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1.
珊瑚礁岩土的工程地质特性研究进展 总被引：1，自引：0，他引：1
文章综述了珊瑚礁岩土工程的研究意义、珊瑚礁岩土的组成、钙质砂的物理性质、钙质砂的静力学特性、珊瑚礁岩土中的桩基工程、珊瑚礁混凝土等方面的研究现状。得出：1）颗粒易破碎是钙质砂最重要的特性,直接影响着钙质砂的其他力学性能,而影响钙质砂颗粒破碎的主要因素有围压、有效应力、颗粒级配、初始孔隙比、颗粒强度、颗粒形状等;2）生物颗粒的易破碎以及成桩过程对钙质砂结构的扰动,导致钙质砂中的桩基承载力远低于普通石英砂;3）在以珊瑚砂为原料的混凝土工程中,利用抗硫酸盐水泥拌养的珊瑚混凝土,其强度和耐久性相对较好。最后指出：加强对钙质砂颗粒破碎发生机理的研究以及建立破碎模型、加强对新型珊瑚礁钢筋混凝土和新型桩基的研究、开展珊瑚礁岩土工程的灾害预防与处理以及工程后期的养护等,是珊瑚礁岩土工程进一步研究的方向。 相似文献
2.
基于水热变化的青藏高原土壤冻融过程研究进展 总被引：1，自引：0，他引：1
青藏高原近地层土壤冻融过程是高原地表最显著的陆面特征之一,也是判断冻土发育、存在以及反映气候变化的重要指标。近地层土壤昼夜、季节性的冻结、融化会导致青藏高原陆—气间能水平衡的变化甚至异常,从而显著影响高原地表水文过程、生态环境、碳氮循环以及高原及其周边区域的天气和气候系统。论文从观测、模拟以及对气候的影响3个角度来探讨1990年以来青藏高原土壤冻融过程的最新研究进展。结果表明：① 在一个完整的年冻融循环过程中,近地表各层土壤大体都经历了夏季融化期、春秋季融化—冻结期、冬季冻结期4个阶段。受局地因素的影响,不同站点的冻结或消融起止时间、速率、类型均有差异。② 多年冻土区和季节冻土区的日冻融循环过程差异较大,主要体现在日冻融循环持续时间上。③ 不同陆面模式都可以很好地抓住冻融过程中物理量的时空变化,但都需要针对高原陆面过程的特点进行参数化改进。④ 规避不稳定的迭代计算并根据热力学平衡方程确定冻融临界温度可以改进不合理的冻融参数化方案。基于已有研究回顾,发现增加高质量的观测站,利用卫星遥感等多种手段来反演高原土壤冻融过程以及加强陆面模式与区域气候模式和全球气候模式的耦合,并立足于高原冻融过程的特点发展相适应的参数化方案以及模拟结构的调整,能够有助于高原冻融过程的模拟。 相似文献
3.
Construction of power transmission lines is becoming an important part of permafrost engineering in China.This paper reviews the construction status and problems of transmission lines in different countries,as well as corresponding solutions that would be of practical significance for sustainable engineering practices.Russia has the longest history of transmission line construction in permafrost areas,with transmission lines（mainly 220 kV and 500 kV） spanning approximately 100,000 km.However,all countries suffer from permafrost-related tower foundation stability problems caused by freezing-thawing hazards such as frost heave and thaw settlement,frost lifting,and harmful cryogenic phenomena.As point-line transmission line constructions,the lines,poles and towers should be reasonably selected and installed with a comprehensive consideration of frozen soil characteristics to effectively reduce the occurrence of freezing-thawing disasters.Reinforced concrete pile foundations are widely used in the permafrost regions,and construction in winter is also a universal practice.Moreover,facilitating engineering measures like thermosyphons are an effective way to reduce freezing-thawing hazards and to maintain the stability of tower foundations. 相似文献
4.
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°C and annual precipitation is over 1700 mm. On the one hand, there always experiences a period of periglacial action with
temperature oscillating near 0°C 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).
Foundation: Regional landform and landscape survey programme of the Zhejiang Institute of Geological Survey
Author: Zhu Cheng (1954–), Professor, specialized in geomorphology and the Quaternary geology. 相似文献
5.
Accounting for the solar radiation in thermal regime prediction for railway subgrade in cold regions
This paper presents a comparative analysis of simulation processes of seasonal freezing-thawing of railway subgrade and permafrost degradation, with and without accounting for solar radiation. Also, the effect of sun screens to reduce the degradation of subgrade permafrost under different climatic conditions is numerically substantiated. And finally, the temperature criterion of the origination of permafrost is illustrated. 相似文献
6.
