Research On Ground Penetrating Radar Technique Applied To The Concealment Engineering Quality Detection And Evaluation

Concealed engineering works mean all constructions that are hidden underground, under water or buried by certain covering. Larger concrete concealment works include groundsill, pile foundation, dam foundation, roadbed, pipe line, culvert, underwater jackstone, anti-seepage wall, and others. It has been long time that the examination and evaluation of the concealed engineering works are made via some conventional methods, such as excavation and drill sampling. Ground Penetrating Radar (GPR) techniques are developed from military radar technology. As early as in 1910 the idea that radar may be applied to detect underground objects was initiated. Through the development of nearly one century, GPR detecting has been widely employed in the detection, exploration, examination and evaluation of constructive foundation, road and bridges, geology, archeology, oil pipeline, culvert prediction, etc.On the basis of the research subject 'Movable Laboratory for Hydro-Engineering Detection' in the project '948' initiation of Ministry of Water Resources, and in association with the Yangtz River Dike Concealment Engineering and Huanghe Xiaolangdi Key Water Control Project, the GPR detecting techniques are applied to the concealment engineering quality detection and evaluation.Taking the consideration of GPR characteristics such as high precision and high resolution, straightforward colorful visualization and on site detecting, geophysical pre-requisites theory and inversion modeling of the GPR applied in the concealment engineering detecting are emphasized in this study. Case studies in the areas of underwater jackstone bank-protection works and anti-seepage wall quality detection are used to demonstrate the effectiveness of GPR detecting techniques facilitated in such area.Based on the detection modeling experiment in the water and underwater, the applied study was carried out for Yangtze Dike Protection through underwater jackstone. The innovative results were obtained by applying GPR in the water to detect the quality of the underwater jackstone engineering works. And the detection of the size and defect of anti-seepage wall was also experimented in order to explore the key techniques in the concealed anti-seepage wall engineering works quality examination. Non-damage detection data with quantified accuracy, which can be used in the anti-seepage wall quality assessment, are obtained in the applied study of Yangtze Dike Concealment Engineering and Huanghe Xiaolangdi Key Water Control Project Quality Detecting. The results have been validated via excavation examination in a number of spots along the walls. This study provides an anti-seepage wall engineering quality detection approach which combines the multiple geophysical detecting and conventional excavation techniques.The main work and achievement are summarized as follows.1. The underwater jackstone bank-protection engineering quality detecting from water surface with GPRThe detection experiment area is located in one construction site for Yangtze River Dike Concealment Engineering works. GPR and seismic imaging in the water are applied in order to investigate the feasibility of detecting the underwater jackstone by GPR. The experiment aims at:1) The feasibility of facilitating GPR in the water;2) The effective reflectance depth of high frequency EM from the river bottom;3) The effectiveness of detecting the attitudes of underwater jackstones.By applying appropriate data processing and mining methods to the GPR data collected in the river water surface, it is feasible to describe the attitudes and the thickness of the underwater jackstones. Therefore the straightforward quantified evaluation for the underwater jackstone can be obtained, which is particularly useful in the concealed underwater jackstone engineering quality detection.The experiment GPR profiles and their interpretation results are acquired with a SIR 2 type instrument manufactured by USA. The experiment frequency is 100MHz. Data acquisition method is to position the GPR on the water surface with a boat and following river flow direction with uniform speed. The GPR detecting effect is much of satisfactory. The results have been accepted by all parties including the construction contractor, monitoring and proprietor.2. Conclusion Summary of The underwater jackstone GPR Detection ExperimentIt is an innovative experiment by positioning a GPR on the water surface to detect underwater concealed engineering body. The experiment GPR profile is able to identify clearly the underwater jackstone body, the thickness, area and scope of burial. The results are briefly described as follows.(1) It is feasible and tangible that the detection of underwater jackstones by GPR in the water surface.(2) The detection depth can reach 6m with a 100MHz antenna. Interfaces of river water, mud, jackstones and riverbed are clearly visible from the GPR section. The attitude of jackstones can be clearly identified, and thus the quantitative interpretation is also possible.(3) Underwater jackstone attitudes can be effectively recognized from the GPR section images. Objects such as river water body, jackstones in the water, mud, jackstones in the mud, riverbed, etc, can be interpreted. The thickness of the jackstones can be interpreted qualitatively and quantitatively.(4) The detecting section shows layers clear and straightforward. The GPR requires relatively less demanding environment and less disturbed from the environment. It is an ideal method so far for detecting the underwater jackstones.3. Study and application of GPR in the anti-seepage wall quality detectingConstructing anti-seepage walls is a widely adopted fundamental anti-seepage method in water conservancy projects. The quality of the walls has great influences on the engineering works and life and property of people. Because the walls are constructed underground and they will be concealed by follow up establishment or exposed only upper portion, it will be difficult to conduct quality checks on the walls by methods conventionally applied in civil engineering. Not only have the excavation or drill hole methods low efficiency and costly, but also they will produce un-restorable destructions to the walls. Therefore facilitating the GPR method for the anti-seepage wall quality detecting has been demanded immensely by the industry.On the basis of a number of comparative experiments and optimized combinations of multiple techniques, an approach of quality detecting for anti-seepage wall is proposed.(1) The parameters that describe the wall status are detected by GPR, which include depth to the wall top and thickness of the wall. For the wall that exceeds 15m in thickness its continuity property along the wall is assessed by GPR.(2) When the wall is buried greater than 15m, the high precision elastic wave imaging method and low strain test method are used to detect the wall depth.(3) Randomly select several positions where samples are taken by excavation and drilling. The strength and infiltration parameters of the samples are measured in laboratory.4. Main conclusions(1) Through GPR detecting principle, working procedures and forward-inversion modeling experiment, a thorough study was conducted on techniques of data acquisition, data processing and image interpretation. And the quality detecting approach for concealed engineering works was then proposed.(2) Aiming at key issues of quality detecting on the underwater jackstone bank-protecting engineering project, GPR techniques are investigated and applied in the detecting. And the results have reached the engineering assessment accuracy for concealed engineering quality detection.(3) For the purpose of solving the quality detecting problem for anti-seepage wall engineering works, special research on non-damage detection method for anti-seepage wall engineering works has been conducted. And the principle based on multiple geophysical methods is adopted. In combination with the state key engineering the applied study was carried out for the quality detecting of anti-seepage walls. The application showed the results very promising.5. Main innovations(1) An innovative method for detecting underwater and water bottom concealed engineering works is proposed and implemented that involves using GPR in the water. On the experiment GPR section the thickness, scope and area of the underwater jackstone bodies and stones buried water bottom are clearly recognized. A brand new detection method and approach for GPR detection of underwater jackstones is initiated and experimented through modeling in water-tanks. The method overcomes the water depth effect and increases the detection depth. The applied results for detection of underwater jackstone engineering quality via the facilitation of GPR in the water are operable and have promotion values. (2) There is no such technique recorded in current standard technical system for the detection of geometrical parameter and local defect in the concealed anti-seepage wall engineering works of shallow burial with thickness less than 15m by using GPR non-damage detection method. In the case that a break through is made at low frequency (20～50MHz) in detection depth study and application, the non-damage GPR detection technique will be widely used, which will change the manner in the anti-seepage wall engineering works quality detection which is now via excavation and drilling.(3) The introduce GPR technique into the concealed engineering quality detection technical system will expand the application field of GPR method and promote the development of the concealed engineering quality detection and evaluation technology.