6200 12TH DR SE Geotech Report 2022-10-25

Catholic Housing Services JN 16298 November 1, 2016 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 pits and borings conducted for this study encountered approximately 13 to 35 feet of loose to medium-dense soil, mostly unengineered fill soils at the ground surface of the site. These soils are not suitable to support building loads without the likelihood of extensive settlement. Therefore, we recommend that the building loads be transferred though these non-competent soils done into the very dense underlying soils using deep foundations. It is our opinion that the deep foundations could consist of driven pipe piles or drilled concrete piles. Information regarding both are included with this report. Another significant geotechnical engineering considerations for this project is the steep slope on the western side of the site that is approximately 25 feet in height. Although there no indications of instability, there is no development near the slope at this time. Based on the condition of the existing fill soil, it is our opinion that any significant development or structures for the project should be held back a distance that equates to an imaginary 2.5:1 (Horizontal:Vertical) slope measured up (eastward) from the base'of the steep slope; we believe that the site is very stable east of this line and has a safety factor that is suitable based on code. The area west of this line projection would not possess an adequate safety factor based on code, and has a potential for movement during events such as extreme precipitation or a large earthquake. Based on the information we have received, this line projection is about 10 feet east of the top of the slope. 111 Placing stormwater from the project is unsuitable from a geotechnical engineering standpoint because it would be discharged into the loose fill soil; because the fill is loose and variable, it the stormwater could cause significant settlement of the fill or destabilize the western steep slope. Therefore, we recommend that the infiltration of stormwater not be done for this project. In addition, no stormwater should be discharged near or on the slope. 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 is necessary to periodically maintain or modify temporary erosion control measures to address specific site and weather conditions. The drainage and/or waterproofing recommendations presented in this report are intended only to prevent active seepage from flowing through concrete walls or slabs. Even in the absence of active seepage into and beneath structures, water vapor can migrate through walls, slabs, and floors from the surrounding soil, and can even be transmitted from slabs and foundation walls due to the GEOTECH CONSULTANTS, INC.