Data-Driven Model for Risk Assessment of Cable Fire in Utility Tunnels Using Evidential Reasoning Approach

Cable fire is one of the most important events for operation and maintenance(O&M)safety in underground utility tunnels(UUTs).Since there are limited studies about cable fire risk assessment,a comprehensive assessment model is proposed to evaluate the cable fire risk in different UUT sections and improve O&M efficiency.Considering the uncertainties in the risk assessment,an evidential reasoning(ER)approach is used to combine quantitative sensor data and qualitative expert judgments.Meanwhile,a data transformation technique is contributed to transform continuous data into a five-grade distributed assessment.Then,a case study demonstrates how the model and the ER approach are established.The results show that in Shenzhen,China,the cable fire risk in District 8,B Road is the lowest,while more resources should be paid in District 3,C Road and District 25,C Road,which are selected as comparative roads.Based on the model,a data-driven O&M process is proposed to improve the O&M effectiveness,compared with traditional methods.This study contributes an effective ER-based cable fire evaluation model to improve the O&M efficiency of cable fire in UUTs.

Study on Gas Explosion Characteristics in Urban Utility Tunnels

In order to study the effects of three factors,namely,premixed gas concentration,number of pressure relief ports and number of obstacles,on the overpressure characteristics of gas explosion and flame structure of gas chambers in utility tunnels,in this paper,a small and narrow experimental platform for gas explosion was constructed to study the evolution mechanism and law of the kinetic characteristics and flame behavior of gas explosion in utility tunnels,with a view to revealing the special influencing mechanism of the overpressure characteristics and flame behavior of gas explosion in utility tunnels.The results show that in the methane concentration of 9.5%when the explosion overpressure reaches its peak,and at the same time by the utility tunnel long and narrow restricted space,the explosion generated by the precursor shock wave along with the flame compression wave were superimposed on both ends of the pipeline back and forth for many times so that the overpressure waveforms are cyclic oscillatory trend,increasing the explosion hazards;compared with the closed conditions,the relief port on the overpressure characteristics of the significant impact of the maximum decrease of 57.7%,when the frequency of overpressure oscillation is reduced,the gas explosion generated by the overpressure damage is reduced;the presence of obstacles significantly affects the flow field,accelerates the flame propagation and leads to greater overpressure peaks and overpressure oscillations.The conclusions of the study can provide a basis for the safety of natural gas in utility tunnels.

Seismic response of underground utility tunnels: shaking table testing and FEM analysis

Underground utility tunnels are widely used in urban areas throughout the world for lifeline networks due to their easy maintenance and environmental protection capabilities. However, knowledge about their seismic performance is still quite limited and seismic design procedures are not included in current design codes. This paper describes a series of shaking table tests the authors performed on a scaled utility tunnel model to explore its performance under earthquake excitation. Details of the experimental setup are first presented focusing on aspects such as the design of the soil container, scaled structural model, sensor array arrangement and test procedure. The main observations from the test program, including structural response, soil response, soil-structure interaction and earth pressure, are summarized and discussed. Further, a finite element model （FEM） of the test utility tunnel is established where the nonlinear soil properties are modeled by the Drucker- Prager constitutive model; the master-slave surface mechanism is employed to simulate the soil-structure dynamic interaction; and the confining effect of the laminar shear box to soil is considered by proper boundary modeling. The results from the numerical model are compared with experiment measurements in terms of displacement, acceleration and amplification factor of the structural model and the soil. The comparison shows that the numerical results match the experimental measurements quite well. The validated numerical model can be adopted for further analysis.

Dynamic response of utility tunnel during the passage of Rayleigh waves

The modeling methodologies and calculation of dynamic response of underground structure under Rayleigh waves is investigated in this paper. First the free field responses under Rayleigh waves are analyzed and the numerical results agree well with the theoretical results. Then, the approximate Rayleigh waves are put forward based on the preliminary re- search, and Rayleigh wave field is obtained through fast Fourier transform technique. Taking a utility tunnel as an example, its dynamic responses under Rayleigh waves is calculated by ABAQUS. The results demonstrate that bending deformation is the main component of structural deformation and the deformation at the top of the structure is about twice as much as that at bottom of the structure. The effect of soil-structure interface and the buried depth of underground structure are also investi- gated via parameter analysis. For the shallow buffed underground structures, Rayleigh waves can be the key factor to control the responses and damage of the structure.

