面板堆石坝砂砾石料填筑碾压试验研究

利用天然砂砾石进行大坝填筑,其碾压参数直接影响到大坝施工进度和沉降变形,也直接影响到大坝施工成本和安全稳定,碾压参数的优化一直是大坝填筑施工技术研究重点。为有效地指导现场施工,以某一工程为案例,通过面板堆石坝砂砾石料填筑碾压试验研究,分析数据成果,提出大坝填筑碾压参数。     

论无粘性砂卵石与堆石的力学性质

无粘性砂卵石与堆石,广泛用于土石坝与面板堆石坝的建设。本文根据我院十余年来大量工程的大三轴试验结果,就抗剪强度、应力应变、剪胀性等性质问题进行了讨论,展现了这些材料性质的某些规律。砂卵石的抗剪强度与堆石相近甚至更好,剪胀性对强度与泊松比有明显影响。本文还讨论了邓肯模型的试验结果,归纳了该模型参数的一些变化性质。     

堆石坝垫层材料的冻胀性能

为研究寒冷地区堆石坝垫层材料的冻胀性能,对不同粉粘粒含量(质量分数)、不同含水率(质量分数)的堆石坝垫层材料进行了不同冻结温度、不同冻结速率的冻胀试验.结果表明:冻结温度越低,垫层材料的冻胀量越小,在冻结温度为-3~-7℃时,冻胀量变化最为显著;垫层材料冻胀量随粉粘粒含量和含水率的增大而增大,随冻结速率的增大而减小,且减小趋势近似线性;在相同粉粘粒含量下,高含水率试样冻胀发展迅速,且发展过程较长.含水率9.0%粉粘粒含量12%或含水率7.5%和9.0%粉粘粒含量15%的垫层材料冻胀级别均为弱冻胀,因此建议工程中选用粉粘粒含量小于12%且含水量小于9.0%的材料作为堆石坝垫层材料.     

堆石料最大指标密度室内试验方法的研究

基于振动合法及表面振动器法的试验条件参数对测定堆石料最大指标密度影响的室内系统试验研究,以及对比相应现场碾压试验资料后,本文提供了这两种试验法试验条件参数的建议值;试验还证实了原型堆石料室内系列相似级配模型料的最大指标密度与最大粒径之间存在半对数线性关系,据此外插得到原型堆石料的最大指标密度。此外,本文推荐采用压实度指标确定堆石料的填筑标准。     

岩石峰后剪胀效应研究综述

岩石破裂后会发生体积膨胀且仍具有一定的承载能力,煤矿中多利用岩石的该性质进行支护.作者从研究岩石峰后特性的重要工程意义着手,叙述了岩石峰后剪胀的概念、发展历史和研究现状,以及目前研究中存在的问题,强调了研究岩石峰后剪胀效应的重要性.     

营造健康：自然和设计的作用

【目的】本研究将人类健康与环境健康视为一个共同体。提出可持续发展的方法,该方法关注个体维度对促进健康的看法,为他们创造条件来应对生活挑战、改善生活质量、增加福祉和与自然的联系。【方法】通过案例研究,讨论了健康本源设计理念,该理念有助于为社区提供健康促进的资源,以及解决更广泛的健康不平等问题。【结果】健康本源理念可以为设计决策提供指导,在大尺度可持续发展方案框架下提升个人体验及健康促进的发展前景。【结论】将健康本源学、自然系统、环境和社会基础设施技术结合的整体性设计方法有助于建立一个健康、活力、有韧性和公平的未来。     

Viscous Behaviour of Unbound Granular Materials in Direct Shear

The viscous properties of a variety of poorly graded unbound granular materials were investigated by direct shear tests on 12 cm-cubic specimens. A number of natural sands having different particle shapes and sizes as well as uniform glass beads having different particle sizes were used. The viscous properties were evaluated by changing the shear displacement rate many times during otherwise monotonic loading (ML) at constant shear displacement rate and normal pressure. Creep loadings were performed in two tests. Different types of viscous properties, which are affected by the particle shape but essentially independent of the particle size, are reported. The viscosity type varies as the shear displacement increases from the pre-peak regime towards the residual state. A new viscosity type, called “Positive & Negative”, was found with relatively round granular materials in the pre-peak regime and with relatively angular granular materials in the post-peak softening regime and at the residual state. Peculiar “rate-independent unstable behaviour” is observed with round natural sands and glass beads in the post-peak regime, which is more significant and frequent with glass beads. Controlled by the particle size, this behaviour is caused by the so-called stick/slip phenomenon. The viscous properties observed in the DS tests are quantified by the rate-sensitivity coefficient defined in terms of the shear and normal stresses, which are then converted to those defined in terms of the major and minor principal stresses, β₁₃. These β₁₃ values are consistent with those directly obtained by the triaxial and plane strain compression tests. The effects of particle size on the β₁₃ value are negligible and the β₁₃ value tends to decrease as the particle shape becomes more round.     

