Based on an underwater shield tunnel project,this study introduces the phenomenon of abnormal shutdown and the measures designed to mitigate problems in construction.On the strength of the analysis of the slurry leaka...Based on an underwater shield tunnel project,this study introduces the phenomenon of abnormal shutdown and the measures designed to mitigate problems in construction.On the strength of the analysis of the slurry leakage causes during re-tunneling,the mech-anism of slurry leakage induced by jack retraction was studied,and treatment measures of leakage at shield tail brushes were elaborated upon.The results show that the sudden change of stratum leads to an abnormal shutdown,and a sharp increase in the slurry pressure at the shield cut location leads to the slurry penetrating the gap between the outer wall of the shield shell and the soil,increasing the risk of instantaneous breakdown at shield tail brushes.The radial displacement of the outer wall of the segments caused by retractions of three jacks and a single jack along the circumferential direction distinctly shows three regions and four regions,respectively.The radial shrink-age of the outer wall of the segments at the jack retraction position decreases the tightness between the shield tail brushes and the outer wall of the segments.The expansion of the outer wall of the segments at the surrounding position,especially at the lower position,increases the slurry level to the radial shrinkage position of the segments,which increases the risk of slurry leakage.Furthermore,when the shield machine faces an abnormal shutdown,re-tunneling,and assembly of segments,the jack can be gradually retracted from top to bottom.The slurry leakage degree can be observed when retracting,and the corresponding measures can be taken for timely plugging.According to the leakage degree,it can be determined whether to replace the shield tail brushes to reduce the risk of large-scale leakage accidents.展开更多
This paper presents a case study of deep excavation adjacent to an existing bridge in karst region of Guangzhou city,China.The movements of retaining structures,settlements of surrounding ground and pipelines,and the ...This paper presents a case study of deep excavation adjacent to an existing bridge in karst region of Guangzhou city,China.The movements of retaining structures,settlements of surrounding ground and pipelines,and the responses of bridge piles were measured and evaluated.A sudden surge of groundwater was recorded at the north pit when excavated halfway.Soil-cement columns using the Metro Jet System(MJS)method was employed along the outer perimeters of the diaphragm wall where water inflow occurred,for the sake of blocking the flow channels.The measured maximum wall deflection dhm in this case ranged from 0.13%H to 0.3%H,with a mean value of 0.2%H(H is the excavation depth),which agreed well with the empirical prediction in mixed ground.During the MJS treatment,the wall and surrounding soils experienced notable lateral deflection and settlement.The bridge piles experienced significant settlement since the excavation commenced,which might be attributed to the inherent deficiency in geological condition and pile length.The soil disturbance induced by the adjacent deep excavation accelerated bridge settlement.The finite element analysis revealed that the excessive settlement of the bridge piles and ground surface resulted from confined-water withdrawal in sand layers.展开更多
The full-field strain of rock material under dynamic compression load was studied using the high-speed three dimensional digital image correlation(3D-DIC)method.The dynamic test was conducted on Laizhou granite using ...The full-field strain of rock material under dynamic compression load was studied using the high-speed three dimensional digital image correlation(3D-DIC)method.The dynamic test was conducted on Laizhou granite using a split Hopkinson pressure bar(SHPB)method.Wave propagation,dispersion and radial inertial effect on the specimen were found by DIC results.A recovery of strain in the post-peak stage was detected on the specimen by DIC,which was unrevealed in the traditional one-dimensional theory method.It can be found that the strain measured by strain gauge was a calculated average one,whereas the strain measured by 3D-DIC could reflect more variation details.Specifically,the testing principle with impact loads and rock dynamic behavior was re-examined using stress wave propagation theory.The theoretical results showed that the specimen reached equilibrium after a series of wave reflections and transmissions and its stress was infinitely close to the initial value of 109.2 MPa.Moreover,the specimen had the calculated maximum strain of 0.52% and strain rate of 15.11 s^(-1),improving the reasonable agreement with the experimental results and requirements of rock mechanical properties measured by SHPB technology.展开更多
Due to the shield tunneling underneath,long-term settlements may develop in the existing metro tunnels.The compensation grouting is applied worldwide to stabilize the settlement of ground and existing structures.Few f...Due to the shield tunneling underneath,long-term settlements may develop in the existing metro tunnels.The compensation grouting is applied worldwide to stabilize the settlement of ground and existing structures.Few field studies concerning large-diameter shield pass-ing tunnel from below have analyzed the interaction between the compensation grouting and the existing tunnel.This paper presents a case study on the response of the operating metro tunnels to the compensation grouting of an underlying large-diameter tunnel in muddy clay stratum.The tunnel deformations before,during,and after the compensation grouting were monitored and analyzed.The long-term tunnel settlements were mitigated and stabilized by the timely compensation grouting.Smaller settlement rates were observed during the grouting treatment,and the settlement was gradually stabilized three months after the grouting.The grouting holes at the tunnel invert were used initially for better grouting efficiency.The horizontal displacement and convergence developed during the grouting construc-tion and remained stable after the grouting process.Moreover,some limitations of the grouting treatment were discussed.The tunnel settlement in the section close to the center-line of the south-line tunnel cannot be prevented effectively.The differential displacement cannot be reduced by this grouting program.展开更多
