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HomeMy WebLinkAboutCT 04-01; YAMAMOTO SUBDIVSION POINSETTIA RIDGE; GEOTECHNICAL REVIEW OF PRECISE GRADING PLANS AND UPDATED FOUNDATION DESIGN RECOMMENDATIONS; 2001-04-13Orange County I Environmental! Corporate 3185.A Airway Avenue Costa Mesa, California 92626 'l 714 549 8921 F:714 549 1438 past + proscirt + future it's ill OIfl $titI?,C [urgiI1ee'. Geoto11isIs F ;iviruu,iuituI at Scientists April 13, 2010 J.N. 155-10 Mr. Torn Tupman WARMINGTON RESIDENTIAL CALIFORNIA 3090 Pullman Street Costa Mesa, CA 92626 Subject: Geotechnical Review of Precise Grading Plans and Updated Foundation Design Recommendations, Lots 1 through 16 Carlsbad Tract No. 04-01, The Poinsettia Ridge Project, Southeast Corner of Black Rail Road and Songbird Avenue, City of Carlsbad, San Diego County, California. Dear Mi. Tupnian: In accordance with your request and authorization, Petra Geotechnical, Inc. (Petra) has reviewed the precise grading plans for Lots I through 16 Carlsbad Tract No. 04-01(Poinsettia Ridge Project) located at the southeast corner of Black Rail Road and Songbird Avenue in the City of Carlsbad; San Diego County, California. The precise grading plans reviewed by Petra consisted of two sheets that were prepared by MLB Engineering and plot-dated March 22, 2010. The purpose of the review is to provide reconunendations for restoring the subject lots to their original as- graded conditions, recommendations for construction of various site improvements, as well as updated foundation design recommendations in accordance with applicable provisions of the 2007 California Building Code (CBC, 2007). PREVIOUS GRADING Petra has reviewed a geotechnical report by Christian Wheeler Engineering dated January 4, 2007 (CWE, 2007) describing the results of their observations and compaction testing during rough grading of the subject tract and construction of various site improvements. Noteworthy findings made from reviewing the CWE report include the following: Rough grading of Tract No. 04-01 reportedly ended approximately 4¼ years ago and the completed earthwork was considered adequate to support foundations for single-family residences. o Results of Expansion Index testing by CWE indicated the onsite soils exhibit Very Low Expansion potentials with expansion indices of less than 20. WARl'HNGTON RESIDENTIAL CALIFORNIA April 13, 2010. Poinsettia Ridge Project . J..N. 155-10 Page 2 SITE RECONNAISSANCE A representative of Petra conducted a site reconnaissance on April 6, 2010 to evaluate the condition of the previously graded lots. The purpose of the Site reconnaissance was to observe and document significant changes that appear to have occurred since the completion of rough. grading and the construction of utilities, retaining walls and streets. A suinniary of our site observations is as follows: A majority of the level pad arias were covered with a negligible to minor growth of vegetation; however, some lots were covered with a light to moderately heavy growth of vegetation (low grasses and weeds). The front yard areas between the level pads and adjacent street sidewalks were typically covered with a light to moderate growth of vegetation. No evidence of significant desiccation was observed on the lot surfaces generally due to the granular and non-expansive nature of the onsite soils. However, erosion gullies varying from about 1 to 3 feet deep, were observed on Lots 3 through 6. The adjacent access streets have been paved to finish grades, and backbone utilities have been installed within the tract itself Stub-outs for utility connections behind the curbs and sidewalks are assumed to -be in place for each lot. Sidewalks, fire hydrants, streetlights and utility access vaults have been installed as well. All driveway approaches have also been constructed in front of each lot. The graded slopes bordering the subject lots are landscaped and irrigated. No evidence of surficial instability such as erosion gullies, rivulets and/or shallow slumps were observed on the slopes. In addition, no evidence of deep-seated instability was observed. An approximately 5 to 6Y2 feet high segmental retaining wall with a geogrid-reinforced backfill exists Along the toe of an ascending slope located at the rear of Lots 5 through 7. This wall appeared intact and no tilting or distress was observed. Geogrid reinforcement was evident within the backfill soils, as observed at several locations within the open spaces between wall cells. Two similar segmental retaining walls also exist along the common property lines between Lots 3 and 4 and Lots 15 and 16. The wall between Lots 3 and 4 is approximately 3 feet high and the wall between Lots iS and 16 is approximately 4¼ feet high. Both retaining walls also appeared intact and no tilting or distress was observed; however, the backfill soils placed behind the walls and between individual wall cells has been washed away in many areas resulting in obvious voids and soil deposits at the base of the walls. PRECISE GRADING PLAN REVIEW Proposed Construction and Lot Drainage Review of the precise grading plans for the subject lots prepared by MLB Engineering indicates that single- family homes with attached garages are proposed within