Past Questions — 2025

Artificial recharge refers to the process of augmenting the natural recharge of groundwater aquifers by intentionally directing surface water (such as rainwater, treated wastewater, or river water) into the ground. Step-by-step reasoning: 1. **Objective of Artificial Recharge**: The primary goal is to increase the water table level and store water underground for future use, especially in areas where groundwater extraction exceeds natural recharge. 2. **Evaluating Option (c)**: 'Replenish groundwater' directly describes the act of filling back the aquifers, which is the fundamental purpose of artificial recharge techniques (e.g., recharge pits, injection wells, percolation tanks). 3. **Evaluating Option (a)**: While reducing surface runoff is often a *method* or a *by-product* of artificial recharge (by capturing runoff to put it underground), the ultimate 'objective' is the storage in the aquifer, not just the reduction of runoff. 4. **Evaluating Option (b)**: Creating open wells is a method of *extracting* groundwater, not recharging it. 5. **Evaluating Option (d)**: Artificial recharge deals with water already present on the surface; it has no scientific mechanism to 'improve' or increase the amount of rainfall.

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 foundation work, making them slow to install and difficult to transport to steep terrains. - Cantilever walls (b): Require precise formwork and significant curing time for reinforced concrete, making them slower to install than modular systems. - Counterfort walls (d): These are complex reinforced concrete structures used for very high walls; they are labor-intensive and slow to construct.

Surface water refers to any body of water found on the Earth's surface, such as streams, rivers, lakes, and reservoirs. 1. Rivers (Option a): These are natural flowing watercourses on the surface of the ground. 2. Lakes (Option c): These are large bodies of surface water surrounded by land. 3. Reservoirs (Option d): These are artificial lakes created by dams to store surface water. 4. Aquifers (Option b): An aquifer is an underground layer of water-bearing permeable rock, gravel, sand, or silt. 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.

Hairline cracks appearing soon after construction in concrete structures (especially water tanks) are typically 'plastic shrinkage cracks' or 'drying shrinkage cracks'. 1. High Water-Cement (w/c) Ratio: A high w/c ratio increases the amount of evaporable water in the concrete mix. As this excess water evaporates, the volume of the concrete paste decreases, leading to shrinkage and the formation of hairline cracks. 2. Improper Curing: Curing is essential to maintain moisture for the hydration of cement. If curing is inadequate, the surface dries out too quickly relative to the interior, creating tensile stresses that result in shrinkage cracks. Analysis of other options: - Option (a): Low cement grade generally affects the ultimate strength and durability, but not necessarily the immediate formation of hairline shrinkage cracks. - Option (c): Reinforcement is used to control cracking and provide tensile strength; its presence prevents rather than causes hairline cracks. - Option (d): Rapid shuttering removal usually leads to structural sagging, honeycombing, or larger structural cracks due to premature loading, rather than widespread hairline shrinkage cracks.

A breast wall is a type of retaining wall specifically designed to support the face of an excavated slope or a hillside to prevent the soil from sliding down onto a road, railway track, or other infrastructure. Unlike a standard retaining wall that holds back a mass of earth from behind, a breast wall is typically built against the slope to provide stability and prevent surface failures of the cut slope. Analysis of other options: - Option (a) 'Withstand water pressure' refers to dams, levees, or seawalls. - Option (c) 'Hold foundation' is a general function of footings or piles, not specifically a breast wall. - Option (d) 'Protect foundations from frost' refers to frost protection layers or deep foundations (below the frost line), not a breast wall.

The Plate Load Test is a standard field test used to determine the ultimate bearing capacity of soil and the probable settlement under a given load. In this test, a steel plate is placed on the soil and loaded using a hydraulic jack until the soil fails or a specific settlement is reached. Why other options are incorrect: - a. Core Cutter Test: This is used to determine the in-situ bulk density (unit weight) of cohesive soils. - c. Vane Shear Test: This is used to determine the undrained shear strength of soft clays in the field. - d. Pycnometer Test: This is a laboratory test used to determine the specific gravity of soil solids.

