Construction mechnical effect of highway tunnelwith four lanes in layered rockmass

Jiangshuiquan tunnel was a highway tunnel with four lanes. Its maximum excavation cross section was 170.1 m2 in Class III surrounding rock. The host rock was horizontal layered limestone, and it have obvious transverse isotropy. Based on laboratory experiments and site survey of rockmass structure, mechnical parameters of rockmass were determined. Numerical simulation and field test were used to study the deformation and failure characteristics of tunnel, pressure of surrounding rock, stress of shotcrete and lattice girder. It was concluded that lateral elasticity modulus of rockmass was obviously bigger than vertical elasticity modulus. Settlement of vault was the main deformation form of surrounding rock. Rock-falling in spandrel and delaminating collapse of roof were the common failure phenomenon. Setting rock bolt in vault was necessary in horizontal layered rockmass. Compared wtith other postions, pressure of surrounding rock, stress of shotcrete and steel frame of the vault were relatively small. (paper)