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HomeMy WebLinkAboutX2021-3462 - Soils (2)ENGINEERS + GEOLOGISTS + ENVIRONMENTAL SCIENTISTS December 5, 2022 J.N. 21-422 NICHOLSON CONSTRUCTION 1 Corporate Plaza, Suite 110 Newport Beach, California 92660 Attention: Ms. Nanci Glass Subject: Geotechnical Report of Rough Grading, Proposed Single -Family Residence, 225 Jasmine Avenue, Corona Del Mar Area, City of Newport Beach, California Reference: Geotechnical Investigation, Proposed Single Family Residence, 225 Jasmine Avenue, Corona Del Mar Area, City of Newport Beach, California; report by Petra Geosciences, Inc., Q.N. 21-422), dated November 10, 2021. Dear Ms. Glass: Petra Geosciences, Inc. (Petra) is submitting herewith a summary of the observation and testing services provided by this firm during rough grading operations within the subject site. Conclusions relative to the suitability of the grading for the planned structures, and foundation design recommendations for the proposed residences and other site improvements, are included herein. The purpose of the grading was to develop an engineered fill pad for the construction of a single-family residence and associated hadscape features. Grading began on November 15, 2022 and was completed on November 16, 2022. SUMMARY OF OBSERVATIONS AND TESTING Site Clearin¢ Structural materials associated with the previous residential structure was removed from the site. Clearing operations also included the removal of previous structural features, such as concrete walkways and patios as well as landscape vegetation. Trees and large shrubs, where removed, were grubbed out to include their stumps and major root systems. Side yard masonry block property line walls were protected in place. Ground Preparation Existing undocumented fill materials and near surface native terrace deposits to a depth of 3 feet were slightly moist to moist and loose to medium dense. The terrace deposits underlying these surficial soil materials remained moist and medium dense to dense. Therefore, in order to provide suitable and relatively uniform support for the proposed structural foundations and exterior site improvements, the existing fill Offices Strategically Positioned Throughout Southern California ORANGE COUNTY OFFICE 3186 Airway Avenue, Suite K, Costa Mesa, California 92626 T: 714.549.8921 F: 714.668-3770 For more information visit us online at w oetma inc.com NICHOLSON CONSTRUCTION December 5, 2022 225 Jasmine Avenue / Corona Del Mar J.N. 21-422 Page 2 and unsuitable terrace deposits were over -excavated to competent terrace deposits at a minimum 2 feet below the bottoms of the proposed structural footings. A brick septic tank was encountered during remedial grading and was removed in its entirety to approximately 7 '/a feet below finish pad grade. Prior to replacing the overexcavated soils as engineered fill, the exposed bottom surfaces were first scarified to a depth of 6 inches, moisture conditioned to achieve a uniform moisture content that was greater than optimum, and then recompacted in place to a minimum relative compaction of 90 percent of the applicable laboratory maximum dry density in accordance with ASTM Test Method D 1557. Horizontal limits of overexcavation and recompaction extended from approximately property line to property line; however, consideration was given to the protection of adjacent property line structures. Existing side yard property line block walls were protected in place. Fill Placement and Testing 1. The fill materials placed within the subject site consisted of on -site soils. 2. The soils were placed in approximately 4- to 6-inch-thick lifts, moisture conditioned as necessary to achieve at or above optimum moisture contents and compacted to a minimum relative compaction of 90 percent of the applicable laboratory maximum dry density in accordance with ASTM Test Method D 1557. The maximum depth of fill placed across the building pad is approximately 7.5 feet. 3. Observations and field density testing were performed during fill placement. Field density and moisture content tests were performed by nuclear methods (ASTM D 6938). Test results are summarized in Table A, and approximate locations of the field density tests are depicted on the enclosed site plan Figure 1. 4. Field density tests were taken at vertical intervals of 1 to 2 feet. 5. Visual and tactile classification of earth materials in the field was the basis for determining if the laboratory maximum density value presented in Table I was applicable for each density test. 6. Fill placement within the subject lot was performed in general compliance with the recommendations of our referenced reports and the Grading Code of the City of Newport Beach. Laboratory Testing Several laboratory tests were previously performed on samples of onsite soil materials obtained near finish pad grade in order to determine their engineering characteristics and chemical activity (Reference). The test results are provided in Table B at the end of this report. ItPETRA SOLID AS A ROCK GEOSCIENCES- NICHOLSON CONSTRUCTION December 5, 2022 225 Jasmine Avenue / Corona Del Mar J.N. 21-422 Page 3 CONCLUSIONS AND RECOMMENDATIONS Regulatory Compliance Removals, overexcavation, processing of exposed surfaces, and placement of engineered fill under the purview of this report have been completed under the part-time observation of, and with selective testing by Petra and are found to be in general compliance with the recommendations provided in the reference report and the grading codes of the City of Newport Beach, California. The completed work within this firm's purview has been reviewed and is considered to be in compliance with project specifications. It is our opinion that the as -graded condition of the subject lot and the proposed building construction will not have an adverse effect on the geologic stability of adjacent properties. Post -Grading Considerations Site Drainage Positive drainage devices such as sloped concrete flatwork, graded swales and area drains should be provided around the new construction to collect and direct all water to a suitable discharge area. Neither rain nor excess irrigation water should be allowed to collect or pond against building foundations. The owner is advised that the drainage system should be properly maintained throughout the life of the proposed development. The purpose of this drainage system will be to reduce water infiltration into the subgrade soils and to direct surface water away from building foundations, and walls. The following recommendations should be implemented during construction. Area drains should be installed within all planter and landscape areas that are located within 10 feet of building foundations to reduce excessive infiltration of water into the foundation soils. Per the 2019 CBC, the ground surfaces of planter and landscape areas that are located within 10 feet of building foundations should be sloped at a minimum gradient of 5 percent away from the foundations and towards the nearest area drains. The ground surfaces of planter and landscape areas that are located more than 10 feet away from building foundations may be sloped at a minimum gradient of 2 percent away from the foundations and towards the nearest area drains. 2. Per the 2019 CBC, concrete flatwork surfaces that are located within 10 feet of building foundations should be inclined at a minimum gradient of 2 percent away from the building foundations and towards the nearest area drains. Concrete flatwork surfaces that are located more than 10 feet away from building foundations may be sloped at a minimum gradient of 1 percent away from the foundations and towards the nearest area drains. 