A method to interpret fracture aperture of rock slope using adaptive shape and unmanned aerial vehicle multi-angle nap-of-the-object photogrammetry

The aperture of natural rock fractures significantly affects the deformation and strength properties of rock masses,as well as the hydrodynamic properties of fractured rock masses.The conventional measurement methods are inadequate for collecting data on high-steep rock slopes in complex mountainous regions.This study establishes a high-resolution three-dimensional model of a rock slope using unmanned aerial vehicle(UAV)multi-angle nap-of-the-object photogrammetry to obtain edge feature points of fractures.Fracture opening morphology is characterized using coordinate projection and transformation.Fracture central axis is determined using vertical measuring lines,allowing for the interpretation of aperture of adaptive fracture shape.The feasibility and reliability of the new method are verified at a construction site of a railway in southeast Tibet,China.The study shows that the fracture aperture has a significant interval effect and size effect.The optimal sampling length for fractures is approximately 0.5e1 m,and the optimal aperture interpretation results can be achieved when the measuring line spacing is 1%of the sampling length.Tensile fractures in the study area generally have larger apertures than shear fractures,and their tendency to increase with slope height is also greater than that of shear fractures.The aperture of tensile fractures is generally positively correlated with their trace length,while the correlation between the aperture of shear fractures and their trace length appears to be weak.Fractures of different orientations exhibit certain differences in their distribution of aperture,but generally follow the forms of normal,log-normal,and gamma distributions.This study provides essential data support for rock and slope stability evaluation,which is of significant practical importance.

Effects of fracture distribution and length scale on the equivalent continuum elastic compliance of fractured rock masses

Fracture systems have strong influence on the overall mechanical behavior of fractured rock masses dueto their relatively lower stiffness and shear strength than those of the rock matrix. Understanding theeffects of fracture geometrical distribution, such as length, spacing, persistence and orientation, isimportant for quantifying the mechanical behavior of fractured rock masses. The relation betweenfracture geometry and the mechanical characteristics of the fractured rock mass is complicated due tothe fact that the fracture geometry and mechanical behaviors of fractured rock mass are stronglydependent on the length scale. In this paper, a comprehensive study was conducted to determine theeffects of fracture distribution on the equivalent continuum elastic compliance of fractured rock massesover a wide range of fracture lengths. To account for the stochastic nature of fracture distributions, threedifferent simulation techniques involving Oda＇s elastic compliance tensor, Monte Carlo simulation （MCS）,and suitable probability density functions （PDFs） were employed to represent the elastic compliance offractured rock masses. To yield geologically realistic results, parameters for defining fracture distributionswere obtained from different geological fields. The influence of the key fracture parameters andtheir relations to the overall elastic behavior of the fractured rock mass were studied and discussed. Adetailed study was also carried out to investigate the validity of the use of a representative elementvolume （REV） in the equivalent continuum representation of fractured rock masses. A criterion was alsoproposed to determine the appropriate REV given the fracture distribution of the rock mass.

Coupled hydro-mechanical effect of a fractured rock mass under high water pressure

To explore the variation of permeability and deformation behaviors of a fractured rock mass in high water pressure,a high pressure permeability test（HPPT）,including measuring sensors of pore water pressure and displacement of the rock mass,was designed according to the hydrogeological condition of Heimifeng pumped storage power station.With the assumption of radial water flow pattern in the rock mass during the HPPT,a theoretical formula was presented to estimate the coefficient of permeability of the rock mass using water pressures in injection and measuring boreholes.The variation in permeability of the rock mass with the injected water pressure was studied according to the suggested formula.By fitting the relationship between the coefficient of permeability and the injected water pressure,a mathematical expression was obtained and used in the numerical simulations.For a better understanding of the relationship between the pore water pressure and the displacement of the rock mass,a 3D numerical method based on a coupled hydro-mechanical theory was employed to simulate the response of the rock mass during the test.By comparison of the calculated and measured data of pore water pressure and displacement,the deformation behaviors of the rock mass were analyzed.It is shown that the variation of displacement in the fractured rock mass is caused by water flow passing through it under high water pressure,and the rock deformation during the test could be calculated by using the coupled hydro-mechanical model.

