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31.
ZHOU Bo GE Hongkui ZHOU Wei WANG Jianbo HAO Hongyong WANG Xiaoqiong LIU Pengyu 《中国地震研究》2020,34(3):430-451
In recent years, with the success of exploration and development of conglomerate reservoirs in Mahu Depression, Junggar Basin, China, it is urgent to study the mechanical properties and its influencing factors of conglomerate which is considered as a new oil and gas reservoir. Based on the investigations of petrologic characteristics, heterogeneity and mechanical properties of conglomerate in Baikouquan formation, the content and geometric characteristics of gravel in conglomerate, the main factors in heterogeneity and the mechanical behavior in the triaxial compression experiment of conglomerate are analyzed in this paper. The results show that the size and content of gravel in conglomerate varies greatly, and conglomerate has strong heterogeneity under the influence of gravel content and size. An analysis of mechanical properties of conglomerate shows that conglomerate is characterized by plasticity. Besides, the sphericity is negatively correlated to the gravel content, while the heterogeneity increases with the increase of conglomerate plasticity. Due to the existence of heterogeneous gravel, local stress may concentrate in conglomerate when the stress is loaded. Consequently, a large number of micro-cracks appear at the edge of gravel, demonstrating the strong plasticity of conglomerate. This paper is of referential significance to the study of rock mechanical properties and the evaluation of engineering properties in conglomerate development. 相似文献
32.
Using analogue model experiments this study investigates the effects of lithostatic pressure and temperature in controlling the pattern of shear localization around rigid inclusions. Compression experiments were conducted on polymethylmethaacrylate (PMMA) by varying confining pressure (P = 30–70 MPa), homologous temperature (To = 0.67–0.80 corresponding to room temperature – 80 °C) and axial strain (yield – 15%) in a triaxial setup. Mechanical data showed temperature has a greater influence on the bulk yield strength and steady-state flow of the analogue material than confining pressure. Increasing confining pressures multiply the shear bands in number, and their overall pattern becomes progressively more complex, leading to composite band structures. On the other hand, under ambient pressure increasing temperature results in a transition from incipient high-strain zones to shear bands with sharp boundaries. Further increase in temperature switches the mode of shear localization, sharp to diffuse type. We finally show the inclusion-induced shear localization as a two-stage process, and provide a micro-mechanical explanation for the P-T dependent shear band patterns, attributed to three mechanically distinct domains of the inclusion-matrix interface: compression, extensional and shear localization. 相似文献
33.
Mechanically-based numerical modeling is a powerful tool for investigating fundamental processes associated with the formation and evolution of both large and small-scale geologic structures. Such methods are complementary with traditional geometrically-based cross-section analysis tools, as they enable mechanical validation of geometric interpretations. A variety of numerical methods are now widely used, and readily accessible to both expert and novice. We provide an overview of the two main classes of methods used for geologic studies: continuum methods (finite element, finite difference, boundary element), which divide the model into elements to calculate a system of equations to solve for both stress and strain behavior; and particle dynamics methods, which rely on the interactions between discrete particles to define the aggregate behavior of the system. The complex constitutive behaviors, large displacements, and prevalence of discontinuities in geologic systems, pose unique challenges for the modeler. The two classes of methods address these issues differently; e.g., continuum methods allow the user to input prescribed constitutive laws for the modeled materials, whereas the constitutive behavior ‘emerges’ from particle dynamics methods. Sample rheologies, case studies and comparative models are presented to demonstrate the methodologies and opportunities for future modelers. 相似文献
34.
