Damage evolution and strength attenuation characteristics of carbonaceous slate under low velocity dynamic impact

Rock is subjected to impact loading during tunnel and subsurface engineering.For understanding the damage evolution of rock under dynamic impact, mechanical research was performed on the carboniferous slate surrounding the Muzhailing tunnel under different influencing factors based on the Split Hopkinson Pressure Bar(SHPB)experimental system. The results show that:(1)carbonaceous slate exhibits a continuous failure process, which develops more rapidly in the presence of joints;simultaneously, a negative correlation was found between the joint density and the dynamic strength of rock;(2) under different impact velocities and wavelengths, the method of using incident energy to represent the dynamic damage threshold of carbonaceous slate under high in situ stress was proposed based on the kinetic energy theorem, and the damage threshold of carbonaceous slate was calculated to be 53 J;(3) impact times is the most critical core variable and negatively correlated with peak strength and positively correlated with strain rate, maximum strain, and cumulative damage. The carbonaceous slate is subjected to repeated load impacts, which is followed by accumulation of damage, continuous strength attenuation, and internal dominant fracture expansion. In particular,when the samples break, there is only one main rupture surface, which is the most significant difference from the single impact rupture form.

Slater条件、BCQ条件、强CHIP性质和限制域最佳逼近的特征

针对广义限制域的最佳逼近问题,在允许有有限个节点的情况下,运用优化理论中的Slate条件、BCQ条件、强CHIP性质的定义,刻划了Slate条件、BCQ条件、强CHIP性质和最佳逼近的特征之间的关系.

Model test on support scheme for carbonaceous slate tunnel in high geostress zone at high depth

The Muzhailing extra-long highway tunnel and corresponding inclined shafts in Lanzhou,Gansu Province,China passes through structurally complex carbonaceous slate that is under high ground stress.Rationally-designed and effective support is of high importance for achieving safe and efficient tunnel construction.The No.2 inclined shaft of Muzhailing Tunnel was taken as the engineering background prototype,for which,a similar model test was conducted to evaluate the effect of highly pretightened constant resistance(NPR,Negative Poisson’s Ratio)anchor cable support provision to the geologically complex carbonaceous slate at different depths.Two schemes were proposed during testing:one scheme was without support and the second was with asymmetric support from highly pre-tightened constant resistance anchor cable.Digital speckle displacement analysis system and micro-groundstress sensors were employed to measure the deformation and shear stress distribution of the tunnel.The results demonstrated that through the second support scheme,the deformation of the surrounding rock could be effectively ameliorated,while this support scheme was applied on the project site of the No.2 inclined shaft,to explore the rationality of the scheme through field engineering tests.On-site monitoring indicated that the deformation of the surrounding rock was within the reasonable design range and the problem of severe tunnel deformation was effectively controlled.The research methods and related conclusions can be used as a reference for the treatment of large deformation problems in deep-buried soft rock tunnels.

Fracture propagation in sandstone and slateeLaboratory experiments, acoustic emissions and fracture mechanics

Fracturing of highly anisotropic rocks is a problem often encountered in the stimulation of unconventional hydrocarbon or geothermal reservoirs by hydraulic fracturing. Fracture propagation in isotropic material is well understood but strictly isotropic rocks are rarely found in nature. This study aims at the examination of fracture initiation and propagation processes in a highly anisotropic rock, specifically slate. We performed a series of tensile fracturing laboratory experiments under uniaxial as well as triaxial loading. Cubic specimens with edge lengths of 150 mm and a central borehole with a diameter of13 mm were prepared from Fredeburg slate. An experiment using the rather isotropic Bebertal sandstone as a rather isotropic rock was also performed for comparison. Tensile fractures were generated using the sleeve fracturing technique, in which a polymer tube placed inside the borehole is pressurized to generate tensile fractures emanating from the borehole. In the uniaxial test series, the loading was varied in order to observe the transition from strength-dominated fracture propagation at low loading magnitudes to stress-dominated fracture propagation at high loading magnitudes.

