Pile-supported embankments are commonly employed for highways in soft soil areas. Extensive studies have been conducted on high embankments under static loading. However, low embankments with lower costs and carbon footprint have not yet been thoroughly studied. This study aims to investigate the performance of pile-supported low embankments under cyclic traffic loading by carrying out two large-scale model tests. The soft soil was constructed using Kaolin clay, and the cyclic traffic loading was simulated using a localized semi-sinusoidal function. The effect of geosynthetic reinforcement on the load transfer mechanism of pile-supported low embankments was investigated by comparing the measured data from unreinforced and reinforced cases. Test results show that geosynthetic reinforcement reduces settlement and leads to faster stabilization of settlement in low embankments. Pile-supported low embankments experience a rapid decrease followed by a stabilization in pile efficacy with increased cyclic loading, and geosynthetic reinforcement increase the pile efficacy and facilitate quicker stabilization. Geosynthetic reinforcement enhances the transfer of static and dynamic stresses to piles, resulting in less stress degradation under cyclic loading. Based on experimental results, pile-supported embankments should account for the adverse effects of cyclic loading, even if they are classified as high embankments according to existing analytical models.
This paper presented a station-subpath metanetwork-based approach for modeling and solving the optimal charging infrastructure location problem.Specifically,this paper proposed a two-phase mixed linear integer programming model,and accordingly developed a two-phase algorithm powered by the branch-and-bound method,decomposing any individual routing-charging decision into two phases.The first phase aimed to find the distance-constrained minimum-cost subpath between each charging station pair in the original network,which was handled by the bi-criterion label-correcting algorithm;while the main algorithmic step of the second phase was to,in the branch-and-bound framework,repeatedly identified the minimum-cost path between each origin-destination pair in the metanetwork,which can be efficiently solved by the classic single-criterion label-setting algorithm.The numerical results from applying the developed metanetwork-based approach for the Yangtze River Delta network reveal that the construction budget limit of charging stations and driving range limit of electric vehicles play important roles in charging station location decisions and individual route-and-charge choices.When applied to three different sizes of numerical networks,the metanetwork-based approach proposed in this paper exhibits dominantly higher computational efficiency than the conventional network-based approach for this type of problems of large size.
The dynamic shear characteristics of the reinforcement-soil interface affect the stability and durability of reinforced soil-rock mixture subgrades.A series of static and dynamic direct shear tests was conducted on the soil-rock mixture-geotextile interface using a large dynamic direct shear apparatus under different rock contents(0％,25％,50％,75％and 100％).The effects of normal stress amplitude(10,20,30,40 and 60 kPa)and normal loading frequency(0.5,1.0 and 2.0 Hz)on the shear response of the interface were analyzed.The test results indicate that the shear strength of the upper and lower boundaries of the interface first increases and then decreases with the increase in rock content.This is positively correlated with the normal stress amplitude,while negatively correlated with the normal loading frequency.An increase in rock content amplifies the interface dilatancy effect,while increases in stress amplitude and loading frequency reduce the interface dilatancy effect.The enhancement of the interface friction effect can be attributed to increased rock content and stress amplitude.An empirical formula for the interface friction coefficient,as a function of rock content,stress amplitude,and loading frequency,has been established.This formula coincides well with the test results.
This paper presents an integrated optimal controller for the tandem intersection with lane function design and signal control, aiming to improve intersection efficiency and service reliability with a multi-objective formulation. The tandem intersection is a type of unconventional intersection that can re-organize the vehicles at entrance lanes with sorting areas, and improve intersection capacity through the coordination of pre-signals and main signals. However, most existing studies related to tandem intersection control assume that the lane functions in the sorting areas for both the through and left-turn movements are the same, and the traffic demand remains static. To fill these gaps, this paper first identifies six different tandem control modes based on the different lane functions and phase sequence schemes in the sorting area, and the corresponding delay models for each mode are derived. Furthermore, an integrated optimization model is developed to minimize the mean and semistandard deviation of the intersection delay, and the Non-dominated Sorting Genetic Algorithm-II is used to obtain the optimal solution. A case study is conducted in a real-world intersection in Melbourne, Australia, under various traffic conditions. The results show that the proposed method can decrease average delay and queue length by 19.61% and 20.94%, respectively, compared with conventional intersection design.
