Graduation Semester and Year

2016

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

Ali Abolmaali

Abstract

The main goal of this research was to gain an in-depth understanding of the behavior of buried large-diameter pipes with controlled low-strength material (CLSM). Design equations were developed based on extensive parametric studies that aimed for an optimized design for designers in industry. Both experimental and numerical methods were espoused in the investigating procedure. The pipe-soil structure characteristics of the experimental analysis were: (a) steel pipe diameter of 108 in., (b) steel pipe thickness of 0.47 in., (c) mortar liner applied at the inner surface of the pipe with thickness of 0.5 +1/6 in., (d) CLSM applied around the pipe at a depth of 70% of the pipe’s diameter, (e) selected compacted soil applied at a depth of pipe’s diameter, and (f) compacted native soil with overall depth of 6ft. applied until the ground level. The staged construction method was applied, which means that the application of each part was done in a specific order. The stages of the construction were: (a) pipe placement, (b) CLSM applied at a depth of 30% of pipe’s diameter (OD), (c) CLSM applied at a depth of 70% OD, (d) compacted select fill layer applied 1 ft. above the pipe’s crown, and (e) consecutive compacted soil layers of 12 in. depth until the ground level. Experimental measurements were conducted at the site to measure the deflection of the pipe during the construction stages. Two methods were applied: MOP-119 and video laser profiler (VLP) method. The MOP-119 is a method based on the ASCE Committee on Buried Flexible (Steel) Pipe Load Stability Criteria and Design of the Pipeline Division. The laser profiler method is based on a laser ring projected at the inner surface of the pipe. Due to physical obstacles inside the pipe, for this research, the VLP was modified to the photo laser profiler (PLP) method to bypass the issues raised. A Finite Element Model (FEM) was developed to mimic the experimental conditions of the pipe tested. The geometrical dimensions, boundary conditions, material properties, and construction stages were all applied based on the site conditions. A model-change algorithm was used for an accurate representation of the staged construction method. Geometry, material, and contact nonlinearities were implemented. A Newton-Raphson algorithm was used for the model convergence. Overall, 28 sections were analyzed with the FEA, and the results for the deflection at springline and invert were compared with the experimental data. The material properties of the CLSM were investigated in the Civil Engineering Laboratory (CELB) at the University of Texas at Arlington. Compression, flexure, and triaxial material tests were conducted based on ASTM D4832, C31, and D 4767, respectively. A material law was developed based on the test results. Unique design equations were developed for large-diameter steel pipes with CSLM. A total of 3500 models were run, and a regression analysis was conducted. The dependent variables were horizontal and vertical deflection, moment, thrust, and shear of the pipe; while the independent variables were pipe diameter, pipe thickness, CLSM layer height, backfill material used above the CLSM layer, trench width, and trench wall stiffness.

Keywords

Buried large diameter steel pipes, Steel pipes, Staged construction, Pipe deflection experimental measurements, MOP_119, Laser profiler, Finite element analysis, Controlled low strength material, Material properties, Compression test, Split cylinder test, Confined triaxial test, Inverse analysis, Multivariate adaptive regression splines, Multilinear regression analysis

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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