采动岩体裂隙分形相关规律的实验研究

利用相似材料模拟实验模拟采动岩体裂隙的形成过程和分布状态,运用分形几何理论研究采空区冒落带、裂隙带和弯沉带岩体裂隙分布的分形规律。实验结果表明:采动岩体裂隙分形维数随开采宽度的增加而增大,岩体碎胀系数、覆岩下沉系数随采动岩体裂隙分形维数的增大而增大。

采动岩体裂隙分形特征的实验研究

利用相似材料模拟实验模拟采动岩体裂隙的形成过程和分布状态 ,运用分形几何理论研究采空区冒落带、裂隙带和弯沉带岩体裂隙的分形特征。实验结果表明 :当采掘工作结束且岩移基本稳定之后 ,采空区冒落带、裂隙带和弯沉带岩体的分形维数分别为 1.17、1.0 6和 0 .98,冒落带分形维数是裂隙带的 1.1倍 ,裂隙带分形维数是弯沉带的 1.0

煤岩孔裂隙结构分形特征及渗透率模型研究

为探究煤岩孔裂隙结构与渗透特性的联动关系,采用扫描电镜、偏光和分形等手段分析煤岩孔裂隙结构分布特征,利用自主研发的出口端正压三轴渗流装置,开展恒定有效应力条件下孔隙压力升高的渗流试验。基于分形理论,考虑煤岩表面孔隙分布情况对煤岩渗透率的影响机理,建立考虑孔裂隙分形特征的煤岩渗透率模型,通过试验验证其合理性,对煤岩孔裂隙下分形维数和渗透率耦合进行定量分析。研究结果表明:①六盘水矿区煤岩表面含有一定数量的孔隙和裂隙,其中四角田7号煤层孔裂隙发育情况最好,具有2条清晰的宽度较大的裂隙,并伴有大量交叉微裂隙及孔隙发育,煤岩结构破坏严重;②通过盒维数法可得煤岩孔裂隙分布具有明显的分形特征,且煤岩孔隙率与分形维数呈正相关关系;③恒定有效应力条件下,煤岩渗透率随孔隙压力升高呈现先急剧降低后趋于平缓的趋势,受孔裂隙结构影响,在相同的孔隙压力下煤岩渗透率存在明显差异。煤岩表面孔裂隙结构越复杂其分形维数越大,有助于瓦斯运移,渗透率呈上升趋势;④考虑孔裂隙分形特征的煤岩渗透率模型计算值与实测值吻合度较高,与前人研究成果相比,无论理论机理的适用性还是对试验点的匹配方面都更加适用,且能较好地反映孔隙压力与渗透率的联动关系。

采动岩体分形裂隙网络研究

采动岩体裂隙网络发展规律和定量描述是当今矿山开采沉陷学科中基本的也是极其重要的难题之一。借助相似材料模型实验，模拟了采动岩体的裂隙分布状态，应用分形几何理论研究采动岩体裂隙分布的自相似规律，继而研究分形裂隙网络随着采宽增加的演化规律。研究结果表明：采动岩体裂隙分布具有分形特征，用分形维数可以综合描述采动岩体裂隙化程度；随着采宽的增加。

采动岩体分形裂隙网络演化规律的试验研究

利用相似材料模拟试验模拟采动岩体裂隙的形成过程和分布状态 ,运用分形几何理论研究采空区冒落带、裂隙带和弯沉带岩体裂隙网络的演化规律。试验结果表明 :采动覆岩裂隙分形维数随工作面推进 ,经历了由小→大→小并趋于稳定的变化过程 ,在工作面推进距离相同情况下 ,冒落带分形维数是裂隙带的 1 0～ 1 2倍 ,裂隙带分形维数是弯沉带的 1 0～ 1