因较好解决了钢桥面疲劳开裂和沥青铺装层易破损问题,钢-UHPC(Ultra-high Perform-ance Concrete,超高性能混凝土)轻型组合桥面在新建斜拉桥中逐步推广;然而,宽幅钢-UHPC轻型组合桥面不可避免地涉及分次浇筑,接缝处钢纤维拉接作用失效,导致接缝抗裂强度显著下降.为了有效降低分次浇筑接缝处UHPC桥面与铺装层的病害风险,开展了多型UHPC接缝的抗裂性能试验与对比分析.采用多尺度有限元仿真分析斜拉桥的全过程受力状态,计算识别出宽幅钢-UHPC桥面在施工和运营阶段的高拉应力区域,据此制定了斜拉桥UHPC分次浇筑接缝的设置原则.设计了五型UHPC分次浇筑接缝供工程比选,包括加粗钢筋接缝、斜向接缝、锯齿接缝、矩形接缝和异形钢板接缝;含对照组,共制作了7组UHPC接缝试件开展直拉试验,根据测试得到的最大裂缝宽度-应力曲线进行了UHPC分次浇筑接缝的抗裂性能对比分析.分析表明:斜拉桥施工阶段的UHPC层高开裂风险区明显不同于运营阶段,施工体系转换将使得最大拉应力峰值达7.543 MPa,超过了传统凿毛接缝的初裂名义应力.试验表明:与整体浇筑试件相比,传统凿毛接缝抗裂性能最差,初裂名义应力降低幅值高达78％;加粗钢筋接缝与斜向接缝的抗裂性能相当,初裂名义应力降低幅值分别为34％与35％;锯齿接缝、矩形接缝与异形板接缝抗裂性能优越,初裂名义应力降低幅值最大仅为16％左右.综合考虑异形钢板接缝的抗裂性能与施工便利性,推荐为应用工程实施方案.
有条件自动驾驶系统无法应对所有驾驶场景,因而需要驾驶人在必要情况下进行接管.驾驶人的接管绩效对于有条件自动驾驶车辆的安全性、驾乘体验与接受度具有重要意义.近年来,大量文献从不同视角对驾驶人接管绩效这一主题进行了广泛研究,但仍然存在一些问题亟待解决.从驾驶人接管绩效影响因素、接管绩效模型与接管绩效评价方法3个方面综述了驾驶人接管绩效的研究现状.首先,从驾驶人因素、交通环境因素和自动驾驶系统因素3个维度对驾驶人接管绩效影响因素的相关研究进行综述.其次,对现有驾驶人接管绩效模型,包括经典统计模型、机器学习模型与结构方程模型进行总结.最后,总结了现有原始接管绩效评价指标以及接管绩效综合评价方法.分析发现:现有接管绩效影响因素的量化指标仍不够全面,现有接管绩效模型的可解释性和预测精度难以兼顾,现有接管绩效评价方法尚需进一步完善.有鉴于此,未来研究首先需要基于驾驶人群体主观评价提出接管绩效的全面评价方法,然后以此为基础从人-机-环境维度全方面探索接管绩效影响因素的量化指标,最后考虑多种影响因素的复杂关联关系,建立高精度接管绩效预测模型,从而为提升驾驶人接管绩效提供理论支持,促进有条件自动驾驶的进一步发展.
针对自动驾驶高精度地图实时动态更新在高精度、高可靠、高安全等方面所面临的挑战,总结当前高精度地图更新面临的困难与挑战,加快自动驾驶高精度地图的大规模商业化落地,从而提升智能汽车的安全性和稳定性,为高级别自动驾驶提供重要支撑.首先描述了 自动驾驶地图的定义与内涵,指出自动驾驶地图的数据特性和功能应用;其次梳理了高精度地图更新的发展现状与趋势,综述了地图集中式更新与众源式更新的优劣,指出众源更新已成为地图更新发展的新趋势;再次,总结了 目前众源更新的基本架构与关键核心模块,并针对关键核心技术展开分析,归纳了众源更新所涉及关键技术的现状及趋势.结果表明:当前技术仍然面临着7个主要方面的挑战,涉及地图模型、高精定位、三维重建、融合更新、数据安全、快速审查、标准法律法规.针对这些挑战,指出自动驾驶高精度地图众源更新技术难题需要政产学研多部门从技术、政策、法律多维度共同推进解决,从而加速自动驾驶地图众源更新技术的发展与应用.
