Influencing factors analysis of hard limestone reformation and strength weakening under acidic effect

Roof disaster has always been an important factor restricting coal mine safety production.Acidic effect can reform the rock mass structure to weaken the macroscopic strength characteristics,which is an effective way to control the hard limestone roof.In this study,the effects of various factors on the reaction characteristics and mechanical properties of limestone were analyzed.The results show that the acid with stronger hydrogen production capacity after ionization(pK_(a)<0)has more prominent damage to the mineral grains of limestone.When pKa increases from−8.00 to 15.70,uniaxial compressive strength and elastic modulus of limestone increase by 117.22%and 75.98%.The influence of acid concentration is manifested in the dissolution behavior of mineral crystals,the crystal defects caused by large-scale acid action will lead to the deterioration of limestone strength,and the strength after 15%concentration reformation can be reduced by 59.42%.The effect of acidification time on limestone has stages and is the most obvious in the initial metathesis reaction stage(within 60 min).The key to the strength damage of acidified limestone is the participation of hydrogen ions in the reaction system.Based on the analytic hierarchy process method,the influence weights of acid type,acid concentration and acidification time on strength are 24.30%,59.54% and 16.16%,respectively.The research results provide theoretical support for the acidification control of hard limestone roofs in coal mines.

顾桥矿顶板水力压裂控制大巷变形技术研究

顾桥煤矿巷道顶板中具有多层关键坚硬岩层,关键岩层传递远场采动应力,致使盘区大巷围岩控制困难;用水力压裂技术切断顶板中的多层关键岩层时,要求精准可控地实现分层致裂,保障施工的有效性和安全性。为此引入成套专用技术装备,在顾桥煤矿北二采区首采工作面开展了顶板水力压裂应力转移保护盘区大巷技术试验。试验结果表明:实时监测的孔口水压力可以反映水力裂缝贯穿目标砂岩层、在其他不同岩性的顶板中扩展的过程,可作为施工过程中的参考。基于孔口压力监测和定点封孔精准致裂,可以有效分层切断顶板关键岩层。分层致裂坚硬顶板后,监测到试验盘区大巷的顶底板及两帮移近量均小于230mm;采动应力得到有效转移,盘区大巷变形得到了有效控制。试验提供了一种精准可控地分层致裂坚硬顶板、保护盘区大巷的工程实例,可为具有类似问题的矿井提供经验参考。

围压作用对爆破裂纹空间形态影响的试验研究

爆破裂纹的空间形态是进行爆破设计的理论依据。地下超深孔爆破炮孔处在围压作用之中,无爆破自由面,此种条件下爆破裂纹空间形态有待进一步的研究。采用4000 kN大型真三轴加载设备和煤矿许用导爆索分别提供围压静载和爆炸动载,并浇筑300 mm×300 mm×300 mm尺寸水泥砂浆立方体试块,采用的等效炸药量均为3 g,围压条件下试块加载的第一、第二、第三主应力分别为8.50 MPa、7.00 MPa、5.75 MPa,对比分析有、无围压两种条件爆破裂纹的空间形态差异。研究发现:围压条件下的爆破裂纹空间形态与拥有爆破自由面条件的爆破裂纹空间形态差异极大,四周拥有爆破自由面条件下试块爆破破碎为碎块,在块度尺寸L<100 mm和100 mm≤L≤200 mm范围内的破碎块度质量分别占试块总质量的30%和70%,其中大尺寸150 mm≤L<200 mm范围内的块度质量占比达到55.32%,但是数量较少,并且都产生于试块表面;围压条件下,在垂直于第二主应力方向产生一个以封孔器为中心对称的宏观破裂面,在试块的其它表面上产生了几条宏观裂纹。试块剖开后,在炮孔壁部产生微裂纹,在预先射孔方向的孔壁处产生明显的裂纹。

基于全程状态监测量的继电保护故障率模型

继电保护的可靠运行对维持电网安全稳定具有重要作用。评估运行中的继电保护故障率是研究继电保护可靠性的一个关键性问题。该文通过分析某一地区的故障率分布,提出基于全程状态监测量与故障数据的广义比例故障率模型,并采用自适应同伦算法估计广义比例故障率模型的参数,求解继电保护故障率表达式。最后,3个算例结果表明:与牛顿同伦算法相比,自适应同伦算法求解故障率参数速度更快,收敛性更好;与威布尔模型相比,采用全程状态监测量与故障数据的广义比例故障率模型可以更好地拟合继电保护故障率,实时反映设备的运行状态,为设备检修类型的选择提供理论基础。

Experimental investigation on basic law of rock directional fracturing with static expansive agent controlled by dense linear multi boreholes

Directional rupture is one of the difficult problems in deep rock mechanics and engineering.A directional fracturing method with static expansive agent controlled by dense linear multi boreholes is proposed.A physical experiment is designed and performed to investigate the basic laws of this method.The fracture initiation and propagation process,and the mechanism of directional fracturing are analyzed.The results indicate that a directional fracture is formed along the direction of boreholes layout through directionally fracturing with static expansive agents controlled by the dense linear multi boreholes.According to the variation of strain and the distribution of associated acoustic emission(AE)events and energy,the experiment can be divided into three stages.In the first stage,the static expansive agent expand slowly with no fracturing inside the rock.In the second stage,some initial micro-fracturing occurs inside the rock.In the third stage,a wide range of fracturing occurs inside the sample.The internal micro-fracturing planes are connected to form a macro-fracture.Finally,it propagates to the surface of the sample.The directional fracturing plane presents a relatively smooth plane with little bias but much local fluctuation.