Excess pore pressure and grain crushing of sands by means of undrained and naturally drained ring-shear tests

An investigation of excess pore-pressure generation of a weathered granitic sand, taken from the source area of a typical landslide caused as a result of liquefaction, and a fine silica sand was conducted, in which grain crushing within the shear zone of ring-shear test specimens was examined as the key phenomenon of rapid long-runout motion of landslides. In order to investigate and explain the low average apparent-friction angle, mobilized in a liquidized landslide, speed-controlled ring-shear tests were conducted under undrained conditions on weathered granitic-sand specimens, formed under a wide range of initial void ratios. It was revealed that very small steady-state shear resistances were obtained irrespective of the initial void ratios, which can explain the low average apparent-friction angle. In addition, two series of ring-shear tests on weathered-granitic and fine-silica sands were conducted under naturally drained conditions by keeping the upper drain valve of the shear box open during the tests. The first series of tests was performed under differing total normal stresses, but at the same shear speed, and the second series was conducted at differing shear speeds, but under the same total normal stress. In order to investigate and analyze excess pore-pressure generation and dissipation within the shear zone that is associated with grain crushing, permeability analyses were conducted by passing water through the sample box of the ring-shear test apparatus before and after shearing. In addition, grain-size distribution analyses of samples taken from the shear zone after shearing were carried out. For the weathered granitic-sand samples, a significant change in bulk permeability and large amount of grain crushing were observed. In these tests on the above soil, a considerable reduction of shear resistance, which increased proportionally to the total normal stress and shear speed, were obtained. It was observed that due to grain crushing, finer grains that lowered the permeability of the soil in the shear zone, were formed. It is likely that the decrease in permeability facilitated the generation of high excess pore pressures by reducing the pore-pressure dissipation rate from the shear zone; thus, flow behaviour was exhibited even under naturally drained conditions.     

Evolution of Shear-Zone Structure in Undrained Ring-Shear Tests

Undrained monotonic torque-controlled tests were conducted on fine-grained silica sand to study the shear-deformation process in granular materials by using a ring-shear apparatus. Shear-zone structures at various stages in the undrained shear tests were observed during a series of tests in which the experiments were terminated at different shear displacement. For undisturbed samples, the shear zone was only developed during the post-failure stage and its thickness increased with progressed shearing. First the shear surfaces had undulating and asymmetric structures; later they gradually became smooth and parallel to the shearing direction. During this process, pore water pressure was generated, and the effective friction angle decreased correspondingly. Generally, the shear zone could be divided into three parts: the compacted core, the adjacent zone above the core, and the adjacent zone below the core. Grain-size analysis on the sample from the shear zone revealed that grain crushing occurred during each stage and the extent of grain crushing differed for different shear stages. An interesting phenomenon occurred during the steady-state deformation where the coarse and fine particles within the shear zone segregated during motions and a parallel orientation structure developed. These results are helpful for understanding the mechanism of progressive failure in granular material as well as the rapid landslide with long runout study.     

高压力下层间错动带残余强度特性和颗粒破碎试验研究

针对某水电站层间错动带的原状样与重塑样,模拟现场地应力条件,在试验法向应力高达10 MPa条件下开展了反复直剪试验。试验结果表明：原状样峰值强度高于重塑样,但强度下降较快,二者残余强度趋于一致;此外,试样发生了大规模的颗粒破碎,采用颗粒相对破碎势Br量化重塑样剪切面附近区域与非剪切面附近区域颗粒破碎程度,对比发现,前者颗粒破碎程度高于后者,且破碎机制不同;剪切面颗粒破碎是高压力下残余强度包线非线性的根本原因：剪切强度的下降（残余强度与峰值强度的比值）与Br和S2（试验前后小于粒径< 2 µm 颗粒含量的比值）呈线性关系,颗粒破碎导致的能量释放和不断产生的黏粒（< 2 µm）降低了剪切强度。     

高速滑坡形成机制： 土粒子破碎导致超孔隙水压力的产生

通过排水剪切试验，揭示出易于产生粒子破碎的土体易于产生体积变化，土体初始结构和粒子破碎难易度对体积变化各阶段的影响。在与之相对应的不排水试验中，产生粒子破碎的土体最终产生了较高的超孔隙水压力，而且孔隙水压力产生的各阶段与排水试验中的体积变化阶段具有良好的对应关系。揭示了不同诱因产生的高速滑坡的共同特征，即在长距离运动中，由于粒子破碎的影响，滑动面土体在不排水条件下，抗剪强度因超孔隙水压力上升而下降，最终导致高速滑坡。同时，由于粒子破碎将导致土体自身渗透系数降低，土粒子破碎因而具有促进超孔隙水压力产生和减缓超孔隙水压力消散的双重效果。     

