465

October-2019

Time-Three hours

(Maximum marks: 75)

Part-A

1. DEFINE VOID RATIO AND POROSITY.

Void ratio:

The void ratio of a mixture is the ratio of the volume of voids to

volume of solids.

Porosity:

The porosity is the ratio of VS is the volume of solids to VT is the total

or bulk volume.

2. DEFINE DARCYS LAW

Darcy's law states that the rate of fluid flow through porous medium is

proportional to the potential energy gradient within that fluid.

The constant of proportionality is the Darcy's permeability of soil.

Darcy's permeability is a property of both porous medium and the

fluid moving through the porous medium.

3. WHAT IS O.M.C

Optimum moisture content (OMC) is the percentage of water present

in soil mass at which a specific compaction force can dry

the soil mass to its maximum dry weight. ... For different types

of soils, OMC and maximum dry density curves are different.

4. WHAT IS EFFECTIVE STRESS

Effective stress is the force at contact particles of soil but divided by

total area. The contact area is very less between the particles here.

It cannot be obtained practically but we can calculate the effective

stress by measuring total stress and pore water pressure.

5. DEFINE SAFE BEARING CAPACITY OF SOIL

Bearing capacity is the capacity of soil to support the loads applied to

the ground.

Ultimate bearing capacity is the theoretical maximum pressure which

can be supported without failure; allowable bearing capacity is

the ultimate bearing capacity divided by a factor of safety is known as

safe bearing capacity of soil.

6. DIFFERENT TYPES OF SHALLOW FOUNDATION

Strip footing

Spread or isolated footing

Combined footing

Strap or cantilever footing Mat or raft Foundation

7. WHAT ARE THE FORCES ACTING ON THE TRANSMISSION

LINE TOWER

Shearing force

Bering force

Uplift pressure

Seapage pressure

8. WHAT IS SOIL EXPLORATION

Soil exploration consists of determining the profile of the

natural soil deposits at the site, taking the soil samples and

determining the engineering properties of soils using laboratory tests

as well as in-situ testing methods.

PART-B

9. Define plasticity index and liquidity index.

Plasticity Index

It is the difference between the liquid limit and plastic limit of the soil.

It shows volume of range of moisture content at which the soil

remains in plastic condition.

PI=LL - PL

Here,

PI - plasticity index,

LL - liquid limit

PL - plastic limit

LiquidityIndex

The relative consistency of a fine grained soil in the original state can

be defined by a proportion called as liquidity index.

LI=(W-PL)/(LL-PL)

Here,

LI - liquidity index,

w -sample water content,

PL -plastic limit

LL- liquid limit.

10. Explain the Mohr-coulomb failure theory

Material fails essentially by shear.

The critical shear stress causing failure depends upon the properties

of the material as well as on normal stress on the failure plane.

The ultimate strength of the material is determined by the stresses on

the potential failure plane (or plane of shear)

When the material is subjected to three dimensional principal stress

(i.e.1, 2, 3) the intermediate principal stress does not have any

influence on the strength of material.

In other words, the failure criterion is independent of the intermediate

principal stress.

The theory can be expressed algebraically by the equation.

f s F()

Where

f =s= shear stress on failure plane,

F () = function of normal stress

11. Brief notes on Quick sand condition.

Quick sand condition or boiling Quick sand condition is a condition of

flow, not a type of soil, in which a vertical upward seepage flow causes

floating condition of a particle in cohesion less soil such as Sand and fine

grave.

Where the effective pressure becomes zero.

12. What are the factors affecting the bearing capacity of the soil?

soil strength

foundation width

foundation depth,

soil weight and surcharge,

spacing between foundations.

These factors are related to the loads exerted on the soil and considerably

affect the bearing capacity

13. Mention any six uses of pile.

If a high groundwater table exists beneath the structure.

If the superstructure load is high and non-uniform.

If highly compressible soil is present at shallow depth.

If the structure is located near the river bed or sea shore etc, pile

foundation is suggested to secure the structure form the possible

scouring.

If a canal or deep drainage systems pass near the structure, pile

foundation is suggested.

If soil condition is very poor and it is not possible to excavate the soil up

to the desired depth.

