碎屑流沿坡面运动的数值模拟

根据Savage提出的碎屑流运动方程,分析了碎屑流沿坡面下滑过程中的运动特性,包括速度分布和高度分布的变化。重点考察了床面摩擦系数、土体内摩擦角、初始运动速度和坡角等因素对碎屑流运动形态的影响。研究表明,在不同的因素组合情况下,碎屑体的运动形态有明显的区别。土体内摩擦角和坡角对碎屑流的运动形态和最大运动距离影响明显。相对来说,床面摩擦角对碎屑流的最大运动距离影响不明显,这可能是因为床面摩擦只影响靠近床面的部分物质的运动     

基于室内模型试验的滑坡碎屑流堆积分布规律研究

本文利用室内物理模型试验,模拟了特定条件下滑坡碎屑流的滑动和堆积过程。获取了滑坡碎屑流堆积物的位置分布,并对其规律进行了分析,且在此基础之上对滑坡碎屑流运动机制进行了简单的分析。结果表明:碎屑流颗粒在滑坡发生后的最终位置分布兼具随机性和规律性;关于坡面中轴对称分布的碎屑流颗粒在滑坡后依然对称分布;堆积体中沿滑坡方向连续分布的颗粒在滑坡结束后最终位置分布在一定程度上并不连续;颗粒滑后位置分布受其滑前在颗粒整体中所处的位置影响较大;在沿坡面下滑过程中,碎屑流颗粒堆积体会发生内部的整体滚动。研究结果为滑坡-碎屑流运动机制的理论研究和复原滑坡初始状态提供了可靠的数据参考。     

辽西黄土陡坡的冲刷破坏机制

以70°辽西黄土陡坡为例,在降雨强度为2.7 mm/min条件下对边坡坡面冲刷破坏特征进行了室内物理试验模拟。试验发现：随着降雨的持续坡面水流能量不断增加,致使侵蚀强度增强;边坡的侵蚀方式从试验初期的片蚀,到中期的细沟侵蚀,最后演化为坡顶部的切沟侵蚀和坍塌。基于试验成果,采用SEEP/W程序对降雨条件下边坡降雨入渗规律进行数值模拟,发现在降雨过程中坡顶部所产生的水头压力最大,随高度降低呈减小趋势;运用PFC2D颗粒流软件从微观角度对坡体土颗粒运动情况进行模拟,结果发现位于坡顶的颗粒最先被径流冲刷带走,且下落速度很快。经对比表明：数值模拟结果和物理模拟试验现象基本一致,可为进一步研究黄土边坡冲刷破坏规律提供参考。     

滑坡-碎屑流物理模型试验及运动机制探讨

滑坡-碎屑流由于高速、远程的特点常常引发灾难性事故,其复杂的运动机制导致预测致灾范围非常困难。通过开展室内模型试验,研究了碎屑粒径、滑床糙率和挑坎对运动特性的影响。试验结果发现,滑坡碎屑运动距离受控于前端碎屑,且随着碎屑的粒径增大而增加,增加滑床糙率、挑坎均可使碎屑的运动距离减小。在前人研究成果的基础上结合碎屑材料的力学特性探讨了滑坡-碎屑流出现流态化的原因和高速远程机制,即高速运动中颗粒间的作用力远小于完整岩体,因此颗粒间的“黏聚力”不能维持滑坡体的整体性,同时致使滑坡体与滑床接触的过程中传递至滑坡体内部的摩阻力减少,从而导致碎屑滑坡的远程结果。     

降雨作用下堆积层滑坡的模型试验研究

通过模型试验,研究不同材料堆积体在降雨作用下的滑坡机理。模型试验中,针对凹形堆积体边坡进行了不同堆积材料的试验。试验结果分别记录了黏性土、砂土以及碎石土边坡随降雨时效的坡面变形特征、边坡内部孔隙水压力变化特征,并对监测结果进行了分析。试验结果表明:孔压的变化规律与坡面变形规律具有一致性,降雨通过影响边坡内部孔隙水压力的变化来影响边坡的稳定性。同时,拟合了降雨量与边坡位移的关系,并对比了不同堆积材料对边坡稳定性的影响。     

