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81.
The experimental programme of Southard and Mackintosh (1981) provides a definitive refutation of the autosuspension criterion as it was originally defined. A simple energy budget for dilute two-phase flow is derived from continuum theory of mixtures; it shows that Bagnold's criterion is based on an arbitrary comparison of two elements of the complete two-phase system. It is recommended that facile, ab hoc criteria for the behaviour of such complex flows be avoided in favour of analyses based on fundamental equations of motion. 相似文献
82.
James R. Rice 《Pure and Applied Geophysics》1983,121(3):443-475
Constitutive relations for fault slip are described and adopted as a basis for analyzing slip motion and its instability in
the form of earthquakes on crustal faults. The constitutive relations discussed include simple rate-independent slip-weakening
models, in which shear strength degrades with ongoing slip to a residual frictional strength, and also more realistic but
as yet less extensively applied slip-rate and surface-state-dependent relations. For the latter the state of the surface is
characterized by one or more variables that evolve with ongoing slip, seeking values consistent with the current slip rate.
Models of crustal faults range from simple, single-degree-of-freedom spring-slider systems to more complex continuous systems
that incorporate nonuniform slip and locked patches on faults of depth-dependent constitutive properties within elastic lithospheric
plates that may be coupled to a viscoelastic asthenosphere.
Most progress for the rate and state-dependent constitutive relations is at present limited to single-degree-of-freedom systems.
Results for stable and unstable slip with the various constitutive models are summarized. Instability conditions are compared
for spatially uniform versus nonuniform slip, including the elastic — brittle crack limit of the nonuniform mode. Inferences
of constitutive and fracture parameters are discussed, based on earthquake data for large ruptures that begin with slip at
depth, concentrating stress on locked regions within a brittle upper crust. Results of nonlinear stability theory, including
regimes of complex sustained stress and slip rate oscillations, are outlined for rate and state-dependent constitutive relations,
and the manner in which these allow phenomena like time-dependent failure, restrengthening in nearly stationary contact, and
weakening in rapidly accelerated slip, is discussed. 相似文献
83.
A. H. Wilson 《Geotechnical and Geological Engineering》1983,1(2):91-187
Summary The characteristics of soft rocks typical of the British Coal Measures are defined and a series of working hypotheses are developed to provide improved design methods for underground roadway and face supports and pillars in coal mines. Proposed design equations are tested against case history data. 相似文献
84.
We analyze flyby-type triple approaches in the plane isosceles equal-mass three-body problem and in its vicinity. At the initial time, the central body lies on a straight line between the other two bodies. Triple approaches are described by two parameters: virial coefficient k and parameter $\mu = \dot r/\sqrt {\dot r^2 + \dot R^2 }$ , where $\dot r$ is the relative velocity of the extreme bodies and $\dot R$ is the velocity of the central body relative to the center of mass of the extreme bodies. The evolution of the triple system is traceable until the first turn or escape of the central body. The ejection length increases with closeness of the triple approach (parameter k). The longest ejections and escapes occur when the extreme bodies move apart with a low velocity at the time of triple approach. We determined the domain of escapes; it corresponds to close triple approaches (k>0.8) and to μ in the range ?0.2<μ<0.7. For small deviations from the isosceles problem, the evolution does not differ qualitatively from the isosceles case. The domain of escapes decreases with increasing deviations. In general, the ejection length increases for wide approaches and decreases for close approaches. 相似文献
85.
Hanifi Canakci 《Environmental Geology》2007,53(4):915-922
This paper focuses on an investigation of the possible causes for the collapse of limestone caves in Gaziantep, Turkey. The
city contains a lot of man-made caves, at a shallow depth, of various width and length. These caves were mainly excavated
to provide work or storage space. As the city has been growing fast with increased population, many structures were constructed
over these caves. Recently, two caves collapsed and five houses were damaged. These caves are all made of limestone and it
was observed after the collapse that the limestone was saturated with water due to sewer pipe leakage and surface water. Tests
were carried out on the limestone and it was determined that the compressive strength of limestone decreases by about 50%
and the tensile strength decreased by about 80% when saturated with water. It was concluded that the reduced strength of the
limestone combined with additional loads due to the factors mentioned above seem to be the main reason for these collapses. 相似文献
86.
87.
浅析山区高等级公路中的边坡工程岩体 总被引:6,自引:1,他引:6
随着山区高等级公路建设的飞速发展,各类边坡工程岩体问题也日益增多。从卸荷岩体力学的基本观点入手,探讨了边坡工程岩体的变形破坏特性、稳定性评价方法以及开挖设计理论。研究表明,边坡工程岩体的变形破坏特性完全符合卸荷岩体力学行为,不同于常规的加载岩体行为;边坡工程岩体的稳定性分析计算中必须重视水力学因素和卸荷作用的影响,并得到了有意义的表达式;边坡工程岩体的开挖设计应在充分认识其工程力学性状的基础上,针对边坡岩体地质特性,结合已有各类稳定边坡的资料,进行既经济又可靠的优化设计。 相似文献
88.
曲石湾滑坡体成因分析及防治措施研究 总被引:4,自引:1,他引:4
滑坡的形成对周围环境造成很大的影响,并严重制约地方经济发展,威胁人民生命财产安全,因此,滑坡成因及防治措施的研究具有重要意义。本文通过实际资料,分析曲石湾滑坡体的形成机理,有针对性的提出曲石湾滑坡的防治措施。 相似文献
89.
90.
为了定量地研究塔里木北部地区区域的层次结构.拆离构造,特别是同油气地质、圈闭构造密切相关的沉积盖层中的层滑倾滑和推覆滑覆等各种构造的形成机制,对该区沉积盖层进行了较系统的岩石物性和岩石力学标本采集和测试(包括三轴参照实验).依其参数结构特点和地质、物探资料,划分出4套7层区域性层滑系统,并与研究程度较高的中、下扬子区的物性参数、岩性组合和构造特征进行综合对比.最后还进一步阐明了塔里木北部地区特征的前列式冲断构造和含油气局部构造等,均受到这7层区域层滑系统的制约. 相似文献