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Storm Drain Calculations Nov. 6 2014
;IVi!. IfJfJ©VA;n0N6r epue Storm Drainage Calculations CITADEL II SELF STORAGE Meridian, ID November 6, 2014 Civil Innovations, PLLC PO Box 170811 Boise, ID 83717-0811 Phone: (208) 884-8181 www.civi]-innovations.com Introduction Citadel II self -storage is a proposed storage unit project located on the east side of Eagle Road, directly south of the Ridenbaugh Canal. The proposed method of stormwater collection and disposal is on-site seepage beds as described below. Existing Storm Drain Conditions The property is currently undeveloped with bare dirt and weeds that are mowed during the growing season. Runoff from the Eagle Road is collected in drop inlets and piped off-site in a public drainage system that is owned and operated by ACHD. Other than the removal of some existing curb cuts, no improvements or modifications to Eagle Road or its drainage system are proposed. Proposed Storm Drain Design Stormwater runoff from this project will be retained in seven on-site in a seepage beds. The seepage beds are sized to hold all runoff from the 100 -year storm event. Water quality treatment is achieved by installation of sand & grease traps and ASTM C-33 filter sand under the drain rock. The sand & grease traps have been designed to limit the flow velocity through the structure to under 0.5 feet per second during the 100 -year storm event. N N c -I N N N N ti ti .--� ti ti ti N rv� m m m m m m 0 0 0 0 0 0 0 ti N ti ti ti ti ti F v m m m m m m m U N m w N 0 p t I .ti V1 M m I- U1 v 0 0 0 0 0 0 0 1. 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Frowt --lam E7rouKd OP Mr. Jim D. Conger Conger Management Group 1627 S. Orchard Street, Ste. 24 Boise, Idaho 83705 iconger@congergroup.com Dear Jim: March 12, 2014 File: B014032A RE: Geotechnical Engineering Evaluation Citadel 2 Storage South Eagle Road Meridian, Idaho STRATA, A Professional Services Corporation (STRATA) is pleased to present our authorized Geotechnical Engineering Evaluation for the proposed Citadel 2 Storage Facility to be located near the northeast corner of South Eagle Road and East Easy Jet Drive (adjacent to the Ridenbaugh Canal) in Meridian, Idaho. Our 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 undocumented fill removal, earthwork activities, foundation considerations and pavement section design. It is our opinion that geotechnical continuity with the project team throughout construction will help identify undocumented fill during earthwork to allow its excavation below proposed infrastructure and building footprint. 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. We appreciate the opportunity to work with Conger Management Group. 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. Geologist SW/AM/am 8653 West Hackamore Drive, noise, Idahn 8"709 Phone.208,376.8200 r-ax.208.376.8201 wvvw.stratageotec h.com REPORT Geotechnical Engineering Evaluation Citadel 2 Storage South Eagle Road Meridian, Idaho Prepared For: Jim Conger Conger Management Group 1627 S. Orchard Street, Ste. 24 Boise, Idaho 83705 Prepared By: STRATA, Inc. 8653 W. Hackamore Drive Boise, Idaho 83709 P.208.376.8200 F.208.376.8201 March 12, 2014 TABLE OF CONTENTS Page INTRODUCTION..............................................................................................................1 PROJECT UNDERSTANDING......................................................................................... 2 ExistingSite Conditions.................................................................................................... 2 Proposed Construction..................................................................................................... 2 SUBSURFACE EVALUATION PROCEDURES...............................................................3 SUBSURFACE CONDITIONS... ... ....... .................... .............. - - ... 3 LABORATORY TESTING................................................................................................. 4 GEOTECHNICAL OPINIONS AND RECOMMENDATIONS............................................4 Geotechnical Constraints..................................................................................................5 Earthwork.......................................................................................................................... 5 Excavation Characteristics............................................................................................ 5 FillRemoval... .............. .......... ...... ......... ---- ... — ....................... ............... ....... ....... 6 Site and Subgrade Preparation..................................................................................... 6 StructuralFill.................................................................................................................. 7 Table 1. Structural Fill Specifications and Allowable Use .......................................... 7 Wet Weather/Soil Construction...................................................................................... 8 Utility Trench Construction............................................................................................. 9 Geosynthetics.............................................................................................................. 10 FoundationDesign.......................................................................................................... 