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Mechanical behavior of EICP-treated calcareous sands under high confining pressures

Journal of Rock Mechanics and geotechnical engineering 2025年第3期17卷 1816-1827页

作者： Qian Zhang Weimin Ye Wei Su Qiong Wang Yonggui Chen Department of Geotechnical Engineering College of Civil EngineeringTongji UniversityShanghai200092China Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education Tongji UniversityShanghai200092China

Calcareous sands are widely distributed on the coral reefs,continental shelf,and seashores between 30north and south latitude and are commonly utilized as filling materials for the construction of artificial islands and infrastructure *** this study,calcareous sands were cemented by enzymatically induced carbonate precipitation(EICP)*** triaxial tests were conducted on the EICPtreated calcareous *** showed that the specimens with different cementation levels exhibited different responses in mechanical *** differences in the sand fabric after consolidation under a relatively high confining pressure resulted in the untreated specimen exhibiting a higher peak strength compared to the lightly cemented *** confining pressures exhibited a strongly inhibiting effect on dilatancy,which could be counteracted by increasing the cementation *** EICP-treated specimen could have one or two yield points(smaller-strain and larger-strain yields).For lightly cemented specimens,the smaller-strain yield stress decreased under high confining pressures due to the partial carbonate bonding degradation during *** stress line of untreated particle breakage(UPB)was a critical boundary to distinguish failure mode in the p′-q *** the EICP-treated specimens,the yield stress located above or below the UPB stress line indicates the simultaneous or sequential breakage of the carbonate bonds and sand particles,***,the EICPtreated specimen exhibited brittle or ductile *** mode transformation could be triggered by increasing cementation level or confining pressure.

关键词： EICP technique Calcareous sand Bonding degradation Yield strength Failure mechanism

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Responses of a short column-supported highrise tower to adjacent deep excavations in water-rich sandy strata and dynamic optimization of protection plans

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Frontiers of Structural and Civil engineering 2024年第11期18卷 1775-1793页

作者： Jun-Cheng LIU Yong TAN State Key Laboratory of Disaster Reduction in Civil Engineering Department of Geotechnical EngineeringCollege of Civil EngineeringTongji UniversityShanghai 200092China

A highrise tower atop short columns in Nantong,China was threatened by excavation of a subway station *** an elaborate protection plan composed of isolation piles,artificial recharge and underpinning was executed throughout the excavations,the tower underwent unacceptable settlements and notable *** combination of field measurements and numerical simulations,this paper investigates the tower’s responses to the adjacent excavations,examines the effects of adopted protection plans and explores potential effective protection ***,the responses of the tower and the effectiveness of the three implemented measures were examined,and the contributory factors triggering intolerable tower deformations were identified;then,the effects of primary protection parameters were quantified,including the length,stiffness and layout of isolation piles,the water level surrounding recharge wells after recharging and the depth and location of wells,and the length of underpinning *** reveals that the underpinning plan had the best protection effect,followed by isolation piles and recharging *** timing of protection measures and termination manners of recharging are two critical factors in restraining tower ***,underpinning the tower with 36-m long steel pipe piles solely before implementation of adjacent excavations could be another optimal protection scheme.

关键词： highrise tower excavation piled-raft footing protection field performance numerical simulation

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Prediction of lateral wall deflections of excavations in water-rich sands by a modified multivariate-adaptiveregression- splines method

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Frontiers of Structural and Civil engineering 2024年第12期18卷 1971-1984页

作者： Dongdong FAN Delujia GONG Yong TAN Yongjing TANG State Key Laboratory of Disaster Reduction in Civil Engineering Department of Geotechnical EngineeringCollege of Civil EngineeringTongji UniversityShanghai 200092China

Machine learning methods have advantages in predicting excavation-induced lateral wall *** to lack of sufficient field data,training data for prediction models were often derived from the results of numerical simulations,leading to poor prediction *** on a specific quantity of data,a multivariate adaptive regression splines method(MARS)was introduced to predict lateral wall deflections caused by deep excavations in thick water-rich *** of lateral wall deflections to affecting factors was *** is disclosed that dewatering mode has the most significant influence on lateral wall deflections,while the soil cohesion has the least *** crossvalidation analysis,weights were introduced to modify the MARS method to optimize the prediction *** of the predicted and measured deflections shows that the prediction based on the modified multivariate adaptive regression splines method(MMARS)is more accurate than that based on the traditional MARS *** prediction model established in this paper can help engineers make predictions for wall displacement,and the proposed methodology can also serve as a reference for researchers to develop prediction models.

