Semester 2_2024 CHAP 1 EARTHWORKS AND LAYERWORKS - LESSON 1.pdf

TRANSPORTATION ENGINEERING 2B TRACIB2  TRANSPORTATION ENGINEERING III TRACIB2 Mr. HH Ndlovu Lecturer: Transportation Engineering III Department Of Civil Engineering Technology Tel: 073 517 8896 Email: [email protected] ...

TRANSPORTATION ENGINEERING 2B TRACIB2  TRANSPORTATION ENGINEERING III TRACIB2 Mr. HH Ndlovu Lecturer: Transportation Engineering III Department Of Civil Engineering Technology Tel: 073 517 8896 Email: [email protected]  HAPT ER 1 C R W OR KS D LAY E R KS AN HW O EART Introduction Objectives: to introduce to the learner: ü the terminology and basic principles used in the design and construction of roadworks. ü the basic principles used in the design and construction of road cuttings, road embankments and layerworks. ü methods used for measurement and payment of earthworks ü Mass Haul Diagrams (MHD) and examples. At the end of each chapter several self-test questions are presented, you should work through them. These will help you understand the contents of the module Earthworks ü A road pavement is made up of layers and these distribute the loads imposed on them by traffic down to the insitu soils beneath the roadway. ü A pavement can carry out its function only if its layers are of sufficient strength to resist the stresses imposed upon it. ü The greatest strength is required at the surface on which the vehicles travel, where the wheels of the vehicles impose both lateral and vertical stresses. ü The thickness of each layer must be sufficient to ensure that the layer immediately below it is not overstressed Earthworks ü Earthworks on a road construction project form a major part of the contract and require careful planning. ü Earthworks must be carried out swiftly in order that the subsequent layerworks can follow on as soon as possible with continuity of work. ü Earthworks are divided into two main categories, namely, that below the formation level and that above the formation level. ü the formation level is taken as the underside of the structural pavement layers (i.e. bottom of selected sub-grade). Earthworks Formation level Earthworks ü When estimating quantities it is assumed that all work above the formation level is constant for a particular project because it consists of the pavement layers of specified thickness. ü For structural consistency the cross-sectional area is usually uniform throughout the work, unless the road cross section changes for a specific reason (e.g. addition of a climbing lane or a taper (widening at an intersection). ü The earthworks required to reach the formation level, which forms the platform on which the pavement is constructed, may consist of excavation (cut) or embankment (fill). Earthworks ü the following is a schematic diagram of a typical longitudinal section along the centre line of a road: Existing ground level Finished road level Formation level Earthworks Typical Cross Section Of A Two Lane Two-way Road ü the terminology used to describe the typical pavement elements. Surfacing Shoulder material Base Subbase Selected subgrade Fill In situ selected subgrade (if Roadbed preparation suitable) Earthworks ü Earthworks is the general term used to describe the process of excavating material down to the formation level in the cuttings and placing this in fill up to the corresponding formation level. CUT FORMATION LEVEL FILL Diagrammatic representation of cut to fill operations Cuttings ü For details of the design and construction of cuttings refer to: TRH 18: The investigation, design, construction and maintenance of road cuttings. Design of cuttings ü A thorough site investigation is essential for long-term stability of cut slopes. ü Trial pits, auguring and/or drilling (if hard material is encountered or suspected) must identify the underlying materials. ü Samples of each horizon must be taken and tested in the materials laboratory. ü attention must be given to discontinuities in otherwise homogeneous materials: joints and bedding planes, lenses of foreign material, fault and slip planes. Cuttings Identification of problem areas is most important. Problems can be encountered where: ü landslides or slips can occur due to the removal of lateral support as or after the cut material is removed. ü layered sedimentary rocks (sandstones and shales) have joint planes or bedding planes sloping towards the roadway. ü boulder formations occur in a matrix of weathered erodible material. ü undercutting of slopes by erosion has taken place. ü seismic (earthquake) forces are applicable. ü sub-surface water seepage is intersected. Cuttings Early identification of problem areas can be made through the following: ü Topography: indications of possible instability can be obtained from the local topography. Evidence of past instability in the form of scars, terracing, hummocky ground, bent trees, displaced fences and landslide debris are good indicators of problems. ü Geology: A thorough understanding of the local geology is necessary. Consult geological and soils maps. ü Water: Most landslides and slips are triggered by water. Thorough investigation for cut slope stability in areas falling within water-surplus zones of the country is essential. CUTTINGS Early identification of problem areas can be made through the following: ü Past experience: Data on past instability in the same or similar materials can often be obtained from case histories. The observation of existing slopes is of utmost importance. ü Erodibility: Certain rock and soil types are very susceptible to erosion and will require special measures to combat erosion. Cuttings ü The slopes of cuts (or batters) should be designed for long-term stability according to the type of material and geological strata encountered within and adjacent to the road prism. ü Cut and fill slopes are generally given as 1:X. For instance 1:2. This means 1 (vertical) to 2 (horizontal). 