7.1.6 Where miscellaneous subterranean improvements are planned Elevator Pits the structures
<br />P p ( ),
<br />may be supported on a conventional foundation system deriving support in the undisturbed
<br />alluvial soils found at and below a depth of 5 feet. If necessary, these miscellaneous
<br />improvements may derive support in a combination of newly placed engineered fill. and
<br />competent alluvium found at and below a depth of 5 feet. It is the intent of the Geotechnical
<br />Engineer to allow miscellaneous subterranean structures to derive support in both engineered
<br />fill and alluvium if project conditions warrant such an occurrence. Recommendations for
<br />elevator pit design are provided in Section 7.15.
<br />7.1.7 It is anticipated that stable excavations for the recommended grading associated with the
<br />proposed structures can be achieved with sloping measures. However, if excavations in close
<br />proximity to an adjacent property line and/or structure are required, special excavation
<br />measures may be necessary in order to maintain lateral support of offsite improvements.
<br />Excavation recommendations are provided in the Temporary Excavations section of this report
<br />(Section 7.17).
<br />7.1.8 Foundations for small outlying structures, such as block walls up to 6 feet high, planter walls
<br />or trash enclosures, which will not be tied to the proposed structure, may be supported on
<br />conventional foundations bearing on a minimum of 12 inches of newly placed engineered fill
<br />which extends laterally at least 12 inches beyond the foundation area. Where excavation and
<br />proper compaction cannot be performed, foundations may derive support directly in the
<br />undisturbed alluvial soils, and should be deepened as necessary to maintain a minimum
<br />12-inch embedment into the recommended bearing materials. If the soils exposed in the
<br />excavation bottom are soft or loose, compaction of the soils will be required prior to placing
<br />steel or concrete. Compaction of the foundation excavation bottom is typically accomplished
<br />with a compaction wheel or mechanical whacker and must be observed and approved in
<br />writing by a Geocon representative.
<br />7.1.9 Where new paving is to be placed, it is recommended that all existing fill soils and soft alluvial
<br />soils be excavated and properly compacted for paving support. The client should be aware that
<br />excavation and compaction of all existing fill in the area of new paving is not required,
<br />however, paving constructed over existing uncertified fill or unsuitable soils may experience
<br />increased settlement and/or cracking, and may therefore have a shorter design life and
<br />increased maintenance costs. As a minimum, the upper 12 inches of soil should be scarified
<br />and properly compacted. Paving recommendations are provided in the Preliminary Pavement
<br />Recommendations section of this report (see Sections 7.11 and 7.12).
<br />7.1.10 Based on the results of percolation testing performed at the site, a stormwater infiltration
<br />system is considered feasible for this project. Recommendations for infiltration are provided
<br />in the Stormwater Infiltration section of this report (see Section 7.19).
<br />Geocon Project No. A9799-88-01
<br />-11-
<br />June 7, 2022
<br />7.1.11 Once the design and foundation loading configuration for the proposed structure proceeds to
<br />a more finalized plan, the recommendations within this report should be reviewed and revised,
<br />if necessary. Based on the final foundation loading configurations, the potential for settlement
<br />should be reevaluated by this office.
<br />7.1.12 Any changes in the design, location or elevation of improvements, as outlined in this report,
<br />should be reviewed by this office. Geocon should be contacted to determine the necessity for
<br />review and possible revision of this report.
<br />7.2 Soil and Excavation Characteristics
<br />7.2.1 The in -situ soils can be excavated with moderate effort using conventional excavation
<br />equipment. Caving should be anticipated in unshored excavations, especially where granular
<br />soils are encountered.
<br />7.2.2 It is the responsibility of the contractor to ensure that all excavations and trenches are properly
<br />shored and maintained in accordance with applicable OSHA rules and regulations to maintain
<br />safety and maintain the stability of adjacent existing improvements.
<br />7.2.3 All onsite excavations must be conducted in such a manner that potential surcharges from
<br />existing structures, construction equipment, and vehicle loads are resisted. The surcharge area
<br />may be defined by a 1:1 projection down and away from the bottom of an existing foundation
<br />or vehicle load. Penetrations below this 1:1 projection will require special excavation measures
<br />such as sloping and shoring. Excavation recommendations are provided in the Temporary
<br />Excavations section of this report (see Section 7.17).
