查看更多>>摘要：The sanding process caused by karstification in dolomite creates a special sandy dolomite stratum,where the frequent catastrophic instability of the surrounding rock occurred during tunnel construction.In this study,the micro-origin and macro-performance of the sandy dolomite stratum are first discussed.Then,a numerical model based on the coupling method between the discontinuous deforma-tion analysis and smoothed particle hydrodynamics is proposed to depict the heterogeneous dolomite formation with different sanding degrees.Following,the mechanical behaviors of the heterogeneous dolomite samples under uniaxial compression are studied after cal-ibrating the numerical parameters with the two single materials sampled from the tunnel site respectively.Further,the instability disas-ters of the dolomite surrounding rock with different sanding degrees are reproduced,and the failure behaviors of tunnels are explained with respect to the stress distribution and plastic zone.The obtained results show that the rotation and dislocation of the remained dolo-mite block contribute to the unsmooth stress-strain curve and deterioration in uniaxial compressive strength.However,the block serves as the skeleton in the transmission of field stress in underground space,which improves the stability of the formation.
查看更多>>摘要：Through the active control of shield thrust system oil pressures,a synchronous shield tunnelling technology combining advancement and segment fabrication was proposed.The key to this technology was to completely exploit the additional stroke of the hydraulic jacks generated by the axial insertion of a key block to assemble the segments.Taking the tunnelling project of the Shanghai Airport Railway Link Line as a demonstration project,this paper uses a large model test platform for this synchronous technology.A single-ring con-struction process along a straight line was simulated,in which the theoretical external loads were implemented on the shield machine.The feasibility and reliability of this synchronous technology were evaluated considering the accuracy of total thrust force control,main-tenance of tunnelling speed and shield postures and segment compression.The effectiveness of the redistribution principle for the missing thrust force due to the withdrawal of cylinders located in the segment fabrication region was discussed.Furthermore,some other inter-esting phenomena were observed in the practical application in addition to the model test.This technology primarily realizes syn-chronous assembly by improving the control of the propulsion system of conventional shield machines without any transformation of the shield machine's primary structure,segment patterns or excavation method.The proposed method has good adaptability and a low construction cost,which will be beneficial for future long-distance tunnelling projects.
查看更多>>摘要：An augmented methodology is developed to estimate the reliability of deep excavations along spatially variable massive rock masses using the cohesion weakening friction strengthening(CWFS)model.Sensitive parameters of the CWFS model were initially identified using Sobol's global sensitivity analysis based on their influence on the displacements and excavation damage zone around excavations.The probability of failure was estimated by performing Mont-Carlo Simulations on random finite difference models of excavations gen-erated via MATLAB-FLAC2D coupling,considering the spatial variation of these sensitive parameters.Spatial variation was modeled by generating anisotropic random fields of sensitive CWFS parameters via the recently developed Fourier series method and updated correlations suggested by Walton(2019).The proposed methodology was demonstrated for a proposed deep nuclear waste repository to be located in Canada.Results from the developed methodology were systematically compared with those of traditional reliability(ig-noring spatial variation)and deterministic methods(ignoring uncertainty).Although the developed methodology was computationally complex,it was judged to be the most realistic due to the realistic consideration of heterogeneous distributions of rock properties.Tra-ditional methodologies underestimate/overestimate the excavation performance due to negligence of uncertainty and spatial variability.Finally,a parametric analysis was performed using developed methodology by varying the initial friction angle,scale of fluctuations(SOFs)and dilation angle.The effect of initial friction angle was observed to be more pronounced on the probability of failures as com-pared to SOFs and dilation angle.Similar observations were made related to the excavation damage zone(EDZ)development quantified using yield area ratio.
查看更多>>摘要：The Hutubi gas field was put into production in 1998 and then converted into an underground gas storage(UGS)facility in 2013,and since then a cluster of earthquakes associated with seasonal injection and extraction activities have been recorded nearby.To evaluate the fault stability and seismic potential,we established a pseudo-3D geomechanical model to simulate the process of seasonal injection and extraction.Reservoir pore pressures from 1998 to 2019 were obtained through multiphase reservoir simulation and validated by history matching the field injection and production data.We then imported pore pressures into the geomechanical model to simulate the poroe-lastic perturbation on faults for over 20 years.The fidelity of this model was validated by comparing the simulated surface deformation with global positioning system(GPS)measured data.We used Coulomb failure stress(CFS)as the indicator for the likelihood of fault slippage.The simulation results show that the location of the induced earthquake cluster was within the positive Coulomb stress pertur-bation(ACFS)area,in which fault slippage was promoted.In addition,ACFS at the earthquake location kept increasing after the injec-tion began.These findings could explain the induced earthquakes with the Coulomb failure stress theory.Furthermore,we conducted a parameter sensitivity study on the dominant factors such as the maximum operating pressure(MOP),frictional coefficient,and dip angle of the pre-existing fault.The results indicate that the magnitude of ACFS caused by seasonal injection and extraction decreases with distance;MOPs are constrained to 32.9,36.2,and 39.5 MPa according to different ACFS thresholds;the critical dip angle ranges are 0-20° and 80°-100°;and strengthening the fault friction can either increase or decrease the seismic potential.This study can help deter-mine the MOP for Hutubi underground gas storage(HTB UGS)and provide a framework for simulating the potential causes of induced seismicity for other sites.
查看更多>>摘要：This paper aims to provide the analytical solutions of the ground settlement for a space curved shield tunnel in the case of yaw con-struction.Settlement inducements include ground loss and construction loads,and two corresponding analytical models have been pro-posed in this study.Three-dimensional image theory has been adopted to calculate the ground settlement due to ground loss.Yaw-related 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 solu-tions 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.