A probabilistic study of a circular tunnel excavated in a soil mass using the response surface methodology(RSM)is presented.A deterministic model based on two-dimensional numerical simulations in a transversal section...A probabilistic study of a circular tunnel excavated in a soil mass using the response surface methodology(RSM)is presented.A deterministic model based on two-dimensional numerical simulations in a transversal section is used,and the serviceability limit state(SLS)is considered in the analysis.The model permits the surface settlement curve and the bending moment on the tunnel lining to be obtained.Only the soil parameters are considered as random variables.Thefirst-order reliability method(FORM)and the response surface methodology(RSM)are utilized for the assessment of the Hasofer-Lind reliability index(bHL)optimized by the use of a genetic algorithm(GA).Two assumptions(normal and non-normal distribution)were used for the random variables.The comparison analysis considering a correlation between the friction angle and the cohesion indicates that the results are conservative if a negative correlation among strength parameters is not taken into account.The assumption of a non-normal distribution for the random variables has an important effect on the reliability index for the practical range of values of surface settlements.展开更多
With the reduction of shallow resources,the degree of damage and the frequency of dynamic hazards,such as deep rock bursts and impact ground pressure,are increasing dramatically.However,the existing support materials ...With the reduction of shallow resources,the degree of damage and the frequency of dynamic hazards,such as deep rock bursts and impact ground pressure,are increasing dramatically.However,the existing support materials are incapable of meeting the safety require-ments of the refuges and roadways under a strong impact force.To effectively solve these problems,a novel negative Poisson’s ratio(NPR)anchor cable with excellent properties,such as impact resistance and the ability to withstand large deformation,is proposed.In the present study,a series of field tests and numerical simulations are conducted to investigate the mechanical and support charac-teristics of NPR anchor cables under blast impact.Laboratory mechanical tests show that NPR anchor cables can maintain constant resistance and produce large deformation under the action of multiple drop hammer impacts.According to the results of field tests,the roadway supported by conventional anchor cables was unable to endure the blast impact,while the roadway supported by NPR anchor cables was able to withstand the severe impact equivalent to a Class 3 mine earthquake.The dynamic response of the NPR anchor cable that supports the roadway under explosion is investigated using the innovative coupled modeling approach that combines the finite element method and the discrete element method,and the support effect of the NPR anchor cable is verified.The study shows that the NPR anchor cable has a superior impact and blast resistance performance,and a broad application prospect in the support of chambers and roadways that are at high risk of rock bursts and impact ground pressure.展开更多
In circular shield tunnels bearing high inner pressure or rectangular shaped shield tunnels,as the axial force at the segmental lining decreases,the bolt load at the segmental joint increases.It is essential to adopt ...In circular shield tunnels bearing high inner pressure or rectangular shaped shield tunnels,as the axial force at the segmental lining decreases,the bolt load at the segmental joint increases.It is essential to adopt high-stiffness segmental joints to improve the bearing capacity and control the deformation at the joint position.When designing high-stiffness segmental joints,the selection of ductileiron joint panel is crucial.In this study,two types of segmental joints with different joint panels were fabricated,and the effects of joint panel stiffness on the mechanical properties of segmental joints were analyzed through full-scale sagging and hogging bending tests.The results showed that the failure mode of high-stiffness segmental joint was similar to that of large eccentric compression section.According to the difference of panel stiffness,the failure modes can be specified into two types.If the stiffness is sufficient,the joint failure occurs due to the yielding of bolts;otherwise,it occurs due to the large deformation of ductile-iron joint panels.As for the design requirement of segmental joint,the stiffness of joint panel should be sufficient,i.e.,the opening and failure of the joints are finally induced by the bolt deformation.Otherwise,before the plastic deformation of the bolts,the large deformation of the joint panels will occur under a bendingmoment-dominant load,and the bearing capacity of the joints will greatly decrease.展开更多
Empirical models provide a practical way to estimate the displacements induced by excavations.However,there are uncertainties associated with the predictions of empirical models owing to:(a)the imperfect knowledge of ...Empirical models provide a practical way to estimate the displacements induced by excavations.However,there are uncertainties associated with the predictions of empirical models owing to:(a)the imperfect knowledge of the model and(b)the uncertainties of the input variables.The uncertainties of these models can be characterized by a bias factor which is defined as the ratio of the actual displacement to the predicted displacement.The bias factors associated with the C&O method and the KJHH model are evaluated using the Bayesian method and a database of 71 excavations in Shanghai.To improve the predictions of the maximum displacement,an adaptive algorithm is proposed using field performance data.The performance of the proposed algorithm is demonstrated by an example in which excavation-induced displacements are generated by finite element method in normally consolidated clays.The example shows that the developed algorithm can significantly improve the predictions by incorporating the field performance data.展开更多
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,t...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 deformation 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 calibrating the numerical parameters with the two single materials sampled from the tunnel site respectively.Further,the instability disasters 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 dolomite 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.展开更多
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 com...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 location 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.展开更多
