Excavation Engineering Summary PDF

Excavation Engineering ====================== The aim of this course is to learn how to choose the right excavation technique, together with the right equipment, in order to respect the project schedule, that are usually tight. Exploration of the rock ----------------------- Performed to get the...

Excavation Engineering ====================== The aim of this course is to learn how to choose the right excavation technique, together with the right equipment, in order to respect the project schedule, that are usually tight. Exploration of the rock ----------------------- Performed to get the geologic and mechanical properties of the rock mass, used to define the factors that are needed to define techniques parameters. Primarily determined by origin, formation and mineralogic composition. - Geophysical methods - Geologic mapping - Drilling and coring - Exploration tests The earth's crust is composed 95% of igneous rock, 5% of sedimentary rock and an insignificant percentage of metamorphic rock, having a depth of aprox. 75km. Being sedimentary and metamorphic the most common on the surface. The major engineering projects take place a few kilometres from the surface, mostly in sedimentary rocks (max 5,5). The exploration data interpretation gives as a result the **stratigraphy** to determine the subsoil components at different depths and its thickness to stablish the **grade of exploitable material.** Can be conducted by means of: - **Direct investigation** → exploratory drilling to get samples to be tested - **Indirect analysis** → geophysical methods to validate results or get more details **Rock Coring Methods** - **Conventional coring**, rotatory (soft rock or soil) or percussive (hard rock) - **Continuous drilling**, long extension tunnels or ducts Excavation works ---------------- The goal is to remove the medium, there are 12 types of different excavation sites, combining: Medium Environment Purposes -------- ------------- ---------- rock open pit mining soil underground civil underwater The excavation can be **cyclic** (discontinuous), where generally no superposition among tasks and a given duration for each task and shift, or **continuous** where operations can nor be divided, all happen at the same time and theres a continuous flow of material from the excavation to the dump. The problems induced by the work are due to: - Vibrations, damage of the nearby buildings - Noice, generated by the equipment employed - Dust - Stability, of the front of the excavation - Flyrocks The solutions are: - Study the propagation of the vibrations in the medium - Definition of an area of respect - Continuous monitoring to check for abnormalities - Modify blasting parameters The target of the exploitation can be, crushed material, given size irregular blocks or regular blocks. Sometimes it is only necessary to specify the maximum size or weight or volume to be excavated, in other cases given percentages of each size, **grainsize distribution**. The **medium** where the work is performed can vary from loose sand to hard rock, since the excavation involves breaking the medium, is necessary to analyse the rock characteristics under mechanical stresses. Mechanical properties of the rock --------------------------------- **Rock strength** → is a mechanical property that mainly depends on the nature of the rock itself, is the intact rock's resistance to failure under load. **Rock cutability** → depends on the rock, the working conditions and the cutting process (depth of cut, cutting speed, axial force, etc.). Systems for rating rock cutability and drillability for specific methods have been developed in separate rating systems for each method not directly connected to each other. [Mechanical rock properties] 1. **Strength**: resistance to failure under stresses, affected by confinement, temperature, strain rates, pore pressure, etc. 2. **Deformability**: resistance to change of shape or volume, depends on elastic and thermal expansion constants. 3. **Hardness:** resistance to local surface failure, evaluated with the Mohs scale. 4. **Fracture toughness:** resistance to fracture propagation 5. **Coefficient of friction:** resistance to sliding of two bodies with planar surfaces in contact 6. **Crushability and millability:** resistance to comminution, reduction of a material to a powder 7. **Extractability:** resistance to fragmentation and disruption by different extraction processes under ideal or standard operating conditions 8. **Abrasivity:** ability of a rock to induce wear on mechanical tools The **abrasivity** is the indicator of the attitude of the medium to wear down the tools. The inevitable friction between medium and tool, that undergoes the tools is primarily a function of the mineral composition of the medium (often related to the % of quartz) and the composition and shape of the tool. The **tool wear** results in progressive deterioration of the performance of machines, due to increased contact area, until the specific pressure exerted by the tool is no longer able to induce failure in the rock. When worn, the tool reduces its geometry, sharpen, face of attack, etc., often a lower productivity is accepted in order to enlarge the tool life and maintenance costs. The **CAI -- Cerchar Abrasivity Index** is obtained by a test performed on steel tools, that gives for a given UCS the feasibility of using that tool or not. A graph showing the economic growth Description automatically generated with medium confidence The **density** of the rock must be differenced between **on site density** and **bulk density**, related to each other through the **bulking factor** (BF ≈ 1,5). After the rock is excavated its apparent volume increases and then its apparent density decreases. [The productivity is always referred to the on site volume!] The **hardness of metals**, microhardness, is determined commonly by the Vickers test by pressing a diamond pyramid indenter with a square base into the surface under a specific load. The size of the indentation left on the material is measured, and the hardness is calculated. Types of interaction --------------------  The graph compares excavation methods based on material type and energy requirements. For **hard rock**, explosives or mechanical excavation are used, depending on the situation. In contrast, **soft ground or soil** requires lower energy and is typically excavated using standard mechanical equipment like excavators and dump trucks. The harder the material, the more energy-intensive the process becomes. Transportation energy is unaffected by the material type or excavation method, dump trucks or conveyor belts are commonly used. This graph shows the correlation between **specific energy consumption** in rock excavation and the **mean particle size**. The left zone covers a range of thin fragmentation, related to the **drilling** activity, the middle zone refers to the **mechanical excavation** and the right zone to the **explosives** that give brittle fragmentation. The left side requires high energy consumption, and the right side gives rise to high levels of vibration. Integrity of the medium ----------------------- The integrity of the medium, physical and lithological, influences on the technique selection. Is essential to know: - state of **natural fractures** - presence of **cavities** - presence of **discontinuities and localized weakening** - **fractures orientation** and **spacing** between them - **stratigraphy** **\\**Any mechanical discontinuity in a rock mass result in zero or very low tensile strength, most masses are controlled by one, two or three sets of primary systematic discontinuities. The rock is considered as a linear elastic material in absence of information about the discontinuities, but most rock formations are fractured so, the effect of intact rock properties is less dominants than the effects of rock mass discontinuities in most cases. Is important to conduct a **structural mapping of rock formations** to identify the rock type, distribution and degree of fracturing and the rating of the predominant discontinuities sets. **Schistosity planes** are formed in metamorphic rocks through intense heat and pressure, aligning platy minerals like mica into parallel foliations, often cutting across pre-existing structures. In contrast, **bedding planes** are sedimentary features created by the deposition of successive layers of sediment, marking boundaries between layers with differences in grain size or composition, typically horizontal and representing original depositional environments. From these parameters, indices that characterize the integrity of the rock mass are used by the rock mass classification systems such as, **RQD**, **RMR**, and **Q**. The mentioned classifications mainly concern the initial decision, whether to use explosives or mechanical excavation, in very poor rock quality, the use of explosives is less productive and more dangerous. **Rock cutability** refers to the ease with which a rock can be mechanically cut, drilled, or excavated. It is influenced by a combination of the rock\'s physical and mechanical properties, which determine how easily equipment can penetrate and break the rock. Geometry of the excavation -------------------------- It evolves over time during the advancement of the work, it includes the **size** and **shape**. And it can be differed 2 situations: - one free surface - more than one free surface **Blast direction** refers to the orientation in which explosives are detonated to control the fracture and movement of rock during excavation or mining.  Explosives ========== An **explosion** is a chemical or chemical-physical transformation that occurs very quickly and releases **energy**, thermic and/or mechanical, and **gas**. The reaction must occur only when the substance experiences an energic **initiation**. It's also necessary that once the reaction is activated it does not stop but proceeds quickly up to the **complete decomposition** of the charge. An **explosive** is a chemical compound or mixture that contains a large amount of energy stored to produce an explosion, when initiated, by heat, impact or friction, it produces a large volume of hot gases in a very short time at high temperature and pressure. The expansion of the hot gas can induce mechanical work by means of shock waves in the surrounding materials. **Classification based on their chemical composition** a. **Chemical compound**, substance formed by a single type of molecule (TNT) b. **Explosive mixture**, substance consisting of two or more compounds, each of them, tanek separately, being not explosive (ANFO) c. **Explosive blend**, substance consisting of two or more compounds with at least one of them being explosive (dynamite) **Historical overview** The modern history of high potential explosives starts with the [technique of nitration] using nitro-glycerine, an unstable with high velocity of reaction explosive. Then the [stabilization] of nitro-glycerine through the creation of a blend, using a non-explosive compound mixed. Further on the development of [blasting agents] such as ANFO, make de field safely manageable and inexpensive. General classification of explosives ------------------------------------ A diagram of explosive agents Description automatically generated Deflagrating explosives ----------------------- **Deflagration** is a slower chemical reaction where the combustion wave propagates at subsonic speeds through heat transfer, resulting in a gradual release of energy. Its propagation velocity depends on the thermical conductivity of the material. A combustion phenomenon where the product burns. (blackpowder, gunpowder, fireworks) The deflagrating explosives burn quickly but [do not detonate], they react with a deflagration. The effect of deflagration under confinement is an explosion, the confinement induces an increase of the reaction velocity, pressure and temperature, it occurs more often accidentally than intentionally. They are used as slow fuse for triggering common detonators or detachment of ornamental stones. Detonating explosives --------------------- **Detonation** is a rapid chemical reaction in which the combustion wave propagates at supersonic speeds, producing a high-pressure shockwave and releasing energy explosively. Detonation explosives are **high explosives**. The reaction is strongly exothermic and continuously provides energy to the reaction zone, allowing the rapid gradient. In an [ideal detonation] the zone of reaction is extremely restricted, and the chemical reactions are completed at the front of detonation. A detonation occurs with an instantaneous decomposition of the charge. A math equations and numbers Description automatically generated They can be divided into **primary** (or initiating) if they can simply detonate with impact, and **secondary** if they require the use of a primary to be initiated.  