Soil - Part 01 and 02 PDF

# SOIL The soil referred to in this study is the material used to build with, or on that acts in combination with other forces of nature to make structures and land forms. The material classified under the field of Geotechnics. Soil may be defined as the accumulation of unconsolidated sediments...

# SOIL The soil referred to in this study is the material used to build with, or on that acts in combination with other forces of nature to make structures and land forms. The material classified under the field of Geotechnics. Soil may be defined as the accumulation of unconsolidated sediments and deposits of solid particles as a result of the integration of rocks. On the other hand rocks may be defined as natural aggregate of minerals connected by strong bonding of attractive forces classified as consolidated materials. ## Scientifically, most of the non-organic materials identified as soil has originated from rocks as the parent material. Rock types are classified into three major classes in accordance with their own origin or method of formations: 1. Igneous rock 2. Sedimentary rock 3. Metamorphic rock ## Igneous Rock is the result from the cooling and hardening of molten rock called magma that has originated from deep within the earth. The rapid cooling of molten magma called lava which was blown up by volcano solidifies into small crystal and possesses fine interlocking texture. The molten lavas that rapidly cooled on the earth surface are volcanic rock types called basalts, rhyolites and andesites. The molten rocks that were trapped deep below the surface of the earth, cooled slowly, and the mineral components forms into large interlocking crystals and coarse textured rocks classified as plutonic types of which, granite is the most common. ## Sedimentary Rocks are formed from accumulated deposits of soil particles or remains of certain organisms that have harden by pressure or cemented by materials. Sedimentary rocks include limestone and dolostone, shale, conglomerate and breccia. Shales are formed from deposited clay and silt particles. Sandstone is predominantly quartz cemented together with mostly silica, but sometimes with calcium carbonate of iron compounds. Conglomerate and breccia are similar to sandstone. ## Metamorphic Rocks are rocks resulted from metamorphism due to changes in temperature, pressure and plastic flow, changing the original rock structure and mineral composition of the rock. Under this processes, limestone is change to marble, sandstone to quartzite, shale to slate or phylite ## Categories of Soil Soil can be divided into two categories, namely: 1. Residual Soil 2. Transported Soil ## Residual Soil or Sedimentary Soil is formed from the weathering of rocks or accumulation of organic materials remained at the location of their origin. Weathering process may be attributed to mechanical or chemical and solution weathering. ## Mechanical weathering refers to physical disintegration due to effects of wind, rain, running water or tectonic forces (earthquake). ## Chemical and solution weathering is decomposition of rock due to chemical reactions that occur as a result of exposure to atmosphere, temperature changes, reaction with water or other materials. Likewise, climate, topography, drainage and vegetative cover have great influences on the chemical or solution weathering process. ## Transported Soils are those materials transported from their place of origin. Transportation may result due to the effects of gravity, wind, water, glaciers of human activity. ## Types of Soil The major categories of soils are gravel, sand, silt and clay. Gravel and sand are universally known as coarse grain soil because of their individual particles that are large enough to distinguish without magnification. On the other hand, silt and clay are considered fine grain soil because of their tiny particles. ## Particles larger than gravel are commonly referred to as cobbles or boulders. Thus, it is apparent that particles size alone is the basis of classifying sand, gravel, cobbles and boulders. On the other hand, fined grain soil is classified as either silt or clay not on the basis of particle size but on the plasticity or nonplasticity of the materials. ## Over a varying range of moisture content, clay soil is plastic and sticky. When dried, possesses strong resistance to crushing\. Silt soil has little or