Anisotropic time-dependent behaviors of shale under direct shearing and associated empirical creep models

Understanding the anisotropic creep behaviors of shale under direct shearing is a challenging issue.In this context,we conducted shear-creep and steady-creep tests on shale with five bedding orientations (i.e.0°,30°,45°,60°,and 90°),under multiple levels of direct shearing for the first time.The results show that the anisotropic creep of shale exhibits a significant stress-dependent behavior.Under a low shear stress,the creep compliance of shale increases linearly with the logarithm of time at all bedding orientations,and the increase depends on the bedding orientation and creep time.Under high shear stress conditions,the creep compliance of shale is minimal when the bedding orientation is 0°,and the steady-creep rate of shale increases significantly with increasing bedding orientations of 30°,45°,60°,and 90°.The stress-strain values corresponding to the inception of the accelerated creep stage show an increasing and then decreasing trend with the bedding orientation.A semilogarithmic model that could reflect the stress dependence of the steady-creep rate while considering the hardening and damage process is proposed.The model minimizes the deviation of the calculated steady-state creep rate from the observed value and reveals the behavior of the bedding orientation's influence on the steady-creep rate.The applicability of the five classical empirical creep models is quantitatively evaluated.It shows that the logarithmic model can well explain the experimental creep strain and creep rate,and it can accurately predict long-term shear creep deformation.Based on an improved logarithmic model,the variations in creep parameters with shear stress and bedding orientations are discussed.With abovementioned findings,a mathematical method for constructing an anisotropic shear creep model of shale is proposed,which can characterize the nonlinear dependence of the anisotropic shear creep behavior of shale on the bedding orientation.

A multifunctional shear apparatus for rocks subjected to true triaxial stress and high temperature in real-time

Deep engineering disasters,such as rockbursts and collapses,are more related to the shear slip of rock joints.A novel multifunctional device was developed to study the shear failure mechanism in rocks.Using this device,the complete shearedeformation process and long-term shear creep tests could be performed on rocks under constant normal stiffness(CNS)or constant normal loading(CNL)conditions in real-time at high temperature and true-triaxial stress.During the research and development process,five key technologies were successfully broken through:(1)the ability to perform true-triaxial compressioneshear loading tests on rock samples with high stiffness;(2)a shear box with ultra-low friction throughout the entire stress space of the rock sample during loading;(3)a control system capable of maintaining high stress for a long time and responding rapidly to the brittle fracture of a rock sample as well;(4)a refined ability to measure the volumetric deformation of rock samples subjected to true triaxial shearing;and(5)a heating system capable of maintaining uniform heating of the rock sample over a long time.By developing these technologies,loading under high true triaxial stress conditions was realized.The apparatus has a maximum normal stiffness of 1000 GPa/m and a maximum operating temperature of 300C.The differences in the surface temperature of the sample are constant to within5C.Five types of true triaxial shear tests were conducted on homogeneous sandstone to verify that the apparatus has good performance and reliability.The results show that temperature,lateral stress,normal stress and time influence the shear deformation,failure mode and strength of the sandstone.The novel apparatus can be reliably used to conduct true-triaxial shear tests on rocks subjected to high temperatures and stress.

Shear creep characteristics and constitutive model of limestone

The characters of limestone in weak interlayer of a high rocky slope in Xuzhou, China, are studied by shear static test and shear creep test. The results show that limestone specimens have attenuation creep properties and constant rate creep properties, almost have no accelerated creep properties. The exponential type empirical formula is selected to fit creep grading curves by polynomial regression analysis method, and the square sums of the fitting results residual are in the order of 10^(-7). Then grade creep curves at every shear loads are set up. Combining creep rate-time curve, the creep properties of limestone are analyzed. As the physical meaning of component model is clearer, the Poytin–Thomson model is set up. Through the least square method, the optimal parameters of Poytin–Thomson model are obtained,and the sums of squared residuals belong to 10^(-3)order of magnitude, which can meet the accuracy requirements of engineering calculation. So the Poytin–Thomson model can reflect the shear creep characteristics of limestone very well.

