Abstract: A light weight structural composite panel adapted for use in a vertical orientation in an underground worker protection system is disclosed. The panel comprises first and second fiberglass reinforced resin matrix facing layers and a balsa-containing core means, weights less than about 5.5 to about 6 lbs. per square foot, and when supported in a vertical plane adjacent an excavation wall, is able to withstand an extended load in Type C solid (OSHA, CFR 1926) of at least 592 pounds per square foot with a minimum safety factor of 3:1. Methods of preparing the panels and methods of assembling the panels into excavation support systems are also disclosed.

Abstract: A light weight structural composite comprised of a cellular core having high dynamic load-bearing properties and a fiber reinforced resinous skin, the panel further comprised of an internally disposed elastomeric membrane which covers the core and acts to disperse shock waves created from impact loads.

Abstract: A light weight structural composite comprised of a cellular core having high dynamic load-bearing properties and a fiber reinforced resinous skin on all edges of the core and on the top and bottom surfaces thereof. The cellular core may comprise an array of balsa wood blocks, the skin may comprise a fiberglass reinforced epoxy or polyester resin, and the core and skin may be formed into a monolithic composite which is particularly suitable for use as a high strength to weight ratio ground opening cover.