the subject lots. The proposed single-family residences will be of wood-frame construction with first floor slabs constructed on-grade. Concrete driveways. will provide access from the adjacent streets and concrete walkways will provide access from the driveways to the front doors. Approximately 4-foot-wide strips of interlocking block pavers are proposed across the WARMINGTON. RESIDENTIAL CALIFORNIA April 13, 2010 Poinsettia Ridge J'roject J.N. 155-10 Page 3 driveways where they abut the adjacent street parkways. Although not indicated on the l)laflS, it is anticipated that concrete patios may be constructed in the rear yard areas. A total of seven new retaining walls varying from 3 to 5'/2 feet high (as-measured from top of footing to top of wall) are proposed on Lots 1, 4, 8, 9, 12 and 16 to increase the size of the level pad areas in order to accommodate construction of the proposed residences. Two retaining walls are proposed on Lot 9 while one retaining wall is proposed on the Lots 1, 4, 8, 12 and 16. Five retaining walls are proposed on or near the tops of adjacent descending slopes and two retaining walls are proposed along the toes of adjacent ascending slopes. Earthen swales designed at a minimum gradient of 1 percent are proposed within the rear, side and front yards to collect surface water and convey it to the adjacent streets. Three- and four-inch PVC area drains with grate inlets are also proposed on Lots 4, 7, 8, 9, 10, 12 and 15 as a supplement to the earthen swales. The PVC area drains on Lots 7, 8,9, 10 and 15 will be exited through the adjacent street curbs. The PVC area drains on Lots 4 and 12 will be eited to an existing concrete drainage ditch located along the southerly tract boundary. Proposed Precise Grading The subject lots are presently in a rough-graded condition with surface elevations at or near planned finish grades. Minor cuts and fills are proposed within the yard areas of the subject lots in order to establish positive drainage away from the. residences and to direct surface water to the eat-then swales and area drains. Some minor re-grading will be required to re-compact the nëar-surfacé soils on the lots that have become weathered and loosened to depths of several inches due to the time that has elapsed since the completion of rough grading. CONCLUSIONS AND RECOMMENDATIONS General Feasibility Based on our review of the precise grading plans and our understanding of the project to date, the proposed precise grading is considered feasible and practical from a geotechnical standpoint if accomplished in accordance with the grading code of the City of Carlsbad and the recommendations provided herein. Site Preparation and Gradhig Clearing and Grubbing The subject lots are covered with vegetation varying in density from slight to locally moderate. All significant vegetation should be stripped and removed from the site. Clearing and grubbing should include the removal of any debris, trash and similar deleterious materials. WARMTNGTON RESIDENTIAL CALIFORNIA April13, 2010 I'oinsettia Ridge Project J.N. 155-10 Page 4 Lot Reconditioning and Precise Grading Remedial grading is recommended to restore the. subject lots to their original as-graded condition by reprocessing the weathered surficial soils and repair the limited erosion damage. The surface of the pads should be scarified to a depth of at least 8 inches, moisture-conditioned to achieve optimum or slightly above optimum moisire conditions, and then recompacted in-place to a minimum relative compaction of 90 percent based on ASTM Dl 557. In addition to the level padsurfaces, the areas between the existing sidewalks and the front of the lots should be similarly scarified and recompacted to achieve a compacted subgrade suitable for construction of driveways and similar improvements. Erosion gullies greater than about 12 inches deep should be repaired by excavating all equipment-width slot cut along the axis of the eroded area to a depth that will expose competent underlying materials. The areas should then be brought to finish grade with fill materials that are placed in approximately 8-inch maximum lifts, watered to achieve optimum or slightly above optimum moisture conditions, and then compacted in-place to a minimum relative compaction of 90 percent. It should be noted that the sequence of precise grading, as recommended above, is left to the grading contractor's discretion. However, our experience indicates that for conditions where site surficial soils exist at a moisture content dryer than optimum moisture, the grading opeiation may be performed more efficiently if the soils are thoroughly moisture conditioned utilizing a temporary sprinkler system prior to scarification and reconipaction. Geotechnical Observations A representative of Petra should be present onsite during scarification and reconlpaction of the existing pad surfaces and front yard/parkway areas to verify proper moisture content and adequate compaction. Existing surfaces and/or exposed bottom surfaces in any areas to receive compacted fill should also be observed and approved by a representative of Petra prior to fill placement. No fills should be placed without prior approval from Petra's representative who should also be