Use of a Probabilistic Neural Network to Reduce Costs of Selecting Construction Rock 总被引：2，自引：0，他引：2
Rocks used as construction aggregate in temperate climates deteriorate to differing degrees because of repeated freezing and thawing. The magnitude of the deterioration depends on the rock's properties. Aggregate, including crushed carbonate rock, is required to have minimum geotechnical qualities before it can be used in asphalt and concrete. In order to reduce chances of premature and expensive repairs, extensive freeze-thaw tests are conducted on potential construction rocks. These tests typically involve 300 freeze-thaw cycles and can take four to five months to complete. Less time consuming tests that (1) predict durability as well as the extended freeze-thaw test or that (2) reduce the number of rocks subject to the extended test, could save considerable amounts of money. Here we use a probabilistic neural network to try and predict durability as determined by the freeze-thaw test using four rock properties measured on 843 limestone samples from the Kansas Department of Transportation. Modified freeze-thaw tests and less time consuming specific gravity (dry), specific gravity (saturated), and modified absorption tests were conducted on each sample. Durability factors of 95 or more as determined from the extensive freeze-thaw tests are viewed as acceptable—rocks with values below 95 are rejected. If only the modified freeze-thaw test is used to predict which rocks are acceptable, about 45% are misclassified. When 421 randomly selected samples and all four standardized and scaled variables were used to train aprobabilistic neural network, the rate of misclassification of 422 independent validation samples dropped to 28%. The network was trained so that each class (group) and each variable had its own coefficient (sigma). In an attempt to reduce errors further, an additional class was added to the training data to predict durability values greater than 84 and less than 98, resulting in only 11% of the samples misclassified. About 43% of the test data was classed by the neural net into the middle group—these rocks should be subject to full freeze-thaw tests. Thus, use of the probabilistic neural network would meanthat the extended test would only need be applied to 43% of the samples, and 11% of the rocks classed as acceptable would fail early. 相似文献
7.
The Stefan equation provides a useful and widely used method for predicting the depth of thawing and freezing in a soil where little site-specific information is available. The original Stefan equation was derived for only a homogeneous medium, and some algorithms have been developed for its use in a multilayered system. However, although the Stefan equation was derived more than 100 years ago, there is not a unified understanding for its use in a multilayered system. This paper examines the use of the Stefan equation in multilayered soil, based on comparing three algorithms(JL-algorithm, NM-algorithm, and XG-algorithm). We conclude that the JL and NM algorithms are incorrect, as they arose from flawed mathematical derivations. Both of these algorithms failed to recognize that the thawing depth in a multilayered soil is a piecewise function and not a continuous function of time. This work asserts that the XG-algorithm is a correct and rigorous method to determine the freezing–thawing fronts in multilayered soil. 相似文献
8.
In seasonally frozen regions, the frost-heave properties of soil play a significant role in its upper-structure performance and durability. To investigate the frost-heave behaviors of saturated, compacted silty clay soil widely used as subgrade material, a series of one-side freezing tests was carried out; and the freezing depth and frozen front effected by the compactness, temperature, overburden pressure, and water-supply condition were analyzed and discussed. The results show that the moving speed of the frozen front and growth rate of the frozen depth are positively correlated. The frost heave is maximum in the frost-heave stability condition. The frost ratio of saturated soil is proportional to the water supply and cooling temperature under a one-side freezing condition. The frost ratio of saturated soil is inversely proportional to the initial compactness of the soil specimen and the overburden pressure. 相似文献
9.
Samantha Jones 《Singapore journal of tropical geography》2000,21(2):131-148
This paper reviews the evidence for and consequences of population pressure in an area of highland Tanzania. While intensification is found to be occurring, both soil improvement and soil productivity decline are evident. A household-level, spatially disaggregated analysis is therefore adopted to understand the variegated pattern of population pressure outcomes. The approach is guided by structuration theory to gain a deeper understanding of the contexts and processes shaping different outcomes. Gender, wealth and land types are found to be influential variables affecting responses to population pressure in this case study. 相似文献
10.
Freezing and thawing during the winter season change soil properties such as density. The density change in the particulate media influences soil stiffness. In addition, freezing of partially or fully saturated soils changes the soil matrix from a particulate media to a continuum. The goal of this study is to investigate the cyclic freezing and thawing effects on elastic waves. Sand-silt mixtures with 10% silt fraction in weight and 40% saturation are prepared. The sand-silt mixtures are placed in a nylon cell, onto which a pair of bender elements and a pair of piezoelectric disk elements are installed for the measurement of shear and compressional waves, respectively. The temperature of the mixtures decreases from 20°C to 10°C to freezing. The frozen sample is gradually thawed at room temperature (20°C). These freezing-thawing processes are repeated three times. The test result shows that the shear and compressional wave velocities significantly increase when the specimen is frozen. When the temperature is greater than 0°C, the elastic wave velocities are lower during thawing than during freezing due to soil structure change. This study demonstrates that soil structure change during the winter season may be effectively estimated from elastic waves. 相似文献
11.
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
12.
