Overcoming Grouting Difficulties during Retaining Wall Stabilization

This paper presents the wall-stabilization design and implementation for a 165-linear-meter masonry and concrete gravity-type retaining wall flanking the west perimeter of a 29,825-square-meter parcel in the Bronx, New York. This paper will discuss the results of static and dynamic stability analyses performed for the pre- and post-excavation phases for the proposed 91-meter-wide excavation extending up to 4.3 meters below the toe of the retaining wall. The wall stabilization consisted of over 74 inclined drilled and grouted anchor dowels, and 55 tiebacks drilled and grouted to the underlying mica-schist bedrock. Three overlapping rows of jet grout columns were used as the foundation stabilization for the existing retaining wall. The jet grout wall served three purposes: (1) as underpinning and excavation support for the removal of contaminated site soils, (2) as a permanent hydraulic barrier, and (3) as resistance against a deep-seated failure within the thick clay layer at the site. The originally designed jet grout wall had unexpected negative effects on the existing retaining wall. The jet grouting program was modified while the observational method was employed to minimize wall movements during installation. This paper discusses the diagnostic methods used to determine the cause of retaining-wall movement; implementation of a remedial ground-improvement program; modification to the jet grout installation procedure; and ultimate performance of the jet grout wall.