A screenshot of a computer Description automatically generated  **Specific energy of the explosions** The specific energy of an explosion refers to the amount of energy released per unit mass of the explosive material. It is typically expressed in units of kiloJoules per kilogram (kJ/kg). Specific energy is a crucial parameter in understanding the efficiency and power of an explosive, as it directly correlates with the amount of work the explosion can do, such as breaking rocks or generating shockwaves. Higher specific energy means that less explosive material is needed to achieve a given result, making it more efficient. **Power of an explosion** Refers to the rate at which energy is released during the detonation process. It is the amount of energy released per unit of time and is typically expressed in Watts (W), where 1 Watt = 1 Joule per second. **Work obtainable by an explosion** 1. One kg of explosive is put into an indestructible and insulates cylinder. 2. Reaction is made start and at its end the cylinder is full of solid remains and smokes at ambient pressure. 3. A piston is put on the cylinder, closing it. 4. The piston is pushed down, the force needed to reach the bottom increases going down. 5. It stops when the smoke is fully compressed in the volume initially occupied with the explosive, having the maximum force needed. The **detonation pressure P~d~**, could be understood as the pressure to apply needed to stop the detonation process. ρ= density of the explosive V~d~= detonation velocity W= velocity acquired by the smokes In a very short time, a mass of explosives transform into an equal mass of fumes with velocity *W*. Measuring *W* might be problematic, but it can be assumed to be ¼ of the detonation velocity. Interaction rock-explosive -------------------------- The **shockwave** initially compresses the material with production of heat and intramolecular fractures, then the formation of gases releases a large quantity of energy allowing the shockwave to propagate. The rock is submitted to compression and reflection waves due to the discontinuities and the free surface. The process produces crushed rock by compression in the vicinity of the blasthole, if the amplitude of the compression wave exceeds the compressive strength of the rock disintegration will occur. Then the shock wave induces radial fractures that reach a certain distance (up to 5Ø), if a free surface is contained in this distance, it generates the fragmentation by overpassing the tensile strength. Free surfaces are needed to generate the wanted fragmentation.  Stages of blasting ------------------ **Stage 1 -- Detonation** The explosive charge detonates, and a shockwave travels through the surrounding material, the material is initially compressed due to the rapid shockwave, causing significant stress and leading to fractures within the rock. The rapid compression leads to the creation of fractures and microcracks in the surrounding rock. This stage is where the initial breakage of the material begins. **Stage 2 -- Refraction and secondary fracturing** As the shockwave continues to travel, its speed decreases. The wave refracts as it interacts with the free surface or changes in the rock\'s composition. The refracted shockwave induces additional fracturing along existing cracks, creating larger cracks that extend further into the material. **Stage 3 -- Material detachment** The material that has been fractured continues to move and break apart, at a lower speed. The detached rock fragments are expelled from the blast site. At this stage, the energy of the shockwave has been dissipated, and the material is now being displaced, forming the blasted rock pile or cavity. A diagram of a crack in a wall Description automatically generated  A drawing of a crack in the ground Description automatically generated  A diagram of a hole in the eye Description automatically generated  Primary explosives ------------------ It compounds are highly sensitive to impact, friction and heat, can be activated with a flame or an electric spark or with impact. Their energy release and velocity of detonation are [low.] Their main function is to **initiate** a secondary explosive. **Ordinary detonators** are the only ones initiated with safety fuse. **Safety fuse** consists of a rope, of diameter 5-7mm covered with substances that make it waterproof with a very thin core layer of blackpowder. It contains **phlegmatized blackpowder,** a chemical process that reduces the combustion velocity of black powder. It is mainly used to activate ordinary detonators and at the same time to give a safety delay to exceed the danger zone of explosion. **Detonating cord** is a thin plastic tube with a core of PENT, which detonates at high velocities. AN-FO ----- It's composed by ammonium nitrate and fuel oil (**94% AN + 6% FO**). It is a low cost, stable mixture (both compounds are not explosive taken separately) with lot of energy. Different reactions depending on the percentages used, it was necessary to find the optimum that does not releases toxic gases like CO, NO or CO~2~.  **ANFO limitations** - Minimum diameter charge of 50mm - Not permitted underground or gassy environments because of toxic gasses - Not permitted in precense of water, AN is very soluble - Recommended usage in a climatic environment from -20°C to +40°C - Its density is 0,8-0,9, lower than the water - Emulsion explosives ------------------- Are a mixture of two liquids, one of them being oil-based and the other water-based, forced to blend together with the appropriate emulsifier and enough energy. Therefore, they are prepared in a **water in oil emulsions**. The internal phase composed of a solution of oxidizer salt suspended as microscopically fine droplets, surrounded by a continuous fuel phase. Emulsion explosives have an excellent water resistance since each AN/water droplet is covered by a thin film of oil which repels the water. The droplet size is extremely small, and the cover thickness is submicron, giving the emulsion a very large surface of contact between the fuel and the oxidizer solution, which elevates the reaction efficiency, making it faster and more homogenous. A diagram of a gassing process Description automatically generated To make the emulsion easier to detonate, small voids are added by mixing in materials like glass microballoons (GMB), perlite, or gas bubbles. These voids act as hot spots during detonation, collapsing under pressure to generate heat and start the explosive reaction. This ensures the emulsion detonates reliably and releases energy effectively. The addition of aluminium or ANFO to an emulsion can be used to increase its energy. Slurries/Watergels ------------------ Consists of oxidizing salts and fuels dissolved or dispersed in a continuous liquid phase, the entire system is thickened and made water resistant by the addition of gellants or crosslinking agents. The explosive may be sensitized by the addition of chemically bubbles, micro balloons, etc. Their performance is like the emulsions, Water resistance and safety are very good. Slurry explosives have lately been replaced by emulsions.  Emulsions have great efficiency (measured with the energy available in detonation / theoretical energy ratio) with respect to the slurries. Its efficiency also remains constant over the time. Its velocity of detonation is comparable too. Diagram of a diagram of water gel and a line of water gel Description automatically generated  In some parts of the world its permited to mix the explosives on site instead of using cartridges. Internationaly, the use of ANFO and dynamite is decreasing, while the emulsion explosives market is increasing and the watergels maintains constant. Explosives important characteristics ------------------------------------ **Trigger Sensitivity**: the ease with which an explosive initiates, typically in response to heat, impact, or friction. **Impedance**: the resistance of the explosive material to the flow of a shock wave, affecting detonation efficiency. \ [*Z*~*e*~ = *ρ*~*e*~   *V*~*e*~ *Z*~*r*~ = *ρ*~*r*~   *V*~prop~]{.math.display}\ (explosive impedance) (rock impedance) The wanted effect is to have the explosive impedance a bit higher than the rock's. The comparison of this parameters allows to evaluate if that explosive is suitable for that medium. **Disruptive Nature**: The capacity of the explosive to fragment or destroy materials upon detonation. It also depends on the specific energy of explosion and the velocity of detonation. Hard to be quantitatively determined. **Critical Diameter**: The smallest diameter at which a steady detonation wave can propagate through the explosive. There is a critical diameter below the one the detonation does not happen, or it is very insufficient (uncertainty zone). The optimum diameter is where the function asymptotizes with the limit velocity. A diagram of a diagram of a curve Description automatically generated with medium confidence The critical diameter conditions the perforation diameter and the explosive type to be used in that hole.  **Detonation velocity:** it decreases with decreasing the charge diameter and by decreasing the confinement level. **Critical Distance**: The minimum distance needed between charges or other components for effective detonation. **Density:** depends on the component substances, (0,8 g/cm^3^ for ANFO) - **density of loading:** ration between the mass of explosive and the hole volume - **density of loose of sensitivity:** density above which explosive can not be initiated. Explosive could become unsuitable for the detonation propagation and also unsensitive to activation for exesive compaction levels**.** **Shot Distance**: aptitude of the explosive to transmit the detonation to other one, is the maximum distance at which a non-charged cartridge detonates due to the detonation of a charged one (charged with the detonator) **Watertight**: The ability of the explosive to remain functional when exposed to water. Internal resistance that depends on the explosive's composition, and external resistance that refers to the cover material of the cartridges. **Healthiness of Smokes**: The toxicity and environmental impact of the fumes generated during detonation. **Sensitivity to Impact, Rubbing, and Heating**: The likelihood of the explosive reacting dangerously under mechanical stress or temperature changes. The **Selection of the explosive type** will depend on many characteristics to choose the most suitable one. A screenshot of a chart Description automatically generated Detonators ========== Inside the blast hole, the charge, the initiation system and the steaming are present.  