3. A watering program should be implemented for the landscape areas that maintain a uniform, near optimum moisture condition in the soils. Overwatering and subsequent saturation of the soils will cause excessive soil expansion and heave and, therefore, should be avoided. On the other hand, allowing the soils to dry out will cause excessive soil shrinkage. As an alternative to a conventional irrigation system, drip irrigation is strongly recommended for all planter areas. The owner is advised that all drainage devices should be properly maintained throughout the lifetime of the development. PETRA SOUV AS A ROCK NICHOLSON CONSTRUCTION December 5, 2022 225 Jasmine Avenue / Corona Del Mar J.N. 21-422 Page 4 Bottomless Trench Drains When gravel filled bottomless infiltration systems are constructed near foundations, a potential exists for oversaturation of the foundation soils which conflicts with the intended purpose of onsite drainage facilities. In addition, it has been our experience that a leading cause of distress to buildings and foundations is due to poor management of water next to building foundations. Petra recommends a setback of at least 15 feet between any infiltration system and building foundations. If this setback distance cannot be maintained, then a modified foundation system may be required to alleviate any distress that could be caused by infiltration of water near the footing. A modified foundation system could consist of constructing deepened footings within 15 feet of the infiltration system and installing extra reinforcement. Design of a modified foundation system is referred to the project structural engineer. Utility Trench Backfill All utility trench backfill should be compacted to a minimum relative compaction of 90 percent. Onsite soils cannot be densifred adequately by flooding and jetting techniques; therefore, trench backfill materials should be placed in lifts no greater than approximately 6 inches in thickness, watered or air dried as necessary to achieve a uniform moisture content that is equal to or slightly above optimum moisture, and then mechanically compacted in -place to a minimum relative compaction of 90 percent. A representative of the project geotechnical consultant should probe and test the backfills to document that adequate compaction has been achieved. For shallow trenches where pipe may be damaged by mechanical compaction equipment, such as under the building floor slab, imported clean sand exhibiting a sand equivalent value (SE) of 30 or greater may be utilized. The sand backfill materials should be watered to achieve near optimum moisture conditions and then tamped in place. No specific relative compaction will be required; however, observation, probing, and, if deemed necessary, testing should be performed by a representative of the project geotechnical consultant to document that the sand backfill is adequately compacted and will not be subject to excessive settlement. Where utility trenches enter the footprint of the building, they should be backfrlled through their entire depths with on -site fill materials, sand -cement slurry or concrete rather than with any sand or gravel shading. This "plug" of less- or non -permeable materials will mitigate the potential for water to migrate through the backfilled trenches from outside of the building to the areas beneath the foundations and floor slabs. PETRA SOLID ASA ROCK NICHOLSON CONSTRUCTION December 5, 2022 225 Jasmine Avenue / Corona Del Mar J.N. 21-422 Page 5 If clean, imported sand is to be used for backfill of exterior utility trenches, it is recommended that the upper 12 inches of trench backfill materials consist of property compacted on -site soil materials. This is to reduce infiltration of irrigation and rainwater into granular trench backfill materials Where an interior or exterior utility trench is proposed parallel to a building footing, the bottom of the trench should not be located below a 1:1 plane projected downward from the outside bottom edge of the adjacent footing. Where this condition exists, the adjacent footing should be deepened such that the bottom of the utility trench is located above the 1:1 projection. FOUNDATION DESIGN CONSIDERATIONS Near -Fault Site Determination Based on our review of the referenced geologic maps and literature, no active faults are known to project through the property. Furthermore, the site does not lie within the boundaries of an "Earthquake Fault Zone" as defined by the State of California in the Alquist-Priolo Earthquake Fault Zoning Act (CGS, 2018). The Alquist-Priolo Earthquake Fault Zoning Act (AP Act) defines an active fault as one that "has had surface displacement within Holocene time (about the last 11,000 years)" The main objective of the AP Act is to prevent the construction of dwellings on top of active faults that could displace the ground surface resulting in loss of life and property. However, it should be noted that according to the USGS Unified Hazard Tool website and/or 2010 CGS Fault Activity Map of California, the Newport -Inglewood fault, located approximately 3 miles southwest of the site, would probably generate the most severe site ground motions and, therefore, is the majority contributor to the deterministic minimum component of the ground motion models. The subject site is located at a distance of less than 9.5 miles (15 km) from the surface projection of this fault system, which is capable of producing a magnitude 7 or larger events with a slip rate along the fault greater than 0.04 inch per year. As such, the site should be considered as a Near -Fault Site in accordance with ASCE 7-16, Section 11.4.1. Seismic Design Parameters Earthquake loads on earthen structures and buildings are a function of ground acceleration which may be determined from the site -specific ground motion analysis. Alternatively, a design response spectrum can be developed for certain sites based on the code guidelines. To provide the design team with the parameters necessary to construct the design acceleration response spectrum for this project, we used two computer applications. Specifically, the first computer application, which was jointly developed by Structural 5tPETRA SOLID AS A ROCK GEOSCIENCES" NICHOLSON CONSTRUCTION December 5, 2022 225 Jasmine Avenue / Corona Del Mar J.N. 21-422 Page 6 Engineering Association of California (SEAOC) and California's Office of Statewide Health Planning and Development (OSHPD), the SEA/OSHPD Seismic Design Maps Tool website, hltps://seismicmus.org, is used to calculate the ground motion parameters. The second computer application, the United Stated Geological Survey (USGS) Unified Hazard Tool website, httns:Hearthguake.usgs.gov/hazards/interactive/, is used to estimate the earthquake magnitude and the distance to surface projection of the fault. To run the above computer applications, site latitude and longitude, seismic risk category and knowledge of site class are required. The site class definition depends on the direct measurement and the ASCE 7-16 recommended procedure for calculating average small -strain shear wave velocity, Vs30, within the upper 30 meters (approximately 100 feet) of site soils. A seismic risk category of II was assigned to the proposed building in accordance with 2019 CBC, Table 1604.5. No shear wave velocity measurement was performed at the site, however, the subsurface materials at the site appears to exhibit the characteristics of stiff soils condition for Site Class D designation. Therefore, an average shear wave velocity of 600 to 1,200 feet per second for the upper 100 feet was assigned to the site based on engineering judgment and geophysical experience. As such, in accordance with ASCE 7-16, Table 20.3-1, Site Class D (D- Default as per SEA/OSHPD software) has been assigned to the subject site. The following table, Table 1, provides parameters required to construct the seismic response coefficient, Cs, curve based on ASCE 7-16, Article 12.8 guidelines. PETRASOLID AS A ROCK GEOSCIENCES" NICHOLSON CONSTRUCTION 225 Jasmine Avenue / Corona Del Mar TABLE I Seismic Design Parameters December 5, 2022 J.N. 21-422 Page 7 Ground Motion Parameters Specific Reference Parameter Value Unit Site Latitude (North) - 33.5957 ° Site Longitude (West) - -117. 