关键词： lateral wall deflection machine learning multivariate adaptive regression splines method excavation database water-rich sand

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A modified smoothed particle hydrodynamics method considering residual stress for simulating failure and its application in layered rock mass

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Journal of Mountain Science 2024年第6期21卷 2091-2112页

作者： XIA Chengzhi SHI Zhenming KOU Huanjia Department of Geotechnical Engineering College of Civil EngineeringTongji UniversityShanghai 200092China Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education Tongji UniversityShanghai 200092China

Residual strength is an indispensable factor in evaluating rock fracture,yet the current Smoothed Particle Hydrodynamics(SPH)framework rarely considers its influence when simulating *** improved cracking strategy considering residual stress in the base bond SPH method was proposed to simulate failures in layered rocks and slopes and verified by experimental results and other simulation methods(i.e.,the discrete element method).Modified Mohr–Coulomb failure criterion was applied to distinguish the mixed failure of tensile and *** fracture markψwas introduced to improve the kernel function after tensile damage,and the calculation of residual stress after the damage was derived after shear *** simulations were carried out to evaluate its performance under different stress and scale conditions and to verify its effectiveness in realistically reproducing crack initiation and propagation and coalescence,even fracture and *** results indicate that the improved cracking strategy precisely captures the fracture and failure pattern in layered rocks and rock *** residual stress of brittle tock is correctly captured by the improved SPH *** improved SPH method that considers residual strength shows an approximately 13%improvement in accuracy for the safety factor of anti-dip layered slopes compared to the method that does not consider residual strength,as validated against analytical *** infer that the improved SPH method is effective and shows promise for applications to continuous and discontinuous rock masses.

关键词： Smoothed particle hydrodynamics Cracking strategy Residual stress Layered rock Crack propagation

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Assessing site investigation program for design of shield tunnels

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Underground Space 2023年第2期9卷 31-42页

作者： Jie Zhang Yuan Sun Jin-zheng Hu Hong-wei Huang Department of Geotechnical Engineering Tongji UniversityShanghai 200092China Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education Tongji UniversityShanghai 200092China

In the design of shield tunnels,it is expected that a design can be more economical as more site investigation data are ***-ertheless,the cost of site investigation will also increase as more site investigation data are *** is thus important to assess the potential benefit of a site investigation program before it is conducted considering the uncertainty in the soil properties and the site inves-tigation *** this paper,a probabilistic framework is suggested to assess the effectiveness of a site investigation program for the design of shield tunnels through the random field *** efficient method based on the generalized extreme value distribution is used to calculate the failure probability of the tunnel,through which the expected benefit from a site investigation program can be estimated *** result shows that a site investigation program is more valuable when a greater target design reliability index is *** expected benefit from a site investigation program increases as the borehole intensity increases,and it also increases as the scale of fluctuation of the soil properties *** method suggested in this paper provides a useful tool for planning borehole layout for the design of shield tunnels,which is promising for the optimization of site investigation.

