Past Questions

Seasoning of timber is the process of reducing the moisture content (sap) of the wood to a level that is in equilibrium with the environment in which the timber will be used. 1. Why Option (b) is correct: Freshly felled timber contains a large amount of water. If used immediately, this water evaporates over time, leading to shrinkage, warping, cracking, and susceptibility to fungal attacks. Seasoning removes this excess moisture, thereby increasing the strength, durability, and dimensional stability of the wood. 2. Why other options are incorrect: - Option (a): Seasoning actually decreases the weight of the timber because water is removed. - Option (c): While seasoning might slightly alter the appearance, its primary engineering purpose is structural stability, not aesthetic color improvement. - Option (d): Seasoning does not make timber fireproof; in fact, dry timber may ignite more easily than green (wet) timber, although it is more stable for construction.

In slope stability analysis, the Factor of Safety (FoS) is a measure of the stability of a soil slope against failure. Failure occurs when the shear stress ($ au$) acting along a potential failure surface exceeds the shear strength ($s$ or $ au_f$) of the soil. Therefore, the Factor of Safety is defined as the ratio of the resisting forces (shear strength) to the driving forces (shear stress). Mathematically: FoS = (Available Shear Strength) / (Mobilized Shear Stress). Why other options are incorrect: - Option (a): The ratio of active to passive pressure is used in the design of retaining walls to check for stability against sliding or overturning, but it is not the definition of the factor of safety for slope stability. - Option (b): Weight and height are parameters used to calculate stresses, but their ratio does not define the stability factor. - Option (d): Cohesion is a component of shear strength (according to Mohr-Coulomb theory), and the slope angle affects the driving stress, but their direct ratio is not the definition of the factor of safety.

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.

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.

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.

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.

Efflorescence refers to the appearance of a white powdery deposit on the surface of bricks or concrete. This occurs when soluble salts present in the brick material or the mortar react with moisture. As water penetrates the brick and subsequently evaporates, these soluble salts are carried to the surface and crystallize, leaving behind the white powder. The efflorescence test is specifically designed to determine the quantity and nature of these soluble salts to ensure the durability and aesthetic quality of the masonry. Why other options are incorrect: - a. Sulphates: While sulphates are a common type of soluble salt that causes efflorescence, the test assesses all soluble salts (including nitrates, chlorides, etc.), not just sulphates. - c. Clay content: Clay content is determined by the composition analysis of the brick earth, not by an efflorescence test. - d. Organic impurities: Organic impurities are typically checked through the burning/firing process or specific chemical analysis, as they cause discoloration or holes (bloating) in the brick, not surface powdering.

In soil mechanics, a compaction curve is plotted by graphing the dry density (ρd) of a soil sample against its moisture content (w) for a constant compactive effort. As moisture is added to a dry soil, the water acts as a lubricant, allowing soil particles to slide over each other and pack more densely, causing the dry density to increase. However, beyond a certain point, the water begins to occupy space that would otherwise be filled by soil solids, causing the dry density to decrease. The peak of this bell-shaped curve represents the Maximum Dry Density (MDD). The specific moisture content at which this peak occurs is known as the Optimum Moisture Content (OMC). Why other options are incorrect: - Option (a): The peak does not represent the maximum moisture content; moisture content can be increased indefinitely (until saturation), but the density will drop. - Option (c): The Zero Air Voids (ZAV) line is a theoretical line that the compaction curve approaches but never crosses; it is not the peak itself. - Option (d): The Liquid Limit is an Atterberg limit related to the consistency of fine-grained soils, not a point on a compaction curve.

Step-by-step reasoning: 1. Concrete is a composite material that is very strong in compression but very weak in tension (its tensile strength is typically only 10% of its compressive strength). 2. Foundations are subject to various loads, including vertical loads from the superstructure and differential settlement of the soil. 3. These loads often induce bending moments within the foundation slab or footing. 4. Bending causes one side of the concrete member to be in compression and the opposite side to be in tension. 5. Since concrete cannot effectively resist these tensile stresses, steel reinforcement (which has high tensile strength) is embedded in the tension zone to carry those loads and prevent the concrete from cracking or failing. Analysis of other options: - (a) Reduce dead load: Reinforcement (steel) actually increases the dead load because steel is denser than concrete. - (c) Prevent shrinkage: While specific 'shrinkage reinforcement' exists, the primary structural purpose of reinforcement in foundations is load-bearing (tensile resistance). Shrinkage is primarily controlled by curing and joint design. - (d) Increase soil strength: Reinforcement is placed within the concrete foundation, not the soil. To increase soil strength, techniques like soil stabilization, compaction, or piling are used, not concrete reinforcement.

According to Indian Standard (IS) specifications and general civil engineering standards for building materials, bricks are classified based on their quality and compressive strength. For a First-Class Brick, the minimum average crushing strength required is 10.5 N/mm². Breakdown of brick classes by strength: 1. First Class Bricks: Minimum crushing strength of 10.5 N/mm². 2. Second Class Bricks: Minimum crushing strength of 7.0 N/mm². 3. Third Class Bricks: Minimum crushing strength of 3.5 N/mm². 4. Fourth Class Bricks: These are generally over-burnt or under-burnt bricks used for temporary structures and do not have a strictly defined high strength requirement. Therefore, option (d) is the correct requirement for first-class bricks, while options (a) and (b) correspond to third and second-class bricks respectively.

