Abstract: When tunneling in soilsand interbeded strata, large deformation often occurs. Hence, the causes and control techniques (such as surrounding rock prereinforcement and arch replacement) of large deformation of Yangcheng tunnel of HaolebaojiJi′an railway are studied. The site monitoring results are used to evaluate the control effect of large deformation section. The research results show the following: (1) The poor properties of soilsand interbeded surrounding rock and uneven strength would cause stress concentration and asymmetrical pressure, and improper countermeasures are adopted, which are the main causes of large deformation. (2) The pressure of surrounding rock and the stress of grid steel frame generally show a fluctuation in the early stage and stabilization in the late stage trend, whereas the shotcrete shows obvious rapid growth, slow growth, and stabilization trend. The variation range of the pressure of surrounding rock and the stress of supporting structure is within the safe state. (3) The material properties of the support structure in large deformation section are not fully utilized. The maximum compressive stress of shotcrete is 1 523 kPa, which is 6.3% of the ultimate strength, and that of grid steel frame is 24 553 kPa, which is 6.1% of the ultimate strength. (4) After the treatment of the large deformation section, the pressure of surrounding rock varies in the range of 0 ~ 85 kPa, the shotcrete stress varies in the range of -2 400 ~ 420 kPa, and the steel frame stress varies in the range of -33 000 ~ 1 600 kPa, indicating that the tunnel structure is in a stable state with large safety reserve. The monitoring results show that the control techniques of large deformation proposed is feasible in controlling the large deformation of tunnel in soilsand interbedded strata.

Key words: HaolebaojiJi′an railway, Yangcheng tunnel, soilsand interbedded strata, large deformation control technology, field test