Pore-Pressure-Coefficient Anisotropy Measurements for Intrinsic and Induced Anisotropy in Sandstone

2010 ◽  
Vol 13 (02) ◽  
pp. 265-274 ◽  
Author(s):  
Ashraf Al-Tahini ◽  
Younane Abousleiman
Keyword(s):  
Pore Pressure ◽  
Elastic Moduli ◽  
Pressure Coefficient ◽  
Induced Anisotropy ◽  
Transverse Anisotropy ◽  
Significant Control ◽  
Bedding Planes ◽  
Rock Structure ◽  
Stress Induced Anisotropy ◽  
The Difference

Summary In this study, we determine experimentally the effect of inherent and stress-induced anisotropy on stiffness components, elastic moduli, and Biot's pore-pressure coefficients (PPCs) for Lyons outcrop Colorado sandstone, which exhibits a clear transverse isotropic rock structure. Both dynamic and quasistatic methods were used under a nonhydrostatic state of stress to perform the measurements on dry core samples. Our assumption of apparent transverse anisotropy was confirmed initially with acoustic velocity measurements and at a later stage in the loading with experimental transverse anisotropic failure analysis. The objective of this study is to identify and isolate the effect of stress-induced anisotropy from the inherent transverse anisotropy on the measured stiffness components, elastic moduli, and Biot's PPCs. The effect of stress-induced anisotropy appears to have significant control on measured stiffness components, elastic moduli, and Biot's PPCs in comparison to the inherent-transverse-anisotropy effect. Our work shows that the stiffness components, Mij and thus the computed elastic moduli, are highly influenced by the stress-induced anisotropy, especially the off-diagonal stiffness components, M12 and M13, where the increase in their magnitudes from the dynamic measurements before failure is determined to be 100 and 81%, respectively. The difference in the magnitude between the axial and lateral Biot's PPCs in line with bedding planes and perpendicular to them is measured to be 24 and 16% from the quasistatic and dynamic methods, respectively; whereas, the effect of stress-induced anisotropy reduced the dynamic average magnitude of the Biot's PPCs along the bedding planes and transverse to these planes by 63% across a stress range of 145 MPa.

Porosity and elastic anisotropy of rocks under tectonic stress and pore-pressure changes

Geophysics ◽  
2005 ◽  
Vol 70 (5) ◽  
pp. N27-N38 ◽  
Author(s):  
Serge A. Shapiro ◽  
Axel Kaselow
Keyword(s):  
Pore Pressure ◽  
Elastic Moduli ◽  
Elastic Anisotropy ◽  
Pore Space ◽  
Tectonic Stress ◽  
Stress Sensitivity ◽  
Seismic Velocities ◽  
Confining Stress ◽  
The Difference ◽  
Stress Dependent

Elastic properties of rocks depend on tectonic stress. Using the theory of poroelasticity as a constraint, we analyze features of these dependencies related to changes in rock pore-space geometry. We develop a formalism describing elastic moduli and anisotropy of rocks as nonlinear functions of confining stress and pore pressure. This formalism appears to agree with laboratory observations. To a first approximation, elastic moduli and seismic velocities as well as porosity depend only on the difference between the confining tectonic stress and pore pressure. However, in general, both the confining stress tensor and the pore pressure must be taken into account as independent variables. The stress-dependent geometry of the pore space fully controls the stress-induced changes in elastic moduli and seismic velocities. Specifically, the compliant porosity plays the most important role, despite the fact that in many rocks the compliant porosity is a very small part of total porosity. Changes in compliant porosity with pressure and stress explain the often observed behavior of elastic moduli: in the low compressive stress regime — say, below 50 to 100 MPa — moduli increase rapidly and then taper exponentially into a flat and linear increase with increasing load. Taking into account the strain of the compliant pore space, we introduce a tensor quantity defining the sensitivity of elastic moduli of rocks to the difference between confining stress and pore pressure. We call it the stress sensitivity tensor. This tensor is an important physical characteristic directly related to elastic nonlinearity of rocks. The stress sensitivity tensor governs the changes in elastic anisotropy of a drained poroelastic system as it depends upon the applied load.

scholarly journals Plastic failure zone characteristics and stability control technology of roadway in the fault area under non-uniformly high geostress: A case study from Yuandian Coal Mine in Northern Anhui Province, China

2020 ◽  
Vol 12 (1) ◽  
pp. 406-424 ◽  
Author(s):  
Yaoguang Huang ◽  
Aining Zhao ◽  
Tianjun Zhang ◽  
Weibin Guo
Keyword(s):  
Numerical Methods ◽  
Numerical Solutions ◽  
Stress Test ◽  
Pressure Coefficient ◽  
Stability Control ◽  
Failure Zone ◽  
Plastic Failure ◽  
Comparison Results ◽  
High Geostress ◽  
The Difference

