Pre-shear effect on liquefaction resistance of a Fujian sand     

《Soil Dynamics and Earthquake Engineering》2015

Pre-shear history has been shown to be a critical factor in the liquefaction resistance of sand. By contrast to prior experimental studies in which triaxial shear tests were used to examine the effects of pre-shear on the liquefaction resistance of sand, hollow cylinder torsional shear tests were used in this study to avoid the influence of the inherent anisotropy that is inevitably produced during the sample preparation process because of gravitational deposition. A series of cyclic undrained shear tests were performed on sand samples that had experienced medium to large pre-shear loading. The test results showed that the liquefaction resistance of sand can be greatly reduced by its pre-shear history, and a pre-shear strain within the range from 0.1% to 5% can cause sand to be more prone to liquefaction. During the cyclic shear tests, the samples that had experienced pre-shear loading exhibited different behaviors when cyclic shear loading started in different directions, i.e., the clockwise direction and the counterclockwise direction. If the cyclic loading started in the identical direction as the pre-shear loading, then the mean effective stress of the sand was almost unchanged during the first half of the loading cycle; if the cyclic loading started in the direction opposite to that of the pre-shear loading, then the mean effective stress decreased significantly during the first half of the loading cycle. However, this anisotropic behavior was only remarkable during the first loading cycle. From the second cycle onward, the speeds of the decrease in the mean effective stresses in the two types of shear tests became similar.  相似文献   

Spatiotemporal variation and driving forces of reference evapotranspiration in Jing River Basin,northwest China   总被引：1，自引：0，他引：1       下载免费PDF全文

Lihong Xu  Zhongjie Shi  Shulan Zhang  Xinzheng Chu  Pengtao Yu  Wei Xiong  Haijun Zuo  Yunni Wang 《水文研究》2015,29(23):4846-4862

Evapotranspiration is an important component of the hydrological cycle, which integrates atmospheric demands and surface conditions. Research on spatial and temporal variations of reference evapotranspiration (ET_o) enables understanding of climate change and its effects on hydrological processes and water resources. In this study, ET_o was estimated by the FAO‐56 Penman–Monteith method in the Jing River Basin in China, based on daily data from 37 meteorological stations from 1960 to 2005. ET_o trends were detected by the Mann–Kendall test in annual, seasonal, and monthly timescales. Sensitivity coefficients were used to examine the contribution of important meteorological variables to ET_o. The influence of agricultural activities, especially irrigation on ET_o was also analyzed. We found that ET_o showed a decreasing trend in most of the basin in all seasons, except for autumn, which showed an increasing trend. Mean maximum temperature was generally the most sensitive parameter for ET_o, followed by relative humidity, solar radiation, mean minimum temperature, and wind speed. Wind speed was the most dominant factor for the declining trend in ET_o. The more significant decrease in ET_o for agricultural and irrigation stations was mainly because of the more significant decrease in wind speed and sunshine hours, a mitigation in climate warming, and more significant increase in relative humidity compared with natural stations and non‐irrigation stations. Changes in ET_o and the sensitivity coefficient of meteorological variables in relation to ET_o were also affected by topography. Better understanding of ET_o response to climate change will enable efficient use of agricultural production and water resources, which could improve the ecological environment in Jing River Basin. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

相对密实度对随机波与定次数波作用下土体变形关系的影响          下载免费PDF全文

孟凡超  袁晓铭  卢滔 《地震工程学报》2015,37(2):476-480

通过砂土的一系列动三轴实验,研究不规则地震荷载作用下与定次数等幅荷载作用下土体变形间的关系,给出砂土相对密实度对二者间关系的影响规律。结果表明:真实地震荷载下土的变形发展与等幅正弦荷载明显不同,应变发展时程的形态主要受地震动的形态控制;应变比C与砂土相对密度间关系具有规律性,随相对密度增大而降低,若采用以20周作为标准作用次数、0.65倍地震波峰值为等幅荷载代替不规则的地震荷载,修正真实地震应力下的残余变形,其应变比C随砂土密实度的增大而减小。同时,冲击型荷载的应变比C`要远大于振动型荷载。  相似文献   

CT扫描技术在我国土工试验中的应用研究进展          下载免费PDF全文

王艳丽  程展林 《地震工程学报》2015,37(S1):35-39

介绍岩土CT可视化系统的特点,总结CT扫描技术在土工试验中的应用情况,包括黄土、冻土、膨胀土、粗粒土等土体的初始结构观测与结构性演化方面的研究进展,指出开发定量的计算机图像分析系统,通过CT细观结构图像来建立土体数值模型和开发研制动态试验CT扫描设备是今后应予以深入关注的研究方向。  相似文献   

