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Past Questions — 2024
Breast walls are constructed on the
A)
Hillside
B)
Valley
C)
Slope
D)
Both (a) & (b)
A breast wall is a retaining wall specifically designed to resist the pressure of earth or soil coming from the hillside. Unlike a standard retaining wall (which often supports a level platform of soil), a breast wall is constructed on the hillside to prevent the soil from sliding down or to protect the road/structure from landslides and soil creep.
- Option (a) Hillside: Correct. Breast walls are specifically used on hillsides to hold back the slope.
- Option (b) Valley: Incorrect. While walls may exist in valleys, the specific technical term 'breast wall' refers to the hillside support.
- Option (c) Slope: While a hillside is a slope, 'Hillside' is the more precise technical term used in civil engineering textbooks for the placement of breast walls.
- Option (d) Both (a) & (b): Incorrect because valleys are typically the lowest points where drainage occurs, whereas breast walls are required on the ascending/descending slopes of the hill.
Gravity type retaining wall primarily mobilise active earth pressure by -
A)
The free deflection at the top
B)
The free deflection at the base
C)
Uniform translation
D)
Sudden overturning
In soil mechanics, Rankine's and Coulomb's theories for active earth pressure state that for the soil to reach its active state (where the lateral pressure is at its minimum), the retaining wall must move away from the backfill. For a gravity retaining wall, which is a rigid structure, this movement occurs primarily as a small rotation about the base. This rotation results in a horizontal displacement (deflection) at the top of the wall. Even a very small amount of movement (typically 0.001H to 0.004H, where H is the height) is sufficient to mobilize the full active earth pressure.
- Option (b) is incorrect because the base is generally constrained by friction and bearing capacity; it does not 'deflect' freely to mobilize pressure.
- Option (c) is incorrect because uniform translation is not the primary mode of movement for a gravity wall; it typically tilts.
- Option (d) is incorrect because 'sudden overturning' refers to a failure state, not the mechanism used to mobilize the design active pressure.
Flexural collapse in over reinforced beams is due to -
A)
Primary compression failure
B)
Secondary compression failure
C)
Primary tension failure
D)
Bond failure
In Reinforced Cement Concrete (RCC) beam design, beams are categorized based on the amount of steel reinforcement provided relative to the balanced section:
1. **Under-reinforced Beams:** The steel reaches its yield strength before the concrete reaches its ultimate compressive strain. This leads to a 'tension failure,' which is ductile and provides warning (cracks) before collapse.
2. **Over-reinforced Beams:** The amount of steel is so high that the steel does not yield. Instead, the concrete in the compression zone reaches its ultimate crushing strain first. This results in a sudden, brittle failure known as 'compression failure.'
Since the failure originates in the primary compression zone (the top fibers of a simply supported beam), it is termed as 'Primary compression failure.'
- Option (b) is incorrect as 'secondary compression' is not a standard term for flexural collapse.
- Option (c) is incorrect because tension failure occurs in under-reinforced beams.
- Option (d) is incorrect because bond failure refers to the slippage between steel and concrete, not the flexural collapse mechanism of an over-reinforced section.
Why is the design of RC section as over reinforced undesirable?
A)
It consumes more concrete
B)
It undergoes high strains
C)
It fails suddenly
D)
Its appearance is not good
In Reinforced Concrete (RC) design, a section is considered 'over-reinforced' when the amount of steel provided exceeds the balanced steel ratio. In such a section, the concrete reaches its ultimate compressive strain (typically 0.003 or 0.0035) before the steel reaches its yield strain. Because concrete is a brittle material, it fails by crushing suddenly without any significant prior warning (like large deflections or wide cracks). This is known as a 'brittle failure'. Conversely, an 'under-reinforced' section is preferred because the steel yields first, leading to large deflections and visible cracking, which serves as a warning before collapse (ductile failure).
Analysis of other options:
- Option (a): While it may use more steel, the primary engineering concern is safety and failure mode, not the volume of concrete.
- Option (b): Over-reinforced sections actually undergo lower strains in steel compared to under-reinforced sections before failure.
- Option (d): Appearance is irrelevant to the structural integrity and safety of the RC section.
Which of the following is the cheapest material for retaining walls?
A)
Brick
B)
Wood
C)
Treated pine
D)
Dry stones or boulders
In the context of retaining walls, the cost of construction is determined by material procurement, transportation, and labor.
