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HomeMy WebLinkAbout25 SEAWATCH - SOILSNMG Geotechnical, Inc. September 16, 2003 Project No. 03022-01 To: Shea Homes P.O. Box 1509 Brea, California 92822-1509 Attention: Mr. Todd Funk, Project Manager Subject: Preliminary Geotechnical Review of Model Precise Grading Plan, Lots 41 through 44, Tract 15811, a Portion of Area C-1 within Pacific Ridge Development, Planning Area 5, Newport Coast, County of Orange, California r INTRODUCTION In accordance with your request, NMG Geotechnica1, Inc. (NMG) has performed a geotechnical review of the proposed model precise grading plan for the subject site within the Pacific Ridge development at Newport Coast, located in the County of Orange, California. The purpose of our review was to evaluate the proposed precise grading and construction in light of the geotechnical conditions at the site. The plans reviewed were Sheets 1 through 3 of 3 sheets of the 20-Scale Model Precise Grading Plan for Lots 41 through 44 of Tract 15811, prepared by Douglas Bender and Associates and received by NMG on September 4, 2003. Currently, NMG is the geotechnical consultant of record during the ongoing preliminary operations conducted by the Irvine Community Development Company (ICDC). The subject site is part of a larger area that is being graded by ICDC within the Pacific Ridge development (Lots 110 through 113 of Tentative Tract 15811). A geotechnical report of our observations will be submitted to the County of Orange Development Services Department (COPDSD) once the preliminary grading (Milestone 3) has been completed. Our scope of work for this study included site visits during preliminary referenced reports and other background materials, review of thegrading, review of the precise grading plan and report preparation. This report presents a summary of our findings and provides our conclusions and preliminary recommendations for design and construction of the subject site. .r ATTACHMENTS Figure 1 — Site Location Map — Rear of Text Figure 2 — Retaining Wall Drainage Detail — Rear of Text Appendix A — References Appendix B — Seismic Data Appendix C — General Earthwork and Grading Specifications T)L7rlTTr /n/n\ /,/,n 1/,/,n rAV /n/.n1 03022-01 September 16, 2003 materials should be scarified; moisture -conditioned and, recompacted. Fills should be compacted to a minimum 90 percent of the maximum dry density, as determined by ASTM Test Method D1557. Fill materials should be placed in loose lifts no thicker than 8 inches. Materials should be moisture -conditioned and processed, as necessary, to achieve uniform moisture content that is within moisture limits required to assure adequate bonding and compaction. Fills placed against ground sloping more than 5:1 should be benched into competent material. 5. Seismic Design Guidelines Seismic design data is provided in the table below based on the 1997 UBC criteria selection. SEISMIC DESIGN VALUES BASED ON 1997 UBC —"—V _VXA%a uvia rlg"o 10-2 4 _- Soil Pro1"ile Type from Table 16-J S Seismic Source Type from Table 16-U D B Closest Distance to Seismic Source 4 miles (6 km) Closest Active Fault Newport -Inglewood (offshore) 6. Foundation and Slab Design '! Shallow foundations and slabs -on -grade (including post -tensioned slabs) may be used for low-rise structures. Based upon our knowledge of the subject site, expansion potentials of the near -surface soils are anticipated to be in the "low" and "medium" ranges. The 1997 Uniform Building Code (UBC) requires specific foundation and slab design for soils having an expansion index of 21 (low) or greater. The design should be post -tensioned slabs per the Post -Tensioning Institute (PTI) method or slab -on -grade per the Wire Reinforcement Institute (WRI) method. Any other foundation and slab designs must be specifically submitted by the geotechnical and structural engineers and approved by the building official. i Geotechnical parameters for the design of post -tensioned slabs in accordance with the PTI method are provided in the following table (Geotechnical Guidelines for Design of Post -Tensioned Slabs). For preliminary design purposes, we recommend the low to medium category (Category 2) be used. Final design parameters will be provided for the subject site based upon the as -graded conditions. For design of the post -tensioned slabs, a soil/concrete coefficient of 0.75 may be assumed when the concrete is underlain by the polyethylene moisture barrier (1997 UBC Section 1816.4.6). Slab subgrades should be at the moisture contents described in the following table just prior to placement of concrete. Presoaking of the soil may be necessary to achieve these moisture contents. If remedial grading is necessary during building pad