黄土陡坡降雨冲刷试验及其三维颗粒流流-固耦合模拟   总被引：2，自引：0，他引：2  

吴谦  王常明  宋朋燃 《岩土力学》2014,35(4):977-985

针对坡角为70°的黄土边坡,进行2.7 mm/min降雨强度下的室内坡面冲刷试验。根据边坡冲刷破坏的过程特征,将边坡侵蚀方式演变过程归纳为试验初期的片蚀、中期的细沟侵蚀、到后期的切沟侵蚀和坍塌。试验中坡顶处侵蚀强度大于其他部位,当坡面形成上下贯通的切沟之后,水流开始掏蚀沟槽底部土体,随着冲刷的持续,切沟两侧土体强度降低,坡顶土体发生坍塌。以此为基础利用三维颗粒流软件PFC3D对边坡降雨冲刷过程进行流-固耦合模拟,在模拟颗粒大变形的同时得到颗粒运动轨迹、孔隙率、流体单元内流速等重要参数,这些参数的定量变化过程反映了降雨过程中边坡遭受侵蚀程度及水流侵蚀能力的分布规律:坡顶处侵蚀最为强烈、水流侵蚀能力最强,且两者随高度降低呈减小趋势,与室内试验结果一致。  相似文献   

无射线追踪层析静校正技术及其应用研究     

季天愚  李澈  李景叶 《物探化探计算技术》2014,(4):475-480

静校正技术在近地表条件复杂地区的地震资料处理中具有重要意义,其校正的准确性直接影响后续的处理和解释工作。在众多静校正方法中,无射线追踪层析静校正法兼具稳定性和灵活性的优点。这里对无射线追踪层析静校正的原理和主要参数进行了分析;而后将其应用于鄂尔多斯盆地某工区黄土塬地区地震资料的处理,把处理效果与其他几种不同静校正方法进行了对比。结果表明,该方法可使单炮记录和叠加剖面的质量得到较大改善,地震记录同相轴的连续性得到增强。  相似文献   

洛川黄土地层渗透性与孔隙性的关系     

李云峰 《地球科学与环境学报》1991,(2)

本文用逐步回归分析方法对洛川黄土孔隙性诸要素进行了变量筛选,选出了影响渗透系数的孔隙要素,并建立了随机数学模型,定量解决了影响渗透系数的孔隙多少和孔隙形状问题,初步确定出了洛川黄土地层透水性与孔隙性的关系。  相似文献   

Climatic implications of loess deposits from the Beijing region     

Shangfa Xiong  Zhongli Ding  Tungsheng Liu 《第四纪科学杂志》2001,16(6):575-582

Variations in magnetostratigraphy, pedostratigraphy, grain size and magnetic susceptibility of the loess deposits near Beijing have been studied at two sections. The sections are about 400 km east of the main loess deposits in China, have a maximum thickness of 100 m and extend back to 1.1 Ma. The sequence consists of 14 loess–palaeosol couplets (S0‐S14), which correlate well with sequences in the Loess Plateau. Susceptibility records from the sites near Beijing are comparable to the Xifeng, Luochuan and Baoji sections located in the middle part of the Loess Plateau; however, the down‐core variations in the grain size in the Upper Lishi Formation exhibit some differences. The median grain size increases by about 25–30 µm from L4 to L2, with the sandy grains (>63 µm) increasing from 10–20 wt% to 40–50 wt% . This implies that the depositional environment of the dust sources in the Beijing loess section is different in some aspects from the Loess Plateau. The Beijing loess may have had a different dust source than the Loess Plateau. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Towards a climate event stratigraphy for New Zealand over the past 30 000 years (NZ‐INTIMATE project)     

Brent V. Alloway  David J. Lowe  David J. A. Barrell  Rewi M. Newnham  Peter C. Almond  Paul C. Augustinus  Nancy A. N. Bertler  Lionel Carter  Nicola J. Litchfield  Matt S. McGlone  Jamie Shulmeister  Marcus J. Vandergoes  Paul W. Williams  NZ‐INTIMATE members 《第四纪科学杂志》2007,22(1):9-35

