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Past Questions — 2025
In India, most of the annual precipitation occurs due to:
A)
Cyclones
B)
Monsoon rains
C)
Snowfall
D)
Convection storms
India's climate is dominated by the monsoon system. The vast majority of the annual precipitation (approximately 75% to 90% in many regions) occurs during the Southwest Monsoon season, which typically lasts from June to September. This is caused by the seasonal reversal of winds, where moisture-laden winds blow from the Indian Ocean toward the landmass.
Why other options are incorrect:
- a. Cyclones: While cyclones cause heavy rainfall, they are seasonal and localized primarily to the coastal regions (East and West coasts) and do not account for the bulk of the national annual precipitation.
- c. Snowfall: Snowfall is restricted to the Himalayan region and high-altitude areas; it represents a very small fraction of the total precipitation of the Indian subcontinent.
- d. Convection storms: These occur frequently (such as pre-monsoon showers or 'Mango showers'), but they are sporadic and provide significantly less total volume of water compared to the sustained monsoon rains.
The unit weight of soil is defined as-
A)
Weight of water per unit volume
B)
Weight of solids per unit volume
C)
Weight of soil mass per unit volume
D)
Weight of solids per unit weight
In soil mechanics, the unit weight (also known as bulk density when expressed as mass) is defined as the total weight of a soil sample (which includes the weight of the solid particles and the weight of the water filling the voids) divided by the total volume of that sample. Mathematically, it is expressed as γ = W / V, where W is the total weight of the soil mass and V is the total volume.
Analysis of options:
- Option (a) refers to the unit weight of water (γw).
- Option (b) refers to the dry unit weight (γd), which considers only the weight of solids.
- Option (c) is the correct general definition of unit weight (bulk unit weight).
- Option (d) is dimensionally incorrect as it describes a ratio of weights rather than a weight per unit volume.
Which soil has the highest permeability?
A)
Silt
B)
Gravel
C)
Clay
D)
Loam
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.
Which of the following is a shallow foundation?
A)
Isolated footing
B)
Pile foundation
C)
Caisson
D)
Pier foundation
In soil mechanics and foundation engineering, foundations are broadly classified into two categories based on their depth: Shallow Foundations and Deep Foundations.
1. Shallow Foundations: These are foundations where the depth (D) is generally less than or equal to the width (B) of the foundation (D/B ≤ 1). They transfer the load to the soil layers near the surface. Examples include isolated footings, combined footings, strip footings, and mat/raft foundations. Therefore, an 'Isolated footing' is a shallow foundation.
2. Deep Foundations: These are foundations where the depth is significantly greater than the width (D/B > 1). 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.
- Pile foundations (Option b) are deep foundations.
- Caissons (Option c) are deep foundations (often used for bridges and piers in water).
- Pier foundations (Option d) are typically deep foundations used to support heavy loads at depth.
Which soil type is best suited for the core of an earthen dam?
A)
Gravel
B)
Coarse sand
C)
Clayey soil
D)
Silty sand
The primary purpose of the core in an earthen dam is to act as an impermeable barrier to prevent water from seeping through the dam body, which could otherwise lead to piping failure or structural instability.
1. **Clayey Soil (Correct):** Clay has very low hydraulic conductivity (permeability) due to its small particle size and cohesive nature. This makes it the ideal material for the core to minimize seepage losses and maintain the stability of the dam.
2. **Gravel (Incorrect):** Gravel is highly permeable. While it is excellent for the 'shell' of a dam to provide structural stability and drainage, it cannot stop water flow.
3. **Coarse Sand (Incorrect):** Like gravel, coarse sand has high permeability and would allow significant water leakage, making it unsuitable for a core.
4. **Silty Sand (Incorrect):** While less permeable than coarse sand, silty sand still lacks the impermeability and cohesion of clay, making it an inferior choice for the core.
An area with impermeable geology faces declining groundwater levels. Which approach is most suitable?
