摘要 软土地基沉降问题一直是国内外学者孜孜以求地寻求着解决的思路和方法的问题，并提出了诸多的理论和技术措施，但迄今还未有一个成熟的理论和技术措施能够得到一致的肯定，这与土体本身的复杂性以及土力学和土动力学理论学科的发展水平有关。本文结合大量现场试验资料、应力波理论和Biot波动理论和动力固结理论的思考，认为无论是在土力学理论和工程技术措施的应对方面，都忽略了移动荷载(包括压实荷载、汽车荷载和列车荷载)对软土地基沉降的影响，这对沉降有时是决定性的，由此引起的问题就是无论是在沉降的机理认识还是在沉降理论的建立中都会忽略这一关键影响因素。本文就是基于这样一个认识，从移动荷载形成的应力波传播理论特征和机理，认为动荷载的作用机理就是应力波（纵波和横波）在软土地基的传播机理，动荷载与静荷载的区别其实是作用频率的高低之分和作用对象的响应不同之分，应用Biot动力固结理论和Biot波动理论，分析了饱和介质和横观各向同性饱和介质中应力波的传播特征，并结合室内外试验重点分析了压实移动荷载在软土地基中的传播及其作用机理，并据此对软土地基的沉降机理进行新的诠释，并对传统总沉降中瞬时沉降、主固结沉降和次固结沉降做出了新的解释。 本文在这一领域内的研究内容和成果主要有： 1）在Lagrange坐标下，用弹性动力学及分析力学的方法，重新推导了Biot动力固结方程及波动方程，对Biot动力固结方程及波动方程的建立有了更深一步的认识。 2）通过编制程序计算所得饱和介质和横观各向同性（简称II）饱和介质中三种体波（P1纵波、P2纵波及S横波）的应力波传播速度与实测波速较接近，同时对两种介质中影响应力波传播的诸因素（渗透系数、粘滞系数、孔隙度及应力波入射角度）进行了详尽的分析研究，为移动荷载对软土地基沉降作用的机理和分析计算提供了保障。 3）利用Zienkewicz判别准则，界定了移动荷载如路基填筑过程中压路机荷载及路基竣工后的汽车荷载对地基固结的影响是不容忽视的。 4）首次建立了压实移动荷载模型，分析计算了移动荷载在软土地基中应力波（三种体波P1、P2压缩波及S剪切波）的传播特征、对软土地基沉降的影响机理以及动荷载的影响深度，计算表明，在常规振动压路机的作用下，剪切波主要作用在软土地基的浅层范围约6m～8m之间，而P2压缩波作用范围在约18m～28m之间，而P1波的作用深度可达58m。 5）从Biot波动理论的角度重新认识了移动循环荷载形成的应力波对沉降的影响，以及影响循环荷载作用效应的重要因素，对软基沉降机理、沉降的组成部分的重新认识提供了理论基础。 6）从移动荷载形成的应力波作用深度推断，公路和道路竣工通车后，汽车荷载对软土地基的反复作用是软土地基产生长期位移变形——剪切变形和压缩变形并由此产生次固结变形的真正原因所在。 7）通过Biot波动理论和室内动三轴试验成果说明了，移动荷载中剪切波的反复作用是引起软土地基侧向变形并由此产生附加沉降的主要原因，此变形及沉降伴随着路基填筑的整个过程甚至运营过程，因此，将移动荷载作用下因剪切波引起的附加沉降定义为瞬时沉降更切合实际，并解决了一直以来瞬时沉降的发生的机理和阶段的争议。 8）我国规范和教材中将沉降分为瞬间沉降、主固结沉降和次固结沉降三阶段是不严谨和不科学的。由剪切变形引起的瞬时沉降伴随着沉降的整个过程，而由压缩变形和剪切变形引起固结变形（包括主固结和次固结）具有相同的物理机理，这一特性决定了固结变形是不同外荷载作用下软土地基不同的变形响应，传统意义上的沉降三阶段中的各沉降组成部分其实存在于沉降变形的整个过程，因此，有必要对沉降三阶段论进行重新审视。 9）提出沉降计算的改进意见及施工控制标准。 关键词：体波，P1纵波，P2纵波，S横波，Biot动力固结理论，Biot波动理论，两相饱和介质，TI饱和介质，移动荷载，沉降，瞬时沉降，次固结沉降。 ABSTRACT The problem of embankment settlement ell saturated soft soil is the issue that many researchers have been working for to find a solution which include theory and technical measure．But there isn’t any mature theory and technical measure that is confirmed，the status maybe caused by the complicated character of saturated soft soil and the soil mechanics and dynamics development level．Based on a large number of experimentation data and the theory of the soil mechanics and dynamics etc，the thesis put forward that the influence of moving load included road roller and automobile and train to the embankment settlement on soft soil should not be neglected，especially in the period of constructing embankment．So according to such a cognition，the thesis has analyzed the propagation characters of stress waves in the soft soil that is derived from the moving load，and formed the viewpoint that the dynamical load’s action mechanism to the soft soil is the process of the propagation of stress waves in the soft soil，and formed another viewpoint that the difference between the dynamical load and the static load is the magnitude of stress wavelength or stress frequency，is the different response from soft soil．Further，based on Blot’s theory of porous media，the propagation characters of stress waves in isotropy and transversely isotropy saturated soft soil are analyzed，especially the propagation and action mechanism of moving load in soft foundation is analyzed emphatically with the field-test and laboratory test．According to the analyzed results，the new explain of settlement mechanism which included the distortion settlement，primary consolidation settlement and secondary consolidation settlement has been achieved． The main works and the achievements of the thesis are listed as the followings： 1) Under the Lagrange coordinates，the Blot dynamical consolidation equation and wave equation is rededuced in the thesis． 