An artificial neural network approach to inhomogeneous soil slope stability predictions based on limit analysis methods

The assessment of soil slope stability is an important task in geotechnical designs. This study uses finite element upper bound (UB) and lower bound (LB) limit analysis (LA) methods to investigate inhomogeneous soil slope stability on the basis of the conventional Mohr–Coulomb parameters. The obtained stability numbers are presented in inhomogeneous soil slope stability charts. In order to minimize manual reading errors when using the chart solutions, an artificial neural network (ANN) is employed to develop a stability assessment tool for the slopes investigated in this paper. The slope stability analysis using the ANN-based tool is convenient, and the predictions it provides are highly accurate.     

拓扑优化研究方法综述

根据两个基本原理把拓扑优化方法分为退化法和进化法两大类,分别介绍了各主要的拓扑优化设计方法,对这些方法进行了比较,并指出各方法适用的范围,介绍了当前拓扑优化的研究热点,并对结构拓扑优化的未来作了展望.     

基于ANSYS的结构优化设计有限元分析

为验证ANSYS对结构优化设计的有效性，从理论上说明了结构优化设计的数学过程，介绍了ANSYS优化的相关概念、过程，结合某设计优化实例，为使用者提供了一套系统的思维模式，创造了良好的条件和方法。     

Bearing capacity and failure mechanism of reinforced foundations based on rigid-plastic finite element formulation

A series of model loading tests on both unreinforced and reinforced foundations have been carried out, and in these tests the ground was modeled by aluminum rods. A rigid-plastic finite element analysis considering the effect of geometrical nonlinearity has been conducted to quantitatively investigate both the increase of calculated bearing capacity and the progress in deformation localization corresponding to the settlement of a loading plate. In the analysis, the reinforcing material and the surrounding soil were modeled as a composite material. Based on the comparative study between the test results and the numerical analysis, it is concluded that the proposed numerical method is capable of investigating quantitatively not only the bearing capacity but also the failure mechanism. In addition, the effectiveness of the proposed numerical analysis has been confirmed.     

基于ANSYS分析的平面桁架结构优化设计

以六杆平面桁架结构为例,利用大型有限元分析软件ANSYS5.7对其按照重量最轻的原则进行了优化分析,实现了利用ANSYS5.7进行结构优化设计的全过程,得到了重量最轻的优化分析结果,在满足工程要求的前提下,节约了大量的工程材料。     

建筑设计方案优化的博弈分析

从委托方的利益角度出发,运用不完全信息静态博弈模型理论分析了委托方的最优策略,并从设计方态度出发,提出了优化建筑设计方案的对策,指出设计主体的项目管理人员应总结设计过程中管理工作的经验与不足,以有效推进建筑设计的管理工作,确保利益相关者的满意.     

Application of generalized regression neural network method for corrosion modeling of steel embedded in soil

In this work, a generalized regression neural network (GRNN) model is used to predict the corrosion potential values and corrosion current densities of ASTM A572-50 steel specimens embedded in nine soils with different physiochemical properties, i.e., pH, moisture content, resistivity, chloride content, sulfate and sulfite contents, and mean total organic carbon concentration. Experiments were conducted, and the corrosion current densities and corrosion potential values of the steel specimens embedded in the different soils were measured. The results obtained with the GRNN model agreed very well with the results of the experiments, suggesting that the proposed model is capable of predicting the corrosion activity of steel specimens embedded in different soils.     

Upper bound limit analysis of collapse shape for circular tunnel subjected to pore pressure based on the Hoek-Brown failure criterion

Based on Hoek-Brown failure criterion and using the upper bound theorem of limit analysis, a numerical solution for the shape of collapsing block in circular tunnel subjected to pore pressure is derived. The effect of water pressure which is assumed to be a work rate of external force is included in the upper bound analysis. By employing variational calculation to minimize the objective function, the upper solution of collapsing block is obtained. In order to evaluate the validity of the method used in this paper, the result for pore pressure coefficient r_u = 0, with no effect of pore pressure taken into account, is compared with previous work. The good agreement shows that the method of calculating the upper solution for the shape of collapsing block subjected to pore pressure is valid.     

