鹿場部落崩積併構土之力學特性

Abstract

地質材料常可見非常不均質的混合體，例如混同層(Melange)、斷層帶的岩石/剪裂帶的岩石、礫岩、崩積層、及火山岩等等。此等岩石常由較強硬的塊體被較軟弱的基質材料包圍所組成，被稱為併構岩bimrocks (block-in-matrix rocks)或併構土，其力學性質極不易評估，國內外研究成果亦有限。本研究以鹿場部落崩積層為標的，利用鑽探結果探討崩積層的組成，及鑽探岩心以實驗室三軸試驗及單壓試驗探討崩積併構土的成岩特性、滲透性、剪力強度等。 試驗前利用表面掃描儀分析結果計算岩塊表面積來預估岩塊體積比，以及了解岩塊分布對破壞形式影響。本研究由崩積併構試體的三軸壓密不排水試驗之壓密排水階段計算試體滲透係數，結果顯示滲透係數介於10^(-6)到10^(-7)(cm/s)，滲透性極差，屬於半透水至不透水材料。利用土壤孔隙與A, B值得關係式，由三軸試驗材料破壞時的孔隙水壓，估算試體的A 值約介於0.1-0.2間，屬夯實黏土礫石，壓密程度低，顯示鹿場崩積層尚處成岩作用中，應為年經崩坍堆積物。三軸試驗結果顯示併構土軸差強度隨岩塊比增加而有上升之趨勢，而由試體破壞形式發現：破壞面為沿著岩塊間發展，並不通過岩塊。高岩塊含量試體使破壞面蜿蜒並造成岩塊互相接觸摩擦，可能提高強度。最後本研究提出以不同岩塊比、不同圍壓下三軸試驗決定特定岩塊比併構土參數之方法，以鹿場崩積併構土岩塊比40%為例，本研究試驗結果估算的強度參數c = 38.59 kPa、ψ= 26.32 ⁰。

Geological materials such as mélanges, fault rocks, coarse pyroclastic rocks, and colluvial deposits are usually considered as inhomogeneous mixtures. The materials, which are chaotic, mechanically and spatially heterogeneous rock masses are composed of relatively strong rock blocks surrounded by weaker matrix. These rock mixtures, known as bimrocks (block-in-matrix-rocks) or bimsoils (when the matrix material is soil-like), are very difficult to evaluate their mechanical parameters. This thesis selects the Luchang colluvial deposits as an example to investigate the mechanical behavior of the colluvial deposits from drilling cores. Then, a series of consolidated, undrained triaxial compression tests is conducted on the core specimens of colluvial deposits to explore the hydrological and mechanical behavior. Then take the bimsoil specimens of cores for triaxial test to study the mechanical characteristic (e.g., diagenesis, permeability, and shear strength). In this research, a rotated scanning machine is adopted for determining the volumetric block ration from the measured surface block ration of the bimsoil . Then, one can reasonably interpret the failure modes of core specimens in uni-axial or tri-axial compression from the obtained distribution of blocks in the specimens. The thesis estimates the hydraulic conductivity of the core specimens from the consolidation-drain step of triaxial tests. The results show that the conductivity of the bimsoil specimen are between10-6 and 10-7(cm/s), From the pore pressure developed at failure under tri-axial compression, we can calculate the pore pressure parameter A and decide the degree of consolidation of the specimen. The results of parameter A are 0.1-0.2 and indicate the degree of consolidation of bimsoil being low. The results of triaxial tests reflect the facts that the tri-axial compression strength of the specimens increases with the increase of the volumetric block ratio. After observing broken specimens, it is found that failure surfaces of cores are tortuously around the blocks. Since the area of failure surface increases with the increase of the volumetric block proportion, the triaxial compression strength is positively proportional to the proportion. Based on the results of triaxial test with vary confining pressure and block proportion, a new approach is proposed for determining the shear strength parameters c and ψfor different block ratio. For example, c = 38.59 kPa、ψ= 26.32 ⁰ is determined based on the approach.