强度参数的不确定性对土石坝坝坡失稳概率的影响

目前对土石坝坝坡的稳定性,主要是在坝料特性的确定参数基础上,采用极限平衡方法求出的坝坡抗滑稳定安全系数来评价。但实际的坝料特性参数往往是具有一定变化范围的变量,因此,安全系数大的坝坡不一定就比安全系数小的坝坡的失稳概率小。在分析研究12座均质土坝坝料强度参数统计特性的基础上,采用蒙特卡罗法对坝坡最危险滑裂面进行失稳概率分析,研究土石坝坝料强度参数的均值、变异性和相关性对坝坡失稳概率的影响。结果表明:强度参数的不确定性对坝坡的失稳概率有较大的影响,失稳概率随强度参数的均值的增大而减小,随变异系数的增大而增大。两个强度参数的相关性对坝坡的失稳概率也有显著的影响。由此可知,土石坝坝坡稳定性评价中,在确定性分析的同时,若能够考虑强度参数的不确定性,给出坝坡失稳概率,有利于更科学合理地评价土石坝的安全。     

土工合成材料在库岸防护中的应用

鞍子坝库岸的主要破坏形式是由于库水位消涨而使岸坡产生的塌岸。应用土工格栅加筋土护坡和土工石笼护脚相结合的方法进行库岸防护设计,且对于多级斜坡式加筋土挡墙的稳定性验算作了一些初步的探讨。     

边坡稳定性有限元直接评价与辅助设计系统

使用VC^ 6.0开发了土体人工边坡稳定性有限元直接评价与辅助设计系统，通过可视化对话方式实现了边坡的开挖、支护等工程的计算机设计，采用基于土体抗剪强度参数析减的有限元法直接评价边坡的稳定性，在迭代计算方案中使用了自适应弧长控制法，通过对多个人工边坡工程的稳定性评价，验证了系统的实用性。     

土质边坡地震稳定性状态判定方法研究

基于有限元强度折减法,对地震作用下土质边坡稳定性状态判定方法进行了研究。探讨了地震作用下坡体内部等效塑性应变区贯通率的计算方法,并利用有限元计算和统计分析方法建立了地震作用下坡体内部等效塑性应变区贯通率与边坡动力安全系数的对应关系。根据《建筑边坡工程技术规范》(GB50330—2013)中边坡稳定性状态与边坡安全系数的对应关系,从而实现了利用坡体内部等效塑性应变区贯通率来判别边坡地震稳定性状态的方法。结果表明:当等效塑性应变区贯通率K=100%时对应边坡稳定性状态为不稳定,当等效塑性应变区贯通率100%K≥90%时对应边坡稳定性状态为欠稳定,等效塑性应变区贯通率90%K≥85%时对应边坡稳定性状态为基本稳定,等效塑性应变区贯通率K85%时对应边坡稳定性状态为稳定。研究结果对于震后边坡稳定性的快速评价将具有重要的借鉴意义。     

Strength Characteristics of Frozen Saline Soils

Methods for determination of the strength characteristics of frozen saline soils (FSS) are examined. The shear parameters C _lt and _lt for typical soils of the Yamal Peninsula are determined over a broad range of negative temperatures (from – sign;1 to – sign;8°C) and salinities (from 0 to 1.5%). Proposed tabular data on strength characteristics of FSS make it possible to use them in calculations to determine limiting loads on bed soils.     

边坡侧向荷载计算方法讨论

《建筑边坡支护技术规范》(GB 50330—2013)采用了极限状态设计法来计算直线滑动模式下的边坡侧向岩土荷载,首先根据库伦土压力原理来计算滑体的剩余下滑力标准值,然后再乘以一个安全系数进行支护结构设计。这种设计方法不满足边坡工程的稳定安全系数设计要求,会造成边坡稳定安全系数为1.0时得到的侧向岩石压力为0。笔者以考虑稳定安全系数的锚杆锚固力计算为例,指出基于强度折减安全系数的侧向岩土荷载计算方法能满足边坡工程的稳定安全系数设计标准,使得支护后的边坡的稳定系数正好是设计安全系数。由此,提出了一个实用计算方法,即仍可采用《建筑边坡支护技术规范》(GB 50330—2013)第6章的计算公式,只是需要对滑面岩体强度c和tan φ按稳定安全系数设计标准进行折减,然后将折减后的参数代入公式计算边坡侧向岩土荷载设计值。     

