Past Questions

Termite resistance in wood is primarily determined by the presence of natural oils, resins, and extractives (like tannins and silica) that act as chemical deterrents to insects. 1. **Teak (Tectona grandis):** Teak is world-renowned for its exceptional durability and resistance to termites and decay. This is due to its high content of natural oils and silica, which make the wood unpalatable and toxic to termites. 2. **Sal (Shorea robusta):** While Sal is a very hard, heavy, and durable wood often used for railway sleepers and heavy construction, it is generally considered slightly less resistant to certain types of termite attacks compared to the high oil content of Teak, although it is still highly durable. 3. **Cedar:** Cedar contains natural oils that repel insects, but it is a softer wood and generally less resistant to heavy-duty termite infestations compared to Teak. 4. **Pine:** Pine is a softwood and is highly susceptible to termite attacks and decay unless it is chemically treated (pressure-treated). Therefore, among the given options, Teak is the most resistant to termite attack.

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.

According to IS 383 (the Indian Standard specification for coarse and fine aggregates from natural sources for concrete), aggregates are classified based on their particle size. Fine aggregate is defined as the material that passes through a 4.75 mm IS sieve. Coarse aggregate is defined as the material that is retained on a 4.75 mm IS sieve. Analysis of options: - Option (a) is correct as it aligns with the standard definition of fine aggregates. - Option (b) is incorrect because while fine aggregates are generally retained on a 75-micron sieve (material passing 75 microns is considered 'silt' or 'clay'), the primary defining boundary for 'fine aggregate' is the 4.75 mm sieve. - Option (c) and (d) are incorrect as 10mm and 2.36mm are specific sieve sizes used for grading and classification of coarse aggregates or specific sand zones, but they do not define the general boundary between fine and coarse aggregates.

Fineness of cement refers to the size of the particles. Finer cement has a larger surface area, which leads to a faster rate of hydration and quicker strength gain. The fineness of cement is typically measured using two methods: 1) Sieve Analysis (using a 90-micron IS sieve) and 2) Air Permeability Method (Blaine's test). Therefore, the Sieve Test is the correct method among the options provided. Why other options are incorrect: - b. Soundness Test: This test is conducted to determine the ability of cement to retain its volume after hardening (checking for excessive expansion due to free lime or magnesia) using the Le Chatelier apparatus or Autoclave test. - c. Consistency Test: This is a preliminary test (usually using Vicat's apparatus) to determine the amount of water required to produce a cement paste of standard consistency, which is necessary for other tests like setting time. - d. Tensile Strength Test: This is generally performed on hardened concrete or steel, not on raw cement powder to determine its fineness.

Artificial recharge is the process of intentionally augmenting the natural recharge of groundwater aquifers. This is typically achieved by directing surface water (such as rainwater or treated wastewater) into the ground through methods like recharge pits, shafts, injection wells, or spreading basins. Step-by-step analysis of options: - Option (a) 'Reduce surface water runoff': While artificial recharge often results in a reduction of surface runoff as a byproduct, the primary *objective* is not the reduction of runoff itself, but the utilization of that water to benefit the aquifer. - Option (b) 'Create open wells': Open wells are structures used to *extract* groundwater; they are not the objective of the recharge process. - Option (c) 'Replenish groundwater': This is the core definition and objective of artificial recharge. It aims to raise the water table, prevent saltwater intrusion in coastal areas, and ensure a sustainable water supply for future extraction. - Option (d) 'Improve rainfall': Artificial recharge deals with water that has already fallen as precipitation; it has no mechanism to influence or improve the atmospheric processes that cause rainfall.

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 that can accurately measure the mass of a known volume of liquid and the mass of soil solids displaced by that liquid is required. A Pycnometer (or a density bottle) is specifically designed for this purpose. 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 as part of Atterberg limits testing. - d. Plate load test: A field test used to determine the ultimate bearing capacity of soil and the settlement characteristics of the ground.