It is widely recognised that the acquisition of high‐resolution palaeoclimate records from southern mid‐latitude sites is essential for establishing a coherent picture of inter‐hemispheric climate change and for better understanding of the role of Antarctic climate dynamics in the global climate system. New Zealand is considered to be a sensitive monitor of climate change because it is one of a few sizeable landmasses in the Southern Hemisphere westerly circulation zone, a critical transition zone between subtropical and Antarctic influences. New Zealand has mountainous axial ranges that amplify the climate signals and, consequently, the environmental gradients are highly sensitive to subtle changes in atmospheric and oceanic conditions. Since 1995, INTIMATE has, through a series of international workshops, sought ways to improve procedures for establishing the precise ages of climate events, and to correlate them with high precision, for the last 30 000 calendar years. The NZ‐INTIMATE project commenced in late 2003, and has involved virtually the entire New Zealand palaeoclimate community. Its aim is to develop an event stratigraphy for the New Zealand region over the past 30 000 years, and to reconcile these events against the established climatostratigraphy of the last glacial cycle which has largely been developed from Northern Hemisphere records (e.g. Last Glacial Maximum (LGM), Termination I, Younger Dryas). An initial outcome of NZ‐INTIMATE has been the identification of a series of well‐dated, high‐resolution onshore and offshore proxy records from a variety of latitudes and elevations on a common calendar timescale from 30 000 cal. yr BP to the present day. High‐resolution records for the last glacial coldest period (LGCP) (including the LGM sensu stricto) and last glacial–interglacial transition (LGIT) from Auckland maars, Kaipo and Otamangakau wetlands on eastern and central North Island, marine core MD97‐2121 east of southern North Island, speleothems on northwest South Island, Okarito wetland on southwestern South Island, are presented. Discontinuous (fragmentary) records comprising compilations of glacial sequences, fluvial sequences, loess accumulation, and aeolian quartz accumulation in an andesitic terrain are described. Comparisons with ice‐core records from Antarctica (EPICA Dome C) and Greenland (GISP2) are discussed. A major advantage immediately evident from these records apart from the speleothem record, is that they are linked precisely by one or more tephra layers. Based on these New Zealand terrestrial and marine records, a reasonably coherent, regionally applicable, sequence of climatically linked stratigraphic events over the past 30 000 cal. yr is emerging. Three major climate events are recognised: (1) LGCP beginning at ca. 28 000 cal. yr BP, ending at Termination I, ca. 18 000 cal. yr BP, and including a warmer and more variable phase between ca. 27 000 and 21 000 cal. yr BP, (2) LGIT between ca. 18 000 and 11 600 cal. yr BP, including a Lateglacial warm period from ca. 14 800 to 13 500 cal. yr BP and a Lateglacial climate reversal between ca. 13 500 and 11 600 cal. yr BP, and (3) Holocene interglacial conditions, with two phases of greatest warmth between ca. 11 600 and 10 800 cal. yr BP and from ca. 6 800 to 6 500 cal. yr BP. Some key boundaries coincide with volcanic tephras. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

