广蓄电站厂房的三维位移反分析

本文采用参数同步变化法对广蓄电站厂房进行全三维的位移反分析,以确定厂房区的地应力和岩体的材料参数。参数同步变化法基于测点埋设时和测试时的几何组构分别进行地应力场和材料参数同步变化的三维计算,取两次计算的位移差值作为优化目标函数的相关变量,与实测值进行比较。这种方法去除了人为的歧意性,适用于各种复杂的地质条件。     

Displacement and stress distributions under a uniform inclined rectangular load on a cross‐anisotropic geomaterial

In practical engineering, an applied rectangular area load is not often horizontally or vertically distributed but is frequently inclined at a certain angle with respect to the horizontal and vertical axes. Thus, the solutions of displacements and stresses due to such a load are essential to the design of foundations. This article yields the analytical solutions of displacements and stresses subjected to a uniform rectangular load that inclines with respect to the horizontal and vertical axes, resting on the surface of a cross‐anisotropic geomaterial. The planes of cross‐anisotropy are assumed to be parallel to the horizontal ground surface. The procedures to derive the solutions can be integrated the modified point load solutions, which are represented by several displacement and stresses elementary functions. Then, upon integrations, the displacement and stress integral functions resulting from a uniform inclined rectangular load for (1) the displacements at any depth, (2) the surface displacements, (3) the average displacements in a given layer, (4) the stresses at any depth, and (5) the average stresses in a given layer are yielded. The proposed solutions are clear and concise, and they can be employed to construct a series of calculation charts. In addition, the present solutions clarify the load inclinations, the dimensions of a loaded rectangle, and the analyzed depths, and the type and degree of geomaterial anisotropy profoundly affect the displacements and stresses in a cross‐anisotropic medium. Parametric results show that the load inclination factor should be considered when an inclined rectangular load uniformly distributed on the cross‐anisotropic material. Copyright © 2008 John Wiley & Sons, Ltd.     

The elastic distortion problem with large rotation in discontinuous deformation analysis

Conventional discontinuous deformation analysis (DDA) results in a change of block volume, which is known as free expansion, during rotation calculations because of the use of a linear displacement function to simulate the behavior of a block with a rigid body and elastic behaviors. This study demonstrates that the linear displacement function also generates unsolved elastic distortion, especially when the block undergoes large rotation in each calculation step. The distortion disturbs the contact judgment in the open–close iteration and update calculations of vertex coordinates, stresses, velocities, etc. at the end of each calculation step. A new procedure follows the flow chart of the original DDA, but it adopts additional codes for the coordinate-transformation calculations in vertex coordinate, stress, and velocity updates. When the vertex coordinates are updated, vertex displacements caused by strains are calculated before involving the block-rotation term in the displacement function to mitigate the elastic distortion. In addition, new codes compile formulas to transform stresses and velocities with block rotation. The new DDA ensures the correctness of rotating elastic calculations to solve practical falling rock problems with a large rotational angle in each calculation step.     

Numerical analysis of the geotechnical behaviour of energy piles

Energy geostructures are rapidly gaining acceptance around the world; they represent a renewable and clean source of energy that can be used for the heating and cooling of buildings and for de‐icing of infrastructures. This technology couples the structural role of geostructures with the energy supply, using the principle of shallow geothermal energy. The geothermal energy exploitation represents an additional thermal loading, seasonally cyclic, which is imposed on the soil and the structure itself. Because the primary role of the piles is the stability of the superstructure, this aspect needs to be ensured even in the presence of the additional thermal load. The goal of this paper is to numerically investigate the behaviour of energy pile foundations during heating–cooling cycles. For this purpose, the finite element method is used to simulate both a single and a group of energy piles. The piles are subjected to a constant mechanical load and a seasonally cyclic thermal load over several years, imposed in terms of injected–extracted thermal power. The soil and the pile–soil interface behaviours are reproduced using a thermoelastic‐thermoplastic constitutive model. The thermal‐induced stresses inside the piles and the additional displacements of the foundations are discussed. The group model is used to investigate the interactions between the piles during thermo‐mechanical loading. The presented results are specific to the studied cases but lead to the conclusion that both the thermal‐induced displacements and stresses, despite being acceptable under normal working conditions, deserve to be taken into account in the geotechnical design of energy piles. Copyright © 2014 John Wiley & Sons, Ltd.     

