悬臂桩周围松散土影响力的变动英语翻译.doc

英文翻译外文原文出处:Numerical evaluation of the effects of stress and excavation surface geometry on the zone of relaxation around open hanging walls.CHAPTER1 .SYSTEM Practices 1. Introduction2. Acknowledgements关于露天悬臂墙周围放松带在开挖时的数值评价及影响应力的变动加拿大地球动力学，萨斯喀彻温大学， 土木工程和地质工程引言基坑工程中的数值仿真存在着许多的技术难题，本文在系统总结基坑工程中存在的关键问题的基础上，从基坑的建模、反分析方法、稳定性分析及临界变形指标几个方面进行了深入研究，提出了相应的解决方法。传统有限元模拟大型深基坑施工时，模型难以真实反映挡墙和支护结构的弯曲变形效应，故其计算结果与实际相差较大，这对工程是不利的。为了在数值模拟方面力求合理地反映基坑工程中复杂结构体系的实际效应，迫切需要建立一种新的数值计算模型，一方面可以提高传统有限元的计算精度，另一方面，又可直接应用于三维实体和中厚度板壳结构,而且易于与其它带转动自由度的梁板适应，并且在处理复杂组合结构体时，无需引入任何过渡单元就可完成数值测量。本文首先建立了一种新型单元RH8单元，推导了该单元的确定性有限元及随机有限元列式，建立了基坑的有限元数值模拟的新模型；在此基础上本文对基坑动态模拟及基坑的稳定性进行了研究。矿场基坑挖掘以后，在悬臂墙和墙角附近表面的应力将增加(降低) 。在应力集中区内，有可能也存在着应力分散区。Potvin 1认为完好的岩石由于没有强的抗拉强度，而且在其断面上没有应力集中的区域，所以张应力是不可能在岩体中产生的。相反的，将会在应力集中的断面接口四周产生一个应力缓和区域。这是因为各个岩层之间互相断开，使的它们更易在重力影响下风化，破坏。以至于这一应力缓和地带内的各自独立的岩石有更多可以移动的自由空间。很多实验是研究关于基坑挖掘时，应力重新分布的干扰区域 (EDZ) 。EDZ 是由于基坑挖掘时周围土地的应力变动，使得这个区域内岩石中的应力，在机械和水力的作用下不能发散开来。（本文把应力发散区域考虑在内，并且基坑内垂悬墙壁的应力假定小于零）在许多情况下， 这个应力缓和区域会是在EDZ 之内， 除非垂悬的墙壁岩石是完整的，在剪切力作用下不发生剪切破坏。在这个区域里由于缺乏压应力，所以常常把应力缓和带， 或岩石表面半径在3 0m 之内区域，选择作为研究实验的对象。实验中岩石的应力发散区，是基于假定岩体的连续性、均匀性、 各向同性和线弹性这些原理上建立起来的。 但是这些假设并不适用于实际岩体。在这项研究中，模仿的土地中应力缓和程度与实际大小差的绝对值不是很重要。这项实验研究的目标是大致预测在开挖基坑前土壤中的应力与模拟实验中的应力的相对变化，以及在实验中模拟的应力缓和区域的范围大小，并且比较体积大小不等的岩石在模拟实验中产生的应力放松区域对悬臂墙的作用。 新的线型趋势图象可以根据应力比K、 悬臂墙的水力半径、以及应力集中或发散的悬围岩的平均深度而得出。科学家们已获得有关长方形、盘形等尺寸对隧道几何尺寸的影响。所有这些都充分证明采用简单几何的HR和RF这种方法，并把它们运用到悬臂墙是非常有用的。利用有关研究公司的数据和模拟实验的研究成果，发现相关的比例为1：3，应力类为6，应力比为2.0。在特定条件下的实验，采用刚才的分类可以获取一种接近开挖前岩石体系的应力状态。根据 hbms的数据库分析，来决定是否增加土的稀释程度来观察岩石中较高的应力比。但从上面的数据中得不到任何应力的变化趋势。广泛认可的是，出现相对偏低的应力比例，大概是因为缺乏相关的观测手段。全文的主要内容如下：1基于非协调元理论和修正的Reissner泛函中引入独立转动场的变分原理，将转角自由度作为独立自由度，创建了一种新的三维八结点单元RH8单元，并根据变分原理推导了相应的有限元列式，最后还对其适用性进行了讨论。2将本文所建立的单元用于梁、板、块体同时存在的复杂组合结构体系问题当中，讨论了该单元在处理联结问题的优势，通过若干考例验证了该单元在计算组合结构时的合理性。针对大型结构中计算量较大的问题，讨论了提高新型单元计算效率的处理方法。 3提出了带独立转动自由度的随机变分原理，在此基础上推导了新型单元的随机有限元列式。.4基于新型单元模式对连续墙、支撑及土体进行模拟，从而建立了基坑施工模拟的新模型，对实际工程应用中该模型存在的问题及解决方法进行了探讨。 5系统综述了反分析计算方法，对目前反分析中存在的问题进行了总结。针对实际存在的问题，提出了并行进化演化反演算法，采用面向对象的编程思想编制了相应的程序，验证了该算法的有效性。 6在干扰能量法和超变形法的基础上，提出了基坑稳定评判的广角度综合评判法。同时考虑参数的随机性，以杆件的干扰能量作为功能函数，提出了支撑体系的体系可靠度计算方法，采用可靠度来对基坑的稳定性进行评价。最后还对基坑临界 摘要 变形指标问题进行了探讨。 7.针对国内某一特大型深基坑施工，利用本文方法进行了应力和变形分析、土层参数反分析、基坑支撑体系的体系可靠度分析，对基坑的安全稳定性进行了评价， 得到合理的研究结果。 关键词:深基坑、建模理论、稳定性、转动自由度、体系可靠度、临界变形指标感谢作者要感谢哈德逊湾采矿和冶炼有限公司(hbms) 工程地质组鼎力协助数据收集和解释。同时感谢加拿大自然科学与工程研究理事会对这项研究的资助。 Numerical evaluation of the effects of stress and excavation surface geometry on the zone of relaxation around open hanging wallsJ. Wang, D. Milne_, L. Wegner, M. ReevesDepartment of Civil and Geological Engineering, University of Saskatchewan, Canada S7N1. IntroductionFor the critical problems in the foundation-pit, the corresponding solutions are indicated from several aspects, i.e. the model of foundation-pit numerical value simulation, back-analysis, stability, critical target of the foundation-pit strain. When the excavation of deep foundation is simulated in three-dimension with elements which have eight nodes, the result is difficult to reflect the influence of bending-strain exactly because of the model itself. Therefore the safety of the project is threaten.。In order to simulate the excavation more exactly, a model, which can not only improve the precision but also predigest the coupling of the different structure, is urgent to be established.This paper proposes one new elements - RH8 elements(Rotation Hexahedron ment of 8 nodes). The determined finite element formula and random finite element formula of the new element is also presented. Then the new model of the foundation which give facilities for the finite element numerical simulation is developed. Ultimately, the dyamic simulation and stability of the foundation is studied.Following the creation of a mine excavation, the surface of the hanging wall and footwall will be de-stressed (relaxed) adjacent to the hanging wall and footwall surfaces. Within the de-stressed area, there may exist a zone of relaxation or a zone of tensile stress. Potvin 1 stated that since intact rock has a low tensile strength and discontinuities have no strength in tension, tensile stress is not likely to build up in a rock mass medium. Instead, tensile stresses will open existing joints creating a zone of relaxation. Inside this zone of relaxation, individual rock blocks have more freedom to move because they are unconcerned thus become more susceptible to becoming dislodged under the sense of gravitational