10 General........................................................................................................................ 10 BearingSoil................................................................................................................. 11 DesignCriteria............................................................................................................. 11 Concrete Slab -on -Grade Floors................................................................................... 11 PavementDesign............................................................................................................ 13 General........................................................................................................................ 13 Trafficand Subgrade................................................................................................... 13 Table 2. Pavement Design Parameters................................................................... 13 Asphalt, Aggregate Base Course and Subbase Materials ........................................... 13 Pavement Section Thickness...................................................................................... 14 Table 3. Asphalt Pavement Design Section............................................................. 14 Pavement Maintenance............................................................................................... 14 SiteDrainage.................................................................................................................. 15 StormwaterDisposal.................................................................................................... 15 Groundwater................................................................................................................ 15 ExteriorGrading........................................................................................................... 15 GEOTECHNICAL DESIGN CONTINUITY...................................................................... 16 EVALUATION LIMITATIONS.......................................................................................... 17 Geotechnical Engineering Evaluation Citadel 2 Storage Meridian. Idaho INTRODUCTION STRATA, A Professional Services Corporation (STRATA) has performed our geotechnical engineering evaluation for the proposed Citadel 2 Storage located in Meridian, Idaho. The proposed development is located near the northeast corner of South Eagle Road and East Easy Jet Drive, adjacent to the Ridenbaugh Canal. Our evaluation's purpose was to explore the subsurface soil conditions at the project site and prepare geotechnical recommendations to assist project planning, design and construction. We accomplished our services referencing our authorized geotechnical proposal dated January 24, 2014. To accomplish our evaluation, STRATA performed the following services: 1. Coordinated exploration with the Idaho Digline utility notification center to help reduce the potential for damage to existing utilities. 2. Observed the excavation of 3 exploratory test pits within the planned development area. Test pit exploration extended 12 feet below existing grade. Temporary standpipe groundwater monitoring piezometers were installed in all test pits. Our field geologist visually described, classified and logged soil encountered referencing the Unified Soil Classification System (USCS). 3. Performed two infiltration tests to evaluate infiltration characteristics of gravel with sand to assist stormwater disposal design. 4. Performed laboratory tests with reference to ASTM International (ASTM) procedures including Atterberg limits, in-situ moisture content, and grain size evaluation. We utilized these laboratory results to help characterize engineering parameters and to correlate soil engineering characteristics used in our design. 5. Performed engineering analyses in order to provide geotechnical design and earthwork construction recommendations. Our engineering analyses provides geotechnical recommendations and opinions for: Earthwork • Excavation characteristics • Fill removal • Site and subgrade preparation • Structural fill criteria • Wet weatherlsoil construction • Utility trench construction • Geosynthetics 8653 West Hackamore Drive, Boise, Idaho 83709 Phone.208.376.8200 rax.208.376.8201 www.stratageotech.com Citadel 2 Storage File: BO14032A Page 2 Foundation Design • Bearing soil • Design criteria • Concrete slab -on -grade floors OF Pavement design • Traffic and subgrade • Asphalt, aggregate base course and subbase materials • Pavement section thickness • Pavement maintenance Site Drainage • Stormwater disposal • Groundwater • Exterior grading 6. Prepared and provided an electronic copy of our final report of geotechnical findings, opinions and recommendations, including exploration logs and an exploration location plan. PROJECT UNDERSTANDING Existing Site Conditions The proposed development area consists of vacant land that is relatively flat and is covered by grassy vegetation. Although the site is currently undeveloped, historic aerial imagery shows that the site was developed up until 2006. The imagery shows a single family residence in the southwest corner of the property and an associated barn/garage near the center of the property. The site is bounded by existing subdivision development to the east, commercial development to the south, South Eagle Road to the west, and Ridenbaugh Canal to the north. Proposed Construction We understand development