軟弱岩石之應力應變行為

Abstract

軟弱岩石之力學特性介於土壤與岩石間，故無法完全採用土壤或岩石力學之實驗設備加以求得。為了能夠進一步瞭解台灣中北部麓山帶地區出露之『極軟弱至軟弱』岩石之力學行為，本研究使用適用於此類材料之三軸試驗裝置。此裝置之試驗能量在一般硬岩與土壤三軸試驗儀器之間，以充分滿足軟弱岩石試驗之需求，並具有飽和試體及量測孔隙水壓之裝置。三軸試體之變形採用三軸室內局部應變以及傳統三軸室外之變形量測，可以量得微應變下試體之線彈性乃至於大應變下材料之屈服行為。 本儀器系統採用局部應變量測之設計，先前學者指出軟岩在應變小於0.01%時，變形性是線性、彈性、與應變速率無關，只與壓密應力有關，此範圍內之楊氏模數 (Young’s modulus) 稱為Emax。三軸室壓與軸向壓力可以用電腦做伺服控制，以進行應力歷史控制之試驗。本研究使用此一試驗裝置對所取得之軟弱岩石試體進行了一系列之壓密不排水，應力歷史控制三軸試驗。 由研究結果顯示，三個研究地區所取得之室內三軸試體受剪時易產生高額孔隙水壓，三軸試驗中在小應變下確實呈現線彈性之行為，且隨著有效圍壓的增加，其線彈性行為會逐漸降低，隨應變量繼續增大，則顯現出非線性變形，其楊氏模數會有遞減情形發生。

The mechanical properties of soft rock are between soil and rock, It is not easy to determine these properties using the conventional soil or rock testing equipment. In order to enhance our understanding of the outcrops of very weak and young rock formations in the central and northern regions of Western Taiwan, the objective of this research projectis to use a triaxial device specifically for soft rocks. To fully fulfill its requirements, the capacity of this soft rock triaxial device lies between those designed for hard rocks and soils. The triaxial cell was equipped with local strain measurement devices and traditional external strain measurement devices capable of monitoring strains less than 0.0001 %, so that the behavior of soft rock from small strain, linear elastic state to yielding could all be observed. The axial and cell pressure could be servo-controlled independently to enable stress path controlled tests to be performed. A series of consolidated undrained, stress path controlled triaxial tests have been conducted using this test device. From the results, it shows the triaxial test speciments from three sites when sheared, the higher pore water pressure will be generated. The results also illustrated the linear elastic behavior of the soft rock during the small strain triaxial tests, and when effect confine pressure increase the linear elastic behavior decrease. As strain increasing, it shows the non-linear strain, and the Young’s module will decrease