B.Tech Civil Notes (8th Semester)

1. Foundations and Pavements - CE367
Written & Composed BY ENGINEER SAQIB IMRAN
WhatsApp & Contact No: 0341-7549889
Email: Saqibimran43@gmail.com
Student of B.TECH(Civil) at Sarhad University of Science &
Information Technology Peshawer.

2. FOUNDATION & FOUNDATION ENGINEERING:
FOUNDATION: A foundation is the lowest part of the building structure.
FOUNDATION ENGINEERING: Foundation engineering applies knowledge of soil mechanics,
rock mechanics, geology and structural engineering to design and construction of foundations
for buildings and other structures.
The most basic aspect of foundation engineering deals with the selection of the type
of foundation, such as using a shallow or deep foundation system. Another important
aspect of foundation engineering involves development of design parameters, such as the
bearing capacity of foundation. OR
FOUNDATION ENGINEERING: The title foundation engineer is given to that person who by
reason of training and experience is sufficiently versed in scientific principles and engineering
judgment (often termed "art") to design a foundation. We might say engineering judgment is
the creative part of this design process.
The necessary scientific principles are acquired through formal educational courses in
geotechnical (soil mechanics, geology, foundation engineering) and structural (analysis, design
in reinforced concrete and steel, etc.) engineering and continued self-study via short
courses, professional conferences, journal reading, and the like.
Because of the heterogeneous nature of soil and rock masses, two foundations—even on
adjacent construction sites—will seldom be the same except by coincidence. Since every
foundation represents at least partly a venture into the unknown, it is of great value to have
access to others' solutions obtained from conference presentations, journal papers, and
textbook condensations of appropriate literature. The amalgamation of experience, study of
what others have done in somewhat similar situations, and the site-specific geotechnical
information to produce an economical, practical, and safe substructure design is application of
engineering judgment.
The following steps are the minimum required for designing a foundation:
1 . Locate the site and the position of load. A rough estimate of the foundation load(s) is
usually provided by the client or made in-house. Depending on the site or load system
complexity, a literature survey may be started to see how others have approached similar
problems.
2. Physically inspect the site for any geological or other evidence that may indicate a potential
design problem that will have to be taken into account when making the design or giving a
design recommendation. Supplement this inspection with any previously obtained soil data.
3 . Establish the field exploration program and, on the basis of discovery (or what is found in
the initial phase), set up the necessary supplemental field testing and any laboratory test
program.
4. Determine the necessary soil design parameters based on integration of test data, scientific
principles, and engineering judgment. Simple or complex computer analyses may be involved.
For complex problems, compare the recommended data with published literature
or engage another geotechnical consultant to give an outside perspective to the results.

3. 5. Design the foundation using the soil parameters from step 4. The foundation should be
economical and be able to be built by the available construction personnel. Take into account
practical construction tolerances and local construction practices. Interact closely
with all concerned (client, engineers, architect, contractor) so that the substructure system
is not excessively overdesigned and risk is kept within acceptable levels. A computer may
be used extensively (or not at all) in this step.
CLASSIFICATION OF FOUNDATIONS:
There are two main types of foundations:
1. SHALLOW FOUNDATIONS
The foundation provided immediately beneath the lowest part of the structure near
to the ground level is known as shallow foundation. Such foundations are mostly placed on
the first hard strata available below the ground level. The depth is generally D/B < 1 but
may be more.
TYPES OF SHALLOW FOUNDATIONS
i. Stepped Footing: The foundation having its bed in the form of steps of concrete is known as
stepped foundation. For this, excavation is done into steps having short length and uniform
height. If there is any possibility of slipping of structure, then RCC piles can be driven along its
base concrete on the slopping side.
Advantages:  Simplicity of design,  Cheap familiar technology,  Less workers required.
Disadvantages:  Comparatively low durability,  High cost in the final stages of construction,
 Inability to make monolithic binding of the floor to the basement.
ii. Mat Foundation: The foundation consisting of a thick RCC slab covering the whole area is
known as mat or raft foundation. It is most suitable foundation when the soil at site is of low
bearing capacity. Mat foundation is constructed of RCC slab covering whole area of bottom of
structure. The slab is provided with steel reinforcing bars in both directions. When column
loads are heavy, the main beams and secondary beams are provided monolithically with raft
slab.
Advantages:  Most suited in clayey soil as the whole area under the foundation contributes to
load distribution and this is more effective.  Economic due to combination of foundation and
floor slab.  Requires little excavation.  Reduces differential settlement.
Disadvantages:  Mat foundation requires specific treatment for point loads.
 Edge erosion occurs if not treated properly.
iii. Spread Footing: The foundation constructed be increasing the area at the base of structure
by means of offsets is called spread footing. In such foundations, spread is given under the base
of wall or column by proving off sets. A spread footing is circular, square or rectangular slab of
uniform thickness.
Advantages:  It is used if bearing capacity of soil is high at shallow depth.  Helps to reduce
settlement.  No piling is required, hence reducing the cost.
Disadvantages:  If weight of structure is high, the load of structure is distributed unequally.
 Bearing capacity of top surface soil is less.

4.  If water level is high, it is uneconomical to pump out the water.
iv. Combined Footing: A combined footing supports two columns when two columns are so
close to each other that their individual footings would overlap. Combined footing is also
provided when property line is so close to one column. It may be rectangular or trapezoidal in
plan.
Advantages:  Can be used when Columns are very near to each other.  Can be used for less
bearing capacity soil.  Uniform pressure below the entire area of footing.
2. DEEP FOUNDATIONS
Foundation constructed sufficiently below ground level with some arrangements
such as piles, wells etc at their base, is called deep foundation. In deep foundation depth to
width ratio is usually greater than 4 to 5. This is usually at depths >3 m below ground level.
TYPES OF DEEP FOUNDATIONS
i. Pile Foundation: A foundation consisting of spread or grillage supported on piles is called pile
foundation. Piles distributes the load of structure to the hard stratum by friction alone or
with bearing at their ends. Two main components of pile foundation are:
 Piles are long and slender members which transfer the load to deeper soil or rock of
high bearing capacity.
 Pile caps are thick slabs used to tie a group of piles together to support and transmit
column loads to the piles.
Advantages:  Piles can be precast to the required specifications.  Piles of any size, length and
shape can be made.  As soil compacts the adjacent soil, the bearing capacity of pile is
increased.
Disadvantages:  Must be properly reinforced to withstand stresses during transportation &
driving.  Advance planning is required for handling and driving.
 Requires heavy equipment for handling and driving.
ii. Well Foundation: The main difference between well and a pile foundation is that, pile is
flexible under horizontal loads while well undergoes rigid body movement under such loads.
Wells have different shapes like circular wells, Double-D wells, double octagonal wells, single
and double rectangular wells, multiple dredged holed wells.
Advantages:  Provides solid and massive foundation for heavy loads,  Greater bearing
capacity because of large area,  Can resist large horizontal forces.
Disadvantages:  Increase cost,  Large number of workers required,
 Use of machineries and equipment’s.
iii. Caisson Foundation: Caisson foundation is also known as pier foundation. Caisson is a
cylinder or hollow box that is sunk into ground to a specified depth by making a deep hole into
the strata. The cylinder or box is then back filled with concrete, thus creating the foundation.
This type of foundation is most often used when constructing bridge piers and other such
foundations that will be beneath bodies of water.
Advantages:  Easily adaptable to varying site conditions,  High axial and lateral load capacity,

5.  Very economical,  Reduce vibrations.
Disadvantages:  Lack of expertise,  Cannot be placed on contaminated sites because of risk of
further contamination throughout the site,  Construction procedures is very sensitive.
GENERAL REQUIREMENTS OF FOUNDATIONS DESIGN:
1. The foundation, including the underlying soil and rock, must be safe against a structural
failure that could result in collapse. For example, the foundation for a skyscraper must
support the great weight of the building above on a relatively narrow base without
danger of overturning.
2. During the life of the building, the foundation must not settle in such a way as to
damage the structure or impair its function.
3. It should be adequately rigid to minimize differential settlement specifically when
superimposed loads are distributed unevenly.
4. The foundation must be feasible, both technically and economically, and practical to
build without adverse effects on surrounding property.
5. The ability of foundation to safely support and transfer combined dead loads, live loads,
horizontal loads such as wind and earthquake to subsurface soil in one of the most
prime design requirements.
6. The depth of foundation should be adequate so that it prevents overturning, and
protects the building against damage or distress caused by swelling or shrinkage of the
subsoil. Soil bearing capacity is good at sufficient depth.
7. Foundation structure should be designed in such as way that possess enough safety
against exceptional future loads for example earthquake and overloading.
8. It should resist attack from chemicals in soil. Various harmful materials like sulfates may
be present in groundwater and soil that deteriorate concrete foundation. Sulphate
attack can usually be offset by using sulphate resisting cement, but even this would not
be a perfect alternative to the problem unless sufficient care is taken in placing the
concrete, by vibrating and curing. OR
GENERAL REQUIREMENTS OF FOUNDATION DESIGN
i. The foundation, including the underlying soil and rock, must be safe against a structural
failure that could result in collapse.
ii. During the life of structure, foundation must not settle in such a way as to damage the
structure or impair its function.
iii. The foundation must be feasible, both technically and economically and practical to build
without adverse effects on surrounding property.
iv. Strength of foundation components shall not be less than that required for load
combinations.
v. The bearing capacity of foundation soil shall be sufficient to support the structure with all
prescribed loads.
FACTORS TO CONSIDER IN FOUNDATION DESIGN AND THEIR DETAILS:

6. FOUNDATIONS: ADDITIONAL CONSIDERATIONS
1. Depth must be adequate to avoid lateral squeezing of material from beneath the foundation
for footings and mats. Similarly, excavation for the foundation must take into account that
this can happen to existing building footings on adjacent sites and requires that suitable
precautions be taken. The number of settlement cracks that are found by owners of existing
buildings when excavations for adjacent structures begin is truly amazing.
2. Depth of foundation must be below the zone of seasonal volume changes caused by freezing,
thawing, and plant growth. Most local building codes will contain minimum depth
requirements.
3. The foundation scheme may have to consider expansive soil conditions. Here the building
tends to capture upward-migrating soil water vapor, which condenses and saturates the
soil in the interior zone, even as normal perimeter evaporation takes place. The soil in a
distressingly large number of geographic areas tends to swell in the presence of substantial
moisture and carry the foundation up with it.
4. In addition to compressive strength considerations, the foundation system must be safe
against overturning, sliding, and any uplift (flotation).
5. System must be protected against corrosion or deterioration due to harmful materials
present in the soil. Safety is a particular concern in reclaiming sanitary landfills but has
application for marine and other situations where chemical agents that are present can
corrode metal pilings, destroy wood sheeting/piling, cause adverse reactions with Portland
cement in concrete footings or piles, and so forth.
6. Foundation system should be adequate to sustain some later changes in site or construction
geometry and be easily modified should changes in the superstructure and loading become
necessary.
7. The foundation should be buildable with available construction personnel. For one-of-a kind
projects there may be no previous experience. In this case, it is necessary that all concerned
parties carefully work together to achieve the desired result. OR
FACTORS IN FOUNDATION DESIGN
1. Loads from Building: The first factor considered is loads from building on the foundation.
This load is a combination of dead load and imposed loads on buildings. Other loads such as
wind loads, earthquake loads, snow loads etc. are also considered.
2. Type of Soil: The soil near surface is called as top soil and below a depth of 30 0mm is called
as sub soil. Generally, subsoil is used as base for foundation for small buildings. However, soil
investigation should be carried out to know the nature of soil and to know the bearing capacity
of soil at different levels.
3. Type of Structure in Neighborhood: The selection of foundation can also have based on type
of foundation selected for neighboring buildings. Based on the success or failure of foundations
for such buildings, decision can be taken for the selection of foundation.
4. Types of Foundation: Types of foundation such as isolated foundations, combined footings,
pile foundations and raft or mat foundations etc. based on the type of soils and loads can be
selected based on suitability and requirement.

7. 5. Water Table fluctuation: A lowered water table increases the effective pressure and may
cause additional settlements. A raised water table may create problems like floating the
structure by making it unstable or tilting it and reducing the effective pressure by causing
excessive settlement.
6. Factors of Safety: Factors of safety represent capacity which a foundation has against
collapse for a given set of loads. Therefore in choosing design approach, designer should
consider significance of project, degree of uncertainty in the design parameters and the
probability of failure due to both collapse and functional errors.
7. Foundations on Permafrost: Permafrost is a condition of permanently frozen ground, where
the ground temperatures are never higher than 0o C. Construction in these areas requires that
the foundations be placed below this material.
INTRODUCTION AND CLASSIFICATION OF DEEP FOUNDATIONS:
Deep foundation is required to carry loads from a structure through weak compressible soils or
fills on to stronger and less compressible soils or rocks at depth, or for functional reasons. Deep
foundations are founded too deeply below the finished ground surface for their base bearing
capacity to be affected by surface conditions, this is usually at depths >3 m below finished
ground level.
Deep foundation can be used to transfer the loading to a deeper, more competent strata at
depth if unsuitable soils are present near the surface.
Types of Deep Foundation: The types of deep foundations in general use are as follows:
1. Basements. 2. Buoyancy rafts (hollow box foundations). 3. Caissons. 4. Cylinders.
5. Shaft foundations. 6. Pile foundations.
1. Basement foundation: These are hollow substructures designed to provide working or
storage space below ground level. The structural design is governed by their functional
requirements rather than from considerations of the most efficient method of resisting external
earth and hydrostatic pressures. They are constructed in place in open excavations.
2. Buoyancy Rafts (Hollow Box Foundations): Buoyancy rafts are hollow substructures
designed to provide a buoyant or semi-buoyant substructure beneath which the net loading on
the soil is reduced to the desired low intensity. Buoyancy rafts can be designed to be sunk as
caissons, they can also be constructed in place in open excavations.
3. Caissons Foundations: Caissons are hollow substructures designed to be constructed on or
near the surface and then sunk as a single unit to their required level.
4. Cylinders: Cylinders are small single-cell caissons.
5. Drilled Shaft foundations: Shaft foundations are constructed within deep excavations
supported by lining constructed in place and subsequently filled with concrete or other pre-
fabricated load-bearing units.
6. Pile foundations: Pile foundations are relatively long and slender members constructed by
driving preformed units to the desired founding level, or by driving or drilling-in tubes to the
required depth – the tubes being filled with concrete before or during withdrawal or by drilling
unlined or wholly or partly lined boreholes which are then filled with concrete.

8. USES AND TYPES OF PILES:
USES OF PILES
i. To carry vertical compression load.
ii. To resist tension or uplift load.
iii. To transmit buildings loads to the foundations and the ground soil layers.
iv. To install loose cohesion less soil through displacement and vibration.
v. To control settlements.
vi. To build a structure within the water and on water river or canal bed.
vii. To increase the bearing capacity of soil by compaction piles. OR
USES OF PILES. The major uses of piles are:
1. To carry vertical compression load. Normally vertical piles are used to carry vertical
compression loads coming from superstructures such as buildings, bridges etc. The piles are
used in groups joined together by pile caps. The loads carried by the piles are transferred to the
adjacent soil. If all the loads coming on the tops of piles are transferred to the tips, such piles
are called end-bearing or point-bearing piles. However, if all the load is transferred to the soil
along the length of the pile such piles are called friction piles. If, in the course of driving a pile
into granular soils, the soil around the pile gets compacted, such piles are called compaction
piles.
2. To resist uplift load. Piles are also used to resist uplift loads. Piles used for this purpose are
called tension piles or uplift piles or anchor piles. Uplift loads are developed due to hydrostatic
pressure or overturning movement.
3. To resist horizontal or inclined loads. Piles are also used to resist horizontal or inclined
forces. Batter piles are normally used to resist large horizontal loads.
TYPES OF PILES
1. BASED ON THEIR FUNCTION
i. Bearing Piles: The piles which rest on hard strata and act as columns to bear the load of the
structure i.e. they acts as a medium to transmit the load from the foundation to the stratum
are known as bearing piles. These piles are used to bear the vertical loads.
ii. Friction Piles: The piles which do not rest on hard strata and bear the loads on account of
frictional resistance between their outer surface and the soil in contact, are called friction piles.
In friction piles, load is carried by friction developed between the sides of pile and surrounding
ground.
iii. Friction-Cum-Bearing Piles: The piles which rest on hard strata and resist the structural load
partly by bearing and partly by their skin friction are known as friction-cum-bearing pile. These
piles are used when bearing capacity of soil strata lying under them is not sufficient to resist the
load of structure.
2. BASED ON MATERIAL
i. Steel piles: The pile consisting of steel section are called steel piles. These pile may be made
in the form of I or H section beams. H section beams are mostly used for steel piles these days.

9. The size of H section varies from 240 to 400 mm depth with thickness of usually 12 mm.
These piles are available in the form of sheet pin piles, sheet piles, disc piles and screw piles.
ii. Timber piles: The timber to be used as a pile should be free from defects, decay etc. and it
should be well seasoned. A main consideration regarding timber piles is that they should be
protected from rotting hence it will last for a long time below the groundwater level. These
piles are driven by blows of drop hammer.
iii. Concrete Piles: Concrete piles may be precast, pre-stressed, cast in place or of composite
construction. Concrete piles are typically made with steel reinforcing and pre-stressing
tendons to obtain strength, to survive handling & driving and to provide sufficient bending
resistance. Pile joints can be used to join two or more short piles to form one long pile.
PILE INSTALLATION METHODS:
1. DROP HAMMER METHOD: It is the simplest method of pile driving. In this method, a
hammer is raised to a suitable height and released to strike the pile head. Hammer is generally
dropped from the height of 1.5 to 4.5 m and its weight is about 2.25 to 9 kN for short piles and
9 to 23.50 kN for long and heavy piles. The hammer is raised by pulling rope manually or by
engine. The pile driving frame is kept in vertical position by suitable ropes.
2. STEAM HAMMER METHOD: In this case, a heavy hammer is dropped on to the pile through a
small height but in quick succession. Single acting or double acting hammers are available.
These hammers are raised with high pressure steam and dropped under gravity or by steam.
Special devices are used to protect the heads of piles from damage due to excessive blows.
3. BORING METHOD: Sometimes piling is done by boring holes of suitable diameter to the
required depth and then dropping piles in them. Generally, cat-in-situ piles are laid by this
method. Boring can be done by:
i. Continuous Flight Auger (CFA); CFA consists of a carrier fitted with a flight auger which is
rotated into the ground to required depth by hydraulic motor. On reaching the required depth,
highly workable concrete is pumped and under the pressure of concrete the protective cap is
detached.
ii. Under Reaming: Under reaming tool is fitted inside pile shaft and then expanded at bottom
of pile to produce under ream. Normally, after installation and before concreting, man carrying
cage is lowered and shaft and the under ream of pile is inspected.
4. WATER JET METHOD: Pile driving can also be done by displacing the material at or near the
foot of pile by means of one or more water jets under pressure. The pressure of jet should be
sufficient to displace soil and removed material for driving piles quickly and satisfactory.
PILE SPACING:
Pile spacing is based on the heat necessary to convert water to ice at no change in
temperature. If the spacing between piles is too close, the zones of stress around pile will
overlap and the ultimate load of pile group is less than the sum of individual capacities of
pile. Generally center to center spacing between piles is kept between 2.5d and 3.5d, where
d is the diameter of the pile.

10. NEGATIVE SKIN FRICTION:
Negative skin friction is a downward shear pull acting on the pile surface due to
relative downward movement of soil surrounding the pile. The following are some of the
causes of negative skin friction:
 Due to pile or pile segment passing through compressible soil
 Due to placement of a fill on compressible soil layer
 Lowering of ground water table causing the shrinkage of expansive soils
 Under consolidated natural or compacted soils
The negative skin friction of a single pile is given by:
Negative skin friction
= Unit frictional resistance (downward)
X Length of the pile above bottom of the compressible layer
X Perimeter of the pile cross section.
And total downward load = negative skin friction load + live load + dead load.
BEARING CAPACITY
The maximum load which the soil can take per unit area without yielding or
displacement is called bearing capacity of ultimate bearing capacity. The stability of
structure depends upon the strength of soil, which is expressed as bearing capacity usually
in terms of tone per square meter. While the workable bearing capacity of soil, which is
considered for design is known as safe bearing capacity.
BEARING CAPACITY EQUATIONS: There is currently no method of obtaining the ultimate
bearing capacity of a foundation other than an estimate:
1. THE TERZAGHI BEARING-CAPACITY EQUATION
One of the early sets of bearing-capacity equations was proposed by Terzaghi in 1943.
Terzaghi's equations were produced from a slightly modified bearing-capacity theory
developed by Prandtl in 1920 to examine punching of a rigid base into a softer material.
 Bearing-capacity equations were intended for shallow foundations.
 All shape factors Si = 1.00, but the Ni factors were computed differently.
 Used α = φ.
 Only used shape factors with the cohesion Sc and base Sγ terms.
 Never explained very well how he obtained Kpγ to compute bearing-capacity.
The general Terzaghi’s equation is:
𝑞 𝑢𝑙𝑡 = 𝑐𝑁𝑐 𝑠𝑐 + 𝑞𝑁𝑞 + 0.5𝛾𝐵𝑁𝛾 𝑠 𝛾
If values of Nq, Nc, Nr, α and Kpγ are not given than use formulas or take values from table 4-2.
𝑁𝑞 =
𝛼2
𝛼𝑐𝑜𝑠2(45 +
𝜑
2
)
𝑁𝑐 = (𝑁𝑞 − 1)𝑐𝑜𝑡𝜑

11. 𝑁𝑟 =
𝑡𝑎𝑛𝜑
2
(
𝐾𝑝𝛾
𝑐𝑜𝑠2 𝜑
− 1)
𝐾𝑝𝛾 = See table
𝛼 = 𝑒
(0.75𝜋−
𝜑
2
) 𝑡𝑎𝑛𝜑
While for 𝑆𝑐 and 𝑆𝑟,
Footing Strip Round Square
𝑺 𝒄 1.0 1.3 1.3
𝑺 𝒓 1.0 0.6 0.8
TABLE 4-2. Bearing-capacity factors for the Terzaghi equations
Values of 𝑁𝛾 for ∅ of 0, 34, and 48° are original Terzaghi values and used to back-compute 𝐾𝑝𝛾.
∅, deg 𝑵 𝒄 𝑵 𝒒 𝑵 𝜸 𝑲 𝒑𝜸
0 5.7* 1.0 0.0 10.8
5 7.3 1.6 0.5 12.2
10 9.6 2.7 1.2 14.7
15 12.9 4.4 2.5 18.6
20 17.7 7.4 5.0 25.0
25 25.1 12.7 9.7 35.0
30 37.2 22.5 19.7 52.0
34 52.6 36.5 36.0
35 57.8 41.4 42.4 82.0
40 95.7 81.3 100.4 141.0
45 172.3 173.3 297.5 298.0
48 258.3 287.9 780.1
50 347.5 415.1 1153.2 800.0
∗ 𝑁𝑐 = 1.5𝜋 + 1.
2. MEYERHOF 'S BEARING-CAPACITY EQUATION
Meyerhof proposed bearing-capacity equation similar to that of Terzaghi but
included a shape factor sq with depth term Nq. He also included depth factors di and
inclination factors ii for cases where the footing load is inclined.
 Obtained his N factors by making trials.
 Using the inclination factors to reduce bearing capacity when the load resultant was
inclined from the vertical.
 When the iγ factor is used, it should be self-evident that it does not apply when φ = 0o.
 All ii factors = 1.0 if the angle θ = 0o.
 The difference becomes more different at larger D/B ratios.
TABLE 4-3. Shape, depth, and inclination factors for the Meyerhof bearing-capacity equations
of Table 4-1

12. Where Kp = tan2 (45 + ∅/2) as in Fig. 4-2
𝜃 = angle of resultant R measured from vertical without
a sign; if 𝜃 = 0 aIl ii = 1.0.
B, L, D = previously defined.
3. HANSEN'S BEARING-CAPACITY METHOD
This equation is further extension of Meyerhof work. Hansen's shape, depth and
other factors makes up general bearing capacity equation. These represent revisions and
extensions from earlier proposals. The extensions include base factors in which footing is
tilted and for possibility of a slope to give ground factors. The equation allows any D/B and
thus can be used for both shallow and deep foundations. Hansen used:
i. For Shallow Foundations
𝑑 𝑐 = 1 + 0.4
𝐷
𝐵
𝑑 𝑞 = 1 + 2𝑡𝑎𝑛𝜑(1 − 𝑠𝑖𝑛𝜑)2
𝐷
𝐵
ii. For Deep Foundations
𝑑 𝑐 = 1 + 0.4𝑡𝑎𝑛−1
𝐷
𝐵
𝑑 𝑞 = 1 + 2𝑡𝑎𝑛𝜑(1 − 𝑠𝑖𝑛𝜑)2
𝑡𝑎𝑛−1
𝐷
𝐵

