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.

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.

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.

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.

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。

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。

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。

A Constitutive Model of Granite Shear Creep under Moisture

Previous constitutive models of granite shear creep have two limitations：（1） although moisture greatly affects granite shear creep behavior, currently there are no constitutive models that include this factor;（2） there are also no models that include an acceleration stage. This paper presents an improved Burgers constitutive model with the addition of a damage parameter to characterize the moisture effect and uses a nonlinear relation equation between stress and strain for inclusion as the acceleration stage. The damage parameter is determined from granite creep experiment under four different moisture contents（0%, 0.22%, 0.49%, and 0.79%）. The nonlinear relation equation is obtained by fitting a dataset of stain versus time under five different loading stages. To verify the presented model, a creep experiment was conducted on other granite samples and the results show that the model agrees well with the experimental observation data.

加筋黄土蠕变特性与改进Burgers模型模拟研究

位于中国西北部的黄土高原为滑坡多发区,具有亚稳态结构、高孔隙率和水敏性等特性的黄土在外界扰动作用下会表现出不稳定性。除了土的剪切特性外,蠕变特性被认为是决定长期抗剪强度的关键因素。合理评价加筋黄土的蠕变规律与长期强度对促进加筋黄土的工程应用具有十分重要的意义。本文利用大型直剪设备进行加筋黄土的蠕变试验得出水平剪位移–时间的变化曲线,研究了加筋黄土在大位移强度状态下的蠕变特性。此外,为了克服传统蠕变模型的不足,本文提出了一种引入非线性参数β的改进Burgers模型。与传统的Burgers模型相比,改进Burgers模型能够更准确地描述非衰减蠕变与黏性流动在加速蠕变阶段的曲线。结果表明:加筋黄土存在三种蠕变行为,包括衰减蠕变、非衰减蠕变和黏性流动;水平剪位移与蠕变时间的关系说明了当受到相同的剪应力比时,未加筋和加筋试件表现出不同的行为,加筋试件在限制颗粒在剪切面内的相对运动优于未加筋试件;蠕变速率与剪应力比的关系证实了在蠕变过程中,剪切应力会导致剪切带中土粒间发生会持续累积的相对位移,最终导致试件沿剪切面破坏。颗粒间接触损失的连锁反应,伴随着黏性位移过大,蠕变抗力迅速减弱,最终加速蠕变位移,为揭示缓慢移动滑坡灾害的形成机理提供了关键证据。

渗透压作用下黄山石灰石矿区炭质泥页岩剪切蠕变特性分析

针对西南地区二叠系软弱夹层在降雨反复作用下蠕变效应明显等问题,以四川省黄山石灰石矿区炭质泥页岩为研究对象进行渗透压作用下的剪切蠕变试验,得到其剪切蠕变试验曲线,通过分析其蠕变特性以及非线性破环规律,基于传统的西原模型,提出了一种能同时描述炭质泥页岩黏弹塑性特性的非线性蠕变模型,并利用该模型进行剪切蠕变参数辨识,结合FLAC3D数值模拟计算,研究了炭质泥页岩变形破坏特征,对比分析了室内试验结果和数值模拟结果,数值模拟结果证实了室内试验的可靠性以及本构模型和参数选取的合理性。研究结果表明:在渗透压、法向压力以及剪切应力的作用下,炭质泥页岩试样经历了完整的蠕变三阶段;改进的西原模型能够很好地拟合炭质泥页岩蠕变的三个阶段,对加速蠕变阶段的拟合效果也很好;运用FLAC3D软件对室内剪切蠕变试验进行计算得到的数值模拟结果与实际结果相吻合。

