Model Tests on the Effectiveness of Slope Protection Works under Rainfalls
Date Issued
2012
Date
2012
Author(s)
Chen, Chih-Shin
Abstract
Rainfall is one of major factors that cause slope failures. In recent years, there have been researches employing model tests on slopes subjected to rainfalls. Instrumentations embedded in the slopes were monitored to investigate the failure mechanism of the slopes. Main variables considered in the researches were as follows: hydrological factors such as water supply conditions (e.g., rainfall or seepage) and rainfall intensity, geometric factors such as slope profile and model dimensions, and geological factors such as the fines content and relative density of soil. However, few have been reported using in-situ soil for research. In this study, the test soil was taken from a site in Tieliku area, located within the catchment area of the Shimen Reservoir in northern Taiwan. The site had experienced slope failures and was under restoration. Before test, the grain size distribution of the in-situ soil was modified in the laboratory to be in accordance with the similarity laws for model test.
The major characteristics considered for simulating the in-situ soil were the grain sizes and their distribution, the shear strength and permeability of the soil, etc. With regard to in-situ conditions, the factors considered were slope profile, the thickness of soil, impervious stratum in slope, and slope protection works such as an anti-erosion geotextile blanket placed on slope face, horizontal drainage pipes embedded in the slope, and a filter blanket under the deposition area near the toe of slope. The aim was to investigate the failure mechanism of the slope and to evaluate the effectiveness of the protection works through model tests. During the tests, the process of slope failure was recorded by three video cameras, and piezometers and moisture sensors measured the variations in pore-pressure and volumetric water content of soil. The eroded soil was collected for weigh measurement and for conducting grain size analysis.
Based on the test results, the unprotected slope with an impervious stratum at shallow depth tended to induce a quicker accumulation of pore water pressure in the slope and to fail earlier than the slope having a thicker layer of soil. However, the geotextile blanket displayed a good effect on stabilizing the slope. The horizontal drainage pipes also showed excellent results not only reducing pore water pressure, but also improving the overall slope stability. Nevertheless, the filter blanket that placed in the area adjacent to the toe of the slope caused shallow slope failures. In this regard, the filter blanket should be used in combination with other protection works or extended into slope so that shallow slope failures as well as deep circular failures would not be induced.
Subjects
slope
model test
rainfall
failure
slope protection works
Type
thesis
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