Loading...
The URL can be used to link to this page
Your browser does not support the video tag.
Home
My WebLink
About
06.02.26 Board Correspondence - FW_ Project Operations Compliance Report submitted in FERC P-2107-000 by Pacific Gas and Electric Company
From:Clerk of the Board To:Clerk of the Board; Connelly, Bill; Cook, Holly; Cook, Robin; Durfee, Peter; Jessee, Meegan; Kimmelshue, Tod; Kitts, Melissa; Krater, Sharleen; Lee, Lewis; Little, Melissa; Pickett, Andy; Ritter, Tami; Stephens, Brad J.; Sweeney, Kathleen; Teeter, Doug; Zepeda, Elizabeth Cc:Loeser, Kamie; Cannon, Jamie Subject:Board Correspondence - FW: Project Operations Compliance Report submitted in FERC P-2107-000 by Pacific Gas and Electric Company Date:Tuesday, June 2, 2026 11:19:06 AM Please see Board Correspondence - Lewis Lee Administrative Technician - Confidential Butte County Administration 25 County Center Drive, Suite 200 • Oroville, CA 95965 T: 530.552.3326 www.buttecounty.ca.gov | lelee@buttecounty.ca.gov -----Original Message----- From: 'FERC eSubscription' <eSubscription@ferc.gov> Sent: Tuesday, June 2, 2026 10:26 AM Subject: Project Operations Compliance Report submitted in FERC P-2107-000 by Pacific Gas and Electric Company .ATTENTION: This message originated from outside Butte County. Please exercise judgment before opening attachments, clicking on links, or replying.. On 6/2/2026, the following Filing was submitted to the Federal Energy Regulatory Commission (FERC), Washington D.C.: Filer: Pacific Gas and Electric Company Docket(s): P-2107-000 Lead Applicant: Pacific Gas and Electric Company Filing Type: Project Operations Compliance Report Description: Pacific Gas and Electric Company submits response to address FERC's 04/20/2026 additional information request re the construction authorization for installing rockfall drapery barrier and anchors at Poe Powerhouse of the Poe Project under P-2107. To view the document for this Filing, click here https://urldefense.com/v3/__https://elibrary.ferc.gov/eLibrary/filelist?accession_num=20260602- 5102__;!!KNMwiTCp4spf!ASI9jTjsDNGdpYPmep9qg353VW3cNpDAZuR- sGab7wizIdinK_ViFPRIqBycpitPG6vutnudZ1OwevT70vaxxlq3wMY0bymrKetn$ To modify your subscriptions, click here: sGab7wizIdinK_ViFPRIqBycpitPG6vutnudZ1OwevT70vaxxlq3wMY0b9A_lLo4$ ------------------------------------------------------------------------ Please do not respond to this email. Online help is available here: https://urldefense.com/v3/__http://www.ferc.gov/efiling-help.asp__;!!KNMwiTCp4spf!ASI9jTjsDNGdpYPmep9qg353VW3cNpDAZuR- sGab7wizIdinK_ViFPRIqBycpitPG6vutnudZ1OwevT70vaxxlq3wMY0b3SZEICI$ or for phone support, call 866-208-3676. Power Generation 300 Lakeside Drive Oakland, CA 94612 Mailing Address: P.O. Box 28209 Oakland, CA 94604 1-FERC Accession Number 20260420-3055 June 2, 2026 Via Electronic Submittal (E-File) Frank L. Blackett, P.E., Regional Engineer Federal Energy Regulatory Commission Division of Dam Safety and Inspections 100 First Street, Suite 2300 San Francisco, CA 94105-3084 RE: Poe Hydroelectric Project, FERC No. 2107-CA Construction Authorization Request for Installing Rock Drapery Barrier and Anchors Responses to Additional Information Request Dear Frank L Blackett: This letter presents Pacific Gas and Electric Company’s (PG&E) responses to address the Federal Energy Regulatory Commission’s (FERC) additional information request (AIR) for PG&E’s construction authorization for installing rockfall drapery barrier and anchors at Poe Powerhouse, which is part of the Poe Hydroelectric Project, FERC No. 2107. PG&E submitted the authorization request on February 24,2026, and PG&E received FERC’s AIR in a letter dated April 20, 20261. PG&E's responses to FERC’s AIR are enclosed with this letter as (Enclosure 1). (Enclosure 2) contains the Slope Reconnaissance and Alternatives Analysis Report, Poe Powerhouse Rockfall Mitigation Project, Butte County, California, dated January 24, 2020. Please contact Gavin Rhoads, project engineer for PG&E, at (530) 370-6685 for any technical questions. For general questions regarding this matter, please contact Anna Urias, license coordinator for PG&E, at (530) 201-1961. Sincerely, Kyle Ingvoldsen, P.E. Supervisor, Power Generation Project Engineering Enclosures: 1. AIR Response 2. Slope Reconnaissance and Alternatives Analysis Report, Poe Powerhouse Rockfall Mitigation Project, Butte County, California. Prepared by Gannet Fleming and dated January 20,2024. ENCLOSURE 1 Poe Hydroelectric Project, FERC No. 2107-CA Responses to FERC Additional Information Request Regarding Construction Authorization Request for Installing Rock Drapery Barrier and Anchors In a letter to Pacific Gas and Electric Company (PG&E) dated April 20, 2026, the Federal Energy Regulatory Commission (FERC) provided an Additional Information Request (AIR) regarding PG&E’s Construction Authorization Request for Installing Rock Drapery Barrier and Anchors for the Poe Hydroelectric Project, FERC No. 2107-CA. For reference, FERC’s comments are copied below, followed by PG&E's responses (in italics). C-1: Submit the report titled “Slope Reconnaissance and Alternatives Analysis Report, Poe Powerhouse Rockfall Mitigation Project, Butte County, California”, prepared by Gannett Fleming Inc., dated January 24, 2020, for our review. PG&E has included the report, “Slope Reconnaissance and Alternatives Analysis Report, Poe Powerhouse Rockfall Mitigation Project, Butte County, California”, as prepared by Gannett Fleming Inc. on January 24, 2020, as Enclosure 2 for FERC’s review. C-2: You indicate that you will provide us with an update on the status of the project by October 29, 2027. This is not acceptable; you must submit the actual date that you plan for the construction to be completed. PG&E plans to mobilize for construction on April 1, 2027 and demobilize on July, 2027. Dates may change due to resource availability and emergent projects in the ar ea. PG&E plans to provide a final construction report within 90 days of completing c onstruction. ENCLOSURE 2 Gannett Fleming, Inc. Suite 200 • 2251 Douglas Blvd • Roseville, CA 95661 t: 916.677.4800 • www.gannettfleming.com January 24, 2020 PG&E PO No. 2700355965 Gannett Fleming Project No. 065601 Jonathan Edwards, PE Senior Project Engineer Pacific Gas & Electric Rogers Flat Service Center Storrie, CA 95980 Re: Slope Reconnaissance and Alternatives Analysis Report Poe Powerhouse Rockfall Mitigation Project Butte County, California Dear Mr. Edwards: Gannett Fleming, Inc. is pleased to submit this report summarizing our reconnaissance of the cut slope located directly above the penstock tunnel portal structure at the Pacific Gas & Electric (PG&E) Poe Powerhouse (Figure 1). This report includes a brief project background; a summary of previous studies; a description of slope observations made during our reconnaissance; conclusions; and an evaluation of rockfall mitigation alternatives. PROJECT BACKGROUND Poe Powerhouse (Powerhouse), which is part of the Poe Hydroelectric Project (FERC Project #2107), is located on the North Fork Feather River approximately 13 miles northeast of Oroville, Butte County, California. The Poe Hydroelectric Project was constructed in the late 1950s. The Poe Tunnel and penstock 1 feed the powerhouse’s two 76,000 horsepower turbine units (Figure 1). An approximately 20-foot-tall concrete tunnel portal structure is located to the east of the turbines and contains a manway for accessing the Poe penstock within the tunnel (Photo 1). 