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

At grade intersection:

• These include all roads which meet at more or less at the same level.
• The traffic manoeuvers like merging, diverging, and crossing are involved in the intersection at grade.
• Some commonly observed at grade intersection are shown below

Confusion Points:

• There is no such thing as a tri-leg junction in at grade junction, there is either Y - Junction or T - Junction, which has 3 roads each.
• Rotary is a type of at grade intersection which can be skewed cross or multi-leg cross depending on the number of roads merging at the rotary.

Concepts:

The energy loss due to hydraulic jump is given as:

Where

y₁ is the pre-jump depth

y₂ is the post jump depth

Calculation:

Given: y₁ = 0.2 m; y₂ = 1.2 m

∴ Energy Loss = E = 1.04 m

Additional Information:

The relation between pre and post jump depth is given as

Where

F₂ is the Froude number after the jump.

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,

Prime coat:

The prime coat is an application of low viscous cutback bitumen to an absorbent surface like granular bases on which binder layer is placed. It provides bonding between two layers. Unlike the tack coat, prime coat penetrates into the layer below, plugs the voids, and forms a watertight surface.

Seal Coat:

Seal Coat Seal coat is a thin surface treatment used to water-proof the surface and to provide skid resistance.

Tack coat:

Tack coat is a very light application of asphalt, usually asphalt emulsion diluted with water. It provides proper bonding between two layers of binder course and must be thin, uniformly cover the entire surface, and set very fast.

The bituminous prime coat is the first application of low viscosity liquid bituminous material over an existing porous or absorbent pavement surface like the WBM base course.

Concept:

Aerosols:

• It is the dispersion of solid or liquid particles of microscopic size in the air.
• Aerosols are minute particles suspended in the atmosphere. When these particles are sufficiently large, we notice their presence as they scatter and absorb sunlight.
• Their scattering of sunlight can reduce visibility (haze) and redden sunrises and sunsets.

Halogens:

• Any of the elements fluorine, chlorine, bromine, iodine, and astatine, occupying group VIIA (17) of the periodic table.
• They are reactive non-metallic elements that form strongly acidic compounds with hydrogen from which simple salts can be made.

Radioactive compound:

• An element can have a number of isotopes, some of which are stable and some are not stable and therefore are classified as radioactive.
• A radioactive isotope, also known as a radioisotope, radionuclide, or radioactive nuclide, is any of several species of the same chemical element with different masses whose nuclei are unstable and dissipate excess energy by spontaneously emitting radiation in the form of alpha, beta, and gamma rays.

Photochemical smog:

• Photochemical smog is a type of smog produced when ultraviolet light from the sun reacts with nitrogen oxides in the atmosphere.
• It is visible as a brown haze, and is most prominent during the morning and afternoon, especially in densely populated, warm cities.

Concept:

• Streamline is an imaginary line or series of imaginary lines in a flow field, such that a tangent to this line at any point at any instant represents the direction of the instantaneous velocity vector at that point.

• There is no flow across streamlines.
• dx/u = dy/v is the differential equation of a streamline for 2D flow, with slope  dy/dx = v/u
• dx/u = dy/v=dz/w is the differential equation of a streamline for 3D flow, where u, v and w are velocities in directions x, y, and z, respectively.
• Streamline flow is also called laminar flow.
• This type of flow is more viscous than turbulent flow.
• Streamline never intersects each other because if they intersect then there will be two tangents for two curves that mean there will be two velocity vector but it is not possible as at a given instant or at a given point there will be a unique velocity vector only.

Path line is the actual path traversed by a given fluid particle.

Streak line is the locus of particles that have earlier passed through a prescribed point.

For steady flow, streamlines, path lines and streak lines are identical because

• For a steady flow, the velocity vector at any point is invariant with time.
• The path line of the particles with different identities passing through a point will not differ.
• The path line could coincide with one another in a single curve which will indicate the streak line too.

Ideal Fluid: An ideal fluid is a fluid that is incompressible and no internal resistance to flow, i.e. zero viscosity. In addition, ideal fluid particles undergo no rotation about their center-of-mass i.e. irrotational. An ideal fluid can flow in a circular pattern, but the individual fluid particles are irrotational. They don't exist.

Real Fluids: They have viscosity and are compressible, and fluid particle can rotate about their center of mass. Real fluids exhibit all of the properties of ideal fluid to some degree, but we shall often model fluids as ideal in order to approximate the behavior of real fluids.

