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1.
Summary. The influence of a simple mountain range on seismic ground motion is studied. A two-dimensional model of the medium and vertically incident plane SH -waves are considered. Attention is devoted not only to the wavefield along the Earth's surface, but also within the medium. The wavefield is computed in two steps: (1) the computation of the impulse response by the finite-difference method, (2) the computation of the response to a time variation of the incident wave. approximately corresponding to a 'hundred-year' local earthquake at the site. Numerical results (the impulse response, the transfer function, the accelerograms, and their spectra) indicate strong spatial variability of the wavefield due to the topographical anomaly. The differences as large as 100 per cent in the peak amplitudes of the accelerograms, and of the order of 5 Hz in their predominant frequencies, at closely (∼ 200 m) spaced internal points of the medium have been found. Attention is focused also on the effect of causal absorption. Even unrealistically strong absorption seems to be unable to reduce significantly the spatial variability of the ground motion, caused by the topography. A variability like this. implying the occurrence of underground differential strains, might be of engineering importance in the antiseismic design of underground structures (tunnels, for example) in mountainous seismic regions. The ground-motion variability along the surface of the mountain is considerably smaller than within the medium. 相似文献
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GIS对空间对象及其关系表达能力的增强以及多源数据集成应用的需要,不仅扩大 了城市空间数据的内涵,而且推动了城市空间数据集成研究.城市空间数据涉及多个学科,主要来源于航空遥感与摄影测量、勘探量测、内插推算和社会统计,可分 为地上、地表、地下3个空间层次类型.城市空间数据具有离散非连续、构造约束、零散分 布、信息隐含和体特征等特殊性,并存在多语义、多尺度和实体拓扑特征.城市空间数据具有灰白二象性,地下空间数据可以灰、白相互转化. 相似文献
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通过野外调研和室内实验,研究了祁连山南坡灌丛草甸地上生物量的生长季变化,并对地上生物量与水热因子的关系进行了探讨。结果表明：在不同区域群落结构有所不同,覆盖度越低,上层和下层的植物高度越低,丰富度和多样性越小。但均匀度还受草场退化阶段的影响,群落结构相对稳定,植物的均匀度越高;地上生物量的年内变化是单峰曲线,乌鞘岭和门源的地上生物量在7月份最大,祁连和野牛沟的地上生物量在9月份最大;地上生物量的积累与前1月和前2月的气温和降水正相关,与前4月的气温也正相关,并且对气温变化的敏感性大于降水,但与地温和土壤水分的相关性不明显,前1月表层地温较高对地上生物量的积累有积极作用;对于地上生物量积累,日气温、日相对湿度、降水量有直接正向作用,而日最高气温、日最低气温、日水汽压有直接负向作用,5 cm、20 cm地温和0~10 cm、20~30 cm土壤水分也有直接正向作用,而10 cm地温和10~20 cm土壤水分也有直接负向作用。 相似文献
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Ground temperature plays a significant role in the interaction between the land surface and atmosphere on the Tibetan Plateau(TP). Under the background of temperature warming, the TP has witnessed an accelerated warming trend in frozen ground temperature, an increasing active layer thickness, and the melting of underground ice. Based on high-resolution ground temperature data observed from 1997 to 2012 on the northern TP, the trend of ground temperature at each observation site and its response to climate change were analyzed. The results showed that while the ground temperature at different soil depths showed a strong warming trend over the observation period, the warming in winter is more significant than that in summer. The warming rate of daily minimum ground temperature was greater than that of daily maximum ground temperature at the TTH and MS3608 sites. During the study period, thawing occurred earlier, whereas freezing happened later, resulting in shortened freezing season and a thinner frozen layer at the BJ site. And a zero-curtain effect develops when the soil begins to thaw or freeze in spring and autumn. From 1997 to 2012, the average summer air temperature and precipitation in summer and winter from six meteorological stations along the Qinghai-Tibet highway also demonstrated an increasing trend, with a more significant temperature increase in winter than in summer. The ground temperature showed an obvious response to air temperature warming, but the trend varied significantly with soil depths due to soil heterogeneity. 相似文献
5.