present onsite during any grading operations to document proper placement and adequate compaction of fill, as well as to observe compliance with the other recommendations presented herein. Post-Grading Considerations Precise Grading and Drainage Facilities Surface drainage systems consisting of sloping concrete flatwork, graded earthen swales and PVC area drains are proposed on the subject lots to collect and directall surface waters to the adjacent streets. In addition; the WARMTNGTON RESIDENTIAL CALIFORNIA April 13, 2010 Poinsettia Ridge Project J.N. 155-10 Page 5 ground surface around the proposed buildings will be sloped at a positive gradient away from the structuies. The purpose of the precise grading is to prevent ponding of surface water within the level areas of the subject lots and against building foundations and associated site improvements. Section 1803.3 of the 2007 California Building Code requires that the ground surface immediately adjacent to building foundations shall be sloped away from the building at a slope of not less than one unit vertical in 20 units horizontal (5 percent slope) for a minimum distance of io feet measured perpendicular to the face of the building wall. Further, the CBC states that swales used-for this purpose shall be sloped a minimum of 2 percent where located within 10 feet of any building foundation. Maintaining compliance with these CBC provisions falls under the purview of the design civil engineer; however, exceptions that allow modifications to these criteria are provided within the same section of the code. Such an exception states that, where climatic or soil conditions warrant, the slope of the ground away from building foundations is permitted to be reduced to not less than one unit in 48 units horizontal (2 percent slope). Since this exemption provision appears to fall under the purview of the geotechnical engineer, we provide the following coninientaiy. It is our understanding that the state-of-the-practice for pojects in San Diego County, as well as throughout Southern California, has been to construct earthen slopes at a 2 percent gradient away from structural foundations, and to maintain earthen swale gradients at a I percent minimum. Dwellings constructed and properly maintained under those criteria;have proven to perform satisfactorily. Therefore, considering the semi-arid climate in the area, site soil conditions and an appropriate irrigation regime, Petra Geotechnical, Inc. considers that the Use of 2 percent slopes away from the building structures and 1 percent swale gradients to be suitable for the subject lots. It should be emphasized that homeowners are to be cautioned that the above-described drainage gradients away from the structures and svales to be properly maintained and not obstructed in any way. In addition, future improvements should not alter the established gradients in any way unless replaced with suitable alternative drainage systems. Further, where the flow -line of any Swale, exists within five horizontal feet of a structural footing, the adjacent footing shll be deepeied appropriately to maintain minimum embedment requirements as measured from the flow line of the swale. Utility 'French Backfill All utility trench backfill should be compacted to a minimum relative compaction of 90 percent. Trench backfill materials should be placed in approximately 8- to 2-inch-thick maximum lifts, moisture conditioned as necessary to achieve near optimum moisture conditions, and mechanically compacted in place with a hydra hammer, pneumatic tamper or similar equipment that can achieve a minimum relative compaction of 90 percent. Flooding or jetting of backfill materials will not provide an adequate level of compaction and thus should not be permitted. A representative of Petra should probeand test the backfills to document that an adequate degree of compaction has been achieved. WARMINGTON RESIDENTIAL CALIFORNIA April 13, 2010 Poinsettia Ridge Project J.N. 155-10 Page 6 For shallow trenches where pipe or utilities might be damaged by mechanical compaction equipment, imported sand having a Sand Equivalent (SE) value of 30 or greatcr may be used, for backfill. Sand backfill materials should be watered to achieve optimum (or above) moisture conditions, and then tamped with hand-operated pneumatic tampers to ensure proper consolidation of the backfill. No specific relative compaction will be required; however, observation, probing and, if deemed necessary, testing should be performed by a representative of this firni to document that the backfill is adequately compacted and will not.be subject to excessive setilement. Where an exterior or interior utility trench is proposed in a direction that is parallel to a building footing, the bottom of the trench should not extend below a 1:1 plane projected downward from the bottom edge of the adjacent footing. Where this condition occurs, the adjacent footing should be deepened or the trench backfilled and compacted prior to construction of the footing. Foundation Design Considerations 2007 CBC Seismic Design Coefficients Structures within the site should be designed and constructed to resist the effects of seismic ground motions as provided in Section 1613 of the 2007 