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Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com GEOTECHNICAL ENGINEERING REPORT of Proposed 4-Lot Subdivision 1180 North Ten Mile Road Meridian, ID Prepared for: LR Geomatics PLLC 2850 West Mirnmont Street Meridian, ID 83646 MTI File Number B190906g 5 June 2019 Page # 2 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection TABLE OF CONTENTS INTRODUCTION ............................................................................................................................................................... 3 Project Description ................................................................................................................................................. 3 Authorization .......................................................................................................................................................... 3 Purpose ................................................................................................................................................................... 3 Scope of Investigation ............................................................................................................................................ 4 Warranty and Limiting Conditions ......................................................................................................................... 4 SITE DESCRIPTION .......................................................................................................................................................... 5 Site Access .............................................................................................................................................................. 5 Regional Geology ................................................................................................................................................... 5 General Site Characteristics .................................................................................................................................... 6 Regional Site Climatology and Geochemistry ........................................................................................................ 6 SEISMIC SITE EVALUATION ............................................................................................................................................ 6 Geoseismic Setting ................................................................................................................................................. 6 Seismic Design Parameter Values .......................................................................................................................... 6 SOILS EXPLORATION ...................................................................................................................................................... 7 Exploration and Sampling Procedures .................................................................................................................... 7 Laboratory Testing Program ................................................................................................................................... 8 Soil and Sediment Profile ....................................................................................................................................... 8 Volatile Organic Scan ............................................................................................................................................. 8 SITE HYDROLOGY........................................................................................................................................................... 9 Groundwater ........................................................................................................................................................... 9 Soil Infiltration Rates .............................................................................................................................................. 9 FOUNDATION, SLAB, AND PAVEMENT DISCUSSION AND RECOMMENDATIONS ............................................................. 10 Foundation Design Recommendations ................................................................................................................. 10 Crawl Space Recommendations ........................................................................................................................... 11 Floor Slab-on-Grade ............................................................................................................................................. 11 Recommended Pavement Sections ....................................................................................................................... 12 Flexible Pavement Section ................................................................................................................................... 12 Pavement Subgrade Preparation ........................................................................................................................... 13 Common Pavement Section Construction Issues ................................................................................................. 13 CONSTRUCTION CONSIDERATIONS ............................................................................................................................... 13 Earthwork ............................................................................................................................................................. 13 Dry Weather ......................................................................................................................................................... 