2) The results of calculated wave velocity of the three volume waves (P1 longitudinal wave，P2 longitudinal wave，S transverse wave) are approached to the tested wave velocity．Meanwhile，the effect factors (included coefficient of permeability，coefficient of viscosity，porosity，angles of stress wave incidence etc) to the stress wave are analyzed elaborately in the two media．The analytical results construct a theory base to analyze the mechanism of soft foundation Settlement which is engendered by the moving load． 3) The compacting moving load model is formed first time in the thesis．The three volume waves propagation characters of stress waves in the soft soil and the effect mechanism to the settlement of soft foundation and the effect depth of dynamic load are calculated and analyzed under the action of compacting moving load．The calculated results show that the effect depth of compression wave and shearing wave to soft soil foundation under the action of vibrational road roller is difference，the shearing wave effect depth is in the range of 6 meter to 8 meter，the P1 compression wave’s effect depth is reached to 58 meter，and the P2 compression wave’s effect depth is in the range of 18 meter to 28 meter． 4) From the viewpoint of Biot wave theory，the effect of stress waves from the moving circulation load to the settlement is cognized in a total new viewpoint，Meanwhile，the key factors of effecting the action result of the moving circulation load to settlement is analysed．The results offer a basic theory to re-know the settlement mechanism and the parts of settlement of soft soil foundation． 5) It is concluded by the stress wave effect depth which is derived from the moving load that the real cause of soft foundation long-term deformation (included the,shear deformation and compression deformation) is produced by the repeating action of the automobile． 6) The Biot wave theory and the laboratory dynamic triaxial test show that the repeating shear wave of the moving load is the key cause of soft foundation’s lateral deformation，which produced additional settlement，and that define the additional settlement as the instantaneous settlement is accorded with the fact，and the disputed definition of the instantaneous settlement is resolved． 7) It is not scientific and precise that the settlement is divided into three stages which included the instantaneous settlement stage and primary consolidation settlement stage and secondary consolidation settlement stage in our specifications and teaching materials．The instantaneous settlement which derived from shear deformation accompany cross the whole settlement process，the primary and secondary consolidation settlement which derived from compressing deformation have same physical mechanism．the character decides that soft soil consolidation deformation is the different deformation response to the different load，so the traditional settlement parts of three—stage settlement are existing in the whole settlement deformation process，so it is necessary to reconsider the traditional three-stage settlement theory． 8) The control of settlement and the control criterion of construction are suggested． Keyword：colum wave，P1 longitudinal wave，P2 longitudinal wave，S transverse wave，Biot dynamic consolidation theory，Biot wave theory，saturated media，TI saturated media，moving load，settlement，instantaneous settlement，secondary consolidation settlement． |
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