破碎砂岩渗透特性与孔隙率关系的试验研究   总被引：5，自引：0，他引：5  

黄先伍  唐平  缪协兴  陈占清 《岩土力学》2005,26(9):1385-1388

利用一种专利装置与MTS815.02型岩石力学试验系统,进行了破碎砂岩的稳态渗透试验,得到了不同孔隙率下破碎砂岩的渗透率和非Darcy流 因子。通过线性回归得到了渗透率、非Darcy流 因子与孔隙率之间的关系。认为破碎岩石的渗透特性主要是由孔隙率决定的,孔隙率不仅与当前的应力有关,更取决于加载历史。研究表明,水在破碎砂岩中的渗流一般不服从Darcy定律,而服从Forchheimer关系,特别是在小孔隙率下,非Darcy性更为突出;渗透率、非Darcy流 因子与孔隙率之间的关系可用幂函数拟合。  相似文献   

水文响应单元法在盐渍化风险评价中的应用   总被引：3，自引：1，他引：2  

章光新  邓伟  何岩  RAMSIS Salama 《吉林大学学报(地球科学版)》2005,35(3):356-360

运用水文响应单元（HRUs）法评价洮儿河流域地下水环境空间变化对盐渍化风险等级的影响过程,利用反映地下水环境空间变化的3个重要参数:水文区权重（HZ）、水位埋深（DTW）和水位上升速率（RR）,由其3个等级网格值算术相乘HRU = DTW*RR*HZ在GIS 平台上生成2001年水文响应单元图。结果表明：（1）洮儿河流域整体上盐渍化风险非常小,低风险区主要分布在水文区A、水文区B和水文区D中的安广镇、烧锅镇一带,主要原因是由于区域地下水位下降、水文区A水文及水文地质条件较好;（2）高风险区主要分布在莫莫格湿地、镇赉县境内和来福-叉干镇一带,主要是由于嫩江排泄通道受阻、地表水体的补给以及水田不合理的灌溉造成的。  相似文献   

Transverse seismic kinematics of single piles by a modified Vlasov model     

Qijian Liu  Fangjun Deng  Yibin He 《国际地质力学数值与分析法杂志》2014,38(18):1953-1968

Within the framework of soil–pile interaction, a novel displacement scheme for the transverse kinematic response of single piles to vertically propagating S waves is proposed on the basis of the modified Vlasov foundation model. The displacement model contains a displacement function along the pile axis and an attenuation function along the radial direction. The governing equations and boundary conditions of the two undetermined functions are obtained in a coupled form by using Hamilton's principle. An iterative algorithm is adopted to decouple and solve the two unknown functions. In light of the governing equation of the pile kinematics, a mechanical model is proposed to evaluate the present method on a physical basis considering material damping. The coefficient of the equivalent Winkler spring is derived explicitly as function of the displacement decay parameter γ and soil Poisson's ratio. A parametric study is performed to investigate the effects of the soil–pile system properties on the kinematic response of single piles. The results show that the dimensionless pile length controls the transverse kinematics of piles. In terms of the theory of beams on elastic foundation, the classification limits of the dimensionless pile length may be π ∕ 4 and π, respectively. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

How do species and data characteristics affect species distribution models and when to use environmental filtering?     

Lukáš Gábor  Vojtěch Barták  Vincent Lecours 《International journal of geographical information science》2020,34(8):1567-1584

ABSTRACT

Species distribution models (SDMs) are widely used in ecology and conservation. However, their performance is known to be affected by a variety of factors related to species occurrence characteristics. In this study, we used a virtual species approach to overcome the difficulties associated with testing of combined effects of those factors on performance of presence-only SDMs when using real data. We focused on the individual and combined roles of factors related to response variable (i.e. sample size, sampling bias, environmental filtering, species prevalence, and species response to environmental gradients). Results suggest that environmental filtering is not necessarily helpful and should not be performed blindly, without evidence of bias in species occurrences. The more gradual the species response to environmental gradients is, the greater is the model sensitivity to an inappropriate use of environmental filtering, although this sensitivity decreases with higher species prevalence. Results show that SDMs are affected to the greatest degree by the species response to environmental gradients, species prevalence, and sample size. Models’ accuracy decreased with sample size below 300 presences. Furthermore, a high level of interactions among individual factors was observed. Ignoring the combined effects of factors may lead to misleading outcomes and conclusions.  相似文献   

Three‐dimensional dynamic response of ground with a poroviscoelastic interlayer to a harmonic moving rectangular load          下载免费PDF全文

S.‐J. Feng  Y.‐C. Li  Z.‐L. Chen  H.X. Chen 《国际地质力学数值与分析法杂志》2017,41(7):1055-1076

Stratification is a basic characteristic of ground. Due to the influence of ground water, saturated weak interlayers widely exist, particularly in soft soil area. An interlayer of high compressibility and low strength has a substantial effect on dynamic response of the ground, especially under high speed moving load. Thus, a comprehensive investigation in the influence of interlayer is essential and useful in geotechnical and transportation‐related engineering. This paper presents a three‐dimensional semi‐analytical approach to study the dynamic response of a layered ground with a soft saturated interlayer. The ground is modelled as a half‐space consisting of three parts: a viscoelastic upper layer, a saturated poroviscoelastic interlayer governed by Biot's theory and a viscoelastic half‐space. An ‘adapted stiffness matrix’ is proposed to obtain the semi‐analytical solution to the system. Comprehensive parametric study is conducted to investigate the influences of existence, geometrical and physical properties of the interlayer. Depth, thickness, hydraulic permeability of the interlayer, load speed and frequency significantly influence the dynamic response of the ground, among which the interlayer depth plays a dominant role. Resonant frequency exists, which is highly affected by the interlayer thickness, especially in low speed regime. Both hydraulic permeability and boundary conditions of the interlayer influence the characteristics of pore pressure distribution. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Precipitation regional extreme mapping as a tool for ungauged areas and the assessment of climate changes          下载免费PDF全文

