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Home My WebLink AboutSgroi Property - Geotechnical Engineering Evaluation:(KJ,9ri4y 6rnwt !kc llf. Providence Properties, LLC Attn: Randy Clarno PO Box 2648 Eagle, ID 83616 Dear Mr. Clarno: July 9, 2013 File: BO13323A RE: Geotechnical Engineering Evaluation Sgroi Property 4405 East Ustick Road Meridian, Idaho Strata, A Professional Services Corporation (STRATA) is pleased to present our authorized Geotechnical Engineering Evaluation for the proposed residential development located at 4405 East Ustick Road in Meridian, Idaho. Our Geotechnical Engineering Evaluation's purpose was to explore the subsurface conditions in the proposed development area and provide geotechnical recommendations to assist project planning, design and construction. The attached report summarizes our field and laboratory test results and presents our geotechnical engineering opinions and recommendations. The following report provides specific geotechnical recommendations for preparing the site, including earthwork activities, pavement design and stormwater design recommendations. It is our opinion that geotechnical continuity with the project team throughout construction will lessen the potential for errors and omissions related to our geotechnical recommendations. The project design, owner, and construction team must read, understand and implement this report in its entirety. Portions of the report cannot be relied upon individually without the supporting text of remaining sections, appendices and plates. Our opinion is the success of the proposed construction will depend on following the report recommendations, good construction practices, and providing the necessary construction monitoring, testing and consultation to verify that work has been constructed as recommended. We recommend STRATA be retained to provide these services to verify our report recommendations are being followed. We appreciate the opportunity to work with you and we look forward to our continued involvement on this project throughout construction. Please do not hesitate to contact us if you have any questions or comments. Sincerely, STRATA, Inc. Steve Worsley, P.G.(W hington) Geologist Cc: Mr. Kevin McCarthy/KM Engineering SW/AM/nm www.stratageotech.com TABLE OF CONTENTS INTRODUCTION............................................................................................................ 1 PROJECTUNDERSTANDING.......................................................................................2 ExistingSite Conditions..................................................................................................2 Proposed Construction...................................................................................................2 SUBSURFACE EVALUATION PROCEDURES..............................................................2 SUBSURFACECONDITIONS........................................................................................3 LABORATORYTESTING............................................................................................... 3 GEOTECHNICAL OPINIONS AND RECOMMENDATIONS...........................................4 Earthwork....................................................................................................................4 Site and Subgrade Preparation................................................................................4 Wet Weather/Soil Construction................................................................................ 5 Excavation Characteristics.......................................................................................6 Utility Trench Construction........................................................................................6 Structural Fill and Compaction..................................................................................7 Table 1. Structural Fill Specifications and Allowable Use ............................................. 7 Geosynthetics........................................................................................................... 8 PavementSection Design............................................................................................ 8 General................................................................................................................... 8 Trafficand Subgrade................................................................................................9 Table 2. Pavement Design Parameters.......................................................................9 Asphalt, Aggregate Base Course and Subbase Materials ........................................ 9 PavementSection Thickness.................................................................................10 Table 3. Asphalt Pavement Design Section............................................................... 