According to the Indian Standard (IS) specifications for Ordinary Portland Cement (OPC), the setting time is divided into two stages: 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 when the cement paste has completely lost its plasticity and has attained sufficient firmness to resist a certain amount of pressure. For OPC, the final setting time should not exceed 600 minutes (10 hours). Comparing the options: - Option (a) 15 minutes: Too short; does not meet IS standards. - Option (b) 20 minutes: Too short; does not meet IS standards. - Option (c) 30 minutes: Correct as per IS specifications. - Option (d) 60 minutes: While 60 minutes is greater than 30, the minimum requirement (the threshold) specified by the code is 30 minutes.

A retaining wall is a structure designed to hold back soil or other materials that would otherwise move due to gravity. The primary engineering purpose of a retaining wall is to resist the 'lateral earth pressure' exerted by the soil behind it, preventing slope failure or landslides and allowing for the creation of level terraces in hilly terrain. Analysis of other options: - Option (a) 'Support roofing' is the function of beams, columns, or load-bearing walls, not retaining walls. - Option (c) 'Anchor piles' refers to a foundation technique; while some retaining walls use anchors (anchored walls), the wall's primary purpose is not to anchor the piles themselves. - Option (d) 'Store water' is the function of tanks, reservoirs, or dams. While some retaining walls may be designed for hydrostatic pressure, their primary definition relates to earth retention.

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 decreases, leading to shrinkage. Since the structure is restrained, this shrinkage manifests as hairline cracks. 2. **Improper Curing**: Curing is essential to maintain moisture for the hydration of cement. If curing is inadequate, the surface dries out rapidly, leading to differential shrinkage between the surface and the core of the concrete, which triggers cracking. Why other options are incorrect: - **Option a (Low cement grade)**: While cement grade affects strength, it is not the primary driver of immediate hairline shrinkage cracks; shrinkage is more closely tied to the water content and curing process. - **Option c (Use of reinforcement)**: Reinforcement is intended to control cracking and provide tensile strength. Its presence generally reduces the width of cracks rather than causing them. - **Option d (Rapid shuttering removal)**: Removing formwork too early typically leads to structural sagging, deflection, or large structural cracks due to the concrete not having reached sufficient strength to support its own weight, rather than widespread hairline shrinkage cracks.

In soil mechanics and foundation engineering, foundations are broadly classified into two categories based on the depth of the foundation relative to its width (D/B ratio): 1. Shallow Foundations: These are foundations where the depth (D) is generally less than or equal to the width (B). They transfer the load to the soil at a shallow depth. Examples include Isolated footings, Combined footings, Strip footings, and Mat/Raft foundations. 2. Deep Foundations: These are foundations where the depth is significantly greater than the width. They are used when the surface soil is too weak to support the load, transferring the load to deeper, stronger strata via skin friction or end bearing. Examples include Pile foundations, Caissons (Well foundations), and Pier foundations. Analyzing the options: - (a) Isolated footing: A type of shallow foundation used to support a single column. - (b) Pile foundation: A deep foundation consisting of long, slender columns. - (c) Caisson: A deep foundation, often used for bridge piers in water. - (d) Pier foundation: A deep foundation used to transfer loads to a deeper bearing stratum. Therefore, only the isolated footing is a shallow foundation.

In Limit State Method (LSM) for reinforced concrete design, the partial safety factor for concrete is typically taken as 1.5 (for concrete strength in design). Hence option b is correct. Option c (1.25) is not the standard value for concrete in LSM; it is sometimes associated with other materials or specific code contexts, but not the usual concrete factor. Option a (1.0) would mean no safety reduction, which is not used for design strength. Option d (2.0) is too high and not the prescribed partial safety factor for concrete in standard LSM design.

