| Summary: | 碩士 === 國立交通大學 === 土木工程系 === 87 === The permeability of weak rock depends on the grain characteristics, pores, cementation, and saturation of material. In this study, a device of constant-flow permeability test was built up for correctly determining the true permeability of weak rock specimen. In the test, a constant-flow pump is developed to control a constant flow through a specimen in a triaxial cell. The head difference between two ends of the specimen is measured. Then, the permeability of the specimen is calculated on the basis of the Darcy''s law. The developed device is able to control the confining pressure and the back-pressure of a specimen; hence, the saturation of specimen can be examined by checking the B value. A series of constant-flow permeability tests on samples of weak sandstone from Ta-kang, Taichung and from Bau-san, Hsinchu were carried out and compared with the in-situ permeability test. The permeability of Ta-kang sandstone lies within 2.9 ×10-5~8.3 ×10-5cm/s. The permeability of Bau-san sandstone lies within 2.7 ×10-4~3.2 ×10-4cm/s, which is found closely consistent with the result from the in-situ lugeon test.
Weak sandstone usually will degrade when it is exposed to unfavorable environmental conditions. The degradation of weak sandstone may results in the reduction in its strength and deformability. This study also attempts to investigate the microstructure change of weak sandstone after the degradation due to seepage through the material. By comparing the microstructure of sample before and after the degradation due to seepage, it was found that the void of sandstone increases significantly after degradation. On the basis of microscopic observation, the reason is possibly due to an increase of void near the grain-matrix interface in the material and/or the dissolution of the cementation/matrix.
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