冻融循环对不同孔隙率页岩相似材料影响的试验研究   总被引：2，自引：2，他引：0  

王永岩  柳雪庆  苏传奇  张余标  魏剑 《冰川冻土》2018,40(1):102-109

基于地质力学模型试验的相似理论,针对寒区岩体工程,分别制作了5种不同孔隙率的页岩相似材料,进行冻融循环试验,探究不同孔隙率的页岩相似材料在冻融前后,其主要物理力学参数的变化规律。试验研究表明：在冻融循环后,页岩相似材料的单轴抗压强度、三轴抗压强度、弹性模量、粘聚力、内摩擦角有不同程度的减小,孔隙率、泊松比有不同程度的增大。页岩相似材料的物理力学参数受冻融循环的影响随孔隙率的增大先增大后减小,孔隙率处于9.4%~13.6%时,受冻融循环影响最大;孔隙率处于5.8%~9.4%时,受冻融循环的影响随孔隙率的增大有增大的趋势;孔隙率处于13.9%~19.1%时,受冻融循环的影响随孔隙率的增大有减小的趋势。研究结果可以为西部寒区的岩土工程建设和减灾提供相关的科学依据。  相似文献   

煤渣改良土的抗冻能力及损伤特性研究     

张向东  任昆 《冰川冻土》2018,40(4):764-772

为研究煤渣改良土作为季节冻土区路基填料的抗冻能力,以不同煤渣掺量及不同养护龄期下的煤渣改良土为研究对象,利用GDS三轴试验系统开展了不同冻融次数下改良土的三轴压缩试验,获得了最佳的煤渣掺量及养护时间数据,提出冻融及加载综合影响下改良土的总损伤变量,并据此建立了损伤本构关系。结果表明：改良土的抗冻能力随着煤渣掺入量的增大出现先增强后减弱的变化趋势,随龄期的增长而逐渐增强。冻融循环对改良土物理力学性质的影响主要集中在前5次循环过程,超过5次后影响逐渐减弱。冻融加载总损伤变量能够较好地反映冻融及加载过程中改良土性质的劣化,据此建立的损伤本构关系具有一定的精度,可以为季节冻土区煤渣改良土路基工程提供参考。  相似文献   

Impacts of Aerosol-Radiation Interactions on the Wintertime Particulate Pollution under Different Synoptic Patterns in the Guanzhong Basin,China     

Naifang BEI  Xia LI  Qiyuan WANG  Suixin LIU  Jiarui WU  Jiayi LIANG  Lang LIU  Ruonan WANG  Guohui LI 《大气科学进展》2021,38(7):1141-1152

The effects of aerosol–radiation interactions(ARI) are not only important for regional and global climate, but they can also drive particulate matter(PM) pollution. In this study, the ARI contribution to the near-surface fine PM(PM2.5)concentrations in the Guanzhong Basin(GZB) is evaluated under four unfavorable synoptic patterns, including "northlow", "transition", "southeast-trough", and "inland-high", based on WRF-Chem model simulations of a persistent heavy PM pollution episode in January 2019. Simulations show that ARI consistently decreases both solar radiation reaching down to the surface(SWDOWN) and surface temperature(TSFC), which then reduces wind speed, induces sinking motion,and influences cloud formation in the GZB. However, large differences under the four synoptic patterns still exist. The average reductions of SWDOWN and daytime TSFC in the GZB range from 15.2% and 1.04°C in the case of the"transition" pattern to 26.7% and 1.69°C in the case of the "north-low" pattern, respectively. Furthermore, ARI suppresses the development of the planetary boundary layer(PBL), with the decrease of PBL height(PBLH) varying from 18.7% in the case of the "transition" pattern to 32.0% in the case of the "north-low" pattern. The increase of daytime near-surface PM2.5 in the GZB due to ARI is 12.0%, 8.1%, 9.5%, and 9.7% under the four synoptic patterns, respectively. Ensemble analyses also reveal that when near-surface PM2.5 concentrations are low, ARI tends to lower PM2.5 concentrations with decreased PBLH, which is caused by enhanced divergence or a transition from divergence to convergence in an area. ARI contributes 15%–25% toward the near-surface PM2.5 concentrations during the severe PM pollution period under the four synoptic patterns.  相似文献   

Invisible face of COVID-19 pandemic on the freshwater environment: An impact assessment on the sediment quality of a cross boundary river basin in Turkey     

Cem Tokatlı 《国际泥沙研究》2022,37(2):139-150

In the current research,the impact of the COVID-19 lockdown period on sediment quality of the MericErgene River Basin was evaluated by determining the potentially toxic elements（PTEs） in sediment samples collected from 25 sampling points in the basin.Also some important ecological indicators including potential ecological risk index（PERI）,contamination factor（CF）,pollution load index（PLI）,biological risk index（BRI）,and geo-accumulation index(I_geo) and some important statistical indica...  相似文献   

