Soil Mechanics And Foundation — Part 1 MCQs with Explanations

The degree of consolidation in soil mechanics is a measure of how much a soil sample has consolidated over time due to applied pressure. It is directly proportional to time because the consolidation process continues as time progresses. It is inversely proportional to the square of the drainage path because longer drainage paths result in slower consolidation. Therefore, Option B correctly describes the relationship between the degree of consolidation, time, and drainage path.

Understanding Consolidation in Saturated Clay: Imagine squeezing a sponge soaked in water. The water needs time to escape. Consolidation is similar; it's the process of water slowly leaving saturated clay under pressure. Neutral pressure is the pressure of the water in the soil pores. Effective pressure is the pressure that the soil particles themselves carry. During consolidation, the total pressure stays the same. It's like the total amount of water in the sponge plus the sponge itself. As the water escapes (reducing neutral pressure), the soil particles take on more of the load (increasing effective pressure). Therefore, the sum of neutral pressure and effective pressure remains constant. The Correct Answer: Based on the above explanation, option B is correct. It accurately describes the reduction in neutral pressure and corresponding increase in effective pressure during consolidation, while maintaining a constant sum.

Relative Density is like a special scale that tells us how "compact" or "dense" sand is. It's a very important property for sandy soils (soils without much clay) because it helps engineers know how stable the soil is. This special scale for Relative Density goes from 0 to 1 , representing the two extreme states of sand packing: 1. Zero (0): If the sand is in its absolute loosest state . This means the sand particles are as spread out as possible, with the maximum amount of empty space (voids) between them. In this scenario, the Relative Density is 0 . 2. One (1): If the sand is in its absolute densest state . This means the sand particles are packed together as tightly as possible, with the minimum amount of empty space (voids) between them. In this scenario, the Relative Density is 1 . 3. Between 0 and 1: If the sand is in any state somewhere between the loosest and densest conditions (which is typically what we find in nature), then its Relative Density will be a value between 0 and 1 (e.g., 0.3, 0.6, 0.8, etc.). Now, let's look at our question: "If the sand in-situ is in its densest state ..." The question clearly states that the sand is already in its most densely packed possible state . As we just learned, when sand is in this extreme densest condition, its Relative Density is 1 . Therefore, the correct answer is Option B: 1 .

Option A: negative This option is incorrect. The plasticity index cannot be negative. It is either zero or non-plastic (NP) in such cases. Option B: zero This option is incorrect. Zero is used when the plastic limit is equal to the liquid limit, not when it is greater. Option C: non-plastic (NP) This is the correct option. When the plastic limit exceeds the liquid limit, the soil is considered non-plastic, and the plasticity index is reported as NP. Option D: 1 This option is incorrect. The plasticity index is not arbitrarily set to 1 in any standard soil mechanics context. In conclusion, the correct answer is Option C: non-plastic (NP) , as this correctly represents the condition when the plastic limit is greater than the liquid limit in soil mechanics.

Effective stress: It is the stress transmitted through soil particles at their points of contact. This is critical in understanding the behavior of soils under load. A physical parameter that can be measured: Effective stress is a measurable quantity calculated as the total stress minus pore water pressure. Importance: Effective stress is a key parameter because it governs the engineering properties of soil, such as shear strength, compressibility, and permeability. Since all the statements are correct, Option D: all of the above is the correct answer.

According to Atterberg, the soil is said to be of medium plasticity if the plasticity index (PI) is 7 < PI < 17 . The plasticity index (PI) is a measure of the plasticity of a soil and is calculated as the difference between the liquid limit (LL) and the plastic limit (PL). Soils with a PI between 7 and 17 are considered to have medium plasticity. This range indicates moderate changes in consistency with changes in moisture content. Therefore, the correct option is 7 < PI < 17 .

Sand particles are made of rock minerals. Sand primarily consists of small fragments of weathered rock and minerals, predominantly quartz, which is a durable and resistant mineral. Kaolinite, illite, and montmorillonite are types of clay minerals, which are much finer in particle size compared to sand and have different properties and compositions. Therefore, the correct answer is that sand particles are composed of rock minerals.

The coefficient of consolidation of a soil is affected by both compressibility and permeability. The coefficient of consolidation ( C v ​) is a measure used in soil mechanics to describe how fast a soil consolidates under load. Compressibility influences how much volume change occurs in the soil when a load is applied. Permeability determines the rate at which water can flow through the soil pores, affecting how quickly excess pore water pressure dissipates. Therefore, the coefficient of consolidation is dependent on both these properties, making Option C the correct answer.