花岗岩残积土复杂次生裂隙的分类与损伤特征

裂隙的萌生、拓展演化对土体的损伤与破坏至关重要。为了研究岩土工程性状复杂的花岗岩残积土在荷载作用下内部细观裂隙的演化规律,利用CT扫描土体的三轴压缩过程,获得一系列重构数字体图像;引入裂隙体积重叠率用于改进笔者提出的裂隙分类方法,提高其在判断变形前后两裂隙团连通性的准确性。研究结果表明:裂隙体积重叠率的变化对湮灭型裂隙和新生型裂隙影响轻微,但对其余类型裂隙有不同程度的影响,表现为试样变形越大其影响也越大,综合选取裂隙体积重叠率为0.05时具有较好效果。随着轴向加载的增大,其中湮灭型裂隙和新生型裂隙的体积含量随着轴向应变的增大而增大,且新生型裂隙的体积含量增长更快,而复合型裂隙的体积含量呈衰减趋势,其余3种裂隙的体积含量均较小。通过分析不同类型裂隙的分形特征显示,裂隙的分形维数与体积含量变化相似,其中湮灭型裂隙、新生型裂隙和合并型裂隙呈增长趋势,新生型裂隙的分形维数增长最快,说明新生型裂隙更能够反映试样的剪切破坏过程。该研究成果将为岩土体的裂隙损伤分析提供理论与技术支持。

岩体裂隙尺度对其变形与破坏的控制作用

岩体是一种含有大量缺陷的天然材料,其中的断层、裂缝和裂隙称为高层次缺陷,微裂隙、孔隙等称为低层次缺陷。首先分析包含宏观和微观裂隙的岩石裂隙数量与尺度之间的分形关系,并按照裂隙尺度进行分级。然后采用数值试验方法,通过逐级增加裂隙,研究岩体裂隙尺度对其变形与破坏的控制作用。研究结果表明,当裂缝、裂隙、微裂隙、孔隙等不同尺度、不同层次缺陷并存时,高层次缺陷对岩体的变形、稳定、破坏起着主导控制作用。

分级循环荷载下保护层开采扰动煤岩强度及裂隙特性研究

针对回采时反复采动作用下的保护层开采扰动煤岩极易诱发巷道围岩失稳的问题,采用分级循环荷载模拟实际回采工程中采动应力的长期作用,研究保护层开采扰动煤岩在循环荷载作用下的力学强度及变形破坏特性.试验结果表明,在加卸载过程中,受保护层开采扰动煤样的体积膨胀变形明显,煤样内部结构破坏程度比未受保护层开采扰动煤样更高.在加卸载后期,受保护层开采扰动煤样表现为塑性破坏,未受保护层开采扰动煤样发生明显的脆性破坏.相比于未受保护层开采扰动煤样,受保护层开采扰动煤样的峰值强度下降,单位体积(直径为50 mm,高度为100 mm)内的煤样裂隙体积显著增加,峰值强度和裂隙体积占比均沿煤层走向分布较为均匀.处于断层带的未受保护层开采扰动煤样的彼此物性差异较大.受保护层开采扰动煤样比未受保护层开采扰动煤样更符合“煤岩破坏时,裂隙空间复杂程度与峰值强度存在反向对应分布”规律.

动荷载巷道围岩裂隙演化的实验研究

运用相似模拟理论,针对巨厚薄层状复合顶板条件, 进行了大比例三维巷道相似模拟实验。实验结果表明,随着 工作面的推进,巷道围岩的动载系数增大,围岩内开始产生 裂隙并扩展、贯通,最后导致巷道破坏。运用分形几何理论 进行分析,认为裂隙分布密度符合分形特征,可定量描述巷 道围岩裂隙的分布,分析结果为制定巷道支护方案,优化支 护设计参数,提供了理论依据。

