The Stability Evaluation Of Rockmass During Subsea Tunneling Ofxiamen In Weathered Trough

The undersea tunnel solves the traffic problem between the cross-strait and the Gulf,it does not occupy the land,and will not hinder the ship’s shipping at the same time.it will not affect the ecological environment,and has many advantages that are difficult to replace.Weathering trough is generally formed under the sea or underwater,which is one of the unfavorable geological phenomena.It has great influence on the construction and stability of submarine tunnels.Based on the full consulting of relevant research contents and taking a submarine tunnel in Xiamen as the actual engineering background,this paper expounds the special features of weathering trough as a submarine tunnel from the aspects of topography,stratigraphic lithology,geological structure and hydrogeological conditions,we know how it affects the construction safety of submarine tunnel.Based on the analysis of mineral composition,wear resistance test,point load test and direct shear test of surrounding rock of weathered channel,the main influencing factors on the stability of surrounding rock of tunnel in weathered channel section are established,the evaluation system of surrounding rock stability is established by using fuzzy analytic hierarchy process,and the stability of surrounding rock of six tunnel sections is evaluated.The results show that the tunnel passes through F9 weathered channel section.The deformation of surrounding rock is the largest in the trough section.The farther the weathering trough is above the tunnel,the smaller the deformation of surrounding rock.The conclusion that the surrounding rock is the most stable when there is no strong weathering layer above the tunnel can provide some reference for the follow-up construction.The stress-seepage coupling model of surrounding rock mass of submarine tunnel under four working conditions is analyzed.It is found that the weathering trough has great influence on the deformation of surrounding rock and seepage field of surrounding rock.In the process of tunnel excavation,the stratum above the tunnel subsides,the bottom of the tunnel heaves,and the existence of weathering trough will increase the deformation of surrounding rock.That is to say,the deformation of surrounding rock is the largest when it passes through the weathering trough,the next is through the weathering trough,and the smallest when it does not pass through the weathering trough.The variation of surrounding rock displacement is related to the location of the tunnel away from the bottom of the weathering trough when the tunnel passes under the weathering trough,that is,the influence of the weathering trough on the surrounding rock displacement is less when the distance between the two is longer.In the case of passing through the weathering trough,the segment displacement changes relatively large,and the pore water pressure at the bottom interface isthe largest.In the comparison of weathering trough types,the minimum principal stress value of segments passing through strong weathering trough is larger than that passing through medium weathering layer,and the maximum and minimum principal stress value of grouting layer is larger than that passing through medium weathering layer.The influence of relative position of weathering trough and tunnel on the stress-strain field and displacement field of surrounding rock is obtained by numerical simulation.Combined with the distribution characteristics of weathering trough and the experimental results,the evaluation system of surrounding rock stability of weathering trough section is established by analytic hierarchy process(AHP)and comprehensive index method.The rationality of the evaluation system is verified,and it has certain reference and auxiliary value for tunnel construction.