The URL can be used to link to this page

Home My WebLink AboutEastwood Sub - Geotechnical Engineering Evaluation�4 sTFtaTa "rHa-c cjrify Frost 4.1, 67ro"nd Up Providence Properties, LLC Attn: Randy Clarno PO Box 2648 Eagle, ID 83616 Dear Mr. Clarno: July 9, 2013 File: BO13253A RE: Geotechnical Engineering Evaluation Eastwood Subdivision Meridian. Idaho Strata, A Professional Services Corporation (STRATA) is pleased to present our authorized Geotechnical Engineering Evaluation for the proposed residential development located to the southwest of the intersection of East Wrightwood Drive and South Locust Grove Road, at 4515 South Locust Grove 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 monitoring, testing, and consultation 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, G%STE STRATA, Inc. Q�c3 Q �Fd 10830 'sm1,-7 9 13 0 Steve Worsley, P.G. ( ashington) 4p Geologist t Geologist ry4 � Cc: Mr. Kevin McCarthy/KM Engineering SW/MGW/nm www.stratageotech.com dworth, P.E. Manager TABLE OF CONTENTS INTRODUCTION............................................................................................................1 PROJECTUNDERSTANDING.......................................................................................2 Existing Site Conditions..................................................................................................2 ProposedConstruction...................................................................................................2 SUBSURFACE EVALUATION PROCEDURES..............................................................2 SUBSURFACE CONDITIONS........................................................................................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..................................................................................6 Table 1. Structural Fill Specifications and Allowable Use.............................................7 Geosynth etics........................................................................................................... 8 Pavement Section Design............................................................................................ 8 General.................................................................................................................... 8 Trafficand Subgrade................................................................................................9 Table 2. Pavement Design Parameters....................................................................... 9 Asphalt, Aggregate Base Course and Subbase Materials........................................9 Pavement Section Thickness................................................................................. 10 Table 3. Asphalt Pavement Design Section............................................................... 10 Pavement Maintenance.......................................................................................... 10 SiteDrainage.............................................................................................................10 ExteriorGrading.....................................................................................................10 InfiltrationRates..................................................................................................... 11 Groundwater........................................................................................................... 11 GEOTECHNICAL DESIGN CONTINUITY.................................................................... 12 EVALUATIONLIMITATIONS... ..................................................................................... 12 Eastwood Subdivision 4515 South Locust Grove Road Meridian, Idaho File: B013253A Page 2 Site Drainage • Exterior grading • Infiltration rates • Groundwater 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 southwest of the intersection of East Wrightwood Drive and South Locust Grove Road. The proposed subdivision will be accessed from East Wrightwood Drive. The site is currently undeveloped, and is bounded by residential properties to the north, south east and west. East Wrightwood Drive parallels the proposed subdivision to the north in an east -west orientation, and South Locust Grove Road parallels the site to the east in a north -south orientation. Proposed Construction We understand the approximate 7.35 -acre development will consist of 22 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 supported floors. 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 3 exploratory test pits extending 14.5 to 15 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. A professional geologist visually evaluated the soil encountered in each test pit and logged the soil profile referencing the USCS. We provide a brief USCS explanation in Appendix www.stratageotech.com Eastwood Subdivision 4515 South Locust Grove Road Meridian, Idaho File: B013253A Page 4 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 Eastwood Subdivision, to be located southwest of the intersection of East Wrightwood Drive and South Locust Grove 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 We currently do not have a grading plan for the proposed subdivision, but we anticipate final grades will generally be within approximately 1 -foot of existing grades. At the time of exploration, surficial vegetation and organic material was observed to a depth of approximately 6 to 10 inches. We recommend a minimum of 10 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. 