{"id":{"repo_id":"cambridge","oai_identifier":"oai:www.repository.cam.ac.uk:1810/371923"},"canonical_url":"https://search.dev.ndltd.org/etd/cambridge/oai:www.repository.cam.ac.uk:1810/371923","repository":{"repo_id":"cambridge","name":"Cambridge University","base_url":"https://api.repository.cam.ac.uk/server/oai/request"},"display":{"title":"Numerical and physical modelling of piled rafts on soft clay under combined loading","abstract":"Piled raft foundations are typically used in cases where a shallow foundation is inadequate to sustain the loads of the superstructure either because of lack of capacity or because of excessive displacement. They consist of two components, namely the raft and the pile group, contributing to the overall response of the foundation. Once the piles are introduced under a raft, the conventional design practice requires that the pile group should be designed to be able to sustain the entire load, ignoring the contribution of the raft, with significant associated financial and environmental cost. In the last four decades, a number of researchers have investigated the behaviour of piled rafts under vertical load, with the objective of defining more rational and economic methods for their design. However, piled rafts are often used for structures that are subject to complex load, involving combinations of vertical, lateral, and moment loading, under cyclic and seismic conditions. Examples of structures commonly founded on piled rafts include, e.g., high-rise buildings, bridge piers and wind turbines on weak soils, where the possibility of high differential settlements or the lack of space make the use of a shallow foundation insufficient or impossible and the use of piles mandatory. At present, research on the behaviour of piled rafts under combined loading is still limited and knowledge on the developed soil-structure interaction mechanisms insufficient to affect practically design codes. This study examined three key aspects of the behaviour of piled rafts in soft clay soil, namely overall capacity, load sharing between the piles and the raft, and failure mechanisms. The problem was tackled by both numerical and physical modelling and different configurations of the system were examined, including the isolated components of the piled raft. An extended numerical parametric study was carried out using the general-purpose finite element code Abaqus to examine systematically the effect of different factors, such as the number of piles, the raft width, and the raft-soil contact, under various load combinations. The principal challenges of the numerical work were to develop a representative model for the reinforced concrete pile section and to model the pile-soil and raft-soil interfaces. These should allow relative displacements between the soil and the structural elements, such as sliding and gapping, ensuring that the correct overall response is predicted. To this end, contact interfaces with damage were introduced with properties varying with depth in accordance with the soil profile. Experimentally, the study examined specific piled raft configurations under different load combinations using centrifuge modelling. In this case, the main challenge was to model miniature reinforced concrete piles, with sections exhibiting realistic moment-axial load failure loci. Traditionally, reduced-scale model of piles for centrifuge testing are made with aluminium hollow sections. In this study, miniature reinforced concrete piles to use in the centrifuge tests were constructed following an original procedure. The miniature piles were initially tested in four-point bending and then inserted in the reduced-scale model foundation for centrifuge testing, successfully predicting the expected failure mechanisms. The findings of this study are organised according to the three key theme areas. As regards the overall capacity, load-displacement curves show the effect of the raft width and the number of piles on the piled raft capacity and on the level of displacement required to fully mobilise the capacity. For the different piled raft configurations, the ultimate response of the system can be described by failure envelopes in the vertical-horizontal and vertical-moment domain with important conclusions about the coupling in different directions of loading. Moreover, the share between the raft and the piles for different load combinations at working or ultimate loading conditions is expressed by establishing load sharing coefficients. The coefficients can be used to predict the overall capacity of the piled raft based on a function of the raft width, the pile spacing and the number of piles. Finally, critical points of the failure mechanism of the piled raft in soft clay under different loading types are highlighted, to provide directions for design.","abstract_html":"Piled raft foundations are typically used in cases where a shallow foundation is inadequate to sustain the loads of the superstructure either because of lack of capacity or because of excessive displacement. They consist of two components, namely the raft and the pile group, contributing to the overall response of the foundation. Once the piles are introduced under a raft, the conventional design practice requires that the pile group should be designed to be able to sustain the entire load, ignoring the contribution of the raft, with significant associated