A new p-y approach to pile foundations with arbitrary dimensions under monotonic load in cohesive soils

authored by

Mauricio Marcelo Terceros Almanza

supervised by

Martin Achmus

Abstract

Offshore wind technology offers great potential to provide clean and renewable energy, representing a potential alternative to the use of fossil fuels. The main obstacle associated with its implementation is the high capital cost. An efficient foundation design consequently means a reduction in cost that ensures the economic feasibility of future wind farms. This thesis makes a contribution to the optimisation of monopile foundation design subjected to lateral loading conditions in cohesive soils. For the geotechnical design of laterally loaded piles, the p-y approaches according to offshore guidelines such as API (2014) and DNVGL (2016) are extensively used due to their simplicity and versatility. An assessment of the horizontal load-bearing behaviour of piles embedded in cohesive soil is carried out to account for a comprehensive analysis of soil resistance. Indeed, pile foundations can be completely founded on cohesive soil despite its low resistance. The layered soils are in any case frequently composed at least partially of cohesive soils. For piles embedded in cohesive soils, a differentiation of the p-y methods is established by means of the soil consistency, i.e. the p-y methods proposed by Matlock (1970) for soft clay and Reese et al. (1975) for stiff clay differ considerably in their complexity from each other. However, the p-y curves specified in the guidelines are based solely on the exponential function proposed by Matlock, whereby different linearisations are recommended by API (2014) and DNVGL (2016) for its general application. Various experimental and numerical investigations demonstrate, however, considerable inadequacies of the stated basic function to accurately model the behaviour of the pile-soil interaction for large-diameter piles. In this sense, several alternative p-y approaches, which explicitly intend to account for the effect of large-diameter piles, are assessed. An extensive comparative study of static p-y approaches with respect to soft and stiff clays as well as unified p-y methods is conducted based on more than 900 three-dimensional simulations using the finite element method. A conclusive validation of the numerical model is accomplished by five field tests introduced in the literature with various pile geometries and soil conditions. Taking into consideration that the results of the p-y approach according to Matlock, the linear approximation according to the API (2014), and the DNVGL (2016) guidelines as well as further alternative approaches are not generally valid for arbitrary pile geometries and soil conditions, a new, generally applicable p-y approach for cohesive soils is developed in a consistent manner, based on the findings from the numerical comparative study.

Organisation(s)

Institute of Geotechnical Engineering

Type

Doctoral thesis

No. of pages

177

Publication date

2021

Publication status

Published

Sustainable Development Goals

SDG 7 - Affordable and Clean Energy

Electronic version(s)

https://doi.org/10.15488/11339 (Access: Open)