A)
Use of artificial recharge structures and recharge wells
B)
Open wells only
C)
Increasing extraction
D)
Reducing rooftop collection
Step-by-step reasoning: 1. Analysis of the problem: The area has 'impermeable geology,' meaning the natural soil or rock layers prevent water from easily seeping down into the aquifers. Simultaneously, groundwater levels are declining, indicating that the rate of extraction exceeds the natural recharge rate. 2. Evaluating Option (a): Artificial recharge structures (such as percolation tanks, check dams, and recharge wells) are specifically designed to bypass impermeable surface layers or increase the residence time of water on the surface, forcing water into the underground aquifers. Recharge wells, in particular, can penetrate through impermeable clay or rock layers to deliver water directly into the water-bearing zone. 3. Evaluating Option (b): Open wells are extraction points, not recharge points. In impermeable geology, open wells may have low yields and do not solve the problem of declining water tables. 4. Evaluating Option (c): Increasing extraction would accelerate the decline of the groundwater level, worsening the crisis. 5. Evaluating Option (d): Reducing rooftop collection would decrease the amount of water available for potential recharge or immediate use, which is counterproductive. Therefore, artificial recharge is the only sustainable engineering solution to replenish the aquifer in such geological conditions.
Pozzolanic materials are primarily added to cement to improve-
A)
Initial setting time
B)
Durability and resistance to sulphate attack
C)
Workability
D)
Heat of hydration
Pozzolanic materials (such as fly ash, silica fume, or volcanic ash) are siliceous or aluminosiliceous materials that possess pozzolanic properties. When added to cement, they react with the calcium hydroxide [Ca(OH)2], which is a byproduct of cement hydration, to form additional calcium silicate hydrate (C-S-H) gel. This process results in several benefits: 1. It densifies the microstructure of the concrete, reducing permeability and increasing overall durability. 2. It consumes Ca(OH)2, which is the primary component that reacts with external sulphates to cause expansion and cracking; thus, it significantly improves resistance to sulphate attack.
Regarding other options:
- (a) Initial setting time: Pozzolans often slow down the initial setting time rather than 'improving' it in a general sense.
- (c) Workability: While some pozzolans (like fly ash) can improve workability due to their spherical shape, this is a physical property of specific materials, not the primary chemical purpose of adding pozzolans to cement.
- (d) Heat of hydration: Pozzolans do reduce the heat of hydration (which is beneficial for mass concreting), but the primary goal of adding them to standard cement blends is to enhance the long-term durability and chemical resistance of the concrete matrix.
Rubble masonry is commonly used for-
A)
Retaining and breast walls in hilly regions
B)
Elevated tanks
C)
Slabs
D)
Road shoulders
Rubble masonry consists of irregularly shaped stones (rubble) laid in mortar. It is highly durable, cost-effective when stone is locally available, and possesses high compressive strength, making it ideal for heavy-duty gravity structures.
1. Why Option (a) is correct: In hilly regions, retaining walls (to hold back soil) and breast walls (to prevent landslides or support road embankments) require massive structures that can withstand significant lateral earth pressure. Rubble masonry is the traditional and most practical choice for these applications due to its strength and the availability of raw materials in mountainous terrain.
2. Why Option (b) is incorrect: Elevated tanks require high tensile strength and water-tightness to handle hydrostatic pressure and structural loads at height. These are almost exclusively constructed using Reinforced Cement Concrete (RCC).
3. Why Option (c) is incorrect: Slabs are horizontal structural elements that must span distances. Rubble masonry cannot provide the necessary tensile strength or structural integrity for a slab; these are made of RCC or steel.
4. Why Option (d) is incorrect: Road shoulders are typically constructed using compacted granular materials (like gravel or crushed stone) or asphalt to allow for drainage and emergency vehicle access, not masonry walls.
Which field test is commonly used to determine the bearing capacity of soil?
A)
Core Cutter Test
B)
Plate Load Test
C)
Vane Shear Test
D)
Pycnometer Test
The Plate Load Test is a standard field test used to determine the ultimate bearing capacity of soil and the settlement under a given load. In this test, a steel plate is placed on the soil surface or at a specific depth and loaded until the soil fails or a specified settlement occurs.
Reasoning for other options:
- a. Core Cutter Test: This is used to determine the in-situ field density (dry density) of cohesive soils, not the bearing capacity.
- c. Vane Shear Test: This is used specifically to determine the undrained shear strength of soft, saturated clays in the field.
