1. The University of Lahore Department of Civil Engineering
11/08/2019
The University of Lahore Department of Civil Engineering
GEOTECHNICAL & FOUNDATION
ENGINEERING
CE4708
Instructors
Engr. Attique ur Rehman (Section C & D)
Engr. Farhan Ali (Section A & B)
Engr. Sadia Kalsoom (Lab Part of Section A, B & D)
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2. GEOTECHNICAL & FOUNDATION ENGINEERING
Credit Hours: 2+1 = 3
Prerequisites: Soil Mechanics
Specific Objectives of course:
To enhance the skills related to baring capacity and settlement evaluation of soils.
To apply principles of soil mechanics to engineering problems pertaining to retaining structures, foundations and embankments.
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3. GEOTECHNICAL & FOUNDATION ENGINEERING
Course Outline: 1. Bearing Capacity of Soils: Definition of: gross, net, ultimate, safe and allowable bearing capacity. Methods of obtaining bearing capacity: Presumptive values from codes, from plate load test. Bearing capacity theories. Bearing capacity from SPT and CPT data. 2. Settlement Analysis: Definition, total settlement, differential settlement, angular distortion, immediate settlement. Primary and secondary consolidation settlements. Oedometer test: Determination of compression index and coefficient of consolidation, magnitude and time rate of consolidation settlement. Causes of settlement and methods of controlling settlement. Allowable total and differential settlement.

4. GEOTECHNICAL & FOUNDATION ENGINEERING
Course Outline:
3. Soil Improvement:
Basic principles, objectives and methods.
4. Slope Stability:
Types of slopes, Factors affecting stability and remedies. Types of failure.
Methods of analysis:
Ordinary methods of slices, Taylor's stability number method, Swedish circle method.
Earth and Rock Fill Dams:
Definition of an earth dam, types of earth and rock fill dams, Components of an earth dam and their functions. General design considerations and typical cross-sections.
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5. GEOTECHNICAL & FOUNDATION ENGINEERING
Course Outline:
6. Introduction to deep foundations:
Types of piles, load carrying capacity of piles, group action, negative skin friction, pile load test.
7. Soil Dynamics:
Sources of dynamic loading, spring-mass-dashpot system, application to machine foundations, liquefaction.
8. Introduction to Geotechnical Computer Software
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6. Chapter-1 Bearing Capacity of Soils
Bearing Capacity of Soils: Definition of gross, net, ultimate, safe and allowable bearing capacity. Methods of obtaining bearing capacity: Presumptive values from codes, from plate load test. Bearing capacity theories. Bearing capacity from SPT and CPT data.
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7. Chapter-1 Bearing Capacity of Soils
11/08/2019
Chapter-1 Bearing Capacity of Soils
Foundation:
The lowest part of a structure is referred to as the foundation.
Its function is to transfer the load of structure to the soil on which it is resting.
A properly designed foundation transfers the load without overstressing the soil.
Overstressing the soil can result in either excessive settlement or shear failure of the soil, both of which cause damage to the structure. Foundations are generally grouped into two categories:
A. Shallow Foundations
B. Deep Foundations
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8. Shallow Foundations
the most common (and cheapest) type of shallow foundations are
SPREAD FOOTINGS
square spread footings to support individual columns (also circular)
McCarthy, 6th Ed.

9. Strip Footings to support wall loads
McCarthy, 6th Ed.
Rectangular and Trapezoidal Footings for two columns (combined footing) or machine base
McCarthy, 6th Ed.

10. RAFT or MAT Foundations
McCarthy, 6th Ed.
To lower the bearing pressure and reduce differential settlement on soils with low bearing capacity or erratic or variable conditions

11. Deep Foundations
used when soil near surface has poor load-bearing capacity
they transmit load through weak soil strata (overburden) to stronger, load-bearing stratum (eg., bedrock, dense sand and gravel, etc.)
loose soil
bedrock

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Definitions :
Ultimate Bearing Capacity (qu):
The maximum pressure that can be supported by a soil mass without causing shear failure is termed as ultimate bearing capacity.
Safe Bearing Capacity (qs):
Ultimate bearing capacity divided by FOS is termed as Safe bearing capacity.
qs = qu/FOS
Ultimate Net Bearing Capacity (qu net):
qu net = qu - γDf
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Definitions :
Safe Net Bearing Capacity (qunet):
qs net = qs - γDf
Safe Gross Bearing Capacity (qs gross):
qs gross = qs net + γDf
Allowable Bearing Capacity (qall):
The allowable bearing capacity adopted in the design of foundation is lesser of the following two;
Safe Bearing Capacity
The maximum allowable bearing capacity that the soil can offer without exceeding the specified limits of permissible settlement.
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14. Modes of Shear failure:
When a uniformly distributed load of q per unit area is applied to the footing, it settles.
If the uniformly distributed load (q) is increased, the settlement of the footing gradually increases.
When the value of q = qu is reached, bearing-capacity failure occurs; the footing undergoes a very large settlement without any further increase of q.
The soil on one or both sides of the foundation bulges, and the slip surface extends to the ground surface.
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15. Modes of failure:
Craig, 6th Ed.

