Environmental Acceptability of Theinstallation of Piles Through the Bottom Clay Barrier at Coastal Landfill Sites

The purpose of this study is to evaluate whether the bottom clay layer at coastal landfill sites will maintain the required barrier function even if piles are installed through the clay layer to ensure the bearing capacity of structures constructed over the landfill sites. The transmissivity of the interface between the clay and the steel was measured with a newly-developed rigid-wall permeameter, which has earth pressure transducers on the top and the bottom caps of the cell so as to determine the side-wall friction. Processed Fukakusa clay (LL = 41.9%, PL = 21.4%) was pre-consolidated at 90 or 180 kPa and was trimmed to have a diameter 2 mm smaller than the 80 mm diameter of the permeameter cell to intentionally create a space between the clay and the side-wall. Vertical pressure levels ranging from 11.25 to 360 kPa were applied, and a hydraulic gradient across the specimen was applied for each vertical pressure. As the vertical stress increased, the friction grew larger between the clay and the steel, and the interface transmissivity decreased. The measured transmissivity was very low, when the clay was under a normal state of consolidation or the OCR (over-consolidation ratio) was smaller than 1.5, and ranged from 0 to 2 x 10^–7 cm²/s. Two different indices of equivalent hydraulic conductivity were proposed, namely, one that considers the total amount of leakage and a second that considers the seepage velocity. Although the work presented in this paper represents the preliminary investigation and the simplicity of the test program limits the application, it is considered that the installation of piles through the bottom clay layer at coastal landfill sites may be environmentally acceptable under the certain conditions in which the clay is deformable enough against the overburden pressure to close the gap between the clay and the pile.