WORK PLANS - Laserfiche WebLink

Home Browse Search

G Gregg In Situ Environmental and Geotechnical Site Investigation Contractors Gregg In Situ CPT Interpretations as of January 7, 1999 (Release 1.00,19) Gregg In Situ's interpretation routine should be considered a calculator of current published CPT correlations and is subject to change to reflect the current state of practice- The interpreted values are not considered valid for all soil types. The interpretations are presented only as a guide for geotechnical use and should be carefully scrutinized for consideration in any geotechnical design. Reference to current literature is strongly recommended. The CPT interpretations are based on values of tip, sleeve friction and pore pressure averaged over a user specified interval(typically 0.25m). Note that[fit is the recorded tip valve, Qc, corrected for pore pressure effects. Since all Gregg In Situ cones have equal end area friction sleeves, pore pressure corrections to sleeve friction, Ps, are not required. The tip correction is: Qt=Qc+(1-a) •Ud where: Qt is the corrected tip load Qc is the recorded tip load Ud is the recorded dynamic pore pressure a is the Net Area Ratio for the cone(typically 0.85 for Gregg In Situ cones) Effective vertical overburden stresses are calculated based on a hydrostatic distribution of equilibrium pore pressures below the water table or from a user defined equilibrium pore pressure profile(this can be obtained from CPT dissipation tests). The stress calculations use unit weights assigned to the Soil Behavior Type zones or from a user defined unit weight profile. Details regarding the interpretation methods for all of the interpreted parameters is given in table 1. The appropriate references referred to in table 1 are listed in table 2. The estimated Soil Behavior Type is based on the charts developed by Robertson and Campanella shown in figure 1. Table 1 CPT Interpretation Methods Interpreted Description Equation Ref Parameter Depth mid layer depth ArrgQt Averaged corrected tip(Qt) AvgQt= ±Qty n,i-t AvgEs Averaged sleeve friction(Fs) 1 AvgF.s=--7,Fs n ,4vgR# Averaged friction ratio(Rf) Avg,gvg]Zf =100%. Fs Qt AvgUd Averaged dynamic pore pressure(Ltd) 1 " AvgUd Ud n SBT Soil Behavior Type as defined by Robertson and Campanella