高速公路砂井地基固结度时空变化规律探讨

软基固结度时空变化规律的研究对解决高速公路软基沉降预测问题具有十分重要的意义。本文在讨论固结度时空变化的实质与计算方法的基础上，结合京珠高速公路广珠段某软基试验资料，初步探讨了高速公路砂井地基固结度的时空变化规律，特别提出固结的滞后效应及其对固结沉降曲线形态的影响，并简要讨论了砂井直径和间距对固结度的影响，认为软基沉降中地下水微观动力学过程的研究将有助于揭示固结度时空变化规律。     

排水固结法加固软基变形简化计算分析

插板和砂井堆载预压是处理软基有效方法之一,现有的沉降变形计算方法大部分采用轴对称理论的解析解和以太 沙基或比奥固结理论为基础的数值解,仍较为复杂。根据软基排水固结机理,采用固结度等效原理,对渗透系数进行调整,把 砂井(插板)地基简化为均质成层地基。运用有限元对某软土路基处理工程进行简化计算,并和监测结果进行对比分析,对简 化计算方法进行验证。发现具有较好的准确性,为实际软基处理工程的沉降变形分析提供了一种简单实用的方法。     

某国际机场试验区软基固结沉降的过程模拟

随着计算技术的发展与普及，土体的固结沉降数据解法已在实际工程中得到推广应用，并取得了较好效果。本文借助剑桥本构模式，对某国际机构试验区软基进行固结沉降的过程模拟研究，并对试验区不 均匀沉降作出评价。     

堆载预压法在某工程中的应用及效果评价

深圳湾填海造地工程采用堆载预压法进行软基处理。根据现场监测结果，从地基最终沉降、固结度和强度等方面对该工程的地基处理效果进行了评价。     

竖井地基热排水固结理论初探

为了加速软土地基固结排水过程,在传统竖井排水固结法的竖井中增设U型导热管,对U型导热管内的水进行预加热,并使其在管内循环,实现管-土之间热传递,以改善土的渗透性状。针对这一新的软基处理技术,本文首先通过研究渗流固结过程中的温度影响因子,建立了渗透系数与温度之间的关系。其次,基于理想竖井地基固结理论,建立基于温度修正的理想竖井地基固结度解析解。最后,分析了温度因素对理想竖井地基固结度及固结时间的影响规律。结果表明:同一时间因素下,温度越高,理想竖井地基的固结度越高,且温差越大,固结度差值越大;温度较高时到达某一固结度所需时间比温度较低时到达同一固结度所需时间少。在固结度较小时,温度因素对固结时间的影响并不显著;而固结度较大时,则固结时间差别较为显著。     

真空预压下软土渗透系数对固结的影响

考虑正常固结状态下前期固结压力对渗透系数的影响,利用ABAQUS软件,将渗透系数随固结应力的变化关系应用于真空预压下单井的三维有限元计算。计算结果表明,考虑渗透系数随固结应力的变化,其表面沉降要比渗透系数保持不变的沉降量小,固结过程较慢,相应的固结时间要长;前期固结压力越大,表面沉降将越小,达到相同固结度时所需固结时间也越长。     

取样扰动对固结系数的影响研究

在软土工程中,地基土的固结系数是重要参数。目前固结系数的选取主要根据室内固结试验得到的沉降与时间曲线得到。但已有的研究成果表明,室内试验获得的固结系数远低于现场资料反演得到的固结系数,取样扰动是一个重要的影响因素。根据Hong & Onitsuka的扰动度定义,推导了取样扰动对固结系数的影响,并引用了大量的试样数据验证了分析的合理性。     

成层软黏土地基的固结沉降计算分析

针对实际工程中软黏土地基的成层特性及竖井有时并未打穿软土层情况,采用太沙基一维固结理论和巴伦固结理论的基本假定,利用固结度联系孔压与变形,提出一种简化成层软黏土地基的固结沉降计算方法,对竖向排水地基的固结度及沉降等进行预测。对计算的几个关键问题进行探讨：如固结系数的反演选择、竖井未打穿土层时,竖井底部成层地基固结度计算、压缩土层厚度选取等问题。在上述理论的基础上,用FORTRAN语言编写排水竖井固结程序CONSOL,在工程实践中得到应用,取得良好的效果。     

确定固结系数的固结速率半对数法

基于太沙基一维固结理论,推导了固结速率与固结时间的解析关系,为固结系数的求解开辟了新方法。该方法避免了图解法的缺陷,消除了初始沉降和次固结的影响。求解中采用最小二乘法原理,便于计算机数据处理。通过与现有方法比较,发现该方法准确、可靠和简便,可以在实际工程中推广应用。     