Comparison of distribution characteristics of asbestos cement slates in rural and urban regions of Korea

The toxicity of asbestos has been constantly an active research topic.Although asbestos has lots of advantages owing to its stable physicochemical properties and economic characteristics,nations enforce policies prohibiting or limiting its use because of its critical impact on human health.Especially in Korea 96% of imported asbestos are slate construction materials and with the influence of Saemaul movement,thatched roofs have been drastically replaced with slate roofs.Efforts to know the distribution characteristics of extensively used asbestos cement slates and to find out the removal method that suits the distribution characteristics are still in an insufficient state.The purpose of this work was to probe into the distribution of asbestos cement slate buildings in Korea and provide basic data of distribution characteristics for policy making in which consideration of the differences between rural and urban regions is necessary based on findings of the studies so far.It is considered helpful in many ways to solving asbestos cement slate related problems in countries where asbestos usage is increasing even after the 2000s including China.

Temperature effects on the mechanical properties of slates in triaxial compression test

High geothermal temperatures appear to be unfavorable for the construction of tunnels in slate rocks with high overburden. To investigate the mechanical characteristics of slates at various levels of geothermal temperature, conventional triaxial compression tests at different levels of confining stress were carried out at 4 different temperatures from 20℃ to 120℃. The obtained results show high confining pressures weaken the thermal effects on rock mechanical characteristics while higher temperatures enhance the effect of confining pressure.At higher levels of confining stress the thermal effects on the rock strength characteristics decrease. The higher the temperature, the larger is the effect of confining pressure on the mechanical characteristics of the slate. Increase of temperature leads to a decrease of the peak strength but increases the deformability and ductility of the slate, the thermo effect on the peak strength and Poisson's ratio is larger than on the elastic modulus. Higher temperatures reduce the shear strength of slate, the decrease is mainly caused by a decrease of the cohesion. In general, the slate samples fail in shear failure.

Alkali-Silica Reactivity and Strength of Mortars with Expanded Slate, Expanded Glass or Perlite

Lightweight aggregates are increasingly used in concrete construction. They reduce concrete selfweight furnishing a structural advantage. In contrast, the mechanical properties and durability of lightweight concrete can become the governing factor on lightweight aggregate replacement ratios. Alkali-Silica Reactison (ASR) and compressive strength of mortar samples with expanded slate, expanded glass or perlite, covering the spectrum of internal porosity and weight of lightweight aggregates, were evaluated. Scanning electron microscopy was utilized to evaluate the contribution of the aggregates’ porosity and chemical composition in inhibiting ASR. Perlite, owing to its highly porous microstructure and lower matter excelled in ASR expansion while chemical composition and denser microstructure of the heavier expanded slate resulted in more signified late ASR expansion and higher compressive strength. An attempt in visual inspection of ASR attack of alkali metal ions on silica-rich expanded glass using an ultra-accelerated exposure to sodium hydroxide solution was made.

高地应力-化学侵蚀耦合作用下炭质板岩蠕变试验及非线性蠕变损伤模型

为克服高程障碍并降低施工风险,可采用长大隧道穿越崇山峻岭,但这些隧道往往处于深埋高地应力环境,并受到化学侵蚀影响。为了解决此问题,以丽江—香格里拉炭质板岩大变形隧道为研究对象,采用室内试验和理论推导,研究深埋炭质板岩隧道受化学侵蚀作用下的围岩变形特性。在Poyting-Thomson体蠕变体的基础上,根据模型元件的力学特性,叠加了损伤元件、化学损伤元件和非线性元件,提出高地应力-化学侵蚀耦合作用下炭质板岩非线性蠕变损伤本构关系。研究结果表明:1)炭质板岩试样受化学侵蚀影响显著,侵蚀90 d试样所产生的轴向蠕变应变为侵蚀0 d试样的2.02倍,侵蚀60 d试样所产生的径向蠕变为侵蚀0 d试样的1.85倍;2)受侵蚀的炭质板岩试样在三轴压缩状态下破裂以斜向贯通裂隙为主,并产生一定的滑移错动裂隙,且沿轴线的拉伸劈裂破坏受围压作用抑制明显,未产生竖向贯通裂隙。

超高沥青混凝土心墙坝砂板岩堆石料试验研究

开展了超高沥青混凝土心墙坝砂板岩堆石混合料的试验研究。研究结果表明:随板岩含量的提升和孔隙率的增大,应力应变曲线软化特性趋弱硬化特性增强、剪切峰值降低,剪切过程中的体变增大且剪胀现象减弱,相应的线性强度c,φ和非线性强度指标φ_(0),Δφ均降低,邓肯模型参数K与Kb减小;建立了同时可反映孔隙率、板岩含量的强度指标及邓肯模型参数经验公式,能较高精度地预测不同板岩含量、不同孔隙率砂板岩堆石混合料的工程力学特性;板岩含量是影响渗透性能的重要因素,随板岩含量的提升渗透系数降低,工程建设中对于含板岩的堆石料应关注排水设计。

