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Past Questions
For house drainage and lateral connections we shall use:
A)
Cast iron sewers
B)
Concrete sewers
C)
Masonry sewers
D)
Stone ware sewers
In environmental engineering and urban drainage design, the selection of sewer material depends on the location, load, and chemical nature of the effluent.
1. **Stoneware (Vitrified Clay) Sewers**: These are the preferred choice for house drainage and lateral connections. They are highly resistant to chemical corrosion (especially from domestic sewage), have a smooth internal surface to prevent clogging, and are cost-effective for smaller diameters typically used in residential connections.
2. **Cast Iron Sewers (Option a)**: While very strong and leak-proof, they are expensive and primarily used for building drains (vertical stacks) or in areas where high structural strength is required, rather than standard lateral connections.
3. **Concrete Sewers (Option b)**: These are generally used for larger main sewers or trunk sewers due to their size and strength. They are more prone to corrosion by sulfuric acid (H2S) produced in sewage compared to stoneware.
4. **Masonry Sewers (Option c)**: These are outdated and used only for very large, old trunk sewers. They are not suitable for small-diameter house drainage due to leakage issues and high construction effort.
Land disposal of sewage will be favourable where:
A)
The rivers run dry or have a small flow during summer
B)
Rainfall is very high
C)
Climate is wet and rates of evaporation is low
D)
The sewage arriving at the out fall point is fresh and non-septic
Land disposal of sewage (such as sewage farming or land application) involves applying sewage to the soil for treatment and disposal. For this method to be favorable and effective, the following conditions must be met:
1. **Fresh Sewage (Option d):** Sewage must be 'fresh' and 'non-septic'. If sewage becomes septic (anaerobic) during transport, it develops foul odors (H2S gas) and becomes difficult to handle, making it unsuitable for land application near populated areas. Fresh sewage contains dissolved oxygen and organic matter that can be more effectively utilized by soil microbes and plants.
2. **Why Option a is incorrect:** If rivers run dry, it might make land disposal a *necessity* due to lack of water bodies for dilution, but it doesn't make the process of land disposal itself 'favorable' or technically efficient.
3. **Why Option b is incorrect:** Very high rainfall is detrimental to land disposal. Excessive rain leads to waterlogging, prevents the soil from absorbing the sewage, and increases the risk of sewage runoff contaminating nearby surface water bodies.
4. **Why Option c is incorrect:** A wet climate with low evaporation rates leads to saturation of the soil. For land disposal to work, the soil must have the capacity to absorb the liquid (percolation) and the environment should ideally support evaporation to prevent the water table from rising too high.
Sewage treatment plant is normally designed to meet the requirement of ___________ period after completion.
A)
15 years
B)
20 years
C)
30 years
D)
50 years
In Environmental Engineering and Urban Planning, the 'design period' is the number of years for which a facility is designed to be adequate to meet the needs of the population. For Sewage Treatment Plants (STPs), the standard design period is typically taken as 30 years. This timeframe is chosen to balance the high capital cost of construction with the expected growth in population and sewage generation. Designing for a shorter period (e.g., 15 or 20 years) would lead to premature obsolescence and frequent expensive expansions, while designing for too long a period (e.g., 50 years) would lead to excessive initial costs and potential inefficiency due to over-sizing of biological processes (which can lead to poor treatment quality if the actual load is too low).
For the sewers of diameter less than 600mm, the type of joint preferred is:
A)
Spigot and socket joint
B)
Collar joint
C)
Bandage joint
D)
Mechanical joint
In environmental engineering and sewerage design, the choice of joint depends on the pipe diameter and the required flexibility/watertightness.
1. **Spigot and Socket Joint**: This is the most common and preferred joint for smaller diameter sewers (typically less than 600mm). It consists of one end of the pipe being expanded (socket) and the other end being slightly tapered (spigot). The spigot is inserted into the socket and sealed with a gasket or cement mortar, providing a secure, watertight seal suitable for smaller pipes.
2. **Collar Joint**: These are generally used for larger pipes or for connecting two pipes of the same diameter where a socket is not provided. They are less common for small-diameter residential or branch sewers compared to spigot and socket joints.
3. **Bandage Joint**: These are typically used for repairs or temporary fixes rather than as a standard installation joint for new sewer lines.
