【作者】 叶四桥；

【导师】 陈洪凯；

【作者基本信息】 西南交通大学 ， 桥梁与隧道工程， 2008， 博士

【摘要】 本文以隧道洞口区段落石灾害为研究对象,在国家自然科学基金(编号:50678182)的资助下,以隧道洞口段落石灾害有效防治为目标,系统进行了落石运动影响因子现场试验,隧道洞口落石危险性分级和风险决策,落石运动路径与运动特性参数计算,落石冲击力计算和落石灾害威胁地段隧道洞口段布置与灾害防治等研究,取得了以下研究成果:(1)通过不同质量、不同形状落石现场试验发现,落石于坡面的运动模式以弹跳和滚动为主,仅在少数落石起始和停止运动阶段有小段滑动情形,且越接近球形该规律越明显。不同形状落石中,球形、方形和短柱状落石在运动过程中会有更大的威胁范围、运动速度和弹跳能力,相应的长方形和片状落石最差,且长径比越大、长细比越大,扁度越大则运动能力越差。不管何种形状及质量大小的落石,在运动可达范围、弹跳高度、横向偏移、运动速度等方面均表现出了极大的随机性,且质量越小随机性越明显。从落石运动模态和运动能力来看,短柱状落石基本能够反映方形、球形落石运动特征,而长柱状落石运动特征与长方形落石相仿,但不管何种形状落石,坡表的碰撞阶段会急剧改变落石运动路径与模式。从落石运动偏移比来看,试验所得结果较已有建议值0.1要大,但均在0.3以内,96%的落石偏移比在0.25以内,89%的落石偏移比在0.2以内,偏移比在0.1以内的约占57%。(2)鉴于落石运动的随机性特征,以及隧道洞口段落石灾害防治决策的需要,建立了隧道洞口段落石灾害危险性分级系统。将隧道洞口段落石灾害危险性以危岩崩落的可能性、崩落后落石到达隧道洞口区域的可能性和致灾能力,以及危害严重性等三个方面进行评价,建立了经验性量化评分系统,将隧道洞口发生落石灾害的危险性等级分为一至四级,一级为隧道洞口受落石灾害威胁最为严重状态,而四级为不受落石灾害威胁状态。(3)通过假定落石为均质圆柱体,将落石于坡表的运动归结为飞行、碰撞和滚动三种模式,以运动学和动力学有关原理来表达各种运动模式下落石运动路径及运动特性参数(弹跳高度、运动速度、总动能等)。并以法向(e_n)、切向恢复系数(e_t)和滚动摩擦系数(μ)等敏感参数的区间变动取值,通过多次计算来反映落石运动随机性特点对落石运动路径及运动特性参数的影响,得到运动特性参数计算结果相应的随机变动区间,并通过统计分析得到不同危险性等级落石防治所需代表参数。建议对于一级落石灾害危险性等级隧道洞口可取相应多次计算结果最不利值作为落石灾害防治依据,对于二级隧道洞口,可取95%保证率参数作为设计依据,对于三级隧道洞口可取计算参数平均值控制设计。(4)落石威胁区域的确定是进行隧道洞口布置、用地规划和防治结构布置的依据。威胁区域可在计算得到落石二维威胁区间后,通过偏移比指标划定落石三维的威胁范围,建议对于一级落石灾害危险性等级隧道洞口,可取偏移比为0.3控制落石横向威胁范围,对于二级洞口可取偏移比为0.25,相应三级洞口可取偏移比为0.2。(5)基于落石冲击过程冲量变化原理,考虑冲击过程中重力项、反弹效应对冲击力的影响,通过有关试验实测数据、不同计算公式对比分析和三维冲击动力数值模拟,并以冲击力放大系数建立平均冲击力和最大冲击力之间的联系,建立了适用于不同冲击速度、不同缓冲土层厚度、不同冲击角度的落石冲击力计算方法,为明洞、棚洞落石冲击力作用下的结构计算提供荷载依据。冲击力计算和比较分析表明,落石冲击角度越小相应冲击力也越小,缓冲土层越厚,不仅计算得到的冲击力越小,而且扩散之后的分布荷载更小,但过大的厚度会增加覆土自重,且仅通过增加缓冲层厚度来抵抗落石冲击作用,对于大尺寸落石防护而言效果不明显,实际工程中,需要依据落石尺寸、冲击力计算结果和洞口结构特征进行优选。冲击力作用的最不利位置对于明洞而言为拱顶或拱腰,而对于棚洞结构通常为跨中。(6)明洞和棚洞既可是隧道进出口结构,也可是线状工程落石灾害防治技术手段,对于落石威胁地段隧道洞口,应在落石灾害威胁区域预测、落石计算的基础上优化布置,可在抗落石冲击设计的前提下以棚洞和明洞结构直接通过落石威胁区域,或者在主动防治落石、被动拦截落石确保安全的前提下,按一般隧道洞口布置即可。主动防治技术适用于勘察确定的危岩体、以及大型崩塌体的治理;被动防护系统可作为主动防治技术的补充,也可单独用来防治小型的、易发生漏勘漏治的或多点、线状、面状分布落石,以被动防护系统自身拦截能力为原则。拦石网和半刚性拦石墙是两种较优的被动防治技术手段,隧道洞口、拦石网和半刚性拦石墙的布设可依据落石威胁区域预测、运动路径、弹跳高度、运动速度、动能、冲击力等计算结果确定。更多还原

