Past Questions — 2025

The Mizoram Water Supply (Control) Act is specifically designed to regulate the distribution, management, and control of water intended for domestic use (drinking water) within the state. Its primary objective is to ensure that the supply of drinking water is managed efficiently and that the use of such water is controlled to prevent wastage and ensure equitable distribution. Why other options are incorrect: - Option (b) Construction of dams: This typically falls under larger infrastructure laws, environmental impact assessments, or central/state irrigation and power department regulations. - Option (c) Water quality testing: While quality is a component of supply, testing standards are usually governed by the Bureau of Indian Standards (BIS) or the Water (Prevention and Control of Pollution) Act. - Option (d) River water disputes: These are generally handled under the Inter-State River Water Disputes Act, 1956, or through constitutional mechanisms involving the Central Government.

In the construction of water tanks, concrete must be kept moist for a specific period to allow the hydration process of cement to complete. This process is called curing. If curing is improper or insufficient, the concrete develops shrinkage cracks (plastic shrinkage or drying shrinkage). Since water tanks are designed to hold liquid, these cracks create pathways for water to seep through, leading to leakage. Analysis of other options: - a. Air pressure: While air pressure can affect pipes or sealed systems, it is not a primary cause of structural leakage in standard concrete water tanks. - c. Strong concrete: High-strength concrete, if properly cured and designed, generally reduces permeability and prevents leakage; it is not a cause of leakage. - d. Too much water: While an excessive water-cement ratio during mixing can increase porosity, 'too much water' as a general term usually refers to the stored content, which does not cause leakage unless the structure is already compromised.

To determine the corrosion-resistant material, we must analyze the chemical properties of each pipe material listed: 1. **DI (Ductile Iron):** While stronger than cast iron, DI is still a metallic material susceptible to corrosion (rusting) when exposed to moisture and corrosive soils. It typically requires internal cement mortar lining and external coatings (like zinc or polyethylene) to prevent corrosion. 2. **CI (Cast Iron):** This is a metallic material highly prone to corrosion and tuberculation over time, which reduces the effective diameter of the pipe. 3. **HDPE (High-Density Polyethylene):** This is a thermoplastic polymer. Plastics are non-metallic and chemically inert to most acids, bases, and salts. Therefore, HDPE does not rust or corrode, making it inherently corrosion-resistant. 4. **ERW (Electric Resistance Welded) Steel:** These are steel pipes. Steel is highly susceptible to oxidation and corrosion unless it is galvanized or coated with special epoxy resins. Conclusion: Among the given options, HDPE is the only non-metallic material and is therefore the most corrosion-resistant.

According to IS 456:2000 (the Indian Standard code of practice for Plain and Reinforced Concrete), the minimum grade of concrete for Reinforced Cement Concrete (RCC) work is specified based on the exposure conditions. For 'Mild' exposure conditions, the minimum grade of concrete for RCC is M20. While lower grades like M10 and M15 are used for Plain Cement Concrete (PCC) or lean concrete, they do not provide the necessary strength and durability required to protect the reinforcement steel from corrosion and to ensure structural integrity in RCC. Therefore, M20 is the baseline minimum grade for any RCC structural member. Options a (M10) and b (M15) are insufficient for RCC, and while d (M25) is used for more severe exposure conditions, it is not the absolute minimum grade for all RCC work.

In open channel hydraulics, the 'most economical section' is defined as the cross-section that provides the maximum discharge for a given cross-sectional area, slope, and roughness. According to Manning's equation, discharge is maximized when the hydraulic radius (R = Area/Wetted Perimeter) is maximized. This occurs when the wetted perimeter (P) is minimized for a constant area (A). 1. Mathematically, for any given area, a circle has the smallest perimeter. Therefore, for an open channel (which is essentially a cut-out of a closed conduit), a semi-circular section provides the minimum wetted perimeter and the maximum hydraulic radius. 2. Among the given options: - Semi-circular: The absolute most economical section. - Trapezoidal: The most economical section among polygonal shapes (specifically when it approximates a semi-circle). - Rectangular: Less efficient than trapezoidal or semi-circular. - Circular: This refers to a closed pipe; for open flow (partially filled), it is not as efficient as a full semi-circle of the same area. Therefore, the semi-circular section is the most hydraulically efficient/economical section.

