【作者】 刘敦平；

【导师】 赵明华； 蒯行成；

【作者基本信息】 湖南大学 ， 岩土工程， 2008， 博士

【摘要】 近年来,随着我国高速公路建设的迅猛发展,软土地基问题日益突出,各种软基处治技术也随之得到了蓬勃发展。双向增强体复合地基法是目前国内外兴起的一种新型的软基处治技术,目前在高速公路路基加固、台背填土加固、不良地质条件的旧路加宽改造等工程中得到了广泛应用,并取得了良好的加固效果。但是该处治技术的理论研究尚欠成熟。为此,本文结合国家高技术研究发展计划(863计划)项目“大面积不均匀公路软弱地基按沉降控制双向增强处治技术”(2006AA11Z104),从双向增强体复合地基的桩土应力比计算、沉降计算及固结分析等方面出发,通过理论分析、数值模拟及室内模型试验进行较深入系统的研究。本文首先针对竖向增强体-水平增强体-桩间土的整体相互作用的特点,将水平增强体视为具有一定刚度的板,竖向桩体及桩间土简化为刚度不同的弹簧系列。以单个竖向桩体影响范围内的复合地基作为典型单元体进行分析,基于Winkler弹性地基圆板理论计算出水平增强体的挠曲函数表达式,推导出双向增强体复合地基桩土应力比计算式。其次,基于薄板变形理论和双参数地基模型,推导了双向增强体复合地基桩土加固区工后沉降的计算公式。研究表明水平加筋垫层的水平抗力作用对控制双向增强体复合地基工后沉降是有利的。为了进一步研究双向增强体复合地基的沉降特性,以近似解析模型为基础,运用剪切位移法建立了竖向增强体中桩与桩,桩与土,土与土之间相互作用的刚度矩阵,引入无单元伽辽金法计算水平增强体刚度矩阵,通过双向增强体复合地基的竖向位移协调条件,建立竖向增强体与横向增强体共同工作的竖向平衡方程,将无单元法的应用推广到双向增强体复合地基的沉降计算。该方法具有不需划分单元,节点布置灵活,节点参数少,计算精度高的特点。根据桩体复合地基固结的特点,将整个桩截面和桩周土截面作为一个研究单元考虑,根据固结过程中孔隙水排出量等于单元体体积减小量的关系和平均超孔隙水压力的概念,推得了考虑桩体的固结变形的桩体复合地基的固结方程。通过等应变假设和初始边界条件,由分离变量法对该固结方程进行求解,得到了桩体和桩间土的平均超孔隙水压力、平均固结度、复合地基整体固结度。进一步完善了桩体复合地基固结解析理论。最后,在相似理论基础上推导了单纯软基模型试验,土工格室垫层路基模型试验以及土工格室垫层+碎石桩复合地基模型试验的相似准则,由此设计并完成了三组室内模型试验。试验数据分析表明,土工格室垫层加固软基能有效扩散和均化上部荷载、减少沉降及不均匀沉降。而土工格室+碎石桩复合地基加固软基则既能减小地基沉降和不均匀沉降,而且能够限制路堤外侧的隆起变形。同时,碎石桩与格室垫层共同构成比较完善的排水体系,有利于加速桩间土排水固结。基于本文桩土应力比解析理论的计算值以及无单元法所获得的沉降值与实测值吻合较好,验证了本文理论分析的合理可行。更多还原

【Abstract】 In recent years, along with the development of the freeway construction, the treatment of soft soil foundation becomes increasingly important, which triggers the development of various soft foundation treatment technology.The double direction reinforced composite foundation method is a new soft foundation treatment technique. This new foundation treatment is widely applied for engineering constructions such as freeway subgrade improvement, filling in the back of the abutment strengthening and widening of existing roads with unfavorable geological conditions. However, the theory about double direction reinforced composite foundation remains immature. This paper researches on bearing characteristic of double direction reinforced composite ground, which includes pile-soil stress ratio, settlement and consolidation of this composite foundation from several aspects of theoretical analysis, numerical simulation and model experiment under the supports of High Technique Research and Development Program of China (863 program)——“The Treatment Technique of Double Diretion Reinforced Foundation Based on The Settlement Control for Large Area and Non-uniform Soft Soil Foundation in Highway Construction”(2006AA11Z104).At first, According to characteristics of interaction of vertical pile, horizontal reinforced cushion and soil, the horizontal reinforced cushion is supposed to be a thin plate, piles and soils are simplified as spring series with different rigidities respectively. A single pile and soils located in the influence area of the pile compose a concentric cylinder. The cylinder is regarded as the typical element to analysis the double direction reinforced composite foundation. A function of the horizontal reinforced cushion deformation is deduced based on a circular thin plate on Winkler foundation, and the formula of the pile-soil stress ratio of the composite foundation is also deduced.Then a biparametric model is adopted to calculate the residual settlement of double direction reinforced composite foundation, in which influences of the horizontal resistant on the residual settlement is taken into account. A formula for calculating the residual settlement is deduced. The results show that the horizontal resistant of reinforced cushion help to reduce the residual settlement, and the effect should be considered.Based on an approximate analytical model, the vertical reinforcement’s stiffness matrix considering interaction between pile and pile, pile and soil,soil and soil is determined by shear displacement method, and the horizontal reinforcement stiffness matrix was calculated by element-free of galerkin method. Then co-working system of double direction reinforcements’vertical balance equation was got through vertical displacement coordinate relationships. The application of element-free galerkin method was extended to calculate settlement of two-reinforced composite foundation. This method has some advantages such as no elements is needed, node arrangement is flexible, node parameters is few and high accuracy is got.The whole cross section of pile and soil around pile were regarded as an element to analyses. According to the equivalent relationship of the seepage discharge to the volumetric change, the equations for the consolidation of composite ground with piles were derived using the concept of average excess pore water pressure, and the consolidation deformation of pile was considered. Through the initial and boundary conditions of the composite foundation and the assumption of the equal strain, the equations were solved by separation of variables. The average excess pore water pressure and average consolidation degree of pile and its surrounding soil were obtained, and the degree of consolidation of the composite foundation was acquired. Consolidation theories for composite ground with piles were further improved.Finally, three comparative model tests including“soft soil foundation model test”,“geocell reinforced gravel cushion on soft soil subgrade model test”and“geocell reinforced gravel cushion+gravel pile composite foundation model test”were designed and carried out under the guidance of similarity theory and similarity criterions. The test results showed that, the geocell reinforced gravel cushion can diffuse and homogenize upper load, the non-uniform settlement was also reduced effectively. The double direction reinforced composite foundation formed by geocell reinforced gravel cushion and gravel pile composite foundation can be used to enhance the bearing capacity of the foundation and reduce its total and non-uniform settlements effectively, the lateral deformation of the embankment was restricted. The geocell gravel cushion and gravel pile constitute a perfection draining system, which is propitious to drainage consolidation of soil around piles. The theoretical results of the pile-soil stress ratio and the settlement coincide with the results from tests.更多还原