大岗山坝区岩体现场剪切蠕变试验及参数反演

现场剪切蠕变试验是了解岩体剪切蠕变特性的最重要手段。针对大岗山水电站坝区"硬、脆、碎"辉绿岩脉进行了现场剪切蠕变试验,分析了岩体的剪切蠕变变形规律和剪切蠕变速率特性。试验结果表明,在剪应力较小时坝区岩体剪切蠕变仅呈现出减速蠕变和稳态蠕变2个阶段;当剪应力接近屈服强度时,坝区岩体剪切蠕变速率由渐变增长转为突变增长,岩体在短时间内即发生破坏,呈现出加速蠕变特性。恒定正应力下辉绿岩体的稳态流变速率与剪应力之间可用指数关系来表征。根据剪切蠕变试验曲线,进行了岩体剪切蠕变模型辨识。辨识表明,西原模型可以较好反映坝区辉绿岩脉的剪切蠕变特性。通过优化反演获得坝区岩体的剪切蠕变参数,为坝基边坡工程稳定性分析和设计提供了重要的力学依据。

黄土剪切蠕变特性试验研究

通过对陕西杨凌地区Q3黄土的直接剪切蠕变试验,研究原状、重塑和饱和黄土的蠕变特性。结果表明:原状、重塑和饱和黄土均具有蠕变特性;相同试验条件下,饱和黄土的蠕变速率最快,蠕变变形量最大,重塑黄土次之,原状黄土蠕变现象较不明显。根据蠕变曲线形态特征,建议一种对数型蠕变模型;选用分数线性蠕变模型模拟杨凌地区Q3黄土的剪切蠕变特性,经验证,该模型能很好地描述杨凌地区Q3黄土的剪切蠕变特性。另外,基于试验数据,拟合出剪切模量和法向应力、时间的关系,为确定剪切模量提供一条新途径。

软弱结构面剪切蠕变特性与含水率关系研究

软弱结构面往往控制着岩体的蠕变变形,含水率又是影响软弱结构面蠕变特性的重要因素,通过开展不同含水率条件下砂岩软弱结构面剪切蠕变试验,得到了不同含水率条件下剪切蠕变曲线,并考虑加载历史对试验曲线进行了修正。在此基础上,通过模型辨识选取Burgers模型描述砂岩软弱结构面蠕变的黏弹性特性。分析了含水率对砂岩软弱结构面剪切蠕变特性的影响,并对含水率影响软弱结构面剪切蠕变特性的机制进行了探讨。

黄石淤泥质土的剪切蠕变特性及模型研究

通过室内剪切蠕变试验,对黄石地区淤泥质土蠕变特性进行了研究。结果表明:黄石淤泥质土的剪切蠕变变形可近似为线性特征;蠕变变形在一定剪应力水平下才能表现出来,剪应力水平越高,剪切蠕变变形越明显;在高应力下,土的粘滞性增加,流动性降低,剪切模量与时间呈下降幂函数关系;粘滞系数的变化受剪应力的影响并不大。针对试验数据采用线性回归分析法确定蠕变参数能取得较高的精度,Burgers体蠕变模型和经验型模型均能较好描述该地区淤泥质土的剪切蠕变规律。比较而言,采用经验型模型更适合于描述软土非线性剪切蠕变特性。

坡积土石混合体蠕变特性的Burgers模型

为探明坡积土石混合体的蠕变特性,利用大型直剪仪对陕西省城固县某边坡的坡积土石混合体进行了剪切蠕变试验,重点研究了分级加载方式下坡积土石混合体的蠕变特性,建立了坡积土石混合体的Burgers模型并确定了其参数获取方式,并建议了在分级加载条件下获取分别加载蠕变终值的方法。结果表明:分级加载方式下土石混合体的蠕变规律呈衰减蠕变特性,且蠕变变形随着垂直应力的减小和剪切应力的增大而增大,不同垂直应力下的t/[ε(t)-ε(t0)]-t的曲线均呈高度线性,且拟合的直线方程斜率和剪切应力没有明显的相关性。本文提出的Burgers模型能够较好地模拟该地区坡积土石混合体的剪切蠕变特性。