A reinforced material is a composite material consisting of a matrix (the bulk material) and a reinforcement (usually fibers or bars) to improve its mechanical properties, particularly its tensile strength. 1. **Reinforced Cement Concrete (RCC)**: Concrete is strong in compression but very weak in tension. To overcome this, steel bars (reinforcement) are embedded in the concrete. The steel carries the tensile loads, while the concrete carries the compressive loads, making it a classic example of a reinforced material. 2. **Plain Cement Concrete (PCC)**: This consists only of cement, aggregates, and water. It lacks any reinforcing agent and is therefore not a reinforced material. 3. **Brick**: This is a ceramic material made from clay and fired in a kiln. It is a homogeneous material (not a composite of a matrix and reinforcement). 4. **Stone**: This is a naturally occurring mineral material. While some stones have natural veins, they are not engineered 'reinforced materials' in the context of construction engineering.

Rainwater harvesting (RWH) is the process of collecting, filtering, and storing rainwater for future use or for recharging groundwater. 1. Roof catchment (Option a): This is the most common method of RWH where the roof surface acts as the collection area for rainwater. 2. Ground recharge pit (Option b): This is a key component of RWH used to direct harvested water back into the aquifer to raise the water table. 3. Storage tank (Option d): This is used to store harvested rainwater for direct domestic or agricultural use. In contrast, a Desalination plant (Option c) is a chemical/mechanical process used to remove salts and minerals from saline water (usually seawater or brackish water) to produce fresh water. It does not involve the collection of precipitation (rain) and is therefore not a part of rainwater harvesting systems.

Step-by-step reasoning: 1. Water-borne diseases (such as cholera, typhoid, and dysentery) are caused by pathogenic microorganisms transmitted through contaminated water. 2. To control these diseases at a population level, the primary goal is to eliminate the pathogens from the water supply. 3. Proper water treatment (filtration, sedimentation) and chlorination (disinfection) are the most effective systemic interventions because they destroy or remove the causative agents before the water reaches the consumer. 4. Analysis of other options: (a) Handwashing is a critical hygiene practice to prevent fecal-oral transmission, but it does not treat the source of the contamination. (c) Wearing masks prevents airborne/respiratory diseases, not water-borne ones. (d) Vaccination provides individual immunity against specific diseases (like Typhoid), but it does not control the environmental source of the contamination across all water-borne pathogens.

In water supply engineering, an intake structure is designed to draw water from a source (like a river, lake, or reservoir) and convey it to a treatment plant. 1. **Direct Pumping Intake (Option b):** This is a common type of intake used in rivers where pumps are installed directly at the intake structure to lift water from the river into the pipeline. It is efficient for sources where the water level is relatively stable or where the distance to the treatment plant requires immediate pressure. 2. **Wet Intake (Option a):** While 'wet wells' are used in pumping stations, 'wet intake' is not a standard classification for a river intake type in the same way direct pumping or infiltration galleries are. 3. **Ground Intake (Option c):** This is a generic term and not a standard technical classification for river intake structures. 4. **Infiltration Intake (Option d):** Also known as infiltration galleries, these are used when the riverbed consists of permeable sand or gravel. While used in rivers, they are specialized structures used primarily to pre-filter water through the riverbed, rather than being the 'common' general-purpose intake used for bulk water withdrawal across various river conditions. Therefore, among the given options, direct pumping is a standard and common method for river water abstraction.

