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HomeMy WebLinkAboutMS 16-05; 1284 PINE AVE; GEOTECHNICAL RESPONSE REPORT; 2020-01-07W. C. HOBBS, CONSUL TING ENGINEER 33892 COPPER LANTERN, UNIT A DANA POINT CALIFORNIA 92629 (951) 660-9800 Date: January 7, 2020 Project No: 1901 4-1-R1 1284 Pine Partners, LLC 1284 Pine Avenue Carlsbad, California 92008 Subject: Response to Report Review Comments from Carlsbad, Geotechnical Update Report with References, As-Graded Conditions, 1284 Pine Avenue, Carlsbad, California 92008, dated Nov. 5, 2019 Gentlemen, This Response report has been prepared to address review comments made during plan check by the City of Carlsbad third party reviewer. Responses are included on an Item by Item bases. The review comments are attached to the back of this response report for easy reference. This response shall become a part of, amend and be considered inseparable from the subject report dated November 5, 2019, and its references. The opportunity to be of service is appreciated. Should questions or comments arise pertaining to this document, or if we may be of further service, please do not hesitate to call our office. Respectfully Submitted, W. C. HOBBS, CONSUL TING ENGINEER Bill t-10b s, Civil Engineer Distribution: Attachments: \.· ./''I/ \~\.~ I -'t,./t.. Addressee (1) electronic pdf Third Party Review Sheets, 2 pages 1284 Pine Partners, LLC., Geotechnical Response Report Project No: 19014-1-R1 Page:2 GEOTECHNICAL RESPONSE REPORT Item 1: The information following in this section has been captured from a variety of published literature on the relevant subject and is believed to represent accurately the conditions at the subject site with respect to geologic conditions, geologic structure and faulting. Regional Geology San Diego County is divided into three distinct geologic areas: the Coastal Plain region, Peninsular Ranges region, and Salton Trough region. The Coastal Plain region includes most of western San Diego County and consists primarily of Mesozoic crystalline rocks underlain by marine and non-marine sedimentary rocks. In this region, drastic land and sea fluctuations have preserved ancient marine rocks up to elevations around 900 feet and ancient river deposits up to 1,200 feet. The Peninsular Ranges region includes much of eastern San Diego County and consists primarily of plutonic rocks that formed from the cooling of molten magmas deep within the Earth's crust between 140 and 90 million years ago. Other sediments are now preserved in this region as marbles, slates, schist, quartzites, and gneiss deposits. The Salton Trough or Colorado Desert region includes the eastern third of San Diego County and is characterized by late Miocene-aged marine sedimentary rocks and Pleistocene aged stream and playa lake deposits (Demere n.d.). Local Geology and Soils Carlsbad is within the coastal portion of the Peninsular Ranges Geomorphic Province, a region characterized by northwest-trending structural blocks and intervening fault zones. Typical lithologies in the Peninsular Ranges include a variety of igneous, intrusive rocks associated with the Cretaceous-age (between approximately 65 and 135 million years old) Southern California Batholith (a large igneous intrusive body). In western San Diego County, batholithic rocks are often intruded into Jurassic-age (between approximately 135 and 195 million years old) metavolcanic and/or metasedimentary units, with these basement rocks locally overlain by Tertiary-age (between approximately 2 and 65 million years old) marine and non-marine sedimentary strata. Tertiary rocks in the western portion of the county are associated primarily with a number of sea level advance and retreat cycles over approximately the last 55 million years, including sedimentary units in Carlsbad and vicinity as described below. W. C. HOBBS, CONSUL TING ENGINEER 1284 Pine Partners, LLC., Geotechnical Response Report Project No: 19014-1-R 1 Page:3 Topographically, the Peninsular Ranges Province is composed of generally parallel ranges of steep-sloping hills and mountains separated by alluvial valleys. More recent uplift and erosion has produced the characteristic canyon and mesa topography present today in western San Diego County, as well as the deposition of surficial