分级连续加载条件下原状膨胀土固结变形研究

由固结系数Cv与有效应力 和孔隙比的关系,推导了考虑固结系数变化的分级连续加载固结控制方程。根据方程的解析解得到了分级连续加载的沉降计算公式。结合云桂高速铁路建设,以高路堤分段堆载方式为研究依据,在GDS三轴试验系统开展原状膨胀土分级连续加载K0固结试验。结果表明：沉降与时间关系在加载期呈折线式发展,稳载期呈双曲线变化;膨胀土的应力-应变关系呈阶梯式变化;当 ≤ 时,固结系数随有效应力呈先增大而后减小,当 ＞ 时,固结系数随有效应力呈波动持续减小。固结度理论计算值与试验结果相比,考虑固结系数变化的固结度计算比固结系数为定值更准确。分级连续加载沉降计算公式可作为分析高速铁路路基沉降-时间关系的参考方法。     

非饱和粉质粘土固结压缩特性及体变试验研究

为进一步研究与基质吸力相关联的非饱和土固结压缩特性,扩展非饱和土固结理论在工程实际中的适用性,通过分析非饱和粉质粘土水土特征曲线变化规律,对非饱和土固结变形机理进行研究。试验结果表明：非饱和土的最终沉降量仅与土骨架的压缩模量有关。对于不同饱和度的非饱和土而言,固结速度随初始饱和度的增加而减小,饱和土固结过程所需要的时间比非饱和土固结过程所需要的时间短。由于孔隙流体的压缩性导致高饱和土体的瞬时沉降比低饱和土体的瞬时沉降小,但高饱和土体的后期固结沉降受饱和度和吸力的影响,比低饱和土体要大得多。      

A Critical Reappraisal of the Average Degree of Consolidation

Since its development in 1925, Terzaghi’s expression for the average degree of consolidation has been extensively used in teaching, research and consulting to determine the consolidation settlement that has taken place at a specific time in a geotechnical problem. Recent research by the authors has revealed that the term degree of consolidation is not very meaningful when the initial pore pressure distribution is highly skewed. In view of these findings, a review of all aspects of Terzaghi’s consolidation theory is required, particularly when considering asymmetric initial pore pressure distributions. An exact method for estimating the consolidation settlement of a clay stratum using the mass flux per unit area out of the drainage boundaries is proposed. Graphical representations of both exact and traditional methods reveal identical average degree of consolidation curves. In light of this, Terzaghi’s expression for the average degree of consolidation was re-examined. Upon application of the original governing one-dimensional consolidation equation, it was found that the traditional and exact methods for calculating the average degree of consolidation are identical. Thus, the widespread proclivity for geotechnical engineers to use Terzaghi’s average degree of consolidation equation to estimate the consolidation settlement of a clay stratum has been validated.     

Consolidation analysis of a cross-anisotropic homogeneous elastic soil using a finite layer numerical method

This paper presents a finite layer procedure for Biot's consolidation analysis of layered soils using a cross-anisotropic elastic constitutive model. The program is first verified using published results. Then, using this program, the influences of cross-anisotropy on the immediate settlement, the final settlement, and the consolidation behaviour are investigated by changing one model parameter at one time. The results obtained using the cross-anisotropic elastic model are compared with results using an isotropic elastic model. It is found that the cross-anisotropy has very large influences on the immediate settlement, the final settlement, and the consolidation behaviour. Curves or tables of the immediate settlement coefficients, the final settlement coefficients, and the average degree of consolidation are obtained and presented in the paper. These curves or tables can be easily used to estimate the immediate settlement, the final settlement, and the consolidation settlement of a cross-anisotropic soil. Copyright © 2004 John Wiley & Sons, Ltd.     

Factors Affecting Consolidation Related Prediction of Singapore Marine Clay by Observational Methods

The use of prefabricated vertical drains with preloading option is the most widely-used ground improvement method for the improvement of marine clays in land reclamation projects. The assessment of the degree of consolidation of the marine clay is of paramount importance prior to the removal of preload in such ground improvement projects. This analysis can be carried out by means of observational methods with the use of field settlement plates and piezometer monitoring. Field settlement monitoring data can be used to ascertain the settlement of the reclaimed fill from the time of initial installation. The field settlement data can be analysed by the Asaoka method to predict the ultimate settlement of the reclaimed land under the surcharge fill. Back-analysis of the field settlement data will enable the coefficient of consolidation due to horizontal flow to be closely estimated. Piezometer monitoring data can be analysed to obtain the degree of consolidation of the improved marine clay. Back-analysis of the piezometer data will also enable the coefficient of consolidation due to horizontal flow to be estimated. The aim of this paper is to highlight the significance and impact of the various factors that affect prediction by the Asaoka and piezometer assessment methods. The authors findings of the Asaoka method reveal that the magnitude of ultimate settlement decreases and the degree of consolidation subsequently increases as a longer period of assessment is used in the prediction. The degree of consolidation predicted by the piezometers is found to be in good agreement with the Asaoka method for the early period of assessment. However as the assessment period increases, the piezometer indicates lower degree of consolidation as compared to field settlement predictions.     