12 kilovolt reserve station service equipment located atop the portal structure is accessed by metal stairs mounted to the south face of the structure (Photo 2). A Union Pacific Railroad Co. (Union Pacific) railroad bench is located 130 feet (approximate slope length) upslope of the portal structure (Figure 1). A roughly 50-foot-tall rock cut slope was excavated during construction of the portal structure (Photos 1 and 2) (E. Steen, personal communication, December 2, 2019; Appendix A). Two small rockfall events (individual blocks or volumes of rockfall debris less than 1 cubic yard) have been reported originating from the cut slope: a 2016/2017 winter season rockfall event (E. Steen, personal communication, December 2, 1 The Poe Powerhouse penstock is an underground structure, constructed within an inclined tunnel section that spans between Poe Tunnel and Poe Powerhouse. The penstock is a steel pipe. Near the portal structure, the penstock is in an open concrete-lined tunnel. Slope Reconnaissance and Alternatives Analysis Report Poe Powerhouse Rockfall Mitigation Project Gannett Fleming Project No. 065601 January 24, 2020 Page 2 of 20 2019; Appendix A) and a spring 2019 event (J. Edwards, personal communication, March 6, 2018; Appendix A). These relatively small, local events caused damage to the metal stairs (2016/2017 event; Photo 3) and a steel cross member of an electrical tower near the portal structure (spring 2019 event; Photo 4). On April 22, 2019, at the request of PG&E, Gannett Fleming’s Matt Buche, P.G., and Syed Ul Haque, P.E., performed an engineering design scoping site visit to observe the portal structure cut slope and discuss rockfall mitigation measures aimed at reducing the vulnerability of the power equipment and metal stairs from rockfalls sourced from the portal cut slope. PG&E authorized Gannett Fleming to provide engineering design services for rockfall mitigation measures under Purchase Order (PO) No. 2700355965 for Engineering Design services on October 31, 2019 (Ref. 1 and Ref. 2). PREVIOUS STUDIES We reviewed an email correspondence (Appendix A) provided by Emily Steen, P.E., G.E., of PG&E Geosciences following her May 29th, 2018, site visit to observe the portal structure cut slope conditions after a reported rockfall event (E. Steen believed the rockfall may have occurred during the 2016/2017 storm season). Ms. Steen’s access was limited to the Powerhouse yard and top of the portal structure. Her key observations, conclusions, and recommendations are summarized below. • The rockfall event damaged the metal stairs on the south side of the portal structure. • The source of the rockfall appeared to be localized within a more weathered and dilated “rind” near the crest of the cut slope, coinciding with the transition to original ground surface. This rind zone appeared to be more susceptible to rockfalls while the lower portion of the slope, though locally overhanging, appeared “tight and generally stable.” • No seepage was observed from the cut slope. The penstock was in operation at the time. • Possible contributing rockfall causation or trigger factors include precipitation and runoff, elevated groundwater level, and/or ice-jacking. Vibration from passing Union Pacific trains to loosen already dilated rock within the rind zone did not appear to be a major contributor to rockfall from the cut slope. It was noted that a tree immediately above the rockfall source area may be loosening the rock mass via root-wedging, and it was recommended that the tree be removed. • Additional small rockfalls from the upper, more weathered and dilated portion of the cut slope would likely continue to be a hazard to personnel and electrical equipment. • Ms. Steen recommended three potential mitigation options: 1. Hand scaling of the slope with facility protection measures in place to prevent damage to existing station service equipment and the portal structure below. 2. Installation of an unsecured rockfall netting (i.e., “simple drapery”) consisting of hexagonal double-twisted wire mesh. 3. Hand scaling to remove hazard blocks, followed by the installation of unsecured drapery (i.e., combination of options 1 & 2, in order). • Ms. Steen recommended that, prior to installing mitigation measures, a pre-construction inspection of the ground surface above the cut slope should be conducted to assess the site for tension features or zones of dilated rock that would indicate potential for a larger/deeper slope failure. Slope Reconnaissance and Alternatives Analysis Report Poe Powerhouse Rockfall Mitigation Project Gannett Fleming Project No. 065601 January 24, 2020 Page 3 of 20 GEOLOGIC SETTING Regional geologic mapping indicates the site is situated within the Pre-Quaternary 2, en echelon branches of the Big Bend fault zone (Ref. 3, 4, 5, and 6), located along the north end of the western metamorphic belt of the Sierra Nevada. The fault zone trends in a west-northwest direction with near vertical to steeply east dipping bedding structure. The site is not within an area evaluated as part of the Alquist-Priolo Act or Seismic Hazards Mapping Act. Typical rocks exposed along the Big Bend fault zone are interbedded metasedimentary and meta-volcanic rocks accompanied by thin long bodies of ultramafic rocks (Ref. 5). Rocks within the Big Bend fault zone are typically strongly deformed. Saucedo and Wagner (1992; Ref. 4) show the site underlain by Mesozoic-Paleozoic aged metasedimentary rock, bounded by approximately located or inferred fault traces of the Big Bend fault zone, which mark geologic contacts with metavolcanic rock to the south and ultramafic rock to the north of the Powerhouse. Hietanen (1973; Ref. 6), did not map the site; however, rock approximately 1.5 miles north of the Powerhouse is mapped as the Horseshoe Bend Formation, which includes metamorphosed volcanic rocks (basalt, andesite, dacite, and tuff), phyllite, and quartzite. Our field observations are consistent with referenced geologic mapping and descriptions. SLOPE RECONNAISSANCE Gannett Fleming performed a slope reconnaissance on November 14, 2019, to make geologic observations and collect slope information for an alternatives analysis and engineering design of rockfall mitigation measures. The reconnaissance was performed by Matt Buche, P.G., and Scott Savko. Our reconnaissance focused on the cut slope above the portal structure (Figure 2; Photo 1). Because of its steepness, discontinuity measurements were collected from areas of the outcrop that were safely accessible by foot. The reconnaissance did not include accessing the slope itself using a crane, man-lift, or rope access techniques. Cut Slope Conditions General The larger Poe Powerhouse cut slope is generally west-facing (Figure 1). The penstock tunnel portal structure cut slope in plan has an asymmetrical horseshoe-type alignment, with a greater than ¼:1 (85ﹾ) northern portion (or segment) facing to the southwest, a central, ¼:1 (78ﹾ) segment, and a ½:1 (62ﹾ) southern segment that faces west. (Figure 2). The max height of the cut slope is around 50 feet, with a max height above the portal structure of about 30 feet. A 30-foot-long, 6.5-foot-tall chain-link fence is present approximately 15 feet upslope of cut slope crest and appears to have been installed to prevent upslope rockfall materials from entering the work area, likely during tunnel excavation (Photo 5). A native (inferred), near 1:1 (~40ﹾ) slope with a thin cover of colluvium (estimated at less than 3 feet) and local rock outcrops continues upslope