Soil resistance predictions from pile dynamics

Observations made during impact driving are widely used to predict the static bearing capacity of piles. The results often do not agree with static load tests due to a lack of knowledge of hammer energy, cushion characteristics, set per blow and other factors. Recent developments in electronics have made it possible to make accurate records of force and acceleration at the pile top during impact driving. Such records, which last only a matter of milliseconds, will be used herein to predict soil resistance effects on the pile. Previous work done on this project by a group at Case Western Reserve University reported the use of force and acceleration records in a simplified model to predict static bearing capacity (4,5,6,11). These results were based on impact records which were taken after a setup period so that strength changes due to soil remolding or pore water pressure dissipation were included. The present work extends the application of the force and acceleration records to the calculation of the distribution of soil resistance along the pile. It also shows how the records are used to predict the magnitude of dynamic resistance that the soil applies to the pile, an important factor in choosing efficient hammer characteristics. A method for obtaining a more accurate simplified prediction of total static bearing capacity is also presented. It should be emphasized that the aforementioned predictions are all made from measurements at the pile top only. The work is correlated by presentation of results for 24 pile tests which include construction static load tests as well as specially instrumented load test piles.