Impact resistance performance and optimization of the sand-EPE composite cushion in rock sheds

Rock sheds are widely used to prevent rockfall disasters along roads in mountainous areas.To improve the capacity of rock sheds for resisting rockfall impact,a sand and expandable polyethylene(EPE)composite cushion was proposed.A series of model experiments of rockfall impact on rock sheds were conducted,and the buried depth of the EPE foam board in the sand layer was considered.The impact load and dynamic response of the rock shed were investigated.The results show that the maximum impact load and dynamic response of the rock shed roof are all significantly less than those of the sand cushion.Moreover,as the distance between the EPE foam board and rock shed roof decreases,the maximum rockfall impact force and impact pressure gradually decrease,and the maximum displacement,acceleration and strain of the rock shed first decrease and then change little.In addition,the vibration acceleration and vertical displacement of the rock shed roof decrease from the centre to the edge and decrease faster along the longitudinal direction than that along the transverse direction.In conclusion,the buffering effect of the sand-EPE composite cushion is better than that of the pure sand cushion,and the EPE foam board at a depth of 1/3 the thickness of the sand layer is appropriate.

Coupled DEM-FDM analyses of the effects of falling rock’s shape and impact angle on response of granular cushion and rock shed

Rock shed is an effective protection measure against rockfall.To investigate the influences of falling rock’s shape and impact angle on the impact effect of the cushioned rock shed,a modeling approach for a rock shed with a cushion layer using PFC-FLAC.The granular cushion is modeled as an aggregate of discrete non-cohesion particles,while the concrete plate and the beam are modeled as zones.The falling rock with different sphericities and impact angles is modeled as a rigid assembly.The numerical model is validated by comparing the simulation results with experimental and numerical results from previous literature.This model is applied to analyze the effects of rock shape and impact angle on the dynamic interaction effects between falling rock and cushioned rock shed,including the impact force,transmitted bottom force,penetration depth,and plate deflection.The numerical results show that the variation in the falling rock’s shape has different effects on the falling rock with different impact angles.These findings could support rock shed design by revealing the limitations of the assumptions in the past research,which may result in unsafe rock sheds for some rockfall cases.

Dynamic response and optimization of an inclined steel rock shed by the graded energy dissipating method

Blocking rockfalls directly by reinforced concrete(RC) flat sheds with thick sand cushions is an outdated method. Such conventional sheds typically accumulate rock heavily, and become progressively damaged and are difficult to repair, and are very costly. To address these problems, we propose a new structure called a Graded Dissipating Inclined Steel Rock(GDISR) shed that utilizes the graded energy dissipation method. Here, we study the dynamic response of the GDISR shed with model test and numerical simulation, and give its optimization design combining with a practical engineering case. Our results show that the optimized modular E-block and corrugated steel tube can deform to sufficiently absorb the energy of different impact intensities. This efficiently and economically provides GDISR sheds with two security lines. Compared with conventional RC sheds, GDISR sheds with optimal incline have a more efficient anti-impact function, are faster and easier to repair, and are much simpler and cheaper to build.

Evaluation of the Impact Force of Dry Granular Flow onto Rock Shed

In the design of rock sheds for the mitigation of risk due to rapid and long landslides, a crucial role is played by the evaluation of the impact force exerted by the flowing mass on the rock sheds. This paper is focused on the influencing factors of the impact force of dry granular flow onto rock shed and in particular on the evaluation of the maximum impact force. The coupled DEM-FEM model calibrated with small-scale physical experiment is used to simulate the movement of dry granular flow coupled with impact forces on the rock-shed. Based on the numerical results, three key stages were identified of impact process, namely startup streams slippery, impact and pile-up. The maximum impact force increases linearly with bulk density, and the maximum impact force exhibits a power law dependence on the impact height and slop angle respectively. The sensitivities of bulk density, impact height, and slope angle on the maximum impact force are: 1.0, 0.496, and 2.32 respectively in the benchmark model. The parameters with high sensitivity should be given priority in the design of the rock shed. The results obtained from this study are useful for facilitating design of shed against dry granular flow.

