Effects of Sampling Disturbance on the Mechanical Properties of Poorly Cemented Sandstone

• Main Authors: Chung-Yi Lin, 林忠義
• Other Authors: Jyh Jong Liao
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/97806044043768431831

碩士 === 國立交通大學 === 土木工程系 === 87 === Due to the poor lithification of soft rocks, the drilling cores obtained from rock triple tubes are easily disturbed. The mechanical properties determined from the disturbed specimens are incorrect and can not be adopted for engineering design. In order to drill reasonable undisturbed cores and investigate the effect of sampling disturbance on the mechanical properties of poorly cemented sandstone, a modified core tube is developed and a series of in situ tests is conducted in this thesis.The inner tube (two pieces of thin steel half-hollow cylinders) of an extensible triple core tube is replaced by a thin plastic hollow cylinder. The modified tube was adopted for sampling at the site of the second reservoir of Bao-San, Hsinchu. The strata are composed of sandstone, mudstone, shale, and their interbeds. The sandstone is poorly cemented. Using the modified tube, the quality of drilling core are improved and the average core recovery is higher than 90 %.In situ tests includes Lugeon tests using a single packer and P and S wave velocity measurements using a suspension PS logging system. Lugeon tests aim to determine the field hydraulic conductivity of rocks. The suspension PS system is adopted for measuring the P and S wave velocity in a borehole. To evaluate the effect of sampling disturbance on the mechanical properties of the sandstone, both of the test results are employed for comparing with the results determined from core specimens in the NCTU laboratory. In general, the value of hydraulic conductivity determined from laboratory is approximately equal to that from fields where the discontinuities (bedding planes and joints) in test sections are not clear. However, for the rock at test section with clear discontinuities, the field conductivity is larger than the laboratory conductivity. This evidence indicates that the hydraulic conductivity is strongly influenced by the existence of discontinuities and the core specimens are undisturbed using the modified tube. The similar trend is obtained from the results of measured velocity from field and laboratory.