Laterally loaded piles in sloping ground

Laterally loaded piles in sloping ground

Verhoef, R.M.

Van Tol, A.F. (mentor)
Broere, W. (mentor)
Bakker, K.J. (mentor)
Azzouzi, S. (mentor)
Jaspers Focks, D.J. (mentor)
Bijnagte, J.L. (mentor)

Civil Engineering and Geosciences

Civil Engineering

Geo Engineering

2015-02-26

The subject of this master's thesis stems from a lack of design rules in the current regulations for dolphins located in sloping ground. Dolphins are very common objects in Dutch waterways, of which a large part are located in sloping ground. The lack of design rules causes difficulties between clients and contractors, possible unfavourable designs, and a potential inefficient use of steel, the material of which dolphins are mostly constructed. In other words, a better understanding of the behaviour of a laterally loaded pile in sloping ground, as a dolphin can be schematized, may save money in the future. The master's thesis starts with a literature review. The literature showed that previous studies already carried out research to laterally loaded piles in sloping ground. Four full scale tests have been conducted, several model scale tests have been performed and three studies carried out finite element analyses. These studies all conclude that reduction of the confining soil, due to a sloping ground, decreases the lateral capacity of the pile. Parameters that influence the amount of capacity's decline are the slope angle, the soil parameters, the pile properties and the roughness of the pile-soil interface. Moreover, in all full scale tests the formation of a gap was observed. This gap indicates that the size of the passive wedge and its offered resistance determine the pile-soil interaction. The method suggested by literature to account for sloping ground in engineering practice, is the reduction of the p-y curves by a multiplier. Several p-multipliers are suggested by the different studies. Georgiadis and Georgiadis are at the most advanced stage with their research, they have developed new p-y curves for the undrained lateral pile response in sloping ground. To better qualify the influencing parameters within the pile-soil interaction of a laterally loaded pile in sloping ground, a parametric study has been conducted. The starting point for this analysis were the conditions of Dutch waterways, to which the varied parameters are connected as much as possible. First, the software programs had to be validated. Nimityongskul's full scale test and Mezazigh's model have been modelled in D-Sheet Piling, D-Pile Group and Plaxis 3D. It has been demonstrated by this validation that the HSsmall model is most suitable in Plaxis 3D to model a laterally loaded pile. In contrast, the Mohr-Coulomb model is not suitable. In the parametric study performed in Plaxis 3D two different soil profiles have been considered; a homogeneous profile consisting of medium dense sand and a layered profile of a clay layer underlain by a deeper sand layer. Two different slope angles with infinite slope have been assessed, 1:3 and 1:4, and 3 different soil parameter sets for both profiles. At the end, an analysis has been performed with a finite slope, where the pile is located at the crest, in the middle and at the toe of the slope. The most important observation of this analysis is the fact that the capacity of a laterally loaded pile in a sand slope is much more affected by the angle of the slope than the capacity of a laterally loaded pile in a clay slope. This difference can be explained by the fact that the strength of sand is stress-dependent and the cohesion of clay is not. The influence of the sloping ground is qualified with the help of normalised curves derived from the load-displacement curves and p-y curves. The normalised curves lead to specific p-multipliers for the conditions in Dutch waterways. Finally, a design recommendation is proposed for laterally loaded piles in sloping ground. A flow chart with 4 design steps is recommended in Chapter 5. First, the original p-y curve for a laterally loaded pile in horizontal level ground need to be selected. Hereafter, an appropriate p-multiplier need to be defined with help of the normalised p-y curves obtained from the Plaxis 3D analysis. The original p-y curves can then be combined with the selected multiplier to form new p-y curves to determine the pile-soil interaction of piles located in sloping ground.

laterally loaded piles
sloping ground
P-Y curve
Plaxis 3D
D-Sheet Piling
D-Pile Group

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Student theses

master thesis

(c) 2015 Verhoef, R.M.