If it becomes impossible to keep the foundation trenches dry by any

measure due to heavy inflow of seepage

14. Define swelling potentials, swelling pressure and free swell.

swelling potentials

Soil swelling is a term generally applied to the ability of a soil to undergo

large changes in volume due to increased moisture content

swelling pressure

The expansive clays increase in their volume when they come in contact

with water owing to surface properties of these clay types.

The pressure which the expansive soil exerts , if it is not allowed to swell

or the volume change of the soil is arrested , is known as Swelling

Pressure of Soil.

free swell

Free swell is the increase in volume of a soil, without any external

onstraints, on submergence in water

15. Distinguish between free vibration and forced vibration.

Free vibrations involve no transfer of energy between the vibrating object

and its surroundings,

whereas forced vibrations occur when there's an external driving force

and thus transfer of energy between the vibrating object and its

surroundings.

16. Write short notes on Isolated Footing.

Isolated footing is the single or individual footing which transfers load to

the underground soil.

It is provided when a single column is to be provided.

Isolated footing is generally provided for shallow depths.

Shallow foundations have their depths less than the widths.

Footing is provided, either as simple footing, sloped footing or stepped

footing.

In simple isolated footing, base of uniform depth is provided.

In sloped footing, base of uniformly sloping downward pattern is

provided.

In stepped footing, base is constructed in steps to distribute the load

uniformly to the foundation soil.

Part-C

17. (A)DESCRIBE SHRINKAGE LIMIT DETERMINATION WITH

NEAT SKETCH

The shrinkage limit of soil is the water content of the soil when the water is just

sufficient to fill all the pores of the soil and the soil is just saturated.

The volume of the soil does not decrease when the water content is reduced

below the shrinkage limit.

Shrinkage limit can be determined from the relation

Where M1= initial wet mass,

V1= initial volume

Ms = dry mass of soil

V2 = volume after drying.

Take a sample of mass about 100g from a thoroughly mixed soil passing 425

micron sieve.

Take about 30g of soil sample in a large evaporating dish.

Mix it with distilled water to make a creamy paste which can be readily worked

without entrapping the air bubbles.

Take the shrinkage dish.

Clean it and determine its mass.

Fill the mercury in the shrinkage dish.

Remove the excess mercury by pressing the plain glass plate over the top of the

shrinkage dish.

The plate should be flush with the top of the dish. And no air should be

entrapped.

Transfer the mercury of the shrinkage dish to a mercury weighing dish and

determine the mass of the mercury to an accuracy of 0.1g. the volume of the

shrinkage dish is equal to the mass of mercury in grams divided by the specific

gravity of the mercury.

Coat the inside of the shrinkage dish with a thin layer of silicon grease or

Vaseline.

Place the soil specimen in the center of the shrinkage dish equal to about one-

third the volume of the shrinkage dish.

Tap the shrinkage dish on a firm cushioned surface and allow the paste to flow

to the edges.

Add more soil and continue the tapping till the shrinkage dish is completely

filled and excess soil paste projects out about its edge.

Strike out the top surface of the plate with a straight edge. Wipe of all soil

adhering to the outside of the shrinkage dish. Dry the soil in the shrinkage dish

in air until the colour of the pat turns from dark to light.

Then dry the pat in the oven at 105 to 110 0C to constant mass. Cool the dry pat

in a desiccator.

Remove the dry pat from the desiccator after cooling, and weight the shrinkage

dish with the dry pat to determine the dry mass of the soil.Place a glass cup in a

large evaporating dish and fill it with mercury.

Remove the excess mercury by pressing the glass plate with prongs firmly over

the top of the cup.

Wipe off any mercury adhering to the outside of the cup.

Remove the glass cup full of mercury and place it in another evaporating dish

taking care not to spill any mercury from the cup.

Take out the dry pat of the soil from the shrinkage dish and immerse it in the

glass cup full of mercury.

Take care not to entrap air under the pat.

Press the plate with prongs on the top of the cup firmly.

Collect the mercury displaced by the dry pat in the evaporating dish and transfer

it to the mercury weighing dish.

Determine the mass of the mercury to an accuracy of 0.1g.

The volume of the dry pat (V2) is equal to the mass of the mercury divided by

the specific gravity of the mercury.Repeat the test atleast 3 times.

Stages for derivation of Shrinkage Limit

(B) DESCRIBE CONSTANT HEAD PERMEABILITY TEST WITH

NEAT SKETCH

Constant Head Permeability Test

The constant head permeability test is a laboratory experiment conducted to

determine the permeability of soil.