16. General Shear Failure
On low compressible (dense or stiff) soils
Heaving on both sides of foundation
Final slip (movement of soil) on one side only causing structure to tilt

17. Local Shear Failure on highly compressible soils
only slight heaving on sides
significant compression of soil under footing but no tilting

18. Punching Shear Failure
on loose, uncompacted soils
vertical shearing around edges of footing
high compression of soil under footing, hence large settlements
no heaving, no tilting

19. Methods of obtaining bearing capacity:
1. Presumptive values from codes 2. From plate load test 3. Bearing capacity theories 4. Bearing capacity from SPT and CPT data.
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20. 1. Presumptive values form codes
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21. 1. Presumptive values form codes
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2. Plate Load Test
In some cases, conducting field-load tests to determine the soil-bearing capacity of foundations is desirable.
The standard method for a field-load test is given by the American Society for Testing and Materials (ASTM) under Designation D-1194 (ASTM, 1997).
Circular steel bearing plates 162 to 760 mm in diameter and 305 mm 305 mm square plates are used for this type of test.
To conduct the test, one must have a pit of depth Df excavated.
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2. Plate Load Test
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2. Plate Load Test
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2. Plate Load Test
The width of the test pit should be at least four times the width of the bearing plate to be used for the test.
The bearing plate is placed on the soil at the bottom of the pit, and an incremental load on the bearing plate is applied.
After the application of an incremental load, enough time is allowed for settlement to occur.
When the settlement of the bearing plate becomes negligible, another incremental load is applied.
In this manner, a load-settlement plot can be obtained, as shown in Figure.
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2. Plate Load Test
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2. Plate Load Test
From the results of field load tests, the ultimate soil-bearing capacity of actual footings can be approximated as follows:
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2. Plate Load Test
For a given intensity of load q, the settlement of the actual footing also can be approximated from the following equations:
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2. Plate Load Test
Numerical Problem:
The ultimate bearing capacity of a 700-mm-diameter plate as determined from fieldload tests is 280 kN/m2. Estimate the ultimate bearing capacity of a circular footing with a diameter of 1.5 m. The soil is sandy.
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30. 3. Bearing capacity theories
Terzaghi’s Bearing-Capacity Equation
Meyerhof's Bearing-Capacity Equation
Hansen's Bearing-Capacity Equation
Vesic's Bearing-Capacity Equation
In this chapter we will only cover these two methods
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31. Terzaghi’s Bearing-Capacity Equation (1943)
Terzaghi presented a classic bearing capacity equation which is still in use in its original form and in many modified forms proposed by various researchers.
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32. Terzaghi’s Bearing-Capacity Equation (1943)
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33. Terzaghi’s Bearing-Capacity Equation (1943)
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34. Meyerhof’s Bearing-Capacity Equation (1951, 1963)
Meyerhof (1951, 1963) proposed a bearing-capacity equation similar to that of Terzaghi
but included a shape factor sq with the depth term Nq.
He also included depth factors di and inclination factors ii for cases where the footing load is
inclined from the vertical.
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35. Meyerhof’s Bearing-Capacity Equation (1951, 1963)
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36. Meyerhof’s Bearing-Capacity Equation (1951, 1963)
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37. Meyerhof’s Bearing-Capacity Equation (1951, 1963)
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38. Effect of Groundwater Table
In developing the bearing-capacity equations given in the preceding section, we assumed that the groundwater table is located at a depth much greater than the width, B, of the footing.
However, if the groundwater table is close to the footing, some changes are required in the second and third terms of BC Eqs.
Three different conditions can arise regarding the location of the groundwater table with respect to the bottom of the foundation.
They are shown in Figures and each of these conditions is briefly described next.
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Case - I
If the groundwater table is located at a distance D above the bottom of the foundation, the magnitude of q in the second term of the bearing-capacity equation should be calculated as
where γ’ = γsat - γw = effective/submerged unit weight of soil. Also, the unit weight of soil, γ that appears in the third term of the bearing-capacity equations should be replaced by γ’.
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Case - II
If the groundwater table coincides with the bottom of the foundation, the magnitude of q is equal to γDf. However, the unit weight, , in the third term of the bearing-capacity equations should be replaced by γ’.
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Case - III
When the groundwater table is at a depth D below the bottom of the foundation, q = γDf. The magnitude of γ in the third term of the bearing-capacity equations should be replaced by γav.
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Numerical Problems
A square foundation is 1.5 m X 1.5 m in plan. The soil supporting the foundation has a friction angle φ = 20°, and C =15.2 kN/m2. The unit weight of soil, γ is 17.8 kN/m3. Use Terzaghi’s and Mayerhof’s equations to determine the safe bearing capacity and safe load on the foundation with a factor of safety (Fs) of 4. Assume that the depth of the foundation (Df) is 1 meter and that general shear failure occurs in soil.
A square foundation is shown in Figure. The footing will carry a gross mass of 30,000 kg. Using a factor of safety of 3, determine the size of the footing—that is, the size of B. Use Terzaghi’s Bearing Capacity equation
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Numerical Problems
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Numerical Problems
3. A square footing is shown in Figure. Determine the safe gross load (factor of safety of 3) that the footing can carry. Use Mayerhof’s equation
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46. 4. Bearing capacity from SPT and CPT data.
To be continued in next lecture ……….
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