For deep excavations in residual soils that are underlain by highly fissured or fractured rocks, it is common to observe the drawdown of the groundwater table behind the excavation, resulting in seepage-induced ground settlement. In this study, finite element analyses are firstly performed to assess the critical parameters that influence the ground settlement performance in residual soil deposits subjected to groundwater drawdown. The critical parameters that influence the ground settlement performance were identified as the excavation width, the excavation depth, the depth of groundwater drawdown, the thickness of the residual soil, the average SPT N value of the residual soil, the location of the moderately weathered rock, and the wall system stiffness. Subsequently, an artificial neural network (ANN) model was developed to provide estimates of the maximum ground settlement. Validation of the performance of ANN model was carried out using additional data derived from finite element analyses as well as with measured data from a number of excavation sites.
Adsorption and separation of carbon dioxide and methane on different carbonaceous adsorbents were analyzed and compared. Coconut shell‐based activated carbon has the highest adsorption capacity for two gases. Sips model describes the adsorption isotherms best. The separation factor on coconut shell‐based activated carbon is the highest under various conditions, reaching about 3.8. The adsorption capacity of the two gases is closely related to the specific surface area and micropore volume of the adsorbent. The adsorbed amount of each component in the mixture is less than that of the pure component under the same condition, indicating that there is a competition in the adsorption process. The total adsorbed amount of the two gases decreases as the proportion of carbon dioxide decreases, implying that the adsorption process is dominated by carbon dioxide adsorption. Additionally, the separation factor decreases with increasing temperature. Understanding the adsorption behaviors of pure and binary carbon dioxide and methane is important in treating biomass gas using carbonaceous adsorbents.
In order to improve the properties of activated carbons in the separation of carbon dioxide/methane mixture, organic acid, namely acetic acid, is used to modify the commercial coconut shell activated carbons. The modified sample 15H‐AC shows greater adsorption capacity than the raw material. To further explore the adsorption mechanism of carbon dioxide and methane on 15H‐AC, adsorption kinetics and thermodynamics are studied and compared with that on R‐AC. According to the results of adsorption kinetic study, it can be observed that the diffusion of both carbon dioxide and methane on 15H‐AC is faster than that on the raw material. The findings obtained in the adsorption thermodynamics indicate that the interaction of both carbon dioxide and methane with the modified sample is stronger and the spontaneity degree is higher. The physical adsorption of carbon dioxide on 15H‐AC indicates that the regeneration of the adsorbents is easy. The modified activated carbon, which possesses higher adsorption capacity, faster adsorption rate and good reproducing property, is promising in the separation of carbon dioxide / methane gas mixtures industrially.
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