Past Questions — 2025

In geotechnical engineering, slope stabilization methods are categorized based on their duration of effectiveness and the purpose they serve. 1. **Shotcrete or Gunite (Correct):** Shotcrete is a process of spraying concrete at high velocity onto a surface. In slope stabilization, it is frequently used as a short-term or immediate measure to seal the slope face, prevent surface weathering, stop immediate raveling of rock/soil, and provide temporary support during construction before more permanent reinforcements (like anchors or deep drainage) are installed. While it can be part of a permanent system, its primary application in stabilization sequences is often for immediate, short-term surface protection. 2. **Soil Nailing (Incorrect):** This is a permanent stabilization technique. It involves installing steel tendons (nails) into the slope and grouting them to create a reinforced soil mass. It is designed for long-term structural stability. 3. **Toe Buttress (Incorrect):** A toe buttress involves placing a heavy mass of material (like rockfill) at the base (toe) of the slope to resist rotational failure. This is a permanent structural modification to the slope geometry. 4. **Gabion Wall (Incorrect):** Gabions are wire mesh cages filled with stone. They are used as permanent retaining structures to provide gravity-based stability and allow for drainage at the base of a slope.

Surface water refers to any body of water found on the Earth's surface, such as rivers, lakes, reservoirs, streams, and oceans. 1. Rivers (Option a): These are natural flowing watercourses on the surface of the ground. They are a primary component of surface water. 2. Lakes (Option c): These are large bodies of surface water surrounded by land. They are a primary component of surface water. 3. Reservoirs (Option d): These are artificial lakes created by dams to store surface water for human use. They are considered surface water bodies. 4. Aquifers (Option b): An aquifer is an underground layer of water-bearing permeable rock, gravel, sand, or silt from which groundwater can be extracted. Since aquifers are located beneath the Earth's surface, they are a component of 'Groundwater', not 'Surface Water'. Therefore, aquifers are not a component of surface water.

The Plate Load Test is a standard field test used to determine the ultimate bearing capacity of soil and the settlement under a given load. In this test, a steel plate is placed on the soil surface (or at a specific depth) and loaded using a hydraulic jack until the soil fails or a specific settlement is reached. Analysis of other options: - a. Core Cutter Test: This is a field test used to determine the in-situ bulk density (unit weight) of cohesive soils, not the bearing capacity. - c. Vane Shear Test: This is a field test used specifically to determine the undrained shear strength of soft, saturated clays. While shear strength is related to bearing capacity, the test itself measures strength, not the overall bearing capacity of the soil profile. - d. Pycnometer Test: This is a laboratory test used to determine the specific gravity of soil solids.

The liquid limit (LL) is the moisture content at which a soil transitions from a plastic state to a liquid state. It is standardly determined using the Casagrande’s Apparatus, where a groove is cut into a soil pat and the number of drops required to close the groove by a distance of 12.7 mm (0.5 inches) is recorded. Analysis of other options: - a. Pycnometer Test: Used to determine the specific gravity of soil solids. - b. Core Cutter Test: Used to determine the in-situ bulk density of cohesive soils. - d. Sand Replacement Test: Used to determine the in-situ dry density of non-cohesive (sandy) soils.

The Indian Standard (IS) classification system for soils (IS 1498) is largely based on the Unified Soil Classification System (USCS). To classify fine-grained soils (silts and clays), the system relies on the 'Plasticity Chart'. This chart plots the Plasticity Index (PI) against the Liquid Limit (LL). The 'A-line' (defined by the equation PI = 0.73(LL - 20)) is used to distinguish between clays (above the A-line) and silts/organic soils (below the A-line). Why other options are incorrect: - b. Ternary diagram: These are used for three-component systems (e.g., sand-silt-clay proportions) but are not the primary tool for the standard IS classification of soil groups. - c. Compaction curve: This is used to determine the Optimum Moisture Content (OMC) and Maximum Dry Density (MDD) of a soil, not for classification. - d. Permeability chart: Permeability is a property of soil, but there is no standard 'permeability chart' used as a basis for the IS classification system.

