3530 COLBY AVE COCOON HOUSE Geotech Report 2022-10-25

Cocoon House JN 16422 November 3, 2016 Page 3 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 generally encountered medium-dense to dense, native silty sand at depths of 2.5 below the existing ground surface. These soils are well-suited to support the proposed building load. Conventional footing foundations are suitable for the building foundation provided they are placed directly on these competent soils, or on structural fill placed that is placed on top of the competent soils. However, there are two situations of note with respect to the footing foundations. One is that there was up to approximately 7 feet of loose, unsuitable fill revealed in Test Boring 3; it is possible that this fill is limited because it is the backfill of an existing or former utility line. In any case, it will need to be removed and replaced with structural fill. Secondly, based on our observations, the existing church has a basement floor with an elevation 4 to 8 feet below the current site grade. Therefore, to construct the building as planned where the basement exists, the void space caused by the existing basement should either be backfilled with structural fill up to the design footing subgrade elevation of the new building, or the footings placed on competent ground below the basement slab. If structural fill is placed, the slab can be left, but it will need to be broken into pieces before the fill is placed. In addition, it will be important that the existing foundations and any loose fill soils that were used to backfill around the exterior of the existing basement walls are removed and the underlying competent bearing soils are exposed prior to constructing footings and/or placing any structural fill. The General Earthwork and Structural Fill section should be reviewed for additional recommendations. We recommend structural fill for the project consist of granular material. Due to the limited planned excavations for the project, we anticipate the structural fill will need to be imported to the site. Appropriate structural fill could consist of gravelly sand with a low fines content, crushed rock or other crushed material. The native silty sand and sand soils could potentially be used as structural fill provided they can be placed and compacted near their optimum moisture content. Any existing fill soils onsite should not be used as structural fill. We recommend a qualified geotechnical engineering firm personnel observe the placement and compaction of approved structural fill below any new foundations. Temporary excavations to remove the existing foundations should be feasible using temporary open cut slopes. Temporary cut slopes in the dense silty sand can be excavated with a maximum inclination of 0.75:1 (Horizontal:Vertical). However, loose fill soils which are likely to be encountered surrounding the existing foundation walls and were encountered in Boring 3 west of the existing building should not be excavated at an inclination steeper than 1:1 (Horizontal:Vertical). If the excavations cannot be completed with these inclinations within the property, temporary excavation easements into the adjacent right-of-ways will be necessary. If temporary excavation easements cannot be obtained, temporary shoring will be needed. The erosion control measures needed during the site development will depend heavily on the weather conditions that are encountered. We anticipate that a silt fence will be needed around the downslope sides of any cleared areas. Existing pavements, ground cover, and landscaping should be left in place wherever possible to minimize the amount of exposed soil. Rocked staging areas and construction access roads should be provided to reduce the amount of soil or mud carried off the property by trucks and equipment. Wherever possible, the access roads should follow the alignment of planned pavements. Trucks should not be allowed to drive off of the rock-covered areas. Cut slopes and soil stockpiles should be covered with plastic during wet weather. Following clearing or rough grading, it may be necessary to mulch or hydroseed bare areas that will not be immediately covered with landscaping or an impervious surface. On most construction projects, it GEOTECH CONSULTANTS, INC.