no plasticity and when dried has very little or no strength at all. If small amount of moist silt sample is shaken on the palm of the hand, water will appear on the surface of the sample but disappear when shaking stops. This phenomenon is called dilatancy. Sand mixed with silt is classified as silty sand, whereas, silt and clay mixture with mostly clay is called silty clay. ## Characteristics of Soil Soil consists largely of minerals formed by disintegration or decomposition of rocks. Disintegration or decomposition into soil may be caused by the action of water or other natural forces like temperature change, or by plant or animal life. ## Soil contains humus and organic acids resulted from decay of vegetation. All soils contain water, either free or absorbed in varying contents. Soil in most cases, are blend or mixture of particles of many sizes, shapes, and parent rock materials making its behavior very difficult to predict. It is very common to encounter five to ten or more distinct types of soil along a kilometer of road. Change of soil types at frequent intervals has become a rule rather than exemption. Behavior of soil mass could be determined based on the characteristics of individual soil particles such as: 1. Grain size 2. Grain shape 3. Surface texture and electrical surface charges, resulted from chemical composition and molecular structures. Regardless of the differences in grain sizes as classified, the common objective is to establish a basis for relating the particle size to soil behavior. ## The General Characteristics and Classification of soil particles: 1. Gravel 2. Coarse Sand 3. Fine Sand 4. Silt Grain 5. Clay 6. Colloidal Clay ## Gravel consist of rock fragments more or less rounded by water action or abrasion classified according to the following types: a) Quartz is the hardest of common rock forming mineral. b) Well Rounded Pebbles and Boulders- those that undergone long period of wear that become almost quartz. c) Slightly Worm Gravel is rough and angular including other materials or rocks like granite, schist, basalt or limestone ## Fine Sand has particles that are more angular than the coarse and fine sand particles. ## Coarse Sand is usually rounded like gravel with which it is found and generally contains the same materials. ## Silt Sand is similar to fine sand with the same mineral composition. They are found as rock flour in glacial moraines. It could be produced by chemical decay. Occasionally, silt contains: 1. Pumice 2. Loess 3. Materials foreign to the associated sand. The presence of silt in fine soil could be detected by its grittiness when small amount is bitten between the teeth. ## Clay is plate like, scale like, or rod like in shape as a result of chemical weathering. Because of their smaller sizes, its performance is influenced by moisture and surface chemistry. ## Colloidal clay is a finer clay particle that remains suspended in water and does not settle under the force of gravity. ## Coarse Grain Materials. For most purposes, coarse grain materials are considered satisfactory construction material. On the other hand, silty soil will create problems in areas where the ground has moisture movement due to capillary action. Soil that contains clay would be troublesome, making the design and construction more difficult. As a rule of thumb, soil with clay should not be used closer to the roadway surfaces. ## Important Grain Shape Characteristics 1. Rounded particles extracted from the stream that has undergone wear, are considered strong materials. 2. Flat and flaky particles that were not subjected to wear, are weak and variable that is not suitable for various used. 3. Angular or roughly cubical shape particles produced from crushing strong and tough rocks, increases the resistance of soil mass to deformation when subjected to load, due to individually interlocking grains. 4. Generally, the rounded particle has the tendency to roll over each other when subjected to load. ## Properties of Soils Soil deposit consists of solid particles and void spaces between particles, either partially or completely filled with water. Void spaces not completely filled with water, are either filled with air or other gases. Therefore, soil deposits are composed of solid, liquid and gas. ## Engineers are interested to know the properties of soil deposit, specially, the strength and compressibility ,because they are necessary in determining the bearing capacity and stability of the foundation. Strength and compressibility of the soil is directly related to: 1. Soil density weight per unit volume. 