Intermittent disturbance mechanical behavior and fractional deterioration mechanical model of rock under complex true triaxial stress paths

Mechanical excavation,blasting,adjacent rockburst and fracture slip that occur during mining excavation impose dynamic loads on the rock mass,leading to further fracture of damaged surrounding rock in three-dimensional high-stress and even causing disasters.Therefore,a novel complex true triaxial static-dynamic combined loading method reflecting underground excavation damage and then frequent intermittent disturbance failure is proposed.True triaxial static compression and intermittent disturbance tests are carried out on monzogabbro.The effects of intermediate principal stress and amplitude on the strength characteristics,deformation characteristics,failure characteristics,and precursors of monzogabbro are analyzed,intermediate principal stress and amplitude increase monzogabbro strength and tensile fracture mechanism.Rapid increases in microseismic parameters during rock loading can be precursors for intermittent rock disturbance.Based on the experimental result,the new damage fractional elements and method with considering crack initiation stress and crack unstable stress as initiation and acceleration condition of intermittent disturbance irreversible deformation are proposed.A novel three-dimensional disturbance fractional deterioration model considering the intermediate principal stress effect and intermittent disturbance damage effect is established,and the model predicted results align well with the experimental results.The sensitivity of stress states and model parameters is further explored,and the intermittent disturbance behaviors at different f are predicted.This study provides valuable theoretical bases for the stability analysis of deep mining engineering under dynamic loads.

Microdynamic mechanical properties and fracture evolution mechanism of monzogabbro with a true triaxial multilevel disturbance method

The far-field microdynamic disturbance caused by the excavation of deep mineral resources and underground engineering can induce surrounding rock damage in high-stress conditions and even lead to disasters.However,the mechanical properties and damage/fracture evolution mechanisms of deep rock induced by microdynamic disturbance under three-dimensional stress states are unclear.Therefore,a true triaxial multilevel disturbance test method is proposed,which can completely simulate natural geostress,excavation stress redistribution(such as stress unloading,concentration and rotation),and subsequently the microdynamic disturbance triggering damaged rock failure.Based on a dynamic true triaxial test platform,true triaxial microdynamic disturbance tests under different frequency and amplitudes were carried out on monzogabbro.The results show that increasing amplitude or decreasing frequency diminishes the failure strength of monzogabbro.Deformation modulus gradually decreases during disturbance failure.As frequency and amplitude increase,the degradation rate of deformation modulus decreases slightly,disturbance dissipated energy increases significantly,and disturbance deformation anisotropy strengthens obviously.A damage model has been proposed to quantitatively characterize the disturbance-induced damage evolution at different frequency and amplitude under true triaxial stress.Before disturbance failure,the micro-tensile crack mechanism is dominant,and the micro-shear crack mechanism increases significantly at failure.With the increase of amplitude and frequency,the micro-shear crack mechanism increases.When approaching disturbance failure,the acoustic emission fractal dimension changes from a stable value to local large oscillation,and finally increases sharply to a high value at failure.Finally,the disturbance-induced failure mechanism of surrounding rock in deep engineering is clearly elucidated.

Anisotropic strength,deformation and failure of gneiss granite under high stress and temperature coupled true triaxial compression

The anisotropic mechanical behavior of rocks under high-stress and high-temperature coupled conditions is crucial for analyzing the stability of surrounding rocks in deep underground engineering.This paper is devoted to studying the anisotropic strength,deformation and failure behavior of gneiss granite from the deep boreholes of a railway tunnel that suffers from high tectonic stress and ground temperature in the eastern tectonic knot in the Tibet Plateau.High-temperature true triaxial compression tests are performed on the samples using a self-developed testing device with five different loading directions and three temperature values that are representative of the geological conditions of the deep underground tunnels in the region.Effect of temperature and loading direction on the strength,elastic modulus,Poisson’s ratio,and failure mode are analyzed.The method for quantitative identification of anisotropic failure is also proposed.The anisotropic mechanical behaviors of the gneiss granite are very sensitive to the changes in loading direction and temperature under true triaxial compression,and the high temperature seems to weaken the inherent anisotropy and stress-induced deformation anisotropy.The strength and deformation show obvious thermal degradation at 200℃due to the weakening of friction between failure surfaces and the transition of the failure pattern in rock grains.In the range of 25℃ 200℃,the failure is mainly governed by the loading direction due to the inherent anisotropy.This study is helpful to the in-depth understanding of the thermal-mechanical behavior of anisotropic rocks in deep underground projects.