An **initiation system** is a way of detonating high explosive charges reliably, at an specific time and following the right sequence. In most works it is required not to detonate a single blast hole, nor many holes simultaneously, but to explode a given number of charges following a sequence of blast timing. Any initiation system is very sensitive to friction, impact, static forces or heat. The importance of the initiation systems in blasting relates to the need of a local mechanical impulse or blow to initiate a charge of high explosive. The only practical way of doing it is to use: - a detonator - a booster and a detonator - a primer and detonating cord - just detonating cord. **Detonators** have the aim to produce a detonation with sufficiently high intensity to initiate the charge. It is composed by a primary charge and a base charge (secondary explosive). When a booster is added to the detonator to increase the energy released, the system is called **primer**. Ordinary detonator ------------------ An **ordinary detonator** is a device used to initiate the detonation of an explosive charge. It is typically a small, highly sensitive explosive device that, when triggered (either electrically or by a fuse), generates a shockwave or heat sufficient to set off the primary explosive. It's composed by a metallic coper, and inside there are the primary and mase charge. The **safety fuse** burns at a rate of 100 s/m, it considered a low explosive fuse. Detonating cord ------------------------------------- Another option is to use **detonating cord**, which is a cord willed with PENT powder and comes in different explosion strengths, its velocity of detonation is around 7000 m/s. They're simple to use but it produces a lot of noise. It requires a primary charge for its initiation. It comes in different diameters and colour according to the amount of PENT containing per meter, from 3,6 up to 100. The **delays** or **timing devices** are used to control the detonation sequence of charges. They ensure that explosions occur in a specific order, often milliseconds apart, to optimize the energy release and reduce ground vibrations or air blasts. Relais can be mechanical, electronic, or chemical. A diagram of a couple of parts Description automatically generated with medium confidence **Advantages** - suitable when there's presence of water, it's no electric - no limit of number of detonators usable in a blast, they're additive - no limits for the distance from the blast - good accuracy of the blasting sequence **Disadvantages** - by interpositioning relais in the line of detonating cord there's danger of unexploded blast-holes due to the cut of detonating cord by fly-rock (previous charge). - Just a visual check possibility Electric detonators ------------------- An **electronic detonator** is a highly precise and programmable device used to initiate explosive charges. Unlike traditional mechanical or pyrotechnic detonators, electronic detonators use an electronic circuit and microchip to control the timing of the explosion with millisecond or microsecond accuracy. There are available **short delay detonators**, for general use with a [maximum amount of use of 20 units], with an interval of 25 milliseconds. And **half second range detonators**, used in tunnels or demolitions, with a [maximum amount of 12 units] and an interval of 0,5 seconds. Electronic detonators have a maximum number of units that can be used in a single blast primarily due to **power supply limitations**, require a precise and adequate amount of electrical energy to function, exceeding this limit can result in some detonators not receiving enough energy to initiate properly, leading to misfires. and **signal integrity considerations**, as the number of detonators increases, the risk of signal loss, interference, or delays in transmission grows, particularly in long or complex blasting circuits. Timing precision is critical in electronic detonators to achieve the desired blast sequence. Managing a large number of detonators may exceed the system's capacity to synchronize them effectively. Also, industry standards and safety protocols often impose limits on the number of detonators that can be used in one circuit to reduce the complexity and risks of a malfunction.  A diagram of a detonator Description automatically generated In order to solve the problem of the limited amount of delays in the electric system, **sequential times** are introduced. Programming a Sequential Timer allows for the definition of the additional delay to be adopted. The important aspect of the system is that between each circuit, for a maximum of 10, can be manually set up a time interval of delay, variable in general between 5ms and 1s, in function of the type of machine used.  The sequence circuit is study according to the **Ohm's Law.** \ [\$\$\\mathbf{Current =}\\frac{\\mathbf{\\text{Voltage}}}{\\mathbf{\\text{Resistence}}}\\mathbf{\\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ I =}\\frac{\\mathbf{V}}{\\mathbf{R}}\\mathbf{\\text{\\ \\ \\ \\ \\ \\ \\ \\ \\ \\ }}\\left\\lbrack \\mathbf{\\ A =}\\frac{\\mathbf{V}}{\\mathbf{\\Omega}} \\right\\rbrack\$\$]{.math.display}\ In **circuits in serial, r**he resistance is added up [ → *R*~*S*~ = *R*~1*d*~   *n*~*d*~]{.math.inline} In **parallel circuits**, the total resistance is [ → *R*~*P*~ = *R*~1*d*~*p*~ = *R*~*s*~*Vol*]{.math.display}\ Functional groups of blastholes ------------------------------- When the wanted result is a given **fragmentation,** a group of blastholes works better than a single one, as it provides a better fragmentation and a more regular profile for the next blasting.  For a higher depth of the exploitation, when again the wanted result is **fragmentation**, different types of holes are classified according to the blasting sequence: - **cut holes:** create a new free surface, opening, to improve the blasting - **production holes:** achieve the main purpose, fragmentation - **contour holes:** provide an even contour on the side and back walls When the wanted result is to **detach** a given volume, the technique applied is **splitting**, which consists on simultaneous blasting, simultaneously groups of holes blast together to apply a given force to the whole surface. Blasting plan ------------- It is the design of the blast, it includes position, diameter, length and orientation of the holes, charge (type and amount of explosive, initiation system, stemming) and timing (sequence, delays).  Grainsize distribution ---------------------- After the blast, the **grainsize distribution** of the product should be analyzed, by means of **screening** or **image analysis**, to determine if it's needed a **secondary fragmentation**, with hydraulic hammer or secondary blasting, to get the max size of the block that the crusher allows. A graph of different colored lines Description automatically generated The concept of **particle size distribution** (A), **cumulative class** (B), and **characteristic size** (C) of fragmented material. In A, the muck pile and its grain size distribution curve (on the *x* the dimensions of the materials, on *y* the cumulative percentage of passing). In B, one of the ways to determine a point of the distribution curve is shown: using a metal grids with an opening di , a passing P is obtained, of which the percentage a% concerning the total can be easily calculated, and a retained or T, whose percentage is also calculated. This way, the curve's a/di point is obtained. The same procedure, applied with grids of different openings, allows for determining the other points on the graph. In C, the relative particle size distributions fully describe two materials, one finer (I) and one coarser (II). The characteristic dimensions d~50I~ e d~50II~ can be used for a less accurate but more convenient description. The aim of the crusher is to change the material curve from II to I. Different blasting designs give different grainsize distributions, empirical correlations have been studied to obtain the following empirical graphs. **Method 1 -- Suitable in limestone or Class III rock (σ~ci~\ - - tunnel dimensions - tunnel geometry - hole size - final quality requirements - geomechanical rock conditions - explosives availability - expected water leaks - vibration restrictions - drilling equipment Tunnel blasting differs from bench blasting in the fact that tunnels only have one free surface available. This restricts the **round length** and the **volume of rock** that can be blasted in one round. The volume to be blasted is the multiplication of the cross section and the pull \ [*V* = *S*   *s*]{.math.display}\ [Specific drilling and charging increases as the tunnel face area decreases], this is because the cut section remains constant for a given section, in a smaller tunnel it occupies a higher percentage of the cross section and therefore the PF and the SD are higher.  A graph of a charge Description automatically generated  When designing a drilling pattern in tunnelling, the main goal is to ensure the optimum number of correctly placed and accurately drill holes. This helps to ensure the successful charging and blasting, ass well as produce an accurate and smooth tunnel walls, roof and floor. A drilling pattern optimized in this way is also the most economical and efficient for the given conditions. Hole size --------- Most tunneling operations are based on hole size between **38 -- 51 mm**. Smaller diameter gives better fragmentation but a smaller pattern and higher specific drilling. Bigger diameter allows better deviation control so, higher pulls and larger volumes to blast. A graph of a graph showing the size of a tunneling Description automatically generated with medium confidence  Only the dami holes are larger than 51 mm and they are realized with **reamers**. If not available, several closed spaced drill holes can be realized to provide the same effect. **Jumbos** rock drills and mechanized drilling equipment used in underground excavations are designed to give optimum performance in this whole range. A yellow machine with black text Description automatically generated Criteria for tunnel driving round design ---------------------------------------- Volume blasted (ideal) [*V*~*t*~ = *s*~*t*~   *S*]{.math.inline} Volume blasted (actual) [*V*~*a*~ = *s*~*a*~   *S*]{.math.inline} Overall drill length [*L* = *V*~*t*~   *SD*]{.math.inline} Total charge [*Q* = *PF*   *s*~*a*~   *S* = *PF*   *V*~*a*~]{.math.inline} Total number of holes [*n* = *L*(*S*   *s*~*a*~)]{.math.inline} (actual volume) Specific drilling [*SD* = *L*/(*S*   *s*~*t*~) ]{.math.inline} (theoretical volume) Specific consumption of detonators [*DC* = *n*/(*S*   *s*~*a*~)]{.math.inline} (actual volume) The factors that affect the design are the cross section, explosive-rock pair and the type of blast pattern. Decomposition of the round -------------------------- Patterns not very often are accurately reproduced by the actual blast; in many cases the blasting scheme is meant rather as a suggestion to the operator than as a design. Surveys show that patterns can tolerate some inaccuracies without significantly affecting the overall result. It\'s common to find a few unexploded explosive cartridges in the muck pile after a good blast, but these should remain within an acceptable limit to ensure efficient blasting performance. Cycle ----- A great part of the shift is consumed in drilling, charging and mucking, while blasting only takes a fer seconds. The aim of a respected schedule is to have a given advancement per day. The efficiency of the whole operation in tunneling is determined by the **duration of the cycle** (time taken for each phase) and the **pull obtained** (the advance made per blast). A well-optimized cycle minimizes time and maximizes pull, ensuring faster progress and cost-effectiveness while maintaining safety and quality.  