Fluid flow through rock fractures is frequently analyzed using models that evaluate permeability while taking into account of the effects of external stress conditions. In this study, a novel fluid flow-stress coupling model (RFFSC model) for rough-walled fractures is proposed. This model considers a revised Hertz contact deformation function in contact zones and an improved finite difference method for Darcy's law and Reynolds equation in void zones. A strong coupling solution scheme is formulated to solve flow field and stress field within fractures. Both numerical simulations and experimental tests under confining pressures are used to valid the RFFSC model, which have demonstrated a good performance of the model in terms of accuracy and efficiency. A series of flow models in fractures with different surface roughness and aperture under normal loadings are then analyzed. The results show that the stress-displacement response is controlled by the dynamic evolution of the surface contact state and exhibits three typical stages: rapid increase, slow increase and levelling off stage. As the normal stress increases, the contact ratio nonlinearly increases. This contact evolution behaviour leads to the reduction in the average aperture and the concentration of smaller apertures within the fracture. Under same normal stress, fractures with higher roughness exhibit lower contact ratios and more heterogenous aperture distributions, forming more high velocity flow channels near the flow inlet. The interaction between geometric complexity and deformation has been identified as the dominant factor controlling fracture closure and fluid flow behaviours. Finally, based on the RFFSC model, an empirical stress-dependent permeability prediction model for roughwalled fractures is proposed, which shows an extremely encouraging performance after cross-validation against some results sourced from published works in the literature.

The thin plate structural characteristics of the concrete panel and the need to control the calculation cost lead to the panel simulation accuracy being too rough compared with the complex working conditions and structural importance of the panel, which seriously affects the reliability of the numerical simulation calculation. [Objective] In order to realize the refined simulation of the concrete face slab of concrete face rockfill dam, [Methods] a transscale finite element simulation technique is developed through introducing arbitrary-node hexahedron element into the finite element calculation of the concrete face rockfill dam, and then this technique is used to make a numerical simulation of a concrete face rockfill dam and the result is compared with that of the conventional finite element simulation. [Results] The result shows that both tensile stress and compressive stress of the concrete face slab significantly increase, in which the increasing amplitudes of the horizontal compressive stress and the tensile stress and compressive stress along the slope reach about 10%, 40% and 70% respectively, while the local horizontal tensile stresses on both the banks even increase by more than 8 times. The stress and deformation through-thickness direction also exhibit that the compressive stress develops toward the surface and the tensile stress and the opening of the structural joint develop toward the bottom, especially the tensile stress along slope with the tensile stress ratio between the surface layer and the bottom layer of over 2.0. The calculation result is mutually coincided with the actual operation performance of the concrete face rockfill dam. [Conclusion] Comparative studies show that, this trans-scale finite element simulation technique can not only delicately reflect the stress change and joint displacement of a single concrete face slab, but can also reflect the changing laws of the deformation and stress of the concrete slab through-thickness direction, and then can provide more reliable basis for the design of complicated structure of concrete face rockfill dam. This technology has high calculation efficiency and simulation accuracy, and has great popularization and application value.

This paper presents a finite element analysis for the behavior of the Lianghekou high earth-core rockfill dam, which was just completed in construction in China. An elastoplastic constitutive model that can account for the degradation of rockfills due to particle breakage (hhu-SH-breakage model) was applied to simulate the mechanical behavior of the rockfills. The earth-core wall was analyzed by using the modified Cam-clay model combined with the Biot's consolidation theory. Numerical results are in good agreement with in-situ measurements during construction, indicating the reasonability of the numerical analysis. Based on the breakage-packing concept, which is able to extract the breakage-induced deformation from the total deformation, numerical analysis showed that the breakage-induced settlement for the extra high rockfill dam is not negligible. Inspired by the sensitivity analysis using the hhu-SH-breakage model, engineering advices were proposed to reduce the settlement of high rockfill dams.

In this paper, a new cross-scale finite element method is developed to study the mechanical response of concretefaced rockfill dams, in which an arbitrary-node hexahedron element is used to deal with the mesh transition between the concrete slab and dam body. By using the proposed method, the mesh sizes of concrete slab and rockfill may be very different. Moreover, since the cross-scale method doesn't change the finite element calculation framework, the proposed method is easy to use. In the simulated CFRD, the mechanical behavior of the concrete slab is described by an elastic-plastic constitutive model, and a nonlinear elastic model is applied to the rockfill materials. The computational accuracy and performance of the proposed method are analyzed. The numerical results and analysis provides an effective approach to study the local behavior of concrete face slabs.