- d. Pycnometer Test: This is a laboratory test used to determine the specific gravity of soil solids.
The main cause of slope failure in hilly terrain is-
A)
Lack of vegetation
B)
High humidity
C)
Excess water infiltration and poor drainage
D)
Wind pressure
Slope stability is primarily governed by the balance between shear strength (resisting force) and shear stress (driving force).
1. Why Option (c) is correct: Water is the most critical factor in slope failure. Excess water infiltration increases the pore water pressure within the soil or rock mass. According to Terzaghi's principle of effective stress (σ' = σ - u), as pore water pressure (u) increases, the effective stress (σ') decreases. Since the shear strength of soil is directly proportional to the effective stress, the strength of the slope is significantly reduced. Additionally, water increases the unit weight of the soil (adding to the driving force) and acts as a lubricant along failure planes.
2. Why other options are incorrect:
- (a) Lack of vegetation: While vegetation helps stabilize slopes through root reinforcement and reducing surface erosion, its absence is usually a contributing factor rather than the 'main' cause of deep-seated slope failure.
- (b) High humidity: Humidity refers to moisture in the air. While it relates to the environment, it does not provide the hydrostatic pressure or saturation levels required to trigger a mass slope failure.
- (d) Wind pressure: Wind can cause surface erosion or blow down trees, but it does not possess the magnitude of force required to cause the structural failure of a geological slope in hilly terrain.
Which of the following plastics is used in making water storage tanks?
A)
Bakelite
B)
Polyethylene
C)
PVC
D)
Nylon
Step-by-step reasoning:
1. Analysis of the requirement: Water storage tanks require materials that are durable, chemically inert (to prevent contamination of water), impact-resistant, and capable of being molded into large shapes.
2. Evaluating Polyethylene (Option b): Polyethylene, specifically High-Density Polyethylene (HDPE) and Linear Low-Density Polyethylene (LLDPE), is the industry standard for water tanks. It is food-grade, resistant to corrosion, UV-stabilized, and possesses high strength-to-density ratios, making it ideal for storing potable water.
3. Evaluating Bakelite (Option a): Bakelite is a thermosetting plastic. It is brittle and used primarily for electrical insulators and heat-resistant handles, not for large fluid storage containers.
4. Evaluating PVC (Option c): While Polyvinyl Chloride (PVC) is widely used for water pipes and fittings due to its rigidity, it is generally not used for the main body of large storage tanks because it is more brittle than polyethylene and can crack under the hydrostatic pressure of a large volume of water.
5. Evaluating Nylon (Option d): Nylon is a polyamide used primarily for fibers, gears, and mechanical parts due to its high strength and wear resistance; it is not used for bulk water storage.
Therefore, Polyethylene is the most appropriate material for making water storage tanks.
Which of the following types of cement is suitable for use in cold weather concreting?
A)
Ordinary Portland Cement
B)
Low Heat Cement
C)
Rapid Hardening Cement
D)
Sulphate Resisting Cement
In cold weather concreting, the primary challenge is the slowing down of the hydration process of cement. Since the rate of chemical reaction decreases as temperature drops, the setting time is prolonged and the strength gain is significantly delayed, which can lead to freezing of the water in the concrete and structural failure.
1. **Rapid Hardening Cement (Correct):** This cement is manufactured to gain strength more quickly than Ordinary Portland Cement (OPC). It achieves higher early strength due to a finer grinding of clinker and a higher C3S (Tricalcium Silicate) content. The increased rate of hydration generates more heat (heat of hydration), which helps maintain the temperature of the concrete mix in cold environments, ensuring the concrete sets and gains strength within a reasonable timeframe.
2. **Ordinary Portland Cement (Incorrect):** While it can be used, it does not provide the accelerated strength gain required to counteract the slowing effects of cold weather.
3. **Low Heat Cement (Incorrect):** This cement is specifically 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.
4. **Sulphate Resisting Cement (Incorrect):** This is used in environments where the concrete is exposed to high concentrations of sulphates (e.g., coastal areas or certain soils) to prevent chemical attack; it is not designed for temperature-related acceleration.
Which soil property is most important for slope stability?
