非均质各向异性软基上管桩基础承载力分析

对于非均质各向异性软土地基上管桩基础的承载力,基于塑性极限分析理论考虑软土强度的非均质与各向异性效应,提出了一种改进的三维极限分析上限解法。利用有限元分析软件ABAQUS,采用Hill理想弹塑性模型,对软基上管桩水平承载力进行了数值模拟,由此所得到的破坏模式与极限分析方法中的假设失稳机制基本一致。通过变动参数对比分析,探讨了软黏土不排水抗剪强度的各向异性和非均质性对于管桩基础承载力的影响。     

华北地台中元古代碳酸盐岩中的微生物成因构造及其生烃潜力

华北地台中元古界主要由环潮坪石英砂岩、浅海碳酸盐岩和浅海—泻湖相暗色页岩3种沉积相组合构成,以陆表海浅水碳酸盐岩占主导。碳酸盐岩中除含有丰富的微古植物、宏观藻类和微生物建隆外,还发育大量的微生物成因构造(MISS)和微生物诱发的碳酸盐沉淀(MMCP)。微生物席和MISS构造在高于庄组上部(约1.6 Ga)和雾迷山组下部(约1.45 Ga)碳酸盐岩中尤为发育,表明活跃的微生物活动和高有机质产量。在石化微生物席中,发现有丝状、球状细菌化石和草莓状黄铁矿;围岩中发现有针状文石、花瓣状重晶石、放射状菱铁矿、铁白云石和葡萄状碳酸盐胶结物等多种自生碳酸盐矿物,指示甲烷厌氧氧化(AOM)导致的自生碳酸盐沉淀。中元古代的温暖气候和海洋分层、缺氧、硫化条件有利于微生物的高生产量和高有机质埋藏率。气隆构造和核形石状碳酸盐结核反映浅埋藏条件下活跃的成烷作用和甲烷排放,围岩和MMCP中富沥青质。华北地台中元古界富微生物席碳酸盐岩有良好的生烃潜力,有可能形成重要的烃源岩。据微生物席、MISS构造及MMCP的研究,初步估算华北地台中元古代碳酸盐岩的概略生烃潜力约为10×108t石油当量。     

微生物成矿

微生物对生命元素如碳、氮、硫、氧和金属离子的代谢作用能显著的改变微生物周边的外部环境和其内部环境。在一系列的生物地球化学过程中,微生物参与了矿产的沉积(生物成矿)或参与了矿石和岩石的溶解(生物风化)。生物成矿作用有两个途径：一个叫生物诱导成矿,通过这个过程,微生物分泌出代谢产物导致了之后的矿物颗粒的沉积;另一个叫生物控制成矿,在这个过程中,微生物在控制矿物成核和生长上起到了显著作用。微生物成因的矿物总体来说颗粒都很小和／或有着独特的同位素特征。最普遍的生物成因矿物有碳酸盐、硫化物和铁的氧化物。细胞表面和其分泌的胞外聚合物的结构可以为离子的浓缩、聚合和矿化提供模板,并起到重要作用。地球材料的仿生合成帮助我们了解了在人工条件下的生物成矿机制。此外,在地质环境中生物成因的矿物还可以作为一种生物信号,用来重建地球和其他行星的起源和演化。     

Simplified Method for the Assessment of the Stiffness Anisotropy of Rocks at Small Strains

Summary A new, practically applicable method for characterizing the stiffness anisotropy of rocks is presented. The anisotropy of geo-materials is often ignored in engineering applications, with potentially serious ramifications, because of the number of parameters required for characterization. The elastic anisotropy has often been considered to be a function of mathematical symmetry, and the restrictions due to layering, microcracking and granularity of the materials have not been considered in the assessment of the anisotropy. The practicality of the method proposed here is achieved by rationally reducing the number of independent anisotropy parameters, typically 9 for orthotropic anisotropy, to a system of 4 independent parameters through a systematic theoretical and experimental analysis of these structural restrictions. These 4 parameters are shown to be sufficient for describing the anisotropy of some rocks and sands at small strains, and parameter determination by back-analysis is demonstrated to be stable using appropriate measurement systems involving 9 elastic wave velocities even when the directions of anisotropic axes are unknown and the velocity data contains appreciable error.     

