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 (2). The cohesion structure includes an expansion element (6) having a wall of flexible material, inside which there is injected along an injecting pipe (7) unreacted polymer (8), which reacts in the expansion element (6). The expansion element (6) with the reacted polymer (8) therein constitutes the cohesion pillar (5). The polymer (8) is water absorbing material and the wall of the expansion element (6) is of water-permeable material, whereby the cohesion pillar (5) is arranged to absorb water from the surrounding ground (2) so as to improve the adhesion between the expansion element (6) and the surrounding ground (2).