Time domain reflectometry (TDR) potential for soil condition monitoring of geotechnical assets

Abstract

The performance of geotechnical assets is influenced by various external factors including time and changing loading and environmental conditions. These changes could reduce the asset’s ability to maintain its function, potentially resulting in failure, which could be extremely disruptive and expensive to remediate; thus, the ability to monitor the long-term condition of the ground is clearly desirable as this could function as an early-warning system, permitting intervention prior to failure. This study demonstrates, for the first time, the potential of using time domain reflectometry (TDR) for long-term monitoring of the relative health of an asset (via water content and dry density) in a field trial where a clayey sandy silt was exposed to leaking water from a pipe. TDR sensors were able to provide detailed information on the variation in the soil conditions and detect abrupt changes that would relay a prompt for asset inspections or interventions. It is proposed that TDR could be used alone or together with other shallow geophysical techniques for long-term condition monitoring of critical geotechnical assets. Early-warning systems could be based on thresholds defined from the values or the relative change of the measured parameters.

Surface wave surveys for imaging ground property changes due to a leaking water pipe

“…The three central arrays were located over the excavated zone, with outer array pairs to the east and west located over the host formation. The findings in this paper are supported by some observations made on the sensor network (Curioni et al, 2019) and over the electrical resistivity grid (Inauen et al, 2016) also undertaken over this trench. The sensor network was installed during the backfilling process, at the leak location around the pipe at various depths within the soil column.…”

“…The trench (Trench 2 in Fig. 2) was excavated and backfilled 20-23 Oct 2015 (along with another trench used for further tests discussed in Curioni et al, 2019), which was when the formation and backfill samples were gathered for the geotechnical property tests (Fig. 3).…”

“…3c). During the leak VWC's of 50-55% are observed, suggesting that suctions would dissipate rapidly to a few hundred kPa, before recovering slightly post-leak, where an increased VWC of 35-40% is observed (after Curioni et al, 2019).…”

“…a network of sensors installed in the trench to monitor the temporal changes in moisture content, temperature and electrical conductivity at specific point locations about the water pipe. While this paper focuses on the MASW method, associated papers by Curioni et al (2019) and Inauen et al (2016) describe the methods and results arising from observations on the sensor network and the Electrical Resistivity Tomography (ERT) array respectively.…”

“…Monitoring instrumentation configurations for MASW, sensor network and electrical resistivity tomography. (For method and full results of sensor network monitoring seeCurioni et al, 2019).…”