基于TIMA全扫描技术分析白云鄂博矿床板岩特征

内蒙古白云鄂博矿床是世界最大的稀土矿之一,其矿床内部及周边出露有大量板岩并且板岩具多种颜色(黑色、黄绿色、深绿色等),板岩的研究程度相对较低。为了厘定板岩的矿物组成,本次研究应用玻片全扫描、TIMA(TESCAN Intergrated Mineral Analyzer)全扫描、电子探针、LA-ICP-MS(激光剥蚀电感耦合等离子体质谱仪)对其矿物组合特征和成分特征进行分析。玻片全扫描和TIMA全扫描比对表明板岩虽颜色各异,但主要由正长石组成,正长石体积比可达86.37%;在白云鄂博矿床范围内正长石有隐晶质、单晶集合体和单晶三种赋存形态。电子探针分析表明正长石中SiO_(2)为59.44%~64.76%、Al_(2)O_(3)为16.89%~19.73%、K_(2)O为13.96%~17.90%,K_(2)O/Na_(2)O为15.86~45.71;环带结构正长石K_(2)O的含量较其它正长石较低,K_(2)O/Na_(2)O为15.86~20.85。LA-ICP-MS分析表明正长石中Ba含量为700.08×10^(-6)~47 606.91×10^(-6),其它微量元素和稀土元素含量很少且差异不大。板岩整体颜色和正长石色带均具有随着Ba含量增多而颜色变深的现象,因此正长石的颜色深浅与Ba含量多少呈正相关关系。

寒区露天矿板岩冻融力学特性及边坡稳定性研究

为了探究寒区板岩边坡在冻融条件下的力学参数劣化规律及其失稳机理,通过室内冻融循环力学试验,并基于广义Hoek-Brown强度准则计算岩体内聚力和内摩擦角随冻融循环次数的衰减规律,以此修正未考虑冻融损伤的白云鄂博南帮内聚力和内摩擦角块体模型,实现南帮岩体力学参数的时空演化表征,最后通过数值模拟分析白云鄂博铁矿主矿区南帮边坡在冻融效应下的循序破坏机理。结果表明:经20次冻融循环后,矽质板岩、云母化板岩、碳化板岩、断层岩内聚力降低率分别为21.64%、22.66%、28.09%、28.53%,内摩擦角降低率分别为12.76%、14.72%、19.37%、21.35%;在冻融效应下,南帮边坡稳定系数由1.19逐渐降至0.92,1650~1570 m区域剪应变逐渐增大,最终滑体于1570 m平台滑移剪出。

东川泥石流源区板岩表生细菌生物多样性

选取云南省昆明市蒋家沟泥石流物源区低风化(LT组)和高风化(MT组)岩石样品以及流通区岩石(F组)样品为研究对象,利用细菌16Sr RNA基因序列高通量测序技术研究岩石表生细菌群落结构与多样性,并通过冗余分析(RDA)探究岩石样品理化性质对岩石表生细菌群落变异的驱动作用。结果表明:该区域岩石属于板岩;LT组岩石样品细菌群落α多样性指数(包括Faith’s系统发育多样性指数(PD)、Shannon指数、Chao1指数和每个样品具有的独特OTU数目)均显著高于MT组和F组岩石样品,且α多样性指数与板岩有机质含量呈显著正相关(r=0.80~0.91,P<0.01)。该区域板岩表生细菌的优势种群包括Firmicutes(厚壁菌门,相对丰度66%)、Proteobacteria(变形菌门,15%)和Actinobacteria(放线菌门,11%)。PCoA和UPMGA聚类分析结果显示3组岩石样品的表生细菌群落存在显著差异。Firmicutes菌门的相对丰度由高到低分别为MT组>F组>LT组,Actinobacteria和Proteobacteria菌门的相对丰度由高到低分别为LT组>F组>MT组。RDA结果显示板岩理化性质解释了该区域岩石样品93%的群落变异,其中有效态Ca含量是板岩表生细菌群落结构变异的最主要驱动因素,解释了36.6%的群落结构变异。相关性结果表明优势菌门(除Firmicutes外)的相对丰度均与有效态Si和Mn含量呈显著正相关,而与有效态Ca含量呈显著负相关。本研究进一步丰富了岩石表生微生物物种资源及表生微生物群落变化的驱动机制。

