突变理论在工程地质中的应用   总被引：28，自引：2，他引：28  

黄润秋  许强 《工程地质学报》1993,1(1):65-73

本文说明了突变理论应用于工程地质中的一般方法。着重通过实例介绍尖点突变理论在工程地质中的应用现状,其中包括用突变理论评价层状结构斜坡、地下洞室的顶板冒落及活断层的稳定性,以及斜坡失稳的时间预报等问题。同时对其应用前景作了展望。  相似文献   

Winds and sand movements in the Namib Sand Sea     

N. Lancaster 《地球表面变化过程与地形》1985,10(6):607-619

Wind regimes in the vicinity of the Namib Sand Sea are high energy unimodal near the coast, becoming bimodal or complex inland. There is an overall decrease in wind energy and sand transport rates from south to north and west to east, such that sand moves from coastal and southern source areas to accumulate in the northern and central parts of the sand sea. Such a pattern can explain much of the observed spatial variability in dune types, sizes, and sediment characteristics and lends support to a climatic model of sand sea formation in this region. Seasonal and daily cycles of wind velocity and direction give rise to episodic sand transport, most of which is generated by winds of moderate velocity and frequency.  相似文献   

上海地区超高层建筑桩基沉降计算方法探讨     

施云华 《上海国土资源》1997,(1):31-37

本文根据已有的建筑经验,应用明特林应力分布理论及双层地基概念和土的临界应力的分析,提出了更符合实际的沉降计算方法,并论证了在第三类土层排列区(即埋深30～40mm的⑦层粉砂层)超高层桩基设置的可能性,以大大减少工程造价。  相似文献   

Prediction method of sand-movement direction in water by geochemical elements     

K. Mizumura  T. Nishimoto  H. Tsutsui  T. Yamamoto 《Environmental Geology》1995,25(2):100-108

The analysis of sand samples by x-ray fluorescent spectroscopy (XRF) gives the ratio of the geochemical elements to construct the sand samples. The x-ray analysis therefore shows the geochemical characteristics of sand in the sampled area. In this study, sand is sampled on coasts and rivers of the Noto Peninsula to determine the geochemical elements and to show the geological characteristics that occur, especially iron and calcium. The experiments show the effect of rivers and Kotogahama beach on iron and calcium, respectively. Applying the method of ratio matching to the measured data of the geochemical elements, the direction of movement of sand on the coast is determined by considering the correlation matrix and the ratio of geochemical elements between sand samples at two locations. The predominant longshore direction movement of sand offshore in the study area is from south to north. Sand in rivers is not directly transported to adjacent beaches; however, offshore sand is transported to beaches. The estimated direction of movement of sand longshore near coastal structures agrees with observations. The proposed method to predict the direction of movement of sand gives the correct one in comparison with the observed data in rivers.  相似文献   

Interfacial instability of sand patterns induced by turbulent shear flow   总被引：1，自引：0，他引：1  

Sk Zeeshan Ali  Subhasish Dey 《国际泥沙研究》2021,36(4):449-456

When a turbulent shear flow above a plane sand surface entrains sand grains,it generates a variety of sand patterns.Fluvial sand forms two major interfacial patterns:meso-scale dunes and antidunes,and large-scale bars.Measurements have evidenced that under erosive conditions,meso-scale patterns either change to or coexist with large-scale patterns.However,it remains elusive what exactly drives the switching of interfacial patterns and how the switching occurs.Here,we showdcombing a flow model with a grain transport model,allowing for both the surface and suspended sand fluxes dthat the switching of patterns emerges from the shear-driven complex feedback between grain transport and topographic perturbations.The switching predominantly depends on the magnitudes of the Rouse number and the grain size to undisturbed flow depth ratio.The model offers quantitative predictions of the maximum amplification of sand patterns and unveils a new attraction erepulsion phenomenon.  相似文献   

MM5和ETA相似理论近地层方案对农田下垫面通量模拟比较研究     

王寅钧  周明煜  徐祥德  孙绩华 《气象学报》2013,71(1):677-691

近地层湍流通量计算对于中尺度数值模式有重要意义, 湍流通量的参数化是当前大气边界层研究的重要课题之一。选择青藏高原东缘大理观象台边界层通量观测系统, 离线测试了WRF区域模式中的两种常用的近地层参数化方案(MM5相似理论非迭代方案A和ETA 相似理论迭代方案B), 并将参数化方案计算结果与边界层铁塔涡动相关法的观测值进行对比分析。在大理观象台观测场不同植被随季节交替的状况下, 根据边界层铁塔4层高度风速拟合, 发现近地层空气动力学粗糙度随季节变化特征明显。将拟合的空气动力学粗糙度输入模式参数化方案进行通量计算。结果表明:稳定度是影响近地层参数化方案精度的重要因素, 在不稳定条件下方案B低估了动量通量, 方案A优于方案B, 而在稳定条件下方案A低估了动量通量, 方案B优于方案A, 两种方案总体来看误差不大。对于大理边界层通量观测场地农田植被交替的环境条件, 不同季节下垫面植被类型的差异, 以及植被的稀疏对近地层参数化方案湍流通量计算结果的精度有显著影响。方案B考虑了空气动力学粗糙度z₀和热量粗糙度z_0h的差异, 不稳定条件下感热通量计算结果在裸土或稀少植被条件下明显优于方案A。针对方案B不稳定条件下感热通量计算结果在裸土下垫面仍出现高估的现象, 在使用了(Zeng, et al, 1998)提出的对于使用辐射地表温度在裸土下垫面时的订正方法后, 计算结果也有明显改善。  相似文献   