The prediction of shield tunnel face support pressure is one of the core issues for the stability analysis of tunnel engineering. Current studies mainly focused on the failure mechanism of horizontal shield tunnel face. The impact of longitudinal inclination angles on the tunnel face was rarely considered. In this study, a series of three-dimensional analytical models were conceived based on the observations of previous laboratory tests and the limit equilibrium theory, which can calculate the active limit face support pressure of shield tunnel in dense sand stratum within three tunneling conditions, i.e., upward tunneling, horizontal tunneling and downward tunneling. The expression of limit face support pressure was deduced combining with the earth pressure theory of Terzaghi. The characteristics of failure mode and face support pressure with different longitudinal inclination angles were investigated by finite difference method Flac3D 5.0 . The core parameters（the height coefficient of log-spiral and the inclination angle of the slip surface） of the proposed model are determined by numerical simulations and previous laboratory tests. The efficacy of the proposed model was evaluated by comparing with the solutions of other analytical methods. The results indicate that the area of failure zone is gradually enlarged from the downward slope to upward slope, and the corresponding limit face support pressure linearly increases within two stages. The increment of face support pressure is obviously enhanced from horizontal to upward slope. In addition, the face support pressure increases simultaneously with the increasing of tunnel diameter, and the impact of tunnel diameter on face support pressure is more significant for the upward tunneling condition. This study can provide some reference for the tunneling of shield machines.
The pipe roof-box culvert integration tunnel structure is a novel underpass structure that solves the traffic bottleneck formed by the intersection of new urban roads and existing roads,its shear behavior is crucial to ensure the safety of the tunnel.To study the shear behavior of this structure,a full-scale shear test was conducted to verify the shear resistance and determine the failure mode.Finite element analysis models were established to analyze the effects of the filling concrete strength,steel plate strength,web plate thickness,and CT-shaped integrated joint length on the shear bearing capacity.And a theoretical calculation formula for shear bearing capacity was derived based on the test phenomena and finite element analysis results.The experimental and theoretical analysis results indicate that the void failure of the CT-shaped integrated joint leads to a significant reduction in structural rigidity,leading to structural failure;The main structural failure modes are critical diagonal crack penetration failure,mid span vertical shear crack penetration failure,and shear failure in the CT shaped integrated joint area;The shear bearing capacity increases with the increase of material strength.Compared to filling concrete,the strength improvement of steel plates has a more significant effect on the shear bearing capacity;The thickness of the web plate has the most significant impact on the shear bearing capacity,with an increase of 66.67％in web plate thickness leading to an increase of 44.54％in bearing capacity;The smaller the length of the CT-shaped integrated joint,the greater the shear bearing capacity,but the effect is relatively small.53.33％of the joint length change can only cause 7.71％of the bearing capacity change;Based on reasonable theoretical assumptions summarized from experimental phenomena and finite element analysis results,the shear bearing capacity theoretical calculation formula derived from the force transmission mechanism of concrete diagonal compression strut and the triangular area failure around the joint takes into account the influence of web plates and CT-shaped integrated joints,and can predict the shear bearing capacity results of experiments and finite element analysis with very small errors(average error-2.30％,standard deviation 2.75％).
The landscape belt of extra-long highway tunnels serves as a function of safety by awakening drivers and reducing their fatigue,especially for those spanning over 7 km.However,the abrupt changes in environmental brightness and decoration information in the landscape zone may cause the driver's visual discomfort.To this end,this study proposed a solution with the idea of gradual changes,which including the linear gradient change of lighting and murals,to optimize the balance of safety and comfort in the driving experience.Based on the parameter investigation about the landscape belt of 21 highway tunnels in China,the simulation model of the tunnel landscape belt was constructed to explore the feasibility of twelve optimized schemes of tunnel landscape design,including with or without gradual changes,different gradual directions,and varying gradual lengths.Driving simulation experiments were conducted to test drivers'feedback,with an eye tracker and heart rate band as sensors collecting data on heart rate change,visual distraction frequency,and pupil diameter range change rate.Results reveal that the proposed gradual change design of the tunnel landscape belt does not significantly distract the driver's attention in terms of safety.From a locational perspective,situating the gradual landscape zone in the approaching direction enhances driver comfort,as opposed to positioning it in the leaving direction.This lifting effect is in a power function relationship with the reciprocal of the gradual length in the approaching direction.In terms of length design,parametric analysis suggests that three schemes-setting the 200 m,250 m of gradual change areas in the approaching direction,or bidirectional 150 m-can significantly reduce the uncomfortable feeling caused by visual mutation issues,without compromising safety.Moreover,it is recommended to set 200 m gradual change areas in the approaching direction for tunnel landscape belt with lengths of 300 m.