Thermal effects on clay rocks for deep disposal of high-level radioactive waste

Thermal effects on the Callovo-Oxfordian and Opalinus clay rocks for hosting high-level radioactive waste were comprehensively investigated with laboratory and in situ experiments under repository relevant conditions:(1) stresses covering the range from the initial lithostatic state to redistributed levels after excavation,(2) hydraulic drained and undrained boundaries, and(3) heating from ambient temperature up to 90℃-120℃ and a subsequent cooling phase. The laboratory experiments were performed on normal-sized and large hollow cylindrical samples in various respects of thermal expansion and contraction, thermally-induced pore water pressure, temperature influences on deformation and strength, thermal impacts on swelling, fracture sealing and permeability. The laboratory results obtained from the samples are consistent with the in situ observations during heating experiments in the underground research laboratories at Bure and Mont-Terri. Even though the claystones showed significant responses to thermal loading, no negative effects on their favorable barrier properties were observed.

Size effects in the uniaxial compressive properties of 3D printed models of rocks:an experimental investigation

Transparent physical models of real rocks fabricated using three-dimensional(3D)printing technology are used in photoelas-tic experiments to quantify the evolution of the internal stress and deformation fields of rocks.Therefore,they are rendered as an emerging powerful technique to quantitatively reveal the intrinsic mechanisms of rock failure.The mechanical behav-ior of natural rocks exhibits a significant size effect;however,limited research has been conducted on whether transparent physical models observe similar size effects.In this study,to make the transparent printed models accurately demonstrate the mechanical behavior of natural rocks and reveal the internal mechanism of the size effect in rock mechanical behavior,the size effect in 3D printed models of fractured and porous rocks under uniaxial compressive loading was investigated.Transparent cylindrical models with different sizes that contained different fractured and porous structures were printed using the fracture and porous characteristics extracted from natural coal and sandstone.The variation in uniaxial compres-sive strength and elastic modulus of fractured and porous models for increasing model sizes were obtained through uniaxial compression experiments.Finally,the influence of internal discontinuous structural features,such as fractures and pores,on the size effect pertaining to the mechanical behavior of the model was analyzed and elaborated by comparing it with the mechanical properties of the continuous homogeneous model without fractures and pores.The findings provided support and reference to analyze the size effect of rock mechanical behavior and the effect of the internal discontinuous structure using 3D printed transparent models.

The influencing factors and mechanisms of the electromagnetic radiation during rock fracture

Based on the laboratory experiments this paper presented that the primary influence factors about the electromagnetic radiation during rock fracture are the rock mechanics characters and mineral components. The brittle samples and samples contained quartz, pyrite, chalopyrite produce electromagnetic radiation easily. There are three fracture radiation effects. The crystal fracture effect produces the high frequency electromagnetic signals, the piezoelectric effect produces low frequency signals and the natural semiconductor effect produces middle frequency signals possessed distinct wave shapes.

A simple method for determining independent fracture toughness and tensile strength of rock

This paper develops a model that only requires two sets of small-size rock specimens with the ratio of the structural geometry parameter maximum to minimum ae,max:ae,min≥3:1 to determine the rock fracture and strength parameters without size effect and predict the actual structural performance of rock.Regardless of three-point-bending,four-point-bending,or a combination of the above two specimen types,fracture toughness KICand tensile strength ftof rock were determined using only two sets of specimens with ae,max:ae,min≥3:1.The values KICand ftwere consistent with those determined using multiple sets of specimens.The full structural failure curve constructed by two sets of small-size specimens with ae,max:ae,min≥3:1 can accurately predict large-size specimens fracture failure,and±10%upper and lower limits of the curve can encompass the test results of large-size specimens.The peak load prediction curve was constructed by two sets of specimens with ae,max:ae,min≥3:1,and±15%upper and lower limits of the peak load prediction curve can cover the small-size specimen tests data.The model and method proposed in this paper require only two sets of small-size specimens,and their selection is unaffected by the specimen type,geometry,and initial crack length.