Fractal evolution mechanism of rock fracture in undersea metal mining

Through rock mechanics test, similar simulation experiment, borehole photographic observation of rock fissure, numerical simulation calculation of plastic zone distribution and deformation monitoring of rock mass during undersea mining, the fractal evolution mechanisms of rock fracture in undersea metallic deposits of Sanshandao Gold Mine were studied by fractal theory. The experimental researches on granite mechanics test in undersea deposit indicate that with the increase of load, the granite deformation energy and the fractal dimension of acoustic emission(FDAE) increase gradually. However, after reaching the peak stress of specimen, the fractal dimensions of acoustic emission(FDAEs) decrease and the granite specimen fails. Therefore, the fractal dimension evolution of rock failure can be divided into four stages, which are fissure inoculation stage, fissure growth stage, fissure expansion stage and fracture instability stage, respectively. By calculating and analyzing the damage photographs of rock specimens in Sanshandao Gold Mine, the fractal dimension of rock fissure is 1.4514, which is close to the average value of FDAE during granite destruction, i.e., 1.4693. Similar simulation experiments of undersea mining show that with the excavation proceeding, the FDAE in rock stratum increases gradually, and when the thickness of the isolation roof is less than 40 m, the FDAE begins to decrease, and meanwhile the sign of water inrush emerges. The numerical simulation researches on the plastic zone distribution of undersea mining in Sanshandao Gold Mine indicate that the fractal dimension of plastic zone(FDPZ) where the failure characteristics occur is 1.4598, close to the result of similar simulation experiment of 1.4364, which shows the sign of water inrush. Meanwhile, the thickness of the isolation roof for undersea mining should be more than 40 m, which is consistent with the results of similar simulation experiment. In Sanshandao Gold Mine, the rock fissures in undersea mining were observed by borehole photography and the rock mass deformation was monitored by multi-point displacement meters, and at the same time the fractal dimensions of strata borehole fissure distribution and energy release ratio(ERR) of rock mass were calculated by fractal principle, which are 1.2328 and 1.2685, respectively. The results demonstrate that rock deformation and fissure propagation are both in the second stage of fissure growth, and have not reached the fourth stage of fracture instability. Therefore, the conclusion can be obtained that the undersea mining in Sanshandao Gold Mine is safe at present.

Dissociation, culture and morphologic changes of interstitial cells of Cajal in vitro

AIM: To study the method of dissociation, culture and investigate its morphologic changes in vitro of interstitial cells of Cajal (ICC).METHODS: Enzymatic digestion and Ficoll density centrifugation were used to dissociate ICC from the ileal segment of mice. Factors including contamination, Ca2+, Mg2+ and collagenase, and stem cell factor, etc., were investigated.ACK2, the antibody of c-kit, was used to identify the cultured ICC. Both light microscope and fluorescence microscope were used to observe the changes of ICC in vitro.RESULTS: The method for dissociation and culture of ICC in vitro was successfully established. After 24 h, cultured ICC exhibited a few axis-cylinders, and longer axis-cylinders were observed to form synapse of each other after 3 d. More widespread connections formed within 7 d in vitro. The changes of its morphologic character were obvious within 7 d; however, there were no obvious morphologic changes after 30 d.CONCLUSION: Many factors can influence the dissociation and culture of ICC.

3-D fracture network dynamic simulation based on error analysis in rock mass of dam foundation

Accurate 3-D fracture network model for rock mass in dam foundation is of vital importance for stability,grouting and seepage analysis of dam foundation.With the aim of reducing deviation between fracture network model and measured data,a 3-D fracture network dynamic modeling method based on error analysis was proposed.Firstly,errors of four fracture volume density estimation methods(proposed by ODA,KULATILAKE,MAULDON,and SONG)and that of four fracture size estimation methods(proposed by EINSTEIN,SONG and TONON)were respectively compared,and the optimal methods were determined.Additionally,error index representing the deviation between fracture network model and measured data was established with integrated use of fractal dimension and relative absolute error(RAE).On this basis,the downhill simplex method was used to build the dynamic modeling method,which takes the minimum of error index as objective function and dynamically adjusts the fracture density and size parameters to correct the error index.Finally,the 3-D fracture network model could be obtained which meets the requirements.The proposed method was applied for 3-D fractures simulation in Miao Wei hydropower project in China for feasibility verification and the error index reduced from 2.618 to 0.337.

