极限分析有限元法讲座——Ⅰ岩土工程极限分析有限元法

经典岩土工程极限分析方法一般采用解析方法,有些还要对滑动面作假设,且不适用于非均质材料,尤其是强度不均的岩石工程,从而使极限分析法的应用受到限制。随着计算技术的发展,极限分析有限元法应运而生,它能通过强度降低或者荷载增加直接算得岩土工程的安全系数和滑动面,十分贴近工程设计。为此,探讨了极限分析有限元法及其在边坡、地基、隧道稳定性计算中的应用,算例表明了此法的可行性,拓宽了该方法的应用范围。随着计算机技术与计算力学的发展,岩土工程极限分析有限元法正在成为一门新的学问,而且有着良好的发展前景。

岩土工程极限分析有限元法及其应用

经典岩土工程极限分析方法一般采用解析方法 ,有些还要对滑动面作假设 ,不适用于非均质材料 ,尤其是强度不均的岩石工程 ,从而使极限分析法的应用受到限制。随着计算机技术的发展 ,极限分析有限元法应运而生 ,它能通过强度降低或者荷载增加直接算得岩土工程的安全系数和滑动面 ,十分贴近工程设计。本文探讨了极限分析有限元法的一些基本原理 ,包括安全系数的定义、岩土体整体失稳的判据、屈服准则的选用等 ,并将该方法应用于边坡、地基、隧道稳定性计算 ,算例表明了此法的可行性 。

某高层建筑基坑塌方分析及极限分析有限元法模拟

某高层建筑基坑在施工过程中由于没有严格按照设计施工、基坑边坡土层没有完全封闭、边坡项部和底部裸露,致使雨水从坡顶排水沟下部渗到边坡面层内,经雨水浸泡后的土体抗剪强度降低,大量土块失稳落下,喷射混凝土面层内形成了大片空洞,锚索的预应力损失,最终导致整个面层坠下,造成塌方事故。采用二分法改进的极限分析有限元法对该基坑边坡进行模拟,得到了基坑边坡的安全系数和滑动面,用二分法对土体强度参数进行折减,提高了极限分析有限元法的求解效率。

岩土工程极限分析有限元法及其应用

极限分析有限元法是通过强度降低或者荷载增加直接计算演示工程安全系数和滑动面的一种方法,在岩石工程中广泛的被应用。本文将对极限分析有限元法的基本原理详细的分析,并且对其在岩石工程中的应用做一些讨论,以期能够进一步拓宽该方法的使用范围。

岩土工程极限分析有限元法及其应用

近年来,在多方面利好因素的影响下,使得我国社会综合国力得到了显著的提升,从而也为各个领域的发展壮大创造了良好的机遇,推动了科学技术的发展,大量的新型科学技术被人们研发出来,并在实践运用中取得了良好的成绩。其中有限元法是当前最先进的一种实践方法,将有限元法与电子计算机技术融合在一起,能够高效的解决各类问题。鉴于此,这篇文章主要围绕岩土工程极限分析有限元法的实践运用展开全面深入的研究分析,希望能够对我国岩土工程行业的未来良好发展有所帮助。

岩土工程极限分析有限元法及其应用

在20世纪70年代,英国科学家zienkiewicz提出了一种计算岩土安全系统的方法,方法是增加外部荷载和降低地质强度。然而,随着计算机技术的发展,影响有限元分析发展的因素逐渐减少,成为一门新的极限分析领域。这种分析方法运用到很多地方,有很大的作用。

极限平衡有限元法在边坡稳定分析中的应用

目前,边坡稳定分析常用的定量分析方法主要为刚体极限平衡法和有限元数值分析法,二者各有优缺点。将两种传统方法相结合,应用极限平衡有限元法和自编程序分析某边坡实例的稳定性。结果分析表明,该法计算的安全系数较为可靠,且作为两种传统方法的结合,能扬长避短,既可满足较高的分析精度要求,又能较好的适应现有的边坡稳定评价体系。

极限平衡理论在加筋土结构设计中应用的评述

为分析加筋土结构设计目前大都采用的极限平衡理论的保守问题,在介绍国际上若干现行规范要点的基础上,以国内外若干工程的实测资料说明这种保守的程度。还对加筋土结构的破坏模式和稳定校核的内容作了叙述,建议从筋材本身的安全与加筋土结构整体稳定2方面进行稳定计算,认为复合滑动面可能是结构稳定安全系数最小的滑动面,该滑动面可能穿过筋材并沿筋材表面滑动。目前常用的所谓"外部稳定校核"、"内部稳定校核"等分析方法,不可能找到整个结构所有可能的滑动面。最后对加筋土结构的合理设计方法提出了建议,认为对结构物的应力应变分析是设计的最基本、最有用的资料,但极限状态下结构物性状也需掌握,因此最合理的是采用有限元分析法和极限平衡分析法相结合的设计方法。

