McMahon & Mann drilled test borings throughout the proposed high school addition footprint and found a deposit of loose sand that, if left untreated, would require large footings due to the low allowable bearing pressure. We recommended a program to densify the loose sand to increase the allowable bearing pressure and improve liquefaction resistance.

We designed a program to improve the loose sand deposit by using a heavy vibratory roller. The first step was to build a working platform of crushed stone on the subgrade and to place settlement platforms on the subgrade to measure the response of the loose sand from the vibrations.

Once the working platform was in place, the contractor made repeated passes over the subgrade with the vibratory roller while McMahon & Mann measured the elevation of the settlement platforms. The contractor continued operating the vibratory roller over the working platform until the monitoring data from the settlement platforms showed no additional settlement to the subgrade surface.