The minimum depth of a shallow foundation is determined by several geotechnical and environmental factors to ensure the stability and longevity of the structure. 1. **Shear Strength**: The foundation must be placed at a depth where the soil possesses sufficient bearing capacity (shear strength) to support the structural loads without undergoing shear failure. If the surface soil is loose or weak, the foundation must be taken deeper to reach a more competent stratum. 2. **Depth of Water Table**: The presence of groundwater significantly affects the bearing capacity of the soil. A high water table reduces the effective stress and the shear strength of the soil (often by nearly half in sandy soils). Therefore, the depth of the foundation is governed by the need to avoid buoyancy effects and the reduction in bearing capacity caused by the water table. 3. **Other Factors (Contextual)**: While not listed as the primary answer here, depth is also governed by the 'frost line' (in cold climates) and the 'shrink-swell' zone of expansive soils. Why other options are incorrect: - **Option a**: The type of structure determines the load, but the *depth* is governed by the soil's ability to support that load, not the structure itself. - **Option b**: Settlement criteria usually govern the *size* (width/length) of the foundation rather than the minimum depth. - **Option d**: Grain size influences the soil type, but it is the resulting shear strength and permeability (water table interaction) that directly govern the depth requirement.

In Reinforced Concrete Cement (RCC) design, columns are classified as 'short' or 'slender' based on their slenderness ratio. The slenderness ratio is defined as the ratio of the effective length of the column to its least lateral dimension. 1. Short Columns: A column is considered short if its slenderness ratio is less than a specific limit (typically 12 according to IS 456:2000). Short columns primarily fail due to direct crushing of the material. 2. Slender (Long) Columns: A column is considered slender if its slenderness ratio exceeds the limit. These columns are prone to buckling before the material reaches its ultimate crushing strength. Why other options are incorrect: - a. Cross-sectional shape: While the shape affects the moment of inertia, the classification of 'short' vs 'slender' depends on the ratio of length to dimension, not the shape itself. - b. Diameter: Diameter is only a parameter for circular columns; it is a component used to calculate the slenderness ratio, but not the defining criterion on its own. - d. Material type: Both short and slender columns can be made of the same material (e.g., concrete); the classification is a geometric property related to stability.

The Plate Load Test is a standard field test used to determine the ultimate bearing capacity of soil and the settlement characteristics of the soil 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. 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, saturated clays, not the overall bearing capacity of various soil types. - d. Pycnometer Test: This is a laboratory test used to determine the specific gravity of soil solids.

Water tanks are liquid-retaining structures that require high durability and low permeability to prevent leakage and protect reinforcement from corrosion. According to standard engineering practices and codes (such as IS 456 and IS 3370), concrete used for water-retaining structures must be dense and high-strength to ensure water-tightness. 1. **Durability Requirements**: Water tanks are often exposed to severe environmental conditions or aggressive chemicals in water. High-grade concrete (M30 and above) provides a denser matrix with fewer interconnected pores, reducing the permeability of the concrete. 2. **Crack Control**: Higher grades of concrete, when combined with appropriate reinforcement and design (as per IS 3370), help in controlling crack widths, which is critical for liquid-retaining structures. 3. **Comparison with other options**: - M10 and M15 are lean concretes used for leveling courses or PCC (Plain Cement Concrete) and lack the strength and density required for structural water tanks. - M20 is a general-purpose grade for basic RCC work but is generally considered insufficient for the stringent permeability and durability requirements of specialized water-retaining structures. Therefore, M30 or above is the standard recommendation for ensuring the longevity and functionality of water tanks.

Lubrication is essential in construction equipment to reduce friction, wear, and heat between moving mechanical parts. 1. **Grease (Option a):** Grease is a semi-solid lubricant consisting of a thickening agent (usually soap) and a lubricating oil. It is widely used in construction machinery for joints, bearings, and open gears because it stays in place (adheres to the surface) better than liquid oils, providing long-term protection against wear and contamination from dust and water. 2. **Diesel (Option b):** Diesel is a fuel used to power internal combustion engines. While it is a hydrocarbon, it lacks the viscosity and additive properties required to act as an effective lubricant; using it as a lubricant would lead to rapid wear and tear of components. 3. **Cement slurry (Option c):** Cement slurry is a mixture of cement and water used in construction for grouting or lubrication of piles during driving (in specific geotechnical contexts), but it is not a mechanical lubricant for equipment parts. In fact, once it hardens, it would seize any moving part. 4. **Paint (Option d):** Paint is a protective coating used to prevent corrosion and provide aesthetic appeal. It is not a lubricant and would actually increase friction if applied to moving mechanical interfaces.

