Jet Grouting Diameter Measurement Using Electrical Resistivity Tomography
|關鍵字:||地電阻法;高壓噴射灌漿;灌漿柱徑檢測;Electrical Resistivity Tomography (ERT);jet grouting;jet grouting diameter measurement|
Jet grouting method is currently among the common ground improvement technique, which performance is closely related to the integrity of improved columns (diameter and continuity). Therefore, column integrity assessment is necessary for quality control. Electrical Resistivity Tomography (ERT) imaging method is capable of detecting or monitoring spatial distribution of resistivity in 2D or 3D stratum. Considering detection accuracy, economy, workability and other aspects, in-hole ERT which has high application potential, was selected as integrity assessment of the improved column in terms of qualitative and quantitative evaluation. In this research, a 3D numerical model was constructed to simulate ERT measurement profile for improved columns. Axial-symmetrical 2D resistivity imaging profile of the improved columns under different circumstances was analyzed. In order to accurately identify the variation of column diameter, diameter quantification method was proposed and its accuracy and restriction was appraised. Results showed that in case the improved column is highly asymmetrical, only qualitative analysis is reliable and effective column diameter cannot be measured precisely. For those axial symmetrical columns, column integrity can be examined accurately and is shown feasible. However, for hollow improved columns, the resistivity variation of the material under test around the electrodes is too large, leading to quantification misjudgment as the effective resistivity is not of geometrical average, yet ERT can still realize this averaged resistivity phenomenon. To verify the feasibility of this approach and the result of numerical simulations, both laboratory sandbox experiment and field test were conducted. Both experimental result verified that column integrity assessment using in-hole ERT is feasible for columns that are near axial symmetrical. The position and appearance of the improved columns were clearly detected by this approach and the column diameters were also accurately quantified. Currently, there is lack of commercial electrode cable designated for in-situ borehole ERT. Therefore, this study aimed at developing a modularized portable electrode cable for in-situ borehole ERT, which would meet the requirements of durability, functionality, convenience, versatility and others. The feasibility of this cable design concept is tested feasible through a series of experiment in this study.
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