BPSC AE Civil Paper 6 (Civil) Mock Test - 2 - Civil Engineering (CE) MCQ

Concept:

Sewerage system:

The entire system developed for the collection, treating, and disposing of the sewage safely is called the sewerage system. Modern sewerage systems fall under mainly three categories-

1). Combined sewerage system:

• A combined sewer system is a sewer that accepts stormwater, sanitary water (sewage), then the sewage is treated in the sewerage treatment plant.
• This system is mainly used in towns where streets are narrow and rainfall is less than moderate.

2). Separate sewerage system:

• In this system, the sanitary sewage and stormwater are carried separately in two sets of sewers.
• The sewage is conveyed to the wastewater treatment plant and the stormwater is discharged into rivers without treatment.

3). Partially Separate sewerage system:

• A partially separate system is a combination of a combined sewerage system and separate sewerage systems.
• This type of sewerage system helps decrease the load from a combined sewerage system because only the water from initial rainfalls (water from acid rain) is added to sewage water and after that this system work as a separate system.
• It is generally used in small towns.

Concept:

The hardness of stone:

For determining the hardness of a stone, the test is carried out as follows:

1). A cylinder of diameter 25mm and height 25mm is taken out from the sample of stone. It is weighed.
2). The sample is placed in Dorry’s testing machine and it is subjected to a pressure of 1250 gm.
3). An annular steel disc machine is then rotated at a speed of 28 rpm.
4). During the rotation of the disc, coarse sand of standard specification is sprinkled on the top of disc.
5). After 1000 revolutions, the specimen is taken out and weighed.
Coefficient of hardness = 20 – (Loss of weight in gm/3)

Important Points

14 < coefficient of hardness > 17, for building construction

17 < coefficient of hardness, for road work.

According to Lacey’s, the design formulas to build canal is as follows:

1) Silt factor ⇒ f = 1.76√d_mm

2) Velocity of flow 

3) Hydraulic mean depth ⇒ R = 5V²/2f

4) Wetted perimeter ⇒ P = 4.75√Q

5) Bed slope

Given,

Canal:

• A canal is an artificial channel generally trapezoidal in shape constructed on the ground to carry water to the fields (or irrigation fields) either from the river or from the reservoir.
• Canals have played an important role in creating assured irrigation supplies to agricultural fields and contributed substantially to the green revolution in the country.

Canal Alignment:

• A canal has to be aligned in such a way that it covers the entire area proposed to be irrigated, with a shortage of possible length, and at the same time, its cost including the cost of drainage works is a minimum.
• For a detailed topographical investigation of a canal, a canal is aligned along the ridge line.
• Irrigation Canals are generally aligned along the ridge line.
• Irrigation canals are generally aligned along the ridge line as this ensures gravity irrigation on both sides of the ridge.

Width of Pavement or Carriageway:

• The pavement width depends upon the number of lanes and the width of single-lane required. The lane width determines on the basis of the width of the vehicle and minimum side clearance.
• The maximum permissible width of the vehicle as per IRC specification is 2.44 m.

Important Points

• Intermediate carriageway is more than one lane but less than two lanes. This is only provided to allow manouvering.

Check valves or reflux valves: It prevent water to flow back to opposite directions. They are provided on the delivery side of the pumping set and at interconnections between a polluted water system and a potable water system. These are generally provided on the delivery side of the pump. These valves work automatically.

Pressure reducing valve: In hydraulics, a pressure reducing valve serves the same purpose as a "pressure regulator" valve in a compressed air system. It is one of a variety of pressure control valves available for hydraulic circuits. It is always used in a branch circuit and never in the full pump flow line.

Air Relief Valve: it is a type of safety valve used to control or limit the pressure in a system, pressure might otherwise build up and create a process upset, instrument or equipment failure, or fire. The pressure is relieved by allowing the pressurized fluid to flow from an auxiliary passage out of the system.

Scour valve: This valve is used to drain the water out of the pipe system.

Sluice valve: These valves are used to regulate the flow of water in the pipe system by dividing into a number of sections.

