【作者】 马强；

【导师】 郑俊杰；

【作者基本信息】 华中科技大学 ， 岩土工程， 2011， 博士

【摘要】 高填方涵洞广泛应用于山区和黄土地区高速公路建设中,高填方涵洞上覆填土荷载较大,且其受力影响因素众多,其受力特性不仅与自身的埋设方式(上埋式或者沟埋式)有关,还与上覆填土高度、地形条件、地质条件、路堤填料的性质、结构物的几何尺寸等因素有关。由于对高填方涵洞土压力及其影响因素认识不清,工程中经常出现涵顶开裂等病害。新型三向土工格栅具有独特的物理力学性能,将其用作加筋材料对高填方涵洞进行加筋减载,可获得良好的经济效益和社会效益。本文在对高填方涵洞土压力及其影响因素分析的基础上,对新型三向格栅加筋减载进行了系统的研究,主要内容如下：(1)通过现场试验对涵顶竖向土压力进行了测试,研究了涵顶竖向土压力的变化规律。通过数值模拟对影响涵洞受力特性的若干因素进行了分析,研究了沟谷宽度、边坡角度、地基刚度、路堤填料性质、拱圈弧度、涵洞结构型式和尺寸对涵洞受力状态和位移的影响。结果表明涵顶土压力随填土高度非线性增长；沟谷设涵非对称性,会引起其两侧土压力差异；沟谷对涵洞有效影响范围约为3倍涵洞宽度；涵顶土压力在边坡为15°和75°左右时较小；地基模量越大,涵顶土压力集中现象越严重；与模量相比,填土内摩擦角和黏聚力对涵顶土压力和涵体位移的影响要小得多；基础型式对涵体位移和压力有显著影响,应根据填土高度合理选择；采用“宽矮涵”比“窄高涵”涵顶土压力小；拱圈弧度对涵体沉降和涵顶土压力影响较小。(2)考虑涵—土相互作用,分析了涵洞减载机理。采用数值模拟的方法研究了减载后涵顶竖向土压力与位移的分布规律,分析了涵洞采用中松侧实法、柔性填料法、先填后挖法等方法时的减载效果,并分析了地基处理后的刚度和处理宽度对降低涵顶压力的作用。结果表明在路堤一定高度范围内适当采用中松侧实或柔性填料的方法可减弱涵顶的土压力集中；采用先填后挖的施工措施时开挖面宜竖直,开挖的宽度最好与涵洞宽度相当,可有效降低涵顶土压力的集中程度；涵洞地基处理后,地基刚度不宜太高,并且应延伸至基底以外一定的范围,以降低涵顶土压力集中。(3)通过现场试验对高填方涵洞采用新型三向格栅加筋减载后的涵顶土压力进行了测试,研究了涵顶土压力的分布规律及变化规律。通过对涵洞位移的监测,研究了减载后涵体位移随填土高度的变化规律。结果表明涵顶加筋减载将涵顶荷载转移至其两侧土体,涵顶压力减小,格栅的“提兜效应”提高了荷载转移效率；涵顶减载孔高度越高,减载效果越好。(4)通过理论分析建立了加筋减载涵洞的力学计算模型,考虑格栅下部松散填料的支承作用,推导了格栅上覆填土的土压力及涵顶压力的解析表达式。并对格栅锚固端进行了分析,计算了格栅的锚固长度。通过参数分析,对填土高度、松散填料模量及格栅刚度等影响涵顶减载效果的因素进行了研究。并利用数值模拟分析了减载孔高度、格栅层数、减载孔宽度、减载孔边坡角度和松散填料模量、内摩擦角及黏聚力对涵顶压力的影响。结果表明本文方法能够准确计算减载后的涵顶土压力；松散填料模量对涵顶土压力有较大影响,宜将其控制在一定的范围之内；格栅刚度较大时,才能进一步有效减小涵顶土压力；格栅刚度较大时,多层格栅与单层相比对减载效率提高作用不大；减载孔填料的黏聚力对涵顶压力影响不大,而内摩擦角影响较大。本文的研究成果对高填方涵洞的设计和施工,及其采用加筋减载法进行高填方涵洞的设计与施工具有重要的参考价值。更多还原

