Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.
Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.
Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.
Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.
Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.
Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.
Bearing capacity of shallow foundations by abhishek sharma ABHISHEK SHARMA
elements you should know about bearing capacity of shallow foundations are included in it. various indian standards are also used. Bearing capacity theories by various researchers are also included. numericals from GATE CE and ESE CE are also included.
Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.
Geotechnical Engineering-I [Lec #14: Lab Compaction of Soil]Muhammad Irfan
Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.
Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.
Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.
Geotechnical Engineering-II [Lec #17: Bearing Capacity of Soil]Muhammad Irfan
Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.
Geotechnical Engineering-II [Lec #19: General Bearing Capacity Equation]Muhammad Irfan
Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.
Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.
Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.
Bearing capacity of shallow foundations by abhishek sharma ABHISHEK SHARMA
elements you should know about bearing capacity of shallow foundations are included in it. various indian standards are also used. Bearing capacity theories by various researchers are also included. numericals from GATE CE and ESE CE are also included.
Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.
Geotechnical Engineering-I [Lec #14: Lab Compaction of Soil]Muhammad Irfan
Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.
Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.
Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.
Geotechnical Engineering-II [Lec #17: Bearing Capacity of Soil]Muhammad Irfan
Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.
Geotechnical Engineering-II [Lec #19: General Bearing Capacity Equation]Muhammad Irfan
Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.
Bearing failure and its Causes and Countermeasuresdutt4190
A brief review about bearing and failure of its various parts due to other possibilities than design such as manufacturing, improper service and handling and other similar aspects.
All mat-raft-piles-mat-foundation- اللبشة – الحصيرة العامة -لبشة الخوازيق ( ا...Dr.Youssef Hammida
اللبشة – الحصيرة العامة
-لبشة الخوازيق ( الأوتاد )
لبشة الخوازيق( الأوتاد) والتربة
Mat foundation- Raft foundation
Mat- Pile Foundation
Mat & Piles Foundation-
- Do you have access to a computer program that can do a finite elements analysis?
If so, you can model the mat as a concrete plate, subdivided into finite elements, on soil
springs.
Check service load soil bearing pressures qs against the allowable soil bearing
pressure q , and design the mat for factored pressures
design of piled raft foundations. مشاركة لبشة الأوتاد الخوازيق و التربة في ...Dr.youssef hamida
Of the most important paragraphs of design should study the effect of the Joint Working Group of the falling pile and fall of the soil and find a formula and factor common reaction one between sub grade reaction smart spring worker and worker response pile reaction called spring factor smart In the case of soil subsidence greater than the drop pile will move full load
piles and breaks down to piles or mat and vice versa
In the event of high rises and soil carried acceptable but not enough for the transplant can mat- piles
Regular spacing and share the soil with piles represent the programs work as usual spring network
And the introduction of sub grade reaction as factor in mat alone as well as the added factor reaction pile at each pile
But the application of this method takes the soil report by the impact of joint work between the soil decline and fall of the stake and the coefficient of reaction and give him carrying a load of soil and allowed the pile needs
Also must make sure that the applicable tag allows participation in this way the soil and pile in the joint
Assume springs for soil and piles
getting modulus of sub grad
Regarding Types of Foundation, Methods, Uses of different types of foundation at different soil properties. Methods of construction of different types of foundation, Codal Provisions etc.
This document will help you learn an introductory part and some detailed information on Shallow Foundations. As I am presenting this document to you I wish you all a Happy learning arena. It is highly recommended for students taking a bachelor degree in Civil Engineering, also it is a good document for students who are doing final touches for their examinations.
Prepared by madam rafia firdous. She is a lecturer and instructor in subject of Plain and Reinforcement concrete at University of South Asia LAHORE,PAKISTAN.
Prepared by madam rafia firdous. She is a lecturer and instructor in subject of Plain and Reinforcement concrete at University of South Asia LAHORE,PAKISTAN.
Prepared by madam rafia firdous. She is a lecturer and instructor in subject of Plain and Reinforcement concrete at University of South Asia LAHORE,PAKISTAN.
Prepared by madam rafia firdous. She is a lecturer and instructor in subject of Plain and Reinforcement concrete at University of South Asia LAHORE,PAKISTAN.
