脆性土石混合体单轴压缩特性的影响因素研究

土石混合体在我国分布广泛且力学性质差异极大,研究其单轴压缩特性的影响因素至关重要。借助量纲分析,阐明了土石混合体单轴压缩特性与各影响因素间的无量纲关系。提出了一种块石随机生成技术,可产生指定级配的随机块石系统。借助连续-非连续数值模拟方法 CDEM(Continuum Discontinuum Element Method),探讨了具有一定结构性的脆性土石混合体材料的宏观力学特性及其影响规律,并重点分析了该类土石混合体的含石量、土石交界面强度与其宏观本构曲线、单轴抗压强度以及破坏模式的对应关系。研究结果表明,随着含石量的增加,脆性土石混合体的宏观单轴抗压强度迅速减小,含石量超过15%之后,单轴抗压强度基本不变。相同含石量及块石分布的情况下,随着交界面比强度的增大,宏观单轴抗压强度逐渐增大;当交界面比强度大于20时,单轴抗压强度基本不变;当交界面比强度小于1时,主要出现贯穿整个试样的裂缝;当交界面比强度大于1时,主要在试样中上部出现局部的压剪破碎。     

块石形状对土石混合体力学行为影响的颗粒流模拟

考虑块石形状为球体、正方体和长方体三种情况,通过正方体与球体相比较来探究块石棱角度不同对土石混合体力学特性的影响,通过长方体与正方体相比较来探究块石球度不同对土石混合体力学特性的影响。首先,提出特定形状块石三维离散元精细建模的方法;接着建立含石量为30%和80%的块石形状分别为球体、正方体和长方体的土石混合体三维颗粒流数值模型;然后,对土石混合体大三轴试验进行颗粒流模拟,获得了不同含石量及不同块石形状的土石混合体试样的宏观力学特征;最后,详细分析了块石形状对土石混合体力学行为影响的细观机理。结果表明,块石形状会影响土石混合体的力学行为,其影响的程度与含石量密切相关;配位数、块石颗粒平均旋转量和摩擦功的演化规律能够很好地从细观水平上反映块石形状的作用机理。     

含石量对土石混合体压桩承载力影响的离散元分析

土石混合体是介于土体和岩体之间的一种非均质、非连续和非线性的特殊工程地质材料,其在压桩贯入过程中的承载力受含石量的影响非常显著。本文分别采用球形颗粒和非规则镶嵌组合颗粒模拟土体颗粒和块石,对不同含石量下压桩贯入过程进行离散元数值分析。计算结果表明,桩柱阻力及其波动规律在不同含石量下有很大的差别。高含石量下的阻力要明显大于低含石量下的阻力,且其波动性也更加明显。通过对土石混合体内部力链结构的细观分析,揭示了压桩贯入过程中承载力随含石量变化的内在机理。以上研究有助于分析土石混合体材料的宏观力学行为,深入研究其在复杂工程条件下的力学特性。     

循环荷载下土石混合体力学特性野外试验研究

土石混合体是一种物理、力学性质非常复杂的不连续介质。以云南某高速公路土石混合体边坡为例,分别对选取的3个试验点进行了单调加载、循环加载一次及多次循环加载试验,获取了其相应的剪切位移-剪切应力关系曲线,并对其曲线特征进行分析研究。通过对试样三维滑动面的形态分析,指出由于土石混合体三维滑动面的不规则性,利用传统的二维计算方法难以得到较为准确的强度参数。基于三维极限平衡理论,提出了土石混合体水平推剪试样强度参数的三维数据计算方法。并利用该方法得到了研究区土石混合体的相应的强度参数及残余强度参数。     

基于离散元模型的土石混合体直剪试验分析

土石混合体是由高强度块石和低强度土体组成的一类特殊工程地质材料,其力学性质可通过直剪试验进行确定.论文针对土石混合体的细观材料特性,分别采用球形颗粒单元和非规则组合颗粒单元模拟土体和块石材料,对其在不同含石量和颗粒粘结强度下的直剪试验过程进行离散元分析.计算结果表明,土石混合体的抗剪强度随着含石量和粘结强度的增加而增加;通过不同法向应力下直剪试验的离散元分析,确定了不同含石量下土石混合体材料的内摩擦角和粘聚力.论文研究结果有助于进一步揭示土石混合体的抗剪强度特性.     

