SOIL MECHANICS
PHASE RELATIONSHIPS: 1. 2. 3. 4. 5. 6. 7. 8.
Moisture/Water Content Void Ratio Porosity Degree of Saturation Density Unit Weight Specific Gravity Relative Density
PHASE RELATIONSHIP SAMPLE PROBLEM: 1. In its natural state, a moist soil has a volume of 0.025 m3 and weighs 490 N. The oven-dried weight of the soil is 400 N. If the specific gravity of the soil solids is 2.71, calculate its (a) moisture content, (b) moist unit weight, (c) dry unit weight, (d) void ratio, (e) porosity, and (f) degree of saturation. Answers: (a) 22.50 (b) 19.60 (c) 16.0 (d) 0.667 (e) 0.40 (f) 0.92
PHASE RELATIONSHIP SAMPLE PROBLEM: 2.
In the natural state, a moist soil has a volume of 0.882 ft3 and weighs 110 lb. The oven-dried weight of the soil is 90 lb. If the specific gravity of soil solids is 2.71, calculate its (a) moisture content, (b) moist unit weight, (c) dry unit weight, (d) void ratio, (e) porosity, and (f) degree of saturation.
Answers: (a) 22.22 (b) 127.7 (c) 102 (d) 0.66 (e) 0.40 (f) 0.92
PHASE RELATIONSHIP SAMPLE PROBLEM: 3. A soil sample has a specific gravity of 2.67 with moisture content of 25% and degree of saturation of 89%. Determine the void ratio of the sample. Ans. 0.75 4. A soil has a saturated weight of 19.68 kN/m3. Its moisture content is 25%. Determine the void ratio of the soil. Ans. 0.67
PHASE RELATIONSHIP SAMPLE PROBLEM: 5. A cubic meter of soil in its natural state is 18.90 kN. After oven drying, it weighs 15.75 kN. Assuming a specific gravity of 2.71, determine the (a) moisture content, (b) void ratio, (c) porosity, and (d) degree of saturation of the soil. Answers: (a) 0.20 (b) 0.69 (c) 0.41 (d) 0.79
PHASE RELATIONSHIP SAMPLE PROBLEM: 6. A container with a saturated soil has a mass of 107 g. After being dried, it weighs 98 g. The soil has a specific gravity of 2.70. The container alone weighs 45 g. Determine the soil’s (a) water content, (b) void ratio, and (c) porosity. Answers: (a) 0.17 (b) 0.46 (c) 0.31
PHASE RELATIONSHIP SAMPLE PROBLEM: 7. A saturated soil has a unit weight of 130 lb/ft3. The water is gradually removed by oven drying the sample. Its unit weight when dry is 110 lb/ft3. Compute its unit weight when the degree of saturation is 0.30. Ans. 116 lb/ft3 8. A sample of dry sand having a unit weight of 15.90 kN/m3 and a specific gravity of 2.71 is placed in the rain. During the rain, the volume of the sample remains constant but the degree of saturation increases to 30%. Determine the unit weight of the soil after being in the rain. Ans. 17.08 kN/m3
PHASE RELATIONSHIP SAMPLE PROBLEM: 9. A sample of saturated soil has a weight of 15 kN. After oven drying, it weighs 10.7 kN. Its specific gravity is 2.68. Compute the effective unit weight of the soils. Ans. 7.94 kN/m3 10. At zero air voids, a soil with a specific gravity of 2.71 has a moisture content of 34 percent. Compute the dry unit weight of the sample. Ans. 13.84 kN/m3
CONSISTENCY OF SOILS: ATTERBERG LIMITS: 1. Liquid Limit 2. Plastic Limit 3. Shrinkage Limit These limits are named after the Swedish scientist Albert Atterberg. But according to the textbook in Soil Mechanics by Muni Budhu, only the liquid limit and plastic limit were considered as Atterberg Limits.
CONSISTENCY OF SOILS: LIQUID LIMIT: - Defined as the water content at which the groove cut into the soil pat in the standard liquid limit test requires 25 blows to close along a distance of 13 mm. (Casagrande Cup Method) - Defined as the water content at which 20 mm of soil is penetrated by an apparatus. (Cone Penetration Test) - Liquid state to Plastic state
CONSISTENCY OF SOILS: LIQUID LIMIT: CASAGRANDE CUP METHOD
CONSISTENCY OF SOILS: LIQUID LIMIT: CONE PENETRATION TEST
CONSISTENCY OF SOILS: PLASTIC LIMIT: - Defined as the water content at which the soil begins to crumble when rolled into a thread 3 mm in diameter. - Two or more determinations are done and the average water content is recorded as the plastic limit. - Plastic state to Semi-solid state
CONSISTENCY OF SOILS: SHRINKAGE LIMIT: - Defined as the water content when the soil changes from the semi-solid state to the solid state. The solid state is the state at which no further change in volume occurs since almost all of the water has already been removed.
