Sacramento Modesto Roseville Pleasanton September 19, 2013 Marcia Medina GHD Inc. 417 Montgomery Street, Suite 700 San Francisco, CA 94104 Subject: GEOTECHNICAL REPORT AMENDMENT Stonybrook Creek Crossings Improvements Palomares Road at P.M. 8.60 and 8.75 Alameda County, CA Dear Ms. Medina: Crawford & Associates, Inc. (CAInc) prepared this amendment to the Preliminary Foundation Investigation prepared by Rick Sowers (Blackburn Consulting, March 28, 2005) for the structures located along Palomares Road at Post Mile (PM) 8.60 and 8.75. The 2005 report was based on 30% conceptual designs by Winzler & Kelly (now GHD, Inc). The project has been modified per the July 2013 50% Basis of Design Report by GHD. SCOPE OF WORK CAInc performed the following to complete this amendment: 1. Reviewed the 2005 preliminary foundation report and the current (50%) design plans by GHD. 2. Reviewed current geologic hazards mapping, including California Geologic Survey (CGS) Seismic Hazard Zones Mapping. 3. Contacted Alameda County Department of Public Works regarding seismic hazard mapping and compliance. 4. Conducted a site review at the current bridge replacement site (PM 8.60) and along the section of proposed channel grading (PM 8.75). 5. Prepared this amendment to address: a) Updated bridge foundations at PM 8.60 b) Impacts of channel grading at PM 8.75 c) Geologic hazards, including earthquake- induced landslide hazard.
Sacramento Modesto Roseville Pleasanton PROJECT DESCRIPTION The current project is shown in GHD s 50% Basis of Design Report as follows: PM 8.60 Bridge The existing culvert will be replaced with a pre- fabricated, clear- span, concrete bridge. The abutments and wing walls will consist of modular concrete blocks set on pre- cast spread footings anchored into bedrock. Precast deck panels will span the bridge opening. Figure 1 shows the site plan of the proposed bridge. Figure 1: Post Mile 8.60 Plan View Corporate Office: 4030 S. Land Park, Suite C, Sacramento, CA 95822 (916) 455-4225 Modesto: 1165 Scenic Drive, Suite B Modesto, CA 95350 (209) 312-7668 Roseville: 1340 Blue Oaks Boulevard, Suite 110 Roseville, CA 95678 (916) 455-4225 Pleasanton: 1811 Santa Rita Road Suite 224 Pleasanton, CA 94566 (925) 401-3515 2
Sacramento Modesto Roseville Pleasanton PM 8.75 Culvert The existing concrete box culvert will be retrofitted with angled baffles throughout the culvert. The upstream channel will be re- graded to remove the severe boulder jam in front of the existing culvert inlet. Channel grading will extend about 237 feet from Station 4+77 (inlet) upstream to Station 7+14 at a gradient of 9.99%. The grading will provide a 14 ft bottom width (8 ft near the culvert inlet) with 1.4:1 (H:V) side- slopes. The creek alignment will be straightened some by shifting south (away from the road). Maximum excavation depth along the new alignment will be about 10 feet. Figure 2: Post Mile 8.75 Plan View Corporate Office: 4030 S. Land Park, Suite C, Sacramento, CA 95822 (916) 455-4225 Modesto: 1165 Scenic Drive, Suite B Modesto, CA 95350 (209) 312-7668 Roseville: 1340 Blue Oaks Boulevard, Suite 110 Roseville, CA 95678 (916) 455-4225 Pleasanton: 1811 Santa Rita Road Suite 224 Pleasanton, CA 94566 (925) 401-3515 3
Sacramento Modesto Roseville Pleasanton SITE GEOLOGY Both sites are underlain by Cretaceous- age sedimentary rocks of the Panoche Formation. The Geologic Map of the San Francisco- San Jose Quadrangle (Wagner, et al., 1991) describes these rocks as marine sandstone, shale, siltstone and conglomerate. Mapping by Graymer, et al., (USGS Open File Map 94-132, 1994) shows the sites to be underlain by distinctly bedded and well lithified Cretaceous sandstone and shale. Rock bedding is shown to strike uniformly northwesterly and dip southwest at 70. Figure 3 shows the site geology. Figure 3: Geologic Map Source: California Geological Survey, Regional Geologic Map No. 5A, 1:250,000 scale Compilation by D.L. Wagner, E.J. Bortugno, and R.D. McJunkin 1991 Corporate Office: 4030 S. Land Park, Suite C, Sacramento, CA 95822 (916) 455-4225 Modesto: 1165 Scenic Drive, Suite B Modesto, CA 95350 (209) 312-7668 Roseville: 1340 Blue Oaks Boulevard, Suite 110 Roseville, CA 95678 (916) 455-4225 Pleasanton: 1811 Santa Rita Road Suite 224 Pleasanton, CA 94566 (925) 401-3515 4
