Past Questions — 2025

The amount of rainwater that can be harvested from a roof is determined by the volume of water that falls on the surface and the efficiency with which that water is collected. The standard formula used for calculating rainwater harvesting potential is: Harvested Water = Catchment Area × Annual Rainfall × Runoff Coefficient. 1. Roof Area (Catchment Area): The horizontal projection of the roof surface that intercepts the rain. 2. Rainfall: The depth of precipitation over a specific period. 3. Runoff Coefficient: A dimensionless factor (ranging from 0 to 1) that accounts for losses due to evaporation, absorption by the roofing material, or leakage. For example, a concrete roof has a higher runoff coefficient (approx. 0.7-0.9) than a thatched roof. Why other options are incorrect: - a. Permeability of soil: This affects how water infiltrates the ground, but not how much is collected from an impermeable roof surface. - c. Catchment slope: While slope affects the velocity of runoff, the total volume of water harvested depends on the horizontal area, not the slope angle. - d. Groundwater table depth: This is relevant for well design or drainage, but it does not determine the amount of rain falling on a roof.

Slope stabilization methods are categorized based on their duration of effectiveness and the mechanism of support. 1. **Shotcrete or Gunite (Option a):** This involves spraying concrete at high velocity onto a slope surface. It is primarily used as a surface treatment to prevent weathering, erosion, and the loosening of surface rocks. Because it is a thin shell that can crack over time and does not provide deep structural reinforcement to the overall mass of the slope, it is considered a short-term or temporary stabilization measure, often used to stabilize a face before permanent works are installed. 2. **Soil Nailing (Option b):** This is a permanent reinforcement technique where steel bars are drilled and grouted into the slope to create a coherent mass of reinforced soil. It is a long-term structural solution. 3. **Toe Buttress (Option c):** This involves placing a heavy mass of material (like rockfill or concrete) at the toe of the slope to resist rotational failure. This is a permanent structural modification to the slope geometry. 4. **Gabion Wall (Option d):** These are wire mesh cages filled with rocks. They provide permanent gravity-based support and allow for drainage, making them a long-term stabilization method. Therefore, Shotcrete/Gunite is the only option listed that serves as a surface-level, short-term stabilization method.

Step-by-step reasoning: 1. Understanding Material Properties: 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). 2. Foundation Behavior: Foundations are subjected to various loads. Due to the upward pressure exerted by the soil (bearing pressure) against the downward load of the structure, the foundation often behaves like an inverted beam. This causes bending, which induces compressive stresses on one side and tensile stresses on the other. 3. Role of Reinforcement: Steel reinforcement (rebar) is added to concrete because steel has high tensile strength. By placing steel in the zones where tension occurs, the reinforcement carries the tensile loads that the concrete cannot handle alone. 4. Evaluating Options: - (a) Reduce dead load: Reinforcement actually increases the dead load slightly because steel is denser than concrete. - (b) Resist tensile stresses: Correct. This is the primary structural purpose of adding steel to concrete. - (c) Prevent shrinkage: While specific 'shrinkage reinforcement' exists to control cracking, the primary purpose of structural reinforcement in foundations is to handle load-induced stresses. Shrinkage is a secondary concern compared to structural failure. - (d) Increase soil strength: Reinforcement is placed inside the concrete foundation, not the soil. To increase soil strength, techniques like soil stabilization, compaction, or piling are used, not concrete reinforcement.

Relative density (also known as density index, $I_D$ or $D_r$) is a physical property used specifically for cohesionless or granular soils (like sands and gravels) to describe the degree of packing or compactness of the soil particles. It is defined as the ratio of the difference between the maximum and minimum void ratios to the difference between the minimum void ratio and the actual void ratio of the soil in its current state. Formula: $D_r = \frac{e_{max} - e}{e_{max} - e_{min}} \times 100\%$ Why other options are incorrect: - Option (a): Moisture content is measured by the water content ratio, not relative density. - Option (c): Relative density is not applicable to cohesive soils (clays) because their structure is dominated by surface chemistry and plasticity rather than simple mechanical packing of grains. - Option (d): Plasticity is measured by the Plasticity Index ($I_p$), which is the difference between the liquid limit and plastic limit.

