Field,experimental, and numerical investigation of a rockfall above a tunnel portal in southwestern China

Combining the results of detailed field investigation, laboratory tests, and numerical simulations, this paper studies the rockfall problem above a tunnel portal. The mechanism of potential rock instability was analyzed, and model tests were conducted based on geological conditions and described in detail, so as to study the restitution coefficients used in programs simulating rockfall trajectory. Improvements in the tests were made in terms of experimental techniques and creative similar materials. A newly developed test bench was built by steel frames and can be assembled or disassembled at will according to requirement of model size. An innovative block-release device was adopted and controlled by computer to change the release position of block. During the model construction, the slope and blocks were fabricated with similar materials developed through quantities of mixing proportion tests. Then experiments were conducted with varied shape, mass, and release height of blocks to clarify their effect on restitution coefficients. Results indicate that restitution coefficients are apparently related to these factors and their values decrease when block mass and releasing height increase. Restitution coefficients of the wedge block are larger than those of a sphere or cuboid block. Subsequently, numerical simulations adopting the calibrated parameters were performed, and the velocities, bounce heights, and kinetic energies of rockfall along the slope profiles were obtained. Based on the research, this paper provides a useful reference for practical remediation design.     

Rock slope deformation mechanism in the Cihaxia Hydropower Station,Northwest China

Complex block-flexure slope toppling is observed in interbedded sandstone and slate in the upper Yellow River, China. Block toppling is observed in the relatively hard sandstone and flexural toppling is observed in the relatively soft slate. The evolution of toppling slope deformation is characterized by long-term progress and spatial variability. In order to study these characteristics, field investigations, adit prospecting, borehole drilling, sonic tests and numerical simulation were carried out. In addition, the effect of the structure, the composite mode of the rock mass, the unloading fissures and geomorphology are discussed. Furthermore, we explored the toppling mechanisms and simulated it numerically; on this basis, the slope evolution is divided into four stages. Results obtained from the numerical simulation compared well with field investigation data (investigation data, rock sonic survey and strata dip statistics). Comparative studies have demonstrated that the analytical methods presented in this paper are appropriate for back analysis of the toppling evolution process. The result showed that this toppling slope has not yet entered the later progressivity failure stage and is currently limited to collapse at shallow levels, whereas the deep-seated rock mass will remain stable for a long time. This study might provide reference for a stability evaluation and hazard prevention analysis for rock toppling.

     

Bender element test and numerical simulation of sliding zone soil of Huangtupo landslide

Bulletin of Engineering Geology and the Environment - The stiffness property of soil at the low level of strain was often encountered in landslide. In order to study the effect of different...     

高校学生公寓楼单室火灾调查的数值模拟应用

采用数值模拟方法分析某高校火灾案例,研究火势增长和烟气蔓延过程,对火灾烟气主要组分的浓度、氧气浓度、温度等参数进行规律性揭示.模拟结果表明,公寓楼发生单室火灾时,如果阳台门开启,通风状况较好,燃烧速度会非常快,受火灾的影响比较严重的阳台区域处有害气体和温度均超出人体的承受限度,威胁人员的生命安全.因此,通风状况对受限空间单室火灾的发展过程影响很大.     

数值模拟在滑坡危险滑动面中的应用

利用FLAC3D对潜在的滑坡体进行模拟,划分出滑坡体的结构,确定危险滑动面的位置,并应用极限平衡法计算得出重新划分后的潜在滑坡体的稳定系数,判断滑坡体的稳定性,验证了数值模拟方法的正确性,为类型工程设计提供依据和参考。     

New insights into the failure mechanism and dynamic process of the Boli landslide,China

Bulletin of Engineering Geology and the Environment - The study of landslide initiation mechanisms and dynamic process analysis is important for monitoring, predicting, and controlling landslide...     

