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Home My WebLink AboutMS 16-04; VIASAT BRESSI RANCH CAMPUS; RESPONSE TO CITY COMMENTS; 2020-06-08I15 jtJL- S GEOCON INCORPORATED GEOTECHNICAL • ENVIRONMENTAL • MATE RIALS) Project No. G1928-52-02 June 8, 2020 Viasat 6155 El Camino Real Carlsbad, California 92009 Attention: Mr. Ryan Hatch Subject: RESPONSE TO CITY COMMENTS VIASAT BRESSI RANCH - PHASE 5 BUILDINGS 16,17 AND PARKING STRUCTURE 3 SOUTHWEST CORNER OF GATEWAY ROAD AND ALICANTE ROAD CARLSBAD, CALIFORNIA References: 1. Update Geotechnical Investigation, Viasat Bressi Ranch - Phase 5, Southwest Corner of Gateway Road and Alicante Road, Carlsbad, California, prepared by Geocon Incorporated, dated August 23, 2019 (Project No. G1928-52-02). Precise Grading Plans for: Viasat Bressi Ranch Campus, Phase 5, Carlsbad, California, prepared by Pasco Laret Suiter & Associates, dated June 1, 2020 (Project No. MS 16-04, Drawing No. 497-41)). Third-Party Geotechnical Review (First), Proposed New Commercial Development, Viasat Bressi Ranch Campus Phase 5, Carlsbad, California, prepared by Hetherington Engineering, Inc., dated March 12, 2020 (Project No. 9083.1). Dear Mr. Hatch: In accordance with the request of Mr. Ryan Taylor with PLSA, we prepared this letter to address the third-party geotechnical review comments prepared by Heatherington Engineering, Inc. and provided by the City of Carlsbad regarding the subject project. The geotechnical review comment is included with our response immediately following. Comment 1: The consultant should provide an updated geotechnical report addressing the plans, and provide updated grading, seismic design, and foundation recommendations consistent with the 2019 California Building Code and ASCE 7-16. Response: Based on our review of the referenced grading plan and the limited changes to the major components of the site design, we consider the recommendations provided in our referenced geotechnical report to still be applicable to site. However, the additional grading and foundation recommendations provided herein should be used for the ancillary structures and site improvements that have been added or revised on the site plan. 6960 Flanders Drive 0 San Diego, California 92121-2974 a Telephone 858558.6900 0 Fax 858.558.6159 Additionally, we previously provided updated seismic recommendations in accordance with the 2019 California Building Code requirements to the design team. The following excerpt provides the updated seismic recommendations provided in our letter dated February 3, 2020: Table 1 summarizes site-specific design criteria obtained from the 2019 California Building Code (CBC; Based on the 2018 International Building Code [IBC] and ASCE 7-16), Chapter 16 Structural Design, Section 1613 Earthquake Loads. We used the computer program Seismic Design Maps, provided by the Structural Engineers Association (SEA) to calculate the seismic design parameters. The short spectral response uses a period of 0.2 second. We evaluated the Site Class based on the discussion in Section 1613.2.2 of the 2019 CBC and Table 20.3-1 of ASCE 7- 16. The values presented herein are for the risk-targeted maximum considered earthquake (MCER). Sites designated as Site Class D, E and F may require additional analyses if requested by the project structural engineer and client. TABLE I 2019 CBC SEISMIC DESIGN PARAMETERS Parameter ( Site Class I D I Section 1613.2.2 MCER Ground Motion Spectral Response 0.956g Figure 1613.2.1(1) Acceleration - Class B_(short),_S5 MCER Ground Motion Spectral Response 0.350g Figure 16 13.2.1(2) Acceleration - Class B (1 see), Si Site Coefficient, FA 1.117 Table 1613.2.3(1) Site Coefficient, Fv 1.950* Table 1613.2.3(2) Site Class Modified MCER Spectral 1.069g Section 1613.2.3 (Eqn Response Acceleration (short), SMS . 16-36) Site Class Modified MCER Spectral 0.682g* Section 16 13.2.3 (Eqn Response Acceleration - (1 see), SM! 16-37) 5% Damped Design 0.712g Section 16 13.2.4 (Eqn Spectral Response Acceleration (short), SOS 16-38) 5% Damped Design 0.455g* Section 16 13.2.4 (Eqn Spectral Response Acceleration (1 see), SDI 16-39) * Using the code-based values presented in this table, in lieu of a performing a ground motion hazard analysis, requires the exceptions outlined in ASCE 7-16 Section 11.4.8 be followed by the project structural engineer. Per Section 11.4.8 of ASCE/SEI 7-16, a ground motion hazard analysis should be performed for projects for Site Class "E" sites with Ss greater than or equal to 1.0g and for Site Class "D" and "E" sites with SI greater than 0.2g. Section 11.4.8 also provides exceptions which indicate that the ground motion hazard analysis may be waived provided the exceptions are followed. Table 