Numerical study on rock fracture and vibration due to blasting

Fracture and ground vibration of rock subjected to different decoupling decked charges are investigated based on the numerical simulation. The dynamic pressure value is studied, which demonstrates that simulation of fracture zone is feasible. Attenuation index of dynamic pressure is 2.06, 2.05 and 1.93 for air, water and sand intervals respectively. The small attenuation of sand in- terval results in the large ground vibration. The predicted vertical vibration waveform and peak parti- cle velocities （PPV） in far-field are in agreement with the monitoring results. The results show that the air and water decked charges can improve the effect of rock fracture in near-field and reduce ground vibration in far-field.

A generalized nonlinear three-dimensional failure criterion based on fracture mechanics

Based on fracture mechanics theory and wing crack model,a three-dimensional strength criterion for hard rock was developed in detail in this paper.Although the basic expression is derived from initiation and propagation of a single crack,it can be extended to microcrack cluster so as to reflect the macroscopic failure characteristic.Besides,it can be derived as HoekeBrown criterion when the intermediate principal stress σ_(2) is equal to the minimum principal stress σ_(3)(Zuo et al.,2015).In addition,the opening direction of the microcrack cluster decreases with the increase of the intermediate principal stress coefficient,which could be described by an empirical function and verified by 10 kinds of hard rocks.Rock strength is influenced by the coupled effect of stress level and the opening direction of the microcrack clusters related to the stress level.As the effects of these two factors on the strength are opposite,the intermediate principal stress effect is induced.

基于液电效应的高压电脉冲岩体致裂特征及机理

基于液电效应的高压电脉冲致裂技术是一种新型的岩体致裂技术,具有安全高效、绿色环保、能量可控等特点,在煤矿井下围岩应力调控方面拥有广阔的应用前景。由于井下岩体往往处在较为复杂的应力环境,为深入研究该技术在井下不同围岩应力环境下对坚硬岩体的致裂效果,通过LS-DYNA软件对基于RHT损伤本构模型建立的岩石试样进行高压电脉冲岩体致裂数值模拟试验,对岩体内部的损伤和有效应力演化过程进行采集,分析岩体的致裂特征及其裂缝扩展机理,通过数值模拟弥补在室内试验中因放电过程快、电磁干扰大而导致的致裂过程中岩体内部难以有效监测的问题。利用自主研发的高压电脉冲岩体致裂试验平台,开展了不同围岩应力条件下的高压电脉冲岩体致裂试验,通过获得的岩体表面破裂特征验证数值模拟结果的可靠性。获得以下结论:①基于RHT本构模型建立了LS-DYNA高压电脉冲岩体致裂数值模型,根据炸药爆破与高压电脉冲的能量等效关系,构建了高压电脉冲数值模拟等效参数。通过实验室试验与数值模拟结果进行对比,验证了数值模型与等效参数的可靠性;②对试样上表面裂纹扩展情况进行分析,发现裂纹会向最大压初始应力方向偏转。在此过程中,裂纹总长度先是逐渐减小。当所有裂纹与最大初始压应力夹角均小于45°时,裂纹总长度开始逐渐增大;③通过数值模拟,发现在致裂初期,高压电脉冲放电产生的动态应力远大于围岩应力,对试样的破坏起主导作用。随着动态应力在传播过程中的快速衰减,初始围岩应力与动态应力的大小逐渐接近,并最终由初始围岩应力主导裂纹的萌生与扩展。研究结果表明,围岩应力是决定岩体裂缝发育和扩展特征的重要因素,特别是对裂缝的扩展方向有显著影响,在采用高压电脉冲致裂技术对深部岩体进行致裂时,应考虑岩体所处应力状态,科学制定致裂方案,以实现对岩体的高效致裂。

基于三维裂隙网络的岩体剪切特性尺寸效应分析

为研究复杂裂隙岩体剪切特性的尺寸效应,以西藏怒江松塔水电站PDC3平硐为例,在现场采集裂隙信息的基础上,基于颗粒流PFC3D软件通过统计学方法及蒙特卡洛原理生成三维裂隙网络,构建等效岩体,进行大尺度直剪模拟试验得到裂隙岩体的抗剪强度、内摩擦系数及内聚力,分别研究其尺寸效应并确定不同参数下的REV尺寸,继而对相关参数和试样尺寸分别进行非线性回归拟合,探究其函数关系。结果表明:抗剪强度、内聚力及内摩擦系数随着试样尺寸的变化而趋于稳定,且不同参数得到的REV大小不同;综合分析不同参数的REV尺寸,得出研究区裂隙岩体的剪切特性REV尺寸为11 m×11 m×11 m;通过函数关系拟合,抗剪强度、内聚力和内摩擦系数与试样尺寸之间均存在指数函数关系。该成果为研究复杂裂隙岩体的力学REV以及合理确定力学参数提供了依据。