Fractal characterization for the mining crack evolution process of overlying strata based on microseismic monitoring technology

In order to study the evolution laws during the development process of the coal face overburden rock mining-induced fissure,we studied the process of evolution of overburden rock mining-induced fissures and dynamically quantitatively described its fractal laws,based on the high-precision microseismic monitoring method and the nonlinear Fractal Geometry Theory.The results show that:the overburden rock mining-induced fissure fractal dimension experiences two periodic change processes with the coal face advance,namely a Small→ Big→ Small process,which tends to be stable;the functional relationship between the extraction step distance and the overburden rock mining-induced fissure fractal dimension is a cubic curve.The results suggest that the fractal dimension reflects the evolution characteristics of the overburden rock mining-induced fissure,which can be used as an evaluation index of the stability of the overburden rock strata,and it provides theoretical guidance for stability analysis of the overburden rock strata,goaf roof control and the support movements in the mining face.

循环渐进升压对页岩压裂效果的影响

为了揭示循环渐进升压对页岩压裂效果的影响规律,开展页岩真三轴水力压裂试验,对比分析一次性压裂与循环渐进升压致裂的破裂效果。试验结果表明:(1)基于泵压曲线、声发射能量对比分析,一次性压裂方式,倾向于单次造缝;循环渐进升压致裂方式,倾向于多次造缝和沿着不同方向造缝。(2)基于声发射定位展布特征对比分析,一次性压裂声发射定位,呈现条带状分布,对应单一裂缝;而循环压裂声发射定位呈现离散化分布特征,对应更大压裂体积范围。(3)基于宏观裂纹形态、数量和分形维数对比分析,循环压裂方式能显著提高页岩缝网密度和改善页岩渗透特性,可以优化和改进现场水力压裂施工方法。(4)基于扩展有限元数值模拟分析,循环注入方式能产生更加偏转和路径更长主裂缝,沿途倾向支生更多次生裂隙,可以增加缝网密度并提升体积压裂的效果。

An experimental investigation on the mechanism of fluid flow through single rough fracture of rock

The structure of fractures in nature rock appears irregular and induces complicated seepage flow behavior.The mechanism and quantitative description of fluid flow through rock fractures is a difficult subject that has been greatly concerned in the fields of geotechnical,mining,geological,and petroleum engineering.In order to probe the mechanism of fluid flow and the effects of rough structures,we conducted a few laboratory tests of fluid flow through single rough fractures,in which the Weierstrass-Mandelbrot fractal function and PMMA material were employed to produce the fracture models with various fractal roughnesses.A high-speed video camera was employed to record the fluid flow through the entire single rough fracture with a constant hydraulic pressure.The properties of fluid flow varying with the fracture roughness and the influences of the rough structure were analyzed.The components of flow resistance of a single rough fracture were discussed.A fractal model was proposed to relate the fluid resistance to the fracture roughness.A fractal equivalent permeability coefficient of a single rough fracture was formulated.This study aims to provide an experimental basis and reference for better understanding and quantitatively relating the fluid flow properties to the structures of rock fractures.

MRT-LBM-based numerical simulation of seepage flow through fractal fracture networks

The study on seepage flow passing through single fractures is essential and critical for understanding of the law of seepage flow passing through fracture networks and the coupling mechanisms of seepage field and stress field in rock masses.By using the fractal interpolation to reconstruct a natural coarse fracture,as well as taking into account the microstructure of the fracture,the numerical simulation of seepage flow passing through the coarse fractures with two distinct vertical scaling factors is conducted based on the MRT-LBM model of the lattice Boltzmann method.Then,after obtaining the length of the preferential flow pathway,the permeability of the two kinds of fractures is estimated respectively.In view of difficulties in locating the preferential flow pathway of natural fracture networks,by numerical tests a transect permeability weighted algorithm for estimating the fracture network permeability is proposed.The algorithm is not specific to one or more particular preferential flow pathways,but considers the contribution of each section to hinder the fluid passing through the medium.In order to apply the new algorithm,by capturing the structure of fracture networks based on the image-processing technique,the numerical simulations of seepage flow passing through two groups of natural fracture networks is carried out,the permeability is forecasted and the partial flows are reproduced for both cases.It is found that the preferential flow pathway emerges at the beginning of evolution,then is strengthened subsequently,and finally reaches a steady status.Furthermore,by using the proposed method some details on local flow can be clearly observed such as backflows and vortices at local branches can exist simultaneously and so forth,suggesting the validness of the proposed method for multiscale simulations of seepage flow.