2. Water content of the soil. 3. Void ratio. 4. Degree of saturation. ## Weight and Volume Relationship Soil is an assemblage of particles, and thus there are separate volumes of solid and void. The voids are occupied with air and water. | | | | | | | | :---: | :----------- | :--: | :------------- | :--: | :-------------------- | | V | Air | W | 0 | V | Air | | V | Water | W | W | V | Water | | V | Solid | W | W | V | Solid | | | | | | | | | | | Wt | | Vv | Total Volume | | | | | Weight of | | | | | | | Air = 0 | | | | | | | Weight of | | | | | | | Water = Ww | | | | | | | Mass of | | | | | | | water = Mw | | | | | | | Weight of | | | | | | | solid = Ws | | | | | | | Mass of | | | | | | | solid = Ms | | | | | | | | | | | | Tree phase model | | | | | ## Porosity and Void Ratio Relationship ### Porosity Volume of Void ---------------------- Total Volume Vv - Va + Vw ---------------------- V ------- e n = ------- 1 + e | | | | :----: | :----: | | 1.0 | n | | | | | | 1 - n | | | Solid | | | Void = | | | Air + Water | ### Void Ratio Volume of void ---------------------- Volume of solid Vv - Va + Vw ---------------------- Vs n --- e = ------- 1 - n | | | | :----: | :----: | | 1 + e | e | | | | | | 1.0 | | | Solid | | | Void = | | | Air + Water | ## Water Content The water content for completely dry soil is 0% and normally up to several tens of percentages for fully saturated soils. However, the value may go up to more than 200% for highly open-structured clay formed under a marine environment and for organic soils as unusual cases. weight of water ---------------------- Weight of solid/dry Ww = ------ x 100 Ws ## Degree of Saturation The S value changes from 0% for completely dry soil conditions to 100% for fully saturated soil. The soils with 0 < S < 100% are called partially saturated soils. Note that on many occasions, “saturated" soils are interpreted as "fully saturated" without spelling out “fully”. Volume of water ---------------------- Volume of void Vw = ------ x 100 Vv a NOTE: V₂ = 0 if S=1 ## Total Unit Weight Total Weight ---------------------- Total Volume W = ------- V Ws + Ww ---------------------- Vs + Vw + Va ## Dry Unit Weight weight of solid ---------------------- Total volume Ws -------- V GsYw --------- Ya = ------- 1 + e Ym --------- Ya = ------- 1 + ω Note that ya is not necessarily physical dry unit weight of soils; rather, it is treated as a case by mathematically removing water while maintaining constant total volume V without shrinkage, which takes place during the physical drying process. ## Moist Unit Weight (Bulk Unit Weight) (Gs + Se)Yw -------- Ym = ------- 1 + e Total weight ---------------------- Total volume W = ------- V Ws + Ww ---------------------- Vs + Vw + Va ## Saturated Unit Weight Wsat -------- Ysat = -------- Vtotal (Gs + e)Yw -------- = ------- 1 + e ## Bouyant Unit Weight Yb = Ysat - Yw Yb = (Gs - 1)Yw ---------------------- 1 + e ## Zero Air Voids Unit Weight (applied if saturated Gsw -------- Yzav = ------- 1 + ωGς ## Air Void Ratio Avr = n (1 - S) ## Critical Hydraulic Gradient icr = Yb ------- Yw = Gs - 1 -------- 1 + e ## Specific Gravity of Solids 1 ------- Gs = ---------------------- 1 SR SL -------- 100 ## Shrinkage Ratio 1 m2 ----- SR = -------- Pw V2 ## Relative Compaction R = Yd (field) ---------------------- Yd (max) x 100 ## % Compaction Dry density of soil ---------------------- Maximum dry density x 100 ## Suitability Number 3 ------- SN = 1.7 + ------- √D50² 1 ------- + ------- D20² 1 ------- D10² ## Sorting Coefficient So = √D75 ------- D25 | Suitability no. | Rating as backfill | | :------------- | :----------------- | | 0 - 10 | Excellent | | 10 - 20 | Good | | 20 - 30 | Fair | | 30 - 50 | Poor | | > 50 | Unsuitable | ## Relative Density of granular soils Compaction is the process of increasing the density of soil by packing the particles closer together with a reduction in the volume of air; there is no significant change in the volume of water in the soil. 1 ------- Dr = ------- emax - e 1 ------- Ydmin = ------- 1 Yd 1 ------- emax - emin Where: emax = void ratio of the soil in loosest state emin = void ratio of the soil in densest state e = void ratio of the soil deposit (in-situ state) Ydmax = dry unit weight in densest state Ydmin = dry unit weight in loosest state Ya = dry unit weight (in-situ state) | Relative density (%) | Description of Soil Deposit | | :------------------- | :-------------------------- | | 0 - 15 | Very Loose | | 15 - 50 | Loose | | 50 - 70 | Medium Dense | | 70 - 85 | Dense | | 85 - 100 | Very Dense | ## MASS DENSITY, p (RHO) - THE DENSITY OF SOIL IS ITS MASS PER UNIT OF VOLUME. p = mass of soil, M ---------------------- Volume, V ## UNIT WEIGHT OR SPECIFIC WEIGHT y = weight of soil, W ---------------------- Volume, V ## SPECIFIC GRAVITY Pliquid ------- S = ------- Pwater Yliquid -------- Ywater For water at 4 °C y = 62.4 lb/ft³ = 9.81 kN/m³ p= 1.94 slugs/ft³ = 1000 kg/m³ ## Conversion of Units 1 kN = 1000 N 1 kg = 9.81 N 1 kg = 2.205 lbs. 1 kg = 1000 g ## Atterberg's Limits When clay particles are in a large amount of water, it is like a lean soup (liquid) and, at a slightly drier state, it becomes like a soft butter (plastic). At a further dried stage, it behaves like a cheese (semi-solid). At a very dry stage, it is like a hard candy (solid). | | | | | | :------------------------------- | :---------------------------- | :---------------------------- | :---------------------------- | | Solid phase (Hard candy) | Semi-solid phase (Cheese) | Plastic phase (Soft butter) | Liquid phase (Lean soup) | | | | | | | Dry | Shrinkage Limit | Plastic Limit (PL) | Liquid Limit (LL) | | | | | | | PI = LL - PL | | | | ## II. Types of Indices ### PLASTICITY INDEX PI = LL - PL ### LIQUIDITY INDEX ω - PL -------- LI = ------- LL - PL | LI | | | | :-------------- | :------------- | :-------------------------------------------------------------------------------------------------------------- | | LI < 0 | Brittle Solid | High strength, brittle (sudden) fracture is expected | | LI < 1 | Plastic | Intermediate strength, soil, deforms like a plastic material | | LI > 1 | Liquid | Low strength, soil deforms like a viscous fluid | ## DESCRIPTION OF SOIL BASED ON PLASTICITY INDEX | PI | Description | | :--- | :-------------- | | 0 | Nonplastic | | 1 - 5 | Slightly Plastic | | 5 - 10 | Low Plasticity | | 10 - 20 | Medium Plasticity | | 20 - 40 | High Plasticity | | > 40 | Very High Plasticity | Atterberg's limit are also used to asses the potential swell of given soil. | LL | PI | Potential swell classification | | :--- | :-- | :--------------------------- | | < 50 | < 25 | Low | | 50 - 60 | 25 - 35 | Medium | | > 60 | > 35 | High | ## CONSISTENCY INDEX LL - ω -------- CI = ------- LL - PI ## FLOW INDEX ω1 - ω2 -------- FI = ------- log (N2/N1) Default: N₁ = 15 blows; N2 = 25 blows ## TOUGHNESS INDEX TI = PI -------- FI ## III. Types of Limits ### LIQUID LIMIT A portion of the cap is filled with a thoroughly mixed wet clay specimen, and a groove is cut with a special grooving tool on the center portion of the specimen. The cranking handle, which lifts and drops the cup, is then rotated with two revolutions per second until the opening the groove closes with 13mm (1/2 in.) length ``` Groove ------- Specimen ------- Cup ------- 10 mm Hard base ``` <br /> &#x20; Front view <br /> &#x20; Top view <br /> Groove width at top = 11 mm Groove width at bottom = 2 mm Groove height = 8 mm The number of revolutions (blow counts) is recorded, and the water content at this stage is measured. Several trials with slightly different (usually a few percentages) water content specimens are performed. LL is then defined as the water content with 25 blows in the flow curve. ### PLASTIC LIMIT A PL test is run in a more primitive way (ASTM D 4318). A drier specimen is rolled into a thread by human palms on a glass plate. PL is defined as the water content at which a rolled thread just crumbles with 3 mm (1/8 in) diameter. ### SHRINKAGE LIMIT where: Mi - Mf ------- SL = ------- Mf x 100 - ( (Vi - Vf)/Mf (pw) ) x 100 * M₁ = mass of wet (saturated) soil * M2 = mass of oven-dried soil * V₁ = volume of wet soil * V2 = volume of oven-dried soil * Pw = density of water ## SPT N Value TCP Blows/0.3 m (12 in) Density | :---------------- | :------------------------- | :--------------- | | :---------------- | :------------------------- | :--------------- | | Less than 4 | Less than 8 | Very Loose | | 4 to 10 | 8 to 20 | Loose | | 10 to 30 | 20 to 60 | Medium Dense | | 30 to 50 | 60 to 100 | Dense | | Greater than 50 | Greater than 100 | Very Dense |