13. 4. VESIC'S BEARING-CAPACITY EQUATIONS
The Vesic procedure is essentially the same as the method of Hansen with select
changes. The Nc and Nq terms are those of Hansen but Nγ is slightly different. There are also
differences in the ii, bi and gi terms. The Vesic equation is somewhat easier to use than
Hansen's because he uses i terms in computing shape factors si whereas Vesic does not.
BEARING CAPACITY PROBLEMS:
EXAMPLE 1: What will be the gross and net safe bearing pressure of sand having  equal to
36o & effective unit weight of 1.8 g/cc under the following cases ?
i. 1.0 m wide strip footing. ii. 1.0 x 1.0 m square footing. iii. Circular footing of 1.0 m dia.
Given Data:  = 36 o, C = 0,  = 1.8 g/cc = 1.8 T/m2, Df = 1 m (Assumed).
Required: CASE-I: 1.0 m wide strip
qu = , qs = , qnet = , When,  = 36o, Nq =49.5, N =55.9.
For strip footing, Sc = 1, S = 1
𝑞 𝑢 = 𝑆 𝐶 𝐶𝑁𝐶 + 𝑞𝑁𝑞 +
1
2
𝛾𝑁𝛾 𝐵𝑆 𝛾
𝑞 𝑢 = 1.8(1.0) (49.5) +
1
2
(1.8) (1) (55.90) (1) ⇒ 𝑞 𝑢 = 139.41 T/m2
𝑞 𝑠 = 𝑞 𝑢/F.O.S ⇒ 𝑞 𝑠 = 139.41/3 ⇒ 𝒒 𝒔 = 46.47 T/m2.
𝑞 𝑛𝑒𝑡 = 𝑞 𝑠 – q ⇒ 𝑞 𝑛𝑒𝑡 = 46.47 – (1.8) (1) ⇒ 𝒒 𝒏𝒆𝒕 = 44.67 T/m2.
CASE-II: 1.0m x 1.0 m square footing
qu = , qs = , qnet = , When,  = 36o, Nq = 49.5, N = 55.9.
For square footing, Sc = 1.3, S = 0.8
𝑞 𝑢 = 𝑆 𝐶 𝐶𝑁𝐶 + 𝑞𝑁𝑞 +
1
2
𝛾𝑁𝛾 𝐵𝑆 𝛾
𝑞 𝑢 = 1.8(1.0) (49.5) +
1
2
(1.8) (1) (55.90) (0.8) ⇒ 𝑞 𝑢 = 129.34 T/m2
𝑞 𝑠 = 𝑞 𝑢/F.O.S ⇒ 𝑞 𝑠 = 129.34/3 ⇒ 𝒒 𝒔 = 43.116 T/m2.
𝑞 𝑛𝑒𝑡 = 𝑞 𝑠 – q ⇒ 𝑞 𝑛𝑒𝑡 = 46.116 – (1.8) (1) ⇒ 𝒒 𝒏𝒆𝒕 = 41.316 T/m2.
CASE-III: 1.0m x 1.0 m circular footing
qu = , qs = , qnet = , When,  = 36o, Nq = 49.5, N = 55.9.
For Circular footing, Sc = 1.3, S = 0.6
𝑞 𝑢 = 𝑆 𝐶 𝐶𝑁𝐶 + 𝑞𝑁𝑞 +
1
2
𝛾𝑁𝛾 𝐵𝑆 𝛾
𝑞 𝑢 = 1.8(1.0) (49.5) +
1
2
(1.8) (1) (55.90) (0.6) ⇒ 𝑞 𝑢 = 119.286 T/m2
𝑞 𝑠 = 𝑞 𝑢/F.O.S ⇒ 𝑞 𝑠 = 119.286/3 ⇒ 𝒒 𝒔 = 39.762 T/m2.
𝑞 𝑛𝑒𝑡 = 𝑞 𝑠 – q ⇒ 𝑞 𝑛𝑒𝑡 = 39.762 – (1.8) (1) ⇒ 𝒒 𝒏𝒆𝒕 = 37.962 T/m2. Ans.
EXAMPLE 2: What will be ultimate Bearing capacity of a soft sensitive clay, in which, when
a vane shear test was conducted (vanes of 10 cm height & 8 cm diameter), the soil
failed at a maximum Torque of 500 kg / cm. consider a footing of square shape and

14. density of soil as 1.7 gm/cm3. Use Terzaghi’s Theory.
Given Data: 𝜏 = 500 kg/cm =
500
1000
×
1
100
= 0.005Tm.
Height of vane H = 10 cm = 0.1 m. Diameter of vane D = 8 cm = 0.08 m
Density of soil δ = 1.7 g/cm3 = 1.7 T/m3. Df = 1.0 m (assumed).
Required: qult = ?. qs =?
C =
𝑇
𝜋𝐷2(
𝐻
2
+
𝐷
2
)
= 2.762. C’ = 2/3C = 1.84.
Ø = 0 (Soft clay), Nγ = 0, Nc = 5.7, Nq = 1.0.
𝑞 𝑢 = 𝑆 𝐶 𝐶𝑁𝐶 + 𝑞𝑁𝑞 +
1
2
𝛾𝑁𝛾 𝐵𝑆 𝛾
qu = (1.3 x 1.84 x 5.7) + (1.7 x 1 x 1.0), 𝒒 𝒖 = 15.33 T/m2
𝑞 𝑠 = 𝑞 𝑢𝑙𝑡/F.O.S ⇒ 𝑞 𝑠 = 15.33/3 ⇒ 𝒒 𝒔 = 5.11 T/m2.
EXAMPLE 3: What will be the maximum safe load for Υ is 1.6 T/m3 , Φ is 27° , footing size is
2.5 x 2.5 m , Df is 1.5 m and the soil is loose sand?
Solution: For Local Shear Failure and Φ = 27° we have from chart,
N’c = 17.0 , N’q = 7.0 , N’Υ = 4.0
qult = 1.3CN’c + ΥDN’q + 0.4ΥBNΥ’
= (1.3) (0) (17) + (1.6) (1.5) (7) + (0.4) (1.6) (2.5) (4) = 23.2 T/m2
qs = Qult/3 = 23.2/3 = 7.73 T/m2.
Safe Load = 7.73 x 2.5 x 2.5 = 48.33 T
EXAMPLE 4: A strip fisting 1m wide at its base, at a depth of 0.8m, r=18t/m, c = t/m, angle =
20 degree. If n/T is 1.5m below the ground surface find out bearing capacity of soil.
Solution: As angle <28 Df = 0.8m, So it is a local shear failure.
When the ground water table is located at a depth below the foundation less than width of
foundation then we will use the equation;
qu = C’Nc + Qn’v + 1/2BN’r rav, Where rav = 1/B{rD + r’(B - D)](for D<B)
C’ = 2/3C = 2/3*3 = 2T/m
Angle = 1/tan(2/3tan angle) = 13.63o and, Nc’ = 0.86 Nq’ = 230 Nr’ = 0.75 * (0.8)
So, qu = (2) (0.86) + (1.8) (2.30) + (0.5) (1) (0.75)*1/1[(1.68 * 0.7) + (1/2.31)(1 - 0.7)
qu = 21.644T/m.
EXAMPLE 5: A strip footing of width 3m is founded at a depth of 2 m below the ground
surface in a (C-Ø) soil having γ = 18 KN/m3, C= 30 KPa, Ø = 36°. Determine the
ultimate bearing capacity of soil by Rankine method.
Solution: According to Rankine method;
q =
1
4
× 𝛾 × 𝐵√N∅(𝑁∅2
− 1) + 2𝐶√∅(𝑁∅ + 1) + 𝛾𝐷𝑁∅2
Where, NØ = tan2 (45 + Ø/2). NØ = tan2 (45 + 36/2) = 3.85o.
qu = ¼ × 18 × 3 × √3.85 (14.83 − 1 ) + (2 × 30)√3.85 (3.85 + 1) + (18 × 2)(3.85)2
qu = 1471.20 KN/m2.
EXAMPLE 6: A square footing of size 3 x 3 m rests at a depth of 2 m in medium dense sand.

