大直径桩沉降敏感性的数值分析

以某桥梁大直径桩为例,采用弹塑性有限元法分析了桩周土、桩端土以及桩土界面特性等因素对大直径桩沉降的影响。土体本构关系采用Drucker—Prager弹塑性模型,桩身混凝土采用线弹性模型,而桩土界面采用接触面单元进行模拟。结果表明：该桩的荷栽一沉降曲线为缓变形,无陡降段,其极限承栽力应以桩顶沉降来控制,在10．2MN的设计荷载作用下,桩顶沉降仅为14．94mm,具有较大的安全储备;在各影响因素中,桩周土对该桩沉降的影响最敏感,其次为桩端土;在工程实践中,提高桩周土强度、合理选择持力层以及避免破坏桩土界面强度是减少桩基沉降、保证上部结构安全性的有效手段。     

膨胀黏土增长曲线的运动学分析

通过大量室内试验,从运动学角度对4种击实膨胀黏土样的胀缩规律进行了深入研究．研究认为,膨胀曲线、收缩曲线可统称为增长曲线,其特征表现为在最初阶段增长得快,以后逐渐减慢并趋于稳定;通过对试验数据的非线性最小平方回归分析,提出了增长曲线的回归方程;通过对增长曲线速度、加速度特征进行深入研究,揭示出膨胀、收缩过程具有许多相似性,但在本质上两者不是可逆过程,其吸水膨胀速度远大于失水收缩速度．研究结果为膨胀黏土地区的工程建设提供了重要依据．     

高速下过渡段路基动响应特性研究

通过现场实测,对秦沈客运专线动力分散型机车在某路桥过渡段高速行车条件下的动响应(动应力、动应变)规律进行了研究。研究表明:路基最大动响应曲线与平均动响应曲线变化趋势相同;对于相同行车速度,纵向(沿线路基床水平方向上)动响应曲线呈"V"形变化、动响应增量曲线呈不规则"N"形变化,而垂向(与地面铅垂方向上)则是随深度的增加动响应呈衰减趋势,并且在基床面浅处(0.6m左右)衰减幅度较大;纵向、垂向上的动响应都有随车速提高而减小的趋势,并且其减小幅度与车速高低紧密相关。同时,提出了预测过渡段路基动响应变化趋势的列车轴重变化系数计算公式,以及"超高"填筑路基减小过渡段沉降差值和动响应的设计思路,研究结果为高速铁路过渡段的设计与施工提供了重要基础。     

人工神经网络模型及其在隧道围岩分类中的应用

应用神经网络的联想记忆功能，以隧道围岩5个类别作为训练标本，建立隧道围岩与分类指标之间对应关系的BP判定模型,伙隧道围岩分类提供了一条新途径。     

Expansive soil-structure interaction and its sensitive analysis

Several groups of direct shear tests of Nanning expansive soil samples were carded out by improved direct shear apparatus. The results of the characteristics of the ultimate shear stress and residual shear stress at the interface of expansive soil-structure are presented as follows： linear relation can approximately reflect changes between the both shear stress and the three factors： vertical load, water content and dry density, just different degrees from each other; increasing the vertical load from 25 kPa to 100 kPa （up by 300%） can cause the average increase of ultimate shear stress from 58% （for samples with 1.61 g/cm^3） to 80% （for samples with 1.76 g/cm^3）, and an close average increase of 180% for the residual shear stress; increasing the water content from 14.1% to 20.8% （up by 47.5%） can cause the average decrease of the ultimate shear stress from 40% （for samples with 25 kPa） to 80% （for samples with 100 kPa）, and the average decrease from 25% （for samples with 25 kPa） to 30% （for samples with 100 kPa） for the residual shear stress; increasing the dry density from 1.61 g/cm^3 to 1.76 g/cm^3 （up by 9.3%） can cause the average increase of ultimate shear stress from 92% （for samples with 25 kPa） to 138% （for samples with 100 kPa）, and an average increase of 4% for the residual shear stress. Sensitive analysis was further made to explain reasons causing the differences of the both shear stress induced by the three factors.     

Analytical method of load-transfer of single pile under expansive soil swelling

The elastic differential equations of load-transfer of single pile either with applied loads on pile-top or only under the soil swelling were established,respectively,based on the theory of pile-soil interaction and the shear-deformation method.The derivation of analytic solution to load-transfer for single pile in expansive soil could hereby be obtained by means of superposition principle under expansive soils swelling.The comparison of two engineering examples was made to prove the credibility of the suggested method.The analyzed results show that this analytic solution can achieve high precision with few parameters required,indicating its' simplicity and practicability in engineering application.The employed method can contribute to determining the greatest tension along pile shaft resulting from expansive soils swelling and provide reliable bases for engineering design.The method can be employed to obtain various distributive curves of axial force,settlements and skin friction along the pile shaft with the changes of active depth,vertical movements of the surface and loads of pile-top.