approximately 130 feet (slope length) to the Union Pacific railroad bench (Figure 1). The tree that was identified by Ms. Steen near the top of the cut slope crest was removed prior to our site visit. Damage to the access stairs appeared similar to earlier photos (Photo 3). A steel cross member of the electrical tower structure closest to the southwest corner of the portal structure is bent (Photo 2 Older than 1.6 million years or fault without recognized Quaternary displacement (Ref. 3). Slope Reconnaissance and Alternatives Analysis Report Poe Powerhouse Rockfall Mitigation Project Gannett Fleming Project No. 065601 January 24, 2020 Page 4 of 20 4), which does not appear to have been previously documented, and may have been damaged by the more recent, spring 2019 rockfall event. Of the rockfall debris and rock fragments observed along the cut slope toe and gravel switchyard, most of the blocks have come to rest within approximately 14 feet of the slope toe (assuming the debris and fragments were not relocated by PG&E personnel). Rockfall blocks typically had maximum dimensions of 12 inches or less. Along the northern portion, the largest rockfall blocks included a 3 x 0.5 x 0.5 foot (approximate) block along the toe of the slope (Photo 6) and a 2.5 x 0.5 x 2 foot toppled block near the northeast corner of the portal structure (Photo 7). We did not observe any free surface water or seepage emanating from the cut slope at the time of our site visit. Seepage from the penstock tunnel is captured by conduit/gutter and piped to the switchyard’s subsurface drainage system. Rock Description 3 As described previously, the rock exposed within the cut slope is comprised of interbedded metavolcanic, metasedimentary, and ultramafic rocks. The rock has been strongly deformed and altered by the Big Bend Fault Zone, and due to the fine-grained nature of the rocks, rock identification is difficult without thin-section analysis (beyond the scope of this reconnaissance). The rock within the cut slope is typically slightly weathered to fresh, moderately hard to hard, and strong. The rock exposed along the upper portions of the cut slope and locally along discontinuities with the rock is increasingly weathered, with slightly lower hardness and strength. Structure The rock bedding and discontinuity orientations recorded during our reconnaissance and measured within lidar scan data provided by PG&E are included on Figure 2 and on the stereonet provided on Figure 3. The orientation of relict bedding across the site varies but is generally consistent with regional mapping by others and is oriented N57°W, dipping approximately 50° to the northeast (Ref. 4 and 6; Figure 2). The thickness of the bedding observed varied from very thickly (2 to 10 feet) to thinly bedded. Bedding locally forms overhanging conditions, for example, upslope of the station service equipment (Photo 8). Interbedded meta-volcanic and ultramafic rock was found to be locally very soft and relatively more weathered and more thinly foliated/laminated along bedding contacts. Bedding was occasionally serpentinized. We also observed a more thinly bedded zone with a yellowish color that is commonly associated with hydrothermal alternation (Photo 9). Discontinuities give the cut slope a blocky or tabular appearance. Jointing is more intense and dilated near the upper portion of the cut slope, particularly in the area interpreted to be the potential source location of recent rockfall events (Photo 10). The rock bedding and discontinuity orientations recorded during our reconnaissance and measured within the lidar scan data provided by PG&E are included on Figure 2. In addition, Table 1 below includes a description of the primary cut slope structural discontinuities. 3 Rock descriptions are based on criteria from Engineering Geology Field Manual, Second Edition, Volume 1, published by the U.S. Department of the Interior, Bureau of Reclamation, dated 1998, reprinted 2001. Slope Reconnaissance and Alternatives Analysis Report Poe Powerhouse Rockfall Mitigation Project Gannett Fleming Project No. 065601 January 24, 2020 Page 5 of 20 Table 1 – Primary Cut Slope Structural Discontinuities portion of cut slope that dips towards portal structure (Photo 9). joint sets J1 and J4. The stereonet provided on Figure 3 includes the collected structural orientations and slope data. Based on a review of the stereonet and our onsite observations, we believe that the four primary rock slope failure modes could kinematically occur within the subject slope. These failure modes include planer sliding, wedge sliding, direct toppling, and flexural toppling. Rock Laboratory Testing We collected two boulder-sized rock samples, S-1 and S-2, for unconfined compressive strength (UCS) and unit weight laboratory testing. The approximate field location of each sample is shown on Figure 2. The samples were transported to Gulf Shore Construction Services, Inc. (Gulf Shore) in Rancho Cordova, California, on November 26, 2019. The laboratory reports for unconfined compressive strength and unit weight test reports are included as Appendix B, and the results are summarized in Table 2 below. Note that UCS testing of sample S1 was unsuccessful because the sample fractured due to a structural discontinuity during loading. Table 2 – Rock Laboratory Testing Summary Sample ID Strength (psi) Dry Density (pcf) DISCUSSION The recent rockfall events from the penstock tunnel portal structure cut slope followed inclement weather and appear to be relatively small in magnitude, mobilizing less than 1 cubic yard of rock and rock block fragments less than 3 feet in maximum dimension. The crest (or brow) of the cut slope appears to be the source area of the recent rockfall events and exhibits a greater degree of fracturing. The crest of the cut slope is likely to continue to produce similar rockfall events, and other areas of the slope contain bedding Slope Reconnaissance and Alternatives Analysis Report Poe Powerhouse Rockfall Mitigation Project Gannett Fleming Project No. 065601 January 24, 2020 Page 6 of 20 and joint interactions that could also promote localized sliding-, wedge-, or toppling-type failures. The volumes of these future events are expected to be similar to the previous rockfalls. However, larger volume events originating from beyond the top of the cut slope, which has not been directly viewed, could be possible. Because of the cut slope’s steep inclination and relatively short slope height, rockfall runout distances appear to be less than 20 feet from the toe of the slope. Although small in magnitude with short runout distances, the rockfall potential of the cut slope puts the portal structure, reserve station power equipment, metal stairs, and the proximal nearby switchyard tower structure at risk of damage. PG&E operational personnel are periodically and temporarily exposed to the hazard when accessing or servicing the reserve station equipment, but their exposure and risk are less than the permanent equipment. The likelihood of damage to equipment in the switchyard is relatively higher due to its constant exposure. RECOMMENDATIONS The following recommendations and alternatives discussion are based on our slope reconnaissance and rockfall project experience. Rockfall Mitigation Measures - Alternatives Analysis The limited distance between the cut slope and the structures that need protection present unfavorable conditions for the installation of a rockfall barrier system (e.g. flexible rockfall fence, berm, k-rail) at