To date,the accurate prediction of tunnel boring machine(TBM)performance remains a considerable challenge owing to the complex interactions between the TBM and ground.Using evolutionary polynomial regression(EPR)and r...To date,the accurate prediction of tunnel boring machine(TBM)performance remains a considerable challenge owing to the complex interactions between the TBM and ground.Using evolutionary polynomial regression(EPR)and random forest(RF),this study devel-ops two novel prediction models for TBM performance.Both models can predict the TBM penetration rate and field penetration index as outputs with four input parameters:the uniaxial compressive strength,intact rock brittleness index,distance between planes of weakness,and angle between the tunnel axis and planes of weakness(a).First,the performances of both EPR-and RF-based models are examined by comparison with the conventional numerical regression method(i.e.,multivariate linear regression).Subsequently,the performances of the RF-and EPR-based models are further investigated and compared,including the model robustness for unknown datasets,interior relationships between input and output parameters,and variable importance.The results indicate that the RF-based model has greater prediction accuracy,particularly in identifying outliers,whereas the EPR-based model is more convenient to use by field engineers owing to its explicit expression.Both EPR-and RF-based models can accurately identify the relationships between the input and output param-eters.This ensures their excellent generalization ability and high prediction accuracy on unknown datasets.展开更多
Energy piles are a new type of heat exchange systems with buried pipes in a pile foundation,which optimize a ground source heat pump system for the utilization of shallow geothermal energy.In this study,based on the p...Energy piles are a new type of heat exchange systems with buried pipes in a pile foundation,which optimize a ground source heat pump system for the utilization of shallow geothermal energy.In this study,based on the principle of similarity,the thermo-mechanical behavior of the model energy pile with a large cross-section in saturated sandy soil was experimentally evaluated.The pre-cast model concrete pile with a diameter of 0.2 m and length of 1.5 m was buried in saturated sand in a steel box with dimensions of 2.5 m×2.5 m×2.0 m(length×width×height).The pile was heated using water in the polyethylene(PE)pipe,which was connected to a water cycle temperature controller.At a constant inlet water temperature of 55℃,three thermal cycles were carried out with the same heating and cooling periods and different water flow rates.The temperature distributions in the pile and soil,in addition to the pore pressure,soil pressure,and displacement of the pile,were monitored to clarify the thermo-mechanical behavior of the pile and soil.The heat transfer efficiency was analyzed based on the temperature difference and water flow rates.The measured strain at different locations in the pile under cyclic thermal loading revealed that the uneven strain that developed in a pile body should be considered for its long-term application.Furthermore,focus should be directed toward the long-term unrecoverable displacement of the energy pile due to the thermal plastic strain and thermal consolidation of the soil.展开更多
Stress changes in the soil induced by tunnel excavation may cause excessive ground settlement.However,high-quality experimental data on ground settlement due to tunnel excavation are limited.In this study,centrifuge t...Stress changes in the soil induced by tunnel excavation may cause excessive ground settlement.However,high-quality experimental data on ground settlement due to tunnel excavation are limited.In this study,centrifuge tests are conducted to investigate the threedimensional ground surface settlement,considering different intersection angles and cover-to-tunnel diameter ratios.The results indicate that the major influence zone along the longitudinal direction on the ground surface settlement is±1.25D,where D is the tunnel diameter.When the monitoring section is perpendicular to the tunneling direction,the transverse ground settlement due to the tunnel excavation is symmetrical with respect to the tunnel centerline.In contrast,an asymmetric ground settlement profile is observed when the monitoring section intersects the tunneling direction at an angle of 60.Applying a Gaussian curve to fit the ground surface settlement curve,the width parameter,K(i.e.,the distance between the tunnel centerline and the inflection point of the settlement trough to the tunnel burial depth),varies from 0.33 to 0.39.The ground surface settlement induced by twin tunnel excavation can be captured reasonably by superimposing two identical Gaussian curves.When the cover to tunnel diameter ratios(C/D)are 1.5 and 2.7,the maximum ground surface settlements are 0.67%of D and 0.35%of D,respectively.It is clear that the maximum ground surface settlement decreases with an increase in the C/D ratio.展开更多
Although significant advancement has been made over recent years with respect to three-dimensional upper bound calculations of tun-nel facing,a considerable difference still exists between analytically and empirically...Although significant advancement has been made over recent years with respect to three-dimensional upper bound calculations of tun-nel facing,a considerable difference still exists between analytically and empirically based stability values.The current work suggests that the difference may well be the outcome of the traditional use of Tresca yield criterion for the upper bound calculations,which,by definition,does not distinguish among the shearing modes(compression,extension,plane strain).Consequently,this paper suggests and discusses a new yield function,which allows for asymmetric yielding.Such yielding is only beneficial in the case of three-dimensional and continuous velocity fields,and therefore a numerical procedure that generates relevant kinematically admissible fields for classical upper bound cal-culation is suggested.The procedure involves conversion from a load controlled boundary value problem to a velocity controlled problem at the limit state of collapse.The analysis results in significantly lower upper bound values than those presented earlier(for Tresca mate-rial),and the values are much closer to the stability curves of Kimura and Mair(1981),which are commonly used in design.展开更多
Metro-led underground space(MUS)plays a crucial role in modern underground space utilisation.Recent studies have shown its great potential for high-quality urban development.However,limited evidence about MUS was avai...Metro-led underground space(MUS)plays a crucial role in modern underground space utilisation.Recent studies have shown its great potential for high-quality urban development.However,limited evidence about MUS was available on a national scale,resulting in incomplete and unsystematic knowledge of MUS utilisation.The interaction relationship between MUS and the surrounding built environment also remains unclear.To fill the research gap,an automatic method for MUS identification and development features extraction was proposed based on point of interest data.We applied the method to identify the MUS in 28 Chinese cities and estimated the development status of MUS in China for the first time.The nationwide statistics of MUS and correlation analysis of development features were conducted.Results show that complex MUS(CMUS)share is significantly lower than that of simple MUS.Besides,CMUS development in China is primarily dominated by public transport and does not have a solid functional link to its surroundings.The comparative analysis of MUS development in four primary urban agglomerations was also conducted,and their development char-acteristics were discussed.The study aims to expand the planning toolkit and construct the MUS database,which sheds light on the data-driven planning for MUS.展开更多