Considering the limitations of the traditional resistance strain gauge method for on-site testing the strain of feet-lock pipe,a φ50 Fiber Bragg Grating(FBG)feet-lock pipe was designed and manufactured based on FBG sensing technology.A field test of the FBG method for testing the strain of feet-lock pipe was carried out.The stress features and supporting function of the feet-lock pipe in soft rock tunnel were analyzed.Then,a mechanical analysis model of feet-lock pipe in soft rock tunnel was established,and the formula for calculating the support stiffness of feet-lock pipe on the feet of primary support was derived.The influence law and sensitivity of each parameter of feet-lock pipe on the support stiffness were quantitatively analyzed.The results of this analysis show that the strain variation law at each measuring point of the feet-lock pipe was very complicated owing to the construction disturbance and connection method of the feet-lock pipe.From the overall strain distribution of the pipe,the strain of the feet-lock pipe near the steel rib significantly exceeds those of other parts of the pipe,and the change amplitude of the strain at the end of the pipe near the steel rib obviously exceeds that near the surrounding rock.The feet-lock pipe is primarily subjected to lateral bending deformation in the upper and lower directions,and is subjected to compressive load transmitted by the tunnel feet in the axial direction.As the angle of the feet-lock pipe increases,its axial compression characteristics become increasingly significant.The axial anchoring effect of the feet-lock pipe is very small,primarily exerting lateral bending and shear resistance to constrain the settlement of the tunnel feet,and the constraint effect on the horizontal convergence deformation of tunnel feet is limited.Increasing the diameter of the feet-lock pipe is the most effective way of enhancing the vertical support stiffness of tunnel feet.When the axial support condition of feet-lock pipe is poor,increasing its angle significantly reduces the vertical support stiffness of tunnel feet.At this time,the steel rib should be closely attached to the surrounding rock.As the length of the feet-lock pipe increases,the vertical support stiffness of the tunnel feet provided exhibit rapid growth initially,followed by gradual growth.Considering the stress characteristics of the feet-lock pipe and the engineering economy,a length of 2.5 m is recommended for the φ50 feet-lock pipe.
In order to master the mechanical characteristics of karst tunnel lining structure under heavy rainfall,the water pressure and mechanical response characteristics of karst tunnel lining structure were analyzed by field test and numerical analysis.Among them,based on lining water pressure test data about 15 months during tunnel operation,the water pressure characteristic indexes such as the total duration of water pressure rise and fall,the time of water pressure rise,the time of water pressure peak and dissipation,the water pressure distribution form and the water pressure peak after three rainfalls were analyzed emphatically.And the load-structure model of tunnel was established for 12 load conditions of three load states,such as single pressure state,multiple pressure state and expanded water pressure range state,and the axial force,bending moment and safety factor changes of tunnel lining structure were calculated and analyzed.The results show that the difference of the peak water pressure of the lining of the two test sections is about 1.83 times,and the total duration of water pressure rise and fall is 20-57 h and 4-9 h respectively,which basically conforms to the rule that the larger the peak water pressure is,the earlier the time of beginning to rise,the earlier the time of reaching the peak,and the later the time of water pressure dissipating.In the whole process of rainfall,the water pressure distribution pattern of tunnel lining shows a"three-stage"time-varying law,which are partial pressure,more uniform distribution,and partial pressure,and the peak water pressure mainly appears in the stage of more uniform distribution.Safety factor of lining structure under single pressure state is larger than under expanding water pressure range state and smaller than under multiple pressure state.Any part of the tunnel lining structure may be damaged when the water pressure of the tunnel lining is very high or high,and the main damage parts of the lining structure are the arch waist and arch foot when the water pressure is relatively high.The research results can provide reference for the design of karst tunnel lining structure,civil structure inspection and disease treatment design in heavy rainfall area.