【Abstract】 High embankment culverts are widely used in constructions of expressway in mountainous and loessial regions. Large loads are usually exerted in the crown of the high embankment culverts, and the mechanism of the fill-culvert interaction is complex, it has a lot of influencing factors, including not only installation conditions of the structure(embankment installation or trench installtion), but also heights of embankment fill, terrain conditions, geological conditions, properties of filling material, sizes of structure and many others. Because the influencing factors of the earth pressure are not clearly understood, there are frequent occurrences of cracking on the crown of the high embankment culverts. TriAx geogrid has unique physical and mechanical properties, when it is used as reinforcement material for imperfect trench method, it can reduce the earth pressure on the crown of high embankment culvert and obtain good economic and social benefits. In this dissertation, the load reduction process of imperfect trench covered with TriAx geogrid is studied systematicly on the basis of the investigation of the earth pressure and its influencing factors on high embankment culvert, which mainly contains:(1) The variation of vertical earth pressures on the crown of the high embankment culvert is studied by field tests. Numerical simulations are also carried out to investigate the influencing factors on the vertical earth pressure and displacement of culvert. The results show that the vertical earth pressure increases nonlinearly with the height of embankment. Asymmetric installation of the culvert causes different earth pressures on both sides. The width of the trench which effectively impacts the culvert is approximately three times of the width of culvert, and the slopes angles of 15°or 75°result in less vertical earth pressures. Larger moduli of the subgrade result in more severe stress concentration. Compared with the moduli, the internal friction angles and cohesions of the filling material have much less influences on the earth pressures and the displacements of the culvert. The types of culvert foundations have significant effects on the displacements and earth pressures, thus the appropriate choice of the foundation type should be made in accordance with the requairements of the earth pressure and the displacment. The earth pressures on wide-and-short culverts are less than those on narrow-and-tall culverts. The settlements and earth pressures are less affected by the curvatures of the arch of the culvert.(2) Considering the interaction between culvert-soil, the mechanism of load reduction for high embankment culvert is analyzed. Numerical simulations are carried out to investigate the effect of different load reduction methods by studying the vertical earth pressures and displacements of the culverts. The results show that the compressible materials can be filled within a certain area above the crown of the culvert, or the embankment fill above the culvert can be compacted loosely in the center to alleviate the concentration of the vertical earth pressure on the crown of the culvert. Excavation after filling method can be also used to reduce the vertical earth pressure, the width of the excavation should be eaqual to that of the culvert and the slopes should be vertical in order to achieve a better load reduction effect. In ground improvement, a relatively flexible composite foundation is preferred and the improvement width should extend a certain range wider than the culvert foundation, thus it can alleviate the pressure concentration on the crown of the culvert effectively.(3) Field tests are carried out to study the distribution and the variation of earth pressures with the increase of the embankment height. The variation laws of the displacement of the culvert with load reduction treatment are also investigated by field monitoring. The results show that the earth pressure on the crown of the culvert underneath an imperfect trench covered by a geogrid layer is transferred to the lateral soil prisms, so that the purpose of load reduction is achieved, and the load transfer efficiency is increased by the "tensioned membrane effect". The load reduction efficiency is related to the height of the load reduction ditch, a higher ditch results in lower vertical earth pressures.(4) The calculation model of the culvert underneath an imperfect trench covered by a geogrid layer is established by theoretical analysis, considering the support of the compressible fill below the geogrid, the analytical expressions of the earth pressures on the upper surface of geogrid layer and the crown of the culvert are derived. The anchorage forces at each end of the geogrid layer are obtained as well. Parametric analyses are performed to investigate the influencing factors of the vertical earth pressure. The results show that the vertical earth pressure on a culvert underneath an imperfect trench covered by a geogrid layer can be accurately calculated by the proposed method. The modulus of the compressible material in the trench has greater impact on the vertical pressure, the modulus is suggested within a appropriate range. The geogrid has significant effect on further reducing the vertical earth pressure, only if the geogrid with sufficient stiffness. Compared with the single layer of geogrid, the increase of efficiency of load reduction with multilayer geogrids is neglectable. The cohesion of the material in the trench has little effect on the vertical earth pressure, while the internal friction angle has a greater impact.The achievements of this research can provide valuable references for the design and construction of high embankment culverts.更多还原