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.

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.

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。

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。

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.

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。

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。

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。

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.

钢-混组合结构桥梁混凝土的收缩徐变效应

首先讨论混凝土收缩作用的等效降温取值问题,分析了构件理论厚度、环境平均相对湿度、预制板存梁期等因素对混凝土收缩的影响。然后探讨收缩徐变应力计算方法,并结合工程实例分析了混凝土徐变、抗剪连接键滑移和次内力对收缩应力的影响。最后提出了补偿收缩混凝土应用于钢-混组合梁桥时的注意事项。结果表明:对于我国大多数地区按等效降温15℃计算的收缩效应值较实际值偏小;抗剪连接键滑移主要影响距梁端1/10跨径范围内的应力分布;连续梁的混凝土板由收缩二次内力引起的结构应力远大于收缩一次内力引起的结构应力;补偿收缩混凝土的限制膨胀率宜根据收缩应变预测值和微膨胀对结构的不利影响综合确定。

红层泥岩剪切蠕变特性及非定常本构模型研究

滇中红层泥岩具有显著的流变特性,会给当地工程建设带来安全隐患。选取狮子山隧洞段的红层泥岩进行分级加载蠕变试验,对其蠕变特性开展研究。结果表明,在较低应力状态下,岩样主要表现为衰减蠕变,而在较高应力状态下,岩样将发生从衰减蠕变、等速蠕变直至加速蠕变破坏的全过程蠕变。对岩样各阶段变形数据进行回归分析,建立拟合方程,发现岩样各阶段变形具有显著的非线性变形特性。根据岩样的非线性变形特性提出了1个指数型加速元件,通过与Bingham体中的黏性元件串联形成改进的Bingham体,使其能克服传统Bingham体模拟加速阶段存在的不足,并同时对Hoek体及Kelvin体进行非线性改进,然后通过将非线性Hoek体、Kelvin体与改进Bingham体串联,建立了1个能够描述滇中红层泥岩蠕变特性的非线性、非定常黏弹塑性岩石蠕变模型。通过与不同剪应力下红层泥岩的蠕变试验曲线进行比较,发现理论模型得到的结果与试验数据吻合较好,表明所建模型对于滇中红层泥岩具有较好的适用性。

波形钢腹板钢底板混凝土组合梁的挠度分析

研究目的:为精确分析波形钢腹板钢底板混凝土组合梁在长期荷载作用下的挠度变化,在纳入组合梁剪切变形效应、剪力滞效应及收缩徐变效应对挠度计算影响的基础上,采用能量变分法推导出波形钢腹板钢底板混凝土组合梁的控制微分方程与自然边界条件,得到波形钢腹板钢底板混凝土组合简支单箱双室箱梁分别在跨中集中荷载和满跨均布荷载作用下的挠度计算公式;利用所得公式计算荷载作用7 d、1000 d和3650 d时的挠度值,与ANSYS数值解以及不考虑收缩徐变效应的计算值进行对比,并通过了模型试验结果的验证。研究结论:(1)本文挠度计算值与ANSYS数值解及模型试验结果吻合良好;(2)波形钢腹板钢底板混凝土组合简支箱梁在跨中集中荷载和满跨均布荷载作用1000 d后,跨中挠度分别增大了9.12%和12.94%;(3)在3650 d后,跨中挠度分别增大了14.69%和18.32%,显然收缩徐变效应对组合箱梁挠度计算的影响不可忽略;(4)本文研究可为同类波形钢腹板钢底板混凝土组合梁的挠度计算提供参考。

长期效应下不同边界钢-混凝土组合梁挠度分析

为了研究长期荷载效应对钢-混凝土组合梁挠度的影响,本文对不同边界钢-混凝土组合梁进行分析。考虑组合梁的剪切变形、层间滑移及剪力滞效应,引入长期荷载下的混凝土收缩徐变作用,运用能量法和变分原理推导出均布荷载作用下不同边界条件的组合梁长期挠度解析解,并通过有限元和试验结果验证了解析解的正确性。通过简支组合梁、固结组合梁和连续组合梁3个算例的挠度分析结果表明:长期荷载作用对组合梁总挠度影响较大,对两跨连续梁尤其显著;除长期荷载影响外,简支组合梁挠度主要受层间滑移作用的影响,两端固结梁挠度主要受剪切变形和层间滑移作用的影响,两跨连续组合梁挠度主要受层间滑移作用的影响;3种不同边界条件的钢-混凝土组合梁挠度受剪力滞效应的影响最小。

竖向荷载作用下预制叠合剪力墙收缩徐变效应研究

为研究预制叠合剪力墙在竖向荷载作用下的收缩徐变效应,制作了一片小尺寸预制叠合剪力墙,对试件施加竖向荷载,得到了预制叠合剪力墙的收缩徐变反应.基于龄期修正有效弹性模量法(AEMM),考虑剪力墙结构长期收缩徐变效应引起的截面内力重分布,建立了长期竖向荷载作用下叠合剪力墙的收缩徐变及截面应力计算模型.经过比较,采用GL2000收缩徐变预测模型计算得到的结果与试验曲线吻合良好.在此基础上,比较了十年服役周期内,混凝土强度等级、纵向钢筋配筋率、环境湿度、初始加载龄期和轴压比对预制叠合剪力墙的收缩徐变效应的影响.

分级加卸载作用下冻结界面黏弹塑性剪切蠕变解耦分析研究

桩-土界面间冻结力及荷载作用下界面的剪切力学行为是决定冻土区桩基础承载性能和荷载传递的关键。由于冰的显著流变性及高含冰量冻土区上限附近厚层地下冰的广泛分布特征,桩基础中上位具有的冰冻结界面剪切蠕变特性对桩基础的承载性能有显著影响。为研究桩冰冻结界面剪切变形特征及其内在机制,开展了-3℃、-5℃下冰-钢管结构分级加卸载剪切蠕变试验。通过对变形曲线的分段独立解耦,分析了冻结界面的黏弹塑性剪切变形行为。结果表明,界面剪切变形可分解为瞬弹性(Sie)、瞬塑性(S_(ip))、黏塑性(S_(vp))以及黏弹性变形(S_(ve))。广义弹性剪切模量随分级荷载的增加逐渐变大,表明加卸载过程中结构未加速破坏前界面存在明显的强化效应。界面剪切蠕变特征随剪应力水平的增加由衰减向非衰减过渡。其中,黏弹性变形和低剪应力水平下黏塑性变形均表现为衰减性,且荷载越大,黏弹性变形越大。高应力水平下黏塑性表现为非衰减性,且变形速率随剪应力水平增加显著提升。整体而言,冻结界面塑性变形值占总累计变形的比例先减小,后增大,其中瞬塑性变形主要存在于应力水平较小的加载阶段。蠕变过程中冻结界面的强化效应可能与剪应力作用下界面接触带压密、负温环境下界面重冻结有关。