6300 MERRILL CREEK PKY BASE FILE 2018-01-01 MF Import

Quadrant JN 97092 August 13, 1997 Page 3 strength and bearing capacity, and is very suitable to use as struct�.ual fill provided it is placed in periods of dry weather and when its moisture condition is near opi;mum. Based on our recent observations, it appears that the on-site, native soil is generaily near its optimum moisture condition, and lhe placement of structural fill is proceeding suitably. Our personnel is making daily visits to ensure the placement of structural fill is being performed per our recommendations. As noted in the subsurface section of this report, some loose fill soil �vas revealed in the area of Test Pit 1. Because a building is proposed in this area, we recommend that the loose fill be removed and replaced with adequately compacted structurai fill. The removed fill can be used as structural fill in that area or other areas on the site if it can be compacted. We understand that mass grading and utility instaliations are proposed to be done before the normally-wet period begins in the Puget Sound region (usually in October). Work on the site buildings will subsequently proceed following this time. It is important that if the building slabs or driveway and parking lot pavements are not in place by the wet period that at least 12 inches of pit- run gravel be placed over the silly, glacial till subgrades to protect the subgrade from disturbance. The glaciai till soil is very sensitive to moisture and becomes very difficult to work on if wet. A geotextile filter fabric should be placed over subgrade prior to pavement subgrade because it can be easily disturbed due to equipment traffic. Tt�e use of the fabric and pit-run gravel could be delayed or possibly eliminated if the pavement subgrade was done next summer. In addition, asphalt-treated base (ATB) could be used in lieu of crushed rock as pavement subbase to provide a suitable winter cover in the pavement :,reas. We understand that some structural fill will be placed within 25 feet of steep slope at the site in pavement areas and berms for detention ponds. Because of the stability of the native, glacial till soil and structural fill that consists of glacial till, it is our opinion that the use of structural fill is suitable within 25 feet of the steep slope. However, it is important that structural fill that is placed on slopes be "keyed in' at the base of the fill, and successive, level lifts of compacted fill be installed. In the berm areas, we recommend that topsoil and alI weathered soils be removed down to the dense, glacial till soil before any structural fill is placed. Conventional Foundations The proposed structure can be supported on conventional continuous and spread footings bearing on undisturbed, native soil or on structural fill placed above this competent, native soil. See the 12ter sub-section entitled General Earthwork and Structurai Fill for recommendations regarding the placement and compaction of structural fill beneath structures. We recomrtiend that continuous and individual spread footings have minimum widihs of 12 and 16 inches, respectively. They should be bottomed at least 12 inches below the lowest adjacent finish ground surtace for frost protection. The local building codes should be reviewed to determine if different footing widths or embedment depths are required. Where the building pads are to be raised with structural fill above the native, stripped ground, the first layer of structural fill sh�uld be placed outside �f the proposed building envelepe a distance equal to the needed height of the structural fi!I. Footing subgrades must be cleaned of loose or disturbed soil prior to pouring concrete. Depending upon site and equipment constraints, this may require rernoving the disturbed sail by hand. GEOTECH CONSULTANTS,INC.