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HomeMy WebLinkAbout1998 - GME consult. inc - recom. for retaining wall 1770 GME CONSULTANTS, INC. IG,9 CONSULTING ENGINEERS E 14000 21st Ave.No./Minneapolis,MN 55447 Phone 1612)559-1859 / Fax(612)559-0720 October 7 1998 Mr. David Klein — :71e1 Aspen Landscaping 5260 Independence Street Maple Plain, Minnesota 55359 GME Project No. 7940 RE: Recommendations for retaining wall construction at the Brakken Residence in Long Lake, Minnesota Dear Mr. Klein: This report presents our recommendations for the proposed retaining walls at the above referenced project . This work has been performed in accordance with your verbal authorization, confirmed through our contract dated September 21, 1998 . Project Information Four retaining walls are proposed for this project, having maximum heights ranging from 6 to 9 feet . Three of the walls will be faced with boulders and the remaining wall would be faced with limestone slabs . The limestone slab wall generally has a height of about 3 feet, however at one location, namely the cul-de-sac turn-around area, the slab wall be tiered for a total height of 7 feet with the WILLIAM C. KWASNY, PE. THOMAS P. VENEMA, PE. WILLIAM E. BLOEMENDAL, PE. GREGORY R. REUTER, RE. CHARLES M. ALLGOOD, PE. MERVYN MINDESS, PE. MARK D. MILLSOP, PG. TIMOTHY F. McGLENNEN STEVEN J. RUESINK, RE. An Equal Opportunity Employer , Mr. David Klein 2 October 7, 1998 GME Project No. 7940 lower wall having a height of 4 feet and the upper wall a height of 3 feet . The horizontal distance between the two walls will be 3 to 4 feet . The grade in front of the slab wall will be horizontal . These walls are cut into the existing hillside which consists of stiff sandy clay. The grade in front of the boulder walls will range from horizontal to no steeper than 4 horizontal : 1 vertical . Soil borings have not been performed for this project . However, based on our site observations and our observation of the exposed soil in the cut hillside at the location of the limestone slab wall/cul-de-sac, we assume that the foundation and retaining soils will consist of stiff sandy clay glacial till . Design Recommendations Since specific soil testing has not been performed, we have had to make assumptions concerning the engineering properties of the existing soils . We assume that the soils retained by the walls will consist of stiff sandy clay having a drained friction angle of 27° and a maximum moist unit weight of 125 pounds per cubic foot . We also assume that the soils would have a net allowable bearing capacity of at least 2000 pounds per square foot . GME CONSULTANTS,INC. Mr. David Klein 3 October 7, 1998 GME Project No. 7940 Included with this report are representative cross-sections of the boulder wall and the limestone slab wall . Geogrid reinforcement is required within the backfill behind all walls for this project . We understand that you plan to use Huesker Fortrac 35/20-20 geogrid. Boulder Wall Construction We recommend that the geogrid be placed at a maximum vertical separation of 2 feet between layers . The geogrid lengths should be equal to or greater than the exposed wall height at that particular location. Each geogrid layer should extend out of the compacted backfill and should be wrapped up along the face the 2 foot distance . The geogrid should then be placed back into the reinforced zone to provide a minimum overlap of 3 feet . (Please refer to the attached cross section drawing. ) This will form a "wrapped face" wall, onto which will be placed the boulder facing. The wrapped face should be inclined 5 degrees from vertical, or flatter. On the inside of the geogrid layer along the wall face and extending back into the backfill no more than 1 foot we recommend placing a layer of geotextile filter fabric to prevent migration of the soil out of the backfill and through the wall facing. Within 1 foot of the back of the geogrid wrapped face, and extending vertically up GME CONSULTANTS,INC. Mr. David Klein 4 October 7, 1998 GME Project No. 7940 from the elevation of the grade in front of the walls to within 1 foot of the top of the walls, we recommend placing a layer of free draining sand or sand and gravel such as 3/4 inch crushed rock to form a drainage layer. The boulders should be placed along the inclined geogrid wrapped backfill . The boulders should consist of durable angular rock. Each rock should rest on two rocks in the layer below, with at least a 3 point bearing. The lowest boulder should be embedded at least 1 foot below final exterior grade . The base width to height ratio of the boulders should be at least 0 . 