Development of methods for evaluating the earthquake resistance of earth dams

The more complete methods that we have developed for evaluating the earthquake resistance of earth dams, which make it possible to account for the following, are discussed: the actual parameters of seismic effects in solving linear or nonlinear problems of the theory of elasticity; the actual properties of the soils comprising the body of the dam, and the characteristic features of the behavior under static and dynamic effects, as well as all basic factors involving the construction and operating periods: the sequence employed in building the structure and filling the reservoir; the consolidation process in the dam-seepage component with allowance for initial moisture and air saturation; and, the interaction between the skeleton material and rock and the fluid in the saturated components of the dam under static and dynamic effects, treating the saturated soil as a multiphase medium.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 6, pp. 10–15, November–December, 1992.     

Static and dynamic stability assessment of slopes or dam foundations using a rigid body–spring element method

A rigid body–spring element method is used to evaluate the static and dynamic stability of slopes or dam foundations. The versatility of the method applies well to both static and dynamic problems for blocks of arbitrary polyhedral shape with various re-entrant surface features. Examples show that the safety factor obtained in this way agrees well with theoretical solutions. The dynamic safety factor determined with this method varies with time, which differentiate it from the results of the limit equilibrium method or the finite element method. The method also makes it possible to search for the most probable sliding mass.     

Estimating the excavation disturbed zone in the permanent shiplock slopes of the Three Gorges Project, China

The stability and deformation of the permanent shiplock slopes are among the key issues in the design and construction of the Three Gorges Project. The permanent shiplock slopes, formed by deeply and steeply cutting into weathered and fresh granites, are 1607 m in length and 50–170 m in height. The disturbed zone in the permanent cut slopes induced by excavation is therefore one of the most important aspects in slope stability and deformation evaluation. A comprehensive investigation including non-linear finite element analysis, in-situ testing, instrumentation and monitoring, back analysis and rock mass quality rating has been carried out for the identification and evaluation of the excavation disturbed zone in the permanent cut slopes. The results of the investigation confirmed the existence of such an excavation disturbed zone in the permanent cut slopes. This zone is characterized by a considerable weakening in the mechanical properties of the rock mass. From the cut surface to the deeper region of the permanent cut slopes, the excavation disturbed zone can be further divided into a damaged zone, an affected zone and a slightly affected zone according to the extent of weakening in the rock mass. The damaged zone and the affected zone have thicknesses of 5–10 m and 10–20 m, respectively. The exact pattern of the excavation disturbed zone is variable in different parts of the permanent cut slopes and are generally similar to that of the plastic zones estimated by using the non-linear finite element analysis. The present investigation has provided both factual data and insights for the stability and deformation evaluation of the permanent shiplock slopes. The approach and methodology developed in the paper can be used to assess similar excavation disturbed zones in other large cut slopes.     

Results of investigation of the stress state of a sandy bed for rigid plates

Conclusions 1. As compared with corresponding solutions of the theory of elasticity, significant stress concentration is observed in compacted and loose sandy beds under any vertical load along the central vertical of rectangular plates. The degree of stress concentration depends on the properties of the medium (the density of the sand), the shape of the plate (the relationship between the dimensions of its sides), the external load, and, evidently, on a number of other factors. In the cases under consideration, the stresses increased nearly proportionally to the load (simple loading).2. Maximum vertical deformations of the sandy bed under small loads occur directly at the lower surface of the plates. As the load increases, maximum deformation appears at a certain depth below the lower surface of the plate. The relation between stresses and relative vertical deformations is nonlinear over the entire range of load variation.3. The more precisely defined results of study of the stress-strain state of the bed make it possible to evaluate more reliably the validity of existing and newly developed theoretical solutions employed in designing beds from first and second groups of limiting states.Novosibirsk Civil Engineering Institute. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 24–27, May–June, 1981.     

