Siow Wei Jaw

Accuracy of data acquisition approaches with ground penetrating radar for subsurface utility mapping

Ground penetrating radar (GPR) is widely used in subsurface utility mapping for extracting the position (x, y) and depth (z) information of the utility. This information is crucial for subsurface facility management, in particular as reference in excavation works. The locational and depth information of the utility features is therefore of very important in subsurface mapping, apart from the reliability of the entire data acquisition and information retrieval method. This study investigates the effects of GPR data acquisition techniques to the locational and depth accuracy retrieved. The techniques examined are: (i) widely used perpendicular to pipe scanning; (ii) along pipe scanning; and (iii) variation angles scanning. Results indicated that along pipe scanning reported better penetrative power, higher detectability and best detection accuracy. Most importantly, this acquisition accuracy conforms to Quality Level A utility data requirements of the utility industries, hence offers the opportunities of GPR as measuring tool for underground cadastre system.

Ground penetrating radar data processing for retrieval of utility material types and radius estimation

Commercial type reflective ground penetrating radar (GPR) systems have been widely used in subsurface utility mapping for extracting position and depth of the utility features lay underneath todays city street. However, the utility of GPR for subsurface utility mapping is not fully exploited for retrieval of material recognition and geometrical properties of the utility features. This paper highlights the results of an approach for extracting information on subsurface material types and radius estimation from GPR backscatters. Results of study confirmed uniqueness coherent mean vectors of radar backscatter of tested features - mild steel, high density polyethylene (HDPE), medium density polyethylene (MDPE), and PVC pipes. The derived radius of these pipes and in-situ measurements also reported strong correlation (r2=0.9). Both these results offer new applications of GPR for reporting status of utility features and conditions, such defects of pipes or cables caused by aging and weathering processes.

Detection of precast concrete beam defects using finite-difference time-domain modelling

Structural failures and concrete structure collapses still remain as an unsolved issue in the building and construction industry although many researches has been done on it. In recent years, ground penetrating radar (GPR) emerged as one of the most promising nondestructive testing (NDT) techniques for civil engineering applications, especially in concrete structures inspection. Although the use of precast concrete beam is gaining its popularity in building and construction industry, there are lacks of publication focusing on defects detection of precast concrete beam with GPR. Therefore, this study is conducted to test the capability of 2 GHz high frequency GPR antenna in monitoring the inner structure and detecting defects in precast concrete beam. The aim of this study is to detect the defects, such as cracks or voids in the precast concrete beam with the assistance of Finite-Difference Time-Domain (FDTD) numerical modelling. Results indicated that defects with different sizes can be detected; even fine cracks with 3mm can be detected. This proved that 2 GHz high frequency GPR antenna is an ideal NDT solution for concrete surveying, particularly for small size cracks. Results from this study offer new applications of GPR for building structural health assessment and maintenance.