落石形状和尺寸对恢复系数影响的室内试验研究

为了研究落石形状和尺寸对恢复系数的影响,通过专门设计的落石碰撞测试装置,分别展开10种不同形状和5种不同尺寸的试块与坡面的碰撞测试。基于冲击动力学理论对试验结果进行分析,法向恢复系数R_n对试块形状的变化非常敏感,且非棱角状试块的R_n值明显高于棱角状试块。非棱角状试块R_n值大小依次为球形椭球球底圆锥圆柱圆盘,棱角状试块的R_n值大小依次为正二十面体正方体正四面体长方体三角板。综合考虑试块的几何构型和表面积分布特征,引入一个新的形状量化指标——形状因子η,其与非棱角状试块和棱角状试块的R_n值分别呈强线性正相关。相较于R_n,试块形状对切向恢复系数R_t的影响较弱,且棱角状试块的R_t值整体略大于非棱角试块。试块尺寸对R_n和R_t的影响均较为显著,且与R_n和R_t均呈良好的线性负相关关系。这些获得的规律可为落石灾害的准确预测提供重要参考。     

边坡落石运动轨迹计算新方法

考虑落石形状对落石运动轨迹的影响,将落石近似成椭圆形。根据落石运动的5种常见形式,即自由落体运动、斜抛运动、碰撞、滑动和滚动,分别得到了各种运动形式的运动速度计算公式。在碰撞阶段考虑了地面的弹塑性变形,得到了与碰撞前速度、落石形状和地面材料有关的恢复系数计算公式,并根据接触力学的有关理论得到了碰撞冲击力的计算公式,给出了落石连续滚动的判别条件。将理论公式应用于重庆万州首立山落石运动轨迹预测,验证了理论公式的可行性和有效性。     

基于重庆某高速公路的岩崩落石数值模拟与防护研究

重庆某高速公路边坡因岩层裂隙切割、岩体差异风化、岩体卸荷等原因,形成陡崖和危岩。陡崖上发育的危岩崩塌方向均为线路所在方向,严重影响线路安全,因此合理设置防护措施十分必要。由于落石属于概率事件,具有很强的随机性,所以其冲击动能、弹跳高度以及拦石网受到落石冲击时,拦石网与防护对象之间的安全距离难以准确确定。通过现场调查、理论分析、并利用rockfall软件对岩崩落石进行稳定性分析,设定危岩体的碰撞恢复系数、坡面摩擦角度和坡面粗糙度等参数,获得边坡潜在的落石坠落轨迹,为被动防护网的设计防护等级、高度和安装位置提供依据。     

落石冲击混凝土棚洞力学特性研究

落石冲击棚洞结构作用过程复杂,缺乏统一的落石冲击力表达式。首先,将落石简化为刚性球体,基于Hertz接触理论,推导得到落石冲击力半正弦算法的理论表达式,考虑落石冲击下棚洞的非弹性特征,根据落石与材料碰撞过程中落石加速度曲线特征,采用函数拟合法推导得到落石法向冲击下其冲击力的理论计算方法;然后,基于ANSYS/LS-DYNA软件建立落石冲击棚洞数值计算模型,研究不同冲击速度下落石冲击棚洞动力特征;最后,与现存常见的多种方法进行对比,得出以下结论：Hertz半正弦法得到的落石冲击力远大于函数拟合法和数值法,而函数拟合法和数值法得到的落石冲击力时程曲线相接近,表明函数拟合法更能反映落石与棚洞接触碰撞动力关系;对比其他计算方法可以得到,Hertz算法适用于分析无能量损失下的弹性碰撞问题,而Logistic算法适用于材料大塑性变形的情况,弹塑性接触理论结果和动力有限元结果存在差异,而采用函数拟合推导的计算方法得到的落石最大冲击力和落石冲击作用时间与动力有限元法更接近,更能反映落石冲击棚洞动力响应特征,推导的落石冲击力计算方法可为工程实践中棚洞防护设计提供理论参考。     

