基于双荷载箱自平衡法的黄土地区桩基承载特性试验研究

为探究双荷载箱自平衡法在黄土地区的适用性,以陕西地区某城市立交工程2根抗压试桩为研究对象,对桩基竖向承载力进行检测,分析了桩底压浆前、后桩基承载力的提升程度及组成差异,并从桩身轴力、桩侧摩阻力及桩端阻力3个方面对荷载传递规律进行研究。结果表明:压浆后桩基极限承载力相较于压浆前提升了51.74%,其中桩端阻力值增加到压浆前的2.5倍,且占桩基承载力的比重明显增大;双荷载箱自平衡试验中,桩身轴力在上荷载箱处产生并达到最大值,向桩顶和桩底逐渐衰减,轴力向下衰减速率明显更快;桩侧摩阻力由上荷载箱处开始发挥,沿桩身传递过程中,由于桩土相对位移逐渐减小,最终衰减至最小值;下部桩身桩端反力-位移曲线与传统静载试验的荷载-位移曲线类似,但两者桩周土应力场存在差异。

软土地区桥梁桩基注浆加固效果及影响参数研究

文章以某软土地区桥梁桩基加固工程为研究背景,对桩基周围土体开展室内试验,研究注浆压力与注浆液水灰比对浆脉宽度、抗压强度、粘聚力、内摩擦角的影响,结合室内试验数据,基于FLAC3D数值模拟软件,采用桩基侧面注浆方法,分析不同注浆深度、注浆长度、注浆压力等条件下桩基荷载-沉降曲线,研究其对桩基极限承载力的影响。结果表明:(1)浆脉宽度随注浆压力的增大在逐渐增大,且增大速率也在逐渐变大,但当注浆压力从1 MPa增加到2.5 MPa,浆脉宽度增加幅度随水灰比的增加在降低,同时随着水灰比的增加,浆液扩散范围在降低;(2)随着水灰比的增大,加固土体的抗压强度、粘聚力、内摩擦角等出现先增大后减小的现象,说明应存在一个最优水灰比;(3)桩基极限承载力随注浆长度、注浆压力的增加在逐渐增大;(4)随着注浆长度的增大,桩基极限承载力在不断提升。

基于三剪统一强度准则的太沙基地基极限承载力

基于三剪统一强度准则考虑中间主应力影响的特点,对太沙基地基极限承载力计算公式进行了修正。在修正式中,强度准则中的中间主应力效应参数b对地基极限承载力有影响。算例分析表明:当地基土的内摩擦角较大,b取其较大值时;当地基土的内摩擦角较小,b取其较小值时,修正式都能较好地反映地基极限承载力的真实情况。

统一强度理论下桩基极限承载力讨论

基于Mohr-Coulomb准则的太沙基深基础承载力公式未考虑中间主应力的影响,因而与实际极限承载力有出入,而统一强度理论通过系数b考虑了中间主剪应力和中间主应力的影响。因此,利用统一强度理论,结合滑移线场理论,以太沙基深基础计算模型为基础建立了考虑中间主应力时的桩基极限承载力的统一解形式,应用Matlab软件画出了地基极限承载力qu与b值的关系曲线,考虑中间主应力时桩基的极限承载力将提高,可以充分发挥材料的承载能力,可以节约造价。

下伏岩溶与桩基耦合作用研究

为探求下伏岩溶与上方桩基之间的耦合作用,对岩溶顶板与桩基作用体系进行抽象概化,建立8种力学模型,基于弹性力学薄板理论及材料力学梁理论进行理论力学分析,并结合工程实践对比分析各力学模型下岩溶顶板安全厚度及桩基极限承载力。计算结果表明:不同力学计算模型适用于不同实际工程;同一条件下各力学模型计算结果差别较大。因此,合理选择适合于实际工程的溶洞顶板及桩基作用体系力学模型至关重要。

多种检测技术在旋挖成孔钻孔灌注桩基桩检测中应用分析研究

旋挖成孔混凝灌注桩由于施工工艺的特殊性,桩身的完整性是决定桩的桩承力主要因素,文章通过低应变法辅以声波透射法进行桩身完整性检测,并对选定工程桩进行承载力检测。检测结果显示,低应变法检测的工程桩均为Ⅰ类桩,平均波速为3543m/s;本次声波透射法检测工程桩亦均为Ⅰ类桩;基桩极限承载力均为最大试验荷载值3700kN。结果表明,桩身完整性为Ⅰ类桩的单桩竖向抗压承载力均对应满足设计要求。

滤基的收敛及其应用

引入滤基和滤基收敛的概念,解决了在一般拓扑空间中讨论点列极限的不能问题,并进一步用滤基的收敛统一了数学分析中的各种极限和黎曼积分的滤基极限.

