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



Question 1 (30%)

Following are the variation of the field SPT values with depth in a sand stratum. The ground water table is located at a depth of 5 ft from ground surface; unit weight of sand above water table is 100 pcf while it becomes 122 pcf below water table.

|Depth |SPN |

|(ft) | |

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

|5 |5 |5 |5 |

|10 |7 |8 |10 |

|15 |8 |10 |10 |

|20 |10 |12 |15 |

|25 |15 |25 |25/10 |

|30 |15 |25 |25/10 |

Calculate the corrected SPT values and the average friction angle of the sand strata using the following relations

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1. Indicate, with explanation, if the soil sample retrieved from SPT is disturbed or undisturbed.

2. List three laboratory tests that can be performed on SPT soil samples

Ans:

Navg = 34, Φ avg = 46

Disturbed, due to use of hammer

Grain size distribution, compaction, classification, LL, PL lure surface in each of the both cases.

n can carry if:

constructed on that soil at a depth of 5ft, and

Question 2 (35%)

For the soil profile shown in Question 1, a square footing (5ft x 5ft) is to be constructed on that soil at a depth of 5ft, and load is inclined with 80° with horizontal. Using FS of 3, what will be the net allowable load the foundation can carry if:

a) Water table is at 5ft depth from GS

b) Water table is at 10ft depth from GS

Discuss the effect of water table on the bearing capacity of the foundation.

Use Myrhof Equation

Ans:

a) qu = 166750 psf,

Qall net = 1385 Kip

b) qu = 179000 psf,

Qall net = 1488 Kip

Question 3 (35%)

A rectangular footing (2m x3m) is embedded in the soil shown below. Determine the gross ultimate bearing capacity of the footing in the following cases:

a) H= 1m

b) H= 10 m

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

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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

γ=17.5kN/m3

Φ=40

Sat clay

γ=16.5kN/؀ࠁࠒऌऍजझटडऩफळव़ऽॅॆॐ॑ड़ढ़३४ॹॺউঌ৿਀ਂ਄ਈਊ୔ୖ���뿍뾲꒲꒲꒲뾲뾲뾲뾲뾲뾲뾲雍熈ᔠ畨ᨯᘀŨ笎䌀᱊伀͊儀͊帀ъ愀᱊̭屪ᔀ穨쀖ᘀ湨켈䌀⁊䔀챈俿͊儀͊唀Ĉ䩞䩡 ᘚ穨쀖䌀⁊伀͊儀͊帀ъ愀⁊ᘚ籨捬䌀⁊伀͊儀͊帀ъ愀⁊ᔛ畨ᨯᘀ籨䠀Ī䩏䩑䩞ᔘ畨ᨯᘀ籨伀͊儀͊帀ъᘚ籨䌀⁊伀͊儀͊帀ъ愀⁊ᔠm3

C=75kN/m2

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