To further enhance the strength of the field of automotive engineering and promote the development of automotive technology in China,this study systematically analyzes the academic research status,cutting-edge hot issues,latest research results,and future development prospects in the field of automotive engineering at both domestic and international levels from six aspects:automotive electrification and energy saving,intelligent and connected vehicles,vehicle dynamics and control,automotive NVH(noise,vibration,harshness)control and lightweight control,automotive electronics and electrical(E&E)and software technology,and automotive testing and evaluation technology.Automotive electrification and energy saving constitute key aspects of pure and plug-in hybrid electric vehicles,hydrogen fuel cell vehicles,extended-range electric vehicles,and energy-saving vehicles.Intelligent and connected vehicles are objectives of the research on intelligent driving environment perception technology,autonomous driving positioning technology,intelligent vehicle decision-making and planning,motion control technology,vehicle-road coordination,intelligent safety technology,Internet-of-vehicles safety technology,and intelligent cockpit and human-computer interaction technology.Vehicle dynamics and control are addressed by the research on brake-by-wire,steer-by-wire,suspension-by-wire,and chassis-by-wire cooperative-control technologies.Automotive NVH control and lightweight control involves the prediction and optimization of automotive aerodynamic noise,NVH control of pure electric vehicle systems,acoustic metamaterials and automotive structural vibration control,automotive noise active control,and automotive lightweight and collision safety technologies.Automotive E&E and software technology is addressed by the research on automotive E&E architecture,automotive software technology and OTA(over the air)upgrade,chip and system function integration,etc.Automotive testing and evaluation technology is addressed by the research on testing and evaluation technology of fuel vehicles,new energy vehicles,and intelligent and connected vehicles.This review provides a reference for further development of automotive engineering research in China,and guidance for the innovation in key technologies of the automotive industry.
Examining the trend of drivers'multidimensional mental workload characteristics over time is important to develop dynamic assessment methods for mental workload during long-term driving tasks.However,a lack of in-depth research exists on the dynamic changes in mental workload,and the trend of multidimensional mental workload characteristics over time has not been fully understood.In this study,a long-term driving experiment was designed based on different levels of mental workload under simulated driving scenarios.A two-factor(three task difficulty levels X six time periods)within-subjects experimental design was used.Data on drivers'subjective mental workload,driving behaviors,and multimodal physiological characteristics(i.e.,measures of eye movements,electro-dermal activity,and electrocardiogram)were collected.The changing trend of each characteristic of mental workload in long driving tasks was systematically analyzed using repeated measures analysis of variance.The results show that,as driving time increases,mental workload increases.Similarly,pupil diameter decreases rapidly and then remains constant.Skin conductance level increases rapidly and then remains constant.Heart rate variability(i.e.,pNN20)decreases slowly over time.The low-frequency to high-frequency component ratio(LF/HF)in heart rate variability first remains constant and then increases during the last time period.Task difficulty significantly affects mental workload,driving behaviors,eye-tracking measures,and skin conductance.The changing trends in characteristics of mental workload for different task difficulty levels vary with time.The results reveal the changing trends in mental workload during long-term driving tasks and provide implications for developing dynamic assessment methods for mental workload in these scenarios.
Traditional methods of identifying bridge mode shapes often have limitations such as time-consuming,labor-intensive,and weak anti-noise ability.To change the weaknesses of previous identification methods,this paper proposes a new bridge mode identification method based on statistical moment theory.Theoretical and numerical experimental analyses are conducted.Two test vehicles installed with accelerometers were used to synchronously collect signals at the preset measuring points on the bridge deck at a fixed distance.After about 30 s of acquisition,the test vehicle moved to the next position to continue the test until the signal acquisition of all bridge deck measuring points was completed.Subsequently,the collected acceleration signal was used to calculate the statistical moment value of each measuring point of the entire span bridge,and finally,the fundamental mode curve of the whole span bridge was constructed by calculating the corresponding relationship between the statistical moment and fundamental mode.The equivalent relationship between the statistical moment ratio and fundamental mode value is theoretically expounded for the first time,and numerical simulations were conducted to analyze the effects of different factors.Furthermore,the distinctions between the proposed and existing mode shape identification methods were compared.Finally,the new method in this article was further proved using an actual bridge test.The results show that,compared with traditional mode-shape identification methods such as stochastic subspace identification and transmissibility,the first mode-shape error of the bridge obtained using the proposed method is smaller,the time efficiency is higher,resistance to noise is better,and no human factors such as preset parameters are involved in the identification process.It can effectively compensate for the limitations of traditional mode shape identification methods in direct measurement technology.