4. **Mechanical Joint**: While highly secure, mechanical joints are more expensive and complex to install. They are typically reserved for larger diameter pipes, high-pressure lines, or areas subject to significant ground movement, rather than standard small-diameter sewers.
The water of a river has an important property called:
A)
Turbidity
B)
Self purification
C)
Permeability
D)
Infiltration capacity
Step-by-step reasoning: 1. Analysis of the question: The question asks for an 'important property' specific to river water in the context of Environmental Engineering. 2. Evaluating Option (b) Self purification: This is a fundamental ecological and engineering property of flowing water bodies (lotic systems). Self-purification is the natural process by which a river cleanses itself of organic pollutants through mechanisms such as dilution, sedimentation, oxidation (aeration), and biological degradation by microorganisms. This is a critical concept in wastewater engineering (e.g., calculating BOD and dissolved oxygen sag curves). 3. Evaluating Option (a) Turbidity: While river water has turbidity, this is a characteristic or a measurement of water quality (cloudiness), not a functional 'property' that defines the river's behavior or capacity to recover from pollution. 4. Evaluating Option (c) Permeability: Permeability is a property of soil or porous media (the riverbed), not a property of the water itself. 5. Evaluating Option (d) Infiltration capacity: Similar to permeability, infiltration capacity refers to the maximum rate at which soil can absorb water; it is a property of the land/soil, not the river water. Therefore, self-purification is the only option that describes a functional property of the river water system.
The percentage ratio of the oxygen available in sewage to the oxygen required to satisfy one stage of bio-chemical oxygen demand(BOD) is termed as:
A)
Bio-oxygen demand
B)
Oxygen consumed
C)
Chemical oxygen demand
D)
Relative stability
In environmental engineering and wastewater treatment, 'Relative Stability' is a parameter used to assess the stability of sewage. It is defined as the ratio of the oxygen available in the sewage to the oxygen required to satisfy the biochemical oxygen demand (BOD) of the sewage, expressed as a percentage.
Formula: Relative Stability (%) = (Dissolved Oxygen / BOD) × 100.
Why other options are incorrect:
- a. Bio-oxygen demand: This is a misnomer for Biochemical Oxygen Demand (BOD), which is the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material, not a ratio.
- b. Oxygen consumed: This refers to the actual amount of oxygen used up during the degradation process, not a percentage ratio.
- c. Chemical oxygen demand (COD): This is the measure of the capacity of water to consume oxygen during the decomposition of organic matter and the oxidation of inorganic chemicals via chemical oxidants, not a ratio of available to required oxygen.
Venturimeter is used to:
A)
Measure the velocity of a flowing liquid
B)
Measure the pressure of a flowing liquid
C)
Measure the discharge of liquid flowing in a pipe
D)
Measure the pressure of difference of liquid flowing between two points in a pipe line
A Venturimeter is a device used for measuring the discharge (volumetric flow rate) of a fluid flowing through a pipeline. It works on the principle of Bernoulli's Equation. The device consists of a converging section, a throat, and a diverging section. As the fluid passes through the throat (the narrowest part), its velocity increases and its pressure decreases. By measuring the pressure difference between the inlet and the throat using a manometer, the flow rate (discharge) can be calculated using the formula: Q = Cd * A1 * sqrt((2gh) / (1 - (A1/A2)^2)), where Cd is the coefficient of discharge, A1 is the inlet area, and h is the differential pressure head.
Why other options are incorrect:
- Option (a): While velocity changes within the meter, the primary purpose of the device is to find the total discharge (Q), not just the velocity at a point.
- Option (b): A pressure gauge or manometer is used to measure pressure; the Venturimeter uses pressure differences as a means to find flow rate.
- Option (d): While the Venturimeter creates a pressure difference, it is not used to 'measure the pressure difference' as its end goal, but rather uses that difference to calculate the discharge.
The frog of a bricks is normally made on its:
A)
Longer face
B)
Shorter face
C)
Bottom face
D)
Top face
A 'frog' is a depression or indentation made on the top surface of a brick. It serves two primary purposes: first, it provides a key for the mortar to grip, creating a stronger bond between the courses of bricks; second, it is often used by manufacturers to emboss their brand name or trademark.
Analysis of options:
- a. Longer face: This is the side surface; placing a frog here would compromise the structural integrity of the wall.