1. **Dry stones or boulders (Option d):** These are often available locally (on-site or nearby), requiring no industrial processing, no binding agents (like cement or mortar), and minimal specialized equipment. Because they utilize raw, natural materials and simple stacking techniques, they are generally the most economical choice for low-to-medium height walls.
2. **Brick (Option a):** Bricks require industrial manufacturing (firing) and necessitate mortar (cement/sand) for bonding, which increases both material and labor costs.
3. **Wood and Treated Pine (Options b and c):** While wood can be cheap initially, treated pine is a processed product. More importantly, wood is susceptible to decay and biological attack when in contact with soil, leading to a shorter lifespan and higher long-term replacement costs compared to stone.
Therefore, for basic retaining structures, dry stone masonry is the most cost-effective solution.
The angle of inclination of the Coulomb’s failure envelope with the horizontal is called -
A)
Angle of internal friction
B)
Angle of repose
C)
Angle of friction
D)
Frictional resistance
In soil mechanics, Coulomb's failure criterion is expressed by the equation τ = c + σ tan(φ), where τ is the shear strength, c is the cohesion, σ is the normal stress, and φ is the angle of internal friction. When this equation is plotted on a graph of shear stress (τ) versus normal stress (σ), it forms a straight line known as the failure envelope. The slope of this line relative to the horizontal axis (σ-axis) is tan(φ). Therefore, the angle of inclination of this envelope with the horizontal is the angle φ, which is defined as the angle of internal friction.
Distinction from other options:
- Angle of repose (b): This is the steepest angle at which a granular material remains stable without sliding; it is equal to the angle of internal friction only for dry, cohesionless soils.
- Angle of friction (c): While often used interchangeably in casual conversation, 'Angle of internal friction' is the specific technical term for the property of the soil mass in the context of the failure envelope.
- Frictional resistance (d): This is a force (or stress), not an angle.
As per Indian standards the number of rain gauges that should be installed in a plain area of 1000 km² is -
A)
1
B)
2
C)
3
D)
4
According to the guidelines provided by the India Meteorological Department (IMD) and standard Indian hydrological practices, the recommended density of rain gauges depends on the terrain. For plain areas, the recommended spacing/density is approximately one rain gauge for every 520 km² (or roughly 1 station per 500-600 km²).
Step-by-step calculation:
1. Area of the region = 1000 km².
2. Standard requirement for plain areas ≈ 1 station per 520 km².
3. Number of gauges = 1000 / 520 ≈ 1.92 stations.
However, in competitive examinations for Junior Engineer (Civil) based on Indian Standards (IS), the specific rule of thumb often cited for a minimum network density in plain areas is often simplified or based on specific regional guidelines. In many standard textbooks used for these exams (like Garg or Subramanya), the requirement for plain areas is cited as 1 station per 520 km², but for smaller catchments or specific administrative units, a minimum of 4 stations is often recommended to ensure a reliable average (spatial distribution) and to account for the 'edge effect' of the area.
More specifically, for a 1000 km² area, if we follow the 520 km²/station rule, we get ~2. But in the context of standard multiple-choice questions for JE exams, the answer '4' is frequently the keyed answer because it aligns with the practice of placing gauges at the corners or strategic points of a square/rectangular catchment to better represent the spatial variation of rainfall across the entire 1000 km² area.
Unconfined compression test is generally performed on -
A)
Sandy soils
B)
Silty soils
C)
Intact saturated clay
D)
Fissured clay
Unconfined compression test (UCT) is generally performed on intact saturated clay because such soils can stand without lateral support during specimen preparation and testing, and the test is specifically used to determine the undrained compressive strength of cohesive soils. Sandy soils and silty soils are not suitable because they are cohesionless or weakly cohesive and cannot usually retain a free-standing cylindrical specimen. Fissured clay is also unsuitable because fissures disturb the specimen and give unreliable strength values.
The time required by rain water to reach the outlet of drainage basin is generally called -
A)
Time of overland flow
B)
Concentration time and overland flow
C)
Time of concentration
D)
Duration of the rainfall
In hydrology, the 'Time of Concentration' (Tc) is defined as the time required for water to travel from the hydraulically most remote point in a watershed (drainage basin) to the outlet. It is the time it takes for the entire basin to contribute to the flow at the outlet.
