Use of Quarry Byproduct (No. 10 Screenings) to Improve Subgrade Soil

Poor subgrade often requires in-place stabilization or removal by excavation and replacement with suitable material. Chemical stabilization with cement or lime is a common remediation practice. This study investigated the use of No. 10 screenings, a quarry byproduct finer than the 4.75-mm (No. 4) Sieve, as a means to improve poor subgrade conditions. Three sources of screenings with two marginal soil types at various mixture rates were studied in the laboratory to determine an appropriate field application. The engineering improvements were determined by the California bearing ratio (CBR), density, plasticity reduction, drainage characteristics, and resilient modulus. At a mix rate of 50% by weight, increased density and reduced plasticity were observed. But the resilient modulus improvement depended on the moisture condition. When subgrade is not saturated, amendment with screenings could provide a benefit in terms of higher resilient modulus at the equilibrium moisture condition, which is usually lower for amended soil and depends on the depth of the groundwater table (GWT).