Jacking resistance in collapsed body considering buckling of force chain

In order to establish an effective and secure emergency rescue channel within a collapsed structure using the pipe jacking method, understanding the evolution mechanism of jacking resistance is crucial. The evolution characteristics of the jacking resistance and the macroscopic displacement of the collapsed particles during pipe jacking process were analyzed by physical similarity simulation test and numerical simulation test, and the drop characteristics of the jacking resistance were discussed by using 3D force chain identification method and the force chain buckling behavior of the particle material. In order to further determine the intrinsic mechanical mechanism of the jacking resistance drop characteristics, the particle stacking thickness, pipe radius, particle size and effective modulus were selected as orthogonal factors, and the numerical simulation test at different parts of the pipe were carried out. On the basis of the force chain buckling behavior, the change characteristics of the jacking resistance and the macroscopic and microscopic parameters of the particles, such as jacking resistance drop, contact failure, sudden drop in coordination number, particle elastic potential energy release and force chain length change, were studied. The results show that: The macro-displacement of particles primarily occurs around the oblique top of the pipe jacking cut, where a distinct and continuous shear slip zone emerges within the particles. The decrease in jacking resistance is associated with the unstable slip of particles and the localized buckling behavior of force chains. The frequency of dropping jacking resistance positively correlates with pipe diameter and effective modulus, while negatively correlating with particle thickness and size. Notably, the dropping frequency observed in pipe jacking cut tests is higher than that in outer wall tests, and both exhibit cyclic rising-falling patterns with high similarity. As the thickness and size of the overlying particles increase, the length and effective length of force chains also increase. This extension expands the reach of force chains, leading to a broader distribution range of buckling contacts, changes in coordination numbers, degrees of buckling deformation within force chains, and in-creases in elastic potential energy. The buckling and slip of force chains within the collapsed body are key factors contributing to the release of elastic potential energy and the breaking down of extended force chains within particles. The rapid instability, fall, and accumulation of particles along shear planes above the pipe jacking, guided by gravity is the reason why the release of elastic potential energy of these particles has little effect on the overall resistance of the pipe jacking.