块石对土石混合体力学性能的影响研究

土石混合体是一种由强度较高岩块、强度较低的土体充填成分及相应孔隙等多相体系组成的复杂地质材料。我国中西部地区诸多地质灾害的发生均与其抗剪强度密切相关。影响土石混合体力学性能的因素很多。本文采用柔性边界条件下的大型剪切实验,从含石量、块石排列、块石尺寸三个方面研究了块石对土石混合体力学性能的影响。通过正交实验确定了3种因素对土石混合体抗剪强度的影响顺序及各因素的显著性水平,研究发现在这3个影响因素中,块石尺寸对土石混合体抗剪性能的影响最大,含石量次之,块石排列的影响最小。     

土石混合体重塑样制备及其压密特征与力学特性分析

基于土力学与岩石力学的实验室力学试验原理与方法,本文首先探索了土石混合体重塑样的制备、压密特性等问题,初步给出土石混合体重塑样制备的一个标准流程,并揭示了土石混合体的压密特性与机制,即土石混合体压密主要是土体的压密,但块石直接影响其压密效果,并指出本次试验土石混合体50锤次可达到的最佳压密效果,而压密机制随含石量增加而有所变化。运用高精度岩石试验机,首次进行了土石混合体的单轴压缩试验。试验表明,在无侧限条件下块石与土体无胶结,导致了试样实际承载面积减小,使其抗压强度与弹模反而低于土体; 而土石混合体中块石形成骨架结构的力学响应是土石混合体的一个重要的力学特性。     

伺服控制土石混合体压力渗透仪研究

土石混合体渗流特性的研究对于工程建设、土石混合体滑坡的防治有重要意义。总结了前人对于堆石料渗透试验仪的研究,其特点在于渗透筒的大尺寸、供水系统、供水压力的控制;透水板、制样方法、筒壁防渗对于试验的影响。周中等自制的常水头渗透仪,主要对土石混合体渗透系数及其影响因素进行研究。本文研制的伺服控制土石混合体压力渗透仪能够准确伺服控制供水压力和供水速度,提供不超过2MPa的高水压,调节试样渗流速度,操作方便,能够有针对性的研究土石混合体的渗流特性。     

虎跳峡龙蟠右岸土石混合体粒度分形特征研究

应用分维理论对虎跳峡龙蟠右岸分布的土石混合体粒度分布的分维规律进行了研究分析,建立了平均粒径与相应的分维数之间的定量关系模型。通过研究表明,土石混合体具有良好的统计自相似性,由于其本身为级配不良土,在分维曲线上表现为双重分形分布,这种特殊的分维分布与土石混合体的成因及形成过程有关。     

不排水条件下土石混合料双轴压缩离散元模拟

基于离散单元法构建了考虑碎石形状的柔性边界不排水双轴压缩模型,研究了11组不同含石量土石混合料在不排水条件下的宏细观力学特性。研究发现,(1)土石混合料强度随含石量增加先增后减,含石量超过约60%时形成碎石骨架,强度快速增长;含石量约80%时强度和内摩擦角最大;含石量增加,混合料黏聚力逐渐减小。(2)不排水受载下,土石混合料孔隙水压力先正后负、先增后减。含石量较小时,含石量增加,混合料孔隙水压力变化较小,混合料在碎石骨架形成初期孔隙水压力增加;碎石骨架完全形成后最大孔隙水压力减小。(3)含石量小于约30%时,混合料应变局部化呈规则剪切带,随后含石量增加破坏规则剪切带,当含石量约为80%时,混合料再次形成规则剪切带。含石量增加,配位数逐渐减小,颗粒间接触力在含石量小于60%时随含石量增加缓慢增长,超过70%时则快速增长。     

Experimental study and numerical modeling of brittle fracture of carbonate rock under uniaxial compression

The brittle carbonate rock taken from the Tarim Oilfield is tested in laboratory under uniaxial compression. The acoustic emission (AE) is used to monitor the microcracking activity in rock during the experiment. Moreover, the 3D tomograms of carbonate rock after uniaxial compression are obtained by using CT imaging technology, which indicates that microcracks mutually interconnect and eventually form macroscopic fractures after failure. The PFC2D is used to model the behavior of brittle rock including microcracks propagation. The stress–strain curve and cracks distribution in rock model are obtained from the PFC simulation. The numerical results agree with the experimental test well.     