the site. Unsecured and secured rockfall drapery systems are generally suitable for individual rock block sizes of roughly 5 feet and single events less than 10 cubic yards in volume (Ref. 9). If larger events are anticipated, supplemental or alternative mitigation measures are considered (e.g. scaling/removal or in-place stabilization of potential rockfall source material). Unsecured rockfall drapery comprises rockfall netting suspended from upslope rock anchors, while secured drapery comprises rockfall netting with upslope rock anchors and rock anchors installed in a grid pattern on the face of the slope atop the netting. Rockfall netting typically comprises double-twisted hexagonal wire mesh (DTWM) and/or cable net, with DTWM utilized for block sizes < 2 feet; and cable nets for block size < 4 to 5 feet. Since DTWM has a smaller opening than cable net, drapery systems can utilize cable net backed with DTWM to prevent smaller diameter blocks from traveling through the cable net. Based on our reconnaissance, we do not anticipate that the cut slope will generate individual failure events with volumes larger than approximately 10 cubic yards. However, because there is a potential for larger type failures (particularly near the crest of the slope), we recommend a design for typical supplemental rock anchors be included in the construction drawings, to be used “as-needed” based on field observations of the cut slope during construction. Two rockfall drapery system alternatives (both with cable net backed with DTWM) are evaluated below. The measures include: • Alternative 1: unsecured rockfall drapery; and • Alternative 2, a combination of unsecured and secured rockfall drapery. Each alternative is described in greater detail below. The conceptual extents of Alternative 1 and Alternative 2 are shown in Figures 4 and 5, respectively. We anticipate reviewing each of these alternatives with PG&E prior to their selection of a preferred alternative. It is important to clarify that the alternatives presented Slope Reconnaissance and Alternatives Analysis Report Poe Powerhouse Rockfall Mitigation Project Gannett Fleming Project No. 065601 January 24, 2020 Page 7 of 20 below are intended to reduce the rockfall hazard from the cut slope itself; the risk posed by rockfalls originating between the crest of the cut slope and Union Pacific bench will not be reduced. Alternative 1: Unsecured Rockfall Drapery This alternative reduces the rockfall hazard by installing an unsecured rockfall drapery system on the cut slope above and adjacent to the portal structure. The drapery would incorporate a wire rope along the bottom of the netting to contain accumulated rockfall debris and prevent rock blocks from running out toward the facility. This alternative would require periodic clean-out of rockfall debris accumulated underneath the netting and at the toe of the slope by temporarily relaxing the bottom rope. The removed rockfall debris would then have to be transported away from the slope. This alternative may also include supplemental rock anchors to be used “as-needed” to secure potentially unstable rock blocks, based on field observations of the cut slope during construction. This alternative is anticipated to have a lower construction cost relative to Alternative 2, given the reduced number of rock anchors required. However, its long-term maintenance cost is estimated to be greater than Alternative 2. Alternative 2: Unsecured and Secured Rockfall Drapery This alternative reduces the rockfall hazard by installing a secured rockfall drapery on the slope directly above the portal structure, and an unsecured rockfall drapery on the cut slope to the north and south. Rock anchors will be installed in a grid-pattern above the portal structure to secure debris and rock blocks in place, thus preventing them from traveling to the bottom of the drapery. This system would require less frequent clean-out of rockfall debris above the portal structure. This alternative would also include supplemental rock anchors to be used “as-needed” within the unsecured drapery to secure potentially unstable rock blocks, based on field observations of the cut slope during construction. This alternative is anticipated to have a higher construction cost but slightly lower maintenance costs relative to Alternative 1. Rock and Ground Anchor Design Ultimate Rock/Ground Bond Stress Ultimate rock/ground bond stress can be estimated from unconfined compressive strength (UCS) test results 4 (Ref. 10). To account for potential locally weak rock zones, we recommend a rock/grout ultimate bond stress of 300 pounds-per-square-inch (psi) for the design of rock anchors and other mitigation system ground anchorages. Because the rock strength, degree of weathering, and formed block sizes vary locally at the site, we recommend that the upper 30 inches of rock be neglected when considering anchor bond during ground anchor design. We recommend that those portions of ground anchors drilled through talus or colluvium be similarly neglected, and and that the anchor total depth be dependent upon achieving the minimum bond length within competent rock. 4 The ultimate bond stress between the rock and the anchor grout can be approximated using a value of 10% of the UCS of the rock, up to a maximum value of 600 psi (Ref. 10). Slope Reconnaissance and Alternatives Analysis Report Poe Powerhouse Rockfall Mitigation Project Gannett Fleming Project No. 065601 January 24, 2020 Page 8 of 20 Corrosion Protection Based on project expereince in similar environments, we recommend that the exposed elements of the rockfall protection systems be galvanized. Constructability Considerations Facility Protection We agree with PG&E (Appendix A) that temporary facility protection measures should be installed prior to working on the slope and constructing the rockfall protection measures. A temporary facility/personnel protection plan submittal should be required as part of the pre-construction submittals and evaluated by PG&E prior to commencing work. Examples of temporary facility protection structures include k-rail, fencing, hay bales, etc., and are typically employed in conjunction with construction procedures including spotters and systems of warning construction and facility personnel if the potential for rockfall is detected. Naturally Occurring Asbestos (NOA) and Crystalline Silica Exposure Naturally occurring asbestos (NOA) minerals may be present within the ultramafic rock at the site. Asbestos fibers in the ultramafic rock may become airborne when disturbed, for example, during drilling. Crystalline silica exposure during drilling is another potential hazard. A health and safety plan should be developed by the contractor and implemented during construction, including procedures to prevent exposure to NOA and respirable crystalline silica in accordance with PG&E policies and federal, state, and local regulatory requirements related to NOA exposure. Minimum Clearances and Energized Equipment We agree with PG&E that the proximity of existing structures and assets to the site may constrain access and contractor means and methods. Construction work near energized equipment will require minimum safe distance clearances and may require an outage to accommodate installation of rockfall mitigation measures. Drilling means and methods should be used that minimize the generation of airborne dust that could create an increased electrical hazard within the switchyard around energized equipment. In