为明确深部软岩隧道围岩压力机制，指导设计合理的大变形治理方案，以米林隧道工程为依托，基于岩体弹塑性力学，推导出围岩膨胀压力解析式。结合Kastner算式，引入断面径向位移u与塑性区半径Rp之间的函数关系，求解出膨胀压力与形变压力的特征曲线函数解GRC，探明膨胀压力与形变压力在断面径向位移过程中的演化规律。根据收敛－约束法，结合支护特征曲线SCC，分析考虑膨胀压力条件下GRC曲线与SCC曲线交点变化趋势，以设计出合理的软岩大变形控制参数。研究结果表明： 1）仅考虑形变压力而设计的支护结构不满足围岩稳定性要求，当围岩径向位移达到530 mm时，仅考虑形变压力pi时围岩对支护结构的压力为0.82 MPa，考虑膨胀压力pr时支护承载压力增至1.37 MPa，膨胀压力占比达40.1%； 2）采用“钢架+锚喷”初期支护将围岩位移释放至upeak=0.325 m时增设间距d=0.7 m I25b钢架的联合支护方案，能对形变压力进行合理释放，同时有效抑制膨胀压力过度增大； 3）第2层钢架设置23 d后围岩变形收敛为56.1 mm，通过理论计算、数值分析与工程应用验证了支护方案的可行性。

To elucidate the surrounding rock pressure mechanism in deep soft rock tunnels and develop effective deformation control technologies, a case study is conducted on the Milin tunnel. The analytical formula for the expansion pressure of the surrounding rock is derived based on the principles of elastoplastic mechanics applied to rock masses. Based on the Kastner formula, the functional relationship between the radial displacement u of a cross-section and plastic zone radius Rp is introduced. Further, the ground reaction curve (GRC) of the expansion and deformation pressures is established, thus exploring the evolution law of these pressures during radial displacement of the crosssection. Based on the convergenceconstraint method and supporting confining curve (SCC), the variation trends of the intersection of GRC and SCC under conditions of expansion pressure are analyzed to design rational control parameters for large deformations in soft rocks. The key findings are as follows: (1) The supporting structure designed only considering the deformation pressure does not meet the stability requirements of the surrounding rock. When the radial displacement of the surrounding rock reaches 530 mm, the pressure of the surrounding rock exerted on the supporting structure reaches 0.82 MPa when considering only the deformation pressure 〖WT５《TNR#I》〗p〖WT５《TNR》〗i; however, the pressure increases to 1.37 MPa when expansion pressure 〖WT５《TNR#I》〗p〖WT５《TNR》〗r is considered, accounting for 40.1% increased pressure. (2) A strategic approach involving primary support comprising a combination of "steel frame + anchor spray" is utilized to counter the displacement of the surrounding rock to 〖WT５《TNR#I》〗u〖WT５《TNR》〗peak=0.325 m. Incorporating an additional I25B steel frame with a space of 〖WT５《TNR#I》〗d〖WT５《TNR》〗=0.7 m effectively moderates the deformation pressure and mitigates excessive expansion pressure. (3) After introducing the secondlayer steel frame over 23 days, the surrounding rock deformation converged to 56.1 mm. The feasibility of the proposed support scheme was validated through theoretical calculation, numerical analyses, and engineering applications.