由震源机制和地震波各向异性探讨青藏高原岩石圈变形

本文据青藏高原天然地震震源参数和地震波各向异性资料，讨论了高原岩圈不同圈层的变形特性。     

水动力质量实效施加方法及地基-筒型基础-塔筒体系的地震敏感性研究

针对海上风电结构在有限元计算中水动附加质量的施加问题,提出了一种在ABAQUS软件中简便有效易于实现的方法,可以提高有限元分析的前处理效率;建立有限元模型,分析有、无考虑水动附加质量和不同边界条件对海上风电结构自振特性的影响,并从力学角度进行分析;利用有限元模拟地震动作用下的海上风电结构塔筒响应,并对水动附加质量和边界条件进行敏感性分析。通过数值计算并结合理论分析表明：提出的水动附加质量施加方法是合理实用的;水动附加质量的施加使得结构固有频率减小,且随着阶数增大,固有频率减小的绝对值增大;边界条件对体系的模态参数影响比水动附加质量更显著,黏弹性透射边界条件下计算得到结构体系的各阶频率较固定边界均有比较明显的减小;黏弹性透射边界模型在地震动作用下的位移响应比固定边界模型大。分析结果对此类海上风电工程具有借鉴意义。     

复杂地形下高密度激电法2.5维有限单元法数值模拟

目前三维有限元模拟计算量大,计算效率低,对计算机要求较高,2.5维模拟是三维问题的简化,较好地克服了上述问题。在高密度激电法模拟中,模拟的点数一般较大,要求程序计算效率高,因此对高密度激电法2.5维模拟研究是必要的。首先给出了2.5维稳定电流场的边值问题及对应的变分问题;为了能更好模拟复杂地形对极化率异常的影响,采用三角形网格,有利于模拟复杂地形又有利于将其应用于反演计算。推导了基于连续电性介质的2.5维稳定电流场的有限元法,利用等效电阻率法,编制了2.5维高密度激电法有限元模拟程序,计算了水平地形及起伏地形下的极化率异常模型,并验证了方法的可行性,分析得出了山谷地形比山脊地形对极化率观测的影响大的结果。     

An approach to model the mechanical behavior of transversely isotropic materials

The present work proposes an approach to adapt existing isotropic models to transversely isotropic materials. The main idea is to introduce equivalence relations between the real material and a fictitious isotropic one on which one can take all the advantages of the well‐established isotropic theory. Two applications of this approach are presented here: a failure criterion and a damage model that takes into account the load‐induced anisotropy. In both cases, theoretical predictions are in agreement with the experimental data. In the present paper, the developed approach is applied to sedimentary rock materials; nevertheless, it can be generalized to any material that exhibits transverse isotropy. Copyright © 2015 John Wiley & Sons, Ltd.     

Weakness and mechanical anisotropy of phyllosilicate-rich cataclasites developed after mylonites of a low-angle normal fault (Simplon Line,Western Alps)

The Simplon Fault Zone is a late-collisional low-angle normal fault (LANF) of the Western Alps. The hanging wall shows evidence of brittle deformation only, while the footwall is characterized by a c. 1 km-thick shear zone (the Simplon Fault Zone), which continuously evolved, during exhumation and cooling, from amphibolite facies conditions to brittle-cataclastic deformations. Due to progressive localization of the active section of the shear zone, the thermal-rheological evolution of the footwall resulted in a layered structure, with higher temperature mylonites preserved at the periphery of the shear zone, and cataclasites occurring at the core (indicated as the Simplon Line). In order to investigate the weakness of the Simplon Line, we studied the evolution of brittle/cataclastic fault rocks, from nucleation to the most mature ones. Cataclasites are superposed on greenschist facies mylonites, and their nucleation can be studied at the periphery of the brittle fault zone. This is characterized by fractures, micro-faults and foliated ultracataclasite seams that develop along the mylonitic SCC′ fabric, exploiting the weak phases mainly represented by muscovite and chlorite. Approaching the fault core, both the thickness and frequency of cataclasite horizons increase, and, as their thickness increases, they become less and less foliated. The fault core itself is represented by a thicker non-foliated cataclasite horizon. No Andersonian faults or fractures can be found in the footwall damage zone and core zone, whilst they are present in the hanging wall and in the footwall further from the fault. Applying a stress model based on slip tendency, we have been able to calculate that the friction coefficient of the Simplon Line cataclasites was <0.25, hence this fault zone is absolutely weak. In contrast with other fault zones, the weakening effect of fluids was of secondary importance, since they accessed the fault zone only after an interconnected fracture network developed exploiting the cataclasite network.     

The behavior of a multilayered porous thermo-elastic medium with anisotropic thermal diffusivity and permeability

With the aid of integral transform techniques, this paper presents an extended precise integration solution for thermal consolidation problems of a multilayered porous thermo-elastic medium with anisotropic thermal diffusivity and permeability due to a heat source. From the fundamental governing equations, ordinary differential equations are derived by employing Laplace–Hankel transforms. By applying the extended precise integration method, equations in the transformed domain can be solved, and the actual solutions are further obtained by adopting a numerical inverse transformation. The accuracy and feasibility of the proposed theory is demonstrated by contrastive analysis with existing studies. Finally, several examples are carried out to investigate the influence of heat source’s type, axial distance, burial depth of heat source, ratio of thermo-permeability, permeability anisotropy, thermal diffusivity anisotropy and stratification on the thermal consolidation process.