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.