共查询到20条相似文献，搜索用时 15 毫秒
1.
卸荷过程岩体中弹性波波速变化分析 总被引：1，自引：0，他引：1
伴随岩体卸荷过程,岩体内部应力状态要进行调整,同时岩体内部几何结构也要发生变化。由于卸荷过程应力状态变化很复杂,文中利用卸载过程中岩体内部几何结构的变化来反映卸载过程,通过岩体几何结构对弹性波传播的影响来分析卸载过程的波速。为考虑弹性波作用下局部裂纹的相互作用,采用双裂纹模型近似分析。在双裂纹体系内部采用“相互作用”分析法,以部分考虑波在岩体内的多次散射;在双裂纹体系之间采用线性叠加分析法,以考虑岩体中缺陷影响的局部化。通过节理裂隙的张开程度和节理裂隙的张开率描述卸载过程对双裂纹体系的影响,由此,对比分析了开挖卸载过程中四种不同的玄武岩与主频25 kHz和主频1 kHz对应的弹性波波速的变化。结果表明,随着卸载过程的推移,主频25 kHz声波和主频1 kHz地震波对应的相对波速逐渐减小,但声波波速的减小幅度要比地震波减小的幅度小,声波波速可以降低到原来的80%,而地震波波速可以降低到原来的50%。结论对于水利工程、隧道工程等建基面的验收和评价有很好的指导意义 相似文献
2.
Qingfa Chen Tingchang Yin Wenjing Niu Wenshi Zheng Junguang Liu 《Arabian Journal of Geosciences》2018,11(11):286
The determination of representative elementary volume (REV) is critical for mechanical model establishment and the determination of rock mass mechanical properties. Therefore, in this study, the REV range, existence, determinate parameter, and category were discussed. The blockiness level of the rock mass (Bz) was defined as the new index to determine the geometrical rock mass REV. Then, a great variety of multiscale three-dimensional fractured network models with different discontinuity persistences and spacings were developed. Finally, the Bz values of all models were measured, and the geometrical REVs were determined, the correlation between the geometrical REVs and rock mass discontinuity properties were assessed, and size validations of geometrical REVs were performed. In this study, it is shown that the REV is approximately 20–50 times that of the discontinuity spacing when the discontinuity spacing is classified as having extremely close to close spacing and is between approximately 0.3 and 4.0 times the discontinuity diameter when discontinuity spacing is in the range from moderate to extremely wide spacing. Further, there is a fourth-order nonlinear correlation between the geometrical REV and the ratio of the discontinuity diameter to discontinuity spacing. Meanwhile, the validation results confirm that the geometrical REV is slightly less than the sizes at which the elastic moduli tend to plateau, and the rationality of the geometrical REV of a rock mass based on Bz is thus supported from another perspective. 相似文献
3.
A geometrical model, including different geometrical shapes influencing thermal conductivity of snow is proposed. The geometrical
model has been assumed to comprise of unit cells having solid (ice) inclusion as an aggregation of spherical, cylindrical
or cubical shapes with vertical connection, arranged in a cubic packing. From the geometrical model and one-dimensional heat
transfer theory, the effective thermal conductivity has been computed. For this purpose, coupled one-dimensional heat transfer
equations have been solved for steady-state condition to account for conduction in ice, conduction in air and latent heat
transfer due to water vapour sublimation through air. The model demonstrates the dependency of thermal conductivity on density,
grain-spacing, grain contact ratio and temperature. Spherical inclusions give highest conductivity while cubical inclusion
estimates lowest value for the same density. Thermal conductivity has been found increasing sharply near to the packing density
for all three shapes. Empirical model results and results obtained from existing microstructure based models have also been
compared with the present model. 相似文献
4.
Zhang Xing 《国际地质力学数值与分析法杂志》1990,14(5):367-377
Discontinuities that have unfavourable orientation and are continuous within overall engineering rock regions can have a dominant effect on the strength, deformability and permeability of the rock mass. The concepts of geometrical parameters of basic discontinuities and engineering discontinuities are proposed in this communication. Further, the engineering discontinuities are divided into key discontinuities and non-key discontinuities. Within any region of the rock mass, the spacing, trace length and probability of engineering discontinuities can be estimated from the geometrical parameters of the basic discontinuities. In general, the geometrical parameters are different from those of the basic discontinuities. Finally, two examples are given to illustrate how to apply these parameters to rock engineering problems. 相似文献
5.
