Strength criterion for crystalline rocks considering grain size effect and tensile-compressive strength ratio

The macroscopic mechanical properties of rocks are significantly influenced by their microstructure.As a material bonded by mineral grains,the grain morphology of crystalline rock is the primary factor influencing the strength.However,most strength criteria neglect the strength variations caused by different grain characteristics in rocks.Furthermore,the traditional linear criteria tend to overestimate tensile strength and exhibit apex singularity.To address these shortcomings,a piecewise strength criterion that considers the grain size effect has been proposed.A part of an ellipse was employed to construct the envelope of the tensive-shear region on the meridian plane,to accurately reproduce the low tensile-compressive strength ratio.Based on the analysis of experimental data,both linear and exponential modification functions that account for grain size effects were integrated into the proposed criterion.The corresponding finite element algorithm has been implemented.The accuracy and applicability of the proposed criterion were validated by comparing with the experimental data.

基于三轴加卸载试验的花岗岩弹性模量变异与能量演化分析

为了研究岩体的变形特征和能量特征与其所处应力状态之间的关系,开展了5种围压下花岗岩的三轴循环加卸载试验.基于应力-应变曲线,计算了循环加卸载过程中花岗岩的弹性模量和能量密度,分析了应力状态对弹性模量及能量演化规律的影响.研究结果表明:轴向弹性模量随围压的增大而增大,随轴向应力的增大先增大后减小.轴向弹性模量与最大、最小主应力呈现良好的二次函数关系.随着围压的增大,能量密度与弹性能占比(弹性能与输入总能量之比)均显著增大,岩石储能能力提高;随着轴向应力增大,弹性能占比先增大后减小.弹性能占比减小阶段即岩石损伤加剧阶段,围压的增加延长了岩石的损伤演化过程.最后讨论了应力状态、岩石力学参数及能量状态的关联性.

高渗透压和不对称围压作用下深竖井围岩损伤破裂机理

随着矿产资源开采深度的不断增大,地应力、地温和孔隙水压随之显著增大,岩石的非线性力学行为更加凸显.针对高渗透压和不对称围压作用下深竖井围岩损伤破裂问题,构建了流固损伤耦合效应力学分析模型,分析了流固耦合条件下深竖井开挖围岩有效应力,探讨了孔隙水压及地应力场对围岩损伤破裂演化的作用机制.研究结果表明:孔隙水压及孔隙水压梯度越大围岩损伤破裂区面积越大,围岩损伤破裂区面积随围岩渗透率的减小逐渐增大并趋于稳定;地应力场对围岩破裂形态具有重要控制作用,最大水平主应力与最小水平主应力差异较小时,围岩损伤破裂区集中在最小水平主应力方向,以剪切损伤为主,最大水平主应力与最小水平主应力差异较大时,在最大水平主应力方向上会产生拉伸损伤破裂区.值得关注的是,由于孔隙水压的存在,最大有效水平主应力与最小有效水平主应力之间的比值增大,即围岩发生拉伸破坏的风险增大.本文研究表明,竖井选址和设计过程中应避开构造应力大、孔隙水压大的区域,从而保障井筒施工安全.

再生骨料品质和掺量对双掺再生混凝土力学性能的影响

随着我国建筑垃圾资源化利用技术的迅猛发展,利用单一再生骨料制备再生混凝土的相关性能研究逐渐趋于系统化和成熟化.但建筑垃圾的再利用率仍处于较低水平,故同时考虑采用再生粗骨料和再生细骨料以不同的掺量分别替代天然骨料制备了双掺再生混凝土.试验中以双掺再生混凝土处于相同工作性为基础条件,重点研究再生粗骨料、再生细骨料的品质和掺量对其力学性能的影响.结果表明,再生粗骨料、再生细骨料的品质对双掺再生混凝土抗压强度的影响作用由小到大依次为:Ⅰ类<Ⅱ类<Ⅲ类;随着再生粗骨料、再生细骨料掺量的增加,其抗压强度均逐渐减小,当掺量均为50%时抗压强度的最大降低幅度可达57%.相比较单掺再生混凝土或普通混凝土,双掺再生混凝土的力学性能显著降低,但可将其应用于成本要求和强度等级要求较低的混凝土工程中.

模拟冻结法施工环境对大体积混凝土的性能影响

模拟大体积混凝土在冻结法施工环境的状态,将混凝土浇筑7 h后施加-5/60℃和-5/70℃温差,测试施加模拟环境后混凝土的超声波参数、抗压强度、劈裂抗拉强度、氯离子扩散系数和冲击倾向性,分析混凝土的扫描电镜微观形貌.结果表明,冻结施工环境对于混凝土内部会造成一定的损伤,且平行于加温方向的损伤要大于垂直方向,C50混凝土的损伤大于C70混凝土,温度梯度会加剧混凝土内部的损伤.模拟冻结环境会对混凝土抗压强度、劈裂抗拉强度、氯离子渗透性能和冲击倾向性造成不利影响,温差与性能降低率正相关,且这种影响对于低强度混凝土更加显著.模拟冻结环境造成混凝土试块的内部微观结构不均匀,低温端混凝土结构比较疏松,高温端结构比较致密,导致部分混凝土性能的降低.

