Abstract: A panel assembly to be used in an RCC dam structure, or the like, includes a precast concrete panel, a geomembrane liner extending over the full face of the panel and a geotextile sheet backing on the liner directly attached to the panel. The liner seals the panel against water leakage in a manner that allows shifting of the dam structure without placing undue stress on the liner or the interconnecting sealing strips. The geotextile sheet is preferably fabricated of a mat of non-woven polyester fibers and the geomembrane liner is preferably polyvinylchloride. The geotextile sheet is attached by hardened concrete slurry integral with the panel. Once the panel assembly is connected to adjacent panel assemblies by the sealing strip to form the dam structure, stress concentrations are relieved in the event that the panels shift for any reason.