True triaxial behavior of sandy soils under both drained and undrained conditions:A discrete element perspective

An advanced discrete element servomechanism that can simultaneously and independently control the evolution equations of six stress and strain components without introducing severe stress concentration is implemented.Such a comprehensive series of discrete element method simulations of both drained and undrained behavior of transversely isotropic sandy soils are successfully conducted in the true triaxial setting.During the simulation process,the evolution patterns of the load-bearing structure of the granular specimen are tracked using a contact-normal-based fabric tensor.The simulation results show that sandy soils exhibit more significant non-coaxiality between the loading direction and the major principal direction of the fabric tensor under extension than under compression.Therefore,the fabric of the sandy soils under extension has a stronger tendency to evolve toward the loading direction than that under compression,causing a more significant disturbance to the load-bearing structure.Consequently,compared with the extension loading condition,the transversely isotropic specimen under compression exhibits a higher shear strength and stronger dilatancy under drained conditions and a stronger liquefaction resistance under undrained conditions.

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Aspan of twenty-five years,for a company,constitutes a engthy and eventful journey.Twenty-five years ago,a group of oil professionals from the Bureau of Geophysical Prospecting INC (hereinafter referred to as BGP),set foot on the land of Nigeria and embarked on a legendary journey.This is a narrative of resilience,commitment,and heartfelt passion,an inspiring saga that touches the soul.

Shear failure behaviors and degradation mechanical model of rockmass under true triaxial multi-level loading and unloading shear tests

The redistribution of three-dimensional(3D)geostress during underground tunnel excavation can easily induce to shear failure along rockmass structural plane,potentially resulting in engineering disasters.However,the current understanding of rockmass shear behavior is mainly based on shear tests under2D stress without lateral stress,the shear fracture under 3D stress is unclear,and the relevant 3D shear fracture theory research is deficient.Therefore,this study conducted true triaxial cyclic loading and unloading shear tests on intact and bedded limestone under different normal stress σ_(n) and lateral stressσ_(p)to investigate the shear strength,deformation,and failure characteristics.The results indicate that under differentσ_(n)and σ_(p),the stress–strain hysteresis loop area gradually increases from nearly zero in the pre-peak stage,becomes most significant in the post-peak stage,and then becomes very small in the residual stage as the number of shear test cycles increases.The shear peak strength and failure surface roughness almost linearly increase with the increase inσ_(n),while they first increase and then gradually decrease asσ_(p)increases,with the maximum increases of 12.9%for strength and 15.1%for roughness.The shear residual strength almost linearly increases withσ_(n),but shows no significant change withσ_(p).Based on the acoustic emission characteristic parameters during the test process,the shear fracture process and microscopic failure mechanism were analyzed.As the shear stressτincreases,the acoustic emission activity,main frequency,and amplitude gradually increase,showing a significant rise during the cycle near the peak strength,while remaining almost unchanged in the residual stage.The true triaxial shear fracture process presents tensile-shear mixture failure characteristics dominated by microscopic tensile failure.Based on the test results,a 3D shear strength criterion considering the lateral stress effect was proposed,and the determination methods and evolution of the shear modulus G,cohesion c_(jp),friction angleφ_(jp),and dilation angleψjpduring rockmass shear fracture process were studied.Under differentσ_(n)andσ_(p),G first rapidly decreases and then tends to stabilize;cjp,φ_(jp),andψjpfirst increase rapidly to the maximum value,then decrease slowly,and finally remain basically unchanged.A 3D shear mechanics model considering the effects of lateral stress and shear parameter degradation was further established,and a corresponding numerical calculation program was developed based on3D discrete element software.The proposed model effectively simulates the shear failure evolution process of rockmass under true triaxial shear test,and is further applied to successfully reveal the failure characteristics of surrounding rocks with structural planes under different combinations of tunnel axis and geostress direction.