Local scouring is a potential hazard threatening the safe operation of bridges.Compared with river-wading bridges,sea-crossing bridges are susceptible to ocean currents and tidal surges,and the process of foundation scouring is complex.Numerous variables influence local scouring,and the relationship between them and local scouring is highly nonlinear.Most traditional empirical models for predicting scour depth are based on physical experiments and establish the mapping relationship between key parameters and local scour depth using the simple regression method,which has severe limitations and large prediction errors when applied to practical sea-crossing projects.In this study,a systematic analysis and research on the above problems were conducted.First,using the single factor control variable approach,the influences of critical parameters such as approach flow velocity,water depth,pier width,and sediment particle size on the calculation results of the local scouring calculation formula of the Chinese and American codes were compared and studied,and the characteristics of the parameters were analyzed.Furthermore,three dimensionless parameters(height diameter ratio,flow intensity,and Froude number)were constructed using parameter dimension reduction.Second,a non-immersion and dynamic whole-process experimental test method was proposed.This method can acquire the dynamic evolution of the terrain surrounding the pier during the scouring process.Third,15 groups of scale physical model tests were conducted based on the actual physical parameters and hydrological conditions of the cylindrical pier of the sea-crossing bridge.Using the proposed non-immersion and dynamic whole-process experimental test method,the effects of the three non-dimensional parameters on the local scouring dynamic development of the cylindrical pier under 15 experimental condition groups were investigated.Finally,a sample database consisting of 73 groups of monitoring data and 15 groups of experimental data was established.Additionally,random forest scouring prediction models based on dimensionless and high-dimensional parameters were constructed.A comparison of the prediction results with the calculation results of the HEC-18 empirical model reveals that the random forest prediction model with dimensionless parameters has the best performance.The experimental approach and scouring depth prediction model described in this paper can serve as a reference for studying both the mechanisms and predictions of local scouring of sea-crossing bridges.
With the rapid development of artificial intelligence,deep learning algorithms for nonlinear propose a new approach for solving the persistent dilemma of tunnels and underground engineering relying on empirical designs.In this study,by fusing multiple indices(mechanical and deformation control indices)with the correlation coefficient of the support system synergy degree,an evaluation standard for support systems,characterized by the degree of fit,was proposed.Using this evaluation standard,the data of 718 highway and 486 railway tunnel sections were collected to build a database for algorithm training.Eight attributes about the background information of tunnel engineering,including rock hardness degree,integrity degree,rock thickness,underground water volume,buried depth level,geological structure,construction method,and internal contour type,were considered input indicators.Eight attributes of the support system,including shotcrete+steel mesh,rock bolt,steel arch,secondary lining,and auxiliary measures,were considered output indicators.The input and output indicators were then quantified.After comparing the characteristics of the PSO-SVM,SA-PSO-SVM,and CLS-PSO-SVM in the application of the intelligent feedback model of the support system,the generated intelligent feedback model was tested.The results show that the evaluation method first eliminates the weak design scheme.The degrees of fit of the strong support and general support schemes are 4.28 and 4.68,respectively,which verifies that the method can evaluate the material utilization rate while ensuring structural safety.Among the three intelligent algorithms,the CLS-PSO-SVM algorithm,with the broadest search range,had the highest feedback accuracy but the longest time consumption,whereas the PSO-SVM algorithm had the shortest time consumption but the lowest accuracy.Finally,the accuracies of the five output labels designed using the CLS-PSO-SVM algorithm are 93.4％,92.6％,89.3％,91.8％,and 94.3％.The collective accuracy of the five output indices is 81.1％.