易贡滑坡-碎屑流-堰塞坝溃坝链生灾害全过程模拟与动态特征分析

为研究易贡滑坡-堰塞坝溃坝链生灾害的动力学特征,基于遥感影像数据建立三维数值模型,运用DAN3D和FLOW3D对易贡滑坡-碎屑流-堰塞坝溃坝全过程进行模拟研究。运用DAN3D模拟滑坡-碎屑流过程,得到滑坡碎屑堆积分布特征及速度变化规律,滑坡持续时间300 s,平均速度35 m/s。基于DAN3D获得的滑坡碎屑堆积分布建立等比例堰塞坝模型,运用FLOW3D模拟溃坝后洪水演进过程,得到洪水演进过程水流特征变化规律,通麦大桥处洪峰流量130 000 m3/s与实测值接近。对易贡滑坡灾害链全过程的模拟和动态特征分析可为高山峡谷区类似的滑坡-堰塞坝溃坝链生灾害风险评价提供参考。     

离心模型试验与数值模拟相结合研究采空边坡渐进破坏特性

以贵州六盘水地区煤层开采为工程背景,采用离心模型试验与数值模拟相结合的方法研究了采空条件下边坡的渐进破坏过程及破坏模式。基于离心模型试验得到了开采过程中边坡的位移场,并采用FLAC~(3D)对离心模型试验过程进行了数值模拟,数值与试验结果得出的边坡位移时程曲线吻合程度较高,塑性区分布与试验点对分析得到的滑裂面破坏过程与路径基本一致。通过对比、融合离心模型试验观测与数值模拟结果,表明贯通坡脚与采空区的滑裂面由下向上形成,且总体发生剪切错动破坏,贯通坡肩与采空区的滑裂面由上至下发生复杂的破坏过程,初始阶段滑裂面发生张拉破坏,中间阶段同时发生张拉与剪切破坏,末尾阶段发生剧烈的剪切滑移破坏。     

重庆武隆鸡冠岭岩质崩滑-碎屑流过程模拟

1994年乌江重庆武隆段左侧岸坡鸡冠岭发生大型岩质崩滑,崩塌体碰撞解体后沿沟谷形成碎屑流,碎屑流体高速入江激起涌浪,最终形成堰塞湖,造成重大人员伤亡和经济损失。本文在滑坡现场工程地质调查的基础上,阐述了鸡冠岭崩滑-碎屑流的基本特征,对鸡冠岭崩滑-碎屑流运动过程中碰撞和铲刮等现象进行了分析,并基于DAN3D动力分析软件反演了鸡冠岭崩滑-碎屑流运动全过程,得到了崩滑-碎屑流速度分布规律和堆积体分布特征,模拟结果与滑坡的基本特征与堆积体分布特征基本吻合。鸡冠岭的研究成果较少,本文从数值模拟的角度剖析了鸡冠岭崩滑-碎屑流的动力特性,完善了鸡冠岭崩滑的研究。本文的研究结果为崩滑动力特性及滑坡涌浪效应研究提供了依据。     

非均一性斜坡落石运动轨迹

现有的落石运动轨迹研究均将斜坡视为半无限均匀的坡面,而实际的工况下,坡面由不均一材料组成。根据落石不同的运动模式,将坡面简化为多层岩土体材料的结构形式,在滚动阶段,基于Hertz接触理论得到落石在不同坡面条件下运动特征,并给出坡面分层条件下落石切向摩擦系数的计算公式,在碰撞阶段,基于能量守恒定理,采用准静态接触力学理论得到法向恢复系数公式,理论推导得到任意层厚岩土体材料坡面条件下落石法向和切向恢复系数的解析解,然后求解得到碰撞后落石运动参数,并根据碰撞后落石的速度及回弹量关系,给出碰撞后落石运动模式转换的判别条件,最后结合运动学定理,得到3种运动模式任意分层坡面条件落石的运动轨迹,将理论公式应用于某山区落石运动轨迹预测,验证了理论公式的适用性和有效性。     

