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11.
大直径宽浅式筒型基础,阻水宽度大,在位工作期间受波浪海流作用,其周围土体易被冲刷。为研究单侧地基土体受冲刷后筒型基础的竖向极限承载力变化,通过引进冲刷率的概念,采用有限元方法研究了不同冲刷率下筒型基础的竖向极限承载力;并基于Meyerhof理论建立了计算不同冲刷率下筒型基础竖向极限承载力的极限平衡方法。研究结果表明,随着冲刷率增大,筒型基础的极限承载力出现不同程度的下降,当冲刷率为0.8时,即筒型基础单侧土体冲刷深度达6.4 m时,筒型基础的竖向极限承载力折减率为3.28%。建立的极限平衡算法可准确计算冲刷条件下筒型基础的竖向极限承载力。 相似文献
12.
YANG Kai ZHANG Bing WANG Xuben HE Lanfang YANG Hongyu WANG Pengwan TANG Jialin DENG Jixin ZHANG Cong 《《地质学报》英文版》2020,94(5):1531-1546
The Lower Silurian Longmaxi Formation in the south of Sichuan is a key player in the exploration and development of shale gas in China. Due to a highly complex topographic area, electromagnetic methods (EM) become important exploration means in this area. Many studies have been conducted on the shale mineral composition and electrical properties of shale, however, the correlation between sedimentary environments and the electrical properties of shale remain poorly understood. The electrical properties and sedimentary environment of the organic-rich shale of the Longmaxi Formation have been studied by means of X-ray diffraction, organic geochemistry, scanning electron microscopy and complex resistivity measurements. The discovered high quartz content of the Longmaxi Formation shale results in low resistivity. Deep-water shelf biogenic quartz contributes lower resistivity more than that of shallow-water terrigenous quartz. The deep-water anoxic and organic sedimentary environment led to major enrichment of pyrite, leading to a high polarization effect in shale. We present the correlation between the lithofacies types and electrical properties of Longmaxi Formation. The mixed siliceous shale lithofacies is the most favorable among the three lithofacies, which is characterized by high total organic carbon (TOC) content, high brittleness mineral content, high polarization and low resistivity (“three high and one low”). This feature is an effective identification of shale gas reservoirs by electromagnetic prospecting. Our study can provide constraints on electrical parameters of rocks for electromagnetic “sweet spot” exploration of shale gas, and so this has important geological significance to shale gas exploration and development. 相似文献
13.
提出一种确定不等式约束Partial EIV模型解及精度评定的新方法,在总体最小二乘准则下,将附有不等式约束的Partial EIV模型转换为标准最优化问题。采取WHP拟牛顿修正的SQP方法求解,并利用SUT法对参数估值进行精度评定,可以减小迭代次数、提高收敛速度,且精度评定方法简单有效。 相似文献
14.
自然重砂是地质体经自然风化、剥蚀、搬运、沉积等地质作用而分离出的单矿物(或矿物组合)。自然重砂矿物晶体由于仍然保留有许多矿物成因信息,包括颜色、形态、化学成分、物理性质和矿物组合等特征,因此常用于追溯源区地质体或者找矿勘查。这种方法被认为是一种经济实用的找矿方法——自然重砂测量。本文基于全国自然重砂找矿的数据资料,系统梳理了自然重砂的矿物类型、出现频率及其分布等特点,分析了自然重砂的矿物组合和成因矿物学特征,研究了自然重砂矿物的源区烙印、搬运距离及标型指示矿物组合特征,探讨了自然重砂成因矿物学研究意义及其找矿应用前景。自然重砂矿物的颜色、形态及内部结构依然保留着明确的成因矿物学信息:其颜色和晶体形态具有继承性而与其源区母体联系起来,体现源区母体的特性;其矿物组成可分出残余原生重矿物(包括造岩矿物、副矿物、矿石矿物等)和新生重砂矿物两个部分,如赤铜矿、孔雀石等反映着源区岩性体的成分或者赋存状态特征,其矿物组合也在很大程度上继承原生共生矿物而体现诸如有无矿化等意义;重砂颗粒的磨圆度、边界光滑性等表面特征反映搬运距离,有利于明确响应源区母体或者物源,而具有良好的找矿指示意义。 相似文献
15.
Jean‐Michel Brazier Anne‐Dsire Schmitt Eric Pelt Damien Lemarchand Sophie Gangloff Tho Tacail Vincent Balter 《Geostandards and Geoanalytical Research》2020,44(2):331-348
This work presents new 87Sr/86Sr and δ88/86SrSRM987 isotopic values of thirteen mineral, vegetal and animal reference materials. Except for UB‐N, all our results are consistent with previously published data. Our results highlight intermediate precisions among the best presently published and a non‐significant systematic shift with the calculated δ88/86SrSRM987 mean values for the three most analysed reference materials in the literature (i.e., IAPSO, BCR‐2 and JCp‐1). By comparison with the literature and between two distinct digestions, a significant bias of δ88/86SrSRM987 values was highlighted for two reference materials (UB‐N and GS‐N). It has also been shown that digestion protocols (nitric and multi‐acid) have a moderate impact on the δ88/86SrSRM987 isotopic values for the Jls‐1 reference materials suggesting that a nitric acid digestion of carbonate can be used without significant bias from partial digestion of non‐carbonate impurities. Different δ88/86SrSRM987 values were measured after two independent Sr/matrix separations, according to the same protocol, for a fat‐rich organic reference material (BCR‐380R) and have been related to a potential post‐digestion heterogeneity. Finally, the δ88/86SrSRM987 value differences measured between animal‐vegetal and between coral‐seawater reference materials agree with the previously published results, highlighting an Sr isotopic fractionation along the trophic chain and during carbonate precipitation. 相似文献
16.