Shear creep parameters of simulative soil for deep-sea sediment

Based on mineral component and in-situ vane shear strength of deep-sea sediment, four kinds of simulative soils were prepared by mixing different bentonites with water in order to find the best simulative soil for the deep-sea sediment collected from the Pacific C-C area. Shear creep characteristics of the simulative soil were studied by shear creep test and shear creep parameters were determined by Burgers creep model. Research results show that the shear creep curves of the simulative soil can be divided into transient creep, unstable creep and stable creep, where the unstable creep stage is very short due to its high water content. The shear creep parameters increase with compressive stress and change slightly or fluctuate to approach a constant value with shear stress, and thus average creep parameters under the same compressive stress are used as the creep parameters of the simulative soil. Traction of the deep-sea mining machine walking at a constant velocity can be calculated by the shear creep constitutive equation of the deep-sea simulative soil, which provides a theoretical basis for safe operation and optimal design of the deep-sea mining machine.

预应力UHPC-NC组合梁结合面徐变剪应力分析

在恒载应力作用下,预应力UHPC-NC组合梁因两种材料不同的徐变特性及加载龄期的差异导致结合面产生徐变剪应力,分别采用解析法和有限元法对结合面徐变剪应力进行分析。在解析法中,用三角级数表示UHPC-NC结合面的应力分布,基于结合面上的变形协调,利用最小余能原理推导出结合面徐变剪应力计算公式。在有限元法中,将组合梁UHPC层与NC层均划分成四边形平面应力单元,对结合面则采用等效杆单元模拟。以T形截面预应力UHPC-NC组合梁为例进行计算方法的验证,两种方法的计算结果吻合良好,且研究发现徐变剪应力最大值位于梁端;在此基础上对影响结合面徐变剪应力分布的UHPC层压应力、梁高、计算龄期、环境年平均相对湿度等参数进行分析,结果表明:结合面徐变剪应力最大值随着UHPC层压应力、计算龄期、环境年平均相对湿度的增大而增大,但基本不随梁高变化;结合面徐变剪应力最大值的位置随着梁高的增大而逐步向跨中靠近,其他因素不影响应力最大值的位置。研究结果可为UHPC-NC组合梁结合面的抗剪设计提供参考。

某核心筒收进水瓶型超高层结构设计关键问题研究

某超高层建筑位于武汉市汉阳区一线滨江区域,整体造型为下大上小逐渐收分的水瓶型,主体结构高度249m,屋面上设51m高塔冠,地上建筑总高度300m。建筑师要求外框柱贴幕墙边布置,导致塔楼大部分柱均为斜柱,在竖向荷载作用下将对楼面体系产生水平分力,设计中通过在楼面梁设置抗拉钢筋及型钢承担水平拉力。核心筒墙体在17、43层进行了转换收进,通过合理的分析及措施,确保了墙体传力路径的合理性。对主体结构进行了风洞试验并进行了相关论证,减小了设计风荷载,节约了结构造价。对结构进行了施工模拟、收缩徐变分析、墙体有限元分析及塔冠分析,结果表明结构设计安全合理。

高应力状态下两河口堆石料蠕变特性试验研究

堆石料是土石坝的主要填筑材料,其蠕变特性直接决定着土石坝工后变形的大小。对两河口水电站砾石土心墙堆石坝的两种筑坝堆石料,开展室内大型三轴蠕变试验,结果表明:①在低应力水平下,试验侧向应变为正;在高应力水平下,试验侧向应变为负;②采用幂函数外推30 a对应的试验值,将其作为堆石料蠕变试验的极限应变,所得剩余蠕变与时间呈良好的幂函数关系;③最终剪切蠕变与剪应力呈倍数关系,轴向蠕变衰减幂指数与剪切蠕变衰减幂指数基本相等,最终轴向蠕变是最终剪切蠕变的1.5倍。最后,提出了更简洁的两参数幂函数蠕变模型,模型参数物理含义明确,便于在工程中使用。研究可为土石坝工后变形的初步估算提供参考。

