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Optimization-based pore network modeling approach for determination of hydraulic conductivity function of granular soils 基于优化的孔隙网络建模方法确定粒状土的导水函数
IF 3.4 2区 工程技术 Q2 ENGINEERING, GEOLOGICAL Pub Date : 2024-08-29 DOI: 10.1002/nag.3826
Suaiba Mufti, Arghya Das

A wide range of applications of unsaturated hydraulic conductivity is well known in geotechnical, hydrological, and agricultural engineering fields. The standard prediction models for hydraulic conductivity function overlook the complexity of soil pore structure and employ a simplistic approach based on the bundle of capillary tubes. This study proposes an alternative approach employing pore network models calibrated to match soil water retention data to predict the hysteretic hydraulic conductivity function of granular soils. A novel approach to constructing a multidirectional pore network built on an irregular lattice with variable coordination numbers is presented for the realistic representation of soil voids. The geometric and topological parameters of the pore network model are optimized using the genetic algorithm, and adequate pore-scale processes (piston-like advance and corner flow during drainage and piston-like advance, pore body filling, and snap-off during imbibition) are modeled to get reasonable predictions of hysteretic hydraulic conductivity functions over the entire suction range of granular soils. Comparisons between the pore network model results, standard physically based models, and measured data for a variety of granular soils show that the proposed pore network has a superior performance over other models and compares favorably to the experimental data.

众所周知,非饱和导水性在岩土工程、水文工程和农业工程领域有着广泛的应用。标准的导水函数预测模型忽视了土壤孔隙结构的复杂性,采用了基于毛细管束的简单方法。本研究提出了另一种方法,即采用经校准的孔隙网络模型来预测粒状土的滞后水力传导函数,该模型与土壤保水数据相匹配。为了真实再现土壤空隙,本研究提出了一种新方法,即在具有可变配位数的不规则晶格上构建多向孔隙网络。利用遗传算法对孔隙网络模型的几何和拓扑参数进行了优化,并对适当的孔隙尺度过程(排水时的活塞式前进和角流,以及浸泡时的活塞式前进、孔体填充和折断)进行了建模,从而合理地预测了粒状土在整个吸力范围内的滞回水力传导函数。孔隙网络模型结果、基于物理的标准模型和各种粒状土的测量数据之间的比较表明,所提出的孔隙网络比其他模型具有更优越的性能,与实验数据相比也更胜一筹。
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引用次数: 0
Contraction and expansion of a cylindrical cavity in an elastoplastic medium: A dislocation-based approach 弹塑性介质中圆柱形空腔的收缩和膨胀:基于位错的方法
IF 3.4 2区 工程技术 Q2 ENGINEERING, GEOLOGICAL Pub Date : 2024-08-28 DOI: 10.1002/nag.3825
Yue Gao, Emmanuel Detournay

The contraction or expansion of a cylindrical cavity in an elastoplastic medium is usually analyzed from a continuum based approach with a plasticity constitutive model. However, localized deformations, which are rooted in the post-failure softening response of geomaterials, are observed in the form of spiral-shaped fractures in laboratory tests. An alternative approach based on dislocation theory is introduced in this paper for modeling cavity contraction or expansion. In this model, several equally spaced spiral-shaped shear fractures initiate and propagate away from the cavity within the linearly elastic medium. The Mohr-Coulomb criterion and a dilatancy rule are imposed on the shear fractures to constrain the stresses and the displacement jumps. The direction of fracture propagation is determined by minimizing plastic dissipation. The displacement discontinuity method is used to discretize the shear and normal displacement jumps along the fracture and solve the problem numerically. The calculated crack path follows a logarithmic-like spiral, similar to the slip lines predicted by plasticity theory. The relationship between the pressure and radial displacement at the cavity boundary converge towards the classical elastoplastic solution as the number of fracture branches increases.

