基于粒子群算法优化小波支持向量机的岩土力学参数反演

常用的确定岩土力学参数的方法有原位测试和室内试验两种,但都存在一定的局限性,参数选择的合理与否,对设计计算及数值模拟分析结果的有效性影响很大。支持向量机法在理论基础和求解算法方面都具有明显优势,为确保岩土力学参数取值的合理性,采用支持向量机法对岩土力学参数进行反演。先通过小波分析理论构造出支持向量机的核函数,再用粒子群算法(PSO)分别优化Morlet小波、Mexico小波和RBF函数的支持向量机模型参数,通过小波支持向量机模型建立反演参数与沉降值间的非线性映射关系。根据正交试验和均匀试验对需反演的岩土力学参数进行设计,结合有限元软件进行计算分析,得到学习样本和测试样本。分别采用Morlet小波、Mexico小波和RBF函数得出的预测结果和原始数据进行对比分析,发现采用Morlet小波核函数预测效果更佳。使用Morlet小波核函数预测的参数输入到Midas模型中计算建筑物最终沉降量,比较计算值与实际监测值,其相对误差不超过8.1%。研究结果表明,该方法在岩土工程参数的反演中具有良好的应用价值,对今后岩土力学参数的确定及校核提供了一种新方法。     

基于点云数据的围岩力学参数反演方法研究

依托南昌地铁1号线盾构工程,探讨基于三维扫描检测技术的围岩力学参数反演方法应用在隧道施工过程中的可行性。具体流程如下:三维扫描获取测点的点云数据并分析计算出管片的位移场,选取周边收敛作为反演的目标值;建立有限元模型,选取敏感性参数弹性模量、内摩擦角、黏聚力建立多个工况并进行反演计算。结果表明:基于三维扫描技术的监测方式较传统监测方式更高效且精确;同时,当围岩弹性模量取值8GPa、黏聚力为700kPa、内摩擦角为28°时,隧道周边收敛值与检测值最为吻合。反演得到的围岩参数值较勘察设计参数值偏低,因此将围岩参数反演方法应用在隧道施工过程参数动态调整中,可以降低隧道施工成本。     

粒子群算法改进及内变量本构模型参数反演

为了研究深埋煤矿巷道通常存在长时间、大变形问题,拓展岩土工程反分析的手段,改善岩土工程反分析的效率和精度,首先基于自然选择、自适应变惯性权重、异步变化学习因子的策略改进了粒子群算法并完成了程序实现,通过Sphere和Rastrigrin两函数测试了改进算法的优越性;其次以Matlab软件为平台,联合大型有限元软件ABAQUS,编制了岩土反分析程序GeoPSOInverse.m;最后应用所编程序反演了以不可恢复应变为变量的、不显含时间的泥岩蠕变模型参数。结果证实:改进的粒子群算法在岩土工程参数反演计算中体现出了可靠的反演能力和很快的收敛速度,可进行复杂采矿工程的实践应用。      

基于BP神经网络的岩土体细观力学参数研究

目前颗粒流计算方法中所采用的细观力学参数,均需根据岩土体宏观力学参数试验结果反复调试获取,调试效率很低且有较大的盲目性,因此,急需引入一种新方法,建立岩土体宏观力学参数与细观力学参数的关系。基于PFC3D程序,采用BP(back propagation)神经网络方法,建立宏观力学参数与细观力学参数的非线性模型,通过输入宏观力学参数,即可快速、准确地反演岩土体细观力学参数。研究结果表明：(1)根据BP神经网络模型反演确定的细观力学参数,输入数值模型计算其宏观力学参数,结果与试验值相比,精度一般高于90%;(2)当模型最小尺度上的颗粒数RES = 10、隐含层含6个神经元时,BP神经网络模型的反演性能最佳。实例计算表明,BP神经网络模型对于岩土体细观力学参数的确定具有良好的反演性能,该方法为颗粒流理论的推广应用提供了新的技术手段。     

基于遗传算法的岩土力学参数反演及其在 ABAQUS中的实现

岩土工程优化反分析是一个典型的复杂非线性函数优化问题,采用全局优化算法是解决这个问题的理想途径。结合ABAQUS有限元软件,提出遗传算法与有限元联合反演法,将有限元程序作为一个单独模块嵌入到遗传算法程序中,以测点的实测值与计算值建立误差函数,编制了遗传算法反演分析程序。并给出应用实例验证了该法的有效性,表明该方法可应用于岩土工程中的反演分析工作。     

