Mechanism And Evaluation Of Multiple Coupling Effects Of Stratum Uncertainty And Adjacent Engineering Disturbances On Force And Deformation Of Shield Tunnel

With the growth and sustainable development of the urbanization rate,shield tunnels have been densely distributed which are the central part of the urban underground infrastructure.New construction projects will inevitably affect the existing tunnels,commonly including surface surcharge and deep excavation.Meanwhile,the stratum of tunnel embedded has various types of uncertainty,mainly containing: geological uncertainty in the heterogeneous layer and spatial variability of soil properties within one nominally homogeneous layer.The complex and uncertain environment will adversely affect the safe operation of existing tunnels.The uncertain stratum,adjacent loading,and unloading disturbances will undoubtedly have a coupling effect on the existing tunnels.It usually has a typical nonlinear effect for force and deformation of shield tunnel under the coupling action.There are still some challenges with unclear mechanisms and evaluation indicators at home and abroad.Substantially supported by NSFC No.51538009 and No.52130805,the coupling mechanism and influence of tunnel performance under the uncertain stratum and adjacent loading and unloading disturbances is thoroughly studied using different approaches,e.g.,physical model test,theoretical analysis,and numerical simulation.Main contributions and results are abstracted as follows:(1)Established a geological uncertainty simulation method and studied its effect on the force and deformation of the tunnel structure.A new method for estimating the horizontal transition probability matrix of coupled Markov chains is proposed,realizing the effective geological uncertainty simulation.A quantitative evaluation index(Geological Uncertainty Index,GUI)of stratigraphic heterogeneity is presented,and the location and number of boreholes are optimized based on information entropy theory.According to the collected boreholes data of two sites,results show that the site with a larger GUI value has a significantly more substantial influence on the force and deformation of the tunnel than a site with a smaller GUI value.Meanwhile,the boreholes located near the tunnel and the boreholes with larger GUI values have a greater weight on the effect of the tunnel structure’s force and deformation.(2)Constructed an intelligent estimation algorithm of spatial variability characteristic parameters based on CPT.A hybrid deep learning model combining Convolutional Neural Network(CNN)and random field theory is established to realize intelligent estimation of the characteristic parameters of soil spatial variability(vertical and horizontal scale of fluctuation).Only two CPT data are used to complete the practical estimation of the typical random field parameters,which overcomes the shortcomings of traditional methods requiring a large amount of field data.A surrogate model based on the deep learning algorithm is constructed to solve the high computational cost of the random finite difference method.The dropout technology is used to “retrain” the CNN model so that many different outputs can be obtained from the same input.Combined with the confidence interval,the quantitative evaluation of the prediction uncertainty of the machine learning model is realized.(3)Proposed a coupling effect index model considering the loading and unloading sequence effect.Based on the physical model test,a coupling effect index(ρ)is presented,which realizes the quantitative evaluation of tunnel force and deformational amplification effect under the coupling of loading and unloading disturbances.The coupling effect is divided into three parts: favorable coupling(ρ<1),zero coupling(ρ=1),and unfavorable coupling effect(ρ>1).According to the ρ value,it is divided into strong,medium and weak coupling effects.The coupling effects of tunnel deformation under different time-series of loading and unloading belong to the unfavorable coupling group,and the coupling effect index is more significant in the case of first loading and then unloading.(4)Revealed the mechanism of coupling amplification effect from the perspective of nonlinear stress-strain.Based on the Mindlin formula,the horizontal and vertical additional stresses of the surrounding area caused by the surcharge loading and excavation unloading are calculated,and then the maximum and minimum principal stress of the entire study area is obtained.The nonlinear soil stress-strain relationship is established based on the HS-Small constitutive model.Meanwhile,the additional strain is calculated by the additional stress.The ratio of the strain obtained after loading and unloading to the sum of the strain caused by loading and unloading alone is used as an index to measure the coupling effect of the soil element.The mechanism of the coupling amplification effect is expounded from the perspective of nonlinear stress-strain.(5)Quantitatively revealed the nonlinear evolution law of the coupling effect between the soil spatial variability and the multiple disturbances of loading and unloading,and proposed an evaluation method for coupling amplification effect.A stochastic probability analysis model is established considering the soil spatial variability and adjacent loading and unloading disturbances.The nonlinear influence laws of tunnel force and deformation under the multiple coupling effect of soil spatial variability and adjacent loading and unloading are systematically studied.Three simplified methods to simplify consider the soil spatial variability are proposed:reduction factor method,amplification factor method and reliability partial factor calibration method.A method for estimating the coupling amplification effect is presented under the impact of soil spatial variability and adjacent loading and unloading disturbances.Compared with the double coupling effect of adjacent loading and unloading,the coupling amplification effect of force and deformation of shield tunnel is more significant considering the spatial variability of parameters and the triple coupling effect of adjacent loading and unloading.