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A bounding surface model is formulated to simulate the behavior of clays that are subject to an anisotropic consolidation stress history. Conventional rotational hardening is revisited from the perspective of thermodynamics. As the free energy cannot be accumulated infinitely upon critical state failure, the deviatoric back stress must vanish. This requires the rotated yield surface to be turned back to eventually align on the hydrostatic axis in the stress plane. Noting that most of the previous propositions violate this restriction, an innovative rotational hardening rule is formulated that is thermodynamically admissible. The bounding surface framework that employs the modified yield surface is applied to simulate elastoplastic deformations for overconsolidated clays, with which the overprediction of strength on the “dry” side can be greatly improved with reasonable results. Other important features, including contractive or dilative response and hardening or softening behavior, can also be well-captured. It has been shown that the model can simulate three types of reconstituted clays that are sheared with initial conditions over a wide range of anisotropic consolidation stress ratios and overconsolidation ratios under both triaxial undrained and drained conditions. Limitations and potential improvement of the model regarding the fabric anisotropy at critical state have been discussed. 相似文献
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洛阳市旅游资源的空间结构及其演化模式 总被引:1,自引:0,他引:1
通过对洛阳市旅游景点体系的集聚度、通达度和分异度指标分析,认为洛阳市旅游资源空间分布呈现整体均匀、中部集聚态势,景点网络的通达度有待提高。基于洛阳市旅游资源的密度和品位度空间分布等高线图,将洛阳市旅游资源化为3个核心-边缘单元:即洛阳——文化旅游资源体系、栾(川)嵩(县)——山岳旅游资源体系和新安——山水旅游资源体系。根据区域发展的离散阶段、成长阶段和成熟阶段,讨论了3个资源体系目前所处的阶段和边缘地区可能的发展趋势。 相似文献
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通过对华北地台河南鹤壁地区太原组有孔虫动物群的系统研究,共鉴定出有孔虫化石18属33种,建立了一个区域性有孔虫动物组合带:Bradyina—Palaeotextularia组合带,根据有孔虫化石的属种类型、数量,应用数理统计方法得出组合带有孔虫化石在地层中的比例变化情况,并根据化石组合带与国内其它地区的有孔虫动物群进行对比研究,认为鹤壁剖面有孔虫动物群Bradyina—Palaeotextularia组合带归于晚石炭世晚期的早期(C2^2-),进而对研究区石炭-二叠系界线的划分进行探讨,界限应该放在第16层(泥岩)和第15层(灰岩)之间。 相似文献
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OUYANG Jie ZHU Cheng PENG Hua YU Jinbiao LI Lan ZHOU Riliang ZHANG Guangsheng ZHU Guangyao LI Zhongxuan ZHONG Yishun ZHU Qing LV Wen HU Yongqi ZHENG Chaogui LV Zhenrong HU Chang WU Honglin XU Longsheng 《地理学报》2009,19(5):631-640
The prominent types of Danxia landform in Fangyan include enclosed valleys, mesas, peaks, stone columns and grooves etc. Their spatial combinations have regular configurations along the northwest–southeast direction: typical grooves and caves are located in the northwestern Wufengshuyuan mainly; abundant fresh collapsed stones may be observed in central Jimingfeng and Taohuafeng; stone drums and stone columns are in the southeastern Shiguliao particularly; enclosed valleys are encircling joints of peaks and plains from three directions east, west, and south. Their spatial combinations reflect that the developments of Danxia landform have undergone stages of geomorphic cyclical erosion in the form of weathering, collapse, transportation, sedimentation and other processes, together with the “sculpture” of external forces mainly as tectonic uplift. The picturesque Danxia landform began its formation at that point. Danxia landform developed mainly in the strata of Fangyan Formation (K1f) caused by the alluvial fan-braided river phase of anterior fan in the late period of the Early Cretaceous. Regular patterns of weathering of stones and features of braided alluvial phase sediments may be verified by the analysis of three groups of experimental data. Danxia landform of Fangyan is a unique representative of the “adolescent” development type in the application of the World Natural Heritages status in China, by virtue of its outstanding universal aesthetic and scientific value. 相似文献
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浙江方岩丹霞地貌类型及其空间组合 总被引:1,自引:0,他引:1
andform of Fangyan is a unique representative of the "adolescent" development type in the application of the World Natural Heritages status in China, by virtue of its outstanding universal aesthetic and scientific value. 相似文献
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ZHU Cheng CUI Zhijiu LI Zhongxuan GAO Jie WANG Lixin WU Xianglin ZHENG Chaogui SHEN Qingfan ZHENG Xianzhang 《地理学报》2009,19(2):239-248
On top of Shigujian Peak (1477 m a.s.l.) of the Dayangshan Mountain in Jinyun County, Zhejiang Province, large amounts of granite pits with diameters ranging from several dozens of centimeters to around one meter and depth from 10 cm to 45 cm are found on rock surface. These pits mainly appear on the NE and SE sides, and their drainage mouths are in the same direction. The identification results through micropolariscope and X-ray fluorescence spectrometer reveal that bedrock of pits is from middle to fine-grained moyite being apt to be weathered and modified. In Dayangshan region the annual mean temperature is 9.2℃ and annual precipitation is over 1700 mm. On the one hand, there always experiences a period of periglacial action with temperature oscillating near 0℃ for 4 months, i.e., from December to March next year. As a consequence, the freezing-thawing cycles may be remarkable to disintegrate the bedrock. On the other hand, the windward slope of Shigujian Peak meets typhoon of over force 10 on the Beaufort scale in summer, therefore, the blowing makes suspending sands or pebbles grind in swirling form. Based on field investigation and periglacial geomorphic theory, the pits on top of Shigujian Peak are attributed to freezing- thawing of periglacial action. Meanwhile, storm and strong wind accelerate the process. Observation shows that both the actions are still undergoing and variant directions of wind are the main cause for making different shapes of the pits. Because the top of Shigujian is 1500 m lower than the present snow line, some scholars considered that “glacial pothole” formed in the Quaternary is hard to work, even though in the Last Glacial Maximum (LGM). 相似文献
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浙江江郎山丹霞地貌发育的年代与成因 总被引:9,自引:0,他引:9
江郎山位于华南褶皱系、江山-绍兴深断裂和保安-峡口-张村断裂带之间.白垩纪早期这两大断裂的拉张断陷导致峡口盆地的形成,随之主要有下白垩统永康群馆头组(K1g)、朝川组(K1c)和方岩组(K1f)在盆地中的沉积.白垩纪晚期上述两大断裂发生强烈挤压活动,峡口盆地逐渐隆升.新生代以来,峡口盆地在构造抬升中,产生大量张断裂和节理,加速了对岩体的切割,以及岩体被切割后的崩塌,导致了丹霞地貌的发育.江郎山丹霞地貌申报世界自然遗产的主要依据是其特有的壮观而独特的老年期孤峰-巷谷以及生动而逼真的象形石丹霞地貌特征、独特的地台活化现象与重要的岩石学科学研究意义以及该区特有的重要事件地层学和古生物学研究的科学意义.本文根据对江郎山亚峰垂直贯穿于丹霞地貌岩层永康群中辉绿岩脉标本K-Ar法的测年,揭示了当地峡口红层盆地抬升的时代为晚白垩世77.89±2.6Ma BP(K2),这也是我国目前丹霞地貌研究中所测得的可靠年代学数据. 相似文献