Diagnostic and Analysis of Specific Soil with Ground Water Level and Plain Concrete Slab Interaction

This article deals with the selected task soil and structure interaction in case of a thin concrete slab and increased groundwater level. The soil and structure interaction is a complex task applied in cases when necessary to sufficiently consider the proposal's safety and economy. The particular topic dealt with is the performed specific experiment of a concrete slab on the subsoil that is subsequently simulated using 3D computing models. The performed experiment is a concrete slab with dimensions 2000 x 2000 mm. The concrete slab thickness was 150 mm. Computing models are based on the Finite Element Method and non-linear analyses. The specificity of the experiment is that it simulates extreme foundation conditions when the groundwater level almost reaches the foundation base. The experiment confirmed the significant effect of the groundwater level, the reduction of the overall bearing capacity of the slab and the rapid disturbance and collapse of the slab. Numerical models also described very well the occurrence of cracks and slab collapse. The results were in good agreement with the experimental testing. Major specificities include that the measuring and load test records are supplemented with an acoustic emission to identify concrete cracks. Findings from acoustic emission make it possible to describe the formation of cracks at a time when cracks are not visible and to verify the subsequent behaviour of the slab. The research task presented also includes detail laboratory tests of the concrete used. Laboratory tests include tests of compressive strength, modulus of elasticity and tensile strength. Tensile strength was determined based on splitting tensile strength and bending tensile strength tests. In the case of bending tensile strength, test variants were performed, which differed in the test configuration (three-point bending test, four-point bending test), the size of the test specimens and the notch in the middle of their span. Numerical modelling of the slab's interaction with the subsoil is also preceded by modelling a small structural element, a beam with reinforcement. Numerical modelling itself is also based on the use of the concept identification of fracture mechanics parameters by laboratory tests.