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HomeMy WebLinkAboutPA2023-0161_20230911_Basis of Design Memorandum Memorandum 18575 Jamboree Road, Suite 150 Irvine, CA 92612 T: 949.561.9200 F: 949.561.9201 To: Don Bragg and Lisa Congdon, The Prado Group CC: Kari Heavenrich and Brian Howe, Rockpoint From: Christopher J. Zadoorian Date: August 17, 2023 Re: Basis of Design and Associated Updates to Previously Approved Soldier Piles and Landslide Mitigation Measures Previous City of Newport Beach Approval CDP PA 2023-0034 Park Newport Apartment Complex 1 Park Newport Newport Beach, California Langan Project No.: 700128101 Langan Engineering and Environmental Services Inc. (LANGAN) is pleased to submit this memo summarizing our basis of design for installation of the soldier piles needed to protect existing, principal residential structures at the Park Newport Apartment Complex located on 1 Park Newport in Newport Beach, California. The site is located at the northwest corner of Jamboree Road and San Joaquin Hills Road and is bound on the north by Big Canyon Nature Park and on the west by Upper Newport Bay (aka Back Bay) and Back Bay Drive as shown on Figure 1. The site is situated on a coastal bluff that includes descending slopes up to approximately 90 feet in height with gradients commonly ranging from approximately ½:1 to 1½:1 (horizontal:vertical) and in some cases near vertical. The site was developed between 1969 and 1972 and includes large footprint apartment buildings and small footprint townhomes as shown on Figure 2. Since construction, several episodes of mitigation have been implemented to address slope failures primarily along the west and northwest descending slopes. We are currently performing a design-level geotechnical evaluation and will issue the results of our investigation in a report. In the interim, this memorandum summarizes recommended alignment of the soldier piles and conceptual design parameters. Soldier pile have previously been proposed and approved by the City of Newport Beach (CDP PA 2023-0034) along the westerly sides of Buildings 4 and 37. The mitigation structures described herein are substantially the same kind of soldier pile structures as summarized in and authorized by the previously approved CDP, but with nominal changes made to the precise locations and lengths of the installation. The intent of the soldier piles to protect the existing residential structures and account for applicable geotechnical and structural (including seismic) loads. To aid in our evaluation, you furnished us with reports of geotechnical investigation for our review prepared by several firms including LeRoy Crandall & Associates (LCA, 1968, 1969 and MEMO Basis of Design and Associated Updates to Previously Approved Soldier Piles and Landslide Mitigation Measures (City of Newport Beach CDP PA 2023) Park Newport Apartment Complex Langan Project No.: 700128101 August 17, 2023 Page 2 of 3 1979), Hetherington Engineering, Inc. (HEI, 2021) and Rock Solid (2022 and 2023). Pertinent borings from the prior investigations are presented in the attachment for reference. Building 4 Building 4 is a four-level building that includes three above-grade apartment levels and one partial subterranean parking level as shown on Figure 1. The foundation elements of Building 4 are present within the subterranean level and these elements provide critical axial and lateral support for the residential dwellings located in this building. Based on our review of as-built plans, the building is supported on shallow caissons that range from approximately six to 19 feet deep. Mapped landslides, zones of rockfall and/or other portions of excessively steep slope are present along the westerly side of the building as summarized in the prior geotechnical reports. Several exploration borings were performed along the westerly side of Building 4 as shown on Figure 1. Based on our review of the prior boring data, a shear zone (zone of slippage) was logged in prior Borings 2 through 4 at depths ranging from 24 to 37 feet below the ground surface level in the borings (LCA, 1979). Based on our review of the prior geotechnical reports, as-built foundation plans, existing conditions, and our independent site reconnaissance, it is our professional opinion that an approximately 300-foot-long solider pile installation is required to provide adequate lateral support for the existing building. The proposed location of the mitigation structure is shown on Figure 1. The rationale for the current recommended wall length is to provide support to the foundation elements of residential Building 4 within areas of observed distress and/or zones of slope instability. The proposed soldier piles may consist of 24- to 36-inch diameter cast-in-drilled hole (CIDH) shaft solider piles noting that permanent tie-back anchors may also be incorporated. We anticipate solider piles will range on the order of 30 to 60 feet deep and tie-back anchors to extend approximately 50 to 75 feet at a typical inclination of approximately 20 degrees from the horizontal. Solider piles and tie-back anchors will be located below ground. Building 