Inverse modeling of lichen growth curves and implications for lichenometric dating     

《Quaternary Geochronology》2022

Lichenometric dating represents a quick and affordable surface exposure dating method that has been widely used to provide a minimum age constraint on tectonic and geomorphic landscape changes as well as buildings and anthropogenic landscape changes in various settings during the late Holocene. Despite its widespread usage, this method has several limitations. Major problems relate to the sampling of lichen population on any given rock surface and the modeling of growth curves. In order to overcome these issues, it has been suggested to subdivide the rock surface into some areas and measure the largest lichen thallus on each one. However, how to express the data in terms of a probability distribution function and link it to an age of last exposure of the rock surface are still a matter of debate. Here, we propose a novel approach to the modeling of lichen growth curves by treating lichen growth as a continuous-time Markov process with a time-varying rate and additive Brownian noise. Given the growth rates, the probability distribution of the lichen population at any time can then be obtained by solving the Fokker–Planck equation. This method is illustrated using a dataset from the Huashan area of eastern China, which consists of measurements of the largest thalli on 12 rock surfaces of known age. We first build up the probability distribution of the lichen population for each rock surface based on extreme value theory and then use these to optimize the growth curve by minimizing the Jensen–Shannon divergence. A new method is also proposed to use the growth curve to map a sample of size data from an undated rock surface to the calendar age domain so as to yield a fully probabilistic estimate of the exposure age of the undated rock surface rather than a point estimate.  相似文献   

Testing a new combined (U,Th)–He and U/Th dating approach on Plio-Pleistocene calcite speleothems     

《Quaternary Geochronology》2022

The geochronology of cave deposits in the Cradle of Humankind UNESCO World Heritage Site in South Africa provides a timeframe essential for the interpretation of its fossils. The uranium-lead (U–Pb) and uranium-thorium disequilibrium (U/Th) dating of speleothems, mostly flowstones that underlie and blanket the fossil-bearing sediments, have been effective in this sense, but U–Pb is limited by the requirement of ∼1 ppm U concentrations and low common Pb contents, and U/Th has a c. 500 ka limit of applicability. Here we report age results for calcite-aragonite speleothems obtained using a new combined uranium-thorium-helium ((U,Th)–He) and U/Th dating routine. We reproduced within analytical uncertainty, the published U–Pb or U/Th ages for (a) flowstone in three drill core samples in the range 2000–3000 ka, (b) a flowstone hand sample taken at surface with an age of 1800 ka, and (c) five underground flowstone samples in the range 100–800 ka. Calcite retentivity for He under cave conditions is thus demonstrated. In the few cases where helium loss was observed in speleothems, only some of the subsamples were affected, and to varying degrees, suggesting loss by lattice damage not related to diagenetic processes, rather than volume diffusion. In the 100 to 800 ka range, the combined U/Th disequilibrium and (U,Th)–He method also yielded reliable values for initial (²³⁰Th/²³⁸U) and (²³⁴U/²³⁸U) activity ratios. Importantly, most subsamples had high initial (²³⁰Th/²³⁸U) values, ranging from 1.0 to 19.7, although having low Th/U ratios. This is probably due to incorporation of Fe–Mn oxides-hydroxides dust, on which ²³⁰Th was previously adsorbed. Such samples are mostly not dateable by U/Th without the additional input from the He analysis. If not detected and corrected for, such high initial (²³⁰Th/²³⁸U) values can lead to inaccurate U/Th and U–Pb ages. Our study shows that the incorporation of He analysis in U/Th dating has broad potential application, with four methods for calculating the ages, in carbonates from different environments where U-Pb or U/Th dating would not work.  相似文献   

Holocene volcanic activity in Anjouan Island (Comoros archipelago) revealed by new Cassignol-Gillot groundmass K–Ar and 14C ages     