支持向量回归算法在地应力场反演中的应用

地应力场是煤矿深部巷道开挖支护设计的基础数据。针对煤矿深部地层地应力实测值有较大随机误差的特点,提出基于支持向量回归(SVR)优化算法的地应力场反演方法。该方法以特征向量结构风险最小化为原则,将经验风险和置信范围最小化,减小实测地应力随机误差对参数反演的干扰。基于平煤一矿地质及地应力实测资料,建立三维有限元计算模型,引入侧压力系数,使用均匀设计表试验设计方法构造应力边界条件。根据计算分析结果建立学习样本,进而通过支持向量回归算法对边界条件参数进行优化,确定最佳应力边界条件,施加到模型上计算分析得到整个模型的地应力场。地应力测点反演值与实测值对比分析结果表明,反演值与实测值误差在合理范围,反演值比实测值随机性更小;反演地应力场分布规律与平顶山矿区地应力场分布规律一致;反演结果准确可靠。     

基于粒子群算法与混合罚函数法的有限元优化反演模型及应用

岩土工程优化反分析是一个典型的复杂非线性函数优化问题,采用全局优化算法是解决这个问题的理想途径。针对常规反演方法应用于岩土工程参数反演时搜索效率低的缺点,结合粒子群算法和遗传算法的特点,充分考虑二者的互补性,提出一种效率较高的全局优化算法,以测点的实测值与计算值建立一种新的评价函数,将多目标优化问题转化为单目标优化问题,用混合罚函数法将约束问题变为无约束问题,构建了一种新的目标函数,将有限元程序ABAQUS作为一个模块嵌入到优化算法程序中,编制了有限元优化反演分析程序。并给出了应用实例验证了该法的有效性和实用性,是一种可行的参数反演方法,可应用于实际工程中复杂岩土介质初始应力场反演、渗流场以及位移反分析     

PSO-LSSVM模型在位移反分析中的应用

提出了一种基于均匀设计原理、最小二乘支持向量机(LSSVM)和粒子群优化算法(PSO)的快速位移反分析方法。该方法利用均匀设计和有限差分法获得学习样本,再用粒子群算法搜索最优的最小二乘支持向量机模型参数。并用最小二乘支持向量机回归模型建立反演参数与监测点位移值之间的非线性映射关系,最后用粒子群算法从全局空间上搜索与实测位移最吻合的反演参数。该反演模型利用了粒子群算法高效简单、均匀设计构造高质量小样本以及最小二乘支持向量机的小样本、泛化性能好的特点。将该模型应用于龙滩水电站左岸地下厂房区岩体地应力场的反演分析中,计算结果与实测的位移值和地应力值均吻合较好,说明了该模型在岩土工程快速反演分析中具有良好的应用价值。     

三维地质体对AMT二维反演的影响研究

为探究三维地质体对二维反演结果地影响以及二维反演中极化模式的选择问题,设计了一系列二维、三维地电模型进行正演计算,并对正演结果进行二维反演计算。研究结果表明:相位受到三维畸变的影响较小,视电阻率较大;当三维异常体模型走向延伸较小时,TE模式的反演结果误差较大,TM模式的反演结果相对较好,但是反演得到了虚假的下覆构造,TE+TM联合反演结合了TE和TM模式反演的优点,可以较好地反映异常体的赋存位置及电阻率值;当三维异常体模型走向延伸长度增大时,三维数据的二维反演结果是可靠的,用TM和TE+TM模式反演都比较合理。     

基于SLR-ANN的地应力场三维智能反演方法研究

基于黄登引水发电系统区域地应力实测结果及建立的三维数值仿真计算模型,揭示了工程所在区域的三维地应力场分布特征,为地下工程的开挖加固设计提供更加准确的基础资料。分别采用传统多元线性回归方法、人工神经网络方法与考虑地质历史过程的基于逐步回归原理耦合人工神经网络(SLR-ANN)的非线性智能方法获得黄登水电站厂址区域的地应力场,再将地应力的实测值与反演数值解进行对比。结果表明:3种方法下反演所得引水发电系统区域内三维地应力场均与实测结果相一致,表明3种方法较为真实地模拟了整个地下洞室群区域三维地应力场的分布规律及特征。但采用SLR-ANN二次智能反演方法进行地应力反演,模拟效果更加接近监测值,且因减少了反演参数的个数而大幅度地提高了反演效率,可将反演计算结果应用于后续洞室开挖及锚固仿真分析中。     