A)
Plasticity index
B)
Moisture content
C)
Shear strength
D)
Density index
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 oppose this movement. The primary resisting force in a soil mass is its shear strength. According to the Mohr-Coulomb failure criterion, shear strength is a function of cohesion (c) and the internal angle of 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 resisting force against sliding.
- b. Moisture Content: While moisture content significantly affects shear strength (by increasing pore water pressure and reducing effective stress), it is a condition/variable rather than the property that provides the actual stability.
- 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.
Which property is most affected when aggregate with high water absorption is used without accounting for it?
A)
Initial setting time
B)
Workability
C)
Compressive strength
D)
Durability
Step-by-step reasoning: 1. Water-Cement Ratio: The workability of concrete is primarily governed by the amount of free water available in the mix to lubricate the aggregates and facilitate flow. 2. Effect of Absorption: Aggregates with high water absorption act like sponges. If these aggregates are used in a dry state without adjusting the mixing water (accounting for absorption), they will absorb a significant portion of the mixing water intended for the cement paste. 3. Impact on Workability: This reduction in 'free water' leads to a stiffer mix, significantly reducing the slump and overall workability of the concrete, making it difficult to place and compact. 4. Analysis of other options: (a) Initial setting time is primarily a property of the cement chemistry and water temperature, not aggregate absorption. (c) Compressive strength is affected by the water-cement ratio; however, if the aggregate absorbs water, the effective w/c ratio actually decreases, which might theoretically increase strength but would make the concrete unworkable and prone to honeycombing (which then lowers strength). The most immediate and direct property affected is workability. (d) Durability is a long-term property; while absorption can affect it, the immediate impact during mixing is on workability.
A retaining wall is to be built on a silty foundation. Which step should be taken before construction?
A)
Directly cast footing
B)
Replace or stabilize foundation soil
C)
Use heavy machinery
D)
Ignore base conditions
In geotechnical engineering, the stability of a retaining wall depends heavily on the bearing capacity and shear strength of the foundation soil. Silty soils are often problematic because they are compressible, susceptible to settlement, and can lose strength significantly when saturated (due to low permeability and capillary action).
1. Why Option (b) is correct: To prevent differential settlement or bearing capacity failure, the weak silty layer must be either replaced with a structural fill (like well-graded gravel or crushed stone) or stabilized using techniques such as soil nailing, chemical grouting, or compaction. This ensures the wall can support the lateral earth pressure and its own dead load without tilting or sinking.
2. Why Option (a) is incorrect: Directly casting a footing on unstable silty soil risks structural failure or excessive settlement, which could lead to the collapse of the retaining wall.
3. Why Option (c) is incorrect: While heavy machinery is used during construction, simply 'using' it does not address the inherent geotechnical deficiency of the silty soil; in fact, heavy machinery on soft silt can cause 'rutting' or further disturb the soil structure.
4. Why Option (d) is incorrect: Ignoring base conditions is a violation of fundamental engineering principles and would lead to catastrophic failure.
Slope movement can be triggered by-
A)
Excessive rainfall or earthquakes
B)
Vegetation growth
C)
Rock mass only
D)
Clayey texture
Slope stability is governed by the balance between shear strength (resisting force) and shear stress (driving force). Slope movement (landslides) is triggered when the driving force exceeds the resisting force.
1. **Excessive Rainfall**: Rainfall increases the pore water pressure within the soil or rock mass. According to Terzaghi's principle of effective stress (σ' = σ - u), an increase in pore water pressure (u) decreases the effective stress (σ'), which directly reduces the shear strength of the material, triggering failure.
2. **Earthquakes**: Seismic activity introduces dynamic horizontal and vertical forces (inertial forces) that increase the driving shear stress on the slope and can cause liquefaction in saturated sandy soils, leading to immediate slope failure.
Why other options are incorrect:
- **Vegetation growth**: Generally, vegetation stabilizes slopes by providing root reinforcement (increasing cohesion) and reducing pore water pressure through evapotranspiration.
- **Rock mass only**: While rock masses can fail, they are the material being moved, not the 'trigger' itself. A trigger is an external event or change in condition.