农用土地价格初步研究--温州市农用地案例分析 总被引：7，自引：0，他引：7
根据农用土地价格特征,选择适当的方法和评估的操作是研究重点,为此建立农用土地类型、等级、基准地价及变幅的价格体系,为农用土地流转、土地税收等提供依据,促进耕地保护和利用格局调整。并在温州市农用土地管理中的实践,有利于深化土地有偿使用制度改革,建立、健全农村土地市场,强化农用土地资产化管理。 相似文献
13.
构建徐连临成长三角的探讨 总被引：9，自引：0，他引：9
文章概括总结了成长三角的基本特征，并进一步分析了构建成长三角的几个条件。然后运用成长三角理论，从促进区域合作和落后地区发展的角度，提出了建立徐(徐州)连(连云港)临(临沂)成长三角的构想，分析了其对区域发展的意义。并就如何促进该成长三角地区的发展给出了具体的措施，认为协调成长三角参与各方的利益是构建该成长三角成功的关键，同时调整区域内的行政区划也对该成长三角优势的发挥起着重要的作用。 相似文献
14.
15.
Frost heave is one of the major complications in highway construction in cold regions. Laboratory experiments are im-portant in the study frost heave behavior of soils, and one-dimensional frost heave ... 相似文献
16.
武汉市旅游生态安全评价研究 总被引：2，自引：1，他引：1
生态安全是由环境安全理论发展而来的一个新的安全概念,在国内多应用于对土地、水资源和城市进行生态安全评价。本研究基于“压力-状态-响应”（P—S—R）模型和生态安全理论,以2010年的实地调研为依托,尝试构建旅游城市旅游生态安全评价指标体系,采取专家座谈和熵权分析法为各指标赋值。本研究综合当前中国旅游城市的发展现状,以武汉市为例进行实证分析,最终得出武汉市旅游生态安全综合评价值。研究表明,武汉市旅游生态安全综合评价值从2004年的5．8023上升到2010年的6．459,生态安全状态逐年好转,达到了生态安全的“良好”状态。然而生态压力和生态响应却呈现出非相关性,7年间生态响应值远远低于生态压力值,武汉市旅游业的发展还处于粗放式发展状态。研究引入限制性因子的概念,根据公式分析出影响武汉市旅游生态安全的十个影响因素,并探讨未来武汉市旅游生态安全的发展策略。 相似文献
17.
In this paper, the applicability of soil-moisture (SM) datasets of GLDAS (Global Land Data Assimilation System) in an alpine region (Tibet Plateau, TP) is investigated. The relations and discrepancies between the GLDAS-NOAH SM (0~10 cm) and the observations are compared; the possible reasons for errors over the TP are explored. The results show that GLDAS SM biases mainly show up in errors of values in the nonfrozen period (April to October) and changes of SM along with the temperature, especially during the freezing-thawing process in the frozen period (November to March). The biases of GLDAS SM in the nonfrozen period are mainly caused by the GLDAS precipitation-forcing data. The errors of GLDAS SM in the frozen period are speculated to be induced by the freeze-thaw parameterization scheme in the land-surface model. 相似文献
18.
Meteorological excitation of the annual polar motion 总被引：2，自引：0，他引：2
J. B. Merriam 《Geophysical Journal International》1982,70(1):41-56
Summary. Numerous studies have indicated that the annual term in the polar motion cannot be explained in any detail by meteorological/hydrological excitation and no reasonable alternative excitations have been put forward. Part of the problem has been that the hydrostatic adjustment of the oceans to the atmospheric pressure changes has traditionally been computed using the inverse barometer approach. This approach does not properly model the gravitational interaction between the atmosphere and oceans, and the inverse barometer theory is modified in this paper to account for this properly. The information necessary to compute the ocean tide and polar excitation caused by any change in the atmospheric pressure pattern is presented. The results of the application of this theory to two global atmospheric pressure data sets are examined and compared to results of other workers.
It is concluded that the atmosphere is observed well enough to answer the question of the annual excitation of polar motion and it is argued that the ground water excitation is the component with the largest error and remains the chief obstacle to the successful solution of this problem. 相似文献
It is concluded that the atmosphere is observed well enough to answer the question of the annual excitation of polar motion and it is argued that the ground water excitation is the component with the largest error and remains the chief obstacle to the successful solution of this problem. 相似文献
19.
Summary The theory of Reed and Otterman, which describes the propagation of a weak shock wave in an inhomogeneous medium, is extended to include the next higher-order term of relative overpressure. This extension allows a matching of theory to initial starting conditions of the shock at a point closer to the source than the Reed-Otterman theory itself. The modified theory gives a value of the shock pressure that agrees well with the numerical calculation performed by Greene and Whitaker for the upward moving shock wave from a low altitude detonation. 相似文献
20.
县级耕地质量经济评价的理论与方法研究--以江苏扬中市为例 总被引：4，自引：0，他引：4
在借鉴前人研究的基础上,对耕地质量经济评价的理论与方法进行了较为系统的研究;着重探讨了应用现有统计资料进行县级耕地质量经济评价的具体方法,并运用该方法对江苏省扬中市的耕地进行了耕地质量经济评价的实践。 相似文献