California Building Code (CBC). The method of design is dependent on the seismic zoning, site characteristics, occupancy category, building configuration, type of structural system and on the building height. For structural design in accordance with the 2007 CBC, a computer prograni, Earthquake Ground Motion Parameters Version 5.09a, developed by the United States Geological Survey (USGS, 2007) was utilized to provide ground motion parameters for the subject site. The program includes hazard curves, uniform hazard response spectra and design parameters for sites in the 50 United States, Puerto Rico and the United States Virgin Islands. Based on the latitude, longitude and site classification, seismic design parameters and spectral response for both short periods and I-second periods are calculated including Mapped Spectral Response Acceleration Parameter, Site Coefficient, Adjusted Maximum Considered Earthquake Spectral Response Acceleration Parameter and Design Spectral Response Acceleration Parameter. The program is based on USGS research and publications in cooperation with the California Geological Survey for evaluation of California faulting and seismicity (USGS, 1996a; 1996b; 2002; 2007). The following 2007 CBC seismic design coefficients. should be used for the proposed structures. These criteria are based on the site class as determined by existing subsurface geologic conditions, on the proximity of the site to the nearby fault and on the maximum moment magnitude and slip rate of the nearby fault. WARMINGTON RESIDENTIAL CALIFORNIA April 13, 2010 Poinsettia Ridge Project J.N. 155-10 Page 7 2007 CBP'S ection 1613 Seismic Design Coefficients Site Latitude 33.1083 Site Longitude 117.2867 Mapped Spectral Response Acceleration Parameter, S5 (Figure 1613.5(3) for 0.2 second) 1.21 Mapped Spectral Response Acceleration Parameter, S1 (Figure 16 13.5(4) for 1.0 second) 0.45 Site Class Definition (Table 16 13.5.2) Site Coefficient, F. (Table 1613,5.3(1) short period) ,.. 1.02 Site Coefficient, F5. (Table 16 13.5.3(2) 1-second period) 1.55 Adjusted Maximum Considered Earthquake Spectral Response Acceleration Parameter, S (Eq. 16-37) 1.23 Adjusted Maximum Considered Earthquake Spectral Response Acceleration Parameter, SMI (Eq. 16-38) 0.70 Design Spectral Response Acceleration Parameter, SDS (Eq. 16-39) 0.828 Design Spectral Response Acceleration Parameter, S01 (Eq. 16-40) 0,47 Post-Tensioned Slab-on-Grade Results of previous laboratory tests provided in the referenced geotechnical report (CWE, 2007) indicate that onsite soils within Lots 1 through 16 exhibit expansion indices of less than 20 (Very Low Expansion Potential) as determined in accordance with ASTM D 4829. As such, the onsite soils within the subject lots may be considered non-expansive soils per Section 1802.3.2 of the 2007 CBC and are exempt from the requirements provided therein. Petra has reviewed the plans and details for post-tensioned slabs-on-grade prepared for the subject tract by Suncoast Post-Tension LTD (Suncoast, 2010). We understand that the post-tension plans have been prepared in accordance with a design method referred to as the"Spanability" method. From a geotechnical engineering viewpoint, it is our professional opinion that the design is suitable for the onsite soil conditions. In addition to recommendations provided in the referenced report by Suncoast, the following are also presented. It should be noted that the following recommendations replace those in the referenced report that are of similar nature. Living area concrete floor slabs should be underlain with a moisture vapor retarder consisting of a minimum 10-mil polyethylene or polyolefin membrane that meets ASTM E 1745 and ASTM E 96 requirements (such as Husky Orange Guard, Stego, or equivalent). All laps within the membrane 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 removing an additional inch from the pad subgrade and then placing a 1-inch-thick leveling course of sand across the pad surface prior to placement of the membrane. 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 thàroughly moistened to achieve a WARivflNGTON RESIDENTIAL CALIFORNIA Poinsettia Ridge Project April 13, 2010 J.N. 155-10 Page 8 moisture content that is at least equal to or slightly greater than optimum moisture content. This moisture conteit should penetrate to aminimum depth of 12 inches below the bottoms of the slabs. Allowable Soil Bearing Capacities An allowable soil bearing capacity of 1,500 pounds per square foot (psi), including dead and live loads, may be utilized for design of 12-inch-wide 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 widtIand/or depth, to a maximum value of 2,500 pounds per square foot. Recommended allowable bearing values include both dead and live loads, and may be increased by one-third for short duration wind and seismic forces. Footing Settlements Based on the allowable bearing values, total settlement of the footings is anticipated to be less than 1 inch and differential settlement is expected to be less than /2 of an inch over a span of 30 feet, represented by an angular distortion of 1:720. The majority of these settlements are likely to take place immediately after placement of the footing loads. Lateral