1 Vertical X Horizontal Cuttings Steepest slopes generally applicable to the following types of material are: ü Soft material 1: 1.5 (1: 2 where vegetation is to be established) ü Intermediate 1: 1 ü Hard 1: 0,25 Frequently slopes have to be made flatter than the values given above. Recommended Minimum values of factors of safety used in slope stability analysis ü Freeways, major interurban roads 1,50 ü Major rural roads 1,25 ü Lightly trafficked roads 1,10 Source: TRH 18, Table 4] CONSTRUCTION OF CUTTINGS ü the limits of the excavations must be surveyed and pegged out ü the topsoil falling within the excavation area is carefully stripped to the required depth (usually 150 - 200 mm) and stockpiled at a convenient site. ü This topsoil material will be used at a later stage to cover cut and fill slopes to facilitate the restoration of vegetation. ü soft material may be excavated using scrapers or front-end loaders and trucks. ü Intermediate materials or rock will require ripping or blasting before they can be excavated and removed. CONSTRUCTION OF CUTTINGS CONSTRUCTION OF CUTTINGS ü Rock cuttings may need some form of rock-fall protection works. ü During the excavation of rock cuttings, all loose rock must be removed from the cutting face. ü Blasting can open fissures in the rock mass and leave unstable blocks that will fall in due course. ü The rock slope must be “barred down” while it is being excavated: a small team of labourers with crowbars on the slope with orders to pry out all loose rocks. ü This will substantially improve safety during construction and reduce rock falls when the road is under traffic. Construction Of Cuttings ü A ditch may be dug at the foot of the slope to hold fallen rock, which prevents the rock from rolling onto the road and causing accidents. ü The ditch can be fenced with a strong fence to further improve safety from bouncing rocks rolling onto the road ü Retaining walls may be needed to support local areas of instability. ü Retaining walls can be constructed with reinforced concrete or other materials such as gabions. ü Gabion walls made with local stone can be made to blend into the landscape in a way that concrete walls cannot. CONSTRUCTION OF CUTTINGS CONSTRUCTION OF CUTTINGS Retaining Walls & Side Drains CONSTRUCTION OF CUTTINGS Construction Of Cuttings Drainage is essential for all cuttings and should comprise: ü Catchwater drains at the top of the cutting to prevent water flowing down the face of the cutting; ü Side drains through the cutting to carry off all water collected from the road and cutting surfaces. ü Interceptor drains to pick up water from springs or seepage zones. ü Subsurface drains as needed to control groundwater flows. EMBANKMENTS (FILLS) Design: Refer to TRH 10: The design of road embankments. The design of fills requires the application of geotechnical engineering techniques to calculate: ü the effect of the weight of the fill on the insitu sub-grade, which may cause settlement in high fills and/or poor insitu soils, and may give rise to instability of existing slopes. ü Stability of the fill slopes themselves (requiring slip circle analysis). ü Settlement of the fill embankment EMBANKMENTS (FILLS) ü Geological maps should be consulted to establish the rock and soil formations at the positions of embankments. ü Soil behaviour can to some extent be predicted from the origin and type of soil. ü The desk study, using geological and topographical maps, should foresee potential problems. ü The site investigation needed to solve the problems can then be planned: — the number and positions of trial pits and/or bore holes necessary, — the number of samples required to reduce uncertainty. EMBANKMENTS (FILLS) Site investigations ü The positions of large embankments must be identified and the depth and type of soil beneath them noted. ü If problems of stability or excessive settlement are expected, then more extensive trial holes or bore holes will be needed to adequately sample the soils in question. ü Laboratory tests are performed on the samples to establish soil properties. ü Insitu tests may be required, for example, CPT (Cone Penetration Test), SPT (Standard Penetration Test) and Vane Shear Tests. EMBANKMENTS (FILLS) Measures to control pore water pressure: ü The construction of drainage paths by laying a blanket drain or by inserting vertical drains are common measures for relieving excess pore water pressures. ü The same measures can be used to speed up settlements, often used in conjunction with a surcharge on the embankment. ü The surcharge consists of an extra layer of soil placed temporarily on top of the formation to provide additional weight. ü The surcharge can be of any required thickness. However, the surcharge should not be so large as to cause failure of the soil. EMBANKMENTS (FILLS) Design of fills ü Design is divided into stability analysis using computerised calculation and a factor of safety of 1,5 or more and settlement predictions. ü The effects of water predominate in both calculations. ü Pore pressures under or within the embankment may build up during the construction of the embankment to such an extent as to cause sudden failure of a portion of the works. ü The design must identify the probability of increased pore pressures and must make provision for measures to control them. EMBANKMENTS (FILLS) ü Settlement when uniform is not a major problem. ü Differential settlement is the problem. ü Differential settlement of an embankment may cause steps that would disrupt traffic. ü Drainage structures like bridges and box culverts seldom settle the same as the adjacent earth bank and the step up and step down from bank to bridge to bank will need extensive and costly remedial filling. CONSTRUCTION OF EMBANKMENTS Construction Clearing is the removal of all trees, bush, other vegetation, rubbish, fences and all other objectionable material including any structures within the road reserve or borrow areas as shown on the plans or instructed by the Engineer. Grubbing: is when all tree stumps and roots are removed to the depths specified. In the area where the roadbed has to be compacted the holes must be backfilled with suitable material and compacted to the required density. CONSTRUCTION OF EMBANKMENTS Roadbed Preparation ü If unsuitable materials are encountered in areas underlying fills, these are removed and disposed of (spoiled) as shown on the drawings or as directed by the Engineer. ü The Engineer may also order that any material which is too wet to provide a stable platform for construction be removed and replaced with suitable dry material (usually dump rock to form what is called a pioneer layer). ü the area under the roadbed needs to be treated to provide