Combined investigations of fluid inclusions in opaque ore minerals by NIR/SWIR microscopy and microthermometry and synchrotron radiation X-ray fluorescence     

《Applied Geochemistry》2006,21(5):813-819

An alternative IR microscopy system in the NIR (near infrared, up to 10 μm) and SWIR (short wavelength infrared, up to 1.4 μm) ranges has been developed for the study of opaque ore minerals. The system uses either IR LED or IR light bulb sources depending on the degree of opacity of the investigated minerals. This paper presents the methodology and the promising results obtained in studies of opaque ore minerals such as Ag minerals (pyrargyrite) from epithermal deposits and Nb-tantalates (columbite) from pegmatites. It also presents results on the internal features of hematites from Fe ore banded formations and tungstates from granite–greenstone belt deposits. The data obtained on fluid inclusions from pyrargyrite and hematite crystals have been integrated by complementary information from X-ray fluorescence analysis using synchrotron radiation (μ-SXRF) under conditions specifically designed for the study of opaque ore minerals.  相似文献   

A bounding surface model for anisotropically overconsolidated clay incorporating thermodynamics admissible rotational hardening rule     

Yanni Chen  Zhongxuan Yang 《国际地质力学数值与分析法杂志》2020,44(5):668-690

A bounding surface model is formulated to simulate the behavior of clays that are subject to an anisotropic consolidation stress history. Conventional rotational hardening is revisited from the perspective of thermodynamics. As the free energy cannot be accumulated infinitely upon critical state failure, the deviatoric back stress must vanish. This requires the rotated yield surface to be turned back to eventually align on the hydrostatic axis in the stress plane. Noting that most of the previous propositions violate this restriction, an innovative rotational hardening rule is formulated that is thermodynamically admissible. The bounding surface framework that employs the modified yield surface is applied to simulate elastoplastic deformations for overconsolidated clays, with which the overprediction of strength on the “dry” side can be greatly improved with reasonable results. Other important features, including contractive or dilative response and hardening or softening behavior, can also be well-captured. It has been shown that the model can simulate three types of reconstituted clays that are sheared with initial conditions over a wide range of anisotropic consolidation stress ratios and overconsolidation ratios under both triaxial undrained and drained conditions. Limitations and potential improvement of the model regarding the fabric anisotropy at critical state have been discussed.  相似文献   

Constitutive modelling of fine-grained gassy soil: A composite approach     

Zhiwei Gao  Yi Hong  Lizhong Wang 《国际地质力学数值与分析法杂志》2020,44(9):1350-1368

Fine-grained marine sediments containing large undissolved gas bubbles are widely distributed around the world. Presence of the bubbles could degrade the undrained shear strength (s_u ) of the soil, when the gas pressure u_g is relatively high as compared with the effective stress in the saturated soil matrix. Meanwhile, the addition of bubbles may also increase s_u when the difference between u_g and pore water pressure u_w becomes smaller than the water entry value, causing partial water drainage from the saturated matrix into the bubbles (bubble flooding) during globally undrained shearing. A new constitutive model for describing the two competing effects on the stress-strain relationship of fine-grained gassy soil is proposed within the framework of critical state soil mechanics. The gassy soil is considered as a three-phase composite material with compressible cavities, which allows water entry from the saturated matrix. Bubble flooding is modelled by introducing an additional positive volumetric strain increment of the saturated clay matrix, which is dependent on the difference between pore gas and pore water pressure based on experimental observations. A modified hardening law based on that of the modified Cam clay model is employed, which in conjunction with the expression for bubble flooding, can describe both the detrimental and beneficial effects of gas bubbles on soil strength and plastic hardening in shear. Only two extra parameters in addition to those in the modified Cam clay model are used. It is shown that the key features of the stress-strain relationship of three fine-grained gassy soils can be reproduced satisfactorily.  相似文献   

Soil‐pile interaction in the pile vertical vibration considering true three‐dimensional wave effect of soil     

W.B. Wu  K.H. Wang  Z.Q. Zhang  Chin Jian Leo 《国际地质力学数值与分析法杂志》2013,37(17):2860-2876

