【作者】 黄晶；

【导师】 罗强；

【作者基本信息】 西南交通大学 ， 道路与铁道工程， 2008， 硕士

【摘要】 CFG桩复合地基处理技术,具有施工速度快、工期短、质量容易控制及工程造价低廉等优点。由于柔性荷载作用下复合地基承载特性及沉降特性与刚性基础下复合地基的使用情况有着较大的差异;因而,在目前中国客运专线在软土和松软土地基处理中大规模采用高强度桩复合地基技术的大环境下,开展柔性基础复合地基承载特性及沉降特性的研究具有重要的工程价值和理论意义。本论文则主要针对路堤荷载作用下CFG桩复合地基工程特性方面进行了相关研究,所做主要工作及主要结论如下:选取典型断面,于试验现场埋设各种量测仪器和传感器对CFG桩复合地基基础的承载特性和变形特性进行测试,利用测试数据对现场CFG桩复合地基实际处理情况的深层侧向变形、沉降变形、桩身应变沿深度分布、孔隙水压在施工期间的变化规律、桩土应力比及桩间土的发挥系数等方面进行了分析,主要有以下结论:(1)超静孔隙水压的变化与路堤填筑的施工速率成正比,填筑速度快,则超静孔隙水压大,反之则小。(2)侧向位移增长速率与路堤填筑速率基本成正比;另外,可以利用侧向位移曲线的变化趋势来确定加固区设桩的影响深度、可以利用侧向位移曲线的变化线型来评估复合地基处理后的侧向稳定性等。(3)在路堤荷载的作用下,加固区桩身应变的最大值大致产生于距桩顶1/3桩长的位置。(4)复合地基沉降量和土工格栅的张拉应变量与软基的深度成正比,软基越深,沉降与张拉应越大。(5)土压力变化与荷载变化密切相关,荷载越大,土压力值越大,并在恒载期变化平缓。由于现场CFG桩复合地基中的桩体在施工时的成桩质量较差,导致桩土应力比随荷载填筑变化规律出现了异常情况。利用西南交通大学的土工离心试验设备进行路堤荷载作用下高强度桩复合地基离心模型试验,分别为设置3倍桩径间距(M1)和5倍桩径间距(M2)两组,根据试验得到的数据对CFG桩复合地基在路堤荷载作用下的变形特性和受力特征进行了分析。主要结论如下:(1)地基变形随着桩间距的增大而增大,桩间距的变化对地基横向变形的影响尤为显著。两模型的地基加固区并没有受到剪切破坏。(2)路堤中心地表沉降随着桩间距的增大而增大。另外,M2的地基土工后沉降并没有得到有效控制。(3)复合地基中的土压力的增长速率并不是随着加载速率的增加而无限增长的,桩顶和桩间土的土压力变化是相互协调发展的。M1的复合地基处于稳定状态;M2的复合地基处于即将破坏的极限状态。(4)模型的加筋带沿线路横向位置是呈“M型”分布规律,这与高强度桩处理复合地基的良好的效果和其较大的刚度是相互联系的。(5)两模型的桩身受力沿桩长均大致的表现出先增大后减小的变化规律,最大值均出现在距桩顶21.5mm的位置。此外,随着桩间距的变大,桩身应变也表现出增长趋势。通过比较分析两种桩间距情况下复合地基的处理效果,得出结论:当高强度桩复合地基的下卧层为较硬持力层时,宜设置3倍桩径的桩间距;另外,如果既要把桩间距变大,又要使复合地基稳定地发挥其承载力,于桩顶加设桩帽是一个很好的选择。最后对复合地基沉降计算分析的现有成果进行了归纳分析,并对Mindlin解与Bousinesq解联合法计算复合地基沉降的计算方法进行了初步的讨论分析,得出了计算的基本思路。采用联合求解法概念明确,充分考虑了复合地基实际受力和变形特征;计算参数虽然较少,但若需要合理确定仍然需要大量试验和理论的支持。更多还原