In the current research, the ground-penetrating radar (GPR) method has been employed to identify physical and geometrical parameters of buried cylindrical structures using the pattern recognition approach. To achieve this goal, the well-established mathematical relationships between geometrical parameters of cylindrical target (radius, burial depth, and horizontal location) and the associated GPR hyperbolic response characteristics are employed using the template matching method. In order to validate the applicability of the template matching method in providing estimates of such parameters, the method is first examined on GPR responses of synthetic models with known geometrical parameters followed by applying on real data using two different similarity criteria including 2-D spatial convolution and normalized cross correlation in the wave number domain. In the first step, the GPR responses of 71 synthetic models encompassing one, two, and three horizontal cylinders were produced using the improved 2-D finite difference in frequency domain. Then, appropriate preprocessing sequences to reduce random noise caused by forward modeling were applied on synthetic data. The proposed algorithm applied on several synthetic model responses could estimate the known geometrical parameters of the buried cylinders with acceptable accuracy (maximum error of 15%). The template matching algorithm was also used to extract geometrical parameters of water and wastewater pipes buried in Imam Hossein Square, Isfahan city, as real GPR data. Depending on environmental conditions and subsurface host formation, the real GPR data normally contain a variety of noises; therefore, a series of appropriate objective preprocessing and processing stages were designed in order to apply on real GPR images before deploying template matching algorithm. The applicability of the template matching algorithm on real data and validity of the estimated parameters were proved based on assessing the accuracy of the estimated geometrical parameters of respective pipes through GPR response versus the measured parameters. The proposed algorithm was designed in such a way that all steps of estimating geometrical parameters of buried cylindrical targets are automatically carried out. 相似文献
6.
斜井和水平井补偿中子测井分辨率改进及应用 总被引：1，自引：0，他引：1
为了合理提高斜井和水平井条件下补偿中子测井曲线的纵向分辨率,利用蒙特卡罗模拟研究了在不同井斜角情况下CN241补偿中子测井仪器的纵向几何因子,把几何因子作为仪器响应函数系数,在模拟地层和实际地层中利用分辨率匹配技术对测井曲线进行了分辨率提高处理,并对改进前后的处理结果进行了比较。通过研究得到了不同井斜角下的补偿中子测井的纵向几何因子,验证了在斜井和水平井中使用垂直井的几何因子进行分辨率匹配处理存在较大误差,在40 cm厚地层中误差最大达10 p.u,改进后的结果与改进前相比降低了误差、提高了数据精度。研究结果表明：随着井斜角的不同,仪器的纵向几何因子也不同,要在斜井和水平井中合理进行分辨率提高处理,应该使用对应井斜角的几何因子作为响应函数系数。 相似文献
7.
利用地震几何属性和自组织神经网络进行地震相的自动识别 总被引：6，自引：0，他引：6
阐述了2类地震几何属性:①反映地震道空间变化量的属性;②反映地震属性空间相似程度及其衍生的各类参数.运用这些属性来判识地层或反射界面的空间连续性和倾向倾角等地质体的空间几何特征,采用自组织神经网络方法对这些属性进行自动分类来判别地震相.在山东东营凹陷永921井区的应用证明,该方法具有较好的应用效果. 相似文献
8.
节理几何特征对预裂爆破效果影响的数值模拟 总被引：1，自引：0，他引：1
运用有限元软件AUTODYN 2D计算爆炸荷载与离散元软件UDEC模拟节理岩体相结合的方法研究了节理几何特征对预裂爆破的影响。通过计算可知,预裂爆破时炮孔间的节理组对预裂成缝的影响明显,当节理法线与炮孔连线夹角在一定范围内时,预裂缝沿炮孔连线方向的平直程度随节理与炮孔连线夹角的增大而逐渐趋于平直,其中当节理组与炮孔连线夹角为90°时成缝效果最好,裂缝与炮孔连线基本重合,与理论分析较一致;节理间距对预裂爆破有较大影响,相同条件下节理间距越小,越难形成连通裂缝,减小炮孔间距有利于小节理间距情况下的预裂缝贯通 相似文献
9.
The concept of bed-duplication folding, a process of folding by stacking of duplicate beds above a thrust ramp, was introduced by John L. Rich in 1934, and such folding has been studied mechanically and geometrically during the last few years.
This paper introduces two kinematical models to bridge between geometrical and mechanical analyses, so results of the two methods of determining the deformations and geometry of bed-duplication folding can be compared. One kinematical model is required for early stages and the other for late stages of bed-duplication folding, but each involves a simple, domainal, velocity distribution. It is remarkable that such simple kinematical models can produce complex geometrical models. The kinematical models clearly produce the type of bed-duplication fold developed by graphical construction and termed “fault-bend fold”. The kinematical models provide new insights into the essence of the type.
