Study On Deformation Law Of Soil Stratum And Control Technology In Soft Soil Stratum Under Construction Of Shield Tunnel In Ningbo

The paper took construction of subway tunnel down-crossing railway bridge as the engineering background in soft soil stratum in Ningbo.Theoretical analysis,numerical simulation,model test and field test were used.Law of the surface settlement after excavation of shield tunnel,influence of soft soil creep to ground settlement,the influence of stratum deformation under train cyclic loading,interaction of shield tunnel,foundation and upper structure and control standards and construction countermeasures were studied.The key work and conclusions of the paper were as follows:(1)Creep characteristics of Ningbo subway silty clay and silty clay typical soil samples were analyzed by triaxial undrained consolidation rheological test,and the crep test showed that the soft soil creep only stayed a decay phase when stress level was lower,which belonged to the creep stability.With the growth of the stress level,the soil creep deformation increased gradually.When the loading reached 80kPa(silty clay reached 100kPa),the creep law of the soil presented decay creep stage and steady creep stage.(2)Physical and mechanical parameters of soil consolidation and creep characteristics under the condition of drainage of soft soil were obtained in Ningbo by triaxial creep test of soil consolidation and drainage.The test revealed the soft soil consolidation and creep influence of strata deformation.(3)Studied on the effect on train speed to soft soil settlement law.The total cumulative settlement of underlying soil increasing exponentially was by train cyclic loading.The train speed to the long-term settlement of soft soil had a significant effect.Reduced the speed could reduce the soil settlement caused by train the cyclic loading in the stage of shield tunnel construction.(4)Based on triaxial of the soft soil,and Studied on the influences of train cyclic load to the Ningbo soft soil stratum deformation,and the influence law of the train dynamic load to the strata deformation was revealed using modified exponential prediction model,numerical simulation and layerwise summation method.(5)Considering the interaction of creep and cyclic loading of train formation,and settlement control standard and construction control measures of settlement were developed shield tunnel under Xiaoyong railway in Ningbo.The technology for the tunnel under construction and security support was provided.