of the approximate 4.8 -acre site is to be developed with 12 buildings totaling 73,000 square feet of covered storage units, with asphalt paved roads providing access to the development. We understand stormwater will be retained and infiltrated on-site via subsurface infiltration beds or surficial swales. STRATA has not reviewed a grading plan for the development, but we anticipate grading will be limited, with cuts and fills of less than approximately 1 to 2 feet. 04 www.stratageotech.com Citadel 2 Storage File: B014032A Page 3 SUBSURFACE EVALUATION PROCEDURES STRATA accomplished subsurface exploration on February 20, 2014 via 3 exploratory test pits extending 12 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 A to help interpret the terms on the test pit logs. We also provide individual test pit logs in Appendix A. The test pits were backfilled with the excavated material to the ground surface following the completion of the excavations. We performed in-situ infiltration testing to assist in evaluating stormwater disposal infiltration rates in the gravel subsoil. STRATA performed infiltration testing at 6.5 and 8 feet below existing grades. We accomplished infiltration testing referencing the Idaho Department of Environmental Quality Technical Guidance Manual infiltration test method. SUBSURFACE CONDITIONS Topsoil vegetation and rooting was observed to a depth of approximately 6 inches below grade within the test pits. Soil conditions encountered within the test pits generally consist of fill clayey sand or native lean clay overlying clay, silt and gravel. We provide more specific discussion of each soil unit encountered below: 'iiio Fill clayey sand with gravel — Within test pits TP -2 and TP -3 (north and east portions of the site) we encountered surficial fill clayey sand with gravel to depths of 1 to 3 below existing grade. Fill soil is described as brown to tan, medium dense, and moist. Sandy clay/Fat clay — Within test pit TP -1 (southwest portion of the site) and below fill soil (north and east portions of the site) we encountered native surficial sandy clay or native fat clay to depths of 2 to 4 feet. Clay soil was described as brown, stiff to hard, and moist. 6* Silt — Underlying clay soil, we encountered light tan, hard, and moist silt to depths of 3.25 to 5.5 feet. Weak to strong calcium carbonate cementation was observed within the silt. Poorly -graded gravel with sand — Underlying silt, we encountered tan, medium dense to dense, and moist poorly -graded gravel with sand to test pit termination depths of 12 feet. #0 www.stratageotech.com Citadel 2 Storage File: BO14032A Page 4 Groundwater — We did not encounter groundwater within test pit at the time of exploration. We anticipate the depth to groundwater could fluctuate as a function of irrigation, precipitation and development to the project site. Based on our review of well logs in the area, we do not anticipate groundwater to rise above 15 feet below existing ground surface. We provide a USCS classification summary and specific soil contacts and descriptions on individual test pit togs provided as Appendix A to this report. Subsurface variations may exist between exploration locations and may not be apparent until construction. Test pits only allow us to observe a portion of the site subsurface conditions. Where such variations exist, they may impact our opinions and recommendations presented, as well as construction timing and costs. LABORATORY TESTING We returned soil samples collected in the field to our laboratory for further classification and testing. Laboratory testing was accomplished referencing ASTM International (ASTM) procedures. We developed our laboratory testing program for this project primarily to evaluate subsurface characteristics and engineering properties. Specifically, we accomplished moisture content, minus No. 200 wash, and Atterberg limit testing. We present laboratory test results on individual test pit logs located in Appendix A. 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 infrastructure planning, design and construction of the proposed Citadel 2 Storage Facility in Meridian, Idaho as illustrated on Plate 1. This report provides foundation and other geotechnical design criteria for the development, which the structural and civil 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 04 www.stratageotech.com Citadel 2 Storage File: B014032A Page 5 those observed during our field evaluation, we must be notified to review the report recommendations and make necessary revisions. Geotechnical Constraints We have identified the following primary geotechnical issues associated with the planned development: Potential variable subgrade soil/uncontrolled fill: Based on our exploration, we anticipate potential soil variability. This includes variances in soil contacts, as well as the potential for undocumented fill in areas not observed during exploration. Undocumented fill was observed to depths of up to 3 feet. This is also based on aerial imagery depicting previous residential development at the site. It will be critical that STRATA observe the subgrade conditions during site grading to confirm unsuitable soil removal, which may vary from the depths observed within test pits. S Expansive clay: We encountered expansive clay in the eastern portion of the site to a depth of 4.5 feet below grade. Expansive clay may be detrimental to foundation construction. As such, STRATA should confirm the absence of expansive clay at foundation elevation during earthwork construction. Our report specifically outlines our opinions and recommendations regarding these soil conditions and relies on geotechnical continuity, communication between project team members, and good construction practices to achieve the desired project outcome. Earthwork 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 and undocumented fill is expected to be exposed in excavations throughout the development area and should be temporarily sloped at 1.5HA V (horizontal to vertical) for excavations deeper than 4 feet. 