<br />7.2.4 The upper 5 feet of existing site soils encountered during this investigation are considered to
<br />have a "very low" expansive potential (EI =1); and the soils are classified as "non -expansive"
<br />based on the 2019 California Building Code (CBC) Section 1803.5.3. The recommendations
<br />in this report assume that foundations and slabs will derive support in these materials.
<br />7.3 Minimum Resistivity, pH, and Water -Soluble Sulfate
<br />7.3.1 Potential of Hydrogen (pH) and resistivity testing as well as chloride content testing were
<br />performed on representative samples of soil to generally evaluate the corrosion potential to
<br />surface utilities. The tests were performed in accordance with California Test Method Nos. 643
<br />and 422 and indicate that the soils are considered "corrosive" with respect to corrosion of
<br />buried ferrous metals on site. The results are presented in Appendix B (Figure B9) and should
<br />be considered for design of underground structures.
<br />Geocon Project No. A9799-88-01 -12- June 7, 2022
<br />6.8 Oil Fields & Methane Potential
<br />Based on a review of the California Geologic Energy Management Division (Ca1GEM, 2022), the site is
<br />not located near the boundary of an oil field and no oil wells are located in the immediate vicinity of the
<br />site. Due to the voluntarynature of record reporting b the oil well drilling companies, wells may be
<br />p g Y g p Y
<br />improperly located or not shown on the well location map. Undocumented wells could be encountered
<br />during construction. Any wells encountered will need to be properly abandoned in accordance with the
<br />current requirements of the Ca1GEM.
<br />Since the site is not located within the boundaries of a known oil field, the potential for the presence of
<br />methane gas at the site is considered low. However, should it be determined that a methane study is
<br />required for the proposed development it is recommended that a qualified methane consultant be retained
<br />to perform the study and provide mitigation measures as necessary.
<br />6.9 Subsidence
<br />Subsidence occurs when a large portion of land is displaced vertically, usually due to the withdrawal of
<br />groundwater, oil, or natural gas. Soils that are particularly subject to subsidence include those with high
<br />silt or clay content. The site is not located within an area of known ground subsidence. No large-scale
<br />extraction of groundwater, gas, oil, or geothermal energy is occurring or planned at the site. There
<br />appears to be little or no potential for ground subsidence due to withdrawal of fluids or gases at the site.
<br />Geocon Project No. A9799-88-01
<br />7.1 General
<br />-9-
<br />7. CONCLUSIONS AND RECOMMENDATIONS
<br />June 7, 2022
<br />7.1.1 It is our opinion that neither soil nor geologic conditions were encountered during the
<br />investigation that would preclude the construction of the proposed development provided the
<br />recommendations presented herein are followed and implemented during design and
<br />construction.
<br />7.1.2 Up to 5 feet of existing artificial fill was encountered during the site investigation.
<br />The existing fill encountered is believed to be the result of past grading and construction
<br />activities at the site. Deeper fill may exist in other areas of the site that were not directly
<br />explored. It is our opinion that the existing fill, in its present condition, is not suitable for direct
<br />support of proposed foundations or slabs. The existing fill and site soils are suitable for re -use
<br />as engineered fill provided the recommendations in the Grading section of this report are
<br />followed (see Section 7.4).
<br />7.1.3 Based on these considerations, it is recommended that the upper 5 feet of existing earth
<br />materials within the buildingfootprint areas be excavated and properly compacted for
<br />tP P P Y p
<br />foundation and slab support. Deeper excavations should be conducted as needed to remove
<br />any encountered fill or soft soils as necessary at the direction of the Geotechnical Engineer (a
<br />representative of Geocon). The limits of existing fill and/or soft soil removal will be verified
<br />by the Geocon representative during site grading activities. The excavation should extend
<br />laterally a minimum distance of three feet beyond the building footprint areas, including
<br />building appurtenances, or a distance equal to the depth of fill below the foundation, whichever
<br />is greater. Where the recommended lateral over -excavation cannot be performed, such as
<br />adjacent to a property line, foundations should be deepened as necessary to derive support in
<br />the undisturbed alluvial soils found at and below a depth of 5 feet. Recommendations for
<br />earthwork are provided in the Grading section of this report (see Section 7.4).