西藏玉龙铜矿崩塌落石运动特征及数值模拟研究

对玉龙铜矿运矿道路区的地形地貌、岩性和地质构造进行调查,获取危岩体的岩体物理力学指标,分析道路两侧的潜在崩塌落石灾害。在对运矿道路两侧边坡地质灾害进行调查的基础上,分析该区的工程地质条件、边坡特征、崩塌落石特点及形成机制。用Rockfall数值软件对落石进行数值模拟,确定落石的运动轨迹、弹跳高度和总动能指标,对防治运矿道路崩塌灾害提供依据。     

球形砾石碰撞损伤破碎三维离散元模拟研究

落石碰撞损伤破碎和碎片速度对落石运动轨迹准确预测至关重要。为揭示碰撞损伤破碎和碎片速度,采用结晶法及三维离散元建模,针对球板碰撞室内试验,开展球砾碰撞损伤破碎三维离散元模拟。模拟结果表明,球砾损伤破碎模式与室内试验完全吻合;较高碰撞速度使球砾内部产生径向宏观裂纹和二级宏观裂纹,将球砾破碎成较小块体;二级环向裂纹源于橘子状碎片进一步压缩。径向宏观裂纹的产生导致裂纹数显著增加;基于裂纹数的损伤率随碰撞速度的增加呈3个不同阶段,接触力同样受损伤破碎显著影响;球砾碰撞破碎会产生高速碎片,碎片速度可高达碰撞速度的3.2倍,以等效粒径小于0.11的小碎片为主;碰后碎片速度方向随碰撞速度发生显著变化,变化与球砾碰撞破碎模式相对应。     

基于线黏弹性接触的落石冲击地面参量理论研究

落石与坡面或者防护结构接触过程中冲击参量随时间变化特征是描述落石碰撞过程的重要指标,对于揭示落石与坡面相互作用机制以及采取合理的防护措施具有重要的意义。在现有的相关设计规范中,并没有给出关于落石冲击力时程关系的计算方法,仅参照有关规范或经验方法确定一个落石最大冲击力值。为此,首先基于线黏弹性接触理论,建立落石冲击地面力学模型,根据位移-速度组合初始条件以及速度-加速度组合初始条件分别推导得到两种落石冲击特征参量理论解析解;然后基于 ANSYS/LS-DYNA 非线性动力学软件,建立落石冲击地面三维数值模型,研究球体落石冲击地面力学特点;最后将理论结果对比室内试验和已有的研究成果,得出以下结论：（1）Hertz 弹性接触理论结果中各参量变化在加载阶段和恢复阶段均呈现对称的趋势,速度、加速度初始条件下的落石冲击特征参量和动力有限元法非常接近,而位移-速度初始条件组合并不适用于研究落石冲击下的动力特征;（2）不同速度和下落高度下,落石最大冲击力值随落石下落高度和冲击速度的增大而增加,而落石冲击作用时间随下落高度和冲击速度的增加而减小;（3）计算结果得到的落石最大冲击力以及落石冲击作用时间与室内试验结果和已有成果相接近,相比室内试验和有限元结果的震荡性,此结果更能体现落石冲击力变化规律; （4）多种冲击速度下,对比不同方法得到的落石最大冲击力,可知计算结果均在各种冲击力计算结果的范围内,具有很好的可靠性。考虑到现有研究理论的不足,难以求解落石冲击力时程关系,求解结果丰富了落石碰撞理论,可以指导工程有关落石灾害的防护设计。     

Malvern Hills边坡溃曲破坏分析及数值流形法模拟

基于能量法推导了多层岩质边坡临界溃曲长度计算公式。考虑层间和交叉节理采用数值流形法对新西兰Malvern Hills边坡溃曲演变过程进行了模拟,并将理论计算、数值模拟结果与现场实测数据进行了对比。结果表明:通过预制层间和交叉节理,数值流形法可以准确模拟边坡溃曲破坏过程;边坡溃曲变形及失稳破坏过程依次为层间错动—轻微弯曲、坡脚牵引—剧烈隆起、加速滑移—形成滑坡;在自重长期作用下,边坡溃曲形成至破坏演化过程主要分为初始弯曲、急剧弯曲和滑坡形成3个阶段;β为交叉节理与斜坡法向夹角,在0°、15°、30°、45°这4种交叉节理中,β为45°时边坡最容易产生滑移弯曲变形,溃曲程度最大,并且经历滑移弯曲时步最少;β为30°～45°时,数值模拟结果与实际较为吻合。     