Fast shear behavior of granular materials in ring-shear tests and implications for rapid landslides

The high mobility of rapid landslides is one of the most important subjects of both theoretical and practical interest to engineers and scientists. The idea that ultralow resistance could explain the high mobility inspires researchers to examine the shear behavior of granular materials under a wide range of conditions, but the response of granular materials to fast loading rates is largely unknown. The motivation for this study was to examine several fundamental issues of particle properties and mechanical conditions on the fast shear behavior of granular materials. Two granular materials were studied in the oven-dried state and were sheared by employing a ring-shear apparatus. Results indicated that angular particles (silica sand) had higher shear strength parameters than spherical particles (glass beads). In addition, the dilative process was observed during shearing, which depended on normal stress and particle shape. A slightly negative shear-rate effect on shear strength was observed for both granular materials under a certain range of shear rates. Furthermore, cumulative shear displacement had a significant effect on the degree of particle crushing. Fast ring-shear tests also revealed that shear rate had a slightly negative effect on particle crushing. Based on these experimental results, the possible applications of dynamic grain fragmentation theory to assess the high mobility of rapid landsliding phenomena were discussed. It was indicated that the magnitude and release rate of elastic strain energy generated by grain fragmentation played important roles on the dynamic process of landslide mobility.     

高应力下剪切速率对砂土抗剪强度影响研究

应用DRS-1型高压直剪仪,进行了16组法向应力水平、5种剪切速率条件下福建标准砂的抗剪强度试验,试验结果表明,高应力下砂土的抗剪强度受法向应力和剪切速率的共同影响。法向应力和剪切速率通过影响颗粒破碎和颗粒重排列程度等试样的细观参数,决定了砂土宏观上抗剪强度的发挥。当法向应力较小时,砂土抗剪强度与剪切速率基本无关;但是当法向应力较大时,较快剪切速率条件下的砂土抗剪强度变小,且其摩尔强度包线出现了“下弯-上扬”循环波动,因此不可以忽略剪切速率对砂土抗剪强度的影响。     

颗粒形状对粗粒土剪切变形影响的细观研究

颗粒形状是影响粗粒土密实度、力学与渗流等特性的主要因素之一。为了分析颗粒形状对粗粒土剪切特性的影响,采用离散元法生成4种不同形状的颗粒组,进行粗粒土直剪试验模拟与剪切宏细观响应研究,得出了颗粒形状对剪应力-剪位移、体应变-剪位移的影响,分析了粗粒土剪切应力、应变特性与剪胀特性。通过分析剪切带厚度、颗粒旋转量值、平均接触数、孔隙率及接触力系等宏细观参量的演化规律,研究颗粒形状在宏细观尺度上对粗粒土的影响。研究表明:异形颗粒间的咬合自锁作用大于纯圆颗粒,试样的抗剪强度有随形状系数的减小而增大的趋势。试样颗粒在外荷载作用下发生运动,应变主要表现在颗粒运动剧烈、剪胀幅度较大的剪切带内。颗粒形状系数F减小,试样的初始平均接触数增加,内摩擦角φ增大,剪切带内孔隙率增量越大,剪胀幅度越大。剪切过程中强力链聚集于剪切带内并起骨架作用,随着形状系数的减小,力链长度在0～5所占百分比呈增大趋势;剪切带内强力链的数目随着形状系数的减小而增加,峰值含量在30%～35%之间。     

细粒含量对冰碛土抗剪强度影响的实验研究

为研究细粒组颗粒在浸水/降雨条件下产生迁移对冰碛土抗剪强度的影响,从西藏林芝市帕隆藏布嘎隆寺沟流域内采取冰碛土样品,进行7种不同细粒（粒径小于2 mm）含量情况下的冰碛土比重和相对密度的测试,开展了不同围压下的大型饱和固结不排水三轴（CU）实验。结果表明：（1）细粒含量对干密度的影响较小,不同细粒含量的冰碛土孔隙比大致相同,细颗粒对孔隙具有改造作用,不同细粒含量会引起孔隙结构的差异,从而导致冰碛土的结构差异,最终导致抗剪强度的不同;（2）细颗粒迁移导致冰碛堤坡脚和内部一定深度细粒含量较高,达到一定的量值时,抗剪强度明显降低,冰碛堤容易发生剪切破坏;（3）细粒含量对抗剪强度参数的变化具有重要影响,从中还可以反映出冰碛土结构控制的变化：粗颗粒控制→粗细颗粒共同控制→细颗粒控制。研究结果对于评价冰碛堤的稳定性具有重要意义。     