The dynamic response of an end bearing pile embedded in a linear visco‐elastic soil layer with hysteretic type damping is theoretically investigated when the pile is subjected to a time‐harmonic vertical loading at the pile top. The soil is modeled as a three‐dimensional axisymmetric continuum in which both its radial and vertical displacements are taken into account. The pile is assumed to be vertical, elastic and of uniform circular cross section. By using two potential functions to decompose the displacements of the soil layer and utilizing the separation of variables technique, the dynamic equilibrium equation is uncoupled and solved. At the interface of soil‐pile system, the boundary conditions of displacement continuity and force equilibrium are invoked to derive a closed‐form solution of the vertical dynamic response of the pile in frequency domain. The corresponding inverted solutions in time domain for the velocity response of a pile subjected to a semi‐sine excitation force applied at the pile top are obtained by means of inverse Fourier transform and the convolution theorem. A comparison with two other simplified solutions has been performed to verify the more rigorous solutions presented in this paper. Using the developed solutions, a parametric study has also been conducted to investigate the influence of the major parameters of the soil‐pile system on the vertical vibration characteristics of the pile. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

An efficient quasi-Newton approximation-based SORM to estimate the reliability of geotechnical problems     

《Computers and Geotechnics》2016

The first order reliability method (FORM) is efficient, but it has limited accuracy; the second order reliability method (SORM) provides greater accuracy, but with additional computational effort. In this study, a new method which integrates two quasi-Newton approximation algorithms is proposed to efficiently estimate the second order reliability of geotechnical problems with reasonable accuracy. In particular, the Hasofer–Lind–Rackwitz–Fiessler–Broyden–Fletcher–Goldfarb–Shanno (HLRF–BFGS) algorithm is applied to identify the design point on the limit state function (LSF), and consequently to compute the first order reliability index; whereas the Symmetric Rank-one (SR1) algorithm is nested within the HLRF–BFGS algorithm to compute good approximations, yet with a reduced computational effort, of the Hessian matrix required to compute second order reliabilities. Three typical geotechnical problems are employed to demonstrate the ability of the suggested procedure, and advantages of the proposed approach with respect to conventional alternatives are discussed. Results show that the proposed method is able to achieve the accuracy of conventional SORM, but with a reduced computational cost that is equal to the computational cost of HLRF–BFGS-based FORM.  相似文献   

考虑加载过程及桩体固结变形的碎石桩复合地基固结解析解     

郭彪  龚晓南  李亚军 《工程地质学报》2016,24(3):409-417

为了完善碎石桩复合地基固结理论,通过假设从桩体排出的水量等于流入桩体的水量与桩体体积变化之和以及地基扰动区土体水平渗透系数呈线性变化,并考虑上部荷载逐渐施加,推导了考虑桩体体积变化的碎石桩复合地基超静孔压及固结度解析解。当加载时间趋于零时,本文解可退化为瞬时加载情况下的解;当加载时间及桩径同时趋于零时,本文解可进一步退化为Terzaghi一维固结解,这证明了本文解的正确性。通过与已有解的比较,对地基固结性状进行了分析。结果表明,加载过程对地基固结度影响显著,加载历时越长,固结越慢;在各种条件下,不考虑桩体固结变形时地基固结始终比考虑桩体变形时快,并且其影响随着加载历时变小、桩径比变小、桩土模量比变小、桩土渗透系数变小而逐渐增大,这说明在实际工程固结计算中不考虑桩体固结变形是偏于不安全的。  相似文献   

锈蚀钢筋在疲劳荷载作用下压磁场分布研究     

金伟良  周峥栋  毛江鸿  张军  崔磊  潘崇根 《海洋工程》2016,34(5):65-72

针对锈蚀钢筋的疲劳损伤与寿命评估中的难度大、精度低等问题,引入压磁检测技术,对锈蚀钢筋疲劳过程中的压磁场分布进行检测,从宏观与微观相结合的角度分析压磁场分布与疲劳损伤之间的联系。试验结果表明,锈蚀钢筋的压磁场分布能够反映疲劳损伤的演变规律,疲劳后期非线性特征加剧,锈蚀率及应力幅越大则变化越为明显,磁感强度值、磁场分布梯度、"反转"现象等均有助于进行疲劳损伤评价与寿命预测。研究结果可为压磁无损检测技术在钢筋混凝土结构中的应用提供依据。  相似文献   

