BPSC AE Civil Paper 6 (Civil) Mock Test - 3 - Civil Engineering (CE) MCQ

Concepts:

As per Manual on Sewerage and Sewage Treatment Systems – 2013, the population density per hector is given below in the tabulated form:

Concept:

Different methods of Irrigation are as follows:

There are various ways in which irrigation water can be applied to the fields:

Sullage:

The water from the bathroom, kitchens washbasin and washing paces are known as sullage.

Sewage:

The used water mixed with organic and inorganic solids, fluid wastes from houses, factories, and dry weather flow is called sewage.

Dry waste:

The waste which does not contain any moisture is known as dry waste. Garbage, rubbish, and ashes are three forms of dry waste.

Concept:

Properties of Potential functions:

1. If velocity potential (ϕ) exists, the flow should be irrotational.

2. If velocity potential (ϕ) satisfies the Laplace equation, it represents the possible steady incompressible irrotational flow.

Calculation:

Thus (i) is a valid potential function as it satisfies the Laplace equation, whereas (ii) is not a valid potential function as it does not satisfy Laplace equation.

Various tests conducted on bitumen for testing its various properties are as follows:

Marshall Mix Design:

(i) Marshal test is used for designing the bituminous concrete mix for pavement construction

Benkelman Beam deflection method:

(i) Benkelman Beam is a device which can be conveniently used to measure the rebound deflection of a pavement due to dual wheel load assembly or the design wheel load.

Instantaneous Unit Hydrograph(IUH):

• The instantaneous unit hydrograph is defined as a unit hydrograph produced by an effective rainfall of 1 cm and having an infinitesimal reference duration (in other words the duration tends towards zero).
• In terms of the systematic conception, this means that the instantaneous unit hydrograph represents the response of the catchment to an instantaneous impulse.
• It is useful as the IUH can be analytically computed and, on the basis of the "S" curve, a certain unit hydrograph of any reference duration may be derived from it.
• This ordinate of the instantaneous hydrograph is given by.

Where,

I = Intensity of rainfall,

S = ordinate of S-Curve.

Important Points

Uses:

• The development of flood hydrograph for extreme rainfall magnitude for use in the design of the hydraulic structure.
• Extension of flood flow records based on rainfall records.
• Development of flood record based on rainfall
• Development of flood forecasting and warning systems based on rainfall.

Limitations:

• Unit hydrograph cannot be used for catchment are greater than 5000 km2
• Unit hydrograph cannot be used for catchment less than 2 km2
• Precipitation must be in the form of rainfall only ie not be in the form of snow.​

Kinematic Viscosity = Dynamic Viscocity/Density of fluid

v = μ/ρ

Calculation:

Using the relation between Kinematic viscosity, Dynamic viscosity and Density of liquid

ρ =  μ/v 

ρ = 0.04 poise / 0.04 stokes

After substituting the values in the density equation

ρ = 1000kg/m³

Hence, the density of a fluid is 1000kg/m³

Concept:

Hydraulic gradient Line (H.G.L) – Line representing the sum of pressure head and datum head.

Total energy line (T.E.L) – Line representing the sum of pressure head, datum head, and velocity head.

From above, the Hydraulic gradient line (HGL) represents the sum of pressure head and datum head.

Dowel bars:

• Dowel bar acts as a load transfer device across the transverse joint and they keep the two slabs at the same height.
• They are of mild steel round bars, bounded on one side and free on the other side.
• Normally have 25 mm to 40 mm diameter and 400 - 500 mm length.
• The stress in dowel bars is given by Bradbury analysis.

​Additional Information

Tie bars:

• Tie bars used for holding faces of rigid slabs in contact to keep aggregate interlock. They are also used in the plain jointed concrete pavement to connect two lanes.
• They are used to reduce transverse cracking.
• Tie bars avoid separation and differential deflection in lanes.
• They are not designed to work as a load transfer device.

Concept:

Sensitivity (S) is defined as the percent change in the outlet discharge to the percentage change in the canal water depth.

Flexibility (F) is defined as the percent change in the discharge of the outlet to the rate of change in discharge of the distributary channel

Calculation:

Given: S = 0.5

∴ Percent change in the discharge of the outlet is 25%

Additional Information

The reservoir behind a dam is prone to generation of waves produced by the shearing action of wind blowing over the surface resulting wave pressure being exerted on the gravity dam.

The force and dimensions of waves depend mainly on the extent and dimensions of waves depend mainly on the extent and configuration of the surface area of the reservoir, the depth of the reservoir, and the velocity of the wind.

• The total wave pressure P_w per unit length (in KN/m) of the dam is given by the area of the triangle 1-2-3 as given in the figure above.
• The center of application is at a height of 0.375H_w (3/8 × H_w) above the still water level.