Notice that drilling and bolting are the only two operations that could be superimposed because both can be done with the Jambo machine. Cut types --------- The blasting sequence always starts from the cut, a pattern of holes at or close to the center of the face, designed to provide the ideal line of deformation. The placement, arrangement and drilling accuracy of the cut is crucial for successful blasting in tunneling. A wide variety of cut types have been used in mining and construction, but they all fall into two categories **parallel holes** and **inclined v cut holes**. Parallel cut ------------ The basic layout always involves one or several uncharged holes drilled at or very near the center of the cut, providing empty space for the adjacent blast holes to swell into. Uncharged cut holes are typically large, 76 -127mm diameter, large cut holes are normally drilled by reaming. First, a smaller, for example, 45mm diameter hole, is drilled, then reamed to the final size. A less common alternative is to use "small hole" openings (several small holes instead of one or two large holes). Small hole opening makes it possible to use the same bit size throughout the whole drilling pattern. Experience proves that big hole openings give more reliable results than small hole openings. Cut holes are drilled very near to each other, as parallel as possible.  One or more charged holes are placed at a small distance from uncharged (dummy) holes to crush the rock and eject it axially, producing a cylindrical cavity whose length equals the pull. The pull obtainable depends practically only on the diameter of the dummy hole. The larger the diameter of the dummy hole, the greater the allowed distance to the charged holes and the fewer holes to be drilled. It is always necessary to consider the volume increase of the blasted rock: each charged hole, when detonated, must find enough free volume (laterally) to accommodate for the volume increase of the broken rock. It\'s crucial to note that the vibratory disturbance is quite high, especially at the beginning of the round detonation when the free surface is very small. This awareness is key to managing and mitigating potential risks. **[Parallel cut design]** When describing the cut, the following parameters are important to a good design: - diameter of the large hole - burden - charge conditions Drilling position is very important, especially for the holes that are closest to the demi holes. The slightest deviation can cause the blast hole to meet the demi hole or make the burden too big. An exceedingly big burden causes breakage or plastic deformation on the cut. An important parameter for good advance of the blasted round is the diameter of the demi hole. A diagram of a hole Description automatically generated If a reamer is not available several closer drilling holes can substitute a demi hole, a fictitious big diameter must be calculated. \ [\$\$D = d\\sqrt{n}\$\$]{.math.display}\ And the distance from the demi hole to the first round. The distance between the blasthole and the large empty hole should not be greater than 1.5ø for the opening to be clean blasted. If longer, there is merely breakage and if shorter, there is a great risk that the blasthole and empty hole will meet.  There is a given calculation for the cut holes provided by charts where the first one calculates the minimum distance between the demi hole and the first charged hole, then the remaining square is calculated, then the distance from the second round to the square sides and on and on. The sequence must stop in the forth sequential square or after reaching a 1m side. A diagram of a curve Description automatically generated with medium confidence  The **stopping holes**, the holes following the cut holes have a diameter typically between 41 -- 51 mm, smaller than 41mm may require drilling an excessive number of holes to ensure successful blasting, bigger than 51mm can result in excessive charging and an uncontrolled blast. Holes are placed around the cut section in an evenly distributed pattern using a space/burden ration of 1:1.1. If the hole size is between 45 - 51mm, typical spacing and burden are both between 1.0m - 1.3m. The **contour holes** have a lower spacing, between 0.5 and 0.7 m and burden from 1 to 1.25 times the spacing, to achieve a good profile. **Floor holes** have approximately the same spacing as the stop holes but smaller burden, between 0.7 to 1.1m. A small inclination angle of **lookout** is considered to maintain a good profile with the advancement. A black and white drawing of a rectangular object Description automatically generated **Smooth blasting** is always used in tunnelling and increases between a 10 and 15% the number of holes drilled. **[Burn cut]** It is rarely used and if, just for small cross section tunnels. Involves drilling several closely spaced parallel holes, with one or more of them left uncharged (empty). These uncharged holes act as a relief zone or void for the explosive energy to vent. The initial opening is a conical crater, created by one or more charges simultaneously detonated; to obtain a larger pull, a great amount of explosives must be used. V-cuts ------ It is an older but widely used method, effective for tunnels with a medium-large cross section and requires fewer holes than parallel cut technique. Holes are drilled with an inclination, with respect to the tunnel axis, decreasing with the increase of the explosion time, and are detonated by groups. The free surface assigned to the holes exploding first is quite large and the vibratory disturbance is lower than in other methods. The cross-section limitation derives from the fact that the inclination of the holes is generally between 20° and 30° and the drilling machine has a 4m drill slide, with small cross section the amount of cuts that can be performed with a given spacing is lower, **fan cut** can be applied as a solution.  The charge calculation is according to the burden between holes and the height of the cut. A diagram of a triangle with a triangle and a triangle with a triangle Description automatically generated  Firing pattern -------------- Detonators for tunnelling can be electronic or non-electric. Electric could not be used because of the max delay. A diagram of a sequence of strips Description automatically generated  Criteria for a tunnel driving round design ------------------------------------------ Engineers from PoliTo, based on the statistical analysis of a wide collection of data on civil and mining tunnel excavation, proposed a correlation formula to [predict the specific explosive consumption] (P.F.) when the rock type, the explosive type and the round type are known. A, B, C are coefficients accounting for the type of rock, explosive and of round (in particular, of the cut scheme). Referring to the P.F. value that is typically found in surface bench blasting, with fixed toe, and that can be assumed as a minimum P.F. value for a given rock-explosive pair, in lack of other information, PFmin=0.5kg/m3: Diagram of a diagram of a production process Description automatically generated Drilling ======== The drilling result depends on the rock geomechanical characteristics: - rock type - structure - hardness - particle size wanted The drilling activity is made by: **Top hammer:** percussion is generated outside the hole, can be just percussive or rotary-percussive. Less efficient than the others, the energy dissipates from the application point to the attack part. **Down the hole -- *DTH*:** the percussion is performed on the hole; it requires a higher diameter (approx. 90mm) to fit the hammer inside. Percussive or rotary-percussive. **Rotary:** for big diameters, no percussion is performed.  A diagram of rock drills Description automatically generated According to the diameter and the hardness of the rock, the drilling machine is selected.  In drilling machines, two motors are available, one for each main motions: 1. **Feeding Motion**: the linear movement of the drill bit into the material being drilled. It ensures continuous contact with the workpiece for material removal and provides the advancement. 2. **Rotational Motion**: the spinning of the drill bit around its axis. Provides the cutting action needed to penetrate the material. To collect the debris, two mechanisms are available: 1. **Direct circulation**: Drilling fluid (water or air) is pumped down through the drill pipe and exits at the drill bit, carrying debris up the annular space between the pipe and the borehole wall. 2. **Indirect circulation**: Fluid or air is pumped down the annular space (outside the drill pipe) and returns up through the drill pipe along with the cuttings. Diagram of a pipe with text and arrows Description automatically generated with medium confidence The **drilling velocity** and **productivity** is defined by the hole length, the downtime and the drilling speed.  Drilling tools -------------- To select the right straight drilling tools, it must be considered: - optimum bit-rod diameter relationship, in order to avoid deviation - insert face types and edges (spherical, ballistic, retract, etc.) - additional drilling components (guide tubes, pilot roads) Tougher rods (tubes) have mor advantages, they improve precision in drilling, stronger and faster connections, faster drilling, longer service life and improved quality of blasting so, reduced cost. Then can be worn very quickly is they're not suitable for that rock. When worn, they reduce its geometry and have to be discarded. In some cases reshaping and sharpening can be suitable for reuse the bits but, if some premature button fails, they are lost and the tool has to be discarded. Mechanics of rock breaking -------------------------- When a tool is loaded onto a rock surface, stress is built up under the contact area. The way the rock responds to this stress depends on the rock type and the type of loading, drilling method. Rock breakage by **percussive drilling** can be divided into four phases: 1. [Crushed zone]: As the tool tip begins to dent the rock surface, stress grows with the increasing load and the material is elastically deformed, zone III. At the contact surface, irregularities are immediately formed, and a zone of crushed rock develops beneath the indenter (the button or insert of a drill bit). The crushed zone comprises numerous micro-cracks that pulverize the rock into powder or extremely small particles. 70-85% of the indenter's work is consumed by the formation of the crushed zone. The crushed zone transmits the main force component into the rock. 2. [Crack formation]: As the process continues, dominant cracks begin to form in the rock. The placement of major cracks depends on the indenter shape. 3. [Crack propagation]: After the crack formation, spontaneous and rapid propagation follows, zone II 4. [Chipping:] When the load reaches a sufficient level, the rock breaks and one or more large chips is formed by lateral cracks propagating from beneath the tip of the indenter to the surface. This process is called surface chipping and is the goal. Each time a chip is formed, the force temporarily drops and must be built up to a new, higher level to achieve chipping. Crushing and chipping creates a crater.  