ORCID Identifier(s)

0000-0003-0095-1597

Graduation Semester and Year

2019

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

Sahadat Hossain

Abstract

Failure of civil engineering infrastructures due to insufficient bearing and shearing capacity of the unsuitable foundation soil is a common problem in the area of North Texas which results in significant maintenance issues for the Texas Department of Transportation (TxDOT). The major concerns regarding construction over such foundation soil includes excessive total and differential settlement of footing resulting in bearing capacity failure and sliding failure of the Mechanically Stabilized Earth (MSE) retaining structure due to inadequate shear resistance. The most common technique followed by TxDOT to counter such problem is to remove and replace the existing soil with appropriate fill material. However, the excessive cost associated with the remove and replace method led to numerous research to develop sustainable alternative solution. A noble approach to improve the problematic soil could be the use of Recycled Plastic Pin (RPP). RPP is a lightweight material, produced from recycled plastics and other waste materials. It is more durable against chemical and biological degradation compared to other alternatives (e.g. concrete pile or timber pile). The current study summarizes the development of an alternative sustainable solution to the bearing capacity failure by excessive settlement of the structures and sliding failure due to lack of sufficient shear resistant at the base of MSE wall. RPPs provide with additional support to the structures (e.g. embankments) when driven into the weak foundation soil in addition to a layer of geogrid. Geogrid acts as load transfer device which ensures transfer of fill load to the RPP by soil arching effect. The RPP reinforcement in combination to geosynthetic helps to reduce both total and differential settlement of the structure by improving the weak foundation soil. Three identical 6ft. height embankment loading test sections of 15 ft. x 15 ft. were constructed in phase – I; one as control section (without any RPP) while the other two sections were instrumented with 10 ft. long RPP of 4 in. x 4 in. and 6 in. x 6 in. sizes respectively. Based on the field monitoring results, settlement for the control section was found to be about 2.01 inches, while due to the use of 4 in. x 4 in. and 6 in. x 6 in. RPP reinforcement, a reduction in settlement of about 60% and 70% compared to the control section was noticed respectively. As a part of phase –II construction and monitoring, one control section and one 4 in. x 4 in. RPP reinforced section was constructed, and the result was found to be in good agreement with the phase – I observation. The study also endeavored to focus on increasing shear resistance of the base of MSE wall constructed on stiff foundation soil against sliding failure by utilizing RPP similar to a shear key. The research included construction of two identical MSE wall test sections of 24 ft. long and loaded with a backfill soil height of 4 ft.; one had a foundation reinforced with 10 ft. long 4 in. x 4 in. RPP at 3 ft. c/c spacing while the other section served as a control section. The performance monitoring result showed significant lateral movement for the control section (3.8 inches), while almost no movement was observed for the reinforced section. For further evaluation, an increased backfill loading height of 5 ft. showed a lateral movement of 1.76 inches for the control section which was found to be reduced by about 80% (0.29 inches) for the RPP reinforced section. The performance of the test sections was further evaluated in numerical modeling using finite element software PLAXIS 2D and a parametric study was conducted using the calibrated model to evaluate effect of RPP size, length and spacing for both cases. The parametric study indicated that the both vertical and lateral deformation decreases with larger RPP size and narrower RPP spacing. Based on the field monitoring results and FEM analysis, RPPs are expected to be an efficient and cost effective reinforcing material for ground improvement.

Keywords

Sustainability, Ground improvement, Bearing capacity, Shear resistance, MSE retaining structure, Recycled plastic pins

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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