addition, the anchors drilled near the base of the slope should be laid out and oriented to remain a safe distance from the pressurized penstock within the tunnel behind the portal structure. Slope Reconnaissance and Alternatives Analysis Report Poe Powerhouse Rockfall Mitigation Project Gannett Fleming Project No. 065601 January 24, 2020 Page 9 of 20 LIMITATIONS This report has been prepared for the sole use of the Pacific Gas & Electricity, and its designated agents, specifically for design of the improvements described herein for the subject project. The conclusions and recommendations contained in this report are solely professional opinions based upon the information obtained from the references listed below. Gannett Fleming is not responsible for the data presented by others. The information provided in this report is valid for a period of three (3) years from the date of issuance. Conditions may arise that were not apparent at the time of this design (e.g., changes in design geometries, soil design parameters, loadings, etc.). In addition, changes in applicable standard of practice can occur, whether from legislation or the broadening of knowledge. Accordingly, the information provided in this report may be invalidated, wholly or partially, by changes outside of our control. Should changes occur that might affect the design presented herein, Gannett Fleming should be notified to evaluate the validity of this report to those changes. This document may not be reproduced for any other reason than pertains to the project for which it was prepared. Sincerely yours, Gannett Fleming, Inc. Attachments Photos 1 through 11 Figure 1 – Site Plan Figure 2 – Surficial Geologic Reconnaissance Map Figure 3 – Cut Slope Primary Structural Discontinuity Stereonet Figure 4 – Alternative 1 Conceptual Layout Figure 5 – Alternative 2 Conceptual Layout Appendix A – Previous Rockfall Event Reports and Correspondence Appendix B – Kinematic Analyses Results Appendix C – Rock Sample Laboratory Test Reports No. 9405 1/24/2020 No. C77661 VICIL EUQAHLUDEYS 01/24/20 Slope Reconnaissance and Alternatives Analysis Report Poe Powerhouse Rockfall Mitigation Project Gannett Fleming Project No. 065601 January 24, 2020 Page 10 of 20 References 1. Pacific Gas & Electric Purchase Order 2700355965 for Non-Taxable – Engineering Services, dated November 17, 2019. 2. Poe Powerhouse Rockfall Mitigation – Engineering Design, prepared by Gannett Fleming, Inc., dated September 19, 2019. 3. Fault Activity Map of California, published by the California Geological Survey, http://maps.conservation.ca.gov/cgs/fam/, accessed December 2019. 4. Geologic Map of the Chico Quadrangle, Saucedo, G.J., Wagner, D.L., published by the State of California Department of Conservation, published January 1, 2002, scale 1:250,000. 5. Paleozoic-Mesozoic boundary in the Berry Creek quadrangle, northwestern Sierra Nevada, California, Geological Survey Professional Paper 1027, authored by A. Hietanen, published by the U.S. Department of the Interior, dated 1997. 6. Geology of the Pulga and Bucks Lake quadrangles, Butte and Plumas Counties, California, authored by A. Hietanen, published by the U.S. Geological Survey, Professional paper PP-731, scale 1:48,000. 7. Rock Slope Engineering, Civil and Mining, 4th Edition, Table 4.1 Typical ranges of friction angles for a variety of rock types, Chapter 4, pp 81, prepared by Wyllie, D.C., and Mah, C.W., published 2004. 8. Rock Slope Engineering, Civil and Mining, 4th Edition, prepared by Wyllie, D.C., and Mah, C.W., published 2004. 9. Design Guidelines for Wire Mesh/Cable Net Slope Protection, prepared by the B. Muhunthen et al, prepared for the Washington State Transportation Commission, in cooperation with the U.S. Department of Transportation Federal Highway Administration, dated April 2005. 10. Recommendations for Prestressed Rock and Soil Anchors, 4th Edition, published by the Post- Tensioning Institute, 2004. Slope Reconnaissance and Alternatives Analysis Report Poe Powerhouse Rockfall Mitigation Project Gannett Fleming Project No. 065601 January 24, 2020 Page 11 of 20 Photo 1: Poe Powerhouse penstock tunnel portal structure and cut slope. Note the station reserve service power equipment atop the structure and access way to penstock. View from north side of structure. Photo: DSCN5988_stitch.JPG Date: November 14, 2019 Slope Reconnaissance and Alternatives Analysis Report Poe Powerhouse Rockfall Mitigation Project Gannett Fleming Project No. 065601 January 24, 2020 Page 12 of 20 Photo 2: Penstock tunnel portal structure with metal access stairs on south side of the portal. Photo: DSCN5977.JPG Date: November 14, 2019 Photo 3: Damage to top of access stairs caused by recent rockfall events. Photo: IMG_0992.JPG Date: November 14, 2019 Slope Reconnaissance and Alternatives Analysis Report Poe Powerhouse Rockfall Mitigation Project Gannett Fleming Project No. 065601 January 24, 2020 Page 13 of 20 Photo 4: Bent steel cross member and concrete tower footing corner interpreted as rockfall damage (red arrow) caused by the 2018 event. Photo: DSCN6018.JPG Date: November 14, 2019 Photo 5: North-facing perspective of cut slope. Note the existing chain-link fence above the cut slope brow. Photo: DSCN6024.JPG Date: November 14, 2019. Slope Reconnaissance and Alternatives Analysis Report Poe Powerhouse Rockfall Mitigation Project Gannett Fleming Project No. 065601 January 24, 2020 Page 14 of 20 Photo 6: Largest rockfall block observed at toe of northern segment of cut slope (red arrow). Approx. dimensions are 3-ft x 0.5-ft x 0.5-ft. Photo: DSCN6008.JPG Date: November 14, 2019 Photo 7: Toppled rock block (red arrow) near northeast corner of the portal structure. Approx. dimensions are 2.5-ft x 0.5-ft x 2-ft. Photo: IMG_1021.JPG Date: November 14, 2019. Slope Reconnaissance and Alternatives Analysis Report Poe Powerhouse Rockfall Mitigation Project Gannett Fleming Project No. 065601 January 24, 2020 Page 15 of 20 Photo 8: Example of serpentinized relict bedding plane, dipping into the slope (B1, red strike and dip symbol), in an overhanging condition. Photo: IMG_0994.JPG Date: November 14, 2019 Photo 9: Prominent joint along southern segment of the cut slope associated with joint set J2 (green strike and dip symbol). Note band rock potentially weaker rock (dashed red line delineation) along bedding that may represent past hydrothermal alteration. Photo: IMG_0997.JPG Date: November 14, 2019. B1 J2 Slope Reconnaissance and Alternatives Analysis Report Poe Powerhouse Rockfall Mitigation Project Gannett Fleming Project No. 065601 January 24, 2020 Page 16 of 20 Photo 10: Assumed source area of recent rockfall events along the brow of the cut slope (delineated in with red dashed line). Photo: IMG_0995.JPG Date: November 14, 2019 Photo 11: Prominent joints along the southern segment of the cut slope associated with joint sets J1 (orange strike and dip symbol), J3 (yellow call outs of joint surfaces), and J4 (dashed blue lines). Photo: DSCN6036.JPG Date: November 14, 2019. J1 J4 J4 J3 N:\1-PROJECTS\0000 BST Projects\065601_PG&E_Poe PH Rockfall Mitigation (19-040.00)\500-WORKING\508-Maps and Photos\GIS DATE: JAN 2020 BY: MVB PROJ NO: 065601 Slope Reconnaissance - Poe Powerhouse Rockfall Mitigation Butte County, California FIGURE SCALE: 1" = 50' 1 Site Plan TAILRACE N. FORK FEATHER RIVER FLOW FLOW PENSTOCK TUNNEL PORTAL STRUCTURE PORTAL STRUCTURE CUT SLOPE POE POWERHOUSE TURBINE UNITS UNION PACIFIC RAILROAD ACCESS ROAD TO HW70 2018 ROCKFALL SOURCE