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1.
Discontinuous deformation analysis (DDA) is a numerical approach used to simulate the post-failure behavior of a blocky assembly. Three available algorithms incorporate seismic impacts into DDA simulations for earthquake-induced slope failure. The following methods are used: directly applying time-dependent accelerations to falling/sliding blocks (Method 1); adding time-dependent accelerations to base block (Method 2); and time-dependently constraining seismic displacements of the base block (Method 3). However, incorrect absolute movements of falling/sliding and base blocks were obtained using Method 1. Additionally, relative movements between falling/sliding blocks and the base block are opposite to those simulated by the other two algorithms—Methods 2 and 3. Since locating an earthquake-induced landslide before an earthquake is extremely difficult, the seismic movements of base rock are recorded. Method 1 applies recorded seismic data to sliding blocks in conflict with d’Alembert’s principle of mechanics. Additionally, in Method 2, when the computation time step must be longer than the time in seismic data, computational results reveal abnormal base block displacements due to the non-zero velocity recorded at the end time of seismic data in seismic DDA. In this study, a novel algorithm to diminish the velocity of the base rock in the seismic analysis is utilized to modify Method 2. Furthermore, this work confirms that DDA with the modified Methods 2 and 3 is a practical approach for earthquake-induced landslide simulations. 相似文献
2.
Sarma's method of taking a fictitious accerelation as a measure of safety is used to study a two-dimensional slope. The slope is divided into arbitrary slices. The relations among forces acting on the slices and Sarma's acceleration are assumed to be linear. Consequently, a general analytical expression of Sarma's acceleration is derived by means of Cramer's rule. Furthermore, for four commonly used slice methods with simple relations among the forces on each slice and Sarma's acceleration, a general closed-form solution of Sarma's acceleration is given. An example is calculated and the results agree well with those of Hoek. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
3.
Vidar Kveldsvik Herbert H. Einstein Bjørn Nilsen Lars Harald Blikra 《Rock Mechanics and Rock Engineering》2009,42(5):689-728
The unstable 650,000 m2 Åknes rock slope (Western Norway) poses a hazard, as a sudden failure may cause a destructive tsunami in the fjord. In this study the slope was divided into blocks based on displacements measured at the slope surface. Discontinuous deformation analysis (DDA) showed that three or four blocks in the upper half may be considered as potential subareas that may fail catastrophically. The lower half may be divided into two or three blocks, but more limited data introduces more uncertainty into block definition. The Universal Distinct Element code (UDEC) was used for two-dimensional (2D) stability analyses. By varying fracture geometry, fracture friction, and groundwater conditions within reasonable limits based on site-specific data a number of possible models were compared. The conclusions show that models that were unstable to great depths were in closer agreement with shear strength parameters derived from an earlier study than models that were unstable to smaller depths. The length (depth) of the outcropping fracture, along which shear displacements are shown to occur, plays an important role. A (shallow) slide at 30 m, in which displacements have been documented by borehole measurements, will reduce the stability at greater depths. Increased groundwater pressure is demonstrated to be less critical for very deep slope instability. The results of the DDA and UDEC modelling will be useful for planning of future investigations, interpretation of the subsequent results, further development of the early warning system and in the tsunami modelling. 相似文献
4.
The role of interface friction is studied by slow direct shear tests and rapid shaking table experiments in the context of dynamic slope stability analysis in three dimensions. We propose an analytical solution for dynamic, single and double face sliding and use it to validate 3D‐DDA. Single face results are compared with Newmark's solution and double face results are compared with shaking table experiments performed on a concrete tetrahedral wedge model, the interface friction of which is determined by constant velocity and velocity stepping, direct shear tests. A very good agreement between Newmark's method on one hand and our 3D analytical solution and 3D‐DDA on the other is observed for single plane sliding with 3D‐DDA exhibiting high sensitivity to the choice of numerical penalty value. The results of constant and variable velocity direct shear tests reveal that the tested concrete interface exhibits velocity weakening. This is confirmed by shaking table experiments where friction degradation upon multiple cycles of shaking culminated in wedge run out. The measured shaking table results are fitted with our 3D analytical solution to obtain a remarkable linear logarithmic relationship between friction coefficient and sliding velocity that remains valid for five orders of magnitude of sliding velocity. We conclude that the velocity‐dependent friction across rock discontinuities should be integrated into dynamic rock slope analysis to obtain realistic results when strong ground motions are considered. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
5.