A gabion is a cage, cylinder, or box made of galvanized steel wire mesh (or PVC coated wire) that is filled with hard, durable materials. The primary and most common filling material used in gabion structures is rocks or stones. These structures are used extensively in civil engineering for retaining walls, erosion control, and slope stabilization because they are flexible, permeable (allowing water to flow through), and sustainable. Why other options are incorrect: - b. Clay soil: Clay is cohesive and would block the permeability of the structure, leading to hydrostatic pressure buildup, which could cause the wall to fail. - c. Bitumen: Bitumen is a binder used in road construction (asphalt) and is not a structural filling material for mesh cages. - d. Cement mortar: Gabions are designed to be flexible and permeable; filling them with cement mortar would turn them into rigid concrete blocks, defeating the purpose of using a wire mesh cage.

Workability of concrete refers to the ease with which it can be mixed, transported, placed, and compacted without segregation. 1. Slump Test (Option a): This is the most common field test used to measure the consistency and workability of fresh concrete. It involves filling a conical mold (slump cone) with concrete and measuring the vertical subsidence (slump) after the mold is removed. A higher slump indicates higher workability. 2. Compression Test (Option b): This test is performed on hardened concrete cubes or cylinders to determine the compressive strength of the concrete, not its workability. 3. Tensile Test (Option c): Concrete is naturally weak in tension. Tensile tests (like the split tensile test) are used to determine the tensile strength of hardened concrete. 4. Flexural Test (Option d): This test is used to determine the modulus of rupture or the bending strength of hardened concrete beams. Therefore, only the slump test is used for assessing the workability of fresh concrete.

A crib wall is a prefabricated cellular structure made of interlocking precast concrete or timber units, which are then filled with granular material (like crushed stone or gravel). 1. Why it is suitable for steep terrains: Crib walls are flexible and can adapt to irregular ground conditions better than rigid concrete walls. They are also highly permeable, which prevents the buildup of hydrostatic pressure—a critical factor in steep, mountainous terrains where drainage is essential for stability. 2. Why it is suitable for quick installation: Because they consist of prefabricated modular components that are assembled on-site and filled with local materials, they can be installed much faster than cast-in-place concrete walls, which require extensive formwork, reinforcement tying, and curing time. Comparison with other options: - Gravity walls (a): These are massive structures (stone or concrete) that rely on their own weight. They require significant material transport and labor, making them slow to install and difficult to build on very steep, remote terrains. - Cantilever walls (b): These require extensive excavation for the base and precise formwork/curing for the reinforced concrete, making them slower to install than modular systems. - Counterfort walls (d): These are essentially cantilever walls with additional supports for very high walls. They are complex to construct and require significant time for casting and curing.

The hydrological cycle describes the continuous movement of water on, above, and below the surface of the Earth. To quantify this cycle for a specific area (like a catchment or basin) over a specific period, the principle of conservation of mass is applied. This is expressed as the 'Water Budget Equation': Inflow - Outflow = Change in Storage. Why other options are incorrect: - a. Hydrograph equation: A hydrograph is a plot of discharge versus time at a specific point in a river; it describes the response of a watershed to a rainfall event, not the overall cycle. - c. Darcy’s law: This describes the flow of fluid through a porous medium (like soil), specifically relating flow rate to hydraulic gradient. - d. Continuity equation: While the water budget equation is a form of the continuity equation (conservation of mass), in the specific context of hydrology and the global/regional water cycle, it is formally referred to as the Water Budget Equation.

Concrete is a composite material that is very strong in compression but very weak in tension (its tensile strength is typically only about 10% of its compressive strength). Foundations, especially footings, are subjected to bending moments due to the upward pressure of the soil against the downward load of the structure. This bending creates compressive stresses on one side and tensile stresses on the opposite side. Since concrete cannot withstand these tensile stresses, steel reinforcement (which has high tensile strength) is embedded in the concrete to carry the tensile loads and prevent the foundation from cracking or failing. Why other options are incorrect: - a. Reduce dead load: Reinforcement (steel) is denser than concrete; adding it actually slightly increases the dead load, not reduces it. - c. Prevent shrinkage: While specific types of reinforcement (like temperature/shrinkage steel) can control cracking, the primary structural purpose of reinforcement in a foundation is to handle load-induced stresses, not to prevent the chemical/physical process of shrinkage. - d. Increase soil strength: Reinforcement is placed within the concrete structure. It does not change the inherent engineering properties or the bearing capacity of the underlying soil.

