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61.
A pragmatic strain-softening constitutive model, which is based on Modified Cam Clay, was applied to the simulation of the progressive failure of an embankment constructed on a deposit of sensitive (strain-softening) clay in Saga, Japan. A comparison of the predictions for this case indicates that if softening is ignored, only relatively small deflections and consolidation settlements are predicted, especially after construction. In contrast, for the case where softening is included in the analysis, progressive failure within the clay induces large shear deformations and finally failure of the embankment is predicted. This comparison suggests that softening-induced progressive failure should be considered in the design of embankments on such soils, and the residual strength of the deposit may have an important influence on the overall factor of safety of the construction. Detailed analyses of predicted excess pore water pressures, shear strains and shear stress levels in the ground indicate that considering the strain-softening process: (a) is associated with the buildup of excess pore water pressure; (b) promotes strain localization; and (c) results generally in a larger zone of soil involved in the failure. 相似文献
62.
通勤时间、社区活动对社区社会资本的影响:基于北京26个社区的调查研究 总被引:1,自引:0,他引:1
城市扩张和郊区化显著增加居民的通勤时间,减少居民在社区内及周边开展的日常活动,进而可能对居民的社区社会资本产生消极影响。基于2017年北京市26个社区居民的社区融合与活动日志问卷调查数据,通过构建结构方程模型,探讨通勤时间、社区活动对社区社会资本的影响机制。结果发现,控制居民社会经济属性和社区区位后,长时间通勤会减少居民在社区及周边1 000 m范围内开展的活动,并进一步对社区社交网络结构、社会信任和共同价值等社区社会资本的不同维度产生负面影响。此外,社区活动中社交娱乐活动的中介效应显著,而个人和家庭事务活动中介效应不显著。最后,证实了促进职住平衡、减少职住分离的规划政策对于增加居民社区活动及培育社区社会资本的重要意义。 相似文献
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65.
玉米秸秆带状覆盖对西北旱地土壤温度及马铃薯产量的影响 总被引:2,自引:0,他引:2
设黑膜大垄(M1)、玉米秸秆带状平覆(M2)、玉米秸秆带状垄沟覆杆(M3)和不覆盖露地平作(CK)4个处理进行田间小区试验,对比研究不同覆盖方式对西北旱地土壤温度及马铃薯产量的影响。结果表明:M1较CK提高全生育期土壤温度0.98℃,主要提高了块茎膨大期5 cm土层(2015年)及淀粉积累期10 cm土层(2016年)的土壤温度;M2、M3较CK降低全生育期土壤温度1.06℃、0.59℃,主要降低了块茎形成期10 cm土层的土壤温度。两年M1、M2、M3分别平均较CK增产11.68%、21.74%、16.88%。产量与淀粉积累期至收获期单株结薯数、单株产量正相关(r=0.064~0.766),覆盖处理显著较CK提高淀粉积累期单株结薯数及单株产量,平水年以M1最好,偏旱年以M2最好。 相似文献
66.
Geochemistry,Zircon U–Pb Analysis,and Biotite 40Ar/39Ar Geochronology of the Maoling Gold Deposit,Liaodong Rift,NE China 下载免费PDF全文
The Maoling gold deposit is located in the southwestern part of the Liaodong rift, NE China, and has estimated reserves of 25 t. In this paper we present the results of an investigation into the geochronology and geodynamic mechanisms of igneous activity and metallogenesis within the Maoling gold deposit. New zircon U–Pb age data, biotite 40Ar/39Ar age data, whole‐rock geochemistry, and Hf isotopic analyses are presented in order to constrain the petrogenesis and mineralization of the deposit. Zircon U–Pb dating of the Wolongquan biotite monzogranite and Maoling biotite granite yielded mean ages of 194.0 ± 1.1 Ma and 196.1 ± 1.1 Ma, respectively. All the granites are characteristically high‐K calc‐alkaline, enriched in light rare earth elements and large ion lithophile elements, and depleted in high field strength elements, which is consistent with the geochemical characteristics of arc‐type magmas. The Hf isotope characteristics indicate that the granites formed by partial melting of early Paleoproterozoic crustal material. In addition, biotite 40Ar/39Ar dating indicates that the Maoling gold deposit formed at 188.9 ± 1.2 Ma, implying that the mineralization was related to both the granite intrusions. Taking into account previous data on S–Pb–O–H isotopes and our new age data, the Maoling deposit can be classified as an intrusion‐related gold deposit. Taking into account the geology of the study area and adjacent regions, we propose that the Maoling gold deposit and its associated granitic intrusions formed in a geodynamic setting that was dominated by subduction of the Paleo‐Pacific Plate beneath the Eurasian continent. 相似文献
67.