Prepared by madam rafia firdous. She is a lecturer and instructor in subject of Plain and Reinforcement concrete at University of South Asia LAHORE,PAKISTAN.
Prepared by madam rafia firdous. She is a lecturer and instructor in subject of Plain and Reinforcement concrete at University of South Asia LAHORE,PAKISTAN.
Prepared by madam rafia firdous. She is a lecturer and instructor in subject of Plain and Reinforcement concrete at University of South Asia LAHORE,PAKISTAN.
Operation “Blue Star” is the only event in the history of Independent India where the state went into war with its own people. Even after about 40 years it is not clear if it was culmination of states anger over people of the region, a political game of power or start of dictatorial chapter in the democratic setup.
The people of Punjab felt alienated from main stream due to denial of their just demands during a long democratic struggle since independence. As it happen all over the word, it led to militant struggle with great loss of lives of military, police and civilian personnel. Killing of Indira Gandhi and massacre of innocent Sikhs in Delhi and other India cities was also associated with this movement.
The Roman Empire A Historical Colossus.pdfkaushalkr1407
The Roman Empire, a vast and enduring power, stands as one of history's most remarkable civilizations, leaving an indelible imprint on the world. It emerged from the Roman Republic, transitioning into an imperial powerhouse under the leadership of Augustus Caesar in 27 BCE. This transformation marked the beginning of an era defined by unprecedented territorial expansion, architectural marvels, and profound cultural influence.
The empire's roots lie in the city of Rome, founded, according to legend, by Romulus in 753 BCE. Over centuries, Rome evolved from a small settlement to a formidable republic, characterized by a complex political system with elected officials and checks on power. However, internal strife, class conflicts, and military ambitions paved the way for the end of the Republic. Julius Caesar’s dictatorship and subsequent assassination in 44 BCE created a power vacuum, leading to a civil war. Octavian, later Augustus, emerged victorious, heralding the Roman Empire’s birth.
Under Augustus, the empire experienced the Pax Romana, a 200-year period of relative peace and stability. Augustus reformed the military, established efficient administrative systems, and initiated grand construction projects. The empire's borders expanded, encompassing territories from Britain to Egypt and from Spain to the Euphrates. Roman legions, renowned for their discipline and engineering prowess, secured and maintained these vast territories, building roads, fortifications, and cities that facilitated control and integration.
The Roman Empire’s society was hierarchical, with a rigid class system. At the top were the patricians, wealthy elites who held significant political power. Below them were the plebeians, free citizens with limited political influence, and the vast numbers of slaves who formed the backbone of the economy. The family unit was central, governed by the paterfamilias, the male head who held absolute authority.
Culturally, the Romans were eclectic, absorbing and adapting elements from the civilizations they encountered, particularly the Greeks. Roman art, literature, and philosophy reflected this synthesis, creating a rich cultural tapestry. Latin, the Roman language, became the lingua franca of the Western world, influencing numerous modern languages.
Roman architecture and engineering achievements were monumental. They perfected the arch, vault, and dome, constructing enduring structures like the Colosseum, Pantheon, and aqueducts. These engineering marvels not only showcased Roman ingenuity but also served practical purposes, from public entertainment to water supply.
We all have good and bad thoughts from time to time and situation to situation. We are bombarded daily with spiraling thoughts(both negative and positive) creating all-consuming feel , making us difficult to manage with associated suffering. Good thoughts are like our Mob Signal (Positive thought) amidst noise(negative thought) in the atmosphere. Negative thoughts like noise outweigh positive thoughts. These thoughts often create unwanted confusion, trouble, stress and frustration in our mind as well as chaos in our physical world. Negative thoughts are also known as “distorted thinking”.
The French Revolution, which began in 1789, was a period of radical social and political upheaval in France. It marked the decline of absolute monarchies, the rise of secular and democratic republics, and the eventual rise of Napoleon Bonaparte. This revolutionary period is crucial in understanding the transition from feudalism to modernity in Europe.