FAST台址巨石混合体的开挖稳定性对工程的建设和安全运营具有重要的意义。本文选取典型剖面,对FAST台址巨石混合体边坡在开挖后可能发生的坡体内部深层滑动和表层块体失稳两种破坏模式进行研究。结果表明：巨石混合体边坡沿最危险滑动面滑动的稳定系数约为2.8,不会发生坡体内部滑动。开挖后坡体上部较陡部位的表层块体由于失去支撑而发生失稳,再带动后方的块体运动。块体运动过程中重新堆积、咬合,体现出一定的自稳性。研究结果可为FAST台址巨石混合体及类似地质体的稳定性评价提供参考。 相似文献
6.
岩质边坡关键块体的搜索方法及工程应用 总被引：1，自引：0，他引：1
工程边坡开挖所揭露的某些结构面组合块体在破坏原有静力平衡状态后,进行应力重新分配,进而块体会发生失稳、滑动等变形,甚至影响到整个边坡发生破坏,因此,结构面组合块体的稳定性是决定岩质边坡稳定的重要因素。本文通过对某工程开挖边坡地形和结构面三维实体模型的建立,实现了边坡结构面与开挖地形实体模型在AutoCAD平台上的可视化操作,剖切不同位置的二维图形预测分析了边坡开挖后可能存在的结构面组合块体,采用块体计算程序(Swegde)验证关键块体并进行稳定性评价。结果表明:三维实体模型及剖切技术与块体计算方法的结合,易于搜索关键块体。事实证明,该方法操作简便,计算结果准确,搜索方法具备可行性。 相似文献
7.
Block theory has been widely applied to stability analysis of rock engineering due to its clear concept and elegant geometrical theory. For a general block with multiple discontinuity planes, it is assumed that contact is only maintained on a single plane (single-plane sliding) or two intersecting planes (double-plane sliding) in block theory analysis. Since the normal forces and shear resistances acting on the other discontinuity planes are omitted, it can cause unreasonable estimations of block failure modes and incorrect calculation of factors of safety. In this study, a new method is presented that permits to consider the contribution of the normal forces and shear resistances acting on each discontinuity plane to the block stability. The proposed method meets all of the force-equilibrium and moment-equilibrium conditions and provides a rigorous solution for stability of general blocks with any number of faces and any shape. Some typical polyhedral blocks in rock slopes are analyzed using block theory and the proposed method. The results indicate that the traditional block theory may give a misleading conclusion for the predictions of stability and sliding direction of rock blocks when contact occurs on more than two discontinuity planes. 相似文献
8.
层状岩石边坡倾倒破坏过程的数值流形方法模拟 总被引：3，自引：0，他引：3
层状岩石边坡的倾倒破坏是岩石边坡失稳破坏的主要形式之一。本文利用数值流形方法对一层状岩石边坡的倾倒破坏过程进行了模拟。模拟结果表明：在不考虑块体间粘结力的情况下，块体间的摩擦角决定着岩石边坡的稳定性。随着摩擦角的增加，块体间的摩擦系数增大，岩石边坡的稳定性增强，并出现相应的滑动区、倾倒区和稳定区。模拟结果与相应的理论预测结果相吻合。 相似文献
10.
A Boundary Element based Discontinuous Deformation Analysis (BE‐DDA) method is developed by implementing the improved dual reciprocity boundary element method into the open close iterations based DDA. This newly developed BE‐DDA is capable of simulating both the deformation and movement of blocks in a blocky system. Based on geometry updating, it adopts an incremental dynamic formulation taking into consideration initial stresses and dealing with external concentrated and contact forces conveniently. The boundaries of each block in the discrete blocky system are discretized with boundary elements while the domain of each block is divided into internal cells only for the integration of the domain integral of the initial stress term. The contact forces among blocks are treated as concentrated forces and the open–close iterations are applied to ensure the computational accuracy of block interactions. In the current method, an implicit time integration scheme is adopted for numerical stability. Three examples are used to show the effectiveness of the algorithm in simulating block movement, sliding, deformation and interaction of blocks. At last, block toppling and tunnel stability examples are conducted to demonstrate that the BE‐DDA is applicable for simulation of blocky systems. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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12.
