1. Code No: A26A3
B V RAJU INSTITUTE OF TECHNOLOGY, NARSAPUR
(UGC - AUTONOMOUS)
B.Tech III Year II Semester Supplementary Examinations, Sep/Oct 2020
FOUNDATION ENGINEERING KEY
( C i v i l E n g i n e e r i n g )
Max Marks: 70
1. a) Need of soil exploration (8 M)
The information from soil investigations will enable a Civil engineer to plan, decide, design, and
execute a construction project. Soil investigations are done to obtain the information that is
useful for one or more of the following purposes.
1. To know the geological condition of rock and soil formation.
2. To establish the groundwater levels and determine the properties of water.
3. To select the type and depth of foundation for proposed structure
4. To determine the bearing capacity of the site.
5. To estimate the probable maximum and differential settlements.
6. To predict the lateral earth pressure against retaining walls and abutments.
7. To select suitable construction techniques
8. To predict and to solve potential foundation problems
9. To ascertain the suitability of the soil as a construction material.
10. To determine soil properties required for design
11. Establish procedures for soil improvement to suit design purpose
12. To investigate the safety of existing structures and to suggest the remedial measures.
13. To observe the soil the soil performance after construction.
1 b) Procedure of obtaining a chunk sample. (8 M)
2. • A cylindrical container open at both the ends is used for sampling.
• The soil is trimmed to shape at the bottom of the test pit One end of container is closed and
inverted over the soil chunk and the soil sample is removed using spatula
• This method is suitable for cohesive soil. Obtaining chunk sample.
2. Procedure of conducting a standard penetration test:
Standard Penetration Test.: (8 M)
The standard Penetration Test is the most commonly used in –site test, especially for cohesion
less soils which cannot be easily sampled, the test is extremely useful for determining the relative
density and the angle to determine the UCC strength of the cohesive soil.
The standard penetration test is conducted in a bore hole using a standard split spoon sampler,
when the bore hole has been drilled to the desired depth, the drilling tools are removed and the
sampler is lowered to the bottom of the hole. The sampler is driven into the soil by a drop
hammer of 63.5kg mass falling through a height of 750mm at the rate of 30 blows per minutes.
The number of hammer blows required to drive 150mm of the sample is counted.
The sampler is further driven by 150mm and the number of blows recorded. Likewise the
sampler is once again further driven by 150mm and the number of blows recorded. The number
of blows recorded for the first 150mm is disregarded. The plumber of blows recorded for the last
two 150mm intervals are added to give the standard Penetration Number (N). In other words, the
standard Penetration number is equal to the number of blows required for 300mm of penetration
beyond a seating drive of 150mm.
If the number of blows for 150mm drive exceeds 50, it is taken as refusal and the test is
discontinued. The standard Penetration number is corrected for decadency correction and our
3. (a) Dilatancy Correction. (4 M)
Silty fine sands and fine sands below the water table develop pore pressure which is not
easily dissipated. The pore pressure increases the resistance of the soil and hence the Penetration
number (N). Terzaghi and peck recommend the following correction when the observed N value
exceeds 15. The corrected Penetration Number,
Nc = 15 + ½ [NR – 15]
Nc – corrected value
NR – Recorded Value
If NR ≤ 15, then Nc = NR
(b) Over burden Pressure Correction: (4 M)
In granular soils, the overburden pressure affects the penetration resistance. Generally, the
soil with high confining pressure gives higher penetration number. As the confining pressure in
cohesion soil increases with depth, the penetration number for the soils at shallow depths is
under estimated and that at greater depths is over estimated for uniformity, the N values obtained
from field tests under different effective overburden pressure are corrected to a standard effective
For dry or moist clean sand, (Gibbs and Holtz)
𝐍𝐑 𝐗 𝟑𝟓𝟎
̅ 𝟎 +𝟕𝟎
Nc - corrected value
NR - Recorded Value
̅0 - effective over burden pressure
It is applicable for ̅ ≤ 280kN/m2
. Usually the overburden correction is applied first and then
dilatancy correction is applied first and then dilatancy correction is applied.
The value of standard Penetration number N depends upon the relative density of the
cohesionless soil and the unconfined compressive strength of the cohesive soil. If the soil is
compact or stiff, the penetration number is high.
3. a) Static method in bearing capacity of piles: (4 M)
Qup = Qp + Qs
Qup = ultimate load on pile.
Qp = tip resistance= qn x A
4. Qs =skin resistance = 𝜋 𝐷 𝑙 × 𝑙s
Where, fs = unit skin friction between pie and soil.