In soil mechanics, the Atterberg limits define the critical water contents of a fine-grained soil. 1. **Plastic Limit (PL):** This is defined as the water content at which a soil transitions from a semi-solid state to a plastic state. In laboratory testing, it is specifically determined as the water content at which a soil thread, rolled to a diameter of 3.2 mm (1/8 inch), just begins to crumble. Therefore, option (b) is the correct definition. 2. **Analysis of other options:** - **Option (a):** The water content at which soil becomes semi-solid is the transition point between the plastic and semi-solid states, but the 'Plastic Limit' is the boundary itself. The state below the plastic limit is semi-solid. - **Option (c):** The water content at which soil begins to flow is known as the **Liquid Limit (LL)**. - **Option (d):** The water content when soil is completely dry is simply 0% moisture content, which is not a defined Atterberg limit.

In rainwater harvesting systems for household use, the storage tank must be made of materials that are durable, non-toxic, and do not leach harmful chemicals into the water. 1. **HDPE (High-Density Polyethylene)**: This is a food-grade plastic that is corrosion-resistant, lightweight, and does not react with water, making it ideal for potable water storage. 2. **Reinforced Concrete**: This is a traditional and highly durable material for large-scale storage. When properly cured and sealed (often with food-grade liners or waterproof coatings), it provides excellent structural stability and keeps 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 causes lead poisoning; it must never be used for storing drinking water. - **Uncoated Iron (d)**: Uncoated iron is highly susceptible to corrosion (rusting) when in contact with water, which contaminates the water and leads to structural failure of the tank.

In cold weather concreting, the primary challenge is the slow rate of hydration of cement due to low temperatures. This leads to a delayed setting time and a slow gain in early strength, which can increase the risk of freezing and structural failure. Rapid Hardening Cement (RHC) is specifically designed to gain strength quickly. It achieves this through a higher tricalcium silicate (C3S) content and a finer grinding of the clinker, which accelerates the hydration process and generates more heat of hydration. This internal heat helps maintain the temperature of the concrete mix, ensuring that the concrete sets and gains sufficient strength rapidly even in cold environments. Analysis of other options: - Ordinary Portland Cement (OPC): Its hydration rate slows down significantly in cold weather, making it less ideal than RHC for rapid strength gain. - Low Heat Cement: This cement is designed to minimize 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. - Sulphate Resisting Cement: This is used in environments with high sulphate concentrations (like coastal areas or certain soils) to prevent chemical attack; it does not specifically address cold weather hydration issues.

A hydrograph is a fundamental tool in hydrology used to analyze the response of a watershed to a rainfall event. By definition, a hydrograph is a graph showing the rate of flow (discharge) measured at a specific point in a river or stream over a period of time. Step-by-step analysis of options: 1. Option (a) 'Rainfall vs time' describes a Hyetograph, not a hydrograph. A hyetograph represents the intensity of rainfall over time. 2. Option (b) 'Discharge vs time' is the correct definition. The y-axis represents the discharge (usually in m³/s or cfs) and the x-axis represents time. 3. Option (c) 'Evaporation vs time' is a plot used in climatology or water balance studies but does not constitute a hydrograph. 4. Option (d) 'Infiltration vs area' is not a standard hydrological plot; infiltration is typically measured as a rate (depth per unit time) vs time.