G.H. Shi 《Geomechanics and Geoengineering》2014,9(2):80-96
Continuous computation and limit equilibrium computation are the two independent computations for practical rock engineering. For global stability analysis, limit equilibrium is still the fundamental method. For any numerical method, reaching limit equilibrium requires large displacements, discontinuous contacts, precise friction law, multistep computation and stabilised time-step dynamic computation. Therefore three convergences are unavoidable: convergence of equilibrium equations, convergence of open-close iterations for contacts and convergence of the contact forces of dynamic computations. This paper utilises mainly two dimensional discontinuous deformation analysis (DDA) and an available simple version of three dimensional DDA. The applications show DDA has the ability to reach the limit equilibrium of block systems. 相似文献
13.
摘要:岩质高边坡整体稳定性主要受软弱结构面及其组合控制,在组合有利的情况下,边坡主要发生浅表层块体失稳,开挖时的爆破振动作用是影响浅表层块体稳定的重要因素。本文以大渡河中游某岩质块状结构高边坡为例研究浅表层块体的稳定性,在总结浅表层块体失稳特征的基础上,实测爆破振动曲线,进行块体稳定性评价。研究结果表明,开挖后已失稳浅表层块体大多小于10m3,80%受软弱结构面控制,70%集中在马道下缘;实测的浅表层块体爆破振动加速度曲线显示,与邻近围岩相比,浅表层块体振动持续时间长,频率低,峰值小;等效静力法评价结果较爆破参数推算法更适用于临界失稳浅表层块体的稳定性评价。 相似文献
14.
This paper provides the theoretical basis for a forward numerical model of rock block systems. This method was developed to compute stress, strain, sliding and opening of rock blocks; rigid body movement and deformation occur simultaneously. Input data consist of block geometry, loading forces, the deformability constants E and v, and the restraint or boundary conditions of the block system. Output data give the movements, deformations, stresses and strains of each block, and the sliding and detachment or rejoining of blocks. The forces acting on each block, from external loading or contact with other blocks, satisfy the equilibrium equations. Equilibrium is also achieved between external forces and the block stresses. Furthermore, this analysis fulfills constraints of no tension between blocks and no penetration of one block into another. To acheive equilibrium and satisfy these constraints, simultaneous equations are solved repeatdly with partial changes of the coefficients each time the contact constraints are chosen. 相似文献
15.
The high computational costs associated with the implicit formulation of discontinuous deformation analysis (DDA) have been one of the major obstacles for its implementation to engineering problems involving jointed rock masses with large numbers of blocks. In this paper, the Newmark-based predictor-corrector solution (NPC) approach was modified to improve the performance of the original DDA solution module in modeling discontinuous problems. The equation of motion for a discrete block system is first established with emphasis on the consideration of contact constraints. A family of modified Newmark-based predictor-corrector integration (MNPC) scheme is then proposed and implemented into a unified analysis framework. Comparisons are made between the proposed approach and the widely used constant acceleration (CA) integration approach and central difference (CD) approach, regarding the stability and numerical damping features for a single-degree-of-freedom model, where the implications of the proposed approach on open-close iteration are also discussed. The validity of the proposed approach is verified by several benchmarking examples, and it is then applied to two typical problems with different numbers of blocks. The results show that the original CA approach in DDA is efficient for the simulation of quasi-static deformation of jointed rock masses, while the proposed MNPC approach leads to improved computational efficiency for dynamic analysis of large-scale jointed rock masses. The MNPC approach therefore provides an additional option for efficient DDA of jointed rock masses. 相似文献
16.
Discontinuous deformation analysis (DDA) has been widely applied in analyzing various rock engineering problems. As the joint strength play a vital role in the stability of jointed rock mass, this paper makes an attempt to implement the Barton-Bandis rock joint model into the DDA code to replace the original Mohr-Coulomb joint model. The developed Barton-Bandis joint model which is characterized by displacement-dependent shear strength is verified by experimental direct shear tests. An example of a block sliding on an inclined plane is used to demonstrate the capacity of the DDA-BB model in predicting the dynamic motion behavior of sliding blocks. 相似文献
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18.