10 PavementMaintenance..........................................................................................10 SiteDrainage.............................................................................................................10 ExteriorGrading.....................................................................................................10 InfiltrationRates.....................................................................................................11 Groundwater...........................................................................................................11 GEOTECHNICAL DESIGN CONTINUITY....................................................................12 EVALUATIONLIMITATIONS........................................................................................12 Sgroi Property 4405 East Ustick Road Meridian, Idaho File: B013253A Page 2 4s Site Drainage • Exterior grading • Infiltration rates • Groundwater 4i Geotechnical Design Continuity • Groundwater Monitoring • Plan and specification review • Construction observation and testing 5. Prepared and provided an electronic copy of our final report of geotechnical findings, opinions and recommendations, including exploration logs and an exploration location plan. Hard copies are available upon request. PROJECT UNDERSTANDING Existing Site Conditions The proposed construction development is located on the south side of East Ustick Road approximately 1,300 feet west of the intersection of East Ustick Road and North Cloverdale Road. The proposed subdivision will be accessed from the south via East Arch Drive. The site is currently developed with a single family residence and 2 associated detached garage outbuildings in addition to a mobile home unit. These structures are located in the northwest corner of the site. Further, in the central portion of the site, there is a concrete slab that appears to be a remnant of a demolished structure. The site is bounded by West Ustick Road on the north and by residential properties to the east, a school to the west, and East Arch Drive to the south. Proposed Construction We understand the approximate 2.8 -acre development will consist of 16 buildable lots with proposed asphalt paved roadways providing access to the development. Although structures are not currently defined, we anticipate buildings will be supported by shallow foundations and joist floor systems. We also anticipate stormwater will be disposed of via seepage beds or swales. SUBSURFACE EVALUATION PROCEDURES STRATA accomplished subsurface exploration on July 1, 2013 via 2 exploratory test pits extending 14 feet below existing ground surface. The approximate exploration locations are illustrated on Plate 1, Exploration Location Plan, which also delineates the proposed development. Test pit locations were established in the field by taping from existing site features. i4 www.stratageotech.com Sgroi Property 4405 East Ustick Road Meridian, Idaho File: B013253A Page 4 subsurface soil characteristics and engineering properties. Specifically, we accomplished moisture content, minus No. 200 wash and R -value testing. We present laboratory test results on individual test pit logs in Appendix A. R -value graphical results are presented in Appendix B. We will retain soil samples for 90 days and discard after this time period unless we are notified to store the samples for an extended period of time. GEOTECHNICAL OPINIONS AND RECOMMENDATIONS We present the following geotechnical recommendations to assist planning, design and construction of the proposed development planned at the Sgroi Property, located at 4405 East Ustick Road in Meridian, Idaho as illustrated on Plate 1 attached to this report. This report provides geotechnical design criteria for the development which the design and construction teams must review to verify the applicability to the planned construction. We base our recommendations on the results of our field evaluation, laboratory testing, our experience with similar soil conditions and our understanding of the proposed construction. If design plans change or if the subsurface conditions encountered during construction vary from those observed during our field evaluation, we must be notified to review the report recommendations and make necessary revisions. Earthwork Site and Subgrade Preparation STRATA has not reviewed a grading plan for the proposed development, but we anticipate cut and fill will be less than approximately 1 -foot for project site grading. At the time of exploration, surficial vegetation and organic material was observed to a depth of approximately 8 inches. We recommend a minimum of 8 inches of topsoil with organic matter be stripped beneath all planned improvements, including structural fill areas. This topsoil is not suitable for use as structural fill and should be wasted or stockpiled on-site for landscape areas. In the area of the current house, garages, mobile home, and concrete slab area, existing structures must be completely demolished and removed from the site. Test pits have been marked in the field with labeled standpipe piezometers or stakes. Test pit locations should be surveyed prior to any