recertification, the placement of fill at or near this moisture content generally is helpful in reducing (in some cases considerably) the amount of effort required during presoaking. The post -tensioned slabs should also be designed to meet the settlement criteria presented in Section 2 of these recommendations. I030916.doc rl AA r., 03 022-01 I, September 16, 2003 " 'DESIGN ECHMCAL GUIDELINES FOR OF POST -TENSIONED SLARR Parameter Estimated Range of Expansion Classification Center Lift • Edge Moisture Variation Distance, em • Center Lift, ym Edge Lift • Edge Moisture Variation Distance, em • PA— r :,a -- Modulus of Elasticity of Soils, Es Presaturation, as needed, to obtain the minimum moisture down to the minimum depth Category 1 2 3 Very Low to Low to 4 Medium to High to Very Low Medium Niah rr , 4.6 feet 5.3 feet 5.6 feet 2.1 inches 2.5 inches 3.8 inches 6.0 feet 4.0 inches 2.5 feet 3.0 feet 3.5 feet 0.5 inch 0.7 inch 1.0 inch Inn,. 2.000 nci � en 1.2 x — ---- .-' 1.2 optimum optimum down to down to 12 inches IN in,-ho. 50 pci 1,000 psi 1.3 x optimum down to ,0, lo---r.,,... -, 1 lwimg nelow 12 inches -_ — •�•���oa West adjacent grade 18 inches 18 inches * Based on Method zn UBC S 4.0 feet 1.1 inch 25 pci 50--- 0 psi 1A x optimum down to 24 inches 24 iirs es ectton 1616 7. Allowable Bearin g Capacity An allowable bearing pressure of 1,500 psf may be applied to post tension slabs if design and used for convention nee al shallow footings having a minimum embedment in approved for material of 1 foot below the lowest adjacent allowable bearing pressure may be increased by�S00 psf ade or each additional th 1 foot. The ment in approved material and b of y 350 psf for each additional foot of width, to a maximum bale of 3,000 psf Allowable bearing pressure may be increased by one-third for wind , loading. For sliding resistance, the friction coefficient of 0.35 may be used at t 02' seismic soil interface, he concrete and 8. Moisture Mitigation for Concrete Slabs In addition to geotechnical and structural considerations, the project owner should al various other factors that relate to slab design and construction. Please note that these ar consider not within the purview of the geotechnical consultant but we provide the foIlowin e are for your consideration. g info rma tion The intended use of the interior space, type of flooring (if any), and the type of goods with the floor may dictate the need for and design of measures to mitigate potential otent al in contact moisture emission from and/or moisture vapor transmission through the slab. effects of Typically, for habitable structures, a minimum 10-mil Visqueen (or equivalent) vapor t is recommended under the slab to help mitigate moisture transmission through slabs. r The m ost 030916.doc 7 Ia1AAr 03022-01 September 16, 2003 recent guidelines by the American Concrete Institute (ACI 302.1R-96) recommend that the vapor retarder be placed directly under the slab where there is the potential for moisture sensitive flooring. The use of a §nd layer between the vapor retarder and slab has been a common local practice but frequently results in water from rain and other construction operations being trapped between the vapor retarder and slab in the sand layer. Although this granular layer may help protect the vapor retarder from damage and facilitates slab curing, it should be not used unless it can be kept dry prior to the slab pour. If damage to the vapor retarder without a sand layer over it is of significant concern, a higher strength retarder or barrier may be appropriate. A layer of sand may also be needed below the vapor retarder to help protect it from puncturing during concrete placement if the pad contains rocks or other objects that can puncture the sheeting. The thickness of the sand layer(s) should be incorporated in the pad grade design. The vapor retarder, when used, should be overlapped minimum 6 inches at the joints, sealed around pipes and other appurtenances, and repaired when punctured in general accordance with the manufacturer's recommendations. Concrete mix design and curing are also significant factors in mitigating slab moisture problems. Concrete with lower water/cement ratios results in de nser, less permeable slabs. They also "dry" faster with regard to when flooring can be installed (reduced moisture emissions quantities and rates). Rewetting of the slab following curing should be avoided since this can result in additional drying time required prior to flooring installation. Concrete mix and the appropriate location of the vapor retarder should be determined in �a coordination with all parties involvedprouct,. structural engineer, architect, concete subcontractors, hand flooring subcontractors.including the ro�ect owner, 9. Lateral Earth