Shape ratio effects on the mechanical characteristics of rectangular prism rocks and isolated pillars under uniaxial compression

Isolated pillars in underground mines are subjected to uniaxial stress,and the load bearing cross-section of pillars is commonly rectangularly shaped.In addition,the uniaxial compression test(UCT)is widely used for determining the basic mechanical properties of rocks and revealing the mechanism of isolated pillar disasters under unidimensional stress.The shape effects of rock mechanical properties under uniaxial compression are mainly quantitatively reflected in the specific shape ratios of rocks.Therefore,it is necessary to study the detailed shape ratio effects on the mechanical properties of rectangular prism rock specimens and isolated pillars under uniaxial compressive stress.In this study,granite,marble and sandstone rectangular prism specimens with various height to width ratios(r)and width to thickness ratios(u)were prepared and tested.The study results show that r and u have a great influence on the bearing ability of rocks,and thin or high rocks have lower uniaxial compressive strength.Reducing the level of r can enhance the u effect on the strength of rocks,and increasing the level of u can enhance the r effect on the strength of rocks.The lateral strain on the thickness side of the rock specimen is larger than that on the width side,which implies that crack growth occurs easily on the thickness side.Considering r and u,a novel strength prediction model of isolated pillars was proposed based on the testing results,and the prediction model was used for the safety assessment of 179 isolated pillars in the Xianglu Mountain Tungsten Mine.

Control of coal and gas outbursts in Huainan mines in China： A review

An investigation was conducted on the overall burst-instability of isolated coal pillars by means of the possibility index diagnosis method（PIDM）. First, the abutment pressure calculation model of the gob in side direction was established to derive the abutment pressure distribution curve of the isolated coal pillar. Second, the overall burst-instability ratio of the isolated coal pillars was defined. Finally, the PIDM was utilized to judge the possibility of overall burst-instability and recoverability of isolated coal pillars.The results show that an overall burst-instability may occur due to a large gob width or a small pillar width. If the width of the isolated coal pillar is not large enough, the shallow coal seam will be damaged at first, and then the high abutment pressure will be transferred to the deep coal seam, which may cause an overall burst-instability accident. This approach can be adopted to design widths of gobs and isolated coal pillars and to evaluate whether an existing isolated coal pillar is recoverable in skip-mining mines.

Primary study on the ＂θ＂ letter type overlying multi-strata spatial structure of mining face surrounded by mined areas

The overlying strata spatial structure academic viewpoint thinks the primary factor which controls the stope presses is the overlying strata spatial structure movement; the spatial structure above the later period coal pillar surrounded by mined areas is the most complex overlying strata spatial structure and study on its evolution law has the important realistic project significance for strata movement control and production safety. The existing research results indicate that the special structure of the first working face of the mine begins to develop lengthways from stratum movement above mined areas and extends level in the exploitation direction. From existing overlying strata spatial structure fundamental research achievement, the spatial structure above the later period coal column surrounded by mined areas have following characteristic： The spatial structure formation is from the top to the lower and from large to small. According to the findings, a formula with the use of rock layer migration angle delta was put forward to estimate isolated island coal column width on which different stratum structure is gonging to form.