丽香铁路达落双线中桥增设棚洞结构设计

该文以在建丽香铁路蒙古哨隧道出口与七达里隧道进口间达落双线中桥为工程依托,根据地形地质、落石重量、坡面高差、结构跨度及防护等级等基本情况,分析常规明洞、柔性钢网棚洞、拱桥棚洞、纵向刚架棚洞及横向刚架棚洞各自适用条件,选用合理的棚洞型式及结构尺寸。研究结论表明,对隧道坡面危岩落石重量及高差进行详细的调查分析,是确定采用柔性钢网棚洞还是钢筋砼刚性棚洞的前提。钢筋砼刚性棚洞沿线路方向跨度、冲沟排洪要求及基岩完整程度,是确定刚性棚洞具体类型的关键。落石冲击强度选用路基手册计算法较为合适,落石冲击力按移动荷载考虑,移动步距按2 m考虑为宜。棚洞结构内力及构件尺寸计算时,按落石不同位置的弯矩包络图最不利工况考虑。

落石冲击棚洞复合缓冲垫层动力响应研究

为探明棚洞聚乙烯泡沫、混凝土板复合垫层抗落石冲击性能,以框架型棚洞为研究对象,基于模型试验研究了不同高度落石冲击下落石冲击荷载及棚洞动力响应规律。结果表明:随着落石高度的增大,落石冲击力、冲击压力和棚洞顶板位移峰值、振动加速度峰值增大,线性关系明显。与纯砂垫层相比,聚乙烯泡沫和混凝土板复合垫层落石冲击力、冲击压应力、棚洞顶板位移、振动加速度峰值均显著减小;其中,混凝土板复合垫层落石冲击力、冲击压应力峰值最小,聚乙烯泡沫复合垫层棚洞顶板振动加速度峰值最小;落石冲击能量较大时,聚乙烯泡沫复合垫层棚洞顶板位移峰值最小。研究结果可为防落石棚洞复合垫层设计提供参考。

不同形状落石冲击棚洞动力响应试验研究

为探明落石形状对棚洞结构动力响应、落石冲击荷载的影响,以框架型棚洞为研究对象,采用缩尺模型试验研究不同形状落石冲击作用下落石冲击力、冲击压应力、棚洞顶板位移、振动加速度的变化规律。结果表明,落石形状对棚洞顶板位移、振动加速度影响显著,与正方体落石冲击棚洞相比,不同高度球体与椭球体落石冲击作用下,棚洞顶板位移分别减小了41.1%,76.1%,棚洞顶板振动加速度分别减小了35.7%~68.9%,71.7%~87.6%。正方体落石冲击力、冲击压应力最大,球体落石次之,椭球体落石最小。

峡谷区公路桥隧衔接段危岩运动模拟及轻量化防护预警体系探讨

深切峡谷区公路桥隧衔接段危岩落石极为普遍,具有高陡、面广量大、致灾随机性强等特点,存在识别难、绕避难、防治难、养护难等诸多工程难题,使得现有防护措施面临巨大挑战。以巫溪隧道出口危岩为例,采用无人机倾斜摄影测量技术建立山体高精度三维模型,快速准确识别危岩及其分布,利用RockFall及CRSP-3D软件模拟落石运动特征。结果表明:1)落石以自由飞落、滚动、弹跳为主;2)无防护工况下落石最大弹跳高度大于70 m,最大冲击能量9000 kJ,主被动防护工况下,仍有10%的高位落石破网而出;3)LS-DYNA模拟显示,冲击作用下柔性棚洞可拦截破网落石,棚洞各构件处于弹性状态,但拱架基础在低能落石冲击下易破坏。基于此,提出深切峡谷区桥隧衔接段突发型及渐进型危岩落石全寿命周期轻量化预警防护体系,以实现“高能易修、中能无害、低能零损”的防护预警目标。

穿越碳质千枚岩破碎带隧道侵限及塌方的处治

基于316国道某穿越碳质千枚岩破碎带隧道侵限及塌方处治施工过程,根据现场侵限及塌方情况,分别对侵限段和塌方段进行处治。工程实践表明,采用“大管棚+小导管超前支护施工+空腔填充”技术进行超前支护对穿越碳质千枚岩破碎带隧道塌方进行处治较合理,施工效果良好,施工处于安全可控范围内。