以民勤荒漠绿洲过渡带为研究区,通过样方调查,研究了荒漠区、荒漠绿洲过渡区到绿洲内不同梯度生境中灌丛沙堆的形态特征及分布格局。结果表明:(1)3种生境中灌丛沙堆的形态呈极显著性差异(p<0.01);绿洲区灌丛沙堆的平均高度、底面积、纵横断面积和体积均最大,其次为荒漠区,过渡区最小。(2)过渡带3种生境灌丛沙堆的长、短轴之间均呈二次函数关系,但相关程度不同,过渡区相关性最高,相关系数达0.78;绿洲区相关性最低,相关系数为0.57;高度与底面积、体积与高度间均呈幂函数关系,相关系数均在0.59以上;(3)过渡区灌丛沙堆分布密度较大,呈聚集分布,而荒漠区及绿洲区沙堆分布密度较小,均呈随机分布。 相似文献
68.
A three-level nested Regional Ocean Modeling System was used to examine the seasonal evolution of the Copper River (CR) plume and how it influences the along- and across-shore transport in the northern Gulf of Alaska (NGoA). A passive tracer was introduced in the model to delineate the growth and decay of the plume and to diagnose the spread of the CR discharge in the shelf, into Prince William Sound (PWS) and offshore. Furthermore, a model experiment with doubled discharge was conducted to investigate potential impacts of accelerated glacier melt in future climate scenarios. The 2010 and 2011 simulation revealed that the upstream (eastward) transport in the NGoA is negligible. About 60 % of the passive tracer released in the CR discharge is transported southwestward on the shelf, while another one third goes into PWS with close to 60 % of which exiting PWS to the shelf from Montague Strait. The rest few percent is transported across the shelf break and exported to the GoA basin. The downstream transport and the transport into PWS are strongly regulated by the downwelling-favorable wind, while the offshore transport is related to the accumulation of plume water in the shelf, frontal instability, and the Alaskan Stream. It takes weeks in spring for the buoyancy to accumulate so that a bulge forms outside of the CR estuary. The absence of strong storms as in the summer of 2010 allows the bulge continue growing to trigger frontal instability. These frontal features can interact with the Alaskan Stream to induce transport pulses across the shelf break. Alternatively as in 2011, a downwelling-favorable wind event in early August (near the peak discharge) accelerates the southwestward coastal current and produces an intense downstream transport event. Both processes result in fast drains of the buoyancy and the plume content, thereby rapid disintegration of the plume in the shelf. The plume in the doubled discharge case can be two to three times in size, which affects not only the magnitude but also the timing of certain transport events. In particular, the offshore transport increases by several folds because the plume appears to be more easily entrained by the seaward flow along the side of Hinchinbrook Canyon. 相似文献
69.
He-Jun Chai Jun-Jie Wang Sheng-Chuan Tang 《Geotechnical and Geological Engineering》2009,27(3):315-323
The visualization of rock structure is a very useful and important technique in many aspects in geological and geotechnical
engineering such as investigating and evaluating the stability of a high rock slope. The conventional method used to visualize
rock structure is limited to plotting the orientation of individual discontinuities by using the Schmidt stereographic net.
The present paper shows a new technique to visualize the three-dimensional structure of rock masses. The fitting function
for three-dimensional rock structure was established based on data gathered from field survey. Two fitting methods by which
the discontinuous points gathered from a plane and discrete points from field survey were fitted respectively are suggested.
The technique to visualize the three-dimensional structure of rock masses includes many aspects such as projection transformation,
blanking and mutual cutting, are investigated. Based on the visualizing technique, the rock structure at the site of Xilupdu dam which is being built in Southwest of China was investigated. 相似文献
70.
Primary productivity (PP) and phytoplankton structure play an important role in regulating oceanic carbon cycle. The unique seasonal circulation and upwelling pattern of the South China Sea (SCS) provide an ideal natural laboratory to study the response of nutrients and phytoplankton dynamics to climate variation. In this study, we used a three-dimensional (3D) physical–biogeochemical coupled model to simulate nutrients, phytoplankton biomass, PP, and functional groups in the SCS from 1958 to 2009. The modeled results showed that the annual mean carbon composition of small phytoplankton, diatoms, and coccolithophores was 33.7, 52.7, and 13.6 %, respectively. Diatoms showed a higher seasonal variability than small phytoplankton and coccolithophores. Diatoms were abundant during winter in most areas of the SCS except for the offshore of southeastern Vietnam, where diatom blooms occurred in both summer and winter. Higher values of small phytoplankton and coccolithophores occurred mostly in summer. Our modeled results indicated that the seasonal variability of PP was driven by the East Asian Monsoon. The northeast winter monsoon results in more nutrients in the offshore area of the northwestern Luzon Island and the Sunda Shelf, while the southwest summer monsoon drives coastal upwelling to bring sufficient nutrients to the offshore area of southeastern Vietnam. The modeled PP was correlated with El Niño/Southern Oscillation (ENSO) at the interannual scale. The positive phase of ENSO (El Niño conditions) corresponded to lower PP and the negative phase of ENSO (La Niña conditions) corresponded to higher PP. 相似文献