The High Insitu Stress Measurement And The Design Of The Pillar Size

With the rapid development of globalization, the demand of natural resources of every country increases continuously. Nowadays, many energy extraction have entered into the state of deep mining at home and abroad, however, the "three high" problem (high geological stress, high temperature and high water-pressure) usually occurred when in deep work. In this process, a series of problems caused by high geological stress are emerging. So, the study of the setting and the stability of the pillar become particularly important.In some cases, techniques like inelastic strain recovery, acoustic emission, hydraulic fracturing and rock core disking are unsuitable for high geological stress detection. Among the alternatives, core disking appears to be the most effective and traditional approach. Rock core disking judges the magnitude and the direction of geological stress by the caking form and the extent of the extracted rock core. In order to get a more intuitive understanding that the rock core discing is an effective method to measure the high geological stress, this paper reproduced the rock core disking of different stress combinations by numerical simulation, and also analysed the causes of its formation. The results showed that:(1) When the in-situ stress exceeded a certain value, rock core disking occurred. (2) Radial stress (horizontal stress) was the main factors that influenced the rock core disking, while the axial stress (vertical stress) just made the core surface produce local failure. (3) At the same radial stress, rock core disking gradually weakened with the increase of axial stress. At the same axial stress, rock core disking was becoming increasingly obvious with the increase of the radial stress. (4) By rock core discing, the formula of Hou scholars was verified rationality. This method can not only simulate the process of rock core discing, but also help us understand the stress transformation process, providing a reliable theoretical basis for judging the magnitude and the direction of the geological stress by rock core discing phenomenon.Based on the fully understanding of the rock core discing process and also its formation mechanism under high geological stress, we set five pillar size to study the size design of the mine pillar under high geological stress. This paper designed different aspect ratio:0.5,1.0,1.5, 2.0,2.5,5; different angle of pillar model:0°,10°,20°,30°,40°; different lateral pressure coefficients:0.5,1.0,1.5,2.0 to simulate the different geological stress level. This paper tried to find out the instability law through the simulation of these models, so as to provide the basis for the design of pillar size. The simulation results show that:(1) With the increase of the pillar size aspect ratio, pillar failure mode changed from tensile stress failure to compress shearing failure. Therefore, the pillar size should be increased in the actual pillar size design. (2) The angle between σl and orebody was an important factor in pillar rock bursts, and the inclination of the pillar should be minimized in the actual pillar design. (3) As the maximum stress distributed asymmetrically, with the pillar corner playing a supporting role, therefore, the empirical formulas were not applicable for determining the average stress of the pillar. (4) The stress accumulation started to build up at the pillar edges and when the stress accumulation reached the bearing capacity of the pillar, the pillar edge damage occurred, the stress released and shift toward the pillar core, eventually, lead to the overall instability of the pillar. The results of this simulation will provide theoretical basis and references for the pillar size design under high geological stress.