改进的非线性徐变模型及其在混凝土坝施工期温度应力仿真分析中的应用

在目前的混凝土坝温度应力仿真计算分析中,一般采用弹性徐变模型考虑施工期混凝土徐变对温度应力的影响。当坝体内的温度应力比较小时,采用弹性徐变模型计算温度应力是可行的,但当坝体的温度应力超过相应龄期的抗拉强度一半时,混凝土的徐变变形不再与坝体的应力呈线性关系,而是呈现出剧烈的非线性变化趋势。温度应力与抗拉强度越接近,相应的非线性徐变变形越大。根据已有的混凝土徐变试验成果,提出了一个用于混凝土坝施工期温度应力仿真计算的混凝土非线性徐变模型,给出了相应的计算方法。算例表明,采用传统的弹性徐变模型与提出的非线性徐变模型计算的温度应力存在一定的差别,采用传统弹性徐变模型计算的温度应力偏大。     

蠕变条件下吹填软土结构强度形成研究

土体的结构性对土的工程力学性质具有决定性的影响。本文以天津滨海吹填软土为土质材料,进行了蠕变作用下土体结构屈服应力形成试验及相应的微观结构分析。试验结果表明:蠕变对土体结构性的影响是一个综合作用的过程,其中排水条件最为关键,在此基础上,围压及偏压都对土体结构屈服应力的增长起作用,并随时间的增长而增长。反之,土体的结构屈服应力变化不大。微观结构分析表明,小偏应力蠕变作用下结构屈服应力的形成实质是其微观结构逐渐稳定的过程。     

Functioning and precipitation-displacement modelling of rainfall-induced deep-seated landslides subject to creep deformation

We propose an approach to study the hydro-mechanical behaviour and evolution of rainfall-induced deep-seated landslides subjected to creep deformation by combining signal processing and modelling. The method is applied to the Séchilienne landslide in the French Alps, where precipitation and displacement have been monitored for 20 years. Wavelet analysis is first applied on precipitation and recharge as inputs and then on displacement time-series decomposed into trend and detrended signals as outputs. Results show that the detrended displacement is better linked to the recharge signal than to the total precipitation signal. The infra-annual detrended displacement is generated by high precipitation events, whereas annual and multi-annual variations are rather linked to recharge variations and thus to groundwater processes. This leads to conceptualise the system into a two-layer aquifer constituted of a perched aquifer (reactive aquifer responsible of high-frequency displacements) and a deep aquifer (inertial aquifer responsible of low-frequency displacements). In a second step, a new lumped model (GLIDE) coupling groundwater and a creep deformation model is applied to simulate displacement on three extensometer stations. The application of the GLIDE model gives good performance, validating most of the preliminary functioning hypotheses. Our results show that groundwater fluctuations can explain the displacement periodic variations as well as the long-term creep exponential trend. In the case of deep-seated landslides, this displacement trend is interpreted as the consequence of the weakening of the rock mechanical properties due to repeated actions of the groundwater pressure.     

地下采场动态施工损伤演化的数值试验

采用莫尔－库仑准则作为岩体的剪切屈服条件、极限应变作为剪切损伤判据、最大拉应力作为拉伸损伤判据,建立了适合岩体的弹塑性各向异性损伤数值模型。运用该数值模型研究了施工过程不施作支护结构和施作支护结构情况下地下采场覆岩的动态损伤演化过程,并与不施作支护结构时岩体采用弹性模型的数值结果进行了对比。数值试验重现了施工过程地下采场覆岩的动态损伤演化过程,从而为进一步优化支护结构设计、施工以及预防和控制地下采场塌方等工程事故提供了一种新的数值试验手段。     

A practical guide to the study of glacial sediments

Evans, D. J. A. & Benn, D. I. (eds.) 2004: A Practical Guide to the Study of Glacial Sediments . Edward Arnold, London, 266 pp. ISBN 0–340–75959–3 (pb). GBP 19.99.     

经济体制改革时期地质工作如何面向经济建设

从“资源驱动”向“需求驱动”转变,是被当今国际社会普遍认可的推动地质工作向可持续发展方向演进的主导思想。无论从经济学、社会学、政治学、历史学还是从哲学、自然科学的角度看,地球科学的发展历来都是与社会经济的进步相适应的。20世纪80年代,中国尚处于改革开放的初期,然而李春昱先生以其超凡的洞察力和对国家民族兴亡无限关切的社会责任感,敏锐地意识到这一问题的现实存在和它所蕴含着的深远历史意义,果敢提出：地质工作要面向经济建设,积极从事于有关地质方面的建设工作。既考虑到当前的经济建设,也要不断地加强基础研究,提高理论水平,以适应将来经济建设的需要。虽然此论断算不上一个纯粹的科学命题,或许在当时看来更像是一番“预言”．但它却对探究地质科学事业的发展前景乃至深刻认识地质科学的社会意义无疑有着难以估量的潜在价值。今天,当我们再一次重温李春昱先生这篇旧文时,依就可以感悟到它的存在理由、它的生命力之体现和它的远见卓识。斯人已去,思想长存。让我们在历史的回味与未来的憧憬中,永远怀念这位深受世人尊敬的地学前辈吧!     

