Three‐dimensional shakedown solutions for anisotropic cohesive‐frictional materials under moving surface loads

Previous work on three‐dimensional shakedown analysis of cohesive‐frictional materials under moving surface loads has been entirely for isotropic materials. As a result, the effects of anisotropy, both elastic and plastic, of soil and pavement materials are ignored. This paper will, for the first time, develop three‐dimensional shakedown solutions to allow for the variation of elastic and plastic material properties with direction. Melan's lower‐bound shakedown theorem is used to derive shakedown solutions. In particular, a generalised, anisotropic Mohr–Coulomb yield criterion and cross‐anisotropic elastic stress fields are utilised to develop anisotropic shakedown solutions. It is found that shakedown solutions for anisotropic materials are dominated by Young's modulus ratio for the cases of subsurface failure and by shear modulus ratio for the cases of surface failure. Plastic anisotropy is mainly controlled by material cohesion ratio, the rise of which increases the shakedown limit until a maximum value is reached. The anisotropic shakedown limit varies with frictional coefficient, and the peak value may not occur for the case of normal loading only. Copyright © 2013 John Wiley & Sons, Ltd.     

Varying water utilization of Haloxylon ammodendron plantations in a desert‐oasis ecotone

Haloxylon ammodendron is a desert shrub used extensively in China for restoring degraded dry lands. An understanding of the water source used by H. ammodendron plantations is critical achieving sustainable vegetation restoration. We measured mortality, shoot size, and rooting depth in 5‐, 10‐, 20‐, and 40‐year‐old H. ammodendron plantations. We examined stable isotopic ratios of oxygen (δ¹⁸O) in precipitation, groundwater, and soil water in different soil layers and seasons, and in plant stem water to determine water sources at different shrub ages. We found that water acquisition patterns in H. ammodendron plantations differed with plantation age and season. Thus, the main water source for 5‐year‐old shrubs was shallow soil water. Water sources of 10‐year‐old shrubs shifted depending on the soil water conditions during the season. Although their tap roots could absorb deep soil water, the plantation main water sources were from soil water, and about 50% of water originated from shallow and mid soil. This pattern might occur because main water sources in these plantations were changeable over time. The 20‐ and 40‐year‐old shrubs acquired water mainly from permanent groundwater. We conclude that the main water source of a young H. ammodendron plantation was soil water recharged by precipitation. However, when roots reached sufficient depth, water originated mainly from the deep soil water, especially in the dry season. The deeply rooted 20‐ and 40‐year‐old shrubs have the ability to exploit a deep and reliable water source. To achieve sustainability in these plantations, we recommend a reduction in the initial density of H. ammodendron in the desert‐oasis ecotone to decelerate the consumption of shallow soil water during plantation establishment.     

δ18O and δ13C in fossil shells of Radix sp. from the sediment succession of a dammed palaeo‐lake in the Yarlung Tsangpo valley,Tibet, China

A series of confirmed and suspected dammed palaeo‐lake sedimentary successions is scattered within the middle Yarlung Tsangpo valley in Tibet. However, the chronology, the genesis of the dam and its location, the water level of the dammed lake, the process of dam failure and the spatiotemporal relationships between the sedimentary successions remain controversial. Here, we focus on one sedimentary succession of the suspected dammed palaeo‐lake at Xigazê. We measured the grain‐size distribution, magnetic susceptibility, organic and inorganic carbon content, and δ¹³C_org and δ¹⁵N_total ratios of the sediments. In addition, we measured the δ¹⁸O_shell and δ¹³C_shell values of modern and fossil Radix sp. shells, and the δ¹⁸O_water and δ¹³C_DIC values of the ambient water with different hydrological regimes. The results indicate that the δ¹⁸O_shell values of modern Radix sp. and the δ¹⁸O_water of the ambient water body significantly depend on its hydrological status. In addition, a strong positive relationship was observed between δ¹⁸O_shell values of modern Radix sp. shells and the δ¹⁸O_water of the ambient water on the Tibetan Plateau. According to this correlation, the δ¹⁸O_water values of the palaeo‐water body are reconstructed using the δ¹⁸O_shell values of Radix sp. fossil shells in the Xigazê section. Further, based on the δ¹⁸O_shell values of fossil Radix sp., the reconstructed δ¹⁸O_water of the palaeo‐water body and the specific habitats of Radix sp., we infer that the sedimentary succession in the Xigazê broad valley was mainly formed within the backwater terminal zone of a dammed palaeo‐lake and that the elevation of the water level of the lake was approximately 3811 m a.s.l. AMS ¹⁴C dating indicates that the deposits of the dammed palaeo‐lake were formed at about 33–22 cal. ka BP. Finally, the presence of Radix sp. fossil shells within the Xigazê section suggests that Radix sp. survived the late Last Glacial Period on the Tibetan Plateau.     

A two‐dimensional coupled hydromechanical discontinuum model for simulating rock hydraulic fracturing

Within the framework of our discontinuous deformation analysis for rock failure algorithm, this paper presents a two‐dimensional coupled hydromechanical discontinuum model for simulating the rock hydraulic fracturing process. In the proposed approach, based on the generated joint network, the calculation of fluid mechanics is performed first to obtain the seepage pressure near the tips of existing cracks, and then the fluid pressure is treated as linearly distributed loads on corresponding block boundaries. The contribution of the hydraulic pressure to the initiation/propagation of the cracks is considered by adding the components of these blocks into the force matrix of the global equilibrium equation. Finally, failure criteria are applied at the crack tips to determine the occurrence of cracking events. Several verification examples are simulated, and the results show that this newly proposed numerical model can simulate the hydraulic fracturing process correctly and effectively. Although the numerical and experimental verifications focus on one unique preexisting crack, because of the capability of discontinuous deformation analysis in simulating block‐like structures, the proposed approach is capable of modeling rock hydraulic fracturing processes. Copyright © 2014 John Wiley & Sons, Ltd.     

