由虛擬力學試驗探討併構崩積土之力學行為與性質-以梨山地滑區為例

Abstract

地滑區之崩積層組成相當複雜，由軟弱的沈泥質黏土至堅硬的新鮮岩盤均屬於其範疇。由於其組構行為複雜，常具不均質性與高變異性，未必適合以一般土壤或岩石之行為視之，本研究以「併構崩積土」的名稱來描述其組成，針對併構崩積土之行為，藉由數值模擬進行「虛擬力學試驗」，進而討論併構崩積土之力學行為與性質。 本研究以梨山地滑區為研究場址，梨山地滑區內的併構崩積土岩塊與基質的強度與勁度的差異性極大，與以往其他學者所研究之「併構岩」材料間的差異性有甚大差距，因此其力學行為也與他人針對併構岩之研究結果不盡相同。本研究同時以三維與二維之條件進行虛擬三軸試驗，比較三維與二維虛擬三軸試驗結果，探討併構崩積土行為之重要參數。 研究結果顯示：(1) 三維虛擬試體之破壞面較為蜿蜒拉長，故強度比二維結果高，(2) 試體極限強度隨岩塊比之增加而遞增，(3) 岩塊方向影響併構崩積土力學性質之異向性，及(4)模擬二維露頭面二維虛擬三軸試驗結果與謝孟修(2007)所得影響因素趨勢相似，可於現地觀察時初步研判現地之材料參數範圍。

Colluvial materials are often complex mixtures of geo-materials of various sizes, shapes, fabrics, and porosities depending on the parent strata and the slope-failure mechanism. Very often, colluvium from previously failed rock slopes is composed of both hard rock blocks and soft clay matrix, and may be considered as a complex composite geo-material which can be treated as a “blocks-in-matrix (BIM) geo-material. A BIM geo-material contains relative stronger rock blocks embedded in relatively softer and weaker matrix. This type of colluvium is termed as “BIM colluvium” in this study. The present work attempts to simulate and analyze the mechanical behavior of block-in-matrix (BIM) colluvial materials using virtual specimens. This study carried out a series of numerical simulation as virtual mechanical tests in order to look into the important factors that affect the mechanical properties of BIM colluvium. The study site for the thesis is within the Li-Shan huge landslide area. This area has been subjected to repeated and reactivated landslides with various depths of sliding surfaces according to several intensive investigations in the past. The colluvial deposit in this landslide region is often composed of both rigid slate blocks and soft clay, which is the “BIM colluvium”, referred to in this paper. A series of two-dimensional (2D) and three-dimensional (3D) virtual triaxial tests were carried out by varying the block proportion and block orientation to compare the results of 2D and 3D virtual mechanical tests and to identify important factors that control the mechanical behavior and properties of BIM colluvium. Major findings obtained from this study are as follows. (1) Comparing to the 2D case, the failure plane in the 3D tends to be tortuous in 3D; hence, results in higher strength. (2) The strength of BIM colluvium increases with increasing block proportion. (3) Rock-block orientation affects the anisotropy of mechanical properties. (4) The general trends of engineering properties versus block proportion obtained from 3D and 2D virtual mechanical tests are similar at least qualitatively. Due to the inevitable difficulties in obtaining colluvium specimens close to the REV for laboratory tests, it may be possible to adopt virtual mechanical tests to complement insufficient data of laboratory tests, provided an appropriate calibration can be made.