河床地形是影响面板堆石坝应力变形特性的重要因素.应用非线性有限元方法,对坝基倾向下游及河床中部存在凸起的某在建面板堆石坝进行研究,得出存在该地形的面板堆石坝的应力变形规律.结果表明:坝基倾向下游地形会扩大坝体向下游位移区域、增大向下游位移数值并使最大沉降位置向下游偏移;同时会使面板靠近趾板附近产生拉应力;河床中部凸起地形会将坝体位移分布规律在此处分为对称的两个区域,且凸起附近坝体应力等值线较密集,应力数值较大.面板在凸起两侧轴向位移相反,该处面板出现拉应力的同时,垂直缝张开,对止水系统不利.

In this paper, a nonlinear constitutive model for rockfill materials is proposed to account for the coupling influence of the mean effective stress p and the deviatoric stress q on the deformation of rockfill materials. In the model, the stress-dilatancy relationship derived from the microstructural changes of granular materials is adopted, and the strength nonlinearity of rockfill materials is considered by using a logarithmic relationship between the peak friction angle and the mean effective stress. The SMP criterion is incorporated into the model to consider the influence of the intermediate principal stress. The good performance of the proposed model is demonstrated through modelling triaxial tests on rockfill materials from a rockfill dam. In addition, the FEM simulated deformation of a real CFRD using the proposed model agrees well with the monitored data.

介绍了一种可以考虑剪胀效应、中主应力影响以及强度非线性的粗粒料非线性模型(hhu-KG模型).在次弹性理论的基础上将其扩展为一般应力空间中的应力应变关系,并基于土石坝静动力流固耦合可视化分析软件平台开发了该模型的有限元计算程序.采用该模型和邓肯E-B模型对某面板堆石坝进行了三维有限元数值模拟,并对两种模型的模拟结果进行了对比分析.结果显示,相较于邓肯E-B模型,hhu-KG模型计算所得到的最大沉降值与最大面板挠度值略小,而最大顺河向位移值略大,但是两种模型计算所得的坝体与面板变形分布规律大致相同,且符合工程的一般规律,验证了基于次弹性理论推导的刚度系数矩阵的合理性,同时也说明了hhu-KG模型在土石坝静力有限元分析中的适用性.研究成果为粗颗粒土在土石坝的应用提供参考.

Soilbags have a wide range of applications in geotechnical engineering. To explore the compressive strength and deformation behaviour of soilbags, a formula for predicting the strength of soilbags is derived considering the relationship between the tensile force of the bag and the vertical strain. A soilbag under cyclic compression is numerically simulated using the discrete element method to verify the basic stress formula and the derived formula for the tensile force. The results indicate that the increase and distribution of the tensile force in the bag material have an important effect on the compressive strength of soilbags. The derived formula can predict the compressive strength of soilbags under vertical loading, providing a theoretical basis and design methods for structures built with soilbags.

堆石料的强度变形特性与初始孔隙及应力状态等因素相关.建立了能够预测不同初始孔隙与初始围压影响的堆石料弹塑性本构模型.在剑桥类本构模型框架内,模型能够反映随着孔隙与围压的增大,变形特性由剪胀趋于剪缩的规律.模型采用了基于颗粒体材料细观结构变化的屈服函数和非关联流动准则,提出了能够反映堆石料正常固结线不唯一的硬化参数.为了反映状态相关性,假定堆石料存在唯一的临界状态面,探讨了考虑状态相关性需要满足的数学条件,从而对剪胀方程与硬化参数进行了修正.提出了基于粒子群优化算法的模型参数快速确定方法,将某筑坝堆石料不同初始孔隙比与围压条件下模型预测结果与三轴试验结果对比,验证了模型的合理性.

Considering the coupling effect of the mean stress p and the deviatoric stress q on the deformation of coarse-grained materials, a nonlinear elastic K-G-J model that can account for the dilatancy and the intermediate principal stress of coarse-grained materials is established. The dilatancy equation derived from the microstructural changes of granular materials is introduced into the constitutive model to reflect the dilatancy of coarse-grained materials, and the strength nonlinearity of coarse-grained materials is considered by using a logarithmic relationship between the peak internal friction angle and the mean stress. Meanwhile, the SMP criterion is introduced into the model simply by using a transformed stress tensor, so that the model can reflect the influence of the intermediate principal stress. The model prediction of the triaxial compression and the extension tests on Toyoura sands agrees well with the experimental results, illustrating reasonability of the model.