36 / 37 Building 36 and 37 are two-level townhomes established at approximately the existing ground surface level. Based on our review of as-built plans, the building is supported on shallow spread and continuous footings. Mapped landslides and excessively steep slope are present along the westerly side of the building as summarized in the prior geotechnical reports. A temporary mitigation measure consisting of steel-link mesh was installed in response to a surficial landslide that occurred circa 2020. MEMO Basis of Design and Associated Updates to Previously Approved Soldier Piles and Landslide Mitigation Measures (City of Newport Beach CDP PA 2023) Park Newport Apartment Complex Langan Project No.: 700128101 August 17, 2023 Page 3 of 3 Prior Boring 5 (LCA, 1968) does not indicate shear zones but does show relatively steep out of slope bedding planes that appear to be consistent with the 2020 landslide. Based on our review of the prior geotechnical reports, as-built foundation plans, existing conditions, and our independent site reconnaissance, approximately 150 lineal feet of soldier pile are required to stabilize existing Building 37 and approximately 30 lineal feet of soldier piles are required to stabilize existing Building 36. The proposed locations of the soldier piles and related mitigations are shown on Figure 2. The rationale for the recommended soldier piles is to protect the existing residential structures and provide lateral support needed due to the steep out-of-slope dipping condition (that is prone to sudden slippage) specifically at the westerly corner of Building 36. Additionally, the westerly corner of existing Building 37 extends to within approximately 15 feet of the top (aka edge) of the slope and additional protection is required at this location as shown on Figure 2. The proposed mitigation may consist of 24- to 36-inch diameter cast-in-drilled hole (CIDH) shaft solider piles. We anticipate solider piles will range on the order of 60 feet in depth. While tie- back anchors may increase stability, they may not be needed at this location and for the purposes of this basis of design memo have been omitted as access for tie-back anchor installation will be challenging. The protective structures described in this memo are intended to provide the minimum measures required to protect the existing principal residential dwellings. Closing We appreciate the opportunity to provide professional services for you for this project. Please contact us with any questions of comments regarding the information presented herein. Enclosures: Figures 1 and 2 Appendix – Prior Pertinent Boring Logs C:\Users\CZadoorian\Desktop\Projects\Prado-Group-Park-Newport\Report\Basis-of-Design\700128101-geom-basis-of-design-081723.docx FIGURES 4 B-2 51 B-3 51 B-6 20 B-1 51 B-4 51 B-7 21 B-5 21 B-7 100 Filename: \\langan.com\data\IRV\data1\700128101\Project Data\_Discipline\Geotechnical\CAD\OLD VERSIONS\GEOTECHNICAL FIGURES - 7.28 for client.dwg Date: 8/15/2023 Time: 15:36 User: smikolajczyk Style Table: Langan.stb Layout: 11x17 L Bldg 4 Project No. Date Scale Drawn By 700128101 AUGUST 2023 AS SHOWN Figure No.Figure TitleProject ORANGE COUNTY CALIFORNIA 1 PARK NEWPORT NEWPORT BEACH PARK NEWPORT APARTMENT COMPLEX Langan Engineering and Environmental Services, Inc. © 2 0 2 0 L a n g a n 18575 Jamboree Road Suite 150 Irvine, CA 92612 T: 949.561.9200 F: 949.561.9201 www.langan.com CC 1 SOLDIER PILE WALL LOCATION BUILDING 4 LEGEND: PROPOSED SOLDIER PILE WALL (LANGAN, 2023) PROPOSED SOLDIER PILE WALL CURRENTLY PART OF CDP PA2023-0034 (KGI, 2023) EXISTING TENSION CRACKS IN BUILDING 4 FLOOR SLAB APPROXIMATE LOCATION OF SUBTERRANEAN LEVEL OF BUILDING 4 PRIOR BORING LOCATION AND DEPTH IN FEET (LEROY CRANDALL, 1979) PRIOR BORING LOCATION AND DEPTH IN FEET (LEROY CRANDALL, 1968) LANDSLIDE ZONE (ROCKSOLID, 2023) LANDSLIDE ZONE (LEROY CRANDALL, 1968) SURFICIAL FAILURES/ EROSION/ROCKFALL LANDSLIDE DIRECTION BUILDING NUMBERS 4 B-7 100 B-1 51 36 37 B-5 75 B-6 75 Filename: \\langan.com\data\IRV\data1\700128101\Project Data\_Discipline\Geotechnical\CAD\OLD VERSIONS\GEOTECHNICAL FIGURES - 7.28 for client.dwg Date: 8/15/2023 Time: 15:39 User: smikolajczyk Style Table: Langan.stb Layout: 11x17 L Bldg 37 Project No. Date Scale Drawn By 700128101 AUGUST 2023 AS SHOWN Figure No.Figure TitleProject ORANGE COUNTY CALIFORNIA 1 PARK NEWPORT NEWPORT BEACH PARK NEWPORT APARTMENT COMPLEX Langan Engineering and Environmental Services, Inc. © 2 0 2 0 L a n g a n 18575 Jamboree Road Suite 150 Irvine, CA 92612 T: 949.561.9200 F: 949.561.9201 www.langan.com CR 2SOLDIER PILE WALL LOCATION BUILDING 36 & 37 LEGEND: PROPOSED SOLDIER PILE WALL (LANGAN, 2023) PROPOSED SOLDIER PILE WALL CURRENTLY PART OF CDP PA2023-0034 (KGI, 2023) EXISTING SOLDIER PILE WALL, 36-INCH DIAMETER, 60 FEET DEEP, 7 FEET ON CENTER PRIOR BORING LOCATION AND DEPTH IN FEET (LEROY CRANDALL, 1979) PRIOR BORING LOCATION AND DEPTH IN FEET (LEROY CRANDALL, 1968) LANDSLIDE ZONE (ROCKSOLID, 2023) LANDSLIDE ZONE (LEROY CRANDALL, 1968) SURFICIAL FAILURES/ EROSION/ROCKFALL LANDSLIDE DIRECTION BUILDING NUMBERS4 B-7 100 B-1 51 APPENDIX Prior Pertinent Boring Logs