For more information, visit-www.vavaclasses.com
How to Create Map Views in the Odoo 17 ERPCeline George
The map views are useful for providing a geographical representation of data. They allow users to visualize and analyze the data in a more intuitive manner.
Read| The latest issue of The Challenger is here! We are thrilled to announce that our school paper has qualified for the NATIONAL SCHOOLS PRESS CONFERENCE (NSPC) 2024. Thank you for your unwavering support and trust. Dive into the stories that made us stand out!
Unit 8 - Information and Communication Technology (Paper I).pdfThiyagu K
This slides describes the basic concepts of ICT, basics of Email, Emerging Technology and Digital Initiatives in Education. This presentations aligns with the UGC Paper I syllabus.
Students, digital devices and success - Andreas Schleicher - 27 May 2024..pptxEduSkills OECD
Andreas Schleicher presents at the OECD webinar ‘Digital devices in schools: detrimental distraction or secret to success?’ on 27 May 2024. The presentation was based on findings from PISA 2022 results and the webinar helped launch the PISA in Focus ‘Managing screen time: How to protect and equip students against distraction’ https://www.oecd-ilibrary.org/education/managing-screen-time_7c225af4-en and the OECD Education Policy Perspective ‘Students, digital devices and success’ can be found here - https://oe.cd/il/5yV
2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
This webinar will introduce you to my framework, highlighting the key competencies I identified from my research. It will also show how anybody involved in language teaching (any language, not just English!), teacher training, managing schools or developing language learning materials can benefit from using the framework.
CLASS 11 CBSE B.St Project AIDS TO TRADE - INSURANCE
Geotech Engg. Ch#05 bearing capacity
1. GEOTECHNICAL ENGINEERING - II
Engr. Nauman Ijaz
Bearing Capacity of the Soil
Chapter # 05
UNIVERSITY OF SOUTH ASIA
2. FOUNDATION
It is the bottom most structural element of
the sub structure which transmits the
structural load including its own weight on
to and / into the soil
underneath/surrounding with out casing
shear failure or bearing capacity failure
(sudden collapse) and excessive
settlement.
3. CONTACT PRESSURE
The pressure generated by the
structural loading and self weight of
the member on to or into the soil
immediately underneath is called
Contact pressure (σo).
σo = Q / A
The contact pressure is independent of
soil parameters; it depends only on the
load and the x-sectional area of the
element carrying the load.
4. Q = 1000KN
σo = Q / A
= 1000/(0.5 × 0.5)
= 4000 Kpa
A
A
0.5m
Fig # 01
0.5m
Sec A-A
5. Super-Structure and
Sub- Structure
The part of the structure which is above
the GSL and can be seen with naked eye
is known as Super-Structure.
That part of structure which is below the
GSL and can not be seen with naked eyes
is known as Sub-Structure.
7. Foundation Depth (Df)
It is the depth below the lowest
adjacent ground to the bottom of the
foundation.
Need or Purpose of a Foundation
Foundation is needed to transfer the
load to the underlying soil assuming
safety against bearing capacity failure
and excessive settlement.
8. This can be done by reducing the contact
pressure such that it is either equal to or less
than allowable bearing capacity (ABC) of soil.
i.e σo < qa.
In Fig- 1, the contact pressure under the concrete
column is 4000Kpa which is much less than 21MPa
(crushing strength of concrete) but much
greater than 200KPa (ABC) of soil and
needed to be reduced prior to transfer it to
the soil underneath the column.
The reduction can be achieved by;
9. Lateral spreading of load using a large
pad underneath the column (Fig # 02)
σo = 1000 /5 = 200Kpa = ABCof soil
The larger pad is known as Spread footing.
FLOATING FOUNDATION
Balance Partly or completely the load
added to the load removed due to
excavation is known as Floating
foundation.i.e Provide basements.
10. Types of Foundation
Foundation may be characterized as
being either “ Shallow” or “Deep”.
Shallow Foundation
Are those located just below the lowest
part of the super structure which they
support ( and get support from the soil
just beneath the footing) and a least
width generally greater than their
depth beneath the ground surface, i.e
Df / B < 1
Df = 3 m (generally)
11. Deep Foundations
Are those which extend considerably
deeper into the earth ( and get supported
from the side friction (skin friction) and / or
bottom (end bearing) and generally with a
foundation depth to width ratio (D/B)
exceeding five.