STFE膜材力学试验与材料本构研究

STFE膜材是一种新型建筑膜材料,它具有良好的透光和透景性能,并且有较高的抗拉强度,可用于大跨度张拉结构中。本文针对这种新式膜材料,基于国内检测标准改进了单、双轴力学试验方法,并测定了其弹性模量、泊松比、剪切模量、徐变伸长率等力学参数。进一步地,提出了描述STFE膜材应力-应变关系与短期时变(徐变、应力松弛现象)力学性能的材料本构模型。试验结果表明,STFE膜材相对于传统织物涂层膜材,拥有更高的弹性模量和同等水平的徐变伸长率,相对于同样透光透景的ETFE膜材,STFE膜材的强度为其6~7倍,弹性模量为其6倍以上,且徐变伸长率不到其15%。综上所述,STFE膜材具有优异的建筑表现效果和力学性能,适合作为透明张拉膜结构的建筑材料。

固体火箭发动机粘接界面剪切蠕变特性分析与快速预测模型

固体火箭发动机在立式贮存期间,受自重载荷影响,在侧壁粘接界面会产生剪切蠕变行为,威胁发动机的结构安全性和贮存寿命。为研究粘接界面剪切蠕变特性,对某型发动机剪切界面试验件进行了多种温度与应力下的剪切蠕变实验,获得其剪应变-时间关系,分析了粘接界面力学性能随温度与剪切蠕变载荷变化的响应和规律,最终构建了一种适用于线性粘弹性阶段的发动机粘接界面剪切蠕变快速预测模型。结果表明,该快速预测模型构建方式简单,且预测值与实验值相差低于10%,可以较好地预测线性粘弹性阶段粘接界面短期蠕变行为。

隐伏非贯通软弱夹层岩质边坡剪切蠕变特征及稳定性研究

针对隐伏非贯通软弱夹层岩质边坡滑移机理复杂这一关键科学问题。设计一种隐伏非贯通软弱夹层缩尺制备方法,开展考虑夹层埋深、岩层倾角、含水率因素影响下岩体剪切蠕变特性试验。引入多参数岩体渐变损伤变量,分阶段建立剪切蠕变损伤本构模型,并通过相似模拟试验验证模型的合理性,分析此类边坡的稳定性。研究表明:(1)隐伏非贯通含软弱夹层岩体随夹层埋深增加、倾角减小、含水率减小而稳定性升高,反之稳定性降低,且夹层含水率对岩体稳定性影响最大,埋深影响相对较小;(2)考虑多参数渐变损伤本构模型能够反映隐伏非贯通软弱夹层岩体剪切蠕变全过程,且加速蠕变阶段拟合效果优于西原模型;(3)隐伏非贯通软弱夹层缩尺制备方法较为合理,所推剪切蠕变本构模型能够较好拟合边坡蠕变滑移各阶段情况,边坡滑移呈坡脚剪胀、后缘拉裂的整体性滑移,对隐伏非贯通含软弱夹层岩体蠕变滑移具有参考意义。

干湿循环作用下吹填固化轻质土蠕变特性研究

采用新型固化技术对高含水率吹填土进行固化处理,通过三轴流变仪,考虑干湿循环次数、围压和初始静偏应力等因素研究其对吹填固化轻质土蠕变变形和抗剪强度指标的影响规律。试验结果表明:吹填固化轻质土具有密度小、质量轻及强度高等优点。在一定程度上,增大围压可有效缓解吹填固化轻质土的蠕变变形,而初始静偏应力对其影响较小,前7次干湿循环对土体破坏应力的影响最大,而后基本保持不变。抗剪强度指标c、φ值均随初始静偏应力的增加而逐渐降低,随干湿循环次数的增加呈现出先减小而后逐渐稳定的趋势,且前7次干湿循环,二者均呈指数函数降低;7次以后,变化均较小并逐渐稳定。基于c、φ值与时间关系曲线,分别构建了不同偏应力作用下吹填固化轻质土c、φ值的预测公式。根据蠕变曲线发展态势,通过回归分析,引入围压、初始静偏应力和干湿循环次数等因素,建立了吹填固化轻质土蠕变变形预测模型,并验证了其可行性。研究结果可为实际工程场地提供理论依据。