8743 ° Site Class Definition Section 1613.2.2 (I), Chapter 20 (1) D-Default (4) - Assumed Seismic Risk Category Table 1604.5 (1) II - Mw - Earthquake Magnitude USGS Unified Hazard Tool (3) 7.5 (3) - R— Distance to Surface Projection of Fault USGS Unified Hazard Tool (3) 5.0 (3) km S, - Mapped Spectral Response Acceleration Figure1613.2.1(1) 0) 1.358 (4) g Short Period (0.2 second) St -Mapped Spectral Response Acceleration Figure 1613.2.1(2) 0) 0.482(4) g Long Period 1.0 second Fs — Short Period (0.2 second) Site Coefficient Table 1613.2.3(1) (1) 1.2(4) - F,— Long Period (1.0 second) Site Coefficient Table 1613.2.3(2) (1) Null (4) - Sms— MCER Spectral Response Acceleration Parameter Equation 16-36 (1) 1.63(4) g Adjusted for Site Class Effect 0.2 second Sm, - MCER Spectral Response Acceleration Parameter Equation I6-37 0) Null (4) g Adjusted for Site Class Effect (1.0 second) SDs - Design Spectral Response Acceleration at 0.2-s Equation 16-38 0) 1.087(4) g SDI -Design Spectral Response Acceleration at 1-s Equation 16-39 (I) Null (4) g T. = 0.2 SDI/ SDs Section 11.4.6 (z) Null s Ts= SDI/ SDs Section 11.4.6 of Null s TI, - Long Period Transition Period Figure 22-14 (2) 8 (4) s PGA - Peak Ground Acceleration at MCEG (`) Figure 22-9 (r) 0.594 g FPGA - Site Coefficient Adjusted for Site Class Effect (2) Table 11.8-1 (2) 1.2 (4) - PGAM —Peak Ground Acceleration (z) Equation 11.8-1 (1) 0.712(4) g Adjusted for Site Class Effect Design PGA = (% PGAM) - Slope Stability (r) Similar to Eqs. 16-38 & 16-39 (2) 0.475 g Design PGA z (0.4 SDs) — Short Retaining Walls (t) Equation 11.4-5 (z) 0.435 g CRs - Short Period Risk Coefficient Figure 22-18A (2) 0.909 (4) - CRt - Long Period Risk Coefficient Figure 22-19A (2) 0.921 (4) - SDC - Seismic Design Category W Section 1613.2.5 (1) 1 Null (4) - References: 111 California Building Code (CBC), 2019, California Code of Regulations, Title 24, Part 2, Volume I and H. (2) American Society of Civil Engineers/Structural Engineering Institute (ASCE/SEI), 2016, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, Standards 7-16. (3) USGS Unified Hazard Tool - hnpsl/eartliquake.usgs.gov/hazards/interactive/ (') SEI/OSHPD Seismic Design Map Application—hltps://Seisn icmaps.org Related References: Federal Emergency Management Agency (FEMA), 2015, NEHERP (National Earthquake Hazards Reduction Program) Recommended Seismic Provision for New Building and Other Structures FEMA P-1050). Notes: Calculated at the MCE return period o£2475 years (2 percent chance of exceedance in 50 years). t PGA Calculated at Design Level of/3o£MCE; appreximately equivalent to a reurn period of475 yens(10 percent chance ofexceedance in 50 years). PGA Calculated for short, stubby retaining walls with an infinitesimal (zero) fundamental period. The desi ation provided herein maybe superseded by the structural engineer in accordance with Section 1613.2.5.1, if applicable. It PETRA Soon ASA ROCK NICHOLSON CONSTRUCTION December 5, 2022 225 Jasmine Avenue / Corona Del Mar J.N. 21-422 Page 8 Discussion - General Owing to the characteristics of the subsurface soils, as defined by Site Class D-Default designation, and proximity of the site to the sources of major ground shaking, the site is expected to experience strong ground shaking during its anticipated life span. Under these circumstances, where the code -specified design response spectrum may not adequately characterize site response, the 2019 CBC typically requires a site - specific seismic response analysis to be performed. This requirement is signified/identified by the "null" values that are output using SEA/OSHPD software in determination of short period, but mostly, in determination of long period seismic parameters, see Table 1. For conditions where a "null" value is reported for the site, a variety of design approaches are permitted by 2019 CBC and ASCE 7-16 in lieu of a site -specific seismic hazard analysis. For any specific site, these alternative design approaches, which include Equivalent Lateral Force (ELF) procedure, Modal Response Spectrum Analysis (MRSA) procedure, Linear Response History Analysis (LRHA) procedure and Simplified Design procedure, among other methods, are expected to provide results that may or may not be more economical than those that are obtained if a site -specific seismic hazards analysis is performed. These design approaches and their limitations should be evaluated by the project structural engineer. Discussion — Seismic Design Category Please note that the Seismic Design Category, SDC, is also designated as "null" in Table 1. For conditions where the mapped spectral response acceleration parameter at I — second period, SI, is less than 0.75, the 2019 CBC, Section 1613.2.5.1 allows that seismic design category to be determined from Table 1613.2.5(1) alone provided that all 4 requirements concerning fundamental period of structure, story drift, seismic response coefficient, and relative rigidity of the diaphragms are met. Our interpretation of ASCE 7-16 is that for conditions where one or more of these 4 conditions are not met, seismic design category should be assigned based on: 1) 2019 CBC, Table 1613.2.5(1), 2) structure's risk category and 3) the value Of SDS, at the discretion of the project structural engineer. Discussion — Equivalent Lateral Force Method Should the Equivalent Lateral Force (ELF) method be used for seismic design of structural elements, the value of Constant Velocity Domain Transition Period, Ts, is estimated to 0.537 seconds and the value of Long Period Transition Period, TL, is provided in Table I for construction of Seismic Response Coefficient — Period (Cs -T) curve that is used in the ELF procedure. As stated herein, the subject site is considered to be within a Site Class D-Default. A site -specific ground motion hazard analysis is not required for structures on Site Class D-Default with Si > 0.2 provided that ItPETRA SOLID AS A ROCK GEOSCIENCES- NICHOLSON CONSTRUCTION December 5, 2022 225 Jasmine Avenue / Corona Del Mar J.N. 21-422 Page 9 the Seismic Response Coefficient, Cs, is determined in accordance with ASCE 7-16, Article 12.8 and structural design is performed in accordance with Equivalent Lateral Force (ELF) procedure. Allowable Bearing Capacity, Estimated Settlement and Lateral Resistance Allowable Soil Bearing Capacities Pad Footings An allowable soil bearing capacity of 1,500 pounds per square foot may be utilized for design of isolated 24-inch-square footings founded at a minimum depth of 12 inches below the lowest adjacent final grade for pad footings that are not a part of the slab system and are used for support of such features as roof overhang, second -story decks, patio covers, etc. This value may be increased by 20 percent for each additional foot of depth and by 10 percent for each additional foot of width, to a maximum value of 2,500 pounds per square foot. The recommended allowable bearing value includes