Contents lists available at ScienceDirect Tunnelling and Underground Space Technology journal homepage: www.elsevier.com/locate/tust 3D ﬁnite element analysis of pile responses to adjacent excavation in soft clay: Eﬀects of diﬀerent excavation depths systems relative to a ﬂoating pile Mukhtiar Ali Soomro a,1, ⁎ , Dildar Ali Mangnejo b , Riaz Bhanbhro a , Noor Ahmed Memon a , Muneeb Ayoub Memon a a Department of Civil Engineering, Quaid-e-Awam University of Engineering, Science & Technology, Sindh, Pakistan b Department of Civil Engineering, Mehran University of Engineering & Technology, Shaheed Zulﬁqar Ali Bhutto Campus, Khairpur Mirs, Pakistan ARTICLE INFO Keywords: Finite element analysis Excavation depths systems Soft clay Single pile ABSTRACT To gain new insights into single pile responses to adjacent excavations in soft ground, three dimensional nu- merical parametric studies are carried out. An advanced hypoplastic (clay) constitutive model which takes ac- count of small-strain stiﬀness is adopted. The eﬀects of excavation depths (H e ) relative to pile (L p ) were in- vestigated by simulating the excavation near the pile shaft (i.e., H e /L p = 0.67), next to (H e /L p = 1.00) and below the pile toe (H e /L p = 1.33). In addition, the eﬀect of pile head boundary conditions and diﬀerent working loads with FOS = 3.0 and 1.5 were also studied. The model parameters are calibrated and validated against measured results in centrifuge reported in literature. It is found that the pile responses to excavation depend upon for- mation level of the excavation as well as the embedded depth of the wall. With diﬀerent wall depth in each case, the induced settlement, lateral displacement and bending moment in the pile at the same stage of the excavation was diﬀerent in the three cases. Among the three cases, the excavation in case of H e /L p = 1.33 resulted in the largest pile settlement (i.e., 7.6% pile diameter). On the other hand, the largest pile deﬂection was induced in case of H e /L p = 0.67. On contrary, insigniﬁcant bending moment and changes in axial load distribution induced in the pile on completion of the excavation in each case. However, signiﬁcant bending moment (60% of pile BM capacity of 800 kNm) induced in the pile with ﬁxed head condition. The diﬀerent working loads (with FOS = 3.0 and 1.5) inﬂuence induced pile settlement but have relatively minor eﬀect on induced bending moment. 1. Introduction It is well recognised that a pile foundation transfers the load of superstructure to surrounding soil which is adjacent to pile shaft as well as underneath the piled foundation. Consequently, the high eﬀective stress regime (stress bulb) is generated surrounding of the pile. On the other hand, the excavation in the ground inevitably results in the ground movement due to eﬀective stress release. To cope with trans- portation problems in congested cities in the world like Hong Kong, Shanghai, London etc, underground transportation systems (involving tunnels for metros, excavations of metro stations and basement to fa- cilitate inhabitants in the buildings for parking) have been developed. These excavations are sometimes inevitable to be constructed adjacent to existing piled foundations. This condition leads to a big challenge for a geotechnical engineer to assess and protect the integrity of piled foundation. Finno et al. (1991) and Goh et al. (2003) reported case studies in granular soil and Alluvium residual soil respectively. They demon- strated that lateral soil movements due to excavation can be detri- mental to adjacent piles. In both the reported case studies, piles toe level was much deeper than the excavation level and they reported only the lateral behaviour of piles. Apart from ﬁeld monitoring, a number of centrifuge tests were also conducted to investigate the response of single pile (Ong et al., 2006) and pile group in soft Kaolin clay (Ong et al., 2006). They concluded that the induced bending moment and lateral deﬂection of piles were highly inﬂuenced by distance from wall and pile head condition. In studies, lateral response of end bearing piles without initial applied load was reported. In reality, piled foundation in soft clay behave as ﬂoating pile group and subjected to initial applied load from superstructure. In the presence of initial applied load, soil surrounding the pile foundation experience higher eﬀective stress level before the commencement of adjacent excavation. Leung et al. (2000, https://doi.org/10.1016/j.tust.2019.01.012 Received 9 March 2018; Received in revised form 7 January 2019; Accepted 13 January 2019 ⁎ Corresponding author. E-mail addresses: eng.soomro@gmail.com (M.A. Soomro), dildarali72@gmail.com (D.A. Mangnejo), riaz@quest.edu.pk (R. Bhanbhro), nahmedmemon@gmail.com (N.A. Memon), engr.muneebmemon@gmail.com (M.A. Memon). 1 Formerly The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, HKSAR. Tunnelling and Underground Space Technology 86 (2019) 138–155 0886-7798/ © 2019 Elsevier Ltd. All rights reserved. T