弹塑性介质中圆柱形空腔的收缩或膨胀通常采用基于连续体的塑性构造模型进行分析。然而,在实验室测试中,可以观察到螺旋状断裂形式的局部变形,这种变形源于土工材料的破坏后软化响应。本文介绍了另一种基于位错理论的空腔收缩或膨胀建模方法。在该模型中,在线性弹性介质中,几条等间距的螺旋形剪切裂缝从空腔开始并向外扩展。对剪切裂缝施加莫尔-库仑准则和扩张规则,以限制应力和位移跳跃。断裂扩展的方向通过最小化塑性耗散来确定。采用位移不连续法对沿断裂的剪切和法向位移跳跃进行离散化,并对问题进行数值求解。计算得出的裂纹路径呈对数螺旋状,与塑性理论预测的滑移线相似。随着断裂分支数量的增加,空腔边界处的压力和径向位移之间的关系向经典弹塑性解法靠拢。
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引用次数: 0
Instability of binary mixtures subjected to constant shear drained stress path: Insight from macro and micro perspective 二元混合物在恒定剪切排水应力路径下的不稳定性:从宏观和微观角度看问题
IF 3.4 2区 工程技术 Q2 ENGINEERING, GEOLOGICAL Pub Date : 2024-08-28 DOI: 10.1002/nag.3823
Zhouyi Yan, Yang Liu, Debin Zhao

Loose granular materials may also exhibit instability behaviors similar to liquefaction under drained conditions, commonly referred to as diffuse instability, which can be studied through constant shear drained (CSD) tests. So far, the research on CSD in binary mixtures is still insufficient. Therefore, a series of numerical tests using the discrete element method (DEM) were conducted on binary mixtures under CSD path. The possible model of instability is categorized into type I and type II, type I instability occurs prior to reaching the critical state line (CSL), whereas type II instability occurs after exceeding the CSL. The study analyzes the macroscopic instability behavior and the impact of fine content (FC) on macroscopic instability behavior. The numerical results show that as FC increases, the slope of the instability line (IL) increases initially and then falls in the p-q plane. In the e-p plane, the IL decreases initially and then ascends. The instability type of the binary mixtures is influenced not only by relative density but also by FC. The stability index increased first and then decreased with the increase of FC. The microscopic origin of binary mixtures instability is explored by investigating the fabric-stress relationship. The collapse of the weak contact sub-network triggers the specimen instability, while the strong contact sub-network dictates the difficulty of achieving instability. FC influences the evolution of fabric anisotropy of the strong and weak contact networks, thereby controlling the macroscopic instability behavior of binary mixtures.

松散颗粒材料在排水条件下也可能表现出与液化类似的不稳定性行为,通常称为扩散不稳定性,可通过恒定剪切排水(CSD)试验进行研究。迄今为止,对二元混合物中的恒定剪切排水(CSD)研究仍然不足。因此,采用离散元法(DEM)对 CSD 路径下的二元混合物进行了一系列数值试验。不稳定的可能模式分为 I 型和 II 型,I 型不稳定发生在达到临界状态线(CSL)之前,而 II 型不稳定发生在超过 CSL 之后。研究分析了宏观失稳行为以及细粒含量(FC)对宏观失稳行为的影响。数值结果表明,随着 FC 的增加,不稳定线(IL)的斜率开始增加,然后在 p-q 平面上下降。在 e-p 平面上,不稳定线的斜率先减小后增大。二元混合物的不稳定类型不仅受相对密度的影响,也受 FC 的影响。随着 FC 的增加,稳定指数先上升后下降。通过研究织物与应力的关系,探索了二元混合物不稳定性的微观起源。弱接触子网的崩溃引发了试样的不稳定性,而强接触子网则决定了实现不稳定性的难度。FC 会影响强接触网络和弱接触网络的织构各向异性的演变,从而控制二元混合物的宏观失稳行为。
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引用次数: 0
Failure mechanism of fully grouted rock bolts subjected to pullout test: Insights from coupled FDM-DEM simulation 接受拉拔试验的全灌浆岩石螺栓的失效机理:FDM-DEM 耦合模拟的启示
IF 3.4 2区 工程技术 Q2 ENGINEERING, GEOLOGICAL Pub Date : 2024-08-26 DOI: 10.1002/nag.3824
Hongyan Zhao, Kang Duan, Yang Zheng, Qiangyong Zhang, Longyun Zhang, Rihua Jiang, Jinyuan Zhang