a stable platform on which the fill is to be constructed because the insitu densities of the naturally occurring materials are generally low (below 90% mod AASHTO). : CONSTRUCTION OF EMBANKMENTS Roadbed Preparation The following methods (generally specified in the contract documents) may be employed: ü Compaction of the material from the surface using pneumatic-tyred, vibrating or impact rollers. ü The number of roller passes to achieve the desired degree of compaction should be specified, or the required density should be specified. ü Scarifying, watering and re-compacting the in situ material to the specified depth (usually 150 - 200 mm) and density (usually 90% Mod. AASHTO). FILL CONSTRUCTION ü Fills are generally constructed from material excavated from cuttings, if there is insufficient of this available, from borrow sites, generally situated outside the road reserve. ü The fill material is brought up in layers (usually 150 - 200 mm thick). ü Each layer must be thoroughly mixed with the correct amount of water and then compacted to the specified density (usually 90% Mod AASHTO or 95-100% Mod AASHTO ü NB: It is usually very difficult, even impossible at times, to compact soil without the correct amount of water. FILL CONSTRUCTION ü The construction of high fills may require special techniques to prevent the development of excessive pore water pressures and to ensure their stability during and after construction. Special Techniques may include: ü selection of a better class of material in the bottom layers of the fill (strength and free-draining qualities needed). ü construction of sand filter blankets in the fill where these may be necessary. ü strict control of moisture content during construction. ü insertion of drains into the ground beneath the fill. FILL CONSTRUCTION Finishing of slopes ü To present a neat and aesthetically pleasing appearance all slopes (cuts and fills) must be trimmed to the lines and levels specified. ü Loose rocks, stones, and other unwanted material must be removed and disposed of as directed by the Engineer. ü Fill slopes and cut slopes in soft material, must have a slope of 1: 2 or flatter and have the tops and toes rounded. ü The slopes are then covered with the topsoil stripped off before earthworks commenced and planted with suitable vegetation. FILL CONSTRUCTION Finishing of slopes ü In ecologically sensitive areas such as the fynbos areas of the Western and Southern Cape the natural flora must be preserved for replanting after construction is completed. ü A common method of revegetating slopes, which are to be grassed, is by Hydroseeding. ü This is achieved by mixing the grass seeds and fertiliser with water and a glue and spraying this onto the topsoil covered slopes. CLASSIFICATION OF EARTHWORKS MATERIALS Materials encountered in excavation areas are classified as one of the following: ü Soft ü Intermediate ü Hard and different rates will be tendered for the quantities given in the Bill of Quantities. CLASSIFICATION OF EARTHWORKS MATERIALS ü Soft material is material that can generally be excavated by scrapers, front loaders, without having to loosen the in situ material first (i.e. by ripping) ü Intermediate material is generally material like soft or weathered rock, which requires loosening by some means, such as ripping but not blasting, before it can be loaded and carted away. ü Hard material is generally hard rock, which requires blasting or ripping with a very heavy machine before it can be removed. MEASUREMENT AND PAYMENT OF EARTHWORKS ü Most road construction and earthworks contracts specify that measurement for payment purposes will be made according to the fill volumes as shown on the drawings in place and after compaction to the specified density. ü the insitu density of soft material encountered is generally much lower (75 - 88% Mod. AASTHO) than the densities to which they must be compacted in the fill and selected sub-grade (generally 90 - 93% Mod AASTHO but 100% for single sized aeolian sands): the shrinkage factors of the materials become important. ü This fact must be taken into account by the designer when attempting to balance the cut and fill quantities in order to achieve the most economical project and by the contractor when planning the logistics and plant requirements for the job. MEASUREMENT AND PAYMENT OF EARTHWORKS Cross-sections Formation level Layer works Fill Natural ground line Chainage 12 200 Cross section in Fill Natural ground line Cut Layer works Formation level Chainage 12 320 Cross Section in Cut MEASUREMENT AND PAYMENT OF EARTHWORKS Cross-sections Fill Cut Plan view MEASUREMENT AND PAYMENT OF EARTHWORKS Cross-sections ü the areas are not simple regular geometric figures due to the irregularities in the ground line ü straight forward mathematical methods to determine the area of cut or fill cannot be used with confidence. ü The most convenient method is to use a planimeter to measure the areas of the cross-sections. ü Volumes are then calculated by the method of end areas from the cross- sections and from the distance between them ü (see Appendix 3 for a description of the “method of end areas” INTRODUCTION TO MASS HAUL The terminology used in conjunction with mass-haul diagrams. ü Longitudinal section or Profile: is a graphical representation of existing ground and final proposed elevations along the centreline. It is a longitudinal section and therefore any curves in the road on the horizontal plane are not apparent. ü Cross-section: The end view, at any station or chainage, perpendicular to the longitudinal section. It is used for determining the volumes of cut and fill.. INTRODUCTION TO MASS HAUL The terminology used in conjunction with mass-haul diagrams. ü Bank volume (BV): is the volume of the natural insitu undisturbed material that is to be excavated. ü Loose volume (LV): The volume of the transported material, which has swelled due to the action of excavation and loading. In this state the same mass of material will occupy more space than in its bank volume. ü Compacted volume (CV): The final volume of the material after compaction. Compaction invariably causes a reduction in volume. INTRODUCTION TO MASS HAUL The terminology used in conjunction with mass-haul diagrams. Condition Representing Altered condition (m3) Soil type 1 m3 Bank Loose