- b. Shorter face: This is the header end; a frog here would not provide the necessary mortar key for horizontal bedding.
- c. Bottom face: The bottom is typically flat to ensure stability on the base.
- d. Top face: This is the standard location for the frog to ensure that when the brick is laid, the mortar fills the indentation, locking the bricks together.
In preliminary treatment of sewage , the operation which takes place is:
A)
Removal of fine suspended particles
B)
Removal of fine dissolved organic material
C)
Removal of lighter floating material
D)
Removal of harmful bacteria and other organism
Sewage treatment is typically divided into preliminary, primary, secondary, and tertiary stages.
1. **Preliminary Treatment**: This stage is designed to protect the plant equipment (pumps and pipes) and remove large, coarse materials. It involves operations such as screening (to remove large floating debris like plastics, rags, and sticks) and grit removal (to remove heavy inorganic solids like sand and gravel). Therefore, the removal of lighter floating material (via screening) and heavy grit is the primary goal of this stage.
2. **Why other options are incorrect**:
- **Option (a)**: Removal of fine suspended particles occurs during **Primary Treatment** (via sedimentation tanks/clarifiers).
- **Option (b)**: Removal of dissolved organic material occurs during **Secondary Treatment** (via biological processes like activated sludge or trickling filters).
- **Option (d)**: Removal of harmful bacteria and other organisms occurs during **Tertiary Treatment** or Disinfection (using chlorine, UV, or ozone).
The quantity of surface water depends mainly upon:
A)
Permeability of soil
B)
Rainfall
C)
Snow
D)
Climate change
Step-by-step reasoning: 1. Surface water refers to water that collects on the ground surface, including rivers, lakes, streams, and runoff. 2. The primary source of input for the hydrological cycle on land is precipitation. 3. Among the given options, rainfall is the most direct and primary source of water that feeds surface water bodies. 4. While 'Permeability of soil' (Option a) determines how much of that rainfall becomes surface runoff versus infiltration, it does not provide the water itself. 5. 'Snow' (Option c) is a form of precipitation, but rainfall is the more general and dominant driver of surface water quantity globally. 6. 'Climate change' (Option d) is a long-term driver that affects patterns of rainfall, but it is not the immediate source of the water quantity. Therefore, the quantity of surface water depends mainly upon the amount of rainfall received in a catchment area.
The quantity of liquid waste which flows in sewers during rainy season is called:
A)
Storm sewage
B)
Dry weather flow
C)
Sanitary sewage
D)
Domestic waste
In environmental engineering and wastewater management, sewage is categorized based on its source and the weather conditions.
1. **Storm Sewage (Correct):** This refers to the wastewater that enters the sewer system specifically due to precipitation (rain or melting snow). In combined sewer systems, the total flow during the rainy season is the sum of dry weather flow and storm sewage.
2. **Dry Weather Flow (DWF):** This is the average flow of sewage in a sewer during periods of no rainfall. It consists primarily of domestic sewage and industrial waste.
3. **Sanitary Sewage:** This is a general term for wastewater from toilets, sinks, and showers (domestic waste), regardless of the season. While it flows during the rainy season, it is not the specific term for the *additional* liquid waste caused by rain.
4. **Domestic Waste:** This refers to the waste generated from residential activities, which is a component of sanitary sewage, not the rain-induced flow.
Therefore, the liquid waste that flows specifically due to the rainy season is termed 'Storm sewage'.
In india per capita contribution of dry solids to be assumed at:
A)
40 g/day
B)
50 g/day
C)
60 g/day
D)
70 g/day
In Environmental Engineering, specifically regarding the design of sewage treatment plants and the estimation of sludge production, the per capita contribution of dry solids (suspended solids) to domestic sewage is a critical parameter. According to standard Indian standards and textbooks on Environmental Engineering (such as those by S.K. Garg or B.C. Punmia), the average per capita contribution of dry solids in India is generally assumed to be approximately 70 grams per day. This value is used to calculate the total organic load and the volume of sludge that needs to be handled in waste water treatment processes. Options a, b, and c (40g, 50g, and 60g) are lower than the standard design assumption used for Indian urban populations.
A sewer which receives discharge of a number of house sewers is called a:
A)
Common sewer
B)
Trunk sewer
C)
Lateral sewer
D)
Branch sewer
In a sewerage system, sewers are categorized based on their position and the volume of discharge they carry.