Fully grouted rock bolts are widely used in mining, tunneling, and pit support, and thus the study of their anchorage performance is beneficial for optimizing the anchorage system design. In this study, an FDM-DEM coupled numerical model is established to simulate the whole process of rock bolt pullout test and to investigate the failure mechanism of fully grouted rock bolts. The accuracy of the model is verified by comparison with existing laboratory test results. Virtual experiments are conducted on different models by eliminating the anchor plate, changing the layered rock strata condition, and adding bolts. The results show that the presence of an anchor plate will reduce tensile stress to restrain the rupture of surrounding rock and thus improve the strengthening effect. Due to the different bond strength and tensile strength of the soft and hard rock mediums, the layer sequence of the rock strata affects the maximum pullout force. The upper-soft and lower-hard composite rock strata (S-HCR) exhibits single-cone damage while the upper-hard and lower-soft composite rock strata (H-SCR) exhibits double-cone damage. The superposition effect of the anchor group on the stresses and displacements is the reason leading to the reduction of the maximum load-bearing capacity of the rock bolts.

全灌浆岩石螺栓广泛应用于采矿、隧道和基坑支护,因此对其锚固性能的研究有利于优化锚固系统设计。本研究建立了 FDM-DEM 耦合数值模型,模拟岩石螺栓拉拔试验的全过程,研究全灌浆岩石螺栓的破坏机理。通过与现有实验室测试结果的对比,验证了模型的准确性。通过取消锚板、改变分层岩层条件和增加螺栓,对不同模型进行了虚拟试验。结果表明,锚固板的存在会降低拉应力,抑制围岩破裂,从而提高加固效果。由于软硬岩介质的粘结强度和抗拉强度不同,岩层的层序会影响最大拉拔力。上软下硬复合岩层(S-HCR)表现为单锥破坏,而上硬下软复合岩层(H-SCR)则表现为双锥破坏。锚杆组对应力和位移的叠加效应是导致岩石锚杆最大承载能力降低的原因。
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引用次数: 0
Lateral kinematic properties of offshore pipe piles embedded in saturated soil considering soil plug effect 考虑土塞效应的饱和土壤中嵌入的近海管桩的横向运动特性
IF 3.4 2区 工程技术 Q2 ENGINEERING, GEOLOGICAL Pub Date : 2024-08-24 DOI: 10.1002/nag.3819
Jiaxuan Li, Xiaoyan Yang, Hao Liu, Libo Chen, Wenbing Wu, M. Hesham El Naggar, Dagang Lu

This study establishes a theoretical framework for analyzing the lateral oscillation of marine pipe piles. The additional mass model is introduced herein to consider the inertial fluctuation effect of the soil plug. Analytical mathematical methods are used to determine the complex impedance variation of the pile over a range of frequency effects. An investigation is performed to determine how the presence of soil plugs changes the lateral complex stiffness and natural frequency of pipe piles. Additionally, comparisons of the applicability of the plane strain model and continuous medium model have been conducted to enable the easy use of the theoretical model. The main conclusions can be drawn as (1) if the fluctuation inertia effect of the soil plug is not taken into consideration, the dynamic active length and the dynamic stiffness of the pipe pile will be underestimated; (2) for the soft soil, the plane strain model may give rise to substantial calculation errors attributed to them regardless of the vertical continuity of the soil, nevertheless, the calculation error decreases rapidly with the increase of soil shear modulus and vibration frequency.

