Geotechnical Monitoring and Analyses on the Stability of Highway Tunnel Constructed in Carbonaceous Slate Stratum

Abstract

There were several damaging behaviors observed in a highway tunnel under construction, caused by the large deformation of rock mass. For this reason, a laboratory test to analyse the mineral composition was implemented, which aims to figure out the cause of the large deformation when tunneling in carbonaceous slate stratum. The laboratory test shows the reactivity of clay minerals with water is one of the important reasons lead to large deformation. Especially, field test was adopted to evaluate the structural stability and safety, affected by large deformation resulted from carbonaceous slate stratum. Displacement of primary lining, internal force of steel arch, pressure between primary lining with rock mass, internal force of secondary lining and seepage pressure of tunnel bottom were monitored and presented during tunneling. The results demonstrate that the mechanical response and stress state of the tunnel reflect the influence of the large deformation. For primary lining, large and asymmetrical deformation, which may result in the failure of steel arch, shows high risk in safety. Moreover, according to the calculated criterion of bearing capacity, once the secondary lining starts to bear pressure from rock mass, unsafety and minor safety reservation of the secondary lining were obtained in two regions of this structure. The result in this paper can provide valuable guidance for the subsequent construction and the similar engineering projects located in this area.