軟岩強度尺寸效應與現地邊坡誘發破壞試驗

Abstract

軟弱岩石之強度界於一般硬岩與土壤之間，為瞭解此等軟弱岩石之力學特性，以低擾動完整試體進行室內力學實驗為必然手段。為降低擾動影響，本研究先以泡沫取代鑽探水取樣獲得一批低擾動的NX及HX尺寸之完整軟岩試體，繼而利用特別為軟岩開發之三軸力學試驗裝置，進行一系列壓密不排水三軸試驗，以探討軟岩之強度尺寸效應問題。由比較不同尺寸軟岩試體之強度差異，若取樣試體的完整性均類似，較大試體相對於較小試體其強度略低，顯示軟岩強度略受尺寸效應之影響。推論其原因，可能歸因於較大的試體相對於小試體存在相對較多的微裂縫，因而使其強度會略低於較小的試體。 除探討軟岩之強度尺寸效應問題，本研究亦探討軟岩邊坡產生漸進式破壞之破壞機制及其過程。本研究引用了交大防災中心於人工開挖大型試坑內所進行之邊坡誘發破壞試驗，做為漸進式破壞之模擬對象。本研究考慮軟岩應變軟化行為，嘗試利用FLAC程式來定性模擬軟岩邊坡於不同加載階段發生漸進式破壞之發展過程。由研究結果顯示，軟岩邊坡漸進式破壞源於邊坡內部先有局部破壞，出現局部張力或塑性降伏區，局部降伏區域之應力產生釋放或轉移，使其附近區域岩體應力進一步重新調整，而造成張力或塑性降伏區域逐漸擴大，並互相延伸相連而使邊坡破壞面擴大。綜而言之，軟岩邊坡漸進式破壞的機制衍生於連續發展之應力調整所伴生之位移與降伏區域之發展。

This research aims to study the size effect of the strength of soft rock and to model the progressive slope failure in soft rock formation. Undisturbed NX and HX size specimens were obtained for laboratory tests. A series of CU triaxial tests were carried out using a triaxial test device specially designed for soft rock. From test results, it appeared that the strength of a larger specimen is relatively lower than a smaller one. The existence of relatively more micro-fissures contained in a larger specimen may be responsible for the size effect. This research also attempted to study progressive slope failure in soft rock formation. The results of a field experiment of induced slope failure carried out by the Natural Hazard Mitigation Research Center, National Chiao-Tung University were adopted for modeling the progressive slope failure. Numerical simulation made use of the commercial code FLAC was carried out to model the field tests. The numerical model took into the strain-softening mechanism of soft rock into account. It was found that the progressive slope failure would initialize at certain tensile and shear yielding zones; the yielding zones tended to expand as a result of stress redistribution. It was demonstrated that the numerical simulation presented in this research could reasonably modeled the process and mechanism of the progressive failure of soft rock slope.