Civil Engineering ETDs

Publication Date

Fall 12-15-2017

Abstract

Drilled shafts have proven to be cost-effective, excellent performing, deep foundation systems where large loads and lateral resistance are major factors. The available design methods that are recommended by FHWA (2010) for drilled shafts are mostly empirical and are developed based on generalized data which sometimes can be conservative for a particular soil. The main objective of this study is to develop a design methodology for estimating the side resistance of an axially loaded drilled shaft based on the current and the unique properties of the soil. The objective was met through using the discrete element method (DEM) to investigate the behavior of soil at particulate level.

Discrete Element Modeling (DEM) is an explicit numerical model that approximates the mechanical behavior of an assembly of particles. DEM is a way to simulate the movement of granular matter through a series of calculations that trace the movement of individual particles. For the study of macro scale behavior of granular material around a drilled shaft, a modified DEM program was developed and entitled as ELLIPSE3D-shaft. For that purpose, several algorithms were developed and implemented in the modified program. Three new contact detection methods of ellipsoidal particles with a cylindrical wall were developed. The modified DEM program was parallelized with Open MP implementation to improve the computing time for numerical analysis. The modified program was used to study the soil-shaft interaction.

The numerical results revealed that the side resistance is dependent on the void ratio of the soil. A general trend of side resistance and void ratio or relative density of soil was found with the results obtained from the DEM experiments. The new design method was evaluated by comparing its performance against the most commonly used design methods.

Finally, two new drilled shaft side resistance design models were proposed using the critical state approach of soil. According to critical state soil mechanics, soil with a mineralogy has two unique properties which are invariant with initial conditions and other soil properties, critical state friction angle and critical state line (CSL). A correlation of the side resistance, critical state friction angle, peak friction angle, and vertical stress of soil was proposed in the first model. A correlation of side resistance and state parameter was subsequently proposed in the second model.

Keywords

numerical method, discrete element method, drilled shaft, DEM, cylindrical DEM

Document Type

Dissertation

Language

English

Degree Name

Civil Engineering

Level of Degree

Doctoral

Department Name

Civil Engineering

First Committee Member (Chair)

Dr. Tang-Tat Ng

Second Committee Member

Dr. Rafiqul A. Tarefder

Third Committee Member

Dr. Arup Kanti Maji

Fourth Committee Member

Dr. Yu-Lin Shen

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