Influence of confined water on the limit support pressure of tunnel face in weakly water-rich strata

In the process of shield tunneling through soft soil layers,the presence of confined water ahead poses a significant threat to the stability of the tunnel face.Therefore,it is crucial to consider the impact of confined water on the limit support pressure of the tunnel face.This study employed the finite element method(FEM)to analyze the limit support pressure of shield tunnel face instability within a pressurized water-containing layer.Subsequently,a multiple linear regression approach was applied to derive a concise solution formula for the limit support pressure,incorporating various influencing factors.The analysis yields the following conclusions:1)The influence of confined water on the instability mode of the tunnel face in soft soil layers makes the displacement response of the strata not significant when the face is unstable;2)The limit support pressure increases approximately linearly with the pressure head,shield tunnel diameter,and tunnel burial depth.And inversely proportional to the thickness of the impermeable layer,soil cohesion and internal friction angle;3)Through an engineering case study analysis,the results align well with those obtained from traditional theoretical methods,thereby validating the rationality of the equations proposed in this paper.Furthermore,the proposed equations overcome the limitation of traditional theoretical approaches considering the influence of changes in impermeable layer thickness.It can accurately depict the dynamic variation in the required limit support pressure to maintain the stability of the tunnel face during shield tunneling,thus better reflecting engineering reality.

基于改进动态规划算法的堆积体滑坡稳定分析

应用图论将堆积体滑坡稳定性分析中最危险滑动面搜索及安全系数计算问题转化为数学领域求最短路径问题。对动态规划算法进行改进,建立基于改进动态规划算法的极限平衡有限元方法,给出该方法的基本方程和路径上应力计算过程,避免引入辅助函数需给定初始安全系数进行迭代计算的缺陷。将该方法应用于溪洛渡左岸谷肩堆积体的稳定性分析,基于滑坡产生、发展、蠕变条件对其稳定性进行判断,对该堆积体的变形破坏机制进行分析和滑面形成条件探讨;借助监测资料揭示的滑面分布,验证改进动态规划算法搜索滑面位置与计算安全系数的准确性;在此基础上提出基于滑坡征兆的堆积体滑坡稳定性分析技术路线,可用于复杂滑坡堆积体边坡的稳定性分析。

锚索布置对长短双排桩的受力影响分析研究

双排桩支护结构作为一空间组合支护结构,受力复杂,影响其支护性能的因素较多,将原单排锚拉桩方案调整为“前桩短,后桩长”的双排桩支护结构形式,为研究基坑支护中不同锚索竖向间距布置对长短双排桩桩身受力的影响及桩身传力规律,通过极限有限元分析法对结构支护体系进行了分析计算,结论如下:(1)双排桩与单排桩支护结构桩身弯矩图存在明显不同,后排桩弯矩图朝坑内方向变形,呈“反C”型,桩身最大弯矩位于在0.45H~0.55H范围内,桩身受力以基坑内方向受拉为主。前排桩弯矩图受锚索分布影响呈“WW”型,桩身最大弯矩位于0.3H~0.6H范围内,桩身受力以基坑外方向受拉为主。(2)后排桩呈受的弯矩是前排桩的1.5~2倍。后排桩主要呈受承载土压力的作用,前排桩起到挡土和传递土压力的作用;(3)采用不同的锚索布置方案时,前排桩嵌固深度不足时,应采用锚索加密布置的方案有利于桩身的整体变形稳定,也有利于基坑开挖安全。

局部破碎带下海底岩体隧道稳定性分析

以局部破碎带的某海底岩体隧道为例,采用有限元极限分析法分析了海底隧道岩体注浆加固前后的稳定性。计算表明,对于整体较为安全的隧道,当存在局部破碎带时,安全度降低,破碎带越宽,注浆堵水圈厚度越小,安全系数越小。与完整围岩破裂面位于两侧相比,含倾角45°破碎带围岩的堵水部分最先失稳。因此,必须做好破碎带的超前注浆堵水,以减少其渗水量,并对破碎带进行局部加固,此种情况下,隧道衬砌原则上可按无水压设计,衬砌厚度与采用全水头设计相比可以大大降低。

Stress based forming limit diagram for formability characterization of 6061 aluminum

Two numerical criteria of forming limit diagram（FLD） criterion and ductile fracture criterion（DFC） are presented for FLD prediction of 6061 aluminum. The numerical results are compared with the experimental FLD and also punch＇s load-displacement curve of experimental samples. Experimental FLD of this study is calculated using hemispherical punch test of Hecker. Experimental FLD is converted to FLSD and imported to the Abaqus software to predict necking of samples. Numerical results for FLSD prediction were compared with experimental FLSD. Results show that ductile fracture criterion has higher accuracy for FLD and FLSD prediction of 6061 aluminum. Comparison of numerical and experimental results for force-displacement curve of punch shows that numerical results have a good agreement with experiment.