15. The water table is at the base level of the footing. The corrected average SPT value is
30 for the soil below the base for a depth equal to the width of foundation. Compute
the net ultimate bearing capacity of soil by Teng’s Method.
Solution: N = 30 , B = 3 m , D = 2 m, Rw = 1.0 , R’w = 0.5.
qult = 0.32 [N2 B Rw + 3(100 + N2)D R’w ] = 0.32 [(30)2 (3) (1) + 3(100 + (30)2) (2) (0.5) ]
= 0.32 [ 2700 + 3000]. qult = 1824 KN/m2.
EXAMPLE 7: At what depth should a raft of size 6 * 9 m be founded to provide a factor of
safety 3, if the soil is stiff clay having an unconfined compressive strength of 120
KN/m2. The unit weight of the soil is 18 KN/m3. The pressure transferred by the raft
to its base is 150 KN/m2.
Given Data: Rectangular footing = 6 * 9 m, F.O.S. = 3, qu = 120 KN/m2,
γ = 18 KN/m3, qs = 150 KN/m2, Ø = 0˚ (for stiff clay), Df = ?
Solution: tanØ' = ⅔(tanØ) = 0 → Ø' = 0o
for Ø' = 0; Nc' = 5.7, Nq' = 1, Nγ = 0
For rectangular footing, Sc = 1 + .2 (B/L) = 1 + .2 (6/9) = 1.13.
c = qu/2 = 120/2 = 60 KN/m2. c’ = ⅔ (c) = ⅔ x 60 = 40 KN/m2.
𝑞 𝑢𝑙𝑡 = 𝑞 𝑠 x F.O.S = 150 x 3 = 450 KN/m2. 1 + .3 (B/L) = 1 + .3 (6/9) = 1.2.
Again using formula,
qult = Scc' Nc'[1 + .3 (B/L)] + 𝛾DfNq' + ½γBNγ'Sγ = (1.13 × 40 × 5.7 × 1 .2) + (18 × Df x 1) + 0.
= 309.17 + 18 Df. or, Df = (450 – 309.17)/18 = 140.83/18 = 7.82 m.
EXAMPLE 8: A strip footing, 1m wide at its base, at a depth of 0.8m, γ = 1.8 T / m2, C = 3
T/m2, Ø = 20, if W/T is 1.5m below the ground surface, find out bearing capacity of soil.
Given data: B = 1m, Df = 0.8m, γ = 1.8 T/m, C = 3 T/m2, Ø = 20.
Solution: Nc = 17.5 , Nq = 7.4 , Nγ = 5, Sc = 1 , Sγ = 1.
qult = Sc CNc + γDfNq + 0.5γBNγSγ
= 1(3) (17.5) + (1.8) (0.8) (7.4) + (0.5) (1.8) (1) (5) (1), qult = 67.656 T/m2.
FOOTING DESIGN PROBLEMS:
PAVEMENTS AND ITS TYPES
PAVEMENT: Highway pavement is a structure consisting of superimposed layers of selected and
processed materials whose primary function is to transmit loads to the sub-base and underlying
soil. It is a structure which separates the tires of vehicles from the under lying foundation.
TYPES OF PAVEMENT
1. FLEXIBLE PAVEMENT: Flexible pavement consists of a mixture of asphaltic or bituminous
material and aggregates placed on compacted granular material in layers over the sub-grade. A
flexible pavement distributes load to the sub-grade and depends on aggregate interlocking,
particle friction and cohesion.
STRUCTURE OF FLEXIBLE PAVEMENT

16. Typical flexible pavement structure consists of:
i. SURFACE COURSE; This is the top layer and the layer that comes in contact with traffic and
normally contains the high quality materials. It provides characteristics such as friction,
smoothness and drainage. In addition, it also prevents the entrance of excessive quantity of
surface water into the underlying layers. Surface Course is sometimes subdivided into two
layers:
 Wearing Course: This is the layer in direct contact with traffic loads. The wearing course can
be rehabilitated before distress propagates into the underlying intermediate/blinder course.
 Intermediate/Binder Course: This layer provides the bulk of the Hot Mix Asphalt (HMA)
structure. Its main function is to distribute load.
ii. BASE COURSE: This is the layer directly below the surface course and generally consists of
aggregates. It provides additional load distribution and contributes to drainage and frost
resistance. Base courses are usually constructed of:
 Aggregates: Base courses are most typically constructed from durable aggregates that will not
be damaged by moisture or frost action. Aggregates can be either stabilized or un-stabilized.
 HMA: In certain situations where high stiffness is desired, base courses can be constructed
using a variety of HMA mixes. It usually contains larger aggregate sizes, more graded and is
subjected to more moderate specifications.
iii. SUB-BASE COURSE: This is the layer under the base course and is not always needed. The
sub-base course is between the base course and the sub-grade. A pavement constructed over a
low quality soil such as clay may require the additional load distribution characteristic that a
sub-base course can offer. Its primary functions are:  Improves drainage,  Minimize frost
action damage,  Provides a working platform for construction.
iv. SUB-GRADE: The sub-grade is the material upon which the pavement structure is placed. It
provides support to the overlying structure. If it is of good quality then base course can be
laid after its compaction without providing sub-base otherwise if it is poor then a sub-base
layer should be included.
2. RIGID PAVEMENT: A rigid pavement is constructed from cement concrete or reinforced
concrete slabs. Rigid pavements are those, which reduces the stress concentration and
distributes the reduced stresses uniformly to the area under the slab. Rigid pavements contain
sufficient strength to be able for sub-grade failures and areas of insufficient support.
STRUCTURE OF RIGID PAVEMENT

17. The typical rigid pavement structure consists of:
i. SURFACE COURSE; This is top layer which comes in contact with traffic load and normally
constructed of PCC or RCC. It provides characteristics such as friction, smoothness and
drainage. In addition, it also prevents the entrance of excessive quantity of surface water into
the underlying layers. The surface course can vary in thickness but is usually between 6 inches
for light loading and 12 inches for heavy loads.
ii. BASE COURSE: This is the layer directly below the surface course and generally consists of
aggregates. It provides additional load distribution and contributes to drainage and frost
resistance. Base courses are usually constructed out of:
 Aggregates base: A simple base course of crushed aggregates is a common option since the
early times and is still used in many situations.
 Stabilized aggregate or soil: Stabilizing agents are used to bind loose particles to one another
and provides strength and cohesion. Cement treated bases (CTB s) can be built to as much as 20
- 25 percent of the surface course strength.
 Dense-graded HMA: In situations where high base stiffness is desired, base courses can be
constructed using a dense-graded HMA layer.
 Permeable HMA: In certain situations where high base stiffness and excellent drainage is
desired, base courses can be constructed using an open graded HMA.
 Lean concrete: It contains less Portland cement paste than a typical PCC and is stronger than
stabilized aggregates. Lean concrete bases (LCB s) can be built to as much as 25 - 50 percent of
the surface course strength which requires construction joints.
iii. SUB-BASE COURSE: This is the layer under the base course and is not always needed. The
sub-base course is between the base course and the sub-grade. A pavement constructed over a
low quality soil such as clay may require the additional load distribution characteristic that a
sub-base course can offer. It functions primarily as structural support but it can also:
 Improves drainage,  Minimizes frost action damage,
 Provides a working platform for construction.
iv. SUB GRADE: Sub grade provides support to the overlying structure. If it is of good quality
then base course can be laid after its compaction without providing sub-base otherwise if it is
poor then a sub-base layer should be included.

18. STRUCTURAL DETAILS OF RIGID AND FLEXIBLE PAVEMENTS:
COMPOSITION AND STRUCTURE OF RIGID PAVEMENT
Rigid pavements support loads through rigidity and high modulus of elasticity of concrete slab.
The loads will distribute to natural soil layer through different layers of rigid pavement. The
composition and structure of rigid pavement tells us about the function of each layer of rigid
pavement as explained below.
COMPOSITION OF RIGID PAVEMENT
In general, Portland cement concrete is used as primary structural element for rigid pavement.
The reinforcement is provided in the slab depending upon the soil strength and loading
conditions. Pre-stressed concrete slabs can also be used as surface course. The concrete slab
usually lies on a compacted granular or treated subbase, which is supported, in turn, by a
compacted subgrade.
Better results of pavement are obtained when the support layers under the pavement are
uniform. The strength of rigid pavement is Rigid pavement is mostly depending upon the
concrete slab so, it should be laid strongly while the bottom layers are constructed using low
cost materials to make it economical.
Fig 1: Transfer of Wheel Load to Subgrade in Rigid Pavement
STRUCTURE OF RIGID PAVEMENT: The structure of a rigid pavement consists following layers.
• Concrete slab or surface course, • Granular base or stabilized base course.
• Granular subbase or stabilized subbase course, • Frost protection layer, • Subgrade soil.
Fig 2: Typical Rigid Pavement Structure
• Concrete Slab: The concrete slab is the top most layer of rigid pavement which is in direct
contact with the vehicular loads. This is also called as surface course. It is water resistant and

19. prevents the water infiltration into the base course. It offers friction to the vehicles to provide
skid resistance. The thickness of concrete slab is kept between 150 mm to 300 mm.
Fig 3: Concrete Slab Laying
• Granular Base or Stabilized Base Course: The base course or granular base or stabilized base
is the second layer from the top and is constructed using crushed aggregates. This course helps
the surface course to take additional loads. It provides stable platform to construct rigid
pavement. It is also useful to provide sub surface drainage system. In frost areas, the frost
action can be controlled by the stabilized base course. It helps to control swelling of subgrade
soil. The base course thickness should be minimum 100mm.
Fig 4: Providing Base Course
• Granular Subbase or Stabilized Subbase Course: It is the third layer from the top and is in
contact with the subgrade soil and base course. It is constructed by using low quality
aggregates than the base course but they should be better quality than subgrade.
Generally, subbase course is not required when the traffic loading is light. When the loading
exceeds 100000 pounds it should be constructed. Its primary function is to provide support for
the top layers and it also serves as frost action controller and prevents the intrusion of fines
from subgrade to top layers. The drainage facility will also improve when there is a subbase
course.