Residual soils are formed by the weathering and decomposition of rocks at the same place where they originally existed . They remain at their place of formation and are not transported by external agents. Agents such as glaciers, wind, and water are responsible for transporting soils from one location to another, producing transported soils rather than residual soils. Therefore, residual soils are not formed by glaciers, wind, or water , making Option D the correct answer.

The correct answer is (A) decreases. Here's why: A consolidated drained (CD) test means we're testing a soil that is: * Consolidated: The soil has been compressed and excess pore water pressure has dissipated. * Drained: Water is allowed to escape freely during the shearing process. A normally consolidated clay is a clay that has never experienced a stress greater than its current stress. When a normally consolidated clay is sheared under drained conditions, the soil particles tend to rearrange themselves into a denser configuration. This rearrangement and compression of the soil structure causes the overall volume of the soil sample to decrease . Because water is allowed to drain, this volume change can occur. Therefore, the answer is decreases .

In soil mechanics, the shear strength of a soil is a unique function of both effective stress and total stress . The shear strength of soil depends on both the effective stress and the total stress acting on the soil mass. Effective stress refers to the stress carried by the soil grains themselves, while total stress includes the stress carried by both the soil grains and the pore water. Therefore, the correct option is both effective stress and total stress .

The correct answer is C: ML . Let's break down why: Soil Classification : In soil mechanics, we use a system to classify different types of soil. This helps us predict how the soil will behave. Inorganic vs. Organic Soils : Inorganic soils are made of minerals, like sand, silt, and clay. Organic soils contain a lot of decomposed plant and animal matter. Compressibility : Compressibility refers to how much a soil's volume decreases under pressure. Low compressibility means the soil doesn't shrink much when you put weight on it. The Options Explained : MH : This represents inorganic silts with high compressibility. SL : This is not a standard soil classification symbol. ML : This represents inorganic silts with low compressibility. This is exactly what the question is asking for! CH : This represents inorganic clays with high compressibility. Therefore , ML (inorganic silts with low compressibility) is the right answer.

First, let's understand some terms: Saturated Soil : Imagine a sponge completely soaked in water, so much that there are no air bubbles left in it. That's what "saturated" means for soil – all the tiny spaces (called pores or voids) between the soil particles are completely filled with water. Pore Pressure : This is simply the pressure of the water that is trapped within these tiny spaces inside the soil. Skempton's Pore Pressure Coefficient B : This is a value that helps us understand how much the pore pressure changes when we apply an overall squeezing pressure (called isotropic stress or all-around stress) to the soil from all directions. Think of it as a ratio: how much the pore water pressure increases for every unit of all-around pressure you apply . Now, let's consider a saturated soil (our sponge full of water). When you apply an external squeezing pressure from all sides to this saturated soil, what happens to the water inside? 1. The water is almost incompressible . It cannot be squashed into a smaller volume easily. 2. The soil particles themselves are also relatively incompressible. 3. There is no air in the pores to compress. Because of these reasons, if you apply, say, 1 unit of pressure from all directions, the water trapped inside the soil pores has nowhere to go immediately. It has to take almost the entire impact of that applied pressure. So, if you increase the all-around stress by a certain amount, the pore water pressure will also increase by almost the same amount . This means the ratio of the change in pore pressure to the change in applied all-around stress is approximately 1. Therefore, for a saturated soil , Skempton's pore pressure coefficient B is 1 . So, if you apply 1 unit of all-around pressure, the pore water pressure will also increase by approximately 1 unit. The correct answer is Option A: 1 .

Here's the core idea: * Shear strength is the soil's ability to resist sliding or shearing. * Normal stress is the force pressing down on the soil (perpendicular to the shearing plane). Think of it as the weight pushing the soil particles together. * Angle of internal friction (φ) represents how much the soil particles resist sliding against each other due to friction. A higher angle means more friction. The relationship: The shear strength (τ) of a soil is described by the Mohr-Coulomb equation: τ = c + σ * tan(φ) where: c = cohesion of the soil σ = normal stress φ = angle of internal friction Explanation of each option: A: Is directly proportional to the angle of internal friction of the soil * This is correct . As the angle of internal friction (φ) increases, the shear strength (τ) also increases because tan(φ) increases. B: Is inversely proportional to the angle of internal friction of the soil * This is incorrect . Inversely proportional means one increases as the other decreases, which is the opposite of what happens. C: Decreases with increase in normal stress * This is incorrect . The formula (τ = c + σ * tan(φ)) shows that as normal stress (σ) increases, the shear strength (τ) also increases. D: Decreases with decrease in normal stress * This is incorrect . If the normal stress (σ) decreases, the shear strength (τ) decreases as well. Therefore, the correct answer is A.