Concept:

Time headway:
It is defined as the time interval between the passage of successive vehicles moving in the same lane and measured from head to head as they pass a point on the road.

Where,

q = traffic volume in vehicles/hour

Time Headway is also given by H_t =  3600/q_max

where q_max is the Theoretical maximum capacity

Calculation:

Given

Traffic stream u = 70 - 0.7 k

we Know

Traffic volume = Traffic Density × u

q = ku

q = k × ( 70 - 0.7 k)

q = 70k - 0.7 k²

For maximum q

dq/dk = 0

dq/dk = 70 - 1.4k = 0

k = 70/1.4 = 50

Maximum q = 70k - 0.7 k2 = 70 × 50 - 0.7 × 50²

q = 1750 veh/hr

So Theoretical maximum capacity is 1750 veh/hr

Now Time Head way is

Time Headway given by H_t = 3600/1750 = 2.057 sec

∴ Time Headway = 2.057 sec ≈ 2.1 sec

Water logging:

• Water logging of the land occurs when the water table rises and the soil in the root zone of the plants gets saturated and the air circulation is stopped.
• Water logging generally occurs because of intensive irrigation and inadequate drainage of the irrigated land.
• Waterlogging affects the productivity and fertility of the land and causes a reduction in crop yield.

Causes of waterlogging -

• Over-Irrigation
• Inadequate surface drainage
• Obstruction of natural surface drainage
• Obliteration of a natural drainage
• Obstruction of natural subsurface drainage
• Impervious top layer
• Seepage from canals
• Construction of a reservoir
• Defective methods of cultivation
• Defective irrigation practice

Effect of waterlogging -

• Reduction in the growth of plants
• Difficulty in cultivation
• Accumulation of salts
• Weed growth
• Increase in plant diseases
• Lowering of soil temperature
• Increase in incidence of malaria

Hence statements B and D are incorrect.

Divide wall: These is much like a pier and is provided between the sets of under sluice or river sluice or spill bays.

The main functions of a divide wall:

• It separates the turbulent floodwaters from the pocket in front of the canal head.
• It helps in checking parallel flow (to the axis of the barrage) which would be caused by the formation of deep channels leading from the river to the pocket in front of the sluices.

∴ The main functions of a divide wall is to separate the under sluices.

Concept:

Looseness factor = Actual width/Regime width

Regime width (w) = 4.75√Q ………… (Lacey’s Theory)

Calculation:

Given: Actual width = 360 m

Regime width (W) = 4.75√Q

W = 4.75√7000

W = 397.41 m

∴ Looseness factor = 360/397.41 = 0.90

Concept:

Rain gauge is an instrument used to measure the rainfall at the location where it is installed. It is known by various other names such as – Pluviometer, ombrometer, hyetometer, and odometer.

In order to have a correct estimate about the amount of rainfall over a particular area, proper distribution of rain gauge stations are required. For this, a term called rain gauge density is defined which means that no. rain gauge stations required per square km².

As per IS a recommendation, the rain gauge density depending on the terrain of the area and it is given below:

∴ Number of required rain gauge stations = Area × Rain gauge density

Calculation:

As it can be seen from the above table, for plain 1 no of rain gauge required for an area of 520 km².

Hence, number of rain gauge stations required for an area of 5200 km² in planes

∴ N = 5200/520 = 10 stations.

• Temporary hardness is due to the presence of soluble bicarbonates of calcium and magnesium in water which can be removed by boiling the water.
• Calcium hydrogen carbonate decomposes when heated. This happens when water is boiled, resulting in the formation of insoluble calcium carbonate. The precipitation reaction is as –

Ca(HCO₃)₂ → CO₂ + H₂O + CaCO₃↓

• Permanent hardness is due to the presence of sulphates and chlorides of calcium and magnesium.

Limit State Method

• The Acceptable limit for safety and serviceability requirements before failure occurs is called a limit state.

It is further divided into two parts:

Limit state of collapse:

• It deals with strength and stability of the structure under maximum design load.
• As per Clause 36.4.2 of IS 456, the material partial safety factor (γm) for concrete and steel should be taken as 1.5 and 1.15, respectively when assessing the strength of the structures or structural members employing limit state of collapse.