1. **Lateral Sewer**: This is the smallest sewer that collects waste directly from a single house or building and carries it to a branch sewer.
2. **Branch Sewer (or Sub-main sewer)**: This sewer receives discharges from a number of lateral sewers (house sewers). Therefore, a sewer that receives discharge from several house sewers is defined as a branch sewer.
3. **Trunk Sewer**: These are larger sewers that collect discharge from several branch sewers and carry it toward the main sewer or treatment plant.
4. **Common Sewer**: This term generally refers to a combined sewer system that carries both sanitary sewage and storm water in a single pipe, rather than referring to a specific hierarchical level of collection.
Since the question asks for the sewer that receives discharge from a number of house (lateral) sewers, the correct answer is the Branch sewer.
One cubic metre of water weighs:
A)
100 litres
B)
250 litres
C)
500 litres
D)
1000 litres
Step-by-step reasoning:
1. Understanding the units: The question asks for the 'weight' (though it uses volume units in the options) of one cubic metre (1 m³) of water.
2. Volume Conversion: By definition, 1 cubic metre is equal to 1,000 litres (1 m³ = 1000 L).
3. Mass/Weight Relationship: For pure water at standard temperature and pressure, the density is approximately 1000 kg/m³. Therefore, 1 m³ of water has a mass of 1000 kg.
4. Litre-to-Mass Correlation: Since 1 litre of water weighs approximately 1 kilogram, 1000 litres of water weigh 1000 kilograms.
5. Analysis of Options: The options provided are in 'litres', which is a unit of volume. In the context of basic fluid mechanics questions of this type, the question is testing the fundamental conversion between cubic metres and litres.
- Option a (100 L), b (250 L), and c (500 L) are mathematically incorrect conversions of 1 m³.
- Option d (1000 L) correctly identifies the volume equivalent of 1 m³ of water.
Grit chambers of sewage plant are usually changed after:
A)
1 day
B)
1 week
C)
2 weeks
D)
4 weeks
In a sewage treatment plant, grit chambers are designed to remove inorganic solids (such as sand, gravel, and eggshells) through sedimentation. These materials are non-biodegradable and highly abrasive. If allowed to accumulate for long periods, they can cause significant wear and tear on downstream pumps, clog pipes, and reduce the effective volume of subsequent treatment units (like primary clarifiers). Therefore, to maintain operational efficiency and prevent equipment damage, grit chambers are typically cleaned or 'changed' (emptied of accumulated grit) on a daily basis. Options b, c, and d (1 week to 4 weeks) are incorrect because allowing grit to accumulate for such durations would lead to operational failure and excessive mechanical wear.
The breaking up of cohesion in a mass of concrete is called:
A)
Workability
B)
Bleeding
C)
Segregation
D)
Creep
Step-by-step reasoning:
1. Definition of Segregation: Segregation in concrete occurs when the coarse aggregates separate from the cement paste (mortar). This represents a loss of homogeneity and a 'breaking up of cohesion' within the concrete mass, often caused by over-vibration, dropping concrete from a height, or improper mix design.
2. Analysis of other options:
- Workability (a): This refers to the ease with which concrete can be mixed, placed, consolidated, and finished. It is a property of fresh concrete, not a failure of cohesion.
- Bleeding (b): This is a specific form of segregation where water (a liquid) rises to the surface of freshly placed concrete. While related to segregation, bleeding refers specifically to the movement of water, whereas the general breaking up of cohesion of the mass is termed segregation.
- Creep (d): This is the time-dependent permanent deformation of concrete under a sustained constant load. It is a long-term structural property, not a phenomenon occurring during the fresh state of concrete.
3. Conclusion: The process of the concrete mass losing its cohesive unity and separating into its constituent parts is defined as segregation.
The area of longitudinal steel reinforcement in column should not be:
A)
Less than 0.8% of the area of concrete section required for direct load alone
B)
More than 6% of gross sectional area of column
C)
Less than 1 % of the area of concrete section
D)
Both (a) & (b)
According to IS 456:2000 (the Indian Standard code of practice for Plain and Reinforced Concrete), the requirements for longitudinal reinforcement in columns are as follows:
1. Minimum Reinforcement: Clause 26.5.3.1 states that the area of longitudinal reinforcement shall not be less than 0.8% of the gross cross-sectional area of the column. This is to prevent sudden failure and to handle accidental eccentricity.
