Linear thermal expansion of granitic rocks: influence of apparent porosity,grain size and quartz content

Values for the linear thermal expansion coefficients () of some Brazilian granitic rocks commercially used as facings for building are presented. The coefficients were determined within a temperature range of 0 to 50 °C, with the temperature raised at a rate of 0.3 °C/min. The values obtained were related to the apparent porosity, grain size and quartz content of the rocks. It is concluded that while increases with an increase in quartz content, it decreases with increases in apparent porosity and mineral grain size.     

建筑石膏组成及颗粒度对其性能的影响

随着石膏制品的逐步发展,建筑石膏作为石膏制品的基础原料,对其性能要求也越来越高,企业及科研单位对影响其性能的研究也越来越多,本文仅从建筑石膏的相组成、比表面积、杂质等对其性能的影响作简单论述,作为对建筑石膏进行改性和生产控制的参考。     

Generalized crack initiation and crack damage stress thresholds of brittle rock masses near underground excavations

The rock mass failure process is characterized by several distinct deformation stages which include crack initiation, crack propagation and coalescence. It is important to know the stress levels associated with these deformation stages for engineering design and practice.Extensive theoretical, experimental and numerical studies on the failure process of intact rocks exist. It is generally understood that crack initiation starts at 0.3 to 0.5 times the peak uniaxial compressive stress. In confined conditions, the constant-deviatoric stress criterion was found to describe the crack initiation stress level.Here, generalized crack initiation and crack damage thresholds of rock masses are proposed. The crack initiation threshold is defined by σ₁−σ₃=A σ_cm and the crack damage threshold is defined by σ₁−σ₃=B σ_cm for jointed rock masses, where A and B are material constants and σ_cm is the uniaxial compressive strength of the rock masses. For a massive rock mass without joints, σ_cm is equal to σ_cd, the long-term uniaxial strength of intact rock. After examining data from intact rocks and jointed rock masses, it was found that for massive to moderately jointed rock masses, the material constants A and B are in the range of 0.4 to 0.5, 0.8 to 0.9, respectively, and for moderately to highly jointed rock masses, A and B are in the range of 0.5 to 0.6, 0.9 to 1.0, respectively. The generalized crack initiation and crack damage thresholds, when combined with simple linear elastic stress analysis, assist in assessing the rock mass integrity in low confinement conditions, greatly reducing the effort needed to obtain the required material constants for engineering design of underground excavations.     

岩石材料裂纹尖端起裂特性研究

 通过综合考虑Williams展开式中奇异应力项和非奇异应力项(T应力),运用断裂力学方法深入探讨远场拉–压、压–压应力组合下裂纹尖端起裂特性。在最大周向应力准则中考虑T应力的影响作用,并将其作为拉伸破裂判据;在剪切破裂方面,提出考虑法向应力影响的最大剪应力准则。通过对拉伸和剪切破裂发生条件的探讨,进一步阐明剪切破坏与裂纹倾角、内摩擦角、抗拉强度、黏聚力等参数之间的关系。研究结果表明,Williams展开式中非奇异应力项对于裂纹起裂角有重要的影响,所提出理论比传统理论计算的起裂角与实验结果更加吻合。随着内摩擦角的增大,剪切破裂减弱而拉伸破裂增强。随着黏聚力增大或者抗拉强度降低,拉伸破裂增强而剪切破裂减弱。     

基于全应力–应变曲线及起裂应力的岩石脆性特征评价方法

脆性作为岩石重要的力学指标,准确评价岩石脆性特征对岩体工程稳定性具有重要意义。目前,常用的岩石脆性指数评价方法主要基于岩石压缩过程中峰后应力–应变曲线变化规律,而对岩石峰前应力状态关注较少。综合考量峰后应力跌落速率及起裂应力值至峰值应力值之间的应力增长速率,建立一种基于岩体应力–应变全过程的脆性指数计算方法,更加准确、合理地描述岩体脆性特征。试验结果表明:单轴条件下当全程采用轴向位移控制时,脆性较强的岩石难以准确获得其峰后曲线,容易降低基于峰后应力曲的常规脆性评价方法的准确性,而所建立的脆性指标可根据峰前曲线进行判断,能够准确评价岩石脆性程度。在三轴条件下,该脆性指标更为全面地反映了围压对大理岩脆性的抑制作用。建立的脆性指标基于岩石整个压缩过程的应力状态,能够更加显著地体现不同因素对岩石脆性特征的影响。试验结果很好地验证了该指标的准确性与优越性,研究结果对丰富与完善岩体脆性评价体系具有重要的作用。     

粗集料粒径和级配对混凝土抗折强度的影响

利用正交设计的方法,研究了粗集料最大粒径和级配、水灰比、砂率对卵石混凝土路面抗折强度离散性的影响,结果表明,砂率对卵石混凝土路面抗折强度的离散性影响不显著,而水灰比、卵石最大粒径和级配对卵石混凝土路面抗折强度的离散性影响十分显著。     