both dead and live loads, and may be increased by one-third for short duration wind and seismic forces. Continuous Footings An allowable soil bearing capacity of 1,500 pounds per square foot may be utilized for design of continuous footings founded at a minimum depth of 12 inches below the lowest adjacent final grade. This value may be increased by 20 percent for each additional foot of depth and by 10 percent for each additional foot of width, to a maximum value of 2,500 pounds per square foot. The recommended allowable bearing value includes both dead and live loads, and may be increased by one-third for short duration wind and seismic forces. Estimated Footing Settlement Based on the allowable bearing values provided above, total static settlement of the footings under the anticipated loads is expected to be on the order of Y: inch. Differential settlement is estimated to be on the order of 1/4 inch over a horizontal span of 40 feet. The majority of settlement is likely to take place as footing loads are applied or shortly thereafter. Lateral Resistance A passive earth pressure of 210 pounds per square foot per foot of depth, to a maximum value of 2,100 pounds per square foot, may be used to determine lateral bearing resistance for footings. In addition, a coefficient of friction of 0.35 times the dead load forces may be used between concrete and the supporting soils to determine lateral sliding resistance. The above values may be increased by one-third when designing for transient wind or seismic forces. It should be noted that the above values are based on the condition PETRASOLID ASA ROCK GEOSCIENCES" NICHOLSON CONSTRUCTION 225 Jasmine Avenue / Corona Del Mar December 5, 2022 J.N. 21-422 Page 10 where footings are cast in direct contact with engineered fill or competent native soils. In cases where the footing sides are formed, all backfill placed against the footings upon removal of forms should be compacted to at least 90 percent of the applicable maximum dry density. Guidelines for Footings and Slabs on -Grade Design and Construction The results of our laboratory tests performed on representative samples of near -surface soils within the site during our -investigation indicate that these material predominantly exhibit expansion indices that are less than 20. As indicated in Section 1803.5.3 of 2019 California Building Code (2019 CBC), these soils are considered non -expansive and, as such, the design of slabs on -grade is considered to be exempt from the procedures outlined in Sections 1808.6.2 of the 2019 CBC and may be performed using any method deemed rational and appropriate by the project structural engineer. However, the following minimum recommendations are presented herein for conditions where the project design team may require geotechnical engineering guidelines for design and construction of footings and slabs on -grade the project site. The design and construction guidelines that follow are based on the above soil conditions and may be considered for reducing the effects of variability in fabric, composition and, therefore, the detrimental behavior of the site soils such as excessive short- and long-term total and differential heave or settlement. These guidelines have been developed on the basis of the previous experience ofthis firm on projects with similarsoil conditions. Although construction performed in accordance with these guidelines has been found to reduce post -construction movement and/or distress, they generally do not positively eliminate all potential effects of variability in soils characteristics and future heave or settlement. It should also be noted that the suggestions for dimension and reinforcement provided herein are performance -based and intended only as preliminary guidelines to achieve adequate performance tinder the anticipated soil conditions. However, they should not be construed as replacement for structural engineering analyses, experience and judgment. The project structural engineer, architect and/or civil engineer should make appropriate adjustments to slab and footing dimensions, and reinforcement type, size and spacing to accountfor internal concrete forces (e.g., thermal, shrinkage and expansion), as well as external forces (e.g., applied loads) as deemed necessary. Consideration should also be given to minimum design criteria as dictated by local building code requirements. ��O PETRA SOLID ASA ROCK GEOSCIENCES- NICHOLSON CONSTRUCTION December 5, 2022 225 Jasmine Avenue / Corona Del Mar J.N. 21422 Page I Conventional Slabs on -Grade System Given the expansion index of less than 20, as generally exhibited by onsite soils, we recommend that footings and floor slabs be designed and constructed in accordance with the following minimum criteria. Footings 1. Exterior continuous footings supporting three- and four-story structures should be founded at a minimum depth of 18 inches below the lowest adjacent final grade, respectively. Interior continuous footings may be founded at a minimum depth of 10 inches below the top of the adjacent finish floor slabs. 2. In accordance with Table 1809.7 of 2019 CBC for light -frame construction, all continuous footings should have minimum widths of 15 inches for three-story construction. We recommend all continuous footings should be reinforced with a minimum of two No. 4 bars, one top and one bottom. 3. A minimum 12-inch-wide grade beam founded at the same depth as adjacent footings should be provided across garage entrances or similar openings (such as large doors or bay windows). The grade beam should be reinforced with a similar manner as provided above. 4. Interior isolated pad footings, if required, should be a minimum of 24 inches square and founded at a minimum depth of 15 inches below the bottoms of the adjacent floor slabs. Pad footings should be reinforced with No. 4 bars spaced a maximum of 18 inches on centers, both ways, placed near the bottoms of the footings. 5. Exterior isolated pad footings intended for support of roof overhangs such as second -story decks, patio covers and similar construction should be a minimum of 24 inches square and founded at a minimum depth of 24 inches below the lowest adjacent final grade. The pad footings should be reinforced with No. 4 bars spaced a maximum of 18 inches on centers, both ways, placed near the bottoms of the footings. Exterior isolated pad footings may need to be connected to adjacent pad and/or continuous footings via tic beams at the discretion of the project structural engineer. 6. The minimum footing dimensions and reinforcement recommended herein may be modified (increased or decreased subject to the constraints of Chapter 18 of the 2019 CBC) by the structural engineer responsible for foundation design based on his/her calculations, engineering experience and judgment. Building Floor Slabs 1. Concrete floor slabs should be a minimum 4 inches thick and reinforced with No. 3 bars spaced a maximum of 24 inches on centers, both ways. All slab reinforcement should be supported on concrete chairs or brick to ensure the desired placement near mid -depth. Slab dimension, reinforcement type, size and spacing need to account for internal concrete forces (e.g., thermal, shrinkage and expansion) as well as external forces (e.g., applied loads), as deemed necessary. 