202 ALDER ST Geotech Report 2018-01-02 MF Import

1 ' P�oposed View Podge Subsurface F_cploration, Geofogic Hazards, Infilrrarion Porential, Elenlenrary School Repincement and Preliminary Georechnical Ertgineering Report Everett, Washrngron Preliminary Design Recommenda�ions , Final exterior grades should promote free and positive drainage away from the buildings at all times. Water must not be allowed to pond or collect adjacent ro foundations or within the ' immediate building area. We recommend that a gradient of at least 3 percent for a minimum distance of 10 feet from the building perimeters be provided, except in paved locations. In ' paved tocations, a minimum gradient of 1 percent should be provided, unless provisions are included for collection and disposal of surface water adjacent to the structures. ' 9.2 Subgrade Protection If building construction will proceed during the winter, we recommend the use of a working , surface of sand and gravel, crushed rock, or quarry spalls to protect exposed soils, particularly in azeas supporting concentrated equipment vaffic. In winter construction staging areas and areas that will be subjected to repeared heary loads, such as those that occur during ' construction of masonry Nalls, a minimum thickness of 12 iuches of quarry spalls or 18 inches of pit run sand and gravel is recommended. If subgrade conditions are sofr and silty, a geotextile separation fabric, such as Mirafi 500x or approved equivalent, should be used ' between the subgrade and the new fill. For building pads where floor slabs and foundation construction will be completed in the winter, a similar working surface should be used, ' composed of at least 6 inches of pit run sand and gravel or crushed rock. Construction of working surfaces from advancing fill pads could be used to avoid directly exposing the subgrade soils to vehicular traffic. ' Foundation subgrades may require protection from foot and equipment traffic and ponding of runoff during wet weather conditions. Typically, comF�cted crushed rock or a lean-mix ' concrete mat placed over a properly prepared subgrade provides adequate subgrade protection. Foundation concrete should be placed and excavations backfilled as soon as possible to protect the bearing surface. i ' 9.3 Proof-Rolling and Subgrade Compaction II ' Following the recommended demolition, site svipping, and planned excavation, the stripped subgrade within [he building areas should be proof-rolled with heavy, rubber-tired construction , equipment, such as a Gully loaded, tandem-axle dump truck. Proof-rolling should be performed prior to struccural fill placement or foundation excavation. The proof-roll should be monitored by the geotechnical engineer so that any soft or yielding subgrade soils or areas of ' remaining existing fill can be identified. Any sofUloose, yielding soils or existing fill should be removed to a stable subgrade. The subgrade should then be scarified, adjusted in moismre content, and recompacted to the required densiry. Proof-rolling should only be attempted if ' soil moisture contents are at or near optimum moisture content. Proof-rolling of wet subgrades could result in further degradation. L.ow areas and excavations may then be raised to the ISeptember 22, 2010 ASSOClATF.�EARTH SClENCF.S, lNC. . BwGnb�KFl00255�1�P�ojrne!20100155iCFiwV Page 14 '