Estimating in-situ soil permeability from CPT & CPTu

Engineers often want to estimate profiles of soil permeability (hydraulic conductivity) as part of the site characterization process. Several methods have been proposed to estimate the coefficient of permeability (k) using CPT results. These methods are generally based on two approaches: (1) estimated soil type and (2) rate of dissipation during a CPTu dissipation test. This paper presents updated correlations to estimate the coefficient of permeability from CPT and CPTu dissipation test results. The proposed correlations are briefly evaluated with available published results. 2 PERMEABILITY ESTIMATES BASED ON SOIL TYPE Lunne et al (1997) suggested that soil permeability (k) could be estimated using the Soil Behaviour Type (SBT) charts proposed by either Robertson et al (1986) or Robertson (1990). A range of k values was suggested for each SBT. Table 1 shows the updated recommended range based on the Robertson (1990) normalized SBTn chart. Table 1 Estimated soil permeability (k) based on normalized CPT soil behavior type (SBTn) by Robertson (1990) (Modified from Lunne et al., 1997) SBTn Zone SBTn Range of k (m/s) SBTn Ic 1 Sensitive fine-grained 3x10 to 3x10 NA 2 Organic soils clay 1x10 to 1x10 Ic > 3.60 3 Clay 1x10 to 1x10 2.95 < Ic < 3.60 4 Silt mixture 3x10 to 1x10 2.60 < Ic < 2.95 5 Sand mixture 1x10 to 1x10 2.05 < Ic < 2.60 6 Sand 1x10 to 1x10 1.31 < Ic < 2.05 7 Dense sand to gravelly sand 1x10 to 1 Ic < 1.31 8 *Very dense/ stiff soil 1x10 to 1x10 NA 9 *Very stiff fine-grained soil 1x10 to 1x10 NA *Overconsolidated and/or cemented Manassero (1994) reported good results using Table 1 to estimate k values for quality control purposes in a slurry wall. Jefferies and Davies (1993) identified that a Soil Behavior Type Index, Ic, could represent the SBT zones in the normalized CPT SBTn chart where, Ic is essentially the radius of concentric circles that define the boundaries of soil type. Robertson and Wride, (1998) and updated by Robertson (2009), modified the definition of Ic, as follows: Ic = [(3.47 log Qtn) + (log Fr + 1.22)] (1)