3535 RIVERFRONT BLVD Geotech Report 2023-02-22

September 24, 2018 IHWA Project No. 2015-061-21 I based on engineering judgment, our experience in the vicinity of the 3-Acre Park project and correlations with settlement plates elevation data collected from the site. Our analyses indicated an estimated settlement across the 3-Acre Park site of up to 4 inches due to 3 feet of grade I increase across the site. We estimated an additional 12 to 18 inches of settlement could occur as a result of construction of the restroom structure (assuming a 2,000 psf foundation bearing pressure). Due to these large magnitudes of anticipated settlement HWA recommended Iconstruction of a preload surcharge over the footprint of the proposed restroom structure to reduce future settlement. IPreload Surcharge Recommendations Preloading involves placing a specified amount of soil or weight over a given area and allowing I the weight to consolidate the underlying compressible soils prior to construction of the proposed improvements. Given the magnitude of anticipated settlement associated with the proposed improvements, HWA recommended a preload consisting of a 15-foot surcharge be constructed Iacross the general area of the restroom structure. The lateral extent of the recommended preload surcharge was limited by the presence of the utilities along Eclipse mill road and the CSO I overflow structure to the south of the site. HWA provided recommendations for preloading of the site in early 2016. KLB Construction Inc. constructed the preload with glacial till derived fill between June 14th and July 14th 2016. Six settlement plates were installed along the centerline of I the preload surcharge to monitor settlement throughout the preload period. HWA indicated that the preload would likely have to remain in place for approximately 9 to 12 months to achieve the desired effect. However, the actual preload duration would be determined through monitoring of the settlement plates. Preload Surcharge Monitoring IFrom June of 2016 to August of 2017, all six settlement plates were monitored on a biweekly to monthly basis. Settlement plate data has been provided to HWA, for evaluation, throughout this I time period. No settlement plate data was collected after August of 2017. A plot of settlement vs log time for each settlement plate is provided on Figure 16. As can be seen on Figure 16, the north end of the preload surcharge experienced less settlement than the south end of the preload I surcharge. We expect that this observed trend is due to the location of past debris stockpiles at the site. We expect that the north end of the preload surcharge area was covered by an undocumented debris stockpile sometime in the past, whereas, the south end of the preload area was not. HWA has evaluated the trend of each settlement plate to determine if primary consolidation is I completed. Given the magnitude of secondary settlement associated with the compressible organic soils, it is difficult to determine if primary consolidation is complete using the standard I log time vs settlement plots shown on Figure 16. However, when the data is plotted as square root time vs settlement the distinction between primary and secondary settlement becomes much more pronounced. Using Taylor's square root method, we were able to determine that all of the I Final Geotechnical Report-3-Acre Park.docx 13 HWA GeoSciences Inc.