Retaining walls are designed to resist the lateral earth pressure exerted by the soil behind them. When water accumulates behind the wall (due to rain or groundwater), it exerts an additional lateral force known as hydrostatic pressure. This pressure significantly increases the total load on the wall, which can lead to structural failure or overturning if not managed. Drainage systems (such as weep holes, perforated pipes, and granular filter material) are provided to allow water to escape, thereby relieving this hydrostatic pressure and ensuring the stability of the wall. Analysis of other options: - Option (a): Making soil heavier would increase the lateral pressure on the wall, which is undesirable. - Option (c): Drainage does not add cohesion; in fact, saturation usually reduces the effective shear strength of the soil. - Option (d): Drainage is used to manage water within the soil mass; it does not change the physical slope angle of the terrain.

Rainwater harvesting (RWH) is the process of collecting, filtering, and storing rainwater for future use or for recharging groundwater. 1. Rooftop collection (Option a): This is a primary method of RWH where rain falling on the roof is collected via gutters and pipes and stored in tanks. 2. Recharge pits (Option c): These are artificial pits designed to direct rainwater into the ground to replenish the water table, which is a core component of groundwater harvesting. 3. Percolation tanks (Option d): These are small reservoirs that hold rainwater, allowing it to slowly seep (percolate) into the ground to recharge aquifers. In contrast, Irrigation from canals (Option b) involves the distribution of water from a river or a large reservoir through a network of man-made channels. This is a method of water distribution for agriculture, not a method of harvesting rainwater. Therefore, it does not fall under the definition of rainwater harvesting.

In soil mechanics, the phase relationship of a soil mass is defined by several key parameters. The correct answer is determined as follows: 1. **Void Ratio (e):** It is defined as the ratio of the volume of voids (Vv) to the volume of solids (Vs). Formula: e = Vv / Vs. This matches the definition provided in the question. 2. **Porosity (n):** It is the ratio of the volume of voids (Vv) to the total volume of the soil mass (Vt). Formula: n = Vv / Vt. While similar to void ratio, the denominator is the total volume, not the volume of solids. 3. **Degree of Saturation (S):** It is the ratio of the volume of water (Vw) to the volume of voids (Vv), expressed as a percentage. Formula: S = (Vw / Vv) × 100%. 4. **Water Content (w):** Also known as moisture content, it is the ratio of the weight of water (Ww) to the weight of solids (Ws). Formula: w = (Ww / Ws) × 100%. Therefore, the parameter defined as the volume of voids to the volume of solids is the Void Ratio.

A crib wall is a type of retaining wall consisting of a network of interlocking prefabricated units (usually timber, concrete, or steel) that form a 'crate' or 'crib' which is then filled with granular material (like crushed stone or gravel). 1. Why Option (c) is correct: One of the primary aesthetic and functional advantages of crib walls is that the open structure allows for the planting of vegetation within the fill. Once the vegetation grows, the roots help bind the soil/fill, and the foliage covers the structure, allowing the wall to blend naturally into the landscape. 2. Why Option (a) is incorrect: While RCC panels can be used in some modular walls, crib walls are characterized by their open-grid framework rather than solid panels. 3. Why Option (b) is incorrect: Crib walls can be designed as permanent structures, especially when using treated timber or precast concrete. 4. Why Option (d) is incorrect: While they are stable, their primary design purpose is to resist lateral earth pressure, not wind. In fact, their open nature makes them less relevant to wind resistance compared to solid walls.

The hydrological cycle is governed by the principle of conservation of mass. For a given catchment area or a specific volume of control, the change in storage is equal to the difference between the total inflow and total outflow. This is mathematically expressed as: (Inflow - Outflow = Change in Storage). This fundamental relationship is known as the Water Budget Equation. 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 is a tool for analysis, not the governing equation of the entire cycle. - c. Darcy's law: This describes the flow of a fluid through a porous medium (like soil), specifically relating flow rate to hydraulic gradient; it is a subset of groundwater hydrology, not the overall cycle. - d. Continuity equation: While the water budget equation is a specific application of the continuity equation (conservation of mass), in the context of hydrology and the hydrological cycle, the term 'Water Budget Equation' is the standard and specific terminology used.

In the context of construction materials and timber engineering, resistance to termites and decay is primarily determined by the presence of natural oils, resins, and the density of the wood. 1. **Sal (Shorea robusta):** Sal is a heavy, hard, and durable hardwood. It contains high concentrations of natural resins and tannins that make it highly resistant to termite attacks and fungal decay. It is widely used in heavy construction, railway sleepers, and door frames specifically because of its superior durability in harsh conditions. 2. **Teak (Tectona grandis):** While Teak is highly prized for its durability and natural oils that resist water and rot, in many comparative engineering standards for termite resistance in the Indian subcontinent, Sal is often rated higher for structural resistance against subterranean termites due to its extreme density. 3. **Cedar:** Cedar is naturally resistant to decay and insects, but it is a softwood and generally lacks the structural density and extreme termite resistance of Sal. 4. **Pine:** Pine is a softwood and is generally very susceptible to termite attacks and decay unless chemically treated. Therefore, among the given options, Sal is recognized as the most resistant to termite attack.