粗粒土大型剪切试验剪切带变形特征分析

采用含有叠环的大型粗粒土直剪试验设备进行试验,叠环作为剪切盒的重要组成部分,可以在剪切时根据粗粒土的结构形成多组剪切面,能够明显地展现出粗粒土的剪切变形特征.为了分析硬质岩粗粒对粗粒土的剪切强度和变形的影响,对粗粒岩性为花岗岩的粗粒土进行大型叠环式直剪试验.通过分析得到试验特征规律,研究粗粒土在剪切过程中的颗粒运动,得出花岗岩粗粒对其组成的粗粒土的剪切强度和变形有很大的影响.硬质岩性的花岗岩颗粒在剪切时不易被剪碎,在剪切过程中主要做错位、翻滚运动.低轴压下,剪切带位移会出现阶梯现象,而在高轴压下,剪切带位移为线性变化,并表现出更加明显的剪胀现象.粗粒土在剪切破坏后依然具有较高的抗剪强度和稳定性,为工程建设中土石体材料的选取提供了一定的借鉴.     

珠海海积软土剪切带微观结构试验研究

天然软土剪切带性状分析一直是岩土力学界的一个研究重点。采用电镜扫描和压汞法对珠海海积软土剪切带内外以及带边缘微观结构进行定量分析,研究结果表明：珠海软土的应力-应变曲线在低围压下表现出明显应变软化特征;软土在剪切破坏后,剪切带内的微观参数变化率最大,其次是剪切带边缘,最后是剪切带外;剪切带边缘上的颗粒逐渐沿着剪切应力的方向呈定向排列,而剪切带内,由于颗粒发生破碎、折断,颗粒排列是随机的,在剪切带外,颗粒的排列受剪切破坏的影响较小;珠海海积软土的孔隙入口孔径分布为主单峰分布,其主峰峰值的位置是沿着剪切带外--带边缘--剪切带内转移;Roscoe理论和Arthur经验公式预测的剪切带倾角与实测值相比都偏小,不适宜黏性土的剪切带倾角预测计算;Mohr-Coulomb理论计算出的倾角与实测值比较一致。     

Structures,kinematic analysis,rheological parameters and temperature-pressure estimate of the Mesozoic Xingcheng-Taili ductile shear zone in the North China Craton

The NE to ENE trending Mesozoic Xingcheng-Taili ductile shear zone of the northeastern North China Craton was shaped by three phases of deformation. Deformation phase D₁ is characterized by a steep, generally E–W striking gneissosity. It was then overprinted by deformation phase D₂ with NE-sinistral shear with K-feldspar porphyroclasts forming a subhorizontal low-angle stretching lineation on a steep foliation. During deformation phase D₃, lateral motion accommodated by ENE sinistral strike-slip shear zones dominated. Associated fabrics developed at upper greenschist metamorphic facies conditions and show the deformation characteristics of middle- to shallow crustal levels. In some parts, the older structures have been in turn overprinted by late-stage sinistral D₃ shearing. Finite strain and kinematic vorticity in all deformed granitic rocks indicate a prolate ellipsoid (L-S tectonites) near plane strain. Simple shear-dominated general shear during D₃ deformation is probably of general significance. The quartz c-axis textures indicate prism-gliding with a dominant rhomb <a> slip and basal <a> slip system formed mainly at low-middle temperatures. Mineral deformation behavior, quartz c-axis textures, quartz grain size and the Kruhl thermometer demonstrate that the ductile shear zone developed under greenschist facies metamorphic conditions at deformation temperatures ranging from 400 to 500 °C. Dislocation creep is the main deformation mechanism at a shallow crustal level. Fractal analysis showed that the boundaries of recrystallized quartz grains had statistically self-similarities. Differential stresses deduced from dynamically recrystallized quartz grain size are at around 20–39 MPa, and strain rates in the order of 10⁻¹² to 10⁻¹⁴ s⁻¹. This indicates deformation of granitic rocks in the Xingcheng-Taili ductile shear zone at low strain rates, which is consistent with most other ductile shear zones. Hornblende-plagioclase thermometer and white mica barometer indicate metamorphic conditions of medium pressures at around ca. 3–5 kbar and temperatures of 400–500 °C within greenschist facies conditions. The main D₃ deformation of the ENE-trending sinistral strike-slip ductile shearing is related to the roll-back of the subducting Pacific plate beneath the North China Craton.     