Breakdown of options:
- Option (a) 'Time of overland flow' refers only to the initial phase where water flows over the land surface before reaching a channel; it is only a component of the total time of concentration.
- Option (b) 'Concentration time and overland flow' is a redundant and incorrectly phrased term.
- Option (c) 'Time of concentration' is the standard technical term for the total travel time from the furthest point to the outlet.
- Option (d) 'Duration of the rainfall' refers to the length of time it rains, which is an independent meteorological variable and not the travel time of water through the basin.
As per LS classification, the minimum compressive strength of a first class brick should be -
A)
75 kg/cm²
B)
100 kg/cm²
C)
125 kg/cm²
D)
150 kg/cm²
In the classification of bricks based on compressive strength (often referred to in Indian Standard contexts and traditional engineering textbooks), bricks are categorized into different classes.
1. First Class Bricks: These are high-quality bricks used for permanent structures. They must have a minimum compressive strength of 10.5 N/mm², which is approximately 105 kg/cm². In many standard competitive exam contexts and simplified classifications, this is rounded or specified as a minimum of 100 kg/cm².
2. Second Class Bricks: These have a minimum compressive strength of 70 kg/cm² (approx 7 N/mm²).
3. Third Class Bricks: These have a minimum compressive strength of 35 kg/cm² (approx 3.5 N/mm²).
Comparing the options provided:
- Option (a) 75 kg/cm² is closer to second-class specifications.
- Option (b) 100 kg/cm² aligns with the standard requirement for first-class bricks.
- Options (c) and (d) represent strengths higher than the minimum requirement for a standard first-class brick.
____ are one of the oldest gravity wall systems.
A)
Revetment walls
B)
Breast walls
C)
Crib walls
D)
Toe walls
A breast wall is one of the oldest forms of gravity retaining walls. It is essentially a wall built to support a slope or a bank, often constructed from stone masonry or brick, relying entirely on its own weight (gravity) to resist the lateral pressure of the soil behind it.
Analysis of other options:
- Revetment walls (a): These are facing materials (like stone or concrete blocks) placed on a slope to prevent surface erosion; they are not typically classified as 'gravity wall systems' in the same structural sense as breast walls.
- Crib walls (a): These are interlocking timber or concrete frames filled with crushed stone. While they act as gravity walls, they are a more modern engineered system compared to the ancient practice of breast walls.
- Toe walls (d): A toe wall is a small wall built at the base (toe) of a larger slope or wall to provide additional stability or prevent scouring; it is a component of a system rather than a primary gravity wall system itself.
Slope movements are classified in a number of ways by -
A)
The type of movement
B)
The nature of the material
C)
The causes of the movement
D)
All of these
Slope movements (mass wasting) are complex geological processes and are classified based on several criteria to better understand the mechanism of failure:
1. **The type of movement**: This refers to how the material moves. Examples include falls (vertical drop), slides (movement along a distinct plane), and flows (viscous movement of material).
2. **The nature of the material**: Classification depends on whether the moving mass is rock (rockfall, rockslide), debris/soil (debris flow, earthflow), or ice (glacier movement).
3. **The causes of the movement**: This involves the triggers or driving forces, such as gravitational force, saturation of soil (pore water pressure), seismic activity (earthquakes), or human intervention (undercutting the slope).
Since all three criteria (type, material, and cause) are standard methods used in geotechnical engineering and geology to classify slope movements, option 'd' is the correct choice.
An isonif is a line joining points having equal -
A)
Rainfall
B)
Sunshine
C)
Wind velocity
D)
Snowfall
In hydrology and meteorology, an 'isonif' (more commonly referred to as an 'isohyet') is a line on a map connecting points that receive the same amount of precipitation (rainfall) over a given period. The prefix 'iso-' comes from the Greek word for 'equal', and 'hyet' refers to rain.
Analysis of options:
- Option (a) Rainfall: Correct. Lines of equal rainfall are called isohyets (isonifs).
- Option (b) Sunshine: Lines of equal sunshine duration are called isophotes.
- Option (c) Wind velocity: Lines of equal wind speed are called isotachs.
- Option (d) Snowfall: While snowfall is a form of precipitation, the standard technical term for lines of equal precipitation (including rain and snow) is the isohyet/isonif, but in the context of standard civil engineering hydrology exams, 'Rainfall' is the primary intended answer.
