The effects of daily cyclic temperature variations on the thermal response of an energy pile built under a six-level residential building are examined. The axial and radial thermal strains along the length of the pile followed stable, linear reversible paths during daily active heating and cooling cycles corresponding to a pile temperature range of 10 to 23°C (∆T of-8°C to 5°C) around a baseline temperature of 18°C. The stable responses of the thermal strains indicate that plastic deformations did not occur in the pile during the daily cyclic temperature changes coupled with the mechanical load in the pile corresponding to 52% of its estimated ultimate capacity. A complex distribution of axial thermal stresses with depth was observed in the pile with higher stress magnitudes near the pile ends particularly at the end of cooling due to larger temperature changes in the cooling cycle. The magnitudes of radial thermal stresses were considerably smaller than the axial thermal stresses along the length of the pile and are not anticipated to play a significant role in the development of thermo-mechanical loads in the pile. The temperatures over the cross-section of the pile were uniformly distributed at the end of cooling and heating at all depths while the axial thermal stresses had a non-uniform distribution but with magnitudes less than the calculated ultimate capacity of the pile.

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This study investigates the performance of bentonite components of geosynthetic clay liners (GCLs) when exposed to aggressive leachates using the fluid loss test and provides a possible quick method for estimating the effect of acidic conditions on hydraulic conductivity. Fluid loss generally increases with increasing acid concentrations. Hydraulic conductivity values back-calculated from the fluid loss tests (kFL) are compared with the values measured using a flexible-wall permeameter (kTri). Generally, the predicted hydraulic conductivity values are conservative (kFL/kTri > 1) under water and low acid concentrations (≤0.015 mol/L). However, the back-calculated hydraulic conductivity is shown to be nonconservative (kFL/kTri < 1) at high acid concentrations (≥0.125 mol/L).

Methane emissions from the Jiangcungou municipal solid waste landfill in China were examined using a static chamber. The monitoring results were compared firstly with those obtained from the California Landfill Methane Inventory Model (Calmim). The monitoring results show that average methane emission flux from the temporary cover is one to two orders of magnitude greater than those from the final cover and the working face. This is because the methane generation rate reaches its maximum at less than 1 year after the wastes were landfilled. The observed methane fluxes are comparable with those obtained by Calmim. The observed results are lower than those predicted by Calmim, which were 74.98 and 98.64 (g/m2)/day, respectively. The difference is reasonable because the results obtained by field monitoring are transient, while those simulated by Calmim are the average daily flux. Moreover, Calmim considers only one-dimensional gas transport through the cover and neglects lateral gas migration. The model results indicate that there is a strong seasonal variability due to the variation in rainfall amount in different months. The methane emission amount was greatly reduced with the increase in vegetation coverage due to the increase in the volumetric water content of the soil induced by the water retention capability of vegetation.

This paper examines the effects of monotonic and cyclic temperature changes of a model energy pile (diameter = mm and length = 264 mm) on the variations in temperature and volumetric water content of surrounding unsaturated sand. Water flowed away from the pile during heating to 36°C and towards the pile during cooling to 5°C, causing soil drying and wetting near the pile, respectively. The change in volumetric water content was timedependent, non-linear and slower than the change in soil temperature and continued to evolve after the soil temperature changes stabilized. Cyclic heating/cooling induced lower thermohydraulic changes in the soil than monotonic heating and cooling. The most significant changes in soil temperatures and volumetric water content were closest to the pile at a radial distance of 20 mm from the edge of the pile and reduced with increasing radial distance for all cases.The largest change in the degree of saturation was near the pile and was up to 6% for monotonic heating. Cyclic heating/cooling induced irreversible cyclic hydraulic responses near the pile with consecutive thermal cycles and caused a permanent reduction in the soil volumetric water content. However, these irreversible cyclic effects were dominant at a radius of 20 mm and reduced with increasing radial distance from the energy pile. The change in volumetric water content was time-dependent, indicating that the ratio of heating to cooling times during cyclic heating/cooling will have a significant effect on the reversibility of hydraulic responses under temperature cycles.