关键词: 防渗墙, 膨润土, 渗透系数, 压缩系数, 最优掺量

Abstract: Soil-bentonite cutoff walls have been widely used for municipal sanitary landfill in United States. However, there are less engineering applications in China and domestic bentonites and stratum have been mixed and formed to cutoff walls under the consolidation of self-weight stress. Less information is known to how the porosity, permeability and compressibility of cutoff walls are influenced by the addition of bentonite. To solve this problem, the effects of bentonite content on the k, n and av of sand-bentonite backfills are investigated based on several improved flexible wall permeability tests and consolidation tests using Fujian Standard sand as the simulated stratum and three typical bentonite mixtures as additional material. The results show that when bentonites and sand are mixed into cutoff walls, there is a critical bentonite content Copt, where the n and the av are lowest. If the bentonite content is less than or equal to Copt, k decreases rapidly and av reduces slowly with the increase in bentonite content. As the bentonite content is larger than Copt, reduced rate k slows down and av increases rapidly with the increase in bentonite content. In theory, when the bentonite content is much lower, clay particles only fit within the sand pore space and without disturbing the sand pack pattern. However, after bentonite content reaches Copt, sand grains become disconnected and are suspended in the bentonite, resulting in increased porosity of the backfill increases with bentonite content, which may be the main reason of the optimum bentonite content at the macro level.

Key words: cutoff wall, bentonite, hydraulic conductivity, coefficient of compressibility, optimum bentonite content