3. b) Classification of piles: (10 M)
Piles can be classified according to
1. The material used
2. The mode of transfer of load
3. The method of construction
4. The use and
5. Displacement of soil
1. Classification according to material used
There are four types of piles according to materials used
(i) Steel piles
(ii) Concrete piles
(iii) Timber piles
(iv) Composite piles
2. Classification based on mode of transfer of load
Based on the mode of transfer of loads, the pile can be classified into three categories:
(i) End bearing piles
(ii) Friction piles
(iii) Combined end bearing and friction piles
3. Classification based on method of installation
Based on the method of construction, the piles may be classified into the following 5 categories
(i) Driven pile
(ii) Driven and cast in situ piles
(iii) Bored and cast in situ piles
(iv) Screw piles
(v) Jacked piles
4. Classification based on use
The piles can be classified into the following 6 categories depending upon their use.
(i) Load bearing piles
(ii) Compaction piles
(iii) Tension piles
(iv) Sheet piles
(v) Fender piles
(vi) Anchor piles
6. 5. Classification based on displacement of soil:
Based on the volume of the soil displacement during installation the piles can be classified into 2
(i) Displacement piles
(ii) Non- displacement piles
5. Components of a well foundation
Well Components: (10M)
• Cutting Edge
• Well Curb
• Well steining
• Bottom Plug
• Sand Fill
• Top Plug
• Well cap
Sharp edge which is provided at the lower end of the well or open and pneumatic caisson for
accelerating sinking operation is called cutting edge. It is made up steel or it is made in R.C.C.
Its angle to vertical is 30 0 and normally slope of 1 horizontal to 2 vertical given better result.
It is made of concrete or brick. Cutting edge of well or caisson is attached to well curb. During
sinking operation well curb impart to the well-stening and facilities the formation of bottom
7. Well Steining
Steining is constructed in concrete or masonary work.
Use of stening is to provide dead load during sinking operation
Covering provided over the well or caisson is called as topping.
Sand is filled in between topping and bottom plug. Topping also acts as a part of shuttering for
laying the well cap.
The lower portion of well is sealed by the concrete is called as bottom plug.
R.C.C Slab covering provided over the top of well is termed as well cap.
The portion between top and bottom plug is filled with sand so as to increase the self weight of
the well and makes safe during earthquake.
6. a) Different shapes of well foundations: (8 M)
Caisson are constructed into two basic shapes and
combination of basic shape.
Shapes of Caissons:
(I) Basic Shape
(II) Combination of Basic Shape
8. 6 b) Rectifying methods of tilts & shifts in well foundations (8M)
Following are the remedial measures to be carefully implemented to avoid tilting of caisson
during sinking process:
Water Jetting: This is the one of the method used to prevent tilting. In this method, water jet is
forcedly applied on tilt.
Eccentric loading: The caisson is normally given the additional loading called kentledge in
order to have necessary sinking effort. In this method, eccentric loading or kentledge is applied
in higher side so as to have greater sinking effort.
Excavation under cutting edge: During sinking process, filled caisson will not set or straighten
due to unbroken stiff strata on its higher side. In such situation, dewatering is preferably done to
loosen stiff strata. If dewatering is not possible or unsafe, then drivers are sent to loosen the stiff
Regulation of Excavation: Sinking of caisson on higher side due to excess excavation is more.
This is all right in the early stages, otherwise dewatering of caisson or well is needed and open
excavation may be done on higher side.
Providing temporary obstacles below the cutting edge: Rectification of tilt can be done by
inserting the wooden sleeper temporarily as an obstacles below the cutting edge on the lower
side so as to prevent further tilt of the well or caisson.
Strutting the caissons or well: Method of strutting the caisson or well is used to prevent any
further and possible rise in tilting of the caisson or well.
Pushing the caissons or well with jack: Mechanical jack or hydraulic jack can be used to
rectify the tilt of well or caisson. Well or caisson can be pushed by jack to bring it a vertical
7 a) Different types of retaining walls:
An earth retaining structure can be considered to have the following types:
9. 1. Gravity wall
2. Semi gravity wall
3. Cantilever wall
4. Buttress wall
5. Counter fort walls
7 b) Stability analysis of a retaining wall.
1. Check for sliding
2. Check for overturning
3. Check for bearing capacity failure
4. Check for base shear failure
The minimum factors of safety for the stability of the wall are:
1. Factor of safety against sliding =1.5
2. Factor of safety against overturning = 2.0
3. Factor of safety against bearing capacity failure = 3.0
To ensure the stability of a retaining wall, the following conditions or requirements must be met:
• The wall should be structurally capable of resisting the pressure applied to it.
• The wall should be so properly proportioned that it will not get overturned by the lateral
• The wall should be safe from consideration of sliding, i.e., the wall should not be pushed
out by the lateral pressure.
• The weight of wall together with the force resulting from the earth pressure acting on it,
should not stress its foundation to a value greater than safe bearing capacity of the soil.
• It is important to prevent accumulation of water behind a retaining wall. The backing
material should be suitably drained by providing weep holes.
• Long masonry retaining walls should be provided with expansion joints located at 6 to
• Weep holes may be provided to relieve water pressure.