Stability of a circular tunnel in cohesive-frictional soil subjected to surcharge loading

The stability of circular tunnels in cohesive-frictional soils subjected to surcharge loading has been investigated theoretically and numerically assuming plane strain conditions. Despite the importance of this problem, previous research on the subject is very limited. At present, no generally accepted design or analysis method is available to evaluate the stability of tunnels/openings in cohesive-frictional soils. In this study, continuous loading is applied to the ground surface, and both smooth and rough interface conditions are modelled. For a series of tunnel diameter-to-depth ratios and material properties, rigorous lower- and upper-bound solutions for the ultimate surcharge loading are obtained by applying finite element limit analysis techniques. For practical use, the results are presented in the form of dimensionless stability charts with the actual tunnel stability numbers being closely bracketed from above and below. As an additional check on the solutions, upper-bound rigid-block mechanisms have been developed and the predicted collapse loads from these are compared with those from finite element limit analysis. Finally, an expression that approximates the ultimate surcharge load has been devised which is convenient for use by practising engineers.     

考虑堆石体流变效应的高面板坝最优施工程序研究

考虑高面板坝堆石体的流变变形效应对堆石体的最优施工碾压进度方案进行了研究。结果表明,堆石体的本身流变变形特性对不同施工碾压进度方案下的面板垫层变形影响较大。堆石坝不同材料分区的特点从客观上决定了高堆石坝必然存在一个较优的施工填筑上升方案。堆石体均匀上升的填筑进度方案的面板垫层法向最大位移较小,且沿面板坡向的分布比较均匀,对面板与垫层间的协调变形有利。从最优填筑方案的角度来看,建议高堆石坝采用均匀上升的碾压施工程序。     

泥岩蠕变行为的实验研究及其描述

利用自行研制的岩石三轴蠕变仪,对泥岩进行了系统的三轴蠕变试验。试验中考虑了轴压σ1和围压σ3对蠕变的影响。结果表明,当围压σ3一定时,轴向应力σ1增加,蠕变加快,在稳态蠕变阶段的应变率增大,试件的寿命缩短。而当应力差?σ=σ1–σ3保持不变时,围压σ3增加,蠕变减慢,稳态蠕变阶段的应变率也减小,试件的寿命增加。利用非经典粘塑性损伤本构模型对试验现象进行了分析,得到了较为满意的结果。     

浅谈建设项目设计阶段的价值管理

社会经济的发展,给人们带来很多新的理念,一些传统的思维和工作方法受到了挑战和冲击.建设工程项目的价值不能简单的认为仅是功能与成本的关系,它表示的应该是一种信仰、哲学、意识形态、理解、目的或建设工程项目所应有的某些深层理念,而且对设计工作产生影响.建设工程项目设计阶段的价值管理,是建立在对项目利益相关者的需求分析基础之上的,在设计过程中充分考虑项目的各方价值,考虑建设项目全寿命周期成本,给项目利益相关者提供一个双方和多方沟通的平台,从而真正实现项目的价值.     

A practical method to estimate crack openings in concrete structures

Numerical modelling of concrete cracking requires robust models able to describe opening and propagation of cracks. Structural concrete codes provide practical relations to describe crack openings. However, these empirical methods were developed for specific structures and cannot be used for general applications. Here, a continuous modelling approach based on damage mechanics is used to compute crack openings in a tie‐beam concrete structure. We propose a post‐processing method to extract crack openings from a continuum damage finite element computation. This method can be applied to all continuum damage/plasticity models. The tie‐beam concrete is characterized by a weak stress gradient; this aspect complicates predictions of crack positions and number. A stochastic method is used to take into account the spatial variability in concrete properties and create a spatially correlated random property field. Copyright © 2010 John Wiley & Sons, Ltd.     

A displacement discontinuity approach to modelling the creep behaviour of rock and its discontinuities

Using the correspondence principle of viscoelasticity the Displacement Discontinuity Method has been extended to model the rate-dependent behaviour of a jointed rock mass. The intact rock is assumed to behave as a linear viscoelastic material while, in general, a non-linear rate-dependent behaviour of the rock joints can be accounted for. A number of numerical examples are presented which illustrate the accuracy and potential of the method for analysing complex engineering problems.     

隧道水平冻结施工期地表融沉的历时预测模型

隧道冻结工程中所形成的人工冻结壁为临时支护结构,隧道衬砌结构施工后,冻结壁要进入解冻期,由于冻结壁解冻过程中的地层融沉现象对隧道周边环境影响较大,因此,应建立合理的方法对地表融沉量进行预测,以便于实际施工中采取相应的融沉控制措施。为此,考虑冻结壁的自然解冻过程,基于随机介质理论,建立了隧道水平冻结施工期地表融沉的历时预测模型。并提出冻结壁自然解冻条件下瞬态温度场由平板解冻理论近似求解,基于平板解冻理论和一维情况下已融土层的稳定融沉量计算公式,确定了预测模型中解冻锋面半径和融缩区域内半径这2个关键参数的取值方法。将所建立的预测模型应用于隧道全断面水平冻结工程中,得到了地表融沉随解冻时间的变化规律。研究结果表明,地表融沉在解冻初期增长速度较快,而在解冻后期增长速度减缓,地表历时融沉量与崔托维奇通过试验得出的天然冻土历时融沉量变化规律相一致。     

