TLDR;
This YouTube video features a comprehensive review of Geotechnical Engineering questions from the past five years of the GATE exam. The instructor provides time limits for each question, offers solutions, and shares tips for efficient problem-solving. The session covers soil water relationships, soil classification, stress analysis, consolidation, shear strength, and earth pressure theories.
- Focus on Geotechnical Engineering for GATE exam preparation.
- Includes time-managed solutions for past exam questions.
- Covers key topics: soil relationships, classification, stress, consolidation, shear strength, and earth pressure.
Introduction [0:23]
The instructor welcomes everyone to the session, emphasising the importance of Geotechnical Engineering, which carries 13 marks in the GATE exam. The goal is to secure full marks in this section through focused effort, including short notes, the Infinity 50 series, and solving the last five years' worth of GATE exam questions. The approach involves setting a timer for each question based on its difficulty, followed by a detailed solution. The session is expected to be long, covering 85 questions.
Soil Water Relationships - Question 1 (GATE 2021) [3:02]
The first question involves a partially saturated soil with given natural moisture content and bulk unit weight. The task is to find the unit weight of the soil sample at full saturation, given the specific gravity and water content. The instructor allocates three minutes for this one-mark question. The solution involves using the formula relating bulk unit weight, water content, specific gravity, and void ratio to find the void ratio, then substituting it into the formula for saturated unit weight. The correct answer is 19.03 kN/m³.
Soil Water Relationships - Question 2 [8:15]
The next question provides laboratory investigation data, including liquid limit, plastic limit, natural moisture content, and flow index, and asks for the toughness index. The instructor gives two minutes for this question. The solution involves applying the formulas for the toughness index (IP/IF) and the liquidity index to arrive at the answer, which is option C.
Soil Water Relationships - Question 3 (GATE 2022) [11:49]
This question from GATE 2022, worth one mark, presents an uncompacted heap of soil with a given volume and void ratio. The soil is then compacted to a smaller volume, and the task is to find the corresponding void ratio. The instructor allows one and a half minutes for this question. The solution is based on the principle that the volume of solids remains the same before and after compaction, leading to the calculation of the new void ratio as 0.5.
Soil Water Relationships - Question 4 (GATE 2023) [14:19]
A one-mark question from GATE 2023 provides the specific gravity of soil and its degree of saturation, along with the water content. The task is to find the void ratio. The instructor allocates one minute for this question. The solution involves applying the formula Se = wG to find the void ratio, which is calculated to be 0.78.
Origin of Soil - Question 5 [16:14]
This question explores the origin of soil, focusing on mechanical weathering and the activity of clay. The instructor emphasises that although the origin of soil is not explicitly in the syllabus, it's important to understand. The question requires identifying the correct statement regarding soil particle shape near the origin and the significance of clay activity. The correct answer is D, where P is false and Q is true.
Soil Water Relationships - Question 6 (GATE 2024) [18:56]
This one-mark question from GATE 2024 deals with soil to be constructed with a degree of saturation of 75%. Given the specific gravity and moisture content, the task is to find the unit weight of the compacted soil. The instructor allows one and a half minutes for this question. The solution involves using the given values to find the void ratio and then calculating the dry unit weight, which is approximately 16.67 kN/m³.
Soil Water Relationships - Question 7 & 8 (GATE 2024) [23:21]
This section covers two-mark questions from the GATE 2024 exam. The first question involves the density index of sand, given its in-situ percentage of voids and maximum and minimum densities. The instructor allocates three minutes for this question. The solution involves using the formula for density index, which requires calculating the dry density of the in-situ sand. The relative density is found to be approximately 0.113.
Soil Water Relationships - Question 9 (GATE 2025) [31:00]
This two-mark question from GATE 2025 presents a clay soil with a given moisture content, specific gravity, and degree of saturation. After a rain event, the degree of saturation increases, and the task is to find the new moisture content, assuming the volume change is negligible. The instructor emphasises that there is no chance of approximation here. The new moisture content is calculated to be 23.59%.
Soil Water Relationships - Question 10 [37:00]
This question involves a partially saturated soil deposit at a construction site. Given the water content, degree of saturation, void ratio, and specific gravity, the task is to find the required weight of water to fully saturate a 5-meter layer of this soil. The instructor encourages a direct approach using basic principles. The required weight of water is calculated to be approximately 6 kN.
Soil Classification - Question 1 [43:56]
The instructor transitions to soil classification, noting that questions in this area are less frequent but still important. The first question asks for the soil type represented by MH according to the Unified Soil Classification System. The answer is inorganic silt with high plasticity, with a liquid limit greater than 50%.
Soil Classification - Question 2 [45:29]
This question presents a soil lying above the A-line in a plasticity chart with a liquid limit greater than 50%. The task is to identify the soil type. The answer is inorganic clay with high plasticity or high compressibility.