Diagram of a rock breaker Description automatically generated Percussive drilling ------------------- **[Percussion power]** Is produced by the rock drill's impact energy and frequency. Compared to pneumatic drills, hydraulic drills are capable of higher percussion power and faster penetration rates. The net penetration rate achieved with hydraulic rock drills as a function of drill hole diameter and rock drillability. One limitation in percussion drilling is the capacity of the drill steel to transmit energy. Only maximum kinetic energy is transmitted through a particular steel before excessive drill string deterioration occurs. For field drilling, the optimum percussion pressure setting depends on financial aspects. Higher penetration rates are achieved through increased percussion power; however, the drill steel's lifetime simultaneously decreases. Possible increased hole deviation and its impact on burden and spacing must also be considered. **[Feed]** Feed force is required to keep the shank in contact with the drill and the drill bit in contact with the rock. This ensures maximum impact energy transfer from the piston to the rock. When percussion pressure is increased, feeding pressure must also be increased. Optimum feed force depends on the percussion pressure levels, rock condition, hole depth, drilling angle, and the size and type of drill steels. Broken rock should be drilled at low percussion and feed pressures. The required feed force is transferred to the rock drill cradle by chains or cylinders. Optimal feeding pressure can easily be observed by monitoring penetration, bit wear and steel thread wear. Quite often, visual monitoring of feed and rotational "smoothness" during drilling is sufficient to determine the optimum feed pressure. Low feed force results in: - Poor transmission of percussion energy, shank damage and increased wear, since couplings tend to loosen - Reduced penetration rates due to poor percussion energy transfer through the drill string - Almost no resistance to rotation and low torque - Increased inner bit button wear - Overheated and rattling coupling Very high feed force leads to: - Unnecessary bending and drill steel and shank wear - Flushing problems - Rapid buttons wear on the bits due to increased drag against the hole bottom and because bit is forced to work in inclined position when drill string bends - Increased hole deviation - Uncoupling becomes difficult due to excessively tight threads - Lower penetration rates **[Bit rotation]** The main purpose of bit rotation is to index the drill bit between consecutive blows. After each blow, the drill bit must be turned to ensure there is always fresh rock under the inserts or buttons. Bit rotation speed is adjusted to the point where the penetration rate is at its maximum. Insufficient bit rotation speeds result in energy loss due to recutting and result in low penetration rates. However, sometimes bit rotation speed is intentionally set under its optimum value since lower RPMs reduce in-hole bit deviation and may be required in very abrasive rocks to maintain gauge button velocity under critical wear speed Excess rotational speeds result in excessive bit wear as rock is forced to break by rotation instead of percussion. High rotational speeds also lead to excessively tight couplings, which result in uncoupling problems. **[Flushing]** Flushing is used to remove rock cuttings from the drillhole and to cool the drill bit. The flushing medium (air, water, mist or foam) is forced to the bottom of the drillhole through the steel's flushing hole and the holes in the drill bit. Insufficient flushing leads to low penetration (increased recutting), decreased drill steel life (bitwear and jamming of the steels) and high bit wear. Air flushing is typically used in surface drilling, in a closed space requires excellent dust collection systems. Experience shows that the minimum required flushing velocity for successful cuttings removal is 15 m/s for air and 1.0m/s for water flushing. Over flushing is also a risk. Pneumatic drilling ------------------ The power source for the pneumatic rock drill is existing compressed air lines or a portable compressor. For tunnelling water is preferred in flushing as it does not generate dust. Hydraulic drilling ------------------ These new, high-power rock drills not only doubled drilling capacities but also improved the drilling environment. The introduction of hydraulics to rock drilling also led to improvements in drilling accuracy, mechanization and automation.  Down the hole drilling ---------------------- DTH hammers are used in underground benching operations. In DTH hammers, the rock drilling bit is a continuation of the shank, which the rock drill piston strikes directly. DTH machines are driven by compressed air and require a large compressor to operate effectively. Since the piston is in almost direct contact with the drill bit, just little energy is lost. This gives a nearly constant penetration rate regardless of hole length. Hole accuracy is also good. DTH machines are limited by their relatively low penetration rates and poor mobility, because they require a large separate compressor. Rotation is usually hydraulic. Energy consumption is also large compared to top-hammer drills. The hole sizes most commonly used for underground DTH drilling are 89 - 165 mm in diameter. Hole lengths in underground benching operations vary up to 60 meters. Rotary percussive drilling -------------------------- In rotary percussion drilling, a variety of blades, or roller bits, mounted on the end of a rotating string of rods, cuts and breaks the rock. A percussion or hammer action in conjunction with chisel bit can be used to penetrate hard material. In the case of rotary percussive drilling with top hammer, the drill rods are driven into the rock and turned at the same time. The flushing can be direct or reverse. Rotary percussive drilling is based on the same rock breaking principle as top-hammer drilling except that feed force, rather than percussion force, is used to dent the rock. When the bit is pressed against the rock and rotated, the cutting force promotes chip formation and rock cutting. Cuttings are removed via air or air-mist-flushing. Underground rotary percussive drilling techniques are most applicable in soft or semi-soft formations. Rotation and thrust set special requirements not only for feed and rotation systems but also on drill steels and tool design. Drilling efficiency ------------------- It can be measured by taking into consideration the following parameters: - The way the drilling tool acts upon the bottom hole (percussive, rotary or percussive rotary) - The forces and the rate with which the drilling tools act upon the hole bottom - Hole diameter and its depth - The method and speed with which the drilling cuttings are removed from the hole When using a **percussive drill**, the compressive forces prevail and, when **rotary** **drilling**, shearing forces prevail. The magnitude of these forces with respect to the drillability in a given rock is considered to be almost equal. Therefore, the compressive strength σ~c~ and shear strength σ~share~ of decisive importance. Since breaking of rock is possible only when the cuttings of rock are removed from the bottom of the hole, the bulk density of rock must also be therefore accounted. The drillability index can be assessed by the formula:  Loading and Hauling equipment ============================= The selection of the loading and transport system is a parameter that strongly influences the global economy of an excavation site. The external factors that influence the selection are: - local topography - stability conditions - grainsize distribution of the material - maximum size accepted by the primary crusher The size of the machines can differ greatly in tunnel sites compared to surface sites. **LHD machines** (Load, Haul, Dump) are mainly used underground, but they can also be used on surface sites. **Hydraulic excavators** and **wheel loaders** are the most used in quarries. Selecting the right machine for the job depends on feed material, production requirements, operating conditions and following operations. When selecting a **loader** is important to consider: - amount of rock to be loaded, production requirement - loading cycle time - size limit of the machine - turning and loading space availability - bucket size and fill factors Loading and hauling equipment affects one another and should be matched to get an efficient system. The selection is made considering production and economic aspects, mainly considering: - optimization of the loading system - optimization of the hauling system - optimization of maintenance programs and availability of the systems Time flow --------- Flow sheet that shows the distribution of total hours for an equipment at an excavation site operation, it can be represented as a series of nodes at which the flow is split in productive and no productive hours. A diagram of a work flow Description automatically generated The ratio of the productive flout out of a node over the total flow into the node can be considered as the **efficiency ratio**. Hauling equipment ----------------- The **distance to cover** must be considered on the machine selection. In case of [short distances] (metric to decametric) usually the same machine that collects the material from the pile performs also the hauling. For [medium distances] (decametric to hectometric) the alternative is to use the same machine for loading and hauling or separate equipment, depending on the technical suitability. For [large distances] (hectometric to kilometric) separate equipment is used, almost always discontinuous but in some cases conveyor belts are used, where a mobile crusher is interposed between the machine that collects the material and the belt. Of course, it is better to avoid more steps (unloading the material from a vehicle and loading into another vehicle) because it involves more machines and more people; however, there are special cases where a multi-step system is advantageous. There are available different **types of engines** like pneumatic, diesel, diesel combined with electric/hydraulic/pneumatic, electric or electric-hydraulic. Diesel is more spread in open pit excavations and electric more in underground. **[Productivity]** The goal of an excavation work is the **removal**, in one shift of a given volume of rock from its original site and transferred to another place. To this result, which is the **productivity of the site**, different machines cooperate: each one of them works for a certain fraction, different from case to case, of the working shift. Referenced to volume in place/in situ/ (m^3^ or t), because the amount of excavated rock must be defined unambiguously; loading & hauling are obviously carried out on a fragmented rock and the volume removed must be referred to that of the rock in place. Loading machines ---------------- For these machines it is necessary to consider that each m^3^ of rock in place gives rise, following the blast, to a volume greater of fragmented rock; the relationship between the two volumes (fragmented rock / rock in place) is the **bulking factor**, about 1.5, but it can vary between 1.3 and 1.6. Loading and hauling machines ---------------------------- The distance to cover is limited by considerations of productivity and energy costs. The relationship between a machine\'s production capacity and the distance it needs to cover is not perfectly parabolic. This means that as the distance (L) approaches zero, production capacity does not become infinite. This happens because, at very short distances, the start and stop phases of the machine take up a larger portion of the cycle time. As a result, the machine operates at a lower average speed, reducing its efficiency.  