12. TYPES OF FOUNDATION
Shallow foundations may be classified
in several ways as below;
SPREAD FOOTING OR
INDIVIDUAL FOOTING
This type of foundation supports one column
only as shown below. This footing is also
known as Pad footing or isolated footing. It
can be square or rectangular in shape. This
type of footing is the easiest to design and
construct and most economical therefore.
13. For this type of footing, length to
breadth ratio (L/B) < 5.
PLAN
GSL
ELEVATION
15. CONTINUOUS FOOTING
If a footing is extended in one direction
to support a long structure such as
wall, it is called a continuous footing or
a wall footing or a strip footing as
shown below.
Loads are usually expressed in force
per unit length of the footing.
For this type of footing , Length to
Breadth ratio (L/B) > 5.
16. A strip footing is also provided for a row
of columns which are closely spaced that
their spread footings overlap or nearly
touch each other.
In such a case it is more economical to
provide a strip footing than a number of
spread footing in one line.
17.
18. COMBINED FOOTING
A combined footing is a larger footing
supporting two or more columns in one row.
This results in a more even load distribution
in the underlying soil or rock, and
consequently there is less chances of
differential settlement to occur.
While these footings are usually rectangular
in shape, these can be trapezoidal ( to
accommodate unequal column loading or
close property lines)
19.
20. STRAP FOOTING
Two or more footings joined by a beam (called Strap)
is called Strap Footing.
This type is also known as a cantilever footing or
pump-handle foundation.
This form accommodates wide column spacing's or
close property lines.
Strap is designed as a rigid beam to with stand
bending moments, shear stresses.
The strap simply acts as a connecting beam and does
not take any soil reaction.
To make this sure, soil below is dug and made loose.
21.
22. MAT OR RAFT FOOTING
A large slab supporting a number of
columns not all of which are in a straight
line is known as Mat or Raft or Mass
foundation.
These are usually considered where the
base soil has a low bearing capacity and /
or column loads are so large that the sum
of areas of all individual or combined
footings exceeds one half the total building
area ( to economize on frame costs).
23. Furthermore, mat foundations are useful in
reducing the differential settlements on
individual columns.
A particular advantage of mat for basement
at or below ground water table is to provide
a water barrier.
24.
25. SELECTION OF FOUNDATION TYPE
The selection of the type of foundation for a
given structure-subsoil system is largely a
matter of judgment/elimination based on
both an analysis of scientific data and
experience.
It is not possible to establish rigorous
regulations and detailed recommendations
for the solution of all soil problems, as the
planning and designing of foundations for
structures is more of an art than a science.
26. 1.
The type of foundation most appropriate for a
given structure depends on several factors
but commonly the principal factors are three
which are as follow:
The function of the structure and the
loads it must carry.
– Purpose of the structure i.e residential, office,
industrial, bridge etc
– Service life
– Loading number of stories, basement.
– Type i.e framed RCC, masonry, column
spacing etc.
– Construction method and schedule.
27. 2.
Sub-surface Condition.
– Thickness and sequence of soil strata
with subsoil parameters.
– GWT position and function limits.
– Presence of any underground
anomalies.
3.
The cost of foundation in
comparison with the cost of the
super structure i.e funds available
for the construction and foundation.
28. COMPARISON OF SHALLOW
AND DEEP FOUNDATIONS
Sr/No
DESCRIPTION
SHALLOW FOUNDATION
DEEP FOUNDATION
1
Depth
Df / B < 1
Df / B > 4+
2
Load Distribution
Lateral Spread
Lateral and/or Vertical
spread.
•For end bearing lateral
spread.
•For frictional vertical
spread.
•Generally both.
3
Construction
•Open pit construction.
•Easy control and the best
QA/QC.
•Less skill labour is required.
•Min. Disturbance.
•During construction
dewatering is required for
shallow GWT.
•In hole or driven
•Difficult QA/QC.
•Very skilled labour is
required.
