松软厚煤层异型开切眼新型预应力锚注支护研究与应用

Research and application of new prestressed anchor-grouting support for special open-off cut in soft-thick coal seam

普通水泥基浆液加固煤体由于其自收缩常造成浆煤界面松弛及充填空隙,以综放厚煤层异型开切眼松软煤体加固为工程背景,提出基于预应力锚和自应力注的松软煤体锚注加固方法。基于该新型预应力锚注加固煤体原理分析,对比研究普通硅酸盐水泥和超细硅酸盐水泥的基本性能,为自应力浆液原材料的选取提供依据;通过浆液纵向自由膨胀率试验获得自应力浆液的最佳膨胀剂掺量;进行预制裂隙煤体普通硅质浆液和硅质自应力浆液加固试验,对比分析自应力浆液加固煤体的力学性能优势和破坏特征;通过数值模拟和现场监测分析新型预应力锚注加固异型开切眼的有效性。结果表明:通过浆液结石体的膨胀应力和注浆锚杆的轴向约束应力,能够使松软破碎煤体处于准三维的受力状态,实现了其强化与损伤修复;超细硅酸盐水泥浆液由于流动性更大、结石体强度更高而更能满足自应力浆液的加固要求;随着膨胀剂掺量增大,水泥浆液最大纵向膨胀率呈先增大后减小的趋势,自应力浆液的最佳膨胀剂掺量为10%;约束条件下自应力浆液加固煤体的峰值强度比普通浆液加固煤体提高4.6%,说明自应力浆液加固裂隙煤体的效果优于普通浆液;普通浆液和自应力浆液加固煤样初始宏观裂纹均出现在浆煤界面处,最终破坏形态均为以预制裂隙为基础的整体劈裂弹射破坏,但其裂纹发展过程有所不同,自应力浆液加固煤样的裂隙数量少于普通浆液加固煤样;在数值模型中,仅锚杆索支护时煤体悬臂梁结构下沉量较大,新型预应力锚注后其下沉量明显减小;现场监测中锚杆索受力相对稳定,加固煤体下沉量较小,说明新型预应力锚注加固松软破碎煤体的效果较好。

In the ordinary cement-based slurry-reinforced coal body,the self-shrinkage of slurry often causes voids at the interface between slurry and coal body.Taking the reinforcement of soft coal with special open-off cut in thick coal seams as the engineering background,a method for the anchor-grouting of soft coal based on prestressed anchors and self-stress groutingwas proposed.Based on the principle analysis of the new prestressed anchor-grouting for strengthening coal,the basic properties of ordinary Portland cement and ultra-fine Portland cement were comparatively studied to provide a basis for the selection of raw materials for self-stress slurry.Through the longitudinal free expansion rate test of the slurry,the optimum content of the expansion agent in the self-stress slurry was obtained.The tests of ordinary siliceous slurry and siliceous self-stress slurry to reinforce pre-fabricated cracked coal body were carried out.The mechanical advantages and failure characteristics of coal body strengthened by the self-stress slurry grouting for strengthening special open-off cut was compared and analyzed.Through the numerical simulation and on-site monitoring,the effectiveness of new prestressed anchor-grouting were studied.The results showed that the expansion stress of the slurry stone and the axial restraint force of the high-strength grouting anchor can make the broken coal body in a quasi-3D state of stress and realize its strengthening and damage repair.The ultra-fine Portland cement slurry can meet the reinforcement requirements of self-stress slurry due to its greater fluidity and higher strength.As the content of expansion agent increased,the maximum longitudinal expansion rate of the slurry increased first and then decreased.The optimum content of the expansion agent for the self-stress slurry was 10%.The peak strength of coal body strengthened by the self-stress slurry under constrained conditions was 4.6%higher than that of coal body strengthened by the ordinary slurry.It showed that the effect of self-stress slurry to strengthen fractured coal was better than ordinary slurry.The initial macro-cracks of coal samples reinforced by ordinary slurry and self-stress slurry both appeared at the slurry-coal interface.The final damage form was the whole split ejection damage based on pre-fabricated cracks.But their crack development process was different.The number of cracks in the coal samples reinforced by self-stress slurry was less than that in the coal samples reinforced by ordinary slurry.In the numerical model,the settlement of the cantilever coal body was larger when it was supported only by anchor cable.After the new prestressed anchor-grouting,the amount of sinking was significantly reduced.During the on-site monitoring,the stresses of the anchor and cable were relatively stable,and the sinkage of the reinforced coal body was relatively small.It showed that the new prestressed anchor-grouting had better effect on strengthening soft and broken coal.