Pressures and Retaining Wall Design Conventional footings for retaining walls should be designed using the lateral earth pressures presented below for backfill material derived from approved pp oved on site sorts in drained conditions: Equivalent Fluid Pressure psf/ft. Conditions Level 2:1 Slope Active 40 65 Al Rest 60 85 Passive 360 165 (if slo ing in front of wall) If clean sand, having a sand equivalent equal to or greater than 30, is used for backfill, lower equivalent fluid pressures may be utilize d. ze. The equivalent fluid pressure of 30 psf/ft for level backfill and 43 psf/ft for 2H:1 V sloping backfill may be used for the active conditions. i Oversized rock and soils that have high expansion potential should not be used in the wall backfill. To design an unrestrained retaining wall, such as a cantilever wall, the active earth pressure may be used. For a restrained retaining pressure should be used. Passive pressure ishused to cas a lompute lateral soils t or at restrained aresis resistance ll corners, developed the at -rest against lateral structural movement. Further, for sliding resistance the friction coefficient of 0.35 030916.doc leiAAf,- 03022-01 September 16, 2003 may be used at the concrete and soil interface. In combining the total lateral resistance, either the passive pressure or the frictional resistance should be reduced by 50 percent. In addition, the passive resistance is taken into account only if it is ensured that the soil against embedded structure will remain intact with time. The retaining walls may also need to be design for additional lateral loads if other structures or walls are planned within a 1:1 projection. Our typical retaining wall drainage detail is included as Figure 2 (rear of text). Proper surface drainage, such as a concrete V-ditch, should also be provided along the top of walls. Down drains (outlets) for surface drainage should not be tied into the subdrain system for walls the should be outlet separately. y 10. Retaining Wall Subdrains Future retaining structures should be provided with a subdrain system approved by the geotechnical consultant. In general, retaining walls are susceptible to minor seepage out of the faces of walls if subjected to significant amounts of infiltration, even with a subdrainage system. If such conditions are unacceptable from an aesthetic standpoint, we recommend the walls be waterproofed and provided with a geocomposite "sheet" drain,. such as Miradrain 6000 (or approved equivalent) behind the wall. Typical retaining wall subdrain recommendations are provided on Figure 2 at the rear of text. Proper surface drainage, such as a concrete V-ditch, should also be provided along the top of walls. Down drains (outlets) for surface drainage should not be tied into the subdrain system for walls, they should be outlet separately. 11. Structural Setbacks COPDSD requires that footings of structures located above descending slopes be setback from the slope face in accordance with the minimum requirements of the County of Orange building code or the UBC criteria, whichever is greater. The setback distance is measured from the outside edge of the footing bottom along a horizontal line to the face of the slope. The table provided below summarizes the minimum setback criteria for structures above descending g Structural Setback Requirements for Footings Above Descending Slopes Slope Height[H] Minimum Setback (feet) from Slope Face(feet) Less than 10 5 10to20 %2*H 20 to 30 10 More than 30 '/ * H (maximum of 40') For the subject site, the maximum descending slope height is approximately 250 feet. Therefore, the maximum required setback from the slope face should be 40 feet. A waiver for this setback criteria within the PA 2C, 5 & 6 site will be submitted at the completion of preliminary grading. The waiver will request a maximum 20-foot setback for structures at the top of descending 030916.doc KlAAr 03022-01 September 16, 2003 slopes over 60 feet in height. Based upon review of the subject plan, the setback criteria to be requested in the waiver appear to be satisfied for the residential structures. p 12. Slope Creep, Lateral Fill Extension and Improvements Near Tops of Slopes Both manufactured and natural slopes can undergo deformations over time due to changes in moisture content and gravitational forces. Slope creep is the tendency of the outer portion of slopes to move downhill over time under the force of gravity as the near surface soils shrink and swell with moisture variations. Lateral fill extension is thought to be the result of deeper wetting of expansive soils. It is sometimes referred to as "lot stretching" since the resulting movement at the pad surface near top of slope includes a lateral component. These phenomena are not