<br />7.1.4 All excavations must be observed and approved in writing by the Geotechnical Engineer (a
<br />representative of Geocon). Prior to placing any fill, the upper 12 inches of the excavation
<br />bottom must be scarified, moistened, and proof -rolled with heavy equipment in the presence
<br />of the Geotechnical Engineer (a representative of Geocon West, Inc.).
<br />7.1.5 Subsequent to the recommended grading, the proposed structures may be supported on a
<br />conventional shallow spread foundation system deriving support in newly placed engineered
<br />fill and/or the competent alluvial soils found at and below a depth of 5 feet. It is the intent of
<br />the Geotechnical Engineer to allow building foundations to derive support in both engineered
<br />fill and competent alluvial soils for this project if conditions warrant such an occurrence. Any
<br />exposed soft soils should be compacted to a dense state or penetrated by proposed foundations
<br />at the direction of the Geotechnical Engineer (a representative of Geocon West, Inc.).
<br />Geocon Project No. A9799-88-01 _10- June 7, 2022
<br />The Maximum Considered Earthquake Ground Motion (MCE) is the level of ground motion that has a
<br />2 percent chance of exceedance in 50 years, with a statistical return period of 2,475 years. According to
<br />the 2019 California Building Code and NEHRP-2015, the MCE is to be utilized for the evaluation of
<br />liquefaction, lateral spreading, seismic settlements, and it is our understanding that the intent of the
<br />Building code is to maintain "Life Safety" during a MCE event. The Design Earthquake Ground Motion
<br />(DE) is the level of ground motion that has a 10 percent chance of exceedance in 50 years, with a
<br />statistical return period of 475 years.
<br />Deaggregation of the MCE peak ground acceleration was performed using the USGS online Unified
<br />Hazard Tool, 2014 Conterminous U.S. Dynamic edition (v4.2.0). The result of the deaggregation analysis
<br />indicates that the predominant earthquake contributing to the MCE peak ground acceleration is
<br />characterized as a 6.67 magnitude event occurring at a hypocentral distance of 15.03 kilometers from the
<br />site.
<br />Deaggregation was also performed for the Design Earthquake (DE) peak ground acceleration, and the
<br />result of the analysis indicates that the predominant earthquake contributing to the DE peak ground
<br />acceleration is characterized as a 6.61 magnitude occurring at a hypocentral distance of 21.16 kilometers
<br />from the site.
<br />Conformance to the criteria in the above tables for seismic design does not constitute any kind of
<br />guarantee or assurance that significant structural damage or ground failure will not occur if a large
<br />earthquake occurs. The primary goal of seismic design is to protect life, not to avoid all damage, since
<br />such design may be economically prohibitive.
<br />6.4 Liquefaction Potential
<br />Liquefaction is a phenomenon in which loose, saturated, relatively cohesionless soil deposits lose shear
<br />strength during strong ground motions. Primary factors controlling liquefaction include intensity and
<br />duration of ground motion, gradation characteristics of the subsurface soils, in -situ stress conditions, and
<br />the depth to groundwater. Liquefaction is typified by a loss of shear strength in the liquefied layers due
<br />to rapid increases in pore water pressure generated by earthquake accelerations.
<br />The current standard of practice, as outlined in the "Recommended Procedures for Implementation of
<br />DMG Special Publication 117, Guidelines for Analyzing and Mitigating Liquefaction in California" and
<br />"Special Publication 117A, Guidelines for Evaluating and Mitigating Seismic Hazards in California"
<br />requires liquefaction analysis to a depth of 50 feet below the lowest portion of the proposed structure.
<br />Liquefaction typically occurs in areas where the soils below the water table are composed of poorly
<br />consolidated, fine to medium -grained, primarily sandy soil. In addition to the requisite soil conditions,
<br />the ground acceleration and duration of the earthquake must also be of a sufficient level to induce
<br />liquefaction.
<br />Geocon Project No. A9799-88-01 -7- June 7, 2022
<br />A review of the State of California Seismic Hazard Zone Map for the Tustin Quadrangle (CGS, 2001)
<br />indicates that the site is not located in an area designated as "liquefiable". A review of the Safety Element
<br />of the General Plan for the City of Santa Ana indicates that the site is located in an area designated as
<br />having the `Potential for Liquefaction' (City of Santa Ana, 2010). However, as stated previously, the
<br />historic high groundwater level is reported to be in excess of 40 feet below the existing ground surface.
