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.

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.

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.

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.

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.

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.

Effect of ventilation on thermal and humidity environment of the underground utility tunnel in the plum rain season in southern China:Field measurement and CFD simulation

The underground utility tunnel(UUT)is one of the typical urban underground structures,which usually requires mechanical ventilation 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 humidity inside the UUT,and on this basis,the humidity control strategy for UUT in the plum rain season is proposed.

Seismic behaviors of utility tunnel-soil system: With and without joint connections

Seismic responses of utility tunnel-soil system were studied via shaking table model tests with considerations of two kinds of double box utility tunnels:with and without joint connections.These two testing utility tunnel models were made of galvanized iron wire and micro-concrete,and the ground was simulated by the dry standard sand through layered tamping treatment.The utility tunnel-soil system was subjected to horizontal vibration in uniaxial direction perpendicular to the longitudinal direction of tunnel model.Via instrumentations of earth pressure gauges,accelerometers and strain gauges,the earth pressure response,acceleration response and bending moment response were measured.The testing results show that the joint connections in the utility tunnel along the longitudinal direction play an important role in determining the characteristic of earth pressure response and bending moment response,whereas the effect of joint connections on acceleration response is less significant.In addition,the partition wall exhibits the consistent acceleration response with the side-wall of double box utility tunnel model under seismic condition.Based on the testing results,it is suggested that the joint connection should be taken reasonably into consideration during design and construction for engineering practice.

基于BIM+技术的城市地下综合管廊智能运维管理研究

城市地下综合管廊是保障城市正常运转的“生命线”,关系着广大民众的日常生活和社会的稳定,如何使其平稳、高效运行已成为社会各界广为重视的问题。综合管廊运维管理涉及的主客体众多,以人工监管方式为主的传统运维方式效率低、准确率不足、安全性难以保障,因此,本文基于BIM+技术视角,为城市地下综合管廊的智能运维管理提供一种新思路,以期实现综合管廊管理的标准化、规范化,提高管理效率、降低管理成本。本文包括引言与结语共分为五个部分。首先,介绍本文的研究背景、意义,以及研究思路。其次,阐述综合管廊传统运维管理模式的现状及存在问题。然后,提出综合管廊运维管理的基本目标,并基于BIM+技术,尝试构建城市地下综合管廊的智能运维管理系统。最后,对文章进行总结并提出展望。

Experimental analysis on the interaction between underground structures and sand layer under groundwater level change

Groundwater level change stands a momentous role in affecting the geotechnical construction stability and safety of underground structures.Global warming and active underground construction cause conspicuous changes in the groundwater level,which further leaves an impact on the underground structures’serviceability.To reveal the interaction between underground structure and soil under groundwater level change in the sand layer,model tests of circular transportation tunnel and rectangular utility tunnel were carried out.With the self-designed experimental equipment and innovative experimental methods,the changes in tunnel stress,bending moment,buoyancy,and vertical displacement of the rise and drawdown of the groundwater level in the sand layer were studied.The results revealed the developments of concentrated structural forces during the rising and falling process of the groundwater water level,indi-cating critical locations that should be strengthened.Meanwhile,both tunnels showed the same movement trend:settling first,floating afterwards and settling at last.And it is concluded that no reduction is required when calculating buoyancy in sands using measured pore pressure.Conclusions can provide a notable reference for future related research and engineering designs.

Long rectangular box jacking project:A case

Rectangular pipe jacking or box jacking has become more popular in municipal applications because of its better adaptability to shallow overburdens and its higher structural section utilization than the conventional circular pipe jacking.This case study presents a utility tunnel constructed by using rectangular box jacking in Suzhou,China.The utility tunnel,which has a cross section of 9.1 m in width and 5.5 m in height,was jacked 233.6 m,which is the longest known single jacking length of a rectangular box jacking project in China.The box jacking mainly passed through a silty sand layer with high groundwater levels with a minimum depth of cover of only 3.5 m underneath the Yuanhetang River.In this zone,the structures on the surface are sensitive to external disturbance,thus increasing the challenges of construction.A series of measures were taken during the jacking process,and the project was successfully completed.This paper provides an overview of this project and introduces key techniques in the construction of working shafts as well as in the installation and retrieval of the box jacking machine.In addition,the use of lubrication to reduce friction resistance,navigation and application of an anti-buoyancy slab under the Yuanhetang River,and analyses of soil deformation caused by box jacking are described.