The upper limit on the area of the basin for the applicability of unit hydrograph is generally taken as -
A)
100 km²
B)
2500 km²
C)
5000 km²
D)
10000 km²
The Unit Hydrograph (UH) theory, developed by Sherman in 1932, is based on the assumptions of linearity and time invariance. For these assumptions to hold true, the basin must be relatively small and homogeneous. In hydrology, it is generally accepted that the Unit Hydrograph method is applicable to basins where the area is not so large that spatial variations in rainfall (non-uniformity) become significant. The generally accepted upper limit for the area of a basin for the practical application of the unit hydrograph is 2500 km². If the basin area exceeds this limit, the assumption that rainfall is uniform over the entire catchment area is typically violated, making the UH method unreliable. Therefore, option (b) is the correct technical limit.
The basement walls are generally designed for -
A)
Active pressure
B)
Passive pressure
C)
At rest pressure
D)
None of these
In soil mechanics, lateral earth pressure is categorized into three states: Active, Passive, and At-Rest.
1. **Active Pressure (Ka):** Occurs when the retaining wall moves away from the backfill. This requires a significant displacement of the wall to mobilize.
2. **Passive Pressure (Kp):** Occurs when the wall is pushed into the soil. This also requires significant displacement.
3. **At-Rest Pressure (Ko):** Occurs when the wall is completely rigid and there is no lateral movement (displacement) of the wall relative to the soil.
Basement walls are typically designed as rigid structures (often reinforced concrete) that are integrated into the overall building frame. Because these walls are not intended to move or tilt significantly, the soil behind them remains in its natural state of equilibrium. Therefore, the lateral pressure exerted on basement walls is the 'At-Rest' earth pressure. Designing for active pressure would be unsafe because the wall would need to tilt away from the soil to achieve that lower pressure state, which is not permissible for a building foundation.
A clay sample has a void ratio of 0.50 in the dry condition. The grain specific gravity has been Determined as 2.70. What is the shrinkage limit of this clay?
A)
18.51%
B)
17.5%
C)
19.51%
D)
16.51%
To find the shrinkage limit (SL) of the clay, we use the relationship between the void ratio at the shrinkage limit and the specific gravity of the soil solids.
1. **Understanding the Shrinkage Limit**: The shrinkage limit is the water content at which the soil remains at a constant volume even if the water content is further reduced. At this point, the soil is fully saturated, and the void ratio is equal to the void ratio in the dry condition (since no further volume change occurs).
2. **Given Data**:
- Void ratio in dry condition ($e_{dry}$) = 0.50
- Specific gravity of solids ($G$) = 2.70
3. **Formula**: For a saturated soil at the shrinkage limit, the water content ($w_{SL}$) is given by:
$w_{SL} = \frac{e_{SL}}{G} \times 100$
Since the volume remains constant from the shrinkage limit to the dry state, the void ratio at the shrinkage limit ($e_{SL}$) is equal to the void ratio in the dry condition ($e_{dry}$).
$e_{SL} = 0.50$
4. **Calculation**:
$w_{SL} = \frac{0.50}{2.70} \times 100$
$w_{SL} = 0.185185... \times 100$
$w_{SL} = 18.5185...\%$
Rounding to two decimal places, we get 18.51%.
Therefore, option (a) is the correct answer. Options (b), (c), and (d) are incorrect as they do not match the calculated value based on the provided soil properties.
The state of shear failure accompanying a minimum earth pressure is called -
A)
At rest state
B)
Active state
C)
Passive state
D)
None of these
In soil mechanics, lateral earth pressure refers to the pressure exerted by soil against a retaining wall. There are three primary states of earth pressure:
1. **At-rest state (a):** This occurs when the retaining wall is completely stationary (no movement). The lateral pressure is denoted as K₀.
2. **Active state (b):** This occurs when the retaining wall moves *away* from the soil mass. As the wall moves away, the soil expands laterally, and the internal shear resistance is mobilized. This leads to a decrease in lateral pressure until it reaches a minimum value known as the 'Active Earth Pressure' (Kₐ). Therefore, the state of shear failure accompanying minimum earth pressure is the active state.
3. **Passive state (c):** This occurs when the retaining wall is pushed *into* the soil mass. This compresses the soil, increasing the lateral pressure until it reaches a maximum value known as the 'Passive Earth Pressure' (Kₚ).
Since the question specifically asks for the state accompanying 'minimum earth pressure', the correct answer is the Active state.