AbstractIn order to explore the effective support method for deep broken roadway, based on the in situ stress test results, the analytical and numerical solutions of the stress and the range of plastic failure zone (PFZ) in a circular roadway subjected to non-uniform loads were obtained using analytical and finite difference numerical methods based on the elastoplastic theory, respectively. Their comparison results show that the analytical and numerical methods are correct and reasonable. Furthermore, the high geostress causes the stress and range of PFZ in roadway roof and floor to increase sharply while those in roadway ribs decrease. Moreover, the greater the difference of horizontal geostress in different horizontal directions is, the larger the range of PFZ in roadway roof and floor is. The shape of PFZ in roadway varies with the ratio of horizontal lateral pressure coefficient in x-direction and y-direction. Finally, according to the distribution characteristics of PFZ and range of PFZ under the non-uniformly high geostress, this paper has proposed a combined support scheme, and refined and optimized supporting parameters. The field monitoring results prove that the roadway deformation and fracture have been effectively controlled. The research results of this paper can provide theoretical foundation as well as technical reference for the stability control of deep broken roadway under non-uniformly high geostress.

scholarly journals A hyperelastic model for soils with stress-induced and inherent anisotropy

2021 ◽  
Author(s):  
Marcin Cudny ◽  
Katarzyna Staszewska
Keyword(s):  
Small Strain ◽  
Induced Anisotropy ◽  
Dynamic Simulations ◽  
Inherent Anisotropy ◽  
Directional Model ◽  
Model Response ◽  
Hyperelastic Model ◽  
Stress Induced Anisotropy ◽  
Stress Invariant ◽  
Independent Model

AbstractIn this paper, modelling of the superposition of stress-induced and inherent anisotropy of soil small strain stiffness is presented in the framework of hyperelasticity. A simple hyperelastic model, capable of reproducing variable stress-induced anisotropy of stiffness, is extended by replacement of the stress invariant with mixed stress–microstructure invariant to introduce constant inherent cross-anisotropic component. A convenient feature of the new model is low number of material constants directly related to the parameters commonly used in the literature. The proposed description can be incorporated as a small strain elastic core in the development of some more sophisticated hyperelastic-plastic models of overconsolidated soils. It can also be used as an independent model in analyses involving small strain problems, such as dynamic simulations of the elastic wave propagation. Various options and features of the proposed anisotropic hyperelastic model are investigated. The directional model response is compared with experimental data available in the literature.

The Magnetic Anisotropy of Co-Base Amorphous Alloys

1991 ◽  
Vol 232 ◽  
Author(s):  
Wu-Xin Zhang ◽  
Xi-Ming Li ◽  
Nan-Ping Chen
Keyword(s):  
Magnetic Anisotropy ◽  
Amorphous Alloys ◽  
Induced Anisotropy ◽  
Pair Model ◽  
Mn Content ◽  
Stress Induced Anisotropy

ABSTRACT4 Co–base amorphous alloys prepared by rapid quenchling are stress–annealed under different temperature (Ta) balow its crytalline temperature Tcry, after pre–annealing. The effect of magnetic anisotropy with Ta shows the mechanism of stress–induced anisotropy is changed from single ionic modal to pair model as Ta inereases. The effect of Mn content may exaggerate the model changing.

Finite Element Analysis of Creep Damage Behavior Near the Cavity on Bimaterial Interface

2006 ◽  
Vol 324-325 ◽  
pp. 951-954 ◽  
Author(s):  
Qing Min Yu ◽  
Zhu Feng Yue ◽  
Yong Shou Liu
Keyword(s):  
Finite Element ◽  
Elastic Moduli ◽  
Elastic Stress ◽  
Creep Damage ◽  
Ductile Material ◽  
Bimaterial Interface ◽  
Modulus Ratio ◽  
Element Analysis ◽  
Damage Law ◽  
The Difference

Fracture along an interface between materials plays a major role in failure of material. In this investigation, finite element calculations with Kachanov–Rabotnov damage law were carried out to study the creep damage distribution near the interface cavity in bimaterial specimens. The specimens with central hole were divided into three types. The material parameters of K-R law used in this paper were chosen for a brittle material and ductile material. All calculations were performed under four load cases. Due to the difference between elastic moduli of the bounded materials, the elastic stress field as a function of the Young’s modulus ratio (R=E1/E2) was determined. At the same time, the influence of model type on elastic stress distribution near the cavity was considered. Under the same conditions, the material with larger modulus is subjected to larger stress. The creep damage calculations show that the location of the maximum damage is different for each model. The distributions of creep damage for all three models are dependent on the material properties and load cases.

