MODEL TESTS ON DEFORMATION BEHAVIOR OF BENTONITE MIXED SOIL LAYER SUBJECTED TO A LOCAL SUBSIDENCE IN LANDFILL

摘要

Compacted soil mixed with bentonite having a low hydraulic conductivity of less than 10-6 cm/s is commonly used as barrier layer in waste landfill in Japan. But it is afraid that the bentonite mixed soil may have cracks when the base ground experiences a local subsidence. The authors conducted trap door tests of bentonite mixed soil under a surcharge pressure of 107.8kN/m2. The sizes of the compacted soil layer mixed with 10 % bentonite are 800 mm in length, 200 mm in width and 100 or 200 mm in thickness. The width of trap door was changed as 30, 40 and 50 cm. The rate of lowering the door was 1.0 mm/day. It was found that bentonite mixed soil had a crack in the middle height of soil layer when the trap door subsided between 12 and 13 mm. And then the crack reached at top and bottom surfaces when the door was lowered between 13 and 27 mm. Therefore the shear crack is predominant than bending crack. In the study the image analysis for the tests with a lowering rate of 0.5 mm/min was also conducted by recording the deformation on the video. The amount of calculated shear strain at the cracked position was lager than 20%.