IPCC AR6报告解读：气候系统对太阳辐射干预响应     

曹龙 《气候变化研究进展》2021,17(6):671-684

IPCC第六次评估报告（AR6）第一工作组报告评估了太阳辐射干预（Solar radiation modification,SRM）对气候系统和碳循环的影响。在大幅度减排基础上,太阳辐射干预有潜力作为应对气候变化的备用措施。目前,对于太阳辐射干预气候影响的评估都是基于模式模拟结果。评估主要结论如下：太阳辐射干预可以在全球和区域尺度上抵消一部分温室气体增加造成的气候变化（高信度);但是太阳辐射干预无法在全球和区域尺度上完全抵消温室气体增加引起的气候变化（几乎确定);有可能通过适当的太阳辐射干预设计,同时实现多个温度变化减缓目标（中等信度);在高强度温室气体排放情景下,如果太阳辐射干预实施后突然终止,并且这种终止长时间持续,将会造成快速的气候变化（高信度);如果在减排和CO₂移除的情况下,太阳辐射干预的实施强度逐渐减小至零,将显著降低太阳辐射干预突然终止产生的快速气候变化风险（中等信度);太阳辐射干预会通过降温作用,促进陆地和海洋对大气CO₂的吸收（中等信度),但是太阳辐射干预无法缓解海洋酸化（高信度);太阳辐射干预对其他生物化学循环影响的不确定性大。由于对云-气溶胶-辐射过程的相互作用和微物理过程认知有限,目前对平流层气溶胶注入、海洋低云亮化、高层卷云变薄等太阳辐射干预方法的冷却潜力和气候效应的认知还有很大的不确定性。  相似文献   

Drought prediction using in situ and remote sensing products with SVM over the Xiang River Basin,China     

Zhu  Qian  Luo  Yulin  Zhou  Dongyang  Xu  Yue-Ping  Wang  Guoqing  Tian  Ye 《Natural Hazards》2021,105(2):2161-2185

Natural Hazards - Droughts have caused many damages in many countries and might be aggravated around the world. Therefore, it is urgent to predict and monitor drought accurately. Soil moisture and...  相似文献   

花岗岩风化料弃土快速堆填过程中不排水抗剪强度评估     

詹良通  孙倩倩  郭晓刚  陈锐  陈云敏 《岩土力学》2021,(1):50-58

沿海沿江城市地下开挖产生的工程渣土含泥量大、含水率高且较松散,主要运往渣土场进行堆填处置。由于产量巨大而处置场地有限,许多渣土场在运营过程中存在堆填速度快、缺乏排水设施、超高超库容堆填等问题,容易引发堆填体失稳事故。目前对于非饱和工程渣土堆体在快速堆填过程中的失稳机制认识尚不清晰,尤其是对这一过程中的高饱和度工程渣土强度增长规律缺乏足够的认识。以深圳红坳渣土场填料——花岗岩风化料(CDG)填土为研究对象,对不同初始饱和度土样进行三轴不排水不排气等向压缩和剪切试验,结果表明:非饱和CDG填土不排水抗剪强度随围压增大呈非线性增长,增长速率与试样初始饱和度密切相关;当土样压缩后的饱和度超过0.7,不排水强度随围压的增长速率显著降低。基于有效固结应力法的原理,结合Hilf孔压公式和修正剑桥模型,提出了一种工程渣土不排水抗剪强度估算方法,并通过与试验结果对比验证了该方法对初始饱和度高于0.6的CDG填土的适用性。利用该方法确定的不排水强度cu与正应力σn的关系可应用于高饱和度工程渣土快速堆填中的稳定性分析。  相似文献