The velocity distributions assumed in the kinematical models are similar to those predicted by a first-order, mechanical model for thrust ramps with low slopes (less than about 20 degrees) and zero drag. The fold forms computed from the two sets of models are also similar, so geometrical construction roughly reproduces a simple, low-amplitude bed-duplication fold.
The approximation is poorer for steeper thrust ramps. The upper limit of the kinematical fold. and geometrical construction is 30 degrees and, at that ramp angle, the dip of the distal limb of the fold is twice the dip of the thrust ramp. Results of the mechanical analysis of relatively steep ramps, carried to second-order accuracy, indicate that the 30-degree limit of the ramp angle is an artifact of the geometrical analysis and that the block being thrusted is subjected to general simple shearing. The simple shear is absent in the kinematical models and the geometrical construction. Nevertheless, both the kinematical and mechanical models predict asymmetry of fold limbs. 相似文献
10.
Lekan Olatayo Afolagboye Jianming He Sijing Wang 《Geotechnical and Geological Engineering》2018,36(1):105-133
Crack initiation and coalescence behavior of rock or rock-like specimens containing artificial flaws under uniaxial compression have been subjects of intensive investigation in the past. Most of these investigations however focused on crack initiation and coalescence between two or more parallel flaws. Although there have been few experimental studies on non-parallel flaws, these studies did not address the influence of geometrical factors such as ligament length and ligament angle on the crack initiation and coalescence behavior of non-parallel flaws. To investigate whether the individual geometrical factors have similar effects on the crack initiation and coalescence behavior of both parallel and non-parallel flaws, we conducted uniaxial compression tests to investigate crack cracking and coalescence processes in rock like material containing two non-parallel flaws. The paper presents the influence of individual geometrical factors on the crack initiation process and coalescence pattern of non-parallel flaws. Initiation of primary first cracks from all the tips of the two flaws did not occur simultaneously in all the flaw configurations. The flaw configuration of the non-parallel flaws influences the crack initiation, crack trajectories and coalescence behavior. The crack coalescence pattern changes with an increasing ligament angle from indirect to shear crack or mixed tensile-shear crack to tensile crack coalescence. The chance of direct coalescence is reduced with an increase in ligament length. In conclusion, the crack initiation and coalescence behavior of prismatic rock-like specimens with non-parallel flaws, as influenced by the geometrical factors, are analogous to the cracking and coalescence pattern observed in specimens with parallel flaws. 相似文献
11.
Numerical simulation of liquefaction-induced lateral spreading in gently sloped sandy layers requires fully coupled dynamic hydro-mechanical analysis of saturated sandy soil subjected to seismic loading. In this study, a fully coupled finite element model utilizing a critical-state two-surface-plasticity constitutive model has been applied to numerically investigate the effects of surface/subsurface geometry on lateral spreading. Using a variable permeability function with respect to excess pore pressure ratio is another distinctive feature of the current study. The developed code has been verified against the results of the well-known VELACS project. Lateral spreading phenomenon has been the focus of an extensive parametric study using the developed code. Numerical modeling of three different geometrical forms of surface and subsurface of liquefiable layer indicates that the amount and direction of lateral spreading are noticeably affected by the geometrical conditions. Also, parametric studies by the developed numerical model show that the effects of layer height, maximum ground acceleration, and loading frequency on the level of lateral spreading are significantly different for the examined geometrical condition. 相似文献
12.
J. C. Butler 《Mathematical Geology》1981,13(1):53-68
Proper analysis of transformed data arrays (such as percentages) requires paying special attention to the effects of the transformation process itself. Effects of several commonly used transformations (including percentage formation, row and column normalization, and the square root transformation) have been examined with emphasis placed on changes in the statistical and geometrical properties of column vectors that accompany the application of the transformation. Even though many transformations, including taking the square root, open up the percentage array, this does not allow one to ignore the fact that percentage formation may have considerably modified the statistical and geometrical properties of the columns of the matrix. In preparing to analyze percentages one should give serious consideration to using the row normalized form of the data matrix. The individual elements in such a matrix are the direction cosines of the vector in M-dimensional space, the row vectors are of unit length, and the row normalized matrix computed from the closed array is equal to the row normalized, open matrix that is unobservable. Application of a column transformation (such as range restriction and proportion of the maximum) destroys the equality of the open and percentage row normalized matrices. Despite repeated claims to the contrary, one can not deduce the statistical and geometrical properties of the open matrix given only the statistical and geometrical properties of the closed matrix. 相似文献
13.