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 for future remediation. 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. The stripped subgrade in proposed structural fill, pavement and sidewalk areas should be proof -rolled with a minimum of 5 passes from a heavy 5 -ton roller or equivalent. If weaving or pumping is observed, those areas should be removed and replaced with structural fill. www.stratageotech.com Eastwood Subdivision 4515 South Locust Grove Road Meridian, Idaho File: B013253A Page 6 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 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. Structural Fill and Compaction All fill placed for the development must be placed as structural fill. The structural fill requirements described in Table 1 below, in general, correlate to ISPWC material specifications. Project structural fill products are described in Table 1 below. 1!4 www.stratageotech.com Eastwood Subdivision 4515 South Locust Grove Road Meridian, Idaho File: BO13253A Page 8 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 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 District substitution ratios. STRATA estimated traffic loading and design parameters based on our proposed construction understanding and our understanding of the subsurface conditions. 04 www.stratageotech.com Eastwood Subdivision 4515 South Locust Grove Road Meridian, Idaho File: B013253A Page 10 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, snowmelt, or leaking water lines. These water sources can be transmitted to the foundation stem wall and pond beneath the structure via precipitation, roof downspout discharge, and snowmelt. Possible conduits for water to enter into crawlspaces can include loose or porous www.stratageotech.com Asphalt Aggregate Base Granular Asphalt Pavement Application Concrete Course (inches) Subbase (inches) (inches) Local Roads (TI = 6) 2.5 4.0 12.0 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, snowmelt, or leaking water lines. These water sources can be transmitted to the foundation stem wall and pond beneath the structure via precipitation, roof downspout discharge, and snowmelt. Possible conduits for water to enter into crawlspaces can include loose or porous www.stratageotech.com Eastwood Subdivision 4515 South Locust Grove Road Meridian, Idaho File: 6013253A Page 12 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: ISF Groundwater Monitoring: The groundwater level should be monitored during the current irrigation season to verify the seasonal high groundwater level beneath the site. Piezometers were 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. 5 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 Eastwood Subdivision to be located at 4415 South Locust Grove 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 time of this report. The geotechnical recommendations provided herein are based on the premise that appropriate geotechnical consultation during subsequent design phases is implemented and an adequate program of tests and observations will be conducted by 04 www.stratageotech.com I I I I ��c _ 3 r m,vOA a �9 m 0 3 m m Fb� oN:o W r7F D I --- ----- II II If I —J L I I---- I I---- LOCUST GROVE ROAD �9 m 0 3 m m 9 y UNIFIED SOIL CLASSIFICATION SYSTEM MAJOR DIVISIONS GRAPH SYMBOL LETTER SYMBOL TYPICAL NAMES Ba99ie Sample 0:' ., GW Well—Graded Gravel, California Modified 3—Inch OD Split—Spoon Sample CLEAN BK Bulk Sample Gravel—Sand Mixtures. Reading GRAVELS ( O GP Poorly—Graded Gravel, Q Groundwater RG Ring Sample v. ° • . : Gravel—Sand Mixtures. GRAVELS Shelby Tube 3—Inch OD Silty Gravel, Gravel— Undisturbed Sample 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 SW Gravelly Sand. • • • • • • Poorly—Graded Sand, SANDS • • • • • • SP Gravelly Sand. SANDS :' :' :• Silty Sand, SANDS • ; • ; • • SM Sand—Silt Mixtures. WITH • • Clayey Sand, FINES. • • • SC Sand—Clay Mixtures. • 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 Organic Clay of Medium GREATER THAN 50% OH 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 Ba99ie 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 RG Ring Sample =_ at Time of Drilling Shelby Tube 3—Inch OD Undisturbed Sample Shorthand Notation: BGS = Below Existing Ground Surface N.E. = None Encountered J' � q REMARKS USCS Description a Cj0 3 m a.a E, a,� m N d o a "� w w Ground Note: BGSSurface LU v j U y in t- N g. a z m Z 2 0 o" U 4 U a SANDY SILT, (ML) brown, stiff, ' 2.5 Grass roots to 6 inches BGS moist to dry ML >4.5 SILT, (ML) tan, hard, moist to dry >4.5 2.5 j3� >as >4.5 Moderate cementation 5 to 8 5.0 I feet BGS ML 7.5 Strong cementation from 8.0 to. 11.0 feet BGS Difficult excavation 8.0 -11.0 i I feet BGS i � 10.0 i I i i ' ' i POORLY GRADED GRAVEL, With = Sand And Silt, (GP) tan, very dense, moist Q O i QO. _ 12.5 GP - .o 0 Q (� � Test Pit Terminated at 14.0 Feet: c 0 Client: KM ENGINEEERING Test Pit Number: TP -2 . r...' -'� -k EXPLORATORY TEST PIT LOG - Project: B013253A Date Excavated: 07-01-2013T`�' z Backhoe: CASE 580K Bucket Width: 2' r Depth to Groundwater: N.E. Logged By: SW Sheet 1 Of 1 APPENDIX B