1: Proctor needle in field Compaction Control) 2. Compaction of Soils.

Ans: the field compaction control consist of Ans : Compaction of the Soil is the simplest
the deter method of improving the bearing capacity of
-water content at which the soil has been soil structure
compacted. ii) It increase the Performance various
- (b) Day density (b). c) for proper compaction desirable. Characteristics or properties of soil
Control rapid test methods must be used like which are. Ultimately beneficial for bearing
calcium carbide method and proctor needle. load of the required structure. the maximum.
Method iii) In Compaction method the Soil Particles are
-d) The proctor needle consists of the needle made to make closed packed by applying the
point attached to graduated needle shank force or vibration So as to increase the density
which in tuan is attached to a spring loaded of soil and finally resulting into the
plunger improvement of bearing capacity of soil to
-c) The needle point of varying cross-sectional Sustain the required load.
area are available so that a wide range of
Penetration resiston Can be measured. 3. Vane Shear Test: IS 2720
-(P) The penetration force is read on a loaded Ans : - Thes test is Suitable to determine the
gauge fixed over the handle To use the needle undrained Shear strength (e) of clay,
in the field. a Calibration curve is plotted in the - Note that it is such test which can be
laboratory betw the penetration resistance as performed in.laboratory as well as in the field
the ordinate and the also
Water Content as the absciassa -It is very difficult to obtain undisturbed
-a) The laboratory penetration resistance is sample for some solls and in such situation the
measured by inserting the proctor needle in vane shear test is more suitable in the field. iv)
the Compacted soil in the Proctor mould. There is a appartus usually used on the field
-The penetration resistance Corresponding to This. appratus consist of four bladed vane or
various water contents are thus noted at the four thin steel
end of each Proctor Compaction and a Plates on one end of a rod as shown in fig The
colibration curve in plotted height of the vane (H) is taken twice its width
re diameter.
vi) The hole is made at which the test is to be
carried. Out The four bladed vane is
penetrated into soil at the bottom of the hole
and shaft is gentely or Slowly rotated at a rate
of 6° per minute then forque
4. ReRhann's Graphical Method of 5. Factors of Slope Stability.
Determination of Earth presure. Ans: Stope Stability is therefore function of
Ans : In 1871 Rebham's represented a i) Material
graphical method, to determine the total active ii) Strength of rock or soil in
Pressure (P₁) based on Coulomb's theory on a iii) slope angle
Cohesionless homogenous and inclined backfill iv) Climate
rough wall with a v) Vegetation and
vil Time Each of these factors may play a
procedure of graphical method. significant role. in controlling driving or
1) Draw a retaning wall to a suitable scale and resisting forces
measu. a the backfill surface angle for required
position as shown in
2) Draw a d-line EG Such that it interset the 6. Taylor's Stability Number
backfill Surface at G. Ans : i) The slipping along the slip are at
3) Draw Semi-circle EQG by taking diamete as. critical equilibri is resisted by the total
EG₁ cohesive force (CL) This force is proportional
4) Draw the pressure line 'EO' at an angle of (α- to the Cohesion 'C' and the height H of the
5)With respect to &-line. 5) Draw FT parallel to slope.
pressure line 'EO! ii) The force responsible for instability of the
6) Draw a perpendicular to EG at I such that it slope is the weight of the wedge which is
cut the Semi-circle at T equal to the unit weight' y' ii) Let (FS) be the
7) with centre E and radius ET draw an are such factored of Safety fox cohesion
that. it Cut EG at 3 iii)We know.
C×H/(F.S)c×yH^2=C/(P.S)c×yH=Sn- Here .C is
the dimensionless quantity which is
(F-S YH Called as Taylor's Stability number (Sn)
iv) Consider Cm be mobilized unit cohesion
which is essential so as to have the
equilibrium of a slope having heigh H.
7. Write a short notes Landslide 8. Triaxial Compression Test
Ans: - A Casagrande invented the triaxial Compression test so as
Ans : Discuss the remedial measures to be remove the diasdvantage of the direct she ar test.
taken to reduce the effect of these factor ii) The triaxial compression test is most efficent and versatile of
all the shearing testing methods of any type of soil In this
1) Due to seepage Pressure of perocolating
method drainage condition can be controlle pore water pressure
ground. Water can be measured accurately and also volume changes can be
2) During rainy season water content increases measured with the help of triaxial test.
iii) Note that there is no rotation of the principal. Stresses during
which -may lead to land slides. the test and the failure plane is not forced the soil sample can
(3) Because of alternative swelling and fall on any weak plane or can simply bulge In short the soil
shrinkage of soil mess hair cracks are sample may subject to brittle failure or Plastic failure.