<br />Based on these considerations, it is our opinion that the potential for liquefaction at the site is low.
<br />6.5 Slope Stability
<br />The topography at the site is relatively level and the site is not within an area identified as having a
<br />potential for slope stability hazards (City of Santa Ana, 2010) or seismic slope instability hazards
<br />(CDMG, 2001). No landslides have been identified at the site or in close proximity to the site. Also, the
<br />site is not in the path of any known or potential landslides. Therefore, the potential for slope stability
<br />hazards to adversely affect the proposed development is considered low.
<br />6.6 Earthquake -Induced Flooding
<br />Earthquake -induced flooding is inundation caused by failure of dams or other water -retaining structures
<br />due to earthquakes. A review of the Safety Element of the Orange County General Plan (2004) and the
<br />City of Santa Ana Seismic Safety Element (2010) indicates that the site is not located within the
<br />inundation boundaries of upgradient dams, rivers, creeks, or reservoirs. The probability of earthquake -
<br />induced flooding is considered very low.
<br />6.7 Tsunamis, Seiches and Flooding
<br />The site is not located within a coastal area. Therefore, tsunamis, seismic sea waves, are not considered
<br />a significant hazard at the site.
<br />Seiches are large waves generated in enclosed bodies of water in response to ground shaking. No major
<br />water -retaining structures are located immediately up gradient from the project site. Flooding from a
<br />seismically -induced seiche is considered unlikely.
<br />The site is in located within an area of minimal flooding potential (Zone X) as defined by the Federal
<br />Emergency Management Agency (FEMA, 2022).
<br />Geocon Project No. A9799-88-01 - 8 - June 7, 2022
<br />6.2 Seismicity
<br />As with all of Southern California, the site has experienced historic earthquakes from various regional
<br />faults. The seismicity of the region surrounding the site was formulated based on research of an electronic
<br />database of earthquake data. The epicenters of recorded earthquakes with magnitudes equal to or greater
<br />than 5.0 in the site vicinity are depicted on Figure 4, Regional Seismicity Map. A partial list of moderate
<br />to major magnitude earthquakes that have occurred in the Southern California area within the last
<br />100 years is included in the following table.
<br />LIST OF HISTORIC EARTHQUAKES
<br />Earthquake
<br />(Oldest to Youngest)
<br />Date of Earthquake
<br />Magnitude
<br />Distance to
<br />Epicenter
<br />(Miles)
<br />Direction
<br />to
<br />Epicenter
<br />Near Redlands
<br />July 23, 1923
<br />6.3
<br />39
<br />ENE
<br />Long Beach
<br />March 10, 1933
<br />6.4
<br />11
<br />SW
<br />Tehachapi
<br />July 21, 1952
<br />7.5
<br />108
<br />NW
<br />San Fernando
<br />February 9, 1971
<br />6.6
<br />55
<br />NW
<br />Whittier Narrows
<br />October 1, 1987
<br />5.9
<br />25
<br />NW
<br />Sierra Madre
<br />June 28, 1991
<br />5.8
<br />36
<br />NNW
<br />Landers
<br />June 28, 1992
<br />7.3
<br />87
<br />ENE
<br />Big Bear
<br />June 28, 1992
<br />6.4
<br />67
<br />ENE
<br />Northridge
<br />January 17, 1994
<br />6.7
<br />50
<br />NW
<br />Hector Mine
<br />October 16, 1999
<br />7.1
<br />1.08
<br />ENE
<br />Rid ecrest
<br />July 5, 2019
<br />7.1
<br />140
<br />N
<br />The site could be subjected to strong ground shaking in the event of an earthquake. However, this hazard
<br />is common in Southern California and the effects of ground shaking can be mitigated if the proposed
<br />structures are designed and constructed in conformance with current building codes and engineering
<br />practices.
<br />6.3 Seismic Design Criteria
<br />The following table summarizes the site -specific design criteria obtained from the 2019 California
<br />Building Code (CBC; Based on the 2018 International Building Code [IBC] and ASCE 7-16), Chapter
<br />16 Structural Design, Section 1.613 Earthquake Loads. The data was calculated using the online
<br />application Seismic Design Maps, provided by OSHPD. The short spectral response uses a period of
<br />0.2 second. We evaluated the Site Class based on the discussion in Section 1613.2.2 of the 2019 CBC
<br />and Table 20.3-1 of ASCE 7-16. The values presented below are for the risk -targeted maximum
<br />considered earthquake (MCER).