灌溉方式对现代绿洲影响的数值模拟 总被引：8，自引：3，他引：5
灌溉是农业发展的根本,没有灌溉就没有荒漠区农业。利用美国NCAR中尺度模式MM5V3模拟了喷灌与不同水量地灌以及没有灌溉对绿洲土壤湿度、地下径流以及感热、潜热通量的不同影响。结果表明:①地灌后地表蒸发与植被层的蒸腾更旺盛,散失的水分更多;而喷灌可以抑制地表蒸发与植被层的蒸腾,对土壤水的保持更有利。②喷灌试验要在土壤湿度达饱和以后才会形成地下径流量,而地灌试验则是土壤湿度与地下径流量同时增长。总之,喷灌方式是一种高效节水的灌溉方式,它比其它灌溉方法更有利于绿洲农业生态系统的温度整体降低,不论土壤湿度还是大气湿度都会相应增大,抑制地表土壤水分的蒸发,有利于绿洲农业维持。 相似文献
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There are numerous methods to prevent seepage flow and ground improvement methodologies such as cement grouting, sheet piling, and the membrane method. In this paper, we present case histories of freezing technology applications in the construction of a deep tunnel sewerage system, undersea highway tunnel, and liquefied natural gas tank. Heaving pressure measurements for various soil types around a liquefied natural tank are compared with existing data. In this paper, we present temperature variations at the bottom and side of a liquefied natural gas tank. Our findings show that ground-freezing technology is very effective in controlling ground water infiltration into underground structures as well providing soil reinforcement in the soft ground. 相似文献
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数字高程模型（DEM）在表达地貌形态、认知地表过程、揭示地学机理等研究中发挥着基础性的作用,是重要的地理空间数据模型,广泛地应用于地学分析与建模中。但是,传统DEM具有属性单一的天然缺陷,难以支撑面向地学过程与机理挖掘的地球系统科学研究。亟待在传统DEM的基础上实现其数据模型的增值,服务于新地貌学研究范式和新对地观测技术背景下的数字地形建模与分析。立足于以上问题,本文构建了DEM增值的理论框架,主要包括DEM增值的概念、内涵、内容、类别、不同增值类别之间的相互关系,以及此理论框架的研究意义和应用范畴。提出了DEM增值的构建方法,包含：① 强调地上地下一体化、时间空间相耦合的DEM空间维度和时间维度增值方法;② 重视地下、地表和地上物质构成,形态属性耦合的物质属性和形态属性增值方法;③ 顾及自然过程、人工作用的地物对象、地貌形态的地物要素和形体要素增值方法。最后,分别以数字阶地模型、数字坡地模型和数字流域模型为例,阐释DEM在面向地貌学本源问题时的不同增值方法及应用场景。期望通过对DEM进行维度、属性和要素3个层面的增值,实现现代对地观测技术背景下数字高程模型表达方法的突破,并支撑知识驱动的数字地貌问题分析。 相似文献
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Adopting the quasi-three-dimensional (Quasi-3D) numerical method to optimize the anti-freeze design parameters of an underground pipeline usually involves heavy numerical calculations. Here, the fitting formulae between the safe conveyance distance (SCD) of a water pipeline and six influencing factors are established based on the lowest water temperature (LWT) along the pipeline axis direction. With reference to the current widely used anti-freeze design approaches for underground pipelines in seasonally frozen areas, this paper first analyzes the feasibility of applying the maximum frozen penetration (MFP) instead of the mean annual ground surface temperature (MAGST) and soil water content (SWC) to calculate the SCD. The results show that the SCD depends on the buried depth if the MFP is fixed and the variation of the MAGST and SWC combination does not significantly change the SCD. A comprehensive formula for the SCD is established based on the relationships between the SCD and several primary influencing factors and the interaction among them. This formula involves five easy-to-access parameters: the MFP, buried depth, pipeline diameter, flow velocity, and inlet water temperature. A comparison between the analytical method and the numerical results based on the Quasi-3D method indicates that the two methods are in good agreement overall. The analytic method can be used to optimize the anti-freeze design parameters of underground water pipelines in seasonally frozen areas under the condition of a 1.5 safety coefficient. 相似文献
9.
