Method of deformation analysis for composite structures of soils and masonry stones

The coupled numerical manifold method (NMM) and discontinuous deformation analysis (DDA) are enhanced to simulate deformations of continuous soil and discontinuous masonry structures. An elasto-plastic NMM-DDA is formulated that incorporates elasto-plastic constitutive laws into incremental forms of the equation of motion. A node-based uniform strain element is applied to avoid volumetric locking, which often occurs in conventional NMM-DDA. The proposed method is applied to three fundamental boundary value problems: a beam bending problem, a bearing capacity problem of a footing, and a bearing capacity problem of a masonry structure. The method is verified through comparisons with conventional solutions.     

Empirical assessment of the critical time increment in explicit particulate discrete element method simulations

This contribution considers the critical time increment (Δt_crit) to achieve stable simulations using particulate discrete element method (DEM) codes that adopt a Verlet-type time integration scheme. The Δt_crit is determined by considering the maximum vibration frequency of the system. Based on a series of parametric studies, Δt_crit is shown to depend on the particle mass (m), the maximum contact stiffness (K_max), and the maximum particle coordination number (C_N,max). Empirical expressions relating Δt_crit to m, K_max, and C_N,max are presented; while strictly only valid within the range of simulation scenarios considered here, these can inform DEM analysts selecting appropriate Δt_crit values.     

Numerical 3D modeling of the effects of strain rate and confining pressure on the compressive behavior of Kuru granite

This paper deals with numerical modeling of the compressive behavior of granite rock under high strain rate dynamic loading and wide range of confining pressure. For this end, a constitutive model based on damage mechanics and viscoplasticity for rock is formulated and implemented in explicit dynamics FEM. The viscoplastic part is based on a simple power law type yield criterion that incorporates the rate-dependency with a linear viscosity term. Moreover, a Rankine type of tensile cut-off is employed. The damage part of the model is formulated with separate scalar damage variables in tension and compression. The model is calibrated for Kuru granite and validated with the experimental data from dynamic compression tests at the strain rate of 600 1/s up to 225 MPa of confining pressure. The numerical simulations demonstrate that, despite the underlying continuum modeling approach, the model captures the correct experimental failure modes, including the transition from single-to-multiple fragmentation, as well as the dynamic compressive strengths at different confining pressures.     

A simple critical state interface model and its application in prediction of shaft resistance of non-displacement piles in sand

A simple semi-hyperbolic state-dependent constitutive model for sand-structure interfaces is proposed. The model formulation is consistent with critical state soil mechanics since void ratio evolves continuously with shear strain from initial state towards asymptotic critical state at extremely large shear strains. The model takes into account influence of normal stiffness on volume change and stress path. The proposed interface model is implemented in a pile segment analysis scheme for simulation of shaft resistance mobilization in non-displacement piles. Results reveal that the proposed pile segment analysis can well predict shaft resistance of model piles embedded in different sands.     

Multi‐slicing strategy for the three‐dimensional discontinuity layout optimization (3D DLO)

Discontinuity layout optimization (DLO) is a recently presented topology optimization method for determining the critical layout of discontinuities and the associated upper bound limit load for plane two‐dimensional and three‐dimensional (3D) problems. The modelling process (pre‐processing) for DLO includes defining the discontinuities inside a specified domain and building the target function and the global constraint matrix for the optimization solver, which has great influence on the the efficiency of the computation processes and the reliability of the final results. This paper focuses on efficient and reliable pre‐processing of the discontinuities within the 3D DLO and presents a multi‐slicing strategy, which naturally avoids the overlapping and crossing of different discontinuities. Furthermore, the formulation of the 3D discontinuity considering a shape of an arbitrary convex polygon is introduced, permitting the efficient assembly of the global constraint matrix. The proposed method eliminates unnecessary discontinuities in 3D DLO, making it possible to apply 3D DLO for solving large‐scale engineering problems such as those involving landslides. Numerical examples including a footing test, a 3D landslide and a punch indentation are considered, illustrating the effectiveness of the presented method. © 2016 The Authors. International Journal for Numerical and Analytical Methods in Geomechanics published by John Wiley & Sons Ltd.     

