Reliability research on the 5-cm-thick insulation layer used in the Yuximolegai tunnel based on a physical model test

•The model test system (a refrigeration system, a circulation system and a temperature control system) was established.•The effect of the 5-cm-thick insulation layer on the Yuximolegai tunnel is studied.•The freezing depth of the Yuximolegai tunnel is approximately 1.5–2 m away from the lining.•The maximum frost heave force behind the lining is 0.5–0.6 MPa based on the physical model test.

The Yuximolegai tunnel was built in the Tianshan mountain of Xinjiang. A 5-cm-thick insulation layer designed by engineering analogy was laid to project the surrounding rocks. To investigate the reliability of the design, a model test, primarily including a refrigeration system, a circulation system and a temperature control system, was developed. Two tests were designed and conducted: (1) a tunnel without insulation layer is studied using the freezing test; (2) a tunnel with a 5-cm-thick insulation layer is studied using the same test. The results show that the 5-cm-thick insulation layer employed in the field can only stop 86.5% of the lowest temperature to transfer to the surrounding rocks on average. On the basis of the analysis for the temperature law from in situ monitoring results and the model test results, the freezing depth is approximately 1.5–2 m away from the lining. When the 5-cm-thick insulation layer is laid, the freezing depth still reaches 0.5 m, which indicates that the preservation measure cannot fully protect the rocks surrounding the tunnel against freezing damage. In addition, comparing the frost heave force from the model test is found to have good consistency with the in situ test. The results obtained can serve as a guide for the design and the numerical simulation research of cold-region tunnels.