混凝土面板堆石坝蠕变沉降经验模型及其应用

根据岩土材料Merchant、Bergers和Butterfield蠕变模型的基本形式,建立3种预测混凝土面板堆石坝蠕变沉降经验模型。以蒲石河混凝土面板堆石坝为例,采用非线性有限元方法数值模拟堆石坝的顺序填筑过程。根据堆石坝沉降现场观测数据,采用回归分析方法确定3种沉降经验模型中的待定参数,确定堆石坝的蠕变沉降随时间的变化关系。工程实践应用结果表明,所提出的堆石坝蠕变沉降经验模型具有较高的拟合和预测精度,堆石坝的蠕变沉降除与时间有关之外,还与观测点的应力状态和位置以及堆石料的变形模量有关。     

基于响应面法的高堆石坝瞬变-流变参数反演方法

如何准确确定原级配堆石体的力学参数是高堆石坝建设中亟待解决的一个关键问题,参数反演是解决这一问题的可行方法之一,传统的参数反演方法因需要进行大量的有限元正分析,其计算工作量大,反演效率较低。响应面法可以有效克服以上问题,但已有方法仅针对堆石体的瞬变参数,未考虑流变参数,不能满足堆石坝长期变形预测的需要。综合考虑瞬变和流变参数,通过构造更加合理的响应面函数,提出了基于响应面法的高堆石坝瞬变-流变材料参数反演方法,大大提高了反演的效率和精度。以水布垭面板堆石坝为例,采用该方法对坝体瞬变和流变参数进行了反演分析。反演结果表明,计算值与实测值在数值和变化规律上总体符合较好,反演结果合理可靠且更加高效。     

基于堆石坝竣工期沉降观测数据的材料非线性本构模型参数反演

为了高效和准确地确定堆石料的非线性本构模型参数,提出了基于响应面方法的参数反演方法。采用有限元方法数值模拟了堆石坝的分层填筑过程。建立了堆石坝变形观测点沉降的响应面函数,确定了多项式响应面函数的系数。根据堆石坝竣工期变形观测数据和确定的响应面函数,采用优化方法反演确定了堆石料本构模型参数。工程实际应用结果表明,该方法具有较高的计算效率,预测的堆石坝沉降变形与现场观测值吻合较好。     

高堆石坝瞬变-流变参数三维全过程联合反演方法及变形预测

利用反演分析得到的参数进行高面板坝的应力、变形分析来预测长期变形。由于堆石坝的施工过程和变形机制比较复杂,很难将瞬时变形和流变变形分开,因此,有必要对静力本构模型参数和流变模型参数进行综合反演。利用实测位移资料,以对堆石坝变形较敏感的静力本构模型和流变模型参数为待反演参数,采用基于粒子迁徙的粒子群算法和径向基函数神经网络构建参数反演平台,该方法克服了粒子群算法易陷入局部最优和早熟收敛的缺点,采用经过训练的神经网络来描述模型参数和位移之间的映射关系,节省了参数反演的计算时间。对水布垭高面板坝的反演结果表明,基于反演参数的沉降计算值与实测值吻合得很好,坝体变形在合理范围以内并趋于稳定。     

Study on wetting deformation characteristics of coarse granular materials and its simulation in core-wall rockfill dams

The wetting deformation of coarse granular materials is often considered to be an important cause of the core wall rockfill dam cracks during impounding. By analyzing existing research results, this paper proposes a hyperbolic relationship between the wetting axial strain and wetting stress level and puts forwards a warped surface relationship among spherical stress, shear stress, and the ratio of wetting volumetric strain to wetting axial strain. To illustrate its practicability, the wetting strain model's parameter determination process is introduced and the rockfill materials wetting parameters are determined using the triaxial wetting test data. Moreover, the collapse settlement of Guanyinyan rockfill dam during first impounding is numerically simulated using the proposed method to calculate rockfill wetting deformation and verified by field measurements and monitoring data. The results show that the calculative method of wetting deformation proposed in this paper is reasonable and practical; the wetting deformation of upstream rockfill materials would cause an adverse deformation trend, which may lead to crack occurrence at the upstream slope and dam crest; and the Guanyinyan rockfill dam cracks on the top of junction mainly caused by the wetting deformation of upstream rockfill.     

