scholarly journals Influence of Bedding Planes on the Mechanical Characteristics and Fracture Pattern of Transversely Isotropic Rocks in Direct Shear Tests

2018 ◽  
Vol 2018 ◽  
pp. 1-14
Author(s):  
Lei Xia ◽  
Yawu Zeng ◽  
Rong Luo ◽  
Wei Liu
Keyword(s):  
Mechanical Characteristics ◽  
Numerical Models ◽  
Transversely Isotropic ◽  
Bedding Plane ◽  
Particle Flow Code ◽  
Fracture Plane ◽  
Direct Shear ◽  
Geometrical Properties ◽  
Bedding Planes ◽  
Fracture Patterns

Bedding planes are the primary control on the anisotropy of mechanical characteristics and fracture patterns in rock. To analyze the influence of the geometrical properties of bedding planes on the direct shear strength characteristics and fracture patterns of transversely isotropic rocks, numerical models were established using an improved modeling method using Particle Flow Code. The results of the numerical model were in good agreement with those of the physical experiments of an artificial rock mass containing a single bedding plane. The results show that the shear fractures with a range of bedding plane geometries can be divided into two patterns. When the inclination angles of the bedding planes were larger or smaller, a thoroughgoing fracture plane was formed near the preexisting shear fracture plane. On the other hand, the intact rock was broken into many parallel sheets.

Karst generation in three-dimensional jointed layered rocks

2021 ◽  
Author(s):  
Chuanyin Jiang ◽  
Xiaoguang Wang
Keyword(s):  
Carbonate Rocks ◽  
Numerical Models ◽  
Three Dimensional ◽  
Dissolution Kinetics ◽  
Bedding Plane ◽  
Fracture Aperture ◽  
Fracture Networks ◽  
Aperture Ratio ◽  
Bedding Planes ◽  
Fractured Carbonate

<p>We use numerical models to investigate the generation of incipient karst in layered geological systems, and specifically to investigate the effects of the structural and hydraulic properties of both joints and bedding planes on the distribution of the developed karst cavities. We develop a numerical model which couples the processes of fluid flow, mass transport and dissolution kinetics that govern the growth of fracture aperture, based on three-dimensional discrete fracture networks. The synthetic fracture networks made up of two jointed layers separated by a horizontal bedding plane are generated to represent the typical layered fracture systems often formed in carbonate rocks. We assume a relatively uniform aperture field with a small variance for each joint set and for the bedding plane, but different joint sets and the bedding plane can have non-identical mean apertures. Results show that the aperture ratio of the joint sets to the bedding plane is found to dominate the flow heterogeneity on the bedding plane, leading to various behaviors of karst development. We further suggest that the distinct flow regimes, i.e., joint-dominated, transitional and bedding plane-dominated, controlled by the magnitude of the aperture ratio, are responsible for the different types of incipient karst morphologies. Our investigations have an important application on the understanding of clustering behaviors of karst cavities in layered fractured carbonate rocks.</p><div> </div>

scholarly journals Research on the Strength Characteristics and Crack Propagation Law of Noncoplanar Nonthrough Jointed Rock Mass by PFC2D

2021 ◽  
Vol 2021 ◽  
pp. 1-28
Author(s):  
Qingzhi Chen ◽  
Yuanming Liu ◽  
Shilong Mei ◽  
Kai Cao ◽  
Bin Du ◽  
...  
Keyword(s):  
Rock Mass ◽  
Numerical Models ◽  
Jointed Rock ◽  
Jointed Rock Mass ◽  
Strength Characteristics ◽  
Particle Flow Code ◽  
Direct Shear ◽  
Direct Shear Tests ◽  
Relief Angle ◽  
Propagation Law

In this study, five groups of numerical models with different conditions were established by using PFC2D (particle flow code) to simulate the direct shear tests of noncoplanar nonthrough jointed rock mass. It is proved that normal stress and shear rate, as well as the connectivity rate, relief angle, and inclination angle of joints, have significant influence on the strength characteristics, number of cracks, and the stress of the rock mass according to measurement taken at five different measurement circles in the rock mass. Moreover, it is determined that in the process of shearing, no matter which group of tests are conducted, the number of cracks in the rock mass caused by tension is far more than that caused by the shear action. In other words, the failure of rock mass with different planes and discontinuous joints is mainly caused by the tension in the process of the direct shear test.

scholarly journals Parameterization of elastic stress sensitivity in shales

Geophysics ◽  
2011 ◽  
Vol 76 (3) ◽  
pp. WA147-WA155 ◽  
Author(s):  
Marina Pervukhina ◽  
Boris Gurevich ◽  
Pavel Golodoniuc ◽  
David N. Dewhurst
Keyword(s):  
Elastic Properties ◽  
Anisotropy Parameter ◽  
Transversely Isotropic ◽  
Bedding Plane ◽  
Stress Sensitivity ◽  
Crack Orientation ◽  
Fluid Identification ◽  
Orientation Anisotropy ◽  
Characteristic Pressure ◽  
Stress Dependency