欧标及API规范桩基承载力设计

欧洲标准作为当前较新的设计标准应用逐渐广泛,其在桩基设计上采用分项系数法取代了传统标准中采用的安全系数法。分项系数可选择多个路径,并且可根据试桩情况,调整分析系数的数值,对于缺乏试桩的情况需对数值计算进行校正,设计方法先进。API-RP2A方法在桩基极限承载能力的计算上应用最为广泛。总结了几内亚力拓铁矿码头项目和几内亚阿联酋铝业码头项目中的设计经验,介绍了将欧标与API规范相结合进行桩基承载力设计的方法,并与国内2012版港口工程桩基规范进行了比较。

遗传算法在单桩极限承载力预测中的应用研究

结合灰色预测的检验方法,将后验差比值作为目标函数,采用遗传算法对单桩极限承载力进行了预测。应用实例表明,与传统灰色预测法相比,该方法能有效减小预测结果的后验差比值,并能得出更合理的桩基极限承载力。

Ne-HF分子间势的从头计算研究(英文)

在用非迭代的三重激发项来校正CCSD的CCSD(T)的理论水平下,采用aug cc pVQZ基函数对Ne NF的分子间势进行了系统的研究。结果表明:Ne-HF以线型结构存在。在极限基的情况下,复合物线型极小点结构Ne H F势阱深为80 77cm-1对应Ne原子到HF分子质心的距离R为0 320nm。相对于第一极小点,在R=0 309nm,Θ=180°处(势阱深为54 443cm-1)有一个第二极小点存在。最后讨论了不同的基函数和理论方法在研究此类弱束缚态复合物的分子间势时的可靠性及其对结果的影响。

曹妃甸浅滩表层砂体插桩深度研究

曹妃甸浅滩原为古滦河三角洲,三角洲废弃后,海底表层沉积物在波浪潮流的簸选及自重应力作用下,沉积物颗粒粗化,粒度单一,且堆积紧密,工程强度较高。平台在该海区插桩时往往难以贯穿该层,其实际插桩深度较预定深度存在较大偏差。本文对此类砂体的形成机制、插桩过程中土体的压实作用对砂体强度的影响进行了分析,在对砂体力学参数做出适当调整后,运用太沙基地基极限荷载公式进行计算,得到了与实际情况较为一致的结果。

子坝高度对膏体尾矿初期坝坝体稳定性的影响

由于尾矿排放量的急剧增加,有必要在一些尾矿库上筑建子坝,扩大库容,但随着坝体高度的增大,在一定程度上影响了坝体稳定性。为此,以内蒙古某尾矿库为例,首先基于太沙基地基极限承载力公式计算了膏体尾矿沉积固结后具有的承载力以及不同高度的子坝对基底产生的应力;然后利用Geo-studio软件的slope模块分析了膏体尾矿沉积固结后在其上建5,7,9 m高度子坝的坝体稳定性,结果表明,坝体安全系数虽有所降低,但大于1.2,满足现有规范。研究表明:(1)膏体尾矿沉积固结后在垂直方向总体呈现上软下硬的特征,在水平方向呈坝前硬、向库内逐渐变软的特征;(2)子坝越高,在基底产生的应力越大,故该膏体尾矿库所筑的子坝高度不宜超过9 m;(3)待膏体尾矿入库固结后,可在库上继续筑子坝,子坝的高度需经计算方可确定,但膏体尾矿的上部固结速度较慢,若需赶工期,则需进行坝基处理,以达到筑子坝的地基承载力要求;(4)膏体尾矿在未固结之前,应视为软土地基,而膏体尾矿软基处理技术仍需进一步研究。

Effect of consolidation parameters on mechanical properties of Cu-based bulk amorphous alloy consolidated by hot pressing

Cu50Zr40Ti10 bulk amorphous alloys were fabricated by hot pressing gas-atomized Cu50Zr40Ti10 amorphous powder under different consolidation conditions without vacuum and inert gas protection. The consolidation conditions of the Cu50Zr40Ti10 amorphous powder were investigated based on an L9（34） orthogonal design. The compression strength and strain limit of the Cu50Zr40Ti10 bulk amorphous alloys can reach up to 1090.4 MPa and 11.9 %, respectively. The consolidation pressure significantly influences the strain limit and compression strength of the compact. But the mechanical properties are not significantly influenced by the consolidation temperature. In addition, the preforming pressure significantly influences not the compression strength but the strain limit. The optimum consolidation condition for the Cu50Zr40Ti10 amorphous powder is first precompacted under the pressure of 150 MPa, and then consolidated under the pressure of 450 MPa and the temperature of 380 °C.

