Investigations of vertical bearing capacity of open-ended piles in cohesive soils with respect to soil-plug formation

目前对开放式桩的堵土研究主要集中在颗粒土中。在本研究项目中，目的是研究在粘性土中安装开放式桩时土塞的形成机制。因此，拟对管桩在粘性土中安装进行现场试验和离心试验。一方面，在现场测试过程中，可以考虑一个真实的应力状态。另一方面，离心机试验用于可重复条件下的试验以及明确定义的土壤力学边界条件下的试验。特别是，离心机试验非常适合于岩土工程的模型试验，因为所施加的应力状态真实地再现了现场条件。此外，在离心机测试过程中，可以研究各种影响土壤堵塞倾向的参数（如固结状态、安装方法、桩径）。该试验是评价内部应力发展的开放式桩作为指标的拱和后土塞的形成。在此基础上，从主要影响参数出发，对粘性土中土壤堵塞机理进行了一般性的探讨。随附的实验室和单元试验有助于更好地理解所研究的粘性土，特别是在桩-轴-土相互作用的背景下。此外，还对在粘性土中数值模拟开孔桩堵漏过程的可能性进行了可行性研究。在此框架下，离心机和现场测试的结果用于研究不同数值模拟方法（CEL， DEM， SPH）在粘性土壤中桩安装过程中的土壤堵塞的可能性和局限性。本工作包的主要目的是验证数值模型，以便它们可以在未来的研究中使用。最后，对所有结果进行综合，建立了一种考虑油堵塞及其主要影响参数的粘性土中开放式桩竖向阻力预测的分析方法。因此，将开发一种方法，根据可能的土塞区域的内部有效土压力系数来预测粘性土壤中塞的垂直容量，因为该方法是由申请人在之前的dfg研究项目中成功开发的，该项目涉及在颗粒材料中安装开放式桩。

Soil plugging in open-ended piles until now was mainly investigated regarding installation in granular soils. In the present research project, the aim is to investigate the mechanisms of soil plug formation during the installation of open-ended piles in cohesive soils.Thus, it is planned to carry out in-site as well as centrifuge tests regarding the installation of tubular piles into cohesive soils. On the one hand, during the in-site tests a realistic stress state can be considered at the best. On the other hand, centrifuge tests are used for tests under reproducible conditions as well as well defined soil mechanical boundary conditions. Especially, centrifuge tests are well suited for model testing in geotechnical engineering as the applied stress-state realistically reproduces in-site conditions. Furthermore, during centrifuge testing it is possible to investigate a wide range of influencing parameters (e.g. consolidation state, installation method, pile diameter) regarding soil plugging tendency.The tests are evaluated regarding the internal stress development inside the open-ended piles as indicator for arching and following a soil plug formation. Out of these results, general conclusions regarding the mechanisms of soil plugging in cohesive soils with respect to the main influencing parameters are drawn.Accompanying laboratory and element tests lead to better undestanding of the investigated cohesive soils especially in context with pile shaft-soil-interaction.Besides, a feasibility study regarding the possibilities to numerically simulating the soil plugging process during installation of open-ended piles into cohesive soils is carried out. In this framework, the results of centrifuge as well as in-site testing are used to investigate possibilities and limitations of different numerical modelling approaches (CEL, DEM, SPH) regarding soil plugging during pile installation in cohesive soils. Main aim of this work package is to validate the numerical models such that they can be used in future research.Finally, all results are consolidated to develop an analytical approach for prognosis of vertical pile resistance of open-ended piles installed in cohesive soils with respect to sthe oil plugging and its main influencing parameters. Thus, an approach will be developed to predict vertical capacity of a plug in cohesive soils based on an internal effective earth pressure coefficient in the area of a possible soil plug as it was succesfully developed by the applicant during a preceding DFG-research project regarding the installation of open-ended piles in granular material.