Large scale shaking table model test and analysis on seismic response of utility tunnel in non-homogeneous soil

Underground utility tunnels are the most fundamental and reliable lifeline network in urban cities,and are widely constructed throughout the world.In urban areas,most utility tunnels usually encounter the non-homogeneity of subsoil condition due to various construction effects.Studies have shown that the damage mechanism of shallow underground structures mainly depends on the inhomogeneity of the subsoil conditions.This would become a considerable factor for the stability of the underground utility tunnel structures.However,this type of research still needs to establish the vulnerable seismic design.In this study,a series of shaking table tests were conducted on non-homogenous soils to investigate the performance of seismic interaction between utility tunnels,surrounding soils and interior pipelines.The dynamic responses measured from the test account for the boundary condition of non-homogeneous soils,the internal forces,displacement of tunnel joints,the dynamic characteristics on interior pipelines and the reasonable spring stiffness with damping in the seismically isolated gas pipeline model inside the tunnel.The vulnerability of underground utility tunnel in non-homogeneous soil zone and the mechanism of the stability of interior facilities are the main topics discussed in this paper.

Blast resistance evaluation of urban utility tunnel reinforced with BFRP bars

To improve corrosion-resistance of shallow-buried concrete urban utility tunnels(UUTs),basalt fiber reinforced polymer(BFRP)bars are applied to reinforce UUTs.As the UUT must have excellent survival capability under accidental explosions,a shallow-buried BFRP bars reinforced UUT(BBRU)was designed and constructed.Repetitive blast experiments were carried out on this BBRU.Dynamic responses,damage evolutions and failure styles of the BBRU under repetitive explosions were revealed.The tunnel roof is the most vulnerable component and longitudinal cracks develop along the tunnel.When the scaled distance is larger than 1.10 m/kg1/3,no cracks are observed in the experiments.When the BBRU is severely damaged,there are five cracks forming and developing along the roof.The roof is simplified as a clamped-supported one-way slab,proved by the observation that the maximum strain of the transverse bar is much larger than that of the longitudinal bar.Dynamic responses of the roof slab are predicted by dynamic Euler beam theory,which can consistently predict the roof displacement under large-scaleddistance explosion.Compared with the UUT reinforced with steel bars,the BBRU has advantages in blast resistance with smaller deflections and more evenly-distributed cracks when the scaled distance is smaller than 1.260 m/kg1/3 and the steel bars enter plastic state.Longer elastic defamation of the BFRP bars endows the UUT more excellent blast resistance under small-scaled-distance explosions.

Dynamic-Response Analysis of the Branch System of a Utility Tunnel Subjected to Near-Fault and Far-Field Ground Motions in Different Input Mechanisms

There are few studies on the dynamic-response mechanism of near-fault and far-field ground motions for large underground structures,especially for the branch joint of a utility tunnel(UT)and its internal pipeline.Based on the theory of a 3D viscous-spring artificial boundary,this paper deduced the equivalent nodal force when a P wave and an SV wave were vertically incident at the same time and transformed the ground motion into an equivalent nodal force using a self-developed MATLAB program,which was applied to an ABAQUS finite element model.Based on near-fault and far-field groundmotions obtained fromtheNGA-WEST2 database,the dynamic responses of a utility tunnel and its internal pipeline in different inputmechanisms of near-fault and far-field groundmotions were compared according to bidirectional input and tridirectional input,respectively.Generally,the damage to the utility tunnel caused by the near-fault ground motion was stronger than that caused by the far-field ground motion,and the vertical ground motion of near-fault ground motion aggravated the damage to the utility tunnel.In addition,the joint dislocation of the upper and lower three-way joints of the pipeline in the branch systemunder the seismic action led to local stress concentrations.In general,the branch system of the utility tunnel had good seismic performance to resist the designed earthquake action and protect the internal pipeline fromdamage during the rare earthquake.