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Experimental and numerical study on dynamic mechanical behaviors of shale under true triaxial compression at high strain rate

High-energy gas fracturing of shale is a novel,high efficacy and eco-friendly mining technique,which is a typical dynamic perturbing behavior.To effectively extract shale gas,it is important to understand the dynamic mechanical properties of shale.Dynamic experiments on shale subjected to true triaxial compression at different strain rates are first conducted in this research.The dynamic stress-strain curves,peak strain,peak stress and failure modes of shale are investigated.The results of the study indicate that the intermediate principal stress and the minor principal stress have the significant influence on the dynamic mechanical behaviors,although this effect decreases as the strain rate increases.The characteristics of compression-shear failure primarily occur in shale subjected to triaxial compression at high strain rates,which distinguishes it from the fragmentation characteristics observed in shale under dynamic uniaxial compression.Additionally,a numerical three-dimensional Split Hopkinson Pressure Bar(3D-SHPB),which is established by coupling PFC3D and FLAC3D methods,is validated to replicate the laboratory characteristics of shale.The dynamic mechanical characteristics of shale subjected to different confining stresses are systematically investigated by the coupling PFC3D and FLAC3D method.The numerical results are in good agreement with the experimental data.

THE ETERNITY OF TRUE FRIENDSHIP EXCLUSIVE INTERVIEW WITH CHINESE AMBASSADOR TO MALAYSIA OUYANG YUJING

China and Malaysia established diplomatic ties fifty years ago.Over the past half-century,the bilateral relationship has made great progress in various fields,delivering tangible benefits to the people of the two countries and making positive contributions to the peace,stability,and prosperity of the region.

数字产业化与产业创新效率——基于TrueFESFA模型的估计

党的二十大强调要加快实施创新驱动发展战略,提高科技投入效能和科技成果转化水平。文章基于数字核心产业的内涵,构建相关指标体系并利用主成分分析法测算了反映地区数字经济核心产业发展水平的指数--数字产业化指数,在分析数字产业化赋能产业创新效率的作用机理的基础上,利用2003-2020年我国省级面板数据,实证检验了数字产业化对高技术产业创新效率的影响。研究发现:1)2003年以来,中国数字产业化指数呈显著上升趋势,但区域发展差异和“数字鸿沟”特征明显。2)数字产业化能够显著提升高技术产业的研发效率和成果转化效率。但这种赋能主要来自于数字技术应用业和数字要素驱动业,数字产品制造业和服务业的影响较小。3)数字产业化的影响具有显著的区域异质性,对西部东北部的研发效率和东中部的成果转化效率的促进效应更大;本地数字核心产业的发展对邻近地区的空间溢出效应较弱。4)基于真实固定效应随机前沿模型(TrueFE SFA)的效率估计表明,2003年以来中国高技术产业的研发效率和成果转化效率均存在显著上升趋势,中西部追赶趋势明显,区域差距不断缩小。最后,根据研究结论提出相关对策建议。

Failure properties of rocks in true triaxial unloading compressive test

Slabbing failure often occurs in the surround rock near a deep underground excavation. The mechanism of slabbing failure is still unclear. In order to reveal the influence of the intermediate principal stress （σ2） on slabbing failure, true triaxial unloading compressive test was carried out based on the stress path of the underground engineering excavation, i.e., unloading the minimum principal stress （σ3）, keeping σ2, increasing the maximum principal stress （σ1）. The initiation and the propagation of slabbing fracture in rock specimens were identified by examining the acoustic emission （AE） and the infrared radiation characterization. The test results show that the failure modes of the granite and red sandstone specimens are changed from shear to slabbing with the increase of σ2. The AE characteristic of rock specimen under low σ2 is swarm type which is the main shock type under high σ2. The infrared radiation properties of rock specimen under different σ2 are also different. The temperature change area is just along the shear fracture such as the uniaxial compression. With the increase of σ2, the temperature change area is planar of rock specimen which proofs that the failure mode of rock specimen turns into slabbing.

MRI单次激发快速自旋回波序列及true FISP序列在前置胎盘并胎盘植入的研究

目的:对比分析半傅立叶采集单发涡轮自旋回波(HASTE)序列、平衡式真实稳态进动快速成像(true FISP)序列在前置胎盘并胎盘植入异常(PIA)中的诊断价值。方法:选取经医院手术病理证实的29例前置胎盘并PIA孕产妇患者,对其均行MRI HASTE序列和true FISP序列检查,对比分析两种序列的图像清晰度及其在前置胎盘、PIA中胎盘突入子宫肌层、子宫结合带中断和胎盘内血管影增多增粗的诊断准确率。结果:HASTE序列和true FISP序列图像清晰度优良率分别为88.9%和72.6%,差异有统计学意义(x^2=4.560,P<0.05)。HASTE序列对前置胎盘、胎盘突入子宫肌层、子宫结合带中断和胎盘内血管影增多增粗的显示率分别为100%、79.5%、58.3%和60.3%;true FISP序列分别为100%、52.7%、40.9%和76.8%;两个序列对胎盘突入子宫肌层、子宫结合带中断和胎盘内血管影增多增粗的显示率比较,差异有统计学意义(x^2=4.380,x^2=6.007,x^2=5.228;P<0.05)。结论:HASTE序列图像清晰度高,对胎盘子宫分界显示较好,true FISP序列对胎盘对比度显示较好,两者结合应用可提高前置胎盘并PIA的诊断准确率。