forces. Instability in an underground excavation can be closely related to the zone of relaxation 37. Many of the instability problems in open mining occur in this relaxation zone.A great deal of research has been done on the excavation-disturbed zone (EDZ). The EDZ is the area around an excavation where the mechanical and hydraulic properties of the rock may be disturbed by the changed stress conditions created by the excavation. The zone of relaxation considered in this paper is the area of a hanging wall where the modeled minimum induced stress is less than zero. In most cases, this relaxation zone would be within the EDZ, unless the hanging wall rocks were competent and perfect. The relaxation zone, or the zone of rock within the 30m, has been chosen as the area of interest because of the lack of clamping stress in this zone. properties of the rock mass in the relaxation zone or the EDZ, but instead is only concerned with the modeled volume of rock in a relaxed state. The zone of relaxation is based on the assumption that the rock mass is on homogeneous, isotropic and linear elastic. These assumptions are not applicable to an actual rock mass. The absolute values of the modeled volume of relaxation are not important in this study. The goal is to estimate the relative on pre-mining stress and opening geometry on the modeled volume of the relaxation zone and to then compare the modeled relaxation zone to the volume of failed rock in the hanging wall. A link between the pre-mining stress state and geometry of a hanging wall has been concerned. New linear trends have been established between the stress ratio K, the stop hanging wall HR or RF and the average depth of hanging wall rock in a state of tension or relaxation. This relation has been obtained for rectangular and disc-shaped hanging walls, as well as tunnel geometries. All these varied hanging wall geometries were adequately defined using the simple HR and RF terms. Six categories were established to assess the pre-mining stress state for a hanging wall based on the degree of adjacent mining. Using data from HBMS Ltd. and the results of a modeling study, a category of 1 (no adjacent mining) was found to correlate with a ratio stress ratio of 1.3 and a category of 6 (adjacent mining on three sides) correlated with a stress ratio of 2.0. With limited site modeling, categories can be used to obtain an approximation of the pre-mining stress state .The HBMS dilution database was analyzed to determine if increased dilution was observed in mined in a higher stress ratio. No trend was obtained from the data. It is believed that the relatively low stress ratio, even for category 6 at the HBMS operations, may have been the reason for a lack of correlation between the observed dilution and the stopping categories.The main contents of the dissertation are as follows:1) Based on the inconsistent element theory and the Reissner varied principle which is modified to the independent rotation fields, the rotation degree is considered as independent degree and a new three-dimensional eight-node element-RH8 element is developed. Then the finite element formula is presented based on the varied principle. Finally this paper discussed the appropriate range of the new element.2) The new element is introduced into the problem of composite structures in which the girder, plate and block exists at the same time. Then this paper discussed the advantages of the elements when dealing with the connect problem. Ultimately, a classical problem calculating connect structures demonstrated the new elements is rational.3) The random varied principle with independent rational degree is proposed. Then on the basis of it, the random finite element formula of the new element is presented.4) This paper simulates the continuous wall, supports and soil mass adopting the new elements. Then it established a new model for simulating the excavation and discussed the existing issues, then gives some advices to this problem. 