completely or well understood. They appear to be related to the height of the slope, the steepness of the slope and the composition of the slope (soil type). Higher slopes, steeper slopes, and slopes composed of more expansive soils are believed to have a greater tendency to experience such slope deformations. The depth of the creep zone seems to be greater as these factors increase. Improvements at or near the tops of slopes that are within the creep zone may be subject to effects such as leaning (walls parallel to slope) and differential settlement slabs Perpendicular to slope). Depending upon the tolerances of improvements to such effects, vari uls forms and degrees of distress can result. Mitigation measures can take various forms, depending upon the sensitivity of the improvements and the type of improvements. Mitigation is typically by means of setbacks, deeper foundations for. structures, specialized jointing, and/or stiffening the improvements. g of As a result of the predominately low to medium expansion potential of materials within the slopes, we estimate that surficial materials in the upper 1 to 2 feet of slopes over 30 feet in height may experience movements as a result of slope creep. Additionally, the zone of influence may extend approximately 10 to 15 feet laterally away from the top of descending slopes. We anticipate that the minimum setback criteria for structural footings, provided in Section 11, should provide sufficient mitigation for the slope creep phenomenon. Additional recommendations for to -of - slope walls and fences are provided within the following Section 13. p 13. Walls and Fences The design of walls and fences is ultimately the purview of the structural engineer. Desi loading. Provided in the table ground conditionsbelow, are should accommodate for wind and seismic e recommendations for minimum footing depths and slope -face setbacks for top of slope and level .. 030916,doe 10 KLkAr I 03022-01 September 16, 2003 Wall/Fence Footing Depth and Slope Face Setback Criteria Level Ground and Slopes Less Than 20 Type of eet High Top of Slope Greater Structure Minimum Footin Than ZO eet In Hi h De th (ft.) g Slope Face Minimum Footing Slope Face MasonryPilaster ( ) Setback (ft.) 2 Depth (ft.) Setback (ft.) 1% 8 iz Tube -Steel Fence 2 5 12 5 3 8 For freestanding walls are located near tops of slopes, we recommend that the wall footings be designed with a grade beam and caisson foundation system. In front of the top of slope walls, the slope creep phenomenon generally decreases the passive resistance of the footing ystem as the result of soils moving down the slope and loosing firm contact with the footin elem Behind the top of slope walls, the grade beam portions of the system should be designedits. to withstand retained soil conditions as a result of slope creep movements in front of the all. j Design should accommodate a retained condition that is, at minimum, the depth beam and, at maximum, 2 feet deep (the depth of the slope creep zone). of the grade Passive resistance of soil in front of wall foundations is taken into account �± that the ma unt o materials embedded against the structure will remain intact with time. For held sign of caisson footings for walls atop descending slopes, we recommended the use of a passive pressure of 165 pounds per square foot per foot (psf/ft) of burial in the upper 5 feet. this 5-foot zone should be neglected for passive resistance. Below 5 feet the e upper p feet ressurof e for caisson footings may be increased to 360 psf/ft of burial. Behind the wall, the retained soils should be designed for an active force of 40 psf/ft of depth. It is our o used for designpinion that these strengths are more than .the creep limiting strength of the onsite material; therefore, continuous creep will not occur behind the wall under these lateral earth pressures. 14. Cement Type and Structural Concrete �. We anticipate that the onsite soils should have a "negligible" soluble su1 (based on the classification for concrete exposed to sulfates in the 1997 UBC Table 19-A-4 level recommend that all cement in contact with onsite soil shall be "Type II" unless otherwise e i specified, ise Structural concrete elements are considered to be footings, slab -on -grade foundations, and floors. Table 19-A-4 also establishes the structural concrete requirements for maximum water -cement ratio and minimum compressive strength based on the sulfate exposure level. Additional provisions for the design of concrete structures in Chapter 19 of the 1997 UBC and/or the governing agency requirements may also be applicable. The near -surface subgrade soils should be tested at the completion of preliminary adin operations in order to verify to soluble sulfate content of the onsite