Firstly the Site is defined at clause 11.2 and the 'boundaries of the site' is stated in Contract Data Part 1, although there is usually cross referencing between the two (wording of 'above and below' etc). Notwithstanding any planning and access rights, which should be the responsibility of the Employer, your main concern is whether the worksite is within the Working Areas.
You further mention the GBR Report, which is a useful document for defining any allocation of risk, although may not ultimately be the definitive baseline, depending on how such allocation of risk is actually worded and whether it sensibly dovetails with the assessment of such matters under clause 60.1 (12), 60.2 and 60.3.
Where you are working outside the confines of the GBR Report then any assessment of 'physical conditions' would revert back to the contract clauses, although if any principles have been established by the GBR report you could apply these, where appropriate, to determine such matters.
You further mention the GBR Report, which is a useful document for defining any allocation of risk, although may not ultimately be the definitive baseline, depending on how such allocation of risk is actually worded and whether it sensibly dovetails with the assessment of such matters under clause 60.1 (12), 60.2 and 60.3.
Where you are working outside the confines of the GBR Report then any assessment of 'physical conditions' would revert back to the contract clauses, although if any principles have been established by the GBR report you could apply these, where appropriate, to determine such matters.