CONSISTENCY OF SOILS: PLASTICITY INDEX: - Defined as the range of water content at which the soil behaves like a plastic material. - PI = LL – PL LIQUIDITY INDEX: - Relative consistency of a cohesive soil in the natural state - A measure of soil strength - LI = (w – PL)/PI
SOIL CONSISTENCY SAMPLE PROBLEMS: 1. Determine the natural moisture content in percent of a soil given the following properties: PL = 27%, PI = 29%, and LI = 0.30. Ans. 35.70% 2. The results of the Liquid Limit test and Plastic Limit test are shown in the figure. (a) Liquid Limit, (b) Plasticity Index. Ans. (a) 52%, (b) 31%
SOIL CONSISTENCY SAMPLE PROBLEMS:
SOIL CONSISTENCY SAMPLE PROBLEMS: 3. The following were obtained from the Atterberg Limit tests for a soil: LL = 41% and PL = 21.1%. Find the following: (a) PI, (b) If the in-situ water content of the soil is 30%, what is its liquidity index?, (c) What would be the nature of the soil? Answers: (a) 19.90% (b) 0.447 (c) Plastic
SOIL CONSISTENCY SAMPLE PROBLEMS: 4. The following are the results of the shrinkage limit test: Initial volume of soil in saturated state = 24.6 cc Final volume of soil in dry state = 15.90 cc Initial mass in saturated state = 44 g Final mass in dry state = 30.1 g Determine the following: (a) Dry density of the soil, (b) Void ratio, and (c) Shrinkage limit Answers: (a) 1.22 g/cc (b) 1.30 (c) 17.28%
SOIL CLASSIFICATION: Definition: A soil classification system is the arrangement of different soils having similar properties into groups or subgroups based on their application. It provides a common language to express briefly the general characteristics of soils.
SOIL CLASSIFICATION: 1. 2. 3. 4. 5. 6.
Textural Classification Grain Size Analysis Triangular Classification Chart (USDA) AASHTO Classification System USCS System Sieve Analysis
SOIL CLASSIFICATION: Textural Classification: • Clay – particle diameter less than 0.002 mm • Silt – particle diameter in between 0.002 mm and 0.05 mm • Sand – particle diameter in between 0.05 mm and 2 mm
SOIL CLASSIFICATION: Triangular Classification Chart (USDA): • United States Department of Agriculture • Uses a triangular chart to classify soils.
SOIL CLASSIFICATION: AASHTO Classification System: • When classifying soils using the table, classification should start from left to right. • The group index is written to the right of the classification enclosed in parentheses. • The group index ranges from 0 to 20 and rounded off to the nearest whole number • For groups A-2-6 and A-2-7, only the partial group index is used.
SOIL CLASSIFICATION: Unified Soil Classification System (USCS)
SOIL CLASSIFICATION: Sieve Analysis: • Uses a stack of sieves of different opening sizes. • The larger openings are put on top of the smaller openings.
SOIL CLASSIFICATION: Sieve Analysis: • Effective size (D10) – the diameter of the particle size distribution cure corresponding to 10% finer • Coefficient of Uniformity (Cu) = D60/D10 • Coefficient of Curvature/Concavity/Gradation (Cc) (Cc) = D302/[(D10)(D60)] • Cu > 4 and 1 < Cc < 3 for well graded gravel • Cu > 6 and 1 < Cc < 3 for well graded sand
SOIL CLASSIFICATION SAMPLE PROBLEMS: 1. The result of the sieve analysis is shown below:
(a) What % of soil is retained in the No. 200 sieve? (b) What is the effective grain size? (c) Determine the uniformity coefficient.
SOIL CLASSIFICATION SAMPLE PROBLEMS: SOLUTION:
Answers: (a) 95.62% (b) 0.149 mm (c) 1.68
SOIL CLASSIFICATION SAMPLE PROBLEMS: 2. A soil has the following particle-size distribution: • Gravel = 20% • Sand = 10% • Silt = 30% • Clay = 40% Classify the soil according to USDA textural classification system. Ans. Clay
SOIL CLASSIFICATION SAMPLE PROBLEMS: 3. The laboratory results of a soil test are as follows:
Determine the group index in accordance with the AASHTO Classification System. Ans. 12
SOIL CLASSIFICATION SAMPLE PROBLEMS: 4.
Classify the following Classification System.
Ans. For Soil A: A-1-b (0) For Soil B: A-7-5 (20) For Soil C: A-1-a (0)
soils
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AASHTO
SOIL CLASSIFICATION SAMPLE PROBLEMS: 5. The table below shows the laboratory results of the sieve analysis of a soil sample.
Determine the ff: (a) Effective size, (b) coefficient of uniformity, and (c) soil classification according to USCS. Ans. (a) 0.149 mm (b) 14.23 (c) Well graded sand (SW)
USCS TABLE
