Experimental research on mechanical characteristics and strength criterion of rock of triaxial unloading tests under different stress pathsEI北大核心CSCD

By carrying out triaxial unloading test under different stress paths on rock, the complete stress-strain curves, deformation characteristics and its strength criterion are studied. The test results show that the relation between lateral strain and confining pressure firstly is linear, and then is nonlinear in the total stage of unloading confining pressure. And its growth rate is about 3 to 5 times the growth rate of the axial strain. It shows obvious lateral dilatancy, and the degree of dilatancy is related to the unloading path. According to the area that is enclosed by confining pressure and volumetric strain curve, it can be seen that the greater the confining pressure is before unloading, the more the energy releases. Deformation modulus decreases gradually with the unloading confining pressure, and increases with the initial confining pressure; the relation between deformation modulus and confining pressure shows negative exponential distribution overall. At the same unloading paths, the reduction of the deformation modulus increases with the increase of initial confining pressure. The Poisson's ratio rises up continually, and the variation law with the confining pressure can be well described by nonlinear. Failure characteristics of rock are mainly shear failure. The strength characteristics of rock can be well characterized by using the Mohr strength criterion of power function. These conclusions provide reliable theoretical reference and guiding significance for the deep mining of the underground metal mine.     

目标样本粒度判据在海湾环境演变研究中的运用——以福建前湖湾为例

高密度采集福建前湖湾海岸剖面133个泥沙样品做粒度分析,其频率曲线显示多种粒度分布特征,预示多种沉积环境的变化。采集研究剖面周边海滩、河口浅滩、河口、滨海沼泽和海岸沙丘等已知环境的样品作为目标样本。将目标样本沉积参数平均粒径(Mz)、标准偏差(σ)、峰态(Kg)设为判别参数,利用Excel计算海岸剖面样品与目标样本参数的距离,筛选最小距离样品,归为已知目标样本的同类。据此,分析了海岸剖面蕴含的6个沉积环境变化阶段。利用剖面底部淤泥测年14C=(328 15±170)a BP,和剖面上部泥炭测年14C=(24 130±100)a BP,了解这一变化发生的年代。自(32 815±170)a BP以来,前湖湾经历了河口浅滩-河口、沙丘-河口-滨海沼泽-海滩-沙丘等海岸环境演变过程。     

象山港余流特征数值研究

基于Delft3D-Flow模块建立了象山港海域的三维斜压潮流数值模型,结合实测水文资料,研究了象山港的潮(余)流特征,对欧拉余流场的时空分布进行了定量的比较和分析,并与潮流测站计算分析得到的欧拉余流分布对比,很好的模拟了象山港的余流特征。结果表明:由湾外至湾顶,余流呈减小的趋势,湾外余流最大为33 cm/s,湾顶最小,余流平均仅5 cm/s。垂向上,表层余流大于底层余流,表层余流指向湾外,而底层余流则指向湾内。对比斜压、正压两种模式下的欧拉余流分布,可以看出湾顶附近主要受径流控制,两种模式得到的结果基本一致,口门至西沪港区域受径流和潮流的共同影响,斜压模式更准确地模拟出了水体层化和垂向余环流结构。     

点蚀损伤下桩基式平台腿柱轴压极限承载力研究

采用圆柱体点蚀损伤模型,建立含细观尺度点蚀损伤的桩基式平台腿柱多尺度精细化数值模型,研究壁厚损伤度、点蚀损伤强度以及点蚀体积损伤强度影响平台腿柱轴压极限承载力的规律。研究结果表明,壁厚损伤度及点蚀损伤强度明显削弱平台腿柱的极限强度,且随点蚀损伤强度增大壁厚损伤度的影响加剧;点蚀体积损伤强度由于综合考虑了壁厚损伤度和点蚀损伤强度的耦合因素,相比于独立考虑后两者,其更能合理地描述点蚀损伤对平台腿柱极限强度的影响,故点蚀体积损伤强度体现了点蚀损伤的关键特征。本方法不仅适用于研究点蚀损伤构件的极限承载力,其所提出的点蚀损伤模型的构建方法,可拓展于研究受点蚀损伤的整体平台结构的极限承载力,且确定点蚀体积损伤强度为描述点蚀损伤特征的关键参数后,有望将其用于修正点蚀损伤平台腿柱的承载力设计公式。     

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A diagnostic analysis on the effect of the residual layer in convective boundary layer development near Mongolia using 20th century reanalysis data

Although the residual layer has already been noted in the classical diurnal cycle of the atmospheric boundary layer,its effect on the development of the convective boundary layer has not been well studied. In this study, based on 3-hourly20 th century reanalysis data, the residual layer is considered as a common layer capping the convective boundary layer. It is identified daily by investigating the development of the convective boundary layer. The region of interest is bounded by(30°–60° N, 80°–120° E), where a residual layer deeper than 2000 m has been reported using radiosondes. The lapse rate and wind shear within the residual layer are compared with the surface sensible heat flux by investigating their climatological means, interannual variations and daily variations. The lapse rate of the residual layer and the convective boundary layer depth correspond well in their seasonal variations and climatological mean patterns. On the interannual scale, the correlation coefficient between their regional averaged(40°–50°N, 90°–110° E) variations is higher than that between the surface sensible heat flux and convective boundary layer depth. On the daily scale, the correlation between the lapse rate and the convective boundary layer depth in most months is still statistically significant during 1970–2012. Therefore, we suggest that the existence of a deep neutral residual layer is crucial to the formation of a deep convective boundary layer near the Mongolian regions.     

