K+A performed a geotechnical engineering study and provided design phase geotechnical consultation throughout the design of the Module 4 West parking structure at Denver International Airport (DIA). The proposed parking structure is located just south of the existing Module 3 West parking structure, which is located west of the south end of the existing Terminal. The structure consists of a 5-level reinforced concrete structure with a footprint of approximately 140,000 square feet.

Prior to construction, the site of the proposed structure consisted of a hillside sloping down to the west away from the existing Level 4 West access road. As a result of that condition, significant excavation was required for the structure, and a retaining wall up to about 45 feet in height was required to provide the grade separation between the existing Level 4 roadway and Level 1 of the new structure. The project also required horizontal realignment of the existing Level 1 and Level 2 access roads, with a new bridge provided from the Level 2 access road into the west side of the new module.

The geotechnical study included 15 borings drilled throughout the proposed structure footprint as well as other borings along the alignments of proposed roadways and retaining walls. In general, the subsurface conditions beneath the structure consisted of high to very high swelling claystone bedrock. As a result of the close proximity of the main east retaining wall to the existing Level 4 road, a top-down construction technique utilizing soil nails and/or tiebacks was necessary. The geotechnical exploration for this system included coring of the claystone bedrock and laboratory shear strength testing to develop design parameters for this specialized wall system. A complicating factor is due to its high plasticity, the claystone bedrock is not generally considered to be a good material for a tied-back type of wall system and additional precautions were necessary.