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. www.stratageotech.com Citadel 2 Storage File: BO14032A Page 6 Fill Removal Any existing, non-native soil at the project site is considered undocumented fill that should be removed below planned pavement and building areas. Undocumented fill has the potential to settle below foundations and pavements, and such settlement could negatively impact their performance. Existing undocumented fill must be completely removed and/or remediated. If any utilities will be capped and remain in place, and/or if any other existing utility trench backfill will remain, such utility trench fill may settle under foundation loads. For these reasons, we recommend existing utilities be properly removed from below the planned buildings. Site and Subgrade Preparation We anticipate site grading will likely be limited to roadway areas, and cut and fill is not anticipated within building areas, with the exception of removal of undocumented fill. At the time of exploration, vegetation and organic material was observed to a depth of approximately 6 inches. We recommend this topsoil with organic matter be stripped beneath all planned improvements, including structural fill areas. In our opinion, this topsoil is not suitable for use as structural fill and should be wasted or stockpiled on-site for landscape areas. We anticipate that some undocumented fill soil could be encountered during site grading, especially in the area of the pre-existing residence and barn in the southwestern and central portions of the site, respectively. Up to 3 feet of surficial clayey sand with gravel fill was observed in test pit TP -3. All undocumented fill associated with previous construction on-site must be completely removed below all planned improvements and replaced with structural fill as indicated in this report. The stripped and/or over -excavated subgrade in proposed building, structural fill, pavement, and sidewalk areas must be proof -rolled with a minimum of 5 passes from a heavy 5 -ton roller or equivalent. If any weaving or pumping is observed, those areas must be removed to firm soil and replaced with structural fill. Test pits have been marked in the field by labeled standpipe piezometers. The test pits should be surveyed prior to any earthwork site grading, and test pits which are located beneath paving, structural fill or building areas should be re -excavated and replaced with structural fill in accordance with the recommendations in this report. 1!4 www.stratageotech.com Citadel 2 Storage File: B014032A Page 7 Structural Fill All fill placed for the development must be placed as structural fill. Soils encountered within the test pits are suitable for reuse as structural fill, provided they meet structural fill criteria as presented in Table 1 below. The structural fill requirements described in Table 1 below, in general, correlate to Idaho Standards for Public Works Construction (ISPWC) material specifications. Table 1. Structural Fill Specifications and Allowable Use Structural Fill Product • Allowable Use Material Specifications Sieve Size Passing • Soil classified as GW, GP, GP -GM, GM, SW, SP, SP -SM, SM or ML according to the USCS. General Structural Fill • Maximum particle size must be less than 6 inches. • General site grading • Soil consisting of inert earth materials with less than 3 percent organics or other deleterious substances wood metal, plastic, waste, etc). Granular Structural Fill • General structural fill Over -excavations • Pavement section • granular subbase • Soil classified as GW, GP, GP -GM, according to the USCS, and meeting the gradation provided. • Soil meeting requirements stated in the latest edition of the Idaho Standard for Public Works Construction (ISPWC), Section 801 —Aggregate Subbase. 6 Inch 100 3 Inch 90-100 No. 4 30-60 No. 200 <10 • Soil may not contain particles larger than 1 inch in 1 Inch 100 3/4 Inch 80-100 median diameter and must meet the required Utility Trench Bedding gradation. 3/8 Inch 20-70 • Utility trench • Soil meeting requirements stated in the latest No. 4 5-20 construction edition of the Idaho Standard for Public Works No. 8 0-5 Construction (ISPWC), Section 305 — Pipe No. 200 0-3 Bedding. • Soil may not contain particles larger than 1 inch in 1 Inch 100 Aggregate Base Course • Granular structural fill median diameter and must meet the required gradation. % Inch 90-100 No. 4 40-65 • Slab support base • Soil meeting requirements stated in the latest No. 8 30-50 • Pavement section edition of the Idaho Standard for Public Works base course Construction (ISPWC), Section 802—Aggregate No. 200 3-9 Base. • Soil classified as CL, CH, MH, OH, OL or PT may Unsatisfactory Soil not be used at the project site for structural fill. • No structural • Soil not maintaining moisture contents within 3 applications percent of optimum moisture. • Landscaping per • Any soil containing