14 Wet Weather ......................................................................................................................................................... 14 Soft Subgrade Soils .............................................................................................................................................. 14 Frozen Subgrade Soils .......................................................................................................................................... 15 Structural Fill ........................................................................................................................................................ 15 Backfill of Walls ................................................................................................................................................... 16 Excavations ........................................................................................................................................................... 16 Groundwater Control ............................................................................................................................................ 17 GENERAL COMMENTS .................................................................................................................................................. 17 REFERENCES ................................................................................................................................................................. 18 APPENDICES ................................................................................................................................................................. 19 Acronym List ........................................................................................................................................................ 19 Geotechnical General Notes ................................................................................................................................. 20 Geotechnical Investigation Test Pit Log ............................................................................................................... 21 AASHTO Pavement Thickness Design Procedures ............................................................................................. 24 Plate 1: Vicinity Map ............................................................................................................................................ 25 Plate 2: Site Map ................................................................................................................................................... 26 5 June 2019 Page # 3 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection INTRODUCTION This report presents results of a geotechnical investigation and analysis in support of data utilized in design of structures as defined in the 2015 International Building Code (IBC). Information in support of groundwater and stormwater issues pertinent to the practice of Civil Engineering is included. Observations and recommendations relevant to the earthwork phase of the project are also presented. Revisions in plans or drawings for the proposed development from those enumerated in this report should be brought to the attention of the soils engineer to determine whether changes in the provided recommendations are required. Deviations from noted subsurface conditions, if encountered during construction, should also be brought to the attention of the soils engineer. Project Description The proposed development is in the western portion of the City of Meridian, Ada County, ID, and occupies a portion of the SW¼NW¼ of Section 11, Township 3 North, Range 1 West, Boise Meridian. This project will consist of the development of a 4-lot residential subdivision. An existing residence is present on the site and will remain. In addition, a shared driveway will be developed for both access and parking. The site is approximately 1.434 acres in size. Total settlements are limited to 1 inch. Loads of up to 4,000 pounds per lineal foot for wall footings, and column loads of up to 50,000 pounds were assumed for settlement calculations. Additionally, assumptions have been made for traffic loading of pavements. Retaining walls are not anticipated as part of the project. MTI has not been informed of the proposed grading plan. Authorization Authorization to perform this exploration and analysis was given in the form of a written authorization to proceed from Mr. Aaron Rush of LR Geomatics PLLC to Clint Wyllie of Materials Testing and Inspection (MTI), on 14 May 2019. Said authorization is subject to terms, conditions, and limitations described in the Professional Services Contract entered into between LR Geomatics PLLC and MTI. Our scope of services for the proposed development has been provided in our proposal dated 13 May 2019 and repeated below. Purpose The purpose of this Geotechnical Engineering Report is to determine various soil profile components and their engineering characteristics for use by either design engineers or architects in: • Preparing or verifying suitability of foundation design and placement • Preparing site drainage designs • Indicating issues pertaining to earthwork construction • Preparing residential pavement section design requirements 5 June 2019 Page # 4 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection Scope of Investigation The scope of this investigation included review of geologic literature and existing available geotechnical studies of the area, visual site reconnaissance of the immediate site, subsurface exploration of the site, field and laboratory testing of materials collected, and