Consider the new parking lot being constructed adjacent to Marston Hall (on the

Question

Consider the new parking lot being constructed adjacent to Marston Hall (on the west side). The existing soil, which was unsuitable as a foundation material for the parking lot, was excavated down to 1.5 meters below grade and removed off-site. The excavation was then backfilled with a well graded compacted gravel (= significantly better foundation soil). Assuming the parking lot is 45 m x 45 m, the removed soil had a unit weight t = 16 kN/m3 and the backfill gravel has a compacted unit weight t = 25 kN/m3, compute the following:

Total weight of soil removed.

Total weight compacted backfill gravel placed.

Stress at depth of 1.5 meters before excavation

Stress at depth of 1.5 meters after placement of the compacted gravel.

It rained heavily after the excavation was completed which filled the open excavation

with water to a depth of 35 cm before placement of the compacted gravel. What was the total weigh of water in the excavation and the stress at the bottom of the excavation?

Explanation / Answer

Weight of soil to be removed= 45x45x1.5x16= 48600 Kn

Weight of gravel to backfield is 45x45x1.5x25= 75398 Kn

Stress at 1.5 m before excavation is (force/area)=(48600/(45*45))=24 Kn/sqmt

Stress at 1.5 m after placing gravel is {force/area}= {75398/(45*45)}=37.50 Kn/sqmt

Weight of water= 45x45x0.35x10 = 7087.50 Kn

Stress at the bottom of the excavation is (7087.50/(45*45))= 3.5 Kn/sqmt

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