1.5m is the correct answer to “The hydraulic head that would produce a quick condition in a sand stratum of thickness 1.5 m, specific gravity 2.67 and voids ratio 0.67 is equal to”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

3 months is the correct answer to “Clay layer A with single drainage and coefficient of consolidation Cv takes 6 months to achieve 50% consolidation. The time taken by clay layer B of the same thickness with double drainage and coefficient of consolidation $$\frac{{{\text{Cv}}}}{2}$$ to achieve the same degree of consolidation is”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

0 ≤ 1D ≤ 1 is the correct answer to “Select the correct range of density index, 1 D”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

ultimate strength is same but peak strength of dense sand is greater than that of loose sand is the correct answer to “For a loose sand sample and a dense sand sample consolidated to the same effective stress”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

50% is the correct answer to “Rise of water table in cohesionless soils upto ground surface reduces the net ultimate bearing capacity approximately by”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

angle of internal friction only is the correct answer to “Terzaghi’s bearing capacity factors Nc, Nq and Nr are functions of”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

0 ≤ S ≤ 100 is the correct answer to “Valid range for S, the degree of saturation of soil in percentage is”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

plastic state is the correct answer to “If the natural water content of soil mass lies between its liquid limit and plastic limit, the soil mass is said to be in”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

0.00018 m3/sec is the correct answer to “The flownet for an earthen dam with 30 m water depth consists of 25 potential drops and 5 flow channels. The coefficient of permeability of dam material is 0.03 mm/sec. The discharge per meter length of dam is”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

Parallel to stratification is always greater than that perpendicular to stratification is the correct answer to “The average coefficient of permeability of natural deposits”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

calcium carbide method is the correct answer to “For proper field control, which of the following methods is best suited for quick determination of water content of a soil mass”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

falling head method is the correct answer to “Which of the following methods is more suitable for the determination of permeability of clayey soil”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

equal to specific gravity of soil is the correct answer to “If the water content of a fully saturated soil mass is 100%, then the voids ratio of the sample is”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

face to face or parallel orientation is the correct answer to “Dispersed type of soil structure is an arrangement comprising particles having”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

both viscosity and unit weight is the correct answer to “Physical properties of a permeant which influence permeability are”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

0.05 N/mm2 and 0° is the correct answer to “A cylindrical specimen of saturated soil failed under an axial vertical stress of 100 kN/m 2 when it was laterally un-confmed. The failure plane was inclined to the horizontal plane at an angle of 45°. The values of cohesion and angle of internal friction for the soil are respectively”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

0.5 and 1.0 is the correct answer to “If the volume of voids is equal to the volume of solids in a soil mass, then the values of porosity and voids ratio respectively are”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

undrained test is the correct answer to “Unconfmed compressive strength test is”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

consolidated undrained test is the correct answer to “In a triaxial compression test when drainage is allowed during the first stage (i. e. application of cell pressure) only and not during the second stage (i.e. application of deviator stress at constant cell pressure), the test is known as”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

10 mm is the correct answer to “A normally consolidated clay settled 10 mm when effective stress was increased from 100 kN/m 2 to 200 kN/m 2 . If the effective stress is further increased from 200 kN/m 2 to 400 kN/m 2 , then the settlement of the same clay is”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

less than the sum of the discharges from individual wells is the correct answer to “The total discharge from two wells situated near to each other is”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

only in fixed ring type consolido-meter is the correct answer to “Direct measurement of permeability of the specimen at any stage of loading can be made”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

cohesion and effective unit weight of soil is the correct answer to “The rise of water table below the foundation influences the bearing capacity of soil mainly by reducing”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

12° is the correct answer to “A retaining wall 6m high supports a backfill with a surcharge angle of 10°. The back of the wall is inclined to the vertical at a positive batter angle of 5°. If the angle of wall friction is 7°, then the resultant active earth pressure will act at a distance of 2 m above the base and inclined to the horizontal at an angle of”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

0.5 kg/cm2 and zero is the correct answer to “The total and effective stresses at a depth of 5 m below the top level of water in a swimming pool are respectively”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.

increases by 50% is the correct answer to “Due to a rise in temperature, the viscosity and the unit weight of the percolating fluid are reduced to 60% and 90% respectively. If other things remain constant, the coefficient of permeability”. This question is standard in competitive examination syllabi for Soil Mechanics And Foundation.