engineering analysis and evaluation of foundation materials. Warranty and Limiting Conditions MTI warrants that findings and conclusions contained herein have been formulated in accordance with generally accepted professional engineering practice in the fields of foundation engineering, soil mechanics, and engineering geology only for the site and project described in this report. These engineering methods have been developed to provide the client with information regarding apparent or potential engineering conditions relating to the site within the scope cited above and are necessarily limited to conditions observed at the time of the site visit and research. Field observations and research reported herein are considered sufficient in detail and scope to form a reasonable basis for the purposes cited above. Exclusive Use This report was prepared for exclusive use of the property owner(s), at the time of the report, and their retained design consultants (“Client”). Conclusions and recommendations presented in this report are based on the agreed-upon scope of work outlined in this report together with the Contract for Professional Services between the Client and Materials Testing and Inspection (“Consultant”). Use or misuse of this report, or reliance upon findings hereof, by parties other than the Client is at their own risk. Neither Client nor Consultant make representation of warranty to such other parties as to accuracy or completeness of this report or suitability of its use by such other parties for purposes whatsoever, known or unknown, to Client or Consultant. Neither Client nor Consultant shall have liability to indemnify or hold harmless third parties for losses incurred by actual or purported use or misuse of this report. No other warranties are implied or expressed. Report Recommendations are Limited and Subject to Misinterpretation There is a distinct possibility that conditions may exist that could not be identified within the scope of the investigation or that were not apparent during our site investigation. Findings of this report are limited to data collected from noted explorations advanced and do not account for unidentified fill zones, unsuitable soil types or conditions, and variability in soil moisture and groundwater conditions. To avoid possible misinterpretations of findings, conclusions, and implications of this report, MTI should be retained to explain the report contents to other design professionals as well as construction professionals. Since actual subsurface conditions on the site can only be verified by earthwork, note that construction recommendations are based on general assumptions from selective observations and selective field exploratory sampling. Upon commencement of construction, such conditions may be identified that require corrective actions, and these required corrective actions may impact the project budget. Therefore, construction recommendations in this report should be considered preliminary, and MTI should be retained to observe actual subsurface conditions during earthwork construction activities to provide additional construction recommendations as needed. 5 June 2019 Page # 5 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection Since geotechnical reports are subject to misinterpretation, do not separate the soil logs from the report. Rather, provide a copy of, or authorize for their use, the complete report to other design professionals or contractors. Locations of exploratory sites referenced within this report should be considered approximate locations only. For more accurate locations, services of a professional land surveyor are recommended. This report is also limited to information available at the time it was prepared. In the event additional information is provided to MTI following publication of our report, it will be forwarded to the client for evaluation in the form received. Environmental Concerns Comments in this report concerning either onsite conditions or observations, including soil appearances and odors, are provided as general information. These comments are not intended to describe, quantify, or evaluate environmental concerns or situations. Since personnel, skills, procedures, standards, and equipment differ, a geotechnical investigation report is not intended to substitute for a geoenvironmental investigation or a Phase II/III Environmental Site Assessment. If environmental services are needed, MTI can provide, via a separate contract, those personnel who are trained to investigate and delineate soil and water contamination. SITE DESCRIPTION Site Access Access to the site may be gained via Interstate 84 to the Ten Mile Road exit. Proceed north on Ten Mile Road approximately 1.5 miles. The site is east of Ten Mile and north of Forecast Street. Presently the site exists as a residence and garage structure with an empty field east of the structures. The location is depicted on site map plates included in the Appendix. Regional Geology The project site is located within the western Snake River Plain of southwestern Idaho and eastern Oregon. The plain is a northwest trending rift basin, about 45 miles wide and 200 miles long, that developed about 14 million years ago (Ma) and has since been occupied sporadically by large inland lakes. Geologic materials found within and along the plain’s margins reflect volcanic and fluvial/lacustrine sedimentary processes that have led to an accumulation of approximately 1 to 2 km of interbedded volcanic and sedimentary deposits within the plain. Along the margins of the plain, streams that drained the highlands to the north and south provided coarse to fine-grained sediments eroded from granitic and volcanic rocks, respectively. About 2 million years ago the last of the lakes was drained and since that time fluvial erosion and deposition has dominated the evolution of the landscape. The project site is underlain by the “Gravel of Whitney Terrace” as mapped by Othberg and Stanford (1993). Sediments of the Whitney terrace consist of sandy pebble and cobble gravel. The Whitney terrace is the second terrace above modern Boise River floodplain, is thickest toward its eastern extent, and is mantled with 2-6 feet of loess. 