Investigating the Detection of Subsurface Ruins and Structure Defects using NDT

Abstract

Investigating the Detection of Subsurface Ruins and Structure Defects using NDT (Extended Abstract) Chen Liang-Yu Wu Jian-Hong & Lee Der-Her Department of Civil Engineering National Cheng Kung University SUMMARY Generally non-destructive testing is detected by a single method The professional experience of the experts and the limitation of the instrument often govern the accuracy of the detection results In this case the study attempted to combine Ground Penetrating Radar and Resistivity Image Profiling with the literature records of the survey area In this way except for the applicability of mutual verification non-destructive testing the better credibility detection method is summarized in parallel and it is also used as a reference for future related research This research can be broadly divided into two parts: underground ruins detection and structural damage detection The underground ruins detection includes Tainan City Elementary School with the underground ruins in the Qing Dynasty and the Dongmen section ruins of the Taiwanese city next to the Taiwan Railway The structure damage detection part includes the Taichung City food processing plant suspected of having a hollowing out phenomenon in the base bottom and the Pingtung County Reservoir where the earth embankment structure needs to be tested the safety The ruins' location is to use Ground Penetrating Radar to detect then determine the ruins' signs in Ground Penetrating Radar image map and determine the other ruins' location according to the signs Using the Ground Penetrating Radar and Resistivity Image Profiling confirm hollow position and the earth embankment structure and compared the results to determine the hollow position and the earth embankment structure show non-destructive testing for the formation condition the understanding of the underground seepage direction and the approximate location can be applied and it's also used as a reference for future research Keyword: Non-destructive testing Ground Penetrating Radar Underground foundation detection Resistivity Image Profiling Seepage Reservoir INTRODUCTION First the study integrates the collected non-destructive testing literature and applies it to field detection The results of the analysis will be used in the following situations: (1) Tainan City Elementary School with underground ruins in the Qing Dynasty; (2) Ruins of the Dongmen section of Tainan City; (3) Taichung Food Processing Factory; (4) Pingtung County Reservoir This content of this thesis covers Chapter 2: Literature survey of NDT Chapter 3: Introduction of the NDT instrument used theoretical formulas and relevant parameters Chapter 4: Detection route planning and detection results of NDT in actual conditions Chapter 5: Conclusion and suggestion MATERIALS AND METHODS Ground Penetrating Radar (GPR) mainly uses the electromagnetic wave emitted by the coil in the antenna to detect the position of the object through the reflected wave signal caused by the difference in the dielectric constant of different materials in the underground and then analyzes it by using software (Radan7) The frequency of the radar wave can be adjusted with the antenna The high-frequency antenna has a shallow depth of detection but the resolution is high The low-frequency antenna has a deep depth of detection and a low resolution Resistivity Image Profiling (RIP) is mainly used to introduce a pair of electrodes from the detection point as a current pole into the surface of the earth by a direct current When the current flows through the formation an artificial electric field is established and then another pair of electrodes is used The potential difference (?V) and current intensity (I) of the potential electric field are measured However the data after the measurement is the apparent resistivity before being processed The true resistivity needs to be stimulated by the positive calculation model before the simulation Perform an inversion calculation analysis When the electrode is applied the distance between the electrodes will affect the analytical ability and the depth of exploration of the profile imaging The smaller the spacing the better the resolution but the depth of detection is also shallow RESULTS AND DISCUSSION In the first case carried out excavation is after the third survey The survey results are shown in Fig 1 and the excavation results are shown in Fig 2 The excavation results are compared with the survey results It can be found that the high similarity between the two results There are two complete ruins on the north side of the excavation In addition the south side has a continuous foundation and gradually moves northward Therefore it can be seen that the Ground Penetration Radar has good applicability in the detection of the ruins and has considerable precision Figure 1 The survey results Figure 2 The excavation results In the third case the survey is divided into 5 zones according to the survey line distribution as shown in Fig 3 the soil layer with high water content is suspected in the test area or the location of the groundwater seepage channel is densely distributed in the A zone southern half the B zone west side the C zone south side and the north side and the E zone Also suspected the soil layer is a strong affected disturbance or grouting position located on the B zone east side the C zone north side and the south side the A zone middle section to the south section and the E zone Through the detection compared the places with strong disturbance or stratum grouting and the places suspected of The high water content or the underground seepage channel location it can be found the location is high similarity it is suspected maybe the groundwater seepage concentration area The two non-destructive test results are roughly the same shown in Fig 4 and the reflections are stronger when the resistance value is higher so it can be known that the resistance value is positively correlated with the reflected wave Figure 3 survey result Figure 4 Compared with GPR and RIP CONCLUSION 1 Using Ground Penetrating Radar to survey and to verify the excavation in Tainan City Elementary School The survey results are quite similar to the test results shows the applicability of the Ground Penetrating Radar to the ruins survey is good 2 In the survey of ruins the two sites have been destroyed and their structures are not complete The obtained signs have broken and discontinuous which must be assisted by literature and site data to make the results of a more powerful explanation 3 According to two non-destructive testing in the Taichung Food Processing Plant the two NDT results are high similarly and showed it can be applied to the condition of the underground stratum the direction of underground seepage and the approximate location Understanding 4 The RIP can be measured to be deeper than the GPR but the resolution is that the GPR has higher RIP Therefore different detection methods can be selected according to the target size and the survey depth such as hollowing out seepage etc A large-area or deep-depth survey can be used by RIP If the depth of the underground pipeline or site is shallow or the range is small it can select the higher resolution GPR

Date of Award	2019
Original language	English
Supervisor	Jian-Hong Wu (Supervisor)