2320 106TH ST SW Geotech Report 2022-10-25

October 14, 2015 Project No.T-6116-2 oundwater seepage should be anticipated within excavations during the wet winter season. We anticipate that the volume of water and rate of flow into the excavation will be relatively minor and are not expected to impact the stability of the excavations when completed, as described. Conventional sump pumping procedures, along with a system of collection trenches, if necessary should be capable of maintaining a relative dry excavation for construction purposes. The above information is provided solely for the benefit of the owner and other design consultants, and should not be construed to imply that Terra Associates, Inc. assumes responsibility for job site safety. It is understood that job site safety is the sole responsibility of the project contractor. Shoring The detention vault is located within seven feet of the southern property line. Based on the drawings, the excavation depth to achieve the foundation elevation of 540.5 is between 9 and 19 feet. These depths cannot be achieved using conventional excavation techniques unless an excavation easement with the adjacent property owners is obtained. If the excavation easement cannot be obtained, the excavation will need to use temporary shoring. Based on the limited height, a conventional cantilevered soldier pile shoring with timber lagging would be the most cost effective shoring system, in our opinion. Recommended soil parameters for design of the shoring are shown on attached Figure 3. Drilling obstructions, such as boulders, may also be encountered in the native soils. Caving or collapse of opened drilled shafts may occur. The contractor must be prepared to case the —illed shafts, as needed,to prevent collapse and maintain a relatively clean,open hole. 5.4 Foundations The building may be supported on conventional spread footings bearing on competent native soils or on structural fill placed above competent native soils. Foundation sub_ :de should be prepared as recommended in Section 5.2 of this report. Perimeter foundations exposed to the weather should bear at a minimum depth of 18 inches below final exterior grades. Interior foundations can be constructed at any convenient depth below the floor slab. Foundations can be dimensioned for a net allowable bearing capacity of 3,000 pounds per square foot(psf). For short-term loads, such as wind and seismic, a one-third increase in this allowable capacity can be used. With structural loading as anticipated and this bearing stress applied,estimated total settlements are less than one-inch. For designing foundations to resist lateral loads, a base friction coefficient of 0.4 can be used. Passive earth pressure acting on the sides of the footings may also be considered. We recommend calculating this lateral resistance using an equivalent fluid weight of 350 pounds per cubic foot(pcf). We recommend not including the upper 12 inches of soil in this computation because they can be affected by weather or disturbed by future grading activity. This value assumes the foundations will be constructed neat against competent native soil or backfilled with structural fill, as described in Section 5.2 of this report. The recommended values include a safety factor of 1.5. Page No. 8