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 ac...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 poroelastic 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 perturbation(DCFS)area,in which fault slippage was promoted.In addition,DCFS at the earthquake location kept increasing after the injection 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 DCFS caused by seasonal injection and extraction decreases with distance;MOPs are constrained to 32.9,36.2,and 39.5 MPa according to different DCFS 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 determine the MOP for Hutubi underground gas storage(HTB UGS)and provide a framework for simulating the potential causes of induced seismicity for other sites.展开更多
Groundwater plays an essential role in stabilizing underground structures.However,hydrostatic uplift forces from groundwater can create safety hazards.This paper obtained the groundwater buoyancy reduction coefficient...Groundwater plays an essential role in stabilizing underground structures.However,hydrostatic uplift forces from groundwater can create safety hazards.This paper obtained the groundwater buoyancy reduction coefficients of 36 types of clays through model tests and conducted a finite element simulation to obtain the buoyancy reduction coefficients of additional clays with varying soil properties.Machine learning methods,including extreme gradient boosting(XGBoost)and random forest(RF)algorithms,were used to analyze and identify the soil parameters that have a significant impact on the reduction of groundwater buoyancy.It was found that the permeability coefficient and saturation are the primary factors that influence the reduction of groundwater buoyancy.Additionally,the prediction models developed by XGBoost and RF were compared,and their accuracy was evaluated.These research findings can serve as a reference for designing underground structures that can withstand the potential risk of buoyancy in clay.展开更多
The increasing demand for resources and depletion of near ground mineral resources caused deeper mining operations under highstress rock mass conditions.As a result of this,strain burst,which is the sudden release of ...The increasing demand for resources and depletion of near ground mineral resources caused deeper mining operations under highstress rock mass conditions.As a result of this,strain burst,which is the sudden release of stored strain energy in the surrounding rock mass,has become more prevalent and created a considerable threat to workers and construction equipment.It is,therefore,imperative to understand how strain burst mechanism and stored excess strain energy are affected due to the high confinement in deep underground conditions.For this purpose,post-peak energy distributions for brittle rocks were investigated using a newly developed energy calculation method associated with acoustic emission(AE).A series of quasi-static uniaxial and triaxial compression tests controlled by the circumferential expansion were conducted.Snap-back behaviour known as Class-II behaviour associated with energy evolution and the material response under self-sustaining failure were analysed on granites under a wide range of confining pressures(0–60 MPa).The experimental results underline that the energy evolution characteristics are strongly linked to confinement.Stored elastic strain energy(dUE),energy consumed by dominating cohesion weakening(dUCW)and energy dissipated during mobilisation of frictional failure(dUFM)showed a rising trend as the confining pressure was increased.An intrinsic ejection velocity was proposed to express the propensity of strain burst that was purely determined by the excess strain energy released from Class II rock.展开更多
A novel and computationally efficient method for developing a nonparametric probabilistic seismic demand model(PSDM)is pro-posed to conduct the fragility analysis of subway stations accurately and efficiently.The prob...A novel and computationally efficient method for developing a nonparametric probabilistic seismic demand model(PSDM)is pro-posed to conduct the fragility analysis of subway stations accurately and efficiently.The probability density evolution method(PDEM)is used to calculate the evolutionary probability density function of demand measure(DM)without resort to any assumptions of the dis-tribution pattern of DM.To reduce the computational cost of a large amount of nonlinear time history analyses(NLTHAs)in the PDEM,the one-dimensional convolutional neural network(1D-CNN)is used as a surrogate model to predict the time history of struc-tural seismic responses in a data-driven fashion.The proposed nonparametric PSDM is adopted to conduct the fragility analysis of a two-story and three-span subway station,and the results are compared with those from two existing parametric PSDMs,i.e.,two-parameter lognormal distribution model and probabilistic neural network(PNN)-based PSDM.The results show that the PDEM-based PSDM has the best performance in describing the probability distribution of seismic responses of underground structures.Differ-ent from the fragility curves,the time-dependent fragility surface of the subway station shows how the exceedance probability of damage state changes over time.It can be used to estimate the escape time and thus the number of casualties in an earthquake,which are impor-tant indexes when conducting the resilience-based seismic evaluation.展开更多
In this study,the pseudo-discontinuum modeling technique,called continuum Voronoi block model(CVBM),was applied to repre-sent the behavior of hard-rock pillars from underground mines subjected to high field stresses.T...In this study,the pseudo-discontinuum modeling technique,called continuum Voronoi block model(CVBM),was applied to repre-sent the behavior of hard-rock pillars from underground mines subjected to high field stresses.The CVBM’s ability to produce numerical results consistent with the observed behavior of pillars is demonstrated through the numerical analysis of a hypothetical case and a back analysis of the Creighton mine pillar.The results show that the model can capture convergence displacements and explicitly show the formation of macro-fractures parallel to excavation walls,intact rock slabs,and V-shaped notches.These components are characteristics of brittle failure induced by highly stressed ground conditions.The studies presented in this work confirm the CVBM as a convenient tool for the numerical modeling of intact rock pillars excavated in deep underground mines.展开更多
基金conducted with funding provided by the National Natural Science Foundation of China(Grant Nos.51878060,52108360).
