ABSTRACT
As a building material widely used in the engineering field, the in-situ strength test of sandy cobble is a hot issue in geotechnical engineering research, but its in-situ strength test is still a difficult problem. Using the research method combining theoretical analysis, device development, experimental research, and engineering testing, the theoretical analysis of rotary cone penetration cutting through soil is carried out, and the theoretical model between drilling parameters (torque, thrust) and the bearing capacity of sand cobble soil is established. Based on the self-developed rotary cone penetration rock-soil strength parameter test device and 3d flexible boundary loading device, a total of 75 groups of rotary cone penetration model tests are carried out under 5 kinds of water content and 5 kinds of drilling confining pressure. Using the multiple linear regression analysis methods, 5 types of quantitative relationship models of torque, thrust, and bearing capacity distinguished by different water content are established, and the reliability of the mathematical model is evaluated using four indicators: Adj.R, VAF, RMSE, and MAPE. In order to test the applicability and accuracy of the quantitative relationship model, a confirmatory application is carried out on a sand cobble foundation. The research results show that under the conditions of rotational speed and rate of penetration, the torque, thrust, and bearing capacity of sandy cobble are in line with multiple linear fitting relationships. In practical engineering applications, the consistency between the calculated value of the bearing capacity model and the calibration value is higher than 85%, and the root-mean-square error of the calculated value is less than 10, which proves the validity of the experimental model applied to in-situ strength measurement and provides a scientific basis for further research on the relationship model of mechanical response and force parameters under different materials and various conditions.