滚石冲击碰撞恢复系数研究

在研究滚石的运动规律过程中,滚石的碰撞恢复系数是重要的控制参数,它不仅与滚石的冲击速度、质量有关,还与滚石、坡面覆盖层的物理力学性质密切相关,目前尚无合理的计算理论,这是滚石灾害研究的一个难点问题。根据Hertz接触理论、Cattaneo & Mindlin切向接触理论,在考虑材料弹塑性特性的基础上研究了滚石法向碰撞恢复系数和切向碰撞恢复系数的计算模式,给出了具体的计算公式,并阐明了影响滚石碰撞恢复系数的主要控制因素。通过一算例的计算分析并与已有结论的比较,表明该计算模式的合理性。     

明棚洞落石冲击荷载计算方法研究

根据落石冲击回填土明棚洞过程中的基本力学和运动学规律,采用Laplace变换,从落石冲击半无限土体、落石冲击有限厚度土体、考虑回填土与下部结构相互作用3个方面推导了落石冲击荷载的理论计算公式,通过数值模拟和相关试验数据对理论公式进行了验证,并与目前常见落石冲击荷载计算公式进行了对比研究。研究表明：所提出的公式理论计算结果与数值模拟结果和相关试验结果均有较稳定的规律,理论计算值比数值模拟值大6%～41%,与Pichler现场试验的95%分位值差值仅在6%以内;尽管所提出的公式计算值比目前所有公式计算结果均偏大,但与数值模拟和试验数据更吻合,更能反映出真实的落石冲击荷载;所提出的计算公式可以反映缓冲层厚度和缓冲层性质的影响,缓冲层厚度越小,落石冲击荷载越大,缓冲层厚度影响系数可根据h/r查表确定;缓冲层和结构的动力相互作用导致结构承受冲击荷载相较缓冲层顶部冲击荷载增大,结构动力放大系数与缓冲层厚度相关,缓冲层厚度越大,结构动力放大系数越小。所提出的计算公式可以反映落石大小、落石形状、落石冲击能量、缓冲层厚度、缓冲层性质等因素对冲击荷载的影响,计算荷载值可直接用于明棚洞结构设计。     

Field Evidence and Kinematical Back-Analysis of Block Rebounds: The Lavone Rockfall,Northern Italy

This paper reports the field evidence and the kinematical study of the motion of two blocks (A and B) mobilised by a rockfall in Lavone (Valtrompia, northern Italy) on 14th February 1987. The two sequences of impact marks left by the blocks on the ground surface were measured and the lithostratigraphical features of the debris slope were surveyed. On the basis of the field-collected input data, several computer simulations were carried out to calculate the coefficients of restitution (E) satisfying the trajectory conditions. The computed output values, obtained by running a specific automatic program for rockfall modelling, show that rebound trajectories require high coefficients of restitution (0.8 ≤ E ≤ 0.9). Back-calculated impact velocities range from 9.2 to 19.8 m/s. Trajectory heights vary from 0 to 2.4 m above the slope surface. Block trajectories differ considerably according to the circumstances of initial air projection, i.e. to the initial rebound angle (α _r). The calculated values of α _r denote a considerable range (36°), emphasising the high variability and the random nature of this parameter. The described case history shows that rockfall computer analyses can be an effective tool to describe the bouncing propagation of single blocks, but care must be taken in choosing the restitution coefficient E and the geometrical parameters of initial air projections.     