天然岩石裂隙面粗糙度尺寸效应及方向性研究

为探究岩石裂隙粗糙面尺寸效应及方向性,对立方定律修正公式中表征天然岩石粗糙裂隙性质的粗糙度修正系数C进行分析。采用高精度3D扫描仪扫描天然岩石样品,得到其表面粗糙度数据,结合网络公开发布的高精度粗糙岩石裂隙CT扫描数据,生成空间坐标,采用公式法和数值法计算分析粗糙度修正系数C。根据公式法计算结果得出粗糙度具有尺寸效应;根据数值法结果得出粗糙度具有方向性,且粗糙度方向性可使用张量形式来表达。通过计算粗糙裂隙JRC值、表面及隙宽分形维数对研究结果进行印证,证明裂隙面粗糙度具有尺寸效应和各向异性。进一步研究发现:可采用粗糙度修正系数张量或粗糙度张量结合裂隙平均隙宽,形成单裂隙渗透张量,量化复杂粗糙裂隙网络中模型的粗糙面。

多工作面连续开采地表沉陷与强矿震联动响应规律

深部矿井多工作面大空间开采导致大能量强矿震事件频发,同时地表伴随剧烈的下沉变形,掌握具体地层条件下地表移动与强矿震时空分布响应规律对于深部矿井动力灾害防控意义重大。以兖州矿区东滩煤矿63_(上)04,63_(上)05,63_(上)06工作面为工程背景,基于关键层理论与复合破断原理,对东滩煤矿复杂地层进行了科学划分,现场实测了深井厚硬岩层下多工作面开采地表沉降规律及强矿震时空分布特征,分析了多工作面连续开采下关键层组运移演化规律,揭示了关键层组破断演化、地表沉陷规律与大能量强矿震分布的联动效应。研究结果表明:(1)东滩煤矿六采区地层可以划分出4个关键层组,每个关键层组包含一层关键层和若干坚硬岩层,相比单一关键层,关键层组发生复合破断时的矿震能量更高、破断步距更大,对上覆岩层的运移及地表下沉影响也更为突出。(2)地表沉陷观测结果显示,63_(上)04,63_(上)05工作面开采结束,地表下沉系数分别为0.189,0.458;63上06工作面当前已开采808.29 m,地表下沉系数为0.492,受多关键层组地质赋存特征影响,东滩煤矿六采区地表下沉系数远小于兖州矿区其他矿井平均地表下沉系数(0.75~0.85),地表未达到充分采动,下沉趋势为:无明显下沉–下沉空间显著–下沉空间逐渐增大。(3)矿震监测结果显示,63上04工作面开采时,大能量强矿震事件主要集中在低位关键层组Ⅰ,Ⅱ层位,随着多工作面连续开采,大能量强矿震逐渐向高位转移,逐渐集中至关键层组Ⅱ,Ⅲ层位。(4)由地表沉陷及大能量强矿震实测数据可知,东滩煤矿六采区多工作面连续开采下关键层组复合破断覆岩结构呈“断悬”结构–“铰接”结构交替上升,逐层演化过程验证了覆岩运动、地表沉陷及大能量强矿震3者之间存在一定的联动效应。研究成果可对类似工程地质条件下多关键层组复合破断研究及大能量强矿震预控提供一定参考。

注浆加固在破碎煤岩体中的应用与研究

破碎煤岩体注浆加固对控制围岩稳定具有重大意义,分层注浆效果检验是检测注浆工程合格的重要环节。通过设计分层注浆方案,选择合理的注浆材料、注浆压力以及注浆量,从浆液填充率、钻孔电视探测、分段注水、巷道检测4个方面进行注浆效果检验。结果表明,分层注浆工艺裂缝的浆液填充率可达90%以上,孔隙率低于10%,填充效果优于传统注浆工艺。

Experimental study on influencing factors of acid-fracturing effect for carbonate reservoirs