- **Clayey texture**: This is a material property (inherent characteristic), not a trigger. While clayey soils may be more prone to failure due to low permeability or swelling, the movement is triggered by an external factor like water infiltration.
Which of the following tests is conducted to determine the fineness of cement?
A)
Sieve Test
B)
Soundness Test
C)
Consistency Test
D)
Tensile Strength Test
The fineness of cement refers to the size of the cement particles. Finer cement hydrates faster and generally provides higher early strength. There are two primary methods to determine fineness: 1) Sieve Analysis (using a 90-micron IS sieve) and 2) Air Permeability Method (Blaine's test). Among the given options, the Sieve Test is the correct method for determining fineness.
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 delayed expansion caused by free lime or magnesia), typically using the Le Chatelier apparatus or Autoclave test.
- c. Consistency Test: This is a preliminary test (using the Vicat apparatus) to determine the amount of water required to create a cement paste of standard consistency, which is necessary before performing other tests like setting time and soundness.
- d. Tensile Strength Test: This is generally performed on hardened concrete or steel, not on raw cement powder to determine its physical properties like fineness.
PVC used in building works is a type of-
A)
Composite material
B)
Natural polymer
C)
Synthetic polymer
D)
Ceramic
PVC stands for Polyvinyl Chloride. To determine the correct classification, we analyze the material's composition:
1. **Polymer**: A polymer is a large molecule (macromolecule) composed of many repeated subunits (monomers). PVC is formed by the polymerization of vinyl chloride monomers.
2. **Synthetic**: Unlike natural polymers (such as cellulose, rubber, or DNA) which occur in nature, PVC is man-made through chemical synthesis in industrial processes. Therefore, it is a synthetic polymer (specifically a thermoplastic).
Evaluating the other options:
- **Composite material**: A composite consists of two or more chemically distinct phases (e.g., reinforced concrete). Pure PVC is a single polymer, not a composite.
- **Natural polymer**: PVC is not found in nature; it is produced chemically.
- **Ceramic**: Ceramics are inorganic, non-metallic solids (e.g., bricks, glass, porcelain). PVC is an organic plastic material.
The factor of safety in slope stability analysis is defined as the ratio of-
A)
Active to passive pressure
B)
Weight to height of slope
C)
Shear strength to shear stress
D)
Cohesion to slope angle
In slope stability analysis, the Factor of Safety (FoS) is a dimensionless ratio used to determine the stability of a soil or rock slope. It is defined as the ratio of the resisting forces (or strengths) to the driving forces (or stresses) acting along a potential failure surface. Specifically, it is the ratio of the available shear strength of the soil (the maximum resistance the soil can offer) to the actual shear stress acting on the failure plane (the stress tending to cause the slope to slide).
Mathematically: FoS = (Available Shear Strength) / (Mobilized Shear Stress).
- If FoS > 1, the slope is stable.
- If FoS = 1, the slope is in a state of limiting equilibrium (critical).
- If FoS < 1, the slope is unstable and will fail.
Analysis of other options:
- Option (a): Active and passive pressures are used in retaining wall design, not as the general definition of slope stability FoS.
- Option (b): Weight and height are parameters used to calculate stresses, but their ratio does not define the factor of safety.
- Option (d): Cohesion is a component of shear strength, and the slope angle affects the shear stress, but their direct ratio is not the definition of FoS.
The crushing strength of first-class bricks should not be less than-
A)
3.5 N/mm²
B)
7.0 N/mm²
C)
5.0 N/mm²
D)
10.5 N/mm²
According to Indian Standard (IS) specifications and general civil engineering standards for brick classification, bricks are categorized based on their compressive (crushing) strength.
1. First-Class Bricks: These are the highest quality bricks used for load-bearing walls. Their minimum average compressive strength should not be less than 10.5 N/mm².
2. Second-Class Bricks: These have a minimum compressive strength of 7.0 N/mm².
3. Third-Class Bricks: These have a minimum compressive strength of 3.5 N/mm².
Comparing this to the options provided:
- Option (a) 3.5 N/mm² corresponds to Third-Class bricks.
- Option (b) 7.0 N/mm² corresponds to Second-Class bricks.
- Option (c) 5.0 N/mm² does not align with standard class definitions.