Boundary element analysis of transversely isotropic bi-material halfspaces with inclined planes of isotropy and interfaces

In this paper, a single-region boundary element method (BEM) is presented for the analysis of transversely isotropic bi-material halfspaces with arbitrarily inclined planes of isotropy and material interfaces. The proposed BEM uses the fundamental solution of a transversely isotropic bi-material fullspace and five boundary element techniques. Infinite boundary elements are introduced to consider the far-fields of a transversely isotropic bi-material halfspace. The effective integration methods are proposed for dealing with various integrals in the discretized boundary integral equation. The stresses at internal points are obtained using the coordinate transformation of kernel functions, and the stresses on the boundary surface are calculated using an improved traction recovered method. Numerical verifications of displacements and stresses for a benchmark problem are conducted, and excellent agreement with previously published results is obtained. Numerical examples are presented to illustrate the influence of non-horizontal or horizontal planes of isotropy in bi-material halfspaces on the displacements and stresses induced by the tractions on the horizontal boundary surface. Results reveal that the elastic fields vary clearly with the dip angle of the isotropic plane and the stresses across the bi-material interface are closely related to the ratios of the elastic parameters of the bi-material.     

Analyses on granular mass movement mechanics and deformation with distinct element numerical modeling: implications for large-scale rock and debris avalanches

A large-scale avalanche of Earth material is modeled here as a granular flow using a distinct element numerical model PFC ^2D. Such failures occur in a variety of geological settings and are known to occur frequently over geologic time-scales transporting significant volumes of material basinward. Despite this, they remain poorly understood. The model used here begins with a listric failure, typical of the flank collapse of a volcanic cone, and describes the movement of an assembly of several thousand particles from failure to deposition. Within the model, each particle possesses its own material properties and interacts with its immediate neighbors and/or the basal boundary during emplacement. The general mechanics of the particle assembly are observed by monitoring the stresses, displacements, and velocities of distinct sections of the avalanche body. We monitor the avalanches’ energy regime (e.g., gravitational influence, energy dissipation by friction, kinetic energy evolution, and avalanche body strain). The addition of colored markers of varying geometry to the pre-failure avalanche was also used to make qualitative observations on the internal deformation that occurs during avalanche emplacement. A general stretching and thinning of the avalanche is observed. Monitoring of vertical and horizontal variations in stress, strain, porosity, and relative particle stability indicate that the lower more proximal sections of the avalanche are subject to higher stresses. These stresses are observed to be most significant during the initial phases of failure but decline thereafter; a situation likely to be conducive to block fragmentation and in developing a basal shear layer in real-world events. The model also shows how an avalanche which is initially influenced purely by gravity (potential energy) develops into a fully flowing assemblage as downslope momentum is gained and kinetic energy increases. The horizontal transition where the failure meets the run-out surface is recognized as a key area in emplacement evolution. The model has particular relevance to volcanic flank collapses and consequently the implications of the model to these types of failure and the geological products that result are considered in detail although the model is relevant to any form of large-scale rock or debris avalanche.     

A dynamic large deformation finite element method based on mesh regeneration

In this paper, a large deformation finite element (LDFE) approach termed ‘remeshing and interpolation technique with small strain (RITSS)’ is extended from static to dynamic soil-structure interaction applications. In addition, a technique termed ‘element addition’ is developed to improve the computational efficiency of both static and dynamic LDFE analyses that involve moving boundaries. The RITSS approach is based on frequent mesh generation to avoid element distortion. In dynamic RITSS, the field variables mapped from the old to the new mesh involve not only the stresses and material properties, but also the nodal velocities and accelerations. Using the element addition technique, new soil elements are attached to the domain boundaries periodically when the soil near the boundaries becomes affected by large displacements of the structure. The procedures of this Abaqus-based dynamic LDFE analysis and element addition technique are detailed, and the robustness of the techniques is validated and assessed through three example analyses: penetration of a flat footing into a half-space and movement of rigid and deformable landslides down slopes.     