贵州西北部基性侵入岩锆石U-Pb年代学、岩石地球化学特征 及其与铅锌成矿关系初探

贵州西北部发育多处基性侵入岩,总体规模较小(约0.25 Km2),多沿深大断裂侵位,出露于铅锌矿点外围,本文对猫猫厂、凉山两处矿点附近的儿马冲和白岩庆两地小型基性侵入岩进行了重点研究。侵入岩主要岩性为细粒辉长岩,造岩矿物主要为拉长石、普通辉石。SiO2范围为49.60-51.09 wt%,MgO从3.88-4.27 wt %,TiO2为3.69-3.85 wt %。LA-ICP-MS锆石U-Pb定年结果为268.3±7.4 Ma,显示岩浆侵位于二叠纪。基性侵入岩的微量元素蛛网图呈OIB型特征,富集大离子亲石元素（LILE）、轻稀土元素（LREE）,亏损重稀土元素（HFEE）,相对亏损高场强元素（Nb,Ta）,有Sr、Y亏损,Pb富集。(87Sr/86Sr)i范围0.706749～0.707069,(143Nd/144Nd)i范围0.512313～0.512363,εNd(t)范围0.2～1.2;源区熔融深度处于石榴石橄榄岩相深度,可能经历了1-3 %的部分熔融,处于亏损石榴石二辉橄榄岩相向原始石榴石二辉橄榄岩相的过渡区。成岩过程中发生了单斜辉石、斜长石等矿物分离结晶,受到了有限的地壳混染作用,未经历明显的AFC过程。地壳物质在地幔源区中的加入可能是造成地幔富集的主要原因。侵入岩与成矿作用之间的关系,主要通过两方面所表现。一方面是二者间构造活动上的耦合性。另一方面是基性岩在成矿过程中可能发挥了重要的化学屏障层作用。     

多尺度细节增强的遥感影像超分辨率重建

鉴于现有超分辨率重建方法难以突显重建影像细节信息的问题,提出多尺度细节增强的遥感影像超分辨率重建模型框架。首先,通过最小二乘滤波方法将序列影像分解成包含大尺度边缘的平滑信息和包含中小型尺度的细节信息;其次,利用插值方法得到相应的高分辨率细节信息和平滑信息,构造纹理细节增强函数,提升中小型细节的增强幅度;最终,融合细节信息和平滑信息,得到初始的超分辨率重建结果,并利用局部优化模型进一步改善重建影像质量。选取同时相和多时相遥感影像作为试验数据。试验结果表明,本文重建结果与插值方法、TV方法和MAP方法相比,在客观评价指标上均有显著提高,明显改善了重建影像的纹理细节。论文提出的多尺度细节增强的超分辨率重建方法,可以使重建影像提供更多高频细节信息,具有较好鲁棒性和普适性。     

起伏地形条件下的磁异常二维聚焦反演及应用

地形对磁异常的反演和解释有很大的影响,特别是磁异常体贴近地表分布时更是如此,为了降低这种影响,笔者推导出了基于有限延深的二度厚板状体的带地形的磁异常正演公式,并提出了一种基于起伏地形的地下网格模型剖分的新方法。同时,聚焦反演对物性体有很强的聚焦效果,如果能够预先判断磁异常主要由地下浅层的强磁性体所引起,则可以考虑采用聚焦反演的方法得到磁性体的位置,显然这种方法非常适合铁矿体的反演。笔者将带地形的二维磁异常正演与聚焦反演结合起来,进行了相应的模型试验,并与水平地形下的聚焦反演及起伏地形下的光滑反演进行对比,验证了这种结合的有效性。最后,将该方法应用于新疆特克斯的磁异常剖面,对该剖面的磁性体分布做出了合理的解释。     

滇东北毛坪铅锌矿床的成矿时代:闪锌矿Rb-Sr定年

毛坪铅锌矿床是滇东北地区代表性矿床之一,目前尚缺乏精确的成矿年代学数据。该文对选自块状铅锌矿石的4件闪锌矿单矿物样品进行了Rb-Sr同位素定年,获得等时线年龄为321.7±5.8 Ma(MSWD=1.5),表明毛坪铅锌矿床的主成矿作用发生于石炭纪。此外,闪锌矿~(87)Sr/~(86)Sr初始值为0.712166±0.000017,低于大陆地壳~(87)Sr/~(86)Sr平均值(0.719)且高于地幔Sr初始值(0.707),暗示成矿物质主要来源于大陆地壳并混有少量地幔物质。综合前人研究成果,作者认为毛坪铅锌矿属后生矿床,与晚二叠世峨眉山大火成岩省玄武岩浆活动无成因联系,类似于典型的MVT矿床,且滇东北地区可能发育多期铅锌矿化作用。     

基于FLUENT的内孤立波质量源造波方法

为研究内孤立波质量源数值造波方法,本文采用两个点源形式的质量源,分别放置于两层流体的上下层中作为内孤立波激发源。推导源项表达式,从不可压缩流体的Navier-Stokes方程出发,结合内孤立波Kd V、e Kd V理论,基于商业软件FLUENT发展了一种内孤立波质量源数值造波方法。通过数值模拟,分析了质量源造波过程中内孤立波的生成过程,并将数值模拟结果同理论及实验作对比。结果表明:基于此方法生成的内孤立波波形、波高及波致水平速度与理论及实验吻合度较好,该方法是可行的,并且耗时短、效率高。