Resistance A passive earth pressure of 250 psf, per foot of depth, to a maximum value of 2,500 psf may be used to determine lateral bearing resistance for footings. In addition, a coefficient of friction of 0.40 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 short duration wind or seismic forces. The above values are based on footings placed directly against compacted fill. In cases where the footing sides are formed, all backfill placed against the footings should be compacted to at least 90 percent of maximum dry density. Foundation Excavation Observations Foundation excavation should-be observed by a representative of this firm to document that they have been excavated into competent bearing soils prior to the placement of forms, reinforcement or concrete. The excavations should be trimmed neat, level and square. All loose, sloughed or moisture-softened soils and/or any construction debris should be removed prior to placing of concrete. Excavated soils derived from footing and/or.utility trenches should not be placed in building slab-on-grade areas or exterior concrete flatwork areas unless the soils are compacted to at least 90 percent of maximum dry density. 1,541,4111 WARMTNCTON RESIDENTIAL CALIFORNIA April 13, 2010 Poinsellia Ridge Project J.N. 155-10 Page 9 Soil Corrosivity Laboratory tests to determine sulfate and chloride contents, pH and electrical resistivity were not performed by CWE to evaluate the potential corrosive effects that onsite soi1s may have on concrete and buried metallic elements. Therefore, an evaluation of soil corrosivity should be performed during scarification and reconipaction of (he existing pad surfaces. Retaining Walls Foundation Setbacks OIL Descending Slopes The retaining walls on Lots 1, 4, 9, 12 and 16 are proposed on or near the tops of descending slopes. Therefore, the foundations for these retaining walls should be deepened to provide a inininium horizomtal setback of 5 feet between the outside bottom edges of the foundations and the face of the descending slope. Bearing Value and Lateral Resistance Retaining wall footings may be designed using the allowable bearing values and lateral resistance values provided previously for building foundations; however, when calculating passive resistance, the upper 6 inches of the footings 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. * In addition, retaining wall footings proposed on or nearthe tops of descending slopes shouldbe designed using a reduced passive earth pressure of ISO psf, per foot of depth, to a maximum value of 1,500 psf. Active Earth Pressures Onsite soils consist of granular, non-expansive materials and are considered suitable for use as wall backfill. Therefore, if onsite soils are utilized for backfill, active earth pressures equivalent to fluids having densities of 35 and 52 pounds per cubic foot ()co should be used for design of cantilevered walls retaining a level backfill and ascending 2: 1backfill, respectively. These values are for retaining walls that are provided with a proper backdrain system. All retaining walls should also be designed to support any adjacent structural surcharge loads imposed by other nearby wails or footings in addition to the recommended active earth pressures. Drainage and Waterproofing Perforated pipe and gravel backdrains should be installed behind all retaining walls to prevent entrapment of water in the backfill. Perforated pipe should consist of 4-inch minimum diameter PVC Schedule 40, or ABS WARMINGTON RESIDENTIAL CALIFORNIA April 0, 2010 Poinsettia Ridge Project J.N. 155-10 Page 10 SDR-35, with the perforations laid down. The pipe should be encased ma 1-foot-wide column of 3/4 inch to P/2-inch open-graded gravel. If onsite soils are used as backfill, the open-graded gravel should extend above the wall footings to a minimum height equal to one-half the wall height, or to a minimum height of 1.5 feet above the fooling, whichever is greater. 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 backdrains and then routed to .a suitable area for discharge of accumulated water. Thebackfilled sides of retaining walls should be coated with an approved waterproofing compound or covered with a similar material to inhibit migration of moisture through the walls. Wall Bacidill Wall backfill materials should be placed in approximately 6- to 8-inch-thick maximum lifts, watered as necessary to achieve optimum or slightly above optimum moisture cnditions, 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 Petra should observe the backfill procedures and test the wall backfill to verify adequate compaction. Temporary Excavations Based on the physical characteristics of the onsite soils, temporary excavations associated with construction of retaining walls should be cut back at a maximum gradient of I 1 (h:v), or flatter. The temporary excavations should be observed by a representative of Petra for any evidence of potential instability. Depending on the results of these observations, a revised slope configuration may be necessary. Other factors that should be considered with respect to the stability of temporary slopes include construction traffic and storage of materials on or near the tops of the slopes, construction scheduling, presence