more than 3 percent organics landscape engineer by weight or other deleterious substances (wood, metal, plastic, waste, etc) is unsatisfactory soil. All structural fill must be compacted to a minimum of 95 percent of the maximum dry density of the soil referencing ASTM D 1557 (Modified Proctor). Fill placed outside any 14 www.stratageotech.com Citadel Storage File: B014032A Page 8 building or pavement envelope can be placed as non-structural fill (i.e. landscape fill) providing there are no structures (sidewalk, curbs, signs, etc.) planned directly above the landscape fill. We recommend landscape fill be compacted to a minimum of 85 percent of the maximum dry density of the soil according to ASTM D 1557. Any structural fill products must be moisture -conditioned to near optimum moisture content and placed in maximum 10 -inch -thick, loose lifts. The above assumes large, appropriate compaction equipment with drum energy of at least 10 tons or greater is used to attempt compaction. If smaller or lighter compaction equipment is provided, the lift thickness may have to be reduced to meet the compaction requirements presented herein. Wet Weather/Soil Construction We strongly recommend earthwork construction take place during dry weather conditions. Clayey soil is susceptible to pumping or rutting from heavy loads such as rubber -tired equipment or vehicles when the soil is above optimum moisture content. Earthwork should not be performed immediately after rainfall or until soil can dry sufficiently to allow construction traffic without disturbing the subgrade. During and after achieving subgrade elevation, the contractor must take precautions to protect the subgrade from becoming disturbed or saturated. We recommend the contractor limit construction traffic to any prepared subgrade and reduce exposure to precipitation and water. Specifically, the contractor should: 6 Grade subgrades to aggressively direct surface water away from construction areas that could be adversely affected by infiltration. 0 After adequate moisture conditioning efforts have flailed, remove exposed subgrade soil that becomes soft or begins to pump to firm soil and replace it with structural fill as described above for over -excavations. • Never attempt structural fill placement during or immediately following a significant precipitation event. •r Never allow subgrades to freeze or become saturated prior to fill placement. The final subgrade conditions and careful construction procedures are critical to the long-term project performance. We recommend earthwork specifications specifically identify the contractor's responsibility to protect and maintain prepared subgrades. It may improve project economy to retain STRATA to observe the subgrade preparation activities to identify i4 www.stratageotech.com Citadel 2 Storage File: BO14032A Page 9 techniques or construction activities that may be attributing to unstable subgrades and contributing to the need for over -excavations. Contractors should also anticipate isolated zones of wet soil, particularly below previous residential areas that may require removal and replacement with granular structural fill in proposed foundation or slab areas. Therefore, the contractor should plan contingencies to remove and replace wet and disturbed soil with granular structural fill after adequate moisture conditioning is attempted. If significant soft/wet soil conditions are encountered, the use of a woven geotextile fabric may be necessary. These material requirements are presented in the Geosynthetics report section. Allowing time for proper moisture -conditioning during dry weather is critical to reducing excessive over -excavations and importing granular structural fill. However, depending on the weather and moisture conditions during construction, drying fine-grained soil may not be practical, and over -excavation in conjunction with the use of geosynthetics may be necessary to 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. Utility Trench Construction Structural fill for backfilling utility trenches and all bedding should conform to 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 Citadel 2 Storage File: B014032A Page 10 Geosvnthetics 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 D 6241) and 200 pounds (Grab Tensile Strength ASTM D 4632). 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). Foundation Design General We recommend STRATA will be retained to observe the foundation system installation prior to placing concrete forms or concrete. Reviewing the final foundation bearing surfaces helps confirm our allowable bearing pressures and settlement estimates and is an important part of the geotechnical design process. Exterior footings must extend at least 24 inches below the final exterior ground surface to help protect against frost action. Interior foundations must extend at least 18 inches below final slab -bearing elevations and maintain at least 4 inches of gravel between slabs and the top of the footing to reduce the reflective cracking potential. Foundations must be structurally designed to conform to the latest edition of the International Building Code (IBC). The foundation bearing pressures presented below can be increased 30 percent to account for transitory live loads such as seismic and wind. Our analysis utilizes a factor of safety against 14 www.stratageotech.com Citadel 2 Storage File: B014032A Page 11 bearing capacity failure of 3.0 or greater. Settlement