富水环境下强–中风化硅质板岩吸水特性及微观演化规律

为探讨富水环境下强–中风化硅质板岩的吸水特性及吸水过程微观演化规律,以玉溪至楚雄段国家高速公路旧寨隧道中的强–中风化硅质板岩为研究对象,开展浸水试验、电镜扫描试验和X射线衍射试验。试验结果表明:富水环境下强–中风化硅质板岩吸水过程可分为急速吸水阶段(0~2 h)、缓速吸水阶段(2~24 h)和平衡吸水阶段(超过24 h)等3个阶段。急速吸水阶段,岩石结构变得较为松散、孔隙及微裂隙逐步延伸发展;缓速吸水阶段,胶结物溶解、脱落,岩石结构进一步松散、孔隙及裂隙进一步发育,逐渐形成显著的贯穿性裂隙;动态平衡吸水阶段,岩石结构松散程度、孔隙及裂隙发育程度基本达到稳定状态。强–中风化硅质板岩主要矿物组成为石英和黏土矿物,随着浸水试验的进行,石英相对含量增加,黏土矿物含量不断减小;伊利石、伊蒙混层等黏土矿物遇水极不稳定,既能与水发生化学反应,转化成石英和其他黏土矿物,又能与水发生物理反应,表现出膨胀、破碎和分解等特性。研究成果可为开展强–中风化硅质板岩吸水软化特性的理论研究提供参考。

高应力炭质板岩隧道开挖支护结构受力评价研究

为探究高应力下炭质板岩隧道开挖过程中围岩位移、支护结构内力变化规律,依托渭武高速木寨岭公路隧道,采用有限差分软件FLAC3D建立三台阶七步开挖法下炭质板岩隧道的数值模型,提出强、中、弱3种支护方案;分析开挖距离对围岩位移、支护结构内力等因素的影响,并对支护设计参数合理性评价。研究结果表明:开挖过程中围岩累计沉降和收敛变形量比较:强支护<中支护<弱支护;开挖相同距离下,随着支护强度上升,支护提供的弹性抗力越强,围岩沉降和收敛变形减小;以强支护为例,支护结构轴力呈现先增大后减小的趋势,最终轴力不断上升但趋势变缓的特征,开挖距离50 m趋于稳定;支护设计参数评价时,开挖距离(50 m)结束,强、中、弱3种方案钢架受压安全系数最小值分别为3.903、3.718、3.264,#1拱顶处强支护钢架较喷射混凝土先破坏,混凝土安全系数最小值分别为3.491、2.987、2.666,#2左拱腰处喷射混凝土较钢架先破坏,故选择中支护方案,材料I25b×C25、初衬厚度26 cm、钢架距离0.8 m。研究成果可为类似软岩隧道开挖和支护结构的设计提供一定参考。

Model test of the mechanism underpinning water-and-mud inrush disasters during tunnel excavation in sandstone and slate interbedded Presinian strata

Water-and-mud inrush disasters have become a major challenge in underground engineering for the construction of tunnels in sandstone and slate interbedded Presinian strata.Disaster prediction and prevention rely in part on realistic modeling and observation of the disaster process,as well as the identification and examination of the underlying mechanisms.Based on the geological conditions and the historical records of the Xinping Tunnel on the China–Laos Railway,an engineering geological model of the water-and-mud inrush was established.A physical model test that accurately reproduced water-and-mud inrush during tunnel excavation in sandstone and slate interbedded strata was also carried out.Then,testing was conducted that examined the stress and strain,seepage pressure,and high-leakage flow of the surrounding rock.The results indicated that the water-and-mud inrush proceeded through three stages:seepage stage,high-leakage flow stage,and attenuation stage.In essence,the disaster was a catastrophic process,during which the water-resistant stratum was reduced to a critical safety thickness,a water-inrush channel formed,and the water-resistant stratum gradually failed under the influence of excavation unloading and in situ stress–seepage coupling.Parameters such as the stress and strain,seepage pressure,and flow of the surrounding rock had evident stage-related features during water-and-mud inrush,and their variation indicated the formation,development,and evolution of the disaster.As the tunnel face advanced,the trend of the stress–strain curve of the surrounding rock shifted from sluggish to rapid in its speed of increase.The characteristics of strain energy density revealed the erosion and weakening effect of groundwater on the surrounding rock.The seepage pressure and the thickness of the water-resistant stratum had a positive linear relationship,and the flow and thickness a negative linear relationship.There was a pivotal point at which the seepage pressure changed from high to low and the flow shifted from low to high.The thickness of the water-resistant stratum corresponding to the pivotal point was deemed the critical safety thickness.

