Finite element simulation of the cone penetration test in uniform and stratified sand.

Abstract

The research presented herein utilized finite element method based on a large strain formulation to study cone penetration in uniform normally consolidated (NC), uniform overconsolidated (OC) and stratified NC sands. An accurate but practical approach for practitioners to interpret CPT test results was developed. An auto-adaptive remeshing technique was utilized for handling very large mesh distortions in zones of high strain concentration around the cone tip. A frictional contact interface utilizing Mohr-Coulomb's theory was chosen to represent interactions between the surface of the cone and sand. To model the sand's response to penetration, a non-associated Drucker-Prager constitutive model was selected. ABAQUS, a commercial finite element software package, was used to implement the model. The explicit solution algorithm was chosen due to its effectiveness in solving complicated contact problems. A series of experimental tests on a half axisymmetric cone against plexiglass wall were performed to investigate and verify the deformed shapes of interfaces between two sand layers. Analysis results proved that the finite element model with an auto-adaptive remeshing scheme successfully modeled cone penetration in NC, OC, and stratified NC sands. A chart for prediction of angles of internal friction, &phis;<super> '</super>, based on the cone bearing q_c and the initial effective vertical stress, sigma_vo<super>' </super> for NC sands has been developed. Two charts for prediction of &phis;<super> '</super> in OC sands, have also been developed: (a) a chart based on q_c, sigma_vo<super>'</super> and OCR, (b) a chart based on q_c and sigma_ho<super>'</super>. A practical method to correct the apparent &phis;<super>'</super> of thin layers of sand has also been developed. The method was presented for two broad soil sequence groups: high &phis;<super>'</super> - low &phis;<super> '</super> - high &phis;<super>'</super> (HLH) and low &phis;<super> '</super> - high &phis;<super>'</super> - low &phis;<super>' </super> (LHL). This work also presents tip resistance - penetration relationships for uniform NC, uniform OC, and stratified NC sands; typical interface displacement shapes between two sand layers due to cone penetration; a typical non-uniform distribution of sleeve resistance along the length of the friction sleeve in NC sands; and typical contours of vertical, horizontal, and shear stresses in NC sands surrounding an advancing cone.