一次“晴天霹雳”致死事件分析

对2017年广州从化地区一次"晴朗"天气下的闪电致死事件进行调查分析发现,这次事件是闪电首先击中一棵大树,然后击中附近人员头顶致死。根据目击者描述的时间和位置,利用闪电低频电场变化探测阵列的定位数据和广东电力等系统的雷电定位数据,结合广州番禺雷达观测资料,确定此事件是由一次含有7次回击的地闪过程的首次回击造成,其电流峰值强度为-30.9 kA。闪电起始于13.0 km高度的云内,经约600 ms云内发展过程后闪电通道从云体延伸出来,云砧区边缘（0 dBz）到回击点水平距离约300 m,降水区边缘（18 dBz）到回击点水平距离约1.8 km。使用雷击现场等效电路模型,计算旁络闪击空气击穿场强可击穿空气与人头部连接为通路,根据电路分流原理,如果雷电流击中13 m高的大树后流经到"跳点"（树干上方1/4）处后,则有13.2 kA雷电流直接闪击到受害者身上,同时还承受了78.3 kV跨步电压伤害,而距离雷击点10 m远的目击者仅承受1.3 kV跨步电压。      

锚杆对节理围岩稳定性影响的离散元研究

本文针对巷道围岩多被节理切割的特点,利用离散元研究了全长锚杆对节理围岩稳定性的影响。结果表明,尽早锚固,有利于围岩的稳定;同时,巷道各部位围岩的变形与破坏具有明显协同性或关联性,应预以系统考虑对围岩的加固。     

巷道围岩塑性状态判定分析方法

本文依照莫尔-库仑屈服条件和非关联流动准则, 从地应力场及地下巷道开挖工程特点出发, 提出对围岩塑性屈服状态进行判定的方法。对无支护巷道和水泥锚杆支护巷道围岩进行有限元分析表明, 巷道开挖以后及时支设锚杆, 对出现塑性屈服的围岩起到了等效提高其刚度和强度的作用, 从而增加了围岩稳定性。与现场实测结果对比说明, 非关联流动准则比关联流动准则更符合实际。     

MEMS传感器在锚杆加固边坡监测中的应用研究

滑坡破坏各种建筑工程,严重影响了人民生产生活以及国民经济的发展。锚杆作为边坡治理的主要手段之一,其施工质量与锚固效果难以直接监测。随着微机电系统(MEMS)技术的兴起与不断发展,MEMS传感器具有体积小、造价低和精度高等优点,使其从常规监测手段中脱颖而出,为地质工程监测提供了新的可能。通过设计模型试验,基于MEMS传感器探讨锚杆对边坡的加固作用。试验采用天然河砂,通过撒砂法堆坡,边坡坡角为45°,分有锚杆加固和无锚杆加固2组。以降雨触发滑坡,将MEMS传感器布设在边坡内部,实现对边坡内部各点的加速度、角度和角速度的实时连续监测。研究表明:当未加固边坡蠕滑开始时,边坡内部和坡脚处的加速度与角度发生渐变,边坡后缘与表面处的加速度和角度变化不明显,表明边坡蠕滑主要发生在边坡内部与坡脚处;滑坡发生时,边坡内部与坡脚处的加速度和角度率先发生突变,边坡后缘与表面的参数随后发生突变,表明砂土坡破坏的瞬间,其内部与坡脚处先发生滑动,边坡后缘与坡面随后滑动,为典型的牵引式滑坡。采用锚杆加固后,边坡只发生蠕滑,边坡内部、坡脚处与坡面的加速度和角度有明显渐变,边坡后缘的各指标几乎无变化,表明降雨条件下,加固后的边坡发生整体蠕滑,边坡坡角降低,不发生破坏。MEMS传感器能够实现低成本、高精度的连续实时监测边坡蠕滑的渐变规律,捕捉到滑坡发生时运动的明显突变,对研究边坡的滑动机制及滑坡预警有一定的应用价值,在地质工程监测领域具有广阔的应用前景。     

An empirical method for design of grouted bolts in rock tunnels based on the Geological Strength Index (GSI)

The procedure presented in this paper has been developed for the design of grouted rock bolts in rock tunnels during preliminary design stage. The proposed approach provides a step-by-step procedure to set up a series of practical guidelines for optimum pattern of rock bolting in a variety of rock mass qualities. For this purpose, a new formula for the estimation of the rock load (support pressure) is recommended. Due to its wide-spread acceptance in the field of rock engineering, the Geological Strength Index (GSI) is adopted in support pressure equation. For poor and very poor rock mass where the GSI < 27, the use of Modified-GSI is, instead, recommended. The supporting action is assumed to be provided by rock bolts carrying a total load defined by the rock load height. The mechanism of bolting is assumed to rely on roof arch forming and suspension principle. Integrated with support pressure function, the bolt density parameter is modified in order to provide an optimized bolt pattern for any shape of tunnel. The modified bolt density can also be used in analysis of a reinforced tunnel in terms of Ground Reaction Curve (GRC) in such a way as to evaluate the reinforced rock mass and the tunnel convergence. By doing so, the effectiveness of the bolting pattern is well evaluated. The proposed approach based on GSI is believed to overcome constrains and limitations of existing empirical bolt design methods based on RMR or Q-system, which are doubtful in poor rock mass usage. The applicability of the proposed method is illustrated by the stability analysis and bolt design of a rail-road tunnel in Turkey.     

