Interaction investigation of the free-standing foundations with sandy basement under rapid additional loading

The influence of fast additional loading on the force interaction of foundations with the subgrade soil has not been investigated sufficiently for the development of foundation calculation methods. The study of the interaction peculiarities between foundations and the subgrade soil is necessary for the foundation calculation methods development to improve the calculation of frame buildings for progressive collapse, the calculation of new foundations when buildings are transplanted on them in the reconstruction process, and to assess the safety of buildings foundations subjected to fast loading. In order to reveal the peculiarities of force interaction between foundations and the subgrade soil, the authors conducted experimental studies in a soil flume with reinforced concrete and metal models of foundations under different modes of slow loading and fast additional loading. The studies experimentally revealed such peculiarities of the fast loading effect on the force interaction of freestanding foundations with the subgrade soil as a decrease in the bending bearing capacity of the foundations, changes in the value of settlement and the shape of the normal subgrade stresses. The main reason for the decrease in the bending load-bearing capacity of foundations under fast additional loading is the relative increase in normal subgrade stresses under the boundary zones of foundations, which leads to an increase in the bending moment in the design cross-sections of the structure. Based on the research results, the authors have proposed a methodology for the calculated epure determination of the normal subgrade stresses under the foundation base, taking into account the level of slow loading and fast loading, based on the improved Fuss-Winkler model with variable modulus of foundation bed rigidity. The paper compares the calculated data according to the proposed methodology and the experimental values, showing a good precision of results.