soils. gr g 030916.doc 11 KLkA r 03022-01 September 16, 2003 15. Exterior Concrete Table 201-1.1.2 of the 1997 Standard Specification for Public Work Construction (Green Book) provides concrete class and compressive strength requirements typically used for street surface improvements. Exterior concrete elements that are considered to be nonstructural (i.e., Pavements, curbs, gutters, sidewalks, etc.) may be based on this specification provided more stringent requirements by governing agency or designer are not given. Additional geotechnical recommendations for design of nonstructural exterior concrete elements constructed over expansive soils also need to be considered. Exterior concrete elements are very susceptible to lifting and cracking when constructed over expansive soils. For this project, the subgrade soil is anticipated to have "low" to "medium" expansion potential. We recommend that the provisions in the "medium" category in the following table be used during design and construction. TYPICAL RECOMMENDATIONS FOR CONCRETE FLATWORK/HARDSCAPE R nsion Potential ecommendations Very Low Low Medium High Very High (< 20) Slab Thickness (Min.); nominal (20 — 50) (51— 90) (91-130) (5130) thickness exce t where noted. 411 411 411 4" 4" Full Subbase; thickness of sand or gravel layer below concrete N/A N/A Optional 2" — 4" 2" — 4" Presaturation; degree of optimum moisture content (opt.) and depth Pre -wet 1.1 x opt. 1.2 x opt. 1.3 x opt. 1.4 x opt. of saturation Only to 6" to 1211 to 18" to 24" Joints; maximum spacing of control joints. Joint should be % of 10, 10, S' 6' total thickness 6' Reinforcement; rebar or equivalent welded wire mesh Optional N/A N/A placed near mid -height of slab (WWI' 6 x 6 — No. 3 rebar, 24" O.C. both ways No. " rebar, W1.4/W1.4) Restraint; slip dowels across cold or equivalent wire mesh 24 O.C. both ways y s joints; between sidewalk and curb N/A N/A Optional Across cold Across cold joints joints (and into curb) The subgrade for the concrete areas should be competent material approved, properly compacted, and that has been geotechnically moisture -conditioned in accordance specifications. For reducing the potential adverse with project affects of expansive recommend a combination of presaturation of subgrade soils; soils on reinforcement concrete, we and restraint; moisture barriers/drains; and a sub layer of granular material. Though these types of measures may not completely eliminate adverse impacts, application of these measures .can significantly reduce the impacts from post -construction expansion of soil. Please note that reducing concrete problems is also a function of proper design and construction practices. We recommend that the design and construction be performed in adherence with the 2 ('1 03OR 16.doc 12 kIAAr 03 022-01 September 16, 2003 American Concrete Institute (ACI) guidelines for site paving. The amount of post-constrction u watering or lack thereof can have a significant impact on the adjacent concrete flatwork, particularly when onsite'soils are expansive. Design and maintenance of proper surface is important for reducing potential problems in hardscape/flatwork areas as a result of wetting ■ and expansion of the subgrade soils. Additional measures, such as additional subdrains, root barriers and/or moisture barriers, should be considered where planter or natural areas with irrigation are located adjacent to the concrete improvements. 16. Street Pavement and Temporary Model Parking Lot Th e final recommended pavement sections for the site are the purview of the County of Orange Public Works Department. Pavement design should be based on the expected Traffic Index (TI) for the streets and the R-values of exposed subgrade soils. For preliminary Purposes, section on the order of 4 inches of asphalt concrete over 6 inches of aggregate base may be assumed. This is based on a TI of 5 and an R-value of 20. The pavement section for the temporary model parking lot may consist of 3 inches of asphaltic concrete over compacted native subgrade soils. The compaction criterion for the native subgrade soils is 95 percent relative compaction in accordance with ASTM Test Method D 1557. N 17. "Utility Construction Trenches, including interior utility, should be either backfilled with native soil and compacted to 90 percent relative compaction or backfilled with clean sand (SE 30 or better), which may be densified with water flooding or jetting. Exterior trenches should at be capped with a minimum of 12 inches of native soils and compacted to a minimum of 90 percent relative compaction. Trenches excavated on a graded slope face for utility or irrigation lines and/or for an y Purpose should be properly backfilled and compacted in order to obtain a minimum 90 percent relative compaction to the slope face. Observation/testing should be performed by the geotechnical consultant during all trench backfill. 