Discrete modelling of time‐dependent rockfill behaviour

This modelling study deals with the time‐dependent behaviour of rockfill media, which is of particular interest during the life of rockfill dams. Breakage of rock blocks and crack propagation are the main processes responsible for rockfill creep and collapse. The modelling procedure presented here is performed on two scales: on the rock block scale, where the grain is taken to be an assembly of rigid particles initially endowed with cohesive bonds, and on the rockfill scale, which is taken to involve a set of breakable grains interacting via contact and friction processes. The grain breakage process is described in term of a thermodynamically consistent damage interface model, where the damage is a gradual delayed process. This model was implemented in a non‐smooth contact dynamics code. The effects of the main parameters involved were analysed by performing numerical studies. The ability of the model to predict the creep behaviour of rockfill media is confirmed by presenting several simulations. Copyright © 2008 John Wiley & Sons, Ltd.     

考虑颗粒强度尺寸效应的原型堆石料破碎特性研究

高土石坝中,堆石体颗粒破碎是导致坝体变形的主要因素之一。但是由于原型坝料的颗粒尺寸较大,其破碎程度难以直接通过室内试验度量,因此通常要将原型级配缩尺为60 mm以下的小粒径级配堆石料,然后才能进行室内试验。而由于原型和试验级配差异较大,导致试验测得的参数往往和原型坝料实际参数有较大差异,因而影响了原型坝料力学特性的深入研究。这里提出了一种新的实时预测原型坝料破碎的方法。首先在颗粒尺度上,基于单粒强度的Weibull分布理论和颗粒分形破碎理论,阐述了原型堆石料级配演化的推求过程;然后通过单粒强度试验测得了相关参数,并与三轴试验测得的试样级配曲线对比,验证了参数选取的合理性;之后分析了颗粒强度离散程度对于原型坝料级配曲线形状的影响;最后,讨论了加载过程中原型级配和试验级配堆石体的相对破碎参量和受力状态的关系。     

The Effect of Impervious Clay Core Shape on the Stability of Embankment Dams

One of the most important dangers that treat earth dams which can lead to interior failure over a prolonged period is the hydraulic fracturing factor. In the case of zoned dams, due to differences in stiffness of the core and its abutment zone, differential settlements occur between them. This factor is responsible for the arching phenomenon. Differential settlements between core and shell cause cracks within the core initially sub-surface, Those cracks may develop the first impounding causing internal erosion on the dam core. In this research, using a computer modeling of Ghavoshan rockfill dam (located the west part of Iran) as a case study computed by SIGMA/W program, the role of the dam core shape on those factors is demonstrated. It is found that an inclined core shape is preferred in a condition that is especially important settlements of construction during for dam body. The result of finite element analysis indicates desired conditions from the point of view of stress, deformation and resistance against hydraulic fracturing for the same width of dam designs. Moreover, this can be higher priority for embankment dam designs.     

Probabilistic analysis of collapsing soil by indicator kriging

Collapsing soils, which undergo a large decrease in bulk volume virtually instantaneously upon saturation and/or load application, are found in arid and semi-arid regions of the world. In the western and midwestern U.S., problems resulting from collapsing soils are being recognized due to rapid industrial and urban developments. A probabilistic analysis of the distribution of such soils would be a rational approach for quantifying risk involved for a project in an area where such soils are found. Indicator kriging was applied to seven sets of collapse and collapse-related soil parameters to obtain the probability that a certain parameter is more or less than a predefined critical value for low, medium, and high collapse susceptibility. Results are presented in the form of probability contour plots with known variance of estimation of the probability. The ability to predict the probability of occurrence of collapse and collapse-related soil parameters for different critical values with a known degree of certainty is invaluable to planners, developers, and geotechnical engineers.     

