Modeling Pile Setup for Closed-Ended Pipe Piles Driven in Cohesive Soils

Date of Award

2023

Degree Name

Ph.D. in Materials Engineering

Department

Department of Chemical and Materials Engineering

Advisor/Chair

Ömer Bilgin

Abstract

This research study focuses on modeling pile setup for closed-ended pipe piles (CEP) driven in cohesive soils. Pile setup can be defined as an increase in pile resistance over time after installation due to an increase in soil resistance. Pile setup was rarely considered in the Ohio Department of Transportation, ODOT, standard driven pile design procedures. If significant pile driving losses occur during pile installation, either pile driving is halted for a short period of time to determine whether pile setup will occur, or pile length is increased to achieve the required ultimate bearing value. This would negatively affect not only the piling and projects costs, but also the project schedule. Thus, incorporating pile setup into the design stage can lead to saving in pile quantity and avoid construction delays, as well as help to avoid change orders. In order to better predict pile driving losses during design stage, this research project aimed to develop more reliable pile setup models. To fulfill the objectives of this research, a database was established to collect data from existing projects in the State of Ohio. In addition, several field projects were selected to investigate the pile setup phenomenon. Comprehensive statistical analyses were conducted to investigate the mechanism of pile setup. Effect of the construction activities on the resistance of adjacent piles was also investigated by performing dynamic and static load tests on CEP piles driven in a fine-grained soil profile. The cone penetration tests (CPT) were performed at three locations at the project sites to gain more knowledge of the soil layers. Data obtained from piezometer measurements showed an increase in water pressure at the site during pile driving, which in turn reduced the effective soil strength. This investigation revealed that pile driving and restrikes should be scheduled such that the effect of construction activities on load tests results will be avoided or minimized. This could be implemented by conducting the dynamic load test on the first pile driven at a site and avoiding any construction activities until after the time of the restrike. The effect of construction activities on the resistances of adjacent piles was observed at distances of seven times the pile diameter. The results also indicated that silty clay soil exhibits higher setup than other soil types encountered at the project site. Side and tip resistances obtained from the static load tests were compared with estimates made using well-known CPT-based pile design methods. Overall, these methods achieved satisfactory predictions of the side and tip resistances with some exceptions. Multiple variable regression analyses performed by using the dataset compiled showed that the resistance mobilized at the end of pile installation, time passed after the installation, pile shaft surface area, and average silt content along the pile length are the most influential parameters in predicting the total pile resistance of driven piles. Multiple regression analyses were also carried out by using the collected database of side resistance demonstrated that initial side resistance, time passed since installation, soil volume displaced, clay and water contents along the pile length are the significant variables on predicting pile side resistance. New models for total and side resistances were developed to predict pile setup for CEP piles driven in fine-grained soils using gene expression programming (GEP). The results showed that the proposed models of pile total and side resistances can predict pile setup quite well. An attempt to evaluate the setup, for both total and side resistances, with time using the database has been made. The total and side setup ratios were also analyzed based on various restrike times. Since the database contains piles with multiple restrikes, another analysis was carried out to evaluate the ultimate total and side setup ratios. One of the main goals of this research was to evaluate pile side setup for individual layers using the unit side resistance with the aid of available dynamic load test data. Effect of soil properties on setup ratios for individual soil layers was also investigated. The results revealed that the recommended setup factor for the pile total and side setup ratios of 2.0 and 3.0, respectively, would cover almost all the piles' long term behavior. The results also showed that side friction setup factors for the piles driven in fine-grained Ohio soils are about 50 to 100% more than the factors currently recommended in the ODOT Bridge Design Manual.

Keywords

Civil Engineering, Pile setup, Pile resistance, Dynamic load test, Static load test, CAPWAP, Gene Expression Programming, Soil properties, Pile properties

Rights Statement

Copyright © 2023, author

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