【作者】 耿建宇；

【导师】 蒋鑫；

【作者基本信息】 西南交通大学 ， 道路与铁道工程， 2013， 硕士

【摘要】 公路路基成功拓宽改建的关键在于,在保证路基安全稳定的前提下,控制新旧路基顶面差异沉降在允许范围内。围绕着这一工程目的,本文采用数值模拟的方法开展了平原软土地区和山区公路路基拓宽改建力学行为及典型工程对策的研究。在地下水位较高的平原软土地基上进行高速公路路基拓宽,极易产生路基失稳、新旧路基顶面差异沉降过大等现象,而既有研究多集中于某一种路基拓宽方式的分析。基于PLAXIS弹塑性平面应变有限元分析,综合运用Biot固结理论和phi/c剪切强度折减法,对拼接式拓宽(双侧对称式拓宽、双侧非对称式拓宽、单侧式拓宽)和分离式拓宽逐一建立数值分析模型,综合比较四种拓宽方式的潜在滑动面形态、稳定安全系数、超孔隙水压力、竖向位移、侧向位移等力学响应。分析表明,双侧对称式拓宽更有利于提高路基稳定安全系数,在削减新旧路基顶面差异沉降及地基侧向位移方面表现良好,而单侧式拓宽新旧路基顶面差异沉降较大。针对单侧拼接式拓宽,采用桩网结构进行加固处治,建立模拟桩体、土工格栅(网)施工及新路基逐层分步填筑的精细化有限元模型,开展了相应结构变形特性以及土体力学响应变化的研究。研究表明,经桩网结构处治后,新旧路基顶面差异沉降显著减小,能有效减缓新路基对旧路基的侧向扰动,土工格栅拉力峰值出现在桩顶边缘处,潜在滑动面由新路基侧转移至老路基侧,稳定安全系数保持相对较高,软基内超孔隙水压力峰值大幅减小,消散时间明显缩短,桩网结构可用于软土地基旧路拓宽工程的快速安全处治。结合山区特殊的地形地貌特性,依托挡土墙处治山区二级公路路基拓宽改建工程,利用非线性有限元法,开展了衡重式挡土墙的修建、新路基逐层分步填筑的动态施工力学行为数值模拟,针对新路基是否加筋、筋材的铺设层位以及衡重台上下方新路基填土压实度差异性对新旧路基稳定安全性、滑动面形态、沉降以及挡土墙变位等力学响应的影响开展参数敏感性分析,并结合室内模拟墙体不同主动位移模式下拓宽路基土工离心模型试验成果,探究了新旧路基顶面沉降与挡土墙变位的动态耦合关系。研究表明,衡重台下方新路基填土压实不足会导致新旧路基顶面差异沉降增大,挡土墙主动外倾诱发新旧路基顶面产生较大附加(差异)沉降,宜对新路基自重作用造成的差异沉降予以适当修正放大后进行上承路面结构设计。根据既有公路路基拓宽改建工程实践,初步提出了公路路基拓宽改建工程实施的基本技术思想,并着重总结路基拓宽工程中控制新旧路基顶面差异沉降的工程处治对策,总结了包括复合地基法、排水固结法、沉降隔离墙等地基处理方法；结合面、路基填料、压实度、加筋材料、挡土墙等路基处理方法,以及相关工程处治对策的技术要点及其适用范围,可为后续公路路基拓宽工程实践提供一定参考。更多还原

【Abstract】 The key point of successfully broadening the highway subgrade is to control the differential settlement of the new and old subgrade top surfaces within permissible range on the premise of ensuring the safety and stability of subgrade. For this reason, the research on the mechanical behavior of plain soft soil area and mountain highway subgrade while broadening and rebuilding as well as the representative engineering countermeasures are conducted by means of numerical simulation.Expressway embankment widening may produce instability and different settlement on soft ground with high under ground water level. The existed research focus on a certain kind of widening type. Based on elastic-plastic plane strain finite element analysis using PLAXIS, Biot consolidation theory and shear strength reduction method were comprehensively applied to study the mechanical behaviors comparisons of four widening types. Some critical responses, such as potential slip surface, safety factor, excess pore water pressure, vertical displacement and lateral displacement were compared. The analysis results show that broadening subgrade in bilateral symmetry style is advantageous to improving the stability safety factor and gets good results for diminishing the differential settlement of the new and old subgrade top surfaces and the lateral displacement of foundation. The unilateral broadening however leads to the large differential settlement.For broadening subgrade in the way of unilateral matching, the pile-net structure is adopted to consolidate foundation. The refined finite element model used to simulate the filling process of pile body, geogrid and new subgrade in layers is formulated to study the characteristics of structural deformation and soil mechanical responses. Results show that pile-net structure could significantly decrease the post construction settlement and differential settlement at the top of old and new embankment, effectively slow down the old embankment lateral disturbance impacted by new embankment, geosynthetic tension reach peak on pile top edge, critical slip surface changes to old embankment from new embankment, stability safety factor keeps relatively high in the full process, excess pore water pressure peak and dispersing time significantly decrease. Pile-net structure can be used in the soft ground old road widening project quick safety treatment.With consideration of the landform of mountain area, the retaining wall is applied for the mountain-area secondary highway subgrade broadening and rebuilding project. Non-linear finite element method was conducted to simulate the dynamic construction of balance weight retaining wall building and new embankment fractional filling considering the mountain region highway embankment widening particularity. The effects of new embankment geosynthetic reinforcement and fill compaction condition on the embankment stability, slip surface behavior, settlement and retaining wall displacement were discussed. The dynamic coupling relationship between embankment settlement and retaining wall was investigated combined with the geotechnical centrifuge model tests which simulate the retaining wall different displacement modes in mountain region embankment widening project. The retaining wall displacement and embankment settlement, differential settlement are intercoupling. The analysis results show that the embankment differential settlement will increase for the insufficient compaction under the equilibrator. The retaining wall leaning toward will induce additional embankment differential settlement. The pavement structural design should consider the magnitude modification of differential settlement induced by new embankment self-weight.According to the engineering practice on subgrade broadening and rebuilding for the existing highway, the basic techniques for the project are put forward initially. The countermeasures to control the differential settlement of the new and old subgrade top surfaces including the technical essentials and scope of application of related projects are emphasized and summarized. More specifically, the foundation treatment method includes composite foundation, consolidation by dewatering, settlement separating wall, etc. And the subgrade treatment method includes junction surface, subgrade filling, compactness, reinforced materials and retaining wall and so on. The whole research can provide a reference for the following highway subgrade broadening projects.更多还原