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Technology and Engineering
- ISSN: 2333-2581
- Modern Environmental Science and Engineering
Slope Stability of Solid Waste Layers in Japan and Asia
Atsushi Yamawaki1, Kiyoshi Omine2, Yoichi Doi3 and Mikio Kawasaki4
1. Japan Industrial Waste Management Foundation, Japan
2. Nagasaki University, Japan
3. Nagano Prefectural College, Japan
4. Center of Environmental Science in Saitama, Japan
Abstract: The present research aims to develop methods for assessment of slope stability of deposits of industrial solid waste that have been formed as a result of illegal dumping or similar acts in Japan. For this purpose the authors studied the patterns of slope failures by surveying 23 sites with reported threat of slope failure in Japan and studied cases of actual failures inside and outside of Japan with a focus on differences in the conditions under which the large-scale slope collapse occurred.
Strength tests including on-site loading test, in-site direct shear test, tensile test and a newly-developed repose angle test were performed at 8 sites in Japan, 1 site each in China, Indonesia and Turkey. A slope (height = 9 m, slope angle = 63°, load weight = 8.6 kN/m2) was formed so that the safety factor for possible failure predicted by the conventional soil ground slope stability analysis would be 0.56. However no collapse or even any displacement occurred.
The present research has revealed that solid waste layers that contain fibrous materials possess tensile resistance, which must be taken into account in addition to the angle of internal friction (φ) and cohesion (c) that are used in conventional circular slip analysis. Therefore, we propose a simplified equation of the infinite slope method that takes into consideration the tensile resistance.
The results of the direct shear tests showed that all the sites investigated had significantly large friction resistances comparable to normal soil; the data of sites in Japan containing fibrous materials were φ = 46-51° and c = 3-4 kN/m2. The repose angle tests every case resulted in the repose angle after avalanching being nearly equal to the φ value obtained by the direct shear test.
The results of the infinite slope method and the circular slip surface analysis correlated well. In addition, the results of these calculations correlated well with the situations of the sites.
These tests and analyses enabled to quantitatively assess the slope stability of illegal dumping sites, reflecting the real situation better than by conventional assessment methodologies. The study explains the slope stability sufficiently well insofar as the dumping is on flat ground and is of typical composition with fibrous materials without containing excess water. With respect to dump sites sitting on inclined ground, however, large-scale failure is possible regardless of the front slope angle or of the composition of the solid waste. Furthermore, large-scale collapse can occur at a relatively mild angle inside nearly-saturated waste layers that are typically found in landfills in Southeast Asia and elsewhere.
Key words: solid waste layers, slope failure, repose angle test, slope stability analysis, infinite slope method, excess moisture