非线性Hoek-Brown强度折减技术

为精确执行非线性Hoek-Brown(HB)强度折减,首先在p-q空间分析了HB曲线任意点切线与Mohr-Coulomb(MC)准则的对应关系,推求了HB屈服函数材料折减系数和强度折减系数的关系,提出了潜入强度折减系数的HB弹塑性分析模型,介绍了在Flac3D平台上二次开发实现非线性HB强度折减的基本思路。对一边坡算例用本文方法和简化Bishop法进行了对比分析,计算结果表明,潜入强度折减系数的HB弹塑性模型计算获得的边坡潜在滑动面形态、位置和相应的安全系数,与简化Bishop法计算结果很接近。     

Distribution and invasion of Spartina alterniflora within the Jiaozhou Bay monitored by remote sensing image

Spartina alterniflora as an alien invasive plant, poses a serious threat to the ecological functions of the coastal wetland of the Jiaozhou Bay. As of 2019, the distribution area of S. alterniflora in the Jiaozhou Bay has reached more than 500 hm². For this reason, combined with field surveys, remote sensing monitoring of the invasion S.alterniflora in the Jiaozhou Bay has been carried out. To accurately identify S. alterniflora within the Jiaozhou Bay coastal wetland, we used a new m...     

Warmer-Get-Wetter or Wet-Get-Wetter? A Criterion to Classify Oceanic Precipitation

In this study, the temporal and spatial variations of observed global oceanic precipitation during 1979–2010 are investigated. It is found that the global trend in precipitation during this period varies at a rate of 1.5%/K of surface warming while the rate is 6.6%/K during 2006–2010. The precipitation is highly correlated with Sea Surface Temperature(SST) in both the temporal and the spatial patterns since the strong 1997–98 El Nino event. Considering the distributions of precipitation and SST, seven oceanic regions are classified and presented using the observed Global Precipitation Climatology Project(GPCP) data and Extended Reconstructed Sea Surface Temperatures, version 3(ERSST.v3) data. Further examining the mechanisms of the classified oceanic precipitation regions is conducted using the Tropical Rainfall Measuring Mission(TRMM) satellite, GFDL-ESM-2G model precipitation and SST data and Hadley Center sea ice and SST version 1(Had ISST1) data. More than 85% of global oceanic precipitations are controlled by either one or both of the warmer-get-wetter mechanism and wet-get-wetter mechanism. It is estimated that a 0.5 SST signal-to-noise ratio, representing the trend of SST time series to the standard deviation, is a criterion to distinguish the mechanism of a region. When the SST ratio is larger than 0.5, the precipitation of this region is controlled by the warmer-get-wetter mechanism. SST, rather than the humidity, is the pivotal factor. On the other hand, when the SST ratio is less than 0.5, the precipitation is controlled by the wet-get-wetter mechanism. The SST variability is a significant factor contributing to the precipitation variation.     

Experimental research on the mechanical properties of methane hydrate-bearing sediments during hydrate dissociation

This paper describes studies of the effect of hydrate dissociation on the safety and stability of methane hydrate-bearing sediments. Methane hydrates within the sediments were dissociating under the conditions of a confining pressure of 0.5 MPa, 1 MPa, 2 MPa and a temperature of −5 °C. After 6 h, 24 h, or 48 h, a series of triaxial compression tests on methane hydrate-bearing sediments were performed. The tests of ice-clay and sediments without hydrate dissociation were performed for comparison. Focusing on the mechanical properties of the sediments, the experimental results indicated that the shear strength of the ice-clay mixtures was lower than that of the methane hydrate-bearing sediments. The strength of the sediments was reduced by hydrate dissociation, and the strength tended to decrease further at the lower confining pressures. The secant modulus E_S of the sediments dropped by 42.6% in the case of the dissociation time of the hydrate of 48 h at the confining pressure of 1 MPa; however, the decline of the initial yield modulus E₀ was only 9.34%. The slower hydrate dissociation rate contributed to reducing the failure strength at a declining pace. Based on the Mohr–Coulomb strength theory, it was concluded that the decrease in strength was mainly affected by the cohesive reduction. Moreover, the mathematical expression of the M–C criterion related to the hydrate dissociation time was proposed. This research could be valuable for the safety and stability of hydrate deposits in a permafrost region.