锚杆支护围岩附加压应力场空间分布规律研究与应用

Research and application of spatial distribution law of additional compressive stress field in surrounding rock of bolt support

  • 摘要: 煤巷锚杆支护已得到广泛应用,锚杆支护作用于围岩内的附加压应力场大小与空间分布范围是量化支护参数、优化支护方案的关键。为研究锚杆(索)相关参数对围岩附加压应力场空间三维分布影响规律,从理论方面分析了锚杆作用下围岩所受托锚力和黏锚力产生附加压应力机制,建立了围岩附加压应力模型,空间表征了附加压应力场分布特征,进一步通过模拟与理论对比,验证了模型的正确性;以围岩附加压应力≥0.02 MPa为基准,量化研究了锚杆(索)支护关键参数即锚杆(索)预紧力、长度和锚固长度对围岩附加压应力场空间分布的形态、最大扩散半径、高度(间距)及体积的影响。锚杆支护下随着预紧力增大,空间附加压应力场分布形态由竖向“椭球体”发展为横向“椭球体”;锚杆长度增加,形态从近似“椭球体”变成“葫芦型”;锚固长度增大,形态从“葫芦型”变成近似“椭球体”。随着锚杆预紧力和长度增加,锚杆支护产生的附加压应力场的半径、高度及体积增大,而锚固长度对附加压应力场影响相反。锚索支护下随着锚索长度增加,围岩附加压应力场的空间分布形态从近似“椭球体”变成“葫芦型”,当锚索长度超过5 m时,变成间断的上下2个“椭球体”且上小下大,即使预紧力和锚固长度增加,分布形态没有明显变化。随着锚索预紧力增加,锚索支护所形成的围岩附加压应力场的最大半径增加,体积增加,上下压应力场间距减少;随着锚索长度增加,围岩附加压应力场高度增加,随后间断成上下2个压应力场,其间距不断增大,半径及压应力场体积先增加后减少;随着锚索锚固长度的增加,围岩附加压应力场间距逐渐减小,半径先增加后减少,体积增加不明显。进一步分析了锚杆(索)组合支护下围岩高/低附加压应力对巷道顶板的作用,结合组合梁及悬吊理论的部分理念,确定了高/低阈值计算公式,通过对比围岩附加压应力场体积大小来确定锚杆支护方案优劣。以葫芦素煤矿21204工作面回风巷和城郊煤矿LW21106工作面运输巷为验证对象,分析了原/新支护方案特点,计算得到2条典型巷道围岩附加压应力场的高/低应力阈值及其在顶板覆盖的总体积。结果显示优化后方案锚杆(索)能在顶板形成有效连续的围岩附加压应力场,高/低压应力场体积均增加显著,围岩变形得到有效控制。

     

    Abstract: The application of coal mine roadway bolt support has been widely adopted. The additional stress field due to the support action of the bolts on the surrounding rock is crucial for quantifying support parameters and optimizing support schemes. In order to study the influence of bolt (cable) related parameters on the spatial three-dimensional distribution of the additional compressive stress field of the surrounding rock, the mechanism of the additional compressive stress generated by the entrusted anchor force and the sticking anchor force of the surrounding rock under the action of the bolt was analyzed theoretically, and the additional compressive stress model of the surrounding rock was established, and the distribution characteristics of the additional compressive stress field were spatially characterized. Further, the correctness of the model is verified through simulations and theoretical comparisons. Using an additional stress threshold of ≥0.02 MPa in surrounding rock as a baseline, the research quantifies the key parameters of bolt (cable) support, namely, pre-tensioning force, length, and anchorage length, and their effects on the spatial distribution form, maximum diffusion radius, height (spacing), and volume of the additional stress field in surrounding rock. Under bolt support, as the pre-tensioning force increases, the distribution pattern of the spatial additional stress field transforms from a vertical “ellipsoid” to a horizontal “ellipsoid”. When the bolt length increases, the shape changes from an approximate “ellipsoid” to a “gourd shape”, and as the anchorage length increases, it transitions from a “gourd shape” back to an approximate “ellipsoid”. As the pre-tensioning force and length of the bolts increase, the radius, height, and volume of the additional stress field generated by the bolts increase, whereas the influence of the anchorage length on the additional stress field is the opposite. Under cable support, as the cable length increases, the spatial distribution of the additional stress field in the surrounding rock changes from an approximate “ellipsoid” to a “gourd shape”. When the cable length exceeds 5 m, it becomes two intermittent “ellipsoids” with a smaller upper part and a larger lower part, showing no significant change in distribution even with increases in pre-tensioning force and anchorage length. With increasing pre-tensioning force, the radius and volume of the additional stress field generated by cable support increase, while the spacing between the upper and lower stress fields decreases. As the cable length increases, the height of the additional stress field in the surrounding rock rises, subsequently becoming two intermittent stress fields, with increasing spacing, while the radius and volume of the stress fields first increase and then decrease. With the increase in cable anchorage length, the spacing of the additional stress field in the surrounding rock gradually decreases, with the radius initially increasing and then decreasing, and the volume showing little increase. The study further analyzes the effects of high/low additional stress on the roadway roof under the combined support of bolts (cables) based on some principles from composite beam and suspension theory, establishing calculation formulas for high/low thresholds. Comparing the volume size of the surrounding rock’s additional stress field helps determine the advantages and disadvantages of the bolt support scheme. The research subjects include the 21204 return airway of the Hulusulu Coal Mine and the transportation roadway of the Chengjiao Coal Mine LW21106 working face, analyzing the characteristics of the original/new support schemes and calculating the high/low stress thresholds and their total volume covering the roof of the two typical roadways. The results show that the optimized scheme with bolts (cables) can create an effective and continuous additional stress field in the roof, significantly increasing both the high and low stress field volumes and effectively controlling the deformation of the surrounding rock.

     

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