Viscosity: The viscosity of a fluid is a measure of its resistance to deformation at a given rate. Denoted by μ.
τ = μ(du/dy)

Here μ = Coefficient of dynamic viscosity; (du/dy) = Velocity gradient;

Kinematic Viscosity: It is a measure of a fluid's internal resistance to flow under gravitational forces. It is determined by measuring the time in seconds, required for a fixed volume of fluid to flow a known distance by gravity through a capillary within a calibrated viscometer at a closely controlled temperature. Denoted by ν.

v= μ/p

Compressibility: If compression and expansion have a significant effect on the fluid density, the fluid is called a compressible fluid. Mathematically,

Here β = Compressibility factor; V = Volume of fluid; p = Applied pressure;

If β = 0, it means fluid is incompressible.

Irrotational Flow: It is a flow in which each element of the moving fluid undergoes no net rotation with respect to a chosen coordinate axes from one instant to other. Curl of the fluid velocity is zero.

Rotational Flow: Flow of a fluid in which the curl of the fluid velocity is not zero, so that each minute particle of fluid rotates about its own axis. Also known as rotational motion.

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:

When a body is either wholly or partially immersed in a fluid, a lift is generated due to the net vertical component of hydrostatic pressure forces experienced by the body. This lift is called the buoyant force and the phenomenon is called buoyancy.

The Archimedes principle states that the buoyant force on a submerged body is equal to the weight of the liquid displaced by the body and acts vertically upward through the centroid of the displaced volume.

Thus, the net weight of the submerged body, (the net vertical downward force experienced by it) is reduced from its actual weight by an amount that equals the buoyant force.

FB = ρghA = ρgV

Weight of cube = buoyancy force

ρiceViceg = ρwVVDg

Calculation:

Given:

ρice = 920 kg/m3, ρw =1000 kg/m3

Let the x be the volume of iceberg floats above the water surface.

ρiceVg = ρwg(V - x)

920 × V × g = 1000 × g × (V - x)

0.92V = (V - x)

x = 8%

Concept:

Deep water bodies have more heat storage than shallow ones. A deep lake may store radiation energy received in summer and release it in winter causing less evaporation in summer and more evaporation in winter compared to a shallow lake exposed to a similar situation.

However, the effect of heat storage is essential to change the seasonal evaporation rates and the annual evaporation rate is seldom affected.

So here both Statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I).

Other Important Points-

Estimation of evaporation is of utmost importance in many hydrologic problems associated with the planning and operation of reservoirs and irrigation systems. In arid zones. This estimation is particularly important to conserve scarce water resources.

The amount of water evaporated from a water surface is estimated by the following methods:

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

According to the Central Pollution Control Board (CPCB), the upper limit of sound for a residential area is 55 Decibels.

• The intensity of sound is measured in decibels.
• It is named in honour of Alexander Graham Bell.

Central Pollution Control Board (CPCB) has declared the permissible noise level in India for different areas:

• In industrial areas, it is 75 dB for daytime and 70 dB for the night.
• In commercial areas, it is 65 dB for daytime and 55 dB for the night.
• In residential areas, it is 55 dB for daytime and 45 dB for the night.

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.

Triangular weir:

The expression for the discharge over a triangular weir or notch is

Q =

From this expression flow through the weir depend upon the vertex angle (θ) and coefficient of discharge (Cd) is constant for all the heads, the value of Cd is nearly equal to 0.6.

Rectangular weir:

The expression for the discharge over a rectangular weir or notch is

Q =

Advantages of triangular weir over rectangular weir:

A triangular weir is preferred to a rectangular weir due to the following reason.

(1) The expression for discharge for a right-angled V- a notch or weir is very simple.

(2) For measuring low discharge, a triangular weir gives more accurate results than a rectangular weir.

(3) In the case of the triangular weir, only one reading, (H) is required for the computation of discharge.

(4) Ventilation of triangular weir is not necessary.

• 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.

Flow over weir and notches follow the Froude model law and the Froude model state that the gravity force is the only predominant force in addition to the inertia force, which controls the motion.