高斯投影正反算与换带计算TrueBASIC程序

实际测量工作中,经常需要进行高斯投影正、反算与换带计算,如果用手工完成,则计算量庞大,且容易出错。为此,利用TrueBASIC编写了计算程序,只需输入高斯平面坐标,就能在克拉索夫斯基和IUGG-1975参考椭球面上进行高斯投影正、反算和换带计算,还可将计算成果导入CASS中展点,或上传到全站仪内存中使用。

TrueTable在管网水力模型数据转换中的应用

为了提高排水管网属性数据转换的效率、保证数据转换的质量,提出了应用Ture Table软件进行管网数据转换的方法。利用Ture Table软件将管网纵断面图的属性数据由CAD批量输出到Excel,再在Excel中转置后批量输入到GIS数据库,从而实现快速有效的管网属性数据转换。该方法在宁波市鄞州区智能排水信息管理系统的数据库建设中得到了应用。结果表明,该方法简单易行,极大提高了工作效率,保证了数据转换的质量。

3D-SPACE、3D-True FISP序列测量膝关节软骨缺损面积的比较研究

目的 :比较三维可变翻转角快速自旋回波序列(3-dimensional sampling perfection with application optimized contrast using different flip angle evolutions,3D-SPACE)、三维真稳态进动快速成像序列(3D-true fast imaging with steady-state precession,3D-True FISP)测量膝关节软骨缺损面积的准确性。方法:选取38例膝关节软骨缺损患者,在1.5 T MRI仪上对比3D-SPACE、3DTrue FISP序列对膝关节软骨的显示质量,并将2组序列测量的缺损软骨面积(52处)与关节镜测量结果进行比较。结果 :3DSPACE、3D-True FISP序列测量的膝软骨缺损面积平均每膝分别为(2.337±0.868)cm2、(1.423±0.560)cm2。3D-SPACE序列比3D-True FISP序列在对膝关节软骨显示质量上更优(P<0.05),且对软骨缺损面积的显示更准确(P<0.05)。结论 :3D-SPACE序列比3D-True FISP序列能更好地显示膝关节软骨,对膝关节缺损软骨面积测量的准确性更高。

贵州古彝文True Type字体开发与设计

按照"易读性、艺术性和思想性"的字体设计原则,结合古彝文字形特征,设计出结构间架平正、比例协调、圆润饱满、字形清晰的古彝文true type印刷字体,以确保古彝文字符传递信息的准确性和完整性。

某医院True beam直线加速器使用效益分析

该文研究了True beam直线加速器的运营情况,应用盈亏平衡分析方法,分析了True beam直线加速器的经济效益情况,得出了该院True beam直线加速器使用率较高、经济效益显著的结论。从合理配置设备、优化诊疗方式、控制设备维修支出成本等方面提出建议,为医院优化设备资源配置,提高大型设备使用率提供科学决策依据。

针对TrueBeam医用直线加速器的质量控制方法

美国瓦里安公司全新设计的医用直线加速器True Beam的质量控制方法与传统直线加速器的质量控制方法存在一些不同。本文将介绍专门针对True Beam直线加速器的常用的质量控制方法。

True Type中文字符的数控插补

通过提取 True Type字体以直线段及二次 Bezier样条曲线描述的字符轮廓信息 ,可以实现对字符的任意放大、缩小、旋转和变形等特殊效果 ,曲线轮廓可以进行填充。经逼近、节点划分处理后 ,由数控机床进行插补加工。

True-Load载荷反求算法研究与应用

利用True-Load软件提供True-Load载荷反求算法,结合有限元技术从应变测量中获得载荷,对天线基座进行了研究.结果表明,如果想要这种方法取得成效,必须具备两个必要条件:有限元模型与试验对象必须具有较高的一致性;由该软件优化出来的应变片贴片点必须与实际的贴片位置保持一致.研究结果为根据应变反求出载荷这种算法的可靠性提供了一些参考价值.