The soils that are suitable for this tests are sand and gravels.

Soils with silt content cannot be tested with this method.

The test can be employed to test granular soils either reconstituted or disturbed.

Objective and Scope

The objective of constant head permeability test is to determine the coefficient of

permeability of a soil.

Coefficient of permeability helps in solving issues related to:

Yield of water bearing strata

Stability of earthen dams

Embankments of canal bank

Seepage in earthen dams

Settlement Issues

The coefficient of permeability, k is defined as the rate of flow of water under

laminar flow conditions through a porous medium area of unit cross section under

unit hydraulic gradient.

Procedure

Remove the collar of the mould. Measure the internal dimensions of the mould.

Weigh the mould with dummy plate to the nearest gram.

Apply a little grease on the inside to the mould. Clamp the mould between the base

plate and the extension collar and place the assembly on a solid base.

Take about 2.5kg of the soil sample, from a thoroughly mixed wet soil, in the

mould. Compact the soil at the required dry density using a suitable compacting

device.

Take a small specimen of the soil in a container for the water content

determination.

Remove the collar and base plate. Trim the excess soil level with the top of the

mould.

Clean the outside of the mould and the dummy plate. Find the mass of the soil in

the mould.

The mould with the sample is now placed over the permeameter. This will have

drainage and cap discs properly saturated

Test Procedure

Through the top inlet of the constant head reservoir, the specimen is connected.

The bottom outlet is opened and a steady flow is established

For a particular time interval, the quantity of flow can be collected.

Measure the difference of head (h) in levels between the constant head reservoir

and the outlet in the base.

For the same interval, this is repeated three times.

18. (A)EXPLAIN WITH NEAT SKETCH THE STANDARD PROCTOR

COMPACTION TEST TO DETERMINE THE DENSITY OF SOIL

Compaction is the process of densification of soil by reducing air voids.

The degree of compaction of a given soil is measured in terms of its dry

density.

The dry density is maximum at the optimum water content.

A curve is drawn between the water content and the dry density to obtain the

maximum dry density and the optimum water content.

Dry density of soil:

Where M = total mass of the soil, V= volume of soil, w= water content.

Proctor Soil Compaction Test Procedure:

Take about 20kg of air-dried soil. Sieve it through 20mm and 4.7mm sieve.

Calculate the percentage retained on 20mm sieve and 4.75mm sieve, and

the percentage passing 4.75mm sieve.

If the percentage retained on 4.75mm sieve is greater than 20, use the large

mould of 150mm diameter. If it is less than 20%, the standard mould of

100mm diameter can be used. The following procedure is for the standard

mould.

Mix the soil retained on 4.75mm sieve and that passing 4.75mm sieve in

proportions determined in step (2) to obtain about 16 to 18 kg of soil

specimen.

Clean and dry the mould and the base plate. Grease them lightly.

Weigh the mould with the base plate to the nearest 1 gram.

Take about 16 – 18 kg of soil specimen.

Add water to it to bring the water content to about 4% if the soil is sandy

and to about 8% if the soil is clayey.

Keep the soil in an air-tight container for about 18 to 20 hours for maturing.

Mix the soil thoroughly. Divide the processed soil into 6 to 8 parts.

Attach the collar to the mould. Place the mould on a solid base.

Take about 2.5kg of the processed soil, and hence place it in the mould in 3

equal layers. Take about one-third the quantity first, and compact it by

giving 25 blows of the rammer. The blows should be uniformly distributed

over the surface of each layer.

The top surface of the first layer be scratched with spatula before placing

the second layer. The second layer should also be compacted by 25 blows

of rammer. Likewise, place the third layer and compact it.

The amount of the soil used should be just sufficient to fill the mould ad

leaving about 5 mm above the top of the mould to be struck off when the

collar is removed.

Remove the collar and trim off the excess soil projecting above the mould

using a straight edge.

Clean the base plate and the mould from outside. Weigh it to the nearest

gram.

Remove the soil from the mould. The soil may also be ejected out.

Take the soil samples for the water content determination from the top,

middle and bottom portions. Determine the water content.

Add about 3% of the water to a fresh portion of the processed soil, and

repeat the steps 10 to 14.

