特定场地下土工构筑物的几何可靠性分析     

吴兴征  王瑞凯  辛军霞 《岩土力学》2020,41(6):2070-2080

针对特定场地下土工构筑物的正常使用极限状态，采用近年发展的几何可靠性方法计算了多种构筑物的可靠度指标。考虑同一场地下的钻孔灌注桩、抗浮锚杆和CFG桩单桩加载变形测试曲线的离散性，各曲线回归参数呈现差异并可作为随机变量，进而探讨了各曲线回归参数间的相关性及联合分布特性。基于这些回归参数的联合发散概率密度等值线，即随机变量刚好达到极限承载能力状态，该几何可靠性算法可在随机变量的原始空间求得土工构筑物的可靠度指标。通过比对该几何可靠度指标与常规的一次可靠性算法成果，验证了该几何可靠性计算技术的可行性。计算表明，几何可靠性评价模型实施简便，易于被工程技术人员接受。  相似文献   

基于级配方程的粗粒料压实特性试验研究     

吴二鲁  朱俊高  郭万里  陆阳洋 《岩土力学》2020,41(1):214-220

级配显著影响着堆石料的压实特性，定量表述级配对堆石料压实特性的影响至关重要。基于连续级配土的级配方程，设计了16组不同级配的试验粗粒料，进行了表面振动压实试验和侧限压缩试验，定量研究了级配对粗粒料压实特性的影响。研究表明：由表面振动压实（动应力）试验和侧限压缩（静应力）试验得到的干密度与级配曲线面积之间均呈二次函数关系，且干密度中的最大值对应的级配曲线面积均在0.9附近；无论是表面振动压实试验还是侧限压缩试验，堆石料都存在干密度最优（最大）的级配。依据试验成果，给出了所试验堆石料的最优级配区间（级配上、下包络线）；同时，利用相似级配法论证了实际级配粗粒料的最优级配区间，并根据国内外多座土石坝粗粒料的设计级配验证了该最优级配区间的普遍适用性，为土石坝粗粒料的级配设计提供了理论依据。  相似文献   

西昌盆地上三叠统白果湾组富有机质泥页岩沉积岩相古地理与孔隙特征     

客昆  秦建华  牟必鑫  魏洪刚  何伟  雷玉雪  陈杨  刘治成 《沉积与特提斯地质》2020,40(3):140-150

海陆过渡相富有机质泥页岩是页岩气勘查开发的重要领域。本文以西昌盆地上三叠统白果湾组富有机质泥页岩为研究对象，对研究区内富有机质泥页岩的沉积岩相古地理特征、微观孔隙类型、孔隙结构特征进行研究。白果湾组富有机质泥页岩段沉积相主要为湖泊相、三角洲相、河流相。发育不同类型的微孔隙，孔隙主要以小孔为主，微孔次之，平均孔径分布在5.56~56.89nm之间，比表面积平均为9.44m²/g，总孔体积平均为0.0187cm³/g。页岩气主要形成于滨浅湖亚相及半深湖亚相中，并主要吸附于富有机质泥页岩的小孔、微孔内；西昌盆地白果湾组富有机质泥页岩储集空间较好，具有良好的勘探潜力。  相似文献   

路网约束条件下热力规则设计与试验     

杜晓  周玉秀  周琦  郑义  张俊辉  林尚纬  陈利军 《测绘通报》2020,(7):18-21

热力图是一种能直观准确展示空间观测值的有效工具，在多个领域具有广泛应用。本文在分析设定不同道路层权重、道路技术等级分类的基础上，以反距离权重、直方图均衡化、密度补偿、参数多次迭代等方法，研究构建了以热力方式展示道路网分布及发达程度的相关规则体系。热力规则通过道路赋权、路线曲面化、密度协调、图面综合等多套规则的有机结合，实现了道路网总体发达水平信息的提取与展示，并以全球地理信息资源建设项目路网成果中的亚洲和非洲部分国家数据为例，进行了信息提取与热力分布试验。  相似文献   

Species Diversity Characteristics of a Natural Pinus taiwanensis Community with Different Diameter Classes and Forest Densities     