长期直接剪切作用下钙质砂的颗粒破碎特性研究

长期直接剪切作用下钙质砂的颗粒破碎特性是影响钙质砂剪切蠕变变形的重要因素。为了探寻钙质砂在长期直接剪切作用下的颗粒破碎特性,在不同应力水平下对具有特定分形维数的钙质砂进行直剪蠕变试验。试验结果表明:钙质砂的剪切蠕变可以分为快速剪切、减速蠕变和稳态蠕变等3个阶段;大粒径组的颗粒相比小粒径组的颗粒更容易被剪切破碎,大粒径组的颗粒破碎后向相邻的小粒径组迁移,且粒径越相近迁移量越大;钙质砂的破碎程度与法向应力和应力水平正相关,但最终的破碎程度由两者共同作用决定;长期直接剪切作用下相对颗粒破碎率和分形维数之间存在线性相关性,法向应力越大相关性越好;相对颗粒破碎率与输入总功之间呈双曲线关系。

硅质板岩剪切蠕变特性及边坡变形机理研究

为研究硅质板岩的时效蠕变效应和高边坡变形破坏演化规律,该文采用室内岩体剪切蠕变试验,通过绘制不同法向应力下硅质板岩的剪切蠕变历时曲线、剪切位移‒时间曲线和不同法向荷载及剪切荷载下蠕变速率‒时间曲线,研究了硅质板岩平均蠕变速率与剪切荷载变化规律,并采用稳态蠕变速率法确定了硅质板岩长期抗剪强度参数。研究表明:蠕变试验中,黏聚力敏感度高于内摩擦角;以十堰至巫溪高速公路ZK33+450硅质板岩高边坡为例,基于摩尔‒库仑模型采用有限差分法对该典型硅质板岩高边坡剪切蠕变条件下的变形破坏机制进行了研究分析。

收缩徐变对钢-混凝土组合梁界面行为影响的有限元分析

为研究混凝土收缩徐变对长期荷载作用下钢-混组合梁界面剪力和相对滑移的影响,提出一个简单实用的有限元分析方法。在假定荷载-滑移为线性以及钢梁与混凝土层之间无掀起的前提下,基于混凝土收缩徐变分析的初应变法,建立部分剪力连接钢-混凝土组合梁长期性能分析的有限元模型,其中界面行为通过建立混凝土板与钢梁之间对应节点的主从关系及特殊单元予以模拟。对比集中荷载作用下简支梁的计算结果与已有文献,验证所提方法的有效性。在此基础上研究收缩徐变对钢-混组合梁界面剪力和相对滑移的影响。结果表明,收缩徐变共同作用使得简支钢-混组合梁的界面滑移随着时间有较大程度地增加,但单独的收缩效应反而使界面滑移减小,尽管变化量可忽略不计;同时,由于界面剪力与滑移的正相关性,收缩徐变效应也使得端部界面剪力随时间增大,呈现出前期增长很快而后期增长缓慢的特点。

PVA纤维沥青路面高温蠕变特性分析

为研究沥青混合料的黏弹性特征对PVA纤维路面车辙的影响,基于沥青混合料蠕变过程中应变随时间变化结果,利用有限元软件对PVA纤维对沥青路面高温稳定性能的影响进行了数值模拟研究。研究显示:(1)增加沥青混合料表面强度并不能显著地改进层间的剪切情况,但加大其厚度却能有针对性地降低层间的剪应力,从而大大提升了层间的剪切稳定性。(2)当处于黏弹性阶段时,添加纤维能够使沥青公路路面的车辙深度、每一层次的相对位移及蠕动应变大幅度下降,较未掺PVA纤维沥青公路路面的下降程度都超过了30%。(3)掺入纤维后,轮迹位置处沥青路面的剪切变形得到显著改善,面层剪切变形的发展阶段、稳定阶段持续时间长,采用纤维沥青混凝土作为路面结构的加铺层更有益于提高路面层间的结合与变形性能。