Slope reliability and back analysis of failure with geotechnical parameters estimated using Bayesian inference

A Bayesian approach is proposed for the inference of the geotechnical parameters used in slope design. The methodology involves the construction of posterior probability distributions that combine prior information on the parameter values with typical data from laboratory tests and site investigations used in design. The posterior distributions are often complex, multidimensional functions whose analysis requires the use of Markov chain Monte Carlo (MCMC) methods. These procedures are used to draw representative samples of the parameters investigated, providing information on their best estimate values, variability and correlations. The paper describes the methodology to define the posterior distributions of the input parameters for slope design and the use of these results for evaluation of the reliability of a slope with the first order reliability method (FORM). The reliability analysis corresponds to a forward stability analysis of the slope where the factor of safety (FS) is calculated with a surrogate model from the more likely values of the input parameters. The Bayesian model is also used to update the estimation of the input parameters based on the back analysis of slope failure. In this case, the condition FS = 1 is treated as a data point that is compared with the model prediction of FS. The analysis requires a sufficient number of observations of failure to outbalance the effect of the initial input parameters. The parameters are updated according to their uncertainty, which is determined by the amount of data supporting them. The methodology is illustrated with an example of a rock slope characterised with a Hoek-Brown rock mass strength. The example is used to highlight the advantages of using Bayesian methods for the slope reliability analysis and to show the effects of data support on the results of the updating process from back analysis of failure.     

高层建筑地基基础概念设计的思考

基于高层建筑箱、筏、桩筏基础变形、反力等实测资料的分析指出,按传统理念设计的箱基、筏基、桩筏基础有两个缺陷:一是呈现明显的碟形沉降引起上部结构的较大次应力;二是基底马鞍形反力分布导致基础板或承台冲剪力和弯矩显著增大。为使差异沉降和箱、筏承台的内力减至最小并改善上部结构受力性状,提出变刚度调平概念设计。对于框筒、框剪结构,应强化核心筒区的桩土刚度(调整桩长、桩径或桩数),相对弱化外围刚度;对于主裙连体建筑,应强化主体,弱化裙房(采用天然地基、复合地基和疏短桩基);对于箱、筏基础,可局部强化核心筒区(采用桩基或刚性桩复合地基)。对于上述变刚度调平概念设计,进行上部结构—基础—桩—土共同作用分析,进一步优化布桩和承台配筋。通过大比例现场模型试验对上述优化设计理念进行了验证,并应用于10余项工程,取得了良好的技术经济效果。     

Homogeneous generalized yield criterion based elastic modulus reduction method for limit analysis of thin-walled structures with angle steel

A homogeneous generalized yield criterion (HGYC) expressed by piecewise polynomial is given for angle section. The element bearing ratio (EBR), reference EBR, and uniformity of EBR are defined in term of the HGYC. Then, a HGYC based elastic modulus reduction method for limit analysis of thin-walled structures with angle steel is presented based on the modulus adjustment strategy established on the EBR and the conservation criterion of energy. The method proposed can overcome the disadvantage of the conventional elastic modulus adjustment procedure where the nonhomogeneous generalized yield criterion is employed and the proportional loading condition is not satisfied.     

基于改进群搜索优化算法的桁架结构拓扑优化研究

对桁架结构拓扑优化设计方法进行了研究,基于和声搜索方法和边界粘附机制,提出了用"启发式拓扑"或"拓扑变量离散化"处理变量的改进群搜索优化方法,分别对一个10杆桁架和一个15杆桁架进行了拓扑优化设计,计算结果与已有的文献结果进行了对比分析.研究表明,该算法不受传统的桁架拓扑优化中"基结构"的限制,避免了奇异最优解的问题,表现出较强的适用性,采用本文提出的方法对桁架结构进行拓扑优化是可行和有效的.     

