共查询到20条相似文献，搜索用时 250 毫秒
1.
通过介绍Ｊ．Ｐ．Ｋｅｎｎｅｔｔ为代表的“洋流说”阐述了大洋钻探２５年来约１０个航次研究所揭示的南极地区显生宙晚期气候演变的历史。晚白垩世时南极地区和全球一样暖和无冰，末期变冷，古新世开始后不久又转暖，早始新世－中始新世早期达顶峰，以后变冷。渐新世为主要冷却期，南极东部形成冰盖，中，晚中新世为另一重要冷却期，南极西部以至全部南极在中新世晚期－上新世早期最终形成稳定冰盖。德雷克海峡打开，环南极洋流（Ａ 相似文献
2.
3.
通过野外实地考察、实验模拟，在黄河三角洲发现了一种非常特殊的、冰-（水-）泥共同作用而形成的冰携泥现象。冬末春初，冰雪融化，位于冰层底部的细粒碎屑沉积物质（粉砂或粘土）常被冰向上携起。研究认为，冰携泥的发育过程可以分为三个阶段：沉积物的破碎、冰层底部融化-泥沙被冰垂向搬运及泥沙下落-冰成球粒等的形成。在冰携泥的整个过程中可产出冰劈裂缝、冰成球粒和冰成泥沙片等特殊的沉积现象（构造），它们是冰携泥现象留下的重要的地质记录，对于恢复这一特殊现象及其形成的环境条件具有重要的指示意义。另外，初步探讨了冰携泥现象形成的两种可能机制：毛细作用和冰融水对流作用，并认为在冰融水能及时渗漏或排出的开放系统中，只有毛细作用机制发生作用；在冰融水不能被渗漏或排出的密闭系统中，两种机制共同发生作用。 相似文献
4.
雪冰中微量有机物的生物地球化学研究进展 总被引：2，自引：0，他引：2
雪冰中微量有机物的生物地球化学研究进展龙江平，秦大河（中国科学院冰川冻土研究所，兰州７３００００）关键词雪冰，有机物，生物地球化学雪冰中微量有机物的生物地球化学主要研究雪冰中有天然来源的微量有机物和由人类活动、工业化发展带来的人为污染有机物。通过雪冰... 相似文献
5.
随着全球气候变暖，青藏高原冰崩灾害日益加剧.通过大量遥感解译及数据分析，系统查明青藏高原冰崩隐患数量、类型、发育规律及危险性:(1)40 269条冰川共发育冰崩隐患581处.按失稳方式分为滑移式和崩落式；按成灾模式分为冰崩直接灾害、冰崩-堵江溃决和冰崩-冰湖溃决灾害.(2)冰崩敏感坡度40°~50°，集中分布高程为4 500~5 500 m，坡向具有“亲北性”.(3)区域分布差异大.西藏和新疆区域分布共占89.5%，雅鲁藏布江和塔里木河流域分布共占80.4%，念青唐古拉山脉和横断山脉分布共占49.4%.(4)空间分异明显.冰崩前缘高程以喜马拉雅东构造结为界，以西呈自西向东增大的趋势，以东呈先减小后增大的“V”型趋势，40.1%的冰崩前缘高程4 500~5 000 m、位于雪线附近，受山脉控制具有气候带交界“群聚性”特点.(5)高危险的冰崩隐患点36处、中等危险215处、低危险330处. 相似文献
6.
ＪＪＹ型井径仪测量臂释放方法的改进天津市津新岩土工程有限公司刘士江ＪＪＹ型井径仪测量臂的开后，是由束缚盒在泥浆中的反力作用打开的，使用时测量臂的开启经常没有保证，有时不得不中断测量。在实际工作中，我们通过总结经验，对测量臂束缚盒的释放方法进行了改进（... 相似文献
7.