文摘Based on an underwater shield tunnel project,this study introduces the phenomenon of abnormal shutdown and the measures designed to mitigate problems in construction.On the strength of the analysis of the slurry leakage causes during re-tunneling,the mech-anism of slurry leakage induced by jack retraction was studied,and treatment measures of leakage at shield tail brushes were elaborated upon.The results show that the sudden change of stratum leads to an abnormal shutdown,and a sharp increase in the slurry pressure at the shield cut location leads to the slurry penetrating the gap between the outer wall of the shield shell and the soil,increasing the risk of instantaneous breakdown at shield tail brushes.The radial displacement of the outer wall of the segments caused by retractions of three jacks and a single jack along the circumferential direction distinctly shows three regions and four regions,respectively.The radial shrink-age of the outer wall of the segments at the jack retraction position decreases the tightness between the shield tail brushes and the outer wall of the segments.The expansion of the outer wall of the segments at the surrounding position,especially at the lower position,increases the slurry level to the radial shrinkage position of the segments,which increases the risk of slurry leakage.Furthermore,when the shield machine faces an abnormal shutdown,re-tunneling,and assembly of segments,the jack can be gradually retracted from top to bottom.The slurry leakage degree can be observed when retracting,and the corresponding measures can be taken for timely plugging.According to the leakage degree,it can be determined whether to replace the shield tail brushes to reduce the risk of large-scale leakage accidents.
基金National Natural Science Foundation of China(Grant Nos.51808230,52020105002,51808150)Science and Technology Project of Guangzhou(Grant No.20210202588).
文摘This paper presents a case study of deep excavation adjacent to an existing bridge in karst region of Guangzhou city,China.The movements of retaining structures,settlements of surrounding ground and pipelines,and the responses of bridge piles were measured and evaluated.A sudden surge of groundwater was recorded at the north pit when excavated halfway.Soil-cement columns using the Metro Jet System(MJS)method was employed along the outer perimeters of the diaphragm wall where water inflow occurred,for the sake of blocking the flow channels.The measured maximum wall deflection dhm in this case ranged from 0.13%H to 0.3%H,with a mean value of 0.2%H(H is the excavation depth),which agreed well with the empirical prediction in mixed ground.During the MJS treatment,the wall and surrounding soils experienced notable lateral deflection and settlement.The bridge piles experienced significant settlement since the excavation commenced,which might be attributed to the inherent deficiency in geological condition and pile length.The soil disturbance induced by the adjacent deep excavation accelerated bridge settlement.The finite element analysis revealed that the excessive settlement of the bridge piles and ground surface resulted from confined-water withdrawal in sand layers.
基金the Key Project of National Natural Science Foundation of China(No.51574248)the National Natural Science Foundation of China(Grant Nos.52074300 and 51704120)+1 种基金the National Key Research and Development Program of China(Grant No.2016YFC0600901)the Fundamental Research Funds for the Central Universities(2021YJSSB11).
文摘The full-field strain of rock material under dynamic compression load was studied using the high-speed three dimensional digital image correlation(3D-DIC)method.The dynamic test was conducted on Laizhou granite using a split Hopkinson pressure bar(SHPB)method.Wave propagation,dispersion and radial inertial effect on the specimen were found by DIC results.A recovery of strain in the post-peak stage was detected on the specimen by DIC,which was unrevealed in the traditional one-dimensional theory method.It can be found that the strain measured by strain gauge was a calculated average one,whereas the strain measured by 3D-DIC could reflect more variation details.Specifically,the testing principle with impact loads and rock dynamic behavior was re-examined using stress wave propagation theory.The theoretical results showed that the specimen reached equilibrium after a series of wave reflections and transmissions and its stress was infinitely close to the initial value of 109.2 MPa.Moreover,the specimen had the calculated maximum strain of 0.52% and strain rate of 15.11 s^(-1),improving the reasonable agreement with the experimental results and requirements of rock mechanical properties measured by SHPB technology.
基金support from the National Natural Science Foundation of China(Grant Nos.51778575)the Zhejiang Provincial Science and Technology Department(Grant Nos.2019C03103)the Science and Technology Committee of Shanghai Municipality(Grant Nos.16QB1403400).
文摘Due to the shield tunneling underneath,long-term settlements may develop in the existing metro tunnels.The compensation grouting is applied worldwide to stabilize the settlement of ground and existing structures.Few field studies concerning large-diameter shield pass-ing tunnel from below have analyzed the interaction between the compensation grouting and the existing tunnel.This paper presents a case study on the response of the operating metro tunnels to the compensation grouting of an underlying large-diameter tunnel in muddy clay stratum.The tunnel deformations before,during,and after the compensation grouting were monitored and analyzed.The long-term tunnel settlements were mitigated and stabilized by the timely compensation grouting.Smaller settlement rates were observed during the grouting treatment,and the settlement was gradually stabilized three months after the grouting.The grouting holes at the tunnel invert were used initially for better grouting efficiency.The horizontal displacement and convergence developed during the grouting construc-tion and remained stable after the grouting process.Moreover,some limitations of the grouting treatment were discussed.The tunnel settlement in the section close to the center-line of the south-line tunnel cannot be prevented effectively.The differential displacement cannot be reduced by this grouting program.
