Force states of soils under shield cutting in excavation face based on Kӧtter equation

To calculate the forces between shield scraper and soils as well as the cutting torque caused by them with different tunneling parameters in different soils, a modified Kӧtter equation is introduced as a supplement to solve the stress distribution on the sliding face when the soils in excavation face are being passively cut to a damage state. A mechanical model for cutting soils is established, and the pressure and friction between the soils and the surface of shield scraper and the lateral shear resistance are solved. Then the method for calculating the cutting torque of cutter head is derived. It can be acquired that the pressure, friction and lateral shear resistance increase with the cohesive force and internal friction angle and decrease with the rotation rate, which illustrates that a properly coarser scraper surface makes the soils easier to be cut, and a lower rotation rate can reduce the force of the tools. The pressure and friction increase linearly with the shield support pressure, which is more obvious in sand. Some cutting torques in different soil types are given as engineering references ultimately.