Author : Hui Loo
Release : 2017-01-27
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Book Synopsis Reactivation of an Old Landslide in Response to Reservoir Impoundment and Fluctuations by : Hui Loo

Download or read book Reactivation of an Old Landslide in Response to Reservoir Impoundment and Fluctuations written by Hui Loo. This book was released on 2017-01-27. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation, "Reactivation of an Old Landslide in Response to Reservoir Impoundment and Fluctuations" by Hui, Loo, 盧慧, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled REACTIVATION OF AN OLD LANDSLIDE IN RESPONSE TO RESERVOIR IMPOUNDMENT AND FLUCTUATIONS Submitted by LOO Hui for the degree of Doctor of Philosophy at The University of Hong Kong in April 2006 Reservoir landslides have long been recognized as a key issue by the Government of the People's Republic of China even before the construction of the Three Gorges Reservoir. A total of 2490 landslides have been identified in this reservoir area. The possibility that these landslides will be reactivated by reservoir impoundment and subsequent fluctuations has become a major concern. The objective of this research is to study the influence of reservoir impoundment and fluctuations on the reactivation of 6 3 old landslides. An old landslide at Xietan of volume 6.24 x 10 m in the Three Gorges reservoir areas was chosen for the study. Xietan site is a typical colluvial deposited landslide underlain by a layer of clayey soil (slip soil). Insitu and laboratory tests were conducted to determine the physical properties, hydraulic properties and shear strength characteristics of the soil. Effective shear strength tests of slip soil were carried out on both undisturbed and reconstituted samples. A preliminary study on the influence of degree of saturation on the effective strength was also carried out. From the test results, it can be seen that the effective friction angle of the slip soil is 22, and the cohesion value is influenced significantly by the inherent structure and degree of saturation of slip soil. A comprehensive instrumentation system was established to monitor the long-term performance of the site in response to reservoir impoundment and fluctuations. The data for the period from 1 April 2003 to 31 July 2005 were analysed. The results show that the changes of groundwater level follow the reservoir level closely as the observation point approaches the reservoir bank, but the influence of rainfall on the rise of groundwater level is negligible. Seepage analysis was carried out to model the changes of groundwater level corresponding to reservoir level. A satisfactory correlation is found between the numerical results and the monitoring results. In response to reservoir impoundment, a shear plane in slip soil is observed. The displacement is greater as the observation point approaches the reservoir bank. The changes of displacement in response to rainfall infiltration are negligible. The rate of Xietan landslide movement is still very slow to extremely slow which is less than 40 mm/year, indicating that the landslide is in a creeping state. However, local failure is observed after the impoundment. A stability analysis of the site was carried out. The results show that the shear strength of slip soil above the reservoir level and the groundwater table in the slope has significant influence on the stability of the slope. It is concluded that the slope would be in a critical state and reactivation of the landslide could happen when (1) the loss of cohesion of slip soil below reservoir level associated with the low cohesion of slip soil above the reservoir level happens; or (2) rapid drawdown occurs without dissipation of pore water pressure in the slip soil; or (3) the reservoir bank changes under the fluctuations of reservoir level between 145 m and 175 m. DOI: 10.5353/th_b3665297 Subje