关键词： Shied tunnel Site investigation Uncertainty Spatial variability

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Interpreting random fields through the U-Net architecture for failure mechanism and deformation predictions of geosystems

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Geoscience Frontiers 2024年第1期15卷 209-224页

作者： Ze Zhou Wang Jinzhang Zhang Hongwei Huang Department of Civil and Environmental Engineering National University of SingaporeSingapore 117576Singapore Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education and Department of Geotechnical Engineering Tongji UniversityShanghai 200092China

The representation of spatial variation of soil properties in the form of random fields permits advanced probabilistic assessment of slope *** many studies,the safety margin of the system is typically characterized by the term“probability of failure(Pfailure)”.As the intensity and spatial distribution of soil properties vary in different random field realizations,the failure mechanism and deformation field of a slope can vary as *** only can the location of the failure surfaces vary,but the mode of failure also *** information is equally valuable to engineering *** this paper,two slope examples that are modified from a real case study are *** first example pertains to the stability analysis of a multi-layer-slope while the second example deals with the serviceability analysis of a multi-layer c-φ*** addition,due to the large number of simulations needed to reveal the full picture of the failure mechanism,Convolutional Neural Networks(CNNs)that adopt a U-Net architecture is proposed to offer a soft computing strategy to facilitate the *** spatial distribution of the failure surfaces,the statistics of the sliding volume,and the statistics of the deformation field are *** results also show that the proposed deep-learning model is effective in predicting the failure mechanism and deformation field of slopes in spatially variable soils;therefore encouraging probabilistic study of slopes in practical scenarios.

关键词： Deep-learning Spatial variability Slope stability Failure mechanism Sliding volume

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Longitudinal shaking of culvert-frame combined underground structure

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Frontiers of Structural and Civil engineering 2025年第1期19卷 123-142页

作者： Yong YUAN Xuzhao LAN Department of Geotechnical Engineering Tongji UniversityShanghai 200092China State Key Laboratory for Disaster Reduction in Civil Engineering Tongji UniversityShanghai 200092China

The underground structure with stiffness mutation at the culvert-frame connection suffers from discrepant dynamic responses when earthquakes *** paper studies the seismic responses of an underground structure consisting of two portions of box frames and twin jacked culverts in soft *** two portions of box frames(Part A and Part C)have the same 2-storey and 3-span cross sections,rigidly connected to the two parallel jacked culverts(Part B)with F-type sockets between joints.A series of 1g shaking table tests is conducted on the modeled soil−structure *** are installed within the model soil,upon culverts,and on the top of mid slabs of box *** extensions and closures of culverts are *** white noise case is carried out to assess dynamic characteristics of the model *** synthetic earthquake cases are conducted to investigate the model system’s seismic responses under earthquakes with varying *** acceleration responses of the model soil at different distances from Part A are *** extent of discrepancy in acceleration of culverts and box frames is quantified by the correlation *** characteristics of the joint extension and closure are summarized.

关键词： shaking table test underground structure culvert-frame metro station soft soil

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Self-initiated static-dynamic state transition behavior and triggering mechanism of strain rockburst using three-dimensional discrete element method

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Underground Space 2024年第3期16卷 143-163页

作者： Yuan Qian Cheng Zhao Rui Wei Rui Zhang Lin Huang Huiguan Chen Department of Geotechnical Engineering College of Civil EngineeringTongji UniversityShanghai 200092China Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education Tongji UniversityShanghai 200092China School of Engineering Tibet UniversityLhasaTibet850000China

The accurate understanding of rockburst mechanism poses a global challenge in the field of rock *** for strain rockburst,achieving self-initiated static-dynamic state transition is a crucial step in the formation of catastrophic ***,the state transition behavior and its impact on rockburst have not received sufficient attention,and are still poorly ***,this study specifically focuses on the state transition behavior,aiming to investigate its abrupt transition process and formation mechanism,and triggering effects on *** facilitate the study,a novel burst rock-surrounding rock combined laboratory test model is proposed and its effectiveness is validated through experiment ***,corresponding numerical models are established using the three-dimensional(3D)discrete element method(DEM),enabling successful simulation of static brittle failure and rockbursts of varying intensities under quasi-static displacement loading ***,through secondary development,comprehensive recording of the mechanical and energy information pertaining to the combined specimen system and its subsystems is *** a result of numerical investigation studies,the elastic rebound dynamic behavior of the surrounding rock was discovered and identified as the key factor triggering rockburst and controlling its *** impact loading on the burst rock,induced by elastic rebound,directly initiates the dynamic processes of rockburst,serving as the direct ***,the transient work and energy convergence towards the burst rock resulting from elastic rebound are recognized as the inherent cause of ***,it has been observed that a larger extent of surrounding rock leads to a stronger elastic rebound,thereby directly contributing to a more intense *** findings can provide novel theoretical insights for the exploring of rockburst mechanism and the development of monitoring and