有限元强度折减法在边坡稳定性分析中的应用

借助ANSYS分析软件,基于Drucker-Prager（D—P）屈服准则,采用力和位移的收敛标准作为破坏判据,进行了边坡稳定性分析,分析结果表明与传统方法相比,有限元强度折减法能更真实地反映边坡的状态,求得的折减系数更接近于实际情况,在边坡稳定性分析中具有一定的优势。     

Stability Chart for Zero Tensile Strength Hoek-Brown Materials—The Variational Solution and its Engineering Implications

Most conventional slope stability calculations are based on the linear Mohr-Coulomb failure criterion. A substantial amount of experimental evidence suggests however that failure criterion of most soils is not linear particularly in the range of small normal stresses. Particulate media like soils usually have very small tensile strength; and the present work focuses attention on zero tensile strength materials obeying a limiting form of the non-linear Hoek and Brown empirical strength criterion. Previous investigations of the effect of strength function non-linearity on results of slope stability calculations were based on limiting equilibrium procedures that include various approximations and static assumptions. The present study presents complete results (safety factors and failure modes) of a rigorous variational limiting equilibrium analysis which does not include kinematical or static assumptions. Linear and non-linear failure criteria depend on different strength parameters and significant comparison of the effect of strength function non-linearity on stability of slopes is possible only for a given state of experimental information (i.e. a given data set). By performing such a comparison it is shown that strength function non-linearity has very significant effect on the results of slope stability calculations for relatively steep and very gentle slope inclinations. In both of these inclination ranges the non-linear analysis results in conservative slope design compared with the conventional Mohr-Coulomb criterion. In the range of intermediate slope inclinations, analysis based on the Mohr-Coulomb criterion is acceptable, resulting in more conservative results than the present non-linear analysis.     

Investigation of the operation of pile foundations with dynamic loads

Static and dynamic tests of two single piles and a cluster of four piles with a high foundation mat were conducted in full-scale conditions. A procedure is suggested for processing tests to evaluate the seismic stability of pile foundations, and coefficients are derived for reduction of the load on piles, which fully agree with analogous seismic coefficients of the conditions of operation given in Construction Standard and Rules and make it possible to choose the optimum variant of a pile foundation.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 6, pp. 26–27, November–December, 1992.     

库水位升降条件下边坡失稳离心模型试验研究

 三峡库区频发的滑坡地质灾害已愈来愈引起学者的高度重视,其受水位反复升降的影响是库区边坡不同于其他陆地自然边坡的一个显著特点。以离心模型试验为手段,基于三峡库区典型滑坡的工程地质特征,建立相应的土质边坡离心模型。在试验过程中实现对库水位循环升降的控制,模拟库区边坡在水位升降作用下的失稳过程。通过数码摄像、数字图像处理和传感元件测试,获得该试验条件下的土坡在水位升降过程中典型位置的孔隙水压力变化、全断面位移矢量演化(水平位移和沉降)、滑面形态及裂缝形成发展过程,并详细分析边坡在这种外部水环境影响下的变形演化、失稳和破坏模式。试验结果表明,若仅考虑水位升降作用的影响,该试验条件下的库区土质边坡的变形呈现典型的渐进牵引破坏模式,并具备较强的水土软化影响特征;裂缝在变形演化过程中出现交替张开和闭合现象,该失稳模式下的滑面呈折线形态,并在变形破坏过程中次生多级滑面。研究结果为库区滑坡地质灾害机制的深入认识、以及滑坡预防和控制提供了重要依据。     

Stability charts for rock slopes based on the Hoek–Brown failure criterion

This paper uses numerical limit analysis to produce stability charts for rock slopes. These charts have been produced using the most recent version of the Hoek–Brown failure criterion. The applicability of this criterion is suited to isotropic and homogeneous intact rock, or heavily jointed rock masses. The rigorous limit analysis results were found to bracket the true slope stability number to within ±9% or better, and the difference in safety factor between bound solutions and limit equilibrium analyses using the same Hoek–Brown failure criterion is less than 4%. The accuracy of using equivalent Mohr–Coulomb parameters to estimate the stability number has also been investigated. For steep slopes, it was found that using equivalent parameters produces poor estimates of safety factors and predictions of failure surface shapes. The reason for this lies in how these equivalent parameters are estimated, which is largely to do with estimating a suitable minor principal stress range. In order to obtain better equivalent parameter solutions, this paper proposes new equations for estimating the minor principal stress for steep and gentle slopes, which can be used to determine equivalent Mohr–Coulomb parameters.     