Local failure(loss of concrete or reinforcement)will significantly affect the bearing capacity of the shield segment,and even lead to the damage of the tunnel structure.To clarify the influence of local failures on the bearing capacity,full-scale tests were carried out on the standard segment,mid-span and side opening segments respectively.Displacements and concrete strains of these segments were monitored during the loading procedure.The loading process of the segment can be divided into four stages,and each stage has a critical load that can be defined as the characteristic load.According to each characteristic load value,the bearing characteristics of the segment were compared and analyzed.The analysis results show that the bearing capacity of the opening segment is lower than that of the standard segment,and the opening position has a strong influence on the bearing characteristics.To further clarify the accuracy of test results,numerical simulations were conducted by using the elastoplastic damage constitutive behavior of concrete,and the reasonableness of the experiment results were verified by comparing with the simulation.According to the bearing characteristics of the standard segment,the influence of the opening diameter and position on the bending bearing characteristics of the partially failed segment was quantitatively analyzed.This paper preliminary proposed a calculation model of the bearing characteristics for the local failed shield segment which can provide a theoretical basis for the safety assessment and reinforcement design of shield tunnels under extreme conditions.
With the continuous development of artificial intelligence,the rapid and nondestructive tunnel rock mass feature recognition method based on intelligent algorithms provides a new idea for the investigation of excavation face structures in the event of geological disasters of tunnels under construction and in service.Based on the three-dimensional panoramic image of the excavation face,an improved algorithm is proposed for three-dimensional simple linear iterative clustering superpixel segmentation.It groups the basic elements of the three-dimensional mesh image,the triangle,according to color,spatial coordinates,normal vector,and other indicators and obtains a three-dimensional superpixel of the excavation face.A structural surface extraction algorithm based on the angle difference is proposed,and the superpixels are screened individually to obtain joint fracture identification results for the surrounding rock of the excavation face.A multilevel clustering surrounding rock structure feature fusion algorithm based on unsupervised cluster learning is proposed.The identification results of the surrounding rock joint fractures are clustered to obtain the dominant structural quilt and large cross-mileage structural quilt of the excavation face.The proposed algorithm is verified using 21 sets of excavation face 3D panoramic image data from the Huxitai Tunnel in Zhejiang Province.The results show that the recognition results of the proposed algorithm are consistent with the two main structural plane directions in the geological exploration data.The angle deviation of the inclination error does not exceed 14.8°,and the inclination deviation does not exceed 17.8°,verifying that the proposed algorithm can accurately reflect the structural surface information of the surrounding rock of the tunnel.The proposed method provides a new method for the recognition and evaluation of three-dimensional information regarding the structural surface of a tunnel excavation face.
Caissons are important platforms and prerequisites for the smooth construction of deep-water bridges.Hydrodynamic loads are key factors affecting the precise positioning,sinking,and landing of the caisson in its segmental construction.To reduce the hydrodynamic load of steel caissons under current loads,this paper proposes a restrain method for rectangular steel caissons by adding a certain length of splitter plate at the rear end.First,a two-dimensional simplified model of a steel caisson was established based on the open source analysis platform OpenFOAM using the computational fluid dynamics method.A modified k-ε model was introduced to solve the Navier-Stokes equation of the steel caisson under ultra-high Reynolds numbers.The accuracy of the proposed method was verified using square and rectangular cross-section bluff columns.Subsequently,based on the full-scale steel caisson model,the influence of splitter plate setting on the hydrodynamic drag and lateral fluctuation force of the steel caisson was analyzed,and the inhibition effect of different lengths of the splitter plate and front/back end splitter on hydrodynamic load was clarified.An optimized and feasible splitter plate setting scheme is proposed.The results show that the standard k-ε model cannot accurately capture the vortex shedding process of square and rectangular bluff bodies at high Reynolds numbers,and the hydrodynamic load would be significantly underestimated.The modified k-ε model can accurately simulate the flow characteristics of a rectangular bluff body,which is in good agreement with the experimental data,and can be used to calculate and analyze steel caissons.The rectangular steel caisson with rounded corners can effectively reduce the hydrodynamic drag and lateral swing amplitude but increase the swing frequency.Adding a central splitter plate at the rear end of the steel caisson can significantly reduce the hydrodynamic drag and lateral swing force.When the length of the splitter is within 1/10 of the longitudinal length of the steel caisson,the inhibition effect is the highest.When the length of the splitter plate is more than 0.75 times the longitudinal length of the steel caisson,the wake begins to oscillate,which results in an increase in the lateral swing force;adding a front splitter can restrain such an increase.The effect of the front splitter on the hydrodynamic action can be ignored.A field flow trace test verified that the formation of the wake vortex can be reduced and delayed using rear-end splitter plates,and the hydrodynamic drag and lift loads of a steel caisson can be effectively restrained.
