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21.
Conditions for instabilities in collapsible solids including volume implosion and compaction banding
Ronaldo I. Borja 《Acta Geotechnica》2006,1(2):107-122
We review conditions for material instabilities in porous solids induced by a bifurcation of solution into non-unique strain rate fields. Bifurcation modes considered include jumps in the strain rate tensor of ranks one and higher representing deformation band and diffuse instability modes, respectively. Eigenmodes (e-modes) are extracted for each type of instability to fully characterize various frameworks of deformation in collapsible solids. For diffuse instability these e-modes are determined from a homogeneous system of linear equations emanating from the condition of zero jump in the stress rate tensor, which in turn demands that the tangent constitutive tensor be singular for the existence of nontrivial solutions. For isotropic materials we describe two types of singularity of the constitutive tensor: (a) singularity of the constitutive matrix in principal axes, and (b) singularity of spin. Accordingly, we derive the e-modes for each type of singularity. We utilize the singularity of the constitutive matrix in principal axes as a precursor to volume implosion in collapsible solids such as loose sands undergoing liquefaction instability and high-porosity rocks undergoing cataclastic flow. Finally, we compare conditions and e-modes for volume implosion and compaction banding, two similar failure modes ubiquitous in granular soils and rocks.Supported by U.S. Department of Energy, Grant DE-FG02-03ER15454, and U.S. National Science Foundation, Grants CMS-0201317 and CMS-0324674. 相似文献
22.
Theocharis Baxevanis Euripides Papamichos Olav Flornes Idar Larsen 《Acta Geotechnica》2006,1(2):123-135
The mechanical behavior and permeability of the Tuffeau de Maastricht calcarenite were studied. Compactions bands were found to form in the “transitional” regime between brittle faulting and cataclastic flow. In order to predict the formation of compaction bands, bifurcation analysis was applied on a model developed by Lade and Kim. The numerical results proved to be in good agreement with the experimental ones where the localization point was identified to be the onset of shear-enhanced compaction (a threshold in differential stress after which significant reduction of porosity is induced). Before the onset of shear-enhanced compaction, permeability was primarily controlled by the effective mean stress, independent of the deviatoric stresses. With the onset of shear-enhanced compaction, however, coupling of the deviatoric and hydrostatic stresses induced considerable permeability and porosity reduction. 相似文献
23.
油气充注对成岩作用的影响 总被引:5,自引:0,他引:5
油气充注对成岩作用的影响有三个方面 :抑制石英和伊利石的胶结作用、油气中所有机酸对深部孔隙的溶蚀改造作用、油气超压对压实的缓冲作用。英国北海Miller油气藏等的资料显示 ,油气充注较早时 ,油区的石英胶结速率比水区的明显要低 ,石英的胶结丰度比一般预测值低 ,而孔隙度比一般的预测值要高。我国渤海湾盆地东营凹陷油田资料显示 ,无论浅部或深部 ,凡是含油砂岩 ,其长石类及碳酸盐类矿物的溶解都十分强烈 ,次生孔隙很发育 ,而不含油的砂岩 ,其矿物溶解及次生孔隙发育一般较差 ;油层的方解石、白云石含量一般比水层低 ,深层尤为明显。干酪根生成油气时的流体体积增加 ,可大大增加孔隙流体压力 ,产生超压 ,并可传递到储集层 ,因而大大增加对压实作用的抵抗能力。上述三方面实质上都为深部油气成藏改善了储层基础 ,对深部油气勘探具有非常现实的意义。 相似文献
24.
25.
《Engineering Geology》2000,56(3-4):293-303
This study aims at investigating the utilization of bottom ash obtained from four different power stations as a construction fill and landfill bottom liner. For the matrix material, commercial powdered bentonite, construction lime and natural clay were used. Compaction tests (Standard Proctor and vibratory hammer) were carried out on the different ratios of bottom ash and matrix material. The optimum water content ranged from 40 to 45% yielding a dry density mostly ca 1 Mg m−3. Uniaxial compressive strength of mixtures ranges from 0.1 to 0.5 kgf cm−2 which showed a 3–20-fold increase when tested on 28-day cured specimens. Triaxial compression tests yield varying rates of shear strength which also showed as high as an 11-fold increase for cured specimens. The hydraulic conductivity of those mixtures was mostly ca 10−4 cm s−1, which is not considered to be low enough for landfill lining. Leaching tests using deionized water were also performed to investigate the possible effect of leachate produced from the mixtures on the environment. In conclusion a light density and environmentally friendly mixture is determined and proposed as construction filler. 相似文献
26.
