Large-scale model test study of the mechanical characteristics on sprayed ECC layer of highway tunnel under confining pressure

Abstract

As the geological environment of highway tunnels becomes increasinlgy complex, sprayed engineered cementitious composites (ECC) has broad application prospects in the field of highway tunnel support. This study focuses on the shotcrete layer in the initial support of Wulingtou extra-long highway tunnel, the 1:4 scale model test of sprayed ECC layer under confining pressure was prepared. Its mechanical properties and real-time joint monitoring are determined using strain gauges, distributed optical fibers, and cameras. The results show that the maximum confining pressure of the sprayed ECC layer is 0.975 MPa with the maximum displacement of 15.497 cm, which outperforms ordinary shotcrete. The loading process of steel bars and sprayed ECC can be divided into three stages, with the change rate of these three stages showing an ascending trend. The failure mode is ductile, involving normal section, oblique section compression shear failure and bending shear failure. In addition, based on the similarity theory, the real mechanical characteristics of the sprayed ECC layer at the tunnel site can be predicted according to the experimental model.