This paper presents robust algorithms for application in polyhedral modelling of rock mass structure based on discrete fracture networks. The algorithms improve the robustness of current polyhedral modellers to challenging or degenerate geometries and geometrical errors. These issues are inevitably encountered when the fracture network realisations incorporate large numbers of fractures, or regions of densely packed fractures are modelled, or when the number of fracture network realisations interrogated is large. Several stages in the polyhedral modelling process which are sensitive to geometrical errors are reviewed and algorithms which are robust and capable of handling topological errors in the input fracture network geometry are presented. 相似文献
14.
圆形板基础下地基强度和变形非线性性状研究 总被引：3，自引：1，他引：3
采用Drucker弹塑性模型、SAP91非线性有限元程序、Vizi CAD微机有限元前后处理系统计算、分析了轴对称问题，即圆形板情况下，基础板几何尺寸、基础刚度、边界条件、基础埋深对基础沉降量、塑性区开展的影响，结果表明基础沉降随基础几何尺寸增大而增大，随基础刚度、埋深的增大而减小；基础刚度、几何尺寸、埋深的加大都能提高地基承载力。 相似文献
15.
岩石节理表面几何特性的三维统计分析 总被引：2，自引：0，他引：2
在利用三维非接触式高精度激光表面形状测定仪精确测量岩石节理的表面粗糙形状并进行数值化表达的基础上,应用地理信息系统(GIS)技术,实现了岩石节理粗糙面的三维可视化。再对岩石节理粗糙面的三维几何特性参数（诸如表面粗糙度、裂隙张开度和粗糙高度等）进行统计分析并计算频数分布的特征数字。最后,根据频率直方图的分布趋势和频数分布的特征数字研究各几何特性参数的分布规律。结果表明,花岗岩节理粗糙表面起伏比砂岩大,但二者几何特性参数的分布规律相似,节理粗糙高度和裂隙张开度分布近似于正态分布规律,而节理粗糙面倾斜角分布近似于Γ分布规律。 相似文献
16.
岩石几何损伤模型是建立统计损伤本构模型的重要基础。在岩石变形力学特性基础上对现有岩石几何损伤模型进行了回顾性分析，针对它们难以较好地反映初始损伤特征和峰后变形破坏特征的缺陷与不足，首先，将岩石材料视为由未损伤部分、初始损伤部分和后继损伤部分组成，提出了考虑初始损伤的岩石几何损伤模型；然后，通过探讨Weibull分布参数m和F0对损伤变量变化产生的影响，构建了参数型岩石几何损伤模型，在此基础上建立了应变软化类岩石统计损伤本构模型并进行了修正，给出了模型参数的确定方法；最后，通过模型验证和参数分析表明，修正后模型能够较好地模拟岩石变形破裂全过程，参数l和h对损伤变量变化产生的影响与m和F0等效，解决了现有岩石几何损伤模型存在的共性问题，该模型和方法具有一定的合理性和可行性。 相似文献
17.
Thomas Kalbacher Wenqing Wang Chris McDermott Olaf Kolditz Takeo Taniguchi 《Environmental Geology》2005,47(7):1017-1027
18.
Fracturing of rock under compression is a product of a series of processes, including nucleation, growth, interaction and coalescence of multiple microcracks. The formation of echelon arrays of microcracks and macrocracks is one of the crucial rings in the processes. We use a superposition and asymptotic approximation technique to analyse the interaction of multiple cracks with various geometrical configurations. It is shown that crack geometry has a strong influence on crack interaction. Echelon crack arrays produce the strongest interaction and are the preferred geometrical configuration for multiple cracks prior to the formation of through-going shear fractures. This technique provides parameter-dependent global behaviour, and is more efficient and easier to use. 相似文献
19.
20.
马维俊 《沉积与特提斯地质》1988,8(6):15-20
盆地的地层格架(stratigraphic framework)是盆地分析最基本、最重要的参数之一(李思田等,1983),它是指沉积盆地的外部和内部几何形态以及组成盆地的层的堆积性质。概括地说,地层格架不仅指盆地的固体几何形态和盆地所包含的地层单元或单元序列的固体几何形态,而且涉及到单个地层单元的性质,最终体现了沉积环境(Conybeare,1979)。衡量地层格架这一参数应从以下几方面来考虑: 1.盆地的外部几何形态盆地的外部几何形态应该为其真实的固体空间形态所反映,应该包括盆地的平面几何 相似文献