Concrete cover is the distance between the outer surface of the concrete and the nearest surface of the reinforcing steel. Its primary purposes are: 1. Corrosion Protection: Concrete is naturally alkaline, which creates a passive oxide layer on the steel. The cover acts as a physical and chemical barrier against moisture, chlorides, and carbonation that would otherwise lead to rust (corrosion) and subsequent spalling of the concrete. 2. Fire Resistance: Steel loses its strength rapidly at high temperatures. The concrete cover acts as an insulating layer, delaying the heating of the reinforcement during a fire, thereby maintaining the structural integrity of the building for a longer period. Why other options are incorrect: - (a) Appearance: While a smooth finish is desirable, the cover is a structural requirement, not an aesthetic one. - (b) Cost: Providing cover does not reduce the cost of reinforcement; in fact, it slightly increases the volume of concrete required. - (d) Weight: Adding concrete cover increases the total weight of the structure; it does not make it lighter.

In water supply engineering, water demand is categorized based on the end-use of the water. 1. **Domestic Demand**: This refers to water used for household activities such as drinking, cooking, bathing, and flushing (e.g., residential use). 2. **Institutional Demand**: This refers to water used in schools, hospitals, offices, and government buildings. 3. **Public Demand**: This category includes water required for the general welfare and safety of the community. This encompasses watering public parks, cleaning public streets, and, most critically, water for firefighting (fire hydrants). Firefighting is a public safety service and is therefore classified under public demand. 4. **Agricultural Demand**: This refers to water used for irrigation and livestock. Since firefighting is a community-wide safety requirement managed by public utilities, it falls under 'Public Demand'.

The Arithmetical Increase Method is used for population forecasting in water supply planning. It assumes that the population increases by a constant amount each decade. 1. Why option (b) is correct: The primary merit of this method is its simplicity. It requires only basic arithmetic (calculating the average increase per decade) and is easy to apply to stable populations or old cities where growth has leveled off. 2. Why option (a) is incorrect: The arithmetical method assumes a linear increase indefinitely; it does not account for saturation limits (carrying capacity). The Logistic Curve method is used for saturation limits. 3. Why option (c) is incorrect: This method does not specifically account for migration patterns; it simply looks at the historical numerical trend of the total population. 4. Why option (d) is incorrect: The arithmetical method predicts linear growth, not exponential growth. The Geometric Increase Method is used for predicting exponential growth, which is typical for rapidly developing cities.

RCC stands for Reinforced Cement Concrete. Concrete is a composite material composed of aggregate, cement, and water. While concrete is very strong in compression, it is weak in tension. To overcome this deficiency, steel bars (reinforcement) are embedded into the concrete. The steel provides the necessary tensile strength, while the concrete provides the compressive strength, resulting in a composite material capable of resisting both types of stresses. Analysis of other options: - 'Rolled Cement Concrete' is not a standard engineering term; 'Roller Compacted Concrete' (RCC) exists but is a specific type of paving concrete, not the general definition of RCC in structural engineering. - 'Ready Cement Concrete' is incorrect; the term for pre-mixed concrete is 'Ready-Mix Concrete' (RMC). - 'Rapid Cast Cement' is not a standard term for RCC.

GI (Galvanized Iron) pipes are made of steel coated with a layer of zinc. 1. **Analysis of Option (a):** Steel is known for its high tensile strength, which allows GI pipes to withstand significant mechanical stress and external loads, making this a distinct advantage. 2. **Analysis of Option (b):** Being 'prone to rust' is a disadvantage. While the galvanization (zinc coating) protects the pipe from rust, once the coating is breached, the iron underneath rusts. Regardless, 'prone to rust' is never an advantage. 3. **Analysis of Option (c):** 'Heavy maintenance' is a disadvantage. An advantage would be 'low maintenance'. 4. **Analysis of Option (d):** 'Cannot withstand pressure' is incorrect. GI pipes are specifically used in water supply systems because they can withstand high internal hydraulic pressures. Therefore, the only positive attribute listed that serves as an advantage is high tensile strength.

