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Faculty of Graduate Studies

Wanli Qi

  • BEng (Nanjing Tech University, 2020)

Notice of the Final Oral Examination for the Degree of Master of Applied Science

Topic

Numerical Analyses of Seismic Response of HDPE Liftstation

Department of Civil Engineering

Date & location

  • Wednesday, August 26, 2026

  • 2:30 P.M.

  • Virtual Defence

Reviewers

Supervisory Committee

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

  • Dr. Min Sun, Department of Civil Engineering, UVic (Member) 

External Examiner

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

Chair of Oral Examination

  • Dr. Jim Christian, School of Earth and Ocean Sciences, UVic 

Abstract

Shallow-buried integrated lift stations are critical components of wastewater networks, yet their seismic response remains insufficiently understood, particularly when the structural shaft is manufactured from high-density polyethylene (HDPE). This thesis develops a three-dimensional numerical framework to distinguish soil-controlled global motion from material-dependent local response in concrete, HDPE, and fiber reinforced polymer (FRP) lift-station shafts. 

The framework combines strain-compatible equivalent-linear soil properties, viscoelastic artificial boundaries, equivalent nodal-force seismic input, and an automated computational workflow. A nonlinear strain-rate-dependent HDPE UMAT is verified against published uniaxial tests, while the soil–boundary–input implementation is assessed using a dynamic centrifuge experiment. Concrete, HDPE, and FRP configurations are compared in a common layered-soil profile at PGA levels of 0.32g and 0.55g. Paired nonlinear and linear-elastic HDPE analyses quantify constitutive-model bias. 

The results show that earthquake-induced soil deformation governs the gross translation and tilting of the shafts, whereas the clay–sand interface concentrates longitudinal curvature, cross-sectional distortion, stress, and damage. Concrete develops a damage-dominated response at 0.55g. HDPE accommodates the imposed movement through comparatively distributed bending and smooth ovalization while remaining below the adopted stress limit. FRP remains below its directional material strengths but develops a more localized and asymmetric sectional distortion at the higher PGA, raising a potential geometric-stability concern. Increasing PGA amplifies soil nonlinearity and local structural demand. The linear-elastic HDPE model reproduces global translation reasonably well but is not uniformly conservative for local response; its bias depends on excitation intensity and the governing demand parameter. 

These findings demonstrate that seismic evaluation of vertical lift-station shafts should combine global kinematic indicators with material-specific local deformation, stress, damage, and stability measures. 

Keywords: integrated lift station; seismic soil–structure interaction; finite element analysis; high-density polyethylene; rate-dependent constitutive model; soil-layer interface; cross-sectional distortion

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