Dynamic limit equilibrium analysis of sliding block for rock slope based on nonlinear FEM

Traditional rigid body limit equilibrium method （RBLEM） was adopted for the stability evaluation and analysis of rock slope under earthquake scenario. It is not able to provide the real stress distribution of the structure, while the strength reduction method relies on the arbitrary decision on the failure criteria. The dynamic limit equilibrium solution was proposed for the stability analysis of sliding block based on 3-D multi-grid method, by incorporating implicit stepping integration FEM. There are two independent meshes created in the analysis： One original 3-D FEM mesh is for the simulation of target structure and provides the stress time-history, while the other surface grid is for the simulation of sliding surface and could be selected and designed freely. As long as the stress time-history of the geotechnical structure under earthquake scenario is obtained based on 3-D nonlinear dynamic FEM analysis, the time-history of the force on sliding surface could be derived by projecting the stress time-history from 3-D FEM mesh to surface grid. After that, the safety factor time-history of the sliding block will be determined through applying limit equilibrium method. With those information in place, the structure＇s aseismatic stability ean be further studied. The above theory and method were also applied to the aseismatic stability analysis of Dagangshan arch dam＇s right bank high slope and compared with the the result generated by Quasi-static method. The comparative analysis reveals that the method not only raises the FEM＇s capability in accurate simulation of complicated geologic structure, but also increases the flexibility and comprehensiveness of limit equilibrium method. This method is reliable and recommended for further application in other real geotechnical engineering.

The Challenges of Designing a Wooden Beam of Composed Section

This work describes details about the challenges and solutions encountered in the timber structure beam. The choice for wood is due to the fact that it is a better material suited for environments with high salinity and, in this context, to reduce maintenance costs. The entire roof was supported only by four columns, which forced the side and frontal beams to exceed spans over 18 meters without intermediate supports. This was the most important challenge of the project： to find a section to the beam which can attend the ultimate limit state and serviceability in wood to the dimensions in project. The answer was clear： It would need to have composed section. A computational model was constructed using the finite element method in order to obtain the efforts on the structural elements. It is important to emphasize that the design of a wood structure requires not only knowledge, but creativity as well, to overcome the challenges posed by the distinctive needs to the detailing of this material. In addition to that, it requires special attention during the construction execution, because of the difficulty that the carpenters have to read the specific plans.

Hybrid method of limit equilibrium and finite element internal force for analysis of arch dam stability against sliding

A hybrid method of limit equilibrium and finite element internal force for analysis of arch dam stability against sliding is presented.The finite element internal force method(FEIFM) is used to provide more accurate thrust forces acting on the faces of a slip body,and the limit equilibrium method(LEM) is employed to evaluate the factor of safety of the slip body.The method presented can deal with a slip body with large amount of geometrically complex slip faces.In addition,compared with the traditional LEM,it can meet the balance condition of the forces in the slip faces.An example shows that the factor of safety obtained by the method presented agrees well with the theoretical solution.A practical example is also presented to demonstrate the application of the method in the stability analysis of an arch dam project.The results from the examples show that the method is promising in analysis of arch dam stability against sliding.

Penetration of disk fragments following impact on thin plate

To investigate the ballistic resistance and failure pattern of aeroengine casing following the impact of disk fragments, and to determine the optimum case structure, the phenomena of a 1/3rd disk fragment impact on single and double-layered thin plate targets were simulated using nonlinear dynamical analysis software MSC.Dytran. Strain rate effect was introduced in a Johnson-Cook (JC) material model for the disk fragment and the plate. Impact modeling was based on the Arbitrary Lagrange-Eulerian method, and simulated using explicit finite element method (FEM). Simulation results showed that the major failure pattern of the plate is shearing and tensile fracture with large plastic deformation. It was also concluded that the ballistic limit velocity increases with the standoff distance when it is beyond a certain value, and that greater resistance is obtained when the front plate has either a proportionately low or high thickness. The impact resistance of a double-layered plate may exceed that of a single plate if the thicknesses and standoff distance of the two plates are set appropriately.