舒兰韧性剪切带应变分析及石英动态重结晶颗粒分形特征与流变参数估算

舒兰北东向韧性剪切带位于佳木斯-伊通断裂带(佳-伊断裂带)中南段, 剪切带内糜棱岩具有明显左行走滑特征, 片麻理产状近NNE向.糜棱岩中长石有限应变Flinn图解判别岩石类型为L-S型构造岩, 属拉长型应变.石英C轴EBSD组构分析表明, 石英组构以中低温菱面为主, 滑移系为{0001} < 110>.剪切带内糜棱岩的剪应变为0.44, 不同方法计算所得运动学涡度值均大于0.95, 指示剪切变形以简单剪切为主.综合矿物变形温度计、石英C轴EBSD组构、石英的粒度-频数图及Kruhl温度计综合估计该韧性剪切带变形机制以位错蠕变机制为主, 变质相为低绿片岩相, 发生韧性变形和糜棱岩化温度范围在400~500 ℃之间.糜棱岩内石英动态重结晶新晶粒边界普遍具有锯齿状或港湾状结构, 利用分形方法对其重结晶新晶边界研究表明, 这些晶粒边界具有自相似性, 表现出分形特征, 分形维数值为1.195~1.220.根据石英重结晶粒径估算差应力值为24.35~27.59 MPa, 代表了舒兰韧性剪切带糜棱岩化作用过程的差异应力下限.使用不同实验方法估算、比较和分析了该剪切带古应变速率, 认为该速率应为10-12.00~10-13.18 s-1, 与区域性应变速率10-13.00~10-15.00 s-1对比, 说明舒兰韧性剪切带的应变速率与世界上大多数韧性剪切带中的糜棱岩应变速率一致, 是缓慢变形的结果, 其形成可能与早白垩世伊泽纳崎板块向欧亚大陆俯冲发生转向有关.      

节理岩体锚杆的综合变形分析

在总结国内外对节理岩体中锚杆加固机制的试验研究和理论探讨基础上,综合考虑锚杆的切向和轴向变形能力,建立节理锚固锚杆在剪切荷载作用下的变形模型,将节理锚固锚杆的变形区划分为弹性变形段和挤压破坏段,引入表征挤压破坏段长度的变量,对锚杆与岩体的相互作用机制进行理论分析,推导了剪切荷载与剪切位移和轴向荷载与轴向位移的关系。通过分析锚杆的屈服破坏形式,得到了确定挤压破坏段长度的方法。最后,通过算例分析了挤压破坏段长度与锚杆直径、岩体强度、锚固角度等参数的关系,得到了以下结论：（1）节理锚固锚杆抗剪作用的实质是锚杆调动岩体的抗压强度抵抗节理切向荷载。在抗压强度较高的硬岩中,挤压破坏段局限于节理面附近,锚杆影响范围小;而在抗压强度较低的软岩中,挤压破坏段较大,而且会产生较大的剪切变形,锚杆影响范围较大。（2）锚杆屈服破坏形式与岩质和锚杆直径有关。硬质岩体发生剪切屈服,而较软岩体中容易发生弯曲屈服;小直径锚杆一般直接剪切屈服,而大直径锚杆可能发生弯曲屈服。锚杆屈服破坏后出现塑性铰,挤压破坏段范围在节理一侧约为直径的1～2倍,继续增加剪切荷载,挤压破坏段长度不再增大。（3）随岩质的不同,锚杆锚固节理的最优锚固角变化较大。岩质较硬时,最优锚固角度较小,反之则较大。     