关键词： Strain rockburst Static-dynamic state transition Self-initiation Triggering mechanism Elastic rebound Discrete element method

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A review of fracture mechanic behaviors of rocks containing various defects

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Underground Space 2023年第5期12卷 102-115页

作者： Fei Zhao Zhenming Shi Songbo Yu Hongchao Zheng Department of Geotechnical Engineering College of Civil EngineeringTongji UniversityShanghai 200092China Key Laboratory of Geotechnical and Underground Engineering Ministry of EducationTongii UniversityShanghai 200092China

The existence of defects in a rock mass is a vital factor complicating the mechanical response of the rock mass under *** characteristics of defects control the rock mass’s mechanical *** report reviews the experimental studies on the influence of simulating the internal defects of rock mass’s mechanical *** effects of preexisting defects(shape,size,number,angle,and other factors)on the mechanical properties and failure modes of the rock are investigated from the perspectives of rock failure and fracture *** fracture propagation mechanisms of different defective rock masses are analyzed by studying the stress state of different defective rock masses under uniaxial *** the defective rock samples with varying inclination angles are destroyed,the relationship among the compressive strength,the fracture propagation,and the failure characteristics is *** primary findings are as *** increase in the size and number of defects rapidly damages the mechanical properties of the rock and intensifies defect penetration and *** rock mechanics characteristics of fissured rocks with different inclination angles show two primary variations:one is a continuous increase,and the other is a decrease followed by an *** result is strongly related to the failure pattern of rocks with preexisting *** investigation is crucial for further studying the failure modes of complex defective rock masses and the geotechnical engineering related to defective rocks.

关键词： Rock mechanics Preexisting defects Failure patterns Fracture characteristics

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Novel hybrid method to predict the ground-displacement field caused by shallow tunnel excavation

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Science China(Technological Sciences) 2023年第1期66卷 101-114页

作者： KONG FanChao LU DeChun MA YiDing TIAN Tao YU HaiTao DU XiuLi Institute of Geotechnical and Underground Engineering Bejing University of TechnologyBejing 100124China Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education Tongji UniversityShanghai 200092China

Based on machine-learning(ML) and analytical methods, a hybrid method is developed herein to predict the ground-displacement field(GDF) caused by tunneling. The extreme learning machine(ELM), as a single hidden layer feedforward neural network, is used as an ML model to predict maximum settlement smaxof the ground surface. The particle swarm optimization(PSO) algorithm is applied to optimize the parameters for the ELM method, namely, weight and bias values from the input layer to the hidden layer. The mean square error of the k-fold cross validation sets is considered the fitness function of the PSO algorithm. For 38 data samples from published papers, 30 samples are used as the training set, and 8 samples are used as the test set. For the test samples, the error of five samples ranges between-5 and 5 mm. The error of only one sample is slightly greater than 10 mm. The proposed PSO-ELM method demonstrates good prediction performance of smax. A deformation parameter of the nonuniform displacement mode for the tunnel cross-section is calibrated based on predicted smax. When the determined nonuniform displacement mode is used as the boundary condition of the tunnel cross-section, the GDF of a shallow circular tunnel is analytically predicted based on the complex-variable method prior to tunnel excavation. For a specific engineering case,i.e., the Heathrow Express tunnel, the proposed PSO-ELM-analytical method can well predict the surface-settlement trough curve, horizontal displacements at different depths, and vertical displacements above the tunnel.

关键词： extreme learning machine particle swarm optimization complex-variable method analytical solution of a shallow tunnel prediction method of ground-displacement field

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