考虑配合比的砂泥岩混合填料剪切蠕变力学特性

砂泥岩混合填料的配合比是影响码头地基承载性能及稳定性的关键因素。为研究不同配合比下砂泥岩混合填料土的蠕变力学特性,开展剪切蠕变试验。结果表明,在同一配合比下,随着剪应力加载等级的提高,瞬时、蠕变应变量及初始、稳态蠕变速率均呈逐渐递增趋势;当处于同样加载等级时,初始、稳态、极限加速蠕变速率及瞬时、蠕变应变量均随配合比中泥岩颗粒占比增大而呈递增趋势;混合填料长期强度折减较大,折减范围为50.53%~66.95%,长期强度随配合比中泥岩颗粒占比增大而递减。研究成果可为码头砂泥岩混合填料地基长期稳定性评价提供一定参考。

A new shear rheological model for a soft interlayer with varying water content

The rheological behavior of a soft interlayer is critical to understanding slope stability, which is closely related to the water content of the soft interlayer. This study used the soft interlayer of the Permian Maokou Formation in Southwest China as an example to perform ring shear creep tests with different water content amounts. The effect of water content on the creep properties of the soft interlayer was analyzed, and a new shear rheological model was established. This research produced several findings. First, the ring shear creep deformation of the soft interlayer samples varied with the water content and the maximum instantaneous shear strain increment occurred near the saturated water content. As the water content increased, the cumulative creep increment of the samples increased. Second, the water content significantly affected the long-term strength of the soft interlayer, which decreased with the increase of water content, exhibiting a negative linear correlation. Third, a constitutive equation for the new rheological model was derived, and through fitting of the ring shear creep test data, the validity and applicability of the constitutive equation were proven. This study has developed an important foundation for studying the long-term deformation characteristics of a soft interlayer with varying water content.

Study of electromagnetic and acoustic emission in creep experiments of water-containing rock samples

Based on biaxial shear creep tests conducted on rock samples with different water contents, we present the results of our study on the regularities of electromagnetic and acoustic emission during the process of creep experiments in which we have analyzed the contribution of water to the occurrence of electromagnetic radiation. The result shows that in the creep-fracturing course of rock samples, when the water content increases, the initial frequency and amplitude of electromagnetic and acoustic emission also increases, but at a decreasing growth rate caused by loading stress. This can be used as a criterion for the long-term stability of rock masses under conditions of repeated inundation and discharge of water.

Creep Modeling of Magnesia-chromite Bricks in a RH Snorkel During a Process Cycle

In this paper both experimental and analytical approaches to provide the inputs for creep modeling of refractories including a newly developed high temperature compressive creep machine and an inverse estimation procedure of creep law parameters are briefly introduced.Besides,a modified shear test is applied to determine the cohesion and friction angle of refractories under shear state. A RH snorkel equipped with magnesia- chromite bricks is chosen for a case study of thermomechanical simulation applying the classical creep model and Drucker-Prager creep model available in the finite element code ABAQUS,respectively. Afterwards,thermal stresses and joint opening of magnesia- chromite bricks during a process cycle are compared to distinguish the impact of these two creep models.

Rate-dependent inhomogeneous creep behavior in metallic glasses

Creep deformation can be classified as homogeneous flow and inhomogeneous flow in bulk metallic glass(BMG).In order to understand the conversion conditions of the two types of creep deformation,the effect of loading rate on the creep behavior of a Ti_(40)Zr_(10)Cu_(47)Sn_(3)(at.%)BMG at ambient temperature was investigated using nanoindentation and molecular dynamic simulation.Results indicate that at low loading rates,many serrations appear in loading stage,leading to inhomogeneous serrated flow in the creep stage.When the loading rate is high enough,the creep deformation tends to be homogeneous.The related mechanism responsible for the rate-dependent creep behavior is attributed to the number of pre-existing major shear bands which is influenced significantly by the loading rate.