A retaining wall is a structure designed to hold back soil or other materials that would otherwise slide or collapse due to gravity. The primary force acting on a retaining wall is the 'lateral earth pressure,' which is the horizontal pressure exerted by the soil mass behind the wall. The wall is engineered to resist this pressure to ensure the stability of the slope or the area behind it. Analysis of other options: - Option (a) 'Support roofing' is the function of beams, columns, or trusses. - Option (c) 'Anchor piles' refers to a specific foundation technique used to resist uplift or lateral loads, but it is not the primary purpose of a retaining wall itself. - Option (d) 'Store water' is the function of tanks, reservoirs, or dams (though dams are a specialized type of retaining structure, a general 'retaining wall' is defined by its relationship with soil/earth pressure).

Step-by-step reasoning: 1. Water absorption is the ability of an aggregate to absorb water into its pore structure. 2. In a concrete mix, the water-cement ratio is carefully calculated to ensure a specific consistency and strength. 3. If aggregates have high water absorption and this is not accounted for (i.e., the aggregates are not pre-saturated to a Saturated Surface Dry (SSD) condition), the aggregates will absorb a portion of the mixing water intended for lubrication and hydration. 4. This reduction in 'free water' available in the mix leads to a significant decrease in the fluidity and ease of placement of the concrete, which is defined as 'Workability'. 5. While compressive strength (c) and durability (d) can be affected if the water-cement ratio is altered during correction, the most immediate and direct effect of using dry, absorbent aggregates is the loss of workability. Initial setting time (a) is primarily a function of the cement chemistry and additives, not the absorption of the aggregate.

Pozzolanic materials (such as fly ash, silica fume, or volcanic ash) are siliceous or aluminosiliceous materials which, in themselves, possess little or no cementitious value but will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide [Ca(OH)2]—a byproduct of cement hydration—to form compounds possessing cementitious properties (C-S-H gel). 1. Why Option (b) is correct: The reaction consumes calcium hydroxide, which is the most soluble and weakest part of the hydrated cement paste. By replacing Ca(OH)2 with additional C-S-H gel, the pore structure becomes denser (reducing permeability), which significantly increases the durability of the concrete and enhances its resistance to sulphate attack (as there is less Ca(OH)2 available to react with sulphates). 2. Why other options are incorrect: - Option (a): Pozzolanic materials generally slow down the early strength gain and do not primarily aim to 'improve' (speed up or stabilize) the initial setting time; in fact, they often retard it. - Option (c): While some pozzolans like fly ash (spherical particles) can improve workability via the 'ball-bearing effect', this is a physical property of specific materials, not the primary chemical purpose of adding pozzolans to cement. - Option (d): While pozzolans do reduce the overall heat of hydration (which is beneficial for mass concreting), the term 'improve' in the context of building materials usually refers to enhancing the performance characteristics of the hardened state, such as durability and chemical resistance.

The specific gravity (G) of soil solids is defined as the ratio of the unit weight of the soil solids to the unit weight of distilled water. To determine this, a device called a Pycnometer (or a density bottle) is used. The process involves weighing a known volume of the pycnometer filled with water, then weighing it with a known mass of soil solids and water, and finally calculating the volume of the solids by displacement. Why other options are incorrect: - a. Triaxial apparatus: Used to determine the shear strength parameters (cohesion and angle of internal friction) of soil under controlled drainage and pressure conditions. - c. Casagrande apparatus: Used to determine the Liquid Limit (LL) of a soil sample (Atterberg limits). - d. Plate load test: A field test used to determine the ultimate bearing capacity of soil and the modulus of subgrade reaction.

In geotechnical engineering and geology, slope movement (mass wasting) refers to the downward movement of soil and rock under the influence of gravity. The primary types of slope movements are classified based on the type of material and the nature of the movement: 1. **Slides (Option a):** This occurs when a distinct mass of material moves along a well-defined surface of rupture (e.g., translational or rotational slides). 2. **Falls (Option b):** This occurs when material detaches from a steep slope or cliff and descends primarily by free-fall, bouncing, or rolling. 3. **Flows (Option c):** This occurs when material moves as a viscous fluid, often saturated with water (e.g., mudflows or debris flows). 4. **Creep:** (Another common type) The slow, imperceptible downward movement of soil. **Lifts (Option d)** is not a recognized term for a type of slope movement. In engineering, 'lift' usually refers to the thickness of a layer of soil placed during compaction (e.g., filling in layers), but it does not describe a mechanism of slope failure or movement.

