Wet Soil Mixing to Stabilize Highly Variable Subsurface Soil for the Reconstruction of Hemet Elementary School

摘要

Originally constructed 1927, Hemet Elementary School was closed in 2009 and demolished in 2015 as a result of continued long-term settlement and structural damage. The cause of the settlement was evaluated to be hydro-collapse of loose alluvial foundation soils that extend deeper than 50 feet below existing grades. The new Hemet Elementary School will be located on the same site. The primary geotechnical design issue for the new Hemet Elementary School is the potential for more than 20 inches of seismically-induced settlement due to the presence of the San Jacinto fault less than one mile from the site. To mitigate the seismic settlement potential, multiple foundation options were evaluated, including piles, vibro-stone columns (VSCs), and ground improvement using the deep mixing method (DMM). DMM was selected as the preferred alternative since it could reduce potential seismic settlement to acceptable levels and accelerate the overall reconstruction schedule. The DMM-stabilized ground allowed the proposed structures to be supported on conventional shallow foundations. This paper highlights the ground improvement design and implementation methods.