Experimental investigation and numerical simulation of a furnished office fire

Experiments were conducted in a full-scale model room equipped with both movable and fixed fire loads to explore fire growth and spread via heat release rates, indoor air temperature and species concentration. The room space is a brick structure that measures 5.7 m in interior length, 4.7 m in width and 2.4 m in ceiling height. The northeast and southeast corners each feature a 2.1 m × 0.9 m open doorway. Numerical simulations with parameter adaptation were carried out using FDS software to predict the fire features and were compared with the experimental results. In this study, the material properties and oxygen limit settings in the FDS software were tested to explore their influence on the tendency of heat release rate and on the total amount of heat release. The results show that the heat release rate from the FDS simulations is comparable to the full-scale experiment results during the fire growth period. Temperature profile near ceiling can be modeled well. In the full-involvement burning and decaying periods, the qualitative trends were identical, although the simulated value differed greatly from the experimental result.     

Downie Slide: numerical simulation of groundwater fluctuations influencing the behaviour of a massive landslide

Groundwater levels at Downie Slide have varied during the development of and over the operating life of the Revelstoke Reservoir. Drainage system construction successfully lowered groundwater levels through the central portion of the slope; reservoir filling resulted in water table rise near the inundated toe, and over the operating life of the hydro-electric facility gradual, minor losses to the drainage system capacity have resulted in a slow rise in water table levels. Calibrated models capable of reproducing observed deformation patterns at Downie Slide have been tested with changing groundwater levels. Models perform well, adequately reproducing observations of global slope response to changes in piezometric boundary conditions. These models have also been used to test potential trigger scenarios, including rapid reservoir drawdown and a total loss of drainage system capacity.     

武隆鸡尾山滑坡形成机理数值模拟研究

2009年发生的重庆武隆鸡尾山滑坡,因滑源区斜坡岩层整体缓倾山内,缺乏有效的临空面和滑移空间,因此,在滑坡孕育过程中存在前缘岩溶带压缩变形、底部剪切滑移、后缘拉裂以及最终前缘关键块体(岩溶带)侧向剪断滑出等一系列的复杂动力学行为。这一过程存在显著的连续变形向非连续变形的过渡与转化,单纯用连续介质的有限元和离散介质的离散元来分析模拟都很难取得较好的效果。为探究鸡尾山滑坡的孕育过程和失稳机理,运用将连续–非连续单元有机耦合的大型数值模拟软件CDEM,模拟鸡尾山滑坡的失稳过程和形成机制。研究表明:滑体前方岩溶发育带具有"可压缩性",为滑体运动提供了一定的变形空间;滑源区下方的采矿活动产生应力重分布,滑带抗剪强度降低,滑体沿其底部软弱带发生剪切蠕滑,并逐渐形成滑体后缘拉裂缝;滑动块体在向前滑移过程中不断挤压向前缘"易压缩带",坡体应力自组织调整,并逐渐在前部三角区形成垂直的第二破裂面,前缘抗力体(关键块体)形成,最后剪断岩溶带个别与稳定山体咬合岩块,整体失稳破坏。数值模拟结果较好地揭示了武隆鸡尾山滑坡前缘视倾向展布岩溶带"软基效应"所提供"准临空面",重现了鸡尾山滑坡"蠕滑—拉裂—压缩(压碎)—剪切滑出"的致灾机理。     

强震区隧道施工塌方段震害机理及处治技术研究

汶川地震公路隧道普通段衬砌垮塌震害均发生在施工塌方段。依托汶川地震公路隧道普通段震害调查资料,对强震作用下隧道施工塌方段进行震害特征、震害机理及处治技术研究具有重要的意义。揭示了汶川地震区公路隧道施工塌方段震害特征:软弱围岩施工塌方段均出现了二衬垮塌震害,严重段落甚至出现衬砌整体垮塌震害。探明了强震区隧道施工塌方段震害机理:地震惯性力影响明显;强制位移影响较小。强震区隧道施工塌方段采取"回填注浆+交错设缝"的处治措施后,主应力和内力的减震率均在35%以上,这说明"回填注浆+交错设缝"处治措施对隧道施工塌方段抗减震具有明显效果,是一种行之有效的处治措施。研究结论对于高烈度艰险山区交通生命线的抗减震技术具有重要的意义。     

