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2 E�auirronment�l Anr�ly�is <br /> implement one of three oprions to stabilize the subgrade soil.s fox the joint-use path profi�e that is <br /> above an elevation of 7 feet. The first option is lime treatment,which reduces the e�pansion of soils <br /> by chemically reacting with soils containing clay mixierals {CE&G,2013). The second opt�on the City <br /> could implement is encapsulatian of the subgrade soils,which would xeduce moisture-content <br /> changes within the soi� (CE&G,2013). The third option the City could implement is ta incorporate <br /> tensile elements into the structura�section through use of a bia�al geogrid,which would reduce <br /> expansion and cont�acrion of the subgxade soils. <br /> Fox the joint-use path profile that would be below seven feet elevarion with wet and very satu�ated <br /> sails,the CitF would c�eate a compacted crushed rock foundation and then drill the micropiles <br /> through the compacted rock to provide an adequate foundation for the joint-use path�rofile.This <br /> would reduce the uplifung buoyant forces and sett�ement of the soi�.Tl�erefore, the implementatian <br /> these measures wauld reduce the project impacts from expansive soils to a less than significant le�el. <br /> Mitigation Measure GEO 1: Geotechnical Report Recornmendations <br /> Cal Engineering and Geology has prepared a geotechnical report containing site-specific <br /> geotech,n.ical recommendatio�s for the proposed US 101 undercrossing project. The design <br /> team shall itnplement the following kep recommendations into the final design of the project <br /> • Joint-use path profile above an elevation of 7 feet: Stabilize the expansive subgrade soils <br /> £or the portions of the joint-use path profile above an elevation of 7 feet using one of <br /> three opt�ons: lime treatment of the subgxade, encapsularing the subgrade mate�ial with an <br /> impervious membrane ar incorporating a geogrid reinfoxcement into the structura� <br /> secrion and using a nominal�y reinforced aggregate base layer. <br /> • Joint-use patl�profile belaw an elevation of 7 feet: Create a working platform by over- <br /> excavaring the subgrade soil a mini.mum af 12 inches and placing a layer of woven <br /> geotextile fabric on top of the over-excavated s�bgrade and a layer of bia�al geo-grid <br /> placed directly on top of the fabric. A minimutn of 12 inches of 3/a inch compacted <br /> crushed rock sl�all be placed on top of tl�e geo-grid. <br /> • The structural concrete slab foundation shall be supported using micropiles. The <br /> micropiles shall be advanced to a tip elevauon between-15 to -45 feet.The final pile <br /> diameters and tip elevations shall be detemuned by a stnictutal engineer in conforniance <br /> with the Federal Highway Administration's Micmpile Deseg�a asad Construction Gsridelines <br /> Manual(August 20d0). <br /> + The retaining wall adjacent to the north abutment will be snpported by tieback anchars <br /> that should be installed between the existing abutment piles. Install tieback anchors at a <br /> �0-degree inclination below horizontal with a mir,imum unhounded length of 10 feet with <br /> permanent Class I corrosion pxotection. The tieback wall shall be in conformance with <br /> the FHWA's Geotechnical Engineering Circular No.4,tit�ed GroundAnchor�s andArachored <br /> Systems(�une 1999�. <br /> ? :i' US 901 Pede.rtrzran Undet�crossing and Baar <br /> ,Tsdand Aoad Storm Drain Pump Stataora Pmjec•t <br />