Where

H_w = height of the wave

The hydraulic jumps in horizontal rectangular channels are classified into five categories based on Froude number F1 of the supercritical flow as:

As per IS 456: 2000, the minimum percentage of reinforcement required will be:

Mild Steel:

P_t = 0.15 % of BD (Total cross - sectional area)

HYSD Bar

P_t = 0.12 % of BD (Total cross - sectional area)

Where

B = width of the slab and

D = overall depth of the slab

Now,

B = unit width given= 1 m = 1000 mm

D = 100 mm

Turbidity:

• Turbidity is the measure of the relative clarity of a liquid which is caused by suspended solids.
• Devices used to measure the turbidity in water are as follows:

1. Jackson’s Turbidimeter

• It is used to measure high turbidity, i.e 25 – 1000 mg/l
• It cannot measure the turbidity less than 25 mg/l

2. Bayli's meter

• It is used to measure low turbidity, i.e less than 10 mg/l

3. Ratio Turbidimeter

• When a turbidity meter is measuring with “ratio on” it will use data from several detectors and take an average, in order to correct for changes caused by this particle size difference

4. Nephelometer

• This works on the principle of light scattering.
• It is a digital electronic device that measures low turbidity in water with very high precision in no time
• It measures the turbidity in terms of NTU (Nephelometric Turbidity Unit)

The sources of generation of hazardous waste are given below:

Clark's method is one of the earliest and simplest methods of removing hardness (i.e., Ca²⁺ and Mg²⁺ ions) from water. It is a lime-soda process and was first proposed by Dr. Clark in the year 1841. Here's how the process works:

Step 1 - Adding Slaked Lime: In this method, slaked lime [Ca(OH)₂] is added to hard water, which precipitates calcium ions as calcium carbonate and magnesium ions as magnesium hydroxide. The chemical reactions are as follows:

For Calcium: Ca²⁺ (aq) + CO₃^2- (aq) ⇌ CaCO₃ (s)

For Magnesium: Mg²⁺ (aq) + 2 OH⁻ (aq) ⇌ Mg(OH)₂ (s)

This process can reduce the hardness from water up to a considerable extent but not completely. This means the water is still hard after this treatment.

Step 2 - Adding Soda Ash: The remaining calcium and magnesium ions are then treated with 'soda ash' (sodium carbonate, Na₂CO₃), which precipitates the remainder of the calcium ions as calcium carbonate and the magnesium ions as magnesium hydroxide:

For Remaining Calcium: Ca²⁺ (aq) + CO₃^2- (aq) ⇌ CaCO₃ (s)

For Remaining Magnesium: Mg²⁺ (aq) + CO₃^2- (aq) ⇌ MgCO₃ (s)

After these precipitation reactions occur, the precipitates are allowed to settle and are then filtered out, resulting in softened water.

Concept:

Different methods of irrigating lands are as follows:

Check flooding: Small check areas are formed by construction of small levees and they are flooded with water. It is recommended for close growing crop.

Basin flooding: Circular basin is constructed around a tree and water is supplied by dedicated channel. It is suitable for irrigating trees.

Furrow irrigation: Furrows are small ditch, which carry the water and plants are grown at the raised boundary of furrow. It is recommended for plants like carrot, potato, etc.

Sprinkler irrigation: Water is applied as a rain drop with a sprinkler. It is an efficient surface irrigation method but not suitable for trees.

According to IS 456-2000, a beam shall be deemed to be a deep beam when the ratio of effective span-to-overall depth, l/D is less than:

1) 2.0, for simply supported beam; and

2) 2.5, for a continuous beam.

Though different codes define deep beams in different clear span-to-depth ratios, as a general rule deep beams are recognized by their relatively small span-to-depth ratio.

Hence, Deep beams are designed for bending moment and checked for shear.

If the hydraulic gradient at exit is more than the critical gradient for the particular subsoil, the soil particles will move with the flow of water thus causing progressive degradation, resulting in cavities and ultimate failure. This is called undermining or piping or sand boiling.

As per Khosla’s theory, the Undermining of the floor started from the tail end because at tail end head loss due to seepage is maximum and which in turn creates maximum hydraulic gradient.

∴ It is essential to have a deep vertical cut off at the downstream end to prevent undermining.

Sliding failure is nothing but sliding of wall away from backfill when there is shearing failure at the base of wall.

As per IS: 1904 – 1986 (CODE OF PRACTICE FOR DESIGN AND CONSTRUCTION OF FOUNDATIONS IN SOILS) clause 17.1

Sliding -

• The factor of safety against sliding of structures which resist lateral forces (such as retaining walls) shall be not less than 1.5 when dead load, live load and earth pressures are considered together with wind load or seismic forces.
• When dead load, live load and earth pressure only are considered, the factor of safety shall be not less than 1.75.

Overturning -

• The factor of safety for shallow foundation against overturning shall be not less than 1.5 when dead load, live load and earth pressures are considered together with wind load or seismic forces.
• When dead load, live load and earth pressures only are considered, the factor of safety shall be not less than 2.

There are mainly two types of joints provided in the cement concrete pavement:

(i) Longitudinal joint

(ii) Transverse joint

• Expansion joint
• Contraction joint
• Construction joint
• Warping joint

Longitudinal joint

These are provided along the length of the pavement.

They are provided if the pavement width is more than 4.5 m.

It reduces the warping stress and uneven settlement of subgrade.