本研究为分析海洋管桩的横向振荡建立了一个理论框架。本文引入了附加质量模型,以考虑土塞的惯性波动效应。分析数学方法用于确定桩在一系列频率效应下的复阻抗变化。通过研究确定土塞的存在如何改变管桩的横向复刚度和固有频率。此外,还对平面应变模型和连续介质模型的适用性进行了比较,以便于使用理论模型。得出的主要结论有:(1)如果不考虑土塞的波动惯性效应,管桩的动活度长度和动刚度将被低估;(2)对于软土,无论土的垂直连续性如何,平面应变模型都可能产生较大的计算误差,但计算误差会随着土的剪切模量和振动频率的增加而迅速减小。
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引用次数: 0
Synthesizing realistic sand assemblies with denoising diffusion in latent space 利用潜空间中的去噪扩散合成逼真的沙粒组合体
IF 3.4 2区 工程技术 Q2 ENGINEERING, GEOLOGICAL Pub Date : 2024-08-14 DOI: 10.1002/nag.3818
Nikolaos N. Vlassis, WaiChing Sun, Khalid A. Alshibli, Richard A. Regueiro

The shapes and morphological features of grains in sand assemblies have far-reaching implications in many engineering applications, such as geotechnical engineering, computer animations, petroleum engineering, and concentrated solar power. Yet, our understanding of the influence of grain geometries on macroscopic response is often only qualitative, due to the limited availability of high-quality 3D grain geometry data. In this paper, we introduce a denoising diffusion algorithm that uses a set of point clouds collected from the surface of individual sand grains to generate grains in the latent space. By employing a point cloud autoencoder, the three-dimensional point cloud structures of sand grains are first encoded into a lower-dimensional latent space. A generative denoising diffusion probabilistic model is trained to produce synthetic sand that maximizes the log-likelihood of the generated samples belonging to the original data distribution measured by a Kullback-Leibler divergence. Numerical experiments suggest that the proposed method is capable of generating realistic grains with morphology, shapes and sizes consistent with the training data inferred from an F50 sand database. We then use a rigid contact dynamic simulator to pour the synthetic sand in a confined volume to form granular assemblies in a static equilibrium state with targeted distribution properties. To ensure third-party validation, 50,000 synthetic sand grains and the 1542 real synchrotron microcomputed tomography (SMT) scans of the F50 sand, as well as the granular assemblies composed of synthetic sand grains are made available in an open-source repository.

沙粒集合体的形状和形态特征对许多工程应用具有深远影响,如岩土工程、计算机动画、石油工程和聚光太阳能。然而,由于高质量三维颗粒几何数据的可用性有限,我们对颗粒几何形状对宏观响应的影响的理解往往只是定性的。在本文中,我们介绍了一种去噪扩散算法,该算法使用从单个沙粒表面采集的点云集合来生成潜空间中的沙粒。通过使用点云自动编码器,首先将沙粒的三维点云结构编码到低维潜在空间中。通过训练生成式去噪扩散概率模型来生成合成沙粒,使生成的样本属于原始数据分布的对数似然最大化(通过库尔贝-莱布勒发散测量)。数值实验表明,所提出的方法能够生成形态、形状和大小与从 F50 沙数据库中推断出的训练数据一致的真实沙粒。然后,我们使用刚性接触动态模拟器将合成砂倒入密闭容积中,在静态平衡状态下形成具有目标分布特性的颗粒集合体。为确保第三方验证,我们在一个开源资源库中提供了 50,000 个合成砂粒和 1542 个 F50 砂的真实同步辐射微计算机断层扫描(SMT)扫描结果,以及由合成砂粒组成的颗粒集合体。
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引用次数: 0
Cover Image, Volume 48, Issue 13 封面图片,第 48 卷第 13 期
IF 3.4 2区 工程技术 Q2 ENGINEERING, GEOLOGICAL Pub Date : 2024-08-13 DOI: 10.1002/nag.3822
Xuejian Li, Kang Duan, Moli Zhao, Qiangyong Zhang, Luchao Wang, Rihua Jiang

The cover image is based on the article Competition among simultaneously stimulated multiple hydraulic fractures: Insights from DEM simulation with the consideration of fluid partitioning by Xuejian Li et al., https://doi.org/10.1002/nag.3801.