Sacramento Modesto Roseville Pleasanton GEOLOGIC HAZARDS Fault Rupture Figure 4 shows Quaternary and younger faults located in the vicinity of the site. In general, faults showing displacement within Historic (approximately last 200 years) or Holocene (approximately last 11,000 years) time are considered "active." Faults showing evidence of displacement during Late Quaternary (last 700,000 years) or Quaternary (last 1.6 million years) time are often referred to as "potentially active." Figure 4: Regional Fault Map Source: USGS/CGS online database Historic fault displacement Holocene fault displacement Late Quaternary fault displacement Quaternary fault displacement 5 Corporate Office: 4030 S. Land Park, Suite C, Sacramento, CA 95822 (916) 455-4225 Modesto: 1165 Scenic Drive, Suite B Modesto, CA 95350 (209) 312-7668 Roseville: 1340 Blue Oaks Boulevard, Suite 110 Roseville, CA 95678 (916) 455-4225 Pleasanton: 1811 Santa Rita Road Suite 224 Pleasanton, CA 94566 (925) 401-3515
Sacramento Modesto Roseville Pleasanton The sites are located between the Hayward fault (approximately 3.3 miles southwest) and the Calaveras fault (approximately 2.9 miles northeast). The California Geologic Survey has mapped both of these faults as active and established Earthquake Fault Zones (EFZ) as shown on Figure 5. Since the site is not within an EFZ and no active faults are shown to cross the project site, we consider the potential for surface rupture due to faulting to be low. Figure 5: Alquist-Priolo Fault Zone Map Source: USGS/CGS online database Corporate Office: 4030 S. Land Park, Suite C, Sacramento, CA 95822 (916) 455-4225 Modesto: 1165 Scenic Drive, Suite B Modesto, CA 95350 (209) 312-7668 Roseville: 1340 Blue Oaks Boulevard, Suite 110 Roseville, CA 95678 (916) 455-4225 Pleasanton: 1811 Santa Rita Road Suite 224 Pleasanton, CA 94566 (925) 401-3515 6
Sacramento Modesto Roseville Pleasanton Ground Shaking The sites are subject to strong ground shaking from earthquakes on the nearby Hayward and Calaveras faults. According to the CGS web site, the peak horizontal ground acceleration (PGA) with a 10% probability of being exceeded in 50 years is approximately 0.60g. The modal (most probable) magnitude and distance for this event is a moment magnitude of about 6.8 at a distance of approximately 3 miles. Liquefaction Liquefaction can occur when loose to medium dense, granular, saturated soils (generally within 50 feet of the surface) are subjected to ground shaking. The sites are underlain by bedrock that is not susceptible to liquefaction. Slope Stability The canyon slopes are steep and subject to landslides. We observed several debris-flow slides within the canyon walls near the two project sites. These slides typically involve only the upper 5-10 feet and we did not observe evidence of deep-seated translational or rotational landslides within the project limits. The CGS Seismic Hazard Zones map (Niles Quadrangle, 2004) shows the canyon slopes to be susceptible to earthquake-induced landslides. We show this mapping on Figure 6: Corporate Office: 4030 S. Land Park, Suite C, Sacramento, CA 95822 (916) 455-4225 Modesto: 1165 Scenic Drive, Suite B Modesto, CA 95350 (209) 312-7668 Roseville: 1340 Blue Oaks Boulevard, Suite 110 Roseville, CA 95678 (916) 455-4225 Pleasanton: 1811 Santa Rita Road Suite 224 Pleasanton, CA 94566 (925) 401-3515 7
Sacramento Modesto Roseville Pleasanton Figure 6: Seismic Hazard Zone Map Source: CGS Seismic Hazard Zones, Niles Quadrangle- 10-19- 04 8 Corporate Office: 4030 S. Land Park, Suite C, Sacramento, CA 95822 (916) 455-4225 Modesto: 1165 Scenic Drive, Suite B Modesto, CA 95350 (209) 312-7668 Roseville: 1340 Blue Oaks Boulevard, Suite 110 Roseville, CA 95678 (916) 455-4225 Pleasanton: 1811 Santa Rita Road Suite 224 Pleasanton, CA 94566 (925) 401-3515