南宁市防洪堤岸坡岩土材料的本构模型试验研究

根据南宁市防洪堤岸坡岩土材料的特性,对典型堤段的岸坡岩土材料进行了试验研究。根据试验数据拟合得到体积屈服面和剪切屈服面,基于广义塑性力学原理,建立了岸坡岩土材料的本构模型。使用MATLAB程序进行数值计算,通过对比试验曲线和理论曲线的拟合程度检验了模型的合理性。     

尾矿库溃坝运动特征模拟研究

尾矿库是一个具有高势能的人造危险源,一旦溃坝,将严重威胁下游人民生命财产安全和生态环境保护。由于尾矿库溃坝因素和条件的复杂性,以及溃坝体在下游沟道或场地运动及滞留特征的不确定性,导致尾矿库溃坝后的运动特征预测成为一个难点。本文基于连续介质和非连续介质力学理论,考虑当前流固耦合数值模拟能力和特征,运用Massflow和PFC3D软件,结合无人机精细测量、现场调查和验证分析等手段,开展了多手段相结合的尾矿库溃坝运动特征模拟研究。研究发现,基于PFC3D和Massflow两种数值方法模拟溃坝后的尾矿砂运动过程有所不同。Massflow模拟结果显示,大部分尾砂体沿着尾矿库下游的曲折沟道运移,在沟谷与张唐铁路交汇的涵洞处堆积;而PFC3D模拟结果显示,尾矿库溃坝后大部分尾矿砂沿着尾矿库主体朝向溃决漫流,少部分进入其下游曲折沟道。研究认为,考虑地质体和运动过程的不确定性,对于尾矿库溃坝的运动特征模拟宜结合两种不同理论基础的模拟方法,并结合实际尾矿库情况进行综合分析预测。     

粗粒料强度及变形特性的细观模拟

粗粒料是一定级配的岩石颗粒集合体,具有独特的物理力学特性。以粗粒料室内三轴固结排水试验成果为基础,基于离散元颗粒流理论,从细观角度出发,以PFC3D为工具,通过自编程及二次开发,得到按级配生成的粗粒料三轴试验数值模型。引入clump颗粒考虑颗粒形状对粗粒料强度及变形的影响,分析剪胀、颗粒形状、颗粒重排的关系。结果表明：颗粒形状是影响粗粒料强度与变形的主要因素,在其他细观参数一定的情况下,改变颗粒形状,可以显著影响粗粒料的力学行为;BPM模型的应力-应变关系只在低围压下与试验值吻合,随着围压的增大,偏差越来越大;而引入clump颗粒的PFC3D数值模型能很好地模拟粗粒料室内三轴固结排水试验的应力-应变特性,但由于BPM及clump都是刚性颗粒,没有考虑颗粒变形及破碎,造成应变剪胀偏大。     

A hypoplastic constitutive model for debris materials

Debris flow is a very common and destructive natural hazard in mountainous regions. Pore water pressure is the major triggering factor in the initiation of debris flow. Excessive pore water pressure is also observed during the runout and deposition of debris flow. Debris materials are normally treated as solid particle–viscous fluid mixture in the constitutive modeling. A suitable constitutive model which can capture the solid-like and fluid-like behavior of solid–fluid mixture should have the capability to describe the developing of pore water pressure (or effective stresses) in the initiation stage and determine the residual effective stresses exactly. In this paper, a constitutive model of debris materials is developed based on a framework where a static portion for the frictional behavior and a dynamic portion for the viscous behavior are combined. The frictional behavior is described by a hypoplastic model with critical state for granular materials. The model performance is demonstrated by simulating undrained simple shear tests of saturated sand, which are particularly relevant for the initiation of debris flows. The partial and full liquefaction of saturated granular material under undrained condition is reproduced by the hypoplastic model. The viscous behavior is described by the tensor form of a modified Bagnold’s theory for solid–fluid suspension, in which the drag force of the interstitial fluid and the particle collisions are considered. The complete model by combining the static and dynamic parts is used to simulate two annular shear tests. The predicted residual strength in the quasi-static stage combined with the stresses in the flowing stage agrees well with the experimental data. The non-quadratic dependence between the stresses and the shear rate in the slow shear stage for the relatively dense specimens is captured.     