Compacted Sand Natural state 1 1,11 0,95 Loose 0,9 1 0,86 Compacted 1,05 1,27 1 Average soil Natural state 1 1,35 0,81 Loose 0,8 1 0,72 Compacted 1,22 1,29 1 Clay Natural state 1 1,43 0,9 Loose 0,7 1 0,63 Compacted 1,11 1,59 1 INTRODUCTION TO MASS HAUL The terminology used in conjunction with mass-haul diagrams. ü Shrinkage is the reduction of the volume of a material that has been excavated when it is used as fill in an embankment. ü A small proportion of this loss may be attributed to spillage during transport from the cut to the fill, but the main loss occurs during compaction because soil particles are packed together as voids are reduced and the density increase. ü This Shrinkage Factor (SF) must be determined for the material concerned and must be included in the calculations of the earthworks cost estimate and claims for payment. ü The factor is usually not applicable to rock but significant for most soils. INTRODUCTION TO MASS HAUL To illustrate the foregoing notes consider the following diagram. Bulking factor (1,11 to 1,43) Loose Volume Volume of material after excavation, to be transported Compaction factor (0,86 - 0,63) Bank Volume or In-situ volume. In place in cut or borrow pit Compacted Volume Shrinkage factor (0,9 - 0,95) Volume in place after compaction INTRODUCTION TO MASS HAUL ü Bulking Factor (BF) = Loose Volume (LV) / Bank Volume (BV) LV BF = BV ü Compaction Factor (CF) = Compacted Volume (CV) / Loose Volume (LV) CV CF = LV ü Shrinkage Factor (SF) = Compacted Volume (CV)/Bank Volume (BV) CV SF = BV INTRODUCTION TO MASS HAUL ü Bulking Factor (BF) = Bank Density (BD) / Loose Density (LD) BD BF = LD ü Compaction Factor (CF) = Loose Density (LD) / Compacted Density (CD) LD CF = CD ü Shrinkage Factor (SF) = Bank Density (BD) / Compacted Density (CD BD SF = BD INTRODUCTION TO MASS HAUL Therefore the Densities diagram: Loose Bulking factor Density (1,11 to 1,43) Compaction factor (0,86 - 0,63) Bank Density Compacted Density Shrinkage factor (0,9 - 0,95) INTRODUCTION TO MASS HAUL Swell ü Swell is the converse of shrinkage; ü Swell Factor (SF) is usually only applicable to rock where the bank volume of the rock prior to excavation is less than the final compacted volume of the broken rock in the embankment. ü This factor should also be included in costing calculations. ü Swell Factor (SF) = Compacted Volume (CV)/Bank Volume (BV) and is greater than 1 for rock. CV SF = BV INTRODUCTION TO MASS HAUL Haul ü Haul (the transportation of material) is the distance over which the material is moved. ü For cut to fill earthworks the distance hauled is measured along the centre line of the road. ü For material carted to the road from a borrow pit, or cut to spoil material hauled to a dumping site, haul is measured along the shortest route determined by the Engineer as being feasible and satisfactory. INTRODUCTION TO MASS HAUL Free haul ü Free haul is the distance specified in the contract documents over which the contractor is paid a specified price per m3 for excavating, hauling and dumping the material, irrespective of the distance involved (within the freehaul distance). ü For small works free haul is about 150 m and for large contracts the distance may exceed 500 m. ü If the actual haul distance exceeds free haul, this extra distance is called overhaul and the contractor is paid an additional rate for the overhaul INTRODUCTION TO MASS HAUL Overhaul ü Overhaul is measured only on the volume of material that must be carted over a distance greater than the freehaul distance. ü The contractor is paid additional money for overhaul beyond the freehaul distance. ü Measurement of overhaul is calculated by multiplying the volume of material carted by the distance hauled which gives a unit of m3.m or m3.km. ü The unit price of overhaul is based on the cost per m3.km of moving the material beyond the free haul distance. ü The length of measurement begins at the end of the free haul distance. Overhaul is listed as a separate item in the bill of quantities. INTRODUCTION TO MASS HAUL Economic haul ü Economic haul is when the cost of excavating from cut and hauling to fill is equal to the cost of borrowing and spoiling. ü When the haul distances are large, it is very often more economical to dump excavated material to waste and to borrow more convenient materials closer to the fill than to pay for expensive overhauling. ü On any given scheme, the economic haul distance will vary considerably, as it depends an the availability of suitable borrow materials and of nearby sites where excavated material can be dumped. INTRODUCTION TO MASS HAUL Consider Example 1 1. Plan View 2. Compacted Volumes: ─ Base = ─ Subbase = ─ SSG = 3. Number of Truck Loads: ─ Base = ─ Subbase = ─ SSG = INTRODUCTION TO MASS HAUL Consider Example 1 4. Subbase: ─ Bank Volume ─ Shrinkage Factor 5. Overhaul: ─ Base = ─ Subbase = ─ SSG = 6. Economic Haul Distance : ─ SSG = MASS-HAUL DIAGRAMS ü The Mass Haul Diagram (MHD) is a graphical tool used by planners and designers to determine the most economical balance of excavation and embankment fill and therefore the selection of the vertical alignment of the roadway. ü The MHD is used in costing because once the formation level has been fixed, the cost of earthworks can be arrived at. MASS-HAUL DIAGRAMS ü To enable the contractor to have knowledge of the amount and extent of free haul and overhaul on a project so that he can submit an accurate bid, it is common practice to include a mass-haul diagram in the plans for the scheme. ü This diagram represents graphically the amount of earthworks involved in the road works and the manner in which they may be most economically handled. ü It shows the accumulated volume at any point along the proposed centreline and from this the economical directions of haul and the positioning of borrow pits and spoil heaps can be estimated. MASS-HAUL DIAGRAMS Characteristics of a mass haul curve: ü The ordinate at any station along the curve represents the earthwork accumulation to that point. ü A rising curve at any point indicates an excess of excavation (cut) over embankment fill material at this point. A falling curve indicates the fill. ü A steeply rising or falling curve indicates heavy cuts or fills. ü Flat curves show that the earthwork quantities are small. MASS-HAUL DIAGRAMS Characteristics