急倾斜夹持煤体承载特征及地面斜井压裂防冲方法

Load-bearing characteristics of clamped coal and ground inclined-borehole hydraulic fracturing method for rockburst control in steeply inclined coal seams

  • 摘要: 我国西北部地区作为“一带一路”沿线的重要枢纽,同时作为国家煤炭资源的主产区,其能源安全保障意义重大。受复杂地质构造演化影响,该区域广泛发育急倾斜煤层。独特的地质赋存条件导致这类煤层开采过程中形成特殊的顶底板“夹持”结构,采场冲击地压灾害频发。然而,当前对“夹持”作用下煤体应力与能量分布仍缺乏定量分析,现有防治技术存在明显局限。为此,构建了基于Timoshenko梁理论的急倾斜悬臂顶板弹性支撑力学模型,结合Winkler弹性地基支撑力与挠度的定量关系,推导出煤体荷载与能量分布解析式,量化分析了顶板悬臂长度、厚度及倾角对两者的影响。创新提出了地面斜井区域压裂改造“夹持”结构、调控应力环境的冲击地压防治新方法,初步明确了该方法的防冲机理与效果。研究表明:煤体荷载与能量峰值随顶板悬臂长度和厚度的增加显著提升。悬臂长度由15 m增至45 m,煤体峰值荷载增长13倍,能量增加168倍;顶板厚度由10 m增至22 m,荷载与能量峰值分别增至11.5×109 N和3.9×1010 J,且峰值位置向远离煤壁端偏移。相比之下,岩层倾角对煤体荷载与能量分布影响较小。地面斜井区域压裂通过构建网格化裂缝,将完整顶板分割为规则岩段,使覆岩运动模式由传统悬顶结构周期性破断转变为压裂岩段沿裂缝面滑移失稳,从根本上弱化了顶底板对煤层的“夹持”作用,并将顶板破断动载由突发性冲击转变为渐进式释放,有效削弱了冲击地压风险。压裂后形成“采动−压裂”协同破裂效应,使致冲关键层提前破断,消除大跨度悬顶结构,缩短悬顶时间,煤层剪切应力峰值降低41.9%。此外,压裂裂缝的“通道”效应促进覆岩裂隙发育高度增加31.4 m,垮落矸石量增多,碎胀性作用下采空区充填质量增强,形成更稳定的“矸石−顶板”承载体系,有效抑制顶板弯曲变形,促使覆岩应力通过矸石向底板岩体转移。

     

    Abstract: Northwestern China, a vital hub for the Belt and Road Initiative and the nation's primary coal producing region, holds significant importance in ensuring energy security. Due to the influence of complex geological evolution, steeply inclined coal seams are widely developed in this region. The unique geological conditions lead to a distinctive “clamping” structure formed by the roof and floor during the mining process, which frequently leads to rockburst hazards. However, the current understanding of the stress and energy distribution of coal under the “clamping” effect and its influencing factors remains insufficient, and current prevention technologies face significant limitations. To address these scientific challenges, based on Timoshenko beam theory, an elastic support mechanical model for the cantilevered roof of steeply inclined coal seams is established. By integrating the quantitative relationship between Winkler elastic foundation support force and deflection, analytical equations for coal load and energy distribution are derived. The effects of roof cantilever length, thickness, and inclination angle on coal load and energy distribution are quantitatively analyzed. Furthermore, an innovative method for mitigating rockburst hazards in steeply inclined coal seams is proposed, involving ground-inclined well regional fracturing to modify the “clamping” structure and regulate the stress environment. The mechanism and effectiveness of this method were preliminarily clarified.. The results indicate that coal load and energy exhibit an unimodal distribution, significantly increasing with the extension of cantilever length and roof thickness. When the cantilever length increases from 15 m to 45 m, the peak load rises by a factor of 13 times, while the energy increases by 168 times. Similarly, as the roof thickness increases from 10 m to 22 m, the peak load and energy reach 11.5×109 N and 3.9×1010 J, respectively, with the peak position shifting away from the coal wall. In contrast, the roof inclination has a relatively minor influence on load and energy distribution. Ground-inclined well regional fracturing constructs a grid-like fracture network, segmenting the intact roof into regular fractured rock blocks. This process transforms the traditional periodic roof failure mode from a suspended roof structure into a sliding instability mechanism along fracture planes. Consequently, the “clamping” effect exerted by the roof and floor on the coal seam is fundamentally weakened. Additionally, the dynamic impact load induced by roof failure shifts from sudden impact to progressive release, effectively mitigating rockburst risks. The induced “mining-fracturing” synergistic failure effect leads to the early breakage of critical burst-prone layers, eliminating large-span suspended roofs, shortening the duration of roof suspension, and reducing peak coal seam shear stress by 41.9%. Moreover, the “channeling” effect of fracturing enhances overlying strata fracture development by 31.4 m, increasing the collapse of gangue and improving the filling quality of the goaf under expansion effects. This leads to the formation of a more stable “gangue-roof” bearing system, which not only effectively restrains roof bending deformation but also facilitates stress transfer from the roof to the floor strata.

     

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