脆性岩石受載損壞與聲射特性之探討

Abstract

脆性岩石在受載的過程中，當荷載逐漸增高，將造成微裂縫的生成與擴展 ，並伴隨聲射現象的發生。隨著荷載的繼續進行，裂縫間終究將相互連接 成一主要裂面(即巨觀裂面)，最後導致崩潰破壞。本研究以聲射量測技術 監測岩石單 軸壓縮試驗之進行，並將擷取的聲射資料加以分析。經試驗 結果之分析，得到以下之結論 ： 1.凱撒效應(Kaisereffect)在較低的應 力時成立；在較高之應力時，凱撒效應不明顯，而呈現 felicity現象。 2.將脆性岩石加壓至某一應力(本研究為單軸壓縮強度之74%∼84%)後解壓 ，靜置相當時間後再壓，凱撒效應不再明顯，顯示聲射的復原性。 3.軸 向應變速率在開始加壓時最大，隨著荷重的增加而逐漸減少至定 率在加 壓初期約為定值(即應變呈線性增加)，直到聲射發生率明顯上升時，側向 應變速率隨之明顯增加。 4.以Walsh的損壞模式配合聲射累計估計損壞參 數推算岩石之應力-應變曲線，與實測應力 -應變曲線之前段較為相符， 而後段則有出入。 The microfractures in a brittle rock may expand when the material is subjected to loading. Microfracturing process in a material results in energy dissippation and acoustic emission. The gradual loss of integrity due to microfracturing is also the cause of material damage due to loading. This thesis investigate the damaging process and the acoustic emissionof brittle rocks subjected to various loading conditions. Uniaxial tests with acoustic emission measurement on brittle rocks quartzite and marble) were performed. Conclusions were drawn from as follows: (1) For the samples used in the study, the Kaiser effect is valid for stress level lower than 60% of the peak strength. (2) Acoustic emission tends to recover if the time interval between unloading and reloading is long and the loading high enough. (3) Duing stress-controlled uniaxial compression, axial strain rate gradually reduced to a constant. The lateral rate remains constant in the early stage of loading, but increases significantly when the hit rate of acoustic rises. (4) Back calculation of the stress-strain curves of unixail compression tests based on the Walsh's damaging model fromacoustic emission measurement data was attempted. The and the measured results agree satisfactorily only in the pre-prak range of stress-strain curve.