Following are the variation of the field SPT values with ...



Question 1 (20%)

1.1 If you, as a geotechnical engineer supervising the drilling work in the site, were asked weather to obtain a disturbed or undisturbed sample at a certain depth for the purpose of conducting consolidation test, which should you select and why?

Ans

Undisturbed sample, because the structure of the soil, which required for such test is maintained.

1.2 List one major difference between conventional soil explorations by drilling versus the geophysical exploration?

1.3 In a two –layered soil under a foundation, if the thickness of the top layer is thin compared to foundation width, discuss the type of shear failure in the soil. Enhance your answer by drawing the shear failure surface.

1.4 List the modifications that the GBCE added to the original Terzaghi Equation.

Question 2 (50%)

A square column foundation (B x B) is embedded 4ft depth in a sand layer as shown below, if the gross allowable load that foundation will carry is 300 kips making 80° with horizontal. Water table is at 4ft depth from GS, Unit weight of sand above water table is 100 pcf while it becomes 122 pcf below water table.

If factor of safety 3 is desired, use GBCE to determine the size of footing?, if the gross allowable load that foundation will carry is 300 kips makin

|Depth |SPN |

|(ft) | |

| |1st 15 cm |2nd 15 cm |3rd 15 cm |

|5 |5 |5 |10 |

|10 |5 |5 |5 |

|15 |10 |10 |5 |

|20 |10 |10 |10 |

|25 |10 |10 |10 |

[pic]

Ans:

Navg = 21, Φ avg = 40, B=4.4 ft

Question 3 (30%)

For the soil profile shown in Question 2, a square column foundation (B x B) is loaded with a vertical load but with 0.5ft eccentricity along one side of the footing.

Determine the net gross allowable load that the footing can carry.

Use Myrhof Equation

B’ = B-2e, A’=B’x L

Ans:

qu = 50400 psf,

Qall net = 333.3 Kip

a) H= 1m

b) H= 10 m

Describe the type of failure surface in each of the both cases.

[pic][pic]

[pic]

[pic]

Ans:

a) Failure Type = Punishing failure in top layer, General failure in bottom layer

qu = 624 kPa

qt = 3507 kPa

b) Failure Type = General failure in top layer

qu = 6534 kPa

qt = 2506 kPa

*** Plot sketch for the shape of failure !!!

-----------------------

1.2m

H

Sand

[pic]

Ç

r &

/

0

2

4

7

T

U

V

W

f

p

ã

q

òÞÍÞ¿±¿±œ±ˆwˆwˆi[i[i[i[J hu/h§)¾CJOJQJ^JaJh*v#CJOJQJ^JaJhúF¦CJOJQJ^JaJ húF¦5?CJ OJQJ\?^JaJ &h[pic]

{húF¦5?CJ OJQJ\?^JaJ )hì$3hì$3B*CJOJQJ^JaJphÌÿhì$3CJOJQJ^JaJh*h[pic]

{h[pic]

{5?CJ OJQJ\?^Jaγ=17.5kN/m3

Sat clay

γ=16.5kN/m3

C=75kN/m2

2

/

:

20

20

1

2

ft

ton

N

C

v

cor

v

N

−

−

+

’

Φ

+

’

σ

σ

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