Effects of installation method on the behavior of driven piles and piles bored using a manual auger in tropical collapsible soil

Understanding the effects of installation method on a deep foundation is fundamental for analyzing load test results and improving foundation design based on soil profile characteristics. This study analyzed 40 load-displacement curves of driven piles and piles bored using a manual auger, measured 20 cm in diameter and 3 or 6 m in length. Piles were constructed at the Experimental Field of Geotechnical Engineering, State University of Londrina. The soil is classified as silty clay, exhibits collapsible behavior up to a depth of 7 m, and has low resistance in surface layers, according to the results of particle size analysis and the standard penetration test. Load tests were carried out under static conditions using mixed loads. Natural moisture conditions were used in the test, and pre-wetted conditions in the retest. For three bored piles, these conditions were reversed. Pre-wetted conditions resulted in loss of failure load, highlighting the collapsible nature of the soil. Conversely, piles tested under natural moisture conditions exhibited higher failure load. Load-displacement curves showed shapes consistent with the expected for the analyzed pile types. This consistency supports the discussion on the effect of the construction method on pile behavior, demonstrating that soil removal during excavation for pile boring mobilizes side friction, whereas, in driven piles, soil compaction enhances toe resistance, particularly for piles constructed by concrete pounding as compared with concrete casting.