考虑发育薄弱区对管涌发展影响的数学模型研究

为了揭示发育薄弱区对管涌发展的影响机制,进行了管涌砂槽模型试验和颗粒流数值模拟,建立了3组模型,以研究孔隙通道的空间发育对颗粒运移过程的影响,分析了土体内部细颗粒运移引起管涌破坏的动态过程。根据数值模拟结果,分析了管涌发展过程中试样细观及流体的变化规律,并与砂槽模型试验结果进行了比较,模拟与模型试验结果较吻合。结果表明,薄弱区越发育,压力分布调整的趋势越强,颗粒运移的趋势相应增加,达到破坏需要的时间越短。数值模拟获得的临界水力梯度与室内试验以及理论分析结果均比较接近,证明了采用颗粒流程序研究管涌问题是合理的,对研究存在薄弱区的砂土管涌现象具有明显的优势和广阔的应用前景。所揭示的结果有益于管涌机制的更深入研究。     

颗粒级配对粗粒土强度与变形特性影响的研究

采用三维颗粒流软件PFC3D的内置FISH语言,进行二次开发,模拟粗粒土级配,建立一个研究高铁填方路基粗粒土变形特性的颗粒流模型。通过粗粒土三轴试验,标定了表征粗粒土细观力学性质的模型参数,并验证了模型的有效性。考虑粗粒土曲率系数和不均匀系数对颗粒级配的影响,模拟并研究了5种不同级配下粗粒土在3种不同围压下的变形特性。试验结果表明,曲率系数对粗颗粒土变形特性影响较大,当其有效粒径与中值粒径及限制粒径的差距过大时,粗粒土中颗粒填充及致密性将变差,变形增大,强度降低。以较大曲率系数与较大不均匀系数组合的粗粒土受力性能较好,但此种级配的粗粒土压缩性大。级配良好且不均匀系数较大,其应力链分布越均匀,颗粒的挤压效果越显著,力的传递和分配也越均匀。     

Deformation analysis of sands in cubical and hollow cylinder devices

For discrete materials like sands, the continuum field variables, stress and strain, are defined in terms of micro-level quantities by considering the deformation mechanism of granular soils from a microscopic point of view. Under the application of load, soil is considered to deform due to the movement relative to each other of clusters of particles. Based on this deformation mechanism, the kinematics of soils are developed and a strain tensor for granular soils, in terms of local displacements and geometric measures, is introduced. A local constitutive law relating local displacements and local tractions is defined. Using the local constitutive law, the relationships between stress and strain for the media are developed. The developed model incorporates the influence of strain hardening and material anisotropy on the deformation behaviour of the media. Comparisons of the model predictions and experimental results from tests conducted in cubical and hollow cylinder devices are presented.     

3D analysis of kinematic behavior of granular materials in triaxial testing using DEM with flexible membrane boundary