南昆铁路施工阶段遥感工程地质调查的应用

以往铁路遥感技术是用于勘测阶段，文章扼要地叙述了遥感技术在南昆铁路施工地质调查中应用的概况及效果。这是遥感技术首次用于施工的一次尝试。文中首先对沿线地形、地质概况进行介绍，然后结合施工部门的要求，开展全线陆地卫星TM图像的断裂构造判释，利用全黑白像片开展主要隧道、部分地段岩溶、八渡桥位地区等的判释，利用不同时期航片对段家河流域的泥石流沟进行动态分析。文中还列出该线部分地段地质遥感图像判释意见与施工验证结果对比一览表。从该表得知遥感判释成果绝大部分是有效的。在结论中归纳出几点认识，并提出施工阶段在特定条件下有针对性地应用遥感技术是有益的。同时指出，施工阶段应用遥感技术是有条件的，并非任何情况下均可应用遥感技术。     

Undrained stability of a single circular tunnel in spatially variable soil subjected to surcharge loading

The stability of tunnels is an important problem in geotechnical engineering. Most of the previous studies dealing with the stability of unlined tunnels are deterministic in nature and do not consider the soil spatial variability. This study investigates the influence of spatial variability on the undrained stability of an unlined circular tunnel, using Random Adaptive Finite Element Limit Analysis (RAFELA). The effect of spatial variability is investigated for tunnels having two different ratios of γD/c_u, for different spatial correlation lengths and tunnel depths. The results indicate that the effect of spatial variability depends on γD/c_u and the depth of the tunnel.     

Geotechnical evaluation of residual gravels in pavement construction

The paper discusses the laboratory and pavement constructional evaluation of residual lateritic gravels over phyllite.

Laboratory classification, compaction and bearing test results indicate that the natural materials are unsuitable by standard gravel acceptance specifications for road base construction. However, the bearing properties can be improved to meet base-material specifications through treatment with about 5% cement. Results of construction control studies also revealed that the laboratory compaction properties of both the raw and cement-stabilised gravels are easily reproduced in the field using fairly light, smooth-wheel rollers. This means that the complaints by contractors of difficulty in achieving design specifications using similar plants during construction is not justified.

Notwithstanding the results of the studies reported herein, it is not possible at the moment to suggest any construction control specifications for these gravels until more data on their in-service performance in the roadway has been collected and analysed over a number of years.     

江苏矿产资源潜力评价重力专题属性库结构

介绍了基于MapGIS平台的重力测量工作程度图、布格重力异常图、剩余重力异常图和重力推断地质构造图属性库结构及字段要求,属性库规范、有序,已在江苏矿产资源潜力评价中得到应用。     

A rheological model to simulate the shear creep behavior of rockfills considering the influence of stress states

Rockfills have been extensively used in the construction of high-fill embankments and dams, which exhibit complex time-dependent behavior. This paper presents a rheological model to simulate the shear creep behavior of rockfills based on the classic Burgers model, in which a nonlinear elasto-damage unit, a modified Newton unit, and a modified Kelvin unit are connected in series. By analyzing the results of large-scale triaxial creep tests on different rockfills, the influence of stress states (i.e., the deviator stress level and confining pressure) on the shear creep behavior of rockfills is revealed. A method to modify the key model parameters is proposed to consider such influence and is incorporated into the proposed model. Furthermore, the accelerated creep behavior of rockfills is reproduced by a nonlinear elasto-damage unit. Despite its simplicity, the model can simulate the essential aspects of the shear creep behavior of rockfills, and reasonable consistency is found between the simulation results and the large-scale triaxial creep test results.     

考虑时效的高填石路堤工后沉降有限元及反馈分析研究

把填石体作为粘弹性介质,提出采用三参数本构模型来描述填石体的蠕变特性,在此基础上引入遗传算法与有限元分析,建立了填石体三参数本构模型参数确定的优化反演方法,结合某高填石路堤得实测工后沉降数据进行参数反演,并利用反演参数对类似断面进行工后沉降分析,结果表明,本文建立的填石路堤工后沉降计算方法能准确的预测工后沉降,参数便于求取,为寻求合理的路面铺筑时间和制定施工控制条件提供依据。     

吹填软土经验流变模型研究

传统的本构模型多是在重塑土或饱和砂土的基础上建立起来,考虑结构性影响较少。自然界中土体大多具有结构性,这样就使得按传统方法计算的结果与工程实际有一定的差别。基于此,本文以Mesri模型为基础,将结构损伤变量引入模型中,建立了考虑结构性影响的流变模型。通过对天津滨海新区吹填场地经过真空预压处理的结构性吹填软土进行三轴流变试验,分析比较计算结果表明,本文建立的模型能够较好地反映结构性软土的应力应变随时间的变化关系。