High-Frequency Monitoring Results of a Piled Raft Foundation under Wind Loading

Authors: Laurent Pitteloud, Jörg Meier

Abstract:

Piled raft foundations represent an efficient and reliable technique for transferring high vertical and horizontal loads to the subsoil. Piled raft foundations were success­fully implemented for several high-rise buildings world­wide over the last decades. For the structural design of this foundation type the stiffnesses of both the piles and the raft have to be deter­mined for the static (e.g. dead load, live load) and the dynamic load cases (e.g. earthquake). In this context the question often arises, to which proportion wind loads are to be considered as dynamic loads. Usually a piled raft foundation has to be monitored in order to verify the design hypotheses. As an additional benefit, the analysis of this monitoring data may lead to a better under­standing of the behaviour of this foundation type for future projects in similar subsoil conditions. In case the measurement frequency is high enough, one may also draw conclusions on the effect of wind loading on the piled raft foundation. For a 41-storey office building in Basel, Switzerland, the preliminary design showed that a piled raft foundation was the best solution to satisfy both design requirements, as well as economic aspects. A high-frequency monitoring of the foundation including pile loads, vertical stresses under the raft, as well as pore water pressures was performed over 5 years. In windy situations the analysis of the measure­ments shows that the pile load increment due to wind consists of a static and a cyclic load term. As piles and raft react with different stiffnesses under static and dynamic loading, these measure­ments are useful for the correct definition of stiffnesses of future piled raft foundations. This paper outlines the design strategy and the numerical modelling of the aforementioned piled raft foundation. The measurement results are presented and analysed. Based on the findings, comments and conclusions on the definition of pile and raft stiffnesses for vertical and wind loading are proposed.

Keywords: Dynamic loading, high-frequency monitoring, piled raft foundations, wind loading.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.2643504

References:

[1] Randolph & Wroth, “An analysis of the vertical deformation of pile groups”, Géotechnique 29, 1979, No. 4, pp. 432-439.
[2] M. F. Randolph, "Design of piled raft foundations", CUED/D – Soils TR 143, Cambridge University, 1983.
[3] M. F. Randolph, P. Clancy, "Efficient design of piled rafts". Proceedings of Deep Foundations on Bored and Auger Piles, 1993, Ghent, pp. 119-130.
[4] M. F. Randolph, "Design methods for pile groups and piled rafts", Proceedings of 13th ICSMGE, 1994, New Delhi, 5, pp. 61-82.
[5] H. G. Poulos, "An approximate numerical analysis of pile–raft interaction", International Journal for Numerical and Analytical Methods in Geomechanics, 1994, 18(2), pp. 73-92.
[6] H. G. Poulos, J. C. Small, L. D. Ta, J. Sinha, L. Chen, "Comparison of some methods for analysis of piled rafts", Proceedings of 14th ICSMGE, 1997, Hamburg, 2, pp. 1119-1124.
[7] H. G. Poulos, "Piled raft foundations: design and applications",. Géotechnique, 2001, 51(2), pp. 95-113.
[8] B. Lutz, Y. El-Mossallamy, Th. Richter, "A simple and handy method for the estimation of the load settlement behaviour of piled raft foundations", Bauingenieur 2, 2006, pp. 61 66.
[9] R. Katzenbach, D. Choudhury, "ISSMGE Combined Pile-Raft Foundation Guideline", Technische Universität Darmstadt, Institute and Laboratory of Geotechnics, Darmstadt, Germany, 2013.
[10] M. H. El Naggar, M. Novak, "Nonlinear analysis for dynamic lateral pile response", Soil Dynamics and Earthquake Engineering, 15, 1996, pp. 223 224.
[11] U. Smoltczyk, " Beispiel für die Kombinierte Pfahl-Plattengründung einer Windenergie-Anlage (1,5 MW)", Bautechnik 82, 2005, Heft 4, pp. 247 250.
[12] S. Bhattacharya, S. Adhikari, "Experimental validation of soil–structure interaction of offshore wind turbines", Soil Dynamics and Earthquake Engineering, Volume 31, Issues 5–6, 2011, pp. 805 816.
[13] D. Lombardi, S. Bhattacharya, D. M. Wood, "Dynamic soil–structure interaction of monopile supported wind turbines in cohesive soil", Soil Dynamics and Earthquake Engineering, Volume 49, 2013, pp. 165 180
[14] M. Damgaard, V. Zania, L.V. Andersen, L.B. Ibsen, "Effects of soil–structure interaction on real time dynamic response of offshore wind turbines on monopiles", Engineering Structures, Volume 75, 2014, pp. 388 401
[15] N. Ravichandran, S. Shrestha, K. Piratla, "Robust design and optimization procedure for piled-raft foundation to support tall wind turbine in clay and sand", Soils and Foundations, 2018.
[16] Yamashita, K., Hamada, J., Onimaru, S. and Higashino, M. (2012), Seismic behavior of piled raft with ground improvement supporting a base-isolated building on soft ground in Tokyo. Soils and Foundations, 52, 1000-1015.
[17] S. J. Shukla, A. K. Desai, C. H. Solanki, "A dynamic behavioural study of structure with piled raft foundation by time histories finite element model", International Journal of Advance Research in Science and Engineering, Vol. No. 3, Issue No. 3, 2014.
[18] A. S. Hokmabadi, B. Fatahi, B. Samali, "Assessment of soil-pile-structure interaction influencing seismic response of mid-rise buildings sitting on floating pile foundations", Computers and Geotechnics 55, 2014, pp. 172 186.
[19] V. T. Nguyen, G. Hassen, P. de Buhan, "Assessing the dynamic stiffness of piled raft foundations by means of a multiphase model", Computers and Geotechnics 71, 2016, pp. 124 135.
[20] B. R. Jayalekshmi, S. V. Jisha, R. Shivashankar, "Wind load analysis of tall chimneys with piled raft foundation considering the flexibility of soil", Int J Adv Struct Eng, 2015, No. 7, pp. 95 115.
[21] L. Pitteloud, “Baugrube und Fundation des höchsten Hauses der Schweiz (Roche Bau 1)” in Mitteilung 165, Herbsttagung der Geotechnik Schweiz (Fall Conference proceedings of Swiss Geotechnical Society), 2012, pp. 23-36.
[22] J. Nyfeler, “Geologisch-Geotechnischer Bericht inkl. Sondierbohrungen SB1 bis SB6”, Version 1.2, Neues Bürogebäude Bau 1, Pfirter, Nyfeler + Partner AG, Muttenz, 2010 (unpublished)
[23] GeoExpert AG, “Seismischer Crosshole-Test, Baugrube Roche Bau 1”, 2011 (unpublished)
[24] L. Pitteloud, “Pfahlbemessung nach SIA 267 - Erfahrung aus der Praxis” in Mitteilung 164, Frühjahrstagung der Geotechnik Schweiz (Spring Conference proceedings of Swiss Geotechnical Society), 2012, pp. 77-90.
[25] L. Pitteloud, “Basels neues Hochhaus auf festem Grund” in TEC 21, issue 19, 2014, pp. 13-14.