Revisiting the existence of an effective stress for wet granular soils with micromechanics 下载免费PDF全文
A possible effective stress variable for wet granular materials is numerically investigated based on an adapted discrete element method (DEM) model for an ideal three‐phase system. The DEM simulations consider granular materials made of nearly monodisperse spherical particles, in the pendular regime with the pore fluid mixture consisting of distinct water menisci bridging particle pairs. The contact force‐related stress contribution to the total stresses is isolated and tested as the effective stress candidate for dense or loose systems. It is first recalled that this contact stress tensor is indeed an adequate effective stress that describes stress limit states of wet samples with the same Mohr‐Coulomb criterion associated with their dry counterparts. As for constitutive relationships, it is demonstrated that the contact stress tensor used in conjunction with dry constitutive relations does describe the strains of wet samples during an initial strain regime but not beyond. Outside this so‐called quasi‐static strain regime, whose extent is much greater for dense than loose materials, dramatic changes in the contact network prevent macroscale contact stress‐strain relationships to apply in the same manner to dry and unsaturated conditions. The presented numerical results also reveal unexpected constitutive bifurcations for the loose material, related to stick‐slip macrobehavior. 相似文献
17.
The energy saving performance of contra-rotating azimuth propulsor (CRAP) is investigated based on low order potential-based panel method. The hydrodynamic interactions among the forward propeller (FP), rear propeller (RP) and the pod unit (PU) which includes the pod body and the strut are considered through induced velocities which are obtained by panel method. In order to have a better understanding about the energy saving performance of CRAP, the hydrodynamic performance of a conventional propeller (CP) supplying the same thrust with CRAP at design condition is also calculated. At design condition, CRAP has a decrease in delivered power by approximately 8% comparing with CP, and the tangential induced velocities in slipstream show that CRAP recovers the rotational energy of slipstream effectively. At off-design conditions, the rotational speed of CRAP is adjusted to supply the same thrust with CP. In general, the delivered power of CRAP is significantly smaller than that of CP, and the energy saving performance of CRAP increases with the decrease of inflow velocity. 相似文献
18.
大量的钻孔资料表明,平原地区及其海域沉积物中普遍有硬质粘土层的存在。硬质粘土层在工程地质、地理学研究等方面具有重要的价值,它不仅是高层建筑的持力层,而且是研究全球环境变化事件、古气候演变的良好载体。该文阐述了硬质粘土层的一般特征、成因以及在粒度、地球化学元素、年代学、沉积环境等方面的研究进展,并展望了硬质粘土层在年代、物质来源和沉积环境等方面的研究方向,认为黄河三角洲硬质粘土层研究较少,需要开展大范围的、系统深入的、多学科的宏观和微观综合分析,挖掘硬质粘土层蕴含的古环境意义和应用价值。 相似文献
19.
为了确定山西台网基于“山西2015速度模型”的相对固定的定位方法,选择2010~2016年最大空隙角小于45°、参与定位台站数大于40的103个地震事件,分别采用单纯形法、Hypo2000、Hyposat结合PTD等3种方法重新测定。结果显示,单纯形法和Hyposat结合PTD测定的残差以及网缘地震的震中距两方面均优于Hypo2000;在震源深度方面,Hyposat结合PTD的结果较为可信。综合分析认为,基于“山西2015速度模型”定位地震时,山西台网应固定使用Hyposat结合PTD的方法。 相似文献
20.
喀斯特露石常常占据一定比例的地表面积,且具有许多已知或未知的水文—生态功能,对于喀斯特地区的植被恢复和环境改善发挥着重要的作用。本实验运用样线法和拍照法识别喀斯特断陷盆地不同位置(盆缘和盆地边坡)露石的数量特征和外部形态特征,同时比较了两种方法测量样地岩石裸露率的精准度。结果发现:盆地边坡与盆缘的露石数量和外部特征存在显著差异,盆缘露石分布密度(0.54个·m-2)>盆地边坡(0.39个·m-2);但盆地边坡露石的长宽比大于盆缘,单体占地面积为盆缘露石的两倍,接近40%的盆地边坡露石与山体等高线平行。样线法和拍照法测量样地岩石裸露率的结果存有差异,但并不显著,且这种差异呈现出随着岩石裸露率的增加而逐渐增加的趋势,拍照测量结果具有较小的变异系数。这些结果说明了研究区露石具有较强的空间异质性,对解释地表水土运移规律和植物分布提供重要参考。拍照法能准确地测量岩石裸露率,并提供露石外部形态特征的精准数据,可以作为喀斯特样地露石调查的新方法加以推广。 相似文献