2 presents the mapped maximum considered geometric mean (MCEG) seismic design parameters for projects located in Seismic Design Categories of D through F in accordance with ASCE 7-16. Geocon Project No. G1928-52-02 -2- June 8, 2020 TABLE 2 ASCE 7-16 PEAK GROUND ACCELERATION Parameter Site Class Value I D ASCE 7-16 Reference I Section 1613.2.2 (2019 CBC) Mapped MCEG Peak Ground 0.417g Figure 22-7 Acceleration, PGA Site Coefficient, FPGA 1.183 Table 11.8-1 Site Class Modified MCEG Peak 0.493g Section 11.8.3 (Eqn 11.8-1) Ground Acceleration, PGAM Conformance to the criteria in Tables 1 and 2 for seismic design does not constitute any kind of guarantee or assurance that significant structural damage or ground failure will not occur if a large earthquake occurs. The primary goal of seismic design is to protect life, not to avoid all damage, since such design may be economically prohibitive. The project structural engineer and architect should evaluate the appropriate Risk Category and Seismic Design Category for the planned structures. The values presented herein assume a Risk Category of II and resulting in a Seismic Design Category D. Table 3 presents a summary of the risk categories. TABLE 3 ASCE 7-16 RISK CATEGORIES CategoryRisk 1(J Building Iir Exa mples Low risk to Human Life at I Barn, Storage Shelter Failure Nominal Risk to Human Life at Failure (Buildings Residential, Commercial and Industrial Not Designated as I, III or Buildings IV) Theaters, Lecture Halls, Dining Halls, Substantial Risk to Human Schools, Prisons, Small Healthcare Life at Failure Facilities, Infrastructure Plants, Storage for Explosives/Toxins Hazardous Material Facilities, Hospitals, Fire and Rescue, Emergency Shelters, IV Essential Facilities Police Stations, Power Stations, Aviation Control Facilities, National Defense, Water Storage Comment 2: The Consultant should review the project grading, shoring and foundation plans, provide any additional geotechnical recommendations considered necessary, and confirm that the plans have been prepared in accordance with the geotechnical recommendations. Geocon Project No. G1928-52-02 -3 - June 8, 2020 Response: We will prepare a plan review letter under separate cover. Comment 3: The Consultant should provide an updated geotechnical map/plot plan utilizing the latest grading plan for the project to clearly show (at a minimum) a) existing site topography, b) proposed structures/improvements, c) proposed finished grades, d) locations of the subsurface exploration, e) geologic contacts, and J remedial grading limits, etc. Response: The updated Geologic Map and Fill Thickness and Settlement Map (Figures 2 and 4, respectively) have been attached herein. Comment 4: The Consultant should provide a geologic cross-section utilizing the current grading plan to clearly show (at a minimum) a) existing site topography, b) proposed structures/improvements, c) proposed finished grades, d) geologic contacts, e) geologic structure, J) locations of the subsurface exploration, g) temporary construction slopes, and h) remedial grading limits, etc. Response: The updated Geologic Cross-Sections (Figure 3) has been attached herein. Comment 5: The project plans indicate additional improvements are proposed north of the parking structure and south of proposed building E5. The Consultant should provide a description of the proposed improvements and provide grading/ foundation recommendations. Response: We understand that the proposed project will consist of construction of Building E5 (previously designated Building 16), Parking Structure P-3 and associated site improvements. Additionally, the building pad for Building E6 (previously designated Building 17) will be pad-graded and developed at a later date. The proposed site improvements include a pavilion area (open-air structure), "treehouse" patio area, outdoor meeting rooms, paved drive and walking paths, landscaping and other associated improvements. We understand that the "treehouse' patio area will be supported by deep foundations, and the remaining improvements will be supported by shallow foundation systems. The grading for the ancillary structures that are supported on a shallow foundation system should consist of removal of the upper 5 feet of materials from pad grade or 2 feet below proposed foundation bottoms (whichever results in a deeper removal) and replacement with properly compacted fill. The foundations for the shallow foundations should be designed using the recommendations provided in Sections 7.9 of the referenced report. Additionally, the ancillary structures should be designed to accommodate the potential fill-related settlements provided on the Fill Thickness and Settlement