利用锚杆轴力量测定围岩破坏区的方法

本文系统总结了锚杆轴力分布型式,分析了各轴力分布型式的力学机理。结果表明,在围岩不同区内,锚杆所受剪切力具有不同的特点,而且,锚杆所受剪切的特点在锚杆轴力分布中得到了反映。根据以上关系,提出了利用锚杆轴力量测确定围岩破坏区的方法。     

水平旋转不变平均持时特征分析

地震动持时对结构低周疲劳、破坏累积效应以及非弹性破坏具有显著影响,合理确定地震动持时至关重要。基于汶川地震记录资料,分析旋转不变平均持时与测点记录持时的大小比值关系和相关性,探讨其随断层距的空间变化规律。结果表明:旋转不变平均持时在数值上不恒等于测点记录持时、两水平分量持时的算术平均值及矢量和时程持时的任一量。旋转不变平均能量持时和相对Bolt持时将随断层距的增大而增加,旋转不变平均绝对Bolt持时则将随断层距的增大而减小。旋转不变平均持时与测点记录持时具有强相关性;相比较而言,90%能量持时的相关性强于70%能量持时;绝对Bolt持时的相关性强于相对Bolt持时;能量持时的相关性强于Bolt持时。     

基于遗传神经网络的锚杆极限承载力预测的研究

针对BP人工神经网络具有易陷入局部极小等缺陷,提出了将遗传算法与神经网络结合,同时优化网络结构的权值与阈值的思想,建立了基于遗传算法的锚杆极限承载力预测的遗传神经网络模型。该模型以低应变动测的5个变量作为输入变量来对锚杆极限承载力进行预测,并与BP神经网络预测结果进行比较。数值算例表明,遗传神经网络在锚杆极限承载力预测中具有较高的计算效率和识别精度。     

Research on the Application of MEMS Sensors to Slope Monitoring Treated by Bolts

The landslide can destroy all kinds of constructions, and seriously hinder people's production and life as well as the development of national economy. Bolt is one of the main methods for slope treatment, but it is difficult to monitor its construction quality and anchoring effect directly. With the rise and development of MEMS (Micro-electro mechanical system) technology, MEMS sensors, with the advantages of small size, low cost and high precision, quickly come out from the conventional monitoring methods and provide new possibilities for the monitoring field in geological engineering. In this paper, based on MEMS sensors, a model test was designed to explore the stability of the slope after treatment by bolts. Natural river sands were used to prepare slopes with angle of 45° through the air-plluviation method. In addition, the tests were divided into two groups (with or without bolts). MEMS sensors were set up in the slope to wirelessly and continually capture the acceleration, angular velocity and angle of slope sliding triggered by simulated rainfall in real-time. It was found that: with no treatment, the acceleration and angle in the interior and the bottom of the slope gradually changed during rainfall, while those parameters in the rear and the surface of the slope had no significant change, which indicated that the slope creep mainly occurred in the interior and the bottom of the slope before failure. When landslides occurred, the movement monitoring indexes in the interior and the bottom of the slope suddenly changed, followed by those in the rear and the surface of the slope, which means that when the sandy slope slides, the interior and the bottom of the slope slides first, and then the rear and the surface of the slope surface fail. This is a typical retrogressive landslide. After the slope was treated by bolts, only creep could be observed during long-term rainfall, and the acceleration and angle in the bottom, interior and surface of the slope gradually changed, while almost no change was found in the rear of the slope, which shows that under rainfall conditions, overall creep occurs for the slope after reinforcement, the slope angle decreases, and there is no landside. The experimental results prove that MEMS sensors can realize low-cost, high-precision, continuous real-time monitoring of slope, and can capture gradual changes of movements before failure and the sudden change when landslide occurs. It should play a certain role in the study of landslide mechanism and landslide warning, and has a broad application in the field of geological engineering monitoring.     

The Dimensioning of Dowels for the Stabilization of Potentially Unstable Rock Blocks on the Walls of Underground Chambers

The analysis of dowels (non pre-stressed passive reinforcements) for the stabilization of potentially unstable rock blocks due to sliding is one of the most interesting problems concerning the static of underground rock chambers. The stabilizing force produced by dowels is not in fact known a priori and it depends on the dowel–rock interaction. The parameters that influence the problem are not only the geometrical ones of the dowel, but also the mechanical characteristics of the rock and the orientation of the displacement vector of the block. A detailed study of the dowel–rock interaction has been carried out in this work. This analysis is able to lead to the evaluation of the axial and shear forces in the dowel in correspondence to the crossed discontinuity of the block. The vectorial composition of these two forces constitutes the stabilization force of the dowel. An extensive parametric analysis then made it possible to determine the great variability of the stabilization force of the dowel in function of the influential parameters of the problem. The graphics that were obtained can be considered a useful design instrument as they quickly allow the dimensioning of the dowels to be done to reach the required safety factor for the rock block.