Exploratory grouting of a subsurface detention/infiltration system NCKRI Symposium 2: Proceedings of the Thirteenth Multidisciplinary Conference on Sinkholes and the Engineering and Environmental Impacts of Karst

pg(s) 53-59 In 2007, a geotechnical investigation was performed for a student center at a New Jersey college. Even after reviewing the results of that study, the Municipality recommended incorporating a subsurface detention/ infiltration system below the parking lot adjacent to the student center. The project area is underlain by solution-prone Beekmantown Formation dolomites. Mapped just to the northwest is the conformable solution-prone Allentown Dolomite. The Allentown likely dips shallowly below the Beekmantown. This local suite of carbonate bedrock lies within a fault-bounded block of these Cambro-Ordovician rocks. Sinkholes formed beneath and adjacent to the basin and parking area and remediation was attempted by others. Repairs reportedly included the removal of basin fill materials, low-mobility grouting and stone backfill placed in subsurface voids. Shortly thereafter, more sinkholes opened, some within the area remediated. Technical problems at the site included a lack of reliable subsurface information; the basin functioning in a manner that allowed infiltration; having the likely need to vary the grout and delivery procedures based upon encountered conditions and probe hole locations in relation to the basin; the need to remediate solution features trending beyond the original area of interest; and the possibility of unrecognized solution features outside the area of interest and below the student center. These potential problems were brought to the attention of the current college administration. They quickly recognized the concerns and requested a different geotechnical firm to develop specifications for remediation and to help in choosing a suitable contractor. To address the concerns, site-mixed grout using cement, water, mason sand and bentonite, in varying proportions, delivered under varying pressures, and using two different grout mixing methods was deemed the most appropriate remedial alternate. During the field operations, liaison and cooperation between the grouting engineers, the grout crew, and the college administration and maintenance personnel provided useful insight and support. The various procedures used and the bases for their use are discussed in this paper. A total of 41 probe holes were drilled where a total of 157 m³ (205 cubic yards) of grout was placed. Voids as large as 5½ m (18 feet) in vertical extent were encountered and a maximum of 18.6 m³ (24.3 cubic yards) of grout were pumped into any single probe hole. Subsurface connection between probe holes was evidenced as grout was seen to travel at least 3 m (10 feet) laterally. Open Access - Permission by Publisher See Extended description for more information