Comparison between the Seismic Performance of Buried Pipes and Pipes in a Utility Tunnel

A utility tunnel system consists of pipes and ancillary facilities.In this paper,a finite element model of a concrete utility tunnel with pipes inside is established.Several tunnel segments were built to simulate a real utility tunnel,while the pipe was fixed by springs on the brackets in the utility tunnel.Using the discrete soil spring element to simulate the soil-structure interaction,actual earthquake records were adopted as excitation to analyze the seismic responses of pipes in a utility tunnel.Moreover,the influences of different parameters,including soil type,earthquake records,and field apparent wave velocity on the seismic responses of the utility tunnel and the pipes inside were studied.Finally,the seismic responses of buried pipes were analyzed and compared with those of pipes in a utility tunnel to evaluate the seismic performance of pipes for two working conditions.

BIM Facility Management on Utility tunnel

With the rise of BIM,Building Information Modeling,technology it subverts process and method of traditional civil engineering industry.It brings different meanings and improve efficacy to each stage of building life cycle.Projects can get different kinds of benefits from BIM technology in plan,design,construction,and operation stages.Utility tunnel,designed according to the variety of pipes and cables,is built under traffic roads,which reduces the traffic impact during maintenance and repair.Establishment of utility tunnel increases urban sustainable development.Through BIM technology,thousands of drawings are turned into one model.Meanwhile,with real-time update,model will reflect the latest situation.When application extends into operation stage,model connected with site sensors becomes a completed database for operation.BIM facility management(FM),the new integrated method,can monitor and control utility tunnel to ensure steadily supply of water,electricity or gas.Further,it assists authorities to guard city safety.

Blast responses of polyurea retrofitted utility tunnel reinforced with basalt fibre reinforced polymer bars

Polyurea coating and carbon fibre reinforced polymer reinforcing techniques were applied to retrofit a severely damaged urban utility tunnel(UUT).The blast responses of the retrofitted UUT were investigated through in-filed explosion experimental tests,and the displacements,strains,accelerations,and damage were compared.The retrofitted UUT exhibited comparable or even better blast resistance than the intact UUT.Although the polyurea coating was flexible,it exhibited excellent performance in improving the blast resistance of the damaged UUT.As the UUT reinforced with basalt fibre reinforce polymer(BFRP)bars has smaller damage compared with the UUT reinforced with steel bars,its retrofitting is simple,and the cost is low.The roof was simplified as an elastically simple support one-way slab.Euler beam theory was adopted to analyse the dynamic responses of UUT roof considering the interaction between soil and structure,which agree well with the experiments in the first three cases.

故障树和模糊贝叶斯网络在管廊运维风险评估中的应用研究

地下综合管廊是城市的生命线,一旦出现问题就会对人们生命财产安全造成巨大损害。为了系统地分析管廊运维风险,建立了基于模糊贝叶斯网络的风险评估框架。首先,通过分析管廊运维风险源与风险形成的原因以确定风险事件和风险类别;其次,建立管廊运维风险故障树来梳理风险因素之间的逻辑关系,将故障树映射为贝叶斯网络;最后,结合专家模糊评价,构建地下综合管廊运维风险评估模型。案例分析结果显示:中间事件“火灾、爆炸”与“危害气体浓度过高”的发生概率较高。敏感性分析结果显示:“运维人员操作和维护不当”是导致管廊运维风险发生的根本事件,因此需要制定严格管理措施及规范,加强对运维人员的素质培训,以降低管廊运维过程中各种风险的发生概率。