Compressibility of soil refers to the decrease in volume of the soil mass when subjected to an applied load. This is primarily governed by the particle size, void ratio, and the nature of the soil particles. 1. **Gravel (Option b):** Gravel consists of coarse-grained particles. Coarse-grained soils have larger particles and generally lower void ratios compared to fine-grained soils. Because the particles are large and often interlock, they offer high resistance to deformation, making gravel the least compressible among the given options. 2. **Clay (Option a):** Clay is a fine-grained soil with a high specific surface area and high water-holding capacity. It is highly compressible due to the process of consolidation (expulsion of pore water over time), making it the most compressible soil listed. 3. **Silt (Option c):** Silt has particle sizes between sand/gravel and clay. While it is less compressible than clay, it is significantly more compressible than gravel due to its smaller particle size and higher potential for rearrangement under load. 4. **Loam (Option d):** Loam is a mixture of sand, silt, and clay. Because it contains a significant fraction of silt and clay, its compressibility is higher than that of pure gravel. Therefore, based on the grain size distribution and mechanical properties, gravel is the least compressible soil.

In cold weather concreting, the primary challenge is the slow rate of hydration of cement due to low temperatures. This slows down the setting time and strength gain, increasing the risk of freezing of the water in the concrete, which can lead to structural failure. 1. **Rapid Hardening Cement (RHC)** is designed to gain strength quickly. It achieves this through a higher tricalcium silicate (C3S) content and finer grinding. Because it generates a higher heat of hydration (exothermic reaction) and sets faster, it helps the concrete reach its critical strength more quickly, protecting it from freezing temperatures. Therefore, it is the most suitable choice for cold weather. 2. **Ordinary Portland Cement (OPC)** has a standard rate of hydration and may set too slowly in very cold weather, leaving the concrete vulnerable to frost damage. 3. **Low Heat Cement** is specifically designed to reduce the heat of hydration to prevent thermal cracking in mass concrete (like dams). Using it in cold weather would be counterproductive as it would further slow down the setting process. 4. **Sulphate Resisting Cement** is used in environments with high sulphate concentrations (like coastal areas or certain soils) to prevent chemical attack; it does not provide the accelerated setting required for cold weather.

Slope stability is fundamentally a balance between the driving forces (gravity, loading) and the resisting forces. The primary resisting force that prevents a soil mass from sliding down a slope is the shear strength of the soil along the potential failure surface. According to the Mohr-Coulomb failure criterion, shear strength is a function of cohesion (c) and the angle of internal friction (φ). While moisture content (option b) significantly affects shear strength (by increasing pore water pressure and reducing effective stress), it is the resulting change in shear strength that directly determines whether the slope fails. Plasticity index (option a) and Density index (option d) are soil classification and state parameters that influence shear strength, but they are not the direct governing property for stability analysis. Therefore, shear strength is the most critical property for assessing slope stability.

A crib wall is a type of retaining structure consisting of an open-work framework of interlocking members (logs or precast concrete beams) that are stacked in a criss-cross pattern to form a 'crib' or cage. This cage is then filled with granular material (such as crushed stone or gravel) to provide the necessary mass to resist the lateral earth pressure of the soil being retained. 1. Why Option (a) is correct: Historically, timber was the primary material used for crib walls due to its availability and ease of assembly. In modern engineering, precast concrete units are preferred for their durability and strength. 2. Why Option (b) is incorrect: Masonry (brick or stone) is used for gravity walls or reinforced masonry walls, but not for the open-framework structure characteristic of a crib wall. 3. Why Option (c) is incorrect: While steel may be used in some specialized industrial applications, it is not the general material for standard crib walls; steel reinforcement is typically embedded in concrete (RCC) rather than forming the primary structural framework of a crib wall. 4. Why Option (d) is incorrect: Plastic cells are used in 'geocells' or geosynthetic reinforced soil systems, which are distinct from the structural framework of a traditional crib wall.

Permeability (hydraulic conductivity) refers to the ease with which a fluid (usually water) can flow through a porous medium. It is primarily governed by the size of the soil particles and the interconnectivity of the void spaces. According to Hazen's formula, the coefficient of permeability (k) is proportional to the square of the effective particle size (D10). 1. Gravel: Consists of the largest particles among the options. Large particles create large, interconnected void spaces, offering minimal resistance to water flow. Therefore, it has the highest permeability. 2. Silt: Has medium-to-small particles. The voids are smaller than in gravel, leading to lower permeability. 3. Clay: Consists of the smallest particles (colloidal size). The voids are extremely small and the particles have a high affinity for water (adsorption), creating high resistance to flow. Clay has the lowest permeability. 4. Loam: A mixture of sand, silt, and clay. While it has better permeability than pure clay, it is significantly lower than that of clean gravel due to the presence of finer particles filling the voids. Ranking of permeability: Gravel > Sand > Silt > Clay.