Study of pore pressure variation during liquefaction using two constitutive models for sand 总被引：1，自引：0，他引：1
Numerical analyses of liquefiable sand are presented in this paper. Liquefaction phenomenon is an undrained response of saturated sandy soils when they are subjected to static or dynamic loads. A fully coupled dynamic computer code is developed to predict the liquefaction potential of a saturated sandy layer. Coupled dynamic field equations of extended Biot's theory with u–P formulation are used to determine the responses of pore fluid and soil skeleton. Generalized Newmark method is employed for integration in time. The soil behavior is modelled by two constitutive models; a critical state two-surface plasticity model, and a densification model. A class ‘B’ analysis of a centrifuge experiment is performed to simulate the dynamic response of level ground sites. The results of the numerical analyses demonstrate the capability of the critical sate two-surface plasticity model in producing pore pressures that are consistent with observations of the behavior of liquefiable sand in the centrifuge test. 相似文献
35.
Behavior of expansive soils stabilized with fly ash 总被引：6，自引：0，他引：6
Expansive soils cause serious problem in the civil engineering practice due to swell and shrinkage upon wetting and drying.
Disposal of fly ash, which is an industrial waste in both cost-effective and environment-friendly way receives high attention
in China. In this study, the potential use and the effectiveness of expansive soils stabilization using fly ash and fly ash-lime
as admixtures are evaluated. The test results show that the plasticity index, activity, free swell, swell potential, swelling
pressure, and axial shrinkage percent decreased with an increase in fly ash or fly ash-lime content. With the increase of
the curing time for the treated soil, the swell potential and swelling pressure decreased. Soils immediately treated with
fly ash show no significant change in the unconfined compressive strength. However, after 7 days curing of the fly ash treated
soils, the unconfined compressive strength increased significantly. The relationship between the plasticity index and swell-shrinkage
properties for pre-treated and post-treated soils is discussed. 相似文献
36.
Practical applications of a nonlinear approach to analysis of earthquake-induced liquefaction and deformation of earth structures 总被引：2，自引：0，他引：2
Zhi-Liang Wang Faiz I. Makdisi John Egan 《Soil Dynamics and Earthquake Engineering》2006,26(2-4):231-252
Seismic stability, liquefaction, and deformation of earth structures are critical issues in geotechnical earthquake engineering practice. At present, the equivalent linear approach is considered the ‘state of practice’ in common use. More recently, dynamic analyses incorporating nonlinear, effective-stress-based soil models have been used more frequently in engineering applications. This paper describes a bounding surface hypoplasticity model for sand [Wang ZL. Bounding surface hypoplasticity model for granular soils and its applications. PhD Dissertation for the University of California at Davis, U.M.I. Dissertation Information Service, Order No. 9110679; 1990; Wang ZL, Dafalias YF, Shen CK. Bounding surface hypoplasticity model for sand. ASCE, J Eng Mech 1990;116(5):983–1001; Wang ZL, Makdisi FI. Implementing a bounding surface hypoplasticity model for sand into the FLAC program. In: Proceedings of the international symposium on numerical modeling in geomechanics. Minnesota, USA; 1999. p. 483–90] incorporated into a two-dimensional finite difference analysis program [Itasca Consulting Group, Inc. FLAC (Fast Lagrangian Analysis of Continua), Version 4. Minneapolis, MN; 2000] to perform nonlinear, effective-stress analyses of soil structures. The soil properties needed to support such analyses are generally similar to those currently used for equivalent linear and approximate effective-stress analyses. The advantages of using a nonlinear approach are illustrated by comparison with results from the equivalent linear approach for a rockfill dam. The earthquake performance of a waterfront slope and an earth dam were evaluated to demonstrate the model's ability to simulate pore-pressure generation and liquefaction in cohesionless soils. 相似文献
37.
