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Mitigation Moraitorirag a�d I�.eportizrag Plan <br /> GEOLQGYAND SOILS <br /> Mit:igation Measure GEO 1: Geotechnical Report Recornrnendarions <br /> Ca1 Engineering and Geology has prepated a geotechnical report containing site-specific <br /> geotechnical recommendations for the proposed US 201 undercrossing project. The design team <br /> shall implement the following key recommendarions into the fir�al design of the project: <br /> • Jaint-use path profit.e above an elevation of 7 feet: Stabilize the expansi�e subgrade soils <br /> far the porrions of the joint-use path prof�le above an elevarion of 7 feet using one of <br /> three options:lime treatment of the subgrade, encapsulating the subgrade material with <br /> an imperviaus mem�rane,or incorporating a geogrid reinforcement into the structural <br /> section and using a nominally reinforced aggregate base laye�. <br /> + Joint-use path prafile below an elevation of 7 feet: Create a working platfarm by over- <br /> excavating the subgrade soil a mir,imum of 12 inches and placing a layer of woven <br /> geotextile fabric on top of the over-excavated subgrade and a].ayer af biaxial geo-grid <br /> placed direcdp on top of the fabric. A muiunum of 12 inches of 3/4 inch compacted <br /> crushed rack sha11 be placed on top of the geo-grfd. <br /> • The structLU�a1 concrete slab foundation shall be supported using xnicropiles. The <br /> micropiles sha,ll be advanced to a tip eZevation between-15 to-45 feet.The final pile <br /> diacneters and tip elevations shall be determi.ned by a structural engineer in conformance <br /> with the Federal Highway r'ldmuustration's Micropile De�agn and Co�astructiorr Guidelines <br /> Manual(August 2000). <br /> � The xetauung wa.tl adjacent to the north abutment will be supparted by rieback anchors <br /> that should be installea between the e.xisting abutment pi�es. Install rieback anchors at a <br /> 10 degtee inclination below horizontal with a minimum unbounded length of 10 feet <br /> wi�h permanent Class I coxrosion protection. The tieback wall shall be in conformance <br /> with the FHWA's Geotechrucal Engineering Circular No.4�itled, Ground.�rrchors and <br /> Anchored 5`y.rtems�un� 1999). <br /> • Footings for the cantilevered xetaining wall that bear on subgrade soils below an <br /> elevation of 7 feet should derive aIl vertical.resistance (downwards and upwards) from <br /> micropiles.Any resistance to verticalloads for footings bearing on subgxade soils below <br /> an elevarion of 7 feet should be neglected. <br /> • Foorings that bear on subgrade soils above an elevation of 7 feet may be designed using <br /> an allowable bearing pressure of 1,000 psf. <br /> * The Contractox shall be responsible £ar the design of the temporary shoring needed for <br /> the construction of the wet well and retaining walls in conformance with the Caltrans <br /> �'renching and Shorirag Maraual. The Contractor's shoring design shouZd be perfortned by a <br /> registered civil engineer and submitted to the City for review prior ta construction. <br /> • The Contractor shall be responsible for the design of the temporary cofferdam needed <br /> to dewater t�e site to construct the joint-use path under US 101. The Contxactor's <br /> ]��t3 15, 3i�I � �x-r:� US 101 Pedestrlan Undercros.ca�ag and <br /> B�ir Isl�nd 5'torm lY�ater Pump Stataon Project <br />