黄河源区草地农牧化对气候环境影响的数值模拟 总被引：5，自引：2，他引：3
利用中尺度数值模式MM5,设计了一个控制试验和一个敏感性试验。模拟分析黄河源区草地农牧化对局地气候环境的影响,得到一些初步结论:在全球增暖的大背景下源区草地农牧化引起源区平均气温和地表温度升高,平均日较差增大;源区农牧区降水以增加为主,周围地区以减少为主;源区空气湿度、土壤湿度明显减小;地表径流增加,地下径流减小,增加的降水大部分随地表径流流失;农牧区感热通量增加,潜热通量减小,有效通量增加。源区植被改变对气候环境的影响状况不同于其他地区。 相似文献
10.
城市地下管网信息管理问题研究 总被引：2，自引：0，他引：2
随着城市信息化进程的加速,城市生活的节奏大大加快,城市供水、供电、供暖等地下管道设施的使用频率也大幅增加.各种管道纵横交错、结构复杂,这就使得城市地下管网信息的现代化管理面临严峻的考验.地下管网具有埋于地下不透明、信息量大、保存期长、要求不问断运行使用等特点,故仅靠图纸、图表等形式记录保存管网资料,并在此基础上进行的人工管理已经不能适应规模日益扩大、经济社会活动日益加快的现代城市发展的要求.针对以上问题,阐述了城市地下管网信息管理的现状,重点分析了管网信息管理的技术发展历程以及管理中存在的问题,最后对地下管网信息的管理提出了相应对策. 相似文献
11.
城市地下空间开发利用容量评估的基础研究 总被引：10，自引：1，他引：9
该文探讨了城市地下空间开发利用容量评估的必要性,容量评估研究的基本内容及其关键技术。指出当前城市地下空间容量评估基础研究包括指标体系、评估模型、评估平台与评估示范四方面。城市地下空间容量评估研究不仅有利于城市地下空间的合理利用和有序开发,也有利于引导城市地面设施的合理布局与科学规划,对保障现代城市的可持续发展具有重要意义。 相似文献
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Stefan W. Grab Charles K. Gatebe Antony M. Kinyua 《Geografiska Annaler: Series A, Physical Geography》2004,86(2):131-141
This paper presents and compares ground thermal regimes at 4200 and 4800 m a.s.l. on Mount Kenya's southern aspect. Temperatures were recorded using Tinytalk? data loggers, installed at the ground surface and at depths of 1 cm, 5 cm, 10 cm and 50 cm. Temperatures were logged at 2‐hour intervals over a period of 12 months (August 1998 to July 1999). The study is designed to demonstrate near‐surface freeze conditions, which would have implications for contemporary periglacial landform production. Although ground freeze at 4200 m a.s.l. occurs during most nights (c. 70% at 1 cm depth), freeze penetration is restricted to the top 2 to 3 cm, such that no freeze was recorded at 5 cm depth. At 4800 m a.s.l., the diurnal frost frequency at the surface is 365 days (100%), whilst that at 10 cm depth is 165 days (45%). The paper demonstrates that a greater longevity of contemporary thin snow cover at 4800 m a.s.l. permits progressive sub‐surface cooling with depth. However, the near‐surface ground temperature profiles suggest that conditions are not conducive to permafrost development at the sites. 相似文献
15.
