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

j Proposed Modernization nnd Addirloi�s to Subsurface Exploration, Geologic Hazardr, Eisenhower Middle School and Geotechniad Engineering RepoR Evei�rr, WarhinRron Des`gn Recommendations foundations at a given point, the overexcavation lateral limit should extend 3 feet beyond the building footprint up to a maximum of 4 feet. Removal of existing fills should not undermine or compromise the support soils of existing founuations or slab-on-grade. Once suitable native soils have been reached, strucmral fill can be placed to restore the desired building pad elevation. Fill material should be selected and placed in accordance with recommendations in the Structural Fill section of this report. If pin piles are to be used for foundation support in areas underlain by deeper existing fill, and the slab is co be supported on underlying soil, the building pad should be overexcavated to approximately 2 feet below slab subgrade. The overexcavated surface should be proof-rolled or compacted. Any soft, loose, or yielding areas should be excavated to expose firm, unyielding soils. The subgrade should then be ,:ompacted to at least 95 percent of tne modified . Proctor maximum dry densiry as determined by the ASTM:D 1557 test procedure. Two feet of strucmral fill to support the proposed slab-on-grade can then be placed. Where pin piles are to be used for foundatio❑ support and where the foundation slab is to be designed as a strucmral slab and supported on the piles, no subgrade preparation beneath the pile-supported structure will be required. Recommendations for pin piles are presented in the Foundations section of this report. If GeopiersT°' or rock trenches will be used to support foundations in areas underlain by deeper existing fiil, the building pad should be excavated to approxicrately 2 feet below slab subgrade. The surface should be proof-rolled or compacted. Any soft, loose, or yielding areas should be excavated to expose firm, unyielding soils. The subgrade should then be compacted to at least 95 percent of the modified Proctor maximum dry densiry as determined by the ASTM:D 1557 test procedure. Two feet of structural fill to support the proposed slab-on-,q,rade can be placed followine the installation of GeopiersT" or rock trenches. Additional recommendations for GeopiersT"as� rock trenches are presented in the Foundations section of this report. If construction will occur durinQ winter weather conditions, we recommend that the upper 6 to 12 inches of the buiiding pad consist of railroad ballast, crushed concrete, or sand and gravel that contains less than 5 percent passing the U.S. No. 200 sieve, based on chat fraction passing the U.S. Na 4 sieve. The purpose of this select fill is to provide a working surface that is compatible with moderately wet site and weather conditions. Depending on field conditions, geotextile fabric, such as ,�tirafi SOOX or equivalent, might be needed beneath areas where heavy traffic is expected. In our opinion, stable construction slopes should be the responsibiliry of the contractor and should be determined �iurine cons[ruction. For estimating purposes, however, we anticipare that temporary, unsupportecl�cut slopes in the existing fill can be made a[ a slope of I.SH:1V. The underlying till can be excavated at an�ies ot' ?'+H:I V or flatter. These slope angles assur:ie that a,round wa[er seepa��e is not strone enoueh [o reduce siope stability and that surface water is not allawed to t7ow across the temporary slope faces. If eround or surface warer is present Janunn' I3. _'OOd ASSOClATE�E.iRTN SC/E.VCES, INC. I � .1fTIJ. .:�q0!'JB�IJ-Y.,qrcrsLl,h,r?IyiXE�tPP- It^K page 11