•Max.disturbance.
•Dewatering may or may
not be required.
29. Sr/No
DESCRIPTION
SHALLOW
FOUNDATION
DEEP
FOUNDATION
4
Cost
Less as compared
with deep
foundations.
Usually 3 times or
more costly than
shallow.
5
Structural Design
Consideration
Flexural bending
Axial Compression
6
Settlement
More than that of
deep foundation.
Usually 50% of the
shallow foundation
for similar loading.
7
Environmental Suitability
Does not suit to all
environments
specially for off
shores sites.
Suitable for all
environment
including off shore.
30. CRITERIA FOR FOUNDATION
DESIGN
1.
2.
When designing foundation; there are two
criteria which must be considered and
satisfied separately.
There must be accurate factor of safety
against a bearing capacity failure in the
soil i.e soil shouldn’t fail in shear.
The settlement and particularly the
differential settlement must be kept within
reasonable limits.
31. Causes of Deformation
Deformation of an element of soil is a function
of a change in effective stress (change in
volume) not change in total stress. Various
causes of deformation of a structure are listed
as follow;
1.
2.
3.
4.
5.
Application of structural loads.
Lowering of the ground water table.
Collapse of soil structure on wetting.
Heave of swelling soils.
Deterioration of the foundation ( Sulphate attack
on concrete, corrosion of steel piles, decay of
timber piles).
32. 6. Vibration of sandy soil.
7. Seasonal moisture movement.
8. The effect of frost action.
33. DEFINITIONS OF
BEARING PRESSURE
Gross Bearing Pressure (q gross):
The intensity of vertical loading at the base
of foundation due to all loads above that
level.
2. Net Bearing Pressure: (q net):
The difference between q gross and the total
overburden pressure Po at foundation level
(i.e q net = q gross – Po). Usually q net is the
increase in pressure on the soil at
foundation level.
1.
34. 3. Gross Effective Burden Pressure (q’gross):
The difference between the qgross and the
pore water pressure (u) at foundation level.
(i.e q’gross = qgross – u).
4. Net Effective Bearing Pressure (q’net):
The difference between q’gross and the
effective over burden pressure Po at
foundation level. (i.e q’net = q’gross – Po).
5. Ultimate Bearing Pressure (qf):
The value of bearing pressure at which the
ground fails in shear. It may be expressed as
gross or net or total effective pressure.
35. 6. Maximum Safe Bearing Pressure (qs):
The value of bearing pressure at which the risk
of shear failure is acceptably low; may be
expressed as gross or net or effective pressure.
7. Allowable Bearing Pressure (qa):
Takes account the tolerance of the structure to
settlement and may be much less than qs.
8. Working Bearing Pressure (qw):
Bearing Pressure under working load. May be
expressed as gross or net or total or effective
pressure.
36. FAILURE MODES
A soil underneath any foundation may fail in
one or a combination of the following three
modes;
1. General Shear Failure.
2. Punching Shear Failure.
3. Local Shear Failure. (an intermediate mode of
failure between conditions a and b)
38. Failure usually accompanied by tilting and
failure signs are imminent around the
footing.
The soil adjacent to the footing bulges
Failure load is well defined on the load
settlement graph.
Shallow foundations on dense/hard soil
and footing on saturated NCC under undrained loading.
Relative density RD > 70%
Void Ratio < 0.55 dense.
39. PUNCHING SHEAR FAILURE
Failure Mechanism, relatively slow ,no
lateral expulsion, failure is caused by
compression of soil underneath the
footing.
40. Failure is confined underneath the footing and no
signs of failure are visible around the foundation.
No tilting the footing settle almost uniformly.
Failure load is difficult to be defined from the shape
of load-settlement graph. There is continuous
increase in load with settlement.
Foundation in and/or on loose/soft soils placed at
relatively shallow depth undergoes such type of
failure.
Footing on saturated NCC under drained loading.
RD < 20%, Void Ratio > 0.75 loose.
41. LOCAL SHEAR FAILURE
Failure is between the
General shear and
Punching shear.
Footing on saturated
NCC under drained
loading undergoes
such type of failure.
