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The effect of grain size distribution on the unconfined compressive strength (UCS) of bio-cemented granular columns is examined. Fine and coarse aggregates were mixed in various percentages to obtain five different grain size distributions. A four-phase percolation strategy was adopted where a bacterial suspension and a cementation solution (urea and calcium chloride) were percolated sequentially. The results show that a gap-graded particle size distribution can improve the UCS of bio-cemented coarser granular materials. A maximum UCS of approximately 575 kPa was achieved with a particle size distribution containing 75% coarse aggregate and 25% fine aggregate. Furthermore, the minimum UCS obtained has applications where mitigation of excessive bulging of stone/sand columns, and possible slumping that might occur during their installation, is needed. The finding also implies that the amount of biochemical treatments can be reduced by adding fine aggregate to coarse aggregate resulting in effective bio-cementation within the pore matrix of the coarse aggregate column as it could substantially reduce the cost associated with bio-cementation process. Scanning electron microscopy results confirm that adding fine aggregate to coarse aggregate provides more bridging contacts (connected by calcium carbonate precipitation) between coarse aggregate particles, and hence, the maximum UCS achieved was not necessarily associated with the maximum calcium carbonate precipitation.

This paper examines the effects of multicycles of desorption/adsorption on the water isotherms of a typical cement–bentonite mixture. These water isotherms were evaluated over a relative humidity (RH) range of 90% and 0.3%. This study shows that, after the first adsorption–desorption cycle, the subsequent cycle shifted the water isotherm curves upward, particularly at RH < 70%, with a high degree of hysteresis. In contrast, at RH > 70%, the water isotherm curves shifted slightly downward with a low degree of hysteresis. The overall degree of hysteresis slightly decreased with the subsequent cycles. It is postulated that multi-adsorption–desorption cycles led to microstructural changes in the CB porous system as the CB material’s water retention ability was enhanced by increasing isotherm cycles.

The leakage of chemical compounds in landfill leachate led to serious environment pollution, especially, the compounds termed endocrine disruptors such as bisphenol A (BPA). It is very important to study the adsorption behavior of endocrine disruptors in modified soil for predicting and evaluating the potential harm of endocrine disruptors to the soil. Bentonite-amended Chinese loess mixtures, with various proportions of bentonite, were used for the removal of BPA from an aqueous solution. A batch test was used to investigate the adsorption properties of bisphenol A on bentonite and Chinese loess mixtures. The influences of bentonite proportion, temperature, reaction time, pH, and soil-water ratios on the adsorption process were considered. The Fourier transform infrared spectra (FTIR) was used to clarify the change of functional groups before and after the adsorption of BPA on soil. The adsorption mechanism of BPA on soil was discussed preliminary. The results show that the addition of bentonite to the loess can improve the adsorption rate of BPA. The adsorption of BPA was mainly a spontaneous, exothermic, entropy decreasing physical adsorption process. The interaction between bentonite content and reaction concentration had a beneficial effect on BPA adsorption. The linear relationship between bentonite content and adsorption capacity was obtained. The results indicate that bentonite amended loess can provide a good liner for BPA.

Baffles and check-dam systems are often used as granular flow (rock avalanches, debris flows, etc.) control structures in regions prone to dangerous geological hazards leading to massive landslides. This paper explores the use of numerical modelling to simulate large volume granular flow and the effect of the presence of baffles and check dam systems on granular flow. In particular, the paper offers a solution based on the smoothed particle hydrodynamics numerical method, combined with a modified Bingham model with Mohr–Coulomb yield stress for granular flows. This method is parallelised at a large scale to perform high-resolution simulations of sand flowing down an inclined flume, obstructed by rigid control structures. We found that to maximise the flow deceleration ability of baffle arrays, the design of baffle height ought to reach a minimum critical value, which can be quantified from the flow depth without baffles (e.g. 2.7 times for frictional flows with friction angle of 27.5°). Also, the check-dam system was found to minimise run-out distances more effectively but experiences substantially higher forces compared to baffles. Finally, flow-control structures that resulted in lower run-out distances were associated with lower total energy dissipation, but faster kinetic energy dissipation in the granular flows; as well as lower downstream peak flow rates.

This paper explores the effect of particle rolling resistance on the mechanical behaviour of silty sand under various shearing conditions. The elastic–plastic spring–dashpot rolling resistance model was employed, and drained and undrained triaxial tests were conducted on silty sand with various fines contents and rolling resistance. It was found that the rolling resistance of fines contents had a strong impact on the critical state, peak state, phase transformation state as well as zero-dilatancy state of silty sands. Moreover, depending on the correlation between rolling resistance of coarse and fine particles, fines can positively or negatively contribute to the overall structure of silty sand. Increasing the rolling resistance of fines enhances the liquefaction resistance of silty sands. Thus, the presence of fines of high rolling resistance in the sand can result in a marked decrease in collapsibility or liquefaction susceptibility compared with the presence of fines of lower rolling resistance.