(B) WRITE NOTES ON MECHANICAL AND CHEMICAL

STABILIZATION

MechanicalStabilization:

Mechanical stabilization is the methodology, which improves selected

engineering properties of soils without the addition of agents or other

particle binding energy.

The methodologies are as follows, compaction, blasting, dynamic

compaction, preloading, sand drains, etc.

Factors affecting the mechanical stabilization are, aggregate mechanical

strength, mineral composition, gradation, compaction, and properties of

soil.If the mixture is not properly designed or not compacted well, the

mechanical stabilization will get affected.

The composition of the mineral is linked with the mechanical stability of the

mixed soil.

The mineral present in the soil should resist weathering action.To attain a

high density in the mixed soil, the pore space between the coarse aggregate

have to be filled with the fine aggregate.Effective compaction is necessary in

the mixed soil to produce high density and stability mix.Plasticity index in

the soil has to be in control, as it reduces the soil stability.

When the clayey soil is in the saturated condition, plasticity index can affect

the stability.

Chemical stabilisation

soil stabilization is the process of altering properties of soil by changing the

gradation through mixing with other oils or chemicals to improve strength

and durability.

Mechanical stabilization and chemical stabilization are the main two

methods employed in stabilization.

Chemical processes such as mixing with cement, fly ash, lime, lime by

products and blends of any one of these materials can be used to alter soil

properties such as strength, compressibility, hydraulic conductivity, swelling

potential and volume change properties.

The additives are combined with the help of machines.

The method used depends on the location and availability of the machine.

There are many types of additives used for chemical stabilization.

But the selection of additive is based on the type of soil.

A single additive act differently with different type of soils.Cement

stabilization offers better strength and improves soil quality.

Normally Portland cement isused for this purpose.

Stabilization using lime creates long-lasting changes in soil properties.

Lime reacts with medium, moderately fine and fine-grained soils to produce

decreased plasticity, increased workability, reduced swelling, and increased

strength.

To enhance the effectiveness of cement, lime, fly ash stabilization or a

combination of the three are used in required proportion.

Fly ash is the byproduct of combustion of coal and contains Silicon and

Aluminum and is mainly used as a filler product to reduce voids.

The silicate aluminates-amide system is widely used for strength

improvement and water cut-off as this system can be used in acidic soils as

well.

19.(A)SHOW THE FLOWNET DIAGRAM BY SKETCH AND ALSO

EXPLAIN THE VARIOUS TYPES OF FLOWS

Flow net is a graphical representation of flow of water through a soil mass.

It is a curvilinear net formed by the combination of flow lines and

equipotential lines.

Properties and application of flow net are explained in this article.Flow lines

represent the path of flow along which the water will seep through the soil.

Equipotential lines are formed by connecting the points of equal total head.

Properties of flow net are, the angle of intersection between each flow line

and an equipotential line must be 90o which means they should be

orthogonal to each other.

Two flow lines or two equipotential lines can never cross each

other.Equal quantity of seepage occurs in each flow channel.

A flow channel is a space between two flow lines.

Head loss is the same between two adjacent potential lines.

Flow nets are drawn based on the boundary conditions only.

They are independent of the permeability of soil and the head causing flow.

The space formed between two flow lines and two equipotential lines is

called a flow field.

It should be in a square form.Either flow lines or equipotential lines are

smoothly drawn curves.

Applications of FlowNet

Flow net is useful to determine the following parameters in seepage analysis of soil

Rate of Seepage loss

Seepage Pressure

Uplift Pressure

Exit Gradient

(B) DESCRIBE ABOUT TERZHAGHI ANALYSIS WITH SKETCH

Terzaghi analysis theory, column load P is resisted by shear stresses at edges of

three zones under the footing and the overburden pressure, q (=γD) above the

footing.

The first term in the equation is related to cohesion of the soil.

The second term is related to the depth of the footing and overburden pressure.

The third term is related to the width of the footing and the length of shear

stress area.

The bearing capacity factors, Nc, Nq, Nγ, are function of internal friction angle,

φ. Terzaghi's Bearing capacity equations:

Strip footings: Qu = c Nc + γ D Nq + 0.5 γ B Nγ

Square footings: Qu = 1.3 c Nc + γ D Nq + 0.4 γ B Nγ

Circular footings: Qu = 1.3 c Nc + γ D Nq + 0.3 γ B Nγ

20. (A )HOW DO YOU DETERMINE LOAD CARRYING CAPACITY OF

PILES?EXPLAIN

The ultimate bearing capacity of a pile is the maximum load which it can carry

without failure or excessive settlement of the ground.