Rockfall-induced block propagation on a soil slope,northern Italy

This paper reports the field evidence and the kinematical study of the motion of two blocks (A and B) mobilised by a rockfall in Lavone (Valtrompia, northern Italy) on 14 February 1987. The two sequences of impact marks left by the blocks on the ground surface were measured and the lithostratigraphical features of the debris slope were surveyed. On the basis of the field-collected input data, several computer simulations were carried out to calculate the coefficients of restitution (E) satisfying the trajectory conditions. The computed output values show that rebound trajectories require high coefficients of restitution (0.8 ≤ E ≤ 0.9). Back-calculated impact velocities range from 9.2 to 19.8 m/s. Trajectory heights vary from 0 to 2.4 m above the slope surface. Block trajectories differ considerably according to the circumstances of initial air projection, i.e. to initial rebound angle (α_r). The calculated values of (α_r) denote a considerable range (36°), emphasising the random nature of this parameter. The described case-history shows that rockfall computer analyses can be an effective tool to describe the bouncing propagation of single blocks but care must be taken in choosing the restitution coefficient E and the geometrical parameters of initial air projections.     

滚石在平台上的运动特征分析

危岩体;滚石;平台;运动距离;现场试验;滚动摩擦系数     

Computer simulation-based evaluation of rock fall roll-out distances for catchment ditch design in Ohio,USA

Catchment ditches along highways are designed to contain hazardous rock falls from cut slopes. RocFall, a rock fall simulation software, was used to evaluate the maximum roll-out distances of rock falls in order to determine rock fall catchment ditch dimensions for Ohio's cut slopes. Based on stratigraphy, cut slopes in Ohio were classified into five types. The parameters required for simulation process included friction angle between rock fall and slope face, coefficient of normal and tangential restitution, slope roughness and average weight of rock falls. A total of 400 simulations were performed for various slope heights, slope angles and catchment ditch slopes. The results are useful in designing catchment ditch for Ohio and neighbouring states where the stratigraphy consists of sub-horizontal, inter-layered hard and soft rock units. The widely used guidelines developed by the Oregon Department of Transportation do not work well for Ohio's stratigraphy.     

层状岩石边坡倾倒破坏过程的数值流形方法模拟

层状岩石边坡的倾倒破坏是岩石边坡失稳破坏的主要形式之一。本文利用数值流形方法对一层状岩石边坡的倾倒破坏过程进行了模拟。模拟结果表明：在不考虑块体间粘结力的情况下，块体间的摩擦角决定着岩石边坡的稳定性。随着摩擦角的增加，块体间的摩擦系数增大，岩石边坡的稳定性增强，并出现相应的滑动区、倾倒区和稳定区。模拟结果与相应的理论预测结果相吻合。     

A fractal fragmentation model for rockfalls

The impact-induced rock mass fragmentation in a rockfall is analyzed by comparing the in situ block size distribution (IBSD) of the rock mass detached from the cliff face and the resultant rockfall block size distribution (RBSD) of the rockfall fragments on the slope. The analysis of several inventoried rockfall events suggests that the volumes of the rockfall fragments can be characterized by a power law distribution. We propose the application of a three-parameter rockfall fractal fragmentation model (RFFM) for the transformation of the IBSD into the RBSD. A discrete fracture network model is used to simulate the discontinuity pattern of the detached rock mass and to generate the IBSD. Each block of the IBSD of the detached rock mass is an initiator. A survival rate is included to express the proportion of the unbroken blocks after the impact on the ground surface. The model was calibrated using the volume distribution of a rockfall event in Vilanova de Banat in the Cadí Sierra, Eastern Pyrenees, Spain. The RBSD was obtained directly in the field, by measuring the rock block fragments deposited on the slope. The IBSD and the RBSD were fitted by exponential and power law functions, respectively. The results show that the proposed fractal model can successfully generate the RBSD from the IBSD and indicate the model parameter values for the case study.     

