Study And Application Of Detection Techniques And Methods Of Urban Underground Pipelines

Urban underground pipelines are the bottleneck in the development of city,and also the basic guarantee of the normal operation for a modern city. Urbanunderground pipelines are changing greatly in compositive material, layingmeans and the quantity, with the accelerating process of urbanization. Atpresent, various types of underground pipelines appears. Different pipelines arecrossed or parallel, weaved like a spider web. The function of urbanunderground pipelines has become more and more significant.For geological and historical factors, the urban underground pipelinesbecome old, dense, and disorderly. And the contradiction of the backwardpipeline management and existing pipeline detection technology to the rapid citydevelopment is increasingly acute. At the same time, science and technology are adouble-edged sword, which can bring the Gospel to pipeline networkconstruction, and bring a large number of pipeline detection problems as well.For example, a common trench technology leads to more dense parallel pipelines;the development of new pipeline compositive material makes non-metallic pipesgradually replace metal ones; trenchless technology produces various types ofdeep buried pipeline and so on, all of which trigger a series of pipeline detectionproblems. At present, the development and utilization of urban subsurface spaceare the inseparable the supported by urban underground information, so theenhancing the research on detection methods and techniques of urban pipeline, isnot only the neccessary for the economic and social development of city, butalso for urban planning, construction and management, which have greatpractical significance and far-reaching historical significance.The environment of urban pipeline detection has become increasingly harshwith the rapid urbanization development. More overground buildings arebuilded, and the underground facilities laid more densely. Various types ofinterferences from space, ground and underground appear and become andserious, and different models of the interferences (sources) are manifold. Pipeline laying technology develops diversely, and the laying time is different. Subsurfacephysical parameters are heterogeneous and varied. Therefore, how to obtain theaccurate information of under pipeline is the key problem which needs to besolved immediately.The detection of parallel underground pipelines with small intervals,non-metallic and deep buried pipelines is a difficult issues right now. First, theexisting pipeline detection methods are analyzed and summarized theoretically.Second, different detection methods and experimental parameters are used todetect and analyze the parallel underground pipelines with small intervals,non-metallic pipelines and deep buried pipelines, in engineering examples. Themain conclusions are summarized as follows.(1)Electromagnetic induction method is a common method for pipelinedetection, which should be used based on the type and depth of the pipeline aswell as the field condition to choose the frequency parameters and differentto-wire methods to test for detection of parallel pipelines with small interval Weshould use grab method priority, when there are exposed pipelines orappurtenances of pipelines in site, and then select appropriate detection methodsto detect other lines under the construction condition. Tilt to-wire method is avery effective and practical detection method, and can be used as one of the mainmethods in the detection of parallel pipelines with small interval, which is lessaffected by the site condition, simple to operate, and bears good detection resultscomparing with other methods,.High frequency should be chosen for impulse. Itusually requires to penetrate a wire in the pipelines, and then by using chargingmethod or grab method, achieves the detection purpose for detection ofnon-metallic pipelines and deep buried pipelines.(2)Ground Penetrating Radar (GPR) is a nondestructive detection method,which have good detection results for both shallow metal pipelines and shallownon-metallic pipelines. With the depth increasing of the buried pipelines, thedetection is unstable by interferences of the pipeline types and environment,and cannot get the desired results for some special circumstances. Meanwhile,GPR method can only be used to detect the profile of the pipelines but cannottrack the pipelines, which is only suitable as a supplement other detectionmethods, not as the primary detection method.(3)Transient Rayleigh wave method has a good application in thedetection for deep buried pipelines not only in the plane loacation but also in the depth measurement. Transient Rayleigh wave method can be used to detect thecement water pipe culverts, but the precision requirement of the depthmeasurement should be reduced in the technical provision. Facing plasticpipelines, transient Rayleigh wave method can determine the plane position butthe detection accuracy is out of the requirements. It is difficult to determine thedepth. Transient Rayleigh wave method can be applied to detect large diameterdrainage water and gas pipelines. Compare with seismic imaging method, thediffraction surface wave generated by the pipes is not more clear than that byseismic imaging method. However, the depth of the pipeline can be determinedby the abnormal velocity zones which taking the advantage of dispersioncharacteristics of surface waves. Stratum condition can also affect theprospecting of surface wave method, like seismic imaging method, the results aregood when subsurface strara are consistent and uniform.(4)Seismic imaging method is a common detection techniques in theunderground pipeline detection. We can obtain fine results when use it to detectthe deep buried and large diameter metallic or non-metallic pipes. The abnormaldiffraction waveform of one pipe is interfered by the diffraction wave generatedby the other parallel pipes with small interval. The diffraction waveformsgenerated by the lines with large intevals are clear, with which we can moreclearly determine the location of the pipeline. Impulse and stratum condition canaffect seismic imaging method. Near surface thick concrete layer, and lowimpulse energy can generate weak wave groups, which make it difficult to locatethe pipes. Heterogeneity also can interfere the waveform.(5)The location of trenchless pipeline can be measured accurately by highdensity resistivity method. But for the pipeline buried in the center of the city,the layout of high density resistivity method is restricted, especially for the deepburied trenchless pipeline which need long survey line arrangement. We usuallycannot get good results because of the limitations of survey site conditions. Thecoupling effect of electrode to ground, especially to rigid road, is an importantfactor affecting the test results in the center of the city. High density resistivitymethod with the advantage of electrode arrangements can efficiently get largeamount of observation signals. Through analysis the information andappropriate inversion, it can clearly distinguish the location, direction andgeneral scope of the targets(underground pipelines) where we cannot distinguishby DC method (6)High-precision magnetic method can directly determine the location ofmagnetic anomalies, and can obtain good results to determine the position of thepipeline. It is an effective method to detect the parallel trenchless pipeline withsmall interval. which opens up a new idea to the detection of non-metallictrenchless pipeline. However, the data gotten by this method is the magnetic fieldintensity value stacked of the magnetic field value of a magnet and the magneticbackground field value. How to remove the background magnetic effects ininversion, and calculate the depth of a magnet still need further research.(7)Magnetic gradient method can effectively detect parallel pipelines withsmall interval and deep buried pipelines, which can accurately determine thelocation and depth of the pipelines. However the detection accuracy of thismethod is affected by the quality of the pore-forming. It need to be applied withother methods to determine the location of the pipelines and of avoid largeamount of work on drilling and excessive damage on pipes. Usually, magneticgradient method was used as an auxiliary and proving method for pipelinedetection.(8)Generally, the detection accuracy of the70%method is higher than thedirect-reading method, and we should priority select70%method to measure thedepth of the pipeline, especially when the target is large-diameter pipelines. Mostof the measurement results can not meet the required accuracy by using whetherthe direct-reading method or the70%method with different impulse modes andwork frequencies in most cases. In order to obtain fine results, furtherexperimental work to sumarize is needed.In a word, the urban underground pipeline is the lifeline of the cityeveryday life. To enhance the research of the urban pipeline detection methodsand techniques is neccessary to face the increasing rigorous detectionenvironment, and substantial detection problems.