2. Living area concrete floor slabs and areas to receive moisture sensitive floor covering should be underlain with a moisture vapor retarder consisting of a minimum 10-mil-thick polyethylene or polyolefin membrane that meets the minimum requirements of ASTM E96 and ASTM E1745 for vapor retarders (such as Husky Yellow Guard®, Stego® Wrap, or equivalent). All laps within the membrane ItPETRA SOLID ASA ROCK GEOSCIENCES" NICHOLSON CONSTRUCTION 225 Jasmine Avenue / Corona Del Mar December 5, 2022 J.N. 21-422 Page 12 should be sealed, and at least 2 inches of clean sand should be placed over the membrane to promote uniform curing of the concrete. To reduce the potential for punctures, the membrane should be placed on a pad surface that has been graded smooth without any sharp protrusions. If a smooth surface cannot be achieved by grading, consideration should be given to lowering the pad finished grade an additional inch and then placing a 1-inch-thick leveling course of sand across the pad surface prior to the placement of the membrane. To comply with Section 1907.1.1 of the 2019 CBC, the living area concrete floor slab should also be underlain with capillary break consisting of a minimum of 4 inches of gravel or crushed stone containing not more than 10 percent of material that passes through a No. 4 sieve. The capillary break should be placed below the 10-mil moisture vapor retarder. At the present time, some slab designers, geotechnical professionals and concrete experts view the sand layer below the slab (blotting sand) as a place for entrapment of excess moisture that could adversely impact moisture -sensitive floor coverings. As a preventive measure, the potential for moisture intrusion into the concrete slab could be reduced ifthe concrete is placed directly on the vapor retarder. However, if this sand layer is omitted, appropriate curing methods must be implemented to ensure that the concrete slab cures uniformly. A qualified materials engineer with experience in slab design and construction should provide recommendations for alternative methods of curing and supervise the construction process to ensure uniform slab curing. Additional steps would also need to be taken to prevent puncturing of the vapor retarder during concrete placement. Garage floor slabs should be a minimum 4 inches thick and reinforced in a similar manner as living area floor slabs. Garage slabs should also be poured separately from adjacent wall footings with a positive separation maintained using'/4-inch-minimum felt expansion joint material. To control the propagation of shrinkage cracks, garage floor slabs should be quartered with weakened plane joints. Consideration should be given to placement of a moisture vapor retarder below the garage slab, similar to that provided in Item 2 above, should the garage slab be overlain with moisture sensitive floor covering. 4. Presaturation of the subgrade below floor slabs will not be required; however, prior to placing concrete, the subgrade below all dwelling and garage floor slab areas should be thoroughly moistened to achieve a moisture content that is at least equal to or slightly greater than optimum moisture content. This moisture content should penetrate to a minimum depth of 12 inches below the bottoms of the slabs. 5. The minimum dimensions and reinforcement recommended herein for building floor slabs may be modified (increased or decreased subject to the constraints of Chapter 18 of the 2019 CBC) by the structural engineer responsible for foundation design based on his/her calculations, engineering experience and judgment. Foundation Observations All foundation excavations should be observed by a representative of the project geotechnical consultant to verify that they have been excavated into competent fill materials. These observations should be performed prior to the placement of forms or reinforcement. The excavations should be trimmed neat, level and square. All loose, sloughed or moisture -softened materials and/or any construction debris should be removed prior IFPETFM SOLID AS A ROCK NICHOLSON CONSTRUCTION December 5, 2022 225 Jasmine Avenue / Corona Del Mar J.N. 21422 Page 13 to the placement of concrete. Excavated soils derived from footing and utility trenches should not be placed in slab -on -grade areas unless they are compacted to at least 90 percent of maximum dry density. General Corrosivity Screening As a screening level study, limited chemical and electrical tests were performed on samples considered representative of the onsite soils to identify potential corrosive characteristics of these soils. The common indicators associated with soil corrosivity include water-soluble sulfate and chloride levels, pH (a measure of acidity), and minimum electrical resistivity. It should be noted that Petra does not practice corrosion engineering; therefore, the test results, opinion and engineering judgment provided herein should be considered as general guidelines only. Additional analyses would be warranted, especially, for cases where buried metallic building materials (such as copper and cast or ductile iron pipes) in contact with site soils are planned for the project. In many cases, the project geotechnical engineer may not be informed of these choices. Therefore, for conditions where such elements are considered, we recommend that other, relevant project design professionals (e.g., the architect, landscape architect, civil and/or structural engineer) also consider recommending a qualified corrosion engineer to conduct additional sampling and testing of near -surface soils during the final stages of site grading to provide a complete assessment of soil corrosivity. Recommendations to mitigate the detrimental effects of corrosive soils on buried metallic and other building materials that may be exposed to corrosive soils should be provided by the corrosion engineer as deemed appropriate. In general, a soil's water-soluble sulfate levels and pH relate to the potential for concrete degradation; water-soluble chlorides in soils impact ferrous metals embedded or encased in concrete, e.g., reinforcing steel; and electrical resistivity is a measure of a soil's corrosion potential to a variety of buried metals used in the building industry, such as copper tubing and cast or ductile iron pipes. Table 2, below, presents a single value of individual test results with an interpretation of current code indicators and guidelines that are commonly used in this industry. The table includes the code -related classifications of the soils as they relate to the various tests, as well as a general recommendation for possible mitigation measures in view of the potential adverse impact on various components of the proposed structures in direct contact with site soils. The guidelines provided herein should be evaluated and confirmed, or modified, in their entirety by the project structural engineer, corrosion engineer and/or the contractor responsible for concrete placement for structural concrete used in exterior and interior footings, interior slabs on -ground, garage slabs, wall foundations and concrete exposed to weather such as driveways, patios, porches, walkways, ramps, steps, curbs, etc. PETRASOr117 AS A ROCK GEOSCIENCES"° NICHOLSON CONSTRUCTION 225 Jasmine Avenue / Corona Del Mar TABLE 2 Soil Corrosivity Screening Results December 5, 2022 J.N. 21-422 Page 14 Test Test Results Classification General Recommendations Soluble Sulfates 0.0087 % SO' Min. f c= 2,500 psi Cal 417 pH 7.72 Type I-P (MS) Modified or Type II Modified cement Cal 643 Allkal' e Soluble Chloride C12 Residence: No max water/cement ratio, f e = 2,500 psi Cal 422 300 ppm C2 Spas/Decking: water/cement ratio 0.40, f c = 5,000 si Resistivity 8,100 Moderately Consult a Corrosion Engineer Cal 643) ohm -cm Corrosives Notes: 1. ACI 318-14, Section 19.3 2. ACI 318-14, Section 19.3 3. Pierre R. Roberge, "Handbook of Corrosion Engineering" 4. Exposure classification C2 applies specifically to swimming pools/spas and appurtenant concrete elements Retaining Wall Design and Construction Considerations Provided herein are geotechnical design and construction recommendations for exterior retaining walls, should they be proposed for construction onsite. Footings for retaining walls proposed on level ground may be designed in accordance with the bearing and lateral resistance values provided previously for building footings; however, when calculating passive resistance, the resistance of the upper 6 inches of the soils should be ignored in areas where the footings will not be covered with concrete flatwork, or where the thickness of soil cover over the top of the footing is less than 12 inches. Active and At -Rest Earth Pressures Active and at -rest earth pressures to be utilized for design of any retaining walls to be constructed within the site will be dependent on whether on -site soils or imported granular materials are used for backfill. For this reason, active and at -rest earth pressures are provided below for both conditions. 