Dynamic prediction of over-excavation gap due to posture adjustment of shield machine in soft soil

The probability analysis of ground deformation is becoming a trend to estimate and control the risk brought by shield tunnelling.The gap parameter is regarded as an effective tool to estimate the ground loss of tunnelling in soft soil.More specifically,x,which is a gap parameter component defined as the over(or insufficient)excavation due to the change in the posture of the shield machine,may contribute more to the uncertainty of the ground loss.However,the existing uncertainty characterization methods for x have several limitations and cannot explain the uncertain correlations between the relevant parameters.Along these lines,to better characterize the uncertainty of x,the multivariate probability distribution was developed in this work and a dynamic prediction was proposed for it.To attain this goal,1523 rings of the field data coming from the shield tunnel between Longqing Road and Baiyun Road in Kunming Metro Line 5 were utilized and 44 parameters including the construction,stratigraphic,and posture parameters were collected to form the database.According to the variance filter method,the mutual information method,and the value of the correlation coefficients,the original 44 parameters were reduced to 10 main parameters,which were unit weight,the stoke of the jacks(A,B,C,and D groups),the pressure of the pushing jacks(A,C groups),the chamber pressure,the rotation speed,and the total force.The multivariate probability distribution was constructed based on the Johnson system of distributions.Moreover,the distribution was satisfactorily verified in explaining the pairwise correlation between x and other parameters through 2 million simulation cases.At last,the distribution was used as a prior distribution to update the marginal distribution of x with any group of the relevant parameters known.The performance of the dynamic prediction was further validated by the field data of 3 shield tunnel cases.

Analytical solutions to ground settlement induced by ground loss and construction loadings during curved shield tunneling

This paper focuses on the ground settlement induced by the construction of a curved shield tunnel.Ground loss and construction loadings are the two factors causing ground settlement,and two corresponding analytical models were developed.First,the ground settlement due to ground loss was analyzed based on 3D image theory.The"integrative gap at shield tail"(IGST)and overcutting gap of a curved tunnel were considered.Second,the ground settlement due to construction loadings was analyzed by modifying Mindlin's solutions.The additional thrust,frictional force,and grouting pressure were considered.Subsequently,a case study and a parameter analysis were conducted.Finally,the obtained solutions were compared with a classical analytical solution,numerical simulations,and monitored results.The proposed model could effectively predict the ground settlement in-duced during curved shield tunneling.

Analytical solutions of ground settlement induced by yaw in a space curved shield tunnel

This paper aims to provide the analytical solutions of the ground settlement for a space curved shield tunnel in the case of yaw construction.Settlement inducements include ground loss and construction loads,and two corresponding analytical models have been proposed in this study.Three-dimensional image theory has been adopted to calculate the ground settlement due to ground loss.Yawrelated parameters are introduced into the calculation model to deduce the relevant laws of the ground settlement.Based on modified Mindlin solutions,analytical models are established to calculate the ground settlement induced by construction loads,such as the frontal additional thrust,axial friction of shield shell,and the grouting pressure.The method of calculating the position of the shield machine in the ground is refined,and the influence area of construction loads from the shield machine is optimized.Subsequently,the obtained solutions are validated by a numerical model and field data.Besides,a comparison reveals that the proposed model is the composition of three classical analytical models,thus it excels them in solving the problem mentioned.Finally,parametric analyses of yaw are conducted to examine yaw angle and pitch angle on ground settlement.The proposed model can effectively predict ground settlement caused by the spatial linear shield tunneling process.

Surface settlement caused by twin-parallel shield tunnelling in sandy cobble strata

City metro tunnels are usually constructed as twin-parallel tunnels and their adjacent construction may lead to surface deformation,affecting the surface environment and the safety of the tunnels.Due to its strong dispersion,sandy cobble strata can be easily disturbed by shield tunneling.Based on the project of the Chengdu Metro Line 1,field and model tests were carried out to study the surface settlement caused by shield tunneling in sandy cobble strata by measuring surface settlement curves,ground loss ratios and construction influence zones.The discrete element method(DEM) was used to study the factors affecting the formation of ground arches in sandy cobble strata at the microscopic level.Results show that the shape of the surface settlement curve in sandy cobble strata is different from that in soft soil.The buried depth and clear spacing of the two tunnels had a significant impact on the formation of ground arches.

Three-dimensional numerical analysis of the interaction of two crossing tunnels in soft clay

Recently,with the development of underground construction,multi-tunnel engineering has become a matter of concern since the interaction between tunnels at close ranges could cause additional deformation in strata as well as surrounding structures and even serious damage to surface buildings.These tunnel displacement and soil deformation problems can be effectively predicted using numerical methods considering the influence of various factors,such as the anisotropic nature of soft clay.To this end,the anisotropic elastoplastic constitutive S-CLAY1 is implemented in finite element code to investigate deformation problems in the strata and nearby structures caused by the excavation of multi-tunnels.This paper focuses in particular on configurations of two crossing tunnels.Multiple 3D numerical simulations using ABAQUS enable successive analyses conducted for tunnels at different spacings(1.5D,2.5D,3.5D and 4.5D,where D is the tunnel diameter)of configurations aligned vertically.The results,including the ground settlement,lining force and moment,and tunnel convergence,are analyzed.For each aspect,the most unfavorable case is determined by comparing the results of different simulations.This investigation can provide a reference for multi-tunnels design and construction.