ARCHIVED REPORTS XR0012551 - Laserfiche WebLink

Home Browse Search

L.Y 3.2.2 Permeability Estimates of soil permeability can be derived from piezocone pore pressure dissipation data. According to geotechnical theory, the rate of pore pressure dissipation is directly related to the coefficient of consolidation of the soil, which in turn is a function of the compressibility and permeability. Therefore, in order to estimate permeability based on pore pressure dissipation data,the soil's compressibility and consolidation behavior must first be determined. An estimate of the coefficient of permeability can be obtained as follows (Gillespie & Campanella, 1381); kh — ch my yw ($) Where kh = coefficient of permeability in the horizontal direction, ch = coefficient of consolidation in the horizontal direction, my = 11M = volumetric compressibility, M = constrained modulus, and yw = unit weight of pore liquid (usually water). The computed value of kh represents the horizontal permeability as a discrete depth interval corresponding to the location of the piezocone filter. The soil consolidation parameter, ch, is derived from theoretical solutions of excess pore pressure dissipation rates. Tim determination of my is guided by empirical correlations between cone tip resistance, qc and constrained modulus, M, and is subject to a range of uncertainty. The uncertainty that is carried over to the permeability prediction as a result of the possible range of rnv is often less than one order of magnitude for silty sands and finer grained soils. Greater uncertainty exists in the permeability predictions for more permeable soils. - � 11