分段管廊装载供水管道穿越地裂缝适宜性研究

在活动地裂缝影响下,供水管道拉裂、错断现象时有发生,并引发严重的次生灾害。本文以西安市西南郊水厂拟建球墨铸铁管道穿越地裂缝为工程背景,建立管道45°穿越活动地裂缝的数值模型,分析地裂缝影响下管道的内力响应与变形特征,结果表明:地裂缝作用会使管道接口偏转角过大而导致其防水失效。因此提出一种分段管廊装载供水管道穿越地裂缝的方法,建立分段管廊装载供水管道穿越地裂缝的数值模型,分析管道与管廊通缝、错缝两种工况、不同分段管廊长度、不同地裂缝位置、不同穿越角度下管廊与管道的内力响应与变形特征。得出管廊装载管道穿越地裂缝的最佳方案为管道与管廊通缝布设,采用单节长度为18 m的分段管廊,使地裂缝位于管廊的2/3处,并尽量以小角度穿越地裂缝。研究成果对城市供水管道穿越活动地裂缝的工程建设与灾害防治具有实际意义。

基于多因子量化分析的综合管廊规划布局研究

传统综合管廊规划选线多从定性和经验角度出发,缺乏定量分析和数据支持,具有较大的主观性。因此以重庆市广阳湾智创生态城为例,构建了综合管廊布局多因子量化评价体系,包括线性因子和区块因子2条主线,采用GIS分析软件将影响综合管廊布局的各类因子在空间上进行叠加,然后对线性因子和区块因子2条主线的评价结果进行再次叠加,形成综合管廊选线的最终评价结果,使其更加科学、客观地形成了综合管廊的系统布局。该研究成果可为类似综合管廊布局提供一定参考。

基于故障树和贝叶斯网络的管廊运维风险评估

城市地下综合管廊在运维过程中事故时有发生,为了量化管廊运维风险并分析关键风险因素,提出一种基于故障树和模糊贝叶斯网络的城市地下综合管廊运维风险评估方法。在综合考虑管廊风险因素的基础上构建故障树模型,将其映射为贝叶斯网络。基于ALARP准则划分风险因素状态等级,根据模糊数和模糊子集计算底事件的发生概率,利用最大似然估计法求解中间事件的条件概率,构建管廊运维风险贝叶斯网络模型,精准评估城市地下综合管廊运维风险。结果表明:所评估的管廊运维过程风险等级为High的概率为28%,接近30%的风险阈值,因此需要及时对管廊风险进行管控。该方法能够科学、合理地评价风险水平并确定关键因素,可为管廊运维安全保障和管理提供参考。

不同受限条件下综合管廊电缆桥架火灾烟气温度分布特性研究

为了更有效地防控综合管廊电缆桥架火灾,在全尺寸综合管廊中开展了电缆桥架火灾试验,系统研究了电缆层数和卷吸条件对电缆桥架火灾烟气温度分布的影响。在电缆桥架附近垂直和水平布置一系列热电偶,分别用于测量管廊内垂直和顶棚水平温度分布。基于管廊内的垂直温度分布,揭示了火灾场景下管廊垂直温度分层规律。结果表明,管廊内发生电缆桥架火灾时,管廊内从上往下可以分为三部分:顶部射流层、中间热烟气过渡层和下部冷空气层。通过分析管廊不同端口的顶棚横向温度分布,发现顶棚温度在半封闭端的衰减速度比全封闭端更快,建立了考虑热释放速率和火源距离顶棚距离的全封闭端顶棚下方无量纲纵向温度分布模型。最后根据卷吸条件与顶棚最大温升的对应关系,发现整体火源功率越大的电缆桥架火灾受到侧壁和端壁的热反馈影响越强烈,针对不同卷吸条件下的电缆桥架火灾分别建立了顶棚最大温升预测模型。通过将模型预测值与试验值对比,发现模型误差在16%以内。

预制拼装综合管廊承插式接头扭转力学性能

为研究节段预制拼装综合管廊承插式接头扭转力学性能,利用ABAQUS有限元软件建立预制拼装管廊节段与土体纵向三维模型,对管廊正向扭转与反向扭转进行模拟,分析管廊扭转承插式接头应力分布规律,得到管廊承插式接头扭矩随横向差异沉降变化规律及管廊横向极限差异沉降量。研究结果表明:管廊节段正向扭转与反向扭转沉降量相同时,承插式接头应力、最大主应力与切应力分布规律基本相同。管廊扭转接头插口端侧壁应力较大,接头顶底板中间与腋角处应力较小,接头最大主应力集中在承口端侧壁距顶板外侧1 m处与插口端顶底板,接头切应力在顶底板中间与侧壁中间最小,向两侧逐渐增大至腋角处切应力最大。管廊承插式接头横向极限差异沉降为1.2 mm,管廊插口端极限扭矩与采用箱型截面计算的结果相差不大,工程实际中可采用箱型截面对管廊插口端抗扭设计。研究结果为预制拼装管廊安全运营提供科学依据。