复杂应力路径下邓肯-张EB模型适用性研究

目前国内研究堆石体应力-应变关系特性主要是在常规三轴试验的基础上,对复杂应力路径上堆石体本构模型的验证工作尚不充分。但坝体在填筑期和蓄水期有着明显的应力路径相关性。利用堆石料常规和复杂应力路径大型三轴试验成果,对国内常用的堆石体本构模型——邓肯-张EB模型进行了验证。结果表明,邓肯-张EB模型对常规三轴试验适应性比较好;对复杂应力路径常会夸大堆石体的体积压缩变形,其加卸载准则无法正确判别一些复杂应力路径的加卸载状况。     

Behaviour of Granular Materials in Relation to Their Fabric Dependencies

The roles of dilatancy and fabric on the behaviour of granular materials are both numerically and experimentally explored for the study of material instability and failure. This investigation has two basic ingredients: namely a stress dilatancy model with microstructural information embedded through a fabric tensor, and an experimental rendition of force transmission and structure in an assembly of 2-D photoelastic disks. In order to highlight material instability, model simulations of sand behaviour are carried out in axi-symmetric stress conditions along proportional strain paths with varying degrees of controlled dilation (or compaction) including isochoric deformations as a special case. It is shown that sand, otherwise stable under isochoric (undrained) conditions, can actually succumb to an instability or a liquefaction behaviour under other loading paths. This suggests that flow type of failures in soils may not be necessarily restricted to the classic saturated loose sand case in undrained conditions, but could manifest itself under other conditions as well.     

乳胶粒径对聚合物改性水泥基材料性能的影响

合成了3种数均乳胶粒径分别为138,202,251nm的聚合物乳液,考查了乳胶粒径对聚合物在水泥表面吸附量、水泥净浆凝结时间、新拌砂浆流动度和含气量、硬化砂浆力学性能的影响.结果发现:在相同聚灰比(mP/mC)条件下,随乳胶粒径减小,聚合物在水泥表面的吸附量降低,水泥净浆的凝结时间变长,新拌砂浆流动度增大,硬化砂浆抗折强度提高,抗压强度下降;新拌砂浆含气量在mP/mC5%时随乳胶粒径减小而增大,在mP/mC≥5%时随乳胶粒径减小而减小;在饱和吸附量下单位质量水泥表面所吸附的3种聚合物覆盖面积与其粒径无关,分别为1 918,2 111,1 963cm2/g,比水泥的勃氏比表面积(3 530cm2/g)小.     

循环建造的诗意 建造一个与自然相似的世界

无论中国还是西方,它们的建筑传统都曾经是生态的。而当今,超越意识形态,东西方之间最具普遍性的问题就是生态问题,建筑学需要重新向传统学习,这在今天的中国更多意味着向乡村学习。不仅学习建筑的观念与建造,更要学习和提倡一种与自然彼此交融的生活方式,这种生活的价值在中国被贬抑了一个世纪之久。我们相信,一种超越城市与乡村区别,打通建筑与景观,打破专业与非专业界限,强调建造与自然的关系的新建筑活动必将给建筑学带来一种触及其根源的变化。建筑学正在经历从传统景观意识到现代景观观念的变迁,我们特别需要一种对建筑的深远思考,而正是这种思考将会振兴新的观念和方法。     

Modelling and Simulation of Rate-Dependent Stress-Strain Behaviour of Granular Materials in Shear

A constitutive modelling of the elasto-viscoplastic stress-strain behaviour of geomaterials in shear that has been developed within a non-linear three-component model framework is validated by simulating a comprehensive series of drained triaxial compression (TC) and direct shear (DS) tests on a wide variety of granular materials. Illustrative simulations of rate-dependent stress-strain behaviour of geomaterial under typical laboratory test conditions were performed to analyse the structure of the model. The versatility of the proposed model and its applicability to a wide variety of shear loading histories is examined and demonstrated by these simulations. The following results are shown. Commonly with different basic viscosity types, Isotach, TESRA and P&N, the viscous stress component has a positive component that increases with an increase in the irreversible strain rate, which makes feasible stable and realistic simulations of rate-dependent stress-strain behaviour, including creep deformation, based on the proposed model. With different unbound granular material types having similar relative densities, the creep strain in TC tests and creep shear displacement in DS tests that develop by sustained loading at a given shear stress level for a given period tends to decrease with an increase in the particle roundness. This trend of behaviours is explained by a decrease in the viscosity type parameter, θ, associated with an increase in the particle roundness based on the simulations of these tests.     