Step-by-step reasoning: 1. **Revetment Wall**: A revetment is a facing of stone, concrete, or other materials placed on a slope (like a riverbank or shoreline) to protect it from erosion caused by water currents or wave action. Its primary purpose is to prevent the scouring of the bank. 2. **Toe Wall**: A toe wall is a small wall constructed at the base (toe) of a larger retaining wall or embankment to prevent the soil from sliding out from underneath the structure (scour protection at the base), but it is not the primary structure used for overall riverbank erosion protection. 3. **Breast Wall**: A breast wall is a retaining wall built to support the sides of a bridge abutment or a road cutting to prevent the soil from sliding into the waterway or road. It is designed to resist lateral earth pressure rather than surface erosion from flowing water. 4. **Anchor Wall**: An anchor wall is a type of retaining wall that uses anchors (cables or rods) driven into the ground to provide additional stability against overturning. It is used for high-pressure soil retention, not specifically for riverbank erosion protection. Conclusion: Since the question specifically asks for protection against erosion along riverbanks, the 'Revetment wall' is the correct technical term.

Run-off is the portion of precipitation that flows over the land surface to reach streams or rivers. It is governed by the water balance equation: Run-off = Precipitation - Infiltration - Evapotranspiration - Storage. 1. **Steeper slopes (Option c):** On a steep slope, gravity pulls water down the surface more quickly. This reduces the time available for water to infiltrate into the soil, thereby increasing the volume and velocity of surface run-off. This is the correct answer. 2. **More vegetation cover (Option a):** Vegetation acts as a barrier that slows down the flow of water and promotes infiltration. Roots also create pores in the soil, increasing its capacity to absorb water. Therefore, more vegetation decreases run-off. 3. **Highly permeable soil (Option b):** Permeability refers to the ability of soil to transmit water. Highly permeable soils (like sand) allow water to seep into the ground quickly, which significantly reduces the amount of water remaining on the surface as run-off. 4. **Higher infiltration (Option d):** Infiltration is the process by which water on the ground surface enters the soil. Since run-off and infiltration are inversely related (for a given amount of rainfall), higher infiltration directly leads to lower run-off.

To calculate the amount of rainwater that can be harvested from a roof, the standard formula used is: Harvested Water = Catchment Area × Annual Rainfall × Runoff Coefficient. 1. Roof Area (Catchment Area): The horizontal projection of the roof surface that collects the rain. 2. Rainfall: The total 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, and leakage. For example, a concrete roof has a different coefficient than a galvanized iron sheet roof. Why other options are incorrect: - a. Permeability of soil: This relates to how water infiltrates the ground, which is relevant for groundwater recharge but not for calculating the volume of water collected from a roof. - c. Catchment slope: While slope affects the velocity of runoff, the volume of water collected is based on the horizontal projection (area), not the slope. - d. Groundwater table depth: This is a hydrological characteristic of the subsurface and has no impact on the amount of rain falling on and being collected from a roof.

A toe wall is a structural element 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 soil from sliding outward, which would otherwise lead to the failure of the entire slope. 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 at the bottom, it is a specific structural feature of the slope's geometry, not a general foundation layer (like a raft or pile). - Option (d) is incorrect because while bridges have foundations (piers/abutments), a 'toe wall' is a specific term related to slope stability and retaining structures, not a general bridge component.