陕北风沙区大保当煤矿开采的生态影响分析     

钱者东  秦卫华  李道进 《西部资源》2012,(1):84-86

陕北风沙区位于毛乌素沙地东南缘,是毛乌素沙地向黄土高原的过渡地带,自然环境十分脆弱。本文通过对陕北风沙区大保当井田进行实地调查研究,结合遥感影像,运用图形叠置法、类比分析法和生态机理法分析了在该地区进行煤矿开采对当地自然植被、野生动物以及神木臭柏自然保护区的影响,并提出相应的生态保护措施。  相似文献   

End Bearing Capacity of Drilled Shafts in Sand: A Numerical Approach     

M. M. Ahmadi  M. Khabbazian 《Geotechnical and Geological Engineering》2009,27(2):195-206

In this paper, a modeling procedure is carried out to numerically analyze the end bearing capacity of drilled shafts in sand. The Mohr–Coulomb elastic plastic constitutive law with stress dependent elastic parameters is used for all numerical analyses performed in this study. The numerical results are compared with the available experimental equations. It is seen that numerical results are in good agreement with experimental equations. The variation of the end bearing capacity of drilled shafts versus embedment depth is also studied. Numerical results show that with increase in pile embedment depth, the end bearing capacity increases. However, the rate of increase becomes smaller as the pile embedment depth increases. Also, numerical analyses show that, for equal settlement, the end bearing decreases with increase in the pile diameter. Finally, a sensitivity analysis is performed to obtain the separate effect of each sand parameter on the end bearing capacity of drilled shafts, and the parameters that are most influential are identified.  相似文献   

A study on the limit void ratio characteristics of medium to fine mixed graded sands     

Y. Yilmaz   《Engineering Geology》2009,104(3-4):290-294

The minimum and maximum void ratios, corresponding to states of densest and loosest packing, of 111 systematically prepared mixed graded sand samples are determined with Method 2A and Method B according to ASTM D 4253 and ASTM D 4254 standards, respectively. Although, those standards are applicable to soils that may contain up to at most 15% fines content, for the harmony of the results even for samples having fines content greater 15%, no other methods are used throughout the experimental program. The test results show that 3rd degree polynomial equations derived from existing experimental data, as a function of packing material percentage, are quite reasonable (R² ≈ 1.0) to estimate the variation of minimum and maximum void ratios for the sands considered. Furthermore, error analysis of the limit void ratios is also carried out. It is found that predictability of maximum void ratio for the soil types and gradations considered is more accurate than that of minimum void ratio.  相似文献   

Source-area controls on the composition of beach and fluvial sands on the southern side of the Gibraltar Strait and Western Alboran Sea (Flysch Basin, Internal and External, Domains, Northern Rif Chain)     

M.N. Zaghloul  H. Reddad  S. Critelli 《Journal of African Earth Sciences》2009,55(1-2):36

The southern side of Gibraltar and the Western Alboran Sea of the northern Rif coasts and rivers provide a natural field laboratory for sampling modern sand at different scales: small catchment basins (first order) and rivers draining mountain belts (second order). The Rifian chain represents a deformed and uplifted thrust-belt and related forelands composed of Palaeozoic nappes, metamorphic and plutonic basement, and their sedimentary Mesozoic and Cenozoic siliciclastic and carbonate cover, respectively. The present physiography of the Rif Chain is shaped by a rugged mountainous relief drained by different scale catchment basins that supply the nearby coastal and marine deep-sea environments. The analysis of the composition of modern fluvial and beach sands is useful for the interpretation of transported sediments by surface processes from the continent toward coasts and later to deep-water environments.Modern beach and fluvial sands of the southern side of Gibraltar and the Western Alboran Sea display three distinct petrologic littoral provinces, from the east to the west and from the north to the south, respectively, designated as: (i) the Tangier–Bel Younech Littoral Province with 90% of sand derived from erosion of Flysch Nappes (Flysch Basin Domain); (ii) the Bel Younech–Sebta Littoral Province with 64% of sand fed mainly by the metamorphic Units of Upper Sebtides and (iii) the Sebta–Ras Mazari Littoral Province with 74% of sand supplied from the epimetamorphic Palaeozoic Ghomaride Nappes and Alpine cover rather than Mesozoic and Cenozoic sedimentary successions of the “Dorsale Calcaire” Units. Comparison of detrital modes of fluvial and coastal marine environments highlights their dispersal pathways and drainage patterns of actualistic sand petrofacies.  相似文献