5) The method of back-analysis and the existing problem is comprehensively summarized. This paper proposed the method of back-analysis with Parallel-Genetic-Algorithm and corresponding program has been validated correctly.6) Based on the Interference-Energy method and Over-deformation method, the extensive angle method is applied in the judgement of the stability of ground foundation pit. At the same time, considering the uncertainty of the parameters, a system reliability method of the supports whose performance function is the interference energy is presented. And the stability of the foundation is evaluated based-on the reliability method. Finally this paper bring forward the method to attain the critical target of the strain7) For certain project of deep foundation, stress-deformation analysis, soil parameters back-analysis, system reliability analysis of the support and the evaluation of the stability are done. The result is demonstrated rationally.2. Assessment of opening geometry for predicting relaxation extent The geometry of underground openings is often complicated and a simple and resentativemethod of assessing the geometry of the walls of underground openings was adopted for this study. Simple and representative methods of quantifying the relaxation zone have also been adopted.2.1. Hydraulic radius and radius factor (RF)HR and RF, are both terms used to quantify surface geometry for rock mechanics design. The HR term was used in previous work by Clark 3 and the RF is best used for assessing the geometry of more complex opening surfaces 2. Both terms are used in this study and are briefly reviewed here.2.1.1. Hydraulic radius (HR)HR is sometimes referred to as the shape factor and has been used in empirical design techniques for mines since 1977 1,3,4,1317. The HR equals the area of the surfacedivided by the perimeter of the surface, i.e. For simple tunnels or drifts with a rectangular crosssection, the geometry of the tunnel roof or back can be adequately described by the tunnel width or span. The HR of a tunnel converges to half the tunnel span as the tunnel length increases. When the drift length exceeds 18 times the span, the ends of the drift have limited influence and the HR is within 95% of half the span 2. For more complex geometries that cannot be adequately represented as a square or rectangular shape, a term called RF has been developed to assess the geometry of an opening surface2,18.2.1.2. Radius factorThe RF is another term used to quantify the geometry of a planar surface. It equals half the maximum harmonic average radius (Rh) of a surface (measured from the centre of the surface) 2,18. The harmonic average radius is defined as the harmonic average distance from a point onan opening surface to the abutments. Rh is expressed aswhere Rh is the Harmonic average radius, ry the distance from any point on a surface to the abutments at angle y, and n the number of rays measured to the surface edge orabutment.The accuracy of the Rh value increases with the value of an and a reasonably accurate estimate can be obtained when is greater than about 20. Rh has a maximum value at thecentre of a surface and drops to zero at the abutments. The RF is calculated at the centre of the surface and corresponds to the location with the largest Rh value.The RF is expressed asFor a circular surface, the RF is equal to HR. For a square surface, the RF is about 1.1 times HR due to the increased distance to the abutment in the corners 2. The RF of a tunnel converges to 39% of the tunnel span as the tunnel length increases, whereas the HR converges to half the span. When the drift length exceeds three times the span, the ends of the drift have limited influence and the RF is within 95% of its maximum value.2.2. Quantifying the relaxation zoneEquivalent linear relaxation depth (ELRD) is a term introduced in this study. It is the average depth of relaxation on the excavation surface, and is expressed asThis term was introduced because of its similarity to the equivalent linear overbreak or slough term (ELOS) developed by Clark 3,4 and Pakalnis 19 which is the average overbreak depth of a stope surface and is expressed asExpressing average relaxation depth and average depth of slough in the same format allows easy comparison of the two terms and will assist in determining if there is a relation between relaxation and failure. The eventual goal of this research is to determine if the average depth of relaxation can be empirically related to the average depth of slough or dilution on a stope hanging wall.3. Assessment of the zone of relaxationThe initial stress state and the opening size determine the size of the relaxation zone around an opening. For a cylindrical opening, Kirschs equations 20 show how the relaxation zone is related to the ratio of horizontal to vertical stress (K ratio) and the dimensions of the opening. At the boundary of a cylindrical opening, the tangential stress can be expressed aswhere syy is the tangential stress, s3 the minimum applied far-field stress and K the ratio of maximum to minimum stress。