WANG Yang  JIANG Xiongbo  WU Dezhi 《资源与生态学报(英文版)》2020,11(4):349-357

Pinus taiwanensis is a species endemic to China. This study selected four typical plots of Pinus taiwanensis in the natural secondary forest around Macheng City, in order to reveal the characteristics of and the relationships between different diameter classes (determined based on the diameter at breast height or DBH), forest densities and species diversity, as well as the similarities of species diversity of different plots within the community. The result showed that Pinus taiwanensis was the dominant species in the community. The ratio of Pinus taiwanensis trees of diameter class IV reached a peak of 19.46% of the total followed by diameter class VII at 18.92%. The study recorded 156 species of vascular plants from 130 genera of 71 families; Pinus taiwanensis was the dominant species in the community. When the forest density was 1200 trees ha ^-1 with the largest average diameter of DBH=36.779±4.444 cm, the diversity (Shannon index H'=1.6716) and the evenness (Pielou index E=0.6727) of the tree layer was the highest. When the forest density reached 1525 trees ha ^-1 with the lowest average diameter of DBH=18.957±5.141 cm, the richness (D_ma=5.4308), the diversity (H'=2.9612) and the evenness (E=0.8985) of all shrub layers climbed to the maximum. When the forest density was 1325 trees ha ^-1, the richness (D_ma=5.8132), the diversity (H'=3.0697) and the evenness (E=0.9025) of all herb layers peaked. In terms of vertical structure, the average diversity indexes were herb layer>shrub layer>tree layer. High canopy density weakened light intensity in the community, causing a reduction in the species diversities of herbs and shrubs. The average similarity coefficient between the sample plots was 0.3356, which was at the medium dissimilarity level. External disturbances and improper management were major contributors to the low species diversity of the community. The implementation of scientific management measures is urgently needed to optimize the forest structures of Pinus taiwanensis, create a benign community environment, and promote species diversities and establish a stable forest community structure.  相似文献   

Gamma-Hadron Separation using Čerenkov Photon Density Fluctuations     

V. R. Chitnis  P. N. Bhat 《Experimental Astronomy》2002,13(2):77-100

In the atmospheric Čerenkov technique γ-rays are detected against the abundant background produced by hadronic showers. In order to improve the signal to noise ratio of theexperiment, it is necessary to reject a significant fraction of hadronic showers. Traditional background rejection methods based on image shape parameters have been extensively used for the data from imaging telescopes. However, non-imaging Čerenkov telescopes have to develop very different means of statistically identifying and removing cosmic ray events. Some of the parameters, which could be potentially important for non-imaging arrays, are the temporal and spectral differences, the lateral distributions and density fluctuations of Čerenkov photons generated by γ-ray and hadron primaries. Here we study the differences in fluctuations of Čerenkov photon density in the light pool at the observation level from showers initiated by photons and those initiated by protons or heavier nuclei. The database of simulated events for the PACT array has been used to evaluate the efficiency of the new technique. Various types of density fluctuations like the short range and medium range fluctuations as well as flatness parameter are studied. The estimated quality factors reflect the efficiencies with which the hadrons can be rejected from the data. Since some of these parameters are independent, the cuts may be applied in tandem and we demonstrate that the proton rejection efficiency of ∼90% can be achieved. Use of density fluctuations is particularly suited for wavefront sampling observations and it seems to be a good technique to improve the signal to noise ratio. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

利用自回归模型检测地球极移重力效应     

杨学峰  孙和平  徐建桥 《大地测量与地球动力学》2004,24(2):110-114

同时采用4个台站的国际超导重力仪长期连续重力观测资料和国际地球自转服务中心提供的同步地球自转参数，研究了极移引起的地球重力场变化特征。利用自回归模型估计了各序列的功率谱密度和积谱密度，结果表明极移导致的重力效应的主要能量集中在Chandler摆动和周年项附近，叠积后实际重力观测与极移重力信号理论值之间的差异分别为0．4％和3．9％，说明超导重力仪可有效监测极移导致的重力变化。  相似文献   

A critical state model for sands dependent on stress and density     

Y.P. Yao  D.A. Sun  T. Luo 《国际地质力学数值与分析法杂志》2004,28(4):323-337

An elastoplastic model for sands is presented in this paper, which can describe stress–strain behaviour dependent on mean effective stress level and void ratio. The main features of the proposed model are: (a) a new state parameter, which is dependent on the initial void ratio and initial mean stress, is proposed and applied to the yield function in order to predict the plastic deformation for very loose sands; and (b) another new state parameter, which is used to determine the peak strength and describe the critical state behaviour of sands during shearing, is proposed in order to predict simply negative/positive dilatancy and the hardening/softening behaviour of medium or dense sands. In addition, the proposed model can also predict the stress–strain behaviour of sands under three-dimensional stress conditions by using a transformed stress tensor instead of ordinary stress tensor. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

GRADATION AND ASSESSMENT OF DAMAGE DEGREE OF NATURAL LANDSCAPE IN XING, AN COUNTY, GUANGXI     

李家永  李昌华 《中国地理科学(英文版)》1992,(4)

A new technique designed to help quantify the degree of damage to the landscape from one area to another shows a close relationship between population density and the degree of landscape damage. The technique establishes a scale of damage from 0 to 5 (zero = no damage; 5 = severe damage) using data from aerial photographs, land-use maps, and field data. The related formula allows one to compare the relative degree of damage across regions using a combination of an absolute index, a theoretical index, a relative index, and population density. Xing'an County is used to demonstrate the technique.  相似文献   

滇西北和邻区均衡重力异常特征及其壳内构造     

袁果田  项爱民 《大地测量与地球动力学》1992,(2)

本文以爱黎-海斯卡宁均衡补偿假设模式为基础,利用圆模板编制了滇西北及邻区均衡重力异常图。分析了异常的基本特征与壳内构造的关系,并初步探讨了均衡重力异常和强震活动的相关性。  相似文献