【作者】 黄文锋；

【导师】 莫海鸿；

【作者基本信息】 华南理工大学 ， 岩土工程， 2014， 博士

【摘要】 刚性网格-桩加筋路基类似于桩承式加筋路堤，是一种由路堤填土、加筋垫层、软土层、持力层、刚性网格和预制或现浇混凝土桩即刚性桩组成的复合地基。该复合地基是基于厚路堤工况下路堤边缘处毁桩破坏而设置的一种更新型复合地基形式，其设计目的是通过筋材的抗拉模量增强桩体荷载分担比和利用刚性网格减小边桩弯矩和剪力；其内部结构形式的不同，为研究提供了新的内容。基于该复合地基的结构特点，利用数值分析方法研究了桩身和软基的受力变形特征；根据土拱理论，推导了在考虑基土反力的情况下筋材力学及变形的解析表达式；并研究了布桩形式和土堤加固方法。主要工作如下：（1）根据Midas/GTS前处理中产生的桩-土单元节点分离，研究桩端处几何瞬变的形成过程；通过桩端边界条件改造，建立有持力层工况下不同类型刚性桩加固路堤的基本模型，比较分析中桩、边桩和网织物的受力变形特点，分析各对象的优缺点，阐明提出刚性网格-桩加筋路基的原因。（2）针对刚性桩加筋路基和桩承式路堤在有持力层刺入工况下的薄弱部位，分析刚性网格–桩加筋路基中筋材、刚性网格和附加桩对薄弱处的加固作用，研究有、无持力层刺入2种工况下刚性网格–桩加筋路基受力和变形在不同桩长影响下的变化特征，对刚性网格–桩加筋路基是否适用于无持力层工况进行可行性探讨。（3）基于Hewlett和Randolph的空间半球拱模型假设刚性网格-桩加筋路基路堤荷载传递途径、虎克定律和平衡条件，获得了筋材受力变形的解析表达式，并利用该方法分析了桩距和软土层弹性模量及深度对筋材的影响，揭示土拱、筋材拉力及桩体荷载分担比的受力机理。（4）提出单向布置混凝土梁下刚性桩加筋路基的混凝土梁和筋材的布置方式；根据“Hewlett&Randolph”和“LOW”的平面土拱理论，求解在考虑了筋材下土体屈服、单向布置混凝土梁下刚性桩加筋路基筋材上下应力差、土拱所占的桩体荷载分担比和筋材所占的桩体荷载分担比，并对两种理论所得结果进行比较，探讨产生差异的原因。（5）探讨了刚性网格-桩加筋路基在有无持力层刺入工况下的布桩优化方式。（6）论证刚性网格-桩加筋路基土堤的主要破坏形式；根据土堤破坏形式，建立草被、土工网、护坡以及支护桩加固状态下土堤受力平衡方程，分析不同土堤坡角下土堤内摩擦角对加固材料厚度的影响。本文主要成果如下：（1）有无持力层两种工况下桩身受力分布规律；（2）薄弱部位的确定；（3）考虑筋材下地基反力的筋材受力及变形、土拱部分所占的桩体荷载分担比和筋材部分所占的桩体荷载分担比的解析解；（4）布桩方式；（5）土堤加固的分析方法。基于上述工作和成果，本文所取得主要结论如下：（1）桩帽或刚性网格的加固减小褥垫层刺入量和筋材的拉力，刚性网格的设置减小了边桩弯矩和剪力。（2）无持力层工况下的刚性网格-桩加筋路基，桩长的增加能增大中桩桩体荷载比，减小边桩上部弯矩及剪力、体系的最大沉降和路堤外侧竖向位移变异，并使体系竖向变形由竖向剪切型部分地向水平扩散型转化；应通过增加桩长，利用预制薄壁混凝土管桩(PTC管桩)放宽中桩截面，减小附加桩桩径实现优化。（3）刚性网格的设置为土拱构架提供一定的厚度，承担一部分桩体荷载分担比；路堤填土内摩擦角的增加有利于增强土拱部分产生的桩体荷载分担比；筋材的增强设置，承担另一部分桩体荷载分担比，并减小筋材与刚性网格的不均匀沉降；地质条件越差越有利于发挥筋材的作用。（4）在有持力层工况下采取‘中桩疏边桩密’的布桩方式；在无持力层刺入工况下，应采用‘中心稍疏其余密’的布桩方式。（5）应结合坡角的大小，可分别利用草被、土工格栅的拉力和护坡的自重对土堤进行加固，堤坡角度越大，加固物厚度越大。更多还原

