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181.
Subsurface dams are rather effective and used for the prevention of saltwater intrusion in coastal regions around the world. We carried out the laboratory experiments to investigate the elevation of saltwater wedge after the construction of subsurface dams. The elevation of saltwater wedge refers to the upward movement of the downstream saltwater wedge because the subsurface dams obstruct the regional groundwater flow and reduce the freshwater discharge. Consequently, the saltwater wedge cannot further extend in the longitudinal direction but rises in the vertical profile resulting in significant downstream aquifer salinization. In order to quantitatively address this issue, field-scale numerical simulations were conducted to explore the influence of various dam heights, distances, and hydraulic gradients on the elevation of saltwater wedge. Our investigation shows that the upward movement of the saltwater wedge and its areal extension in the vertical domain of the downstream aquifer become more severe with a higher dam and performed a great dependence on the freshwater discharge. Furthermore, the increase of the hydraulic gradient and the dam distance from the sea boundary leads to a more pronounced wedge elevation. This phenomenon comes from the variation of the freshwater discharge due to the modification of dam height, location, and hydraulic gradient. Large freshwater discharge can generate greater repulsive force to restrain the elevation of saltwater wedge. These conclusions provide theoretical references for the behaviour of the freshwater–seawater interface after the construction of subsurface dams and help optimize the design strategy to better utilize the coastal groundwater resources. 相似文献
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中国地震局地震科学联合基金会办公室于 1999年 10月 19日至 2 0日在山西省太原市太原钢铁 (集团 )有限公司地震台召开了合欢树地震观测与试验研究课题验收会。验收组听取了课题组关于合欢树地震观测与试验的研究报告 ,查看了观测现场 ,观测仪器、设备及观测环境 ,查阅了观测资料、图件 ,及山西省科学技术情报研究所出具的科技查新检索报告 ,并对有关问题进行了询问 ,验收组经过认真的评议讨论 ,认为 :利用合欢树生物电位进行地震短临观测、探索 ,在国内属首次进行 ,具有新颖性、实用性 ,课题组重点观测、研究的不同树种、不同树龄、不同传… 相似文献
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Dynamic analysis of slab track on multi-layered transversely isotropic saturated soils subjected to train loads 总被引:1,自引:0,他引:1
The dynamic responses of a slab track on transversely isotropic saturated soils subjected to moving train loads are investigated by a semi-analytical approach. The track model is described as an upper Euler beam to simulate the rails and a lower Euler beam to model the slab. Rail pads between the rails and slab are represented by a continuous layer of springs and dashpots. A series of point loads are formulated to describe the moving train loads. The governing equations of track-ground systems are solved using the double Fourier transform, and the dynamic responses in the time domain are obtained by the inverse Fourier transform. The results show that a train load with high velocity will generate a larger response in transversely isotropic saturated soil than the lower velocity load, and special attention should be paid on the pore pressure in the vicinity of the ground surface. The anisotropic parameters of a surface soil layer will have greater influence on the displacement and excess pore water pressure than those of the subsoil layer. The traditional design method taking ground soil as homogeneous isotropic soil is unsafe for the case of RE 1 and RG 1, so a transversely isotropic foundation model is of great significance to the design for high train velocities. 相似文献
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对重大工程结构进行强地震作用下的连续倒塌全过程分析并建立相应的设计与控制方法,已成为当前地震工程领域的发展趋势。目前,由于数值求解方面的困难,绝大多数针对极端作用下的结构连续倒塌的研究止步于数值临界状态的界定,在分析过程中不能实时地对结构构件的损伤状态进行监测并根据构件的损伤状态对分析模型进行修改。为了实现连续倒塌过程中构件的逐步失效,在OpenSees程序中,基于Beam with Hinges Element构建了端部带附属节点的Beam with Hinges Element,并根据构件失效情况对附属节点的多点约束进行控制。采用三次静力凝聚方法和Newmark-beta法,给出了对此改进建模技术可信的理论背景,方法的准确性通过一个简单框架算例得到了验证。 相似文献
189.
Using modern census and environmental factor data,this study first identified the environmental factors that significantly affect the population distribution through Geodetector analysis and then constructed a population spatial distribution model based on the random forest regression algorithm.Finally,with this model and historical population data that were examined and corrected by historians,gridded population distributions with a spatial resolution of 10 km by 10 km in the traditional cultivated region of China(TCRC,hereafter)were reconstructed for six time slices from 1776 to 1953.Using the reconstruction dataset,the spatiotemporal characteristics of the population distribution were depicted.The results showed that(1)the environmental factors that significantly affected the population density differences among counties in the TCRC mainly consisted of elevation,slope,relief amplitude,distances to the nearest prefectural and provincial capitals,distance to the nearest river and the climatology moisture index.(2)Using the census data of 1934 counties in the TCRC in 2000 and the abovementioned environmental factor data,a random forest regression algorithm-based population spatial distribution model was constructed.Its determination coefficient(R2)is 0.81.In 88.4%of the counties(districts),the relative errors of the model predictions were less than 50%.(3)From 1776 to 1953,the total population in the study area showed an uptrend.Prior to 1851,the population increased mainly in the Yangtze River Delta.During this period,the number of grid cells in which the population densities were greater than 500 persons per km2 increased from 292 to 683.From 1851 to 1953,the population increased extensively across the study area.In the North China Plain and the Pearl River Delta,the number of grid cells in which the population densities were greater than 500 persons per km2 increased from 36 to 88 and from 4 to 35,respectively.The spatial clustering pattern of the population distribution varied temporally.The potential reasons included the shifts in economic development hot spots,traditional beliefs,wars,famine,and immigration policies.(4)Between our reconstructions and the HYDE dataset,there are large differences in the data sources,selected environmental factors and modeling methods.As a consequence,in comparison to our reconstructions,there were fewer populations in the eastern area and more populations in the western area from 1776 to 1851 and more populations in urban areas and fewer populations in rural areas after 1851 in the HYDE dataset. 相似文献
190.
从断裂强度到临界点──重整化群理论在地震预报中的应用述评 总被引:1,自引:0,他引:1
介绍了临界自组织现象和重整化群方法的基本原理,对地震的自组织临界行为作了较为深入的讨论,并就这一领域中的一些概念和观点发表了作者自己的见解。 相似文献