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:

Superelevation:

• It is the transverse slope to counteract the centrifugal force and to reduce the tendency of the vehicle to overturn or skid.
• It is the rise of the outer edge of the pavement w.r.t inner edge on a horizontal curve thus providing a transverse slope throughout the length of the horizontal curve
• It is also known as cant or banking.

Rate of Superelevation = e = tan θ = E/B

Where,

E = Total superelevated height of the outer edge

B = Width of the pavement

General equation,

where,

f = Coefficient of lateral friction = 0.15

R = Radius of horizontal curve

Impoertant Points: 

1. Equilibrium superelevation is that superelevation at which pressure at the inner and outer tyre will be equal. If the coefficient of friction is neglected, f = 0.

e_equilibrium = V²/127R

2. For mixed traffic condition, the superelevation is calculated corresponding to 75 % of design speed and neglecting the role of friction.

3. Maximum superelevation is given by

Concept:

Different methods of Irrigation are as follows:

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

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.​

Convective precipitation:

As a result of heating of the ground surface, the air warms and this warm air expands and forced to rise to a great height and it is replaced by colder air. As the air rises, it cools and becomes saturated and condensed and then clouds will form. By further cooling, precipitation takes place.

Note:

Cyclonic precipitation occurs when the warm and moist air mass meets a cool and dry air mass.

Orographic precipitation: It occurs when a large mass of air is forced to rise across landform barriers, such as high mountain ranges, plateau, and hills. The leeward side of such a mountain barrier where the air is ascending and warming are drier are called rain shadow regions.

Concept-

Salient features of the revised guideline “IRC: 37-2001 – Guidelines for the Design of Flexible Pavements” are:

The flexible pavement is designed as a four- layer structure – bituminous surfacing consisting of two courses -wearing course and binder course, granular base and granular sub-base over the soil subgrade.

Soils having CBR-values in the range of 2 to 10% are covered.

Traffic volumes up to 150 million standard axles (msa) are considered in two ranges, 1 to 10 msa and 10 to 150 msa.

Pavement failure criteria or the critical strains considered are:

Vertical compressive strain on top of the subgrade under the centre of the dual wheels is correlated with ‘rutting’ or the vertical permanent strain of the pavement, the allowable rut depth being 20 mm.

Horizontal tensile strain at the bottom of the bituminous binder course under the centre of a wheel of the dual wheels is correlated with ‘fatigue failure’ or cracking, with the limit of fatigue being 20% cracked surface area.

Flow measuring equipment that is used to measure discharge through pipes are:

• Pitot tube and cross section area of pipe
• Venturimeter
• Orifice meter

​But here Notches and weir can be used for measuring the discharge in an open channel.

So, The Triangular notch cannot be used for measuring the discharge through pipes.

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

The fluids which obey Newton’s Law of viscosity i.e. shear stress is directly proportional to velocity gradient are called Newtonian Fluids. Examples are: Water, air, Petrol, Kerosene, and Mercury.

Mathematical relation between shear stress and rate of deformation in Newtonian fluids are expressed as:

The fluids which do not follow Newton’s law of viscosity are called Non- Newtonian fluids. They have nonlinear shear-stress Vs deformation-rate relationship.

The mathematical model for describing the behavior of non-Newtonian fluids is the Power-Law model, which is given as:

For n < 1; these fluids called Pseudoplastic fluids. Example: blood, milk.

For n > 1; these fluids called dilatants fluids. Examples are Sugar in water, rice starch solution.

The hypothetical fluids having a zero viscosity ( μ = 0) is called an ideal fluid and the resulting motion is called an ideal or inviscid flow.

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

Key Points

• The filter over which sewage is sprinkled is called a Trickling filter.
• It is an artificial bed of stone or broken brick material over which wastewater or sewage is allowed to sprinkle or trickle.
• Trickling filters (TFs) are used to remove organic matter from wastewater.
• Trickling filters can treat domestic blackwater or brown water, greywater or any other biodegradable effluent.

Additional Information

• Intermittent sand filters (ISF) remove contaminants in wastewater through physical, chemical, and biological treatment processes.
  • Although the physical and chemical processes play an important role in the removal of many particles, biological processes play the most important role in sand filters.
• Contact beds are also called contact filters.
  • ​They are in general similar to intermittent sand filters.
  • A contact bed consists of a watertight tank filled with filtering media.