Limit state of serviceability:

• It deals with the deflection and cracking under service loads, durability, stability, fire resistance etc.

Depth area duration (DAD) relationship:

(i) A rain gauge station gives the point rainfall, which does not actually represent the rainfall in that area. To find how much rainfall will occur in an area by converting the point rainfall data to areal rainfall data, the depth area duration curve is used.

(ii) A depth area duration curve express graphically the relation between the progressively decreasing average depth of rainfall over a progressively increasing area from the center of the storm outward to its edges for a given duration of rainfall.

(iii) The depth area curve for a particular storm can be calculated with the help of the equation as,

P̅ = Po e-(K/An)

From the above graph, it is clear that at the same area when the time period decreases then the average rainfall depth decreases.

Slow sand filter:

• The filtration rate of a slow sand filter is usually one-twentieth (or less) of the rate of a rapid sand filter or pressure filter.
• These filters require large areas of land and a correspondingly large quantity of filter media (sand) and base material (gravel).
• Cleaning of the filter is done by surface scrapping which may involve a lot of labor. A slow sand filter is suitable when the availability of land, labor, and filter media is at a low cost.
• A distinguishing property of slow sand filters is the availability of a thin layer, called the schmutzdecke, which results on the surface of the sand bed and contains a large variety of biologically active microorganisms. It is a very simple and effective technique for purifying surface water.
• It will remove practically all of the turbidity from the water as well as most of the pathogens without the addition of chemicals. If the turbidity of raw water is high then plain sedimentation would be required to reduce turbidity to some extent so that the fillers are not unduly loaded.
• Depth of filter is 2.5 m to 3.5 m.
• Plan area of filter is 100 to 200 m².
• 0.2 ≤ D₁₀ of sand ≤ 0.3 mm
• Depth of sand is 90 to 110 cm.
• Frequency of cleaning 1 to 3 months.
• Rate of filtration is 2400 to 4800 lit/m²/day

So backwashing is used for cleaning the filter bed is the wrong statement, hence option (2) is correct.

Wake:

• Wake is defined as the region downstream of the streamline or blunt-body where the flow is disturbed and maybe turbulent or separated from the boundary.

Additional Information:

• Drag is defined as forceful pull experienced by the flat plate while the fluid flows over it.
• Pressure drag comes from the eddying motions that are set up in the fluid by the passage of the body. This drag is associated with the formation of a wake in the flow.
• Frictional drag comes from friction between the fluid and the surfaces over which it is flowing.

Mach number (M):

It is defined as the square root of the ratio of the inertia force to the elastic force.

Where Fi = Inertia force

F_e = Elastic force

This number is important following situations:

• Compressible flow at high velocities.
• Launching action of the apron.
• Motion of high-speed projectiles and missiles.

Thomas Number:

• The Thomas number is useful when analyzing fluid flow dynamics problems where cavitation may occur.
• It is also called the cavitation number.

Reynolds Number (R):

It is defined as the ratio of the inertia force to the viscous force.

R_e = ρvd / u

Where ρ = density of water

v = velocity of flow

d = Diameter of pipe

μ = Dynamic viscosity of the fluid

This number is important following situations:

• Motion of submarine completely underwater
• Low-velocity motion around automobiles and aeroplanes.
• Incompressible flow through pipes of smaller sizes.
• Flow through low-speed turbomachines.

Weber Number (W_e):

It is defined as the square root of the ratio of the inertia force to the surface tension force.

Where F_i = Inertia force

F_s = Surface tension force

This number assumes importance in the following flow situations:

• Capillary movement in water soils.
• Flow of blood in veins and arteries.
• Liquid atomisation.

Concept:

Specific speed (N_s) of the turbine:

Where N_s = specific speed of the turbine

P = Power developed

H = Head of water

Calculation:

Given

Power produced by turbine A (P_A) = 400 kW

Speed in turbine A (N_A) = 1000 rpm

Power produced by turbine B (P_B) = 100 kW

Speed of turbine B (N_B) =?

