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Three mixtures of cement-bentonite slurry containing 28, 36 and 44 % PFA (as a proportion of cementitious materials) were tested using the unconfined compressive strength and triaxial apparatus to determine the stress-strain and shear strength relationships for samples cured for various periods. The samples were batched using 4 % bentonite and 20 % cementitious materials (by mass of water) and allowed to cure underwater once extruded from sealed moulds. Curing periods of 14, 28 and 90 days were selected to investigate the changes in behaviour at durations commonly specified (28 and 90 days) as well as providing insight into changing behaviour with curing (additional curing periods of 7 and 60 days were investigated on a smaller number of samples to increase understanding). Two rates of displacement were used (1.0 and 1.3 mm/min) and four confining pressures (0, 50, 100 and 200 kPa). Shear strength and strain at peak deviator stress of the samples do not appear to vary considerably with confining pressure. For samples containing 28 % PFA, the majority of physical properties exhibited by the cement-bentonite samples change with curing period up to 60 days, where after the properties become similar to those cured for 90 days.

The successful operation of buried infrastructure within urban environments is fundamental to the conservation of modern living standards. Open-cut methods are predominantly used, in preference to trenchless technology, to effect a repair, replace or install a new section of the network. This is, in part, due to the inability to determine the position of all utilities below the carriageway, making open-cut methods desirable in terms of dealing with uncertainty since the buried infrastructure is progressively exposed during excavation. However, open-cut methods damage the carriageway and disrupt society's functions. This paper describes the progress of a research project that aims to develop a multi-sensor geophysical platform that can improve the probability of complete detection of the infrastructure buried beneath the carriageway. The multi-sensor platform is being developed in conjunction with a knowledge-based system that aims to provide information on how the properties of the ground might affect the sensing technologies being deployed. The fusion of data sources (sensor data and utilities record data) is also being researched to maximize the probability of location. This paper describes the outcome of the initial phase of testing along with the development of the knowledge-based system and the fusing of data to produce utility maps.

Time domain reflectometry (TDR) can be used to measure the dry density of compacted soils, although it is believed that TDR could also be used to monitor the long-term performance of aging geotechnical assets. Understanding the deterioration of aging assets (earth dams, embankments) can be problematic; monitoring the relative condition with time may prove advantageous. In such applications, it would be likely that commercially available TDR probes and multiplexers would be used, and this paper illustrates that the current method does not perform particularly well with these. Therefore, an alternative method has been developed that, when applied to six fine-grained soils (exhibiting a range of plasticities), can deal with the impacts of multiplexers and commercial probes. It is shown that the dry density and gravimetric water content can be predicted with an accuracy of AE5 and AE2%, respectively. The accuracy can also be improved by correcting the TDR parameters for temperature. The new method is robust, relatively independent of the compactive effort and only marginally affected by the presence of multiplexers, making it suitable for field-monitoring applications.

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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.

This study demonstrates the use of Multi-channel Analysis of Surface Waves (MASW) to measure changes in Rayleigh wave velocity relating to both the initial trench construction and subsequent simulated failures (water leaks) of a buried water-pipe. The MASW field trials were undertaken in conjunction with a wider suite of geophysical monitoring techniques at a site in Southwest England, within an area of clayey sandy SILT. The Rayleigh wave velocity through a soil approximately equals the shear wave velocity, which in turn is predominantly dependant on the shear modulus of the soil (G) and this can be inferred to give a measure of the relative strength of a soil. It is proposed that the time-lapse measurement of Rayleigh wave velocity may be used to monitor ongoing changes in soil strength and therefore the MASW technique could perform a significant role in monitoring the initiation/progression of any internal processes within a geotechnical asset, before they would otherwise be identified through visual inspection alone.