靖远地区大厚度黄土地基浸水湿陷过程及土中竖向应力特征试验研究     

刘德仁  安政山  徐硕昌  王旭  张转军  金芯  张严 《岩土力学》2023,44(1):268-278

为了研究靖远大厚度黄土在浸水条件下的水分入渗规律和自重湿陷变形特征,在中兰铁路沿线的靖远北站黄土自重湿陷场地进行了不打注水孔的现场浸水试验,监测并分析了地表及地下湿陷变形、试坑周围裂缝、含水率和土中竖向应力变化情况,对水分扩散规律、自重湿陷特性和土中竖向应力变化规律进行了研究,并对地区修正系数β0值和浸润角进行了探讨。结果表明：体积含水率变化分为浸水稳定（2个）、快速增加（1个）和缓慢增加（1个）共4个阶段;浸水过程中,水分在21m处竖向入渗加快、径向扩散减缓,湿润峰最终形态呈现为椭圆状。根据探井和钻孔含水率测试结果,推算出浸润角最大为41°。该场地黄土自重湿陷过程历经剧烈湿陷、缓慢湿陷和固结稳定3个阶段。试验结束时共计发展了13圈环状裂缝,裂缝最远处距试坑边缘26m。根据室内试验和现场测试结果,建议地区修正系数沿土层深度进行修正,0～10m内β0值取1.05,10～27 m内β0值取0.95。在地表至21 m深度范围内,地基土浸水饱和且湿陷充分,土中竖向应力沿深度呈线性增加,土中竖向应力接近饱和自重应力,21m以下的地基土未能充分湿陷,土中竖向应力逐渐减小。该研究成果可应用于中兰铁路...  相似文献   

兰州第四纪黄土/古土壤序列物源演变: 来自于碳酸盐矿物的证据^*          下载免费PDF全文

蔡青松  杨光亮  范育新  颜雪域  高敏敏  张青松  王荣华  郭雪莲 《古地理学报》2022,24(3):583-598

黄土/古土壤的物源研究对于揭示第四纪气候变化和青藏高原隆升历史具有重要意义。本研究以位于黄土高原西部1.4 Ma以来的兰州黄土/古土壤沉积序列为研究对象,基于X射线衍射技术分析了黄土/古土壤中的主要矿物组成,侧重于碳酸盐矿物含量,追溯了兰州黄土/古土壤的直接物源。结果显示: (1)1.4 Ma以来兰州地区黄土/古土壤沉积物的主要直接源区为柴达木盆地沙漠区和阿拉善干旱区。(2)基于二元混合模型计算的潜在原始源区对兰州黄土白云石和总碳酸盐矿物的相对贡献率以及长石与石英比值结果一致支持1.4 Ma以来兰州黄土原始物源发生了多次变化。1.4~1.1 Ma和0.9~0.3 Ma青藏高原东北缘造山带(昆仑山、祁连山)和中亚造山带对兰州黄土的贡献相当,而1.1~0.9 Ma和0.3 Ma以来,中亚造山带对兰州黄土的物源贡献增加,这可能分别是对中更新世气候转型和0.3 Ma以来青藏高原及邻近地区干冷气候增强的响应。1.15 Ma和0.8 Ma兰州黄土/古土壤中高的白云石含量、碳酸盐矿物总含量以及0.8 Ma长石与石英比值的快速升高可能是对“昆黄运动”的响应,进而造成了昆仑山、祁连山对黄土高原物源贡献的增加。  相似文献   

青藏高原东缘湖相沉积和黄土高原黄土沉积磁化率与粒度相关性对比^*          下载免费PDF全文

时伟  蒋汉朝 《古地理学报》2022,24(3):599-610

为探讨构造稳定地区(如黄土高原)和构造活跃地区(如青藏高原东缘)粉尘沉积物中磁化率(SUS)与粒度的相关性及其对环境事件的指示意义,本次研究分析了黄土高原蓝田剖面黄土—古土壤样品和青藏高原东缘湖相沉积样品的粒度和磁化率记录。黄土高原黄土—古土壤沉积SUS与2~10 μm粒度组分最强正相关,青藏高原东缘湖相沉积的SUS与2~10 μm粒度组分最强负相关,反映2~10 μm粒度组分为黄土高原和青藏高原乃至亚洲干旱—半干旱地区连续稳定敏感的背景沉积组分。黄土高原黄土—古土壤沉积的SUS与32~63 μm粒度组分最强负相关,青藏高原东缘湖相沉积的SUS与32~63 μm粒度组分最强正相关,反映32~63 μm粒度组分不仅是黄土高原尘暴事件沉积的敏感指标,也是青藏高原东缘湖相沉积记录的地震事件敏感指标。SUS与粒度组分的相关性在青藏高原东缘地区地震事件层开始部分高于结束部分,也较好地反映地震事件为研究区添加新鲜沉积物后随地形地貌恢复逐步减少的过程。SUS与粒度组分相关性也受当地物源的影响。  相似文献   