数字滑坡技术及其在天台乡滑坡调查中的应用

“数字滑坡”技术,是在我国前期滑坡遥感工作基础上,在现代先进信息技术支持下发展起来的滑坡遥感新技术。利用“数字滑坡技术”和滑坡前后的高分辨率卫星数据对2004年9月5日发生在中国四川省的天台乡滑坡,进行了详细调查。获取了滑坡边界、规模、各部分的滑动方向和滑动距离、运动方式、加载和减载部位及方量等数据。基于滑坡地学原理进行的分析认为义和村斜坡虽具有发生滑坡的岩性、构造及临空面基本条件,但在2004年9月5日滑坡前其总体上为一稳定斜坡,这次滑坡性质为义和村斜坡上的首次大规模滑动,滑坡的滑动方式为牵引式,规模约为2300万方,一年前修筑公路是滑坡潜在的诱发因素;滑坡发生前连续强降雨是直接触发因素。     

The role of active faults and sliding mechanism analysis of the 2017 Maoxian postseismic landslide in Sichuan,China

A giant, high-position rockslide occurred in Xinmo village of Maoxian County, Sichuan, China, on June 24, 2017. It was the largest rockslide recorded since the 2008 Wenchuan earthquake, and caused great loss. We use field survey data and relevant information to describe the geometric and zoning of the Maoxian landslide, and we discuss its sliding mechanism and the role of active faults in its formation. The sliding mode of the Maoxian landslide involves a plane failure mechanism (sliding rupture), while the slipping process can be divided into two stages: a rock cracking and deterioration stage, and a high-speed sliding stage. The role of active faults (earthquake and fault movement) is probably the most important factor in the Maoxian landslide formation, while lithology played a catalytic role and rainfall acted as an inducing factor. The fault vertical combination model (“back thrust” dynamic model) proposed in this paper provides a reasonable explanation for the different distribution of the coseismic landslides caused by the 1933 M 7.5 Diexi earthquake. We consider that a steep slope near the active fault, especially where the active fault intersects, just like the “locked segment” of a fault, is the uppermost area to develop a large landslide.

     

FDS数值模拟技术在某“商住合用”建筑火灾调查中的应用

采用FDS数值模拟的方法,再现了某典型“商住合用”建筑底层商铺火灾蔓延和烟气传播的过程。针对火灾现场调查和数值模拟实验研究结果,对“商住合用”建筑的消防安全提出了建议。     

沟埋式涵洞非线性土压力试验研究与数值模拟

现行公路桥涵设计通用规范中线性土压力理论未能准确反映沟埋式涵洞涵顶垂直土压力变化规律,土压力计算结果与实际情况存在差异,导致涵洞在施工或使用过程中出现不同程度的病害。结合现场试验和数值模拟研究了沟埋式涵洞垂直土压力的变化规律,以及涵顶填土内部的土拱效应,分析了涵顶平面土压力及不均匀沉降的分布规律。研究结果表明,并非所有沟埋式涵洞涵顶垂直土压力都小于按线性土压力理论计算结果,它与填土高度、沟谷宽度、沟谷坡角、涵洞几何尺寸、填料性质及地基刚度等因素有关,涵顶垂直土压力随各影响因素呈非线性变化。填土达到一定高度后,涵顶填土内部产生土拱效应,该效应能够缓解涵顶应力集中现象,但其具有不稳定性。沟埋式涵洞的设计与施工应综合考虑各因素对涵洞受力状态的影响。     