论内蒙古第四纪冰川和冰臼群的成因 总被引：5，自引：0，他引：5
通过内蒙古林东地区第四纪冰川地质和冰臼群成因专项调查工作，发现了晚更新世冰碛泥砾层的龟背石、熨斗石、龟裂石等典型的冰碛砾石及冰斗、刃脊、角峰、冰川槽谷中的表皮构造等山谷冰川遗迹。在花岗岩体中发的岩臼群，可划分为冰期冰雪融水形成的冰臼、现代季节性降水形成的瓯穴和风蚀作用为主形成的风翕3种类型。本区冰臼同山谷冰川相伴随，未发现远源巨型漂砾等大陆冰盖证据。 相似文献
8.
雪冰中重金属的研究进展 总被引：4，自引：1，他引：4
文章概述了雪冰样品中重金属分析的发展状况，以及在样品分析中出现的困难，方法，并简要介绍了常用的分析方法及雪冰样中重金属分析的发展方向。 相似文献
9.
中国内蒙古哈马尔太碱湖Ha01孔岩心13000a以来的古气候记录 总被引：1，自引：0，他引：1
通过对内蒙古哈马尔太碱湖Ｈａ０１孔岩心古气候记录的研究，划分出１３０００ａ以来的１０个气候期及若干气候阶。对比表明，与全球气候变化是一致。在末次冰期盛冰期之后，冰后期之前，有三次明显的急速降温，先后有老仙女木冰阶、中仙女木冰阶和新仙女木冰队；冰后期以来，有两次大幅度的降温事件，均具有全球性，一次冷点是７６４０ａＢ．Ｐ．，一次冷点为５０００ａ．Ｂ．Ｐ．，前者相当Ｄｅｎｔｏｎ称作的第一新冰期，后者相当 相似文献
10.
随着全球气候的变暖,青藏高原地区冰川消融、退缩加剧,稳定性降低,增加了冰崩灾害的发生频率。西藏地区作为青藏高原的主体部分,其冰川的稳定影响着我国及周边国家的水源及生命财产安全。文章通过梳理国内外冰崩的研究现状,整理了西藏地区冰崩灾害的定义;从地形因素、构造运动和气候作用角度分析了冰崩形成机制;归纳分析了冰崩—冰湖溃决—泥石流链式灾害、冰崩—堵溃—泥石流链式灾害、冰崩—直接型泥石流（山洪）灾害3种类型冰崩灾害链的特征;阐述了目前冰崩灾害监测预警的手段及特点,认为多种监测方式联合是冰崩灾害监测的发展趋势,展望了冰崩灾害的研究体系,以期能为后续的研究工作提供思路。 相似文献
11.
12.
The cracked chevron notched semi-circular bending (CCNSCB) method falls into a significant testing category of chevron notched specimens for measuring the mode I fracture toughness, of which the progressive fracture mechanism deserves to be further assessed under intermediate dynamic loading rate (IDLR). In this study, the discrete element method (DEM) is adopted to depict the three-dimensional fracture processes of the CCNSCB specimens subjected to different IDLRs considering different supporting spans. The results demonstrate that the crack front of the CCNSCB specimen with any loading condition is prominently curved, which violates the straight-through crack propagation assumption and may induce some errors in the fracture toughness measurements. For each IDLR, the peak force of the CCNSCB specimen evidently increases with decreased supporting span, and the effect of loading rate on this parameter is more prominent for a smaller supporting span. For a relatively large span, the crack grows restrictively in the notched ligament, which conforms to the ideal assumption of the fracture process and contributes to an accurate measurement of the mode I fracture toughness. Thus, a large supporting span is suggested for the semi-circular bend tests. Additionally, the critical crack length and peak force are found dependent on the loading rate, and they are larger for the higher loading rate. Thus, the critical crack length determined under quasi-static conditions is not strictly suitable for the specimens under different IDLRs, especially for the much higher IDLR. This study calls for more attention on how to accurately determine the fracture toughness via chevron notched samples. 相似文献
13.