文化记忆理论下传统村落建筑的保护研究——以镇宁高荡村布依族石板房为例

石板房作为布依族传统建筑的代表,肩负着传统村落民族文化记忆传承的重担。随着城镇化的快速发展,传统村落面临文化记忆遗忘危机。在乡村振兴的大背景下,以石板房为传承民族文化记忆的符号,深入理解石板建筑的文化与价值,借助文化记忆理论提出石板房的保护与创新路径,传承与重构传统村落建筑的文化记忆,可为传统村落文化的可持续发展提供理论和实践指导。

考虑层理倾角的炭质板岩蠕变损伤本构模型

针对层状岩体的各向异性特征,以炭质板岩为研究对象,开展不同层理倾角炭质板岩的蠕变力学试验.基于蠕变试验结果,建立可以描述不同层理倾角炭质板岩加速蠕变的改进Nishihara非线性损伤蠕变本构模型,推导该模型的一维、三维本构方程.研究结果表明,炭质板岩的蠕变过程存在明显的应力阈值.当应力小于阈值时,炭质板岩只发生衰减蠕变;当应力达到或大于阈值时,开始发生稳态蠕变;当应力达到或超过破坏应力时,炭质板岩发生加速蠕变并发生蠕变破坏.模型参数反演辨识结果表明,改进Nishihara蠕变模型能够很好地描述炭质板岩的整个蠕变过程.基于参数辨识结果,对模型参数与围压和层理倾角的关系进行探讨,得到损伤参数c与层理倾角的关系式,分析损伤参数d与黏滞系数对加速蠕变阶段的影响.

炭质板岩横观各向同性强度准则及参数辨识方法

为探究层理状岩石的横观各向同性力学特性,以炭质板岩为研究对象,通过室内试验和理论分析对其强度准则和参数辨识方法进行研究。首先,对水平与垂直层理岩样开展不同围压的常规单、三轴压缩试验,探讨不同应力状态炭质板岩的强度特性与破坏模式。其次,对比分析试验结果,建立适用于炭质板岩的横观各向同性弹塑性本构模型;基于Pariseau强度准则确定模型的屈服函数,用以描述炭质板岩不同方向的强度特性;基于相关联流动法则确定模型的塑性势函数,用以描述炭质板岩塑性变形阶段的流动方向。在各向同性假定下,该模型可退化为描述各向同性岩土材料的Drucker-Prager模型。最后,提出模型参数辨识方法,即通过常规三轴压缩试验和经验公式求解弹性参数;通过基于Duveau数值计算程序的最小二乘法常规三轴试验和直线型Mohr-Coulomb准则确定岩样的抗压、抗拉和剪切强度,再代入所推导公式求解塑性参数;结合试验结果验证了所提横观各向同性强度准则的合理性。结果表明:不同围压的水平岩样的抗压强度均高于垂直岩样,且抗压强度随着围压的增大基本呈线性增大;炭质板岩在压缩过程中多呈脆性破坏,水平层理岩样呈滑移-剪切破坏,垂直层理岩样呈张拉-剪切破坏。

冻融循环作用下板岩力学及表观特性劣化研究

为确保川西高原大型露天采场高陡板岩质边坡的稳定性,有必要对不同介质中冻融循环作用下高寒地区板岩劣化损伤特性的发展规律展开研究。将板岩分别置于空气和水中进行冻融试验,在达到相应循环次数后测定试样质量、饱和含水率和纵波波速,进行单轴抗压强度测试,并观察岩样宏观形貌,综合分析其在冻融作用下相关力学特性的劣化规律。结果表明:冻融作用下板岩各力学参数表现出明显的劣化效应,随着暴露在冻融环境中时间的增长,试样质量损失速率、吸水速率波动上升,纵波波速、单轴抗压强度和弹性模量呈下降趋势,饱和含水率曲线呈负指数增大;岩样因温度变化自身产生的胀缩、内部黏土矿物吸水聚集膨胀是板岩破坏的主要原因;随着冻融循环次数的增加,试样劣化速率减缓,最后趋于稳定;水分是板岩劣化的重要因素,相同冻融循环次数下,水中进行冻融循环的岩样劣化程度更大,劣化速度更快。