Helical pile behavior in a silty soil at varying thermal and hydraulic conditions

Nawaz, Kamran

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https://hdl.handle.net/2142/117608 Copy

Description

Title

Helical pile behavior in a silty soil at varying thermal and hydraulic conditions

Author(s)

Nawaz, Kamran

Issue Date

2022-12-09

Director of Research (if dissertation) or Advisor (if thesis)

Baser, Tugce

Department of Study

Civil & Environmental Eng

Discipline

Civil Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Helical piles
• Frozen soil
• Temperature
• Bonny silt

Abstract

This thesis focuses on the axial behavior of single- and double-helix helical piles installed in ice-poor unsaturated Bonny Silt layers. A physical modeling approach was conducted to develop an experimental setup for estimating the uplift capacity of helical piles in permafrost in laboratory conditions. A series of tensile load tests were performed to predict the uplift capacity of piles. Physically meaningful relationships were established between the results from pile load tests and their corresponding ambient environmental conditions. The effect of degree of saturation, embedment depth, and temperature variation on the pull-out capacity and adfreeze bond were investigated. Laboratory experiments were used to determine what mechanism causes the variability of helical pile capacity in Bonny Silt. Physical scale models of single and double helix helical piles were embedded in a silty layer inside a test tank. Pull-out tests were conducted for the frozen and unfrozen conditions at different temperatures and volumetric water contents. The water contents were measured using a capacitance sensor embedded in the silt layer. This experimental campaign consists of 30 tests at varying soil temperatures, four degrees of saturation (Sr), and embedment depth ratio. The displacement rate (0.5 mm/min) was applied and kept constant throughout the testing campaign to sustain a uniform loading condition. The results from the pull-out test revealed that strain softening was the main stress-strain behavior observed for the pile in frozen conditions, while strain hardening was prevalent for the piles tested at room temperature. The initial degree of saturation significantly affected the pull-out capacity of the piles. The pile capacity in frozen conditions was higher for higher Sr and decreased with increasing Sr for the unfrozen conditions. The adfreeze strength was predicted from the load-displacement curves for the first time in this study. As expected, the adfreeze strength was observed to be higher for piles with higher Sr. When the embedment/depth ratio decreased, the piles exhibited lower strength for both single and double helix helical piles. The results from the experimental campaign and main conclusions drawn from this thesis directly contribute to the helical pile design in a changing subsurface in cold regions and will be instrumental in developing sustainable built environments in which the impact of climate change is considered at-large scales.

Graduation Semester

2022-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Kamran Nawaz

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