of nearby walls or structures, and weather conditions at the time of construction. All applicable requirements of the California Construction and General Industry Safety Orders, the Occupational Safety and Health Act of 1970,, and the Construction Safety Act should also be followed. Exteilor Concrete Fltwork Thickness and Joint Spacing To reduce the potential of unsightly cracking, concrete walkways, patio-type slabs and concrete subslabs lobe covered with decorative payers should be at least 4 inches thick and provided with construction joints or expansion joints every 6 feet or less. Concrete driveway slabs should beat least 4 inches thick and provided with constructioli joints or expansion joints every 10 feet or less, UJ WARMINGTON RESIDENTIAL CALIFORNIA April 13, 2010 Poinsettia Ridge Project J.N. 155-10 Page 11 Rein foiceiiieii All concrete patio-type slabs, driveways and walkways greater than 10 feet in width should be reinforced with a minimum of No. 3 bars spaced 24 inches on centers, both ways. Alternatively, the slab reinforcement may consist of welded wire mesh of sheet type (not rolled) with 6x6/W2.9xW2.9 designation in accordance with Wire Reinforcement Institute (WRT), The reinforcement should be properly positioned near the middle of the slabs. Should the project architect determine that more stringent reinforcement is appropriate, the architect's specifications would supercede the recommendations provided' herein. Subgrade Preparation As a further measure to reduce cracking of concrete flatwork, the subgrade soils below concrete flatwork areas should first be compacted to a minimum relative compaction of 90 percent and then thoroughly vetted to achieve 'a moisture content that is at least equal to, or slightly greater than, optimum moisture content. This moisture should penetrate to a depth of 12 inches into. the subgrade and should be maintained in.the soils during placement of concrete. Pre-watering of the soils is intended to Promote uniform curing of the concrete and reduce the development of shrinkage cracks. A representative of this firm should observe and document the density and moisture content of the soils, and the depth of moisture, penetration prior to pouring concrete. Iiiter1ocldng Block Payers Approximately 4-foot-wide strips of interlocking block payers are proposed across the driveways where they abut the adjacent street park'ays. In consideration of the intended usage, it is recommended that the payers be underlain with 4 inches of aggregate base and a I to I Y2-inch layer of bedding sand. This section was determined in accordance with Interlocking Concrete Pavement Institute (ICPI) Technical Spec Number 4 Detailed specifications for the design and construction of interlocking payers are available at the ICP1 website (www.icpi.org). Prior to placing the aggregate base, the subgradc soils to aminimuni depth of inches should be compacted to 90 percent, or more, relative compaction based on ASTM D155.7. The subgrade should be firm and unyielding prior to placement of base, as exhibited by proof-rolling. Base materials should consist of Class 2 aggregate base conforming to Section 26-1.02B of the State of California Standard Specifications or crushed aggregate base conforming to Section 200-2 of the Standard Specifications for Public Works Construction (Greenbook). Base materials should be compacted to 95 percent or more relative compaction based on ASTM D1557. The base materials should be at or slightly above optimum-moisture content when compacted. Care must be taken that the aggregate base is properly compacted to the correct grades, since irregularities in the base surface will eventually be reflected in the paver surface. WARMINGTON RESIDENTIAL CALIFORNIA April 13, 2010 Poinsettia. Ridge PiOject J.N. 15540 Page 13 4. Interlocking Payers Observe and test preparation of subgrade soils below aggregate base materials to verify adequate compaction. Observe and test placement of aggregate base materials to verify material specification compliance, adcquate thickness and compaction. Observe placement of the bedding sand to verify material specification compliance and adequate thickness S. Retaining Walls Observe temporary excavations for any evidence of potential instability. Observe all footing trenches when first excavatedto verify adequate depth and competent soil bearing conditions. Re-observe all footing trenches, if necessary, if trenchesarefound to be excavated to inadequate depth and/or are found to contain significant slough, saturated or compressible soils. Observe instillation of subdrains. Observe and test placement of backfill materialsto verify adequate compaction. 6. Utility Trench Backfill Observe, probe and test placement of all utility treich backfill to verify adequate compaction. CLOSURE This report is subject to review by the controlling authorities for this project. We sincerely appreciate this opportunity to be of service. Please do not hesitate to call the undersigned if you have any questions regarding this report. Respectfully submitted, PETRA GEOTECHNICAL, INC. Siamak Jafroudi, PhD,GE 2024 Senior Principal Engineer SJfkg W'20101OO\l35-I0 Waanüngcon Rsdniial California (Mick Rail)lO\Precisc Grading Plan Rcsicwdoc