The specific speed and working head of both the turbines are the same, so we can write the above formula for specific speed in the following form

Speed of turbine B (N_B) = 2000 rpm

Hence option (2) is correct.

Concept:

An estimate of the theoretical maximum or basic capacity of a single lane may be made from the relation:

q_c = 1000V/S,

Where q_c = Basic capacity of single lane, vehicles per hour per lane

V = Speed kmph

S = Average centre-to-centre spacing of vehicles, m

Calculation:

Given

S = 30 m

V = 60 kmph

The basic capacity of the traffic lane is

q_c = (1000 x 60) / 30 = 2000 vehicles per hour

q_c = 2000 vehicles per hour

The most economical or most efficient or best section of the channel :

• A channel is said to be economical when it can pass a maximum discharge for a given cross-sectional area, resistance coefficient, and bottom slope.
• Discharge,
• Discharge is maximum when Hydraulic radius (R) is maximum and wetted perimeter is minimum
  R = A/P 
• A section of a channel is said to be most economical when the cost of construction of the channel is minimum.
• But the cost of construction of a channel depends upon the excavation and the lining.
• To keep the cost down or minimum, the wetted perimeter, for a given discharge should be minimum.
• This condition is utilized for determining the dimensions of a economical sections of a different forms of channels.
• So all these conditions will be satisfied by the semi-circular section.
• Hence for open channel flow best hydraulic section is semi-circular.

Chlorination:

• Chlorination is the process of disinfecting water to make it fit for consumption by adding chlorine or chlorine-containing substances.

• Chlorine inactivates a microorganism by damaging its cell membrane. once the cell membrane is weakened, chlorine can enter the cell and disrupt cell respiration and DNA activity.

Types of chlorination:

1. Plain chlorination:

• If only one treatment is given to water is chlorination it is termed plain chlorination.
• It removes Taste, Odour, color, and microorganisms from water.

• The normal dose of chlorine for plain chlorination is 0.5 mg/l.

2. Pre-chlorination:

• If the chlorination is done during coagulation or filtration it is termed as pre-chlorination.
• It is adopted when the quality of water is poor i.e. water contains a high amount of organic matter and microorganisms.

• Pre-chlorination is always succeeded by post-chlorination.

​3. Post-chlorination:

• If chlorination is done after filtration or it is the last treatment given to the water it is termed as post chlorination.

• The dose of chlorine in this case should be such that 0.2 mg/l of residual chlorine is ensured at a contact period of 10 min to safeguard the water against future contamination.

4. Double chlorination:

• if pre-chlorination and post-chlorination are both done it is termed double chlorination.

• It is adopted when higher efficiency of chlorination is needed.

5. Super chlorination:

• If excess chlorine is added in the range of 5-15 mg/l to ensure residue of 1-2 mg/l at a contact period of 10 min during an epidemic. it is termed super chlorination.

6. De-chlorination:

• The process of removing excess chlorine from the water is termed de-chlorination.
• It is done by activated carbon, sodium thiosulphate (Na₂S₂O₃), etc. ​​

Highway Pavement

• Highway pavement is a type of hard surface made from durable surface material laid down on an area that is intended to carry vehicular or foot traffic.

• Based on the material used in pavement highway pavement is classified as 1. Flexible pavement 2.Rigid pavement 3. Semi-rigid pavement 4. Composite pavement

Composition of highway pavement:

Surface course:

• This layer of pavement is in direct contact with traffic therefore good quality aggregate and highly dense bitumen is used.
• The main function of the surface course is to provide skid resistance surface, and friction for moving vehicles.
• It should be water tight against surface water infiltration.

• generally the thickness of surface course is 25 mm - 50 mm.

Base course:

• The base course is provided below the binder course.

• It is constructed with hard and durable aggregates.

• The main function of the base course is to provide structural support to the pavement and distribute loads from the top layers to the underneath sub-base and sub-grade.

• The minimum thickness of the base course provided is 100 mm.