文摘A probabilistic study of a circular tunnel excavated in a soil mass using the response surface methodology(RSM)is presented.A deterministic model based on two-dimensional numerical simulations in a transversal section is used,and the serviceability limit state(SLS)is considered in the analysis.The model permits the surface settlement curve and the bending moment on the tunnel lining to be obtained.Only the soil parameters are considered as random variables.Thefirst-order reliability method(FORM)and the response surface methodology(RSM)are utilized for the assessment of the Hasofer-Lind reliability index(bHL)optimized by the use of a genetic algorithm(GA).Two assumptions(normal and non-normal distribution)were used for the random variables.The comparison analysis considering a correlation between the friction angle and the cohesion indicates that the results are conservative if a negative correlation among strength parameters is not taken into account.The assumption of a non-normal distribution for the random variables has an important effect on the reliability index for the practical range of values of surface settlements.
基金supported by the National Natural Science Foundation of China(Grant No.41941018).
文摘With the reduction of shallow resources,the degree of damage and the frequency of dynamic hazards,such as deep rock bursts and impact ground pressure,are increasing dramatically.However,the existing support materials are incapable of meeting the safety require-ments of the refuges and roadways under a strong impact force.To effectively solve these problems,a novel negative Poisson’s ratio(NPR)anchor cable with excellent properties,such as impact resistance and the ability to withstand large deformation,is proposed.In the present study,a series of field tests and numerical simulations are conducted to investigate the mechanical and support charac-teristics of NPR anchor cables under blast impact.Laboratory mechanical tests show that NPR anchor cables can maintain constant resistance and produce large deformation under the action of multiple drop hammer impacts.According to the results of field tests,the roadway supported by conventional anchor cables was unable to endure the blast impact,while the roadway supported by NPR anchor cables was able to withstand the severe impact equivalent to a Class 3 mine earthquake.The dynamic response of the NPR anchor cable that supports the roadway under explosion is investigated using the innovative coupled modeling approach that combines the finite element method and the discrete element method,and the support effect of the NPR anchor cable is verified.The study shows that the NPR anchor cable has a superior impact and blast resistance performance,and a broad application prospect in the support of chambers and roadways that are at high risk of rock bursts and impact ground pressure.
基金supported by the National Natural Science Foundation of China(Grant No.52090083)the Postdoctoral Innovative Talents Supporting Program(Grant No.BX20200247)the Shanghai Sailing Program(Grant No.20YF1451400).
文摘In circular shield tunnels bearing high inner pressure or rectangular shaped shield tunnels,as the axial force at the segmental lining decreases,the bolt load at the segmental joint increases.It is essential to adopt high-stiffness segmental joints to improve the bearing capacity and control the deformation at the joint position.When designing high-stiffness segmental joints,the selection of ductileiron joint panel is crucial.In this study,two types of segmental joints with different joint panels were fabricated,and the effects of joint panel stiffness on the mechanical properties of segmental joints were analyzed through full-scale sagging and hogging bending tests.The results showed that the failure mode of high-stiffness segmental joint was similar to that of large eccentric compression section.According to the difference of panel stiffness,the failure modes can be specified into two types.If the stiffness is sufficient,the joint failure occurs due to the yielding of bolts;otherwise,it occurs due to the large deformation of ductile-iron joint panels.As for the design requirement of segmental joint,the stiffness of joint panel should be sufficient,i.e.,the opening and failure of the joints are finally induced by the bolt deformation.Otherwise,before the plastic deformation of the bolts,the large deformation of the joint panels will occur under a bendingmoment-dominant load,and the bearing capacity of the joints will greatly decrease.
文摘Empirical models provide a practical way to estimate the displacements induced by excavations.However,there are uncertainties associated with the predictions of empirical models owing to:(a)the imperfect knowledge of the model and(b)the uncertainties of the input variables.The uncertainties of these models can be characterized by a bias factor which is defined as the ratio of the actual displacement to the predicted displacement.The bias factors associated with the C&O method and the KJHH model are evaluated using the Bayesian method and a database of 71 excavations in Shanghai.To improve the predictions of the maximum displacement,an adaptive algorithm is proposed using field performance data.The performance of the proposed algorithm is demonstrated by an example in which excavation-induced displacements are generated by finite element method in normally consolidated clays.The example shows that the developed algorithm can significantly improve the predictions by incorporating the field performance data.
基金This work was supported by China Scholarship Council(Grant No.202108050072)Japan Society for the Promotion of Science KAKENHI(Grant No.JP19KK0121)the State Key Laboratory of Geohazard Prevention and Geoenvironment Protection open fund(Grant No.SKLGP2018K009)。
文摘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 deformation 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 calibrating the numerical parameters with the two single materials sampled from the tunnel site respectively.Further,the instability disasters 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 dolomite 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.
基金supported by the National Science Foundation for Distinguished Young Scholars of China(Grant No.52025091)the National Natural Science Foundation of China(Grant No.52109127)+2 种基金the Joint Funds of the National Natural Science Foundation of China(Grant No.U1934218)the National Natural Science Foundation of China(Grant No.52009076)the Young Elite Scientists Sponsorship Program by China Association for Science and Technology(Grant No.2021QNRC001).
文摘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 location 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.
基金supported by the research project of Zhongtian Construction Group Co.Ltd.(Grant No.ZTCG-GDJTYJS-JSFW-2020002).