Settlement analysis of the Shuibuya concrete-face rockfill dam

Settlement is one of the most important deformation characteristics of a high concrete-face rockfill dam (CFRD) and is regarded as a key indicator of dam safety. The time-dependent settlement behavior of the Shuibuya CFRD is studied on the basis of in situ settlement-monitoring records and displacement back-analysis. The goal of this work is to characterize actual deformation of the dam and to verify the back-analysis method used in this paper. The settlement-monitoring records were from seven control stations at the crest and 38 monitoring points inside the body of the dam and covered the construction period, the initial filling of the reservoir and 2 years of operation. A displacement back-analysis for parameters is performed by hybrid generic algorithms (HGAs) and finite element method (FEM). Comparative studies of monitoring data and back-analysis show good agreement between measured settlements and computed settlements. Furthermore, the deformation in the next 3 years is predicted on the basis of back-analysis. Overall, it is demonstrated that the deformation of the Shuibuya CFRD is basically stable and that the technique used to control the dam deformation is successful.     

改进的遗传算法在堆石体参数反演中的应用

在研究堆石坝问题中,堆石体参数的合理估计非常重要,根据工程实测值反演堆石体参数不失为一种有效估计参数的新思路。在传统遗传算法操作过程中,引入模拟退火的Metropolis接受准则,并结合系统识别的基本原理改进了遗传算法。将改进的新算法应用于堆石坝主要堆石料的参数反演,结果显示其误差很小、收敛速度快、精度高的优越性,克服了传统的梯度优化方法和单纯形法所具有的搜索速度随反演参数增多呈级数减慢、容易陷入局部极值点和误差传递导致不收敛等缺点,值得在本领域参数优化中推广。     

Influence of Different Stress Conditions on Behavior of Rockfill Materials

Rockfill material is the most readily available and the most flexible material for the construction of dams especially in the seismic prone regions. The material is obtained either by blasting available rock or is collected from the alluvial deposits of the river. During construction of the dam, the available rockfill material is compacted to required density layer by layer using various sophisticated compactors to achieve the required density and slope. Gradually the vertical load on the lower layers goes on increasing due to placement of subsequent layers of the materials to achieve the desired height. This may result in variation of grain size distribution of the lower layers due to the breakage of particles. This will certainly influence the shear parameters. Present studies have been carried out to find the influence of loading the rockfill materials under two different stress conditions i.e. multistage loading and single stage loading on the grain size distribution and its subsequent effect on its shear parameters. Consolidated drained triaxial shear tests have been conducted on the materials obtained by blasting available rock as well as on the materials collected from the alluvial deposits of the river which are generally used for construction of rockfill dams. Test data have been analyzed to study the breakage factor and corresponding shear parameters under both conditions.     

On the distinct element parameters used for earthquake ground motion simulation

To overcome the difficulties in the choice of parameters used for the distinct element method, some hints are presented with a main focus on earthquake ground motion simulation. As a natural period of vibration, especially the fundamental period is an important factor in any earthquake response, nature of the fundamental period of distinct element systems is closely investigated. Meanwhile, nature of the least period of vibration is also investigated because of its importance in the selection of time step of a direct integration scheme. Reduction in elastic wave velocity due to discontinuity is described on the basis of experimental measurement on aluminum blocks. In addition to analytical formulation on damping properties, accelerograms observed on a rockfill dam model are compared with simulated ones, giving a useful suggestion on the viscous damping.     

循环荷载作用下考虑颗粒破碎的堆石体本构模型

中国西部兴建的很多200～300 m高的堆石坝处于高烈度地震区。应力水平高时堆石体的颗粒破碎对其在循环荷载作用下的应力、应变特性有重要的影响。基于广义塑性理论,通过引入状态参数,建立了循环荷载作用下考虑颗粒破碎的堆石体的本构模型,并给出了模型参数的确定方法。与堆石体在400、800、1 500、2 200 kPa围压作用时的试验结果对比,表明所提出的本构模型可以较好地模拟循环荷载作用下颗粒破碎时堆石体的动应力和动应变响应。     