earthwork site grading activities. Test pits which are located beneath paving, structural fill or building lot areas should be re -excavated and replaced with structural fill in accordance with the recommendations in this report. www.stratageotech.com Sgroi Property 4405 East Ustick Road Meridian, Idaho File: B013253A Page 6 help maintain project schedule. In short, using site soil may be impractical during certain weather or soil conditions and we recommend contingencies to remove and replace wet soil. Excavation Characteristics Based on exploration results, it appears the near -surface soil encountered in exploratory test pits may be excavated with conventional equipment. Excavations can cave and slough and must be sloped back in accordance with Occupational Health and Safety Act (OSHA) guidelines. Fine to coarse-grained soil is expected to be exposed in excavations throughout the development area and should be temporarily sloped at 1.5H:1V (horizontal to vertical). Due to the potential for varying soil conditions at the time of construction, we recommend earthwork contractors evaluate each excavation configuration specific to OSHA guidelines and to seek appropriate professional guidance to ensure excavation safety and stability. Utility Trench Construction Structural fill for backfilling utility trenches and all bedding should conform to Idaho Standards for Public Works Construction (ISPWC) specifications, except that all trench backfill must be placed and compacted to the structural fill requirements presented herein. Loose soil must be removed from the base of utility trenches prior to placing pipe bedding. In addition, if water is encountered, it must be removed from the base of the utility trench before placing pipe bedding. We recommend utility pipes be placed on at least 4 inches of bedding placed over undisturbed native soil, structural fill or otherwise supported according to the pipe manufacturer's specifications and ISPWC requirements. After bedding the pipe, place structural fill and compact it from the pipe invert to 1 -foot above the top of the pipe with tamping bars and/or plate compactors to render the backfill in a firm and unyielding condition. Thoroughly place and compact bedding below pipe haunches or the zone between the pipe invert and the spring line. To accomplish backfilling, the distance between the side of the pipe at the spring line and the trench wall should be at least 12 inches. The remainder of the utility trench should be backfilled in accordance with the Structural Fill section of this report. www.stratageotech.com Sgroi Property 4405 East Ustick Road Meridian, Idaho File: B013253A Page 8 above specification. Coarse fill must be compacted using a "method specification" developed during construction, based on the material characteristics and the contractor's means and methods. It is common that "method specifications" are developed during construction, specific to the materials and conditions encountered. At a minimum, STRATA recommends coarse, granular fill be placed in maximum 10 -inch lifts and compacted with 6 complete passes of a 10 - ton vibratory or grid roller. Vibratory rollers must have a dynamic force of at least 30,000 pounds per impact per vibration and at least 1,000 vibrations per minute. Coarse fill must be compacted to a dense, interlocking and unyielding surface. We recommend STRATA review the soil and aggregate material planned for fill use and monitor compaction effort during construction. Geosynthetics If earthwork contractors are unable to achieve subgrade compaction requirements outlined in this report's Site Preparation section, geosynthetic fabrics may be used to improve subgrade support when constructing on soft or wet soil. We recommend woven geosynthetics at pavement subgrade elevation where moisture -conditioning and re -compaction as recommended in the Site Preparation section of this report is not possible due to wet soil conditions. Where required, apply geosynthetics directly on approved subgrade, taut, free of wrinkles and over -lapped at least 12 inches. Woven geosynthetic fabrics for subgrade stabilization and soil improvements shall have the following minimum properties of 700 pounds (CBR Puncture, ASTM D6241) and 200 pounds (Grab Tensile Strength ASTM D4632). STRATA must be consulted prior to using geosynthetics for subgrade stabilization. Further, we recommend contractors carefully review subsurface conditions prior to bidding and recommend the design team include a unit price for woven geosynthetics for the earthwork portion of the project. We recommend non -woven geosynthetic fabrics for filtration and for stormwater facilities. Non -woven fabrics and should have a maximum apparent opening size equivalent to the U.S. No. 70 sieve (ASTM D4751), a minimum weight of 3.5 ounces per square yard and minimum CBR puncture resistance of 200 pounds (ASTM D6241). Pavement Section Design General The following flexible asphalt pavement section design is provided referencing the Idaho Transportation