Method for founding of a building-or plant-construction and apparatus for the use of the method

A method for laying a foundation for an existing building structure, said method comprising the steps of:

• excavating a space under an existing foundation;
• removing an upper part of an existing foundation pile after excavation to provide a carrier surface on a remaining sub-foundation pile;
• establishing a core between the carrier surface on the remaining sub-foundation pile and a carrier surface on the existing foundation by means of a cylinder;
• wherein the core between the carrier surface on the existing foundation and the carrier surface of the sub-foundation pile is a cast core;
• introducing to said cylinder a fluid for establishing the cast core formed of a curable casting material, the curable casting material being supplied to said cylinder under pressure;
• filling the cylinder with the curable casting material under pressure so that pressure of the fluid is established in the cylinder until a top piston and a bottom piston housed in said cylinder are situated in respective support positions, and curing the casting material, wherein the cylinder is arranged between the carrier surface on the sub-foundation pile and the carrier surface on the existing foundation with said top piston being directed towards the carrier surface on the existing foundation and said bottom piston being directed towards the carrier surface on the sub-foundation pile, so that when a fluid under pressure is let into the cylinder, the cylinder is filled with the fluid under pressure until the top piston is in contact with the carrier surface on the existing foundation and until the bottom piston is in contact with the carrier surface on the sub-foundation pile;
• said pressure established in the cylinder being greater than the gravitational pressure of the building structure on the sub-foundation pile so that the sub-foundation pile is able to assimilate such pressure without sinking.