堆石料Gudehus-Bauer亚塑性本构模型改进及参数确定方法

研究了Gudehus-Bauer亚塑性本构模型和模型参数的求取方法。采用侧限压缩试验曲线求取模型参数颗粒硬度hs和指数n。根据模型方程的推导,建立了拟合指数 和 与围压之间的关系,并提出了新的拟合参数。考虑到堆石料具有明显的剪胀、剪缩性,在Gudehus-Bauer模型线性项中增加了主要控制体积应变项 ,以改善模型对堆石料体积应变曲线的描述。采用堆石料大型侧限压缩试验、常规三轴试验分别验证了新的拟合参数和改进后的Gudehus-Bauer亚塑性本构模型。与堆石料试验成果比较,提出的新拟合参数与改进后的Gudehus-Bauer亚塑性本构模型可以较好地模拟堆石料的应力-应变特性,并较好地改善了堆石料体变曲线的模拟结果。对改进后的模型作了常规三轴加、卸载模拟,模拟结果反映了改进的Gudehus-Bauer亚塑性本构模型具有一定的卸载适应性。     

Stress deformation properties of macroporous loess soils

Milovic, D., 1988. Stress deformation properties of macroporous loess soils. Eng. Geol., 25: 283–302.

Herein are presented the results of laboratory and field tests which were carried out on loess in Yugoslavia.

Experience gained during recent decades show that the loess soil in some cases undergoes structural collapse and subsidence due to inundation. In order to find the explanation of such behaviour, numerous laboratory and field load tests on loess soil have been performed. Using the obtained results, several correlations have been established.

On the basis of the unconfined test results, a correlation between the initial dry density, initial water content and unconfined compression strength has been established.

A relatively large number of the consolidation subsidence tests (about 550), carried out on undisturbed loess samples, made possible the determination of the degree of subsidence and the corresponding values of the dimensionless coefficients of subsidence. These coefficients have been determined for several values of the initial dry density, for various degrees of saturation and for several stress levels upon wetting. Using these coefficients, the values of the additional settlement caused by flooding of loess under the foundation can easily be calculated. It is of particular interest to note that, in general, water penetrates under one part of the building, producing differential settlements, which are in most cases very dangerous.

By the comparative laboratory investigation of the undisturbed loess samples obtained by thin walled sampler and samples obtained from pits, it has been shown that the mechanical disturbance is an extremely important factor which governs the shear and deformation parameters of loess soils.

The laboratory test results obtained on undisturbed loess samples, cut from blocks in the vertical and horizontal direction, have shown that this soil exhibits anisotropic properties. For this reason a stress deformation problem in an anisotropic medium has been treated by the finite element method.

Static penetration tests and field load tests in loess soils with natural water content and also after saturation have been performed and are described.

The results of the observed settlements for two statically identical multi-storey buildings are also presented. Using the coefficients of subsidence for the undisturbed samples cut from blocks, very good agreement between the calculated and the observed settlements has been obtained.     

Tunnelling in difficult ground: a case study from Dranaz tunnel, Sinop, Turkey

This paper presents a case study of the instability mechanisms, and the excavation sequence, re-qualification and reinforcement methods adopted to pass through a short segment of a nearly 2-km tunnel built as part of a new 55-km state highway in northern Turkey. The instability problems were encountered during tunnel excavation due to the failure to recognize the fact that alteration in stress field and resulting deformation could cause dilation and increase in the permeability of claystone-shale layers and local fault gouge zones, and in turn significant reduction in shear strength. Change in natural drainage pattern and capillarity exacerbated saturation and the consequent strength reduction. The 92-m³ loose material flowed into the tunnel due to the collapse and caused 2.5 months of delay in completion of the tunnel. Longitudinal and oblique cracks observed in shotcrete were attributed to the reduction in modulus upon saturation, which caused a large cumulative deformation of approximately 110 mm at a section about 30 m behind the collapse face.