Variations in the sensitivity of the optically stimulated luminescence from quartz in the Xifeng section: A spatiotemporal comparison across the Chinese Loess Plateau since the last interglaciation     

《Quaternary Geochronology》2022

The sensitivity of the optically stimulated luminescence (OSL) from quartz is thought to be mainly influenced by source rock (crystallization temperature and quartz defect types) and depositional history (irradiation/bleaching cycles). In this study, the OSL sensitivity of quartz of different grain sizes from loess (L1) and paleosol (S1) layers at the Xifeng section of the Chinese Loess Plateau was analyzed. The OSL sensitivity of the samples from the Xifeng section shows a distinct difference between glacial and interglacial cycles, which is consistent with the patterns observed from magnetic susceptibility (MS) and grain sizes. The highest OSL sensitivity is observed in S1, which is twelve times the lowest sensitivity observed in L1. Moreover, the contribution of the fast component of quartz OSL from the paleosol accounts for more than 90% of the total OSL signal. In contrast, the middle and slow components contribute more in loess, and a significant variation among different aliquots was observed.Comparison of the data obtained from loess sections from different regions, including Xifeng, Luochuan, Jingyuan and Shimao, show significant differences in the magnitudes of OSL sensitivity but a similar pattern between glacial and interglacial periods. The results of this study suggest that, except for the wildfire model proposed to interpret the high OSL sensitivity in paleosol (Zhang, 2018), the shift of wind pattern of westerly wind (i.e., transporting “dim” source from North Tibetan Plateau and northwesterly wind (i.e., transporting “bright” source from Alxa Arid Lands and the subsequent mixture from the different sources may partially contribute to the different OSL sensitivities observed for Xifeng and Luochuan. In contrast, the OSL sensitivity of Shimao samples from L1 was affected by the input from the Mu Us Desert, and those of Jingyuan may affected by the contribution from the Yellow River.  相似文献   

A detailed luminescence chronology of the Lower Volga loess-palaeosol sequence at Leninsk     

《Quaternary Geochronology》2022

We present a detailed luminescence chronology of the loess-palaeosol sequences in the Lower Volga region of Russia at the Leninsk site – an important palaeogeographic archive describing the climate and environmental conditions of regressive stages of the Caspian Sea. The chronology of these sediments has received very little attention compared to the under- and overlying marine deposits. The degree of bleaching was addressed by making use of the differential resetting rates of quartz and feldspar. Our results show that the quartz OSL and feldspar pIRIR_50,290 signals were sufficiently bleached before deposition and uncertainties in bleaching have a negligible impact on the reliability of the luminescence ages. The combined quartz OSL and K-feldspar pIRIR_50,290 chronology constrains the main stages of the Northern Caspian Lowland evolution during the Late Quaternary. During early MIS 5 (130–120 ka), the northern part of the Lower Volga was covered by a shallow brackish water estuary of the warm Late Khazarian Caspian Sea transgression. After ∼122 ka, the Volga incised the Northern Caspian Lowland surface following sea-level decrease and the start of subaerial conditions at Leninsk. Loess accumulation rate increased towards the end of MIS 5 and two palaeosols of presumably MIS 5с and MIS 5a age formed, exhibiting features evidencing a dry, cold climate, influenced by long seasonal flooding by the Volga River. Cryogenesis affecting the MIS 5a soil is a regional phenomenon and is dated to between ∼70 and 90 ka. The overlying thick Atelian loess unit formed during the cold periods of MIS 4 and MIS 3. Clear erosional features at the top of the Atelian loess are constrained by luminescence to ∼35 to ∼24 ka, allowing reconstruction of erosion of 150–200 cm of loess.  相似文献