Abstract: The influence of multifield coupling action on the plastic loose circle of surrounding rocks in high ground stress zone is investigated using an analytical model. For this purpose, a case study is conducted, and the established analytical model is based on the unified strength theory. Furthermore, the influence of initial crustal stress, ground temperature, tunnel excavation radius, and intermediate principal stress on loose circle radius is examined. The primary findings of the study are as follows: (1) Under the thermalforce coupling effect, the radius of the loose circle is primarily affected by the initial crustal stress and has a nonlinearly relation with this stress. (2) An increasing ground temperature expands the influence of initial crustal stress, tunnel excavation radius, and intermediate principal stress on the loose circle. (3) The radius of the plastic loose circle increases almost linearly with an increase in the tunnel excavation radius and decreases with increasing intermediate principal stress coefficient. Moreover, the sensitivity of the stability state of the surrounding rocks to the intermediate principal stress increases with decreasing intermediate principal stress coefficient. (4) The engineering practice shows that the error of the calculated loose circle radius of surrounding rocks based on the unified strength theory is less than 1.4% under the action of thermalforce coupling, demonstrating the rationality and feasibility of the proposed calculation method.

Key words: deepburied tunnel, surrounding rock, thermalforce coupling, plastic loose circle, loose circle radius, unified strength theory