文摘To date,the accurate prediction of tunnel boring machine(TBM)performance remains a considerable challenge owing to the complex interactions between the TBM and ground.Using evolutionary polynomial regression(EPR)and random forest(RF),this study devel-ops two novel prediction models for TBM performance.Both models can predict the TBM penetration rate and field penetration index as outputs with four input parameters:the uniaxial compressive strength,intact rock brittleness index,distance between planes of weakness,and angle between the tunnel axis and planes of weakness(a).First,the performances of both EPR-and RF-based models are examined by comparison with the conventional numerical regression method(i.e.,multivariate linear regression).Subsequently,the performances of the RF-and EPR-based models are further investigated and compared,including the model robustness for unknown datasets,interior relationships between input and output parameters,and variable importance.The results indicate that the RF-based model has greater prediction accuracy,particularly in identifying outliers,whereas the EPR-based model is more convenient to use by field engineers owing to its explicit expression.Both EPR-and RF-based models can accurately identify the relationships between the input and output param-eters.This ensures their excellent generalization ability and high prediction accuracy on unknown datasets.
基金This work was supported by the national Natural Science Foundation of China[Grant No(s).5137215551678369]the Technical Innovation Foundation of Shenzhen[Grant No.JCYJ20170302143610976].
文摘Energy piles are a new type of heat exchange systems with buried pipes in a pile foundation,which optimize a ground source heat pump system for the utilization of shallow geothermal energy.In this study,based on the principle of similarity,the thermo-mechanical behavior of the model energy pile with a large cross-section in saturated sandy soil was experimentally evaluated.The pre-cast model concrete pile with a diameter of 0.2 m and length of 1.5 m was buried in saturated sand in a steel box with dimensions of 2.5 m×2.5 m×2.0 m(length×width×height).The pile was heated using water in the polyethylene(PE)pipe,which was connected to a water cycle temperature controller.At a constant inlet water temperature of 55℃,three thermal cycles were carried out with the same heating and cooling periods and different water flow rates.The temperature distributions in the pile and soil,in addition to the pore pressure,soil pressure,and displacement of the pile,were monitored to clarify the thermo-mechanical behavior of the pile and soil.The heat transfer efficiency was analyzed based on the temperature difference and water flow rates.The measured strain at different locations in the pile under cyclic thermal loading revealed that the uneven strain that developed in a pile body should be considered for its long-term application.Furthermore,focus should be directed toward the long-term unrecoverable displacement of the energy pile due to the thermal plastic strain and thermal consolidation of the soil.
基金supported by the Natural Science Foundation of Jiangsu Province(project number:BK20160863)research funding provided by Shenzhen Ploytechnic(project number:601822K28024).
文摘Stress changes in the soil induced by tunnel excavation may cause excessive ground settlement.However,high-quality experimental data on ground settlement due to tunnel excavation are limited.In this study,centrifuge tests are conducted to investigate the threedimensional ground surface settlement,considering different intersection angles and cover-to-tunnel diameter ratios.The results indicate that the major influence zone along the longitudinal direction on the ground surface settlement is±1.25D,where D is the tunnel diameter.When the monitoring section is perpendicular to the tunneling direction,the transverse ground settlement due to the tunnel excavation is symmetrical with respect to the tunnel centerline.In contrast,an asymmetric ground settlement profile is observed when the monitoring section intersects the tunneling direction at an angle of 60.Applying a Gaussian curve to fit the ground surface settlement curve,the width parameter,K(i.e.,the distance between the tunnel centerline and the inflection point of the settlement trough to the tunnel burial depth),varies from 0.33 to 0.39.The ground surface settlement induced by twin tunnel excavation can be captured reasonably by superimposing two identical Gaussian curves.When the cover to tunnel diameter ratios(C/D)are 1.5 and 2.7,the maximum ground surface settlements are 0.67%of D and 0.35%of D,respectively.It is clear that the maximum ground surface settlement decreases with an increase in the C/D ratio.
文摘Although significant advancement has been made over recent years with respect to three-dimensional upper bound calculations of tun-nel facing,a considerable difference still exists between analytically and empirically based stability values.The current work suggests that the difference may well be the outcome of the traditional use of Tresca yield criterion for the upper bound calculations,which,by definition,does not distinguish among the shearing modes(compression,extension,plane strain).Consequently,this paper suggests and discusses a new yield function,which allows for asymmetric yielding.Such yielding is only beneficial in the case of three-dimensional and continuous velocity fields,and therefore a numerical procedure that generates relevant kinematically admissible fields for classical upper bound cal-culation is suggested.The procedure involves conversion from a load controlled boundary value problem to a velocity controlled problem at the limit state of collapse.The analysis results in significantly lower upper bound values than those presented earlier(for Tresca mate-rial),and the values are much closer to the stability curves of Kimura and Mair(1981),which are commonly used in design.
基金the support provided by National Natural Science Foundation of China(NSFC)(Grant Nos.42071251,52090083).
文摘Metro-led underground space(MUS)plays a crucial role in modern underground space utilisation.Recent studies have shown its great potential for high-quality urban development.However,limited evidence about MUS was available on a national scale,resulting in incomplete and unsystematic knowledge of MUS utilisation.The interaction relationship between MUS and the surrounding built environment also remains unclear.To fill the research gap,an automatic method for MUS identification and development features extraction was proposed based on point of interest data.We applied the method to identify the MUS in 28 Chinese cities and estimated the development status of MUS in China for the first time.The nationwide statistics of MUS and correlation analysis of development features were conducted.Results show that complex MUS(CMUS)share is significantly lower than that of simple MUS.Besides,CMUS development in China is primarily dominated by public transport and does not have a solid functional link to its surroundings.The comparative analysis of MUS development in four primary urban agglomerations was also conducted,and their development char-acteristics were discussed.The study aims to expand the planning toolkit and construct the MUS database,which sheds light on the data-driven planning for MUS.