Settlement behaviour of a concrete faced rock-fill dam

Settlement behaviour of a concrete faced rock-fill dam (CFRD), Kurtun dam, located in the East Black Sea Region, Turkey, is investigated. This is the first instrumented CRDF in the Country. Two dimensional plane strain finite element analyses were carried out to assess the total stresses and displacements in the dam both for construction and reservoir filling stages by using computer program PLAXIS. Predicted stresses and settlements are compared with those observed and overall the results are found to be in good agreement for the construction stage. Due to the relatively steep abutment slopes, cross-valley arching has a significant effect on stresses and displacements in the dam body. For the reservoir filling condition, it is seen that, predicted settlements are larger than the observed values, which indicates that during reservoir filling the rock-fill embankment responds more stiffly than it does during the construction stage. The hardening soil model is used to represent the non-linear, inelastic and stress dependent behaviour of rock-fill material. The model parameters are selected from the appropriate values in the literature investigating comparable cases.     

金属矿山采空区群形成过程中围岩扰动规律研究

以石人沟铁矿为工程背景,选取典型矿段,采用相似材料模型试验和数值模拟计算相结合的方法,对该区域内采空区群形成过程中围岩的应力应变的演变规律进行研究。首先,利用相似材料试验,对采空区顶板的应力和位移以及矿柱的应力演变规律进行系统分析。然后,用数值模拟软件,对采空区群形成过程中开采对围岩的扰动范围进行系统研究。研究结果表明,在采空区群形成过程中,围岩应力-应变演变规律与采空区单独开采差异较大,每个采空区的围岩应力应变始终处于动态变化中,尤其是处于群区域中间部位的采空区,该处围岩的应力-应变状态也是最差的。群区域中,由开采对围岩造成的扰动较单独开采时急剧增大,且最终的影响范围并不是单独开采的简单相加,说明在区域内形成一种采空区的“群效应”,加剧采空区的危险程度。     

A theoretical study of reinforcement influence on the stability of a tunnel face

Summary The problem of tunnel face stability is studied and the analysis of the stabilizing effect achieved by pre-reinforcement of the core which has to be excavated is dealt with. In Italy, the insertion of longitudinal fibreglass pipes in the ground has proved to be efficient in solving face instability problems. A thorough review of other applications of the technology has been carried out.The results of a series of parametric, three-dimensional, elasto-plastic finite element analyses are presented. The tunnel excavation with or without support and face reinforcement is simulated in the models. The stresses, plastic zones and displacements in the ground, pipes and lining have been studied. The support effect of the pipes is demonstrated by the results. Face reinforcement significantly reduces the displacements of the face. The stresses in the material at the face are also charged from tension to compression, thus enhancing face stability.     

Numerical modelling of large deformations associated with driving of open‐ended piles

This paper presents a ‘Eulerian‐like’ finite element technique to simulate the large accumulated displacements of piles subjected to multiple hammer blows. For each hammer blow, results are obtained using a standard small strain finite element model and, at the end of each hammer blow, material flow is taken into account with reference to a fixed finite element mesh. Residual stresses calculated at the Gauss integration points of the deformed finite element mesh are mapped on to the fixed finite element mesh, and these stresses are used as initial stresses for the next hammer blow. At the end of each hammer blow, stiffness and mass matrices are recalculated for the volume of material remaining inside the fixed finite element mesh. Results obtained with and without allowing material to flow through the fixed mesh are compared for several hammer blows. Build up of residual stresses, soil flow and yielded points around the pile are presented for plugged, partially‐plugged and unplugged piles. Using the new finite element technique, the driving of a pile from the soil surface is studied. The ability to analyse this and other large deformation problems is the main advantage of the new finite element technique. Copyright © 2000 John Wiley & Sons, Ltd.     

2-D deformation analysis of a half-space due to a long dip-slip fault at finite depth

Closed form analytical expressions of stresses and displacements at any field point due to a very long dip-slip fault of finite width buried in a homogeneous, isotropic elastic half-space, are presented. Airy stress function is used to derive the expressions of stresses and displacements which depend on the dip angle and depth of the upper edge of the fault. The effect of dip angle and depth of the upper edge of the fault on stresses and displacements is studied numerically and the results obtained are presented graphically. Contour maps for stresses and displacements are also presented. The results of Rani and Singh (1992b) and Freund and Barnett (1976) have been reproduced.     