In civil engineering, specifically in the context of retaining structures, a 'breast wall' is a type of retaining wall built on the side of a slope or an excavation to prevent the soil from sliding down or to support the face of an excavated slope. Unlike a standard retaining wall that holds back a mass of earth from behind (backfill), a breast wall is typically constructed to stabilize the 'breast' or the front face of a cut slope to prevent landslides or erosion of the slope face. Analysis of options: - Option (a) 'Withstand water pressure' refers to dams or seepage walls. - Option (b) 'Support excavated slope face' is the primary function of a breast wall. - Option (c) 'Hold foundation' is not a standard definition for a breast wall; foundations are supported by footings or piles. - Option (d) 'Protect foundations from frost' refers to frost protection layers or insulation, not a breast wall.

According to Indian Standard (IS) specifications for bricks, bricks are classified into various classes based on their minimum compressive crushing strength. 1. First-Class Bricks: These are the highest quality bricks used for load-bearing walls. The minimum average crushing strength required for first-class bricks is 10.5 N/mm². 2. Second-Class Bricks: These have a minimum crushing strength of 7.0 N/mm². 3. Third-Class Bricks: These have a minimum crushing strength of 3.5 N/mm². 4. Fourth-Class Bricks: These are generally used for temporary structures and have a strength lower than 3.5 N/mm². Therefore, for first-class bricks, the crushing strength should not be less than 10.5 N/mm².

Stability under loading in soil mechanics is primarily governed by the soil's shear strength and its resistance to compression (settlement). 1. **Well-graded soil**: A well-graded soil contains a wide variety of particle sizes. In such a distribution, smaller particles fill the voids between larger particles. This results in a denser packing arrangement, higher interlocking between grains, and a higher internal angle of friction. Consequently, well-graded soils exhibit higher shear strength and lower compressibility, making them more stable under loading. 2. **Uniformly graded soil**: These soils consist of particles of nearly the same size. This leads to larger void spaces and less interlocking between particles, making them more susceptible to settlement and failure under load compared to well-graded soils. 3. **Higher void ratio**: A higher void ratio implies more empty space and less solid material per unit volume. This generally leads to lower strength and higher compressibility, which decreases stability. 4. **Plastic soil**: Plasticity is a characteristic of fine-grained soils (like clays). While they can be strong in some conditions, they are generally more prone to long-term consolidation settlement and volume changes (shrink-swell) compared to well-graded granular soils, making them less 'stable' in a general engineering loading context unless specifically treated. Since both soils in the question have the same dry density, the deciding factor is the grain size distribution. The well-graded soil provides superior mechanical interlocking and stability.

In soil mechanics, the unit weight (also known as bulk density when expressed as mass) is defined as the total weight of a soil sample (which includes the weight of the solid particles and the weight of the water in the voids) divided by the total volume of that sample. Mathematically, it is expressed as γ = W / V, where W is the total weight of the soil mass and V is the total volume. Analysis of options: - Option (a) refers to the unit weight of water (γw). - Option (b) refers to the dry unit weight (γd), which only considers the weight of solids. - Option (c) correctly describes the bulk unit weight (γ), which is the standard definition of 'unit weight of soil' unless specified as 'dry' or 'saturated'. - Option (d) is dimensionally incorrect as it describes a ratio of weight to weight (specific gravity or a similar ratio), not a unit weight (weight per volume).

The triaxial shear test is one of the most versatile and widely used methods for determining the shear strength parameters (cohesion 'c' and angle of internal friction 'φ') of soil. Its primary advantage over other tests (like the direct shear test) is the ability to control the drainage conditions and the pore water pressure. Depending on how the drainage valves are operated and the rate of loading, the test can be conducted as an Unconsolidated Undrained (UU) test, a Consolidated Undrained (CU) test, or a Consolidated Drained (CD) test. Why other options are incorrect: - a. Plasticity: This is determined using Atterberg limits tests (Liquid Limit, Plastic Limit). - c. Specific gravity: This is determined using a pycnometer or a density bottle. - d. Consolidation characteristics: These are determined using an Oedometer (One-dimensional consolidation test).