It is concluded that early detection or prediction of potentially problematic zones (via probe drilling and monitoring) in tunnelling is of paramount importance, especially through mixed or difficult ground conditions characterized by alternating layers, folding, faulting and localized zones of high water pressure. Because mechanical detection methods cannot be fully relied upon, availability of experienced personnel to predict and deal with such instability problems effectively and promptly is the best insurance for successful completion of tunnelling contracts.     

Liquefaction analysis and damage evaluation of embankment-type structures

The increasing importance of performance-based earthquake engineering analysis points out the necessity to assess quantitatively the risk of liquefaction of embankment-type structures. In this extreme scenario of soil liquefaction, devastating consequences are observed, e.g., excessive settlements, lateral spreading and slope instability. The present work discusses the global dynamic response and interaction of an earth structure-foundation system, so as to determine quantitatively the collapse mechanism due to foundation’s soil liquefaction. A levee-foundation system is simulated, and the influence of characteristics of input ground motion, as well as of the position of liquefied layer on the liquefaction-induced failure, is evaluated. For the current levee model, its induced damage level (i.e., induced crest settlements) is strongly related to both liquefaction apparition and dissipation of excess pore water pressure on the foundation. The respective role of input ground motion characteristics is a key component for soil liquefaction apparition, as long duration of mainshock can lead to important nonlinearity and extended soil liquefaction. A circular collapse surface is generated inside the liquefied region and extends toward the crest in both sides of the levee. Even so, when the liquefied layer is situated in depth, no significant effect on the levee response is found. This research work provides a reference case study for seismic assessment of embankment-type structures subjected to earthquake and proposes a high-performance computational framework accessible to engineers.     

基于组合指数型流变模型的堆石坝流变分析

由于3参数、6参数、7参数指数流变模型以及Merchant模型和H-K模型均仅有一个指数式进行堆石坝流变收敛率调节,难以同时合理地反映蓄水初期和蓄水后期的堆石坝沉降变化规律;而9参数幂函数流变模型虽然可以较好地反映堆石坝的沉降变化规律,但数学运算较复杂。类比混凝土热学力学性能变化规律的组合指数式,从唯象角度建议了一种既能较好地反映堆石坝流变变形规律,又便于数学运算的组合指数型流变模型,并推导了组合指数型流变模型有限元计算公式。实例分析表明,组合指数式只需取2项,由于具有2个指数式协调调整,可较好地反映堆石坝流变变形规律且数学运算方便;而一个指数式流变模型是组合指数式流变模型的特例,难以合理反映蓄水后期堆石坝的沉降变化规律。     

堆石料单粒强度尺寸效应的颗粒流模拟方法研究

围绕堆石料单粒强度尺寸效应的颗粒流模拟方法展开研究。首先,基于FISH二次开发建立了堆石料的随机不规则单粒模型,充分考虑堆石料的形状特征和破碎现象;然后,建立了堆石料单粒强度尺寸效应的等效模拟方法,以单粒强度随其粒径的变化规律为基础,推导了堆石料模型中细观黏结强度与堆石料等效粒径的负指数经验公式;其次,基于建立的数值模型对堆石料的室内单粒压缩试验进行仿真模拟,验证数值模型的正确性和合理性,并对较大粒径堆石料的单粒强度进行模拟预测,突出数值试验的优势;最后,基于建立的数值模型对相同粒径不同形状特征堆石料的单粒强度分布特征进行模拟研究。研究结果表明：（1）堆石料内部缺陷含量和尺寸随粒径增加对其单粒强度所产生的尺寸效应,可通过堆石料模型中细观强度参数随粒径折减进行等效模拟;（2）形状特征对堆石料的破裂机制具有重要影响,方形颗粒为压剪破裂,单粒强度较高,而随机不规则颗粒和圆形颗粒为拉剪或劈裂,单粒强度相对较低;（3）拉剪或劈裂条件下,堆石料形状越不规则,其单粒强度的离散程度越高,反之则离散程度越低。相关研究成果可为进一步研究荷载作用下堆石体内各粒径段堆石料的破碎量奠定基础,从而更加真实地反映堆石体的级配演化规律。