Acid fracturing treatment is the key technique for stimulation and stable production in carbonate reservoirs.In order to improve the carbonate reservoirs acid fracturing effect,in this paper,with a large number of experiments as the main research methods,study on influencing factors of acidfracturing effect for carbonate reservoirs from increase the effective distance of living acid,increase acid corrosion eched fracture conductivity,reduce the acid fluid loss,etc.The effective distances of live acid calculated with reacted acid limitations measured in different acid systems are quite different from those calculated according to previous standard.Fracture conductivity is one of the key parameters that affects acid fracturing effects,but it's difficult to be predicted accurately due to the strong randomness of acid-rock reaction as well as various influence factors.Analyses of the impacts on fracture conductivity resulted from the rock embedment intensity,closure stress,acid dosage,rock-acid contact time,acid fluid loss,acid pumping rate through self-developed small-core fracture capacity test instrument.Fluid loss during acid fracture can be well controlled by thickened liquid as well as solid particles,but formation damage occurs inevitably.Foamed acid is a specific fluid with high viscosity,low fluid loss,small friction resistance,good retarding property,strong fracture making ability,easy flowback and low damage,which is an ideal acid system for low pressure and low permeability carbonate reservoirs.In this paper,the theoretical study on percolation mechanism and fluid-loss control mechanism of foam(acid)in porous medium are presented with the help of visual microscopic model fluid drive unit.

基于DA-DE-SVM智能模型的煤岩体SC-CO_(2)压裂效果预测

煤岩体压裂效果是超临界CO_(2)(SC-CO_(2))压裂工程设计的主要依据。为准确预测煤岩体SC-CO_(2)压裂效果,基于多孔相向裂缝动态扩展模拟,筛选确定影响煤岩体SC-CO_(2)压裂效果的6个地质因素和4个施工因素,提出了一种集成支持向量机(SVM)、蜻蜓算法(DA)、差分进化算法(DE)的混合人工智能模型,利用支持向量机构建SC-CO_(2)压裂效果与其影响因素之间的关系,并利用蜻蜓算法、差分进化算法联合优化支持向量机的超参数。以相关系数、均方根误差、平均绝对误差为评价指标对混合人工智能模型性能进行了评估,并采用MIV方法对模型输入变量进行了敏感性分析,结果表明:本文提出的DA-DE-SVM智能模型能很好预测煤岩体SC-CO_(2)压裂效果,其训练集的R值为0.9572,测试集的R值为0.9316。SC-CO_(2)压裂效果影响因素的重要程度从高到低依次为:相邻压裂钻孔水平距离>垂直地应力>压裂液注入速率>相邻压裂钻孔垂直距离>煤体抗拉强度>水平地应力>压裂液温度>煤体渗透系数>煤体初始孔隙压力>煤体弹性模量。研究成果可为SC-CO_(2)压裂工程参数优化设计及工程应用提供重要指导。

变开度岩体裂隙多相渗流实验与有效渗透率模型

岩体裂隙的有效渗透率是描述岩体非饱和或多相渗流的关键参数,而裂隙开度是影响有效渗透率的重要因素.通过自主研发的粗糙裂隙多相渗流可视化实验平台,针对天然岩体裂隙复制而成的裂隙模型开展变开度条件下的多相渗流可视化实验,研究开度变化对多相渗流流动结构以及有效渗透率的影响.研究表明:非湿润相流体运动通道,在低流量比条件下呈现出气泡流流动结构,而在高流量比条件下呈现较为稳定的通道流流动结构.随着开度的增加,非湿润相流动通道的分支变少、等效宽度增加,两相流体的有效渗透率均增大,流动结构趋于稳定.可视化结果还阐明了柱塞流流动结构下,两相流体交替占据裂隙空间的竞争机制:当非湿润相流体通道由连续转变为不连续时,裂隙进出口压差显著增加;反之,当该通道由不连续转变为连续时,压差显著减小.最后,基于分形理论以及渗透率统计建模方法,建立了考虑开度效应的岩体裂隙多相渗流有效渗透率理论模型,并通过实验测定的有效渗透率数据验证了该模型的正确性与有效性.

