The Effect of Smectite Dehydration on Land Subsidence
| Autor: | Wen-Sheng Lin, 林文勝 |
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| Rok vydání: | 2001 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 89 Traditionally, the mechanisms of land subsidence resulting from groundwater over-pumping have been described, and explained often by primary consolidation with the classical elasticity or consolidation theory. The mechanism of secondary compression, also resulting in land subsidence, due to clay interlayer water release is seldom addressed in these studies. Therefore, the purpose of this study is to investigate the effect of smectite interlayer water release on the land subsidence. Two schemes of “hydration state of smectite”, and “solid solution model of smectite dehydration” were developed using thermodynamic solid solution model and the laboratory studies of clay-water systems, e.g. swelling pressure, hydration state and basal spacing in smectite interlayer. Subsequently, these two schemes developed in this study were applied to evaluate the effect of smectite dehydration on the cumulative amount of land subsidence in the Chang-Hua, Yun-Lin coastal area. The analytical results indicated that 9.56% ~ 22.80% of the total cumulative amount of land subsidence within the depth of 300 m resulted from the smectite dehydration due to groundwater over-pumping. This dehydration-related land subsidence occurred often within the depth of 0-60 m. The amount of subsidence due to smectite dehydration amounted to 6.20% ~ 13.32% of that of primary consolidation, which was calculated with ABAQUS model or INTERBED model. In addition, the total subsidence amount resulting both from smectite dehydration and the primary consolidation is consistent with the subsidence amount of observation. This encouraging finding supports that incorporation of the secondary compression from smectite dehydration does provide better modeling results compared to field observation. Therefore, this study showed that both mechanisms of interlayer water release and the primary consolidation, either from Biot 3-D pore-elastic theory or Terzaghi-Jacob 1-D consolidation theory are responsible for the clay compaction due to groundwater over-pumping. The results from this study are applicable to the assessment of smectite dehydration effect on land subsidence. Future works include kinetic studies of smectite dehydration focusing on the time dependency on dehydration which directly affects the amount of consolidation. With these kinetic data, groundwater model incorporated with time-dependent primary consolidation and second compression may be established. Another possible work is the development of the solid solution model for smectite dehydration as functions of pressure and temperature, which is applicable to the safety assessment of radioactive waste disposal site with the backfill clay composed of smectite in the engineer barrier, and to the stress analysis resulting from rapid smectite dehydration triggered by the fault displacement or earthquake. |
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