在使用UHPC加固盾构隧道时，不同位置UHPC层厚度不同可形成变截面加固，从而提高UHPC利用率。为研究采用变截面形式UHPC加固后衬砌结构的力学性能，开展变截面UHPC加固盾构隧道衬砌整环足尺试验，试验结构中变截面UHPC层厚度在隧道顶部和腰部为70 mm，肩部为40 mm，节省肩部UHPC用量的同时扩大了列车与结构间隙。此外基于曲梁理论建立UHPC加固盾构隧道衬砌结构计算方法，分析变截面UHPC加固盾构隧道衬砌结构的内力分配机制。结果表明： 1）变截面UHPC加固结构的破坏模式表现为UHPC开裂、粘结界面破坏，破坏过程包含弹性阶段、弹塑性阶段和塑性阶段3个阶段，呈现良好的延性特征。2）相比等截面UHPC加固方法，变截面UHPC加固结构承载力提升25.0%，可额外多承担4.1 m上覆土荷载。3）等截面UHPC加固结构表现为明显的“超筋”破坏，管片先破坏、后加固体破坏，而变截面UHPC加固结构UHPC和界面先发生破坏，后管片破坏，对于UHPC的利用率提高。4）基于曲梁理论建立的UHPC加固结构计算方法经试验结果验证正确有效，且推导得出加固界面的破坏由剪切破坏主导。
When applying ultra-high-performance concrete (UHPC) to shield tunnel reinforcement, varying UHPC layer thickness at different positions creates a variable cross-section reinforcement, thereby improving UHPC utilization efficiency. To investigate the mechanical performance of tunnel linings reinforced with variable cross-section UHPC, a full-scale test is conducted on a shield tunnel lining. In the test structure, the UHPC layer thickness is 70 mm at the tunnel crown and mid-sides and 40 mm at the shoulders, reducing the amount of UHPC used at the shoulders while increasing the clearance between the train and structure. Moreover, a calculation method for UHPC-reinforced shield lining is established based on curved beam theory to reveal the internal force distribution mechanism. The findings are as follows: (1) The failure mode of the variable cross-section UHPC-reinforced structure is characterized by UHPC cracking and bond interface failure, encompassing three phases—elastic, elastoplastic, and plastic—demonstrating good ductility. (2) Compared with the uniform cross-section UHPC reinforcement method, the load-bearing capacity of the variable cross-section UHPC-reinforced structure increases by 25.0%, allowing for an additional 4.1 m of overburden load. (3) The uniform cross-section UHPC-reinforced structure exhibits a distinct "over-reinforcement" failure mode, where the segments fail first, followed by the reinforcement body. In contrast, in the variable cross-section structure, the UHPC and interface fail first, followed by the segments, thereby improving UHPC utilization. (4) The calculation method for UHPC-strengthened tunnel lining based on curved beam theory is thus validated as accurate and effective through experimental results, demonstrating that shear failure primarily governs the failure of the strengthened interface.
