Peat soil shrinking and swelling associated with ground water table movement
2000
Iiyama, I. (Tokyo Univ. (Japan)) | Miyazaki, T. | Nakano, M. | Imoto, H.
To investigate the shrinking behavior of peat soils associated with drainage, we used undisturbed rectangular parallelepiped shape peat specimens to observe changes of height, vertical strain distributions, matric potential distributions and drainage. Volumetric water content distribution data derived from matric potential distributions and soil water retention curves were applied to estimate the change of vertical stress distribution. Further to investigate the shrinking-swelling behavior of peat soils as a result of repetitive drainage and water supply terms, we analyzed the shrinking-swelling behavior of rectangular parallelepiped shape specimens. Resulting from the increase of vertical stress caused by the loss of buoyancy, three stages of peat soil shrinkage were observed; (1) an abrupt shrinkage according to drainage from macro pores, (2) a moderate shrinkage according to drainage from micro pores, (3) a slow, long term shrinkage due to the decrease of air-filled porosity and solid phase volume without drainage. Differences in bulk densities, pore-size distributions, the degree of saturation and suction force of pore water resulted in the difference in shrinking behaviors of peat soils under unsaturated conditions. We inferred that peat soil swelling above water table resulted from decreasing of suction force with capillary water uptake. We could observe irreversible shrinkage due to residual strain during long term shrinking behaviors of peat soils according to repe
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