The bearing capacity of a pile depends primarily on 3 factors as given below,

1. Type of soil through which pile is embedded

2. Method of pile installation

3. Pile dimension (cross section & length of pile)

While calculating pile load capacity for cast in situ concrete piles, using static

analysis, we need to use soil shear strength parameter and dimension of pile.

The pile transfers the load into the soil in two ways.

Firstly, through the tip-in compression, termed as “end-bearing” or “point-

bearing”; secondly, by shear along the surface termed as “skin friction”.

LOAD CARRYING CAPACITY OF CAST IN-SITU PILES IN COHESIVE

SOIL

The ultimate load carrying capacity (Qu) of pile in cohesive soils is given by the

formula given below, where the first term represents the end bearing

resistance (Qb) and the second term gives the skin friction resistance (Qs).

LOAD CARRYING CAPACITY OF CAST IN-SITU PILES IN COHESION

LESS SOIL

The ultimate load carrying capacity of pile, “Qu”, consists of two parts. One

part is due to friction, called skin friction or shaft friction or side shear denoted

as “Qs” and the other is due to end bearing at the base or tip of the pile

toe, “Qb”.

The equation given below is used to calculate the ultimate load carrying

capacity of pile.

(B)EXPLAIN UNDER-REAMED PILE FOUNDATION.

Under reamed piles are bored cast-in-situ concrete piles having one or more

number of bulbs formed by enlarging the pile stem.

These piles are best suited in soils where considerable ground movements occur

due to seasonal variations, filled up grounds or in soft soil strata.

Provision of under reamed bulbs has the advantage of increasing the bearing

and uplift capacities. It also provides better anchorage at greater depths.

These piles are efficiently used in machine foundations, over bridges, electrical

transmission tower foundation sand water tanks.

Indian Standard IS 2911 (Part III) - 1980 covers the design and construction of

under reamed piles having one or more bulbs.

According to the code the diameter of under reamed bulbs may vary from 2 to 3

times the stem diameter depending upon the feasibility of construction and

design requirements.

The code suggests a spacing of 1.25 to 1.5 times the bulb diameter for the

bulbs. An angle of 45 0 with horizontal is recommended for all under reamed

bulbs.

21. (A) Explain Barkan’s method.

Refer the books………

(B) Explain the choice and types of foundation for transmission line tower.

There are seven basic types of tower foundations:

a) Steel grillage

b) Concrete spread footing

c) Concrete auger or caisson

d) Pile foundation

e) Rock foundation

f) Raft foundation

g) Novel foundations.

The foundation is excavated to the desired depth.

Generally, the depth of foundation is shallow, just sufficient to

accommodate the two tiers of grillage beams and the gusset plates etc.

connecting the stanchion to the base.

However this depth should not be less than 90 cm in any case.

After leveling the foundation base, rich concrete is poured and compacted,

so that the formed thickness is not less than 15 cm.

Compaction should be done properly so that the layer of concrete becomes

an impervious bed.

This would protect the steel joists against ground water.

After levelling the concrete bed, first layer of grillage beams of designed

sizes are laid over it, at proper distances, with the help of separaters.

The upper surface of all the beams should lie in one horizontal plane.

Rich cement grout is then poured all around the lower flanges of the beams

so that they are secured to the concrete bed.

Cement concrete is then poured betwecn and around the beams of the first

tier.

The second tier of beams is then placed at right angles to the first tier and

over the top flanges of the beams of the first tier.

They are properly spaced with the help of separators.

Concrete is then poured between and around the steel beams.

The steel stanchion is then connected to the upper tier with the help of a

base plate, side angles and gusset plate.

These connecting elements are also embedded in the concrete so that joint

becomes rigid.

Steel grillage foundation may also be provided for a masonry wall on soils

of low bearing capacity.

The grillage foundation for such a case consists of only on tier, though in

some circumstances when the wall is wider and it carries heavy loads, two

tiers may also be provided.

TYPICAL GRILLAGE FOUNDATION FOR STEEL STANCHION.

STEEL GRILLAGE FOUNDATIONS FOR WALLS.