estimates and other design criteria are unfactored. Based on the assumed foundation loading conditions, the text below provides recommended design and construction criteria. Bearinq Soil From exploration, we expect the foundation excavations will expose fill clayey sand, native sandy clay and native lean clay. Any undocumented fill (as exposed in TP -2 and TP - 3) exposed during foundation excavations must be completely removed and replaced with structural fill as indicated in the Site and Subgrade Preparation section above. Foundations shall bear on native soil (prepared as indicated in the Site and Subgrade Preparation section above) or structural fill placed over native soil (prepared as indicated above). Desiqn Criteria Foundations constructed on native soil or structural fill over native soil, and prepared as indicated in the Site and Subgrade Preparation section, may be designed using a maximum allowable bearing pressure of 2,000 pounds per square foot (psf). Mass concrete placed on compacted native subgrades can utilize a friction coefficient (fs) of 0.35 to resist lateral loads. Mass concrete placed on granular structural fill or base course can utilize a friction coefficient (Q of 0.5 to resist lateral loads. These coefficients must be reduced by V3 if concrete is not cast directly on soil, such as for pre -cast panels. Using good construction practices and constructing during good weather, we estimate foundations bearing on subgrades prepared as recommended herein will realize 1 inch total and '/2 inch of differential settlement in a 30 -foot span. Our settlement estimates rely on 12 -inch -wide minimum continuous foundations. Foundation dimensions less than these should be analyzed for changes in settlement potential. Where water accumulates at the foundation elevation, settlement can be in excess of our estimates and the building tolerances. Therefore, we recommend exterior grading provide adequate drainage away from the building. Concrete Slab -on -Grade Floors Concrete slab -on -grade floors should be supported by compacted crushed aggregate base course placed on a prepared subgrade, as described in this report's Site and Subgrade #0 www.stratageotech.com Citadel 2 Storage File: B014032A Page 12 Preparation section. We recommend concrete slab -on -grade floors exposed to typical pedestrian and light storage loads be underlain by at least 4 inches of crushed aggregate base course to provide a leveling course and capillary break for the slab. Subgrade areas that become soft, wet or disturbed or that cannot be recompacted to structural fill requirements must be over -excavated to firm soil and replaced with granular structural fill prior to placing aggregate base. Interior floor slabs may be susceptible to moisture migration caused by capillary action and vapor pressure. If floor coverings such as tile, vinyl, or other "impervious coatings" may exist, a vapor retarder is strongly encouraged in these areas. Where utilized, vapor retarders must consist of a thick, 15 -mil, puncture -resistant sheeting consistent with American Concrete Institute (ACI) Section 302.2R-06 specifications. An example of a common vapor retarder is Stego WrapTM, a 15 -mil vapor retarder. The specific location of vapor retarders has been widely discussed in the architectural, structural, construction and geotechnical engineering community, and differing opinions exist. However, current recommendations by the ACI recommend placement of a vapor retarder directly below the concrete slab. However, ultimately, the location of the vapor retarder (if a vapor retarder is specified) should be carefully considered by the owner and architect. Studies have shown that decreased concrete water -cement ratios, higher strength concrete, and good construction finishing practices significantly decrease any negative impacts associated with both of the above options for vapor retarder locations. Installation of form stakes or other sub -slab penetrations must never be allowed to puncture the vapor retarder. Manufacturer recommendations for proper sealing of slab -to - wall connections, plumbing or other penetrations must be strictly followed. Although these recommendations are used, water vapor migration through the concrete floor slab is still possible. Floor covering must be selected accordingly and manufacturer's recommendations strictly followed. Exterior slabs are susceptible to frost action which can generate substantial frost heave at certain times of the year. The potential for frost heave may not be acceptable at entries or other critical areas adjacent to the buildings that will be exposed to weather. One approach to provide partial frost protection requires removing 65 percent of material within the frost depth and replacing it with granular structural fill. If this method is employed, the over -excavated soil must be replaced with aggregate base course as specified in the 14 www.stratageotech.com Citadel 2 Storage File: B014032A Page 13 Structural Fill section. Alternatively, if partial frost protection is unacceptable, over - excavation and aggregate base course replacement must be accomplished to the anticipated frost depth (24 inches). Pavement Design General The following flexible asphalt pavement section design is provided referencing the AASHTO Method. STRATA estimated traffic loading and design parameters based on our proposed construction understanding and our understanding of the subsurface conditions. Traffic and Subgrade The