4. The traixal- test apparatus consists of the following
developed then it may lead to landslides. components:
4) Due to increase load of trafic or (i) loading frame
(iii) proving ring
accumulated Snow: on the road surface.
(v) pressure apparatus
5) Undermining caused by erosion. (vii) loading arm (ix) porous disc
6) Due to earthquakes (ii) triaxial cell
(iv) pressure chambers
7) Due to vibration faults are formed in (vi) sample trimmer
bedding (viii) rubber 'O' ring
Plones of the strata. (x) air release value
5) Triaxial cell is a perspex cylinder, which is attached to the base
8) fissuring of pre-consolidated mass due to with rubber seals so as to make the cell water tight.
release of tateral pressur while doing cutting • Test procedure
of rocks. Following are the various points which explains the
The cylindrical specimen is kept on a saturated porousest
9) Due to failure of a retaining wall or breast procedure disc resting on the pedestal of the triaxial cell The
wall. cylindrical specimen is enclosed by a rubber. membrane and
sealed at the top and bottom by rubber ring The rubber
10) Geological Causes. membrane prevents the penetration of water into the soil
• weak or sensitive materials. specimen
- Weathered materals. -The inaxial cell is filled with water at the required pressure
through cell pressure unit. This water pressure is subjected to
Sheared jointed, or fissured materials. the soil specimen to all-around. Thes water pressure is called as
• Adversely oriented discontinuity (bedding is cell pressure or the confining pressure (,). Cell pressure acts
chistosity. • Contrast in Permeability and for radially on the vertical surface of the specimen and axially at the
top and bottom.
stiffness of. Materials. 4. By keeping constant cell pressure, additional axial stress is
11) mor phological causes applied through the ram gradually until the soil specimen fails.
This additional axial stress is also called as deviator stress
12) Women causes produces shear stresses within the soil sample on all planes
except the horizontal and vertical planes.
9. Pressure Bulb or Isobar:-
Ans : Definition: 'Isobar' is a line or contour joining
points of equal vertical stress inside soil mass
-Isobar is a spatial curve which shows the same
vertical pressure at all points in a horizontal plane
at equal radial distances from the load
-This stress isobar is bulb in shape hence it is called
as pressure bulb. The area outside the pressure
bulb is assumed to have negligible stresses
-The zone within which the stresses have a
significant effect on the settlement of structures is
known as the
pressure bulb. -The Boussinesq Equation for
vertical stress due to point
load is.
: σz=3Q/2π×Z^3/(r^2+z^2)^5/2
-Stress isobar for different vertical stress intensity
can be plotted.
10. Boussinesg's Theory for Point Load. 11. Earth Pressure :-
Ans : The Problem of stress evaluation at a point Ans: -The structure which are used to hold back a
inside soil mass due to point load acting on the soil mass
surface of a homogeneous elastic, isotropic and or earth pressure are called as retaining wall. -
semi- infinite medium of soil mass has solved by Hence the design of structure such as retaining wall
Boussinesq. requires the knowledge of the earth pressure
Assumption made by Boussinesq:- acting on the back of wall due to the soil backfill or
(1) The soil medium is an elastic, homogeneous, earth pressure in contact with it
isotropic and semi-infinite medium. -The magnitude of earth pressure itself is the
(2) The soil medium obeys Hooke's law. function of the magnitude and nature of the
(3) The self weight of the soil is ignored. absolute and relative movement of soil and
(4) The soil is initially unstressed. structures. -Earth pressures are statically
(5) The change in soil volume due to load indeterminate and therefore pose problems in
application is neglected. evaluation. -Following are the various structures
(6) The top surface of the soil is free of shear stress earth pressure
and only point load is acting at a point. Consider a (1) Retaining wall
point load Q acting at point O. Consider point 'S' (ii) Bracing in cuts
inside soil mass where σz is acting. (i) Abutment of a bridge
σz=3Q/2π×Z^3/(r^2+z^2)^5/2 (iv) Anchored sheet pile
(v) Twin retaining walls for cut.
