【作者】 汪攀峰；

【导师】 丁启朔；

【作者基本信息】 南京农业大学 ， 农业生物环境与能源工程， 2009， 硕士

【摘要】 桩基础由于其在竖向承载力、抗拔承载力、抗水平承载力以及抗震能力等方面有着不可替代的优势,在工程中得到了广泛地应用。但还是有很多问题急待解决,如桩侧阻力尤其是负摩阻力、桩基前端及围土的应力场分布、桩基的稳定性问题等等。由于桩-土工况条件的复杂,特别是土的性质差异性很大,给研究工作带来了很大的困难,成为土木研究领域的重点、难点和热点。因此,相关的研究不仅具有十分重要的工程意义,也具有重要的理论意义。室内模型试验存在一个重要的问题,就是土壤基的制备。这方面的研究几乎未有报道,然而一个理想的土壤基往往是模型试验成败与否的关键。特别是粘性土,其性质的复杂性尤其突出,某种因素的变化都会对粘性土的性质产生重大影响,用其制备试验用理想的土壤基更为困难。因此,室内重塑土样地制备具有重要的现实意义。本研究的目的在于寻求制作相对均质重塑土样的方法,并以此制作模型试验土壤基进行多直径模型桩试验,揭示桩基贯入及拔出过程中桩端及桩侧阻力随桩径及深度的变化情况。首先是制作小尺度的土壤基,探索小尺度土壤基制作过程中影响其结构均匀性的条件,获得制作均匀土样的制样方法与工作参数。在此基础上探索大尺度土壤基的制作技术,结合文献中关于大尺度土壤基的报道,制作尺度为30cm左右尺度的土壤基,使用不同直径的模型桩借助液压动力系统在大尺度土壤基上进行动态贯入与拔出试验研究,并利用测试系统测取桩贯入及拔出过程中的阻力,研究不同尺度的桩在相对均质土壤基中阻力随深度的变化情况,并根据结果验证土壤基的均匀性。本论文的主要结论及成果如下：1.提出了以土壤孔隙率(比)作为土壤压实质量的控制指标,目前的规范和规定都是采用压实度这一指标来控制填土工程的质量,但是由于孔隙率(比)更加直观地反映了土壤的压实效果,因此可以尝试用现场压实后土的孔隙率(比)与室内标准击实后土的孔隙率(比)进行比较,以此更加精确的定义压实度指标。并介绍了一种测量土壤孔隙率(比)的简易方法,与现有方法相比较,该方法具有简单易行,成本较低,且结果较准确等特点。2.通过室内非标准小型击实试验,反映了在非标准击实状态下粘土的一些性质与表现,得出了一些特殊的规律。提出了制样因子的概念,制样因子的合理性仍要做深入探讨,重塑土样的性质直接关系到室内模型试验的结果,因此室内模型试验的重塑土样制备也值得做进一步的研究。3.设计制作了移动式液压动力系统,为制作土壤基与模型桩试验提供了动力源。通过室内模型桩贯入与拔出试验,得到桩贯入过程中,桩土间的阻力随位移增长呈线性增大趋势；拔出过程中,桩土间阻力随位移增长也近似呈线性减小趋势。随桩径增大,对应的阻力也明显增大。最大桩端阻力在总阻抗中的比重随桩径及长径比的增大而呈减小趋势,但当长径比达到75时,减小的趋势便放缓,并近似趋于恒定。桩端阻力随桩径增大呈增大趋势,而贯入过程中位移的变化对桩端阻力几乎无显著影响,从侧面验证了土壤基的相对均匀性。更多还原

【Abstract】 Because of its excellent vertical bearing capacity, pull-out capacity, anti-horizontal bearing capacity and anti-seismic capacity, pile foundation has irreplaceable advantages in engineering and thus has been widely used. However, a number of problems remain unresolved, such as the pile side resistance, of particular the negative friction, stress distribution under the pile tip and the surrounded soil, the stability of foundation problems, etc.Due to the complexity of geotechnical conditions, and particularly the unpredictable behavior of soils, researches in these areas generally faced with a lot of difficulties, and in turn these have turned out to be the focus, difficult and hot spots of the research field of civil engineering. Therefore, the relevant research work was not only significant in engineering practices but also has important theoretical implications.One important issue for laboratory model tests is the preparation of remolded soil. Although an ideally remolded soil is generally the key for a successful indoor model test, there was almost no such research work reported. This was true particularly for clay soils. The properties of this type of soils were very much complicated. The change of one or two of its factors can generally lead to the drastic variations of many other properties,making the preparation of ideal test soil unattainable. Therefore the preparation of remolded soil has important practical significance.The purpose of this study is to search the method of preparing relatively homogeneous remolded soil, based on which the target remolded soil base be made for multi-diameter model pile tests.So that the relationship between the pile tip and side resistance and the pile diameters and depths can be illustrated for the dynamical pressing and pulling processes.Mini-scale remolded soil bases were firstly prepared to test the influencing factors on the soil base homogeneity, the results of which provided the relevant working parameters that were governing conditions for homogeneous soil state. Next, the technology of large-scale homogeneous remolded soil preparation was explored. By considering the past reports,the large 30 cm diameter remolded soil base was prepared. This allowed the dynamic penetration test on different sized model piles in the soil bases, under the help of hydraulic power system. The pile resistance changes with depth for different scales were measured in relatively homogeneous remolded soil base, which results also validated the homogeneity of the remolded soil based.Conclusions and main achievements of this paper were listed below:1.Soil porosity (ratio) was proposed as an indicator for quality control on soil compaction. The currently applied regulations and specifications defined the degree of compaction as a controlling indicator. Yet the porosity (ratio) is more intuitive to reflect the degree of soil compaction, and thus it can be used for comparing the porosity of in-situ soil compaction test with that of the standard-laboratory tamping test. This index provide a higher precision quantification on soil compaction.In addition, a simple test method was explained for soil porosity measurement.Comparing with the past methods,this method was benefited with its simplicity, low cost and more accurate.2.The non-standard mini-scale indoor tamping test revealed some special characteristics and behaviors of a clay soil.The concept of soil sample preparation factor was proposed, which reasonability still need investigation.As the property of remolded soil is directly related to the result of the indoor model test, it preparation should be further investigated.3.A hydraulic power system for the preparation of remolded soil and model pile test was designed and constructed. Through the indoor penetration and pull-out test, the pile-soil resistance is enhancing as a linear trend with the increasing of the depth during the pile penetrate into the soil;in the pull-out process,the resistance is in constrast with above.With increasing of the pile diameter, the corresponding resistance also increases. The proportion of the biggest pile tip resistance in the total impedance decreases with the increase of the pile diameter and aspect ratio,but while the aspect ratio is 75,the decrease will slow down, and approximately tends to a constant. Pile tip resistance increases with the pile diameter, but the pile tip resistance is almost no significant increased trend with the change of displacement, it verifies the relative homogeneous of the base on the other hand.更多还原