Effect of Storage Capacity in the Performance of Vertical Drains in Liquefiable Sand Deposits

Pestana, J.M., Hunt, C.E., Goughnour, R.R., and Kammerer, A.M. (1998) "Effect of Storage Capacity in the Performance of Vertical Drains in Liquefiable Sand Deposits, " 2nd International Conference on Ground Improvement Techniques, Singapore, 1998, 373-380.

The use of vertical drains to improve the performance of potentially liquefiable ground during earthquakes has received increased attention over the last two decades. This paper briefly describes the formulation of a finite element code, FEQDrain, developed to analyze the development of excess pore pressure in a layered soil profile, accounting for vertical and horizontal drainage. The code includes equations describing a vertical drain with a non-constant "equivalent hydraulic conductivity" which more accurately describes the flow properties of perforated pipes and wick drains, and head losses due to horizontal flow into the drain. It can also model the presence of a reservoir directly connected to the drain, allowing the accumulation of the water discharged by the drain element as well as head losses in the reservoir itself. In contrast, most analyses used in practice assume the water level in the drain is at the ground surface and therefore all flow into the drain escapes. The accumulation of water within the drain, however, can lead to a significant retardation of flow into the drain, causing an increase in the predicted pore pressures developed during the earthquake.

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