土钉墙支护在电力线路中的应用

介绍某220kV线路铁塔地基为含碎石、块石较多，遇水后易软化的土体，采用土钉墙支护，解决了下边坡土体崩落的问题，取得了较好的经济效益。     

膨胀土用于高速公路路基的改性处理及施工要点

膨胀土是在漫长的地质年代中形成的一种吸水膨胀、失水收缩的高塑性黏性土。膨胀土的矿物成分主要是蒙脱石,具有吸水膨胀、失水收缩和反复胀缩变形、浸水承载力衰减、干缩裂隙发育等特性,性质极不稳定,对工程危害极大。     

如何减少预应力管桩施工时的挤土影响

预应力管桩具有强度高、承压性能好、施工速度快等特点,适用于一般黏性土及填土、淤泥和淤泥质土、粉土、非自重湿陷性黄土等土层中使用,大量应用于各种建筑的基础中.由于挤土、桩距、施工安排不当等因素的影响,使桩的单桩承载力提高,加大了挤土效应.要减少预应力管桩施工时的挤土影响,就得从挤土、施工、承载力等方面考虑.并从这几个方面出发,采取相应的措施来减少挤土影响.     

昆明丘陵地区土体抗剪强度指标分析

现行规范[1⁵]用于支挡设计时规定,土体抗剪强度指标宜采用直剪固结快剪强度指标或按三轴试验确定的固结不排水(快)剪指标,而未明确选取时的适用状态(地下水位以上、以下)。呈贡新区地处昆明盆地的丘陵区,地下水位较低,土体具有一定的弱膨胀性(自由膨胀率<40%,不属于膨胀土,但具有遇水软化的特点),在边坡、基坑设计时极易忽视水的作用,从而出现工程事故。本文以该地区某一工程事故为例,根据极限平衡理论,通过对土体指标进行反演分析,得出变形的主要原因为土体指标取用不当。提出该区域土体宜采用浸水后的固结快剪指标或采用折减后的固结快剪指标。     

二灰土施工中对低液限弱膨胀土的处理应用

针对低液限弱膨胀土在路拌二灰土施工中含水量降低缓慢,粉碎困难,导致混合料灰剂量不匀,成型后强度、压实度离散性大,表面土粒遇水膨胀影响美观,后期干缩裂缝发育等问题,经过试验施工对比总结,研究出对该种土的处理方案,有效的保证了二灰土的内外质量,消除了干缩裂缝的产生。     

膨胀土水泥改性试验浅析

膨胀土作为一种典型的非饱和土,具有显著的吸水膨胀软化和失水收缩开裂特性,它在全世界范围分布较广,对水利、道路等工程建设的危害较大,由于防治困难,膨胀土的工程问题一直以来都受到国内外学术界和工程界的高度重视。     

冻融循环作用下细粒土抗剪强度特性参数的研究

新疆地质条件复杂以及春秋季温度变差较大,使得细粒土冻融循环前、后土体的物理、力学性质发生变化,现通过室内冻融循环试验和剪切试验,对细粒土冻融循环前、后抗剪强度特性参数变化进行研究,对不同冻融循环温度变差范围及不同冻融循环次数条件下,细粒土强度特性参数粘聚力c、内摩擦角Ф值的变化规律进行揭示。     

东改工程C-Ⅱ标段对基础处理的质量控制

东改工程C-Ⅱ标段输水管线地处凤凰岗窑坑地段,地层结构复杂多变,地下水丰富。针对输水管线基坑开挖深度范围内的泥质粉砂岩风化土和纳长斑岩风化土遇水或在潮湿的环境中极易软化的特性,通过试验、探索、创新,因地制宜对该标段地基基础处理进行了有效的控制。     

湿陷性花岗岩残积土地质强夯施工技术及应用

安哥拉卢班戈(LUBANGO)居民新城建设区内浅层地基土主要为花岗岩残积土,具有成分和厚度不均匀、孔隙裂隙较多、结构松散、遇水软化和湿陷的特性;本文通过对土层结构的分析,利用强夯试夯施工充分验证了强夯法对于该类型地质处理的有效性。在本工程实践应用中取得了良好的效果,并对同类型地质状况的工程具有一定的借鉴和推广价值。     

