If the preliminary soil report indicates the presence of critically expansive soils or other soil problems which, if not corrected, would lead to structural defects, a soil investigation of each lot in the subdivision shall be prepared by a civil engineer who is registered by the state. The soil investigation shall recommend corrective action which is likely to prevent structural damage to each dwelling proposed to be constructed on the expansive soil. The report shall be filed with the Building Inspector and City Engineer.
(`67 Code, § 11-9-3)