Quality management of base and subgrade materials with seismic methods.

The acceptance criteria for compacted geomaterials (such as base and subgrade) are typically based on adequate in-place density. Unfortunately, the design of a given project is based on engineering parameters, such as strength and stiffness. A procedure based on seismic techniques to measure the modulus layer by layer shortly after placement is presented. The major advantage of seismic methods is that similar results are anticipated from the field and laboratory tests as long as the material is tested under comparable conditions. This unique feature of seismic methods in material characterization is particularly significant in quality control and quality assurance for ground treatment before, during, and after construction. Simplified field and laboratory tests are suggested that can be performed and interpreted rapidly and nondestructively so that problem materials can be identified before construction and any problems during the construction process can be adjusted. The field and laboratory methods are incorporated so the results can be readily reconciled without any scaling or simplifying assumptions. The simplified laboratory tests can be used to develop the ranges of acceptable properties for a given material. Nondestructive field tests can be performed to determine whether the contractor has achieved the minimum specified stiffness. A concept that uses seismic nondestructive testing technology to evaluate compacted materials and describes the equipment and setups developed for implementing the technology in both field and laboratory tests is presented. The methods have shown promise as practical tools for use by the highway and construction industries. Currently, the procedure is being implemented on a trial basis by the Texas Department of Transportation.