Flexural behaviors of double-reinforced ECC beams

In order to investigate the flexural behaviors of engineered cementitious composites （ECC）, theoretical and experimental researches are done on flexural doublereinforced ECC beams. Based on the assumption of the plane section remaining plane in bending and simplified constitutive models of materials, the calculation methods of load carrying capacities for different critical stages are obtained. Then, these calculation methods are demonstrated by comparing the test results with the calculation results. Finally, based on the proposed theoretical formulae, the effects of the compression strength, compression strain and tension strength of ECC, and the reinforcement ratio on the flexural behaviors of double-reinforced ECC beams are analyzed. The calculated and measured results are in good agreement, which indicates that the theoretical model can be used to predict the momentcurvature response of steel reinforced ECC beams. And the results of parametric studies show that the increase in the compression strength of ECC can greatly improve the flexural performance of beams; the increase in the ultimate compression strain can significantly improve the ultimate curvature and ductility, but has little effect on the load bearing capacity of beams. little effect on the flexural The tensile strength of ECC has behaviors of ECC beams. The increase in the steel reinforcement ratio can lead to significant improvement of the load bearing capacity and the stiffness of beams, but a degradation of the ductility of beams. The theoretical model and parameter analysis results in this paper are instructive for the design of steel reinforced ECC beams.

关于向量值函数RIEMANN积分的二个注记

本文对向量值函数Rismann积分进行了研究。

基于矩法的结构非线性整体抗震可靠性分析

建立了基于极限基底剪力的结构非线性整体承载能力极限状态方程。为了从概率的角度评估结构的整体抗震能力,分别提出了基于Nataf变换的点估计法(PEM)和基于点估计法的随机Pushover分析方法(RPA)。在此基础上,提出了一种将点估计法、Pushover分析和矩法(MM)相结合进行结构整体非线性抗震可靠性分析的统计矩半解析法。将该方法应用于钢筋混凝土框架结构,得到了此类结构整体抗震可靠度随地震作用变异系数变化的规律。算例分析表明,本文提出的方法简单、实用、有效,模拟次数很少,且具有与蒙特卡罗模拟法(MCS)相当的计算精度。

强夯后水位对预制方桩静载试验的影响

以某化工类地基处理项目中预制钢筋混凝土方桩的单桩竖向抗压极限承载力试验为例,分析了单桩竖向抗压极限承载力试验检测预制钢筋混凝土方桩在工程中遇到的问题,指出单桩竖向抗压静载试验适宜安排在地下水位回归正常水位、土体重新固结基本完成之后进行,能够准确判断桩基抗压极限承载力。

Bearing capacity and settlement of strip footing on geosynthetic reinforced clayey slopes

The effect of geosynthetic reinforcing on bearing capacity of a strip footing resting on georeinforced clayey slopes was investigated.The results of a series of numerical study using finite element analyses on strip footing upon both reinforced and unreinforced clayey slopes were presented.The objectives of this work are to:1) determine the influence of reinforcement on the bearing-capacity of the strip footings adjacent slopes,2) suggest an optimum number of reinforcement and 3) survey the effect of friction angle in clayey soils reinforced by geogrids.The investigations were carried out by varying the edge distance of the footing from slope.Also different numbers of geosynthetic layers were applied to obtaining the maximum bearing capacity and minimum settlement.To achieve the third objective,two different friction angles were used.The results show that the load?settlement behavior and ultimate bearing capacity of footing can be considerably improved by the inclusion of reinforcing layer.But using more than one layer reinforcement,the ultimate bearing capacity does not change considerably.It is also shown that for both reinforced and unreinforced slopes,the bearing capacity increases with an increase in edge distance.In addition,as the soil friction angle is increased,the efficiency of reinforcing reduces.

Top Limit Characteristics of New Type Cascade PC on the Basis of Homogeneous Semiconductor

A new type homogeneous planar PC （photoelectric converter） on the basis of multijunction semiconductor n＋-p-p＋-n＋-p-p＋-...-n＋-p-p＋ structure has been investigated. The entire structure is a cascade PC consisting of a number of elements of the structure--single PCs connected in series and illuminated by light that has consistently passed through the previous semiconductor layers. The theory of converter of both monochromatic and solar radiation has been developed and the limiting values of their photoelectric and power characteristics have been determined, including the optimal thickness and number of single PCs layered on a base PC, their spectral sensitivity, current-voltage characteristics and efficiency. The open-circuit voltage grows practically linearly with the number of elements in the cascade. The top efficiency limit for a certain optimal elements number reaches its maximum that exceeds considerably that of the base PC, especially in the range of low collecting coefficient of charge carriers in the base PC.

The Limit to the Liberty of Expression in the Western World from the Perspective of Jurisprudence

The liberty of expression is one of the most important values in the human society, and a tolerant, unconstrained social atmosphere can provide personal development with a healthy and harmonious environment. Since the modern times, the liberty of expression has been gradually deemed by academic circles and all walks of life as a basic human right, and also has been fixed as a basic right of citizens through the legal form. The purpose of this paper is to clearly analyze the kernel and value of the liberty of expression through a historical review, so as to specifically sort out the development course of the liberty of expression and also excavate its implied meanings. In addition, the embodiment of the liberty of expression in both theory and practice since the modern times is analyzed around the limit theory of the liberty of expression, and then the opinions of the author are drawn up. Thus, some new ideas and views are provided for the future development of the liberty of expression from a new perspective.