The mechanical behavior of geo-materials depends on the assemblage structure and fundamental characteristics of constituting particles such as their shape, size and mechanical properties. Anisotropy is an intrinsic macroscopic material property that quantifies the differences in mechanical resistances to loading directions. In this study, the discrete element method (DEM) is used to investigate the anisotropic behavior of geo-materials like rocks. The model considers a fabric tensor characterizing the internal structure of particles associated with the anisotropy. The new fabric tensor proposed in this research is termed the particle stiffness fabric tensor (P-S fabric), which associates the stiffness (k in the traditional DEM) with the anisotropic state parameters. The results show that the discrete nature of the proposed approach allows an effective modelling of the anisotropic behavior of rocks. Numerical experiments are conducted on standard Brazilian tensile strength (BTS) tests with different anisotropic configurations using the PFC2D code. The tensile strength obtained shows that the results based on the proposed particle stiffness fabric tensor have a much better agreement with experimental results compared with conventional numerical modelling approaches.

An axial load-transfer analysis for energy piles is presented in this study that incorporates empirical models for estimating the side shear resistance and end bearing capacity in rock along with associated normalized stress-displacement curves. The analysis was calibrated using results from field experiments involving monotonic heating of three 15.2 m-long energy piles in sandstone. Analyses of the field experiments indicates that poor cleanout of the excavations led to an end restraint smaller than that expected for a clean excavation in sandstone. Specifically, end bearing parameters representative of cohesionless sand were necessary to match the load-transfer analysis to the field experiment results. Parametric evaluations demonstrate the importance of using appropriate rock- or soil-specific empirical models when estimating the side shear resistance and end bearing capacity of energy piles. Specifically, the end bearing capacity and side shear resistance in rock are greater than in soils, leading to more restraint and greater thermal axial stresses. The stiffer side shear restraint in rock was also found to lead to a less nonlinear distribution in thermal axial stress along the length of the energy pile.

This paper presents the results of field and numerical studies on the soil thermal response around a field-scale energy pile. The investigation focuses on the effect of monotonic heating, monotonic cooling, and daily cyclic heating/cooling of the energy pile on the soil thermal response. The soil temperature changes are found to be highest near the edge of the energy pile and reduce with increasing radial distance for all operating modes. The cyclic temperature changes of the energy pile impose lower ground temperature changes compared to monotonic temperature changes due to frequent ground thermal recoveries during each thermal cycle. The soil zone experiencing radial thermal influence is also smaller for cyclic temperature changes of the energy pile. The results generally indicate that cyclic heating/cooling of the energy pile will improve geothermal energy utilization with lower thermal impacts on the ground for long term operations of ground source heat pumps.

Variation of volatile organic compound (VOC) concentration and composition in an active landfill were monitored by a developed static chamber for 2 years. The landfill gas from 82 sampling points including 70 points on working face, 8 points on geomembrane (GMB), and 4 points on final cover were analyzed for VOCs by GC-MS. Twenty-eight types of VOCs were detected, including terpenes, sulfur compounds, aromatics, hydrocarbon, oxygenated compounds, aldehyde compounds, and halogenated compounds. Terpenes were the dominant VOCs recorded in the spring, autumn, and winter seasons, whereas sulfur compounds dominated in the summer season. Limonene, ethyl alcohol, and acetone were identified as the main VOCs emitted from the waste working face of the landfill. Limonene dominated the terpenes with a maximum concentration of 43.29 μg m −3 in the autumn season. Limonene was also the dominant VOC escaping from the defects of geomembrane temporary cover reaching an average concentration 38 μg m −3 . The defects of geomembranes can be a great emission source of VOCs. Emission rate of limonene was 2.24 times higher than that on the working face. VOC concentrations on the final cover can be 166 times less than those obtained on the working face. VOC emitted from the landfill did not represent a health threat for human health. However, concentrations of methyl mercaptan and ethanethiol on the working face were 3.4–22.8 times greater than their odor threshold, which were the main compounds responsible for odor nuisance. Results obtained from CALPUFF model indicated that methyl mercaptan and ethanethiol would not be a nuisance for the residents around the landfill. However, these compounds are harmful to the workers on the landfill.

This paper examines the deformation characteristics of energy piles subjected to horizontal loads in sandy soil. A model energy pile was subjected to ten heating and cooling cycles. The temperature of the pile and soil around the pile, pile top horizontal displacement, pile strain, and horizontal soil pressure in front of the pile were measured. Furthermore, the bending moment and displacement of the pile body were calculated and analyzed. The results show that the horizontal displacement of the pile top consistently increased. The temperature variation caused significant changes in the pile body displacement, which increased in the heating process and decreased in the cooling process, showing an overall increasing trend. However, the increment of pile body displacement gradually reduced. The temperature variation considerably changed the pile's bending moment; the pile body's maximum bending moment appeared at a depth of 3.5 D (D is the pile diameter). The pile bending moment increased during heating but decreased during cooling. The pile bending moment increased with the number of heating–cooling cycles.