基于三维数字图像相关技术钙质砂颗粒运动行为试验研究

桩基附近土颗粒的运动行为与宏观力学表现密切相关,对揭示界面剪切机制具有重要意义。利用自主研制的大型直剪仪,结合三维数字图像相关技术（3D-DIC）全场位移测量分析系统,开展了钢−钙质砂界面循环剪切试验,研究了界面附近砂颗粒的运动行为演化规律。结果表明：界面峰值剪切应力和发挥的界面摩擦角随循环次数的增大而增加,体变特性以剪缩为主;钙质砂颗粒左右移动的幅度与距界面的垂直距离成反比,钙质砂颗粒的位置随循环次数的增大逐渐向正剪切方向移动,试验结束时上剪切盒左侧区域的钙质砂颗粒向正剪切方向移动的距离最大;钙质砂颗粒在单个循环内出现有规律的上下移动,向下移动的幅值更大,位于上层的钙质砂颗粒向下移动的位移值大于下层;钙质砂颗粒的运动速度在沿单方向剪切时,呈现出慢−快−慢的变化规律,位于上剪切盒右侧区域的钙质砂的体变特性较左侧区域更显著;网格位移值和缺失数量随循环次数的增大而增加,在试验后期趋于稳定,试验结束时的破碎带厚度为 6.21 mm。     

基于机器学习的岩体结构面剪切破坏区域预测研究

剪切破坏区域是岩体结构面上下盘相对运动的主要接触区域,对抗剪强度具有重要影响。鉴于结构面剪切破坏区域与形貌特征的高度非线性关系,本文在分析结构面表面形貌特征及剪切机制的基础上,以粗糙度参数倾向、倾角、曲率、高差和孔径分布来描述结构面表面形貌特征。对结构面试样开展法向应力为1.0MPa的直剪试验,通过图像分割技术提取剪切破坏区域,利用多种机器学习方法构建结构面剪切破坏区域预测模型,建立结构面粗糙度参数与破坏状态之间的非线性关系,并采用训练准确率和AUC（Area Under Curve）值等指标对模型预测性能进行评估。结果表明所建立的模型中集成装袋树预测性能最好,其次是K最近邻,其训练准确率最高分别可达98.02%和97.38%,AUC值最高分别可达0.78和0.74。通过敏感性分析发现孔径分布对剪切破坏区域的影响最大。本研究对有效分析结构面的剪切破坏机理和准确评价抗剪强度具有重要意义。     

新近纪软岩质水平滑带的结构与内部黏土矿物聚集规律

新近纪软岩质水平滑带控制了平推式滑坡的滑移过程,其内部黏土矿物的分布规律决定着滑坡能否出现低角度滑移。为分析水平滑带内黏土矿物的聚集规律,论文对典型地质剖面内物质组成、结构、黏土矿物含量与对应力学性质开展了定量测试,试验发现随着累积位移的增大,水平滑带的结构呈碎裂化、劈理化、塑性化、泥化渐进破坏状。滑带上边界的累积位移量最大,中部剪切面、下边界面处累积位移逐次递减。在同一滑带内,累积位移量越大的剪切面,其黏粒含量、含水率就越高。以簸箕山滑坡为例,上边界面、中部剪切面与下边界面的黏粒含量分别达到62. 60%、62. 46%、58. 04%,含水率分别为28. 82%、25. 34%、25. 52%。滑带的剪胀机制控制了上述水岩耦合作用过程。     

泸定大渡河桥冰碛土的结构及现场剪切试验研究

泸定大渡河桥康定岸分布巨厚层冰碛土,为研究土的抗剪强度特性,在不同位置和深度进行了6组现场剪切试验,基于地质勘察和试验结果分析土的结构特征、剪切强度和变形特性及其与土的结构的关系。研究表明:冰碛土的颗粒以粗粒、巨粒粒组为主,骨架颗粒呈悬浮状,混杂、无序堆积,骨架间充填杂基,形成骨架悬浮密实结构。根据颗粒组成和骨架风化程度,划分为骨架悬浮密实结构、软化骨架悬浮密实结构、砂砾土富集结构、大块石包绕结构等4种细观结构类型。冰碛土剪切破坏主要有剪切破碎带、包绕块石边界、锯齿状剪切和切穿软化骨架等4种模式,剪切荷载作用下线弹性变形阶段明显,剪切刚度大,初始屈服历时短。颗粒骨架和杂基形成的悬浮密实结构,是冰碛土强度与变形特性的内在控制因素,剪切荷载作用下骨架颗粒与具有一定胶结的基质间相互作用,剪切破坏时表现为基质的压碎与骨架的变位。骨架颗粒强度、大骨架颗粒分布、基质胶结程度的不同,对冰碛土强度和变形特性都构成一定的影响。土的抗剪强度、剪切刚度和剪胀性随骨架强度和基质胶结程度的提高而增大,而延性随之变差。     