RD < 20%, Void ratio
> 0.75, loose.
42. SOURCES OF OBTAINING
BEARING CAPACITY
VALUES
1.
2.
3.
4.
5.
Building codes, official regulations and civil
engineering handbooks (Prescriptive
method).
Soil Load Test.
Laboratory Testing.
Method based on observations ( used for
embankment design).
Analytical Method (Bearing Capacity
theories)
43. BUILDING CODES
In building codes bearing capacity values
are tabulated for various type of soil. These
values are based on many years of
observation in practice as shown in table
represents presumptive (Presumed) bearing
capacity values of National Building Code
(NBC).
These values may be used for preliminary of
feasibility design.
44. MERITS AND DEMERITS OF
CODE VALUES
MERITS:
1. These values are used for preliminary
design because of their readily
availability and economy.
2. For small jobs in the areas for which the
code values have been listed, final
designs may be based on these values.
45. DEMERITS:
1. The tabulated values neglect to report the
effects of moisture, density and other soil
properties which are known to have influence
on bearing capacity.
2. The Building Codes do not indicate how and
what methods are used to arrive at these
values.
3. Effect of shape, size and depth of foundation
is ignored.
4. Values of building Codes are not usually
updated.
5. Type of structure is not taken into account.
46. PRESUMPTIVE BEARING CAPACITY VALUES
OF NATIONAL BUILDING CODE
SOIL TYPE
MAX. BEARING CAPACITY (TSF)
CLAY:
SOFT
MEDIUM STIFF
1 TO 1.5
2.5
COMPACT (FIRM)
2
HARD
5
SAND:
FINE, LOOSE
2
COARSE, LOOSE
3
COMPACT,COARSE
4 TO 6
GRAVEL:
LOOSE
4 TO 6
SAND – GRAVEL MIXTURE COMPACT
6
VERY COMPACT
10
47. SOIL TYPE
MAX. BEARING CAPACITY (TSF)
SAND-CLAY MIX., COMPACT
3
SAND-CLAY MIX, LOOSE,SATURATED
1
HARD PAN, COMPACTED OR
CEMENTED
10 to 12
ROCK:
SOFT
8
MEDIUM HARD
40
HARD
60
SEDIMENTARY ROCK:
SHALE
8 to 10
HARD SHALE
8 to 10
LIME STONE
10 to 20
SAND STONE
10 to 20
Chalk
8
IGNEOUS ROCKS:
GRANITE,LAVA,BASALT,DIORITE etc
20 to 40 to 100
48. TERZAGHI’S THEORY
Terzaghi modified the Prandtl’s theory and
presented a classic bearing capacity equation
(1943) which is still in use in its original form and in
many modified forms proposed by various
research workers.
ASSUMPTIONS:
1. Footing base is rough.
2. Footing is shallow; i.e Df / B < 1 and shear along CD is
neglected.
3. Footing is a strip footing i.e L/B > 10 and the stress
distribution is assumed to be plain.
50. In fig zone I forms wedge under the footing and moves
downward with footing. The soil in zone II and III are in state of
general shear failure and move up and away from the footing as
it moves down into the soil.
Terzaghi considered the equilibrium of the wedge ABC and
summing up the vertical forces ΣFv = 0 produced the following
equation for (c-ϕ) soil.
qult
=
c Nc
cohesion
+
q Nq
+ 0.5 γ B Nγ
overburden
Friction
Where;
qult = Gross ultimate bearing capacity including the effect of Terzaghi
overburden pressure, q = γDf
Ni = Bearing capacity factors, the values of which depends on angle of
internal friction ϕ.
51. The first term is the cohesion term and accounts
for cohesive resistance along failure surface.
The 2nd term is the surcharge term and accounts
for the resistance supplied by the mass of soil
above the base of footing.
The third term is the self weight term and accounts
for frictional resistance generated along failure
surface. The self weight is a function of the footing
width B because increasing the footing width
increases volume of soil in zone II and III, thereby
increasing the normal forces acting on the failure
surface in turn increases the resistance along the
failure surface.