following tables present our traffic loading, geotechnical design parameters and references, as well as the resulting flexible pavement section design recommendations. Table 2. Pavement Design Parameters Design Parameter Value Used References Traffic Loading 33,000 ESALS Assumed Design Life 20 years Assumed Subgrade Resilient Modulus (Mr) 4,000 Assumed based on R -value correlations see paragraph below Terminal Serviceability Index 2.5 Typical Level of Reliability 95% Typical 'Equivalent Single Axle Loads (ESALS). From correlations to index laboratory testing, subgrade soil consisting of clayey soil and the subgrade soil variability, we estimate the Subgrade for proposed asphalt areas will have an R -value of approximately 5. This correlates to a resilient modulus of approximately 4,000. To help improve subgrade characteristics, the pavement subgrade should be prepared as recommended in this report's Site Preparation section. Subgrades must be shaped (crowned) and graded to facilitate positive drainage and inverted crowns must be avoided. Asphalt, Aggregate Base Course and Subbase Materials Crushed aggregate base course and granular subbase shall conform to the Structural Fill requirements and be placed directly over a properly prepared subgrade. A www.stratageotech.com Citadel 2 Storage File: B014032A Page 14 non -woven geotextile should be used for constructability during wet and inclement weather and to increase performance at the subgrade. The non -woven geotextile should have material properties and be placed as outlined in this report's Geosynthetics section. We recommend STRATA observe final subgrade preparations, geotextile placement and all aggregate placements. Asphalt concrete must be compacted to 92 percent of the maximum density for a Hveem or Superpave mix design. The final traveling surface of asphalt concrete shall meet ISPWC 3/ -inch asphalt mix design requirements. Asphalt mix designs and all appropriate aggregate source certificates should be accepted by STRATA at least 5 days prior to initiating asphalt paving. Asphalt construction and final surface smoothness, joints and density should meet ISPWC specifications. If subgrade conditions appear significantly different during 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 AASHTO 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 traffic loading or subgrade conditions change as design is finalized or during construction, 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 www.stratageotech.com Asphalt Aggregate Base gg G ranu lar Asphalt Pavement Application Concrete (inches) Subbase (inches) (inches) Access Roads 2.5 1 4.0 1 11.0 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 www.stratageotech.com Citadel 2 Storage File: B014032A Page 15 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 Stormwater Disposal We performed infiltration testing in the poorly -graded gravel with sand in test pit TP -2 and TP -3 at depths of 7 and 8 feet, respectively. We observed field infiltration rates of 20 to 25 inches per hour (in/hour). We recommend all subsurface infiltration facilities extend into poorly -graded gravel with sand a minimum of 12 inches. Based on our exploration, we anticipate excavation depths of 3.5 to 5.5 feet may be required to expose poorly -graded gravel soil. Stormwater facilities constructed into poorly -graded gravel with sand may be designed utilizing the allowable infiltration below: SO Allowable infiltration rate (poorly -graded gravel with sand) = 8 in/hr Groundwater Groundwater was not encountered within test pits at the time of site exploration. Although we expect groundwater levels to fluctuate seasonally, based on our review of the nearby water well logs, we do not anticipate groundwater to rise within 15 feet of existing site grades. However, due to the proximity of the site to the Ridenbaugh Canal, we recommend groundwater monitoring be accomplished during the 2014 irrigation season to confirm the absence of groundwater at the site. Standpipe piezometers were installed to maximum depths of 12 feet. Exterior Grading We recommend the ground surface outside of any structure be sloped a minimum of 5 percent away for 10 feet to rapidly convey surface water or roof runoff away from foundations. Remaining landscapes should slope at least 2 percent away from structures. �4 www.stratageotech.com Citadel 2 Storage File: B014032A Page 16 Stormwater should be routed away from disturbed soil areas and should be disposed of in stormwater disposal facilities located at least 20 feet from the proposed buildings. Irrigation adjacent to or within 10 feet of the buildings is discouraged. 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: 'uo Groundwater Monitoring: The groundwater level should be monitored for the 2014 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 April and October. STRATA remains available to perform groundwater monitoring at your request. ft 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. 