Foundation of the Building on Short Concrete Piles in a Thin Layer of Non-Cohesive Soils

Abstract

The paper presents measurable benefits resulting from optimization of selection, appropriate for local ground-water conditions, type of foundation of a high residential and service building with ten residential floors, two service and two underground ones. The original design solution expected the replacement of up to 8.5 m p.p.t. soft cohesive soils (including organic ones) on gravel mixed with sands. The foundation of the high building is planned as a direct foundation on depth of 6.9 m below ground surface on a foundation slab under a residential part and the service part on a foundation framework on the prepared substitute-subsoil. After a detailed analysis of the data, the contractor reported the possibility of engineering optimization initially the pre-engineering adopted in the project foundation, significantly reducing the investment costs. It was proposed to change the direct foundation on indirect on short foundation piles with a diameter of 600 mm, the base of which is located in the subsoil, shallowly located layer of gravel mixed with coarse sands, about 2,0 m thick. Below the granular soilslayer there is at least several dozen meter thick layer of Krakowiec clays. Numerical simulations of the foundation were made, from which it appears that due to the settlement of the building, it is more advantageous to form the piles shallowly in the non-cohesive soils layer rather than deeper. An additional benefit of the adopted solution - foundation of the building on concrete piles - allowed to reduce the trench by 1.5 m and to protect the sheet piles with only one level of struts inside the trench. The settlements values predicted in the numerical model, have been verified by monitoring, which was carried out during construction as well as during the five-year operation of the building. The real settlements of the building reached the level of 45.8% of settlements values of the numerical model, of which 37.5% of real settlements occurred at the stage of completion shell of the building. The discrepancy between the real and model values of settlements may result from the underestimation of the soil medium parameters in the numerical model.