隧道围岩流变参数的粘弹性位移反演与验证

将解析反演和数值反演相结合,对试验毛洞的断面形状和所处应力场做出适当的简化,利用对应性原理求解出洞室位移的Kelvin粘弹性解,并以此去拟合试验洞不同位置处的实测位移而得到多组流变参数;分别将其作为FLAC3D数值模型蠕变模式的输入参数,得出各自对应的实际断面形状和实际应力场条件下试验洞的蠕变位移数值解。然后,利用BP神经网络,对各组流变参数和其对应的试验洞同一位置处的蠕变位移数值解进行训练,建立起两者之间的非线性关系;利用训练好的网络,依据实测蠕变位移值得出了围岩流变参数;最后,利用隧道实测位移数据对反演的流变参数进行了数值正分析验证。     

黄土填方高边坡变形破坏机制分析

本文依据西北某油田倒班基地黄土填方高陡边坡工程勘察, 研究了该边坡的变形破坏机制, 通过对边坡工程地质条件及变形破坏分析, 建立FLAC3D地质模型, 采用数值模拟方法研究了边坡变形破坏机制。研究结果表明, 主要变形区或破坏区为陡坎周围至其沿坡面向下20～25m 的范围之间, 其破坏深度底界为全新世填土层Q4与原状黄土Q3接触面, 但要重点控制沿坡面向下20～25m 的范围之间的变形。数值模拟结果表明, 该边坡目前整体稳定性较好, 不会发生整体变形破坏。     

Folder: A numerical tool to simulate the development of structures in layered media

We present Folder, a numerical toolbox for modelling deformation in layered media subject to layer parallel shortening or extension in two dimensions. The toolbox includes a range of features that ensure maximum flexibility to configure model geometry, define material parameters, specify numerical parameters, and choose the plotting options. Folder builds on an efficient finite element method model and implements state of the art iterative and time integration schemes. We describe the basic Folder features and present several case studies of single and multilayer stacks subject to layer parallel shortening and extension. Folder additionally comprises an application that illustrates various analytical solutions of growth rates calculated for the cases of layer parallel shortening and extension of a single layer with interfaces perturbed with a single sinusoidal waveform. We further derive two novel analytical expressions for the growth rate in the cases of layer parallel shortening and extension of a linear viscous layer embedded in a linear viscous medium of a finite thickness. These solutions help understand mechanical instabilities in layered rocks and provide a unique opportunity for benchmarking of numerical codes. We demonstrate how Folder can be used for benchmarking of numerical codes. We test the accuracy of single-layer folding simulations using various 1) spatial and temporal resolutions, 2) iterative algorithms for non-linear materials, and 3) time integration schemes. The accuracy of the numerical results is quantified by: 1) comparing them to analytical solutions, if available, or 2) running convergence tests. As a result, we provide a map of the most optimal choice of grid size, time step, and number of iterations to keep the results of the numerical simulations below a given error for a given time integration scheme. Folder is an open source MATLAB application and comes with a user-friendly graphical interface. Folder is suitable for both educational and research purposes.     

Dynamic sliding of tetrahedral wedge: The role of interface friction

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.     

大断面黄土隧道初期支护适应性研究

以兰渝铁路大断面黄土隧道为工程背景,采用三维数值模拟结合现场监测实验对现有初期支护设计参数的适应性进行研究,对大断面黄土隧道初期支护的受力与变形特性进行综合分析。通过三维数值模拟得到黄土隧道开挖扰动后初期支护的受力与变形状态,将数值计算结果与现场监控量测对比获得典型断面围岩的应力和位移发展规律并对初期支护安全性进行评价;通过FLAC3D的FISH语言开发程序分析混凝土硬化特性对初期支护受力与变形的影响;现场跟踪量测与数值模拟的计算结果基本吻合,结论可为黄土地区隧道初期支护的设计和施工提供一定的借鉴和参考,积累有益的经验     

矿井层测深三维地电体异常规律研究

依据电磁场理论，构建地电模型，利用有限差分对矿井三维地电异常体进行数值模拟，得到异常体在电阻率不同、至巷道距离不同、及测点不同情况下的层测深曲线，并对其分布规律进行分析研究。通过模拟矿井三维地质异常体地电异常响应特征，并与井下实测层测深曲线对比和分析，论证了矿井三维地电体数值模拟的正确性。     

