Observations/Finding

On the above date, an AS Engineering and Consulting, LLC (ASEC) representative visited the project site at the contractor’s request to observe grading and remedial earthwork activities at the west embankment of the detention pond. The grading contractor was Mathis.

Unsuitable, saturated soils were stripped and undercut within the embankment area. The subgrade was undercut to approximately Elevation 1132, where groundwater was encountered within approximately 2 feet of the exposed surface and seepage was observed.

ASEC recommended placement of a thickened soil layer over the saturated subgrade using onsite undercut residual soils. The contractor placed approximately 3 to 4 feet of fill over the affected areas in general accordance with this recommendation. A D6 track dozer was used to place and spread the material while rubber-tired equipment was kept off the saturated subgrade.

Initial compaction was performed using the track dozer, followed by additional compaction with a Bomag vibratory sheepsfoot roller operated in static mode. Fill performance was further evaluated by observing off-road haul truck traffic during placement, which served as proofrolling. No rutting or deflection was observed under traffic.

Based on observed performance, the stabilized area was considered acceptable for placement of an additional 8 to 12 inches of loose fill, to be compacted using the vibratory sheepsfoot roller operated in vibratory mode.

TESTING AND SAMPLING

In-place density testing was performed at approximately Elevations 1136 and 1137 using a Troxler Nuclear Density Gauge, Model 3430 (Serial No. 91643).
Two bag samples of the fill material were obtained and submitted to the laboratory for moisture-density relationship (Proctor) testing. Laboratory results are pending.

Based on field observations and proofrolling performance, the contractor was advised that placement of compacted fill may continue pending receipt of Proctor results.

RECOMMENDATIONS

Due to the potential for precipitation, ASEC recommended that the exposed fill surface be sealed at the end of the workday by tracking with an off-road dump truck.

Saturated subgrade conditions ,stabilized with fill placement and tested.