Soil Classification - Question 3 [46:48]
This question involves arranging four different soil types (CH, ML, SP, SW) in decreasing order of hydraulic conductivity. The instructor emphasises that knowing the permeability of each soil type is not necessary; instead, focus on identifying the least permeable soil. The correct order is SW > SP > ML > CH.
Permeability and Suction Head [48:32]
The instructor discusses the relationship between moisture content, permeability, and suction head. Increasing moisture content increases permeability because it raises the degree of saturation. However, increasing moisture content decreases suction head because it reduces the meniscus in the capillary tube.
Effective Stress Analysis - Question 1 [52:10]
This question involves a soil sample underlying a water column, and the task is to determine the vertical effective stress at different points. The instructor allocates two and a half minutes for this question. The solution involves applying the principles of effective stress, considering the total stress and pore water pressure at each point.
Permeability - Question 2 [57:18]
This question presents an anisotropic soil with horizontal and vertical permeability coefficients. The task is to determine how the embedment depth of a wall should be scaled to draw a flow net for an equivalent isotropic soil. The solution involves multiplying the vertical coordinate by the square root of the ratio of horizontal to vertical permeability (kx/ky).
Permeability - Question 3 [59:04]
This question involves two soils with different permeabilities placed in a horizontal flow apparatus. The task is to find the discharge through the soil. The solution involves calculating the average permeability using the formula for flow perpendicular to bedding planes and then applying Darcy's law to find the discharge.
Permeability - Question 4 [1:04:32]
This question asks for the most suitable laboratory test for measuring the permeability of clay soil. The answer is the falling head test, which is appropriate for fine-grained soils like clay.
Total Head Calculation - Question 5 [1:05:29]
This question involves calculating the total head at the junction of two soil samples, considering an additional pressure applied to the water. The solution involves first determining the additional head due to the applied pressure. Then, the total head at the junction is calculated by considering the datum head and pressure head, taking into account the head loss through the soil samples.
Soil Structure - Question 1 [1:20:15]
This question presents statements about soil structure and asks which are incorrect. The solution involves understanding the properties of flocculated structures, the phreatic surface, and piping phenomena. The correct answer is that both Q and R are false.
Exit Gradient - Question 2 [1:24:05]
This question involves a homogeneous earth dam with a given water head difference and flow net characteristics. The task is to find the void ratio of the soil for a factor of safety of 2 against piping. The solution involves using the formula for the factor of safety against piping, which relates the critical hydraulic gradient to the exit gradient.
Exit Gradient - Question 3 [1:29:30]
This question involves a flow net under a concrete dam and asks for the factor of safety against quick sand conditions. The solution involves calculating the critical hydraulic gradient using the submerged unit weight and the unit weight of water. The factor of safety is then calculated as the ratio of the critical hydraulic gradient to the exit gradient.
Stress Distribution - Question 1 [1:37:09]
This question involves a concentrated vertical load applied to a horizontal ground surface. The task is to find the ratio of the increase in vertical stress at two different depths below the load. The solution involves applying the Boussinesq theory, considering that the points are along the line of application of the load.
Stress Distribution - Question 2 [1:41:57]
This question involves a concentrated load on a square footing and asks for the maximum depth of the pressure bulb, considering 10% of the vertical load intensity. The solution involves applying the Boussinesq theory, considering the maximum depth occurs directly below the load.
Stress Distribution - Question 3 [1:45:13]
This question provides an expression for the vertical stress within a half-space and asks for the locus where the stress is maximum. The solution involves recognising that the given expression is a form of the Boussinesq equation and recalling that the maximum stress occurs at a specific r/z ratio.
Compaction - Question 1 [1:49:26]
This question presents statements about soil compaction and asks which are incorrect. The solution involves understanding the relationship between compaction effort, optimum moisture content, and dry density, as well as the characteristics of the zero air voids line.
Consolidation - Question 1 [1:51:47]
This question involves an oedometer test on a fully saturated clay specimen. The task is to find the effective stress and pore water pressure immediately after increasing the vertical stress. The solution involves understanding that the initial stress is fully consolidated, and the additional stress is initially taken up entirely by the pore water.
Consolidation - Question 2 [1:59:12]
This question presents a soil profile and asks for the over-consolidation ratio (OCR) at the mid of the clay layer. The solution involves calculating the effective stress in the present and past conditions, considering the groundwater table level. The OCR is then calculated as the ratio of the past to present effective stress.
Consolidation - Question 3 [2:06:44]
This question involves a soil profile at a road construction site and asks for the primary consolidation settlement due to an embankment load. The solution involves applying the formula for primary consolidation settlement, which requires calculating the initial void ratio and effective stress.
