Soil parameters’ numerical back analysis for comparison of driven pile’s capacity assessment methods

Abstract

The paper shows several methods of driven piles capacity assessment. The piling work consisted of driving around 10 000 prefabricated concrete piles for the indirect foundation of National Stadium’s located in Warsaw city center. A total number of 68 investigated piles was divided into three groups, depending on their length, because longer piles tend to be weaker, what is shown in the paper. Results of dynamic load test, CASE and CAPWAP limit capacity and piling reports provided by AARSLEFF company stood the basis for further analysis in this work. The given results of dynamic test were taken as the most reliable data to compare with other methods, as they gave surprisingly close values, while being nondependent. Large amount of displacement piles happened to impact existing soils’ mechanical properties. The difference in maximum resistance force was estimated, by carrying out a numerical back analysis with GEO5 software. The computation shows significant growth of internal friction angle, and compaction index which led to three times higher limit pile capacity. The extra compaction effect during pile driving should be considered, during the design process, both as positive for soil stiffness, and potential impediment for the contractor.