Step-by-step reasoning: 1. Definition of a lubricant: A lubricant is a substance used to reduce friction between two moving surfaces, preventing wear and tear and heat buildup. 2. Evaluating Option (a) Grease: Grease is a semi-solid lubricant consisting of a thickening agent and a base oil. It is specifically designed to adhere to moving parts (like bearings, joints, and gears) in heavy construction equipment, providing long-lasting lubrication and protection against contaminants. 3. Evaluating Option (b) Diesel: Diesel is a fuel used to power internal combustion engines; it is not used as a lubricant because it lacks the viscosity and additive properties required to reduce friction between mechanical parts. 4. Evaluating Option (c) Cement slurry: This is a mixture of cement and water used for grouting or bonding; it hardens over time and would cause mechanical parts to seize if used as a lubricant. 5. Evaluating Option (d) Paint: Paint is a protective or decorative coating; it is not a lubricant and would act as a contaminant in mechanical assemblies. Therefore, grease is the only appropriate lubricant among the choices.

Stability under loading in soil mechanics refers to the soil's ability to resist deformation (settlement) and shear failure. 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 shear strength. Consequently, well-graded soils exhibit lower compressibility and higher stability under loading. 2. **Uniformly graded soil (Option c)**: These soils consist of particles of approximately the same size. This leads to larger void spaces and less interlocking between particles, making them more prone to settlement and less stable compared to well-graded soils. 3. **Higher void ratio (Option a)**: The void ratio is the ratio of the volume of voids to the volume of solids. A higher void ratio indicates a looser packing of soil particles, which generally leads to higher compressibility and lower stability. 4. **Plastic soil (Option d)**: Plasticity is a characteristic of fine-grained soils (like clays). While plasticity allows the soil to deform without cracking, highly plastic soils are often subject to significant consolidation settlement and lower shear strength compared to well-graded granular soils under typical loading conditions. Since both soils in the question have the same dry density, the deciding factor for stability is the grain size distribution. The well-graded soil provides the best mechanical interlocking and structural integrity.

In rainwater harvesting systems for household use, the storage tank must be made of materials that are durable, non-toxic, and resistant to corrosion to ensure the water remains potable and safe for consumption. 1. **HDPE (High-Density Polyethylene)**: This is a food-grade plastic that is lightweight, durable, and does not leach harmful chemicals into the water. It is widely recommended for domestic water storage. 2. **Reinforced Concrete**: This is a standard engineering material for large-scale or permanent household storage. When properly cured and sealed (to prevent seepage), it provides excellent structural stability and keeps the water cool. Why other options are incorrect: - **Asbestos (a)**: Asbestos is a known carcinogen and is strictly prohibited for use in drinking water systems due to health risks. - **Lead (b)**: Lead is a toxic heavy metal that can leach into the water, causing severe neurological damage (lead poisoning). - **Uncoated Iron (d)**: Uncoated iron is highly susceptible to corrosion (rusting) when in contact with water, which contaminates the water with iron oxides and leads to structural failure of the tank.

In India, the Bureau of Indian Standards (BIS) defines the dimensions for modular bricks. A 'modular brick' is a brick whose dimensions are based on a module (standard unit) to ensure uniformity in construction. 1. **Standard Modular Size (excluding mortar):** The nominal size of a modular brick is 200 mm x 100 mm x 100 mm. However, this nominal size includes the mortar joints. The actual size of the brick itself (excluding mortar) is 190 mm x 90 mm x 90 mm. 2. **Nominal Size (including mortar):** When a 10 mm mortar joint is added to one side of the length, width, and height, the size becomes 200 mm x 100 mm x 100 mm. Analyzing the options: - Option (a) 190x90x80 mm is incorrect as the height is not 80 mm. - Option (b) 190x90x90 mm is the correct actual size of a modular brick. - Option (c) 200x100x100 mm is the nominal size (including mortar), whereas the question specifically asks for the size 'excluding mortar'. - Option (d) 230x110x70 mm refers to traditional/non-modular brick sizes used in some regions, not the standard modular size.

