10200 25TH AVE SE Geotech Report 2018-01-02 MF Import

. i Propose�Modernimtion and ddditions m Su6surfare Exp[oration, Geolagic Hazards, Eisenhower b9iddle Schoo! ar.a;eotechnical Engineering Repon Everett, Washington DesiRn Recommendations tvhen the temporary excavation slopes are exposed, flatter slope angles will be required. As is rypicai with earthwork operations, some sloughing and raveling may occur and cut slopes may have to be adjusted in the field. In addition, WISHA/OSHA regulations should be followed at all times. We should be allowed to review excavation cut slopes greater than 8 feet in height. Permanent cut and/or fill slopes should be no steeper .han 2H:IV. The on-site soils contain a high percentage of fine-grained material, which makes them moisture-sensitive and subject to disturbance when wet. The contractor must use care during site preparation and excavation operation� so that the underlying soils ate not sofrened. If disturbance occurs, the softened soils should be remove� and the area brought to g:ade with structural fill. To the extent that it is possible, we recommend that the existing paving along the north portion of the site be used for construction staging. If the existing pavement cannot be used for construction staging, we recommend that crushed rock fill be considered in construction staging areas to form a working surface. If crushed rock is to be used for the access and staging areas, it should be underlain by engineering stabilization fabric such as Mirafi 500X or equivalent to reduc� the potential of fine-grained materials pumping up through the rock and turning the area to mud. The fabric will also aid in supporting construction equipment, thus reducing the amount of crushed roc�c required. We recommend that at least 10 inches of rock be placed over the fabric; however, due to the variable nature of the near-surface soils and differences in wheel loads, this thickness may have [o be adjusted by the contractor in the field. 9.0 STRUCTUR�L FILL Structural fill will be necessary to establish desired grades and to provide a uniform subgrade below new floor slabs and pavement areas. All references to structural fill in this report refer to subgrade preparation, fill type, and placement and compaction of materials as discussed in i this section. If a percentage of compaction is specified under another section of this report, the � vafue given in that section should be used. After stripping, excavation, and any required overexcavat:on has been performed to the satisfaction of the geotechnical engineer/engineering geologist, the upper 12 incLes of esposed ground should be recompacted to 90 percent of the modified Proctor maximum density using ASTM:D 1557 as the stantiard or to a tirm unyieiding condition. If the sabgrade cuntains too much moisture, adequate recompaction may be difficult or impossible to obtain and should probabfy not be attempted. [� lieu of recompaction, the area to receive fill should be blanketed with washed rock or quarry spalls to act as a capillary Lreak between the new fill and the wet suberade. Where the erposed eround remains soft and further overexcava:ion is impractical, Jmumn• 33, 200d ,ISSOCIATED E:RTH SClENCES, INC. �5 .NT,(d-REOi:J3aJ-Pru��Rti_�J;?,9iRFitYP-t�.A" PBQC IZ 1' a