of a mass haul curve: ü The maximum ordinate (+) indicates a change from cut to fill as one proceeds along the centreline from an arbitrarily assumed origin. ü The minimum (-) ordinate represents a change from fill to cut. ü The shapes of the loops indicate the direction of haul. A convex upwards loop shows that the haul from cut to fill is to be from left to right, while a concave upwards loop indicates that the haul is to be from right to left. MASS-HAUL DIAGRAMS Characteristics of a mass haul curve: ü The ordinates of a curve are plotted from cut volumes and adjusted fill volumes ü Any line parallel to the base line which cuts off a loop intersects the curve at two points, amount of cut is equal to the fill between these two points. ü Such a line is called a ‘balancing line' and the intersection points are called 'balancing points'. MASS-HAUL DIAGRAMS Characteristics of a mass haul curve: ü The area between a balance line and the mass-haul curve is a measure of the haul (in m3.km) between the balance points. ü If this area is divided by the maximum ordinate between the balance line and curve, the value obtained is the average distance that the cut material must be hauled in order to make the fill. ü This distance can also be estimated by drawing a horizontal line through the mid-point of this maximum ordinate until it intersects the loop at two points; ü the length of this line is very close to the average haul distance when the shape of the loop is 'smooth'. MASS-HAUL DIAGRAMS Characteristics of a mass haul curve: ü Balance lines need not be continuous; the vertical break between any two balance lines merely indicates unbalanced earthwork between two adjacent points of termination of the lines. ü Balance lines should never overlap, as this means using the same part of the mass diagram twice. MASS-HAUL DIAGRAMS The choice of a balance line is always determined by economic considerations and the following factors should be borne in mind. ü The use of more than one balance line will result in waste and borrow at intermediate points, which will involve increased excavation and transportation. ü Short unconnected balance lines are usually more economical than one continuous line, particularly if each is shorter than the free haul distance, because no overhaul cost will be involved. ü It is cheaper (for the contractor) to haul on downgrades than on upgrades and it is therefore better to waste on hills and borrow in valleys. MASS-HAUL DIAGRAMS The choice of a balance line is always determined by economic considerations and the following factors should be borne in mind. ü The free haul limit should be exceeded as little as possible. ü The haul is given by the area between the curve and the balance line and therefore if the haul can be minimised the overhaul will be at a minimum for the most economical solution, ü but in minimising the area large amounts of waste and borrow result at intermediate points. LIMITATIONS OF THE MASS-HAUL DIAGRAM ü Though the mass haul diagram (MHD) is a good guide and an invaluable estimating tool, quantities and distances could be misleading and the results should not be regarded as perfect Some of the more common limitations of MHD are: ü The MHD is limited to linear construction. ü If the project becomes relatively wide with respect to its length, movement of earth may be transverse as well as longitudinal, which is not indicated on the MHD. ü The MHD is capable of analysing only the potential of balancing within any one phase of the project. ü It cannot deal with two or more adjacent projects simultaneously. LIMITATIONS OF THE MASS-HAUL DIAGRAM ü The MHD assumes that all material excavated is acceptable for embankment (fill). This is not necessarily true, but can be taken care of by eliminating all unacceptable material quantities from the earthwork summary sheet. ü The MHD is applicable to projects on which the balancing of earthwork is desirable. This is normally the case because balancing eliminates double handling. ü However, it is possible that a short distance from an acceptable borrow pit to an embankment section will make it economically wise to use the borrow pit in lieu of a long balancing operation. EXAMPLE OF MASS HAUL DIAGRAM ü The table below gives the ground levels GL and finished road levels FRL at chainages measured along a short road. ü Calculate the volumes of cut and fill earthworks, given that the layerworks comprises three layers of thickness 150 mm each. ü The shrinkage factor is estimated to be 94%. ü Calculate and plot the mass haul diagram and state whether the earthworks are balanced or not. ü As payment is by compacted cubic metre, calculate the MHD in terms of compacted volume. ü What is the approximate average haul distance? EXAMPLE OF MASS HAUL DIAGRAM Cross- Sum of cut Ground Finished Formation Depth of Average Length of Volume of Volume of Adjusted Chainage section and fill level road level level cut area m2 section m fill m3 cut m3 cut vol area vols Ch GL FRL FL GL - FL m2 m2 m m3 m3 m3 m3 0 30.05 30.50 100 31.70 31.50 200 32.55 32.50 300 33.05 33.25 400 34.20 33.85 500 34.00 34.30 600 34.15 34.60 700 33.55 34.75 800 32.90 34.75 900 33.05 34.60 1000 33.40 34.30 1100 33.15 33.85 EXAMPLE OF MASS HAUL DIAGRAM ü Thickness of the layer works = 3 ´ 150 mm = 450 mm = 0,45 m ü Therefore the top of formation is 0,45 m below finished road level. ü The side slopes are at 1:2, meaning that the horizontal width of the slope is twice the height of the slope. EXAMPLE OF MASS HAUL DIAGRAM Cross- Ground Finished Formation Depth of Average Length of Volume of Volume of Adjusted Sum of cut Chainage section level road level level cut area m2 section m fill m3 cut m3 cut vol and fill vols area Ch GL FRL FL GL - FL m2 m2 m m3 m3 m3 m3 0 30.05 30.50 30.05 100 31.70 31.50 31.05 200 32.55 32.50 32.05 300 33.05 33.25 32.80 400 34.20 33.85 33.40 500 34.00 34.30 33.85 600 34.15 34.60 34.15 700 33.55 34.75 34.30 800 32.90 34.75 34.30 900 33.05 34.60 34.15 1000 33.40 34.30 33.85 EXAMPLE OF MASS HAUL DIAGRAM Cross- Ground Finished Formation Depth of Average Length of Volume of Volume of Adjusted Sum of cut Chainage section level road level level cut area m2 section m fill m3 cut m3 cut vol and fill vols area Ch GL FRL FL GL - FL m2 m2 m m3 m3 m3 m3 0 30.05 30.50 30.05 0.00 100 31.70 31.50 31.05 