Geomechanical modelling to assess fault integrity at the CO2CRC Otway Project,Australia

This paper presents the first published 3D geomechanical modelling study of the CO2CRC Otway Project, located in the state of Victoria, Australia. The results of this work contribute to one of the main objectives of the CO2CRC, which is to demonstrate the feasibility of CO₂ storage in a depleted gas reservoir. With this aim in mind, a one-way coupled flow and geomechanics model is presented, with the capability of predicting changes to the in situ stress field caused by changes in reservoir pressure owing to CO₂ production and injection. A parametric study investigating the pore pressures required to reactivate key, reservoir-bounding faults has been conducted, and the results from the numerical simulation and analytical analysis are compared. The numerical simulation indicates that the critical pore fluid pressure to cause fault reactivation is 1.15 times the original pressure as opposed to 1.5 times for the comparable analytical model. Possible reasons for the differences between the numerical and analytical models can be ascribed to the higher degree of complexity incorporated in the numerical model. Heterogeneity in terms of lateral variations of hydrological and mechanical parameters, effect of topography, presence of faults and interaction between cells are considered to be the main sources for the different estimation of critical pore pressure. The numerical model, which incorporates this greater complexity, is able then to better describe the state of stress that acts in the subsurface compared with a simple 1D analytical model. Moreover, the reactivation pressures depend mainly on the state of stress described; therefore we suggest that numerical models be performed when possible.     

Influence of the microstructural properties of biocemented sand on its mechanical behavior

The mechanical efficiency of the biocementation process is directly related to the microstructural properties of the biocemented sand, such as the volume fraction of calcite, its distribution within the pore space, coordination number, contact surface area, and types of contact. In the present work, some of these microscopic properties are computed, from 3D images obtained by X-ray tomography of biocemented sand. These properties are then used as an input in current analytical models to estimate the elastic properties (Young and shear moduli) and the strength properties (Coulomb cohesion). For the elastic properties, the analytical estimates (contact cement theory model) are compared with classical bounds, self-consistent estimate and numerical results obtained by direct computation (FEM computation) on the same 3D images. Concerning the cohesion, an analytical model initially developed to estimate the cohesion due to suction in unsaturated soils is modified to evaluate the macroscopic cohesion of biocemented sands. Such analytical model is calibrated on experimental data obtained from triaxial tests performed on the same biocemented sand. In overall, the presented results point out the important role of some microstructural parameters, notably those related to the contact, on such effective parameters.     

Implementation of a coupled plastic damage distinct lattice spring model for dynamic crack propagation in geomaterials

This paper studies dynamic crack propagation by employing the distinct lattice spring model (DLSM) and 3‐dimensional (3D) printing technique. A damage‐plasticity model was developed and implemented in a 2D DLSM. Applicability of the damage‐plasticity DLSM was verified against analytical elastic solutions and experimental results for crack propagation. As a physical analogy, dynamic fracturing tests were conducted on 3D printed specimens using the split Hopkinson pressure bar. The dynamic stress intensity factors were recorded, and crack paths were captured by a high‐speed camera. A parametric study was conducted to find the influences of the parameters on cracking behaviors, including initial and peak fracture toughness, crack speed, and crack patterns. Finally, selection of parameters for the damage‐plasticity model was determined through the comparison of numerical predictions and the experimentally observed cracking features.     

基于BP神经网络的土体细观力学参数反演分析

利用离散元方法对颗粒材料的细观力学特性研究, 目前确定数值计算模型的细观力学参数大多数通过反复调试获取, 效率低、可重复性差。本文采用开源的颗粒离散元程序LMGC开展了土体双轴压缩数值试验, 通过25组土体细观力学参数计算得到相应的宏观力学参数, 建立了BP人工神经网络反演系统。利用土体物理试验得到的土体宏观力学参数, 输入BP神经网络, 反演得到土体的细观力学参数。将所得细观力学特性参数输入所建立的土体数值计算模型, 得到土体破坏过程中的应力-应变关系曲线, 以及土体颗粒的力链图和旋转变形云图。所建立的土体数值试验模型能够较好地模拟土体变形破坏过程, 利用BP神经网络反演细观力学参数以及数值模型计算得到的土体宏观力学参数与物理试验吻合较好, 误差在10%左右, 土颗粒间力链云图以及旋转变形云图较好地揭示了土体变形破坏的机理。