基于井上下微震联合监测技术的地面水平井分段压裂效果分析

针对深井巨厚岩层动力灾害的防控,我国部分冲击地压矿井采用了地面水平井压裂防控技术。为了有效监测地面水平井压裂期间的压裂效果,提出了井上下微震联合监测方法,通过井上下微震联合监测台网的建设,对地面水平井分段压裂期间产生的微震事件进行有效监测、分析。结果表明,压裂施工与微震事件的发生具有明显的相关性,使用井上下微震联合监测方法,压裂时段微震事件分布在压裂缝网展布范围内的概率高达71%,微震事件分布与压裂缝网在垂直方向的展布范围具有较高的一致性;井上下微震联合监测技术的应用可有效提高微震的垂直定位精度,能够满足地面水平井分段压裂效果的观测。井上下微震联合监测技术的提出和应用可为后续地面压裂效果的观测、分析提供一定参考。

神东矿区采动裂隙岩体自修复特征研究

针对采动裂隙岩体在煤层采后长期演变过程中易发生降渗自修复的客观现象,以神东补连塔煤矿12401工作面和大柳塔煤矿52306工作面为典型试验区,开展覆岩不同区域裂隙岩体自修复规律的工程探测与理论研究,揭示了采后覆岩导水裂隙长期自修复过程的演变规律。结果表明,两矿试验面采动覆岩分别在采后15 a和7.3 a均获得了较好的自修复效果,在原先导水裂隙带范围出现导水的区域已明显减少,垮落带虽仍导水,但高度也已有所降低。通过将覆岩由原先导水变为隔水的自修复区段垂向长度占导水裂隙带高度的比值作为自修复率进行统计,得到12401试验面在开采边界附近及倾向中部覆岩中的自修复率已分别达到59.5%和53.5%,52306试验面在对应区域自修复率分别为25.8%和47.5%;因12401试验面采后年限更长、煤层埋深更大,其裂隙岩体自修复效果明显偏好。受覆岩纵向不同层位岩层赋存差异、横向不同区域初始垮裂程度的影响,自修复区域的分布常易呈现离散非连续性,其中间隔的未修复区一般对应于关键层或厚硬岩层位置,且采后年限越短、距开采边界越近,这种离散性越显著。采动裂隙岩体的自修复实际是多因素综合影响下的降渗演变过程,对于神东矿区开采条件,在煤层采后1.5~2 a时间内,是以应力压实作用引起的残余沉降为主导影响自修复进程,这在采区中部覆岩中体现相对显著;而后则一直以采动地下水与裂隙岩体或采空区CO_(2)等气体发生的水–岩或水–气–岩相互作用为主导影响自修复进程,即相关作用过程产生的衍生物对裂隙的充填封堵效果以及裂隙面受冲蚀后粗糙度降低程度直接影响裂隙自修复效果或程度。因此,采后覆岩中是否长期存在水体渗流决定了裂隙岩体实现自修复的难易程度;神东多数矿井覆岩导水裂隙一般直接沟通第四系松散层或地表,且近年雨水充沛,这为采动覆岩中水–岩或水–气–岩相互作用产生及促进裂隙自修复提供了优越条件。

基于3D打印的裂隙岩体力学特性尺寸效应及各向异性初探

裂隙岩体力学参数的尺寸效应和各向异性是岩石力学与工程领域亟待解决的难点问题。充分利用3D砂型打印技术快速成型、可批量制备复杂内部结构岩体模型的优势,以石英砂和呋喃树脂为打印基材,制备不同尺寸和旋转角的裂隙网络类岩石试件。通过单轴压缩试验研究裂隙网络岩体力学特性的尺寸效应,揭示裂隙密度与强度之间的相关性,分析表征单元体尺度岩体力学特性的各向异性。结果表明:3D砂型打印试件的力学性能与真实岩体相似,应力-应变曲线可划分为初始压密、弹性变形、裂纹萌生与扩展和峰后破坏4个阶段。试件抗压强度与试件边长之间呈指数衰减关系,存在显著尺寸效应性质。裂隙密度与抗压强度之间呈显著的负指数关系,基于裂隙密度与抗压强度确定的岩体表征单元体尺度具有良好的一致性。裂隙岩体的破坏模式和抗压强度具有显著的各向异性特征。研究方法从3D打印角度为复杂裂隙岩体尺寸效应及各向异性的室内试验研究提供了可靠途径。