28 or wider (for example, a 9 foot high wall should have a base width of at least 2 . 5 feet) . Limestone Slab Wall We have included a representative cross-section of the limestone slab wall with this report . This section shows the wall at its highest point along the west side of the cul-de-sac . We assume that the individual limestone slabs would have front to back widths of 1 . 5 to 2 feet and each slab would have a unit weight of 150 pounds per cubic foot . The slabs should consist of hard durable limestone with rough cut sides . We assume that each limestone slab would have a thickness of 6 to 8 inches . GME CONSULTANTS.INC. Mr. David Klein 5 October 7, 1998 GME Project No. 7940 We recommend that the geogrid be placed on the second and fifth courses . The geogrid behind the lowest wall should have a length of 7 feet . Therefore, two geogrid layers would be required behind the lowest tier wall . Geogrid length for the upper wall should be 3 feet . A layer of geotextile filter fabric should be placed along the inside back of the slabs . Within 1 foot of the back of the slabs we recommend placing a granular drainage layer consisting of sand and gravel, or 3/4 inch crushed rock. Wall Backfill The backfill over the geogrid behind the granular drainage layer may consist of excavated on-site non-organic soils, which we estimate would consist of sandy clay. The clay should be moisture conditioned to within 2% of the optimum moisture content as determined by the Standard Proctor compaction test, ASTM: D 698 . Excessively wet clay should not be used as backfill . The fill should be placed in loose lifts not exceeding 4 to 6 inches thick. Each lift should be compacted to at least 95% of the maximum Standard Proctor dry density. We recommend placing approximately 1 foot of compacted clay on top of the granular drainage layer behind the wall to reduce surface water infiltration. GME CONSULTANTS,INC. Mr. David Klein 6 October 7, 1998 GME Project No. 7940 The geogrid layer must be pulled taught and staked prior to and during backfilling. Care must be taken not to damage the geogrid layer while compacting the backfill . Testing Proper observation and testing are an integral part of our recommendations . We strongly recommend that one of our Geotechnical Engineers or Engineering Technicians be present to observe and test the wall foundation subgrade, observe the placement and tensioning of the geogrid, and test the backfill degree of compaction. If soils are observed that are different than we have assumed, we could then determine the effects on our recommendations . Safety Devices Safety is an important concern on this project . The design of safety devices such as guard rails or fencing are not part of our scope of work for this project and are the responsibility of the Owner. GME CONSULTANTS,INC. Mr. David Klein 7 October 7, 1998 GME Project No. 7940 General Comments It is understood by all parties that the contractor is responsible for the methods and results of the work. GME will not direct the contractor' s personnel, or the construction methods used by the contractor. It is the responsibility of the contractor to protect backfill in the tested condition. GME will not warrant, assure, or guaranty the work of contractors on this project . During construction, the contractors will be solely responsible for compliance with the latest OSHA regulations for trench and slope excavation and safety, and general construction site safety. The excavator must designate one employee as the OSHA "Competent Person. " This person must be capable of identifying existing and predictable hazards on the site including temporary slope stability, and must have authorization to take prompt corrective measures to eliminate hazards . GME will not accept any responsibility or liability for construction safety on this project . The recommendations and professional opinions contained in this report are based on our understanding of the project . These opinions were arrived at in accordance with currently accepted engineering practices at this time and location. Other