Dynamic Characteristics And Long-term Settlement Of Basement Soft Soil In Shenzhen Qianhai Tunnel

There is a large amount of deep marine soft soil in the coastal area,and the soft soil layer is prone to accumulate plastic deformation under the long-term action of vibration load.Therefore,the tunnel passing through soft soil often has large settlement and deformation during operation,which will seriously affect the normal operation and structural safety of the tunnel.The problem of long-term settlement of tunnels during operation has gradually become an important issue in the process of transportation planning,design,operation and maintenance.As the first cross sea access in Shenzhen,the construction of Mawan subsea tunnel will bear the important task of traffic diversion in Qianhai,Shenzhen,and play an important role in transport links.However,there are a lot of deep soft soil layers along the Manwan Tunnel,which will bring great challenges to its design,construction and operation.Under the background of Manwan Tunnel,this paper takes the tunnel soft soil as the research object,studies the cumulative deformation rule of soft soil under dynamic load,and predicts the long-term settlement and deformation development trend of tunnel soft soil under vehicle load.The main research contents and related achievements are as follows:(1)In the process of soil parameter parsing,random-fuzzy statistical method is introduced to analyze all physical and mechanical parameters,and it is compared with the traditional stochastic statistical method.It is found that the spatial coefficient of variation of stochastic-ambiguous statistical results is smaller,and related parameters Closer to the actual situation.According to the analysis results,the soft soil characteristics in the line site are summarized and analyzed,which will provide reference for the subsequent design and construction.(2)Based on the DDS-70 dynamic triaxial test instrument,the cumulative deformation development rule of the specimen under different confining pressure,dynamic stress,loading frequency,static bias stress and loading times is analyzed.On the base of the hyperbolic model,the cumulative plastic deformation formula of soft soil under different working conditions is established.Compared with the test results,it is found that the fitting effect is good and can provide service for the long-term settlement prediction of the tunnel.(3)The three-dimensional finite element model is established by Midas/GTS,and the dynamic response rule of tunnel soft soil under different driving speed,vehicle load and segment thickness is analyzed.It is found that the vehicle load has the most significant influence on the vertical dynamic of the tunnel soft soil,and the influence area of the vehicle load is about the depth of 4m below the tunnel base.(4)Based on the cumulative plastic deformation model,the stratified summation method is used to predict the long-term settlement of the soft soil layer at the bottom of the tunnel.The increase of driving speed and vehicle load will cause the increase of long-term settlement of the tunnel.When the vehicle is overloaded 80%,the cumulative settlement of the tunnel increases to nearly 31%.Increasing the slice thickness can reduce the cumulative settlement.However,the effect of increasing the segment thickness only on the cumulative settlement is not obvious.