52. The safe bearing capacity values are
computed by dividing the ultimate values of
gross or net bearing capacity by an appropriate
factor of safety usually 3 or more.
qs net = Safe bearing capacity = qult net / FOS
qs
= Safe gross bearing capacity
= qult net / FOS + γDf
54. Later on Terzaghi proposed shape
factors Sc and Sγ for the first and last
terms of equation to account for the
different shapes of the footings such
as circular, square, rectangular etc.
SHAPE
FACTOR
STRIP
CIRCULAR
Square
Rectangular
Sc
1
1.3
1.3
1 + 0.2 (B/L)
Sγ
1
0.6
0.8
1- 0.2 (B/L)
55. Terzaghi's bearing capacity Eq. has been modified for other types
of foundations by introducing the shape factors. The equations
are:
– Square Foundations:
– Circular Foundations:
– Rectangular Foundations:
57. M A Y E R H O F ’ S B E A R I N G CAPACITY
FACTORS
ϕ
Nc
Nq
Nγ
0
5.1
1
0
5
6.5
1.6
0.1
10
8.3
2.5
0.4
15
11
3.9
1.2
20
14.9
6.4
2.9
25
20.7
10.7
6.8
30
30.1
18.4
15.1
35
46.4
33.5
34.4
40
75.3
64.1
79.4
58. EFFECT OF GROUND WATER TABLE
If there is enough water in the soil to
develop a ground water table, and this
ground water table is within the potential
shear zone, then pore water pressure will be
present, the effective stress and shear
strength along the failure surface will be
smaller and the ultimate bearing capacity
will be reduced.
When exploring the sub-surface conditions,
we determine the current location of the
ground water table and worst case (highest)
location that might reasonably be expected
during the life of the proposed structure.
59. We have three cases that describes the
worst-case field conditions.
Case – I :
Ground water table is at or above base of footing
(Dw < D). We simply compute γ’ = γb = γ - γw
Case – II :
Ground water table is below the base of
the footing, but still within the potential
Shear zone, below the footing (D < Dw <
D+B), we interpolate γ’ between buoyant unit
weight and unit weight using,
γ’ = γ – γw [1 – (Dw – D)/ B]
60. Case # I
Ground water table
above base of
footing
Case # II
Ground water table
In this zone
Case # III
Ground water table
Deeper than D+B
61. Case – III :
Ground water table is below the
potential shear zone below the footing
(D + B < Dw ), no ground water
correction is necessary.
γ’ = γ
62. NUMMERICAL PROBLEM :
Compute the FOS against a bearing
capacity failure for the square spread
footing as shown in the figure with ground
water table at position A.
63. SOLUTION :
D = 2ft
Dw = 7ft
D + B = 6ft
D+B < Dw, so ground water Case#III applies γ’ = γ.
From the table ;
Nc = 40.40, Nq = 25.30, Nγ = 23.70 when ϕ’ = 31o
Terzaghi’s equation for square footing;
qu = 1.3×0×40.4 + 121×2×25.3 + 0.4×121×4×23.70
qu = 10,710 lb/ft2
64. q = P/A + γc D - u
q = 76000/(4×4) + (150×2) – 0
q = 5050 lb/ft2
Factor of safety = FOS = F = qult / q
F = 10,710/5050
F = 2.1
65. NUMMERICAL PROBLEM :
Compute the FOS against a bearing
capacity failure for the square spread
footing as shown in the figure with ground
water table at position B.
66. SOLUTION :
D = 2ft
Dw = 3ft
D + B = 6ft
D < Dw < D+B, so ground water Case#II applies.
γ’ = γ – γw [1 – (Dw – D)/ B]
γ’ = 121 – 62.4 [1 – (3 – 2)/ 4] = 74.2 lb/ft3
From the table ;
Nc = 40.40, Nq = 25.30, Nγ = 23.70 when ϕ’ = 31o
Terzaghi’s equation for square footing;
qu = 1.3×0×40.4 + 121×2×25.3 + 0.4×74.2×4×23.70
qu = 8936 lb/ft2
67. q = P/A + γc D - u
q = 76000/(4×4) + (150×2) – 0
q = 5050 lb/ft2
Factor of safety = FOS = F = qult / q
F = 8936/5050
F = 1.8
68. NUMMERICAL PROBLEM :
A1350KN column load is to be supported on a square
spread footing founded in a clay with Su = 150Kpa. The
depth of embedment, D will be 500mm, and the soil has a
unit weight of 18.5KN/m3.The ground water table is at a
considerable depth below the bottom of the footing.
