【作者】 陈保国；

【导师】 郑俊杰；

【作者基本信息】 华中科技大学 ， 岩土工程， 2008， 博士

【摘要】 山区高速公路建设中,高填方涵洞应用广泛,现行公路桥涵设计通用规范中的线性土压力理论未能准确反映涵洞的受力状态。由于涵顶土压力计算方法和地基处理方法不当,导致涵洞在施工或使用过程中出现不同程度的病害。此外,路线穿越山涧谷地时,软土厚度和成分分布极不均匀,在软土地基上填筑高路堤常常面临地基承载力不足,整体或局部失稳,沉降、差异沉降及水平位移过大等问题。本文针对山区高速公路中高填方涵洞和高填方路基处理两大问题展开系统研究,主要内容如下:(1)通过现场试验、理论分析和有限元数值模拟手段研究了路堤填土—涵洞—地基之间的相互作用机理,系统分析了地形条件、地质条件、路堤填料性质、涵洞几何尺寸、偏载效应等因素对涵—土体系的受力状态和变形特性的影响,讨论了涵洞基础埋深效应、宽度效应和固结对地基承载力的影响,提出了基于变形协调的高路堤下涵洞地基设计方法。(2)将双向增强体复合地基法应用于山区高速公路路基处理,通过理论分析和有限元数值模拟研究了高路堤下双向增强体复合地基的作用机理和作用效果,详细讨论了筋材性质、加筋层数、桩墙性质、桩墙距径比、桩墙深度、路堤填料性质、地基土性质及接触界面强度等因素对双向增强体复合地基工作性状的影响;同时分析了多种条件下,加载和固结过程中,软土地基中超静孔隙水压力的分布特性和随时间的变化规律,探讨了双向增强体复合地基的时效性。通过上述研究,得出了如下主要结论:(1)涵顶土压力随路堤填土高度的增加呈非线性增长,研究结果表明,采用现行公路桥涵设计通用规范计算宽沟谷沟埋式涵洞(B≥3b)和上埋式涵洞的涵顶土压力是不安全的。(2)现场试验和数值模拟验证了涵顶等沉面的存在和填土内部的土拱效应。土拱效应能够缓解涵顶的土压力集中现象,但其具有不稳定性。(3)路堤填土—涵洞—地基作用机理受到地形条件、地质条件、填料性质、涵洞几何尺寸、偏载效应、埋设型式、基础的埋深效应、宽度效应和软土固结的影响,涵洞结构和地基设计应综合考虑上述因素的影响。(4)研究表明,双向增强体复合地基法应用于山区高速公路软基处理,能够很好地控制路堤沉降和不均匀沉降、减小侧向位移、提高路堤的稳定性。(5)受路堤侧向滑移和竖向荷载作用,筋材内部拉力呈非线性分布。从总体变化趋势看,由路堤中心向边缘呈减小趋势,但是在竖向荷载作用下,由于筋材张力膜效应,桩间部分的筋材拉力小于桩顶部分的筋材拉力,在桩顶边缘处筋材拉力突然增大;另一方面,受路堤侧向滑移的影响,路肩附近筋材拉力最大。(6)沿路堤横向,桩顶水平位移随着距路堤中心距离的增大而增加,边桩水平位移最大;桩身最大轴力发生在路堤底面中心处,随着距路堤中线距离增大而减小,但在路肩附近桩身轴力有所增加;由于路堤侧向滑移作用,桩身产生较大弯矩,最大弯矩发生在路肩附近的桩墙内部。(7)高路堤下双向增强体复合地基的工作性状受筋材模量、加筋层数、桩墙模量、桩墙距径比、接触界面强度、路堤填土性质、桩墙深度、地基土性质、固结时间、加载方案等众多因素的影响,双向增强体复合地基设计应综合考虑各因素的影响。(8)桩端未穿透软土层时,中性点深度随着固结时间的增长而上下波动,并最终趋于稳定,一次性加载和分步加载两种方案下,最终中性点位置相差不大。更多还原