In the design of water tanks, the primary objective is to ensure 'watertightness' and durability against seepage and corrosion. According to standard codes of practice (such as IS 3370 for concrete structures for storage of liquids), a higher grade of concrete is required to reduce the permeability of the concrete. 1. Permeability: Lower grades of concrete (like M10, M15, M20) are more porous, which allows water to seep through the structure, leading to leakage and corrosion of the reinforcement steel. 2. Durability: Water tanks are often exposed to aggressive environments or constant moisture. Higher grades of concrete (M30 and above) provide a denser matrix, which significantly reduces the diffusion of harmful ions and water. 3. Code Requirements: For liquid-retaining structures, the minimum grade of concrete is typically specified as M30 to ensure the structure remains leak-proof and durable over its design life. Therefore, options a, b, and d are incorrect as they represent grades that are too porous for the specialized requirements of water-retaining structures.

A Crib wall is a prefabricated cellular structure made of interlocking precast concrete or timber units, which are then filled with granular material (like crushed stone or gravel). 1. Why it is suitable for steep terrains: Crib walls are flexible and permeable. Their ability to drain water freely prevents the buildup of hydrostatic pressure, which is a critical failure mode in steep, mountainous terrains with high rainfall. 2. Why it is suitable for quick installation: Because they are composed of prefabricated modular units, they can be assembled rapidly on-site without the need for extensive formwork, curing time for cast-in-situ concrete, or heavy machinery required for massive gravity walls. Comparison with other options: - Gravity walls (a): Require massive amounts of material and extensive site preparation, making them slow to install and difficult to transport to steep terrains. - Cantilever walls (b) and Counterfort walls (d): These are reinforced concrete structures that require significant formwork, steel reinforcement placement, and curing time, making them slower to install than modular crib walls.

A crib wall is a type of retaining structure consisting of an open-work framework of interlocking members. These members are typically laid in a criss-cross pattern to form a 'crib' or cage, which is then filled with granular material (like crushed stone or gravel) to provide stability through gravity. 1. **Materials**: Historically, timber was the primary material used for crib walls due to its availability and ease of assembly. In modern engineering, precast concrete units are widely used because they offer greater durability and resistance to decay compared to timber. 2. **Why other options are incorrect**: - **Masonry only (b)**: Masonry is used for gravity walls or cantilever walls, but a 'crib' specifically refers to the open-frame structure, which is not the characteristic of solid masonry. - **Steel reinforcement (c)**: While steel may be used in some specialized reinforced earth walls, a standard crib wall is defined by its modular frame (timber/concrete) rather than internal steel reinforcement. - **Plastic cells (d)**: While geocells exist for soil stabilization, traditional crib walls are defined as being constructed from timber or concrete units.

The design of water retaining structures requires specific considerations to prevent leakage and cracking due to hydrostatic pressure and environmental conditions, which are not covered in general RCC codes. 1. **IS 3370** is the specific Indian Standard code for the 'Code of Practice for Concrete Structures for Storage of Liquids'. It provides guidelines on limiting crack widths, specifying concrete grades, and detailing reinforcement specifically for water tanks and reservoirs. 2. **IS 456** is the general 'Code of Practice for Plain and Reinforced Concrete'. While it is the base code for all RCC work, water retaining structures must follow the additional, more stringent requirements of IS 3370. 3. **IS 800** is the 'Code of Practice for General Construction in Steel', which is irrelevant to concrete water structures. 4. **IS 13920** is the 'Ductile Design and Detailing of Reinforced Concrete Structures Subjected to Seismic Forces', used primarily for earthquake-resistant building design.

Step-by-step reasoning: 1. Water absorption refers to the ability of an aggregate to absorb water into its internal pore structure. 2. In a concrete mix, the 'effective water' is the water available to lubricate the aggregates and hydrate the cement paste, which directly determines the workability (slump) of the mix. 3. If aggregates with high water absorption are used without adjusting the mix design (i.e., without adding extra water to compensate for what the aggregate absorbs), the aggregates will soak up a portion of the mixing water. 4. This reduction in free water leads to a drier mix, significantly reducing the workability of the concrete, making it difficult to place and compact. 5. While compressive strength and durability can be affected indirectly if the mix is poorly compacted due to low workability, the most immediate and direct property affected by the absorption of mixing water is the workability. 6. Initial setting time is primarily a property of the cement and chemical admixtures, not the water absorption of the aggregate.