Department (ITD) Gravel Equivalent Design Method using Ada County Highway www.stratageotech.com Sgroi Property 4405 East Ustick Road Meridian, Idaho File: B013253A Page 10 construction, traffic loading conditions change or traffic volumes increase, STRATA should be notified to amend our design accordingly. Pavement Section Thickness STRATA evaluated the pavement sections utilizing the ITD pavement design methodology, soil -engineering parameters from laboratory testing and the estimated traffic - loading conditions. Based on subgrades prepared as recommended and the traffic criteria provided, Table 3 provides the recommended asphalt section for the anticipated pavement application. If subgrade conditions change as design is finalized or during construction, or traffic loading is different than we have assumed, STRATA must review our pavement analyses and resulting sections. Table 3. Asphalt Pavement Design Section Pavement Maintenance We recommend crack maintenance be accomplished on all pavement surfaces every 3 to 5 years to reduce the potential for surface water infiltration into the underlying pavement subgrade. Surface and subgrade drainage are extremely important to the performance of the pavement section. Therefore, we recommend the subgrade, base and asphalt surfaces slope at no less than 2 percent to an appropriate stormwater disposal system or other appropriate location that does not impact adjacent buildings or properties. The pavement's lifespan is dependent on achieving adequate drainage throughout the section, especially at the subgrade elevation. Ponding water at the pavement subgrade surface can induce heaving during the freeze -thaw process. Site Drainage Exterior Grading We recommend the ground surface adjacent to structures slope a minimum of 5 percent away within 10 feet of the structure. The ground surface beyond 10 feet of structures should be sloped at least 2 percent away. Improper management of near -surface water, by not providing an effective grading and drainage design, can result in moisture or water entering foundation areas. Possible sources of near -surface water include pressurized irrigation water, rainwater, www.stratageotech.com Asphalt Aggregate Base Granular Asphalt Pavement Application Concrete Course (inches) Subbase (inches) (Inches) Local Roads (TI = 6) 2.5 4.0 10.0 Pavement Maintenance We recommend crack maintenance be accomplished on all pavement surfaces every 3 to 5 years to reduce the potential for surface water infiltration into the underlying pavement subgrade. Surface and subgrade drainage are extremely important to the performance of the pavement section. Therefore, we recommend the subgrade, base and asphalt surfaces slope at no less than 2 percent to an appropriate stormwater disposal system or other appropriate location that does not impact adjacent buildings or properties. The pavement's lifespan is dependent on achieving adequate drainage throughout the section, especially at the subgrade elevation. Ponding water at the pavement subgrade surface can induce heaving during the freeze -thaw process. Site Drainage Exterior Grading We recommend the ground surface adjacent to structures slope a minimum of 5 percent away within 10 feet of the structure. The ground surface beyond 10 feet of structures should be sloped at least 2 percent away. Improper management of near -surface water, by not providing an effective grading and drainage design, can result in moisture or water entering foundation areas. Possible sources of near -surface water include pressurized irrigation water, rainwater, www.stratageotech.com Sgroi Property 4405 East Ustick Road Meridian, Idaho File: B013253A Page 12 STRATA installed a standpipe piezometer within test pit TP -1 to monitor groundwater levels. We recommend STRATA be retained to perform groundwater monitoring to verify the seasonal high groundwater level for subsurface stormwater disposal design. GEOTECHNICAL DESIGN CONTINUITY Geotechnical design continuity will be an important aspect of this project's successful completion. In our opinion, geotechnical continuity can occur in 4 stages in the planning, design and construction project aspects. Specifically, we recommend STRATA maintain the geotechnical design continuity in the following aspects: 1-4 Groundwater Monitoring: The groundwater level should be monitored during the current irrigation season to verify the seasonal high groundwater level beneath the site. A piezometer was installed to monitor groundwater levels. Monitoring typically should be accomplished on a monthly basis between July and October. STRATA remains available to perform groundwater monitoring at your request. Plan and Specification Review: We recommend STRATA be retained to review final design and construction plans and specifications to verify our geotechnical recommendations are incorporated into project bidding and construction documents as well as to provide additional recommendations based on the final design concepts. These efforts can help provide