基金supported by the National Nat-ural Science Foundation of China(Grant No.42077247)。
文摘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 poroelastic 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 perturbation(DCFS)area,in which fault slippage was promoted.In addition,DCFS at the earthquake location kept increasing after the injection 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 DCFS caused by seasonal injection and extraction decreases with distance;MOPs are constrained to 32.9,36.2,and 39.5 MPa according to different DCFS 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 determine the MOP for Hutubi underground gas storage(HTB UGS)and provide a framework for simulating the potential causes of induced seismicity for other sites.
基金The authors are grateful to the financial support from the National Major Scientific Instruments Development Project of China(Grant No.5202780029)Chongqing Urban Investment Infrastructure Construction Co,China(Grant No.CQCT-JS-SC-GC-2022-0081).
文摘Groundwater plays an essential role in stabilizing underground structures.However,hydrostatic uplift forces from groundwater can create safety hazards.This paper obtained the groundwater buoyancy reduction coefficients of 36 types of clays through model tests and conducted a finite element simulation to obtain the buoyancy reduction coefficients of additional clays with varying soil properties.Machine learning methods,including extreme gradient boosting(XGBoost)and random forest(RF)algorithms,were used to analyze and identify the soil parameters that have a significant impact on the reduction of groundwater buoyancy.It was found that the permeability coefficient and saturation are the primary factors that influence the reduction of groundwater buoyancy.Additionally,the prediction models developed by XGBoost and RF were compared,and their accuracy was evaluated.These research findings can serve as a reference for designing underground structures that can withstand the potential risk of buoyancy in clay.
基金The authors gratefully acknowledge the financial support from the Australian Research Council(ARC)(ARC-LP150100539)OZ Minerals,and the principal geotechnical manager David Goodchild.The authors also wish to thank the laboratory technicians Adam Ryntjes and Simon Golding.
文摘The increasing demand for resources and depletion of near ground mineral resources caused deeper mining operations under highstress rock mass conditions.As a result of this,strain burst,which is the sudden release of stored strain energy in the surrounding rock mass,has become more prevalent and created a considerable threat to workers and construction equipment.It is,therefore,imperative to understand how strain burst mechanism and stored excess strain energy are affected due to the high confinement in deep underground conditions.For this purpose,post-peak energy distributions for brittle rocks were investigated using a newly developed energy calculation method associated with acoustic emission(AE).A series of quasi-static uniaxial and triaxial compression tests controlled by the circumferential expansion were conducted.Snap-back behaviour known as Class-II behaviour associated with energy evolution and the material response under self-sustaining failure were analysed on granites under a wide range of confining pressures(0–60 MPa).The experimental results underline that the energy evolution characteristics are strongly linked to confinement.Stored elastic strain energy(dUE),energy consumed by dominating cohesion weakening(dUCW)and energy dissipated during mobilisation of frictional failure(dUFM)showed a rising trend as the confining pressure was increased.An intrinsic ejection velocity was proposed to express the propensity of strain burst that was purely determined by the excess strain energy released from Class II rock.
基金supported by National Key R&D Program of China(Grant No.2022YFE0104400)State Key Laboratory of Disaster Reduction in Civil Engineering(Grant No.SLDRCE19-B-38)the Fundamental Research Funds for the Central Universities,China(Grant No.22120210572).
文摘A novel and computationally efficient method for developing a nonparametric probabilistic seismic demand model(PSDM)is pro-posed to conduct the fragility analysis of subway stations accurately and efficiently.The probability density evolution method(PDEM)is used to calculate the evolutionary probability density function of demand measure(DM)without resort to any assumptions of the dis-tribution pattern of DM.To reduce the computational cost of a large amount of nonlinear time history analyses(NLTHAs)in the PDEM,the one-dimensional convolutional neural network(1D-CNN)is used as a surrogate model to predict the time history of struc-tural seismic responses in a data-driven fashion.The proposed nonparametric PSDM is adopted to conduct the fragility analysis of a two-story and three-span subway station,and the results are compared with those from two existing parametric PSDMs,i.e.,two-parameter lognormal distribution model and probabilistic neural network(PNN)-based PSDM.The results show that the PDEM-based PSDM has the best performance in describing the probability distribution of seismic responses of underground structures.Differ-ent from the fragility curves,the time-dependent fragility surface of the subway station shows how the exceedance probability of damage state changes over time.It can be used to estimate the escape time and thus the number of casualties in an earthquake,which are impor-tant indexes when conducting the resilience-based seismic evaluation.
基金based upon a R&D Project from ANEEL-National Agency(Grant No.PD-0394–1709/2017)supported by Eletrobras Furnas and University of Brasiliasupported by Conselho Nacional de Desenvolvimento Cientifico e Tecnologico-CNPq and the Brazilian National Department of Transport Infrastructure(Grant No.TED 352/2020).
文摘In this study,the pseudo-discontinuum modeling technique,called continuum Voronoi block model(CVBM),was applied to repre-sent the behavior of hard-rock pillars from underground mines subjected to high field stresses.The CVBM’s ability to produce numerical results consistent with the observed behavior of pillars is demonstrated through the numerical analysis of a hypothetical case and a back analysis of the Creighton mine pillar.The results show that the model can capture convergence displacements and explicitly show the formation of macro-fractures parallel to excavation walls,intact rock slabs,and V-shaped notches.These components are characteristics of brittle failure induced by highly stressed ground conditions.The studies presented in this work confirm the CVBM as a convenient tool for the numerical modeling of intact rock pillars excavated in deep underground mines.
