Report No. : GEO Report No. 228

Report Title : Use of Time Domain Reflectometry to Determine the Length of Steel Soil Nails with Grout Pipe with Embedded Copper Wires (2008), 41 p.

Author : W.M. Cheung, K.W. Shum & F.K. Cheng

Abstract

Time domain reflectometry (TDR) has been identified as a potential non-destructive method for determining the length of installed steel soil nails with pre-installed wires. This report presents the findings of a feasibility study of using a new type of grout pipe with embedded copper wires for grouting and TDR test. By integrating the copper wire and the grout pipe, the procedure of pre-installing a wire alongside the steel bar can be streamlined.

The performance of the newly developed grout pipe with embedded copper wires for TDR test has been studied and benchmarked with that of the conventional wire. The benchmarking includes a precision experiment using prefabricated soil nails and working soil nails at 11 LPM sites. The overall uncertainty of TDR tests using the grout pipe with embedded copper wires is found to be smaller than that of using conventional wire. However, the new grout pipe seems to have a slightly higher material defect rate than that of the conventional wire. In all, the use of grout pipe with embedded copper wires is found to be feasible for both the grouting works and TDR test.

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