Method and arrangement for supporting a structure. Beneath the structure there is arranged a cohesion structure, which transfers the structure load through shaft adhesion to surrounding ground. The cohesion structure includes an expansion element having a wall of flexible material, inside which there is injected along an injecting pipe unreacted polymer, which reacts in the expansion element. The expansion element with the reacted polymer therein constitutes the cohesion pillar. The polymer is water absorbing material and the wall of the expansion element is of water-permeable material, whereby the cohesion pillar is arranged to absorb water from the surrounding ground so as to improve the adhesion between the expansion element and the surrounding ground.