The present invention relates to a gravity based structure 5 with a topside 2 on at least one hollow concrete platform leg 1 with a platform leg wall and a circular cross section. The at least one platform leg, includes an upper leg portion (4) cut off from a lower leg portion 3. The lower leg portion 3 has an upper sloped cut surface 10 inclined at an angle in the range of 1°-10° off a horizontal axis. The upper leg portion 4 has an upper leg sloped cut surface inclined at the same angle as the lower leg sloped cut surface 10 of the lower leg portion 3 whereby the angles are complementary, the sloped cut surfaces forming an inner and an outer obtuse cone with a common vertical longitudinal axis. Furthermore, the invention relates to method of forming a conical cut through a concrete platform leg of a GBS.