In geotechnical and structural engineering, the stability of a retaining wall depends heavily on the bearing capacity and settlement characteristics of the foundation soil. Silty soils are often problematic because they are compressible, susceptible to frost heave, and can lose significant strength when saturated (low shear strength). 1. Why 'b' is correct: To prevent differential settlement or shear failure (sliding/overturning) of the retaining wall, the weak silty soil must be either replaced with a well-graded granular material (like sand or crushed stone) or stabilized using chemical additives (like lime or cement) or mechanical means (like compaction or piles) to ensure it can support the structural load. 2. Why 'a' is incorrect: Directly casting the footing on unstable silty soil risks structural failure due to excessive settlement or bearing capacity failure. 3. Why 'c' is incorrect: While heavy machinery is used during construction, simply 'using' it is not a preparatory step to address the soil's inherent material properties. 4. Why 'd' is incorrect: Ignoring base conditions is a fundamental engineering error that leads to catastrophic structural collapse.

In soil mechanics, the Degree of Saturation (S) is defined as the ratio of the volume of water (Vw) to the volume of voids (Vv) in a soil mass, expressed as a percentage: S = (Vw / Vv) × 100%. 1. When a soil is 'fully saturated', it means that all the void spaces between the soil particles are completely filled with water. 2. In this condition, the volume of water (Vw) is exactly equal to the volume of voids (Vv). 3. Therefore, S = (Vv / Vv) × 100% = 1 (or 100%). Analysis of other options: - Option (a) 0: This represents a completely dry soil where no water is present in the voids. - Option (b) 50% and (c) 75%: These represent partially saturated soils, where only a fraction of the void space is filled with water and the rest is filled with air.

Slope stability is governed by the balance between shear strength (resisting force) and shear stress (driving force). 1. Why Option (c) is correct: Water is the most significant trigger for slope failure. Excess water infiltration increases the pore water pressure within the soil or rock mass. According to the principle of effective stress (σ' = σ - u), an increase in pore water pressure (u) reduces the effective stress (σ'), which directly decreases the shear strength of the material. Furthermore, water increases the unit weight of the soil, thereby increasing the driving force (downward stress) acting on the slope. Poor drainage prevents this water from escaping, leading to saturation and eventual failure. 2. Why Option (a) is incorrect: While vegetation helps bind soil with roots and reduces surface erosion, its absence is usually a contributing factor rather than the primary 'main cause' of deep-seated slope failures. 3. Why Option (b) is incorrect: Humidity refers to moisture in the air. While it relates to the environment, it does not provide the hydrostatic pressure or lubrication required to trigger a mass movement of soil or rock. 4. Why Option (d) is incorrect: Wind pressure can cause surface erosion or blow down trees, but it lacks the magnitude and mechanism to cause the structural failure of a geological slope in hilly terrain.

Brick earth consists of several constituents, each serving a specific purpose: 1. **Silica (SiO2):** It prevents the brick from cracking and shrinking during the drying and burning process. However, an excess of silica can make the brick brittle. 2. **Alumina (Al2O3):** This provides plasticity to the clay, allowing the brick to be molded easily. Excess alumina causes excessive shrinkage and cracking. 3. **Lime (CaO):** It acts as a flux to fuse the sand and alumina. It also helps in preventing shrinkage. However, excess lime causes the brick to disintegrate. 4. **Iron Oxide:** This is primarily responsible for the red or reddish-brown color of the bricks and also helps in the fusion of silica. 5. **Magnesia:** It imparts a yellowish tint to the bricks and reduces shrinkage. Therefore, among the given options, silica is specifically responsible for preventing cracking and shrinkage.

According to the Indian Standard (IS 269) and other international standards for Ordinary Portland Cement (OPC), the setting time is divided into two phases: Initial Setting Time and Final Setting Time. 1. Initial Setting Time: This is the time elapsed between the moment water is added to the cement and the time when the paste starts losing its plasticity. For OPC, the standard requirement is that the initial setting time should not be less than 30 minutes. This ensures that the concrete remains workable long enough for mixing, transporting, placing, and compacting. 2. Final Setting Time: This is the time elapsed between the moment water is added and the time when the cement paste has completely lost its plasticity and attained a certain degree of hardness. For OPC, the final setting time should not exceed 600 minutes (10 hours). Comparing the options: - a. 15 minutes: Too short; does not meet the IS standard. - b. 20 minutes: Too short; does not meet the IS standard. - c. 30 minutes: Correct; this is the minimum required initial setting time for OPC. - d. 60 minutes: While 60 minutes is acceptable (as it is not less than 30), the standard minimum threshold defined in the code is 30 minutes.