5 June 2019 Page # 6 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection General Site Characteristics This proposed development consists of approximately 1.434 acres of relatively flat terrain. A residence with a detached garage is located in the western portion of the site, fronting Ten Mile Road. The remainder of the site is a vacant field with Eightmile Lateral located along the eastern property boundary. Throughout the majority of the site, surficial soils consist of lean clays. Vegetation primarily consists of mature trees, bunchgrass, and other native grass varieties typical of arid to semi-arid environments. Regional drainage is north toward the Boise River. Stormwater drainage for the site is achieved by percolation through surficial soils. The site is situated so that it is unlikely that it will receive any stormwater drainage from off-site sources. Stormwater drainage collection and retention systems are not in place on the project site, but do exist along Ten Mile Road in the form of curbs, gutters, and drop inlets. Regional Site Climatology and Geochemistry According to the Western Regional Climate Center, the average precipitation for the Treasure Valley is on the order of 10 to 12 inches per year, with an annual snowfall of approximately 20 inches and a range from 3 to 49 inches. The monthly mean daily temperatures range from 21°F to 95°F, with daily extremes ranging from - 25°F to 111°F. Winds are generally from the northwest or southeast with an annual average wind speed of approximately 9 miles per hour (mph) and a maximum of 62 mph. Soils and sediments in the area are primarily derived from siliceous materials and exhibit low electro-chemical potential for corrosion of metals or concretes. Local aggregates are generally appropriate for Portland cement and lime cement mixtures. Surface water, groundwater, and soils in the region typically have pH levels ranging from 7.2 to 8.2. SEISMIC SITE EVALUATION Geoseismic Setting Soils on site are classed as Site Class D in accordance with Chapter 20 of the American Society of Civil Engineers (ASCE) publication ASCE/SEI 7-10. Structures constructed on this site should be designed per IBC requirements for such a seismic classification. Our investigation did not reveal hazards resulting from potential earthquake motions including: slope instability, liquefaction, and surface rupture caused by faulting or lateral spreading. Incidence and anticipated acceleration of seismic activity in the area is low. Seismic Design Parameter Values The United States Geological Survey National Seismic Hazard Maps (2008), includes a peak ground acceleration map. The map for 2% probability of exceedance in 50 years in the Western United States in standard gravity (g) indicates that a peak ground acceleration of 0.197 is appropriate for the project site based on a Site Class D. 5 June 2019 Page # 7 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection The following section provides an assessment of the earthquake-induced earthquake loads for the site based on the Risk-Targeted Maximum Considered Earthquake (MCER). The MCER spectral response acceleration for short periods, SMS, and at 1-second period, SM1, are adjusted for site class effects as required by the 2015 IBC. Design spectral response acceleration parameters as presented in the 2015 IBC are defined as a 5% damped design spectral response acceleration at short periods, SDS, and at 1-second period, SD1. The USGS National Seismic Hazards Mapping Project includes a program that provides values for ground motion at a selected site based on the same data that were used to prepare the USGS ground motion maps. The maps were developed using attenuation relationships for soft rock sites; the source model, assumptions, and empirical relationships used in preparation of the maps are described in Petersen and others (1996). Seismic Design Values Seismic Design Parameter Design Value Site Class D “Stiff Soil” Ss 0.289 (g) S1 0.102 (g) Fa 1.569 Fv 2.392 SMs 0.453 SM1 0.244 SDS 0.302 SD1 0.163 SOILS EXPLORATION Exploration and Sampling Procedures Field exploration conducted to determine engineering characteristics of subsurface materials included a reconnaissance of the project site and investigation by test pit. Test pit sites were located in the field by means of a Global Positioning System (GPS) device and are reportedly accurate to within fifteen feet. Upon completion of investigation, each test pit was backfilled with loose excavated materials. Re-excavation and compaction of these test pit areas are required prior to construction of overlying structures. In addition, samples were obtained from representative soil strata encountered. Samples obtained have been visually classified in the field by professional staff, identified according to test pit number and depth, placed in sealed containers, and transported to our laboratory for additional testing. Subsurface materials have been described in detail on logs provided in the Appendix. Results of field and laboratory tests are also presented in the Appendix. MTI recommends that these logs not be used to estimate fill material quantities. 