| Knowledge of the in situ state of stress in the Earth's crust is very important in many problems dealing with rocks in geology, geophysics, as well as civil and mining. In civil and mining engineering, the characteristic of in situ rock stress has potent influence on the failure and deformation behavior around openings and also control the distribution and magnitude of the stresses around underground openings such as mines, shafts and tunnels. As the depth and scale of underground structures tend to increase recently, its importance is getting more attention. The overstressed condition may induce progressive and brittle failures such as spalling, slabbing and rock bursting. In foreign countries, a lot of researches on in situ rock stress have been carried out by in situ tests and data analyses. From them, many empirical and theoretical formulate have been proposed to accurately estimate the initial rock stress such as Korea. In China, on the contrary, a few studies on rock stress have been carried out but their results do not provide with detailed information of the initial rock stress.In this study, the study area was Chuncheon-Yanggu region, the east-north part of Kyeonggi Massif in Korea where most of the study areas are high and rugged mountainous region. The characteristics of initial rock stress there were studied using more than thirty-five field stress measurements in fifteen vertical boreholes were conducted at the depth from 20m to 320m of in situ hydraulic fracturing method test with the help of Geogeny consultants group 1nc.Based on the test data set, it introduces the whole procedure of hydraulic fracturing measurement method, field hydraulic fracturing test system, the technique of geophysical imaging technique and test data analysis to obtain critical pressure parameters from the pressure time records.Based on the measurement data, the main purpose of the study area was that one was to investigate the characteristics of the regional stress state of the target region and the other was to evaluate the potential possibility of stress induced brittle failures at the future excavation work. The study results revealed that the different initial rock stresses had formed with the formation rock type. For the depth less than 320m, the stress ratio (K) had a tendency to decrease and stabilize with the depth. The average orientation of all SH data was approximately 790 from the north (N790E).Based on the collection analyses of predecessors', on the field investigation about the rock mechanics characteristic, the initial stress field, deep architectonic, indoor test analyses as well as analog calculation and field condition, to know the stress and strained condition under different kinds of behavior situation, analysis rock mass engineering failure mechanism in order to direct the construction on the security transport operation, supplying necessary engineering data and holding the engineering work safely.The keynote of this research has three aspects:the first one is to appraise the geologic environment condition of the tunneling region based on the geologic survey of project site; the second one is to determine the relevant parameters and process the data coming from the hydraulic fracturing method; the last one is between the method of determining the initial stress under the measurement of hydraulic fracturing and the analytical procedure of indoor test, using the numerical simulation software to make the simulating in order to research the rock wall's variation under different kinds of stress ratio K and rock types to demonstrate the rationality and feasibility of the tunnel supporting. |
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