NEC3 ECC Op A. Proposed change to works information

C tendered for the main project and at the same time was appointed under a PSC to develop the civils and frame. Upon contract award C would be responsible for the whole of the design. The PSC incl a retaining wall separating an upper and lower plateau. Wall described as brickwork but subject to development of design details. The plans for the retaining wall were incl in PSC but not the main works WI. Between tender and contracts a VE schedule was agreed with changes the retaining wall from brick to gabions. No design was proposed other than a designers intent based on a previous job. C appointed. Upon contract award The WI included a solitary plan with a simple bold line and a note stating retaining wall. The top and bottom levers were noted. The PSC and VE schedule do not seem to be included in the WI but are annexed to the contract. Since award the C issued a design submission which omits the wall in place of a shallower and larger embankment. This cuts into the flatter grasses play areas. The design submission was reject by the PM as none compliant but offered to consider as a proposed change if there was an acceptable quote. The C disagrees stating it’s his risk item and by benefit belongs to him. PM disagrees and refuses to accept the design and suggested a potential defect. Thoughts?