軟弱岩石孔內試驗儀器之研發

Abstract

台灣中北部麓山帶地區出露之地層多屬極軟弱年輕之砂岩層普遍具有固結差，膠結不良之特性。岩層取樣過程對岩樣本身之組織構造可能已造成破壞。而且軟弱岩石中或多或少存在有缺陷，如裂縫、互層與節理等。理想的現地力學試驗應該可以量測缺陷對整個岩體的影響，而且可避免取樣擾動之問題。但傳統之現地試驗需要使用大型儀器，費用昂貴，而且亦有其缺點。本研究試圖研發一套中型系統，稱為多功能孔內試驗儀，其可施作鑽孔千斤頂試驗、鑽孔剪力試驗、及孔底平板載重試驗。經由這些試驗可決定軟弱岩石之現地橫向與縱向的應力-應變-強度之關係，並且能夠感應到岩石中缺陷或互層的影響。多功能孔內試驗儀根據可回收式試驗裝置之概念，再加上Goodman千斤頂儀之構想，使其功能更多。本系統主要單元由一個四片橫向填充板與縱向平板千斤頂兩個單元所組成，橫向填充板在上，縱向平板千斤頂在下。目前多功能孔內試驗儀已經組裝完成，並且完成系統標定之程序，其結果顯示該系統之壓力勁度低，高壓下體積偏差量小。惟因鑽探之孔徑過大，無法施作現地試驗。本論文敘述台灣軟弱岩石之特性、目前適用於軟弱岩石之現地試驗儀器的介紹、以及多功能孔內試驗儀的設計理念、儀器系統、標定程序與其結果、以及初步規畫之試驗流程。

The outcrops in the central and northern regions of Western Taiwan often contain weak, poorly cemented and young rock formations. The typical rock coring process has a tendency to damage the structure that originally existed in situ. Soft rocks are likely to contain defects, such as fissures, bedding and joints. An ideal in situ test method should be able to reflect the effects of these defects on the behavior of the rock mass that is tested. The existing field testing methods for soft rocks often involve large pieces of equipment and are costly to perform. The main objective of this research is to develop a medium sized, versatile in situ testing device specifically for soft rock. The new device, referred to as the multiple-purpose Borehole Testing Device (BTD), is capable of performing lateral jacking test, direct shear test and plate bearing test at the bottom of a borehole. The radial and longitudinal stress-strain relationships can be determined simultaneously using the new device. The design of this new device follows the concept of a "retrievable rig" plus the capability equivalent to a Goodman jack. The new equipment consists of four radial filler plates at the top and a circular bearing plate that moves in the longitudinal direction at the bottom. The design and fabrication of the new BTD have been completed. Preliminary instrument calibration tests have indicated that the device had a low compliance and the possibilities of error in volumetric strain measurement under high stress were low. This thesis gives a brief background of the soft rock in Taiwan and existing technologies in characterizing soft rock in situ. Details of the design concept, functions and calibration performance of the various components of the new BTD are described.