浅埋隧道施工过程中的围岩变形及控制研究

为了探究弹性模量、内摩擦力及粘聚力等围岩参数对隧道围岩施工变形的影响,同时分析管棚布设对围岩变形的控制效果,文章以某公路隧道工程为依托,通过Midas有限元软件建立模型,通过模拟计算得出以下结论:(1)竖向位移发生在围岩各部位,拱顶、拱肩、拱腰处为沉降,拱脚及隧底为隆起;(2)水平位移发生在拱肩和拱腰处,水平位移量及变动幅度小于竖向位移;(3)随着弹性模量增大,各部位的竖向位移减小;拱肩、拱腰处水平位移减小,拱脚处水平位移无变化;(4)随着内摩擦角增大,拱顶、拱肩、拱腰处竖向位移减小,拱脚、隧底竖向位移增大;水平位移均减小,拱肩受影响最为显著;(5)随着粘聚力增大,竖向位移及水平位移均减小,拱腰受影响较为显著;(6)管棚注浆法对围岩变形有限制作用,增大管棚布设范围对拱顶竖向位移的控制效果更明显。

泥化软岩巷道的支护优化设计

为解决采用传统U型钢支架对软岩巷道进行支护所面临的冒顶和两帮移近量增加的问题,对1201工作面基本地质条件分析的基础上,分析了传统U型钢支架支护不到位的原因,并提出了采用管棚进行超前支护和注浆加固进行强化支护的理念,并对优化后的效果进行综合评估,得到理想优化效果。

综采工作面超前应力区围岩控制技术研究

超前用应力区围岩控制是确保综采工作面稳定的关键,做好该项工作意义重大。本文在阐述围岩变形与破坏常见形式基础上,对工程实例,对综采工作面超前应力区围岩控制相关内容进行了探究,以期对相关工作人员有所帮助。

膨胀性软破岩层深竖井施工分级支护研究

境外某铜金矿千米深竖井在通过膨胀性软破岩层(泥灰岩)时,围岩遇水膨胀压力极大,先后出现两次井壁垮塌和开裂的情况,对施工进度及施工人员安全产生极大影响。为解决该问题,查找相关文献资料及国内外类似施工案例,对通过膨胀性软破岩层的井壁破裂机理进行分析,针对性地制定井壁破裂修复方案;在此基础上,进一步调查施工地点的工程地质和水文地质情况,通过分析与总结,提出深竖井不良岩层的施工及分级支护方案,对其所穿过的膨胀性软破岩层的围岩制定分级表,根据不同岩体等级分别提出相应的施工及具体支护方案。通过对两次破裂处井壁的修复,较长时间内未出现裂缝及漏水现象,修复效果良好,达到预期;此外,竖井井筒后续施工中在采用分级支护方案后,井筒顺利通过厚度超过500 m的不良岩层,且在工期、质量、安全三个方面都取得良好效果,保障该深竖井工程的施工质量与施工安全。该工程为膨胀性软破岩层中的深竖井掘进施工积累了宝贵经验,对类似工程具有一定的借鉴意义。

防治危岩落石桥梁棚洞一体化结构设计防护能级划分标准研究

基于铁路工程建设运营安全需求,尤其是中西部山区危岩落石易发的实际情况,分析国内外防治危岩落石防护柔性和刚性棚洞应用现状,对比防护网、明洞、棚洞不同结构类型情况下防护方式的防护能级范围,梳理目前国内铁路典型棚洞设计能级指标实际,针对桥梁棚洞一体化结构特点、常见落石计算防护能级和200、500、1000 kJ 3种防护能级在主梁、棚洞使用钢筋、混凝土用量的经济性比较,提出我国铁路工程防治危岩落石桥梁棚洞一体化结构设计防护能级划分标准建议。

软塑黄土层对浅埋黄土超大断面隧道围岩变形的影响

为解决在建西延高铁洛川隧道长大距离穿软塑黄土层施工中存在的问题,进行围岩变形数值模拟分析,建立三台阶预留核心土法施工模型,软塑黄土层分布在拱顶、边墙、拱底时,不同层厚(1、3、5 m)对拱顶下沉及拱腰收敛变形产生影响,结合监控量测数据提出合理的变形控制措施。研究结果表明:(1)对软塑黄土层不同分布以及不同厚度工况下围岩位移进行对比,发现软塑黄土层的存在增大了围岩位移,软塑黄土层分布较其厚度影响更明显,当软塑黄土层位于隧道拱顶上方且厚度为5 m时,影响最大。(2)浅埋软塑黄土隧道在超前管棚作用下,围岩竖向位移与水平位移相较于无管棚超前支护时位移减小,在穿软塑黄土层施工时要及时做好防护。(3)拱顶下沉及拱腰收敛随开挖均呈断崖式急剧变形、持续缓慢变形和变形趋于平稳3个阶段。因此,实际施工时应及时开展开挖初期急剧变形阶段的变形控制,并加强围岩监控量测。