18. Corrosivity Towards Metals Measures consistent with local practice should be taken to protect metals in contact with soil. Corrosivity of near -source soils at the site should be evaluated following the completion of grading. 19. Surface Drainage and Irrigation In order to mitigate the potential for development of adverse moisture conditions resulting. from rainfall or irrigation water build-up, which would adversely affect the design function of post - tension slabs and foundations in accordance with the Post -Tensioning Institute PTI)method, the following recommendations should be relayed to the future homeowners. ( 030916.doe 13 lei AA P'; o 03022-01 September 16, 2003 22. Geotechnical Observation and Testing Geotechnical observation and testing should be conducted during the following stages: • During site preparation and clearing, prior to site processing; • During precise grading and placement of any fill; • Upon completion of any foundation excavation prior to placement of steel and pouring of concrete; • Upon completion of presaturation of subgrade for structural slabs and/or for sidewalks; • During pavement subgrade preparation; • During aggregate base and asphalt concrete placement; • During backfill for utility trenches; and, • When any unusual or unexpected soil and/or geotechnical conditions are encountered during grading and construction. If you have any questions regarding this report, please contact our office. We appreciate the opportunity to provide our services. Respectfully submitted, NMG GEOTECHNICAL, INC. Darien Osborne, RCE 64108 Project Engineer DAO/TD/er Tom Devine, CEG 2236 Project Geologist Distribution: (2) Addressee (3) Mr. Daniel Kim, Hunsaker & Associates (includes two copies for submittal to COPDSD) p p{iOFESSI w m No.64108 EXP.12/31/06 lA' 1MC ST CIVIL �Y OP CAL1FC�a� 7 ��1GINEER/NG "oPS R. DQFO� cf F w N V No. 2236 � *\ EXP.2/04 /* ��NP\` CALl p� 030916.doc 15 0 NMG Provide proper surface drainage (drain separate from subdraln) 1'to 2�—r Retaining wall Waterproofing (optional) Weep Hole (optionao rrr Provide proper surface drainage (drain separate from subdrain) I'Cover OPTION 1: AGGREGATE SYSTEM DRAIN Native backfill lean sand vertical drain having sand equivalent of 30 or greater (can be densified by water jetting) or other free -draining granular material • min L�tE Minimum 1 W/ft, of 1/4 to 1 1/2" size gravel or crushed rook encased In approved Filter Fabdo r * flinch diameter perforated pipe with proper outlet, (See Notes below for alternate discharge system) Native backflll Alternative: Class 2 permeable filter material (Per Caltrans specifications) may be used for vertical drain and around perforated pipe (without filter fabric) OPTION Z: COMPOSITE DRAINAGE SYSTEM Wrap filter fabrio Retaining wall flap behind core Miradraln 8000, J Drain.100, or equivalent . drainage composite for non -waterproofed walls; . Miradrain 6200 or J Drain 200 for waterproofed walls, Weep Hole (optional) Out back of core to match size of weep hole, Do not out fabrio. 3*^ 4--inch diameter perforated pipe with proper outlet, Peel back the bottom fabric flap,place pipe next to core, wrap fabric around pipe and tuck behind core. (SeeNotes for alternate weep hole discharge system)• NOTES: 1. PIPE TYPE SHOULD BE PVC OR ASS, SCHEDULE 40 OR SDR35 SATISFYING'THE REQUIREMENTS OF ASTM TEST STANDARD D1527, D1785, D2751 , OR 03034. 2. FILTER FABRIC SHALL BE APPROVED PERMEABLE NON WOVEN POLYESTER, NYLON, OR POLYPROPYLENE MATERIAL. 3, DRAIN PIPE SHOULD HAVE A GRADIENT OF 1 PERCENT MINIMUM. . 4. WATERPROOFING MEMBRANE MAY BE REQUIRED FORA SPECIFIC RETAINING WALL (SUCH AS A STUCCO OR BASEMENT WAL S. WEEP HOLES MAY BE PROVIDED FOR LOW RETAINING WALLS (LESS THAN 3 FEET IN HEIGHT) IN LiEU OF A VERTICAL DRAIN AND PIPE AND WHERE POTENTIAL WATER FROM BEHIND THE RETAINING WALL WILL, NOT CREATE A NUISANCE WATER CONDITION. IF EXPOSURE IS NOT PERMITTED, A PROPER SUBDRAIN OUTLET SYSTEM SHOULD BE PROVIDED. G. iF EXPOSURE IS PERMITTED; WEEP HOLES SHOULD BE 24NCH MINIMUM DIAMETER AND PROVIDED AT 25-FOOT MAXIMUM SPACING ALONG WALL. WEEP HOLES SHOULD BE LOCATED 3+ INCHES ABOVE FINISHED GRADE, 7. SCREENING SUCH AS WITH A FiLTER FABRIC SHOULD BE PROVIDED FOR WEEP HOLESIOPEN JOINTS TO PREVENT EARTH MATERIALS FROM ENTERING THE HOLESIJOINTS, 8.OPEN VERTICAL MASONRY JOINTS (I.E., OMIT MORTAR FROM JOINTS OF FIRST COURSE ABOVE FINISHED GRADE) AT 32-INCH -MAXIMUM INTERVALS MAY BE SUBSTITUTED FOR WEEP HOLES. 9 THE GEOTECHNICAL CONSULTANT MAY PROVIDE ADDITIONAL RECOMMENDATIONS FOR RETAINING WALLS DESIGNED FOR SELECT SAND BACKFILL, RETAINING WALL DRAINAGE DETAIL I NMG Gzatachnical, Inc.