David Evans

Topic

Numerical analysis of laterally loaded large pile groups in clays & Influence of improved ground on lateral behaviour of a large pile group supporting an LNG tank

Department of Civil Engineering

Date & location

• Wednesday, August 26, 2026

• 9:00 A.M.

• Virtual Defence

Reviewers

Supervisory Committee

• Dr. Cheng Lin, Department of Civil Engineering, University of Victoria (Co-Supervisor)

• Dr. Min Sun, Department of Civil Engineering, UVic (Co-Supervisor) 

External Examiner

• Dr. Wenbo Zheng, Civil Engineering, University of Northern British Columbia 

Chair of Oral Examination

• Dr. Hong-Chuan Yang, Department of Electrical and Computer Engineering, UVic 

Abstract

Liquefied natural gas (LNG) storage tanks and other major structures constructed over soft coastal deposits may require foundations containing hundreds or thousands of piles. The lateral design of these foundations is complicated by pile–soil–pile interaction, commonly referred to as group effects, and by the limited lateral resistance provided by unfavourable soil conditions. Existing design methods and published studies generally focus on smaller pile groups because physical testing and numerical analysis of groups containing more than 100 piles are resource intensive and their interaction mechanisms are complex. This thesis used three-dimensional continuum finite element analysis to investigate the lateral behaviour of large pile groups in clay and to evaluate ground improvement by material replacement as a means of improving the lateral performance of a 499-pile LNG tank foundation. 

The first part of the study examined the effects of the number of piles, pile spacing, and pile-group configuration on lateral group response. The influence of the numerical modelling approach was also assessed using several soil constitutive models and by representing the piles with both embedded beam and volume elements. The results indicated that group interaction effects generally became more significant as the number of piles increased and were not adequately represented by existing design methods developed primarily for smaller pile groups. Based on the numerical results and available published data, a predictive equation was proposed to estimate the group reduction factor as a function of pile spacing and the number of piles within the group. 

The second part of the study investigated the effects of ground improvement thickness and stiffness on the lateral response of the LNG tank foundation. The modelling approach was benchmarked against a completed field lateral load test, after which parametric analyses were conducted for both single-pile and pile-group configurations. Improvement thicknesses ranging from 0 to 20 m were considered for the single-pile analyses and from 0 to 30 m for the pile-group analyses, while the compression modulus ranged from 12 to 60 MPa for both configurations. Increasing the thickness or compression modulus of the improved material generally reduced lateral pile displacement and bending moment, although the incremental benefits diminished as these parameters increased. For the configurations investigated, the single-pile response was primarily influenced by improvement extending to a depth of approximately 5D, whereas the complete pile group remained sensitive to improvement extending to approximately 20D. Overall, the findings demonstrate the importance of explicitly considering large-group interaction effects and indicate that material replacement can substantially improve the lateral performance of piled LNG tank foundations. The results also highlight the need for project-specific analysis of the complete foundation system when determining appropriate group-reduction parameters and the required depth and properties of improved ground.