After reviewing the dynamic interaction between the soil and structure, it is visible that the piles improve the dynamic characteristics of the weak ground base. A short review of the opportunities toreduce seismic effects on the building project has been made; respectively it decreasedthe construction cost. The thesis about the increase of the soil stiffness after the construction of the pile foundation has been set out. The principles for evaluation of characteristics improvement and the ways for their experimental determination have been exposed. The outcome highlighted that following the construction of the pile foundation, the improved soil characteristics should be measured again and the results obtained should be used as an input to the dynamic analysis of the entire designed structure.