3322 BROADWAY COMPASS HEALTH 2025-10-03

Compass Health June 26, 2019 J N 19178 Page 3 CONCLUSIONS AND RECOMMENDATIONS GENERAL THIS SECTION CONTAINS A SUMMARY OF OUR STUDY AND FINDINGS FOR THE PURPOSES OF A GENERAL OVERVIEW ONLY. MORE SPECIFIC RECOMMENDATIONS AND CONCLUSIONS ARE CONTAINED IN THE REMAINDER OF THIS REPORT. ANY PARTY RELYING ON THIS REPORT SHOULD READ THE ENTIRE DOCUMENT. The test borings conducted for this study encountered dense and very dense glacial till at shallow depths on the east side of the site, and at depths of 9 to 19 feet on the western side of the site beneath a layer of fill that was likely placed as basement backfill. Considering the proposed excavation depths, the glacial till that will very likely be exposed at, or near the base of the excavation. The underlying very dense glacial till is very suitable to support building loads, and conventional footings can be used for the building's foundation provided they bear on the exposed dense and very dense soil. However, the glacial soils are silty and thus are moisture sensitive; they can become easily disturbed if they are wet at the time of foundation construction. If the foundation subgrade is wet at the time of foundation construction, a several -inch -thick layer of imported, angular, clean crushed rock should be placed over the exposed subgrades as protection. Based on the soil types encountered during drilling, excavation inclinations of no steeper than a 1:1 (Horizontal:Vertical) in the upper, loose fill and native soil, and a 9.75:1 (H:V) in the underlying very dense glacial till are appropriate for the project. It does not appear that proposed excavations can be kept within the property boundaries based on these excavation parameters. The next alternative would be to obtain excavation easements/agreements to extend the excavations into the adjacent rights -of -way. If these cannot be obtained, then excavation shoring would be necessary. We anticipate that cantilevered soldier piles will be the most appropriate option along the eastern half of the site considering the depth of excavation. However, due to the deeper planned excavation on the western half of the site, tieback anchors may need to be utilized to provide additional support to the excavation shoring. Easements into the adjacent rights -of -way will be needed if anchors are used. An expanded discussion can be found in the Shoring section of this report. The presence of the tall, existing, perimeter site walls and basement foundation walls will increase the difficulty of installing the shoring. Due to their locations, these walls may need to be left in place during shoring installation, and demolished as the mass excavation progresses so that lagging can be installed as the walls are demolished. The project design and construction teams should closely consider the most efficient option for this issue while conforming to the recommendations presented in this report. The glacial till that underlies the site is cemented, very dense, has a high fines content, and is essentially impervious. For these reasons, it is not feasible from a geotechnical engineering standpoint to utilize stormwater infiltration for this project. Due to the silty nature of these soils, we do not recommend that the onsite soils be re -used as structural fill beneath the buildings, or behind engineered retaining walls. The high fines content of the glacial till will increase the difficulty in achieving adequate compaction, and could cause undue construction delays related to the increased time and labor needed to sufficiently compact the material. If structural fill is needed for the project, imported clean, angular rock should be utilized. We can provide further recommendations for structural fill if needed. GEOTECH CONSULTANTS, INC.