Improvement of the load-deformation behavior of organic soils by means of sand compaction piles

本研究的目的是研究砂桩改良有机土的荷载变形特性。目前，关于密实、无芯砂柱改良有机土壤效率的数据非常有限，特别是关于砂柱不同安装方法的影响。蠕变，特别是在有机土壤中发生的，是一个依赖于时间的过程，并在很长一段时间内发展。这一行为尚未得到调查，因此不是任何设计模型的一部分。置换砂柱安装后随时间变化的应力发展也不是以往任何研究的主题。此外，有机土和砂柱之间差异沉降的可能性也尚未得到令人满意的调查。在1G模型试验和数值分析的基础上，对这些砂桩在安装过程中置换有机土的不同设计方法进行了研究。实验室中的测试将分为两个部分。在第一部分中，将分析和评价地基与砂柱之间的相互作用。有机土壤的行为将在实验室测试的另一部分中进行分析。这些试验的重点是研究荷载集中对不同间距和安装方法的砂柱横截面面积的影响。1G模型试验的主要目的是确定两种不同的安装方法的影响，即通过置换或置换有机土壤来安装压实砂柱。然后，将这些不同规模的试验相互比较，并用来判断大型原型砂柱所需的尺寸。为了对有机土的力学特性有一个基本的了解，并确定有限元分析的输入参数，需要得到土壤力学单元试验的结果。这些元件试验应包括限制侧变形的压缩试验以及固结、不排水的三轴试验。为了研究各向异性有机土壤的特性，我们将在本研究项目的框架内使用一个必须购买的罗氏小室。利用该装置可以准确测量不同排水和加载条件下的荷载变形行为。结合所有实验室试验的结果，根据原型砂柱的安装方法和横截面面积，可以预测原型砂柱的变形行为。然后，可以使用预定义的有限元模型来验证这一预测。

The aim of this research project is to investigate the load deformation behaviour of organic soils improved with uncased sand columns. Data available on the efficiency of organic soil improvement using compacted, uncased sand columns are currently very limited, especially on the influence of different installation methods of the sand columns. Creep, which occurs in particular in organic soils, is a time dependent process and develops over a long period of time. This behaviour has not yet been investigated and is therefore not part of any design model. The time dependent stress development after the installation of the displacement sand columns has also not been the topic of any previous investigations. Furthermore, the possibility of differential settlements between the organic soil and the sand column has also not yet satisfactorily been investigated. Based on the knowledge gained from 1g model testing as well as numerical analyses, different design approaches for these sand columns constructed by displacing the organic soil during their installation shall be developed. Testing in the laboratory will be divided into two parts. In one part the interaction between the subsoil and the sand columns will be analysed und evaluated. The behaviour of organic soils will be analysed in another part of the laboratory testing. The emphasis of these tests is to investigate the dependence of the load concentration to the cross-sectional area of the sand columns according to their spacing and their installation method. The main aim of the 1g model tests is to determine the influence of two different installation methods, namely the installation of the compacted sand columns by displacement or replacement of the organic soil. These tests on different scales shall than be compared against each other and also be used to make a judgement of the dimensions needed for a large scale prototype sand columns. The results from soil mechanical element tests are needed to gain a fundamental understanding of the soil mechanical behaviour of organic soils and to define the input parameters for the finite element analysis. These element tests shall include compression tests with restricted side deformation as well as consolidated, undrained triaxial tests. In order to investigate the behaviour of anisotropic, organic soils, a Rowe cell will be used which has to be purchased in the frame of this research project. Using this equipment, the load-deformation behaviour for different drainage and loading conditions can be accurately measured. Combining the results from all the laboratory tests, a prognosis for the deformation behaviour of prototype sand columns will be possible according to their installation method and cross-sectional area. A validation of this forecast will then be possible using the pre-defined finite element model.