Lined Circular Tunnels in Elastic Transversely Anisotropic Rock at Depth

Closed-form solutions for displacements and stresses of both the liner and the rock are presented for a deep circular tunnel excavated in transversely anisotropic rock above or below the water table subjected to static or seismic loading. The solutions are obtained with the assumption of elastic response of rock and liner, tied contact between rock and liner, impermeable liner, plane strain conditions along the tunnel axis and simultaneous excavation, and liner installation. The liner of a tunnel placed below the water table must support, in addition to the rock stresses, the full water pressure, while a tunnel located above the water table must support only the rock pressures. The solutions presented for static loading show, however, that displacements and stresses of the liner and rock are the same when the tunnel is placed above or below the water table as long as the total far-field stresses are the same. With rapid loading, e.g. seismic loading, excess pore pressures may be generated in saturated rock, which induce a different response than that of a tunnel excavated in dry rock. The analyses indicate that stresses and displacements are more uniform when excess pore pressures are produced, which seems to indicate that pore pressure generation tends to reduce non-uniform response in anisotropic rock.     

Intracontinental mountain building in Central Asia as inferred from satellite geodetic data

The results of longstanding GPS measurements in the northwestern part of Central Asia are discussed. These results impose certain constraints for modeling of intraplate tectonic processes. In the territory covered by observations, the velocity vectors of recent motions of the Earth’s surface relative to the stable portion of Eurasia decrease northward. The plane field of velocities, which rules out the development of extension zones, indicates the impossibility of the mountain building driven by ascending mantle flows beneath the lithosphere of these regions. The nonuniform spatial distribution of the motions is suggestive of the discrete character of the Earth’s crust and its deformation. The crust is brittle, at least in its upper part, and capable of breaking into blocks. The blocks, which move at different velocities, interact with one another and change their original orientation and position, while experiencing independent deformations. This phenomenon has been exemplified in the Tarim Block and the Tien Shan. Within the limits of the constraints imposed by the GPS measurements, the mechanism of intracontinental mountain building related to the lateral flow of asthenospheric material and to the drag of the overlying lithospheric layers is discussed. This mechanism springs from Argand’s ideas [2, 29] and the plate tectonic concept [10, 23]. The upper-mantle convective flow in the direction of the Indian Plate’s motion was the main cause of the crustal deformation. The detachment of the lithospheric mantle from the Indian Plate approximately 25 Ma ago and its subduction beneath the Himalayas and Tibet, along with simultaneous ascent of the remaining crust and uplift of the Tibetan Plateau, allowed the mantle flow to spread far northward beneath the Asian continent. This process is accompanied by consecutive separation and sinking of the cooling asthenospheric material over the entire area from the Himalayas to Siberia as the subcrustal material cools. As a result, the flow velocity decreases, the roof of the active flow plunges, and the lithosphere becomes thicker. The motion and deformation of the lithospheric layers dragged by deep flow cannot follow the asthenospheric flow strictly, owing to the rigidity of the layers. Therefore, a difference of tangential velocities originates between the flow and the lithosphere, thus giving rise to horizontal shear stresses. These stresses affect the overlying lithospheric layers, including the crustal ones, and bring about their drag and tectonic delamination. Simultaneously, the decreasing velocity in the direction of the mantle flow results in bending of the lithospheric layers that is accompanied by local warping of the crust and its stacking and fragmentation into blocks. The different velocities of block motions lead to their mechanical interactions. This scenario of intracontinental mountain building allows an explanation of the many specific features of tectonic processes and orogeny in within-plate mountainous regions.     

Stresses and displacements in an elastic mass due to distributed loading by discretization technique

Numerical solutions have been obtained for stresses and displacements in a linear elastic half space due to distributed loads of circular, rectangular and elliptical shapes. The technique primarily involves use of a multi-dimensional numerical integration technique to integrate point load solutions over the distributed loading after discretizing the area into a finite number of elements. Both uniform vertical and shear loads have been considered as well as vertical conical loads and inward shear loads. The technique evolved facilitates the determination of stresses and displacements by the use of mini-computers and is neither as tedious and cumbersome as the use of tables and charts nor as costly as FEM solutions. A detailed comparison has been presented between the results obtained by the numerical solutions and those of the existing analytical solutions wherever they are available. It is found that the agreement between the two is within one per cent for displacements at all depths for the different cases studied. The matching is also good in the case of stresses, except at shallow depths.     

