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Work herein is focused on evaluating factors affecting tetrachloroethene (PCE) contaminant ingress into the subsurface concrete pipe embedded in the saturated soil profile and assessing the efficacy of permeable reactive barriers (PRB) in mitigating PCE concentration. A three-dimensional groundwater flow and solute transport numerical model is established using MODFLOW paired with reactive transport (RT3D) software, in which the model is developed using a finite-difference numerical scheme. The analyses parameters are developed from data for a site in Wilson, North Carolina, at which subsurface chlorinated organic solvents from a dry-cleaning facility occurred in the presence of subsurface highway concrete drainage pipe. Modeling results after 10 years of simulation period indicated that the natural attenuation process taking place in the native soils with coefficients of KPCE=0.00019 d−1 , and 0.0033 d−1 reduced the PCE concentrations breaking through the concrete pipe by 30.7% and 34.1%, respectively. On the other hand, with a greater percent of the soil sorption as manifested by organic carbon content, the PCE concentration breaking through the pipe increased by 137% for the same simulation period as a result of the prolonged presence of PCE concentration within the pipe trench. The hydraulic conductivity of the PRB (kPRB) modestly affects the level of PCE breaking through the pipe, while the increase in thickness of the PRB was found to be the most effective in decreasing the level of PCE ingress into the pipe. [ABSTRACT FROM AUTHOR]

This investigation examines the effect of clamshell ash (CSA) and lime additives on the physico-mechanical characteristics of kaolinite clay soil stabilized at the optimum silica fume content. Laboratory tests were performed to assess plasticity, shrink-swell characteristics, compaction characteristics, unconfined compressive strength (UCS), shear strength characteristics, mineralogical and morphological microstructure characteristics of stabilized soil specimens. The kaolinite clay soil was stabilized at its optimum silica fume content (6%) to produce the highest strength and was altered with three non-identical proportions of clamshell ash and lime (3%-9%). Cylindrical soil specimens, 76 mm in height and 38 mm in diameter, were moulded and treated for curing periods of 1, 7, 14, and 30 days to examine the strength of the altered soil. The findings revealed that, adding clamshell ash and lime significantly alters the plasticity, shrink-swell, maximum dry unit weights, and optimum moisture contents of the silica fume-stabilized soil. In terms of strength, the beneficial effects of CSA and lime additives were found to be more significant with more extended curing periods. Incremental increases in curing periods resulted in further enhancements in UCS, cohesion, and internal friction angle, indicating continued strength development over time. Microstructural analysis using field emission scanning electron microscopy and X-ray diffraction provided insights into the interparticle bonding mechanisms and microstructural changes induced by the addition of CSA and lime. The emergence of cementitious phases and pozzolanic responses between soil particles and stabilizers contributed to the densification and strengthening of the stabilized soil matrix. The findings of this study provide valuable insights into the potential of clamshell ash and lime additives to enhance the engineering properties of kaolinite clay soil stabilized with silica fume. These results have implications for sustainable soil stabilization practices, offering a promising approach to improve the performance of soils for various engineering applications, including construction and geotechnical projects. [ABSTRACT FROM AUTHOR]

Shear strength of rock masses is critical for geotechnical tasks including tunnel, slope stability, and foundations. Various approaches comprising of back calculation, large-scale testing, experimental parameter, and a rock mass categorization system could be used to define the shear strength of a jointed rock mass. Furthermore, the excavatability features of rocks influence the choice of excavation technique and equipment in geotechnical and mining operations. In this work, the excavatability of rock is assessed using rock mass categorization techniques, such as residual shear strength, rock mass rating system, and updated excavatability graph. Therefore, the residual and peak shear strength envelopes of jointed magmatic rock masses are evaluated through a hybrid ELM-SVM model that combines two soft computing models: support vector machines (SVM) and extreme learning machine (ELM) (objective of study). The shear strength characteristics are studied and predicted using the findings of regression analysis using factors, such as root-mean-square error (RMSE) and coefficient of determination (R2). The findings reveal that the suggested hybrid could be applied to find the peak and residual shear strength values of frequently fractured rocks as well as providing a meaningful relation between the values of shear strength variables of the geotechnical units. [ABSTRACT FROM AUTHOR]