封面图片来自 Xuejian Li 等人撰写的文章《同时刺激多条水力压裂之间的竞争》(Competition among simultaneously stimulated multiple hydraulic fractures:考虑流体分区的 DEM 模拟的启示》,李学俭等著,https://doi.org/10.1002/nag.3801.
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引用次数: 0
Superposition-based concurrent multiscale approaches for porodynamics 基于叠加的并行多尺度孔动力学方法
IF 3.4 2区 工程技术 Q2 ENGINEERING, GEOLOGICAL Pub Date : 2024-08-09 DOI: 10.1002/nag.3813
Wei Sun, Jian-Min Zhang, Jacob Fish, Rui Wang

The current study presents superposition-based concurrent multiscale approaches for porodynamics, capable of capturing related physical phenomena, such as soil liquefaction and dynamic hydraulic fracture branching, across different spatial length scales. Two scenarios are considered: superposition of finite element discretizations with varying mesh densities, and superposition of peridynamics (PD) and finite element method (FEM) to handle discontinuities like strain localization and cracks. The approach decomposes the acceleration and the rate of change in pore water pressure into subdomain solutions approximated by different models, allowing high-fidelity models to be used locally in regions of interest, such as crack tips or shear bands, without neglecting the far-field influence represented by low-fidelity models. The coupled stiffness, mass, compressibility, permeability, and damping matrices were derived based on the superposition-based current multiscale framework. The proposed FEM-FEM porodynamic coupling approach was validated against analytical or numerical solutions for one- and two-dimensional dynamic consolidation problems. The PD-FEM porodynamic coupling model was applied to scenarios like soil liquefaction-induced shear strain accumulation near a low-permeability interlayer in a layered deposit and dynamic hydraulic fracturing branching. It has been shown that the coupled porodynamic model offers modeling flexibility and efficiency by taking advantage of FEM in modeling complex domains and the PD ability to resolve discontinuities.

目前的研究提出了基于叠加的多尺度并发孔隙动力学方法,能够捕捉不同空间长度尺度上的相关物理现象,如土壤液化和动态水力断裂分支。研究考虑了两种情况:不同网格密度的有限元离散的叠加,以及周动力学(PD)和有限元法(FEM)的叠加,以处理应变局部化和裂缝等不连续性问题。该方法将加速度和孔隙水压力的变化率分解为由不同模型近似的子域解,允许在裂缝尖端或剪切带等相关区域局部使用高保真模型,而不忽略低保真模型所代表的远场影响。耦合刚度、质量、可压缩性、渗透性和阻尼矩阵是根据基于叠加的当前多尺度框架推导出来的。针对一维和二维动态固结问题,提出的 FEM-FEM 孔隙动力学耦合方法与分析或数值解决方案进行了验证。将 PD-FEM 孔隙动力学耦合模型应用于层状沉积中低渗透性夹层附近土壤液化诱发的剪切应变累积以及动态水力压裂分支等情况。结果表明,通过利用有限元在复杂域建模方面的优势和 PD 解决不连续性的能力,耦合孔动力学模型提供了建模的灵活性和效率。
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引用次数: 0
Analysis of progressive collapse disaster and its anchoring effectiveness in jointed rock tunnel 节理岩隧道渐进式坍塌灾害及其锚固效果分析
IF 3.4 2区 工程技术 Q2 ENGINEERING, GEOLOGICAL Pub Date : 2024-08-08 DOI: 10.1002/nag.3817
Chengcheng Zheng, Peng He, Gang Wang, Jie Hu, Feng Jiang, Zhiqiang Yan, Zhiyong Xiao, Zhenghu Ma

The complexity and variability of the structural distribution and combination characteristics of jointed rock masses make the response mechanism of tunnel rock collapse different, and there is a lack of systematic research on the existing perimeter rock instability mode and bolt support scheme. Based on numerical simulations of the block system structure of a nodular rock mass, the existing theory of bolt support is compared and analyzed to explore the scope of their respective applications. Combined with the spatial and temporal transport law of block instability, a new batch instability model of jointed rock tunnels is proposed, which reveals the progressive collapse catastrophe evolution mechanism of a collapsed interlocking block system after the instability of the key blocks and elucidates the coupling mechanism between the bolts and the block system structure as well as their anchoring effectiveness. Finally, for the actual tunnel project, the instability batches of the surrounding rock are identified, and the corresponding optimized design of the bolt support is presented, which has achieved good support effects. The research results can provide important theoretical guidance and practical engineering value for risk avoidance, disaster identification and targeted prevention and control of dangerous rock fall and chain collapse instability disasters in jointed rock body tunnels.