AREA (APPROX.) UNION PACIFIC RAILROAD LOCATED FURTHER UPSLOPE POE POWERHOUSE N:\1-PROJECTS\0000 BST Projects\065601_PG&E_Poe PH Rockfall Mitigation (19-040.00)\500-WORKING\508-Maps and Photos\GIS DATE: JAN 2020 BY: MVB PROJ NO: 065601 Slope Reconnaissance - Poe Powerhouse Rockfall Mitigation Butte County, California FIGURE SCALE: 1" = 50' 2 Surficial Geologic Reconnaissance Map MzPz MzPz MzPz MzPz Qc Qc Qc Qc 45 43 82 39 61 NORTHERN CUT SLOPE SEGMENT CENTRAL CUT SLOPE SEGMENT SOUTHERN CUT SLOPE SEGMENT S1 S2 Qls Qls Qaf Qaf Qaf AREA NOT MAPPED AREA NOT MAPPED AREA NOT MAPPED PENSTOCK TUNNEL PORTAL STRUCTURE RESERVE STATION POWER EQUIPMENT ACCESS STAIRS LIGHT POLE FOOTING ELECTRICAL EQUIPMENT TOWER Contour Interval = 2' X X XXX EXISTING CYCLONE FENCE EXISTING WATER LINE VALVE GUY WIRE GUY WIRE EXISTING UTILITY POLE AREA NOT MAPPED EXPLANATION Qc Geologic Units Qls Qaf Rockfall Deposit/Debris Artificial Fill - Switchyard Colluvium Metavolcanic, meta-igneous, metasedimentary, and ultramafic rock MzPz Map Symbols Cut slope crest (approx.) S2 Sample block location 43 Sample block location Joint orientation 45 Joint orientation Bedding orientation Overhead electrical line Geologic contact (approx.) Hillshade and contours developed from terrestrial lidar point cloud provided by PG&E; acquired June 2019. Qls/Qaf Qls/Qaf NOTE: THE OREINTATION AND INCLINATION OF THE CUT SLOPE VARIES. THE MAJOR PLANE IS SHOWN WITH AN AVERAGE DIP OF 75ﹾ AND A DIP DIRECTION OF 248ﹾ. N:\1-PROJECTS\0000 BST Projects\065601_PG&E_Poe PH Rockfall Mitigation (19-040.00)\500-WORKING\508-Maps and Photos\GIS DATE: JAN 2020 BY: MVB PROJ NO: 065601 Slope Reconnaissance - Poe Powerhouse Rockfall Mitigation Butte County, California FIGURE SCALE: -- 3 Cut Slope Primary Structural Discontinuity Stereonet B1, N57W/50NE B1, N57W/50NE CUT SLOPE CUT SLOPE J1, N25W/56SW J1, N25W/56SW J2, N30E/64NW J2, N30E/64NW J3, N01E/80SE J3, N01E/80SE J4, N39E/84NW N:\1-PROJECTS\0000 BST Projects\065601_PG&E_Poe PH Rockfall Mitigation (19-040.00)\500-WORKING\508-Maps and Photos\GIS DATE: JAN 2020 BY: MVB PROJ NO: 065601 Slope Reconnaissance - Poe Powerhouse Rockfall Mitigation Butte County, California FIGURE SCALE: 1" = 50' 4 Alternative 1 Conceptual Layout NORTHERN CUT SLOPE SEGMENT CENTRAL CUT SLOPE SEGMENT SOUTHERN CUT SLOPE SEGMENT Qaf PENSTOCK TUNNEL PORTAL STRUCTURE RESERVE STATION POWER EQUIPMENT ACCESS STAIRS LIGHT POLE FOOTING ELECTRICAL EQUIPMENT TOWER Contour Interval = 2' X X XXX EXISTING CYCLONE FENCE EXISTING WATER LINE VALVE GUY WIRE GUY WIRE EXISTING UTILITY POLE Hillshade and contours developed from terrestrial lidar point cloud provided by PG&E; acquired June 2019. UNION PACIFIC RAILROAD LOCATED FURTHER UPSLOPE POE POWERHOUSE UNSECURED ROCKFALL DRAPERY CONCEPTUAL EXTENT (APPROXIMATE) N:\1-PROJECTS\0000 BST Projects\065601_PG&E_Poe PH Rockfall Mitigation (19-040.00)\500-WORKING\508-Maps and Photos\GIS DATE: JAN 2020 BY: MVB PROJ NO: 065601 Slope Reconnaissance - Poe Powerhouse Rockfall Mitigation Butte County, California FIGURE SCALE: 1" = 50' 5 Alternative 2 Conceptual Layout NORTHERN CUT SLOPE SEGMENT CENTRAL CUT SLOPE SEGMENT SOUTHERN CUT SLOPE SEGMENT Qaf PENSTOCK TUNNEL PORTAL STRUCTURE RESERVE STATION POWER EQUIPMENT ACCESS STAIRS LIGHT POLE FOOTING ELECTRICAL EQUIPMENT TOWER Contour Interval = 2' X X XXX EXISTING CYCLONE FENCE EXISTING WATER LINE VALVE GUY WIRE GUY WIRE EXISTING UTILITY POLE Hillshade and contours developed from terrestrial lidar point cloud provided by PG&E; acquired June 2019. UNION PACIFIC RAILROAD LOCATED FURTHER UPSLOPE POE POWERHOUSE AREA OF SECURED ROCKFALL DRAPERY UNSECURED ROCKFALL DRAPERY CONCEPTUAL EXTENT (APPROXIMATE) APPENDIX A – PREVIOUS ROCKFALL EVENT REPORTS AND CORRESPONDENCE EMAIL CORRESOPNDENCE: NEW PROJECT-POE PH STATION SERVICE PLATFORM PREPARED BY JONATHAN EDWARDS OF PG&E DATED MARCH 6, 2019 1 Buche, Matthew V. From:Steen, Emily <EADf@pge.com> Sent:Monday, June 18, 2018 8:39 AM To:Hill, M. Craig Cc:Edwards, Jonathan; McManus, Bob; Kottke, Albert Subject:Poe Powerhouse Rockfall Attachments:Poe PH Rockfall Photos 2018-06-15 r.pdf; Maccaferri Drapery Info.pdf Craig, As requested, I visited Poe Powerhouse on May 29 to inspect a rock slope above the yard following reported rockfall. Jonathan Edwards and Albert Kottke joined me onsite. All of my observations were from the powerhouse yard and the top of the concrete portal structure. I attempted to hike to the top of the slope above the rockfall area but was not able to do so because the slope was too steep and unsafe. This email summarizes my observations and recommendations for mitigating rockfall hazard in this area. Attached are photos and some reference information. Observations The rock slope is located on the east side of the powerhouse yard and is directly above the concrete portal structure that provides access to a manhole in the Poe Penstock. This structure/access point is commonly referred to as Adit 3 (where Adits 1 and 2 provide access to the Poe Tunnel upstream of the penstock). The structure also serves as a platform for station service electrical equipment (one abandoned and one in‐service lattice dead‐end structure, circuit breakers, and a lamp post). Excavation of the slope was required to facilitate construction of the concrete portal and station service equipment and resulted in a 20‐ to 30‐feet‐high oversteepened area above these facilities. The cut slope exposes metamorphic bedrock that is blocky to massive, moderately to slightly weathered, and strong. The rock quality improves with depth, and there appears to be a more weathered and dilated “rind” at the top of the cutslope near the original ground surface. The recent rockfalls are sourced from this upper rind near the south end of the concrete portal structure. The rockfalls reportedly occurred sometime during the exceptionally wet 2016/2017 winter season, but a precise date is not known. It is also not clear if the entire volume (several cubic feet) failed in one occurrence or if smaller blocks failed intermittently over time. The debris damaged an access stairway on the south side of the concrete portal. The lamp post and abandoned dead‐end structure below the source area do not appear impacted by this or past rockfalls. The near‐slope leg of the in‐service dead‐end structure on the north side of the platform had a small dent near the base, suggestive of past rockfalls. I did not see any seepage coming from the source area or anywhere else on the slope. The remaining rock in the source area, and in the upper rind on the rest of the cutslope, appears more dilated and susceptible to rockfalls. The lower portion of the slope is partially overhanging but looks tight and generally stable. I could not inspect the slope above the rockfall area for dilated blocks or tension cracks, but as observed from the powerhouse yard and the concrete structure I did not see evidence of a larger, global slope failure. The recent and past rockfalls appear localized and the result of construction excavations creating oversteepened slopes in a weathered and dilated zone of the bedrock. The Poe Penstock penetrates the mountain directly below this slope, but it does not appear to be excessively leaking or otherwise raising the groundwater level in the slope. There was no seepage coming from the slope during my inspection and the penstock was in operation. Because these failures occurred during the winter season, it is possible precipitation and runoff, an elevated groundwater level, and/or ice‐ jacking contributed