1. On -Site Soils Used for Backfill If on -site soils are used as backfill, active earth pressures equivalent to fluids having densities of 35 and 51 pounds per cubic foot should be used for design of cantilevered walls retaining a level backfill and ascending 2:1 backfill, respectively. For walls that are restrained at the top, at -rest earth pressures of 53 and 78 pounds per cubic foot (equivalent fluid pressures) should be used. The above values are for retaining walls that have been supplied with a proper subdrain system (see Figure RW-1). All walls should be designed to support any adjacent structural surcharge loads imposed by other nearby walls or footings in addition to the above recommended active and at -rest earth pressures. PETRASOLID ASA ROCK GEOSCIENCE13— NICHOLSON CONSTRUCTION December 5, 2022 225 Jasmine Avenue / Corona Del Mar J.N. 21-422 Page 15 2. Imported Sand, Pea Gravel or Rock Used for Wall Backfill Where imported clean sand exhibiting a sand equivalent value (SE) of 30 or greater, or pea gravel or crushed rock are be used for wall backfill, the lateral earth pressures may be reduced provided these granular backfill materials extend behind the walls to a minimum horizontal distance equal to one-half the wall height. In addition, the sand, pea gravel or rock backfill materials should extend behind the walls to a minimum horizontal distance of 2 feet at the base of the wall or to a horizontal distance equal to the heel width of the footing, whichever is greater (see Figures RW-2 and RW- 3). For the above conditions, cantilevered walls retaining a level backfill and ascending 2:1 backfill may be designed to resist active earth pressures equivalent to fluids having densities of 30 and 41 pounds per cubic foot, respectively. For walls that are restrained at the top, at -rest earth pressures equivalent to fluids having densities of 45 and 62 pounds per cubic foot are recommended for design of restrained walls supporting a level backfill and ascending 2:1 backfill, respectively. These values are also for retaining walls supplied with a proper subdrain system. Furthermore, as with native soil backfill, the walls should be designed to support any adjacent structural surcharge loads imposed by other nearby walls or footings in addition to the recommended active and at -rest earth pressures. Earthquake Loads Retaining Walls Note 1 of Section 1803.5.12 of the 2019 CBC indicates that the dynamic seismic lateral earth pressures on foundation walls and retaining walls supporting more than 6 feet of backfill height due to design earthquake ground motions be determined. It is unlikely that any wall retaining 6 or more feet of backfill will be constructed onsite. Accordingly, dynamic seismic lateral earth pressures are not considered necessary for this project. Subdrainage Perforated pipe and gravel subdrains should be installed behind all basement and retaining walls to prevent entrapment of water in the backfill (see Figures RW-1 through RW-3). Perforated pipe should consist of 4- inch-minimum diameter PVC Schedule 40, or SDR-35, with the perforations laid down. The pipe should be encased in a 1-foot-wide column of %-inch to 1'/z-inch open -graded gravel. I£ on -site soils are used as backfill, the open -graded gravel should extend above the wall footings to a minimum height equal to one- third the wall height or to a minimum height of 1.5 feet above the footing, whichever is greater. If imported sand, pea gravel, or crushed rock is used as backfill, subdrain details shown on Figures RW-2 and RW-3 should be utilized. The open -graded gravel should be completely wrapped in filter fabric consisting of Mirafi 140N or equivalent. Solid outlet pipes should be connected to the subdrains and then routed to a suitable area for discharge of accumulated water. If a limited area exists behind the walls for installation of a pipe and gravel subdrain, a geotextile drain mat such as Mirafi Miradrain, or equivalent, can be used in lieu of drainage gravel. The drain mat should extend the full height and lengths of the walls and the filter fabric side of the drain mat should be placed up against It PETRA SOLID ASA ROCK NICHOLSON CONSTRUCTION December 5, 2022 225 Jasmine Avenue / Corona Del Mar J.N. 21-422 Page 16 the backcut. The perforated pipe drain line placed at the bottom of the drain mat should consist of 4-inch minimum diameter PVC Schedule 40 or SDR-35. The filter fabric on the drain mat should be peeled back and then wrapped around the drain line. Wateraroofine The portions of retaining walls supporting backfill should be coated with an approved waterproofing compound or covered with a similar material to inhibit infiltration of moisture through the walls. Wall Backfill Recommended active and at -rest earth pressures for design of retaining walls are based on the physical and mechanical properties of the on -site soil materials. On -site soil materials may be difficult to compact when placed in the relatively confined areas located between the walls and temporary backcut slopes. Therefore, to facilitate compaction of the backfill, consideration should be given to using pea gravel or crushed rock behind the proposed retaining walls. For this condition, the reduced active and at -rest pressures provided previously for sand, pea gravel, or crushed rock backfill may be considered in wall design provided they are installed as shown on Figures RW-2 and RW-3. Where the onsite soils materials or imported sand (with a Sand Equivalent of 30 or greater) are used as backfill behind the proposed retaining walls, the backfill materials should be placed in approximately 6- to 8-inch-thick maximum lifts, watered as necessary to achieve near optimum moisture conditions, and then mechanically compacted in place to a minimum relative compaction of 90 percent. Flooding or jetting of the backfill materials should be avoided. A representative of the project geotechnical consultant should observe the backfill procedures and test the wall backfill to verify adequate compaction. If imported pea gravel or rock is used for backfill, the gravel should be placed in approximately 2- to 3- foot-thick lifts, thoroughly wetted but not flooded, and then mechanically tamped or vibrated into place. A representative of the project geotechnical consultant should observe the backfill procedures and probe the backfill to determine that an adequate degree of compaction is achieved. To reduce the potential for the direct infiltration of surface water into the backfill, imported sand, gravel, or rock backfill should be capped with at