materials including Quaternary-age (less than approximately two million years old) alluvium, colluvium and topsoil. The geology as shown in the Oceanside Quadrangle, in which the city is located, indicates that the site is underlain by alluvium. This is evidenced in the boring into the proposed building area and logged in the 2012 referenced report of the subject report (Nov. 5, 2019). Earthquake Faults Review of State of California Documents indicates that there are no active faults that run directly through Carlsbad. Additionally, the California Geological Survey does not include Carlsbad on its list of cities affected by Alquist-Priolo Earthquake Fault Zones. The nearest fault to the city is the Newport-Inglewood-Rose Canyon Fault, which runs offshore of the western edge of the city and is considered active. Other faults in the region include the Coronado Bank, La Nacion, Elsinore, Agua Caliente, and San Jacinto. Fault activity has the potential to result in ground shaking, which can be of varying intensity depending on the intensity of earthquake activity, proximity to that activity, and local soils and geology conditions. Carlsbad is located within a seismically active region, and earthquakes have the potential to cause ground shaking of significant magnitude. Although located near fault lines, Carlsbad lies within a medium-low probabilistic peak ground acceleration zone. Historic documents record that an earthquake centered either on the Rose Canyon or Coronado Bank faults struck San Diego on May 27, 1862, damaging buildings in Old Town and causing ground rupture near the San Diego River mouth. This earthquake is believed to have had a magnitude of about 6.0 based on descriptions of the damage it caused. The strongest recorded earthquake in the San Diego area was a magnitude of 5.3 on the Richter scale that struck on July 13, 1986, on the Coronado Bank fault, 25 miles offshore of Solana Beach. There have been several moderate earthquakes recorded within the Rose Canyon Fault Zone as well. On June 17, 1985, three earthquakes hit San Diego measuring 3.9, 4.0, and 3.9, respectively, and on October 28, 1986, a stronger earthquake with a magnitude of 4. 7 occurred. Item 2: Liquefaction can cause the soil beneath a structure to lose strength, which may result in the loss of foundation-bearing capacity. This loss of strength commonly causes the structure to settle or tip. Loss of bearing strength can also cause light buildings with basements, buried tanks, and foundation piles to rise buoyantly through the liquefied soil. Historically, seismic shaking levels in the San Diego region, including Carlsbad, have not W. C. HOBBS, CONSULTING ENGINEER 1284 Pine Partners, LLC., Geotechnical Response Report Project No: 19014-1-R1 Page:4 been sufficient enough to trigger liquefaction. The city has a low liquefaction risk; however, there are areas of the city that have a higher risk of liquefaction due to the presence of hydric soils or soils that are often saturated or characteristic of wetlands. These areas are limited to the immediate vicinity of the Buena Vista, Agua Hedionda, and Batiquitos lagoons. The subject site is not near any of those locations. Due to the density of the earth materials (dense to very dense) encountered in the boring of the referenced investigation(s) dated 2012 and subsequent earthwork performed in 2016 placing compacted fill in the upper 3 to 4 feet at the site, combined with the historical depth to groundwater, the potential for liquefaction at the site is nil. Tsunami inundation maps including the Oceanside and San Luis Rey quadrangles indicate that the subject site on Pine avenue northeast of the interstate 5 freeway is well outside the inundation zone, particularly at elevation 108. Therefore, tsunami is not considered a geologic hazard. Item 3: As a matter of clarification, it shall be stated herein that no surficial recompaction in the upper 1 foot is recommended at this time. This is based on physical observation of the site within the previous month of this writing. Foundations may be excavated into existing soils. It is a forgone conclusion that the recommendations for the soil engineer to observe foundation excavations remains. Item 4: Construction and grading on this site will have