to the rockfalls. The Union Pacific Railroad is about 180 feet upslope of the Adit 3 portal. Its possible vibrations from passing trains contribute to loosening of already dilated rock, but it does not appear to be a major contributor to rockfall from the slope at this time. 2 Recommendations Because of the more dilated rock in the upper part of the cutslope, small rockfalls will continue to be a hazard. The removed blocks and total volume may be small, but these could still injure personnel or damage electrical equipment. There is very limited access for personnel or equipment to perform work on this slope, which limits the possible rockfall mitigation options. Three options are discussed below, each of which could be evaluated by an experienced mining contractor to determine which would be most constructible and cost efficient. In any of the below scenarios, the mining contractor should conduct a pre‐construction inspection of the ground above the cutslope to confirm there are no tension cracks, zones of dilated rock, or similar that would indicate a larger slope failure that could pose a risk to workers or necessitate a more robust repair. The contractor should also remove the tree immediately above the rockfall source area; it’s roots may be loosening the rock mass and could contribute to rockfalls in the future. Hand Scaling The hazard blocks are relatively small (approximately one foot or less in max dimension) and could be scaled by hand by miners on ropes using a pry bar. During scaling operations uncontrolled rockfall could further damage the access stairway, the top of the concrete portal structure, or the electrical facilities, and these would have to be protected by the contractor using barricades or similar. The advantages of scaling are that it removes hazard blocks from the slope, is relatively inexpensive, and doesn’t require engineering or constructing new infrastructure. Periodic rescaling may be required in the future. Rockfall Drapery The slope is not very tall above the concrete platform, and the rock blocks are small, so the station service equipment could be protected from future rockfalls by a drapery net over the slope. This would be constructed of hexagonal double twist wire mesh anchored into competent rock above the cutslope and draped over the slope (see attached reference material). This method does not prevent rockfalls from occurring but does control their decent when they fall, minimizing their consequence to facilities or personnel. Rock debris must be periodically cleaned from the bottom of the net. This option would also require personnel to access the slope on ropes to drill and install drapery anchors, and hang the drapery over the slope. The contractor would work with a rockfall drapery vendor (e.g. Maccaferri) to design the anchorages. Geosciences can assist with reviewing that design if desired. The contract should consider the feasibility of installing anchors in the slope above, which may be made difficult by overburden or the fractured and dilated nature of the rock mass. Scaling and Drapery If the drapery option is selected, it may require only minimal additional effort to thoroughly scale the slope. Some scaling may be required anyway to make the area safe for workers on the slope. This would be the most thorough mitigation approach because it both removes existing hazard rocks and protects station service equipment from future rockfalls, and may not be significantly more expensive than the drapery alone. I can work with you and a contractor to determine your preferred mitigation option, and review the design for a drapery net if you select that solution. I can also give you a list of contractors experienced in mining and hazard rock mitigation for bidding or direct award. Please let me know if you have any comments or questions. Emily Emily Steen, PE, GE | Geotechnical Engineer | PG&E Geosciences 245 Market Street, Mail Code N4C, San Francisco, CA 94105 O: 415.973.3991 | M: 415.314.3805 | emily.steen@pge.com Adit 3 Portal and Station Service Equipment Rockfall Source Union Pacific Railroad Poe Powerhouse Rockfall Sourcebandoned Dead-end In-service Dead-end Damaged access stair dit 3 Entrance Adit 3 Entrance In-service Dead-end bandoned Dead-end Rockfall Source Damaged access stair Rockfall Source, zone of more weathered and dilated rock at top of cutslope, near original ground surface; susceptible to continued rockfalls. More competent, less dilated, less weathered rock lower in the slope Rockfall Source, zone of more weathered and dilated rock at top of cutslope, near original ground surface; susceptible to continued rockfalls. More competent, less dilated, less weathered rock lower in the slope Schematic showing approximate limits of rockfall drapery 06 MACCAFERRI MAC.RO™ SYSTEMS MESH SYSTEMS INTRODUCTION Maccaferri offers a complete range of mesh systems for rockfall protection. Selection of the optimum solution is based upon the analysis of the project site conditions (geology, topography, environment, static and dynamic loading conditions) and client requirements (design life, maintenance). Maccaferri technical software MACRO 1, MACRO 2 and BIOS, enable designers to select the appropriate system and product type. Often the Serviceability Limit State sets the design criteria, in this case deformations and not breaking loads are to be considered, so stiffness is the key design parameter. Another important parameter is the punching resistance, which defines the resistance of the system to the pressure of a punching body. Maccaferri’s wide variety of systems offer a range of values for both stiffness and punching resistance, allowing designers to select the optimum solution. Corrosion resistance of Maccaferri mesh systems is provided by heavily galvanised steel with optional polymer coatings. For aggressive environments, the System Stiffness Strength DT Mesh Moderate Moderate Steelgrid® HR Very High High HEA Panels Extreme Very High Ring Nets Low Extreme polymer coated mesh, Steelgrid® HR and HEA panels are available. The performance of these are often necessary, especially in coastal applications. Solutions Drapery Mesh is hung down the slope face from a secure top rope. Rock debris falling from the slope is contained safely behind the mesh and collects at the toe of the slope. Periodic removal of collected debris is needed. Secured Drapery Surface Stabilisation Pinned Drapery Like drapery, but the mesh system is enhanced by anchors (with or without face ropes) securing the mesh back to the slope. Loads in the system are transferred back to these anchors, enhancing the stability of the slope. 