Time domain reflectometry measurements of localized soil deformation

A conformable coaxial cable-grout composite is developed for transferring the technology of time domain reflectometry (TDR) measurements of rock joint deformation to localized soil deformation along thin shear zones. The existing system uses a stiff cable grouted in cement paste that conforms to rock but is too stiff for soil. Thus TDR measurements of localized soil deformation with the existing composite are inadequate. The compliant composite developed herein can be used to locate single or multiple shear zones, to measure zone thickness, and to monitor small movements along these zones.; An experimental program was conducted to select a commercially available coaxial cable and a bonding grout with strengths to match soils. Self-hardening cement-bentonite slurries were found to meet the criteria designated for pumpable and controllable low strength grouts. A cement-bentonite mixing design procedure was developed from the results of the experimental program. A small diameter braided coaxial cable was found to be the weakest and most compliant cable of those sheared in the experimental program and was seven times more compliant than the existing stiff cable. Fundamental concepts of electromagnetic and mechanical response of coaxial cables to shearing were presented to facilitate design of a more compliant cable.; The most compliant, commercially available cable was embedded in a series of grouts with increasing strengths to determine the minimum strength needed to activate TDR response and the optimum strength at which TDR response was most sensitive to shearing. These experiments showed that the optimum cable-grout composite was weaker and more compliant than the existing composite but TDR response was less sensitive to localized deformation.; The optimum composite was analyzed with a non-linear model developed for laterally loaded piles. This analytical approach was calibrated by simulating cable deflections observed during shearing while encapsulated in grout. It was extended to the analysis of shearing a cable-grout composite encapsulated in soil, which showed that the cable should be sufficiently sheared in a stiff clay but not in a soft to medium clay.