Alluvial Sand Compression Testing and Ground Subsidence Monitoring at the Intersection of Expressway 78 and High Speed Rail of Taiwan
| Autor: | CHUANG,CHAI-FENG, 莊家豐 |
|---|---|
| Rok vydání: | 2017 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 105 Chuoswei River Alluvial Fan-Delta (CRAFD) is the largest and most severe subsiding area in Taiwan. In recent decades, the ground subsidence center in the CRAFD has been gradually moving from the coastline to inlands. The current ground subsidence center is located in Tuku, Huwei, Yuanchang and Baozhong. Per recent data by WRA, Taiwan High Rail (THR) and Directorate General of Highways (MOTC), ground subsidence and compressions are obvious and continuing in all layers within a monitoring depth of 300 m. The observed compressions are related to the variations in groundwater level. Generally, sands would behave immediate compression, with no obvious primary or secondary consolidations (i.e., time-dependent compressions) as clay, when subjected to loading. Evidences in the field have shown considerable compressions in sandy soils. Accordingly, the aim of this study is to examine the compressibility of sandy deposits in the Chuoswei River Alluvial Fan-Delta (CRAFD) in Taiwan. The sandy soil samples for testing are retrieved from the subsurface exploration. The compression tests are performed under various overburdened pressures and cyclic loading conditions by a high-pressure consolidation apparatus designed and fabricated for this study. Based on in-situ monitoring on the CRAFD, all the groundwater has similar pattern in groundwater level fluctuations, which is closely related to the compression of soils at the site. For a three-year monitoring period, we observe the compression is around 9~10 cm in sandy and clayey soils within the 300-m depth range of the study area. We also notice the amount of compression in aquifers (sandy and gravelly soils) appears greater than that in aquitards (silty and clayey soils), indicating the sandy layers would have more contributions to the ground subsidence of the site. Our preliminary study shows the compression characteristics (Cc、Cs、Cr、Cα、Cv、K) of the sandy soils in the CRAFD are influenced by the overburden pressure as well as the fluctuation of groundwater levels. Under low confining pressures, the sandy soils would experience both elastic and plastic deformations when subjected to cyclic loading. Under high confining pressures, however, only elastic compressions are found during cyclic loading, with no permanent deformation accumulated in the soils. In addition, the volumetric strain of sandy soils under cyclic loading would be greater than that due to the static loading. Keywords: sandy soil, overburden pressure, groundwater variation, consolidation test, alluvial soil, Chuoswei River Alluvial Fan-Delta (CRAFD), laboratory testing, insitu monitoring. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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