Dozer ----- The volume that the blade can collect ad haul at each cycle is proportional to its width and to the second power of its height, according to a coefficient of about 0.9 (0.8 - 1). The cycle consists of a loading and hauling phase and in a return phase, usually performed at different speeds and therefore at different durations: if L is the distance to cover and V~1~ and V~2~ are the average speeds of the two trips, the duration of the cycle is L/V~1~ + L/V~2~. By dividing the volume collected at each cycle for the duration of the cycle, in hours, hourly productivity can be calculated (in m^3^/h of fragmented rock, to be converted into rock in place by dividing by the bulk factor). The dozer can be used to cover short distances and convey the material within the range of other vehicles, to bring the material closer to other machines. LHD machines ------------ LHD machines are specially [designed and built to load, haul and dump]. LHD technology provides a profitable solution whether the tunnel is large or small. LHD's loading philosophy is to clean the face and haul the blasted rock to a secondary muck pile or dump truck. If trucks are not available, LHD dumps the material onto the secondary muck pile, which makes the cleaning effective.  In conventional D&B underground excavation projects, fast and effective workplaces are essential. Tunnel advancement depends on the time spent on the [critical path of each operation], which is why contractors try to minimize it. Fast face cleaning increases the demand for more effective leader equipment and face-cleaning methods. LHD offers fast and effective face cleaning because it is flexible and versatile. The cycle includes collecting the material with the bucket (which occurs by pushing the bucket into the muck pile), lifting the bucket when it is full, then the machine takes the hauling position and travels to the unloading site, where it unloads the bucket and returns empty. The duration of the cycle is therefore the sum of fixed times and time dependent on distance, and grows as it grows. The production capacity, expressed in m^3^/h of fragmented rock, is given by the ratio between the bucket's capacity (m^3^) and the cycle's duration (h). The productivity must be referred, anyway, to the on-site volume. The truck loading point and secondary muckpile is placed far enough away, so that it does not disturb other operations near the face such as drilling, charging and roof support. If the tunnel is narrow, the secondary muckpile can be placed in turning/loading niches. A white rectangular object with black text Description automatically generated In larger tunnels, muckpile and loading can be done in the tunnel itself with one or two LHDs. LHD also provides long hauling distances, while still maintaining high capacity.  A diagram of a face cleaning procedure Description automatically generated (one LHD) (two LHD) The features that make LHD superior in tunnel jobs include its suitable weight distribution, big bucket volumes, approximately 50% higher payloads compared to fronted loaders with the same engine size, and along wheel base that gives better stability and allows high tramming speeds with full loads. Self-loading trucks ------------------------------------------- They are vehicles equipped with a tipping body and a front bucket (with rear discharge, from the back), through which the body is filled; depending on the model, the driving position can be regular or lateral. Subsequently, the vehicle goes to the unloading point, unloads the material, overturning the container and returns empty to the pile to carry out the next cycle. It is suitable for relatively low production, for example underground mining. They are essentially characterized by power and speed data, capacity of the bucket, capacity of the box and, eventually, the length of the feed cable. The productivity, in m^3^/h of fragmented rock, is given by the ratio between the capacity of the box (m^3^) and the duration of the cycle (h). Dump trucks ----------- Dump trucks are usually used at underground work sites that have steep inclines. Dump trucks are suitable in ramp driving, underground or to-surface rock transport. LHD and dump trucks match each other in size, working space and capacity and are commonly used together. The greatest advantage of dump truck haulage is its flexibility, which cuts down on long-term planning. The dump truck fleet adjusts easily to production changes. Wheel loaders ------------- Wheel loaders are used only for loading, therefore, they have an easier and more economical design than LHDs. The advantages of the wheel loader are its mobility, versatility and high bucket capacity, which facilitate features not only for loading but also maintenance, short-distance hauling and pile preparing after blasting. The wheel loader also has some [negative properties]. It needs a solid working floor and well-prepared pile. Break force and dump height are small compared to hydraulic excavators. It needs a considerable space for performing the maneuver necessary to load the trucks. The size of the bucket should be well calibrated with the size of the dump truck to reduce the downtime. Continuous loader machine ------------------------- Continuous loading is a method used at tunneling work. The continuous loader needs either a rail or wheel mounted hauling system. One benefit of the continuous loader is that it does not require turning niches. Its disadvantages include poor mobility, low tramming speed and its inability to easily handle big boulders. Muck jams also pose problems.  Hydraulic excavators -------------------- Hydraulic excavators can be divided into two different categories: front shovel category and front dump bucket. 385C FS \| H-CPC  Excavators are mainly used in surface excavation sites. Front shovels are also suitable in large tunnels (more than 40m^2^ face). Some advantages for hydraulic excavators include: - Successful attack of solid that needs blasting before being loaded by wheel loader - Hydraulic excavators operate on rough surface - Wheel excavators move as fast as wheel loaders A disadvantage is that it requires a separate loader for collecting and preparing the rock pile. **[Wheel loaders and Hydraulic excavators]** The choice of the equipment is essentially dictated by the geometry of the excavation site. The [front shovel] is to be preferred with high benches and not too large muckpile, the [backhoe and the loader] with relatively low benches, and muckpile with large horizontal extension; the [backhoe] is normally used in trench excavations (with not excessive depth, in relation to the bucket outreach); the [loader], due to its versatility of use, is the most used machine and can be conveniently used even for short distances; the loader with side discharge can be useful especially in road works, where often the limited width of the construction site complicates the maneuvers. When only one excavator (or loader) and one dump truck is available, the healing time is a dead time for the excavator (or loader), as the loading time is a dead time for the dump truck. To fully utilize the productivity of one of the mentioned machines, more dump trucks are needed for each loading machine, or a continuous hauling system. Otherwise, the ability to muckpile removal is limited by that of the hauling system and the load machines remain underutilized. **[Conclusions on shovel-truck system]** The productivity of the shovel-truck system, therefore the bucket/truck capacity ratio, depends on the mutual position of the two machines, say on the availability of space and the geometrical features of the site, that can make possible one side or both sides loading. When applicable, both-side loading is preferred, making continuous loading possible and avoiding the shovel's idle time due to the dump truck maneuver to get to the loading position. A diagram of a light source Description automatically generated Based on the hourly production required, the capacity of the bucket of the shovel and, therefore, the average cycle time, are identified. Depending on the capacity of the bucket, the capacity of the dump truck is selected. The needed power required for both excavators and dump trucks are found in accordance with the bucket and truck capacities. Conveyor belts -------------------------------------- Belt conveyors are often the most economical transportation mode. Conveyors have traditionally been used for transporting overburden and other materials of limited particle size. Belt conveyors in tunneling and quarrying applications are limited due to its maximum practical particle size of approximately 300mm. The development of mobile and semi-mobile crushing equipment, which enables crushing close to the face, has made it possible to switch from hauling trucks to the more economical method of continuous transportation by belt conveyors. Belt conveyors can be adapted to any loading method. Opposed to other transportation methods, the advantages of belt conveying include its almost unlimited capacity, low operating costs. The conveyor belt is most cost competitive when handling heavy materials, high capacities and big lifting heights. Long distances do not pose problems for the conveyor belt, with lengths up to 15 km. Mechanical excavation on rocks ============================== **Rock excavation** is a phase of decohesion, that is the transformation of the rock into granular material, and a phase of debris removal. In **soft ground excavation** the material has practically no cohesion so there's only the removal phase, the equipment used is not referred to as excavation machines but as earth-moving machines. Rock and soil are two extreme terms, there are also intermediate materials (weak rocks) or hard soil. The **rock-tool interaction** **mechanics** investigates the behavior of the tools to optimize their efficiency in cutting (or disaggregation-disruption), in technical operational-environmental terms. Mechanical excavation is energetically illogical: - It forces the rock to fragment in sizes much finer than is necessary to remove it easily. - It is rigid against the natural changeability of the rock (it is easy to modify a shooting pattern, much less to modify a machine when the work is started). - It engages, at equal production, capital of a greater order of magnitude in machinery. However, it more perfectible and evolves faster. Mechanical excavation is performed with machines that transfer energy (in terms of force) from the tools (cutters, bits) to the rock, generating concentrated stresses. Excavation Specific Energy related to rolling and chisel tools mounted on the head of a TBM. The disruption is obtained by means of **tools**, which locally apply very high pressures to their surface, suitable for breaking down a small thickness of rock ([depth of cut] of the tool). Application of principles like those used in metal or wood working, even if the rock, due to its limited plasticity, does not give rise to chips, but rather to more or less fine irregular debris. Relationship between the advancement or revolution of a TBM and the excavation specific energy, separately for chisel and rolling tools, for different mean values of compressive strength of the rock.  