查看更多>>摘要：The water leakage through segmental joint gaskets has become a major concern that adversely affects the normal serviceability of underwater shield tunnels throughout the construction and operational periods.Therefore,it is of great significance to investigate the sealing performances of the joint gaskets,which directly helps evaluate the waterproof capacity of underwater shield tunnels.To date,the numerical modeling plays an irreplaceable role in the analysis on the waterproof capacity of the joint gaskets.Nevertheless,conven-tional methods tend to ignore the self-sealing effect induced by the water seepage pressurization,thus failing to reveal the progressive evolution of the water infiltration process through the joint gasket.To remedy this defect,this paper proposed a novel numerical model to simulate the penetration process of the sealing gasket based on the Python language-enabled secondary programming in the ABAQUS software,which could fully consider the superimposed seepage squeezing effect.Based on the proposed model,the waterproof failure process and the dynamic contact stress of the gasket's water seepage path subject to excessive hydraulic pressure were thoroughly inves-tigated.Moreover,indoor tests on the waterproof capacity of the gasket were also performed to validate the proposed model.It is found that the numerical results from the developed model are consistent with the experimental results.This research will contribute to better understanding of the gaskets'hydraulic penetration process and more accurate prediction of the maximum waterproof capacity in under-water shield tunnels.
查看更多>>摘要：Estimating average vertical pillar stresses is a critical step in designing room-and-pillar mines.Several analytical methods can be used to estimate the vertical stresses acting on the pillars.However,the present analytical methods fail to adequately account for the influence of abutments on the distribution of vertical stresses,especially when applied to narrow panel widths and pillar layouts comprising evenly spaced barriers.In this study,a multi-layer perceptron neural network(MLPNN)was applied to predict the vertical loads of regular pillars more accurately.Hundreds of room-and-pillar mine layouts were modeled using a displacement discontinuity method(DDM),and a database of 2355 sampled pillar cases was compiled.The MLPNN was trained based on this database,and its prediction capa-bilities were further validated using simulations by a finite difference code(i.e.,FLAC3D).The model predictions and the FLAC3D sim-ulations reasonably agreed with a regression coefficient of 0.99.The model was also adapted for mine cases with evenly spaced barrier pillars,and its application to a real case study mine has shown to provide accurate pillar stress estimations;hence,this model is suitable for practical use at mines.Even though the MLPNN model cannot be applied universally to all mine situations,it seems as a significant improvement over existing analytical techniques in terms of accounting for the influence of abutments on pillar stresses.
查看更多>>摘要：An advanced stability analysis of surrounding rock can assure safe construction in tunnels.However,in traditional analysis methods,geometric information on the rock mass discontinuities is obtained by a geological compass and treated as an infinitely expanded plane in a numerical simulation,which is inaccurate in both geometric and numerical models.To solve this problem,this paper studied a control network and an image stitch method to assess the accuracy of a geometric model and proposed a more accurate method to obtain the geometric information of rock mass discontinuities based on digital photogrammetry.Based on discrete fracture network and discrete element method(DFN-DEM),this paper treated the rock mass discontinuities obtained by digital photogrammetry as finite disk planes and simulated the excavation process of the Qianyu tunnel.According to the simulation results,this paper determined the specific loca-tion of the collapse disaster on the tunnel face,which is of great significance to tunnel support design.Comparing the deformation of the surrounding rock mass on the tunnel face in the simulation results with the actual situation,this paper verified the feasible accuracy of this method in analysing the stability of the surrounding rock mass on a tunnel face in advance.
查看更多>>摘要：In this study,a series of undrained cyclic torsional shear tests were conducted to investigate the effect of cyclic loading frequency f on the pre-liquefaction(shearing contractive(SC)period and initial shearing dilative(ISD)period)and post-liquefaction(late shearing dila-tive(LSD)period)deformation properties of saturated Fujian sand.The secant shear modulus G and damping ratio A in the entire cyclic loading process,and the unloading tangent shear modulus GLi and flow deformation tangent shear modulus GL2 in the ISD and LSD periods were adopted to quantitatively characterize the evolution of hysteresis loop with an increase in shear strain amplitude γa.The test results show that the effect of f on G of saturated Fujian sand in the SC period is not apparent.However,all the G-γa,GL1-γa,and GL2-γa curves in the ISD and LSD periods showed a downward trend with an increase in f.This study also proposes a modified method for calculating 2 to compensate for the analytical error caused by the non-closure of hysteresis loop.Compared with the classical curves that mainly applied in geotechnical engineering,the A first increases and then decreases with the increase of Ya.Furthermore,the A evaluated by the modified method is approximately 10％-15％more than the A evaluated by the traditional method when the A reaches its peak value.
查看更多>>摘要：Geothermal energy is a kind of green and renewable energy.Conventionally,ground source heat pumps can be used to harvest geothermal energy from the subsurface.To reduce the initial investment,a good solution is to use tunnel linings as heat exchangers to extract/dump heat.This special infrastructure is called an energy tunnel.In addition to the thermal performance,the impact of pipe network configuration on thermal efficiency is still challenging in the design of energy tunnels.To solve this problem,this study makes the first attempt to carry out research on the optimization of pipe circuits in energy tunnels by a series of numerical analyses.A fully coupled thermo-hydraulic 3D finite element model is established to investigate the response of tunnel-soil interaction under cyclical ther-mal loading(initial soil temperature varies from 8 ℃ to 18 ℃),as well as the thermal transient interactions among air,absorber pipe,tunnel linings and ground,to quantify the amount of useful heat that can be extracted from the tunnel and the ground.On the other hand,the influence of 3 various heat-carrying pipes layout is also investigated.It is found that higher heat transfer efficiency can be obtained when the entrance and exit of pipelines are located below the tunnel in the study.The spatial location of pipelines will also affect the exchanged heat output.
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