than this no warranty is GME CONSULTANTS,INC. Mr. David Klein 8 October 7, 1998 GME Project No. 7940 implied or intended. Our recommendations are based on certain assumptions stated in this letter. If the project changes or if different soil conditions are observed during construction, we must be notified so we can review our recommendations . Closure If you have questions regarding this report or need further assistance, please contact us . Sincerely, GME C NSULTANTS, INC. 1 /i; '/e?,,I7 / i ,. Gregor R. Reuter, P.E. Erin O'B ien, E. I .T. Senior Project Engineer Project ngineer Enclosures : Cross-Section Views Huesker Geogrid Specifications I hereby ify that this plan,specification, or repo as prepared by me or under my direct rvision a.-,th- am a duly Register d Prof./-1• ,ineer under the laws of a Sta;�o inn: ota 4 Gre ory R.Reuter Date: 19 7 r1 Reg.No.19885 GRR:scr W:\7940 Brakken Wall Rpt GRRscr GME CONSULTANTS,INC. -/- -/- /-- /- BOULDER RETAINING WALLS •1•• ' PROPOSED HOUSE •ORNE BOULDER LIMESTONE SLAB RETAINING WALL RETAINING WALL .'. .•.•.•.• • PROPERTY LINE s. `.\ APPROXIMATE SCALE `\ ,. FEET 40' 7940.GCD GME CONSULTANTS. INC. Ern LOCATION DIAGRAM G.ot.chnicd• Materials •Environmental RESIDENCE 14000 21st Avenue N. MC pis_0 LONG LAKE. MINNESOTA Minneapolis. M inn.sota 55447 i (612) 559-1859 �J VJL GRR SEPT 98 GME Project No. 7940 5• OR FLATTER DRAINAGE AGGREGATE COMPACTED, SOIL DURABLE, ANGULAR ROCK TOPSOIL AND VEGITATION COVER I 9 FT. �> - I MAX. I I MAXIMUM —\ ( 4F I SLOPE I 4H . 1V 1 ' \_ G • EOGRI_; �{ h FT. MIN. HUESKER HUESK J 2.5 ER 35/20-20 MINIMIiiUM BASE WIDTH LENGTH = 9 FEET 12 INCHES THROUGHOUT OVERLAP GEOGRID 3 FEET PLACE GEOTEXTILE FILTER FABRIC ON INSIDE OF GRID LAYER OVER FRONT FENCE AND EMBEDED 1 FOOT INTO BACKFILL TYPICAL SECTION (9 FOOT HIGH BOULDER WALL) APPROXIMATE SCALE 0. FEET S. 7940SEC.000 GME CONSULTANTS. INC. EMI SOL BORNG LOCATION DIAGRAM Gsatechnicd • Materials • Envirormsntd BRAKKEN RESIDENCE 14000 21st Avenue N. /_1 LONG LAKE. MINNESOTA Minneapois. Minnesota 55447 (612) 559-1859 VJL GRR SEPT 98 GME Project No. 7940 EXISTING HILL ONE FT THICK DRAINAGE COMPACTED CLAY SWALE TOPSOIL AND VEGITATION GEOTEXTILE FILTER FABRIC v>' L = 3FT LIMESTONE I--I-- L = 7FT 7 FT. SLAB MAX FACING HUESKER 35/20-20 GEOGRID L = 7FT DRIVEWAY ' f PAVEMENT DRAINAGE AGGREGATE COMPACTED CLAY F1 L TER FABRIC TYPICAL SECTION (7 FEET HIGH LIMESTONE SLAB WALL) APPROXIMATE SCALE FEET 5. 7940SEC2.GCD SOS. BORNG LOCATION DIAGRAM GME CONSULTANTS. INC. um Geotechnicd • Materials •Environmental BRAKKEN RESIDENCE 14000 21st Avenue N_ Imo\ LONG LAKE. MINNESOTA Minneapolis. Minnesota 55447 \` (612) 559-1859 VJL GRR SEPT 98 GME Project No. 7940 r ftp FORTRAC® 35/20-20 GEOGRID FORTRAC GEOGRIDS ARE COMPRISED OF HIGH TENACITY POLYESTER YARNS, WOVEN INTO A STABLE, INTERLOCKING PA11hRN AND THEN COATED FOR PROTECTION FROM INSTALLATION DAMAGE. THEY ARE VERY PLIABLE FOR INSTALLATION AND THEY ARE RESISTANT TO FREFZF-THAW CONDITIONS, SOIL CHEMICALS AND ULTRA-VIOLET EXPOSURE. FORTRAC GEOGRIDS HAVE BEEN DEVELOPED TO STABIT UP POOR SOILS AND REINFORCE STEEP SLOPES. THEY CONFINE AND STRENGTHEN ROAD BASE AGGREGATES AND THEY PROVIDE STABILITY WHILE ALLOWING REDUCED AGGREGATE BASE THICKNESS. ALSO, THEY ALLOW CONSTRUCTION OF STEEPENED SLOPES OR CAN BE UTILIZED AS A TIE BACK MECHANISM FOR WOODEN OR BLOCK WALLS. PHYSICAL PROPERTIES OF FORTRAC 35/20-20 GEOGRID MINIMUM AVERAGE ROLL PROPERTY UNIT TEST METHOD VALUES' Weight oz/sq yd ASTM D-3776 7.0 Aperture Size inch - .8 x .8 Open Area °Io CW 02215 75+ Wide Width Tensile Strength • Machine Direction lb/ft ASTM D-4595 @ Ultimate 2600 @ 5% Strain 1100 • Cross Machine Direction lb/ft ASTM D-4595 @ Ultimate • 1350 @ 5% Strain 550 Elongation at Break % ASTM D-4595 12.0 Long Term Design Load* Machine Direction lb/ft GRI GG4 (b) 100+Yrs. (Creep F.S. = 1.67) • Sand, Silt and Clay 1322 • .75" Minus Well Graded Gravel 1261 • 2.5" Crushed Stone and Gravel 991 I Minimum average roll values are based on a 95%confidence level. *Long Term Design Load(100+Years) = T,+ttownetz TAL.LOWABLE = Tail_TEMA TF BID = partial factor of safety for installation damage FSID • FScR • FScD • FSBD • FSI,-/- FScD = partial factor of safety for creep deformation FScD = partial factor of safety for chemical degradation 2600 FSHD = partial factor of safety for biological degradation 1.05 X 1.67 X 1.1 X 