Full-Scale Field Study of Instrumented Under-Reamed Piles in Clay

The prediction of the pile-bearing capacity of an under-reamed pile is a very complex problem, specifically including local construction practices and installation effects. This paper describes a detailed study of full-scale under-reamed piles. The study includes installation and instrumentation of piles, load tests, and subsequent exhumation of constructed pile shafts. The exhumation is carried out to shed light on local construction practices, bulb formation, shaft mobilization, and end bearing. Two under-reamed piles were installed in similar soil conditions, employing local construction practices. Geotechnical investigations were conducted at the experimental site to get a better understanding of the soil condition around the test piles. Piles were instrumented using embedded-type strain gauges to understand the load transfer of the pile. An innovative approach of simultaneously identifying the shaft resistance and end bearing was adopted by conducting the load testing using bidirectional static load testing. The results of full-scale load testing tests show that the formation of the bulb is a practical problem, and a better construction approach is required to form a pile-shape matching theoretical dimensions. It also demonstrated that the bidirectional load testing approach is a very useful tool to directly determine the end bearing resistance and shaft resistance. The exhumation-constructed piles suggest that the shape of the bulb is not uniform and does not match the theoretical dimensions. Load test results also reveal poor pile toe conditions at the base, thereby affecting the end-bearing resistance significantly.