This paper describes the constitutive behavior and particle-scale kinematics of granular materials in three-dimensional (3D) axisymmetric triaxial testing using discrete element method (DEM). PFC3D code was used to run the DEM simulations using a flexible membrane boundary model consisting of spherical particles linked through flexible contact bonds. The overall deformation behavior of the specimen was then compared with the specimen with rigid boundary and experimental measurements. Computed tomography was used to track the evolution of particle translation and rotation within a laboratory triaxial specimen in 3D. The DEM model of the flexible membrane specimen successfully predicted the stress–strain behavior when compared with laboratory experiment results at different confining pressures. The DEM results showed that the rigid specimen applies a uniform deformation and leads to non-uniformities in the confining stress along the particle-boundary interface in the lateral direction. In contrast, the flexible specimen better replicates the uniformly applied confining stress of a laboratory triaxial experiment. The 3D DEM simulations of the specimen with flexible membrane overpredicted particle translation and rotation in all directions when compared to a laboratory triaxial specimen. The difference between the particle translation and rotation distributions of DEM specimens with rigid and flexible membrane is almost negligible. The DEM specimen with flexible membrane produces a better prediction of the macroscopic stress–strain behavior and deformation characteristics of granular materials in 3D DEM simulations when compared to a specimen with rigid membrane. Comparing macroscale response and particle-scale kinematics between triaxial simulation results of rigid versus flexible membrane demonstrated the significant influence of boundary effects on the constitutive behavior of granular materials.     

颗粒材料剪胀性的微观力学分析

剪胀性是颗粒材料在加载过程中表现出来的重要变形特性。以孔隙胞元描述颗粒材料内部结构的最小单元,通过对单个孔隙胞元进行剪切受力分析,探讨了剪切过程中颗粒材料体积的改变对应力比和单个孔隙胞元形状的依赖关系,解释了排列密实的颗粒材料在剪切过程中先压缩后剪胀的微观机制。用离散元数值模拟得到了在双轴剪切过程中单个孔隙胞元形状以及孔隙胞元体积变形的演化过程。离散元数值结果表明,加载过程中孔隙胞元形状由初始各向同性到沿大主应力方向变大变长、体积变形先压缩后膨胀,并且体积变形在加载过程中存在局部化现象,体积变化大的孔隙胞元在较大变形时,排列成倾斜的窄带。综合孔隙胞元的受力分析和离散元数值结果表明,致密排列颗粒材料的剪胀性与微观尺度上孔隙胞元的几何结构及其内部的力链传递方式密切相关。     

Study of the interaction between dry granular flows and rigid barriers with an SPH model

This study uses an incompressible smoothed‐particle hydrodynamics model to investigate the interaction between dry granular material flows and rigid barriers. The primary aim is to summarise some practical guidelines for the design of debris‐resisting barriers. The granular materials are modelled as a rigid‐perfectly plastic material where the plastic flow corresponds to the critical state. The coupled continuity equation and momentum equation are solved by a semi‐implicit algorithm. Compared with flows in controlled flume experiments, the model adequately reproduces both the kinetic of the flows and the impact force under various conditions. Then the numerical simulations are used to study the detailed interaction process. It is illustrated quantitatively that the interaction force consists of two parts, ie, the earth pressure force caused by the weight of the soil and a dynamic force caused by the internal deformation (flowing mass on top of a dead zone). For the estimation of impact load, this study suggests that an increased earth pressure coefficient depending on the Froude number should be incorporated into the hydrostatic model.     

Simulation of debris flow on an instrumented test slope using an updated Lagrangian continuum particle method

We present an updated Lagrangian continuum particle method based on smoothed particle hydrodynamics (SPH) for simulating debris flow on an instrumented test slope. The site is a deforested area near the village of Ruedlingen, a community in the canton of Schaffhausen in Switzerland. Artificial rainfall experiments were conducted on the slope that led to failure of the sediment in the form of a debris flow. We develop a 3D mechanistic model for this test slope and conduct numerical simulations of the flow kinematics using an SPH formulation that captures large deformation, material nonlinearity, and the complex post-failure movement of the sediment. Two main simulations explore the impact of changes in the mechanical properties of the sediment on the ensuing kinematics of the flow. The first simulation models the sediment as a granular homogeneous material, while the second simulation models the sediment as a heterogeneous material with spatially varying cohesion. The variable cohesion is meant to represent the effects of root reinforcement from vegetation. By comparing the numerical solutions with the observed failure surfaces and final free-surface geometries of the debris deposit, as well as with the observed flow velocity, flow duration, and hot spots of strain concentration, we provide insights into the accuracy and robustness of the SPH framework for modeling debris flows.