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侯泉林,程南南,石梦岩,卢茜. 2018. 不同构造层次岩石变形准则的融合与发展. 岩石学报, 34(6): 1792-1800
不同构造层次岩石变形准则的融合与发展
作者单位
侯泉林 中国科学院计算地球动力学重点实验室 
程南南 中国科学院计算地球动力学重点实验室 
石梦岩 中国科学院计算地球动力学重点实验室 
卢茜 Department of Earth Sciences, Western University, 1151 Richmond Street, London, Ontarioa N6A 3K7 
基金项目:本文受国家重点研发计划深地资源勘查开采重点专项(2016YFC0600401)资助.
摘要:
      岩石变形准则对于构造地质学、工程安全等方面均具有重要的理论价值与实践意义。经典的岩石脆性变形(破裂)准则包括屈特加准则(水平直线型包络线)、库伦准则(斜直线型和抛物线型包络线)、格里菲斯准则(抛物线型包络线)等。近年来最大有效力矩准则在野外韧性剪切带观测与理论计算中都得到了广泛应用,逐渐成为岩石韧性变形的重要准则。然而,这些变形准则在应用过程中还存在一些问题,如有些准则在理论上无法解释、彼此不相协调,最大有效力矩准则在摩尔图解中尚无对应的包络线,部分准则边界条件和应用范围不清等。本文针对这些问题,结合野外实际情况和理论分析,取得了如下认识:(1)水平直线型屈特加准则在地质过程中无法实现。(2)提出了最大有效力矩准则的包络线方程为τ=-0.35(σn-σd),在摩尔图解中为一条反倾斜直线型包络线;进而将脆性变形的格里菲斯准则和库伦准则与韧性变形的最大有效力矩准则统一表述于应力摩尔图解中,使各准则彼此协调和融合。(3)初步明确了各变形准则的适用条件及所对应的构造层次:张性应力存在的构造环境(包括地壳浅表层次、水力压裂等人为张性应力环境),格里菲斯准则比较合适,以张性破裂(θ=~0°)和张剪性破裂(θ=0°~30°)为主;上地壳在一般情况下(3个主应力均为挤压应力),斜直线型库伦准则更为合适,以锐夹角共轭剪破裂(θ=~30°)为主;随着深度的增加,在中地壳,抛物线型库伦准则较合适,以锐夹角脆韧性剪切变形带(θ=30°~45°)为主;进入下地壳及以下,最大有效力矩准则更合适,以钝夹角韧性剪切变形带(θ=~55°)为主。实际地质作用过程中影响岩石变形的因素更为复杂多样,应具体问题具体分析,不能简单地对号入座。
英文摘要:
      The study of rock deformation criteria, including brittle and ductile deformation criteria, has important theoretical value and practical significance for structural geology and engineering safety. The classic brittle deformation (failure) criteria include Tresca criterion, Coulomb criterion and Griffith criterion, which are horizontal line, oblique line or parabola, and parabola envelope in Mohr diagram, respectively. In recent years the maximum effective moment (MEM) criterion has become one important ductile deformation criteria, which is supported by increasingly solid evidence from both observed examples in nature and laboratory experiments. However, we find that it is unfeasible for applying these criteria to actual geological practices. For instance, there are no reasonable explanations for some of the criteria in theory; though the MEM criterion is well functioned in explaining the origin of obtuse conjugate angle (usually ~110°), it is not yet resolved for the accurately corresponding envelope of MEM criterion in Mohr diagram; the applicable limitations of some criteria are unclear which make certain contradictions. Combining with field practices and theoretical analyses, we hold that:(1) It cannot be done for the Tresca criterion with horizontal envelope (the equation is τ=τ0, τ0 is the cohesive strength) in geological processes. Because in compressive regime, the normal stress is positive (σn>0) on the planes in θ=45° direction (θ is the angle between the maximum principal stress σ1 and the potential share planes), the failures will not form in this direction until the shear stress overcomes not only cohesive strength but also internal friction of the rock. Namely the shear stress cannot make rocks fracturing when it just achieves cohesive strength. The case of conjugate shear failures with 90° in the field is merely a coincidence, which is more likely to be the end tip of Coulomb criterion with parabola envelope tending to be horizontal in high confining pressure. (2) We propose that the Mohr envelope equation of the MEM criterion is τ=-0.35(σn-σd), which is corresponding to an anti-oblique line in Mohr diagram. Then we can combine the brittle deformation criteria (the Coulomb criterion and the Griffith criterion) and the ductile criterion (the MEM criterion) in Mohr diagram and make them coordinate with each other. (3) No clear distinctions among the applied conditions (namely the corresponding structural levels) of different criteria are the basic reasons for the contradictions above. For rocks in crust, there are various microscopic deformation mechanisms from brittle to ductile domain, which correspond to frictional sliding and crystal-plasticity (such as dislocation and diffusion creep), respectively. So the transformation of different deformation mechanisms requires the adjustment of corresponding criteria at different structural levels. To cover the full range of critical stress states in the crust, we try to give an unified interpretation to the mechanism of rock deformation at different structural levels and express it in Mohr diagram:the Griffith criterion with a parabola envelope is more appropriate at the tensile settings such as superficial crust and artificial settings like hydraulic fracturing where tensile fractures (θ=~0°) or hybrid fractures (θ=0°~30°) form; the Coulomb criterion with an oblique line envelope is proper at upper crust with axial compressive stresses where acute conjugate shear fractures form (θ=~30°); it is common for the envelope to flatten as the depth increases to the middle crust, and the Coulomb criterion with parabola envelope is suitable at brittle-ductile transition zone where acute conjugate ductile shear bands form (θ=30°~45°); at lower crust and below, the MEM criterion with an anti-oblique envelope is befitting where obtuse conjugate shear bands form (θ=~55°). Since the factors affecting rock deformation are complicated and various in geological processes, such as confining pressure, temperature, fluids, strain rate and so on, we should give concrete analyses to specific issues when using the criteria above.
关键词:岩石破裂准则  最大有效力矩准则  摩尔包络线  构造层次  微观变形机制
投稿时间:2018-01-19  修订日期:2018-03-18
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