| Subfluvial tunnel is usually restricted to the width of the riveris,and the shallow buried form is always used to satisfy the requirement of the slope setting,so it is easy to encounter the weak surrounding rock and even the terrene surrounding rock.The construction methods of the subfluvial tunnel mainly include mine method,shield method and immersed tube method.The mechanical properties are different when taking different construction methods.At present,the subfluvial tunnels which had been successfully completed by the mining method were still less in our country.In addition,to this kind of tunnel,the mature design concept and construction technology,even the systematic technology of the operation management and maintenance are insufficient.The mechanics properties of the tunnel are very complex because of the river water osmosis and the river level change,so it is necessary to explore step by step.At present,the river level changes above the tunnel can be generalized to maintain low river level for a period of time,and maintain high river level for a period of time,then maintain low river level for a period of time again.......The repeated changes of the river level will not only change the stress field of the tunnel again and again,but also change the seepage field of the tunnel repeatedly.Moreover,the strain of the surrounding rock will be changed during the invariable period of the river level.The Liuyang river highway tunnel in Changsha was taken as the research object,the mechanical properties of surrounding rock and lining were researched by laboratory test,numerical simulation and field observation.The main works and achievements are as follows:(1)The triaxial compression test,the uniaxial grade loading test,the uniaxial respectively loading test and the uniaxial low-frequency cyclic load test were carried out on the surrounding rock samples,and the cohesion and internal friction angle of the surrounding rock were obtained.The changing river level was simplified as a low-frequency cyclic load,and the deformation characteristics of the surrounding rock were obtained,in a few cases,it was found that the change of the axial strain of the surrounding rock could be delayed because of the influence of the river level repeated change.(2)The relatively complex numerical model were built.The constitutive model was matched by the laboratory test results of the surrounding rock,and this constitutive model subroutine was embedded into the numerical model.The numerical model have several features: hydromechanical coupling,the construction period of the tunnel connected with the service period,the river level repeated change in the 100 years service period.The mechanical properties of surrounding rock and lining had obtained through the numerical calculation.It was found that the vertical displacement of the river bed and the vertical displacement of the secondary lining vault all behaved fluctuant sinking in the service period of tunnel,and the fluctuation range will be steady after 70 years of service.(3)Many working cases of the numerical simulation had been comparative analyzed by change the design parameters of tunnel,and put forward some engineering suggestions.The lining mechanic properties will be obviously deteriorated,When the double hole interval of the section that the river level is deepest reduced from 1.5B to 1B.So it is should be considered carefully when optimization design the double hole interval.(4)The rationality of the numerical simulation had been verified by the results of field observation,and the seepage characteristics and the causes of tunnel seepage were analysis.Based on the field observation and the knowledge of river hydrology,the experience formula of river level above the Liuyang river tunnel were put forward.And 8 problems were discussed encountered in field observation,which can provide references for the similar subfluvial tunnel. |
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