Stress dependency and anisotropy of dynamic elastic properties of shales is important for a number of geophysical applications, including seismic interpretation, fluid identification, and 4D seismic monitoring. Using Sayers-Kachanov formalism, we developed a new model for transversely isotropic (TI) media that describes stress sensitivity behavior of all five elastic coefficients using four physically meaningful parameters. The model is used to parameterize elastic properties of about 20 shales obtained from laboratory measurements and the literature. The four fitting parameters, namely, specific tangential compliance of a single crack, ratio of normal to tangential compliances, characteristic pressure, and crack orientation anisotropy parameter, show moderate to good correlations with the depth from which the shale was extracted. With increasing depth, the tangential compliance exponentially decreases. The crack orientation anisotropy parameter broadly increases with depth for most of the shales, indicating that cracks are getting more aligned in the bedding plane. The ratio of normal to shear compliance and characteristic pressure decreases with depth to 2500 m and then increases below this to 3600 m. The suggested model allows us to evaluate the stress dependency of all five elastic compliances of a TI medium, even if only some of them are known. This may allow the reconstruction of the stress dependency of all five elastic compliances of a shale from log data, for example.

Tectonic ripples and associated minor structures in the Silurian rocks of Denbighshire, North Wales

1970 ◽  
Vol 107 (1) ◽  
pp. 51-60 ◽  
Author(s):  
P. T. Warren ◽  
R. K. Harrison ◽  
H. E. Wilson ◽  
E. G. Smith ◽  
M. J. C. Nutt
Keyword(s):  
Bedding Plane ◽  
Linear Structures ◽  
Regional Stress ◽  
Bedding Planes ◽  
North Wales ◽  
Tectonic Origin

SummaryStructures affecting certain bedding planes, and simulating sedimentary ripples, have been found at a number of horizons in the Wenlock and Ludlow rocks of Denbighshire, North Wales. The megascopic appearance of the ripples, including their association with linear structures and their miscroscopical fabric are described in detail; and it is concluded that they are of tectonic origin, being manifestations of bedding-plane slip. The orientations of the ripples and other minor structures suggest that the stress responsible was the regional stress that produced folding, faulting and cleavage.

Spatial analytics of self-organized vegetation pattern in semi-arid regions: an example on tiger-bush patterns in Sudan

2021 ◽  
Author(s):  
Christoph Hinz ◽  
Konlavach Nengsuwan ◽  
Daniel Cavieds-Voullieme
Keyword(s):  
Spatial Analysis ◽  
Arid Regions ◽  
Numerical Models ◽  
Google Earth ◽  
Vegetation Patterns ◽  
Strong Positive Correlation ◽  
Positive Correlation ◽  
Geometrical Properties ◽  
Principal Axes ◽  
Semi Arid

<p>The concept of local-scale interactions of spatially periodic vegetation patterns are well known in arid and semi-arid regions. The vegetation patterns are easily observable from aerial and satellite photography. Additionally, various mathematical models have been developed to reproduce the patterns observed in nature, aimed towards understanding the driving factors leading to pattern properties. Several studies exist attempting to analyse spatial properties of these patterns, their spatial distribution and their relationship to  topography and climate. However, there are limitations in how these studies provide spatially-distributed statistics, and on the specifics of vegetation patch and band geometries, making it difficult to compare to model predictions. </p><p>This study proposes  a new workflow (implemented in R) to measure geometric  characteristics of vegetation bands and patches. We use high-resolution satellite imagery as the base dataset. Color filters are used to binarise and identify individual patches/bands of arbitrary irregular shapes. We then compute different geometrical properties, such as  patch-size, separation between them, orientation, among others. Additionally, the principal axes of each patch/band are identified, and used to measure characteristic lengths and widths, for which statistics are then computed, and can be represented in spatial subdomains to allow for spatial analysis at different scales. The strategy can also be easily applied to modelling results, thus facilitating comparison, and the algorithm is flexible enough to yield different forms of patterns and spatial extent.</p><p>As a test case, we apply this workflow to a study site (11.05 N, 28.35 E) in Kordofan, south Sudan (a region previously reported and documented in the literature), using Google Earth Imagery as input. For this domain (3500 x 1400 m), the  results show that the length of the patches has a strong positive correlation with their width. Additionally, the length and the average nearest neighbor distance displayed a small positive correlation to the elevation. Using the available ALOS topography, the results also confirm that that 92% of the bands in our study area are oriented perpendicularly to the slope direction, as is expected from these systems. </p><p>This test is a first step into applying this workflow to a larger extend within Kordofan and other regions known to exhibit vegetation bands (tiger bush in wester Africa, Australia, Nevada) and perform extensive geometric and spatial analysis of the bands, as well as simulated banded systems obtained from numerical models.</p><p>Keywords: Vegetation patterns, Self-organization, Tiger-bush, Geometric analysis, Oriented direction</p>