不同排水条件下饱和砂土快速大剪切力学特性

为探索滑坡灾害中土在复杂条件下的剪切力学特性,本文利用大型环剪试验机,通过进行各种排水条件下的连续大位移剪切试验,对不同法向应力、剪切速率和孔隙水压力等复杂条件下饱和砂土的力学特性及其变化机理进行了研究。结果表明：1）在连续快速剪切条件下,砂土剪切力学特性在干燥、不排水和排水等条件下呈现不同的变化形式。其中在不排水条件下,饱和砂出现一定的应变软化现象。2）在相同正应力和剪切速率的环剪试验中,饱和砂在不同排水条件下（上排水、下排水、上下排水）的抗剪强度出现显著差异。3）在排水环剪试验条件下,砂土剪切应力与强度的差异性变化不仅与土体内细土颗粒运移和结构变化有关,并且受到剪切过程中不同排水条件下孔隙水压力变化的影响和控制。4）排水环剪条件下,饱和砂孔隙水压力的消散变化不仅与不同排水方式下土体内所形成的排水通道顺畅程度有关,并且受到不同剪切速率和法向应力的影响作用。     

Volume strain, strain type and flow path in a narrow shear zone

This study explores the state of finite strain and changes in the mean kinematic vorticity number, grain size, whole-rock chemistry and mineralogy across an upper amphibolite-facies shear zone in a metadiorite, northern Malawi, east-central Africa. P–T conditions during shear-zone formation and deformation were approximately 700–750^?°C and 5–7?kbar and are slightly less than P–T conditions for the regional peak of metamorphism. The major rock-forming minerals, plagioclase, hornblende, biotite, and quartz, were deformed by crystal-plastic processes accompanied by, except for hornblende, dynamic recrystallization. The modal abundance of all four major rock-forming minerals shows no systematic change from the country rock into and across the shear zone, indicating that shear-zone development was not associated with retrograde mineral reactions. The grain size of the major rock-forming minerals decreases within the shear zone. Plagioclase and hornblende, which occur as porphyroblasts outside the shear zone, exhibit a bimodal grain-size distribution within the shear zone. Quartz has a unimodal grain-size distribution in the shear zone. Major and trace element chemistry does not change systematically across the shear zone, implying no volume change in the mylonite. Matrix strain data for plagioclase and hornblende by the Fry method and fabric strain as deduced from R_f/φ analysis of plagioclase and quartz grains demonstrate a slightly constrictional strain type (K≈1.5) across the shear zone. The quantitative finite-strain data for the different residual minerals as obtained by unlike methods show no systematic variation, but recrystallized plagioclase grains record higher strain than the residual grains. The mean kinematic vorticity number changes from approximately 0.3 outside to approximately 0.8 within the shear zone, indicating that the bulk deformation path deviated from progressive simple shear. The estimates for finite strain and the degree of noncoaxiality account for approximately 50% of thinning normal to the shear zone.     

Observation of shear zone development in ring-shear apparatus with a transparent shear box

Using a new ring-shear apparatus with a transparent shear box and video image analysis system, drained and undrained speed-controlled tests were conducted on coarse-grained silica sands to study the shear-zone formation process in granular materials. Velocity distribution profiles of grains under shear at various stages in the ring shear tests were observed through processing the video image by the Particle Image Velocimetry (PIV) program. Shear-zone thickness and type of shear mode (slide-like or flow-like) during shear were observed. Before reaching peak strength in low-speed and drained condition test, a comparatively major part of the sample in the upper shear box showed a velocity distribution profile of structural deformation and dilatancy behavior. After peak strength, the velocity profile changed into a slide-like mode and thereafter showed almost no change. In higher speed tests with drained and undrained conditions, an almost slide-like mode was observed, compared to low-speed test. Apparent shear-zone thicknesses of high-speed tests are thinner than low-speed tests. Unexpectedly, almost no difference was observed in the shear-zone thickness and mode of shear (slide or flow-like) between drained and undrained tests. This study was conducted as part of the International Programme on Landslides (IPL) M101 “Areal prediction of earthquake and rain induced rapid and long-traveling flow phenomena (APERITIF)” of the International Consortium on Landslides (ICL). These results will contribute to understanding the mechanism of shear-zone development in granular materials as a basic knowledge for disaster risk mitigation of rapid long run-out landslides.