台灣西部麓山帶西緣地區廣泛分佈著年輕且膠結不良的沉積岩層，此等軟弱岩層具有強度低、變形性高及遇水極易軟化之特性。影響軟弱岩層破壞之外在環境因素中，水文地質特性為重要關鍵因素之一。因軟弱岩層之強度受到有效應力控制，有效應力受到岩層中孔隙水壓分佈控制，而孔隙水壓分佈又受到岩層之滲透性控制，加上滲透性又為岩層所受應力狀態之函數，故軟弱岩層之破壞，應與其滲透特性的變化極為相關。本研究利用傳統三軸實心試體之透水試驗與中空扭剪滲透試驗儀，配合軟弱岩石材料的中空套鑽技術，進行一系列軟弱岩石滲透性的相關試驗。主要探討項目包括：(1)軟岩滲透異向性；(2)圍壓對軟岩滲透異向性之影響；以及(3)受剪過程軟岩滲透性質的變化。研究結果發現：(1)軟岩存在滲透異向性，尤其是砂岩夾薄層泥岩或砂泥、頁岩薄互層之軟岩材料，其水平與垂直層面之滲透係數比(kh/kv)約為10~100；(2)垂直與水平層面的滲透係數均隨有效圍壓的增加有逐漸降低的現象，而滲透異向性程度則隨圍壓之增加而變大；(3)在受剪過程中，試體的滲透係數隨剪應變量增加有變大的趨勢，特別在應力-應變曲線過尖峰強度後，滲透係數值將明顯上升。本研究的試驗結果顯示，軟岩材料除具有先天滲透異向性以外，同時滲透異向性亦將隨應力狀態改變而改變，因此，軟岩工程之分析與設計宜考慮此一效應之影響。 Anisotropic Permeability of the Sedimentary Soft Rock Chih-Yung Chang ABSTRACT In the west foothill of Taiwan generally distributes young, poorly cemented, sedimentary soft rock.. This material is weak in strength and is easily deformed. The properties will be more obvious while it is watered. The characteristic of hydraulic geology affects the strength of soft rock. The permeability is an important factor in hydraulic geology. It is a function of confining stress, controls pore water distribution, and influences soft rock strength. This research studies the permeability of soft rock. A hollow cylindrical torsional shear device was developed and a series of permeability tests were performed in this device as well as triaxial cell. The skill of coring hollow cylindrical specimen are also discussed. This study includes : (1) the anisotropic permeability of soft rock; (2)the effect of confining pressure upon permeability; (3)the change of permeability during shearing. Results show that there exists anisotropic permeability in soft rock, especially for sandstone stratified mudstone and/or shale. The ratio of horizontal permeability coefficient (flow direction is parallel to the strata, kh) to vertical permeability coefficient (flow direction is perpendicular to the strata, kv) is 10 to 100. The kh and kv decreased, while confining pressure increased. The anisotropic of permeability is increasing with confining pressure. The coefficient of permeability is increasing with shear strain and a obviously raise occurs in the post peak stage of stress strain curve.
