查看更多>>摘要：The horizontally layered or even inclined strata are often encountered in practical shield tunneling.The influence of inclined strata on face stability of shield tunnels is not fully investigated by the existing studies.This paper adopts both theoretical analysis and numerical simulation to carry out research on face stability in inclined strata.The spatial discretization technique is adopted to construct a three-dimensional(3D)kinematic failure mechanism considering intersection between inclined soil interface and tunnel face.An analytical solution for critical support pressure is obtained.Besides,the critical support pressure and 3D kinematic mechanism are compared with numerical results to verify accuracy and effectiveness of analytical model.The influences of dip and position of inclined strata on face stability are thoroughly studied.The proposed failure mechanism can serve as a reference for face stability analysis in inclined strata.
查看更多>>摘要：Buried water pipelines are vulnerable to fail or break due to excessive loading or ground displacements.Accurate evaluation of pipe performance and serviceability relies on the proper understanding of pipe-soil interactions(PSI).Analytical methods are important approaches to studying PSI.However,a systematic and thorough literature review to analyze the existing research trends,technological achievements and future research opportunities is not available.This work investigates analytical methods that analyze the stress and deformation of pipes in terms of cross-sectional,transverse and longitudinal PSI problems.First,scientometric analysis is performed to acquire relevant research works from online databases and analyze the existing data of influential authors,productive research sources and frequent key word occurrence in the fields of interest.Second,a qualitative discussion is performed in the three categories of PSI:(1)cross-sectional,including ovalization and circumferential behaviours;(2)transverse,including seismic fault crossing,weak soil zones,ground settlement and pipe uplift;and(3)longitudinal.Third,six research opportunities are discussed,including the role of friction in cross-sectional deformation,combined effects of bending and compression,choice of soil reaction models and calibration of key param-eters,effect of pipe flaws,soil spatial variability and behaviours of curved pipes.This study helps beginners familiarize themselves with PSI analytical methods and provides experienced researchers with ideas for future research directions.
查看更多>>摘要：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 coeficients 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 perme-ability coefficient and saturation are the primary factors that influence the reduction of groundwater buoyancy.Additionally,the pre-diction 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.
查看更多>>摘要：Rockburst is a kind of common geological disaster in deep tunnel engineering.It has the characteristics of causing great harm and occurring at random locations and times.These characteristics seriously affect tunnel construction and threaten the physical and mental health and safety of workers.Therefore,it is of great significance to study the tendency of rockburst in the early stage of tunnel survey,design and construction.At present,there is no unified method and selected parameters for rockburst prediction.In view of the large difference of different rockburst criteria and the imbalance of rockburst database categories,this paper presents a two-step rockburst prediction method based on multiple factors and the stacking ensemble algorithm.Considering the influence of rock physical and mechanical parameters,tunnel face conditions and excavation disturbance,multiple rockburst criteria are predicted by integrating mul-tiple machine learning algorithms.A combined prediction model of rockburst criteria is established,and the results of each rockburst criterion index are weighted and combined,with the weight updated using the field rockburst record.The dynamic weight is combined with the cloud model to comprehensively evaluate the regional rockburst risk.Field results from applying the model in the Grand Can-yon tunnel show that the rockburst prediction method proposed in this paper has better applicability and higher accuracy than the single rockburst criterion.
查看更多>>摘要：This paper introduces a new prefabricated recyclable double-row piles retaining system for excavations in silty clay ground.Labora-tory model test and numerical simulation are conducted to study the system behavior upon excavation.The horizontal displacement(δh),Von Mises stress(σM),strain(ε),ground surface settlement(δv),and earth pressure are systematically investigated.Furthermore,the monitoring data of 13 excavation cases supported by double-row piles retaining system are presented and discussed.The experimental results can basically match the numerical results,and the maximum σM,maximum bending moment(Mmax),maximum horizontal dis-placement(δhm)of structural members are all less than the tolerance limits.The ground surface settlement model of double-row piles retaining system consists of three zones,i.e.,rebound influence zone,primary influence zone and secondary influence zone.The δhm val-ues are 0.07％-1.42％of the excavation depth(He).The maximum ground surface settlement(δvm)is generally less than δhm.The ratio ofδvm/δhm varies between 0.09 and 0.76,with an average value of 0.5.The observed earth pressure on the retained side of front pile(paf)is about 0.53-0.57 γH below the excavation surface.Above the excavation surface,paf decreases dramatically when getting closer to the ground surface.