国际岩石力学学会建议了4种岩石I型断裂韧度（KIC）测试方法。将建议方法的人字形切槽巴西圆盘试样与直切槽半圆盘试样结合,可以得到具有诸多优点的人字形切槽半圆盘（CCNSCB）三点弯曲试样。近年来,CCNSCB方法受到许多关注,然而,其渐进破坏过程却尚未进行有效的评估。为此,对其进行了数值研究,其内容包括：进行细观损伤力学模拟,直观展现CCNSCB试样渐进断裂过程;考虑不同支撑跨距与直径之比（ ）的影响,发现 愈大,愈加符合测试原理,建议 取0.8;采用有限元子模型技术对CCNSCB方法（ 0.8）中计算KIC的关键参数-临界无量纲应力强度因子（ ）进行了宽范围标定,可供相关研究直接查取;细观损伤力学模拟峰值力对应的临界裂纹与有限元标定 对应的临界裂纹较为一致,证明CCNSCB方法测试原理的合理性,以及数值模拟与 标定结果的有效性。 相似文献
14.
The cracked chevron notched Brazilian disc (CCNBD) specimen has been suggested by International Society for Rock Mechanics for measuring mode I fracture toughness of rocks. Subsequently, this specimen geometry has been widely extended to conduct mixed mode fracture tests on rocks as well. A straight through crack front during the fracturing process upon the root of the chevron notch is assumed in the testing principle, but has never been thoroughly evaluated before. In this study, for the first time, the progressive rock fracture mechanism of the CCNBD rock specimen under mixed mode loading is numerically simulated. Specimens under representative mixed mode loading angles are modelled; and the assumption of the straight through crack front growth is critically assessed. The results show that not only the notch tip but also the saw-cut chevron notch cracks during the experiments, yielding a prominent twisted front, far from being straight. The crack front never grows up to the root of the notch ligament and the straight through crack front assumption is never satisfied in the realistic rock fracture progress of this chevron notched specimen subjected to mixed mode loads. In contrast, the fracture progress features typical three-dimensional wing cracking towards the loading ends. The numerically observed progressive fracture mechanism reveals that the measuring principle of mixed mode fracture tests employing CCNBD specimens is significantly violated and the measures of both modes I and II fracture toughness are uncertain. 相似文献
15.
可压性是衡量页岩气储层对压裂改造响应程度的重要依据,目前针对页岩可压性常用脆性指数对其进行评价。但在实际运用中存在脆性指数相近,实际压裂效果却差别甚远的问题。为了弥补利用脆性指数进行页岩气储层可压性评价的不足,在考虑断裂韧性影响的基础上引入临界机械能释放率,综合了Ⅰ型、Ⅱ型断裂韧性对岩石裂缝发育的影响,并定义平均临界机械能释放率。最后结合平均临界机械能释放率和脆性指数,初步建立了以裂缝发育指数为量化指标的页岩气储层可压性评价模型。基于焦石坝龙马溪组焦页48-2HF井测井资料,计算出其弹性模量、泊松比、Ⅰ型及Ⅱ型断裂韧性,并根据构建的裂缝发育指数模型,得出页岩储层可压性随埋深的变化关系。结合现场微震资料,验证了该模型能有效预测页岩气储层可压性随埋深的变化趋势,为页岩气实际开发过程中优选页岩储层压裂段提供可靠方法。 相似文献
16.
Summary The effect of testing method and specimen geometry such as diameter, thickness, and crack length and type on measured fracture
toughness was investigated using specimens collected from a limestone rock formation outcropping in the Central Province of
Saudi Arabia. Straight Edge Cracked Round Bar Bend (SECRBB), semicircular disk specimens under three point bending, and Brazilian
disk specimens under diametrical compression were used in this investigation. SECRBB specimens were used for the Mode-I study,
and notched Brazilian disk and semicircular specimens were used for the mixed Mode I–II study. The results show that specimen
diameter and crack type have a substantial influence on the measured fracture toughness; however, loading rate, crack size,
and specimen thickness seem to have a negligible effect on the fracture toughness. Mode-I fracture toughness is significantly
influenced by specimen diameter and crack type, while their effects on Mode-II fracture toughness are generally negligible.