关于粗粒土压实特性的试验研究

粗粒土一般是指砂卵石、砂砾石、石渣、堆石料、爆破开采的石料等粗颗粒土石料。具有抗剪强度高、压实密度大、沉陷变形小、透水性能强等工程特性,是一类良好的路基填筑材料。因此,研究它的工程特性对于指导工程设计与施工具有重要意义。从以往对粗粒土的研究上看,仅限于粗颗粒含量与密实度、弹性模量、CBR值等关系的研究,缺乏对粗粒土抗剪强度、水稳定性的研究以及与工程实际的联系。所以重点对粗粒土压实密度特性、抗剪强度特性和水稳定性进行研究。     

Optimality results on orthogonal arrays plus <Emphasis Type="Italic">p</Emphasis> runs for <Emphasis Type="Italic">s</Emphasis><Superscript><Emphasis Type="Italic">m</Emphasis></Superscript> factorial experiments

The optimality of designs obtained by adding p runs to an orthogonal array is studied for experiments involving m factors each at s levels. The optimality criterion used here, is the Type 1 criterion due to Cheng (1978) which is an extension of Kiefer (1975) universal optimality criterion. Unlike what happens with orthogonal array plus one run designs, the behavior of designs obtained via augmentation of an orthogonal array by p runs depends on the particular runs added.     

Measuring process capability index <Emphasis Type="Italic">C</Emphasis><Subscript><Emphasis Type="Italic">pm</Emphasis></Subscript> with fuzzy data

The process capability index C _pm , which considers the process variance and departure of the process mean from the target value, is important in the manufacturing industry to measure process potential and performance. This paper extends its applications to calculate the process capability index [(C)\tilde]_pm{\tilde {C}_{pm} } of fuzzy numbers. In this paper, the α-cuts of fuzzy observations are first derived based on various values of α. The membership function of fuzzy process capability index [(C)\tilde]_pm{\tilde {C}_{pm} } is then constructed based on the α-cuts of fuzzy observations. An example is presented to demonstrate how the fuzzy process capability index [(C)\tilde]_pm{\tilde {C}_{pm} } is interpreted. When the quality characteristic cannot be precisely determined, the proposed method provides the most possible value and spread of fuzzy process capability index [(C)\tilde]_pm{\tilde {C}_{pm} }. With crisp data, the proposed method reduces to the classical method of process capability index C _pm .     

Maximal Rank Minimum Aberration Foldover Plans for 2<Superscript><Emphasis Type="Italic">m</Emphasis>-<Emphasis Type="Italic">k</Emphasis></Superscript> Fractional Factorial Designs

Two level regular fractional factorial designs are often used in industry as screening designs to help identify early on in an experimental process those experimental or system variables which have significant effects on the process being studied. In a recent paper, Li and Lin (2003) suggested a strategy for constructing optimal follow up designs using the well known foldover technique and the minimum aberration criterion. In this paper, we extend the results of Li and Lin (2003) by giving an alternate technique for constructing optimal follow up designs using the foldover technique in conjunction with the maximal rank–minimum aberration criterion suggested in Jacroux (2003).     

Top-<Emphasis Type="Italic">k</Emphasis>-lists

Top-k-lists are introduced as sequences of k-dimensional random vectors with ordered components being k largest observations from a sequence of independent identically distributed random variables. Such lists changing in time are natural stochastic models of ranking tables which appear in many situations in real life, when one wants to keep a track of several best results in a given field. Here we study basic properties of top-k-lists as joint distributions, conditional structures, representations, driving examples of top-k-lists from exponential and uniform distributions, asymptotics and a relation to generalized order statistics.     

¿Está adoptando Asia la «flexiseguridad»?

Incitados por la competencia mundial, muchos países están adaptando la reglamentación laboral al principio de la «flexiseguridad>>, que da a las empresas más flexibilidad para contratar y despedir a los trabajadores, al tiempo que ampara a éstos cuando deben pasar de un empleo a otro. El presente estudio de seis países asiáticos indica que China y República de Corea han promulgado reformas de este género; Singapur y Malasia han implantado algunos elementos de «flexiseguridad>>, pero no un seguro de desempleo, y la India y Sri Lanka han hecho pocas reformas y mantienen un modelo anticuado en el que la protección depende de la empresa. Para prestar apoyo a los trabajadores del sector informal, China, India y Sri Lanka se valen de obras públicas y de programas de fomento del trabajo por cuenta propia y de formación profesional.     

