Analytical Chem Soil HW Solutions 57

Analytical Chem Soil HW Solutions 57 - Application of...

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57 Application of one-dimensional compression and consolidation theory to field problems Q4.6 Figure 4.41 shows a cross section through a long sheet piled excavation. The width of the excavation is b, its depth is h and the sheet piles penetrate a further depth d to a permeable aquifer. A standpipe piezometer is driven into the aquifer, and the water in the standpipe rises to a height H above the bottom of the sheet piles. (a) Show that the base of the excavation will become unstable if H > H crit , where (H crit )>d. γ / γ w . (Note: this is a quicksand problem: see Section 3.11.) (b) Some time after the excavation has been made, and steady state seepage from the aquifer to the excavation floor has been established, it is found that H is indeed very close to H crit . In order to reduce the risk of base instability it is decided to reduce the head in the aquifer to H/2 by pumping. This is done very rapidly. Explain why the pore water pressures in the soil between the sheet piles cannot respond instantaneously.
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This note was uploaded on 12/28/2011 for the course CHM 4302 taught by Professor Stuartchalk during the Fall '11 term at UNF.

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