5 June 2019 Page # 8 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection Laboratory Testing Program Along with our field investigation, a supplemental laboratory testing program was conducted to determine additional pertinent engineering characteristics of subsurface materials necessary in an analysis of anticipated behavior of the proposed structures. Laboratory tests were conducted in accordance with current applicable American Society for Testing and Materials (ASTM) specifications, and results of these tests are to be found on the accompanying logs located in the Appendix. The laboratory testing program for this report included: Atterberg Limits Testing – ASTM D4318 and Grain Size Analysis – ASTM C117/C136. Soil and Sediment Profile The profile below represents a generalized interpretation for the project site. Note that on site soils strata, encountered between test pit locations, may vary from the individual soil profiles presented in the logs, which can be found in the Appendix. The materials encountered during exploration were quite typical for the geologic area mapped as Gravel of Whitney Terrace. Lean clay soils were encountered at ground surface. These soils were dark brown, slightly moist, and medium stiff to very stiff. Organic materials were measured to depths of roughly 2 feet bgs. Underlying the lean clays in test pit 3 were silty sand sediments. The silty sand sediments were light brown, dry to slightly moist, very stiff and contained fine to medium-grained sand and intermittent coarse-grained sand. In test pits 1 and 2 beneath lean clay and in test pit 3 below the silty sand, silt with varying sand contents were noted. The silt soils were light brown to brown or red brown, dry to slightly moist, stiff to hard, and contained fine to coarse-grained sand. In test pits 1 and 2, poorly graded sands with varying silt contents were encountered below the silts. The sand sediments were light brown, dry to slightly moist, loose to medium dense, and contained fine to coarse-grained sand. Silty sand was noted underlying the sands in test pits 1 and 2. The silty sand was red brown, dry to moist, and dense to very dense, with fine to coarse-grained sand. At depth, poorly graded sand with gravel was found. The poorly graded sand with gravel was brown, moist to saturated, medium dense to dense, and contained fine to coarse-grained sand and fine to coarse gravel. Competency of test pit sidewalls varied little across the site. In general, fine grained soils remained stable while more granular sediments readily sloughed. However, moisture contents will also affect wall competency with saturated soils having a tendency to readily slough when under load and unsupported. Volatile Organic Scan No environmental concerns were identified prior to commencement of the investigation. Therefore, soils obtained during on-site activities were not assessed for volatile organic compounds by portable photoionization detector. Samples obtained during our exploration activities exhibited no odors or discoloration typically associated with this type of contamination. Groundwater encountered did not exhibit obvious signs of contamination. 5 June 2019 Page # 9 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection SITE HYDROLOGY Existing surface drainage conditions are defined in the General Site Characteristics section. Information provided in this section is limited to observations made at the time of the investigation. Either regional or local ordinances may require information beyond the scope of this report. Groundwater During this field investigation, groundwater was encountered in test pits at depths ranging from 13.9 to 14.5 feet bgs. Soil moistures in the test pits were generally dry to slightly moist within surficial soils. Within the poorly graded sands with gravel, soil moistures graded from moist to saturated as the water table was approached and penetrated. In the vicinity of the project site, groundwater levels are controlled in large part by residential and commercial irrigation activity and leakage from nearby canals. Maximum groundwater elevations likely occur during the later portion of the irrigation season. During several previous investigations performed from February 2005 through June 2018 within approximately ½-mile of the project site, groundwater was noted within test pits at depths ranging from 7.4 to 14.6 feet bgs. Additionally, during groundwater monitoring of a nearby project, groundwater was noted to fluctuate roughly 5.3 feet bgs throughout the year. Furthermore, according to United States Geological Survey (USGS) monitoring well data within approximately ½-mile of the project site, groundwater was measured at depth of 11.0 feet bgs. Based on evidence of this investigation and background knowledge of the area, MTI estimates groundwater depths to remain greater than approximately 7.5 feet bgs throughout the year. This depth can be confirmed through long-term groundwater monitoring. Soil Infiltration Rates Soil permeability, which is a measure of the ability of a soil to transmit a fluid, was not tested in the field. Given the absence of direct measurements, for this report an estimation of infiltration is presented using generally recognized values for each soil type and gradation. Of soils comprising the generalized soil profile for this study, lean clay and silt soils generally offer little permeability, with typical hydraulic infiltration rates of less than 2 inches per hour. Sandy silt soils will commonly exhibit infiltration rates from 2 to 4 inches per hour. Silty sand sediments usually display rates of 4 to 8 inches per hour. However, calcium carbonate cementation within the sandy silt and silty sands may reduce these values to near zero. Poorly graded sand with gravel sediments typically exhibit infiltration values in excess of 12 inches per hour. High groundwater depth is expected to be higher than the free draining soils through portions of the year and will significantly reduce infiltration rates. Because of this, MTI recommends infiltration testing be performed once infiltration facility locations are determined. 