Jinhui Jeanne Huang  Yu Li  Junxian Yin  Edward Authur Mcbean 《水文研究》2016,30(12):1940-1954

The spatial‐temporal characteristics of mean annual daily maximum precipitation events in the upper Yangtze River basin in China are examined using a framework termed precipitation regional extreme mapping (PREM). The framework consists of regional analyses and mapping methods, which have the capability to assess the presence or absence of climate change. The findings confirm the homogeneous regions identified by Wang (2002) using a heterogeneity measure, where all three regions have heterogeneity less than 1.0. The Pearson type III (PE3) distribution was found to be acceptable for all three regions, while the generalized extreme‐value distribution performs better than PE3 for Region I (eastern portion of the upper Yangtze basin). Two indices, root mean square error and mean bias, were used to access the performance of the extreme map, and the results show that the map of extreme can predict precipitation for ungauged regions with acceptable accuracy. The regional frequency maps were used in conjunction with the Student's t‐test to identify the statistical significance of changes of extremes in precipitation. Results indicate that there have been no significant changes in maximum daily precipitation magnitudes over the past four decades, a finding that is valuable for the safe planning of major hydraulic projects and the management and planning of water resources in the upper Yangtze River basin. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

基于地理国情信息编制自然资源资产负债表技术方法研究     

苏东华 《地理空间信息》2021,19(4):126-130

基于地理国情信息编制自然资源资产负债表,以广安市为研究区开展了编制自然资源资产负债表技术方法研究,从数量、质量和价值3个方面,运用数值统计与空间分布格局相结合的方法探究编制广安市自然资源资产负债表。研究结果表明:(1)地理国情矢量数据作为制作自然资源资产数据集的基础数据,在统计自然资源资产面积和空间分布上有极大的优势,可以直观地反映上述两项指标。(2)多光谱遥感影像数据,可用于部分质量和价值指标核算。(3)自然资源资产负债表的编制,需要多部门专业数据支持。  相似文献   

无人机三维航迹规划改进方法     

冯朝晖  韩留生  李芹 《测绘通报》2021,(3):50-54

在地形起伏的复杂环境下进行遥感观测任务需要进行三维航迹规划以适应多变的自然环境,而且在规划航迹时需要考虑减少飞行时间和能量消耗以提高作业效率。本文提出了一种曲面趋平化算法（CSFA）,首先采用准均匀B样条曲面拟合算法对CSFA算法处理后的目标区域DEM进行插值,构建区域的自然环境地形模型;然后为了减少时间和能量的消耗,采用点边式宽度算法计算最优飞行方向,获得最少转弯次数;最后通过摄影测量中的重叠度约束和区域环境地形模型计算三维航带和曝光点。试验通过在不同的航高下建立约束进行三维航迹规划模拟仿真,试验结果表明,本文提出的方法能够缩短航带长度,降低作业能耗,有效地提高了观测任务效率。  相似文献   

Rapid ecosystem change challenges the adaptive capacity of Local Environmental Knowledge     

《Global Environmental Change》2015

The use of Local Environmental Knowledge has been considered as an important strategy for adaptive management in the face of Global Environmental Change. However, the unprecedented rates at which global change occurs may pose a challenge to the adaptive capacity of local knowledge systems. In this paper, we use the concept of the shifting baseline syndrome to examine the limits in the adaptive capacity of the local knowledge of an indigenous society facing rapid ecosystem change. We conducted semi-structured interviews regarding perceptions of change in wildlife populations and in intergenerational transmission of knowledge amongst the Tsimane’, a group of hunter-gatherers of Bolivian Amazonia (n = 300 adults in 13 villages). We found that the natural baseline against which the Tsimane’ measure ecosystem changes might be shifting with every generation as a result of (a) age-related differences in the perception of change and (b) a decrease in the intergenerational sharing of environmental knowledge. Such findings suggest that local knowledge systems might not change at a rate quick enough to adapt to conditions of rapid ecosystem change, hence potentially compromising the adaptive success of the entire social-ecological system. With the current pace of Global Environmental Change, widening the gap between the temporal rates of on-going ecosystem change and the timescale needed for local knowledge systems to adjust to change, efforts to tackle the shifting baseline syndrome are urgent and critical for those who aim to use Local Environmental Knowledge as a tool for adaptive management.  相似文献   

基于皮尔斯符号三元观的专题地图符号设计     

翁敏  黄谦  苏世亮  亢孟军 《测绘地理信息》2021,46(1):44-47

作为专题地图的重要组成部分,符号始终受到广泛关注,不少学者对符号的设计方法提出了见解,然而少有学者从符号意义的角度系统研究地图符号设计。以皮尔斯的符号三元观为基础,结合专题地图特点,建立了"符号组成要素-符号表现层面-符号结构"的理论基础;并根据视觉变量的特征,阐述不同表现层面下的符号设计方法;以《深圳市地图集》中的3幅地图为例,介绍了具体的符号表达策略。  相似文献