硬頁岩之靜態力學行為

Abstract

本研究嘗試利用多段式三軸壓縮試驗的方法進行硬頁岩之三軸殘餘強 度試驗，以尋求橫向等向性岩石之殘餘強度行為（如三軸殘餘凝聚強度、 殘餘摩擦角等強度參數與破壞型態…等），並且對於硬頁岩之峰前、峰後 曲線做一番探討。從一系列的試驗結果顯示，硬頁岩之三軸殘餘強度亦如 同尖峰強度隨著葉理面與最大主應力軸之間的夾角(β)而變化，在β=30 °附近有最小值，β=0或90°為最大值。而由試驗結果也顯示對於硬頁岩 之多段式三軸殘餘強度試驗，試體因為反覆磨損而造成殘餘強度損失的現 象不大。但是三軸殘餘凝聚強度 卻不像一些學者於直剪試驗下的結果會 趨近於零，也隨著β角而變化。殘餘摩擦角則與β角無關約略為一個定值 。 由於硬頁岩之三軸殘餘強度亦如同尖峰強度隨著β角而變化，其趨 勢相似，故對於三軸殘餘強度的破壞準則則嘗試利用三軸尖峰強度下的破 壞準則修正（如Jager,Hoek & Brown,及黃紹祈與廖志中的強度準則）,結 果顯示以後者強度準則的修正式較為符合。 張力強度的破壞準則，嘗 試利用楊明宗學長的試驗結果作修正，葉理面與水平面之間夾角定義為( α)。由於α＞75°時，試體的破壞面部份會沿著葉理面、部份會貫穿葉 理面而呈現鋸齒狀的破壞型態，表示受到剪應力的作用。若忽略剪應力所 作用的面積而僅考慮實際受到張應力有效面積所分析出來的破壞準則與試 驗結果比較，顯示與試驗趨勢頗為吻合。 至於三軸尖峰下的變形行為 ，則將Wei and Hudson 的建議方法作理論上解析的試誤法，結果顯示在 β≧45°時， 對於角度的變異行為愈不靈敏，也就是說當β≧45°，所 進行的變行性研究一致性會較佳。 In order to investigate the residual behavior of anisotropic rocksin triaxial compression, such as strength characteristics and failuremodes,a laboratory technique called Multiple Failure State of TriaxialTest has been adopted for performing a series of tests on core samples of argillite in this paper. The results show that the triaxial residualcompression strength versus the inclination of cleavage with respect tothe direction of major applied force are concave upward with pronouncedstrength minima at 30 degrees to the anisotropy orientation, and maximumstrength occurs in the 0 degree or 90 degrees orientation. It also showsthat the trend of the residual cohesive strength obtained from the methodof multiple failure state of triaxial test is not to be zero and stronglydepends on its anisotropy orienation, which is different from that done by direct shear tests in some literatures, but residual friction angle has nothing to do with anisotropy orienation, so it can be simplified asa constant. A new failure criterion modified from Huang and Liao is proposed for the triaxial residual compression strength of transverselyisotropic rocks. The testing results show more fitter than others like Jager, Hoek-Brown...etc. Being the failure planes show a sawtoothed mode, which indicates that the specimens fail partly along and partly across the foliation planes forthe specimens with the inclination angle with respect to horizontal plane of 75 to 90 degrees in direct tensile test. A new strength failure criterionin direct tension was also proposed within the range of these angles and shows better for fitting the testing results. A series of parametric study was done for investigating the fitness of the method suggested by Wei and Hudson for obtaining the 5 elastic constants of anisotropic rocks. The results show that E', v' and G' do not seem to be sensitive due to the judgement of the angle when the inclination angle withrespect to the loading direction is greater than 45 degrees.