基于硬脆性岩石特征粒径的锥齿滚刀最优钻压分析

为提高反井钻机锥齿滚刀对硬脆性岩石的破岩效率,需要得到最优钻压,分析岩碴粒径是研究反井钻机锥齿滚刀最优钻压的重要手段。采用直线破岩试验方法,使用锥齿滚刀破碎硬脆性大理岩试样,并通过Rosin-Rammler分布函数对岩碴粒径分布情况进行分析。通过对比多个钻压下岩碴粒径分布的累计概率曲线、特征粒径以及比能,得到钻压与岩碴特征粒径分布规律、特征粒径与比能的关系。当特征粒径最大和比能最小时,分别得到大理岩试样的最优钻压为34.45 kN和35.19 kN,因此最优钻压约为35 kN。据此,建议在实际应用中可将钻压设为35 kN。还分析了在相同钻压下,采用锥齿滚刀破碎硬脆性大理岩和花岗岩时的粒径分布关系,分析得到两种单轴抗压强度岩碴的特征粒径。研究结果表明特征粒径能够反映锥齿滚刀的破岩效果;硬脆性岩石的破碎过程符合黎金格的新表面说,特征粒径与比能呈近似反比关系;在一定钻压范围内,相同钻压下花岗岩特征粒径均大于大理岩,且特征粒径差距随钻压增加而增大。

尾砂胶结含盐冻结充填体力学特性研究

矿山充填开采正逐步向寒区甚至永久冻土区发展,这些区域含盐地下水分布非常广泛。同时,极端寒冷条件下往往需要向充填材料中加入一些防冻盐以防止料浆在输送过程中发生冻结。通过室内测试分析了-6℃环境下不同盐分(Na Cl)膏体充填体力学特性(强度和初始弹性模型)随时间演化特征。利用单轴压力机测得了龄期为7、28、90 d膏体充填体的强度和初始弹性模量,结果表明NaCl的加入会降低冻结充填体的强度,其影响程度取决于胶结料类型。试样的强度随着养护时间的增加而增大。此外,不论盐分浓度、养护时间和胶结料类型,试样的强度与初始弹性模量之间存在显著的线性关系。该研究结果可以为寒区含盐膏体充填技术的开展提供一些依据。

Strength and energy exchange of deep sandstone under high hydraulic conditions

To investigate the influence of confining pressure and pore water pressure on strength characteristics,energy storage state and energy release intensity at peak failure of deep sandstone,a series of triaxial compression tests under hydraulic coupling conditions are carried out.By analyzing the process of rock deformation and failure,the stress thresholds of the rock are obtained.The change trend of total energy density,elastic energy density and dissipated energy density of deep sandstone in the pre-peak stage is obtained by the graphical integration method.By comparing the dynamic energy storage level of rocks under different confining pressures,the influence of pore water pressure on the energy dissipation at stress thresholds of crack closure stress,crack initiation stress,crack damage stress and peak stress is analyzed.Based on the ratio of pre-peak total energy density to post-peak total energy density,the interaction mechanism of confining pressure and pore water pressure for the rock burst proneness of deep sandstone is studied.The experimental results show that the peak stress of sandstone increases with the increase of confining pressure,while the existence of pore water pressure can weaken the peak stress of sandstone.In the stress stage from crack closure stress to peak stress,the dynamic energy storage level of rock presents a trend of the inverse“check mark”.Meanwhile,the larger the confining pressure,the higher the energy storage level of rock.However,the pore water pressure increases the degree of energy dissipation of rock and reduces the energy storage capacity of rock,and the degree of dissipation is linear with pore water pressure.The increase of confining pressure aggravates the instability and failure of deep sandstone,while pore water pressure has the opposite effect.The research results will provide necessary data support for the stability analysis of rock mass excavation in sandstone stratum under high stress and high pore water pressure.

测控设备噪声功率高效控制优化方法仿真

由于目前已有方法未能对设备中的噪声进行识别,导致控制结果不理想,稳态误差增加,音质质量下降。提出一种数字化智能测控设备噪声功率自适应控制方法,通过梅尔频率倒谱系数(MFCC)提取数字化智能测控设备噪声。使用Hannning自卷积窗替换Hannning窗,获取优化后的MFCC,将其作为特征值输入到SVM中进行噪声识别。在上述分析的基础上,将滤波器结构和自适应算法相结合,简化控制器结构,实现数字化智能测控设备噪声功率自适应控制的目的。仿真结果表明,所提方法能够有效提升音质质量,降低稳态误差,获取理想的噪声功率自适应控制结果。