云模型在地下综合管廊运维安全管理绩效评价中的应用研究

为了系统地了解地下综合管廊运维安全管理工作效果,提出一种基于云模型的管廊运维安全管理绩效评价模型。在分析影响管廊运维安全相关因素的基础上,构建了管廊运维安全管理绩效评价指标体系。利用层次分析法和熵权法进行组合赋权从而确定各项评价指标权重,结合云模型进行管廊运维安全管理绩效评价。结果显示:所调研管廊的安全运维工作评价结果在“合格”和“良好”之间,总体趋向于“良好”,并识别出人员培训与提升是运维安全管理工作中的薄弱环节。该模型可以有效地评价管廊运维安全管理工作效果并识别出风险环节,丰富了管廊运维安全管理绩效评价的理论研究。

长距离地下综合管廊局部通风强化换热效果研究

现有的地下综合管廊通风散热方法主要为换气次数法。当管廊长度增加时,要满足规范规定的廊内温度不高于40℃的要求需要非常大的换气量,并会导致管廊前端区域过冷,整体散热效果并不好。本文提出了一种可用于长距离地下综合管廊的局部通风方式,使用CFD方法建立了局部通风数值模型,通过缩尺模型实验验证了其准确性。对增设射流风机后形成的局部通风气流组织进行了研究,结果表明,在总送风量相同的情况下,设置射流风机能够改善管廊局部热环境,在本文所研究工况下,局部截面平均温度降低了0.5℃。对比研究发现:管廊进口风量和射流风机风量之比对管廊内热环境影响不大;风机射流角度对管廊内热环境的优化具有显著影响,射流角度为90°时管廊后端截面平均温度相比0°、45°分别降低了0.41、0.33℃,90°为最优射流角度。

双面叠合装配式管廊侧墙面外抗震性能试验

为研究采用螺旋箍筋套筒底节点连接的预制双面叠合式管廊侧墙在面外荷载作用下的受力变形性能,对2个采用该节点连接的足尺侧墙试件进行了不同轴压比下低周往复加载试验,并与对应2个现浇试件作对比,初步揭示了螺旋箍筋套筒底节点和竖向轴压比对管廊侧墙面外抗震受力变形性能的影响。试验结果表明:两种试件滞回曲线均较为饱满,具有良好的抗震耗能能力,满足装配式结构抗震变形设计要求;叠合装配试件上部区域剪切变形均高于现浇试件,且裂缝遍布整个墙体高度范围,具有良好的面外变形能力。

方拱形波纹钢管廊弯矩解析解及断面参数研究

方拱形结构因空间利用率较高而广泛应用于我国地下综合管廊的建设中,但其结构承载特征、力学机制及相关设计方法研究尚少。为研究方拱形波纹钢管廊结构弯矩的解析计算理论以及合理的断面形式,利用结构力学、土力学基本理论和相关规范,推导方拱形波纹钢综合管廊的弯矩解析解,并用二维平面应变模型对弯矩解析式的正确性进行验证,同时建立不同管顶覆土深度的方拱形波纹钢管廊三维地层-结构有限元数值模型,将数值分析结果与弯矩解析式计算的弯曲应力进行对比,分析弯矩表达式的适用覆土深度,基于弯矩解析表达式对管廊断面参数进行优化分析,并给出推荐断面参数范围。研究表明:1)方拱形波纹钢综合管廊的弯矩解析解与数值解相吻合,理论计算的弯矩与数值解的最大误差为5.79%;2)弯矩解析表达式的适用覆土深度为H≤10 m;3)针对依托工程,计算结果表明管廊断面矢跨比、顶板和侧板跨度比均处于0.6~0.8,管廊结构弯矩分布较合理,有利于保障结构安全。