AgdaPkt 2016-04-25 Closed and Joint SA PFA

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7.B. - Page 117 Mitigation Monitoring and Reporting Plan GEOLOGY AND SOILS Mitigation Measure GEO 1: Geotechnical Report Recommendations Cal Engineering and Geology has prepared a geotechnical report containing site-specific geotechnical recommendations for the proposed US 101 undercrossing project. The design team shall implement the following key recommendations into the final design of the project: • Joint-use path profile above an elevation of 7 feet: Stabilize the expansive subgrade soils for the portions of the joint-use path profile above an elevation of 7 feet using one of three options:lime treatment of the subgrade, encapsulating the subgrade material with an impervious membrane, or incorporating a geogrid reinforcement into the structural section and using a nominally reinforced aggregate base layer. • Joint-use path profile below an elevation of 7 feet: Create a working platform by over- excavating the subgrade soil a minimum of 12 inches and placing a layer of woven geotextile fabric on top of the over-excavated subgrade and a layer of biaxial geo-grid placed directly on top of the fabric. A minimum of 12 inches of 3/4 inch compacted crushed rock shall be placed on top of the geo-grid. • The structural concrete slab foundation shall be supported using micropiles. The micropiles shall be advanced to a tip elevation between-15 to -45 feet. The final pile diameters and tip elevations shall be determined by a structural engineer in conformance with the Federal Highway Administration's Micropile Design and Construction Guidelines Manual(August 2000). • The retaining wall adjacent to the north abutment will be supported by tieback anchors that should be installed between the existing abutment piles. Install tieback anchors at a 10 degree inclination below horizontal with a minimum unbounded length of 10 feet with permanent Class I corrosion protection. The tieback wall shall be in conformance with the FHWA's Geotechnical Engineering Circular No.4 titled, Ground Anchors and Anchored Systems (June 1999). • Footings for the cantilevered retaining wall that bear on subgrade soils below an elevation of 7 feet should derive all vertical resistance (downwards and upwards) from micropiles. Any resistance to vertical loads for footings bearing on subgrade soils below an elevation of 7 feet should be neglected. • Footings that bear on subgrade soils above an elevation of 7 feet may be designed using an allowable bearing pressure of 1,000 psf. • The Contractor shall be responsible for the design of the temporary shoring needed for the construction of the wet well and retaining walls in conformance with the Caltrans Trenching and Shoring Manual. The Contractor's shoring design should be performed by a registered civil engineer and submitted to the City for review prior to construction. • The Contractor shall be responsible for the design of the temporary cofferdam needed to dewater the site to construct the joint-use path under US 101. The Contractor's July 15,2013 A-6 US 101 Pedestrian Undercrossing and Bair Island Storm Water Pump Station Project