Thermal conductivity of plastics is ____ compared with wood.
A)
High
B)
Relatively low
C)
Low
D)
Relatively high
Thermal conductivity (k) is a measure of a material's ability to conduct heat. Materials with low thermal conductivity act as insulators.
1. **Wood**: Wood is a natural insulator with a relatively low thermal conductivity (typically ranging from 0.12 to 0.20 W/m·K depending on the species and moisture content).
2. **Plastics**: Most plastics (polymers) are engineered to be excellent insulators. Their molecular structure consists of long chains that do not conduct heat efficiently. The thermal conductivity of common plastics (like PVC, Polyethylene, or Polystyrene) is generally lower than that of wood, often ranging from 0.10 to 0.30 W/m·K, but specialized insulating plastics and foams are significantly lower (often < 0.05 W/m·K).
In the context of building materials, plastics are categorized as having 'low' thermal conductivity compared to most structural materials, and specifically lower than wood when comparing standard polymer solids to standard timber. Therefore, plastics are more effective thermal insulators than wood.
Working stress method of design for reinforced concrete is -
A)
Not a limit state design
B)
A serviceability limit state design
C)
A limit state for crack width
D)
A collapse limit state
The Working Stress Method (WSM) and the Limit State Method (LSM) are two fundamentally different philosophies of design in reinforced concrete.
1. **Working Stress Method (WSM):** This is a deterministic approach based on the linear elastic theory. It assumes that concrete and steel behave linearly under service loads. It uses a 'Factor of Safety' applied to the material strengths to ensure that the actual stresses do not exceed the allowable (permissible) stresses. It does not explicitly define 'limit states' (the condition beyond which a structure ceases to fulfill its intended function).
2. **Limit State Method (LSM):** This is a probabilistic approach. It defines specific 'limit states'—such as the Limit State of Collapse (strength/stability) and the Limit State of Serviceability (deflection/cracking). It uses partial safety factors for both loads and materials.
Analysis of Options:
- **Option a:** Correct. WSM is a traditional stress-based method, not a limit state-based method.
- **Option b:** Incorrect. Serviceability is a specific category within the Limit State Method (LSM).
- **Option c:** Incorrect. Crack width is a check performed under the Limit State of Serviceability in LSM.
- **Option d:** Incorrect. Collapse (Ultimate strength) is a specific category within the Limit State Method (LSM).
The soil within a soil mass bounded by an isobar of given vertical pressure intensity is called :
A)
Isotropic
B)
Contact pressure
C)
Pressure bulb
D)
Pressure intensity
In soil mechanics, when a load is applied to the surface of a soil mass, the vertical stress increases with depth and spreads laterally. An 'isobar' is a line (or surface in 3D) connecting points of equal vertical pressure intensity. The volume of soil contained within a specific isobar (usually the 10% or 20% of the surface contact pressure) is referred to as the 'Pressure Bulb' or 'Stress Bulb'. This concept is critical for determining the depth of influence of a foundation and assessing potential settlement of adjacent structures.
Why other options are incorrect:
- a. Isotropic: This refers to a material property where physical properties are the same in all directions; it does not describe a volume of soil bounded by pressure.
- b. Contact pressure: This is the pressure exerted at the interface between the foundation base and the soil surface, not the volume of soil below it.
- d. Pressure intensity: This is a scalar value representing the magnitude of pressure at a specific point, not the soil mass bounded by an isobar.
In a combined footing, in the zones where the shear stress are less than 5 kg/cm², stirrups to be provided are generally -
A)
2- legged
B)
4- legged
C)
8- legged
D)
12- legged
In the design of combined footings, shear reinforcement (stirrups) is provided when the factored shear force exceeds the shear strength of the concrete. The number of 'legs' in a stirrup refers to the number of vertical bars crossing the section being considered. For relatively low shear stress levels (typically below 5 kg/cm² or within a moderate range where the concrete's capacity is only slightly exceeded), standard 2-legged stirrups are generally sufficient to carry the remaining shear load. As the shear stress increases significantly, the requirement for more legs (4, 6, or 8) increases to provide more vertical steel area to resist the shear force. Therefore, for the lower threshold of shear stress mentioned in the question, 2-legged stirrups are the standard engineering practice.