【Abstract】 High fill culverts have been widely used in expressway in mountain area. Due to the improper ground treatment and the stresses states of culverts cannot be accurately reflected by linear earth pressure theory in current Chinese General Code for Design of Highway Bridges and Culverts, many problems of culverts frequently take place during the construction process or in service time. Moreover, when the road crosses the soft ground in mountain area, the depth and the composition of the soft soil are not uniform. The constructions of high embankments over soft ground face several challenges, such as potential bearing failure, global or local slope instability, intolerable total or differential settlements, and large lateral movement during both construction and post-construction periods. The objective of this dissertation focus on these problems in the construction of expressway in mountain area, and the main contents are as follows:(1) The full scale experiment, theoretical method and numerical simulation are conducted to investigate the interaction among the embankment fill-culvert-ground soil system. The influencing factors, such as the topographic condition, the geological condition, the characteristics of embankment fill, the dimensions of culvert, the eccentric load effect, and so on, on the stresses states and displacements of culvert-soil system are systemically analyzed by FEM simulation. The influence of embedding effect and the wide effect of the culvert foundation, as well as the consolidation of soft ground on the bearing capacity of ground are also discussed. The compatible deformation-based foundation design methods of high fill culverts are proposed.(2) Horizontal geosynthetic reinforcement combined with vertical reinforcement using piles or pile walls (Biaxial Reinforced Composite Foundation) can provide an economical and effective solution to soft ground improvement to support high embankments. The mechanism and the efficacy of biaxial reinforced composite foundation are studied with theoretical analysis and numerical simulation. The influencing factors on the performance of biaxial reinforced composite foundation are discussed in detail. The distribution characteristics and the dissipation process of excess pore water pressure in the construction process and post-construction period are also discussed under four different conditions. Furthermore, the time-dependent behavior of biaxial reinforced composite foundation is studied in this dissertation.Based on the researches mentioned above, the following conclusions can be drawn:(1) The earth pressure on the top of culvert nonlinearly increases with the height of backfill over the culvert. The results show that the current Chinese General Code Method is unsafe in the calculation of earth pressure on the culvert top for the wide trench installation (B≥3b) and embankment installation culverts.(2) The existences of equal settlement plane and soil arch effect in embankment fill are verified by the full scale experiment and numerical simulation. The soil arch can release the earth pressure concentration on the top of culvert, but it is instable.(3) The interaction among embankment fill-culvert-ground soil is influenced by the topographic conditions, the geological conditions, the characteristics of embankment fill, the dimensions of culvert, the eccentric load effect, the installation conditions, the embedding and the wide effect of culvert foundation, as well as the consolidation of soft ground. The design of the culvert and the foundation should consider these influencing factors comprehensively.(4) The biaxial reinforced composite foundation can obviously reduce the total and differential settlements, minimize the lateral displacement, and enhance the stability of embankment. It can be a preferred method in the soft ground improvement under high embankment.(5) The tension along the geosynthetic layer is not uniform. In general, the tension in the geosynthetic layer decreases with the distance from the centerline of the embankment. In addition, there is an obvious increase in the tension over the pile walls. Moreover, the maximum tension in the geosynthetic layer occurs below the shoulder of the embankment due to the lateral movement of embankment fill.(6) At the cross section of embankment, the maximum horizontal displacement at the level of pile wall head occurs near the most right (or the left) side pile wall and decreases towards centerline of the embankment. The maximum axial force among all pile walls is near the centerline and decreases with the distance from centerline, but it has a little increase below the embankment shoulder, whereas the maximum bending moment occurs below the slope of the embankment.(7) The behavior of biaxial reinforced composite foundation is influenced by the tensile stiffness of geosynthetic, the layers of geosynthetic, the pile wall modulous, the ratio of pile wall distance to the width, the strength of interface, the characteristics of embankment fill and ground soil, the depth of pile wall, the consolidation time and load schemes. The best performance of biaxial reinforced composite foundation can be obtained by optimizing these influencing factors.(8) When the pile walls do not penetrate the soft clay of the ground, the locations of neutral point fluctuate with the increase of the consolidation time, and they are stable finally, the depth of neutral point are closely between one-step load scheme and step by step load scheme.更多还原