Method of construction of bored-injection piles with increased bearing capacityfor foundations in seismic areas

The development of methods for the construction of foundations for buildings and structures using bored-injection piles allows expanding the scope of their application in seismic areas, as well as in complex and especially complex engineering-geological conditions. In this article, bored-injection piles are understood as piles formed in boreholes by injecting fine-grained concrete mixture under pressure through a hollow rod with a perforated drill bit at the end. The disadvantage of such piles in sandy clay soils is the limited bearing capacity of their upper part for the action of horizontal seismic loads and limited crack resistance of the reinforced concrete body. This is explained by the absence of a spatial rigid reinforcement cage or continuous external reinforcement in the pile. The role of reinforcement in these bored-injection piles is performed by a small-diameter (up to 103 mm) hollow metal rod located in the center of the cross-section. In this case, the upper section of the pile does not work effectively in resisting the reinforced concrete section to horizontal seismic loads. The proposed bored-injection piles differ from the known ones in that a reinforcing element made of a hollow metal pipe with a diameter of 0.3-0.4 meters is made in their upper part. To connect the hollow metal pipe with the underlying small-diameter metal rod, a screw-on transition coupling with a diameter equal to the diameter of the hollow metal section to be connected above is used. After installation, the hollow pipe is filled with concrete, and reinforcement bars are placed inside to subsequently form rigid connections with the body of the grillage or foundation slab of the building. This reduces bending deformations of the pile and achieves the required load-bearing capacity both in terms of material and soil during earthquakes.