The axial and radial thermal responses of a field-scale energy pile installed in dense sand and subjected to monotonic and cyclic temperatures are examined. It is found that the axial thermal strains in the pile are more restricted to thermal expansion/contraction compared to radial thermal strains. The radial thermal strains are close to that of a pile expanding/contracting freely, indicating minimal resistance from the surrounding soil in the radial direction. As a result, very low magnitudes of radial thermal stresses developed in the pile compared to axial thermal stresses. The pile–soil radial contact stresses estimated from the cavity expansion analysis are up to 12 kPa for a pile temperature change of 22.5°C and are likely to stay low for the range of commonly encountered operating temperatures for cast-in-place concrete energy piles installed in dense sand. During cyclic heating and cooling, unstable changes in axial and radial thermal strains were observed initially during initial cycles, indicating a ratcheting response. The changes in strains became more stable over further cycles without significant changes in side friction or pile–soil contact stresses.

Biocementation processes rely on microbial-induced calcite precipitation (MICP), which is a naturally occurring biochemical process. Biocement materials are a form of environmental cementitious agents used to improve the mechanical properties of granular soils by physically binding soil particles together. Efficient improvement of the macromechanical behavior of coarse sand treated by various amounts of biocement materials requires an in-depth understanding of its microstructure. This paper examined the effect of a number of bacterial suspension and cementation solution flushes on the macromechanical behavior of coarse sand. Also, X-ray computed tomography (XCT), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were used to investigate changes occurring at microlevels. The results show that compressive strength increased with an increase of biocement materials, and the maximum compressive strength achieved was around 14 MPa. The microscopic investigations were linked to the macromechanical changes, providing unique insight into the causation of the changes. Furthermore, several common soil properties (calcium carbonate content, dry density, void ratio, and porosity) were successfully identified using the XCT technique.

Geosynthetic clay liners (GCLs) are frequently used in lieu of, or as an augmentation to, compacted clay liners as secondary hydraulic barriers in municipal solid waste containment facilities. GCLs are lately being assessed for use in industrial and mining applications, not only for the temporary storage of process waters and permanent disposal of tailings, but also beneath heap leach pads, where their performance will be subjected to loads, hydraulic heads and leachate chemistries outside the normal conditions found in conventional municipal solid waste landfills for which they were designed. This paper considers recent limited research assessing the compatibility of GCLs to leachates having extreme chemistry. Extreme chemistry is here defined as strongly alkaline (pH > 12), strongly acidic (pH < 3) and hypersaline (> 1 M). Based on the limited research available, GCLs cannot be expected to perform for the long-term when in contact with strongly acidic leachates; however there exists some indication for the possibility of inducing conditions for pore clogging that may assist their performance in the short term. Many GCLs probably can exhibit long-term performance objectives for strongly alkaline leachates. In both extreme pH ranges, leachate ionic strength and the potential for cation exchange have the greatest negative effects on bentonite swelling and GCL hydraulic conductivity. Future developments toward improving bentonite resistance to leachates having extreme chemistry should focus on experiments that underpin the potential mid- to long-term performance of GCLs and undertake to evaluate, as far as possible, changes in leachate chemistry and bentonite mineralogy involved in loss of field performance.

Post-construction data from an instrumented geosynthetic reinforced column supported embankment (GRCSE) on drilled displacement columns in Melbourne, Australia, show the time-dependent development of arching over the 2 year monitoring period and a strong relationship between the development of arching stresses and subsoil settlement. A ground reaction curve is adopted to describe the development of arching stresses and good agreement is found for the period observed thus far. Predictions of arching stresses and load-transfer platform behaviour are presented for the remaining design life. Four phases of arching stress development (initial, maximum, load-recovery, and creep strain phases) are shown to describe the time-dependent, and subsoil-dependent, development of arching stresses that can be expected to occur in many field embankments. Of the four phases, the load-recovery phase is the most important with respect to load-transfer platform design, as it predicts the breakdown of arching stresses in the long term due to increasing subsoil settlement. This has important implications in assessing the appropriate design stress for the geosynthetic reinforcement layers, but also the deformation of the load-transfer platform in the long term.