Sacramento Modesto Roseville Pleasanton CONCLUSIONS Foundation Recommendations @ PM 8.60 Footing support for the new bridge is available using reinforced concrete strip footings. Design the foundations using a minimum footing width of 3 feet and install the foundations below new channel invert elevation (approximately elevation 482 feet) and within intact rock, as identified by a CAInc representative during construction. Use an allowable bearing capacity of 5 tons per square foot (tsf), for footings constructed per above. Higher bearing pressures are available with increased rock penetration and/or positive field review during construction by CAInc. We expect rock excavation to be locally difficult but achievable by use of air tools without blasting. Rock blasting would disrupt/degrade integrity of the surrounding rock and should be avoided. If the rock surface is variable along the footing lines, we consider the use of plain concrete appropriate to provide positive contact between the footing elements and suitable rock. Use a coefficient of friction to resist sliding of 0.40 between the footing and weathered rock. Passive pressures in the rock unit can be based on an equivalent fluid weight of 500 pcf. For additional security against sliding (if necessary), or if hard rock precludes reasonable rock excavation, doweling can be utilized to establish a positive connection between the footing and rock (e.g., #8 bars grouted in drilled holes extending 5±ft into rock). Place footing concrete neat, without forming, against trimmed, intact bearing material in clean and dry excavations. Assuming dry season (low flow) construction, we expect de- watering to be achievable by means of diking/diversion of surface water and sump pumping. The alluvial soils overlying the rock are subject to scour and bank erosion. If rock slope protection is placed at the inlet/outlet, or along the banks, construct in accordance with Caltrans Standard Plans. Construction backslopes within the existing fill may require slopes at gradients flatter than 1:1 for stability. Channel Grading @ PM 8.75 The proposed grading will remove the boulder aggradation and restore the channel to a more natural step- pool channel. The alignment shift into the left bank, accompanied by channel excavation to achieve the profile gradient, will locally undercut the left bank and may cause local debris slides and minor rock wedge failures. We do not, however, expect this grading to initiate significant landslides. Corporate Office: 4030 S. Land Park, Suite C, Sacramento, CA 95822 (916) 455-4225 Modesto: 1165 Scenic Drive, Suite B Modesto, CA 95350 (209) 312-7668 Roseville: 1340 Blue Oaks Boulevard, Suite 110 Roseville, CA 95678 (916) 455-4225 Pleasanton: 1811 Santa Rita Road Suite 224 Pleasanton, CA 94566 (925) 401-3515 9
Sacramento Modesto Roseville Pleasanton The canyon slope is subject to seismically- induced landslides (predominately debris slides and/or rockfalls); however, there are no structures along these slopes and this hazard is not a threat to life or habitable property. The existing bank below Palomares Road is steep (greater than 1:1 in places), especially between about Station 6+50 to 7+00. We recommend placing some of the excavated boulders against this bank to protect the roadbed from future erosion. LIMITATIONS CAInc prepared this amendment report in accordance with generally accepted geologic and geotechnical engineering principles and practices currently used in this area. This report should be reviewed and modified if conditions change or if the project is further modified. Crawford & Associates, Inc. Rick Sowers, P.E., C.E.G. Principal Benjamin D. Crawford, P.E., G.E. Principal 10 Corporate Office: 4030 S. Land Park, Suite C, Sacramento, CA 95822 (916) 455-4225 Modesto: 1165 Scenic Drive, Suite B Modesto, CA 95350 (209) 312-7668 Roseville: 1340 Blue Oaks Boulevard, Suite 110 Roseville, CA 95678 (916) 455-4225 Pleasanton: 1811 Santa Rita Road Suite 224 Pleasanton, CA 94566 (925) 401-3515