DETERMINATION OF IN SITU STRESS IN ROCK MASS BY OVERCORING METHOD
由於工程建設的推動，各種地下開挖工程日益普遍，其中現場地應力之大小、方向分佈狀態，以及岩層開挖後應力重新分佈之情況，對地下開挖工程的品質及安全穩定均有極重要立影響。因而本研究乃挑選套鑽法中之USBM法（Overcoring USBM Type Method）來進行對現地應力及變形之量測研究，並以花蓮聯峯石礦場地下坑室做為實際量測研究地點﹔其中包括三個鑽孔之套鑽實驗、雙軸試驗、Factor校正、以及理論地應力分析、量側面應力狀態分析、三維空間主應力分佈計算等。
Based on the 6-years planning of the National Construction, many of the large scale underground engineering projects are developed step by step during the past few years, such as the underground free way tunnels, railway tunnels and the underground stope mining etc. The essential problems for these projects which, affecting the quality and safety concern of underground engineering are the in-situ field stress conditions, such as the magnitude, direction and the redistribution of the field stresses during excavation. The investigation of the in-situ field stress conditions of the underground engineering construction is the first considerations for solving the above problems.
The overcoring tests, using the whole set of the USBM deformation gauges for measuring the magnitude and the directions of the max. and min. principal field stresses, were carried out in the under ground stopes of the Lien-Foung Dolomite mines and the 3-D principal stresses were also analyzed from the data of overcoring tests using the matrix method.
Hydraulic fracturing technique is one of the most widely acceptedin-situ stress determination method in rock strata. The methodutilizes the measurement of pressure required to initiate andreopen fractures in a sealed section of a borehole and theimpression taking of the fracturing plane to determine the magnitudesand orientation of the in -situ rock stresses.
This paper describes the first application of the method inTaiwan in the in-situ stress measurement along Pinglin tunnelalignment. It discusses the equipments, testing procedure, testresults and their inter pretations. The results show that the ratiosof maximum and minimum horizontal stresses to the overburden stressare about 1.1 and 0.6 in average, and the bearing of themaximum horizontal stress is about N30。E. These were found to bein agreement with the results estimated by using theoretical studyand tectonic evidences.
Ground water level has a great impact on the slope stability and land subsidence. We can establish observation wells or piezometers on site to record the variation of ground water level, the number of wells and the distribution and depth for placing observation wells are dependant upon local hydrogeology, topography and engineering requirements. Hydraulic conductivity that represent the ease of flow in the rock is an important consideration for site drainage, seepage, environment protection, and improvement of geologic conditions. The value of hydraulic conductivity for geologic materials varies over a wide range. Currently field test is the most reliable measurement method. Because the applicability of slug test, single-well recovery test, multiple-well pumping test or open hole testvaries with field conditions and engineering requirements , it is essential to evaluate these conditions prior to the field measurement.
The properties of rock mass and in-situ stresses are important parameters for tunnel design. In engineering practice, the underground openings can be considered as large-scale in-situ tests. In this paper, a back-analysis method based on the measured displacements during excavations of pilots or tunnels is introduced to estimate these parameters. The basic concept, analysis procedure, advantages and limitations of the back-analysis method in tunnelling are also described. Three examples of tunnels in central Taiwan are presented to show the efficiency and applicablility of the back-analysis method for estimating the field parameters of rock mass.
The fracture patterns of engineering material are introduced in this paper, including ductile fracture, brittle fracture and rupture. This paper focuses on the fracture of brittle material and the features of the fracture surface, so called fractography. Fractography reveals a lot of useful information such as fracture origin, trace of crack front, development of cracks and associated stress conditions such as opening mode, sliding mode or tearing mode.
Applications of fractography in identifying crack origin and mechanism of fracture to Brazilian tests, uniaxial compression tests, deep penetration and crack coalescence, are presented to demonstrate how information of fractography can be used to identify fracture history.
Tectonofractography is a new branch of tectonophysics, which provides useful information regarding fracture history and mechanism of rock fracture, based on the fractographical features. This paper aims at introducing tectonofractography and its application to site investigation for engineers.
Historical review on the development of tectonofractography is first presented in this paper, followed by introducing basic morphologies of rock fracture, to establish basic understanding of this disci pline to the readers. The application of tectonofractography to site investigation is then presented through three practical cases. With more understanding about tectonofractography, the engineers can thus gain more information- from site investigation.
The properties and behaviors of the rock mass are greatly affected by the existence of discontinuities. In order to promote the quality of rock engineering and enhance its safety, it is necessary to systematically define and describe the characteristics of discontinuities. Based on the suggested methods from International Society of Rock Mechanics (ISRM), this paper provides currently description and evaluation of rock discontinuity characterization techniques with quality and quantity analysis. In this manner the reader will not only see innovative developments but will also be provided with a review of many currently discontinuties characterization techniques. So far, quantitative methods with objective and specific for characteristic parameters of discontinuities except the term of filling have been established.