0.65 200 32.55 32.50 32.05 0.50 300 33.05 33.25 32.80 0.25 400 34.20 33.85 33.40 0.80 500 34.00 34.30 33.85 0.15 600 34.15 34.60 34.15 0.00 700 33.55 34.75 34.30 -0.75 800 32.90 34.75 34.30 -1.40 900 33.05 34.60 34.15 -1.10 1000 33.40 34.30 33.85 -0.45 1100 33.15 33.85 33.40 -0.25 EXAMPLE OF MASS HAUL DIAGRAM EXAMPLE OF MASS HAUL DIAGRAM Area of rectangle + area of triangle ´ 2 (as the triangles are the same) = (12 ´ h) + (2 ´ h ´ h ´ ½) ´ 2 = 12 h + 2 h2 = h(12 + 2h) EXAMPLE OF MASS HAUL DIAGRAM Area of rectangle + area of triangle ´ 2 (as the triangles are the same) = (12 + 1,5 + 1,5) ´ d + (2 ´ d ´ d ´ ½) ´ 2 = (15 ´ d) + 2 d2 = d(15 + 2d) EXAMPLE OF MASS HAUL DIAGRAM Cross- Ground Finished Formation Depth of Average Length of Volume of Volume of Adjusted Sum of cut Chainage section level road level level cut area m2 section m fill m3 cut m3 cut vol and fill vols area Ch GL FRL FL GL - FL m2 m2 m m3 m3 m3 m3 0 30.05 30.50 30.05 0.00 0 5.30 100 31.70 31.50 31.05 0.65 10.60 9.30 200 32.55 32.50 32.05 0.50 8.00 5.94 300 33.05 33.25 32.80 0.25 3.88 8.58 400 34.20 33.85 33.40 0.80 13.28 7.79 500 34.00 34.30 33.85 0.15 2.30 1.15 600 34.15 34.60 34.15 0.00 0.00 -5.06 700 33.55 34.75 34.30 -0.75 -10.13 -15.42 800 32.90 34.75 34.30 -1.40 -20.72 -18.17 900 33.05 34.60 34.15 -1.10 -15.62 -10.71 1000 33.40 34.30 33.85 -0.45 -5.80 -4.46 1100 33.15 33.85 33.40 -0.25 -3.13 EXAMPLE OF MASS HAUL DIAGRAM Use the Method of End Areas (refer to Appendix 3) to calculate Earthworks Volumes Cross- Sum of cut Ground Finished Formation Depth of Average Length of Volume of Volume of Adjusted Chainage section and fill level road level level cut area m2 section m fill m3 cut m3 cut vol area vols Ch GL FRL FL GL - FL m2 m2 m m3 m3 m3 m3 0 30.05 30.50 30.05 0.00 0 5.30 100 530 498 498 100 31.70 31.50 31.05 0.65 10.60 9.30 100 930 874 1372 200 32.55 32.50 32.05 0.50 8.00 5.94 100 594 558 1930 300 33.05 33.25 32.80 0.25 3.88 8.58 100 858 806 2736 400 34.20 33.85 33.40 0.80 13.28 7.79 100 779 732 3468 500 34.00 34.30 33.85 0.15 2.30 1.15 100 115 108 3576 600 34.15 34.60 34.15 0.00 0.00 -5.06 100 -506 3070 700 33.55 34.75 34.30 -0.75 -10.13 -15.42 100 -1542 1528 800 32.90 34.75 34.30 -1.40 -20.72 -18.17 100 -1817 -289 900 33.05 34.60 34.15 -1.10 -15.62 -10.71 100 -1071 -1361 1000 33.40 34.30 33.85 -0.45 -5.80 -4.46 100 -446 -1807 1100 33.15 33.85 33.40 -0.25 -3.13  EXAMPLE OF MASS HAUL DIAGRAM 4000 3000 2000 Sum of cut and fill vols 1000 0 0 100 200 300 400 500 600 700 800 900 1000 1100 -1000 -2000 -3000 MASS-HAUL DIAGRAMS Characteristics of a mass haul curve: 4000,000 2000,000 VOLUME( m3) 0,000 0 300 600 900 1200 1500 1800 2100 2400 -2000,000 -4000,000 -6000,000 -8000,000 CHAINAGE MASS-HAUL DIAGRAMS Consider Example 2 Attached to this example is a mass haul diagram for the bulk earthworks on a 3,0 km long road contract. The freehaul distance, in terms of the contract documents, is 500m. Material that must be carted beyond the freehaul distance is considered to be overhaul. Overhaul distance is measured to the nearest 0,001 km. 1. On the mass haul diagram determine and show clearly all the freehaul sections and the quantity at each section. 2. Determine the total volume of material to be carted from cut to fill within the freehaul range. 3. Calculate the quantity of overhaul at each section where they occur and give the total quantity of overhaul (m3.km). 4. Will there be any borrow or spoil? If so determine the quantities and the start and end chainages where these are required. All borrow pits and spoil areas are within the freehaul distance from the road. LAYER WORKS ü Layerworks can be defined as those layers lying above the formation level ü Selected sub-grade (usually one or two layers 100-150 mm thick) ü Sub-base (one or two layers 100-150 mm thick) ü Base (usually one layer 100-150 mm thick) LAYER WORKS ü Material constructing Layerworks must conform to the design requirements of that particular road. ü The design requirements are based on the ability to withstand loading from the volume and characteristics of the vehicular traffic expected to use the facility. ü the strength of the layers must increase towards the top of the road, as the effects of the wheel loads increase. ü The base is a very strong material and spreads the traffic loads so that the sub-base can carry them. ü The sub-base, in turn, spreads the loads still further so that the sub- grade can carry them. LAYERWORKS ü Layerworks comprising base, sub-base and selected sub-grade spread the traffic loads sufficiently so that the formation materials can carry them without being overstressed. Generally layer works are constructed using the following material types: ü Selected Sub-grade: fair quality natural soils and sands having low plasticity. If the material from cuts is suitable and there is a surplus after the fills are constructed this may be used. ü Sub-base: good quality natural or processed gravels, which may or may not be stabilised with small quantities of lime, cement or other agents. ü Base: suitably graded crushed rock (or high quality natural gravels on low trafficked roads). Refer to TRH 14: Guidelines for road construction materials, for full specifications of the materials that will make up satisfactory layerworks. LAYER WORKS The construction methods employed for layerworks on large projects using mainly mechanised methods are as follows: ü the correct volume of material necessary to achieve the final specified thickness after compaction is placed on the surface of the previously constructed and approved layer (all tests passed and signed for) this material is spread and shaped. ü The correct amount of water, as determined from the dry density/optimum moisture content test (method A7), is applied and thoroughly mixed through the material. ü Mixing is usually carried out by blading the material from side to side using a motor grader while the water is being applied with a water tanker. ü Mixing in this fashion also ensures reasonably uniform material in the layer. LAYERWORKS Correct volume of material is placed on a previously constructed layer LAYERWORKS The correct amount of water is added and thoroughly mixed through the material. LAYERWORKS Mixing is usually carried out by blading the material from side to side using a motor grader. LAYER WORKS The construction methods