《Quaternary Geochronology》2022

The Comoros archipelago has attracted renewed attention since 2018 due to the submarine volcano growing east of the island of Mayotte and the associated ongoing seismic crisis. However, the origin of Comorian magmatism remains controversial, as it is either interpreted as related to a hotspot trail, to a fracture zone, or to a plate boundary. Lying in the central part of the archipelago, Anjouan is a key island to better understand the relationship between volcanism and geodynamics. Together with a careful selection of published whole-rock K–Ar ages, our new set of 13 groundmass K–Ar ages on lava flows and one radiocarbon age on a charcoal from a strombolian deposit, allow us to reassess the volcano-tectonic evolution of Anjouan Island. New groundmass K–Ar ages lie within the last 1 Ma, i.e. from 899 ± 14 to 11 ± 1 ka. They suggest that most of the subaerial volcanism in Anjouan is much younger than previously inferred, and occurred as pulses at 900–750 ka, perhaps 530 ka, 230–290 ka, and since 60 ka, with erosional periods in between. Among our new data, one ¹⁴C age of 7513–7089 yrs calBCE (9.3 ± 0.2 ka) and five K–Ar ages younger than 60 ka show that recent volcanism occurred in Anjouan. Moreover, the concentration of eruptive vents along a N150° alignment, parallel to the maximum horizontal stress, suggests a strong link between regional tectonics and volcanism. Considering the presence of active volcanoes on both the western and eastern extremities of the Comoros archipelago, our discovery of Holocene activity on Anjouan provides strong arguments against a chronological progression of volcanism along the archipelago, and therefore contradicts the hotspot hypothesis for the origin of volcanism.Finally, this study provides a robust geochronological timeframe of the different volcanic stages of Anjouan. It demonstrates that Anjouan is an active island and suggests that volcanism and tectonics can both resume at any time.  相似文献   

场地韧性的概念及有关问题的讨论          下载免费PDF全文

薄景山    张毅毅  薄涛  王玉婷    赵鑫龙  陈亚男 《世界地震工程》2022,38(3):001-9

在韧性城市和建筑抗震韧性等级评价中,需要对场地的韧性给出评价。场地韧性是一个新概念,场地韧性的概念和场地韧性等级评价在学术界还是空白。因此,对场地韧性的概念及有关问题开展讨论,对韧性城市和建筑抗震韧性评价具有重要的理论意义和工程应用价值。本文在分析韧性和场地概念的基础上,讨论了场地的稳定性和抗干扰问题;基于HOLLING建立的适应性循环理论,论述了建立场地韧性概念的理论基础;首次提出了场地韧性概念并解释了其内涵;考虑韧性城市和建筑抗震韧性评价的需求,初步讨论了与场地韧性等级评价有关的问题,提出了建立场地韧性等级评价指标体系的初步设想;建议了场地韧性等级评价的数学方法,为实现场地韧性等级评价提供了途径和方法。本文研究成果对从事韧性城市和建筑抗震韧性研究的科技工作者有一定的参考价值。  相似文献   

多年冻土区输油管道-管周冻土热力相互作用研究进展     

王飞  李国玉  马巍 《冰川冻土》2022,44(1):217-228

冻土区管道工程建设面临冻土工程特性及相关地质问题的严重挑战,开展管道-冻土相互作用研究对于解决管道稳定性问题具有重要的实际指导意义。综述国内外输油管道-冻土热力相互作用研究进展发现,目前研究集中在特定（定值或周期变化）油温下管周土温度场的定量描述以及差异冻胀/融沉下交界面处管道力学响应规律的解耦分析,缺乏完整时空序列的现场综合观测与管土界面特性及其动态演化研究。对管道防融沉措施进行归纳总结发现,各措施应用效果缺乏管道应力与变形数据的有效支持。应加强管道本身与管道沿线次生冻融灾害监测及相关数据获取,以此为校验开展管土界面特性及演化规律的系统研究,以便构建更为合理的管土接触面单元模型,将其和具有普适性的冻土模型相结合,植入有限元软件提高管土相互作用模型计算可靠性,并建议立足管道变形角度对防融沉措施的工程应用效果予以综合评价。  相似文献   

冻融循环作用下含水率对粗颗粒填料水分迁移影响的宏细观试验研究北大核心CSCD     

张玉芝  刘文龙  王海永  张莲海  陈世杰  朱晓东 《冰川冻土》2022,44(2):591-601

冻融循环作用和初始含水率是影响粗颗粒填料水分迁移特征和冻胀融沉变形的两个主要因素。为明确冻融循环作用下,不同初始含水率粗颗粒填料的水分迁移特征及细观机制,采用荧光素为追踪剂,以CT细观机理观测为研究手段,开展了不同初始含水率条件下粗颗粒填料的一系列冻融循环试验,探究了温度场和冻深变化、水分迁移图像、补水量变化、最终含水率分布及CT值变化规律等。试验结果表明,冻深基本随冻融循环的次数增加不断加深,初始含水率越大,不同冻融循环作用下冻深的变化越稳定。外界补水量和液态水迁移高度与初始含水率呈负相关。CT扫描结果分析表明,经历多次冻融循环后,试样中的水分迁移导致土体孔隙结构及颗粒构造发生变化,试样的密度普遍增加,孔隙率以减小为主,进而导致土体发生相应变形。  相似文献