Any structure has to be supported by a foundation. Geotechnical engineering involves such areas as foundation design, earthquake engineering, offshore structures, dam designs, tunneling, and highway subgrades design. Geotechnical engineers provide recommendations for the design of footings, raft foundations, piles and pile bents, piers, earth retaining structures, shoring, and the underpinnings of structures. They also design dams, solid waste landfills and wetland dewatering systems. They work closely with environmental engineers in the areas of solid waste management and groundwater protection.