橫向等向性岩石基礎之承載力解析解－利用滑動線法

Abstract

由於大型荷重結構物漸被採用，以往被視為不會產生破壞的岩石基礎承載 問題漸被重視。傳統上，岩石基礎承載力的分析計算常視岩石為均向均質 、彈性、塑性、和脆性材料。事實上甚多岩石承現異向性特性，例如頁岩 、板岩、片岩等，致使現存考慮均向岩石之基礎承載力分析公式無法試用 。本文考慮具橫向等向特性岩石之強度異向性，採用滑動線法 Slip Line Method及修改後適用於具單一組弱面之Hoek--Brown岩石強度破壞準 則，提出適用於具橫向等向性軟弱岩石之基礎承載力理論解。本理論解可 求取不同水平地表及與坡地交界處不同弱面傾角之基礎承載力及破壞滑動 線。經一系列數例分析得知，在水平地表下，由於弱面存在造成岩石之強 度異向性，致使岩石基礎承載力隨弱面之傾角方向與大小而變化。由本文 中例子可知平地地形狀況下其承載力因數最大值出現於當傾角為60度時， 當傾角為25度其承載力因數有最小值，承載力因數最大與最小相差約有2 ∼3倍。若基礎接近坡地則承載力受坡角、岩石弱面傾角及基礎與坡面距 離等因素影響。另外，Hoek--Brown破壞準則中當m<1 ,s<0.01時，m,s對 承載力影響不顯著。本理論解因採用平面應變條件下之塑性理論推導而得 ，因此僅適用於橫向等向性之岩石，岩層走向與分析平面垂直，且具彈塑 特性。 It is very important for engineering safety to predict the bearing capacity of foundation rock before engineering strctures with large loads are built on the rock. Isotropic solutions for the bearing capacity in foundation rocks cannot be used for rocks that exhibit strength anisotropy. A few analytical solutions for the bearing capacity in anisotropic foundation rocks were proposed. These solutions are limited to rock masses with strength anisotropy because of one set of weak planes and bounded by a flat surface. For the bearing capacities in aniostropic foundation rock on sloping ground or on the crest of sloping ground, analytical solutions were not considered for rocks with strength anisotropy in the literature. In this thesis, new analytical solutions for the bearing capacities and slip line in foundation rock with strength anisotropy on flat surface and on the crest of sloping ground are presented by slip line method. In the solutions, the foundation rocks are modelled as plastic materials and satisfy associate flow rules and modified Hoek-Brown failure critrion. Numerical examples are conducted to investigate the effect of the dip direction and angle of strata, the slope angle, and the location of foundation at the crest of sloping ground on the bearing capacity in the rocks with strength anisotropy.