Seismic bearing capacity of shallow strip foundations in the vicinity of slopes using the lower bound finite element method

The seismic bearing capacity of shallow strip foundations in the vicinity of slopes was investigated by the use of the lower bound limit analysis in conjunction with the finite element method and the linear programming technique. The combination of the most probable failure modes including slope instability and ultimate bearing capacity makes the problem difficult to solve by conventional approximate methods such as the limit equilibrium, the bound theorems of the limit analysis, and the slip line methods since these are based on assumptions about either kinematically admissible failure mechanisms or statically admissible stress fields. The pseudo-static seismic loading scheme was adopted in the presence of both horizontal and vertical acceleration fields, and the soil-foundation interface was assumed perfectly rough. Parametric analyses were conducted to evaluate the most effective factors in the form of the dimensionless strength and geometry parameters. The results of the current study were found comparable with those in the literature, and the consistency of the results confirmed the robustness of the extended finite element lower bound formulation. It was shown that the normalized limit pressure is dramatically reduced as the earthquake acceleration coefficients increases, and that it increases with higher the soil strength parameters. Moreover, the threshold distance at which the influence of the slope diminishes was found to be a function of the soil strength parameters and the slope geometry.     

Application of several optimization techniques for estimating TBM advance rate in granitic rocks

This study aims to develop several optimization techniques for predicting advance rate of tunnel boring machine(TBM)in different weathered zones of granite.For this purpose,extensive field and laboratory studies have been conducted along the 12,649 m of the Pahang-Selangor raw water transfer tunnel in Malaysia.Rock properties consisting of uniaxial compressive strength(UCS),Brazilian tensile strength(BTS),rock mass rating(RMR),rock quality designation(RQD),quartz content(q)and weathered zone as well as machine specifications including thrust force and revolution per minute(RPM)were measured to establish comprehensive datasets for optimization.Accordingly,to estimate the advance rate of TBM,two new hybrid optimization techniques,i.e.an artificial neural network(ANN)combined with both imperialist competitive algorithm(ICA)and particle swarm optimization(PSO),were developed for mechanical tunneling in granitic rocks.Further,the new hybrid optimization techniques were compared and the best one was chosen among them to be used for practice.To evaluate the accuracy of the proposed models for both testing and training datasets,various statistical indices including coefficient of determination(R~2),root mean square error(RMSE)and variance account for(VAF)were utilized herein.The values of R~2,RMSE,and VAF ranged in 0.939-0.961,0.022-0.036,and 93.899-96.145,respectively,with the PSO-ANN hybrid technique demonstrating the best performance.It is concluded that both the optimization techniques,i.e.PSO-ANN and ICA-ANN,could be utilized for predicting the advance rate of TBMs;however,the PSO-ANN technique is superior.     

Seismic analysis of geosynthetic-reinforced retaining wall in cohesive soils

Although a cohesionless backfill is recommended for geosynthetic reinforced earth retaining walls, cohesive soil have been widely used in many regions across the globe for economic reasons. This type of backfill exposes the soil to the crack formation that leads to reduce the stability of the system. In this paper, to investigate the internal seismic stability of reinforced earth retaining walls with cracks, the discretization method combined with the upper bound theorem of limit analysis are used. The potential failure mechanism is generated using the point-to-point method. Two types of cracks are considered, a pre-existing crack and a crack formation as a part of the failure mechanism. The use of the discretization method allows the consideration of the vertical spatial variability of the soil properties. A pseudo-dynamic approach is implemented which allows the account of the dynamic characteristics of the ground shaking. The presented method is validated using the conventional limit analysis results of an existing study conducted under static conditions. Once the proposed technique to consider the cracks is validated, a parametric study is conducted to highlight the key parameters effects on the lower bound of the required reinforcement strength.     

Durability analysis of seashore saline soil bound with a slag compound binder

In this paper, a slag compound binder (hereinafter referred to as the SM binder) was used to bind seashore saline soil. Compressive tests, scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction analytical tests were carried out to measure the unconfined compressive strength, observe the microstructure, analyze the composition of hydration products and evaluate the binding mechanism of the saline soil/SM binder mixture. The results showed that calcium silicate and calcium aluminate hydrates were produced after the hydration of the cinder components in the SM binder. Part of the calcium aluminate hydrate reacted with the gypsum to form ettringite, while the other part reacted with the Cl^? and SO₄^2? in the saline soil to produce Kuzel’s salt. Na⁺ also participated in the hydration reaction and produced zeolite-like substances. These hydration reactions led to the rapid binding of the soil sample. As the surface of the saline soil particles also contained active SiO₂ and A1₂O₃, the Ca(OH)₂ reacted with them to form calcium silicate and calcium aluminate hydrates in a continuously alkaline environment. Such reactions contributed to the third-stage binding of the saline soil, leading to a gradual increase in the strength of the soil samples during the middle and late stages of binding.     