Inference by the <Emphasis Type="Italic">m</Emphasis> out of <Emphasis Type="Italic">n</Emphasis> bootstrap in nonparametric frontier models

It is well-known that the naive bootstrap yields inconsistent inference in the context of data envelopment analysis (DEA) or free disposal hull (FDH) estimators in nonparametric frontier models. For inference about efficiency of a single, fixed point, drawing bootstrap pseudo-samples of size m < n provides consistent inference, although coverages are quite sensitive to the choice of subsample size m. We provide a probabilistic framework in which these methods are shown to valid for statistics comprised of functions of DEA or FDH estimators. We examine a simple, data-based rule for selecting m suggested by Politis et al. (Stat Sin 11:1105–1124, 2001), and provide Monte Carlo evidence on the size and power of our tests. Our methods (i) allow for heterogeneity in the inefficiency process, and unlike previous methods, (ii) do not require multivariate kernel smoothing, and (iii) avoid the need for solutions of intermediate linear programs.     

Two-stage DEA: <Emphasis Type="Italic">caveat emptor</Emphasis>

This paper examines the wide-spread practice where data envelopment analysis (DEA) efficiency estimates are regressed on some environmental variables in a second-stage analysis. In the literature, only two statistical models have been proposed in which second-stage regressions are well-defined and meaningful. In the model considered by Simar and Wilson (J Prod Anal 13:49–78, 2007), truncated regression provides consistent estimation in the second stage, where as in the model proposed by Banker and Natarajan (Oper Res 56: 48–58, 2008a), ordinary least squares (OLS) provides consistent estimation. This paper examines, compares, and contrasts the very different assumptions underlying these two models, and makes clear that second-stage OLS estimation is consistent only under very peculiar and unusual assumptions on the data-generating process that limit its applicability. In addition, we show that in either case, bootstrap methods provide the only feasible means for inference in the second stage. We also comment on ad hoc specifications of second-stage regression equations that ignore the part of the data-generating process that yields data used to obtain the initial DEA estimates.     

Heteroscedasticity diagnostics for <Emphasis Type="Italic">t</Emphasis> linear regression models

The t regression models provide a useful extension of the normal regression models for datasets involving errors with longer-than-normal tails. Homogeneity of variances (if they exist) is a standard assumption in t regression models. However, this assumption is not necessarily appropriate. This paper is devoted to tests for heteroscedasticity in general t linear regression models. The asymptotic properties, including asymptotic Chi-square and approximate powers under local alternatives of the score tests, are studied. Based on the modified profile likelihood (Cox and Reid in J R Stat Soc Ser B 49(1):1–39, 1987), an adjusted score test for heteroscedasticity is developed. The properties of the score test and its adjustment are investigated through Monte Carlo simulations. The test methods are illustrated with land rent data (Weisberg in Applied linear regression. Wiley, New York, 1985). The project supported by NSFC 10671032, China, and a grant (HKBU2030/07P) from the Grant Council of Hong Kong, Hong Kong, China.     

浅谈“三背回填”质量控制

"三背回填"是公路工程的重要组成部分,出现错台、沉降、结构物位移等现象,直接影响到公路路基的稳定性,影响车辆行驶的安全度和舒适度,对此,在公路设计、施工和质量检测方面也提出更高的要求。本文从地基处理、填料选择、施工工艺及加筋土运用四方面对施工进行了改进,达到了质量控制要求。     

Bayesian estimation of log odds ratios from R × C and 2 × 2 × K contingency tables

In this paper, Bayesian estimation of log odds ratios over R × C and 2 × 2 × K contingency tables is considered, which is practically reasonable in the presence of prior information. Likelihood functions for log odds ratios are derived for each table structure. A prior specification strategy is proposed. Posterior inferences are drawn using Gibbs sampling and Metropolis–Hastings algorithm. Two numerical examples are given to illustrate the matters argued.