Rural sanitation primarily focuses on the management of human excreta and the prevention of water-borne diseases through the safe disposal of waste. 1. Soak pits (Option a) are common in rural areas for the disposal of effluent from septic tanks or greywater. 2. Night soil disposal (Option b) refers to the collection and disposal of human excreta, which is a core component of sanitation systems in rural or underdeveloped areas. 3. Septic tanks (Option c) are the standard on-site sanitation systems used in rural areas where centralized sewerage is unavailable. 4. Storm water drains (Option d), while important for civil infrastructure and flood control, are categorized under 'Drainage' or 'Urban Infrastructure' rather than 'Sanitation' (which specifically deals with hygiene and waste/excreta management). In a rural context, storm water is typically managed by natural topography or simple open ditches, whereas sanitation components are specifically designed to treat or isolate hazardous waste.

Lightning protection systems (LPS) are designed to intercept a lightning strike and provide a low-impedance path for the electrical current to travel safely from the roof to the ground, preventing damage to the structure. To achieve this, the materials used must have high electrical conductivity and resistance to corrosion. 1. Copper and Aluminum: These are excellent electrical conductors. Copper is highly conductive and corrosion-resistant, making it a gold standard for lightning rods and down-conductors. Aluminum is also highly conductive, lighter, and more cost-effective, making it a common alternative. 2. Glass (Option a): This is an insulator and would block the flow of electricity, making it useless for a protection system. 3. Rubber (Option b): This is a dielectric/insulator used for electrical safety (e.g., gloves), but it cannot conduct lightning to the ground. 4. PVC (Option d): Polyvinyl Chloride is a plastic insulator used for conduit/piping; it cannot conduct the massive current of a lightning strike.

Waterborne diseases are caused by pathogenic microorganisms that are transmitted through contaminated water. 1. **Cholera (Correct):** It is an acute diarrheal infection caused by ingestion of food or water contaminated with the bacterium *Vibrio cholerae*. It is a classic example of a waterborne disease. 2. **Tuberculosis (Incorrect):** This is an airborne disease caused by *Mycobacterium tuberculosis*, primarily transmitted through droplets in the air when an infected person coughs or sneezes. 3. **Malaria (Incorrect):** This is a vector-borne disease caused by *Plasmodium* parasites and transmitted to humans through the bite of an infected female Anopheles mosquito. While mosquitoes breed in water, the disease is not contracted by drinking the water. 4. **Cancer (Incorrect):** This is a genetic/cellular disease characterized by uncontrolled cell growth, caused by various factors including genetics, lifestyle, and environmental carcinogens, but it is not an infectious waterborne disease.

In open channel hydraulics, the flow is driven by gravity. The slope of the channel (bed slope) provides the gravitational force that overcomes the frictional resistance of the channel walls and bed. According to Manning's Equation (V = (1/n) * R^(2/3) * S^(1/2}), the flow velocity (V) is directly proportional to the square root of the slope (S). Therefore, increasing the slope increases the flow velocity. Why other options are incorrect: - a. Width of pipe: The question refers to an 'open channel', not a pipe. Furthermore, the physical width of a channel is a design geometry parameter, not something affected by the slope of the flow. - c. Temperature: Water temperature is influenced by environmental factors, solar radiation, and heat exchange, not by the gradient of the channel. - d. Odour level: Odour is a result of chemical composition and biological decomposition of organic matter in the water, which is independent of the physical slope of the channel.

The slump test is a standard field test used to determine the consistency and workability of fresh concrete. Workability refers to the ease with which concrete can be mixed, transported, placed, and compacted without segregation. Step-by-step reasoning: 1. **Mechanism**: A conical mold (Abrams cone) is filled with fresh concrete in layers and then lifted vertically. The amount the concrete 'slumps' or drops from its original height is measured. 2. **Interpretation**: A higher slump indicates higher workability (more fluid), while a lower slump indicates lower workability (stiffer mix). Why other options are incorrect: - **a. Strength**: Strength is measured by compressive strength tests on hardened concrete cubes or cylinders after curing (e.g., 7 or 28 days), not on fresh concrete. - **b. Setting time**: Setting time (initial and final) is typically measured using the Vicat apparatus for cement paste, not the slump test. - **d. Water-cement ratio**: While the water-cement ratio significantly influences workability, the slump test measures the *result* (the workability), not the specific ratio of water to cement used in the mix design.