Applications of numerical limit analysis (NLA) to stability problems of rock and soil masses

This work presents formulations and results obtained with computer implementations of an alternative to the more standard techniques for the determination of the state of collapse of geotechnical structures in rock or soil masses. Examples of normally available and used techniques for those purposes are limit equilibrium based procedures and elasto-plastic finite elements. As an alternative to these techniques, the present paper describes Numerical Limit Analysis (NLA). The fundamentals for limit analysis, summarized in the so-called bound theorems, have been known for decades. Analytical solutions obtained with limit analysis are however limited in scope and are seldom used in the engineering practice. NLA on the other hand, by solving the limit analysis equations through numerical methods are general and applicable to a wide range of problems. The paper presents a discussion on available alternatives for the formulation of NLA specialized for the determination of collapse load factors of geotechnical structures in/on rock (fractured or not) and soil masses. Rock masses in particular are modelled as standard continua, Cosserat equivalent continua and true discontinua formed by discrete blocks. Finite elements are used for the solution of NLA equations of standard continua and Cosserat continua. The paper presents derivation of the pertinent equations, the numerical formulations used and details of their numerical implementation in computer programs. Attempt was made to validate all the implementations through existing analytical solutions. The obtained results permit to state that NLA is a promising and very often advantageous numerical technique to establish collapse states of geotechnical structures in rock and soil masses.     

钢托架的优化设计

介绍了工业厂房中钢托架的设计方法,分别对单跨简支托架和连续托架进行了内力分析,得出不同结构形式对托架各杆件的内力影响较大,设计时应根据结构特点进行优化选择.     

Effect of spatial variability of block-type cement-treated ground on the bearing capacity of foundation under inclined load

Deep mixing methods are widely used for stabilizing soft clayey soils and improving their bearing capacity. However, spatial variability in the shear strength of the cement-treated ground introduces uncertainties in estimating the bearing capacity for design. This paper evaluates the reliability of, block-type, cement-treated foundation under inclined load conditions using random field numerical limit analyses. The undrained shear strength is modelled as a random field which is characterized by a log-normal distribution and a spatial correlation length. Monte Carlo simulations are then used to interpret the stochastic bearing capacity factor and failure mechanisms for inclined concentric loading conditions at selected ratios of the shear strength ratio of cement-treated ground to original clay, the coefficient of variation in undrained shear strength and correlation length of the cement-treated zone. Variability of the undrained shear strength can reduce the expected bearing capacity of the cement-treated ground by 50–70% compared to homogeneously mixed clay.     

Probabilistic analysis of site-specific load-displacement behaviour of cement-fly ash-gravel piles

Cement-fly ash-gravel (CFG) piles comprise one of the novel ground-improvement methods. They are attracting considerable attention, as their beneficial role in accessible soft foundations is being increasingly exploited by the surging urban industrial development in China. Despite their recognised significance, however, the load-settlement behaviour of CFG piles is poorly understood, particularly in the context of probabilistic assessments. This study focuses on six full-scale CFG pile load test datasets, consisting of 245 samples collected at six sites in the Beijing region, under static axial compression loading. As a part of this investigation, a regression curve is applied to the load-settlement data for each load test in the database using a two-parametric hyperbolic or power law curve-fitting equation. Moreover, an assessment of the multiple load-displacement curves, based on the full set of pile load measurements conducted at a particular test site, reveals that the scatter observed in the regression parameter values is mainly caused by the inherent soil variability.Thus, a bivariate copula-based mixed distribution is chosen to represent the dependence between these regression parameters. A simple copula-based simulation model is used to estimate the reliability index at any specific allowable settlement for the serviceability limit state (SLS) design. The correlation coefficients in the copula-based distributions of the regression parameters are proven to have an impact on the reliability index of this pile foundation. A scatter analysis of the load-displacement behaviour provides insight into the probabilistic design of site-specific CFG pile foundations.