Soil-rock mixtures (S-RM) are widely distributed in mountainous regions, and there are different genetic types and scales of S-RM slopes. The stability of these slopes is very important for slope safety during the construction and operation of engineering projects. Since the mechanical properties of an S-RM are mainly dominated by its random component, accurately investigating the structure of an S-RM slope is the fundamental basis for evaluating the mechanism of a landslide. In this paper, in situ direct shear tests are used to obtain the “soil” strength parameters of the S-RM, the microtremor survey method (MSM) is introduced to detect the S-RM slope and the numerical method of FEM is utilised to simulate the failure characteristics and stability of the S-RM slope. Based on the MSM, the strata structure and proportions of solitary rock blocks in the S-RM slope are investigated, and three possible models of the S-RM slope are established. By using the strength reduction method in numerical simulations, the potential failure surface and stability of a slope of homogeneous soil and that with solitary rock blocks are discussed. The study results show that the MSM is an effective method to estimate the proportion of rock blocks in the S-RM slope. The presence of solitary rock blocks makes the slope potential slide surface complicated. The factor of safety of the S-RM slope is higher than that of the homogeneous soil slope, the rock blocks at the toe of the slope are favourable for slope stability and the rock blocks near the surface of the slope squeeze the lower soil and improve the safety factor of the slope. 相似文献
19.
公路隧道局部塌方洞段的围岩稳定性评价 总被引：2，自引：0，他引：2
结合某公路隧道工程,以现场地质调查和监测资料为基础,在结构面发育且可能发生大规模塌方的围岩洞段,根据现场实际统计的优势结构面产状,采用关键块体理论、非连续变形方法（DDA）首先确定围岩主要的失稳破坏模式,然后运用连续介质分析程序FLAC,在DDA方法确定的围岩实际变形破坏塌方形态的基础上进行计算分析,评价围岩的整体稳定性及加固措施的有效性。分析表明,围岩破坏的主要模式为受结构面控制的局部块体的失稳,工程开挖后围岩不会发生大变形,这与实际情况基本一致,为安全施工提供了保证。采用非连续变形方法和连续介质计算相结合的分析方法对隧道工程塌方稳定性进行研究,取得了较好的效果,研究方法和经验可为类似工程参考并借鉴。 相似文献
20.
重庆武隆鸡尾山滑坡视向滑动机制分析 总被引：8，自引：0，他引：8
重庆武隆鸡尾山山体为典型的斜倾厚层灰岩山体,其破坏模式不同于常见侧向崩塌-堆积层滑坡,属于真倾向滑移变形转为视向整体滑动的特殊失稳模式。在现场地质调查的基础上,从地层岩性、岩体结构、岩溶及地下水作用、软弱夹层等影响因素分析重庆武隆鸡尾山滑坡形成原因;根据滑坡破坏机制,基于关键块体控制理论,对鸡尾山滑坡进行三维稳定性极限平衡分析;利用三维离散元软件模拟鸡尾山滑坡的初始变形破坏过程,分析了鸡尾山滑坡不同影响因素条件下的视向滑动形成机制和变形破坏特征,并探讨了节理化和溶蚀岩体的参数取值。结果分析认为,在重力的长期作用下,鸡尾山山体初始沿真倾向方向滑移,沿岩溶发育的陡倾节理裂隙逐渐产生后缘及侧向裂缝,形成块状后部驱动块体,由于地下水等因素使软弱夹层软化,驱动块体下滑力增大,前缘阻滑关键块体内部应力积累,并最终沿强度较低的岩溶发育带发生剪切破坏,从而导致整体滑动;在进行滑坡稳定性极限平衡分析时,考虑实际的滑坡机制,将滑体分为驱动块体和关键块体分别进行力的解析,并以关键块体的安全系数代表滑坡的安全系数更加合理。数值模拟显示,软弱夹层强度降低、岩溶发育带剪切破坏后,滑体进入大变形阶段,表明关键块体控制和阻滑作用明显,软弱夹层强度降低是滑坡发生的关键因素。采矿形成的采空区对山体的影响主要是使上覆岩体压应力增大,但对滑体的变形无影响。 相似文献