Constitutive relationship of brittle rock subjected to dynamic uniaxial tensile loads with microcrack interaction effects

A micromechanical model is proposed to describe both stable and unstable damage evolution in microcrack-weakened brittle rock material subjected to dynamic uniaxial tensile loads. The basic idea of the present model is to classify the constitution relationship of rock material subjected to dynamic uniaxial tensile loads into four stages including some of the stages of linear elasticity, pre-peak nonlinear hardening, rapid stress drop, and strain softening, and to investigate their corresponding micromechanical damage mechanisms individually. Special attention is paid to the transition from structure rearrangements on microscale to the macroscopic inelastic strain, to the transition from distribution damage to localization of damage and the transition from homogeneous deformation to localization of deformation. The influence of all microcracks with different sizes and orientations are introduced into the constitutive relation by using the statistical average method. Effects of microcrack interaction on the complete stress-strain relation as well as the localization of damage for microcrack-weakened brittle rock material are analyzed by using effective medium method. Each microcrack is assumed to be embedded in an approximate effective medium that is weakened by uniformly distributed microcracks of the statistically-averaged length depending on the actual damage state. The elastic moduli of the approximate effective medium can be determined by using the dilute distribution method. Micromechanical kinetic equations for stable and unstable growth characterizing the ‘process domains’ of active microcracks are taken into account. These ‘process domains’ together with ‘open microcrack domains’ completely determine the integration domains of ensemble averaged constitutive equations relating macro-strain and macro-stress. Theoretical predictions have shown to consistent with the experimental results.     

DOUBLE-MEDIUM CONSTITUTIVE MODEL OF GEOLOGICAL MATERIAL IN UNIAXIAL TENSION AND COMPRESSION

Based on elasto-plasticity and damage mechanics, a double-medium constitutive model of geological material under uniaxial tension and compression was presented, on the assumption that rock and soil materials are the pore-fracture double-medium, and porous medium has no damage occurring, while fracture medium has damage occurring with load. To the implicit equation of the model, iterative method was adopted to obtain the complete stress-strain curve of the material. The result shows that many different distributions (uniform distribution, concentrated distribution and random distribution) of fractures in rock and soil material are the essential reasons of the daedal constitutive relations. By the reason that the double-medium constitutive model separates the material to be porous medium part, which is the main body of elasticity, and fracture medium part, which is the main body of damage, it is of important practical values and theoretical meanings to the study on failure of rock and soil or materials containing damage.     

单轴压缩条件下溶蚀礁灰岩细观变形破坏特征研究

礁灰岩的溶蚀对海洋工程和岛礁工程的稳定性有明显的影响.孔隙型溶蚀是礁灰岩常见的溶蚀方式.本文通过构建随机溶蚀孔洞的离散元模型,模拟孔洞型溶蚀礁灰岩的细观变形破坏特征,分析其变形破坏规律与裂隙演化特征.结果 表明,基于随机聚类算法构建的溶蚀礁灰岩离散元模型能够很好地模拟孔洞型溶蚀作用,且其变形破坏特征具有明显的规律;随着...     

ANALYSIS OF THE LOCALIZATION OF DAMAGE AND THE COMPLETE STRESS-STRAIN RELATION FOR MESOSCOPIC HETEROGENEOUS ROCK UNDER UNIAXIAL TENSILE LOADING

The mechanical behavior of rock under uniaxial tensile loading is different from that of rock under compressive loads. A micromechanics-based model was proposed for mesoscopic heterogeneous brittle rock undergoing irreversible changes of their microscopic structures due to microcrack growth. The complete stress-strain relation including linear elasticity, nonlinear hardening, rapid stress drop and strain softening was obtained. The influence of all microcracks with different sizes and orientations were introduced into the constitutive relation by using the probability density function describing the distribution of orientations and the probability density function describing the distribution of sizes. The influence of Weibull distribution describing the distribution of orientations and Rayleigh function describing the distribution of sizes on the constitutive relation were researched. Theoretical predictions have shown to be consistent with the experimental results.     

