Study on mechanical response of existing tunnel lining induced by excavation of newly constructed sandy loess tunnel and slipr reinforcement technology

Abstract Soil displacement from the excavation of new sandy loess tunnels tends to cause surrounding deformation and affect existing tunnels, necessitating reinforcement for adjacent construction sections to mitigate risks. Taking Tunnel F as a case study, this paper investigated the stress–strain evolution of sandy loess with varying moisture contents via laboratory triaxial compression tests, analysed the stress characteristics of the existing tunnel’s secondary lining under new tunnel excavation disturbance through numerical simulations, and explored the optimal design parameters of super long interlocked pipe roof (SLIPR) reinforcement. The research results indicated that an increase in water content led to a reduction in the macroscopic mechanical parameters of sandy loess, and simultaneously induced a synchronous rise in the displacement and stress of the secondary lining. The maximum vertical displacement, horizontal displacement, tensile stress and compressive stress of the lining appeared at the left arch waist, right side wall, inverted arch and left wall footing, respectively. Tensile failure occurred when the sandy loess moisture content reached 10%, with the lining’s maximum tensile stress at 2.92 MPa. SLIPR effectively reduced excavation disturbance via arching and interlocking dual mechanisms; the optimal scheme was determined as hot finished seamless steel pipes with an inner diameter of 760 mm and wall thickness of 40 mm, balancing structural safety and construction cost.