2. Maximum Reinforcement: Clause 26.5.3.1 also specifies that the maximum area of longitudinal reinforcement shall not exceed 6% of the gross cross-sectional area of the column. However, in practice, it is often limited to 4% to avoid congestion of reinforcement at lap joints.
Evaluating the options:
- Option (a) refers to the minimum limit of 0.8% (though the phrasing 'required for direct load alone' is a slightly older way of describing the gross area requirement).
- Option (b) refers to the maximum limit of 6% of the gross sectional area.
- Option (c) is incorrect because the minimum is 0.8%, not 1%.
Since both (a) and (b) represent the regulatory limits (minimum and maximum) set by the code, the correct answer is (d).
Which of the following statement is correct?
A)
Sewage if not treated, will create healthy conditions
B)
Secondary treatment of sewage works on hydraulic separation principles
C)
Primary clarifiers are the sedimentation tanks located just after the grit chambers
D)
Trickling filter is different from percolating filter
Step-by-step analysis of the options:
1. Option (a) is incorrect: Untreated sewage contains pathogens, organic matter, and toxic chemicals. If not treated, it leads to water pollution, outbreaks of diseases (like cholera and typhoid), and eutrophication, creating unhealthy conditions, not healthy ones.
2. Option (b) is incorrect: Secondary treatment is a biological process (e.g., Activated Sludge Process, Trickling Filters) that uses microorganisms to decompose organic matter. Hydraulic separation (physical removal of solids based on density/gravity) is the principle used in Primary treatment.
3. Option (c) is correct: In a typical wastewater treatment plant flow, the sequence is: Screening $\rightarrow$ Grit Chamber $\rightarrow$ Primary Clarifier (Primary Sedimentation Tank). The grit chamber removes heavy inorganic solids (sand, gravel), and the primary clarifier follows to remove settleable organic solids.
4. Option (d) is incorrect: In the context of environmental engineering, a trickling filter is essentially a type of percolating filter. Both refer to attached-growth biological processes where sewage is sprayed over a bed of media (rocks, plastic) to allow a biofilm to degrade organic matter.
Curing of concrete for ___________ is satisfactory for normal Portland cement under normal temperature conditions.
A)
24 hrs
B)
7 days
C)
14 days
D)
30 days
Curing is the process of maintaining moisture and temperature conditions in freshly placed concrete to allow the hydration of cement to proceed, ensuring the concrete reaches its intended strength and durability. For Ordinary Portland Cement (OPC) under normal temperature conditions, the standard minimum curing period is generally accepted as 7 days. During this period, the majority of the initial strength gain occurs. While longer curing (14 or 28 days) is beneficial for higher strength or specific environmental conditions (like hot/dry weather), 7 days is considered the satisfactory minimum for standard applications. Option (a) 24 hours is only sufficient for the initial setting phase; options (c) and (d) are ideal for specialized high-strength requirements but exceed the standard 'satisfactory' minimum for normal conditions.
The disposal of sewage into natural water courses such as streams, rivers, sea and lake is known as sewage disposal:
A)
By dilution
B)
By self purification
C)
By sedimentation
D)
By liquidification
Step-by-step reasoning: 1. Definition: Sewage disposal by dilution involves discharging untreated or partially treated sewage into a large body of water (like a river, lake, or sea). 2. Mechanism: The principle is that the large volume of the receiving water body dilutes the concentration of pollutants to a level where they are less harmful and can be processed by the natural environment. 3. Analysis of other options: (b) Self-purification is the natural process (physical, chemical, and biological) that occurs *after* the sewage has been diluted and discharged, but the act of disposal itself is called dilution. (c) Sedimentation is a primary treatment process where solids settle at the bottom; it is not a method of final disposal into water courses. (d) Liquefaction is a physical process (often related to soil or gas) and is not a term used for sewage disposal methods. Therefore, the correct term for the act of discharging sewage into natural water courses is disposal by dilution.