<br />Geocon Project No. A9799-88-01 - 5 -
<br />2019 CBC SEISMIC DESIGN PARAMETERS
<br />June 7, 2022
<br />Parameter
<br />Value
<br />2019 CBC Reference
<br />Site Class
<br />D
<br />Section 1613.2.2
<br />MCER Ground Motion Spectral Response
<br />1.29g
<br />Figure 1613.2.1(1)
<br />Acceleration — Class B (short), Ss
<br />MCER Ground Motion Spectral Response
<br />0.46g
<br />Figure 1613.2.1(2)
<br />Acceleration — Class B (1 sec), SI
<br />Site Coefficient, FA
<br />I
<br />Table 1613.2.3(1)
<br />Site Coefficient, Fv
<br />1.,,;4*
<br />Table 1613.2.3(2)
<br />Site Class Modified MCER Spectral Response
<br />1.29g
<br />Section 1613.2.3 (Eqn 16-36)
<br />Acceleration (short), SMs
<br />Site Class Modified MCER Spectral Response
<br />0.846g*
<br />Section 1613.2.3 (Eqn 16-37)
<br />Acceleration — (1 sec), SMI
<br />5% Damped Design
<br />Spectral Response Acceleration (short), SDs
<br />0.86g
<br />Section 1613.2.4 (Eqn 16-38)
<br />5% Damped Design
<br />Spectral Response Acceleration (1 sec), SDI
<br />0.564g*
<br />Section 1613.2.4 (Eqn 16-39)
<br />Note:
<br />*Per Section 11.4.8 of ASCE/SEI 7-16, a ground motion hazard analysis shall be performed for
<br />projects for Site Class "E" sites with Ss greater than or equal to 1.Og and for Site Class "D" and
<br />"E" sites with S 1 greater than 0.2g. Section 11.4.8 also provides exceptions which indicates that
<br />the ground motion hazard analysis may be waived provided the exceptions are followed. Using
<br />the code based values presented in the table above, in lieu of a performing a ground motion
<br />hazard analysis, requires the exceptions outlined in ASCE 7-16 Section 11.4.8 be followed.
<br />The table below presents the mapped maximum considered geometric mean (MCEG) seismic design
<br />parameters for projects located in Seismic Design Categories of D through F in accordance with ASCE
<br />7-16.
<br />ASCE 7-16 PEAK GROUND ACCELERATION
<br />Parameter
<br />Value
<br />ASCE 7-16 Reference
<br />Mapped MCEG Peak Ground Acceleration,
<br />0.543g
<br />Figure 22-9
<br />PGA
<br />Site Coefficient, FPGA
<br />1.1
<br />Table 11.8-1
<br />Site Class Modified MCEG Peak Ground
<br />0.598g
<br />Section 11.8.3 (Eqn 11.8-1)
<br />Acceleration, PGAM
<br />Geocon Project No. A9799-88-01 - 6 - June 7, 2022
<br />•
<br />Architecture + Planning
<br />17911 Von Karman Ave.
<br />Suite 200
<br />Irvine, CA 92614
<br />ktgy.com
<br />949.851.2133
<br />KTGY Project No: 2017-0934
<br />Project Contact: Debbie Holland
<br />Email: dholland@ktgy.com
<br />Principal: Wil Wong
<br />Project Designer: D. Schoolmeester
<br />Project Director: Debbie Holland
<br />Developer
<br />ED7 OAK
<br />INVES'I'NiEN I'S
<br />4199 CAMPUS DRIVE
<br />IRVINE, CA 92612
<br />PHONE NO. (714) 342-2502
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<br />It is the clients responsibility prior to or during construction to notify the architect in writing
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<br />of any perceived errors or omissions in the plans and specifications of which a contractor
<br />thoroughly knowledgeable with the building codes and methods of construction should
<br />reasonably be aware. Written instructions addressing such perceived errors or omissions
<br />shall be received from the architect prior to the client or clients subcontractors proceeding
<br />jr
<br />with the work. The client will be responsible for any defects in construction if these
<br />procedures are not followed.
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