三軸狀態下硬頁岩之超音波特性

Abstract

本研究利用超音波量測橫向等向性岩石受三軸狀態下波傳速度的變化，並根據異向性波傳 理論，求得動彈性模數的變化，以探討其動態力學行為與受力下岩石之破裂關係。實驗的 結果顯示三軸應力狀態下（靜水壓及加軸差應力），材料分子結構因應力趨於緊密或鬆散 ，是主要影響動彈性係數變化的因素。此外探討試體傾角與量測之周角對波速和動彈性係 數的關係，目的是為了減低實驗上量測的誤差，以求得合理之動彈性常數。因此應用最佳 化方法，提出一套具體可行的實驗及分析流程，以確保利用一個圓柱且具任意傾角之橫向 等向性岩石試體，求取五個動彈性常數方法之合理與準確性。另外在三軸狀態下，於靜水 壓階段，因試體孔隙閉合，波速和動彈性係數隨圍壓增加而漸增，而加軸差應力(s1/s3 = 1~2 )的過程中，波速和動彈性係數的變化趨於平緩，其原因是岩石進入線彈性階段，動 彈性係數漸趨於一致。而所測得的波幅，則隨圍壓增加而漸減，代表岩石受壓下微裂縫逐 漸地形成。 In order to investigate the fracture behavior and the characteristic of sonic velocity of argillite specimens under triaxial compression , a series of triaxial compression tests were conducted . The experimental results reflect the fact that the influence of the applied stress is stronger than the closing of the fissures or the development of new cracks on the variation of sonic velocity of specimens . Based on the proposed method developed by Liao et al., the five dynamic elastic constants under uniaxial or triaxial compression were obtained using a single cylindrical specimen of argillites with inclined dip angle . Also, a mathematical optimization was adopted successfully for data reduction from the experimental data.The results of triaxial compression tests also show that the magnitude of sonic velocities and dynamic elastic constants increases with the increase of the confining pressure during hydraulic compression. However, the variation of those is little while the specimens are loaded in deviator condition with (( 1/(3=1-2) . This is because the rock is linear elastic under the condition.