Anchoring mechanism and application of hydraulic expansion bolts used in soft rock roadway floor heave control

Comparing with the resin bolt, the hydraulic expansion bolt has different anchoring mechanism and application advantage. According to the working mechanism of the hydraulic expansion bolt, its anchoring force is expressed in four forms including support anchoring force, tension anchoring force, expansion anchoring force and tangent anchoring force, and their values can be obtained on the basis of each calculation formula. Among them, the expansion anchoring force, which is the unique anchoring force of the hydraulic expansion bolt, can provide confining pressure to increase the strength of rock. Aiming at solving the problem of stability control in the soft rock roadway in Jinbaotun Coal Mine which has a double layer of 40 U-type sheds and cannot provide enough resistance support to control floor heave, the study reveals the mechanism of floor heave in the soft rock roadway, and designs the reasonable support parameters of the hydraulic expansion bolts. The observed results of floor convergence indicate that the hydraulic expansion bolts can prevent the development and flow of the plastic zone in the floor rock to control floor heave. Research results enrich the control technology in the soft rock roadway.

落石冲击作用下棚洞-拦石墙顶板及缓冲层的动力响应

以黔张常铁路(黔江—张家界—常德)为例,采用离散元软件PFC3D与有限差分软件FLAC 3D进行耦合计算,研究落石冲击棚洞-拦石墙顶板及缓冲层的动力响应,优化棚洞-拦石墙顶板及缓冲层设计,并对掺有轮胎颗粒的缓冲层进行研究。结果表明:可适当减小棚顶厚度,达到减轻结构自重与节省原料的目的,但棚顶厚度不宜小于0.4 m;适当增加缓冲层厚度可以减小落石冲击力,从而减小顶板挠度与应力,且缓冲层厚度不宜低于0.50 m;缓冲层添加20%~30%轮胎颗粒能有效提升缓冲层防护效果。

锚索肋板式拦石墙结构稳定性及动力响应研究

为了满足站场扩线落石防护范围需求,在既有棚洞防护措施基础上,提出了棚洞-拦石墙组合结构。该结构底部为既有棚洞或新建门式基础,上部为锚索肋板式拦石墙。根据受力分析,计算了棚洞-拦石墙组合结构稳定安全系数,并通过ANSYS/LS-DYNA软件对落石冲击该组合结构的动力响应进行了研究。结果表明:棚洞-拦石墙组合结构稳定安全系数较高,能够满足抗滑动和抗倾覆稳定性要求;落石冲击拦石墙面板后,受重力作用,会回弹继续冲击棚洞或新建门式基础顶板缓冲层;该组合结构能够抵抗落石对拦石墙的冲击作用,增加站场扩线防护范围。

巷道掘进过陷落柱技术研究

为确保3103运输巷安全高效掘进通过X1陷落柱,依据现场条件确定掘进及支护方案,并进行工程应用。在过陷落柱期间采用炮掘方式可更好的陷落柱破碎围岩条件并提高掘进安全系数;变更巷道断面后可避免顶板及巷帮交汇位置出现应力集中,降低顶板及巷帮变形量;采用全锚索及钢架棚支护,充分发挥主动支护及被动支护优势,实现陷落柱破碎围岩有效控制。现场应用后,巷道在陷落柱影响区内仍可保持5.0 m/d掘进速度,期间未出现冒顶、片帮等问题同时顶板始终持稳定,顶板、巷帮最大收敛量分别为95 mm、55 mm,采用的掘进及围岩支护方式实现了巷道安全高效过陷落柱。

滑动构造下高应力“三软”煤层巷道支护技术

矿井因受滑动构造应力影响且处于“三软”煤层地质条件下,煤巷支护十分困难,常常需要频繁返修。为了解决巷道容易变形的问题,通过在煤巷采用不同的支护方式进行对比分析,摸索出一套适合矿井该特殊地质条件下的围岩综合控制技术,采用锚网索+U36钢棚复合支护方式有效控制了巷道变形速度,实现了长距离巷道不返修,解决了矿井因煤巷变形快严重影响安全生产的问题。同时,该技术的研究与应用也为滑动构造下高应力“三软”煤巷支护提供了借鉴。