6 Geotechnical Design Confirmation: The potential soil variation may have a significant impact on foundation construction. As such, we recommend STRATA be retained to provide geotechnical engineering oversight during site grading and excavation to observe the potential variability in the soil conditions and provide consultation regarding potential impacts on foundation construction. _i Construction Observation and Testing: We recommend STRATA be retained to observe foundation excavation and concrete placement operations for shallow foundations. Having STRATA provide inspection 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 and special inspection for concrete, masonry, reinforcement, and asphalt. If we are not retained to perform the recommended services, we cannot be responsible for related construction errors or omissions. IS www.stratageotech.com Citadel 2 Storage File: B014032A Page 17 EVALUATION LIMITATIONS This report has been prepared to assist project planning, design and construction of the proposed Citadel 2 Storage Facility to be located 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 report findings and recommendations should not be extrapolated to other future site developments without allowing adequate geotechnical consultation by STRATA. Subsurface variations may exist between exploration locations and may not be apparent until construction. Test pits only allow us to observe a portion of the site subsurface conditions. Where such variations exist, they may impact opinions and recommendations presented in this report, as well as construction timing and costs. 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 STRATA during construction to verify compliance with our recommendations and to confirm conditions between exploration locations. This acknowledgment is in lieu of all warranties either express or implied. The following plate and appendix accompany and complete this report: Plate 1: Exploration Location Plan Appendix A: Unified Soil Classification System (USCS) & Exploratory Test Pit Logs #0 www.stratageotech.com APPENDIX A UNIFIED SOIL CLASSIFICATION SYSTEM MAJOR DIVISIONS GRAPH SYMBOL LETTER SYMBOL TYPICAL NAMES BG Baggie Sample 'California Modified 3—Inch OD Split—Spoon Sample Q ..�.: GW Well—Graded Grovel, IIRock Core CLEAN Groundwater RG Ring Sample Gravel—Sand Mixtures. Shelby Tube 3—Inch OD =_ _ GRAVELSO GP Poorly—Graded Gravel, Gravel—Sand Mixtures. GRAVELS Silty Gravel, Gravel— GRAVELS GM Sand—Silt Mixtures. WITH Clayey Gravel, Gravel— COARSE FINES GC Sand—Clay Mixtures. GRAINED 000000 Well—Graded Sand, SOILS CLEAN 0 0 0 0 0 0 0 0 0 a 0 0 SW Gravelly Sand. ' ' • • • • Poorly—Graded Sand, SANDS SP Gravelly Sand. SANDS SANDS • • • • SM Silty Sand, Sand—Silt Mixtures. WITH FINES .� • •• SC Clayey Sand, •� .� • 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 GREATER THAN 50% ` OH Organic Clay of Medium 9 y � 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 After 24 Hours BG Baggie Sample 'California Modified 3—Inch OD Split—Spoon Sample (7_3_07) Indicates Date of Reading BK Bulk Sample IIRock Core 0 Groundwater RG Ring Sample Shelby Tube 3—Inch OD =_ _ at Time of Drilling Undisturbed Sample Shorthand Notation: BGS = Below Existing Ground Surface N.E. = None Encountered Ulm p a m an c p 'c Remarks USCS Description o U� y F yry> a d mC o o teE 2 � Note: BGS = Below Ground Surface LL PI SANDY LEAN CLAY, (native), (CL) brown, 0.0 stiff, moist Grass roots to 6 inches BGS BG 70.0 25.0 _ 1 CL BG 1 2.5 '% "`' 1.5 o. SILT, (ML) light tan, hard, moist ML Strong cementation observed at 3 feet BGS POORLY GRADED GRAVEL, With Sand, -- (GP) tan, medium dense, moist ° C) o D Q. 1.7 3.8 5.0 o "D Q. . BG 0 0. Q: n ,D. O .. ado, o p:. Q. . 7.5 o p Q GP o 'b. O �p o D' o �o. Q 1a.a p D:. Q' �.' 0 0. Piezometer installed to 12 feet Q. BGS. Test Pit Terminated at 12.0 Feet. i Client: CONGER MANAGMENT Test Pit Number: TP -1 EXPLORATORY i Project: B014032A Date Excavated: 02-20-2014 s-rFR&Y& TEST PIT LOG Backhoe: CASE 580 Bucket Width: 2' AG„_,.,,, Depth to Groundwater: N.E. Logged By: SW Sheet 1 Of 1 USCS Description P v yy U m a E m6 E 'bow m a a ��, y m m = y `m a„ v m ww g E Remarks ❑ v a z Note: BGS = Below e ❑ a a Ground Surface LL PI CLAYEY SAND,. With Gravel (fill), (SC) brown, medium dense, moist Grass roots to 6 inch BGS SC SANDY LEAN CLAY, (native), (CL) brown, hard, moist BG 39 18 CL >4.5 SILT, (ML) light tan, hard, moist 2.5ML >4.5 Moderate cementation observed from 325 to 4 feet POORLY GRADED GRAVEL, With Sand, (GP) tan, dense, moist o a°.:: BGS P fl' Q. . PUa o.. ° �° . 5.0 o D. Q.. °G" . p ,D O a ad o b:' Infiltration test performed at o (T,:: 6.5 feet BGS. Infiltration rate = o � 25 inches per hour measured 7.5 GP P..p 0 �9 o D', a: o'D Q' P D:. O to.o n D. a Q° n ..D Q. . o b' Piezometer installed to 12 feet 41�2 BGS. Test Pit Terminated at 12.0 Feet. Client; CONGER MANAGMENT Test Pit Number: TP -2 EXPLORATORY Project: B014032A Date Excavated: 02-20-2014 STRaTa TEST PIT LOG Backhoe: CASE 580 Bucket Width: 2' '"' - "-"'- ' " Depth to Groundwater: N.E. Logged By: SW Sheet 1 Of 1 Uj a Remarks USCS Description mE aN x a J Note: BGS = Below LL PI Ground Surface 0.0 CLAYEY SAND, With Gravel (fill), (SC) tan, medium dense, moist -- Grass roots to 6. inches. BGS BG SC 2.5 FAT CLAY, (native), (CH) brown, very stiff, moist BG 3.0 63 37 CH Moderate cementation SILT, (ML) tan, hard, moist observed at 4.5 feet BGS 5.0 ML POORLY GRADED GRAVEL, With Sand, (GP) tan, dense, moist a O' e Q°. o..D: O. o D. 7.5 O o ,D Q . Infiltration test performed at 8 a �o feet BGS. Infiltration rate = 20 0 0: inches per hour measured GP o D 0.0 5 Q'. With cobbles at 10 feet BGS Q o..G G. o a" Piezometer installed to 12 feet BGS. Test Pit Terminated at 12.0 Feet. Client: CONGER MANAGMENT Test Pit Number: TP -3 EXPLORATORY Project: B014032A Date Excavated: 02-20-2014 STR�T3 TEST PIT LOG Backhoe: CASE 580 Bucket Width: 2' - ` "' " "' Depth to Groundwater: N.E. Logged By: SW Sheet 1 Of 1