(Fr)model = (Fr)prototype

⇒ = ……..(i)

It is given in the question, Lm/Lp = Bm/Bp = K

From (i),

Since in most of the cases gr = 1

So, Vr = √K = (K)1/2

∵ we know, Discharge (Qr) = area × velocity = Ar × Vr

Qr =

Qr = K2 × K1/2

Qr = K5/2

Concept:

Water at the downstream of a fall has very high energy and it can damage the downstream structure. So, this energy is reduced with the help of some obstructive structure. For e.g. Baffle wall, biff wall, deflector, etc.

Biff wall is an obstructing wall, which is constructed at the end of cistern. It pushes back the water and reduces its energy.

Baffle wall provides a deep pool of water in front of it and by continuously changing the direction of water flow, it reduces its energy.

Deflector also works on the same principle as biff wall. Here it produces a reverse roller of water and hence reduces the energy.

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.

1. Hauled Collection systems:

• Collection systems in which the containers used for the storage of wastes are hauled to the processing, transfer, or disposal site, emptied, and returned to either their original location or some other location are defined as hauled container systems.
• It is the flexibility – many different sizes & shapes for the collection of all types of waste.
• Require one truck & driver to accomplish the collection cycle.
• It is economical.
• It is ideal for the locations where waste generation rate is very high. The use of a large handling system reduces handling time, reduces unsightly accumulations, and avoids unsanitary conditions.

Disadvantages:

• The use of very large containers leads to low-volume utilization unless loading aids are provided.

2. Stationary container systems:

• In this collection system, a container is used for the storage of wastes which remains at the point of waste generation. This type of system is called a stationary-container system.

There are two main types of stationary-container systems:

• Those in which self-loading compactors are used
• Those in which manually loaded vehicles are used.

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 various types of failures in Flexible Pavements are:

1. Failure in Sub-grade: It occurred due to the following reasons:

• If the pavement thickness is inadequate or the loads are more than the design value, excessive stress is developed, and it harms as load repetitions are increased.
• ·The inadequate stability of the subgrade is developed due to the inherent weakness of the soil itself or excessive moisture or improper compaction.

2. Failure in Base or Sub-base courses: It occurred due to the following reasons:

• The poor mix proportioning of material used in the base or sub-base course.
• The inadequate thickness of pavement may lead to the lack of stability or strength of the sub-base or base course.
• The repeated stress applications lead to the internal movements of aggregate in subbase or base courses and thus, the loss of binding action is developed, and it leads to poor load transmitting property of the pavement layer.

3. Failure in Wearing Course: It occurred due to the following reasons:

• If the mix design does not provide adequate binder content, the bituminous surface will exhibit poor performance under the action of traffic.
• Due to oxidation of binder, the bitumen surface may become brittle and which in turn results in cracking on the surface.

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.

A controlled mass or closed system is characterized by a fixed quantity of mass of a given identity, while in an open system or control volume mass may change continuously due to the flow of mass across the system boundary.

The continuity equation is the equation of conservation of mass in a fluid flow.

According to the law of conservation of mass:

Rate of flow in section 1 - 1 = Rate of flow at section 2 - 2

ρ₁ x A₁ x V₁  = ρ₂ x A₂  x V₂

Given:

ρ₁ = 3 kg/m³, ρ2 = 4 kg/m3, A₁ = 0.5 m², A2 = 1 m2, V₁ = 8 m/sec, V₂ = ?

ρ₁ x A₁ x V₁  = ρ₂ x A₂  x V₂
Putting these values, we get

3 x 0.5 x 8 = 4 x 1 x V₂

V₂ = 12/4 = 3 m/sec

Important PointsThis equation is applicable to the compressible as well as incompressible fluid and is called a continuity equation.

If the fluid is incompressible, then ρ₁ = ρ₂; and continuity equation reduces to A₁V₁ = A₂V₂

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:

Types of highway gradients:

1. Ruling Gradient: Ruling Gradient is the maximum gradient which is generally used to design the vertical profile of highway. So it is also called as designer gradient. Ruling gradient depends on the terrain, length of the grade, speed, pulling power of the vehicle and the presence of the horizontal curve.

2. Limiting Gradient: This gradient is provided as shorter stretches in highways. Whenever ruling gradients costs high for the hilly terrains then limiting gradient is provided which will reduce the cost. This gradient is adopted frequently in terrains with limited stretches.

3. Exceptional Gradient: These are very steeper gradients given at unavoidable situations and they are adopted for stretches not exceeding 100m of length.

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