储层建模研究进展及发展趋势

油气田开发的后期进入高含水阶段,为了更加经济准确地进行油气开发,有必要采用储层地质建模的方法对老油气田进行储层研究。详细阐述了国内外储层地质建模的发展史,对储层地质建模的方法进行了细致的分类及论述。方法分类包括确定性建模方法和随机性建模方法。每一种建模方法又有多种子方法。提出了目前储层地质建模研究尚未很好解决的一些问题,如建模的对象局限于常规的碎屑岩储层。虽然有学者对火成岩、裂缝碳酸盐岩进行了相关的探究工作,但目前对非常规储层涉及较少,储层建模的精度也有待提高。     

三维定量预测方法在内蒙古红石山南金矿中的应用

红石山南金矿位于内蒙古阿木乌苏—鹰嘴红山金、锑、铁、钨Ⅳ级成矿带中段南部。为了对红石山南金矿的资源潜力进行定量预测评价,并为下一步勘探工作提供指导,在该地区开展以三维可视化技术和信息量法为核心的三维成矿预测很有必要。通过建立红石山金矿的找矿模型,圈定出3个成矿有利区,将二维勘探工作与三维成矿预测有效结合,将矿产预测拓展到三维空间,为今后研究定量化预测评价方法提供参考。     

基于杨赤中推估法空间插值的三维地质隐式建模

杨赤中推估法是一种对空间域复合变量通过连续的几何滤波过程来建立核函数的最小二乘推估法,建模过程简便且能基于少量已知数据点取得好的建模效果。针对地质勘查中离散、稀疏而不规则分布的地质特征点数据难以构建地质体三维模型的难点问题,提出了一种基于杨赤中推估法的三维地质空间插值与模型建立的自动化方法。该方法首先以地质特征点数据库为基础,选用负幂指数函数模型建立适合三维地质空间插值的杨赤中推估法估值数学模型;在此基础上,构建一套基于杨赤中推估法的三维地质空间插值计算和地质体隐式建模的自动化实现流程与程序;最后以实例矿化插值数据为基础,采用基于移动立方体算法的三维隐式建模方法,快速构建实例矿体三维模型。与人工交互圈定地质体边界和进行矿体推断的三维地质显式建模相比,这种方法能快速直观地分析地质特征并处理样品分析数据,方法可行且高效。     

数值模拟探讨青藏高原东部应力应变场及断裂活动性

青藏高原东部是我国活动构造非常强烈的区域,现今的应力应变状态对活动构造研究有重要参考意义。本文依据地质资料和岩石力学性质构建相应的有限元数值模型,以GPS观测为边界约束,计算得到了青藏高原东部应力应变场,在此基础上探讨了主要断裂的活动特征。结果显示,距离印度板块和欧亚大陆板块碰撞带较近的青藏高原,汇聚速度、最大压应变率和最大压应力均较高,而随着远离碰撞带各个数值相应降低;在青藏高原东部,以喜马拉雅东构造结为旋转中心的一系列弧形断裂滑动速率相对较高,如玉树—鲜水河—小江断裂带,巴塘—金沙江断裂带,嘉黎断裂带等,这些走滑断裂带控制着青藏高原东南缘物质旋转挤出的特征,而其它断裂带滑动速率则相对较低,在块体内部则更低;结果同时表明应变速率分配高的断裂达到屈服的时间短,对应的地震复发周期短。     

三峡重庆地区钻孔应变资料可靠性检验与分析

对三峡重庆地区6个四分量钻孔应变资料进行可靠性分析,利用其增量观测数据进行相对标定,得到各站点测区的应变参数,并分析测区相对应变特征。结果表明,6个站点的钻孔应变观测资料是可靠的,其中1个站点测区面应变呈现张性变化,靠近三峡库首区的5个站点测区面应变呈现压性变化,测点主压应变方向与大范围构造应力场方向较为一致,表明三峡重庆地区呈现压性特征。