Influence of temperature cycling and pore fluid on tensile strength of chalk

Calcite has a highly anisotropic thermal expansion coefficient, and repeated heating and cooling cycles can potentially destabilize chalks by breaking cement bonds between neighboring particles. Based on tensile strength measurements, we investigated how temperature cycles induce weakening of chalk. Tensile strength tests were performed on chalk specimens sampled from Kansas (USA) and Mons (Belgium), each with differing amounts of contact cement. Samples of the two chalk types were tested in dry and water-saturated states, and then exposed to 0, 15, and 30 temperature cycles in order to find out under what circumstances thermally induced tensile strength reduction occurs. The testing results show that the dry samples were not influenced by temperature cycling in either of the chalk types. However, in the water-saturated state, tensile strength is increasingly reduced with progressive numbers of temperature cycles for both chalk samples, especially for the more cemented Kansas chalk. The Kansas chalk demonstrated higher initial tensile strength compared to the less cemented Mons chalk, but the strength of both chalks was reduced by the same relative proportion when undergoing thermal cycles in the water-saturated state.     

高韧性特厚煤层综放开采顶煤弱化处理研究

灵武矿区2号煤层,硬度系数小,但韧性高,煤层厚度大,在开采过程中表现为顶煤悬顶面积大,冒落滞后,冒落块度大。结合磁窑堡二矿综放试验,研究了提高高韧性特厚煤层顶煤松动爆破技术参数,成功地实现了高韧性特厚煤层的综放开采。     

The influence of borehole arrangement of soundless cracking demolition agents(SCDAs) on weakening the hard rock

The hard roof difficult to collapse easily causes gas accumulation, which threatens the production safety of coal mine. Therefore, roof pre-cracking is required. Although blasting and hydraulic fracturing can also crack the roof, blasting can easily induce rock bursts, whereas hydraulic fracturing needs complex equipment. In contrast, soundless cracking demolition agents(SCDAs) with noise-free, dust-free, and safe characteristics have obvious advantages. The main component of SCDA is calcium oxide, which reacts with water to produce higher expansion pressure. In this paper, focused on the angles of the borehole, the effect of SCDA is analyzed by numerical simulation based on Pingdingshan coal mine. The research results showed that the azimuthal angle a(between borehole projection and the roadway direction) does not significantly affect the efficacy of SCDAs, whereas the influence of borehole elevation angle b is far more significant than that of the azimuthal angle. Therefore, the angle b is a dominant factor influencing the effect of SCDAs. Based on different effects of SCDAs at different angle of boreholes, the weakening unit was established, so the SCDAs could give full play to roof fracturing. Moreover, field tests validated the importance of borehole angle on weakening the hard roofs.     

基于LQR直升机模糊滑模跟踪控制

研究直升机系统稳定性优化问题,由于直升机系统的强耦合和非线性特性的影响,使飞行的稳定性和实时跟踪性差。为解决上述问题,对直升机原始数学模型进行近似线性化和解耦处理,采用模糊滑模控制方法实现直升机姿态角度的跟踪控制。首先,在滑模面的设计中引入最优线性二次型调节器,构建一种积分型切换面。其次,以切换面及导数的乘积和滑模切换增益的变化量为模糊系统的变量,实时调整变结构控制项的切换增益。仿真结果表明,通过控制器设计能够实现直升机姿态角度跟踪的稳定性,对外界不确定干扰具有强鲁棒性且控制器输出抖振问题得到明显改善。     

几类强弱缓冲算子的构造方法及其内在联系

基于最基本的缓冲算子x(k)d=∑ni=kωix(i)/∑ni=kωi变形,获得了几类范围大大拓宽的实用缓冲算子的构造方法,并揭示了这几类缓冲算子的内在联系.同时揭示了强化缓冲与弱化缓冲的对应关系,即指数γ由正到0,由0到负的变化,导致缓冲算子由弱(强)化到不变化,由不变化到强(弱)化的过程,揭示了由量变到质变的过程.研究表明,现有的大量缓冲算子都是所构造的缓冲算子的特例,此外还包括许多与常见文献中类型迥然不同的新算子.     

新型复合锚固类结构静力弱化效应试验研究

为研究新型复合锚同类结构的弱化机理及其在静载作用下的特性,进行了静力三轴试验研究。研究表明：①弱化试件同非弱化试件相比,其平均变形量为后者的2.7倍,最大为7.3倍,其平均承载力为后者的1.8倍,最大为3.2倍;②在非弱化试件中的锚杆已达到很高应变状态或试件已产生极限破坏条件下,弱化试件中的锚杆尚处于很低应变状态;③弱化试件荷载～应变关系曲线中的“峡谷”现象是弱化孔间的孔壁介质由于应力集中而出现超载破坏,引起试件产生相对卸载的结果,而多次“峡谷”现象的发生,实质上反映了孔壁介质从破裂、破碎到压实的全过程效应;④复合锚同类结构的弱化效应非常显著,其间存在极大潜能,充分利用这一潜能,将具有巨大的社会、经济和军事效益。     

新型复合锚固结构静力弱化效应影响因素试验研究

在新型复合锚固结构静力单轴试验研究中,进行了3组影响弱化效应的对比试验,即考虑了不同比面积、不同材料强度、不同弱化孔深度3组单因素。试验结果表明：①在3组单因素对比试验中,比面积较大、材料强度较高、弱化孔较深的3组试件,均存在更为明显的弱化效应;②锚固区厚度为第4个影响弱化效应的因素;③比面积、弱化孔深、锚固区厚度均存在最佳值,可使弱化效应最优;④弱化效应的机理是：在锚固区厚度足够条件下,弱化区一般要经历变形—大变形—压裂—压碎—压实的各个阶段,与此同时吸收大量爆炸能,使锚固区（包括洞室表面）的危机得以转移,因而潜藏有巨大的经济技术效果。本次试验研究为新型复合锚固类结构的弱化效应优化设计提供了必要的依据。     

中国城市规划教育的双面观

城市规划专业教育的改革已经取得了可喜的成绩。在拓宽专业领域时既要防止专业知识的虚化,又要防止传统专业能力的弱化。     

关于新的弱化缓冲算子的研究及其应用

在灰色系统理论缓冲算子公理体系下,构造出一类新的弱化缓冲算子.研究其一些特性和内在联系,可有效地解决冲击扰动数据序列在建模预测过程中经常出现的定量预测结果与定性分析结论不符的问题.实例分析结果表明,该类算子是有效而实用的.     

一类新的弱化缓冲算子的构造及其应用

利用灰色系统理论,在对缓冲算子和已有弱化缓冲算子研究的基础上,构造一类新的弱化缓冲算子,并研究其一些特性及内在关系,有效解决了冲击扰动数据序列在建模预测过程中经常出现的定量预测结果与定性分析结论不符的问题.实例分析结果表明,这类新的弱化缓冲算子能显著提高数据预测模型的预测精度.