2701 ROCKEFELLER AVE NIMBUS Geotech Report 2023-12-29

Opportunity Zone Development LLC June 6, 2019 JN 19152 Page 3 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 to very dense silty send (glacial till) below depths of 2.5 to 5 feet beneath the existing ground surface. Very dense sand (glacial outwash) was encountered beneath the glacial till at depths of 15 to 26 feet below grade from west to east across the site. Conventional footings that bear directly on these dense to very dense, glacially -compressed soils are well -suited to as the foundation of the proposed building. However, It will be important that great care be taken during excavation to maintain the high bearing capacity of these soils. Excavation using a toothed bucket usually leaves several inches of disturbed soils. The loosened soll must be entirely scraped out of the base of the footing excavations. This should be accomplished with a flat -bladed bucket, a grade bar that Is dragged with the bucket, or by hand - shoveling the loose soil out of the excavation. A major geotechnical consideration for the project will be the depth of the excavation within close proximity of the property lines. As previously discussed, we understand excavations shoring 20 to 30 feet are needed near property lines. Thus, excavation shoring Is needed. The most suitable type of excavation shoring Is largely dependent on a number of factors under the contractor's control. Therefore, we suggest a shoring contractor be Included in the early discussions with the structural engineer designing the shoring to determine the most appropriate system. Shoring options include soldier piles and tie -back anchors, or soil nails; the soll-nail shoring is the most cost effective. Considering the excavation depths and dense soils conditions, it appears that soil -nail shoring may be used for the project; however, the underlying, poody-graded, outwash sands have a very low fines content which could cause minor sloughing when the 4. to 6400t vertical cut slopes are completed prior to installing each horizontal row of nails. It may be necessary to use sloped cuts/berms in the underlying sands instead of vertical cuts to install the soil nails. The clean sands may affect the soil nail borehole drilling techniques used as well. More discussion of this situation is given in the Shoring section of this report. Again, it is important that a shoring contractor and designer be made aware of this sand soil and are consulted regarding soil -nail shoring. The building on the southern adjacent property, which appears to have little to no setback from the subject site's southern property line, will bean important design consideration for both the proposed building's southern shoring wall and permanent southern foundation wall. The neighboring building has two stories above shallow concrete footings at approximately the elevation of the eastern adjacent alley. The neighboring building is of brick construction over a concrete foundation. It will be very important that the total vertical deflection of the southern shoring wall (and the southern adjacent building's northern perimeter footing) be limited to one -half -inch or less during the excavation and foundation construction of this project. This may require a more rigid shoring system than soil nails (such as tied -back soldier piles) be used along the southern perimeter of the excavation. Again, it ls important that a shoring contractor and designer be made aware of this situation. Regardless of the shoring system used, monitoring the deflection of the neighboring building's foundations will be very Important during excavation. Preliminary design recommendations for both soil nails and tied -back soldier pile shoring systems have been included in the Shoring section of this report. The neighboring building will also apply a surcharge load onto the southern temporary shoring wall and the proposed onsite building's permanent southern aEOTECHCONSULTANTS.INC.