20. Fig 5: Laying of Subbase Course
• Frost Protection Layer: In low temperature regions there is a problem of frost action on the
pavements. If the soil contains high ground water table, during low temperatures the water will
freeze and frost heave will have formed under the subgrade which will cause the pavement to
rise because of non-uniform formation of ice crystals.
Similarly, when the ice melts the pavement will penetrate into the subgrade when load comes
on it. To overcome this frost protection layer should be provided. Generally, a good base course
and subbase course themselves acts as frost protection layers.
Fig 6: Formation of Ice Crystals in Frost-Susceptible Soil
• Subgrade Soil: The subgrade is nothing but the existing soil layer which is compacted using
equipment to provide stable platform for rigid pavement. The subgrade soils are subjected to
lower stresses than the top layers since the stresses will reduce with depth.
Subgrade soils may vary considerably. The stresses coming from the top layers is received by
different soils in different manners. Some soils may resist them and some may not. It is
depending upon the interrelationship of texture, density, moisture content and strength of
subgrade. So, proper examination should be done on subgrade before construction.
At the same time the pavement layers above the subgrade should be capable of reducing
stresses imposed on the subgrade soil to prevent the displacement of subgrade soil layers.
Fig 7: Preparing Subgrade Soil

21. FLEXIBLE PAVEMENT COMPOSITION AND STRUCTURE
The composition and structure of flexible pavement consists of surface course, binder course,
base course, subbase course, frost protection course, subgrade. Flexible pavements contain
bitumen or asphalt layer as wearing course and supports loads through bearing. They have low
flexural strength.
COMPOSITION AND STRUCTURE OF FLEXIBLE PAVEMENT
Fig 1: Layers of Flexible Pavement
1. Surface Course: Surface course or wearing course is the top most layer of flexible pavement
which has direct contact with the vehicular loads. Since it is directly in contact with traffic, good
quality aggregates and high dense bitumen or asphalt is recommended for the construction of
surface course. The main function of surface course is to provide skid-resistance surface,
friction and drainage for the pavement. It should be water tight against surface water
infiltration. The thickness of surface course generally provided is 25 to 50 mm.

22. Fig 2: Surface Course
2. Binder Course
Binder course is also constructed using aggregates and bitumen but with less quality than
materials used for surface course. In general, its thickness is about 50 to 100 mm.
If economy is not a problem, binder course and surface course can be constructed
monotonically using good quality materials with 100 to 150 mm thickness. The function of
binder course is to transfer the loads coming from surface course to the base course.
Fig 3: Binder Course
3. Base Course: The base course is important layer of pavement structure and it distributes the
loads from top layers to the underneath Subbase and sub-grade layers. It provides structural
support for the pavement surface. It is constructed with hard and durable aggregates which
may either stabilized or granular or both.
The thickness of base course must be great enough to reduce the load capacity on sub-grade
and Subbase courses. The minimum base course thickness recommended is 100 mm. sub
surface drainage system can be provided with in the base course.
Fig 4: Laying Base Course
4. Subbase Course: The Sub-base course is provided beneath the base course and it also
functions as same as base course. If the sub-grade soil is strong and stiff, then there is no need

23. to sub-base course. Granular aggregates are used to construct sub-base course. If sub-grade is
weak minimum 100 mm thick sub-base course should be provided.
Fig 5: Laying Sub-Base Course
5. Frost Protection Layer: Frost protection layer is provided for the pavements in colder regions
where temperatures are very low. It is generally provided between Subbase and sub-grade soil.
The function of frost protection layer is to prevent damage of pavement from frost heaves,
which are formed by freezing of groundwater. A good quality base course and Sub-base courses
provided can also serves frost protection layer.
6. Subgrade: Subgrade is the bottom most layer which is nothing but natural soil layer
compacted up to required depth generally about 150 to 300 mm to receive the loads coming
from top layers. This layer is termed as foundation for the pavement system.
The sub-grade should be strong enough to take the stresses and also it is important to keep the
stresses coming from top layers should be within the limit of sub-grade capacity. To reduce the
amount of stress on soil sub-grade, provide thick layers of base course, Sub-base course and
surface course.
Fig 6: Compacting Sub-grade
Apart from the above layers, three types of coats or finishes are provided in flexible pavement
system which are as follows: • Seal Coat, • Tack Coat, • Prime Coat.

24. a. Seal Coat: Seal coat is provided directly on the top of surface course to make it watertight
and to provide skid resistance to the surface. Mixture of Emulsified asphalt, mineral fillers and
water is used as seal coat material.
Fig 7: Seal Coat
b. Tack Coat: Tack coat is provided on the top of binder course to develop strong bond between
the binder course and surface course. Asphalt emulsion diluted with water is used as tack coat
material.
c. Prime Coat: Prime coat is provided between base course and binder course to develop strong
and water tight bong between them. Low viscous cutback bitumen is sprayed on the top of
base course as prime coat material.
STRESS CONSIDERATIONS
Different types of stresses tend to result in deformation of the concrete slab which
causes tensile, compressive and flexural stresses of varying magnitude. The main stresses
in rigid pavements are:
i. WHEEL LOAD STRESSES: Stresses in concrete pavements vary with position of the wheels at
any given time. Therefore, each slab should be analyzed at all points and most severe stresses
evaluated are used for design purpose. Westergaard examined three critical conditions of
loading i.e.:  Corners (Tension at the top),  Edges (Tension at the bottom),
 Interior of the Slab (Tension at the bottom).
ii. TEMPERATURE AND MOISTURE STRESSES: If a pavement slab is subjected to temperature
gradient through its depth, its surface will tend to deform. The tendency to deform is restrained
by the weight of slab itself. These stresses develop due to differential changes in the top and
bottom surfaces of the slab.
iii. STRESSES DUE TO FRICTION: If the slab is free to move (i.e. no friction between the slab and
the sub-grade) stresses will not result. However, if friction exists between the slab and the sub-
grade, stress can result from the friction forces. Stresses in concrete slabs resulting from friction
on the sub-grade vary with slab length.
iv. COMBINED STRESSES: Stresses resulting due to both, wheel load and friction are called
combined stresses.

25. PAVEMENT DESIGN PRINCIPLE:
1. FUNDAMENTAL PARAMETERS: Following are the fundamental parameters to be considered:
i. Wheel loads
ii. Design Factors:  Design of paving mixtures,  Structural design of pavement components.
iii. Types of Distress:  Structural distress,  Functional distress.
iv. Stresses:  Stresses in flexible pavements,  Stresses in rigid pavements.
v. Vehicle and Traffic considerations:  Equivalent Axle Loads,  Equivalent Single-Wheel Loads.
vi. Climate and Environment:  Frost heave,
 Loss of strength during frost modeling,  Permafrost.
vii. Economic Factors
viii. Design Strategies.
2. SECONDARY PARAMETERS: Following are the secondary parameters of pavement design.
i. Soil Classification:  Soil horizons,  Parent materials,  Moisture-solid relationship.
ii. Material Characterization
iii. Materials Considerations
iv. Surfaces:  Functions,  Types of materials,  Skid qualities,  Cracking.
v. Soil and Base Stabilization
vi. Base and Sub base Courses:  Feasibility,  Grading,  Construction.
vii. Sub-grades Strength Studies:  Compaction,  Strength-Density-Moisture Considerations.
STEPS FOR PAVEMENT DESIGNING:
Before going to design the pavement we must know the structure of pavement:
i. Calculate total thickness (T) by different charts
ii. Calculate the thickness of sub-base course (tsb)
iii. Calculate thickness of base and surface course (tb & ts) by:
Thickness of surface and base course = total thickness – sub-base thickness
= T – tsb
iv. Then we can easily calculate the value of thickness of the base course,
Tb = T – tsb - ts
Steps in design process include:
i. Review Pavement Management Data to determine the appropriate scope of work
and treatment type.
ii. Evaluate existing pavement to confirm the scope of work and determine preliminary
design and appropriate construction strategy.
 Research roadway history and traffic data
 Perform field trips to make site inspections
iii. Evaluate sub-base and sub-grade for drainage characteristics and bearing capacity.
iv. Make structural calculations like the traffic, soils and existing pavement data.
v. Set specifications such as pavement materials, construction methods and finished
project requirements.
vi. The Designer must ensure that plans, specifications and estimate are clearly defined.