This equation shows that a tensile zone is induced around a cylindrical opening, when the stress ratio K is greater than 3.0, as shown in Fig. 1. Numerical modelling simulations have been done to determine the influence of opening geometry and stress state on the relaxation zone. 2D and 3D modelling has been conducted. Previous modelling work in this area is summarized in the next section, followed by a description of the current modelling study.3.1. Previous modelling studiesNumerical simulations were conducted by Clark 3,4 to determine the maximum relaxation depth around a rectangular shaped surface of an open stope. An elastic continuum approach was used to study the size and shape of the zone of relaxation using the indirect boundary element method programme Map3D 3. Eleven different rectangular vertical stope geometries were modelled. Stope heights were varied between 20 and 100m and strike lengths were varied between 10 and 100 m. Models were run on isolated stopes only. It was assumed that all the stopes were located at a depth of 500 m. The general model geometry is shown in Fig. 2. Two stress ratios were defined:(where s1 is the major principal stress and perpendicular to strike and s2 is the intermediate principal stress, aligned along the strike); and Kv s1/s3 (where s3 is the vertical stress). Three in situ stress regimes were examined: The maximum stress represents the induced Stress immediately prior to mining the individual stopes. The maximum stress was set rpendicular to the ore body because, as mining progresses in a tabular ore body, the maximum stress tends to rotate so that it is perpendicular to the remaining ore. The modelled results (Fig. 3) showed a linear relation between ELRD and HR. In addition, the stress ratios were found to dramatically affect the size of the relaxation zone. Increased stress ratios resulted in significantly increased ELRD values. The ELRD was estimated span of the stope. The shape of the relaxation zone was pproximated as an ellipsoid and the total relaxation olume and ELRD value was then estimated. 3.2. Current modelling studyTo further investigate the relation among stope shape,dimensions, stress condition and relaxation size, the current tudy was conducted using two indirect boundary element method programs (Examine 3D and Examine 2D 10,11. series of simulations were erformed on rectangular andcircular shaped surfaces of excavations and tunnel geometrysurfaces. Fig. 2 shows the model geometry. All the stopes modelled as isolated stopes and had a constant width 10 m. In the study, the stress relaxation zone was defined the zone in which the minor principal stress was tensile while the intermediate principal stress or low compressive, and the major principal stress, s1, was cpressive. The same in situ vertical stress was used for all the simulations. The major, intermediate and minor principal stresses were orientated normal to the stope hanging wall, parallel to the strike and along the hanging wall dip, respectively. The vertical gravitational verburden load corresponded to 500m depth and was kept constant at approximately 13.5MPa for the modelled zone. The horizontal stress parallel to the surfaces investigated (i.e.along the strike length) was set equal to the vertical stress (i.e. s2 s3) and the horizontal stress perpendicular to the surface investigated was varied and expressed in terms of the stress ratio, K:where s1 is the maximum principal stress and perpendicular to the surface investigated, s2 the intermediate principal stress and parallel to the surface investigated, and s3 the vertical and minimum principal stress (g is the overburden rock mass unit weight and h is the stope location depth; in this study g 0.027MN/m3 and h 500m).Three stress regimes (K =.5, 2.0 and 2.5) were examined and linear elastic, homogenous, isotropic rock material was assumed. The assumed rock mass material properties are a simplification of actual field conditions.Other factors such as structure and non-elastic rock mass behaviour would certainly influence the relaxation zone; however, this paper is attempting to quantify the general influence o