As captioned, to my understanding 'Bedrock level' is the top of solid rock at a site/region. 'Rock head Level' is a level at solid rock where Grade III (Moderately Decomposed Rock) or better (Slightly Decomposed to Fresh) with Total Core Recovery equals to or greater than 85%. And also 'Rock head' is a competent strata as required in a project. Any advice from geotechnical engineers/engineering geologists will be greatly appreciated!!