节理岩体结构分布和组合特征的复杂性和多变性,使得隧道围岩坍塌的响应机理各不相同,现有围岩失稳模式和螺栓支护方案缺乏系统研究。基于对节理岩体块系结构的数值模拟,对比分析了现有的螺栓支护理论,探讨了各自的应用范围。结合块体失稳的时空迁移规律,提出了一种新的节理岩隧道批量失稳模型,揭示了关键块体失稳后互锁块体系统坍塌的渐进式坍塌灾难演化机理,阐明了螺栓与块体系统结构的耦合机理及其锚固效果。最后,针对实际隧道工程,确定了围岩失稳批次,提出了相应的螺栓支护优化设计方案,取得了良好的支护效果。研究成果可为节理岩体隧道危岩落石和连锁坍塌失稳灾害的风险规避、灾害识别和针对性防治提供重要的理论指导和工程实用价值。
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引用次数: 0
A depth-integrated SPH framework for slow landslides 慢速滑坡的深度整合 SPH 框架
IF 3.4 2区 工程技术 Q2 ENGINEERING, GEOLOGICAL Pub Date : 2024-08-08 DOI: 10.1002/nag.3814
Manuel Pastor, Andrei Hernández, Saeid M. Tayyebi, Gustavo A. Trejos, Ginés Suárez, Junwei Zheng

Slow and very slow landslides can cause severe economic damage to structures. Due to their velocity of propagation, it is possible to take action such as programmed maintenance or evacuation of affected zones. Modeling is an important tool that allows scientists, engineers, and geologists to better understand their causes and predict their propagation. There are many available models of different complexities which can be used for this purpose, ranging from very simple infinite landslide models which can be implemented in spreadsheets to fully coupled 3D models. This approach is expensive because of the time span in which the problems are studied (sometimes years), simpler methods such as depth-integrated models could provide a good compromise between accuracy and cost. However, there, the time step limitation due to CFL condition (which states that the time step has to be slower than the ratio between the node spacing Δx$Delta x$ and the physical velocity of the waves results in time increments which are of the order of one-10th of a second on many occasions. This paper extends a technique that has been used in the past to glacier evolution problems using finite differences or elements to SPH depth-integrated models for landslide propagation. The approach is based on assuming that (i) the flow is shallow, (ii) the rheological behavior determining the velocity of propagation is viscoplastic, and (iii) accelerations can be neglected. In this case, the model changes from hyperbolic to parabolic, with a time increment much larger than that of classic hyperbolic formulations.

缓慢和非常缓慢的山体滑坡会对建筑物造成严重的经济损失。由于山体滑坡的传播速度较快,因此可以对受影响区域采取计划性维护或疏散等措施。建模是一项重要工具,可使科学家、工程师和地质学家更好地了解其成因并预测其传播。有许多不同复杂程度的可用模型可用于此目的,从可以在电子表格中实现的非常简单的无限滑坡模型到完全耦合的三维模型。由于研究问题的时间跨度较大(有时长达数年),这种方法成本较高。然而,由于 CFL 条件(规定时间步长必须慢于节点间距与波的物理速度之比)造成的时间步长限制,在许多情况下,时间增量仅为十分之一秒。本文将过去用于冰川演变问题的有限差分或元素技术扩展到滑坡传播的 SPH 深度积分模型。该方法基于以下假设:(i) 流体较浅;(ii) 决定传播速度的流变行为是粘塑性的;(iii) 可忽略加速度。在这种情况下,模型将从双曲线模型变为抛物线模型,其时间增量远大于传统的双曲线模型。
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引用次数: 0
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