Computer program for estimating friction angle and in-situ state parameter using cavity expansion theory and CPT in sands

The Cone Penetration Test (CPT) is a widely used in-situ test. By measuring the cone tip resistance, sleeve side friction and pore water pressure, CPT is used to estimate soil parameters and profiles. Analytical/numerical methods involve tedious arithmetic calculations. A study on developing a computer program for estimation of soil parameters using CPT data is needed. This study, dealt with developing a computer program for estimating friction angle and in-situ state parameter of sands from CPT tip resistance using similarity solutions for cavity expansion. The similarity solutions for stresses and radial speed are presented by replacing the PDEs from stress equilibrium, constitutive law, consistency condition, and continuity equation with first-order ODEs. The Runge-Kutta method with adaptive step-size control was used to solve the first-order ODEs. The large strain similarity solutions for cavity expansion from zero initial radius are presented using an elastic-perfectly plastic Mohr-Coulomb model and a state parameter-based critical state model. A computer programs has been developed using C++ language and used to estimate friction angle and in-situ state parameters. The presented similarity solutions and computer programs are verified by comparing the results of plastic radius and cavity limit pressure with similar previous studies. A good agreement between the results by the presented similarity solutions and those by the previous studies is obtained. Using the results of the spherical cavity limit pressure obtained from the large strain similarity solutions, the friction angle and in-situ state parameter are estimated from the cone tip resistance. The best-fit theoretical correlations are obtained and compared with empirical correlations.