基于转动–平动组合破坏机构的含软弱夹层土坡降雨入渗稳定上限分析

软弱夹层、降雨等因素对边坡的整体稳定性有着很大的影响。软弱夹层会使得边坡的破坏形式发生改变,从而降低其稳定性;而降雨不但会使得边坡的稳定性变差,甚至有可能使边坡内形成更加软弱的夹层。但是目前尚未有一个简单合理的方法来分析这种类型边坡的稳定性。基于转动–平动组合破坏机构,提出了一种用于含软弱夹层边坡降雨入渗稳定性极限分析上限法。采用非饱和非稳定渗流分析计算得到的浸润线位置结合降雨后的土体强度及组合破坏机构分析含软弱夹层边坡降雨入渗的稳定性,通过与弹塑性有限元数值模拟结果进行对比,验证了本文方法的有效性。分析表明,组合破坏机构能够很好的用于含软弱夹层边坡的稳定性分析并为实际工程提供一个简单有效的设计方法。     

A comprehensive method for analyzing the effect of geotextile layers on embankment stability

Commercial software is used widely in slope stability analyses of reinforced embankments. Almost all of these programs consider the tensile strength of geotextiles and soil–geotextile interface friction. However, currently available commercial software generally does not consider the drainage function of nonwoven geotextile reinforcement. In this paper, a reinforced channel embankment reinforced by a nonwoven geotextile is analyzed using two methods. The first method only considers the tensile strength and soil–geotextile interface friction. The second method also considers the drainage function. In both cases, the reinforced embankment is modeled in rapid drawdown condition since this is one of the most important conditions with regard to stability of channel embankments. It is shown that for this type of application, modeling a nonwoven geotextile reinforced embankment using commercial software which neglects the drainage function of the geotextile may be unrealistic.     

软粘土边坡稳定性分析中十字板强度取值的探讨

土体强度指标的确定和选取是正确计算边坡稳定性的关键。对于欠固结、高灵敏度的软粘土地基,获取完全不扰动的土样进行室内试验是相当困难的,对此种软土地基通常采用十字板法来获得其强度指标进而进行边坡稳定性分析。但工程经验表明,由于土体强度具有摩擦特性和明显的各向异性,使得由十字板指标计算的边坡稳定性不能反映实际情况。考虑到上述因素,将十字板强度与土体的抗剪强度指标建立联系,采用经过修正的十字板强度指标进行边坡稳定性分析,通过对若干工程进行对比分析表明,该方法能够比较准确地反映工程的实际情况。     

Technical Transition of Earth Structures for Shinkansen

The paper describes the technical transition of earth structures for the super express known as the Shinkansen. To ensure the safe running of Shinkansen, the earth structures needed to be adequately designed and constructed with consideration of cost effectiveness and high stability. These earth structures include embankments for the slab tracks, reinforced retaining walls, reinforced cut slopes, aseismic abutments, soil improvement and performance-based design. New construction techniques and design methods, model tests, field construction tests and evaluations of these designs were carried out to construct the best possible earth structures. The actual applications of the earth structures listed above to secure the safe running of the Shinkansen are introduced.     

Experimental investigation of the stress-strain state of loess soils in the base of rigid plates

Conclusions 1. The method developed for pressing the pressure cells into the soil mass made it possible to establish for the first time the actual initial stressed state of damp and wet loess bases from the effect of the soil's own weight within the depth of the deformable region under plates.2. The results of measuring the vertical and horizontal stresses along the central axis of the plate established that the lateral earth pressure coefficient varies as a function of the stressed state and water content of the base.3. The results of the full-scale investigations permit a most complete and comprehensive evaluation of the work of a damp and wet loess base under a load. The different character of distribution of stresses and displacements in such soils under foundations indicates that the existing methods of calculating damp and wet loess bases require further improvement.Moscow Civil Engineering Institute (MISI). Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 17–19, May–June, 1979.