兰州高坪湿陷性黄土地基处理方法分析 总被引:2,自引:0,他引:2
根据兰州地区3处大厚度高坪黄土的天然密度、含水量、土粒比重等物理性质指标沿深度变化的统计规律,分析了计算值-天然孔隙比随这些指标的变化规律,得出黄土天然孔隙比简化的计算公式。藉此分析强夯法、挤密桩法等地基处理方法的合理设计参数:对于强夯法,平均夯沉量可以作为初步设计参数和质量检测指标;对于挤密桩法,确定了加固深度和处理后的孔隙比,即可确定桩间距和桩径的比值。 相似文献
27.
Taber Hersum 《Contributions to Mineralogy and Petrology》2009,157(3):285-300
Crystals that form an interconnected porous network can become preferentially oriented both prior to and during compaction
of magmatic mush. This introduces anisotropy in the melt pore-space that can reduce permeability in the direction of compaction
and in turn decrease melt flux and compaction rate. Using a number of grain-scale numerical models, the consequences of end-member
magmatic fabrics on the directional dependence of permeability are tested over a range in melt fraction from 22 to 77%. As
the crystal aspect ratio (i.e. ratio of long to short axis length) increases from 2 to 10, isotropic permeability decreases
by a factor of 2 and 5 for randomly oriented prolate and oblate-shaped crystals, respectively, at a melt fraction of 22%.
With a flattening fabric, permeability is reduced in the compaction direction no more than approximately a factor of 2 relative
to the isotropic permeability at the same melt fraction and crystal shape for both oblate and triaxial prisms. However, permeability
is enhanced in directions orthogonal to the compaction direction. For example, permeability is enhanced up to a factor of
11 relative to the isotropic permeability at a melt fraction of 22% for oblate prisms with a ratio of the long to short axis
length of 10. Anisotropy in permeability increases as the melt fraction decreases and the crystal aspect ratio increases.
Ratios of the principal permeabilities are sufficiently large based on the realistic crystal shapes tested here to warrant
including anisotropic permeability into macroscale melt segregation models including those for compaction. 相似文献
28.
Geomaterials respond to some environmental circumstances through generation of a series of feedback mechanisms of damage, deformation, erosion, and chemical processes or reactions: e.g. osmosis, dissolution and precipitation, mineral transformations. These mechanisms are coupled at different scales. Several natural geomechanical processes, as sediment compaction, rock weathering or landsliding appear to include such sequences of mechanisms. A multi-physics model of sediment compaction is examined from the point of view of feedbacks and feedforwards for the phenomena involved at micro- and meso-scale. Two types of feedback are identified: constitutive feedbacks and boundary condition feedbacks. A numerical sensitivity study points out which feedbacks and feedforwards are strong and which are weak. 相似文献
29.
During specific intervals within Mesozoic and Cenozoic times, several areas of the southwestern Barents Sea were subjected to uplift and erosion. Areas with missing shallow stratigraphic interval sections and major erosion can be seen at several places along interpreted regional profiles in the southwestern Barents Sea. A new Normal Compaction Trend (NCT) for two selected shale– and sandstone–dominated lithologies has been constructed based on sonic logs in the southwestern Barents Sea. The shale– dominated NCT is calibrated to the Cretaceous shales in the northern North Sea and Norwegian Sea and applied to the Cretaceous shales of the Barents Sea. The sandstone–dominated NCT is calibrated to the Lower Jurassic Åre Formation of the Norwegian Sea and applied to the Lower Jurassic–Upper Triassic coastal plain section in the Barents Sea. By utilising the NCT model, the study estimates net apparent erosion in 28 selected Barents Sea wells based on comparison of sonic log velocities. A net apparent erosion map of the study area was constructed by gridding of the well values. The accuracy of the map is limited in areas with little well control, such as in the northwest, where the east–west transition into the southwestern Barents Sea region is poorly constrained. With that in mind, the map clearly shows two regional trends which dominate the erosion pattern in the study area; an increasing amount of erosion towards the north and a sharp decrease of erosion westwards of the hinge zone into the southwestern Barents Sea. The highest erosion estimates are observed towards Svalbard, with values up to 2500 m. The results of this study can be further utilized in petroleum system studies in the eroded areas. 相似文献
30.