least 12 to 18 inches of on -site soil. Filter fabric such as MirafL 140N or equivalent, should be placed between the soil and the imported gravel or rock to prevent fines from penetrating into the backfill. If a thicker cap is desired (for planting or other reasons), consultation with the project structural engineer may be required to ascertain if the wall design is appropriate for the additional lateral pressure that a thicker cap of native material may impose. PETRASOLID ASAROCK GEOSCIENCES"° NICHOLSON CONSTRUCTION December 5, 2022 225 Jasmine Avenue / Corona Del Mar J.N. 21-422 Page 17 Geotechnical Observation and Testing All grading and construction phases associated with retaining wall construction, including backcut excavations, observation of the footing and pier excavations, installation of the subdrainage systems, and placement of backfill should be provided by a representative of the project geotechnical consultant. Masonry Block Walls (Non -Retaining) Footings for free-standing (non -retaining) masonry block walls may be designed in accordance with the bearing and lateral resistance values provided previously for building footings. However, as a minimum, the wall footings should be embedded at a minimum depth of 12 inches below the lowest adjacent final grade. The footings should also be reinforced with a minimum of two No. 4 bars, one top and one bottom. In order to reduce the potential for unsightly cracking related to the possible effects of differential settlement and/or expansion, positive separations (construction joints) should also be provided in the block walls at each corner and at horizontal intervals of approximately 20 to 25 feet. The separations should be provided in the blocks and not extend through the footings. The footings should be poured monolithically with continuous rebars to serve as effective "grade beams" below the walls. Planter Walls Low -height planter walls should be supported by continuous concrete footings constructed in accordance with the recommendations presented previously for masonry block wall footings. General Near -surface engineered fill soils within the site are variable in expansion behavior and are expected to exhibit very low to low expansion potential. For this reason, we recommend that all exterior concrete flatwork such as sidewalks, patio slabs, large decorative slabs, concrete subslabs that will be covered with decorative pavers, private vehicular driveways and/or access roads within the site be designed by the project architect and/or structural engineer with consideration given to mitigating the potential cracking and uplift that can develop in soils exhibiting expansion index values that fall in the low category. The guidelines that follow should be considered as minimums and are subject to review and revision by the project architect, structural engineer and/or landscape consultant as deemed appropriate PETRA SOLID AS A ROCK NICHOLSON CONSTRUCTION December 5, 2022 225 Jasmine Avenue / Corona Del Mar J.N. 21-422 Page 18 Thickness and Joint Spacing To reduce the potential of unsightly cracking, concrete walkways, patio -type slabs, large decorative slabs and concrete subslabs to be covered with decorative pavers should be at least 4 inches thick and provided with construction joints or expansion joints every 6 feet or less. Private driveways that will be designed for the use of passenger cars for access to private garages should also be at least 5 inches thick and provided with construction joints or expansion joints every 10 feet or less. Reinforcement All concrete flatwork having their largest plan -view panel dimension exceeding 5 feet should be reinforced with a minimum of No. 3 bars spaced 24 inches on centers, both ways. The reinforcement should be properly positioned near the middle of the slabs. The reinforcement recommendations provided herein are intended as guidelines to achieve adequate performance for anticipated soil conditions. The project architect, civil and/or structural engineer should make appropriate adjustments in reinforcement type, size and spacing to account for concrete internal (e.g., shrinkage and thermal) and external (e.g., applied loads) forces as deemed necessary. Edge Beams (Optional) Where the outer edges of concrete flatwork are to be bordered by landscaping, it is recommended that consideration be given to the use of edge beams (thickened edges) to prevent excessive infiltration and accumulation of water under the slabs. Edge beams, if used, should be 6 to 8 inches wide, extend 8 inches below the tops of the finish slab surfaces. Edge beams are not mandatory; however, their inclusion in flatwork construction adjacent to landscaped areas is intended to reduce the potential for vertical and horizontal movement and subsequent cracking of the flatwork related to uplift forces that can develop in expansive soils. Subgrade Preparation Compaction To reduce the potential for distress to concrete flatwork, the subgrade soils below concrete flatwork areas to a minimum depth of 12 inches (or deeper, as either prescribed elsewhere in this report or determined in the field) should be moisture conditioned to at least equal to, or slightly greater than, the optimum moisture content and then compacted to a minimum relative compaction of 90 percent. - PETRA SOLID ASA HOCK NICHOLSON CONSTRUCTION December 5, 2022 225 Jasmine Avenue / Corona Del Mar J.N. 21-422 Page 19 Pre-Moistenin¢ As a further measure to reduce the potential for concrete flatwork cracking, subgrade soils should be thoroughly moistened prior to placing concrete. The moisture content of the soils should be at least 1.2 times the optimum moisture content and penetrate to a minimum depth of 12 inches into the subgrade. Therefore, moisture conditioning should be achieved with sprinklers or a light spray applied to the subgrade over a period of few to several days just prior to pouring concrete. Pre -watering of the soils is intended to promote uniform curing of the concrete, reduce the development of shrinkage cracks and reduce the potential for differential expansion pressure on freshly poured flatwork. A representative of the project geotechnical consultant should observe and verify the density and moisture content of the soils, and the depth of moisture penetration prior to pouring concrete. Drainage Drainage from patios and other flatwork areas should be directed to local area drains and/or graded earth swales designed to carry runoff water to the adjacent streets or other approved drainage structures. The concrete flatwork should be sloped at a minimum gradient as discussed earlier in the Site Drainage section of this report, or as prescribed by project civil engineer or local codes, away from building foundations, retaining walls, masonry garden walls and slope areas. Tree Wells Tree wells are not recommended in concrete flatwork areas since they introduce excessive water into the subgrade soils and allow root invasion, both of which can cause heaving and cracking of the flatwork. FUTURE IMPROVEMENTS Should any new structures or improvements be proposed at any time in the future other than those shown on the enclosed grading plan and discussed herein, our firm should be notified so that we may provide design recommendations. Design recommendations are particularly critical for any new improvements that may be proposed on or near descending slopes, and in areas where they may interfere with the proposed permanent drainage facilities. Potential problems can develop when drainage on the pad is altered in any way (i.e., excavations or placement of fills associated with construction of