0707MACCAFERRI MAC.RO™ SYSTEMS MESH SYSTEMS ROCKFALL NETTING Double Twist (‘DT’) steel wire mesh is a highly efficient mesh combining ease and flexibility of use with unsurpassed cost-effectiveness. Used around the world for over 60 years, Maccaferri DT mesh is proven to offer robust, long lasting and cost-effective rockfall protection. Commonly used as ‘drapery’, DT mesh provides a protective curtain on the slope; any rocks and debris detaching from the slope are contained behind the mesh. Maccaferri DT mesh is available in a variety of puncture (punch) resistances and corrosion protection coatings to suit the project design and exposure conditions. It can be supplied with a range of installation accessories including C-rings and installation tools to increase site productivity. Double Twist vs Single Twist Mesh Unlike Single Twist (chain-link) style mesh, the construction of Double Twist (‘DT’) mesh inhibits the propagation of tears in the mesh. Research shows that damage to a DT mesh remains local and the mesh does not unravel/ unzip, due to the Double Twist ‘locked yet flexible’ connection between adjacent wires. Feature Benefit Double Twist mesh construction Does not unravel in the event of wire breakage Flexible in 3 dimensions Excellent containment of debris Easy to install on site Light-weight Ease of installation Variety of coatings Balance commercial and performance requirements C-Rings and tools No overlapping mesh on lateral connections = fast installation and minimal material wastage Variety of lengths and widths of mesh rolls Different lengths and widths are available to suit site conditions, saving install time and waste TECHNICAL DATA SHEET Rev: 01, Issue Date 07.01.2017 ROLLED MESH GALMAC® Figure 1 Figure 2 Figure 3 - Example of Rolled Mesh Figure 4 - Example of Rolled Mesh Product Description Rolled mesh consists of GalMac® coated double twisted steel woven wire mesh manufactured in accordance with ASTM A975. The steel wire used in the manufacture of the mesh is heavily GalMac® (Zinc-5% aluminum-mischmetal [Zn-5% Al-MM] alloy) coated soft temper steel. The standard specifications for the wire-mesh are shown in Tables 2, 3, 4. Rolled Mesh is used for a wide variety of civil applications. It is used in conjunction with other double twisted wire mesh products such as gabions, mattresses, etc. or it is used alone for rockfall applications, repair work, etc. Rolled Mesh is supplied at standard lengths and can be cut to fit on site. Wire All tests on wire must be performed prior to manufacturing the mesh. All wire should comply with ASTM A975, style 1 coating and GalMac®. Wire used for the manufacture of Rolled Mesh and the lacing wire, shall have a maximum tensile strength of 75,000 psi (515 MPa) as per ASTM A856/A856M, soft temper steel. Woven Wire Mesh Type 6x8 and 8x10 The mesh and wire characteristics shall be in accordance with ASTM A975. The minimum mesh properties for strength and flexibility should be in accordance with the following: W D The tolerance on the opening of mesh "D" being the distance between the axis of two consecutive twists, is according to ASTM A975. Mesh Type Nominal Mesh Opening D in (mm) Mesh Tensile Strength lb/ft (kN/m) Mesh Connec- tion to Selvedge lb/ft (kN/m) Punch Test lb (kN) 6x8 2.5 (64) 33.6 (2300) 700 (10.2) 4,000 (17.8) 8x10 3.25 (83) 35,00 (51.1) 1,400 (20.4) 6,000 (26.7) A Table 1 - Sizes for mesh L=Length ft (m) W=Width ft (m) 150 (45.7) 6.0 (1.83) or 12 (3.66) All sizes and dimensions are nominal. Tolerances of +/- 1 % of the length , and 5% of the width shall be permitted. B C Pneumatic Spenax tool Manual tool Lacing Operations Lacing operations are made by using lacing wire specified in Table 3 and described in Figure 5. GalMac ® coated ring fasteners (Figure 6), using the appropriate tools shown in Figure 7 for connection, can be used instead of, or to complement lacing wire. GalMac® coated rings for GalMac® mesh shall be in accordance with ASTM A975 section 6.3. Spacing of the rings shall be in accordance with ASTM A975 Table 2, Panel to Panel connection, Pull-Apart Resistance. In any case, ring fasteners spacing shall not exceed 6 in. (150 mm) (Figure 5). Ring diameter: 0.118 in. (3.00 mm). The maximum spacing of the fasteners is determined by ASTM A975 Table 2, Pull-Apart Resistance test. Table 2 - Standard mesh-wire Type D in. (mm) Tolerance Wire Dia in. (mm) 6x8 2.5 (64) +10% 0.087 (2.2) 8x10 3.25 (83) +10% 0.120 (3.05) Table 3 - Standard wire diameters Lacing Wire Mesh Wire Selvedge Wire 6x8 ø in. (mm) 0.087 (2.2) 0.087 (2.2) 0.106 (2.7) 8x10 ø in. (mm) 0.087 (2.2) 0.120 (3.05) 0.153 (3.9) Table 4 - Wire tolerances and coating Wire diameter in. (mm) 0.087 (2.20) 0.106 (2.70) 0.120 (3.05) 0.153 (3.90) Wire tolerance + ø in. (mm) 0.004 (0.1) 0.004 (0.1) 0.004 (0.1) 0.004 (0.1) 0.70 (214) 0.80 (244) 0.85 (259) 0.90 (275) Min qty/GalMac® oz/ft2/(g/m2) Maccaferri reserves the right to amend product specifications without notice and specifiers are requested to check as to the validity of the specifications they are using. Lacing wire Rings Ma x 6 i n . (1 5 0 m m ) Open Closed Nominal overlap of 1 in. (25 mm) after closure 0. 7 5 i n . (1 9 m m ) 1.75 in. (44 mm) Quantity Request When requesting a quotation, please specify: Number of units, size of units (length x width, see Table 1), type of mesh, type of coating. EXAMPLE: No. 100 rolled mesh, 150 ft (45.7 mm), Mesh type 8x10, Wire diameter 0.120 in. (3.05 mm), GalMac®. Figure 7 Figure 6 Figure 5 1) Pliers 2) Pliers with nipper 3) Nipper Area Offices: AZ, Phoenix MO, St. Louis PR, Caguas CA, Sacramento NJ, Iselin TX, Lewisville FL, Coral Gables NM, Albuquerque WA, Seattle MD, Williamsport OH, Columbus www.maccaferri-usa.com Headquarters: 10303 Governor Lane Boulevard Williamsport, MD 21795-3116 Tel: 800-638-7744 Fax: 301-223-6134 info@maccaferri-usa.com MACCAFERRI INC. ©2012 Maccaferri, Inc. Printed in USA EMAIL CORRESOPNDENCE: POE POWERHOUSE ROCKFALL PREPARED BY EMILY STEEN OF PG&E GEOSCIENCES DATED JUNE 18, 2018 1 Buche, Matthew V. From: Edwards, Jonathan <JWEd@pge.com> Sent: Wednesday, March 6, 2019 5:03 PM To: Darren Mack <dmack@sageengineers.com> Cc: Macleod, Chris <C5Mi@pge.com> Subject: New Project‐Poe PH Station Service Platform Hi Darren, I’ve got a new project this year at Poe PH that will involve mitigating a rock fall that continues to shed rocks on the station service platform. We’ve recently experienced some significant damage to the platform and railing and there are fears that it will eventually take out station service. Once the Advance Authorization is in place, I would like to get SAGE scheduled for a Scoping site visit. Is there a good day during the weeks of April 15th or April 22nd that would work for you or the engineer you assign? Thank you, Jonathan Edwards, PE | Senior Project Engineer | Power Generation Cell: (530)-514-9364 | Office: (530) 896-4400 | jwed@pge.com APPENDIX B – ROCK SAMPLE LABORATORY TEST REPORTS Depth, ft. - PROJECT NUMBER:19-280 Wet Unit MOISTURE CONTENT & UNIT WEIGHT TEST RESULTS December 18, 2019 Sample Moisture Content, % Dry Unit Weight, lb/ft.3 163.5 Identification S1 (49364) Weight, lb/ft.3 165.2 1.0 Poe Powerhouse Test Method: ASTM D2216, ASTM D2937 3362 Fitzgerald Road Rancho Cordova, CA 95742 Phone: (916) 939-4117 FAX: (916) 635-4315 Project Name: Poe Powerhouse Rockfall Mitigation Date: 12/06/2019 Client Job Number: 65601 Sample ID: S1 Gulf Shore Job Number: 19-280 Sample No.: 49364 Rock Coring Core Sample from Rock Sample S1 Rock Sample S1 - Cored Hole Tested By: CHM Checked By: JL UNCONFINED COMPRESSION TEST Project No.: 19-280 Date Sampled: Remarks: Figure Client:Gannett Fleming Project:Poe Powerhouse Location: S2 Sample Number: 49365 Depth: N/A Description: LL = PI = PL = GS= 2.7 Type: Rock Core Sample No. Unconfined strength, psi Undrained shear strength, psi Failure strain, % Strain rate, in./min. Water content, % Wet density, pcf Dry density, pcf Saturation, % Void ratio Specimen diameter, in. Specimen height, in. Height/diameter ratio 1 18603.16 9301.58 2.0 0.050 0.1 166.7 166.5 31.5 0.0123 1.74 3.48 2.00 Co m p r e s s i v e S t r e s s , p s i 0 5000 10000 15000 20000 Axial Strain, % 0 1 2 3 4 1 Project Name: Poe Powerhouse Rockfall Mitigation Date: 12/06/2019 Client Job Number: 65601 Sample ID: S2 Gulf Shore Job Number: 19-280 Sample No.: 49365 Unconfined Compression Before UC Testing After UC Testing