地质与地球物理观测数据表明青藏高原、安第斯山、以及帕米尔等典型造山高原之下均有明显的岩石圈地幔小尺度/分段式减薄现象.这些小尺度岩石圈减薄难以用经典的拆沉或对流减薄理论来解释,一方面,拆沉预示大尺度岩石圈地幔的剥离过程,而对流减薄则在黏度相对低的地幔岩石圈中发生,其主要以小尺度的局部增厚触发并仅减薄地幔岩石圈的底部区域.另一方面,拆沉或对流减薄模型都预测造山带尺度的地幔岩石圈拆离,都假设造山带岩石圈横向均一,然而实际的造山带岩石圈往往由多个不同的地块构成,块体之间岩性、物性、流变结构可能大有差别,即横向不均一性.这些造山带岩石圈地幔的横向不均一性,能否有效解释观测到的局部小尺度减薄现象？为此,我们构建了一系列高精度动力学数值模型,系统模拟了碰撞造山过程中岩石圈地幔的形变和不稳定性.结果表明,在塑性屈服强度很低的情况下,横向不均一的造山带岩石圈有发生分段式/小尺度减薄的可能性;其主要机理是由位错蠕变与强塑性作用所导致的应变集中使得地块间及壳幔间耦合弱化,从而使得较弱地块的岩石圈地幔在增厚时由于重力不稳定性而产生局部剥离,进而诱发小尺度软流圈上涌.模拟结果可以良好地解释发生在青藏高原东北缘、安第斯中部高原、以及帕米尔高原之下岩石圈的局部小尺度/分段式减薄现象. 相似文献
38.
Transmission electron microscopy (TEM) has been used to investigate deformation microstructures of synthetic stishovite specimens deformed at 14 GPa, 1,300°C. Geometrical characteristics of numerous dislocations have been characterized by dislocation contrast and stereographic analyses in order to identify the easy slip systems of stishovite. TEM data allowed us to characterize the following slip systems: 〈100〉{001}, 〈100〉{010}, 〈100〉{021}, [001]{100}, [001]{110}, [001]{210} and
Observation of sub-grain boundaries and scalloped edge dislocations suggest that climb has been activated in the specimens. 相似文献
39.
Continental breakup, or compressive lithosphere scale faulting, requires a physical mechanism for wholesale faulting of the lithosphere. We compared numerical and experimental models for the nucleation of quasi-adiabatic shear bands in polyvinylchloride (PVC) with those in an idealized viscoelastoplastic mantle with olivine rheology. In both materials fault nucleation is caused by elastic stress concentration on pre-existing imperfections, with localized yielding confined to its vicinity. Faulting occurs rapidly after the initial elastic energy in the system is charged sufficiently to cause wholesale yielding. Propagation of the fault, monitored by looking at the dissipation of plastic energy, reveals migration of a sharp, thermal-mechanical “crack”- like instability, which appears in the temperature field as a slightly diffused signal. The initial temperature rise in the crack is subtle but increases suddenly when the plate is severed. This autocatalytic behavior has also been described in ductile polymers, which can be used as mechanical analogues. We suggest that elastoplastic coupling in quasi-adiabatic shear banding is a key for fast (< 1 Ma) nucleation of shear zones. These nonlinear phenomena will be illustrated for both experimental and numerical results by nine movies 相似文献
40.
This paper investigates the cyclic and post-cyclic shear behavior of low-plasticity silt and the impact of additional clay content. Bentonite clay was added to the low-plasticity Mississippi River Valley (MRV) silt (PI=6) to increase the clay content of the soil. A series of triaxial tests were conducted in the laboratory to examine the shear and pore pressure behavior during and after cyclic loading. As the bentonite content in the reconstituted specimens increased, the excess pore pressure developed at a slower rate and the total excess pore pressure decreased at the end of cyclic loading. In contrast to the MRV silt, the specimens modified with bentonite experienced cyclic softening rather than initial flow liquefaction. The cyclic shear strength increased with an increase in bentonite content. The post-cyclic reconsolidation behavior was a similar to a virgin compression process, and not recompression. Adding bentonite to the MRV silt results in changes in permeability, compressibility, undrained shear strength, and initial stiffness. Additionally, the cyclic loading had a marked effect on the shear behavior of low-plasticity soil with a PI<6, but not noticeable with a PI>6. This study suggests that the behavior of the Mississippi River Valley silt changes from contractive sand-like material to clay-like behavior at a PI≈6 due to the addition of clay. 相似文献