financial and environmental cost. In the last four decades, a number of researchers have investigated the behaviour of piled rafts under vertical load, with the objective of defining more rational and economic methods for their design. However, piled rafts are often used for structures that are subject to complex load, involving combinations of vertical, lateral, and moment loading, under cyclic and seismic conditions. Examples of structures commonly founded on piled rafts include, e.g., high-rise buildings, bridge piers and wind turbines on weak soils, where the possibility of high differential settlements or the lack of space make the use of a shallow foundation insufficient or impossible and the use of piles mandatory. At present, research on the behaviour of piled rafts under combined loading is still limited and knowledge on the developed soil-structure interaction mechanisms insufficient to affect practically design codes. This study examined three key aspects of the behaviour of piled rafts in soft clay soil, namely overall capacity, load sharing between the piles and the raft, and failure mechanisms. The problem was tackled by both numerical and physical modelling and different configurations of the system were examined, including the isolated components of the piled raft. An extended numerical parametric study was carried out using the general-purpose finite element code Abaqus to examine systematically the effect of different factors, such as the number of piles, the raft width, and the raft-soil contact, under various load combinations. The principal challenges of the numerical work were to develop a representative model for the reinforced concrete pile section and to model the pile-soil and raft-soil interfaces. These should allow relative displacements between the soil and the structural elements, such as sliding and gapping, ensuring that the correct overall response is predicted. To this end, contact interfaces with damage were introduced with properties varying with depth in accordance with the soil profile. Experimentally, the study examined specific piled raft configurations under different load combinations using centrifuge modelling. In this case, the main challenge was to model miniature reinforced concrete piles, with sections exhibiting realistic moment-axial load failure loci. Traditionally, reduced-scale model of piles for centrifuge testing are made with aluminium hollow sections. In this study, miniature reinforced concrete piles to use in the centrifuge tests were constructed following an original procedure. The miniature piles were initially tested in four-point bending and then inserted in the reduced-scale model foundation for centrifuge testing, successfully predicting the expected failure mechanisms. The findings of this study are organised according to the three key theme areas. As regards the overall capacity, load-displacement curves show the effect of the raft width and the number of piles on the piled raft capacity and on the level of displacement required to fully mobilise the capacity. For the different piled raft configurations, the ultimate response of the system can be described by failure envelopes in the vertical-horizontal and vertical-moment domain with important conclusions about the coupling in different directions of loading. Moreover, the share between the raft and the piles for different load combinations at working or ultimate loading conditions is expressed by establishing load sharing coefficients. The coefficients can be used to predict the overall capacity of the piled raft based on a function of the raft width, the pile spacing and the number of piles. Finally, critical points of the failure mechanism of the piled raft in soft clay under different loading types are highlighted, to provide directions for design.","abstract_has_math":false,"creators":["Katsanevaki, Zacharoula"],"institution":"University of Cambridge","degree_name":"Doctor of Philosophy (PhD)","degree_level":"Doctoral","degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Viggiani, Giulia"],"committee_chairs":[],"committee_members":[],"year":2023,"date_issued":"2023-12-21","date_published":"2023-12-21","updated_at":"2026-07-22T22:24:24Z","subjects":["centrifuge modelling","failure domain","failure mechanism","load sharing","miniature piles","physical modelling","piled rafts"],"languages":["eng"],"rights":[],"rights_urls":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/e819cc21-f017-4780-ae3f-496df6152ed0/download","http://purl.org/NET/rdflicense/allrightsreserved"],"identifier_entries":[]},"links":{"outbound_url":"https://doi.org/10.17863/CAM.110954","outbound_label":"DOI","outbound_source":"dc:identifier.doi"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Viggiani, Giulia"]},{"key":"dc:creator","label":"Author","values":["Katsanevaki, Zacharoula"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.issued","label":"Date","values":["2023-12-21"]},{"key":"dc:publisher.institution","label":"Dc Publisher Institution","values":["University of Cambridge"]},{"key":"dc:relation.isreferencedby.uri","label":"Dc Relation Isreferencedby URI","values":["https://www.repository.cam.ac.uk/handle/1810/371923"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["Doctoral"]},{"key":"dc:type.qualificationname","label":"Dc Type Qualificationname","values":["Doctor of Philosophy (PhD)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["centrifuge modelling","failure domain","failure mechanism","load sharing","miniature piles","physical modelling","piled rafts"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/e819cc21-f017-4780-ae3f-496df6152ed0/download","http://purl.org/NET/rdflicense/allrightsreserved"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.doi","label":"DOI","values":["https://doi.org/10.17863/CAM.110954"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/76fada04-59d3-43ba-bc5c-c462ed84d9c2/download"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Piled raft foundations are typically used in cases where a shallow foundation is inadequate to sustain the loads of the superstructure either because of lack of capacity or because of excessive displacement. They consist of two components, namely the raft and the pile group, contributing to the overall response of the foundation. Once the piles are introduced under a raft, the conventional design practice requires that the pile group should be designed to be able to sustain the entire load, ignoring the contribution of the raft, with significant associated financial and environmental cost. In the last four decades, a number of researchers have investigated the behaviour of piled rafts under vertical load, with the objective of defining more rational and economic methods for their design. However, piled rafts are often used for structures that are subject to complex load, involving combinations of vertical, lateral, and moment loading, under cyclic and seismic conditions. Examples of structures commonly founded on piled rafts include, e.g., high-rise buildings, bridge piers and wind turbines on weak soils, where the possibility of high differential settlements or the lack of space make the use of a shallow foundation insufficient or impossible and the use of piles mandatory. At present, research on the behaviour of piled rafts under combined loading is still limited and knowledge on the developed soil-structure interaction mechanisms insufficient to affect practically design codes. This study examined three key aspects of the behaviour of piled rafts in soft clay soil, namely overall capacity, load sharing between the piles and the raft, and failure mechanisms. The problem was tackled by both numerical and physical modelling and different configurations of the system were examined, including the isolated components of the piled raft. An extended numerical parametric study was carried out using the general-purpose finite element code Abaqus to examine systematically the effect of different factors, such as the number of piles, the raft width, and the raft-soil contact, under various load combinations. The principal challenges of the numerical work were to develop a representative model for the reinforced concrete pile section and to model the pile-soil and raft-soil interfaces. These should allow relative displacements between the soil and the structural elements, such as sliding and gapping, ensuring that the correct overall response is predicted. To this end, contact interfaces with damage were introduced with properties varying with depth in accordance with the soil profile. Experimentally, the study examined specific piled raft configurations under different load combinations using centrifuge modelling. In this case, the main challenge was to model miniature reinforced concrete piles, with sections exhibiting realistic moment-axial load failure loci. Traditionally, reduced-scale model of piles for centrifuge testing are made with aluminium hollow sections. In this study, miniature reinforced concrete piles to use in the centrifuge tests were constructed following an original procedure. The miniature piles were initially tested in four-point bending and then inserted in the reduced-scale model foundation for centrifuge testing, successfully predicting the expected failure mechanisms. The findings of this study are organised according to the three key theme areas. As regards the overall capacity, load-displacement curves show the effect of the raft width and the number of piles on the piled raft capacity and on the level of displacement required to fully mobilise the capacity. For the different piled raft configurations, the ultimate response of the system can be described by failure envelopes in the vertical-horizontal and vertical-moment domain with important conclusions about the coupling in different directions of loading. Moreover, the share between the raft and the piles for different load combinations at working or ultimate loading conditions is expressed by establishing load sharing coefficients. The coefficients can be used to predict the overall capacity of the piled raft based on a function of the raft width, the pile spacing and the number of piles. Finally, critical points of the failure mechanism of the piled raft in soft clay under different loading types are highlighted, to provide directions for design."]