Chapter 3 : problems

Problem 1:

An eccentrically loaded foundation is shown below. Use a factor of 3 and determine

the allowable load that the foundation could carry.

(the factor of safety based on the maximum stress along the base of the footing).

Solution:

1) Determine , and

The foundation is with one-way eccentricity:

Note: always take the smaller of ( , ) as effective width.

2) Calculate and

The water table level is within the depth of foundation ( ) Case

110pcf

( ) 122.4

800

15

sat

o

pcf

c psf

3 ft

7 ft

6 ft

W.T

6ft x 8ft

e=0.5ft

3) Determine Meyerhof's equation parameters

a. Bearing capacity factors

b. Shape factors

c. Depth factors

d. Inclination factors

4) Calculate ultimate bearing capacity using Meyerhof's equation

5) Find the maximum pressure

6) Find the maximum allowable load the foundation could carry

Problem 2

Refer to figure (). The shallow foundation is subjected to a centric load and

a moment. If and and the depth of foundation is , determine

the allowable load the foundation can carry if:

water table level lies at 8ft under ground level?

water table level lies at 5ft under ground level?

Use a factor of safety of 4. For the soil, given: unit weight, ; friction

angle, ; cohesion,

Solution:

( )

115

122

0

35

d

sat

o

pcf

pcf

c

3 ft

4 ft

6ft x 8ft

Qall=??

6 ft eL

eB

1) Determine , and

The foundation is with two-way eccentricity:

Use figure 3.15b to get:

12.72

2.49

5.1

2) Calculate and

Case :

The water table level is so deep that it doesn't affect ultimate bearing capacity

case

Case :

The water table level lies within the distance under foundation base

3) Determine Meyerhof's equation parameters

a. Bearing capacity factors

b. Shape factors

c. Depth factors

d. Inclination factors

4) Calculate ultimate bearing capacity using Meyerhof's equation

Case :

Case :

5) Find the maximum allowable load the foundation could carry

Case :

Case :

Problem 3

A circular footing is shown below. Determine the safe gross load ( with a factor of safety of 3) that the footing can carry.Solution:

1) Calculate and

The water table level lies within the distance under ground level

2) Determine Meyerhof's equation parameters

a. Bearing capacity factors

b. Shape factors

c. Depth factors

d. Inclination factors

3) Calculate ultimate bearing capacity using Meyerhof's equation

4) Find the maximum allowable load the foundation could carry

Problem 4:

A square column foundation has to carry a gross allowable total load of 150 KN. The

depth of the foundation is 0.7m. the load is inclined at an angle of 20 to the vertical.

Determine the width of foundation, use the general equation & F.S=3.

Solution:

1) Calculate and

2) Determine Meyerhof's equation parameters

a. Bearing capacity factors

b. Shape factors

c. Depth factors

d. Inclination factors

3) Calculate ultimate bearing capacity using Meyerhof's equation

4) Calculate the width of foundation

Problem 5:

For the shown rectangular foundation:

a) Compute the net allowable bearing capacity using Meyerhof general equation,

use a factor of safety of 3.

b) If water table is lowered by 2m, what effects on bearing capacity would occur

due to water lowering.

Given Data:

Solution:

1) Determine , and

The foundation is with one-way eccentricity:

3 15 /KN m

3( ) 21 /sat KN m

0.5

m

1.5

m

3 m

W.T

3m x 2m

700 KN

Note: always take the smaller of ( , ) as effective width.

2) Calculate and

The water table level is within the depth of foundation ( ) Case

Case :

Case :

3) Determine Meyerhof's equation parameters

a. Bearing capacity factors

b. Shape factors

c. Depth factors

d. Inclination factors

4) Calculate ultimate bearing capacity using Meyerhof's equation

Case :

Case :

Problem 6:

The figure below shows a continuous foundation.

a) If H=1.5 m, determine the ultimate bearing capacity,

b) At what minimum value of H/B will the clay layer not have any effect on the

ultimate bearing capacity of the foundation?

Solution:

a) H=1.5

This is the special case , because the top layer is strong sand ( ) and the

bottom layer is weak soft clay ( ).

1.2 m

H

B = 2 m

31

01

1

17.5 /

40

0

KN m

c

32

2

32

16.5 /

0

30 /

KN m

c KN m

Sand

Clay

Note: the foundation given is strip, so

Use figure 3.21 (p.190) to get

Use figure 3.22 (p.190) to get

b) H=??

To find the minimum value of H/B will which makes the clay layer not have any

effect on the ultimate bearing capacity of the foundation, let and

Problem 7:

For the design of a shallow foundation given the following:

Calculate the ultimate load, use vesic equation?

Solution:

1) Determine Vesic's equation parameters

a. Bearing capacity factors

b. Shape factors

c. Depth factors

d. compressibility factors

i. calculate rigidity index ( )

ii. calculate critical rigidity index ( )

Since , use the following equations to find

compressibility factors:

2) Calculate ultimate bearing capacity using vesic's equation