In hydrology, the water balance equation for precipitation considers various 'losses'—processes that remove water from the surface or prevent it from becoming surface runoff. 1. Interception (Option a): This occurs when precipitation is caught by vegetation or structures before it reaches the soil surface. It is a primary loss from precipitation. 2. Infiltration (Option b): This is the process by which water on the ground surface enters the soil. It is a major loss component that reduces surface runoff. 3. Evaporation (Option d): This is the process by which water changes from a liquid to a gas and returns to the atmosphere. Together with transpiration (evapotranspiration), it is a key loss. Extraction (Option c) is not a standard hydrological term used to describe the natural losses of precipitation. While 'extraction' might refer to human activities (like pumping groundwater), it is not a component of the natural precipitation loss cycle in the context of hydrology exams. Therefore, it is the correct answer as it is NOT a loss from precipitation.

In civil engineering, the 'grade' of cement refers to its compressive strength after 28 days of curing (measured in MPa). 1. **43 Grade Cement (OPC 43):** This is the most commonly used grade for Reinforced Cement Concrete (RCC) works. It provides a balanced strength-to-workability ratio and is the standard requirement for most structural elements like slabs, beams, and columns in general construction. 2. **33 Grade Cement (OPC 33):** This is a lower grade typically used for general masonry, plastering, or low-strength concrete works where high structural capacity is not required. 3. **53 Grade Cement (OPC 53):** This is a high-strength cement used for high-rise buildings, bridges, and pre-stressed concrete where rapid strength gain and very high compressive strength are essential. While it can be used for RCC, it is not the 'general' choice due to its higher heat of hydration and tendency to crack if not cured strictly. 4. **22 Grade Cement:** This is not a standard grade for Ordinary Portland Cement (OPC) used in structural RCC works. Therefore, for general RCC works, 43 grade cement is the industry standard.

A toe wall is a protective structure constructed at the base (the 'toe') of a slope, embankment, or retaining wall. Its primary engineering purpose is to provide stability to the slope and protect the base from erosion or 'scouring' caused by water flow or soil movement. By reinforcing the bottom of the slope, the toe wall prevents the slope from sliding or being undercut, which would otherwise lead to the failure of the entire embankment. Analysis of other options: - Option (a) is incorrect because structures at the top of slopes are typically called 'crest walls' or 'coping'. - Option (b) is incorrect because while a toe wall is part of the foundation system of a slope, it is not constructed 'below' the foundation; it is the lowest part of the visible structural support. - Option (d) is incorrect because while bridges have foundations (like abutments), a 'toe wall' specifically refers to slope stabilization rather than a general bridge component.

In soil mechanics and foundation engineering, foundations are categorized into shallow and deep foundations. 1. **Pile Foundation (Deep Foundation):** When the surface soil or the immediate layers have low bearing capacity and the strong, stable bearing stratum (hard rock or dense sand) lies at a significant depth, deep foundations like piles are used. Piles transfer the load to the deeper, stronger strata through skin friction or end-bearing. Therefore, it is the correct choice when the bearing stratum is at a greater depth. 2. **Mat/Raft Foundation (Shallow Foundation):** This is used when the soil bearing capacity is low or the column loads are very high, spreading the load over the entire area of the building. However, it is still considered a shallow foundation and is not used to reach deep strata. 3. **Spread Footing (Shallow Foundation):** This is the most common type of shallow foundation used when the bearing stratum is located at a shallow depth. It distributes the load of a single column over a wider area. 4. **Grillage Foundation (Shallow Foundation):** This consists of beams of steel sections used to distribute heavy concentrated loads over a larger area of soil. It is typically used for heavy steel columns and is not intended for reaching deep bearing strata.

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, 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 (consolidation test) to find the compression index and coefficient of consolidation.

A retaining wall is a structure specifically designed to resist the horizontal pressure of soil, waste materials, or water. The primary force acting on a retaining wall is the 'Lateral Earth Pressure,' which is the pressure exerted by the soil mass behind the wall. Failure occurs when this lateral pressure exceeds the wall's capacity to resist it, leading to failure modes such as sliding, overturning, or bearing capacity failure of the foundation. Why other options are incorrect: - a. Wind pressure: While wind can act on the exposed face of a wall, it is negligible compared to the massive force of the soil it is designed to hold. - c. Snow accumulation: Snow may add a small amount of surcharge load, but it is not the primary cause of failure for the structure as a whole. - d. Vertical dead loads: Vertical loads (the weight of the wall itself) actually help stabilize the wall against overturning and sliding; they are generally a stabilizing force rather than a cause of failure.