Analytical solutions for stresses and displacements around tunnels driven in cross-anisotropic rocks

In this paper, closed-form solutions for the stresses and displacements around unlined circular tunnels excavated in an elastic, orthotropic (cross-anisotropic) medium are developed. The effect of both the elastic parameters characterizing the behaviour of the medium and the anisotropy of the initial stress system on the stresses and displacements induced are evaluated. An example of utilizing the theoretical solution for design analysis is given. For convenience of application, design charts are prepared for the determination of stresses and displacements for given values of initial stresses and the elastic parameters. Copyright © 1999 John Wiley & Sons, Ltd.     

复杂条件下隧道支护结构稳定性分析

以方斗山隧道为研究对象,建立三维有限元数值分析模型,模拟分析了隧道支护结构的稳定性。以距离隧道洞口10 m处断面支护结构为例,分析了该断面初次支护和二次衬砌的水平应力、竖向应力、竖向位移、锚杆轴力及支护结构破坏域等随掌子面推进的变化规律,并对该断面支护结构特征点的稳定性进行追踪研究。研究结果表明,当掌子面与断面间距离小于30 m左右时,随着掌子面的推进,支护结构应力及位移等均有一定程度的增长,其后支护结构应力及位移基本收敛,且收敛值均较小,表明支护结构是稳定的。对隧道初次支护应力及锚杆轴力的现场监测结果及数值模拟结果进行对比分析,结果表明,数值模拟与现场监测结果基本一致。     

核废料处置概念库开挖及封闭后近场热-水-应力耦合数值分析

考虑了缓冲层中温度梯度水分扩散、水蒸汽扩散对水连续性及能量守恒的影响,进一步完善了饱和-非饱和介质中热-水-应力耦合现象的控制方程。应用缓冲材料的实验资料,对核废料处置概念库开挖及封闭后近场的热-水-应力耦合过程进行了数值模拟,以考察围岩中的位移、塑性区、主应力、孔隙水压力和温度的分布及变化。认为开挖是引起洞室围岩中的变形及应力重新分布的主要原因,但坑道封闭后的热-水-应力耦合过程对变形及应力状态也产生了明显的影响。     

岗曲河混凝土面板堆石坝三维静力应力变形分析

采用邓肯模型对岗曲河面板堆石坝进行了三维有限元分析,研究软岩填筑层对坝体工作性能的影响,计算混凝土面板与岩石填筑层的位移和应力及周边缝变形。结果表明,由于受到下游堆石3D软岩填筑区的影响,坝体最大横断面最大沉降略偏向下游,总沉降量约为坝高的0.2 %,面板周边缝位移的绝对值一般都小于2 cm,周边缝的止水设计需注意选择合理的止水形式和填缝材料,由于坝址河谷狭窄,受岸坡约束,三维效应对坝体的应力变形影响较明显,为设计施工提供了参考。     

Applicability of the theory of hollow inclusions for overcoring stress measurements in rock

Summary Whenever solid or hollow inclusions are used as instrumented probes in overcoring techniques, residual stresses remain in the overcored rock sample and in the probes. When using such devices for computing the in-situ stress field components from measured strains or displacements, it is common practice to assume that the overcoring diameter is infinite and that there is a perfect bonding between the rock and the probes. The validity of these assumptions depends on the magnitude of the residual stresses at the rock-probe contact as compared to the tensile and shear strengths of the rock-probe bond material. It also depends on the distribution of residual stresses in the overcored sample.In comparison to previous work, new expressions are proposed in this paper for the residual stresses associated with solid or hollow inclusion type stress probes in anisotropic ground. These expressions are presented in dimensionless form and are used to show that the distribution and magnitude of residual stresses depend on the isotropic-anisotropic rock character, the degree and type of rock anisotropy, the orientation of the rock anisotropy with respect to the hole in which the probes are located and the relative deformability of the rock with respect to the deformability of the material comprising the probes. The conditions that are required for neglecting the overcored sample diameter are also discussed. This is shown for rocks that can be described as isotropic, transversely isotropic and orthotropic materials.