employed for layerworks ü The material is then spread and compaction with suitable rollers begins. ü During the early stages of compaction the grader continues to shape the layer until the shape and thickness are to specification. ü Additional water is sprayed onto the layer as necessary to maintain the soil moisture near optimum. ü When complete, the layer is checked by the contractor’s foreman for compliance to the specification (production control) and then by the client’s representative (acceptance control). LAYER WORKS the layer is checked for compliance to the specification CONSTRUCTION Cuttings and borrow pits ü Materials for construction are obtained from cuttings or from borrow pits. ü The vegetation must be cleared and the roots grubbed out and removed. ü Topsoil needs to be removed and stockpiled for later use. If the soil remaining is suitable, it can be excavated and loaded for transport to the fill or layer works where it is needed. ü Borrow Pits often have a top layer of soil that is not suited for the selected sub-grade or sub-base. ü This overburden has to be removed and stockpiled, so that the underlying gravel can be extracted. LAYERWORKS ü Gravels are often too dense for easy loading and are then ripped by bulldozer to loosen the gravel. ü Loading can then generally be done by front-end loader directly into trucks. ü As the final dimensions of the fills and layers are known and the soil characteristics are known, the volumes to be transported can readily be calculated. ü Note that excavation is in bank volume; transport is always in loose volume and placing, compaction and payment is measured in compacted volume. LAYERWORKS Transportation ü Transportation of materials must be done as efficiently as possible. ü Various machines used by contractors have different efficiencies for varying haul distances: eg. ü Wheel-loaders (front-end loaders) can be used for short hauls of up to about 50 m. ü Bulldozers are short-distance earthmovers, highly efficient when dozing distances of 30 m to 200 m. ü Scrapers are efficient medium-haul machines in soft soils and in reasonably flat terrain. They are efficient up to hauls of about 1 km. ü Front-end loader - truck combinations work well for hauls of about 1 km LAYERWORKS Transportation ü Note that the cost of haulage by the different machines depends on quantity as well as haul distance. ü For example, if a very small quantity of material is to be moved say 500 m, it may well pay the contractor to move this with a front-end loader that is available, rather than to hire a scraper for half a day, just because the scraper is more efficient than the loader for that particular distance. ü A contractor must keep an open mind and must be flexible, always carefully costing every operation. LAYERWORKS Compaction objectives There are three main objectives in soil compaction: a) To reduce the void ratio and the permeability of the soil this will also reduce subsequent changes in moisture content. b) To increase the shear strength and the bearing capacity of the soil. c) To make the soil less susceptible to subsequent volume changes and therefore to reduce settlement under the influence of traffic induced vibration. ü For every compactive effort or energy level chosen for compaction, there is an optimum moisture content at which the density peaks. Refer to the figure below: LAYERWORKS ü The Optimum Moisture Content (OMC) is an important characteristic of a soil, as it gives the amount of water that should be present in the soil during compaction, so that the maximum density can be obtained. ü The graph shows how the density of one particular soil varies as the soil moisture at which it is compacted, varies. ü At low soil moisture the density is low. The density increases to a maximum as the optimum moisture content is reached and then reduces as the soil moisture is further increased. ü The graph clearly shows the importance of control of the soil moisture during compaction. LAYERWORKS Optimum Moisture Content (OMC) and Maximum Dry Density (MDD) LAYERWORKS ü The OMC of a soil can be found in the field by firmly squeezing a handful of moist soil. If the soil ball so formed crumbles easily, the moisture content is below OMC. ü If the soil ball is firm the moisture content is close to OMC. ü If the soil ball is wet or glistens with water, the moisture content is above OMC. ü The behaviour of the soil under the compactor should be observed to confirm the correctness of the moisture content of the soil being compacted. If dry, the soil stays loose or is dusty; if wet, the soil moves excessively as the roller passes over it. ü When at OMC, the soil moves a small amount as the roller passes. COMPACTION Methods of Compaction ü Static weight ü Impact ü Vibration ü Manipulation or kneading ü Percolation COMPACTION Compaction process The principles of compaction are simple and are: a) wet the soil or gravel to near optimum moisture content. b) spread and level the material to the correct shape. c) compact the materials efficiently and economically. COMPACTION Factors that influence the compaction process are: a) Material characteristics, i.e. sand or clay; uniform or well graded; plastic or non-plastic. b) The maximum state of compaction attainable for the soil for a particular energy input. c) Maximum amount of compaction attainable under field conditions. d) Moisture content at the time of placing. e) Type of compaction plant being used. COMPACTION Material characteristics ü The compactability of any soil depends on the moisture content, plasticity, particle shape and particle size distribution. ü The shear strength of cohesive fine-grained soils depends on the cohesion. In order to increase the density of the soil, the shear strength must be overcome so that the particles can be pushed closer together. ü High-pressure impact loads are best at increasing the density of such soils. ü Kneading rollers that manipulate the soil can also quickly achieve improved densities. LAYER WORKS Material characteristics ü The shear strength of non-cohesive coarse-grained gravels depends on inter-particle friction. ü The compactability of such gravels is dependent upon the particle shape and surface smoothness and on the grading. ü Well-graded gravel, with a smooth grading curve, is easier to compact than