Abstract: An exemplary method for measuring the impact resistance of polymeric film-based laminates involves a falling dart test using laminates that are essentially fully adhered to an inclined mortar block in emulation of stone impacts in backfill situations. Methods for protecting subgrade vertical walls from stone impacts in backfill operations involve the use of a four-layer laminate having an impact energy of at least 50 lb-ft.sup.2 /sec.sup.2 in accordance with a falling dart test using a mortar block inclined at an angle of 60.degree. from vertical. The film-based laminate, comprising a center film having a Young's modulus of at least 200,000 psi (ASTM D 882), is surprisingly discovered to have synergistic properties to provide an average impact energy, as determined in accordance with the 60.degree. impact test, which far exceeds the additive impact energy of the components and which reflects more accurately the performance of the laminate in the actual backfill situation.