鋼管杭打設粘土地盤と杭境界面における漏水量とその評価

抄録

Bottom clay layer at the coastal landfill site is required to maintain its hydraulic barrier performance even if steel 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 been designed to measure the side-wall friction. Kaolinite clay specimen was pre-consolidated at 90 or 180 kPa, and trimmed with its diameter of 2 mm smaller than that of the permeameter cell to intentionally create a gap between the clay and the steel side-wall. A hydraulic gradient across the specimen was applied under the vertical pressure ranging from 11.3 to 360 kPa. As the vertical stress increased, the friction between the clay and the side-wall grew larger, 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 2×10^-7 cm²/s. Two different indices of equivalent hydraulic conductivity were proposed, namely, one gives the equivalent leakage rate and another gives the equivalent seepage velocity, to verify the adverse effect of the steel pile installation on the barrier performance of the clay layer. Although the experimental 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 not induce the leakage flow 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.