Well Shear Associated with Conventional and Unconventional Operations: Diagnosis and Mechanisms

2021 ◽  
pp. 1-18
Author(s):  
Russell T. Ewy
Keyword(s):  
Cross Sections ◽  
Slip Surface ◽  
Bedding Plane ◽  
Vertical Stress ◽  
Natural Fracture ◽  
Shear Deformations ◽  
Horizontal Fracture ◽  
Bedding Planes ◽  
Shear Slip ◽  
Fluid Pressurization

Summary Wells are sometimes deformed due to geomechanical shear slip, which occurs on a localized slip surface, such as a bedding plane, fault, or natural fracture. This can occur in the overburden above a conventional reservoir (during production) or within an unconventional reservoir (during completion operations). Shear slip will usually deform the casing into a recognizable shape, with lateral offset and two opposite-trending bends, and ovalized cross sections. Multifinger casing caliper tools have a recognizable response to this shape and are especially useful for diagnosing well shear. Certain other tools can also provide evidence for shear deformation. Shear deformations above a depleting, compacting reservoir are usually due to slip on bedding planes. They usually occur at multiple depths and are driven by overburden bending in response to reservoir differential compaction. Shear deformations in unconventional reservoirs, for the examples studied, have been found to be caused by slip on bedding planes and natural fractures. In both cases, models, field data, and physical reasoning suggest that slip occurs primarily due to fluid pressurization of the interface. In the case of bedding plane slip, fracturing pressure greater than the vertical stress (in regions where the vertical stress is the intermediate stress) could lead to propagation of a horizontal fracture, which then slips in shear.

scholarly journals Application of Direct Shear Test to Analysis of Tertiary Landslides Along a Bedding Plane

1992 ◽  
Vol 32 (1) ◽  
pp. 1-12 ◽  
Author(s):  
Shyojiro Aramaki ◽  
Yoshito Kitazono ◽  
Atsumi Suzuki ◽  
Mitsuhisa Kajiwara
Keyword(s):  
Direct Shear Test ◽  
Shear Test ◽  
Bedding Plane ◽  
Direct Shear

Modelling creep deformation in floating ice

2003 ◽  
Vol 30 (1) ◽  
pp. 28-41 ◽  
Author(s):  
K van Steenis ◽  
F E Hicks ◽  
T M Hrudey ◽  
S Beltaos
Keyword(s):  
Large Scale ◽  
Field Experiments ◽  
Numerical Models ◽  
Ice Sheet ◽  
Transversely Isotropic ◽  
Element Model ◽  
Ice Cover ◽  
Load Test ◽  
Drilling Rig

The ability to predict the response of an ice sheet to long-term loading is important in many situations. In northern regions, ice sheets have been used as construction platforms, drilling rig platforms, airfields, parking lots, and festival platforms. Numerical models can be used to predict the deflection of an ice sheet over time and, together with a failure criterion based on allowable deflection, can facilitate the safe use of an ice cover under long-term loading situations. In this study, a two-dimensional axisymmetric finite element model was developed to model the behaviour of a homogeneous, transversely isotropic, infinite ice cover under long-term loading. The model was validated using 33 sets of long-term load test data from large-scale field experiments performed on lake, bay, and reservoir ice and was shown to be capable of reliably predicting deflections under a variety of loading scenarios.Key words: bearing capacity of ice, long-term loading, ice platforms.

A weak-anisotropy approximation to multicomponent induction responses in cross-bedded formations

Geophysics ◽  
2006 ◽  
Vol 71 (4) ◽  
pp. F61-F66 ◽  
Author(s):  
Tsili Wang
Keyword(s):  
Apparent Resistivity ◽  
Transversely Isotropic ◽  
Anisotropy Ratio ◽  
Weak Anisotropy ◽  
Bedding Planes ◽  
Geometric Average ◽  
Induction Logging ◽  
Anisotropic Formation ◽  
The Cross

The multicomponent induction logging response to a cross-bedded formation has been modeled under a weak-anisotropy approximation. With the approximation, a cross-bedded formation can be modeled as a transversely isotropic (TI) medium. The validity of the approximation has been tested for the main (coplanar and coaxial) components of the induction response. The conditions for the weak-anisotropy approximation to be valid depend on the component of the response. For the coplanar components, the approximation is valid for an anisotropy ratio up to 2 if the relative dipping angle between the cross-bedded formation and the borehole axis is below [Formula: see text]. For the coaxial component, the approximation reduces to a previously established result that the apparent resistivity for such a component is the geometric average of the resistivities, parallel and perpendicular to the bedding planes of an anisotropic formation, respectively, if the borehole is ignored. Hence, the approximation holds for the coaxial component regardless of the anisotropy ratio.

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