Consolidation with threshold gradients

Evidence for threshold gradients is reviewed. The consolidation problem, with threshold gradient, is properly formulated and solved numerically. An approximate analytical solution is also developed. The influence of a threshold gradient on the time rate of settlement is examined, and it is shown that by modifying the definition of the degree of consolidation a good approximation to the threshold gradient problem can be obtained directly from the Terzaghi solution. It is also shown that threshold gradients will have no influence on odometer testing and their effect is, therefore, to reduce the primary compression below that predicted from standard tests.     

Approximate Simple Invertible Equations for Consolidation Curves Under Triangular Excess Pore-water Pressures

Approximate but accurate, simple invertible equations for the consolidation curves under triangular excess pore-water pressures are developed. These approximations can be used to calculate the degree of consolidation corresponding to a specified time factor (explicit) or the time factor corresponding to a specified degree of consolidation (implicit). Explicit equations are also developed for estimating the consolidation coefficient and final settlement, from two settlement readings, using the proposed approximations.     

基于室内模拟实验的软土固结沉降的分形几何

为了能够比较准确、简便地计算及预测软土的沉降,在Terzaghi一维固结理论的基础上,结合分形几何理论对软土的沉降计算进行了探讨和研究。首先通过室内模拟实验,获得了不同固结时期试样的孔隙比e、沉降量以及扫描电镜照片（SEM图片）;然后利用WD-5软件对SEM图片进行处理,并计算得到孔隙分布的分数维D_f;最后建立起e与D_f的函数关系,再结合Terzaghi一维固结理论建立了D_f与固结度、沉降量的关系方程并计算得到相应的固结度及沉降量。经分析得出：Df随着沉降量的增加而减小;软土在固结沉降过程中在42.33 h处有一个明显的拐点;利用Df建立的固结沉降模型计算的结果与试验实测的结果基本吻合。     

饱水粘性土主固结理论

对饱水软粘土的预压排水主固结研究应从其排水的本质出发, 即从软土在预压过程的含水量变化上研究主固结量的变化规律, 利用土的基本性质指标导出主固结比基本公式及主固结量(沉降量)、绝对主固结量、绝对固结度等理论计算方法.与传统的算法不一样的地方是这些算法与预压荷载(即固结应力) 无关系, 直接计算出主固结的效果及评价预压排水固结地基处理卸载的可行性.利用上述基本公式亦可导出剩余主固结量、主固结速率等计算式.通过实例的分析, 证明上述理论方法与观测的数据基本相符.      

Theoretical Equations of Vertical and Radial Consolidation by Equating Degrees of Consolidation by Settlement Analysis and Dissipation of Pore Pressure

Degree of consolidation, U, is defined in two ways: (1) by settlement analysis and (2) by dissipation of pore pressure. Equations of vertical and radial consolidations are derived by equating the above two U. The new equations are compared with the existing equations of vertical and radial consolidations. It is shown that new equation of radial consolidation is exactly same as Barron’s equation of equal strain radial consolidation while in case of vertical consolidation it is similar to later part of Terzaghi’s equation of vertical consolidation. A few possible reasons and advantages of comparison are given. The theory of rapid loading methods is based on the equality of these two degrees of consolidations. It is concluded that in rapid loading methods the next load increment can be applied at any time in radial consolidation once the effects of initial compression are over. However, in vertical consolidation it can be applied only after 60% consolidation.     

Model Test on Self-Weight Consolidation of the Red Mud Tailings Placed in the Karsts

The management of tailings depends on its consolidation behavior to great extent. The red mud tailings in Pingguo, Guangxi is of high water content and void ratio. The present paper takes the red mud aluminiferous tailings in Pingguo, Guangxi as prototype. Model tests were carried out to study the consolidation behavior of red mud aluminiferous tailings that were landfilled layer by layer. The layered settlement and the water discharge caused by self-weight consolidation were studied. The influence of the latter landfilled layer of red mud on the previous layer was analyzed. The results show that the settlement at the surface with time can be divided into two stages. During the first stage, a thin layer of water appeared and the thickness kept increasing at the top of the mud surface with the particle of red mud sinking. During the second stage, water drained from the mud and settlement developed slowly. Cracks developed at the surface due to evaporation and the red mud near the surface became unsaturated. When the previous landfilled layer consolidated to the degree that the water content was less than 40%, the later landfilled layer of red mud will have little influence on the settlement of previous landfilled layer.