Frost susceptibility should be considered in the design and construction of foundations and retaining-wall structures in regions with the seasonally freezing-soil ground condition. When planning construction that goes deep into this soil, one has to understand the impact of horizontal forces to an underground wall and realize the potential effect of frost heaving upon, deep foundations. This article presents a few soil tests for frost heaving and the results of those tests show dangerous data for retaining structures under the soil conditions in Kazakhstan. The main parameters of the soil include frost penetration and heaving rate and amount. So, in designing underground structures, one must understand and consider that frost heaving occurs in various directions; this factor is very important for predicting on the restriction of deformations of structures in the seasonally freezing-soil ground condition. 相似文献
16.
石羊河地下水盆地的水资源构成及其合理利用问题 总被引：3，自引：0，他引：3
甘肃西部的石羊河流域是河西走廊三大流域之一, 是一个典型的干旱区地下水盆地。盆地内水土资源比较丰富, 灌溉农业历史悠久。解放30多年来水利建设发展很快, 水资源的利用比较充分, 利用率达到了较高的水平, 获得了显著的经济效益。有效灌溉面积已发展到360多万亩, 配套机井一万余眼, 年产粮食10亿多斤, 成了甘肃省的重要产粮区之一。 相似文献
17.
塔里木河中游土地沙漠化与环境因子关系研究 总被引：13，自引：4，他引：9
根据已有的和大量的调查地贡巴扎地区沙漠化与主导环境因子之间的关系进行了研究,结果表明：沙漠化形成主要因子的重要性依次为地下水位,植被,微地貌类型、土壤质地。以沙漠化研究为基础的维护合理的生态水位应为４．４米左右。 相似文献
18.
中国天山西部季节性森林积雪雪层温度时空分布特征 总被引：3，自引：0，他引：3
利用2009年12月27日～2010年4月2日天山积雪站站区内开阔地和雪岭云杉(Picea schrenkiana)林下6次降雪过程后雪层内时间间隔10 min的温度数据,探讨雪层温度变化特征。结果表明,越接近地表雪层温度越高,且在雪层表面形成冷中心和(局部)暖中心;在积雪稳定期林下雪层温度高于开阔地,融雪期林下低于开阔地;林下雪层冷、暖中心出现时间晚于开阔地,其强度也小于开阔地。林下雪层温度振幅小于开阔地,林下温度振幅拐点以上雪层温度振幅随深度和时间的递减率小于开阔地,拐点以下无明显差异。初冬,林下和开阔地雪层均为较小的正温度梯度,随着气温急剧下降,温度梯度逐渐增大,且从雪表向雪底递减,林下雪层负温度梯度出现时间晚于开阔地。开阔地和林下积雪表层正温度梯度最大值分别达到0.95℃/cm和0.82℃/cm,负温度梯度大值分别达到-0.84℃/cm和-0.35℃/cm;但开阔地全雪层日平均温度梯度小于林下雪层。 相似文献
19.
在粤北石漠化地区选取不同石漠化阶段的样地,对其碳酸盐岩进行室内岩性溶蚀和野外模拟溶蚀试验,研究不同石漠化阶段碳酸盐岩溶蚀特点。结果表明：在轻度→中度→重度→极重度石漠化演化过程中,重度石漠化阶段是碳酸盐岩溶蚀变化的一个重要转折点,在这个阶段中,溶蚀过程从以化学溶蚀转为物理侵蚀为主。不同石漠化阶段不同环境中的碳酸盐岩溶蚀速度在地上50 cm处,轻度石漠化土地>中度石漠化土地;在地面0 cm处,极重度石漠化土地>重度石漠化土地>轻度石漠化土地>中度石漠化土地;在地面下10 cm处,极重度石漠化土地>轻度石漠化土地>中度石漠化土地>重度石漠化土地;在地面下20 cm处,轻度石漠化土地>中度石漠化土地>重度石漠化土地;在地面下30 cm处,轻度石漠化土地>中度石漠化土地。 相似文献