Analysis of the localization of damage and the complete stress-strain relation for mesoscopic heterogeneous brittle rock subjected to compressive loads

A micromechanics-based model is established. The model takes the interaction among sliding cracks into account, and it is able to quantify the effect of various parameters on the localization condition of damage and deformation for brittle rock subjected to compressive loads. The closed-form explicit expression for the complete stress-strain relation of rock containing microcracks subjected to compressive loads was obtained. It is showed that the complete stress-strain relation includes linear elasticity, nonlinear hardening, rapid stress drop and strain softening. The behavior of rapid stress drop and strain softening is due to localization of deformation and damage. Theoretical predictions have shown to be consistent with the exoerimental results.     

人工冻结深部软岩单轴力学性能试验及蠕变模型1）

为了了解深部软岩在冻结条件下的单轴力学性能,以东北地区的原状泥砂岩为试验对象,利用自行研制的WDT-100型人工冻土试验仪器,对其进行不同温度下的人工冻土单轴抗压强度试验和单轴蠕变试验,得到泥砂岩单轴压缩应力-应变关系曲线,各温度下试样的单轴抗压强度以及蠕变曲线.单轴压缩试验结果表明：试样在给定温度和加载速率条件下,单轴压缩应力-应变关系曲线都有较为明显的屈服点,并且都在屈服点后,强度有所提高,出现硬化现象.单轴蠕变试验结果表明：单轴压缩蠕变曲线有非线性特征,单轴压缩蠕变的等时应力-应变曲线向应变轴靠拢;单轴压缩时蠕变模量随时间的增长而降低.最后采用遗传算法优化模型参数,得出泥砂岩蠕变经验方程.与试验结果对比,发现拟合情况较好.     

人工冻结深部软岩单轴力学性能试验及蠕变模型

为了了解深部软岩在冻结条件下的单轴力学性能,以东北地区的原状泥砂岩为试验对象,利用自行研制的WDT-100型人工冻土试验仪器,对其进行不同温度下的人工冻土单轴抗压强度试验和单轴蠕变试验,得到泥砂岩单轴压缩应力-应变关系曲线,各温度下试样的单轴抗压强度以及蠕变曲线.单轴压缩试验结果表明：试样在给定温度和加载速率条件下,单轴压缩应力-应变关系曲线都有较为明显的屈服点,并且都在屈服点后,强度有所提高,出现硬化现象.单轴蠕变试验结果表明：单轴压缩蠕变曲线有非线性特征,单轴压缩蠕变的等时应力-应变曲线向应变轴靠拢;单轴压缩时蠕变模量随时间的增长而降低.最后采用遗传算法优化模型参数,得出泥砂岩蠕变经验方程.与试验结果对比,发现拟合情况较好.     

经历不同高温后砂岩的动态力学特性实验研究

3D打印技术应用于岩石试样制备有着诸多优势,但也存在着传统3D打印材料无法完美模拟岩石材料、3D打印类岩石试样强度偏低和3D打印类岩石试样后处理技术较少等不足。为了使3D打印技术能更好地应用于岩石试样制备,本研究尝试以某典型砂岩真实矿物组成配置的矿物粉末为打印材料,通过3D打印技术制作出2种不同级配的类岩石试样,并探究渗剂渗透后处理方法对3D打印类岩石试样力学特性的影响。研究结果表明：以矿物粉末为打印材料,按不同颗粒级配下制作出的试样的力学性能有很大差异,以水性氨基树脂对3D打印类岩石试样进行渗透处理能进一步提升试样的单轴抗压强度,树脂渗透试样在抗压强度以及破坏模式上与致密砂岩相似。研究成果为通过3D打印制备岩石试样提供了新思路。