In the construction of water-retaining structures like water tanks, construction joints are inevitable due to the pouring of concrete in stages. These joints are potential paths for water leakage. To prevent this, a 'Water bar' (also known as a waterstop) is used. A water bar is a flexible strip made of PVC or rubber that is embedded halfway into one concrete pour and halfway into the next. It creates a physical barrier that blocks the flow of water through the joint. Why other options are incorrect: - a. Steel bars: These provide structural strength and reinforcement against tension but do not create a watertight seal. - c. Formwork: This is the temporary mold used to shape the concrete; it is removed after the concrete sets and does not prevent leakage. - d. Lining: While lining (like epoxy or membranes) can be applied to the interior surface of a tank to reduce permeability, it is a surface treatment rather than a specific component designed to seal construction joints.

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).

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.

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.

Slope stability is fundamentally a balance between the driving forces (gravity, external loads) that tend to cause the soil mass to slide and the resisting forces that hold the soil in place. The primary resisting force in soil is its shear strength. According to the Mohr-Coulomb failure criterion, shear strength is defined by cohesion (c) and the angle of internal friction (φ). If the shear stress induced along a potential failure plane exceeds the shear strength of the soil, the slope will fail. Why other options are incorrect: - a. Plasticity index: While it helps in classifying soil and predicting behavior (like swelling or shrinkage), it is not the direct force resisting slope failure. - b. Moisture content: Moisture content affects shear strength (by increasing pore water pressure and reducing effective stress), but it is a condition/variable rather than the property that provides the actual resistance. - d. Density index: Relative density affects the shear strength of cohesionless soils, but it is a secondary property; the ultimate factor determining stability is the resulting shear strength.

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.

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.

The water-cement (w/c) ratio is the ratio of the weight of water to the weight of cement used in a concrete mix. According to Abram's Law, the strength of concrete is primarily dependent on the w/c ratio; as the ratio increases, the strength decreases due to the formation of more capillary pores. 1. **General Construction Range:** For most general construction purposes, a w/c ratio between 0.40 and 0.60 is typically used to balance workability and strength. A value of 0.5 is considered the standard representative average for general-purpose concrete. 2. **Analysis of Options:** - **0.3 (Option a):** This is a very low ratio, typically reserved for high-strength concrete or specialized pre-cast elements. It often requires the use of superplasticizers to ensure the mix is workable. - **0.5 (Option b):** This is the ideal balance for general construction, providing sufficient strength and adequate workability without excessive shrinkage. - **0.7 (Option c):** This is too high for structural concrete. It leads to high porosity, increased permeability, and significantly reduced compressive strength. - **0.9 (Option d):** This ratio is excessively high and would result in very weak concrete prone to severe segregation and shrinkage cracks.

The correct instrument for measuring precipitation (rainfall) is the Rain Gauge. It collects rainfall over a specific period, and the depth is measured using a graduated cylinder. Analysis of other options: - a. Evaporimeter: Used to measure the rate of evaporation of water from a surface. - c. Barometer: Used to measure atmospheric pressure. - d. Anemometer: Used to measure wind speed and direction.

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.

In soil mechanics, the unit weight (also known as bulk density when expressed as mass) is defined as the total weight of a soil mass (which includes the weight of soil solids and the weight of water filling the voids) divided by the total volume of that soil mass. Mathematically, it is expressed as γ = W / V, where W is the total weight and V is the total volume. Analysis of options: - Option (a) describes the unit weight of water (γw). - Option (b) describes the dry unit weight (γd), which only considers the weight of solids. - Option (c) correctly describes the bulk unit weight, which is the general definition of 'unit weight of soil'. - 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).

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 react with calcium hydroxide [Ca(OH)2]—a byproduct of cement hydration—in the presence of water to form compounds possessing cementitious properties (C-S-H gel). 1. Why Option (b) is correct: The reaction between pozzolans and calcium hydroxide consumes the Ca(OH)2, which is the most soluble and weakest part of the hardened cement paste. By replacing Ca(OH)2 with C-S-H gel, the pore structure becomes denser (reducing permeability), which significantly increases the durability of the concrete and its resistance to chemical attacks, specifically 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 optimize) the initial setting time; in fact, they often extend it. - Option (c): While some pozzolans (like fly ash) can improve workability due to their spherical shape (ball-bearing effect), this is a physical property of specific materials rather than 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 the enhancement of the final structural properties like durability and chemical resistance. Reducing heat is a side effect of replacing clinker with pozzolans, but the primary goal for general cement improvement is long-term durability.

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 earth. 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 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 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.

In civil engineering and hill road construction, retaining structures are categorized based on their position relative to the slope: 1. **Breast Wall (Option a):** This is a wall constructed on the hill side of a road or a cut slope. Its primary purpose is to support the cut portion of the hill to prevent landslides or soil slippage from the upper slope onto the road. It 'breasts' the slope. 2. **Toe Wall (Option b):** This is constructed at the base (toe) of a slope or embankment to prevent the soil from sliding down and to provide stability to the slope's foot. It supports the fill portion rather than the cut portion. 3. **Revetment Wall (Option c):** This is a facing of stone, concrete, or turf used to protect a slope from erosion (e.g., by water or wind). While it stabilizes the surface, it is not specifically designed as a structural wall to support a deep cut portion of a hill in the same way a breast wall is. 4. **Grouted Wall (Option d):** This refers to a method of stabilization where grout is injected into the soil or rock to fill voids and increase strength; it is a technique rather than a specific type of wall used for supporting cut slopes. Therefore, the wall used specifically to support the cut portion of a hill is the Breast Wall.