Surface water refers to any body of water found on the Earth's surface, including natural and man-made sources. 1. Rivers (Option a): These are natural flowing watercourses on the surface of the earth. 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. Because 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.

A normally consolidated (NC) clay is a soil that has never been subjected to a pressure higher than the current effective overburden pressure. In soil mechanics, NC clays are characterized by their tendency to undergo significant volume reduction (consolidation) when additional loads are applied. 1. **Why 'High compressibility' is correct**: Because the soil is at its maximum historical stress, any increase in load will lead to a significant decrease in void ratio, resulting in high compressibility compared to over-consolidated (OC) clays. 2. **Why 'Very low permeability' is incorrect**: While clays generally have low permeability, this is a characteristic of the material (clay) regardless of whether it is normally consolidated or over-consolidated. The question asks specifically what a *normally consolidated* clay will exhibit relative to its state. 3. **Why 'Low compressibility' is incorrect**: Low compressibility is a characteristic of over-consolidated clays, which have been subjected to higher pressures in the past and are therefore 'stiffer'. 4. **Why 'High shear strength' is incorrect**: Normally consolidated clays typically have lower shear strength compared to over-consolidated clays of the same composition because they have a looser structure and higher void ratio.

A retaining wall is subject to significant lateral earth pressure and vertical loads, which can lead to failure through sliding, overturning, or bearing capacity failure. To ensure stability, the foundation must have high shear strength and low compressibility. 1. **Compacted granular base (Correct):** Granular materials (like crushed stone or well-graded gravel) provide high bearing capacity, excellent drainage (reducing hydrostatic pressure), and minimal settlement when properly compacted. This provides the most stable platform for the wall's base slab. 2. **Clay bed (Incorrect):** Clay is cohesive and compressible. It is prone to long-term consolidation settlement and can lose strength when saturated, increasing the risk of wall tilting or failure. 3. **Loose sand (Incorrect):** Loose sand has low bearing capacity and is highly susceptible to settlement and liquefaction under certain conditions. It must be compacted to be suitable. 4. **Silty soil (Incorrect):** Silty soils are often unstable, highly compressible, and sensitive to moisture changes, making them poor foundations for heavy structural loads like retaining walls.

Run-off is the portion of precipitation that flows over the land surface rather than infiltrating into the soil. The relationship between run-off and the given options is as follows: 1. **Steeper slopes (Correct):** On a steep slope, the velocity of water flowing over the surface increases, and the time available for water to infiltrate into the ground decreases. Consequently, more water remains on the surface, leading to an increase in run-off. 2. **More vegetation cover (Incorrect):** Vegetation acts as a barrier that slows down the flow of water and increases the time available for infiltration. Roots also create pores in the soil, enhancing infiltration. Therefore, more vegetation decreases run-off. 3. **Highly permeable soil (Incorrect):** Permeability refers to the ability of soil to transmit water. Highly permeable soils (like sandy soils) allow water to seep into the ground quickly, which significantly reduces the amount of surface run-off. 4. **Higher infiltration (Incorrect):** Infiltration is the process by which water on the ground surface enters the soil. By definition, Run-off = Precipitation - Infiltration - Evapotranspiration. Therefore, as infiltration increases, run-off must decrease.

Permeability (or hydraulic conductivity) refers to the ease with which a fluid (usually water) can flow through a porous medium like soil. It is primarily governed by the size of the soil particles and the connectivity of the void spaces. 1. **Gravel (Option b):** Consists of the largest particles among the choices. Large particles create larger, well-connected interstitial voids (pores), which offer minimal resistance to water flow. Therefore, gravel has the highest permeability. 2. **Silt (Option a):** Particles are smaller than sand and gravel. The smaller pore spaces increase the frictional resistance to water flow, resulting in lower permeability than gravel. 3. **Clay (Option c):** Consists of the smallest particles (colloidal size). While clay may have high porosity (total volume of voids), the pores are microscopic and the water is held tightly by surface tension and electrical charges. This makes clay the least permeable soil (often acting as an aquiclude). 4. **Loam (Option d):** Loam is a mixture of sand, silt, and clay. While it has better drainage than pure clay, its permeability is significantly lower than that of clean gravel due to the presence of finer particles that plug the larger voids. In summary, permeability increases as the effective particle size increases: Clay < Silt < Sand < Gravel.