12. Analyze the stability of Soil Using Method with #Assumption Made by Rankine for Earth Pressure:-
Net Sketch friction :- 1. The soil mass or earth is assumed to be
Ans: -The Friction Circle Method is a graphical homogeneous,
method used to analyze the stability of slopes in dry, and cohesion less 2.The back of structural wall
soil. It involves Plotting the shear strength of the is assumed to be vertical and smooth.
soil against the shear stress acting on the Soil The 3. The ground level or surface is plane which can be
shear strength is represented by the effective angle horizontal or inclined.
of internal friction while. the shear stress is 4. Rankine considered a semi-infinite mass of soil
represented by the inclinatio of the failure plane. by a horizontal surface and a vertical boundary
The friciton circle is Created by drawing a circle formed by the vertical back of a smooth wall
whose diameter is equal to the shear strength of surface.
the soil the point where a Failure Plane intersects 5. Entire mass of soil comes under plastic
the Circle represents the Factor of safety of the equilibrium and
slope If the point falls inside. The Circle The slope is also the various soil element is in state of plastic
stable but if it falls · outside the circle the slope is equilibrium
unstable. The friction Circle method is a useful tool 6. Rankine's theory consider the stress in a soil
for anylyzing the Stabil of slope in a variety of soil mass
types. 7. Back of wall is assumed to be smooth.
13. State The Merits And Demerits of Direct 14. Factor Affecting Compaction:-
Shear Test:- Ans: 1. Type of soil.
Ans: Advantages / Merits:- 2. Amount of compaction.
1. This test is quite simple to perform. 3. Water content.
2. There is quick drainage because of having 4. Admixtures.
lesser thickness of sample. 5. Method of compaction.
3. CD and CU tests takes relatively small 6. Thickness of layer.
period, because of quick drainage and rapid 7. Stone content.
dissipation of pore water pressure. 8. Saturation line.
4. Test is ideally suited for drained tests on 1. Type of soil:-
cohesionless soils. -The maximum dry density depends on the
5. The direct shear test apparatus is relatively type of soil.
cheap. -In general coarse grained soils can be
6. The sample preparation is easy and fast. compacted to higher dry density than fine
7. This test is simple and convenient. grained soils.
-Well graded sand can have higher dry density
#Disadvantages/Demerits:- than a poorly graded soil.
1.There is no uniform stress distribution on 2. Amount of Compaction:-
failure plane. -The amount of compaction is greatly affected
2. There is orientation of the failure plane on the maximum dry density (MDD) and
which is fixed. optimum moisture content (OMC) of a given
3.The stress conditions can be known only at soil.
the failure of soil sample. The condition before -But the increase in MDD is not linear with
to failure are indeterminate. increase of
4.There is very difficult control on drainage compactive effort or compactive energy.
condition. 3. Water content:-
5. It is not possible to measure pore water -The soil becomes stiff at low water content
pressure. and offers great resistance to compaction.
6. There is gradual reduction in the area under -It water content is further increased, the dry
shear as the test in progress. However it is not density decreases.
possible to find the corrected area. The 4. Admixtures:-
stresses are calculated based on the original -Compaction behavior and characteristics of
area. the soils can be improved by adding
7. The side wall do not allow the soil sample to admixtures like cement, lime, bitumen, etc.
deform laterally. -Lime may increase dry density by about 5 to
10%.
5. Method of compaction:-
-Maximum dry density also depends upon the
method of compaction.
6. Thickness of Layer:-
-Thickness of layer is also affecting the
compaction of soils.
-In laboratory, the nicknes of layer of soil is
normally kept 30 to 40 m.
7. Stone content:-
-The density of soil increases by adding the
aggregates
of 20 to 30 mm size upto 40% volume.
Culmann's graphical method" for evalution of Earth pressure:-
-1) Draw the failure plane: Draw the failure plane
18
Passing throught the toe of the retaining wall and extending to the surface of the soil The angle
of the failure. plone is assumed to be equal to the angle of internal friction of the soil.
2) Drow the normal force polygon : Draw a polygon to represent the normal forces acting the
polygon should have sides that are parallel to the on the failure plane. failure plane and
perpendicular to the retaining toall
3) Draw the shear force polygon: Draw a polygon to
represent the shear forces acting on the failure Plane
The Polygon should have sides that are parallel to the
failure plane and perpendicular to the normal force polygon
4) Determine the intersection of the normal and shear
force Polygons: The intersection of the normal and Shear force Polygons represents the resultant
force acting on the failure plane.
5) Determine the earth Pressure Coefficient & The earth. Pressure coefficient is determine by
dividing the horizon. Component of the resultant force by the vertical Component of the
resultant force.
6) Determine the earth Pressure: The earth pressure is determined by multiplying the earth
Pressure Coeffici by the unit weight of the so