Analysis of Mechanical Properties at the Pile-Pisha Sandstone Interface Using Large-Scale Constant Normal Stiffness Cyclic Direct Shear Tests in Seasonally Frozen Regions

This study investigates the mechanical behavior at the interface between pile foundations and Pisha sandstone, crucial for the safe operation of wind turbines and bridge piers in Pisha sandstone regions. Using a cyclic large direct shear apparatus, the dynamic characteristics of the frozen Pisha sandstone–concrete interface are analyzed under various normal loads and vibration amplitudes. The results indicate a progressive decrease in shear stress with an increasing number of cycles, revealing a characteristic strength weakening. This trend highlights the ongoing reduction in interface strength under dynamic loading conditions. Initially, during the dynamic shear tests, the shear stress experiences a sudden increase, followed by a gradual decrease, which is attributed to the overcoming of the freezing force at the interface. Postcyclic shearing tests show further strength reduction, wherein variations in shear amplitude impart significant influence on the shearing behavior. The findings offer significant theoretical support for engineering projects in the Pisha sandstone area.