Experimental Characterisation of the Fire Behaviour of Thermal Insulation Materials for a Performance-Based Design Methodology

A novel performance-based methodology for the quantitative fire safe design of building assemblies including insulation materials has recently been proposed. This approach is based on the definition of suitable thermal barriers in order to control the fire hazards imposed by the insulation. Under this framework, the concept of “critical temperature” has been used to define an initiating failure criterion for the insulation, so as to ensure there will be no significant contribution to the fire nor generation of hazardous gas effluents. This paper proposes a methodology to evaluate this “critical temperature” using as examples some of the most common insulation materials used for buildings in the EU market, i.e. rigid polyisocyanurate foam, rigid phenolic foam, rigid expanded polystyrene foam and low density flexible stone wool. A characterisation of these materials, based on a series of ad-hoc Cone Calorimeter and thermo-gravimetric experiments, serves to establish the rationale behind the quantification of the critical temperature. The temperature of the main peak of pyrolysis, obtained from differential thermo-gravimetric analysis under a nitrogen atmosphere at low heating rates, is proposed as the “critical temperature” for materials that do not significantly shrink and melt, i.e. charring insulation materials. For materials with shrinking and melting behaviour it is suggested that the melting point could be used as “critical temperature”. Conservative values of “critical temperature” proposed are 300°C for polyisocyanurate, 425°C for phenolic foam and 240°C for expanded polystyrene. The concept of a “critical temperature” for the low density stone wool is examined in the same manner and found to be non-applicable due to the inability to promote a flammable mixture. Additionally, thermal inertia values required for the performance-based methodology are obtained for PIR and PF using a novel approach, providing thermal inertia values within the range 4.5 to 6.5 × 10³ W² s K^?2 m^?4.     

蒲石河电站面板堆石坝垫层料冻胀试验

研究级配、粉粘粒含量、含水率、上覆荷载对冻结过程中冻胀量、冻胀速率的影响,以保证冬季面板堆石坝工程的安全。以蒲石河地区的经验冻结速率为条件控制冻结,采用自上而下的冻结模式,冻结速率控制为20 mm/d。当级配石料粉粘粒含量小于12%时,基本为无冻胀或弱冻胀,冻胀量随粉粘粒含量增加呈线性增长;粉粘粒含量相同时不同级配改变了含水量与冻胀量之间的线性关系的梯度。反向压力与冻胀力相平衡,限制了冻胀时的体积膨胀,工程中宜采用7.5%含水率和12%的粉粘粒含量的级配石料,使用密度为59 g/cm3的混凝土面板可以抑制冻害的发生。     

堆石围堰变形特性试验研究

本文用结构模型试验方法,研究了堆石围堰在自重和水荷载作用下的变形特性,给出了自重、正常水荷载、漫坝水荷载(超载)和正常水荷载长期恒载作用情况下的水平位移和垂直位移分布规律。表明在各种正常荷载作用情况下,水平位移均小于垂直位移。水平位移与垂直位移的比值约为0.3。 文中还论述了堆石围堰结构模型试验中的模拟原则、相似常数、模型材料、量测技术等问题。     

翘曲对薄壁结构后屈曲性能的影响

薄壁结构力学性能分析的一维模型,用于分析一些框架结构的初始后屈曲性能。该模型以一种非常简单的方式考虑了翘曲的初始边界条件,而且被证明是分析薄壁框架结构的一种有效模型。基于多物理场耦合分析软件的有限元法,给出许多L型框架的数值分析结果。     

准脆材料动力强度的本质和侧向惯性约束作用

从材料内部结构层次的角度,就准脆材料动力强度的本质和侧向惯性效应的作用问题进行了研究。利用岩体的Maxwell型松弛模型,得到了试样的强度、应变率、试样尺度和松弛速度之间的关系。利用这一关系解释了实验得到的岩石试样的动力强度与应变率成正比、与试件的尺寸成正比的结果。利用这一关系和实验数据拟合,得到了断裂传播速度随试件尺寸的增大而减小的结论。利用这一关系,结合Bazant的静力强度尺寸律,确定了相应的区分动力尺寸效应与静力尺寸效应的特征应变率。进一步的研究表明,岩石试样的动力强度的本质是由于断裂传播速度的有限性,当加载速度足够大时,在试样完全宏观断裂之前所发生的超载。侧向惯性约束的作用可以归结为降低了断裂的传播速度,即降低了松弛速度,从而有更充足的时间保证超载的发生。     

土石围堰边坡安全性研究

结合山西天桥水电站除险加固工程中土石围堰的边坡,提出了采用安全系数和失效概率来综合评价其安全性.采用工程上常用的瑞典条分法建立极限状态方程,考虑土体内摩擦角、粘聚力为随机变量,利用蒙特卡罗法来求解边坡的可靠度指标,并对边坡稳定性分析中最重要的评价指标安全系数与可靠指标的关系进行了探讨.结果表明,采用安全系数和可靠概率综合评价土石围堰边坡的稳定性能更好地了解工程的实际安全状况.该方法为土石围堰边坡的安全性评价提供了一种参考.     

碳达峰、碳中和 大国雄心,建材行业须担当

2020年9月,国家主席习近平在第七十五届联合国大会一般性辩论上提出,中国将采取更加有力的政策和措施,二氧化碳排放力争于2030年前达到峰值,努力争取2060年前实现碳中和。继在联合国大会提出应对气候变化的目标和长期愿景后,习近平在三个月后的气候雄心峰会上又宣布了中国国家自主贡献一系列新举措:到2030年。