Step-by-step reasoning: 1. **Analysis of the Requirement**: The question asks for a structure specifically designed to protect riverbanks from erosion caused by the flow of water. 2. **Evaluating Option (b) Revetment wall**: A revetment is a facing of stone, concrete, or other materials placed on a bank or shoreline to protect it from erosion caused by wave action or currents. It acts as a protective layer (armoring) that prevents the soil from being washed away by the river flow. This directly matches the question's requirement. 3. **Evaluating Option (a) Toe wall**: A toe wall is a wall constructed at the base (toe) of a slope or a larger retaining wall to prevent the sliding or scouring of the base. While it helps in stability, it is not the primary structure used for overall bank erosion protection. 4. **Evaluating Option (c) Breast wall**: A breast wall is a retaining wall built across a slope or at the edge of a road/embankment to prevent the soil from sliding down. It is typically used for slope stability rather than protecting against hydraulic erosion from a river. 5. **Evaluating Option (d) 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 a structural design for stability, not a specific erosion protection measure for riverbanks. Conclusion: The revetment wall is the correct technical term for a structure providing protection against erosion along riverbanks.

The hydrological cycle is governed by the principle of conservation of mass. For a given catchment area or a specific volume of the earth's atmosphere/crust over a specific time interval, the inflow must equal the outflow plus the change in storage. 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), which is only a small part of the hydrological cycle (infiltration/groundwater flow). - d. Continuity equation: While the water budget equation is a specific application of the continuity equation (conservation of mass), in the context of Hydrology, the term 'Water Budget Equation' is the standard terminology used to represent the cycle's balance.

The runoff coefficient (C) is a dimensionless coefficient used in the Rational Method (Q = CiA) to represent the fraction of rainfall that becomes surface runoff. It depends on the permeability of the surface. 1. Concrete surfaces are considered 'impervious' or 'impermeable,' meaning they allow very little to no water to infiltrate into the ground. 2. Because infiltration is negligible, most of the precipitation that falls on a concrete surface becomes runoff. 3. Typical values for the runoff coefficient for concrete range from 0.80 to 0.95, depending on the smoothness and condition of the surface. Analysis of options: - Option (a) 0.1: Typical for sandy soils or heavily forested areas with high infiltration. - Option (b) 0.3: Typical for lawns or parks. - Option (c) 0.85 - 0.95: Correct for impervious surfaces like concrete and asphalt. - Option (d) 1.2: Impossible, as the runoff coefficient cannot exceed 1.0 (you cannot have more runoff than the total rainfall received).

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 into storage tanks. 2. Recharge pits (Option c): These are structures designed to divert rainwater into the ground to replenish the water table, which is a key component of groundwater rainwater harvesting. 3. Percolation tanks (Option d): These are artificial ponds designed to hold rainwater, allowing it to seep (percolate) into the ground to recharge aquifers. In contrast, Irrigation from canals (Option b) involves the distribution of water from a river or reservoir through a network of man-made channels. This is a method of surface water irrigation and does not involve the collection or harvesting of rainwater falling on a specific site. Therefore, it is not a part of rainwater harvesting.

Step-by-step reasoning: 1. **Plywood**: This is an engineered wood product made by gluing together thin layers of wood veneers. These layers (plies) are glued with their grains oriented perpendicular to each other (cross-graining), which provides high strength, stability, and resistance to splitting. 2. **Particle board**: This is made from wood chips, sawmill shavings, or sawdust bonded together with a resin under heat and pressure. It does not consist of 'thin layers' of wood veneers. 3. **Block board**: This consists of a core of solid wood strips (blocks) sandwiched between two layers of veneer. While it uses veneers on the surface, the core is not made of thin layers glued together, but rather solid blocks. 4. **Fiberboard (MDF/HDF)**: This is made by breaking down wood residuals into fibers, combining them with wax and resin, and forming panels under high temperature and pressure. It is a homogeneous material rather than a layered veneer product. Therefore, the product specifically defined by gluing thin layers (veneers) together is Plywood.