Map, Figure 4. We understand that the "treehouse" structure will be supported by a deep foundation system bearing in the previously compacted fill. Remedial grading within the "treehouse" area should consist of removal of existing undOcumented fill and replacement with properly compacted fill. The deep foundations should be designed using an allowable skin friction resistance of 300 psf and an allowable end bearing capacity of 4,000 psf. Pile settlement is expected to be on the order of 1-inch due to the planned loading conditions. Additionally, the proposed pavement areas should be designed in accordance with the pavement recommendations we previously provided in our Supplemental Geocon Project No. G 1928-52-02 - 4 - June 8, 2020 Preliminary Pavement Recommendations letter dated December 29, 2016 (attached herein). Comment 6: The Consultant should clarify if all undocumented fill is to be removed. Response: As indicated in Section 4.1 of the referenced report, the existing undocumented fill at the site is associated with the soil stockpile located in the south/southwest corner of the site. These materials are likely comprised of on-site materials excavated during previous grading of the site and are not considered suitable for support of proposed structures, settlement-sensitive improvements or compacted fill. Based on review of the grading plans, the majority of the undocumented fill is situated within the footprint of Parking Structure P-3, and as such, will be removed during building pad excavations. Undocumented fill exposed at bottom removal elevations should be removed to competent fill materials or formational materials. Comment 7: The Consultant should provide the site risk category and seismic design category. Response: See response to Comment 1, herein. We assume a Risk Category of II; however, the project architect and structural engineer should evaluate the appropriate risk category for the planned structures. Comment 8: Foundation and slab design criteria for soils should be consistent with Section 1808.6 of the 2019 California Building Code. The Consultant should update foundation recommendations, if necessary. Response: We provided updated seismic recommendations in accordance with the 2019 California Building Code herein. The remainder of recommendations provided in the referenced geotechnical report are still considered applicable for the 2019 California Building Code. Comment 9: The Consultant should provide a statement regarding the impact of the proposed grading and construction on adjacent properties and improvements. Response: Based on our review of the project plans, we opine the planned development can be constructed in accordance with our recommendations provided herein. We do not expect the planned development will destabilize or result in settlement of adjacent properties if properly constructed. Comment 10: The Consultant should provide a list of recommended observation and testing during site grading and construction. Response: Geocon Incorporated should provide testing and observation services during the grading operations, foundation construction, utility installation, retaining wall backfill and pavement installation. Table 4 presents the typical geotechnical observations we would expect for the proposed improvements. Geocon Project No. G1928-52-02 -5 - June 8, 2020 TABLE 4 EXPECTED TESTING AND OBSERVATION SERVICES Construction Phase Observations Exiwi I Time ii ii Base of Removal Part Time During Removals Grading Fill Placement and Soil Compaction Full Time Operations Soil Nail Drilling and Installation Full Time Soil Nail Walls Soil Nail Testing Full Time Foundations Foundation Excavation Observations Part Time Utility Backfill Fill Placement and Soil Compaction Part Time to Full Time Operations Retaining Wall Backfill Fill Placement and Soil Compaction Part Time to Full Time Operations Subgrade for Sidewalks, Curb/Gutter Soil Compaction Operations Part Time and Pavement Base Placement and Compaction Part Time Asphalt Concrete Placement and Full Time Pavement Construction Compaction If you have any questions regarding this correspondence, or if we may be of further service, please contact the undersigned at your convenience. Very truly yours, GEOCON INCORPORATED AA , -—h oy Weedon GE 2714 M RCE 84154 MRL:SFW:arm Attachments: Figuresl-4 Supplemental Preliminary Pavement Recommendations (dated December 29, 2016) (e-mail) Addressee (e-mail) PLSA Attention: Mr. Ryan Taylor Geocon Project No. G1928-52-02 -6- June 8, 2020 EEE-E±.i _•- "--I Qpcf/rs I I r-A Qpcfrs, -i Qdf 0 PEf 1Qr Ts Qpcf Ts Ts GEOLOGIC CROSS-SECTION A-A Qudf Ts PC Ts - ' QpCf —V -------- Ts GEOLOGIC CROSS-SECTION B-B TL :::bo TTT '1 2Ptf/rs 'Al zi - I