The different specimens (SECRBB, Brazilian disk, and semicircular) can give comparable results only when the proper span to
diameter ratio is used. The Brazilian disk with a straight notch was found to be the most convenient geometry to use for fracture
toughness determination. A simple method of making a precise notch inside the disk is presented, using the combination of
a drilling machine and a wire saw. 相似文献
17.
ISRM-Suggested Method for Determining the Mode I Static Fracture Toughness Using Semi-Circular Bend Specimen 总被引：5，自引：3，他引：2
M. D. Kuruppu Y. Obara M. R. Ayatollahi K. P. Chong T. Funatsu 《Rock Mechanics and Rock Engineering》2014,47(1):267-274
The International Society for Rock Mechanics has so far developed two standard methods for the determination of static fracture toughness of rock. They used three different core-based specimens and tests were to be performed on a typical laboratory compression or tension load frame. Another method to determine the mode I fracture toughness of rock using semi-circular bend specimen is herein presented. The specimen is semi-circular in shape and made from typical cores taken from the rock with any relative material directions noted. The specimens are tested in three-point bending using a laboratory compression test instrument. The failure load along with its dimensions is used to determine the fracture toughness. Most sedimentary rocks which are layered in structure may exhibit fracture properties that depend on the orientation and therefore measurements in more than one material direction may be necessary. The fracture toughness measurements are expected to yield a size-independent material property if certain minimum specimen size requirements are satisfied. 相似文献
18.
根据围压条件下的断裂力学理论 ,采用双翼裂纹厚壁圆筒 ,对泥岩进行了不同围压和不同泥质含量条件下的人工岩样断裂韧性测试。建立了有限元方法解释断裂韧性的数值模型。在进行大量实验测试的基础上 ,通过回归分析表明 ,断裂韧性与围压、泥质含量有较好的线性统计关系。解决了水力压裂设计中断裂韧性参数的准确获取问题 ,有利于提高压裂设计、预测的精度 相似文献
19.
Yan Jin Jianbo Yuan Mian Chen K. P. Chen Yunhu Lu Huaiying Wang 《Rock Mechanics and Rock Engineering》2011,44(5):621-627
Hydraulic fracture propagation is greatly influenced by mode-II fracture toughness since this is one of the factors which
determine whether a fracture diverts. Direct measurement of rock fracture toughness is constrained by high cost, limited number
of available cores and long turn around time. Therefore, to overcome these constrains, it is necessary to develop an effective
mode-II fracture toughness test which can be used in a prediction analysis for deep rock formations. Consequently, a mode-II
fracture toughness test system was designed for rocks using the straight-notched Brazilian disc (SNBD) test methodology. In
the experiment, this system was used to test 20 rock samples from the WG oilfield. This enabled a fracture toughness prediction
model to be established, based on an analysis of the test data. H341 acoustic, density and gamma-ray logging data were used
to predict horizontal stresses and rock tensile strength. When combined with the mode-II fracture toughness prediction model,
continuous values were predicted, which were successfully confirmed by field fracturing practices. It was confirmed, therefore,
that this successful method met the need of providing continuous fracture toughness data during field fracturing operations. 相似文献
20.
针对含边缘裂缝之砂岩试体受反平面剪力情形进行了III型断裂韧度量测试验,搭配相关所推导之理论公式求取砂岩III型断裂韧度。研究试验条件为无围压及单轴荷重加载下进行III型断裂试验,且针对试体受高温后之性质改变为变量条件加以探讨。研究结果表明,以该方式进行III型断裂韧度之量测,为可靠且稳定;砂岩经历温度在200 ℃前,试体III型断裂韧度会提升,之后呈现下降,到600 ℃,下降趋于平缓;随着烧结温度的提升,单压强度、动态杨氏模量、动态泊松比与III型断裂韧度皆有下降之趋势,且试体出现熔融样态,表面出现明显微裂纹。 相似文献