Using FOS of 3, determine the required footing width.
Case # III applies. As ground water table is at
considerable depth below the bottom of footing.
γ’ = γ
From the table ;
Nc = 5.7, Nq = 1.0, Nγ = 0.0 when ϕ’ = 0o
Terzaghi’s equation for square footing;
qu = 1.3×150×5.7 + 18.5×0.5×1.0 + 0.4×18.5×B×0
qu = 1121 KPa
69. Factor of safety = FOS = F = qult / qa
qa = qult / F = 1121 / 3 = 374 Kpa
qa = P/A + γc D - u
374 = 1350/(B2) + (23.6×0.5) – 0
B = 1.93 m
Round up = 2m
70. STANDARD PENETRATION TEST
One of the oldest and most common in-situ test is
the Standard Penetration test.
It was developed in the late 1920’s and has been
extensively used in North and South America, UK
and Japan.
ASTM Standard D 1586.
It consists of Penetrometer having diameter 51mm
and 600mm long tube.
The penetrometer is connected to the surface with
standard rods and is hammered into the ground
with a tip hammer.
71. TEST PRODEDURE
1.
2.
3.
4.
The test procedure according to ASTM D1586 are as follow;
Drill a 60-200mm (2.5 – 8inch) diameter exploratory boring to
the depth of the first test.
Insert the SPT sampler (also known as SPLIT-SPOON
Sampler) into the boring. Shape and dimensions are shown in
the figure. It is connected via steel rods to a 63.5Kg (140lb)
hammer.
Use either rope or an automatic tripping mechanism.
Raise the hammer to a height 760mm (30inch) and allow it to
fall. This energy derives the sampler into the bottom of the
boring. Repeat the process until the sampler has penetrated a
distance of 460mm (18inch), recording the number of hammer
blows required for each 150mm (6inch) interval. Stop the test if
more than 50 blows are required for any of the intervals or if
more than 100 total blows are required.
72. 5. Either of these events is known as Refusal and is noted on
the boring logs.
6. Compute the N-value by summing the blow counts for the
last 300mm (12inch) of penetration. The blow count for the
first 150mm (6inch) is retained for reference purpose, but
not used to compute N because the bottom of the boring is
likely to be disturbed by the drilling process and may be
covered with loose soil left in the boring.
7. Extract the SPT sampler, then remove and save the soil
sample.
8. Drill the boring to the next test and repeat the same
procedure.
73.
74.
75. IMPORTANT POINTS
Soft or very loose soil typically have NValues less than 5.
Soil of average stiffness generally
have 20< N <40.
Very dense and hard soils have N of
50 or more.
Very high N-values > 75 typically
indicate very hard soil or rock.
76. What is SPT – N value??
Number of blows required to penetrate
split spoon sampler for 12inch
penetration when a standard weight of
140lbs is dropped from a standard
height of 30inches.
77. ADVANTAGES
1.
2.
3.
SPT does have at least three important
advantages over other in-situ methods.
First, it obtains a sample of the soil being tested.
This permit direct soil classification. Most of the
other methods do not include sample recovery.
It is very fast and inexpensive test.
Nearly all drill rigs used of soil exploration are
equipped to perform this test. Whereas other insitu test requires specialize equipment that may
not readily available.
78. ASSIGNMENT
A foundation 3.0m square is placed at 1.5m
below the GSL on a uniform deposit of
sandy gravel having following properties.
1.
2.
3.
4.
c’ = 0, ϕ’ = 32o γ = 19.5 KN/m³ γ’ = 10.5 KN/m³
Calculate the gross ultimate bearing capacity for
the following position of water table:
GWT well below the zone of influence.
GWT at the base of the footing.
GWT rises to the GSL.
GWT at 2m below the footing base.