In the context of environmental engineering and solid waste management, 'Refuse' is a general term used to describe all solid waste materials resulting from human activities. It typically encompasses both garbage (decomposable organic waste) and rubbish (non-decomposable waste like plastics, glass, and metals). Step-by-step analysis of options: - Option (a) is incorrect because refuse specifically refers to solid materials, not liquid waste (which is handled by sewerage or liquid waste management systems). - Option (b) is incorrect because plastic is only one component of refuse; it is too narrow a definition. - Option (c) is correct because refuse is the umbrella term for all types of solid waste generated from residential, commercial, and institutional sources. - Option (d) is incorrect because while industrial waste is a type of solid waste, refuse primarily refers to municipal solid waste (MSW), and the term is not limited solely to industrial sources.

In the context of rural sanitation, 'trenching' refers to the practice of using trench latrines or trenching pits for the safe disposal of human excreta (night soil). This method involves digging a trench and covering the waste with layers of soil or lime to prevent odors, discourage flies, and allow for natural decomposition. Why other options are incorrect: - a. Laying pipelines: While pipelines are laid in trenches, this is a general civil engineering activity and not a specific 'sanitation' purpose in the context of rural waste management. - c. Foundation laying: This is a structural engineering process for buildings, not a sanitation practice. - d. Water harvesting: This typically involves ponds, tanks, or recharge pits, not 'trenching' for the purpose of sanitation.

Disinfection is the process of killing or inactivating pathogenic (disease-causing) microorganisms present in water to make it safe for human consumption. This is typically achieved using chemical agents like chlorine, ozone, or physical methods like UV radiation. Analysis of other options: - Option (a) 'Remove suspended solids' is achieved through processes like coagulation, flocculation, sedimentation, and filtration. - Option (b) 'Improve color' is typically handled by coagulation or activated carbon adsorption. - Option (d) 'Remove dissolved salts' is achieved through processes like reverse osmosis (RO), distillation, or ion exchange (demineralization).

An isolated footing (also known as a pad footing) is a type of shallow foundation used to support an individual column. It is designed to transfer the concentrated load from a single column to the soil over a larger area to ensure the bearing capacity of the soil is not exceeded. Analysis of other options: - Option (a) 'A group of columns' is supported by a Combined Footing or a Raft/Mat Foundation. - Option (b) 'A wall' is supported by a Strip Footing or Continuous Footing. - Option (d) 'A retaining wall' typically uses a specialized strip footing or a reinforced concrete base slab designed to resist overturning and sliding.

A retaining wall is a structure specifically designed to resist the lateral pressure of soil, preventing it from sliding or collapsing. It is commonly used in hilly terrains, basements, and road embankments to create level areas of land. Analysis of other options: - a. Septic tank: A watertight container used for the primary treatment of sewage. - b. Soak pit: A covered pit that allows wastewater to slowly soak into the ground. - c. Infiltration gallery: A horizontal structure used to collect groundwater from a sandy or gravelly aquifer. Therefore, only the retaining wall is built for the purpose of retaining soil.

According to IS 3370 (the Indian Standard code of practice for concrete structures for storage of liquids), the requirements for concrete are more stringent than for general RCC structures to ensure liquid-tightness and durability against seepage. In the updated versions of IS 3370 (specifically Part 2), the minimum grade of concrete for water-retaining structures is specified as M30. This higher grade is required to reduce permeability and increase the resistance of the concrete to chemical attacks and cracking. - M20 and M25 are generally used for standard RCC work but are insufficient for the durability requirements of liquid-retaining structures under IS 3370. - M35 is a valid grade, but it is not the 'minimum' required grade.