Relationship between rock compression strength and torque per unit of depth of cut in one revolution of the head for chisel and rolling tools mounted on a TBM. A diagram of a crack Description automatically generated with medium confidence  A diagram of a thrust and a thrust Description automatically generated with medium confidence Rock-Tool interaction --------------------- The **force** that the tool exerts on the rock is exactly the same which the rock exerts on the tool and that, being such force exchanged on the rock/tool **contact surface**, the same considerations they also apply to **pressure**. Between rock and tool there is a process of mutual destruction (desired on the rock side, suffered on the tool side), the shape and the material constituting the tool are selected according to the rock type, in order to maximize the relationship between the destructive effects, in favor of the tool and against the rock. Rocks and tool materials are characterized by specific values of mechanical strength, that is the unit force (force/section) necessary to cause it to break down. These values depend, as well as on the material, on the type of stress referred to (compression, tension, shear). Moreover, they also depend on the scale to which the operation is considered. Scale effect ------------ The unit strength (MPa) decreases as the size of the resistant body increases. Even when appearing homogeneous on the visual scale, the materials are inhomogeneous at the microscopic examination, as they consist of small elements of different substances or of the same substance but with different crystallographic orientations from point to point or more or less thickly interested by pores, discontinuity or other.  When it is necessary to calculate the force that a tool must apply to cut the rock, or to forecast the service life of the tool, it does not act on medium material, but on small volumes of the individual components, if it meets one that is too hard/strong, it breaks or is worn. The rock must therefore be characterized both by the strength value as a whole, and by an indicator of the distribution of local strength values at a small scale (hardness). The indicator can be found from mineralogical analysis or from the frequency distribution of the hardness values determined through a large number of specific tests. Hardness and toughness of the tool ---------------------------------- The tool is not only asked to be **hard**, not to suffer local abrasions from the components of the rock, but also to be macroscopically **tough**, not to break due to the application of the load. The toughness of a material is expressed by the work necessary to break a unit volume of it. Considered, for example, a unitary cube of the material, a valid indicator of toughness can be given by the product of the pressure necessary to crush it (N/m^2^). What is done to increase the hardness of a material (metallurgical treatments, addition of hardeners to the alloy) does not improve, and more often worsens, the toughness and vice versa. A tool is a force concentrator, it must transfer a considerable force without breaking on a small surface, to achieve a high contact pressure. The rock is not detached in the form of continuous chips, but of separate scraps and the tool does not transfer a constant force, but a succession of very strong peaks of force separated by very short intervals of almost rest, in which it moves for attack and detach the next scrap. So, the tool as it concentrates the action both in the space (small contact surface) and in the time (short successive intervals of effective action), must be hard, strong and tough. Ideally, hardness and toughness are specific characteristics of a material, quantitatively defined by quantities that have the dimensions of pressure: - the **hardness** expresses the pressure to be applied on a very small area to cause a local failure - the **toughness** is the work necessary to break a unit volume of material (and the work/volume ratio is still, dimensionally, a pressure) The difference in hardness and toughness between tool and rock should be related to the amount of excavation work a tool can perform before it needs to be replaced or repaired. The materials used as rock tools are many and can be roughly classified into three categories: **Simple substances:** diamond, natural or synthetic; various abrasive substances such as quartz, corundum, carborundum. **Sintered:** they are materials obtained by compacting under strong pressure, and heating at a temperature insufficient to cause melting but sufficient to cause the welding of the grains, mixtures of very fine powders. To this category belongs the most widespread material for rock tools (the Widia), obtained by sintering tungsten carbide and cobalt **Alloys:** they are obtained by melting together different metals and allowing the solutions thus obtained to solidify. To this category belong many types of hard steels used as rock tools. Tools can become inefficient for two reasons: - Due to **wear**, modification of the original geometry, due to the progressive removal of material by the rock, whose hard components act as tools, to smaller scale, with regard to the actual tool. This phenomenon is essentially dominated by the (punctual) differences in hardness between tool and rock. It can affect both the actual tool and the tool holder. - Due to **breakage**, because they have been subjected to excessive stress, for example because they are expected to have a \"depth of cut\" bigger than that compatible with the type of rock where they work. The breakage can concern the actual tool, the tool holder or the connection between them. Wear and breakage are [interconnected], if the tool wears, it is necessary to exert higher force to make it work and this overload makes it more likely to break. For a given operation (with a certain machine and a certain rock) a **service life** of the tool is defined as the interval, in actual working hours, between the substitutions of the tool itself. To evaluate the impact of tools on the cost of excavation, the operation is characterized by the **specific consumption of tools**, defined by the ratio between the number of tools replaced and the excavation production obtained (expressed in m^3^ in place of rock). Being **v~u~** the **service life** of the tool, **n~u~** the **number of tools** mounted on the machine and **Q** the **hourly excavation production**, the **hourly excavation production by tool** is **Q~u~=Q/n~u~.** The **specific consumption of tools** is **v~u~ / Q~u~.** The **specific consumption of metal** is the weight difference between a new tool and one being replaced divided by the excavation production by tool, **(P1-P2) / Q~u~** , expressed in \[g/m^3^\] is the amount of metal that one cubic meter of rock can destroy. A comparison of different types of lines Description automatically generated with medium confidence Excavation head --------------- The excavation head is the part of the machine to which the tools are applied and which supplies the cutting motion and the feeding motion to them. During the excavation action, the tools travel straight or curvilinear trajectories, which lead them to geometrically interfere with the medium to be removed. Schematically, the motion of the tool can be divided into two parts: - **Cutting motion**: gives rise to chip or splinter separation (rotation) - **Feeding motion**: causes the tool to find something to detach in the next cutting path (advancement) The cutting and feeding motions occur at very different speeds, the first is usually reported in m/s, and the second in m/min or m/h. Simple (approximate) relationships exist between the cutting speed, feeding speed, and productivity of the machine. These relationships are based on the known geometry of the excavation head, providing insights into the factors that influence the efficiency of the machine. The excavation head (body) can be provided with one or more tools (all simultaneously in action during work, or only in part). Each tool follows a certain trajectory, a more or less large part of which is active (gives rise to detachment of material). During the work, there are no tools on the excavation body that follow the same trajectory: the combination of the feeding motion and of the cutting motion requires each of them to follow a different path. However, it may happen that the trajectories of two or more tools differ only with respect to the displacement due to the feeding motion. In this case we are talking about **homologous tools**, some excavation bodies consist of groups of homologous tools, in others none of the tools has homologues, in others there is only one tool.  The **depth of cut** of the single tool is the thickness of rock removed, during the cutting path, by the single tool, corresponds to the distance, in the direction of the feeding motion, between the two successive cutting paths of the same tool, or between those of two subsequent homologous tools. Therefore, being known the velocity of the cutting motion **V~t~**, the distance (along the cutting path) between a tool and its next homologous, **L~t~** , and the speed of the feeding motion **V~a~** , the depth of cut **p** is given by: \ [*p* = (*V*~*a*~ *L*~*t*~)/*V*~*t*~]{.math.display}\ Each tool digs a groove, whose depth of cut depends on the geometry of the excavation body and on the speeds Vt and Va. The groove also has a width that depends on the geometry of the tool, the depth of cut and the behavior of the rock. In the area of interaction between tool and rock, a sort of **pulverization** is observed. At a greater distance from the contact rock/tool, fractures are generally observed in the rock, variously oriented. The way this works is similar to how an explosion acts, a pulverization zone in the immediate adjacency of the charge/rock contact and a fracture zone at greater distances, up to the limit of the so called action radius. The rationally designed excavation bodies satisfy the so-called "coverage of the excavation section" and are very important, if they fail, for example due to a tool\'s breakage, in the trajectory of the missing tool, there would remain a rock outcrop, which would soon interfere with the behavior of the machine itself. Adding the contributions of all the tools, the production of the excavation head is obtained. Tool types ---------- In **drag tools**, the cutting force forms a small angle with the cutting path of the tool itself and detaches rock scales in front of the tool (excavation body must apply transversal forces to the rock with respect to the direction of progress of the excavation). They are frontal detachment tools. Made with a great variety of geometries, but basically, they are related to three groups: - linear, or blade tools - nail tools - pencil, or conical tools  In **rolling tools**, the cutting force is orthogonal to the trajectory and detaches rock scales laterally to the tool (excavation body must apply to the rock forces acting in the direction of advancement of the excavation (thrusts), from which the detachment forces arise. They are side (lateral) detachment tools, they are the only ones suitable for hard rocks with a brittle behavior. **Disk tools**, cutting edge ring in hard steel (sometimes also with widia inserts), keyed on an idle roller. They are the most common. **Roller tools** with widia buttons for very hard rocks. A black metal object with a circular top Description automatically generated  A diagram of a line graph Description automatically generated with medium confidence Dimension stones exploitation techniques ======================================== The morphological and structural variability in deposit structures and stone properties leads to diverse quarry layouts, even within the same area. The main stablished **cutting techniques** are: 1. Dynamic splitting (hard stones) 2. Diamond wire sawing (hard and weak tones) 3. Chain sawing (weak stones)  Dynamic splitting is much cheaper but the smoothness in the faces of the wanted block is not the wanted one, also can be not suitable for some kind of rocks. When the results are not the ones wanted, **recovery** must be done to sell the piece as a commercial block, some mm of the faces need to be softened, which can be considered as material waste. For hard stones, the main block is cut using dynamic splitting and the resizing is made with the diamond wire technique. For weaker stones, the chain cut is the first performed on the bottom part and then the block is cut with diamond wire. A collage of images of a person working on a machine Description automatically generated Quarrying methods and cutting technologies ------------------------------------------ 1. **Cutting**: blocks are separated by means of kerfs. a. diamond wire b. chain saw cutter c. flame jet d. water jet 2. **Splitting**: blocks are separated by fractures induced in predetermined planes. e. explosive (cord, gunpowder) f. hammer and feather, wedging, separating devices g. line drilling 3. **Cautious blasting**: blasting with minimal breakage, suitable pieces are selected from the muck. Diamond wire saw ---------------- Its principle of operation is to cut the rock, according to a predetermined plane by means of a flexible made abrasive. It creates a loop where the wire runs at high speed, always sprinkled with water for cooling, so as to progressively affect the stone to cut it. At a given point, the machine needs to be stopped and the wire shorten, long wire exposed means less efficiency. The cur performed has a width of approximately 30mm.  The goal is to engrave the rock according to a wanted plan, by the movement of a flexible abrasive cable. In the diamond wire, the abrasive action is exerted by the diamond contained in the beads inserted into the wire itself. A close-up of a cable Description automatically generated  The **cutting mechanism** can be outlined, as disruption of the rock by means of micro-tools, mounted on a flexible tool-holder, which locally apply high pressure to thecontact surface, suitable for removing a small thickness of rock (tool\'s depth of cut). **[Traditional diamond wire]** It is a galvanized steel **cable**, 5 mm diameter, made up of 7 strands, wrapped in a helix, of ultra-flexible steel wire, with the task of supporting the diamond beads and absorbing the static and dynamic stresses. The **diamond** **beads**, the real cutting element, are homogeneously distributed along the cable, in variable number according to the different types of wire, 28-34 beads/m (marble) and 32-40 beads/m (granite). The **spacer** **springs** are spiral-shaped, elastic, ultra-flexible and steel made, interposed to the beads; their task is not only to protect the cable, but also to achieve a good amortization of the shocks and of the abrupt variations of friction that the beads undergo during the work phase. There are also available **[Plasticized wires]:** the springs and spacers are replaced by a cover in thermoplastic resin injected at high pressure and particularly resistant to wear. The beads become, in this way, integral with the cable. **[Rubberized wires]:** hot injection of a protective sheath made of rubber material of a traditional wire (with springs and spacers), so as to occlude all the spaces between the different components of the wire.  The **beads** are formed by a cylindrical metal capsule with a length of 8-11 mm, with a 3mm width. On the outer surface there is a 2-3 mm thick layer containing the diamonds. The overall diameter is therefore usually 10-11 mm. **Electroplated beads** the bush is coated with a layer of diamonds on the surface with an electrochemical process and adhered by means of a nickel binder. Most suitable for soft rock. **Sintered beads,** the synthetic diamonds are immersed in an amalgam composed of cobalt, with bronze to calibrate the hardness according to the material to be cut. The distribution of diamonds is homogeneous throughout the thickness of the amalgam. More suitable for hard rock. The wires with electroplated beads and traditional structure allow high cutting speeds with a new tool, but with a progressive reduction in performance with the wear of the surface layer of diamonds. A diagram of a post Description automatically generated For wires with sintered beads, the consumption of the diamonds proceeds parallel to that of the matrix that contains them, therefore allowing the bead to keep constant the cutting capacity up to its total consumption. Although their cost is higher, they guarantee greater versatility, being able to play on the choice of metallic amalgam and of diamonds, in order to obtain \"personalized\" beads according to the material to be cut. **[Operational configurations]**  A diagram of a tunnel Description automatically generated D blind cut for the construction of an opening channel Its **performance** is measured in: - **Cutting speed**: number of square meters that can be cut in one hour (m^2^/h). - **Lifetime** (or durability, productivity, wire yield): number of square meters that can be cut with a linear meter of wire before it is completely worn(m^2^/m). Chain saw cutter ---------------- The **chain saw cutter technique** involves using a chain saw equipped with industrial-grade diamond or carbide-tipped chains to cut natural stone in quarries. It provides precise and efficient cuts, making it ideal for extracting blocks with minimal waste and damage. Commonly used for marble, limestone, and soft to medium-hard stones, this technique is favored for its versatility, reduced environmental impact, and ability to create clean, straight cuts in large stone deposits. When not enough free surfaces are available, it can be combined with **pillows** with compressed air injected.  The arm can be mounted on a tubular gun carriage, separate from the engine. Thanks to the movement on the lifting columns and translation columns, both horizontal and vertical cuts can be performed, simply rotating the arm. A drawing of a bridge Description automatically generated The **cutting** **tools** are cutting platelets of widia or polycrystalline diamond, placed on appropriate supports, in turn fixed on the links of the chain. The plaques are mounted on the chain in series of 6-7 elements, positioned so as to outward at an angle (in the case of small plates prismatic square based) or with part of the outer diameter (if the base is circular).  A diagram of a arch Description automatically generated **Most relevant advantages:** - versatility of use - general healthiness of the operations (absence of dust, vibrations and low noise) - simplicity of operation - little need for labor in the cutting phase (an employee) - absence of injuries induced to the rock mass - regularity and planarity of the cut - essential in the opening and exploitation of underground quarries **Major limits:** - current impossibility to use this machine with hard materials - reduced cutting depth (limited to arm length) - the positioning and the movement of the machine require the availability of powerful shovels or loaders and the presence of at least two workers Water Jet --------- The cutting action is generated by a water jet at high speed and high pressure (up to 400 MPa) with a diameter of the order of mm. The cutting mechanism can be schematized as a chipping of the rock components. The waterjet is currently at an intermediate stage between the experimental and the industrial application stage. The waterjet is used for the primary cut in granites. It can be used both in open pits and underground. There are two types of water jet cutting processes, **pure water cutting**, in which the cutting is performed using only an ultra-high-pressure jet of clean water, and **abrasive water jet cutting** in which an abrasive mineral (typically garnet) is introduced into the high-pressure stream. The machine can be schematically reduced to two components: a pressure generator and a user. The pressure generator is designed to provide a certain flow of water (5-80 l/min) at a given pressure (100-400 MPa). The user is the nozzle, in which the water hydraulic load is transformed into kinetic energy. The nozzle is mounted on an oscillating head (cutting head) supported by a rod, which must have considerable dimensions to support the recoil of a jet coming out of the nozzle at supersonic speeds (up to 800 ÷ 900 m/s). The cut must be a few centimeters wide to accommodate the rod. The cut is created by translating and penetrating the rod with the nozzle, for subsequent switches along the chosen direction. The progress of the machine is automated, and therefore the continuous presence of an operator is not necessary. The depth of cuts achievable: 2.5-3.5 m, up to 8 m with an extension of the rod. Operational aspects ------------------- A diagram of a wire bridge Description automatically generated  A diagram of a rectangular structure Description automatically generated with medium confidence  Underground Mechanical excavation ================================= 11.1 Impact Hammers =================== **Impact hammers** are machines that deliver powerful, repeated blows to break or drive materials. Mounted on special carrier, equipped with a mechanical or hydraulic arm for positioning and impacting the rock and for the lateral movement in the phase of detachment of the rock elements. Hammer weight classes: 500 - 2000 kg. To provide good support, the carrier should be tracked and weigh 10 to 20 times the hammer. Hammers in tunneling -------------------- Hammer in tunneling has proven to be economic and successful compared to drilling and blasting when the fractured rock structure makes controlled blasting hard to achieve. Additionally, hammer tunneling involves only a few work phases and there is less need for skilled work force than in drilling and blasting. In a typical hammer tunneling case, the main advantages over other methods are lower investment costs, lower work force costs, safer job-site conditions (because explosives are not used) and little or no over-excavation with costly refills. Rock types ---------- For achieving a reasonable productivity rate in hammer tunnelling, distance between cracks, joints and other discontinuities should not be more than 30 to 50 cm. The rock to be excavated is compact but soft enough to allow a reasonable productivity rate by tool penetration. Rock strength, abrasion level and general toughness also influence productivity up to a point. Rock is rarely homogenous in long tunnels. If extremely compact rock is encountered, [auxiliary blasting] is recommended. It is often sufficient to fracture the rock, enabling further excavation with a hammer. Auxiliary blasting is applied at the lower middle part of the tunnel where excavation normally would start. Considerably less **ground vibration** is associated with hammer excavating than with the drilling and blasting method. The vibration level caused by hammer excavation is 5 - 10% the level of blasting. This can be a decisive factor when excavating rock in the vicinity of structures that require vibration limitations. Working methods --------------- The working method is dictated by the section area and length of the tunnel. **Areas 30 - 70 m^2^** Hammer tunneling is suitable for tunnels with a cross-section greater than 30 m^2^ due to the necessary space to fit the excavator with the hammer. In a small and narrow width (less than 8m) tunnel profile, only one excavator-hammer combination can work at