Interaction of foundry sands with geosynthetics

Excess foundry sands from gray-iron casting are a mixture of sand, bentonite, and additives that can have properties desirable for structural fills and hydraulic barriers, depending on their bentonite content. To facilitate beneficial reuse of foundry sands, typical strength parameters need to be available so that designers can make comparisons with designs employing virgin earthen materials. To provide typical design parameters, a testing program was conducted to characterize the strength of foundry sands and their interaction with geosynthetics. Small-scale direct shear tests, large-scale multistage interface shear tests, and pullout tests were conducted using foundry sands with bentonite contents representing the range normally found in the casting industry and three geosynthetics (geotextile, geogrid, and geomembrane). The results indicate that foundry sands can be used effectively in geotechnical construction. Friction angles of the as-compacted foundry sands generally ranged between 39 degrees and 43 degrees, and the as-compacted cohesions ranged between 17 and 28 kPa. Drained friction angles were similar to as-compacted friction angles except at high bentonite content. Typical interface friction angles ranged between 25 degrees and 35 degrees, with efficiencies ranging between 0.5 and 0.9. Interaction coefficients from the pullout tests ranged between 0.2 and 1.7.