中国格点化日降水极值统计模型及阈值的选取     

张昕怡  方国华闻昕叶健  郭玉雪 《气候变化研究进展》2017,13(4):346-355

采用年最大值法（AM）及超阈值峰量法（POT）分别构建基于0.5°×0.5°网格的全国地面日降水极值序列,建立基于广义极值分布（GEV）和广义帕累托分布（GPD）的降水极值统计模型,通过K-S检验评估模型拟合效果,研究全国日降水极值的统计规律及其空间分布特征,提出适用于不同地区极端日降水的极值分布模型与阈值选取标准,结果表明：(1)POT序列比AM序列更符合降水极值序列的要求;(2)为便于比较并提高模型拟合效果,POT序列的阈值由百分位数法确定效果较好;(3)阈值方案优选结果在空间分布上与中国干湿区域的划分有很好的相关性,在湿润地区宜将第90～94百分位数作为阈值,在半湿润和半干旱地区宜将第94～97百分位数作为阈值,在干旱地区则使用第97～99百分位数较为合适。  相似文献   

Numerical investigation on the impact resistance of road barriers of Micropile-MSE Wall for subgrade     

《Computers and Geotechnics》2017

The Micropile-MSE Wall, specially designed for mountain roadways, is used to simultaneously increase the MSE wall’s local stability, global stability and impact resistance of road barriers. Model tests were conducted first to validate the viability of the Micropile-MSE Wall. The impact resistance of the road barrier is then studied numerically. The test results indicate that the surcharge-induced earth pressure, base pressure and lateral displacement of Micropile-MSE Wall panels are effectively reduced. The impact loading on the barriers of the Micropile-MSE Wall is actually supported by the whole retaining structure, which increases the impact resistance of the road barrier significantly.  相似文献   

Influence of the intermediate principal stress and principal stress direction on the mechanical behavior of cohesionless soils using the discrete element method     

《Computers and Geotechnics》2017

In this paper, the Discrete Element Method (DEM) is employed to numerically explore the response of hollow cylinder specimens of granular soils under complex stress paths. Two series of numerical tests are conducted to clarify the effects of the principal stress direction α and the intermediate principal stress through the b-value on the mechanical response of granular materials. The effects of α and b-value on the non-coaxiality of the principal stress and the principal plastic strain increment directions are investigated. It is observed that b-value and α significantly affect the non-coaxial behavior of granular materials. Finally, the results are discussed and compared with those obtained from physical laboratory tests.  相似文献   

Determination of microscopic parameters of quartz sand through tri-axial test using the discrete element method     

《Computers and Geotechnics》2017

A calibration procedure, in which coupled effects of microscopic parameters are considered, is proposed to determine the values of the microscopic parameters in the Discrete Element Method (DEM) for Fujian quartz sand. Laboratory tri-axial tests are conducted to be compared with the DEM simulations and the effects of end restraint in the laboratory tests are eliminated through a digital image measurement system. Sensitivities of the macroscopic behaviour of the specimen to the microscopic parameters are analyzed through DEM simulations. Four coupled effects of the microscopic parameters on the macroscopic behaviour are investigated through a graphic method and then considered in the calibration procedure.  相似文献   

SAGD技术应用于陆域冻土天然气水合物开采中的理论研究          下载免费PDF全文

王志刚  张永勤  梁健  王汉宝  吴纪修  李宽  李鑫淼  尹浩  李小洋 《探矿工程》2017,44(5):14-18

天然气水合物被誉为最有研究价值和开采价值的清洁能源,已经成为当今世界能源研究的热点。但到目前为止还未形成成熟稳定的天然气水合物开采技术体系,仍处于研究和试采阶段。陆域冻土天然气水合物开采与海域天然气水合物开采相比相对比较容易,在钻进过程中能够形成较稳定的孔壁。天然气水合物开采的主要方法有热激法、降压法、置换法和化学抑制剂法。SAGD（Steam Assisted Gravity Drainage）技术也叫蒸汽辅助重力驱油技术,在重油、油砂开采中得到了迅速发展,取得了非常有效的成果,被认为是目前重油开采最有效的方法。对SAGD技术应用到陆域冻土天然气水合物开采中进行理论分析研究,经过分析发现将SAGD技术应用到天然气水合物开采中是可行的,但确定两口水平井之间的距离是关键,且在应用时要将上部井变为生产井,下部井变为注汽井。  相似文献   

深井分层真空抽水试验及机理分析          下载免费PDF全文

何计彬  潘德元  李炳平  叶成明 《探矿工程》2017,44(1):18-23

基于某单井分层真空抽水综合试验,使用新型分层抽水试验装置,对试验方法进行技术改进,使分层抽水工作省时高效、安全可靠、经济实用。将该工艺方法监测数据与常规方法监测数据进行对比,研究地层、真空负压对抽水效果的影响,并对其机理进行详细分析,得出真空分层抽水井管周围渗流场的变化性状。对比试验表明,分层真空抽水工艺方法在提高单井出水量、洗井效果上具有明显优势。  相似文献