甘肃甘谷裂隙泥岩剪切蠕变行为及其修正模型研究

岩石在长期荷载作用下表现出典型的蠕变特性,裂隙泥岩在长期荷载作用下的力学性质不同于完整岩石。对甘肃甘谷赵家窑滑坡钻孔取芯的裂隙泥岩开展剪切蠕变试验,探讨轴向压应力、预制裂隙长度等因素对试样剪切蠕变特征的影响。试验结果表明:轴向荷载和裂隙长度对试样剪切蠕变特征有明显的影响。轴向压应力越大,试样剪切蠕变变形越不明显;裂隙越长,试样剪切蠕变变形越显著。应力较低时,如Cvisc模型等蠕变模型能够较好反映泥岩的蠕变力学特性。而在加速蠕变阶段,大多数模型却不能准确体现泥岩蠕变曲线的非线性变化。改进的西原模型克服了传统模型不能对非线性蠕变特征进行描述的缺点,且模型参数较少,能较好地适用工程软弱岩体。不同载荷作用下泥质软岩试样剪切蠕变过程中,裂隙泥岩剪切破坏带形成表现为渐进与突发相结合。泥岩的剪切蠕变力学模型可解释泥岩滑坡的多种现象,边坡潜在滑移带内泥质软岩发生的剪切蠕变则是泥岩滑坡的内在诱因。

三峡泄滩滑坡滑动带土的改进Mesri蠕变模型

为进行滑坡建模和稳定数值分析的需要,进行了三峡泄滩滑坡体滑动带土的三轴排水蠕变试验.在此基础上,给出了排水条件下粘性土的Mesri蠕变模型,即剪应力 应变关系采用双曲线模型、应变 时间关系采用幂函数来描述土体的弹粘塑性;提出了改进Mesri蠕变模型,其应变 时间关系采用分段拟合方法.模型计算曲线与试验数据的比较表明,改进Mesri蠕变模型较Mesri蠕变模型对粘性土蠕变性能的拟合能力得到了显著改善.

重塑粉质黏土的剪切蠕变特性及本构模型研究

通过室内三轴试验,对重塑粉质黏土的剪切蠕变特性进行研究,分析了粉质黏土在不同偏应力水平下和不同偏应力分级方式下的蠕变变形特性。试验表明,粉质黏土的偏应变蠕变变形与对数时间关系具有明显的非线性;在同样的剪切应力水平下,不同的加载分级方式对试样的最终偏应变量有明显的影响,加载分级越多,最终的偏应变量越小。基于试验数据,建立了适合描述重塑粉质黏土蠕变特性的双曲线模型,并对模型参数的物理意义和取值方法进行了讨论。分析表明,模型参数的取值与应力水平及试样的初始孔隙比有关;结合试验结果,给出了粉质黏土剪切蠕变双曲线模型参数取值建议。

镍基单晶合金筏化规律及蠕变持久寿命模型在复杂应力状态下的考核

利用双剪切蠕变试样在受剪切区的筏化试验结果和不同晶体取向试样的蠕变持久寿命试验结果,对镍基单晶合金的蠕变筏化预测模型和蠕变持久寿命模型进行考核,证实此2个模型的合理性。

结构面的剪切蠕变特性及本构模型研究

岩体结构面的蠕变特性研究对解决岩石力学实际问题具有很重要的意义,结构面的蠕变力学性态往往控制着岩体的时效变形和长期强度,研究结构面的剪切蠕变特性是岩石流变学的一项重要内容。通过规则齿形结构面在不同法向应力条件下的剪切蠕变试验,研究了不同角度结构面的剪切蠕变特征,并根据蠕变试验结果,对结构面的剪切蠕变特性进行了描述,对结构面剪切蠕变试验过程中的蠕变速率特性进行了研究。研究表明,结构面在蠕变试验过程中,严格意义下的稳态蠕变是不存在的,常说的稳态蠕变实际上是蠕变速度随时间缓慢减小的近似稳态蠕变过程。最后,提出改进Burgers模型来描述蠕变的剪切蠕变特性,并讨论了改进的Burgers模型对于描述结构面剪切蠕变特性的适用性。