Evaluation of strength characteristics of soils based on piezocone penetration tests and flat dilatometer tests in water areas

In geotechnical engineering investigation, the multivariate in-situ test data fusion method has become the research trend, and it has obvious advantages in improving the accuracy of parameters and the evaluation of strength characteristics of soils. In order to solve the problems of sampling difficulty, spatial variability of geotechnical parameters, and regional and structural mechanical properties of soils in geotechnical engineering investigation in water areas, the Haimen-Taicang Changjiang River crossing project in Jiangsu Province is taken as the research object. Based on the piezocone penetration tests (CPTU), flat dilatometer tests (DMT) and laboratory tests, the undrained shear strength of soft clay, internal friction angle of sandy soil and constrained modulus of layers with different material indices are studied. The results show that both the CPTU and the DMT can provide abundant soil parameters, which are sensitive to the strength characteristics of soils, and it is feasible to characterize the strength of soils using the parameters from the two experiments. The calculated results based on the CPTU tip resistance and the net tip resistance overestimate the effective internal friction angle of sandy soil, while that approximated by K_D is slightly smaller. There is a good correlation between the DMT constrained modulus and the CPTU tip resistance. The stiffness and strength can be linked by fitting their relationship, which also considers the influences of the material indices, and this relationship can be used as a new method to estimate the constrained modulus.