Consolidation - Question 4 [2:17:13]
This question involves an oedometer test and asks for the relationship between void ratio and pressure. The solution involves applying the formula for the coefficient of consolidation, which relates permeability, void ratio, and effective stress.
Consolidation - Question 5 [2:25:32]
This question involves a consolidation scenario and asks to determine the settlement. The solution involves understanding the different stages of consolidation and applying the appropriate formulas for each stage.
Consolidation - Question 6 [2:31:35]
This question involves matching soil conditions with their properties. The solution involves understanding the characteristics of normally consolidated soil, high plasticity clay, quick clay, and dilating sand.
Consolidation - Question 7 [2:33:15]
This question involves a raft foundation and asks for the time required to achieve 25% consolidation settlement. The solution involves applying the theory of consolidation, considering the drainage conditions and the relationship between time and degree of consolidation.
Consolidation - Question 8 [2:42:54]
This question involves a saturated compressible clay layer and asks for the percentage consolidation at a point when the effective stress reaches a certain value. The solution involves understanding the relationship between total stress, pore water pressure, and effective stress during consolidation.
Consolidation - Question 9 [3:00:29]
This question involves an oedometer test and asks for the effective stress and excess pore pressure. The solution involves understanding that the initial stress is fully consolidated, and the additional stress is initially taken up entirely by the pore water.
Shear Strength - Question 1 [3:36:29]
This question involves a drained direct shear test on a sand soil and asks for the effective shear strength parameter. The solution involves applying the Mohr-Coulomb failure criterion, considering that the soil is cohesionless.
Shear Strength - Question 2 [3:39:14]
This question involves an unconfined compression test on a cohesive soil and asks for the undrained cohesion. The solution involves applying the relationship between unconfined compressive strength and cohesion.
Shear Strength - Question 3 [3:40:04]
This question involves a stress path and asks for the correct condition. The solution involves understanding the relationship between vertical and horizontal stress.
Shear Strength - Question 4 [3:52:44]
This question involves a consolidated drained test on a sand sample and asks for the pore water pressure. The solution involves applying the Mohr-Coulomb failure criterion, considering the effective stress parameters.
Shear Strength - Question 5 [4:02:39]
This question involves a soil sample and asks for the value of Skempton's pore pressure parameter B. The solution involves applying the formula for Skempton's pore pressure parameter, considering the changes in cell pressure and pore pressure.
Shear Strength - Question 6 [4:07:01]
This question asks which soil type can attain negative Skempton's pore pressure parameter. The answer is over-consolidated soil.
Shear Strength - Question 7 [4:08:38]
This question involves a drained triaxial test and asks for the angle of the sharing plane. The solution involves applying the Mohr-Coulomb failure criterion, considering the effective stress parameters.
Shear Strength - Question 8 [4:13:26]
This question involves a normally consolidated clay and asks for the value of sin φ. The solution involves applying the Mohr-Coulomb failure criterion, considering the effective stress parameters.
Shear Strength - Question 9 [4:19:50]
This question presents statements about soil and asks which are correct. The solution involves understanding the properties of unconfined compression tests, shear strength parameters, vane shear tests, and UU tests.
Earth Pressure - Question 1 [4:24:10]
This question asks for the maximum depth of an unsupported excavation. The solution involves applying the formula for the depth of unsupported cut.
Earth Pressure - Question 2 [4:26:18]
This question involves a retaining wall and asks for the factor of safety against sliding failure. The solution involves calculating the active earth pressure, considering the tension crack and water filling the crack.
Earth Pressure - Question 3 [4:37:54]
This question asks for the condition for a soil element to reach the passive state under Rankine earth pressure conditions. The answer is that the effective horizontal stress is greater than the effective vertical stress.
Earth Pressure - Question 4 [4:38:47]
This question involves a smooth vertical retaining wall and asks for the lateral earth pressure at the base of the wall. The solution involves applying Rankine's earth pressure theory, considering the surcharge load and the properties of the soil.
Earth Pressure - Question 5 [4:48:15]
This question involves a vertical trench excavated in clay soil and asks for the maximum depth of unsupported excavation. The solution involves considering the surcharge load, the fluid in the trench, and the properties of the clay.
Earth Pressure - Question 6 [5:07:00]
This question involves a force polygon and asks to identify the correct diagram. The solution involves understanding the direction of the forces acting on the wall.
Earth Pressure - Question 7 [5:11:10]
This question involves a smooth vertical rigid retaining wall and asks for the inclination of the failure plane. The solution involves applying Rankine's earth pressure theory, considering the major principal plane.
Earth Pressure - Question 8 [5:13:53]
This question involves a rough retaining wall and asks to identify the correct statement. The solution involves understanding the direction of the forces acting on the wall.
Earth Pressure - Question 9 [5:16:18]
This question presents statements and asks which are correct. The solution involves understanding the properties of soil.