5 June 2019 Page # 10 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection FOUNDATION, SLAB, AND PAVEMENT DISCUSSION AND RECOMMENDATIONS Various foundation types have been considered for support of the proposed development. Two requirements must be met in the design of foundations. First, the applied bearing stress must be less than the ultimate bearing capacity of foundation soils to maintain stability. Second, total and differential settlement must not exceed an amount that will produce an adverse behavior of the superstructure. Allowable settlement is usually exceeded before bearing capacity considerations become important; thus, allowable bearing pressure is normally controlled by settlement considerations. Considering subsurface conditions and the proposed construction, it is recommended that the development be founded upon conventional spread footings and continuous wall footings. Total settlements should not exceed 1 inch if the following design and construction recommendations are observed. Presently, there are 4 lots proposed for the project site. The following recommendations are not specific to the individual structures, but rather should be viewed as guidelines for the subdivision – wide development. Foundation Design Recommendations Based on data obtained from the site and test results from various laboratory tests performed, MTI recommends the following guidelines for the net allowable soil bearing capacity: Soil Bearing Capacity Footing Depth ASTM D1557 Subgrade Compaction Net Allowable Soil Bearing Capacity Footings must bear on competent, undisturbed, native lean clay, sandy silt, silt, and silty sand soils or compacted structural fill. Existing organic materials must be completely removed from below foundation elements.1 Excavation depths ranging from roughly 1.4 to 2.0 feet bgs should be anticipated to expose proper bearing soils.2 Not Required for Native Soil 95% for Structural Fill 1,500 lbs/ft2 A ⅓ increase is allowable for short-term loading, which is defined by seismic events or designed wind speeds. 1It will be required for MTI personnel to verify the bearing soil suitability for each structure at the time of construction. 2Depending on the time of year construction takes place, the subgrade soils may be unstable because of high moisture contents. If unstable conditions are encountered, over-excavation and replacement with granular structural fill and/or use of geotextiles may be required. The following sliding frictional coefficient values should be used: 1) 0.35 for footings bearing on native lean clay, sandy silt, silt, and silty sand soils and 2) 0.45 for footings bearing on granular structural fill. A passive lateral earth pressure of 297 pounds per square foot per foot (psf/ft) should be used for lean clay, sandy silt, and silt soils. A lateral earth pressure of 351 psf/ft should be used for sandy silt and silty sand soils. For compacted sandy gravel fill, a passive lateral earth pressure of 496 psf/ft should be used. 5 June 2019 Page # 11 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection Footings should be proportioned to meet either the stated soil bearing capacity or the 2015 IBC minimum requirements. Total settlement should be limited to approximately 1 inch, and differential settlement should be limited to approximately ½ inch. Objectionable soil types encountered at the bottom of footing excavations should be removed and replaced with structural fill. Excessively loose or soft areas that are encountered in the footings subgrade will require over-excavation and backfilling with structural fill. To minimize the effects of slight differential movement that may occur because of variations in the character of supporting soils and seasonal moisture content, MTI recommends continuous footings be suitably reinforced to make them as rigid as possible. For frost protection, the bottom of external footings should be 24 inches below finished grade. Crawl Space Recommendations Considering the presence of shallow cemented soils across the site, all residences constructed with crawl spaces should be designed in a manner that will inhibit water in the crawl spaces. MTI recommends that roof drains carry stormwater at least 10 feet away from each residence. Grades should be at least 5 percent for a distance of 10 feet away from all residences. In addition, rain gutters should be placed around all sides of residences, and backfill around stem walls should be placed and compacted in a controlled manner. Floor Slab-on-Grade Organic, loose, or obviously compressive materials must be removed prior to placement of concrete floors or floor-supporting fill. In addition, the remaining subgrade should be treated in accordance with guidelines presented in the Earthwork section. Areas of excessive yielding should be excavated and backfilled with structural fill. Fill used to increase the elevation of the floor slab should meet requirements detailed in the Structural Fill section. Fill materials must be compacted to a minimum 95 percent of the maximum dry density as determined by ASTM D1557. A free-draining granular mat (drainage fill course) should be provided below slabs-on-grade. This should be a minimum of 4 inches in thickness and properly compacted. The mat should consist of a sand and gravel mixture, complying with Idaho Standards for Public Works Construction (ISPWC) specifications for ¾-inch (Type 1) crushed aggregate. The granular mat should be compacted to no less than 95 percent of the maximum dry density as determined by ASTM D1557. A moisture-retarder should be placed beneath floor slabs to minimize potential ground moisture effects on moisture-sensitive floor coverings. The moisture-retarder should be at least 15-mil in thickness and have a permeance of less than 0.01 US perms as determined by ASTM E96. Placement of the moisture-retarder will require special consideration with regard to effects on the slab-on-grade and should adhere to recommendations outlined in the ACI 302.1R and ASTM E1745 publications. Upon request, MTI can provide further consultation regarding installation. 