26. PAVEMENT DESIGN METHODS
1. GROUP INDEX METHOD: Group Index method of pavement design is an empirical method
which is based on the physical properties of soil sub-grade. Group Index is number assigned to
the soil based on its physical properties like particle size, Liquid limit and plastic limit. It varies
from a value of 0 to 20, lower the value higher is the quality of sub-grade. By sieve analysis test
we can determine Group index value of soil sub grade from below equation:
GI = 0.2a + 0.005 ac + 0.01bd
Where,
a = percentage of soil passing 0.074 mm sieve in excess of 35 per cent, not exceeding 75
b = percentage of soil passing 0.074 mm sieve in excess of 15 per cent, not exceeding 55
c = Liquid limit in per cent in excess of 40
d = Plasticity index in excess of 10
In G.I. method for designing of pavement, the thickness of pavement depends upon
the G.I. and the type of traffic.
Type of Traffic Commercial Vehicles per day
Light traffic volume <50
Medium traffic volume 50 to 300
Heavy traffic volume >300
2. CALIFORNIA BEARING RATIO METHOD: CBR method is used to determine total thickness of
pavement. California Bearing Ratio (CBR) is a penetration test, wherein a standard piston,
having an area of 3 in2 is used to penetrate soil at a standard rate of 0.05 inch per minute. The
pressure at each 0.1-inch penetration is recorded and its ratio to bearing value of standard
crushed rock is termed as the CBR. Data required for flexible pavement design is:
 CBR value of soil subgrade,  CBR value of sub base course.
 CBR value of base course,  Wheel load in KG or KN.
Wheel load is classified into three groups based on traffic conditions:
 Light traffic (3175 KG),  Medium traffic (4082 KG),  Heavy traffic (5443 KG).
3. AASHTO DESIGN METHOD: The basic objective is to determine significant relationship
between no. of repetition of specified axle loads and performance of different thickness of
pavement layers. The design is based on the equivalent 80kN single-axle load. The original
equation is applicable only to the specific environmental and soil conditions. To make it
applicable to other areas of the nation, the equation is modified by introducing an effective
roadbed soil resilient modulus M R and two drainage coefficients m2 and m3 for granular base
and sub base, respectively. This equation is widely used and has following form:
Log10(𝑊18) = 𝑍 𝑟 × 𝑆 𝑜 + 9.36 × log10
(𝑆𝑁 + 1) − 0.20 +
{log10 (
∆𝑃𝑆𝐼
4.2
− 1.5)}
0.4 + {1094/(𝑆𝑁 + 1)5.19}
+2.32 × Log10(𝑀 𝑅) − 8.07
Where, W18 = predicted number of 80 kN (18,000 lb.) ESALs
Zr = standard normal deviation
So = combined standard error of traffic prediction and Performance prediction

27. ΔPSI = difference between initial design serviceability index po, and design terminal
Serviceability index pt.
MR = sub-grade resilient modulus (in psi)
SN = Structural Number (an index that is indicative of total pavement thickness
Required) which can be calculated by:
SN = 𝑎1 𝑑1 + 𝑎2 𝑑2 𝑚2 + 𝑎3 𝑑3 𝑚3 + ………..
 ai = ith layer coefficient
 di = ith layer thickness (inches)
 mi = ith layer drainage coefficient
FUNDAMENTAL AND SECONDARY APPROACHES TO PAVEMENT DESIGN:
DESIGN APPROACHES: For flexible pavements, design is mainly concerned with determining
appropriate layer thickness and composition. The main design factors are stresses due to traffic
load and temperature variations. Two approaches of flexible pavement structural design are
common today:
1. EMPIRICAL APPROACH OF DESIGN OF PAVEMENTS:
EMPIRICAL APPROACH OF PAVEMENT DESIGN: An empirical approach is based on results of
experiments or experience. Generally, it requires a number of observations to be made to
determine the relationships between input variables and outcomes.
Many pavement design procedures use an empirical approach. Empirical design methods can
range from simple to complex pavements. The simplest approaches specify pavement
structural designs based on what has worked in the past. More complex approaches are usually
based on empirical equations derived from experimentation.
2. MECHANICAL EMPIRICAL APPROACH OF DESIGN OF PAVEMENTS:
MECHANISTIC-EMPIRICAL APPROACH OF PAVEMENT DESIGN: One of the significant changes
with this approach is that, the empirical approach has effectively reversed. In empirical design
methods, various inputs are considered and are use to produce design requirements While in
mechanistic-empirical, design of pavement structure is initially assumed on a trial basis, along
with inputs for traffic and climate.
This method requires the determination of critical stress, strain or deflection in the pavement
by some mechanistic methods and the calculation of resulting damages by some empirical
failure criteria. The failure criterion that is used most commonly for the design of flexible
overlays are fatigue cracking and permanent deformation, but for rigid overlays only fatigue
cracking is considered.
First, the condition or remaining life of existing pavement must be evaluated. Based on the
pavement condition or remaining life, the thickness of overlay is determined so that damages
will be within the allowable limits.
AXLE LOADS
One of the primary functions of a pavement is its load distribution. Therefore, in order
to adequately design a pavement something must be known about the expected loads it
will carry during its design life. Loads, the vehicle forces exerted on the pavement can be

28. characterized by the following parameters:  Tire loads,  Axle and tire configurations,
 Repetition of loads,  Distribution of traffic across the pavement,  Vehicle speed.
STANDARD AXLE LOAD: An axle carrying a load of 18,000 lbs (8160 kg) was defined in the
AASHTO road test as a Standard Axle, with a damaging effect of unity.
EQUIVALENT STANDARD AXLE LOAD: This approach converts wheel loads of various
magnitudes and repetitions to an equivalent number of "standard" or "equivalent" loads based
on the amount of damage to pavement. The commonly used standard load is the 18,000 lb.
Using the ESAL method, all loads are converted to an equivalent number of 18,000 lb. A "Load
Equivalency Factor" represents the equivalent number of ESAL’s:
Load Equivalency Factor (L.E.F) = (Tons/8.2 tons)4.

29. PAST PAPERS
DIFFERENCE BETWEEN SHALLOW AND DEEP
SHALLOW:  Light, flexible structure: older residential construction which include a basement,
and in many commercial structures etc.  Nice soil condition: hard, uniform soil,
 Cheaper than deep foundation,  Easier construction.
DEEP:  Heavy, rigid structure such as large bridge, tower etc.  Poor soil condition:
liquefaction, soft clay and sands,  Typically more expansive,
 More complex to construct and more time than shallow foundation.
DIFFERENCE BETWEEN FLEXIBLE AND RIGID PAVEMENTS
1. In flexible pavements load distribution is primarily based on layered system. While,
in case of rigid pavements most of the load carries by slab itself and slight load goes
to the underlying strata.
2. Structural capacity of flexible pavement depends on characteristics of every single
layer. While, structural capacity of rigid pavement depends on the characteristics of
concrete slab.
3. In flexible pavements, load intensity decreases with the increase in depth. While
in case of rigid pavement, maximum intensity of load carries by concrete slab itself.
4. In flexible pavement deflection basin is very deep because of its dependency on the
underlying layers. While in case of rigid pavement, deflection basin is shallow.
5. Flexible pavement has very low modulus of elasticity (less strength). Modulus of
elasticity of rigid pavement is very high, because of high strength concrete and more
loads bearing capacity of the pavement itself.
SEAL COAT: Sealcoat is a liquid that is applied to asphalt to protect it from oxidation and the
damage caused by winter cracking, as well as UV rays and traffic. It provides:
 A waterproof layer to protect the underlying pavement.
 Increased skid resistance.
 A filler for existing cracks or raveled surfaces.
 An increased reflective surface for night driving.
TACK COAT: A tack coat is sprayed on the surface of an existing asphalt or concrete pavement.
The goal is to achieve uniform coverage over the entire surface. It is also used to seal
together layers of precast concrete (PCC). Tack coats should be applied uniformly across
the entire pavement surface.
PRIME COAT: A prime coat is an application of a low viscosity asphalt to a granular base in
preparation for an initial layer of asphalt. The principal function of prime coat is to protect
the sub-grade from moisture and weathering. The purpose of the prime coat is:
 to coat and bond loose material particles on surface of base
 to harden base surface to provide work platform for construction equipment
 to avoid voids in base course surface to prevent migration of moisture
 to provide adhesion between base course and succeeding asphalt course
DIFFERENTIAL SETTLEMENT: Differential settlement occurs when the soil beneath structure