【Abstract】 The technology of CFG pile composite foundation has such characterisitics of rapid-construction speed, short-period project, easy quality control and economically.The bearing behavior and deformation properties of flexible composite foundation has large difference between the case of rigid composite foundation; so under the great environment of current construction of passenger dedicated lines in the soft soil foundation treating in large-scale use of the technology of high-strength pile in China,the study on the bearing behavior and deformation properties of flexible composite foundation has important project value and theoretical significance.This paper mainly discusses the engineering characteristics of CFG pile composite foundation under embankment,the mian work and the main conclusions are as follows:Selecting a typical cross-section,burying various sensors on test field to test bearing behavior and deformation properties of flexible composite foundation,using the data to analysis the actual treatment of test field such as the deep lateral deformation,the settlement deformation,the Pile’s strain distribution along the depth,the change law of pore water pressure during the period of construction,the pile-soil stress ratio and the mobilization factor of soil between piles and so on. Mainly in the following conclusions: (1)The change of excess pore water pressure is proportional to the construction speed of embankment filling, the construction speed is faster,then the excess pore water pressure is larger, otherwise smaller. (2) The growth rate of lateral deformation is proportional to the construction speed of embankment filling; In addition,we can use the curve’s change tendency of lateral deformation to determine the influence depth of composite ground, use the curve’s change linear of lateral deformation to evaluate the lateral stability of composite ground.(3) under the load of embankment,the maximum pile strain of reinforcement area generates approximately at the place from the pile top 1/3 of the pile length.(4)The settlement of composite foundation and the tension of geotechnical grille are proportional to the depth of soft foundation,the depth is deeper,the settlement and the tension are larger.(5)The change of earth pressure is closely related to the load fluctuation, the greater load,the greater value of earth pressure.Because of the construction quality of the pile of composite foundation on site is poor, the change law of pile-soil stress ratio following the load filling appeared abnormal situation.Using the equipment of Southwest Jiaotong University to do the geotechnical centrifugal model test of high strength pile composite foundation under the load of embankment,3 times the distance of pile diameter between piles (Ml) group and 5 times the distance of pile diameter between piles(M2) group were set, according to the test data, The bearing behavior and deformation properties of flexible composite foundation is analysed. Main conclusions are as follows: (l)The foundation deformation increases with the distance of piles,the pile distance affects markedly the lateral deformation of foundation. The reinforce areas of two models’ foundation was not subjected to shearing failure.(2) The ground settlement of the center of embankment increases with the distance between piles. In addition,the settlement of M2 was not controlled in effect.(3)The growth rate of earth pressure does not increases with the loading rate ad infinitum,the earth pressure on the piles and the soil changes during the coordination and development.The composite foundation of Ml is in stable status, the composite foundation of M2 is at the limit state of destruction.(4)The reinforced band of model shows "M" distribution law along the transverse position of railway,this is related to the good results and the greater rigidity of high strength pile composite foundation.(5)The Pile’s strain distribution along the depth of two models increases then decreases, the maximum is found in the place which distance is 21.5 mm from the pile top. Further, as the distance between the larger pile, pile strain also showed growth trend.Through comparativing analysis of the treatment effect of two models, we draw a conclusion: When the substratum of high-strength pile composite foundation is harder, 3 times the distance of pile diameter between piles shouled be set; in addition,if the distance between two piles is not only larger,but also the bearing capacity of composite foundation perform stably, adding cap on the pile top is a good choice.Finally,the current research achievements of the calculation analysis of composite foundation are summarized, the united method of Mindlin’s solution and Bousinesq’s solution is also discussed in brief,the basic thinking of calculation is then given. The united method features clear concept,the actual loading and the deformation features are fully considered; Although the calculation parameters are less, but the support of large number of tests and theory is still needed to reasonably determine them.更多还原