【Abstract】 A rigid grid-pile reinforced subgrade is similar to a piled embankment comprising athick embankment fill layer, a granular layer with geosynthetic, a soft foundation soil layer, afirm bearing stratum, rigid grids and prefabricated or cast-in-situ concrete piles termed rigidpiles. The composite foundation is an update form based on the pile destruction close to theembankment border in thick embankment. The design purpose is to foreground the tensilestiffness of the geosynthetic to increase the pile efficacy with the intent of making use of therigid grid to decrease the shearing force and bending moment distributing at the side piles.The difference in the interior structural form of this composite foundation from the availablepiled embankments provides a new research direction. Based on the structural characteristicof this composite foundation, the force-deformation behavior of the pile and soft soilfoundation is investigated by numerical analysis. According to the soil arching theories, theanalytical solutions for the load-deflection of the geosynthetic considering subsoil support arederived. The pile arrangement and the reinforced method for the embankment slope areinvestigated. The main work includes of six parts:(1) In terms of the node separation between the pile element and the soil element inMidas/GTS preprocessing, the geometric transient of the pile bottom is investigated. Usingthe improvements to the boundary conditions at the pile bottoms, different types of models ofrigid pile reinforced subgrade with bearing stratum penetration are built, the embankmentforce-deformation bahavior for the middle pile, side pile and geosynthetic are examined by acomparative analysis, the merit and demerit of each type of the embakment is investigated,and the reasons why the rigid grid-pile reinforced subgrade is proposed.(2) According to weak parts of rigid pile reinforced subgrade and piled embankmentswith bearing stratum penetration，the reinforcement for the weak parts by geosynthetic，rigidgrid and additional pile in the rigid gird-pile reinforced subgrade is analyzed. Thecharacteristics of force and deformation of rigid grid-pile reinforced subgrade with andwithout bearing stratum penetration are investigated at different pile lengths；and thefeasibility whether the rigid grid-pile reinforced subgrade is applicable to the case withoutbearing stratum penetration is evaluated.(3) Based on the load-transferring path of the hemispherical soil arching model proposedby Hewlett&Randolph, Hooke’s law and the equilibrium condition, the load-deflection ofthe the geosynthetic is derived. Employing the method, the effect of pile spacing, elasticmodulus and depth of the soft soil foundation on the geosynthetic is investigated, which reveals the mechanism of the soil arching, tesile force of the geosynthetic and pile efficacy.(4) The concrete beam and transverse geosynthetic placement in a rigid pile compositefoundation reinforced by the unidirectional concrete beams, is proposed. Based on the planesoil arching theory proposed by Hewlett and Randolph and modified by Low et al., the loadcarried by the geosynthetic, the pile efficacy due to soil arching, and the pile efficacy due tothe geosynthetic are derived considering subsoil yield. The results between Hewlett andRandolph and Low et al. are compared with each other, and their difference is discussed.(5) The optimized arrangement of the pile is investigated and discussed.(6) The failure mode of the embankment slope in the rigid grid-pile reinforced subgradeis demonstrated. According to the failure mode of the embankment slope, the equilibriumequation of the slope reinforced by grass, geogrid and revetment are built. The influence ofthe internal friction angle of the embankment fill on the thickness of the reinforced at differentslope angles are investigated.The main achievements of this paper are (1) the force laws of the pile with and withoutbearing stratum penetration,(2) the determination of the weak positions,(3)the analyticalsolution for the force-deformation behavior, the pile efficacy due to soil arching and the pileefficacy due to geosynthetic considering the subsoil support,(4) the pile arrangement, and (5)the analytical method for the slope reinforcement.The main conclusions, drawn based on the above work and achievements, are as follows:(1) the pile cap or rigid grid reinforcements decrease the penetration into granular layerand the geosynthetic tension, and the setting of the rigid grid decreases the bending momentand shearing force distributing at the side pile.(2) In a rigid grid-pile reinforced subgrade without bearing stratum penetration, anincrease in pile length increases the pile efficacy of the middle pile, and decreases the bendingmoment and shearing force distributing at the upper-side pile, the maximum settlement in thesystem and the variation in the lateral deformation, which make the vertical deformation inthe system partly converted into lateral diffusion. The optimization can be obtained byincreasing the pile length，applying PTC pile to enlarging the cross-section of central pile, anddecreasing the additional pile’s diameter.(3) The setting of the rigid grid-pile provides the soil arching with a certain thickness tobear a portion of the pile efficacy. An increase in the intenal friction angle can increase thepile efficacy due to soil arching. The geosynthetic reinforcements can regulate the verticalstress below the geosynthetic and bear another portion of the pile efficacy and decrease the differential settlement between the rigid grid and the geosynthetic.The weaker the geologicalcondition, the greater the role of the geosynthetic.(4) The pile arrangement can be ‘sparse in middle pile and dense in side pile’ witbearing stratum penetration, and ‘sparse close to the center and dense in the residual’without bearing stratum penetration.(5) The embankment slope can be reinforced by apllying the tensile force of the grassand geogrid and the revetment weight. The larger the slope angle, the larger the thickness ofthe reinforced thickness.更多还原