公路隧道衬砌裂缝对结构受力分布影响规律研究

近些年我国高速公路隧道规模迅猛增长,与此同时也出现了较多的隧道病害和缺陷,其中二衬衬砌裂缝及渗漏水问题非常突出,大量运营隧道都出现了类似问题。本文结合依托工程,对隧道不同位置出现衬砌裂缝情况下的结构受力分布规律进行了分析与研究,探讨了裂缝对衬砌结构安全性的影响,得出结论如下：(1) 素混凝土隧道衬砌贯通型裂缝,隧道结构成为多铰环形结构,结构在断裂处轴向承载能力变化不大,但不能继续承受弯矩|(2) 通过计算分析发现,结构在某处断裂而不能继续承受弯矩时,其整个受力分布规律会发生改变,在其它局部会产生较大的弯矩,从而诱发新的开裂|(3) 裂缝的存在对隧道周边岩体的受力和变形存在着很大的影响,裂缝的存在改变了既有隧道力学分布规律。在隧道运营过程中,当发现存在裂缝时,必须加强监测并严控裂缝的发展。     

Theoretical and numerical studies of crack initiation and propagation in rock masses under freezing pressure and far-field stress

Water-bearing rocks exposed to freezing temperature can be subjected to freezeethaw cycles leading tocrack initiation and propagation, which are the main causes of frost damage to rocks. Based on theGriffith theory of brittle fracture mechanics, the crack initiation criterion, propagation direction, andcrack length under freezing pressure and far-field stress are analyzed. Furthermore, a calculation methodis proposed for the stress intensity factor （SIF） of the crack tip under non-uniformly distributed freezingpressure. The formulae for the crack/fracture propagation direction and length of the wing crack underfreezing pressure are obtained, and the mechanism for coalescence of adjacent cracks is investigated.In addition, the necessary conditions for different coalescence modes of cracks are studied. Using thetopology theory, a new algorithm for frost crack propagation is proposed, which has the capability todefine the crack growth path and identify and update the cracked elements. A model that incorporatesmultiple cracks is built by ANSYS and then imported into FLAC3D. The SIFs are then calculated using aFISH procedure, and the growth path of the freezing cracks after several calculation steps is demonstratedusing the new algorithm. The proposed method can be applied to rocks containing fillings such asdetritus and slurry.
2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.     

土体粒径对盐生植物根–土复合体抗剪强度影响的试验研究

 为研究盐生植物根系的固土护坡力学效应,探讨土体粒径对植物根系加筋固土作用和提高土体抗剪强度的影响。以青海柴达木盆地大柴旦盐湖区为研究区,选取海韭菜(Triglochin maritima Linn.)和无脉苔草(Carex enervis C.A.Mey.)2种优势盐生植物作为供试种,选取粒径大小分别为颗粒直径d≤0.25 mm和d≤0.5 mm粒径条件下的2种土体,制备根–土复合体扰动试样和不含根系素土扰动试样,分别进行了不固结不排水三轴压缩试验,以探讨2种盐生植物增强土体抗剪强度贡献,以及2种粒径条件下的根–土复合体抗剪强度指标变化规律;在此基础上,探讨土体粒径差异对根–土复合体抗剪强度的影响。试验结果表明：盐生植物根系加筋固土作用主要表现为在2种不同土体粒径条件下,海韭菜根–土复合体与无脉苔草根–土复合体抗剪强度强度均显著大于素土抗剪强度,且垂直布根海韭菜根–土复合体的抗剪强度显著大于水平或倾斜布根无脉苔草根–土复合体抗剪强度;土体粒径的差异可影响植物根系增强土体抗剪强度大小,即主要表现为在相同的含根量条件下,土体粒径愈小,由该粒径土体与根系共同组成的根–土复合体黏聚力值则愈大。同时,进一步研究表明,水平或倾斜布根的无脉苔草根–土复合体的抗剪强度受土体粒径大小的影响,相对大于垂直布根的海韭菜根–土复合体中的土体粒径大小对其抗剪强度影响。研究成果对于进一步探讨盐生植物根–土复合体抗剪强度的影响因素,以及利用盐生植物有效防治研究区水土流失、土壤侵蚀等地质灾害方面具有重要理论指导意义。     

预应力混凝土收缩及其对桥梁裂缝的影响分析

介绍了混凝土收缩类型,分析了混凝土收缩与裂缝之间的关系,从工程实例出发,利用有限元软件论证了这种关系,从混凝土收缩的角度解释了裂缝的产生原因,对工程中减少裂缝的出现有一定的实际作用.     