【Abstract】 With financial support of the National Natural Science Foundation (ID: 50678182), the author chooze rockfall hazards at tunnel entrance as research object, and aimed at its effective mitigation, throw systemic rockfall field experiments, tunnel entrance rockfall hazard rating, rockfall trajectories and movement parameters calculation, rockfall impact forces calculation, tunnel entrance arrangement, rockfall mitigation at tunnel entrance and so on, get the following concludings:(1) Through different quality, different shapes rockfall filed experiments, the auther found that the movement mode of rockfalls are mainly rolling and bouncing, only a small number of rockfall has a short phase sliding at start, and the more spherical the the law is more obvious. For different shape rockfalls, spherical, square, and short cylindrical rockfalls have greater threaten scope, faster speed and stronger jumping ability. But the rectangular and sheet rockfalls have the worst movement ability, and the greater the Slenderness Ratio or the Flat Degree, the rockfalls have worse movement ability. No matter what shape , quality and size of rockfalls, up to the threaten scope, a high bouncing hight, lateral distance, velocity, and so on, have shown great randomness, and the smaller the quality of rockfall, the randomness are more obvious. From the movement mode and ability of rockfalls, the cylindrical rockfalls’ movement features like spherical and square rockfalls. and the cylindrical rockfalls’ like rectangular rockfalls. But no matter what shapes, the inpact on the slope will be a sharp change of rockfall movement trajectories and mode.From the Offset Ratio of rockfall movements, test results have been greater than some proposals value of under 0.1, but all Offset Ratio value is smaller than 0.3. And about 96% of rockfalls Offset Ratio is less than 0.25, about 89% less than 0.2, about 57% less than 0.1.(2) In view of the random characteristics of rockfall movement, as well as the needs of rockfall mitigation decision-making at tunnel entrance, the hazards rating ystem was established. The author evaluated measured the hazard rating by the possibility of rockfall avalanche, the possibility of rockfall reached the tunnel entrance after its avalanche and seriousness of rockfall hazards. A quantitative empirical rating system was founded and divided the risk dgreed into 4 grades named Grade 1 to Grade 4 tunnel entrance, for a tunnel entrance thretened by rockfall hazards Grade 1 means the most serious state, and Grade 4 means the tunnel ertrance has no rackfall hazard.(3) Through the homogeneous cylinder assumption, the author decomposed the rockfall movement mode into flight, collision and rolling, and introduced kinematics and dynamics principles to express movement parameters of rockfall(bouncing hight, movement speed, the total kinetic energy, etc.). Through choosing random value of sensitive parameters such as the normal coefficients of restitution( e_n), the tangential coefficients of restitution(e_t), and rolling friction coefficient(μ) in a identified range, and through a number of calculating by different parameter value to reflect the movement characteristics parameters random range of rockfalls. And through statistical analysis we can get the necessary parameters for the mitigation of rockfalls at the tunnel entrance.The author recommends that, for Grade 1 tunnel entrance, should choose the most adverse value as rockfall mitigation design basis. Accordingly, 95% ensuring rate parameter for Grade 2 tunnel entrance and mean value for Grade 3 tunenel entrance.(4) The threaten area by rockfall hazards is basis of tunnel entrance design, land planing and rockfall mitigation structure design. By 2D rockfall trajectory and movement parameter calculation and combination with the Offset Ratio, the 3D rackfall threaten area can be delineated. The author recommends that, for Grade 1 tunnel entrance, the Offset Ratio is 0.3. Accordingly, 0.25 for Grade 2 tunnel entrance and 0.2 for Grade 3 tunenel entrance.(5) Based on the Impulse Principle, considering gravity and rebounding effect in the rockfall impacting process, throught field experiment data, different formulas calculating results and the 3D dynamic numerical simulation, the author presented rockfall impacting force calculation method. The method can apply in solving impacting forces problem for different impact speed, different thickness of the bufferlayer, different impact angle. And then the impacting force calculation method provided load basis for the design of rockfall mitigation structure such as cut-and-cover tunnel and shed-tunnel. The calculation of impact impacting force and its comparative analysis showed that the smaller the impact angle the corresponding impact force is also smaller, and the thicker the buffer layer, the impact force is smaller. and after the distribution of buffer layer, the impacting force on structure is much more smaller. But with the increasing of the thickness of buffer layer, the weight on the stucture is also increaed. And to enhance the anti-impact capacity only by increasing the thickness of buffer layer is usually expensive. In the actual engineering, the buffer layer design need considered rockfall size, impact force and structure optimization. The adverse location by impacting force for cut-and-cover tunnel is arch crown or arch back. But for shed tunnel the adverse location is usually at mid span.(6) The cut-and-cover tunnel and shed tunnel not only can serve as tunnel entrance or exit, but also one type of rockfall mitigation techniques for linear engineering such as roads. To tunnel entrance and exit which threatened by rockfall hazards, we can design the tunnel based on forecasts of rockfall threaten area, rockfall trajectory and impacting force calculation. And also can be designed like a tunnel in general area in the premise of ensuring safety by mittigation the rockfall hazards using systemtic active and passive mitigation techniques. The active control techniques are applicable to the large scale and well investigated rockfalls. And the passive protection system can be used as supplementary to the active control techniques, or can also be used to prevent and treatment of small, bad investigated, linear distributed rockfalls. The safty net and semi-rigid rockfall barrier wall are two kinds of good passive mitigation system. And the design of passive mitigation techniques or tunnel entrance must be based on the results of rockfall threaten forecasting, trajectories, bouncing hight, velocity, kinetic energy, and impact force calculation.更多还原