大开地铁车站地震破坏模拟与机理分析

1995年日本阪神地震中塌毁的大开地铁车站震害事例引起了人们对地下结构抗震问题前所未有的关注和重视。针对这一震害事例,国内外已开展了大量的理论、数值和试验研究工作,对震害机理和破坏模式等进行了深入、系统的解析,但迄今并未形成一种系统性的共识。基于大开地铁车站三维非线性数值分析模型,采用时域显式整体分析方法,从围岩土体对浅埋地下结构的两种地震作用效应、组成结构构件不同的受力功能,以及关键构件的力学性能与体系受力分配改变导致的侧墙、中柱变形能力不协调等方面,系统阐述了大开地铁车站的地震破坏机理和失效模式,并提出了抗震关键支撑柱概念。     

西南某高位滑坡成因机制及稳定性分析

以西南某高位滑坡为例,通过现场测绘、钻孔揭露、航拍、现场监测及室内现场实验等手段,对该滑坡体的基本特征进行了较深入的研究,并对该高位滑坡的变形特征、成因机制及稳定性进行了初步分析。     

新型大跨索结构避难帐篷现场试验与数值模拟

基于现场试验,对实测风荷载作用下大跨度索结构避难帐篷的顶点位移进行测量,分析风速对顶点位移的影响,得出了实测风荷载与结构顶点位移之间的关系。应用ABAQUS有限元软件对风荷载作用下的大跨度索结构避难帐篷的顶点位移进行有限元计算,有限元计算结果与试验结果具有较好的一致性。通过降低脚手架材料的刚度,模拟不同刚度条件下结构的风载-位移响应;并模拟了雪荷载以及温度荷载作用下大跨度索结构避难帐篷的受力性能。研究结果表明:大跨度索结构避难帐篷的抗风、抗雪荷载性能以及温度荷载作用下的变形幅度均能达到安全使用要求。     

Analysis of landslide stability under seismic action and subsequent rainfall: a case study on the Ganjiazhai giant landslide along the Zhaotong-Qiaojia road during the 2014 Ludian earthquake,Yunnan, China

In a strong earthquake, not only a large number of coseismic landslides are triggered, but relaxation and cracks in the rocks and soils are induced, which make these rocks and soils vulnerable to instability during subsequent rainfall; thus, strong earthquakes always have long-term effects on landslides. The geo-hazards along the Zhaotong-Qiaojia road in the 2014 Ludian earthquake (Ms 6.5) of Yunnan Province, China, were investigated, and the Ganjiazhai giant landslide was chosen as a case study. First, using the limit equilibrium analysis and Newmark method, the critical seismic intensity of the landslide before the earthquake was evaluated. Secondly, the dynamic failure process of the landslide under the measured ground motion was simulated with the discontinuous deformation analysis method. Lastly, based on stress–seepage coupling analysis and precipitation data from Ludian meteorological station, the stability of the landslide during subsequent rainfall after the earthquake was predicted. The results show that the critical seismic intensity was within degrees VIII–IX, which is consistent with the results of the earthquake damage investigation. The dynamic failure process can be divided into four stages, and four scarps formed; the potential sliding zones during the subsequent rainfall were at the first scarp and the fourth scarp, and their critical rainfall amounts were 35–40 mm and 55–60 mm, respectively. In this paper, failure process simulation and stability prediction of the landslide before, during, and after the strong earthquake are presented, which provide analysis methods for the dynamic stability of landslides in the meizoseismal area.

     

铁路客站无组织渗风现状调研及数值模拟研究

通过对全国16个大型铁路客站现场调研,总结了客站主要空间的无组织渗风现状及特点,归纳了目前控制无组织渗风的节能做法。通过调研发现,由于客站建筑及使用特点,大量的无组织渗风量增加了夏季空调和冬季供暖能耗,并且影响室内热舒适。通过数值模拟方法,分析了门斗和空气幕对客站无组织渗风的控制效果,并对各自控制无组织渗风的特性给出了评判和使用建议。