document continuity across the engineering disciplines and reduce the potential for errors as the project concepts evolve. `a Construction Observation and Testing: We recommend STRATA be retained to observe site grading and fill compaction testing. Having STRATA provide testing and oversight during this process will reduce the potential for an unforeseen construction error which may ultimately impact the project. STRATA can also provide construction material testing of pavement sections and asphalt surfaces. If we are not retained to perform the recommended services, we cannot be responsible for related construction errors or omissions. EVALUATION LIMITATIONS This report has been prepared to assist project planning design and construction of the proposed Sgroi Property to be located at 4405 East Ustick Road in Meridian, Idaho. Our geotechnical findings and opinions have been developed based on the authorized subsurface exploration and laboratory testing, as well as our understanding of the project at this time. Our geotechnical design recommendations are specific to the planned design and infrastructure construction and should not be extrapolated to other future site developments without allowing adequate geotechnical consultation by STRATA. Our services consist of professional opinions and findings made in accordance with generally accepted geotechnical engineering principles and practices in southwest Idaho at the www.stratageotech.com \ )ƒ � � � }k \\ {\ }\ � \( - \ { . \» _— L--- ) - —�� ------ k- « o , >!IA- )/}) ! \ m0 111PI MID N \�PE \\ r �� UNIFIED SOIL CLASSIFICATION SYSTEM MAJOR DIVISIONS GRAPH LETTER TYPICAL NAMES Baggie Sample SYMBOL SYMBOL = After 24 Hours California Modified 3—Inch OD Split—Spoon Sample GW Well Gravel, Bulk Sample CLEAN Reading Gravel—Sand Mixtures. IIRock Core GRAVELSO a Sample Poorly—Graded Gravel, =_ at Time of Drilling .°- . GP Gravel—Sand Mixtures. _ GRAVELS Undisturbed Sample Silty Gravel, — GRAVELS GM Sand—Silt Mixtures. WITH Clayey Gravel, Gravel— COARSE FINES GC Sand—Clay Mixtures. GRAINED 0 0 0 0 0 0 Well—Graded Sand, SOILS CLEAN 0 0 0 0 0 0 000000 SW Gravelly Sand. • • • • • • Poorly—Graded Sand, SANDS • • • • • ` SP Gravelly Sand. SANDS : : :• Silty Sand, SANDS SM Sand—Silt Mixtures. WITH FINES SCClayey Sand, Sand—Clay Mixtures. •I Inorganic Silt, Sandy ML or Clayey Silt. SILTS AND CLAYS Inorganic Clay of Low CL to Medium Plasticity, LIQUID LIMIT Sandy or Silty Clay. LESS THAN 50% Organic Silt and Clay OL of Low Plasticity. FINE GRAINED Inorganic Silt, Mica— SOILS MH ceous Silt, Plastic Silt. SILTS AND CLAYS Inorganic Clay of High CH Plasticity, Fat Clay. LIQUID LIMIT GREATER THAN 50% OH Organic Clay of Medium to High Plasticity. Peat, Muck and Other PT Highly Organic Soils. BORING LOG SYMBOLS GROUNDWATER SYMBOLS TEST PIT LOG SYMBOLS IStandard 2—Inch OD Split—Spoon Sample ' Groundwater BG Baggie Sample = After 24 Hours California Modified 3—Inch OD Split—Spoon Sample (7-3-07) Indicates Date of BK Bulk Sample Reading IIRock Core Q Groundwater FRG]Ring Sample =_ at Time of Drilling Shelby Tube 3—Inch OD _ Undisturbed Sample Shorthand Notation: BGS = Below Existing Ground Surface N.E. = None Encountered d p c REMARKS H .+ C1 fN/J m MW V) > tJ N N> N V ✓� c C USCS Description w g g H ¢❑.. N a d N ❑ a o R u 9 Note: BGS = Below Ground ❑ 7 U rYji y u) E— W o z Z' o o Surface 7 U ❑ U a - SANDY SILT, (ML) brown, stiff, 3.5 Grass and roots to 8 inch BGS moist ML B G >4.5 SILT, (ML) tan, hard, moist to dry II >4.5 2.5 ML >4.5 Moderate cementrationfrom 3.0 to 4.0 feet BGS >4.5 POORLY GRADED. GRAVEL, With Sand And Silt, (GP -GM) tan, dense, moist Q s.o O O o O d 7.5 o 0 Q Infiltration test performed at 8.0 o o feet BGS. Infiltration rate = 20 BG inches per hour measured. GP - GM o O i o � O O � Q C D h V e 12.5 O Q 1 O O =Test Pit Terminated at 14.0 Feet. n L Client: KM ENGINEERS Test Pit Number. TP -2 �— 7& „_ ,. •. ,., . EXPLORATORY TEST PIT LOG 1 Project: B013323A Date Excavated: 07-01-2013 i i Backhoe: CASE 580K Bucket Width: 2' Depth to Groundwater: N.E. Logged By: SW Sheet 1 Of 1 RNALUE Idaho T 8 Project: Sgroi Property Project Number: B013323A Client: KM Engineering Lab Number: B13LO715A Sample Identification: TP -1 @ 1 - 1.5 ft Date Received: 7/1/13 Sample Classification: Silt Date Tested: 7/2-3/13 By: [RICK SOIL CONSTANTS R VALUE DATA Percolation: None P°,nt, P°,ntS P°int3 R VALUE: 41 Exudation, PSI 109 207 265 Dry Density, PCF 99.0 99.6 99.7 Moisture Content, % 21.8 21.2 20.8 Exp. Pressure, PSI 0.00 0.03 0.09 O o o _ — GRADATION: AASHTO T-11, T27 SCREEN ASRECEIVED ASTESTED SIZE %PASSING %PASSING O o M O o T' [+i r 2° E d V. ,N N d N o w 3/4.. J ^ v 1/2" 3 � h N N O o N 0 h No.4 100 100 o o c o No.8 V No. 16 No. 30 0 0 0 o Na 50 M No. 100 UDo 0 No. 200 6 N O O 0 0 0 QD 0 0 rn m r m O 0 0 0 R value Note: This report covers only material as represented by this sample and does not necessarily cover all soil from this layer or source. T FR aT a A PROFESSIONAL SERVICES CORPORATION Reviewed by: ��_ �H-Fc9rl-F�- From !-hc E�round UP