제주도 표선리 현무암의 역학적 특성 및 강도에 관한 연구

Abstract

Recently, as the scale of national and international construction has become bigger and also as Jeju island is named as Jeju Special Self-Governing Province, it is inevitable to build large scaled public works for it to be reborn as a free international city in the world. And also with the gathering of population into Jeju city, there will be enlargement of dwelling site and business area, so that skyscrapers will be built and the underground space will be used. As the city is enlarged, the skyscrapers will gradually go upward to the mount. Then it is expected of large scaled public works, big building structures, underground structures, and high earth cut slope therefore there will be a demand for study about earth foundation. At present in the case of Jeju, the study about soil is vivid, but it is not sufficient about rock mass. Therefore it needs mechanical data about basalt, the volcanic rocks, and other various data about engineering trait of the rock mass. So this study researched the physical and mechanical traits of Pyoseonri basalt(the Acicular Feldspar Olivine Basalt; FOB), Trachybasalt, and Scoria and then implemented absorption test, bulk specific gravity test, permeability test, and strength test to see their influence on strength, and at last analysed the failure criterion on rock mass. The result of this study is as following. The basic physical traits of the three intact rock are as the following Table 4.1∼3. As the bulk specific gravity is higher, it showed the tendency of decreased absorption and permeability, and the tensile strength showed as much as 1/9∼1/18 of compressive strength. It showed a little difference between anticipated strength from schmidt hammer test and the real strength from uniaxial compression test, and there were more errors in high strength given intact rock. Therefore I expressed them in exponential function as the following. ,σ_(pre) = a·e^(b·R), a and b are variables accordant to the kinds of intact rocks and are suggested as following. The strength of intact rock is dependant upon various elements but this study took the strength test according to loading speed, anisotropy of the intact rocks, and water content. The result showed a tendency of that the more loading speed is fast, the more they are closing to horizontal or vertical direction, and the less they have water content, the higher is the strength. It showed different result on the failure criterion of rock mass according to each of them. While the failure criterion of Hoek-Brown evaluates cohesion much lower than that of Mohr-Coulomb, it evaluates higher in the aspect of internal friction angle and the failure criterion of Lade evaluates both cohesion and internal friction higher than that of Mohr-Coulomb. As there are different results according to the failure criterion, it needs thoughtful decision to select failure criterion of rock mass.