Important Points

• The tie bars in concrete pavement are provided across the Longitudinal joint.
• Tie bars are not load transfer devices but serve as a means to tie two slabs.
• Hence tie bars must be deformed or hooked and must be finally anchored into the concrete to function properly.
• They are smaller than dowel bars and placed at large intervals.

Roman roads:

Many of the early Roman roads were of elaborate construction. Some of these roads are still in existence after over 2000 years. During this period of Roman civilization, many roads were built of stone blocks of considerable thickness. The Appian Way was built in 312 B.C. extending over 580 km which illustrates the road-building technique used by the Romans.

The main features of the Romans roads are:

• They were built straight regardless of gradients.
• The soft soil was excavated and removed till hard stratum was reached.
• The total thickness of the construction was as high as 0.75 to 1.2 metres at some places, even though the magnitude of wheel loads of animal-drawn vehicles was very low.

The type of construction was much stronger than that required for the animal-drawn carts in those days. The enormous cost of construction cannot be justified at all if this technique is compared with the modern trend of pavement design based on more scientific approaches.

Hence option (1) is correct.

Emergency spillways:

The spillway crest is the uppermost part of the spillway over which water discharge

Different zone of storage of water:

Minimum pool level: The minimum pool level is the lowest level up to which the water is withdrawn from the reservoir under ordinary conditions.

Dead Storage: The volume of water held below the minimum pool level is called dead storage.

Full Reservoir Level (FRL): The FRL is the highest water level to which the water surface will rise during the normal operating conditions.

Maximum Water Level (MWL): The MWL is the maximum level to which the water surface will rise when the design flood passes over the spillway.

Normal Pool Level: For a reservoir with a fixed overflow it is a maximum water level to which water may rise under normal conditions.

The essential requirement of spillway:

1. It must have sufficient capacity
2. Must be hydraulically & structurally adequate
3. Must be so located that it provides safe disposal of water.
4. A spillway is a waterway provided in a dam for carrying the surplus floodwater from a reservoir safely to a downstream river.

Hence spillway crest is located at normal pool level.

Seepage flow through the embankment, foundation, and abutments must be controlled by suitable design provisions so that no internal erosion takes place. The amount of water lost through seepage(seepage loss) must be controlled so that it does not interfere with planned project functions.

The seepage line should be well within the downstream face so that no sloughing of the slope takes place.

The seepage loss through the dam should be minimum.

Additional Information:

The criteria considered for Safe Design of Earth Dam:

• The dam must have sufficient free-board so that it is not over-topping by wave action.
• The embankment must be safe against over-topping during the occurrence of the inflow design flood by the provision of sufficient spillway and outlet works capacity.
• There should be no opportunity for the free passage of water from upstream to the downstream either through the dam or through the foundation.
• The upstream and downstream slopes should be so designed that they are safe during and immediately after the construction.
• The portion downstream of the impervious core should be properly drained.
• The upstream slope should be stable during rapid draw-down conditions.
• The dam as a whole should be earthquake resistant.
• The downstream slope should be so designed that it is safe during steady seepage cases under full reservoir conditions.

For a channel section the depth of cutting is such that the quantity of excavation or cutting is equal to the earth filling required for making the banks, then depth of cutting is known as balancing depth or most economical depth of cutting.

Balancing canal depth comes when the canal is in partially embankment and partially in cutting. It is the depth of the canal (H) which gives equal amount of filling (i.e. earth required for formation of Banks) and cutting (i.e. earth from digging).

Concept:

According to Lacey’s, the design formulas to build a 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

Calculation:

Given,

Q = 27 m³/sec, f = 1.0

As Hydraulic (R) is a function of velocity (v), we need to determine v

Critical velocity of flow

The hydraulic radius of the channel

The difference between Slow Sand Filter (SSF) and Rapid Sand Filter (RSF) is given below:

The Chezy equation can be used to calculate mean flow velocity in open channel.

Chezy’s constant is given by:

f = friction factor

Its unit is  √m/s

So, the dimensions of Chezy coefficient C is L1/2 T-1

When the dam has been newly constructed, and the reservoir has not yet been filled, then the worst combination of vertical and horizontal inertia forces would have to be taken that causes the dam to topple backward i.e. Horizontal earthquake force acting in the upstream direction and Vertical earthquake force acting upwards.

Under the reservoir full condition, the worst combination of the inertia forces is the one which tries to topple the dam forward i.e. horizontal earthquake force acting in the downstream direction and Vertical earthquake force acting downwards.

Probable Maximum Flood (PMF): This is the flood resulting from the most severe combination of critical meteorological and hydrological conditions that are reasonably possible in the region. The PMF is computed by using the Probable Maximum Storm (PMS) which is obtained from the studies of all the storms that have occurred over the region and maximizing them for the most critical atmospheric conditions.

Standard Project Flood (SPF): This is the flood resulting from the most sever combination of meteorological and hydrological conditions considered reasonably characteristic of the region. The SPF is computed from the Standard Project Storm (SPS) over the watershed considered and may be taken as the largest storm observed in the region of the watershed. It is not maximized for the most critical atmospheric conditions but it may be transposed from an adjacent region to the watershed under consideration.