崇左市旅游资源开发研究

发展旅游业是一座城市吸引外商投资、拉动内需、促进经济增长的重要途径。为了发挥旅游业对崇左市经济发展的龙头辐射和带动作用,通过对崇左市旅游资源进行分析和评价可知,崇左市应以打造特色品牌、建设精品线路、整合旅游资源、加强区域合作、完善基础设施和实施营销策略等措施为开发重点,推动当地经济、社会全面发展。     

Numerical investigation of blasting-induced crack initiation and propagation in rocks

To investigate the dynamic fracture mechanism related to blast-induced borehole breakdown and crack propagation, circular rock models containing a single centrally located source of explosive were numerically blasted using the AUTODYN 2D code. According to the material properties and loading conditions, four kinds of equations of state, linear, shock, compaction and ideal gas, are used. A modified principal stress failure criterion is applied to determining material status. The dynamic stresses at the selected target points in a rock sample are computed as a function of time following application of explosive load. It is shown that shear stress (resulting from intense compressive stress) causes a crushed zone near the borehole, the major tensile principal stress causes radial cracks, and the reflected stress wave from free boundary causes circumferential cracks some distance away from the free boundary. The influences of the factors of boundary condition, coupling medium, borehole diameter, decoupling and joint on rock dynamic fracture are discussed.     

光老化对沥青混合料空隙率的影响

通过室内实验方法模拟沥青路面在外界自然条件下的光老化,然后对比不同级配的混合料在老化后的孔隙率的分布情况,得出了开级配和半开级配空隙率在不同光照条件下的变化情况,并分析其原因,对今后沥青路面施工具有一定指导意义。     

The assessment of porosity and pore size distribution of limestone Portland cement pastes

The cement production industry is one of the most energy and raw materials consuming one. Over the last years a great effort is performed in order to substitute clinker for less energy demanding materials. Nevertheless, construction industry needs durable materials with improved properties. Limestone is being used in blended cements widely. The most important parameter that affects all the properties of cement paste is its pore structure. In this study, four different limestone cements were produced and their pore structure was determined by means of mercury intrusion porosimetry (MIP) and nuclear magnetic resonance (NMR) cryoporometry. The conclusion of the study was that limestone addition affects the pore structure of the cement paste by increasing linearly the size of capillary pores from 20 nm to 40 nm when the maximum amount (35%) of limestone that is allowed by EN 197-1 is used. On the other hand the threshold diameter decreases exponentially and it is evident that limestone hardened cement pastes have many pores of the same size due to the filling effect that minerals additives have. Furthermore, limestone decreases the size of gel pores which is related to higher hydration rates. Hence, the use of limestone in cement produces a material that is structurally adequate to be used in construction.     

大体积混凝土温度应力及抗裂验算

通过实例对大体积混凝土在施工期的温度应力及裂缝控制进行了验算,从设计的角度说明其控制温度和有害裂缝控制的技术措施,以指导设计人员合理采取设计措施有效预防裂缝。     

The influence of occupational stress on construction professionals

The majority of the respondents were happy in their work but experienced considerable stress as a result of working practices, contractual arrangements and the demands of projects and their clients. Educationalists still retained their identity as 'construction lecturers' rather than as 'academic staff', and to some extent felt themselves to have the best of both worlds - the interest and variety of construction coupled with the satisfaction of acquiring and imparting knowledge and skills, as well as job security of 'academic tenure'.     

基于COD断裂准则的土体干缩裂隙萌生扩展力学机制

为探究土体干缩裂隙演化力学机制,基于单向干燥开裂试验规律概化了裂隙演化物理模型。在弹塑性断裂力学EPFM理论框架内,考虑裂隙顶端张开位移表征断裂临界参数,建立了裂隙扩展过程中的损伤本构关系,并对其物理过程进行了数值分析。研究表明：容器边界处产生的裂隙仅是边界效应,并非土体开裂自然现象,且边界约束会降低裂隙扩展速率;土体天然缺陷会导致干燥过程中出现收缩应力的集中,优先萌生裂隙;裂隙顶端阻力过大会降低裂隙扩展规模和发展速率,残余收缩阶段的土体干燥裂隙扩展规模有限;基于COD张开位移断裂准则的土体干缩裂隙演化物理模型能很好的反映裂隙扩展过程,单元试验内矩形试样的裂隙角度分布在30°～135°;数值试验中因天然缺陷随机发育较多形成的裂隙分岔较多,且最初萌生裂隙的区域总位移通常较大,为2.573×10-3～4.512×10-3m,分支衍生裂隙周边土体位移较小,仅为1.073×10-3～1.526×10-3m。工程实践中,若能采取合理的约束或保湿控裂措施可适当降低裂隙扩展速率和裂隙规模。     

基于岩石峰前起裂及峰后特征的脆性评价方法

现有研究表明岩石脆性与其内部微裂纹起裂、扩展有密切联系,但考虑岩石起裂特征的脆性评价指数并不多见,在对脆性理论以及起裂特征分析的基础上,提出了一种基于岩石峰前起裂及峰后特征的脆性评价方法.首先,结合George和Tarasov&Potvin等对脆性的描述和定义,从理论上分析了基于岩石峰前起裂及峰后特征脆性评价方法的可行...