Flexural buckling of micro piles - Buigingsknik van ankerpalen

This thesis focuses on the stability of slender micro piles with a diameter of 100-400mm in soft soils when used in compressive situations. In the western part of the Netherlands and many other deltaic areas weak clay and peat deposits overlay stiffer sand layers. In these geological conditions flexural buckling may cause a considerable design constraint. The purpose of this thesis is to enlarge existing knowledge about this phenomenon and use this knowledge to improve the existing design methods. To validate and to further improve the existing models a comparison with the laboratory tests from the TU Munich has been made. In the laboratory research of the TU Munich; GEWI28-100 micro piles (28mm S500 GEWI steel with a 100 diameter groutshell of C20/25) with a length of 4m were used in buckling tests. In this thesis a physical non linear model of the complete GEWI pile is made in INCA. In combination with DSheet 9.2 beta the resulting moment-curvature relations obtained from INCA can be coupled to geometrical non linear (second order) analyses provided by DSheet. The lateral soil springs in DSheet are modelled with p-y curves for soft clays according to the API. Because the use of these p-y springs in a buckling calculation lead to a gross overestimation of the measured buckling loads PLAXIS 3D is used for more advanced modelling of the soil behaviour. The Kaolin (clay) used in the test of the TU Munich has been modelled with the Hardening Soil model. The resulting numerical buckling calculations in PLAXIS 3D have empirically shown that drained analyses on the basis of the undrained shear strength provides a good match with the laboratory results. The renewed model to determine the buckling of a micro pile is based on the analytical solution of the TU Munich. In this renewed version, mathematical superposition is used to determine the buckling load of each individual component of the micro pile (steel, grout and soil). By using empirical relations between strength and stiffness of the three components using numerical tools and literature the design value of the buckling load of a micro pile can be determined with a simple algorithm.Geoscience & EngineeringCivil Engineering and Geoscience