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Subsidence Investigation Mathew/ Aley Rental Property Claim No. 223968 BCI Project No. 03-15564 November 2007 Page 10 5.0 REMEDIAL MEASURES 5.1 Compaction Grouting A program of subsurface compaction grouting is recommended to stabilize the Mathew/ Aley Rental Property against further sinkhole or karst-related settlement. The intent of the grouting is to stabilize the raveled and loose soil zones that may underlie the house and to seal and fill the karst-related fractures and/or cavities in the underlying limestone bedrock surface. The recommended grouting program should consist of a series of vertical and angled grout injection points around the perimeter of the house. A low slump grout (3 to 5 inches) should be utilized to ensure effective treatment of the loose soil zone(s) and reduce migration of grout beyond the affected areas. In conjunction with the grouting, the collapse feature under the front porch should be filled with flowable fill (sand-cement mixture). Sixteen (16) vertical and angled grout injection points are recommended at the locations shown in Figure 6. The grout casings should be installed into firm limestone bedrock, which is estimated to occur at depths ranging from 50 to 75 feet below grade, based on the three SPT borings completed at the site. Due to the variable limestone bedrock, in-filled soil zones, and local zones of soft rock, appropriate drilling equipment should be utilized to ensure the grout injection pipes are installed to the required depths. During grout point installation, care should also be taken to identify the soil materials to ensure the grout pipes are not installed to depths significantly below the limestone surface, and should be limited to a maximum of 10 feet into the limestone formation. The angled drill points should be able to reach the projection of the foundation line at a depth of 25 to 30 feet. We note that additional, intermediate grout points may be necessary if high grout volumes are recorded during the grouting program. In order to improve stabilization of the shallow sandy soils, use of progressively lower injection pressures and smaller diameter grout pipe are recommended at shallow depths above 10 feet. During mobilization and prior to grouting, particular care should be taken to identify subsurface obstructions at the site that could potentially be damaged (underground utilities, septic tanks, etc.). A copy of our recommended specifications for the compaction grouting program and a contractor bidding form are included as Appendix E. Important provisions of the specifications include the following: . Installation of grout casings in a manner to prevent grout leakage and/or uplift of casing during grout injection. The contractors bidding the project should provide a description of their method of installing the grout casings. . Injection of a low-slump grout ranging from 3 to 5 inches, as measured at the hopper. Grout slumps as high as 5 to 7 inches may be acceptable during initial grout injection to fill and seal the limestone bedrock surface, as well as in areas of obvious soil cavities if grout takes are low. . Control of grout pumping rates and quantities, such that for each 2-foot injection interval, injected grout quantities are limited to a maximum of 10 cubic yards (excluding obvious soil cavities). The recommended grouting pumping rate is I to 5 cubic feet per minute. . Reduction of grouting pressures at shallower depths is recommended in order to stabilize any shallow loose soil zones. Use of smaller diameter grouting pipe (0.75-inch minimum diameter) may help to control grout injection pressures and flow . Monitoring to avoid uplift ofthe house and adjacent structures during grouting.