FIELD MONITORING AND ANALYSIS OF MECHANICAL BEHAVIOR OF SECTION STEEL FRAME FOR THE SHALLOW AND SMALL SPACING UNDERWATER TUNNEL

Liuyanghe Tunnel is the first shallow,small spacing underwater road tunnel by mining method in China,bench cut method was adopted and circular section steel frame was used as one of primary support measures in construction.The loading state of the arch frame is one of the key factors to be controlled to the stability of the support system.The stress and displacement of the arch frame were measured on site,and based on the massive measured data,the mechanical behavior of section steel frame was analyzed.The research shows that the stress is larger in vault and invert bottom;the stress is changed due to lower bench excavation,pouring concrete at inverted arch and secondary lining,the local stress for section steel frame of the ahead tunnel chamber is increased because of the laggard chamber excavation;the arch frame stress change is related to time-space effect and river water permeability.The test results of stress and displacement show that the bench length is reasonable.