30. expands, contracts or shifts away and foundation settles unequally. This can be caused by
drought conditions, the root systems of maturing trees, flooding, poor drainage, frost,
vibrations from nearby construction or poorly compacted soil. Differential settlement can
cause:  cracks in a structure’s foundation and interior walls,  bulging walls,  leaking through
openings and sunken slabs,  Bending and deflection of structure supported by foundation.
TOTAL SETTLEMENT: When foundation settlement occurs at the same rate throughout all
portions of a building, it is termed total settlement. If the settlement is total, the structural
failure will not take place. However, if total settlement is very excessive than its function is
impaired. For example, utility services such as water supply and sewage lines, electric and
telephone poles etc. may not function properly even the structure remain sound structurally.
STRAP FOOTING: When the independent footings of two columns are connected by a beam, it
is called a strap footing. It is used when the distance between columns is so great that a
combined footing becomes quite narrow, with high bending moments. In this case the column
is provided with its independent footings and a beam is used to connect the two footings.
PILE GROUP: Group of piles means when we have more than 1 pile in a row. Many factors
influence the pile group stability. The major factors are Geometry of group, soil conditions
and direction of loads.
TRAFFIC REGULATION AND CONTROL: Road traffic regulation and control involves directing
vehicular and pedestrian traffic thus ensuring the safety of emergency response teams,
construction workers and the general public. Traffic control also includes use of CCTV and other
means of monitoring traffic by local or state roadways authorities.
Traffic control devices are markers, signs and signal devices used to inform, guide and control
traffic, including pedestrians, motor vehicle drivers and bicyclists. These devices are usually
placed adjacent, over or along the highways, roads, traffic facilities and other public areas that
require traffic control.
TRAFFIC SIGN: Traffic signs are signs which use words and/or symbols to convey information to
road users. These devices are made with materials that reflect light from headlights back
towards driver's eyes to achieve maximum visibility especially at night. Traffic signs can be:
 Regulatory signs are traffic signs used to convey traffic rules and regulations such as
intersection controls, weight limit, speed limit, one way, no parking and others. These signs are
generally rectangular in shape and uses white, black and/or red as primary colors.
 Warning signs are traffic signs that are used to warn road users about a potential danger.
These signs are usually diamond in shape and have black legends and borders on a yellow
background.
 Guide signs help road users navigate to their destination. These signs are generally
rectangular in shape and have white text on green backgrounds.
TRAFFIC SIGNAL: Traffic control signals are used to assign right-of-way to traffic moving in
conflicting directions at an intersection. Traffic lights feature three different lights that conveys
different meanings. The red light means the vehicle must come to a complete stop. A green
light means the vehicle may proceed when it is safe to do so. A yellow light indicates that a

31. red light will follow and vehicle drivers must stop if it is safe to do so.
PAVEMENT MARKING: Road surface markings are traffic control devices that are applied
directly to the road surfaces. They are used to guide and channel traffic by assigning lanes and
indicating stopping points at intersections. Pavement markings may be permanent or
removable.
HIGHWAY DRAINAGE: It includes collecting, transporting and disposing off surface/subsurface
water originating on or near the highway right of way or flowing in streams crossing bordering
right of way. Drainage of highway is important because water damage highway structure in
many ways. The water which are dangerous for highways are:
 Rainwater,  Groundwater,  Water body.
Merits
 It prevents erosion by runoff from the hill.
 It stop water, not allowing it to enter side drain which may cause greater discharge in side
drains.
 It remove water from the road surface.
 Prevent scour and/or washout of pavement, shoulder, better slopes, water courses and
drainage structures.
DRAINAGE METHODS
1. SURFACE DRAINAGE: Surface drainage is concerned with removing all water that is present
on the pavement surface from which it may flow into the pavement. If not removed, this water
can accumulate underneath and weaken the pavement structure. There are three primary
means used to prevent water infiltration and accumulation:
i. Impermeable pavement surface: An impermeable surface will protect the underlying sub-
grade from water sources above. Permeability surfaces are different for flexible and rigid
pavements.
ii. Slope: The pavement section should be sloped to allow rainwater to sheet flow quickly to
the edge where it is typically collected in a curb and gutter system or a roadside ditch. A
generally accepted standard is a 2 percent cross slope.
iii. Grade: The curb and gutter or roadside ditch must be properly graded to allow flow to
central collection points such as catch basins or detention ponds. A generally accepted standard
is a grade of 0.5 percent or more.
2. SUB-SURFACE DRAINAGE: Subsurface drainage is concerned with removing water that
percolates through or is contained in underlying sub-grade. This water, typically result of high
water table or specially wet weather, can accumulate under the pavement structure by two
chief means:
 Gravity flow: Water from surrounding areas can be absorbed by soil then flow by gravity to
areas underneath the pavement structure. In pavement with high air voids, water can percolate
down through the pavement structure itself.
 Capillary rise: Capillary rise is the rise in a liquid due to a upward force produced by attraction
of water molecules to soil. Capillary rise can be up to 6m or more. In general, smaller the soil

32. grain size, greater the chance for capillary rise.
TYPES OF DEEP FOUNDATION
 Pier foundation,  Well foundation,  Caisson foundation,  Pile foundation.
TYPES OF SHALLOW FOUNDATION
 Spread footing,  Combined footing,  Grillage footing,
 Stepped footing,  Mat or raft foundation.
AASHTO LOADINGS: The American Association of State and Highway Transportation Officials
(AASHTO) has a series of specifications for loadings. In general, loading depends on the type of
bridge, its location and type of traffic anticipated. AASHTO specifications also allow to represent
the truck as a single concentrated load and an uniform load.
There are two basic types of standard truck loadings described in the current
AASHTO Specifications:
 Hypothetical trucks, called the H (with two axles)
 HS (with three-axles)
The first type is a single unit vehicle with two axles spaced at 14 feet and elected as
a highway truck or H truck. The weight of the front axle is 20% of the gross vehicle weight,
while the weight of rear axle is 80% of gross vehicle weight. The second type that is HS
loading, consists of truck with semi-trailer i.e. that pull trailers are chosen as HS.
In many cases, vehicles may bounce or sway as they move over a bridge. This
motion produces an impact load on the bridge. AASHTO has develop an impact factor to
increase the live load to account for bounce and sway of vehicles:
I =
50
𝐿+125
≤ 0.3
Where, L is the span in feet.
Impact loading is intended to transfer loads from superstructure to substructure.
Impact shall not be included in loads transferred to footings or to those parts of piles or
columns that are below ground.
RETAINING WALL
Retaining walls are used to hold back masses of earth or other loose material where conditions
make it impossible to let those masses assume their natural slopes. Such conditions occur when
the width of an excavation, cut, or embankment is restricted by conditions of ownership, use of
the structure, or economy. For example, in railway or highway construction the width of the
right of way is fixed, and the cut or embankment must be contained within that width.
Similarly, the basement walls of buildings must be located within the property and must retain
the soil surrounding the basement.
Freestanding retaining walls, as distinct from those that form parts of structures,
such as basement walls, are of various types. The gravity wall retains the earth entirely by its
own weight and generally contains no reinforcement. The reinforced concrete cantilever wall
consists of the vertical arm that retains the earth and is held in position by a footing or base
slab. In this case, the weight of the fill on top of the heel, in addition to the weight of the wall,

33. contributes to the stability of the structure. Since the arm represents a vertical cantilever, its
required thickness increases rapidly with increasing height. To reduce the bending moments in
vertical walls of great height, counterforts are used spaced at distances from each other equal
to or slightly larger than one-half of the height. Property rights or other restrictions sometimes
make it necessary to place the wall at the forward edge of the base slab, that is, to omit the toe.
Whenever it is possible, toe extensions of one-third to one-fourth of the width of the base
provide a more economical solution. Which of the three types of walls is appropriate in a given
case depends on a variety of conditions, such as local availability and price of construction
materials and property rights. In general, gravity walls are economical only for relatively low
walls, possibly up to about 10 ft. Cantilever walls are economical for heights from 10 to 20 ft,
while counterforts are used for greater heights.