Yi ZengPierre Guy Atangana NjockWang XiongXiao-Long Zhang...
281-300页
查看更多>>摘要：The construction of super-large tunnels generates various safety risks that can hamper the tunneling process and cause severe damages if not properly identified.This paper presents a case study on the identification and management of geological and environmental risks during the construction of the largest(a diameter of 15.8 m)slurry shield tunnel in China.Its ground conditions and settlement control were identified among the most challenging owing to a large area of mixed ground conditions,11 fault zones and tunneling under res-idential areas and the city's Metro Lines 1 and 9.In response to the severity of these risks and challenges,novel monitoring systems,ground treatment,and safety management technologies were successfully implemented throughout the tunneling process.Further,a technical framework was proposed in this study to serve as a risk management guidance for analogous tunneling operations.
查看更多>>摘要：The underground utility tunnel(UUT)is one of the typical urban underground structures,which usually requires mechanical venti-lation systems for forced ventilation.In addition to the ventilation scheme for accident scenarios,the normal operating ventilation scheme deserves equal attention as it has a great impact on the air quality as well as the thermal and humidity environment inside the UUT.In this study,a UUT located in southern China is taken as the research object,and the effect of ventilation on its internal thermal and humidity distribution is explored with a combined use of field measurements and numerical simulations.The results of field measurements show that the average temperature inside the closed UUT is 20.5 ℃ and the average humidity ratio is 14.1 g/kgdry;both are lower than those of the external environment.In the plum rain season,if the tunnel is ventilated without any treatment of the external airflows,surface condensation tends to occur near the air inlet while the region with high relative humidity would be distributed on both sides far from the air inlet.The study also discusses the effect of different temperatures and humidity ratios of the inflow air on the humid-ity inside the UUT,and on this basis,the humidity control strategy for UUT in the plum rain season is proposed.
查看更多>>摘要：According to different geological conditions and engineering disturbance,three dimensional numerical models of anchored jointed rock mass with two kinds of boundary conditions of constant normal load(CNL)and constant normal stiffness(CNS)were constructed considering the ductility damage of rockbolt,the stiffness degradation of grouting layer and the joint surface roughness.The effects of anchorage angle,joint surface morphology,and boundary conditions on the shear performance of anchorage system were analyzed,and the failure characteristics under different working conditions were revealed.Finally,the analytical solution of shear strength of anchored system was established.Results show that the larger the anchorage angle is,the more serious the necking phenomenon of rockbolt will be.The damage degree of the bonding layer and the horizontal displacement of the bedding rock mass decrease with the increase of the joint surface roughness.The CNL condition is to instantaneously apply high normal stress,and the CNS condition is to gradually form a high normal stress environment through the superposition of increment on the basis of the initial value,which can resist greater trans-verse load.This is equivalent to enhancing the ductility of the rockbolt.The shear strength of the system increases with the increase of normal stress and normal stiffness.Ignoring the normal stiffness will underestimate the shear strength.
查看更多>>摘要：Shield machine may deviate from its design axis during excavation due to the uncertainty of geological environment and the complex-ity of operation.This study therefore introduced a framework to predict the attitude and position of shield machine by combining long short-term memory(LSTM)model with attention mechanism.The data obtained from the Wuhan Rail Transit Line 6 project were uti-lized to verify the feasibility of the proposed method.By adding the attention mechanism into the LSTM model,the proposed model can focus more on parameters with higher weights.Sensitivity analysis based on Pearson correlation coefficient was conducted to improve the prediction efficiency and reduce the irrelevant input parameters.Compared with LSTM model,LSTM-attention model has higher accu-racy.The mean value of coefficient of determination(R2)increases from 0.625 to 0.736,and the mean value of root mean square error(RMSE)decreases from 3.31 to 2.24.The proposed LSTM-attention model can provide an effective prediction for attitude and position of shield machine in practical tunneling engineering.
维普
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