Charles County, MD
GTA performed a preliminary subsurface exploration for a planned mixed-use development at the site of an existing sand and gravel mine. As part of the mining operation, wash pond sediments, and other processed mining fines were deposited in several portions of the site. These materials are very soft in nature, and are prone to excessive consolidation settlement when loaded. The preliminary development plans included mixed-retail and townhouse developments in the areas of the wash pond sediments and mining fines. GTA performed a combination of SPT, CPT, and DMT soundings to evaluate the engineering characteristics of these soils and determine their potential impact on development. In addition to SPT/CPT explorations, and laboratory testing, the DMT soundings provided additional soil strength parameters to estimate the magnitude and rate of consolidation settlement. GTA worked with the project team to devise several options/methods for construction of structures in areas which are underlain by the wash pond sediments. Among these, “preloading” of the soft soils was considered as an alternative to a deep foundation system. Accurate estimation of the soil strength parameters will be vital to implement a cost-effective mitigation program.