1.02 X 1.0FSThrr= partial factor of safety for joints(seam and connections) = 1322 lb/ft(min) -Sand,Silt and Clay calculation-per Glu GG4(b) Each roll of Fortrac geogrid delivered to the project site is labeled by Huesker Inc.with a roll label that indicates manufacturer's name,product identification,lot number,roll number and roll dimensions. All rolls of Fortrac are encased in a sturdy polyethylene wrap to shield the product from rain,dirt,dust and ultraviolet light. O HUESKER® inc. P.O. BOX 411529, CHARLOI1L, NC 28241-1529 • (704) 588-5500 • (800) 942-9418 • FAX (704) 588-5988 1/95 MEMBER OF HUESKER I11Ci GIC RESEARCH INSTITUTE FORTRAC GEOGRIDS INSTALLATION GUIDE FOR RETAINING WALLS Fortrac geogrids are comprised of high tenacity polyester yarns, woven into an interlocking pattern and then coated with polyvinyl chloride. They are very pliable for Inst 1lation and they are resistant to freeze-thaw conditions, soil chemicals and ultra- violet exposure. The primary reinforcing direction for all Fortrac geogrids is in the long direction of the roll (also called the machine direction). Fortrac geogrids are shipped to the jobsite in rolls; they are encased in a plastic wrap. Leave the wrap on the rolls until ready for use. This will protect the grid from unnecessary exposure and damage. Site Preparation: The contractor should excavate to the lines and grades shown on the project grading plans. The contractor should take precautions to minimize over-excavation. Foundation Soil Preparation for Reinforced Soil Zone The foundation soil shall be excavated as required for footing dimensions and limits of reinforced soil zone as shown on the construction drawings or as directed by the wall design engineer. The foundation soil should be tested by the owner to assure that the actual foundation soil strength meets or exceeds the assumed design bearing strength. Soils not meeting the required strength should be removed and replaced with soil meeting the design criteria. A compacted drainage aggregate should be placed as shown on the construction drawings. The drainage aggregate base should be compacted to provide a level hard surface on which to place the first course of modular block units. Geogrid Placement The Fortrac geogrid should be installed at the proper elevation and orientation as shown • in the wall details on the project construction plans or as directed by the wall design Engineer. Cut the geogrid to the specified length as shown in the engineers drawings. The primary reinforcing direction should be placed perpendicular to the wall face and should be one continuous piece of material. End pieces of geogrid too short to cover the full expanse of the reinforced section should be discarded or held for use on shorter sections. Adjacent sections of geogrid should be butted in a manner to assure 100% coverage after placement. 11107A South Commerce Blvd.•P.O.Box 411529.Charlotte,NC 28241 •Telephone(704)588-5500/(800)942-9418•Fax(704)588-5988 MEMBER OF HUESKER inc. GEOSYNTHETIC RESEARCH INSTITUTE Fill Placement The reinforced fill should be placed as shown in the construction plans in 6-8 inch lifts and compacted to a minimum 98% of Standard Proctor Density (ASTM D-698). Backfill shall be placed, spread, and compacted in such a manner that eliminates the development of wrinkles and/or movement of the geogrid. Tracked construction equipment should not be allowed to operate directly on the geogrid. A 6" minimum thickness of backfill is required prior to operation of tracked vehicles over the geogrid. Rubber-tired equipment may pass over the geogrid reinforcement at slow speeds less than 6 mph. Sudden breaking and sharp turning should be avoided. Although the PVC coating should protect the geogrid from UV exposure indefinitely,Huesker recommends that the soil cover should be placed over the geogrid within 14 days as an extra precaution. Only hand-operated compaction equipment should be allowed within 3 feet of wall face. Drainage placement shall be placed in accordance with the construction plans or as modified by the wall design engineer. This may consist of a drainage collector pipe in combination with a drainage net in order to maintain gravity flow to the outside of the reinforced soil zone. r 11107A South Commerce Blvd.•P.O.Box 411529•Charlotte,NC 28241 •Telephone(704)588-5500/(800)942-9418•Fax(704)588-5988