Is the risk register a contract document if referred to in the contract particulars? I appreciate the relevant events/ matters account for risk allocation but what if a risk register was included that identified, say contaminated materials, dewatering, hazardous materials as a contractors risk?
In JCT contracts the risk of unexpected ground conditions sits with the contractor as there are no Relevant Events / Matters associated with this risk.
By referring to the risk register in the Contract Particulars then it is part of the Agreement which in turn makes it one of the Contract Documents. However the concept of a risk register is not dealt with in JCT contracts therefore the inclusion of one without any special conditions associated with it could create ambiguity as to it’s function and purpose. However in your case it appears to reflect the natural position of the contract in any case.
One small chink of light for you may be that you may have a claim for misrepresentation if the Employer made representations as to the site conditions in the Employer’s Requirements.