基于摩擦与变形耗能的滚石切向恢复系数影响因素

切向恢复系数是滚石碰撞回弹的重要控制参数,目前的理论公式不能完全反映其作用机制,这是滚石动力学研究的一个难点问题.为此,根据滚石不同的回弹状态,提出基于入射角度变化的切向力模型;进一步,以切向接触理论和动能定理为基础,考虑碰撞过程中切向的摩擦耗能与变形耗能,推导了切向恢复系数的理论公式;最后研究入射速度、入射角、被撞击物体的变形模量对切向恢复系数的影响.结果表明:滚动回弹的切向恢复系数主要受切向变形量的影响;滑动回弹时,入射速度对切向恢复系数的影响参数为\begin{document}$ {v}^{\frac{1}{20}} $\end{document},切向恢复系数随着其增加而缓慢减少;入射角度对切向恢复系数的影响参数为$ \frac{\mathrm{c}\mathrm{o}{\mathrm{s}}^{\frac{1}{20}}{\beta }_{i}}{\mathrm{t}\mathrm{a}\mathrm{n}{\beta }_{i}} $,切向恢复系数随其增加而增大;被撞击物体的变形模量对切向恢复系数的影响参数为$ {E}_{2}^{-\frac{5}{8}} $,切向恢复系数随其增加而增加.基于摩擦与变形耗能的切向恢复系数计算公式为滚石的碰撞回弹过程提供了新的计算模型.      

Rockfall susceptibility zoning at a large scale: From geomorphological inventory to preliminary land use planning

Rockfall, up to several hundreds of cubic meters, is a frequent and rapid landslide which menaces extensive areas in mountainous territories. Rockfall susceptibility zoning map at a large scale (1:5000–1:25 000) can be the first tool for land use planning in order to manage rockfall risk. A methodology allowing to analyze susceptibility in extensive areas with optimum cost/benefit relationship is needed. This work analyzes rockfall susceptibility in an extensive rocky mountain of the Principality of Andorra (Pyrenees Mountains), first on the rock slope and then on the exposed area located below. The rockfall record, obtained by means of geomorphological analysis, supplies the main data to analyze the susceptibility on the rock slope. An additional historical inventory verifies the accuracy of rockfall sizes recorded by means of the geomorphological analysis. According to the classification recommended by the Guidelines of Joint Technical Committee, the density of rockfall features on the rock slope assesses susceptibility in four levels. Subsequently, susceptibility on exposed areas has been analyzed by means of reach probability of rock blocks analysis using empirical models. Data acquired from thirteen recent events, from 1999 to 2004, have been used to verify the accuracy of the two empirical models mainly used (reach angle and shadow angle). Five reach probability limits (1, 0.5, 0.25, 0.01, and 0) establish boundaries between susceptibility levels. The resulting rockfall susceptibility zoning map allows: (a) to identify land areas and human elements exposed to rockfalls and, (b) to establish several exposition levels. This map can be a useful and cost-effective tool for administrations responsible to manage natural risk in order to guide urban grow in extensive areas or decide upon work programs based on in-depth analysis (hazard and risk).     

On the role of sphericity of falling rock clusters—insights from experimental and numerical investigations

In this study, the dynamic behavior of rock clusters falling on rough slopes and impacting a vertical barrier is investigated experimentally and numerically using discrete element analysis. A specially designed laboratory setup that involves a flume of adjustable slope lined with a bumpy surface and equipped with an instrumented wall at the toe is used in the experimental investigation. The velocity profiles and impact forces were measured for three inclination angles using two different rock clusters. Three-dimensional discrete element analysis is then conducted to investigate the mechanical behavior of the rockfall and examine the role of sphericity of the rock cluster on the overall behavior of the system. This was achieved by explicitly simulating the complex shapes of the used rocks and the rough surface of the slope. The material coefficient of friction was measured using heap tests, and the results are compared with those obtained numerically using four different particle sphericities. Conclusions are made regarding the effect of slope inclination angle and the volume of the cluster on the impact forces exerted on rigid barriers. This study suggests that rock sphericity plays important roles on the dynamic behavior of the system and should be taken into consideration in simulating rockfall problems.     

尼泊尔某项目滚石灾害的工程地质调查与评价

滚石灾害是山区常见的地质灾害类型,研究滚石的运动特征对地质灾害调查及危险性评估有着重要意义.通过对尼泊尔某项目滚石灾害后现场进行工程地质调查,分析其灾害成因机制,查明事故原因.调查结果表明:9·15灾害非人类活动的影响,属自然地质灾害,造成事故的主要原因为超高位岩体崩塌,而滚石的范围又超过前期预测的危险区.通过现场痕迹...