new walkways, patios, block walls and planters). Therefore, it is recommended that we be engaged to review the final design drawings, specifications and grading plan prior to any new construction. If we are not given the opportunity to review these documents PETRASOLID AS AROCK GEOSCIENCES- NICHOLSON CONSTRUCTION 225 Jasmine Avenue / Corona Del Mar December 5, 2022 J.N. 21-422 Page 20 with respect to the geotechnical aspects of new construction and grading, it should not be assumed that the recommendations provided herein are wholly or in part applicable to the new construction or grading. POST -GRADING OBSERVATIONS AND TESTING Our firm should be notified at the appropriate times in order that we may provide the following observation and testing services during the various phases of post grading construction: 1. Building Construction • Observe footing trenches when first excavated to verify competent soil bearing conditions. • Re -observe footing trenches, if necessary, if trenches are found to contain a significant accumulation of loose, saturated or otherwise compressible soils. • Observe and test subgrade soils below slab areas to evaluate moisture content and penetration. 2. Masonry Block Walls and Retaining Walls • Observe footing trenches when first excavated to verify competent soil bearing conditions. • Re -observe footing trenches, if necessary, if trenches are found to contain significant slough, saturated or compressible soils. • Observe the subdrain systems installed behind the retaining walls. • Observe and perform field density testing of retaining wall backfill. 3. Utility Trench Backfill • Observe and perform field density testing of utility trench backfill. 4. Concrete Flatwork Construction • Observe and test subgrade soils below spa and concrete flatwork areas to document field density, moisture content, and moisture penetration. 5. Re-Grading/Additional Grading • Observe and perform field density testing of fill placed to proposed grades and any fill to be placed in temporary excavations, as well as above or beyond the grades shown on the accompanying grading plan. REPORT LIMITATIONS A representative of Petra was present on -site during grading operations on an on -call, as -needed basis for the purpose of providing the owner's representative with professional opinions and recommendations. PETRASOLID AS A ROCK GEOSCIENCES"` NICHOLSON CONSTRUCTION 225 Jasmine Avenue / Corona Del Mar December 5, 2022 J.N. 21-422 Page 21 These opinions and recommendations were developed based on field observations and selective testing of the contractor's work. Our scope of services during this project did not include supervision or direction of the contractor, his personnel or his subcontractors. Our observations and testing did not reveal any obvious deviations from the recommendations provided in the referenced geotechnical report by our firm; however, Petra does not in any way guarantee the contractor's work, nor do our services relieve the contractor (or any sub -contractors) of their liability should any defects subsequently be discovered in their work product. Based on our findings, the conclusions and recommendations presented herein and within the referenced report by our firm were prepared in conformance with generally accepted professional engineering practices. No warranty is expressed or implied. As noted above, existing side yard property line block walls were protected in place. These walls were designed and constructed by others; therefore, Petra assumes no responsibility for the long-term performance of these walls. This opportunity to be of service is sincerely appreciated. Please call if you have any questions pertaining to this report. Respectfully submitted, PET E CIENCES, INC. L Don Obert Associate Engineer GE 2872 SNUDO/DR/ly Darrel Roberts Principal Geologist CEG 1972 Attachments: Table A — Field Density Test Results Table B — Laboratory Data Summary Figures RW-1 through RW-3 — Retaining Wall Details Figure 1 — Density Test Location Plan W:Q020-20252021 WOU 1422ai ortsR 1422200 Rough Grade Repou.docx CEI L"DWAN WA lac�.tar� Cl31ia� E3:QBiEERM • 9,0 CAo02 SOLID AS A ROCK NICHOLSON CONSTRUCTION 225 Jasmine Avenue / Corona Del Mar TABLE A Field Density Test Results December 5, 2022 J.N.21-422 Date of Test Test No. Location Depth* (ft.) Moisture (%) Unit Wt. (lbs./cu.ft.) % Rel. Com Soil T e 11/15/2022 1 Building Pad 6.0 12.7 111.2 93 A 11/15/2022 2 Building Pad 4.0 12.2 109.5 92 A 11/15/2022 3 Building Pad 2.0 11.6 110.4 92 A 11/15/2022 4 Building Pad 0.5 12.0 112.4 94 A 11/16/2022 5 Building Pad 2.5 12.9 111.6 93 A 11/16/2022 6 Building Pad 1.5 11.9 112.1 94 A 11/16/2022 7 Building Pad 0.5 12.3 111.3 93 A 11/16/2022 8 Building Pad FP 11.1 112.6 94 A * Depth below finish grade FP — Finish Pad PETRASOLID AS A ROCK Is / e |y»� (/fa \ [ ])« a !/— » ] ! § �c A \ ° \� e± /!E \f� & \\\ \ m; / \ ! / ƒ\ 4 NATIVE SOIL BACKFILL / , Sloped or level ground surface .... 1 ? Compacted on -site soil Recommended backcut* IL y ti `Waterproofing compound M ly i c o ° �` Install subdrain system I / o op Hf3 Minimum 12-inch-wide column of 3/4" - 1 1/2" +y / open graded gravel wrapped in filter fabric. y o / Filter fabric (should consist of Mirafi 140N or equivalent) oo u'an I _-:4 inch perforated pipe. Perforated pipe should consist of 4" diameter ABS SDR-35 or PVC Schedule 40 or approved equivalent with the tg ' perforations laid down. Pipe should be laid on ti at least 2 inches of open -graded gravel. �K Vertical height (h) and slope angle of backcut per soils report. Based on geologic conditions, configuration of backcut may require revisions (i.e. reduced vertical height, revised slope angle, etc.) L PETRA I RETAINING WALL BACKFILL I FIGURE RW-1 I AND SUBDRAIN DETAILS IMPORTED SAND BACKFILL Sloped or level ground surface On -site native soil cap (12"thick) � Z� Non -expansive imported sand, SE>30. —Waterproofing compound y . Install subdrain system 1 cubic foot per foot min. of 3/4" - 1 1 /2" y, open graded gravel wrapped in filter fabric. y 4 Fitter fabric (should consist of w Mirafi 140N or equivalent). 7777 w ° .4 inch perforated pipe. Perforated pipe should N -0 o - y consist of 4" diameter ABS SDR-35 or PVC ' y - Schedule 40 or approved equivalent with the perforations laid down. Pipe should be laid on at least 2 inches of open -graded gravel. 2' mini * At base of wall, the non -expansive backfill materials should extend to a min. distance of 2' or to a horizontal distance equal to the heel width of the footing, whichever is greater. RETAINING WALL BACKFILL PETRA I AND SUBDRAIN DETAILS FIGURE RW-2 IMPORTED GRAVEL OR CRUSHED ROCK BACKFILL / / / Sloped or level ground surface On -site native soil cap (.12" thick) ° Non -e expansive imported >� P `gravel or crushed rock - = u ` ' ° °^ / Install filter fabric (Mirafi 140N ri> c^B. �,i �. . or equal) to prevent migration ' of fines into backfill. Waterproofing compound 4 inch perforated pipe. Perforated pipe should consist of 4" diameter ABS SDR-35 or PVC Schedule 40 or approved equivalent with the ;perforations laid down. If pea gravel used, <; pipe should be encased in 1 cubic foot per foot min. of 3/4" - 1 1/2" open -graded gravel wrapped in filter fabric (Mirafi 140N or equal) 2 Pipe should be laid on at least 2 inches of min.* gravel. *At base of wall, the non -expansive backfill materials should extend to a min. distance of 2' or to a horizontal distance equal to the heel width of the footing, whichever is greater. PETRA I RETAINING WALL BACKFILL I FIGURE RW-3 I w AND SUBDRAIN DETAILS ___ ..__ . _, ._, ____,_,_ 2dogm, �77 /\ \ 4-0 } a f Wave _ § 40 . ; §# \ yy, I - I � I I x