The minimum depth of septic tank is considered to be:
A)
0.5 m
B)
1.0 m
C)
1.2 m
D)
1.5 m
In Environmental Engineering, a septic tank is designed to provide sufficient detention time for the settling of solids and anaerobic digestion of organic matter. According to standard engineering guidelines (such as IS 2470 in the Indian context), the liquid depth of a septic tank is typically maintained between 1.0 m and 1.8 m. The minimum liquid depth is specified as 1.0 m to ensure that there is enough space for the accumulation of sludge at the bottom and the formation of a scum layer at the top without compromising the hydraulic retention time or causing premature solids carry-over into the soak pit or drainage field. Options a (0.5 m) is too shallow to prevent turbulence and allow settling; options c (1.2 m) and d (1.5 m) are common design depths but are not the absolute minimum threshold.
The hydraulic mean depth or the hydraulic radius is the ratio of:
A)
Velocity of flow and area of flow
B)
Area of flow and wetted perimeter
C)
Wetted perimeter and diameter of pipe
D)
Area of flow and diameter of pipe
The hydraulic radius (R), also known as the hydraulic mean depth, is a fundamental parameter in open channel flow and pipe flow analysis. It is defined as the ratio of the cross-sectional area of the flow (A) to the wetted perimeter (P). Mathematically, it is expressed as R = A / P.
- Area of flow (A): The total cross-sectional area through which the fluid flows.
- Wetted perimeter (P): The length of the boundary of the cross-section that is in contact with the fluid.
Evaluating the options:
- Option (a) is incorrect because the ratio of velocity to area does not define a standard hydraulic property.
- Option (b) is correct as it matches the definition R = A/P.
- Option (c) is incorrect as the ratio of wetted perimeter to diameter is not the hydraulic radius.
- Option (d) is incorrect as the ratio of area to diameter is not the hydraulic radius.
The time taken for flow in a sewer to build upto maximum is known as:
A)
Time of flow
B)
Time of concentration
C)
Time of entry
D)
Time of consideration
In environmental and hydraulic engineering, specifically regarding storm sewers and drainage systems, the 'Time of Concentration' (Tc) is defined as the time required for runoff to travel from the hydraulically most remote point of a catchment area to the outlet or the point of interest. It is the time taken for the entire watershed to contribute to the flow at the outlet, meaning the flow at that point reaches its maximum peak.
Breakdown of options:
- Option (a) 'Time of flow' is a generic term and not a technical definition for peak flow timing.
- Option (b) 'Time of concentration' is the standard technical term used in the Rational Method (Q=CIA) for calculating peak discharge.
- Option (c) 'Time of entry' refers to the time it takes for water to flow from the surface into the inlet (inlet time), which is only a component of the total time of concentration.
- Option (d) 'Time of consideration' is not a recognized technical term in hydraulic or environmental engineering.
The centre to centre spacing of vertical stirrups , in a rectangular beam is:
A)
Increased towards the centre of the span of the beam
B)
Decreased towards the centre of the span of the beam
C)
Increased at the ends
D)
Decreased at the ends
In a reinforced concrete rectangular beam, vertical stirrups are provided primarily to resist shear forces. According to the shear force diagram (SFD) for a simply supported beam under uniform or point loads, the shear force is maximum at the supports (ends) and minimum (often zero) at the center of the span. Since the requirement for shear reinforcement is proportional to the magnitude of the shear force, stirrups are placed closer together (decreased spacing) near the supports to handle the high shear stress and further apart (increased spacing) towards the center of the span where the shear force is lower. Therefore, the spacing increases as you move from the ends toward the center.
The minimum grade of concrete for small capacity of tanks upto 50 cum at a locations where there is difficulty in providing M-30 grade of concrete, may be taken as:
A)
M-10 grade of concrete
B)
M-15 grade of concrete
C)
M-20 grade of concrete
D)
M-25 grade of concrete
According to the Indian Standard code for the design of liquid retaining structures (IS 3370), the general requirement for the grade of concrete used in water tanks is M-30 to ensure durability and water-tightness. However, the code provides a relaxation for small-capacity tanks. For tanks with a capacity up to 50 cubic meters, in locations where it is difficult to provide M-30 grade concrete, the minimum grade of concrete permitted is M-20. This allows for practical construction in remote areas while still maintaining a minimum threshold of structural integrity and permeability resistance. Options a (M-10) and b (M-15) are too low for liquid retaining structures as they lack the necessary density and strength to prevent seepage and corrosion of reinforcement. Option d (M-25) is higher than the minimum required relaxation limit of M-20.