Field investigations concerning screw piles and columns have been carried out for the “Bearing capacity and work in the soil of screw piles” research project, financed by the Polish Ministry of Science and Higher Education – project No N N506 369234. The tests of three instrumented screw piles were conducted together with CPTU tests and measurements of pile installation parameters (especially torque). The objectives of field investigations and the entire research project include discovering how screw piles work in the soil, locating and describing the correlations between CPTU results and rotation resistance during pile auger installation and next establishing correlations between CPTU results, rotation resistance and the bearing capacity of this kind of piles. The paper describes the investigation procedure and the basic results of tests carried out in the first of a series of sites.

Predicting the Q–s settlement characteristics of piles is an important element in the designing of pile foundations. The most reliable method in evaluating pile-soil interaction is the static load test, preferably performed with instrumentation for measuring shaft and pile base resistances. This, however, is a mostly post-implementation test. In the design phase, prediction methods are needed, in which numerical simulations play an increasingly popular role. This article proposes a procedure for numerically modeling the interaction of screw displacement piles with soil using the ZSoil 2D FEM program. The procedure takes into account technological characteristics of this type of pile, such as the process of soil expansion during the screwing-in of the auger and the pressure of concrete mix after pile concreting. They significantly affect the soil stress state, which is a key parameter for the pile load capacity. Geotechnical parameters of the subsoil were adopted from CPTU probing and laboratory tests. Due to the physical complexity, a constitutive soil model “Hardening Soil” (HS) was used in the analyses. The modeling procedure was calibrated on the basis of the static load test results of several instrumented piles, which were carried out as part of the “DPDT-Auger” research project. As a result of these calibrations, generalized recommendations were derived for an entire single pile modeling process with the axisymmetric system of ZSoil program. These can be useful in the reliable FEM prediction of the Q–s characteristics for screw displacement piles for practical engineering purposes.