Sub Base course:

• It serves the same function as of base course and distributes the entire load over the subgrade.
• If sub-grade soil is strong and stiff, then there is no need to provide sub-base course.
• It is constructed with granular aggregates to provide drainage function.
• The minimum thickness provided is 100 mm.

• It is also known as the drainage layer.

Sub Grade course:

• It is the bottommost layer of pavement and is responsible for the stability of pavement.
• It is a natural soil layer compacted up to the required depth generally about 150 mm to 300 mm to receive the load coming from top layers.

Given,

Discharge (Q) = 1 cumec = 1 m³/sec

Time = 1 day

We know

Volume (V) = Q x time = 1 m³/sec x 1 day

V = 1 m³/sec x 24 x 60 × 60 sec

V = 86,400 m³

∴ The volume of water resulting from a discharge of 1 cumec per day amounts is 86,400 m³

Anaerobic Sludge Digestion:

• The anaerobic sludge digestion produces a large amount of energy in the form of Methane.
• The sludge digested by this method is less bulky, hence can be dewatered easily.
• Gas production in anaerobic sludge digester: Out of total volatile solids 65 % are induced to gasses and 35 % are formed in digested sludge and out of the total gasses formed 70 % is methane (CH₄) and 30 % is Carbon Dioxide (CO₂).
• Products of digestion: Gases (CH₄, CO₂), Scum (Separable solids), and Supernatant liquid and digested sludge.
• It reduces the nuisance of digested sludge and reduces the vectors such as rodents, flies, etc. attraction towards sludge.

Concept:

• A stagnation point is a point in a flow field where the local velocity of the fluid is zero.
• The Bernoulli equation shows that the static pressure is highest when the velocity is zero and hence static pressure is at its maximum value at stagnation points. Because all the velocity head is converted into the pessure head at stagnation point.
• This static pressure is called the stagnation pressure.

For a fully developed laminar viscous flow through a circular pipe, the maximum velocity is equal to twice the average velocity.

Important Points

For the fully developed laminar flow through the parallel plates, the maximum velocity is equal to the (3/2) times of the average velocity.

i.e. U_max  = (3/2) x U_avg 

For a laminar flow between parallel plates:

The Discharge over an Ogee Spillway is given by

Where,

C is the Coefficient of discharge

L_e is the length of the spillway crest

H_e is the Total head above the crest

Flood routing: It is a technique of determining the flood hydrograph at a section of a river by utilizing the data of flood flow at one or more upstream sections.

The two types of routing are as follows:

a) Lumped/Hydrologic flow routing

b) Distributed/Hydraulic routing

Attenuation: It is the technique of reducing the peak value of the outflow. Decreased peak flows contribute less volume to downstream flood events, and peak flows that are delayed high in the watershed may not coincide with peak flows downstream and therefore contribute less to downstream flooding.

The key parameters that define flood attenuation are:

1) decreased peak flows and 2) delayed peak runoff.

Given,

Duration = 150 days = 150 × 24 × 60 × 60 = 12.96 × 106 sec

Depth of water required = 25.92 cm = 0.2592 m

Area = 100000 ha = 10⁹ m² (1 ha = 104 m2)

Discharge in distributary channel is __?

Q = Area of field × Depth of water required / Duration

∴ Q = 20 cumec

As there will be losses along the supply to get 20 cumec It has to be designed for more than 20 cumecs

Corrosion of sewers due to biological reaction:

• Corrosion in sewer pipes happens primarily due to hydrogen sulfide gas

• H₂S in sewer is usually produced by bacteriological reduction of sulphates.
• In the presence of air, H₂S gets oxidized to H₂SO₄ and this sulphuric acid reacts with cement constituents of concrete.

Factor responsible for sewer corrosion:

• Sewers with low velocities ( insufficient self-cleansing) encourage the growth of anaerobic bacteria in a slime layer.
• Improper composition of sewer material ( like non use of sulphate resistant elements ).
• Due to high BOD.
• Due to high temperature.
• Improper maintenance of sewer.
• Improper ventilation.