Client: Confidential Location: Unionville, Connecticut Geotechnical Investigation for Supermarket Building As part of an overall geotechnical investigation for a large new supermarket building, GeoInsight, Inc. (GeoInsight) assisted an engineering firm with a stability assessment for an existing mortared fieldstone retaining wall located along the Farmington River. The new site development included increasing site grades for new parking areas and these grade changes could not be accommodated without the construction of a new retaining wall. The new retaining was positioned such that it would impart a lateral load to the existing fieldstone retaining wall. GeoInsight was retained to evaluate the affects of the new construction on the existing wall and devise solutions to protect the integrity of the existing wall. Assessing Subsurface Soil Conditions and Construction Scenario Recommendations GeoInsight used historic soil boring data and supplemental test pit excavation data to assess the subsurface soils underlying both the existing and proposed retaining walls. The investigation data identified extensive and variable fill materials. Based upon the lateral and vertical position of the new wall compared to the existing fieldstone retaining wall, slope stability modeling parameters were developed and numerous global stability scenarios performed. Multiple construction scenarios were recommended depending upon the proximity of the new wall to the existing wall, and the character of the soils underlying the new wall. Recommendations Summary Recommendations included: decreasing the base elevation of the new wall to decrease the load on the existing wall; adding geosynthetic reinforcement to the base of the new wall and in its upper layers to improve the uniformity of forces acting on surrounding soils and minimize over-excavation needed; developing minimum setbacks for the new construction compared to the existing wall; and carefully monitoring the condition of the existing wall during construction.

GEOTECHNICAL EVALUATION Retaining Wall Stability Analysis

Case History No. 44