According to Indian Standard (IS) specifications and general civil engineering standards for building materials, bricks are classified into different classes based on their compressive (crushing) strength. 1. First-Class Bricks: These are the highest quality bricks used for load-bearing walls. Their minimum average crushing strength should not be less than 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. Comparing the options: - Option (a) 3.5 N/mm² corresponds to Third-Class bricks. - Option (b) 7.0 N/mm² corresponds to Second-Class bricks. - Option (c) 10.5 N/mm² corresponds to First-Class bricks. - Option (d) 5.0 N/mm² does not align with the standard classification for these specific classes.

The liquid limit (LL) is the moisture content at which a soil transitions from a plastic state to a liquid state. The most widely used standard method to determine this is using the Casagrande’s Apparatus. In this test, a groove is cut in a soil pat, and the cup is dropped from a height of 10 mm. The liquid limit is defined as the water content at which the two sides of the groove close for a distance of 12.7 mm (0.5 inches) after 25 blows. Why other options are incorrect: - a. Pycnometer Test: Used to determine the specific gravity of soil solids. - b. Core Cutter Test: Used to determine the in-situ bulk density (unit weight) of cohesive soils. - d. Sand Replacement Test: Used to determine the in-situ bulk density of sandy or gravelly soils where core cutters cannot be used.

The Indian Standard (IS) classification system for soils (IS 1498) is based on grain size distribution and plasticity characteristics. For fine-grained soils (silts and clays), the 'Plasticity Chart' is the primary tool used to differentiate between them. The chart plots the Plasticity Index (PI) against the Liquid Limit (LL). The 'A-line' (defined by the equation PI = 0.73(LL - 20)) separates clays (above the A-line) from silts (below the A-line). Why other options are incorrect: - b. Ternary diagram: These are used for three-component systems (like soil mixtures or phase diagrams) but are not the standard tool for IS soil classification. - 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.

The strength of concrete is primarily governed by the 'Water-Cement Ratio' (w/c ratio), a principle established by Duff Abrams (Abrams' Law). 1. Why Option (b) is correct: The w/c ratio determines the porosity of the hardened cement paste. A lower water-cement ratio (provided the mix is workable and fully hydrated) results in a denser microstructure with fewer capillary pores, which significantly increases the compressive strength of the concrete. Conversely, excess water creates voids when it evaporates, weakening the concrete. 2. Why other options are incorrect: - (a) Color of cement: The color is a physical characteristic and has no impact on the structural strength or chemical properties of the concrete. - (c) Size of coarse aggregate: While aggregate size affects workability, bonding, and the amount of paste required, it is not the primary determinant of the strength of the cement matrix itself. - (d) Quantity of sand: The proportion of sand (fine aggregate) affects the density and workability of the mix, but it does not dictate the fundamental strength of the concrete in the way the w/c ratio does.

In the context of building materials and aggregate testing, it is crucial to distinguish between toughness, hardness, and soundness: 1. **Toughness** is the resistance of an aggregate to failure under repeated impact or shock loading. The **Impact Test** (specifically the Aggregate Impact Test) is used to determine the toughness of aggregates. It measures the resistance to sudden shock or impact. 2. **Aggregate Impact Value (AIV)** is the *result* or the numerical value derived from the Impact Test, but the test itself is the Impact Test. In many exam contexts, 'Impact Test' is the standard term for the procedure to determine toughness. 3. **Hardness** is the resistance to surface abrasion, scratching, and wearing. This is measured by the **Los Angeles Abrasion Test** (Option d). 4. **Soundness** is the ability of an aggregate to resist volume changes caused by environmental factors like freeze-thaw cycles or chemical reactions. This is measured by the **Soundness Test** (Option c). Therefore, the test used to determine the toughness of aggregates is the Impact Test.