Concepts:

The total head of a liquid (water in this case) particle in motion is the sum of its potential head, kinetic head, and pressure head. Mathematically, it is given as:

Where,

Z is the elevation from the assumed datum

P is the pressure and P/γ is pressure head

γ is the unit weight of water flowing in water

V is the velocity of the flow of water in the pipe

Calculation:

Given:

Pipe Diameter, D = 50 mm, Pressure, P =29.43 × 104 N/m2

Substituting the above values in the expression for the pressure head equation:

Hence, The pressure head = 30 m

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)

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-

Uniform flow-

• Uniform flow is the type of fluid flow in which the velocity of the flow at any given time does not change with respect to space.

Non uniform flow-

• A non-uniform flow is a type of fluid flow in which the velocity of the flow at any given time changes with respect to space.

Steady Flow-

• A flow is defined steady when its fluid characteristics like velocity, density, and pressure at a point do not change with time.

Unsteady flow-

• A flow is defined unsteady, when the fluid characteristics velocity, pressure and density at a point changes with respect to time.

i) Bank Storage: When the reservoir is filled, a certain amount of water seeps into the permeable reservoir bank. This water comes out when the reservoir gets depleted. This volume of water is known as bank storage.

ii) Useful storage: The volume of water stored in the reservoir between normal and minimum pool level is called useful storage.

iii) Surcharge Storage: The volume of water stored between the maximum pool level and normal pool level is called surcharge storage.

iv) Valley Storage: Before the construction of the dam, a variable amount of water is stored in the stream channel is called valley storage.

After construction of the dam, storage increases and there is a net increase in the storage is equal to the storage capacity of a reservoir minus natural valley storage.

Effective storage for flood mitigation = Useful Storage + Surcharge Storage–Valleys Storage

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.

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.

Concept:

The relation between Duty, Delta and Base period are as follows:

Δ → depth of water required (m), D → Duty (hectares per cumec)

B → Base period (days)

Calculation:

Given,

Depth of water (Δ) = 1 m, Base Period = 150 days

From the equation

∴ Duty of water = 1296 ha/cumec.

Potential evapotranspiration (PET) is defined as the evaporation which would occur if there was always an adequate water supply available to a fully vegetated surface. PET is the upper limit of evapotranspiration for a crop in a given climate.

If the water supply available is less than PET,the deficit will be drawn from soil moisture storage until the available soil moisture is reduced to about 50%. Beyond this, actual evapotranspiration (AET) will be less than PET, until the wilting point is reached when evapotranspiration ceases. AET varies from 0 to PET

Surges in open channels:

(i) A surge or surge wave is a moving wave front which brings about an abrupt change in depth of flow.

(ii) A surge is also often referred to as moving hydraulic jump and is caused by sudden increase or decrese in flow. Surges are also classified as:

• Positive surge: is one which results in an increase in depth of flow.
• Negative Surge: is one which causes a decrease in the depth of flow.

(iii) Analysis of a surge in open channel is done by using Continuity and Momentum equation. Due to high turbulence and shear action, some energy lost in the formation of moving hydraulic jump which is initially unknown to us. Hence energy equation is not used in th analysis of surge.

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 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

Ideal fluid

Fluids which don’t have viscosity and are incompressible are termed as an ideal fluid such fluid do not offer shear resistance i.e no resistance is encountered as the fluid moves.

Real fluid

Fluids which do possess viscosity are termed as real fluids. These fluids always offer shear resistance i.e. Certain amount of resistance is always offered by these fluids as they move.

Newtonian fluids

Newtonian fluids (a real fluid) defined as fluids for which the shear stress is linearly proportional to the shear strain rate

Newtonian fluids are analogous to elastic solids (Hooke’s law: stress proportional to strain)

Any common fluids, such as air and other gases, water, kerosene, gasoline, and other oil-based liquids, are Newtonian fluids

where μ is shear viscosity of the fluid

A fluid whose viscosity does not change with the rate of deformation or shear strain is known as Newtonian fluid.

Non-Newtonian fluid

Fluids for which the shear stress is not linearly related to the shear strain rate are called non-Newtonian fluids examples include slurries and colloidal suspensions, polymer solutions, blood, paste, and cake batter

In non-Newtonian, the viscosity is dependent on shear rate (Shear Thinning or Thickening) .