- Option (d) 10.5 N/mm² is the correct minimum requirement for First-Class bricks.
The main objective of artificial recharge is to-
A)
Reduce surface water runoff
B)
Create open wells
C)
Replenish groundwater
D)
Improve rainfall
Artificial recharge is 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. **Definition**: Artificial recharge involves the use of structures like recharge pits, shafts, or injection wells to move water from the surface into the saturated zone of an aquifer.
2. **Primary Goal**: The fundamental objective is to 'replenish' or 'refill' the groundwater table, especially in areas where extraction (pumping) exceeds natural recharge, leading to a drop in the water table.
3. **Evaluating Options**:
- (a) Reduce surface water runoff: While reducing runoff is often a *method* or a *by-product* of recharge (by capturing water that would otherwise run off), it is not the ultimate 'objective'. The goal is what happens to that water after it is captured.
- (b) Create open wells: Open wells are structures used to *extract* water; they are not the objective of recharging the aquifer.
- (c) Replenish groundwater: This is the direct and primary objective of artificial recharge.
- (d) Improve rainfall: Artificial recharge deals with water already present on the surface; it has no mechanism to influence atmospheric conditions or increase rainfall (which would be 'cloud seeding').
Timber is seasoned to-
A)
Increase weight
B)
Reduce moisture content
C)
Improve color
D)
Make it fireproof
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. Freshly felled trees contain a high percentage of water (free water and bound water). If used without seasoning, the timber is prone to warping, shrinking, cracking, and decay. By reducing the moisture content through air seasoning or kiln seasoning, the timber becomes more dimensionally stable, stronger, and more durable.
Analysis of other options:
- Option (a) Increase weight: Seasoning actually decreases the weight of timber because water is removed.
- Option (c) Improve color: While seasoning may slightly alter the appearance, its primary engineering purpose is structural stability, not aesthetic color improvement.
- Option (d) Make it fireproof: Seasoning does not make timber fireproof; in fact, dry timber may ignite more easily than green timber, although it does not change the inherent combustibility of the material.
Gabion structures are filled with-
A)
Rocks or stones
B)
Clay soil
C)
Bitumen
D)
Cement mortar
A gabion is a cage, cylinder, or box filled with rocks, concrete, or sometimes sand and soil, for use in civil engineering, road building, military applications, and erosion control. Specifically, in the context of retaining walls and slope stabilization, gabions consist of galvanized steel wire mesh baskets filled with hard, durable rocks or stones.
Why other options are incorrect:
- b. Clay soil: Clay is cohesive and lacks the internal friction and permeability required for gabion structures; filling them with clay would defeat the purpose of drainage and structural stability.
- c. Bitumen: Bitumen is a binder used primarily in road surfacing (asphalt) and waterproofing, not as a filler for structural cages.
- d. Cement mortar: While 'mattress' gabions exist, the defining characteristic of a standard gabion is its flexibility and permeability. Filling the baskets with cement mortar would turn the structure into a rigid concrete block, removing the primary advantages of gabions (such as permeability and the ability to settle without cracking).
Which of the following is a protective coating for metals?
A)
Whitewash
B)
Lacquer
C)
Galvanization
D)
Emulsion paint
Step-by-step reasoning: 1. The question asks for a protective coating specifically for metals. 2. Galvanization is the process of applying a protective zinc coating to steel or iron to prevent rusting (corrosion). The zinc acts as a sacrificial anode, protecting the underlying metal even if the coating is scratched. 3. Whitewash (Option a) is a mixture of slaked lime and water used primarily for walls and ceilings, not for metal protection. 4. Lacquer (Option b) is a resin-based coating used for aesthetics and some protection on wood or metal, but it is not the primary industrial 'protective coating' in the context of civil engineering and material science compared to galvanization. 5. Emulsion paint (Option d) is a water-based paint used mainly for interior and exterior walls, not as a specialized protective coating for metals against corrosion. Therefore, Galvanization is the most accurate and standard engineering answer for metal protection.
Which of the following is used to calculate rainwater harvested from a roof?
A)
Permeability of soil
B)
Roof area x rainfall x runoff coefficient
C)
Catchment slope
D)
Groundwater table depth
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.