5　Engineering Gedogical Investigation

5.1　General Requirements

5.1.1　Engineering gedogical investigations shall correspond respectively to different engineering design stages.A site selection investigation shall be carried out at the pre-feasibility study stage；a preliminary investigation shall be carried out at the prefeasibility study stage；a detailed investigation shall be carried out at the basic design stage；and，construction investigations shall be carried out at the detailed design and construction stages.

5.1.2　At the investigation stages before the construction，a rock mass quality classification shall be carried out，and at the construction investigation stage，the determined rock mass quality grades shall be verified and accordingly adjusted.