},{"key":"dc:format.checksum.md5","label":"Dc Format Checksum Md5","values":["4d9fcc453c96bfb7d095e3c9bf275fe2","87eda9de84448d1f82354d60eee3eb5f"]},{"key":"dc:title","label":"Title","values":["Numerical and physical modelling of piled rafts on soft clay under combined loading"]}]}],"canonical_facts":{"dc:contributor.advisor":["Viggiani, Giulia"],"dc:creator":["Katsanevaki, Zacharoula"],"dc:date.issued":["2023-12-21"],"dc:description.abstract":["Piled raft foundations are typically used in cases where a shallow foundation is inadequate to sustain the loads of the superstructure either because of lack of capacity or because of excessive displacement. They consist of two components, namely the raft and the pile group, contributing to the overall response of the foundation. Once the piles are introduced under a raft, the conventional design practice requires that the pile group should be designed to be able to sustain the entire load, ignoring the contribution of the raft, with significant associated financial and environmental cost. In the last four decades, a number of researchers have investigated the behaviour of piled rafts under vertical load, with the objective of defining more rational and economic methods for their design. However, piled rafts are often used for structures that are subject to complex load, involving combinations of vertical, lateral, and moment loading, under cyclic and seismic conditions. Examples of structures commonly founded on piled rafts include, e.g., high-rise buildings, bridge piers and wind turbines on weak soils, where the possibility of high differential settlements or the lack of space make the use of a shallow foundation insufficient or impossible and the use of piles mandatory. At present, research on the behaviour of piled rafts under combined loading is still limited and knowledge on the developed soil-structure interaction mechanisms insufficient to affect practically design codes. This study examined three key aspects of the behaviour of piled rafts in soft clay soil, namely overall capacity, load sharing between the piles and the raft, and failure mechanisms. The problem was tackled by both numerical and physical modelling and different configurations of the system were examined, including the isolated components of the piled raft. An extended numerical parametric study was carried out using the general-purpose finite element code Abaqus to examine systematically the effect of different factors, such as the number of piles, the raft width, and the raft-soil contact, under various load combinations. The principal challenges of the numerical work were to develop a representative model for the reinforced concrete pile section and to model the pile-soil and raft-soil interfaces. These should allow relative displacements between the soil and the structural elements, such as sliding and gapping, ensuring that the correct overall response is predicted. To this end, contact interfaces with damage were introduced with properties varying with depth in accordance with the soil profile. Experimentally, the study examined specific piled raft configurations under different load combinations using centrifuge modelling. In this case, the main challenge was to model miniature reinforced concrete piles, with sections exhibiting realistic moment-axial load failure loci. Traditionally, reduced-scale model of piles for centrifuge testing are made with aluminium hollow sections. In this study, miniature reinforced concrete piles to use in the centrifuge tests were constructed following an original procedure. The miniature piles were initially tested in four-point bending and then inserted in the reduced-scale model foundation for centrifuge testing, successfully predicting the expected failure mechanisms. The findings of this study are organised according to the three key theme areas. As regards the overall capacity, load-displacement curves show the effect of the raft width and the number of piles on the piled raft capacity and on the level of displacement required to fully mobilise the capacity. For the different piled raft configurations, the ultimate response of the system can be described by failure envelopes in the vertical-horizontal and vertical-moment domain with important conclusions about the coupling in different directions of loading. Moreover, the share between the raft and the piles for different load combinations at working or ultimate loading conditions is expressed by establishing load sharing coefficients. The coefficients can be used to predict the overall capacity of the piled raft based on a function of the raft width, the pile spacing and the number of piles. Finally, critical points of the failure mechanism of the piled raft in soft clay under different loading types are highlighted, to provide directions for design."],"dc:format.checksum.md5":["4d9fcc453c96bfb7d095e3c9bf275fe2","87eda9de84448d1f82354d60eee3eb5f"],"dc:identifier.doi":["https://doi.org/10.17863/CAM.110954"],"dc:identifier.uri":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/76fada04-59d3-43ba-bc5c-c462ed84d9c2/download"],"dc:language":["eng"],"dc:publisher.institution":["University of Cambridge"],"dc:relation.isreferencedby.uri":["https://www.repository.cam.ac.uk/handle/1810/371923"],"dc:rights":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/e819cc21-f017-4780-ae3f-496df6152ed0/download","http://purl.org/NET/rdflicense/allrightsreserved"],"dc:subject":["centrifuge modelling","failure domain","failure mechanism","load sharing","miniature piles","physical modelling","piled rafts"],"dc:title":["Numerical and physical modelling of piled rafts on soft clay under combined loading"],"dc:type":["Thesis"],"dc:type.qualificationlevel":["Doctoral"],"dc:type.qualificationname":["Doctor of Philosophy (PhD)"]},"updated_at":"2026-07-22T22:24:24Z"}