Developing an in situ, hydromechanical coupling, true triaxial rock compression tester and investigating the deformation patterns of reservoir bank slopes

2021 ◽  
pp. qjegh2021-043
Author(s):  
Lei Fan ◽  
Meiwan Yu ◽  
Aiqing Wu ◽  
Yihu Zhang
Keyword(s):  
Coupling Effect ◽  
Water Pressure ◽  
Pressure Coefficient ◽  
Hydromechanical Coupling ◽  
Rock Interaction ◽  
True Triaxial ◽  
Rock Structure ◽  
Deformation Patterns

Interactions between water and rocks are the main factors affecting the deformation of rock masses on sloped banks by reservoir impoundment. The technology used in laboratory tests of water-rock interaction mechanisms cannot simulate the coupling of water, the rock structure and the initial stress environment. In this work, we develop an in situ hydromechanical true triaxial rock compression tester and apply it to investigate the coupling response of reservoir bank rocks to changing groundwater levels. The tester is composed of a sealed chamber, loader, reactor, and device for measuring deformation, which are all capable of withstanding high water pressures, and a high-precision servo controller. The maximum axial load, lateral load and water pressure are 12 000 kN, 3 000 kN and 3 MPa, respectively. The dimensions of the test specimens are 310 mm×310 mm×620 mm. The test specimens are grey-black basalts with well-developed cracks from the Xiluodu reservoir area. The results show that increasing water pressure promotes axial compression and lateral expansion, while decreasing water pressure causes axial expansion and lateral compression. A water pressure coefficient, K, is introduced as a measure of the hydromechanical coupling effect (expansion or compression) with changing groundwater level. A mechanical tester can be used to perform accurate field tests of the response of wet rocks to hydromechanical coupling. The test results provide new information about the deformation patterns of rock slopes in areas surrounding high dams and reservoirs.Thematic collection: This article is part of the Role of water in destabilizing slopes collection available at: https://www.lyellcollection.org/cc/Role-of-water-in-destabilizing-slopes

Study on Simulation Experiment with Universal Pass Rolling Deformation for Heavy Rail

2012 ◽  
Vol 430-432 ◽  
pp. 525-529 ◽  
Author(s):  
Lin Chen ◽  
Ke Xin Bi
Keyword(s):  
Finite Element ◽  
Pressure Coefficient ◽  
Small Deformation ◽  
Dimensional Accuracy ◽  
Research Unit ◽  
Finite Element Software ◽  
Universal Mill ◽  
The Difference ◽  
Rolling Deformation ◽  
Heavy Rail

Using the finite element software ANSYS/LS-DYNA for the universal rolling machine to simulate,research unit of the universal rolling deformation etc, and the use of universal mill for heavy rail rolling to simulate of lead samples, study of both. By comparing experimental results, the results show rolling simulation of laboratory lead samples and finite element simulations of computer are basically the same, use the universal pass, the difference of pressure coefficient for the rail head and rail base and rail back that work on the workpiece at the universal pass is small, deformation of workpiece is uniformity, it ensure the dimensional accuracy of the finished rail on the rail section.

Anisotropy Energies and Critical Behavior of Ultrathin Ni(111) Films Grown on Smooth and Rough W(110) (invited)

1991 ◽  
Vol 231 ◽  
Author(s):  
Yi Li ◽  
K. Baberschke
Keyword(s):  
Magnetic Properties ◽  
Curie Temperature ◽  
Film Thickness ◽  
Critical Exponent ◽  
Critical Behavior ◽  
Induced Anisotropy ◽  
Effective Anisotropy ◽  
Stress Induced Anisotropy ◽  
Surface Crystal

Abstract6 to 80 Å thin Ni(111) films were prepared on smooth and rough W(110) substrates in UHV and characterized by LEED and Auger spectroscopies. The measurements of the magnetic properties were carried out in situ by ferromagnetic resonance at 9 GHz between 300 and 600 K. We found that the effective anisotropies, which consist of surface, crystal, and stress induced anisotropy, increase with decreasing film thickness and temperature. The roughness of the substrate results in the drastic decrease of the effective anisotropy. This is attributed to the change of the surface structure and the stress within the Ni films. Furthermore we found that the Curie temperature Tc and the critical exponent β of Ni films on the smooth and rough substrates show no change.

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