ORCID Identifier(s)

0000-0001-9174-7246

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

Construction of embankment over soft foundation soils is incredibly a challenging task due to the risk of bearing failure and excessive settlement of foundation soil. Most of the available conventional methods for addressing these problems are either expensive or time-consuming or both. Therefore, research has been striving to develop a sustainable alternative to the current conventional methods. A noble approach to improve the soft foundation soil could be the use of Recycled Plastic Pins (RPP) in combination with geosynthetics. The load transfer efficiency of a geosynthetic-reinforced and RPP supported embankment is influenced by interactions among embankment fill, geosynthetics, and foundation soil. The objective of this study is to investigate the effectiveness of Recycled Plastic Pins (RPP) for controlling ground settlement of soft foundation soil. Two field test sections (6 m × 7.5 m) were constructed over soft soil; one was left unreinforced to use it as a control section, and the other section was reinforced with RPPs. A Load Transfer Platform (LTP), composed of Recycled Crushed Concrete Aggregate (RCCA), sandwiched between two geogrid layers, was placed above the RPPs for transferring load from embankment onto the RPPs. Vertical pressures, settlements, and pore water pressures were monitored. After 260 days, a maximum settlement of 52 mm was observed for the control section, whereas, for the reinforced section, it was 23 mm. Excess pore pressure dissipated faster in the control section. The measured data indicated that the RPP supported a significant percentage of the embankment load. The in-situ measurements have proven the effectiveness of RPPs in combination with LTP in reducing settlement. In the analytical study, an integrated method based on force equilibrium, soil arching, and stress distribution is developed to calculate differential settlement and stresses on RPPs and adjacent soil in between RPPs. The load transfer mechanism accounted for soil arching and tensioned membrane effects were comprehensively studied. The proposed analytical method was validated with measured results from a field study. Furthermore, the method was also compared with other field study and design methods. A parametric study is also conducted to observe the effects of influential factors such as RPP size, spacing, tensile stiffness of geosynthetics, and friction angle of aggregates used in LTP. The results indicate that more efficiency of load transfer can be achieved with larger size and closer spacing of RPPs. The tensile stiffness of geosynthetic also has a greater influence on the load transfer mechanism. Furthermore, a numerical investigation was conducted using finite element software PLAXIS 2D. The model was calibrated against the field measured data in the context of settlement and pressure variations. The performance of the RPP supported embankment was evaluated with maximum consolidation settlement, differential settlement, and soil arching effect. An extensive parametric study was performed to evaluate the effect of RPP size, and spacing, load transfer platform, stiffness of geosynthetics, and shear strength of embankment fill. The present method can be applied for any embankment construction over soft soil, bridge approaches, and widening of a highway where the foundation soil is unsuitable for regular construction.

Keywords

Recycled plastic pins, Embankment, Load transfer platform, Settlement, Soft soil, Consolidation, Arching effect, Numerical modeling

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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