| 摘要: | 地表承受荷重時，應力影響規模隨著岩盤之性質不同而異，是故瞭解應力影響規模實屬必要。Bray(1977)經驗公式為一套處理單組節理下橫向等向性岩體內主應力分佈之簡單公式，但變化岩盤性質時，僅能瞭解參數對主應力分佈之改變，並無法得知參數間之影響比例。而且在多組荷重、多組節理岩體中應力之變化Bray公式之應用仍有多方面的受限。因此本研究擬透過量化分析各參數之影響程度，並釐清各參數間之相依性。
本研究先分析應力影響規模與Bray公式中各參數（節理傾角、勁度比、間距、岩石之彈性模數、柏松比等）之關係，接著擴展到多組荷重、節理組數及斜坡之應力疊加方式，並推估所得應力規模之合理性。在綜合岩體於不同內在應力參數、外在荷重條件範圍分析中所得之應力規模及對影響寬度、深度等結果，共計73,780組假設狀況資料，使用多變量分析求得其影響權重值，並以相對分析佐以探討參數間彼此之差異性。可得致以下幾點結論：
(1) 岩盤最大主應力分佈規模大小主要受節理勁度比、間距、及岩石之彈性模數等三者的控制。而應力分佈形狀之異向性則受節理傾角控制，但傾角大小並不影響應力的分佈規模。(2) 在兩組荷重下，應力影響規模具重疊效果，當荷重大小變化與彼此間距離之遠近，對影響規模之影響極高。(3) 雙組節理時，應力規模之異向性程度較單組節理輕微。而在正交節理岩體之應力規模雖具有異向性，但應力影響規模大小卻不隨著而傾角有改變。(4) 改變外在荷重方向時，影響應力規模之參數主要仍為節理勁度比、間距、及岩石彈性模數三者，但對於影響之深度與廣度仍隨荷重方向改變而不同。(5) 由相對分析發現節理勁度比、間距、與岩石彈性模數三個參數間不僅對應力規模之影響最大，且彼此間之相依性甚高；傾角與前三者之差異性雖高，但對於應力分佈的異向性影響仍最大，柏松比之影響最少。而延伸因子中兩荷重大小比例、兩荷重間距離、兩組節理之夾角三者儘管影響應力規模之權重甚高，但相關性卻不高。
While surface subjected to point load, the stress influenced volume differs from the laccolith’s properties. Therefore it’s essential to understand the stress influenced Volume. Bray (1977) experience formula deal with distribution of principle stress under transversely isotropic rock with single joint, it could interpret distribution of principle stress while changing the laccolith’s properties though, the influence proportion within parameters is hard to know. Besides, the application of Bray formula still have limits in multi-load, multi set of joints. Hence the study aims to rectify correspondence of influenced parameters through weighting analysis.
This study analyzes the relation between stress influenced volume and parameters within Bray formula (such as joint direction, joint stiffness ratio, joint spacing, elastic modulus and poisson''s ratio of the rock material), then expand the formula to multi-load, multi set of joints, and slope condition using superposition of stresses, finally check the rationality of predicted stress volume. To conclude the 73,780 predicted conditions with influenced volume, width, depth under different inherent rock parameters and external loading condition. Using multiple regression analysis and correspondence analysis to obtain the weighing values and the difference between parameters, could get the following conclusions:
(1) The influenced volume of maximum principle stress in rock mainly controlled by joint stiffness ratio, joint spacing and elastic modulus of rock. Although the joint direction controls the anisotropy of stress influenced distribution, it doesn’t influence the stress volume. (2) Under two set of point load, the stress influenced volume has superposition effect. While changing the scale of loadings and their distances, it highly influences the stress volume. (3) The anisotropy of influenced volume in two joint sets is lighter than single joint set. Though the stress volume have anisotropy in orthogonal joints, it doesn’t change with the joint direction. (4) While changing the direction of loading , joint stiffness ratio, joint spacing and elastic modulus of rock still mainly controls the influenced volume, as to the influenced depth and width the volume changes with the loading directions. (5) By using correspondence analysis, joint stiffness ratio, joint spacing and elastic modulus of rock highly influenced the stress scale and have great relationship. In spite of the difference between joint inclination and the former three is high, it influences the anisotropy of stress distribution greatest, while the poisson''s ratio influences least. Besides, the loading ratio, loading distance, and the angle of two set of joints influence the stress scale highly, even though it has little dependence. |
