Analysis of the Water/Cement/Bentonite Ratio Used for Construction of Cut-Off Walls

Abstract

In recent years, because of the continuous expansion of urban areas, an increased necessity to isolate historically polluted sites by means of artificial, flexible, low-permeability barriers has emerged. Moreover, due to cost and efficiency considerations, various combinations of materials that fulfill the previously stated requirements have been proposed. On the basis of a literature review, this paper analyses the relationships between water, cement, and bentonite, and the physical and mechanical properties of the resulting material created in combination with standard sand introduced in the mixture using a ratio of 2:1 with respect to the solid part of the mixture (cement and bentonite). The quantity of standard sand was established following previous research conducted by the authors. The relation between water, cement, and bentonite is analyzed through properties such as viscosity, permeability, and undrained cohesion, and the representation of mixtures and their corresponding parameters was carried out using a ternary diagram. This paper provides a graphical approach to finding the optimum water/bentonite/cement mixture required for barrier design, taking into account permeability, undrained cohesion, and mixture viscosity.

Dewatering Characteristics and Drawdown Prediction of Suspended Waterproof Curtain Foundation Pit in Soft Soil Areas

“…The soil profile and soil properties are shown in Figure 10. The soil layers, from top to bottom, are backfill (11), silty clay (12), coarse sand (13), sandy clay ( 14), fine, chalky sand (15), chalky clay ( 21), fully weathered granite (31), sandy, gravelly soil (41), and strongly weathered granite (51). The project includes a phreatic aquifer (Aq01), two confined aquifers (Aq I and Aq II), and an aquitard (Ad I and Ad II).…”

“…The excavation process in these areas does not isolate the hydraulic connection between the inside and outside of the foundation pit, resulting in a difference in the hydraulic head, which allows groundwater to flow into the pit [10]. To prevent issues such as sand inflow, sudden floor heave, and water inflowing towards the excavation [11,12], it is crucial to implement necessary dewatering measures. Additionally, improper dewatering can lead to rapid ground settlement, potentially causing damage to nearby structures, especially in densely populated urban areas [13,14].…”