no adverse impact on adjacent sites. Item 5: It is believed that all of the exterior hardscape will be constructed with pavers. However, as an alternate, with respect to hardscape on the exterior of the proposed residence structure, all concrete slabs on grade should be 4 inches thick, minimum. They should be underlain by 2 inches of sand or approved non expansive onsite materials. Contractors should be advised that when pouring during hot or windy weather conditions, they should provide large slabs with sufficiently deep weakened plane joints to inhibit the development of irregular or unsightly cracks. Also, 4 inch thick slabs should be jointed in panels not exceeding 8 feet in both directions to augment proper crack direction and development. Exterior slabs should be reinforced with a minimum of number 3 steel bars placed at the center of thickness at 18-inch centers both ways (CBC 2016). Item 6: Based on Table 11.6-1 of ASCE 7-10 for risk category and Sos, Seismic Design Category is D. Item 7: No response required. W. C. HOBBS, CONSULTING ENGINEER HETHERINGTON ENGINEERING, INC. SOIL & FOUNDATION ENGINEERING• ENGINEERING GEOLOGY• HYDROGEOLOGY December 11, 2019 Project No. 8924.1 Log No. 20789 City of Carlsbad 1635 Faraday Avenue Carlsbad, Califotnia 92008 Attention: Subject: Reference: Ms. Kyrenne Chua THIRD-P ARTYGEOTECHNJCAL REVIE:W (SECOND) Proposed 2nd Dwelling · 1284 PiI1e Avenue Cadsbad, Califdrnia Project ID: GR20J9s0024 '--D:WG 518-7A l) "Certification of Pad, Proposed 2nd Dwelfu1g., APN: 205-020-04, Lot 9 of Ti·act Map No 1744, 1284 l>ine Avenue, City. of Carlsbad, San Diego County, California, Work Otdet No. 1931503,22", by South Shore Testing & Envirofuriental, dated May 9, 2016. 2) "Geotechnical Update, As-Graded Conditions, 1284 Pine Avenue, Carlsbad, California 92008", by W. C. Hobbs, Co11sulting Engineer, dated June 6, 2019. 3) "Grading Plan For: 1284 Pine Avenue", by W.C. Hobbs, Consulting Engineer, dated June 6, 2019 (2-sheets} 4) "Third-Party Geotechnical Review (First), . Proposed 2nd Dwelling, 1284 Pine Avenue, Carlsbad, California, Project ID: GR2019-0024 - DWG 518-7A". by Hetherington Engineering, Inc., dated JtHy 16, 2019. .. 5) Geotechnical Update Report with References, As-Graded Conditions, 1284 Pine Avenue, Carlsbad, California", by W.C. Hobbs, Consulting Engineer, dated November 5, 2019. Dear Ms. Chua: In accordance with your request, Hethedngton Engineering, Inc. has provided tlrird-party geotechnical review of Reference 5. The following comments .ate provided for analyses and/or response by the Geotechnical Consultant. 5365 Avenida Encinas, Suite A • Carlsbad, CA 92008-4369 • (760) 931-1917 • Fax (760) 931-0545 333 Third Street, Suite 2 • Laguna Beach, CA 92651-2306 • (949) 715-5440 • Fax (760) 931-0545 www.hetheringtonenglneering.com THIRD-PARTY GEOTECHNICAL REVIEW (SECOND) Project No. 8924. l Log No. 20789 December 11,2019 Page2 1. The Consultant should discuss rc:g1011al geologic conditions, geologic strncture, and faulting. (Second Request) 2. The Consultan:t should address liquefaction and tsunami poterttialat the site. (Second Reqwit) 3. Reference I indicates scarificaijon • and recompaction · of the graded . pad is recommended. ,R_eferenoe 2 indicates. no·. '~fwiher grading requirements". The Consultant should address this appm·ent discrepancy. (Second Request) . . . 4. TI1e Consultant should addtess impacts to adjacent property and improvements as a result of site grading and construction: (Second Request) 5. The. Consultant . should .... ptovide harclscape J'econunendations (thickness, reinforcement, joints, etc.), if necessary. (Second Request) 6. The CoriSultant should provide the seismic design category for the site. 7. It should be noted .that the Conclusions. and Recommendations in the "Certification of Pad .... " repb1t should refer to the 2016 California Building Code and the CUJTertt City of Carlsbad guidelines. N~ tesponse required. Please call if there are any questions. Ci · . Geotechnical En (expires 3/31/20) ,·. ogse Professional Geologist 3772 Certified Enginee1ing Geologist 1153 Certified H:ydrogeologist 591 (expires 3/31/20) · Distribution: 1-via e-mail (Kytenne.Chua@carlsbadca.gov) 1-via e-mail (Cecel!a,Femandez@carlsbadca.gov) HETHERINGTON ENGINEERING. INC.