ORCID Identifier(s)

0000-0002-7696-4717

Graduation Semester and Year

2021

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

Sahadat MD Hossain

Abstract

Mechanically Stabilized Earth (MSE) walls have been widely used as retaining structures due to their flexible nature, a better tolerance against differential settlement, and many other factors. However, external stability problems of MSE walls have been an issue in North Texas over decades. Lateral displacement of the wall occurs, giving rise to sliding failure, when there is insufficient shear strength at the wall base to produce adequate frictional resistance. Such failures can cause significant maintenance, repair, and cost implications for the state department of transportation. Furthermore, MSE walls also undergo global failure due to weak soil conditions along with high lateral pressures. Typical recommended solutions consist of either increasing the weight of the wall, increasing the length of the heel slab, or using wall anchors and helical tiebacks, which are all expensive. On the other hand, incorporating a shear key at the wall base has proven to completely restrict the lateral sliding of walls. However, for MSE retaining structures, incorporating a concrete shear key is challenging due to its expensive cost and rigid nature, which undermines the most important feature of an MSE wall which is the flexible nature of its base. A possible solution could be using recycled plastic pins (RPP) as shear keys. The success of RPPs in providing sufficient lateral support to sliding soil mass in slopes could be imitated in an MSE wall to deliver the required lateral resistance against sliding. As the RPPs are made from recycled plastics, they are highly cost-saving when compared to concrete. They are comparatively flexible in nature and require almost no maintenance. The main objective of the study is to investigate the effectiveness of RPPs in increasing the lateral stability of MSE wall system. Four test sections were constructed, out of which three were reinforced with 10 ft. long RPPs at the wall base. One test section was left unreinforced as a control section. The three test sections were reinforced with 4x4 inches RPP at 3 ft. c/c, 4x4 inches RPP at 2 ft. c/c, and 6x6 inches RPP at 3 ft. c/c. The RPPs inside the wall were extended 2 ft. above the foundation into the reinforced zone. Two rows of RPPs were installed fully flushed to the ground surface in front of the test wall. Vertical and horizontal inclinometer casings along with earth pressure plates were used to monitor the performance of the test sections over a period of almost two years. The field results showed that the lateral resistance of the RPP reinforced sections increased by 75% to 89% in comparison to the control section. The control section failed about 8 months after construction, while the RPP reinforced sections were stable. The vertical settlement of the RPP reinforced sections decreased by 48% to 68% in comparison to the control section, while the maximum lateral earth pressure reduced by 66% to 76% in the RPP reinforced sections. Finite element studies in PLAXIS 2D showed that larger cross-section and closer spacing of RPPs provided better lateral resistance. Lateral displacement and lateral stress reduction prediction models were developed using the modeling results. Based on the performance monitoring results and further analyses, it can be concluded that the RPPs can be effectively used as shear keys in MSE walls. They can be incorporated at the wall base during design for improving the lateral resistance of MSE walls.

Keywords

MSE walls, Base sliding, Lateral displacement, Lateral pressure, Recycled plastic pin, Shear keys, FE modeling, Prediction models, Sustainable

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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