The toughness of aggregate is tested by -
A)
Impact test
B)
Crushing strength test
C)
Abrasion test
D)
Soundness test
In civil engineering and building materials, different tests are conducted on aggregates to determine their mechanical properties:
1. **Toughness (Impact Test):** Toughness is defined as the ability of an aggregate to resist failure under repeated impact or shock loading. The Aggregate Impact Value (AIV) test is specifically used to measure this property. It involves dropping a hammer of a specific weight from a fixed height onto the aggregate sample.
2. **Crushing Strength (Crushing Test):** This test measures the resistance of an aggregate to gradual compressive loading. It determines the 'Crushing Value', which indicates the strength of the aggregate.
3. **Hardness/Wear (Abrasion Test):** The Los Angeles Abrasion test is used to determine the hardness of aggregates, which is their resistance to surface wear and rubbing (abrasion).
4. **Soundness (Soundness Test):** This test evaluates the resistance of aggregates to weathering actions, such as freeze-thaw cycles or chemical reactions (using sodium or magnesium sulfate solutions).
Therefore, the test for toughness is the Impact test.
For shorter storey height, cheaper formwork and better lighting facilities, what is the recommended slab floor?
A)
T beam and slab
B)
Two way slab
C)
Flat slab
D)
Framed structure
A flat slab is a reinforced concrete slab supported directly by columns without the use of beams.
1. **Shorter Storey Height:** Because there are no beams protruding downwards from the ceiling, the overall depth of the floor system is reduced. This allows for a reduction in the total height of the building for the same number of storeys or allows for more headroom within a fixed height.
2. **Cheaper Formwork:** The formwork for a flat slab is simple and flat, unlike beam-and-slab systems which require complex shuttering for the beams. This significantly reduces labor costs and time during construction.
3. **Better Lighting and Ventilation:** The absence of beams provides a clear, unobstructed ceiling. This allows light and air to circulate more freely across the floor area and provides more flexibility for the installation of HVAC ducts and lighting fixtures.
Comparison with other options:
- **T-beam and slab / Framed structure:** These involve beams that increase the floor-to-floor height and require more complex formwork.
- **Two-way slab:** While a two-way slab distributes loads in two directions, it is typically supported by beams on all four edges in a standard framed structure, thus not offering the specific height and formwork advantages of a flat slab.
Quantity of water extracted by gravity-drainage from a saturated water bearing stratum is called -
A)
Groundwater yield
B)
Permeability
C)
Groundwater velocity
D)
Groundwater flow
Step-by-step reasoning:
1. **Definition of Groundwater Yield**: In hydrology, the 'yield' of an aquifer refers to the amount of water that can be extracted from a saturated water-bearing stratum (aquifer) under the influence of gravity. It is the volume of water that can be drained by gravity alone.
2. **Analysis of Option (b) Permeability**: Permeability is a property of the soil or rock that describes the ease with which a fluid can flow through it. It is a coefficient (k), not a quantity of water extracted.
3. **Analysis of Option (c) Groundwater velocity**: Velocity refers to the speed at which water moves through the pores of the aquifer (often calculated using Darcy's Law). It is a rate of movement (length/time), not a quantity of water.
4. **Analysis of Option (d) Groundwater flow**: This is a general term describing the movement of water through an aquifer from an area of higher hydraulic head to an area of lower hydraulic head. While yield is a result of flow, 'flow' itself is the process, whereas 'yield' is the specific quantity extracted.
Therefore, the quantity of water extracted by gravity-drainage is specifically termed as the groundwater yield.
Timber can be made reasonably fire-resistant by -
A)
Soaking it in ammonium sulphate
B)
Coating with tar paint
C)
Pumping creosote oil into timber under high pressure
D)
Seasoning process
Timber is naturally combustible. To make it fire-resistant, it must be treated with fire-retardant chemicals. Ammonium sulphate is a well-known fire-retardant chemical; when timber is soaked in a solution of ammonium sulphate, the chemical penetrates the wood fibers. Upon exposure to heat/fire, it releases gases that help extinguish the flame or slow down the combustion process by forming a protective char layer.
Analysis of other options:
- Option b (Tar paint): Tar is a hydrocarbon-based material and is highly flammable, which would actually increase the fire risk.
- Option c (Creosote oil): Creosote is used primarily as a preservative to protect timber from fungi, insects, and moisture (decay), but it is not a fire retardant.
- Option d (Seasoning): Seasoning is the process of reducing the moisture content of timber to improve strength, stability, and durability, but it does not provide fire resistance.