a poorly-graded gravel with steps or gaps in the grading curve. COMPACTION Material characteristics ü The shear strength of non-cohesive coarse-grained gravels depends on inter-particle friction. ü The compactability of such gravels is dependent upon the particle shape and surface smoothness and on the grading. ü Well-graded gravel, with a smooth grading curve, is easier to compact than a poorly-graded gravel with steps or gaps in the grading curve. ü Compactability of mixed fine and coarse-grained soils depends on the mixture and then to a greater or lesser extent on the cohesion, particle size and shape and grading of the soil. COMPACTION Material characteristics ü compact from the top of the layer downwards. ü the layer thickness must be limited, so that the whole layer thickness will be compacted. ü Thick layers often are much looser at the bottom, as the rollers cannot reach that depth COMPACTION Moisture content ü The moisture density test measures the optimum moisture content. ü Once the in-situ moisture content of the soil or gravel in the layer has been measured, the additional water that needs to be added to raise the soil moisture to OMC can be calculated easily. Consider an example the measurements from a moisture content test are: Mass of wet soil = 967 g Mass of dry soil = 880 g Mass of water = 87 g COMPACTION Moisture content Moisture content = ü If the OMC was 12%, how much water should be added to the soil? ü OMC = 12% and soil moisture is 9,89%, hence 12 – 9,89 = 2,11% should be added. ü However, on a construction site one cannot tell the operator of the water bowser just to add 2,11% to the layer. ü He must be told how many bowser-loads are needed. This needs additional calculation. COMPACTION Moisture content ü Moisture contents are always given as a percentage of the soil mass. In order to add a certain percentage of water, therefore, the soil mass or its density must be known. Continuing the example above: from the moisture: density test the maximum density was 2 000 kg/m3. Note that the soil density used to calculate the water needed is the maximum density after compaction, not the loose soil density. Note also that the density is the mass of 1 m3 of compacted soil. Do the calculation for 1 m3. COMPACTION Moisture content ü Water to be added (litres) per ü For the above example, the density of the soil is 2 000 kg/m3, so the water to be added is: ü Water to be added per cubic metre litres/compacted m3 ü From the water to be added per compacted cubic metre and the dimensions of the layer, the water needed for the section of layerwork can be calculated. LAYERWORKS ü Layerworks comprises the construction of the selected sub-grade, sub- base and base. ü Most of the materials for these layers will come from borrow pits. ü Base may come from borrow (natural gravel base) or may comprise processed material from a rock crusher (crusher run base). ü The quantity of material for one layer must be calculated, correctly ordered, transported, dumped, spread, watered, mixed and compacted. ü Using known productivities the duration, resources required and hence the cost, of every activity can be calculated. LAYER WORKS The following example illustrates some of the principles involved. ü Sub-grade layer width is 12,0 m, layer thickness is 150 mm. 𝐶𝑜𝑚𝑝𝑎𝑐𝑡𝑒𝑑 𝑣𝑜𝑙𝑢𝑚𝑒 𝑝𝑒𝑟 𝑚𝑒𝑡𝑟𝑒 𝑙𝑒𝑛𝑔𝑡ℎ = 12 ∗ 0,150 = 1,80 𝑚3 ü If the compaction factor for this particular material is 0,75, then the loose volume of material to be transported is: 𝐶𝑜𝑚𝑝𝑎𝑐𝑡𝑒𝑑 𝑣𝑜𝑙𝑢𝑚𝑒 𝐿𝑜𝑜𝑠𝑒 𝑣𝑜𝑙𝑢𝑚𝑒 = 𝑐𝑜𝑚𝑝𝑎𝑐𝑡𝑖𝑜𝑛 𝑓𝑎𝑐𝑡𝑜𝑟 1,80 = 0,75 = 2,40 𝑚3 LAYERWORKS ü Knowing the volume of loose material transported, the spacing of the heaps dumped by the chosen transport can be found. ü For example, if trucks of 10 m3 capacity are to be used, the spacing of the loads dumped on the road should be: 10 𝑆𝑝𝑎𝑐𝑖𝑛𝑔 = = 4,1667 𝑚 2,40 !" ü [Check: 10 m3 at 4,1667 m spacing = = 2,40𝑚' /𝑚 run, which is #,!%%& correct] LAYER WORKS ü If the contractor has a large loader (CAT 950F) available and wishes to haul the sub-grade material from the borrow pit with 10 m3 trucks: ü Bucket capacity of a CAT 950F front end loader is 2,55 m3. ü Using a fill factor of 95%, the actual bucket capacity becomes = 2,55 ∗ 0,95 = 2,42 𝑚'. ü Cycle time of the loader (dig, move, dump in truck, move) is estimated at 0,55 minutes; correction for inconsistent operation is +0,04 minutes, giving total cycle time of 0,59 minutes. LAYER WORKS ü Productivity of the loader is therefore (for 60 minute hour): 60/0,59 = 101 𝑐𝑦𝑐𝑙𝑒𝑠 𝑜𝑟 𝑙𝑜𝑎𝑑𝑠, 𝑎𝑡 2,42𝑚' 𝑝𝑒𝑟 𝑙𝑜𝑎𝑑, = 101 ∗ 2,42 = 244𝑚' 𝑝𝑒𝑟 ℎ𝑜𝑢𝑟. ü However, no operator can work continuously, hour after hour, without a break. ü The normal allowance for operator comfort breaks is 10 minutes per (" hour, giving a time efficiency = = 0,83 𝑜𝑟 83%. %" ü For this example, we estimate the time efficiency at 80% (not 83% as recommended). ü Hence loader productivity = 244 ∗ 0,80 = 195 𝑚' 𝑝𝑒𝑟 ℎ𝑜𝑢𝑟. [Source: Caterpillar Performance Handbook, chapter 12] LAYER WORKS ü Using 10 m3 trucks means that the loader can load !)( = 19,5 𝑡𝑟𝑢𝑐𝑘𝑠 𝑝𝑒𝑟 ℎ𝑜𝑢𝑟. !" ü The number of trucks needed for the operation can then be calculated, if the haul cycle time is known or can be worked out. ü For example, if the round trip of a truck is estimated to be 20 minutes (load, drive, dump, return), then (again using a 50 minute hour to allow for driver breaks) 50 = 2,50 𝑡𝑟𝑖𝑝𝑠 𝑐𝑎𝑛 𝑏𝑒 𝑚𝑎𝑑𝑒 𝑝𝑒𝑟 ℎ𝑜𝑢𝑟, 20 2,50 ∗ 10 = 25,0𝑚' 𝑐𝑎𝑛 𝑏𝑒 𝑡𝑟𝑎𝑛𝑠𝑝𝑜𝑟𝑡𝑒𝑑 𝑝𝑒𝑟 𝑡𝑟𝑢𝑐𝑘 𝑝𝑒𝑟 ℎ𝑜𝑢𝑟. LAYER WORKS !)( ü This implies that = 7,8 𝑡𝑟𝑢𝑐𝑘𝑠 are needed to keep up with the loader. *( ü A spread of 8 trucks and one loader is then a good choice. ü The productivity of the chosen spread for a 9¼ hour day would 195 ∗ 9,25 = 1803,75𝑚' 𝑠𝑎𝑦 1800. ü LAYERWORKS ü For continuity of work, the sub-grade compaction team should be able to handle 1800 𝑚' loose per day. Converting this to compacted volume gives: 𝐶𝑜𝑚𝑝𝑎𝑐𝑡𝑒𝑑 𝑣𝑜𝑙𝑢𝑚𝑒 = 𝐿𝑜𝑜𝑠𝑒 𝑣𝑜𝑙𝑢𝑚𝑒 / = 1800 / (1,40) = 1 285,7𝑚' = 1285,7/1,80 = 714,3 𝑚𝑒𝑡𝑟𝑒𝑠 𝑜𝑓 𝑠𝑢𝑏𝑔𝑟𝑎𝑑𝑒 𝑝𝑒𝑟 𝑑𝑎𝑦. ü This length is too much for one team, as the grader travel time from one end to the other while mixing or spreading or cutting level will be too long. Depending on the size and capacity of the graders, disc harrows, water bowsers and rollers available, the contractor would give the work to two or three compaction teams. EARTHMOVING EQUIPMENT EARTHMOVING EQUIPMENT