5 June 2019 Page # 12 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection Recommended Pavement Sections MTI has made assumptions for traffic loading variables based on the character of the proposed construction. The Client shall review and understand these assumptions to make sure they reflect intended use and loading of pavements both now and in the future. Based on experience with soils in the region, a subgrade California Bearing Ratio (CBR) value of 4 has been assumed for near-surface lean clay, sandy silt, and silt soils on site. The following are minimum thickness requirements for assured pavement function. Depending on site conditions, additional work, e.g. soil preparation, may be required to support construction equipment. These have been listed within the Soft Subgrade Soils section. Flexible Pavement Section The American Association of State Highway and Transportation Officials (AASHTO) design method has been used to calculate the following pavement section. A calculation sheet provided in the Appendix indicates the soils constant, traffic loading, traffic projections, and material constants used to calculate the pavement section. MTI recommends that materials used in the construction of asphaltic concrete pavements meet requirements of the ISPWC Standard Specification for Highway Construction. Construction of the pavement section should be in accordance with these specifications and should adhere to guidelines recommended in the section on Construction Considerations. AASHTO Flexible Pavement Specifications Pavement Section Component1 Residential Roadway Asphaltic Concrete 2.5 Inches Crushed Aggregate Base 4.0 Inches Structural Subbase 8.0 Inches Compacted Subgrade See Pavement Subgrade Preparation Section 1It will be required for MTI personnel to verify subgrade competency at the time of construction. Asphaltic Concrete: Asphalt mix design shall meet the requirements of ISPWC, Section 810 Class III plant mix. Materials shall be placed in accordance with ISPWC Standard Specifications for Highway Construction. Aggregate Base: Material complying with ISPWC Standards for Crushed Aggregate Materials. Structural Subbase: Granular structural fill material complying with the requirements detailed in the Structural Fill section of this report except that the maximum material diameter is no more than 2/3 the component thickness. Gradation and suitability requirements shall be per ISPWC Section 801, Table 1. 5 June 2019 Page # 13 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection Pavement Subgrade Preparation Uncontrolled fill was encountered in portions of the site. MTI recommends that these fill materials be excavated to a sufficient depth to expose competent, native soils. MTI personnel must be present during excavation to identify these materials. Common Pavement Section Construction Issues The subgrade upon which above pavement sections are to be constructed must be properly stripped inspected, and proof-rolled. Proof rolling of subgrade soils should be accomplished using a heavy rubber-tired, fully loaded, tandem-axle dump truck or equivalent. Verification of subgrade competence by MTI personnel at the time of construction is required. Fill materials on the site must demonstrate the indicated compaction prior to placing material in support of the pavement section. MTI anticipated that pavement areas will be subjected to moderate traffic. Subgrade clays and silts near and above optimum moisture contents may pump during compaction. Pumping or soft areas must be removed and replaced with structural fill. Fill material and aggregates, as well as compacted native subgrade soils, in support of the pavement section must be compacted to no less than 95 percent of the maximum dry density as determined by ASTM D698 for flexible pavements and by ASTM D1557 for rigid pavements. If a material placed as a pavement section component cannot be tested by usual compaction testing methods, then compaction of that material must be approved by observed proof rolling. Minor deflections from proof rolling for flexible pavements are allowable. Deflections from proof rolling of rigid pavement support courses should not be visually detectable. CONSTRUCTION CONSIDERATIONS Recommendations in this report are based upon structural elements of the project being founded on competent, native lean clay, sandy silt, and silt soils or compacted structural fill. Structural areas should be stripped to an elevation that exposes these soil types. Earthwork Excessively organic soils, deleterious materials, or disturbed soils generally undergo high volume changes when subjected to loads, which is detrimental to subgrade behavior in the area of pavements, floor slabs, structural fills, and foundations. Mature trees, brush, and thick grasses with associated root systems were noted at the time of our investigation. It is recommended that organic or disturbed soils, if encountered, be removed, and wasted or stockpiled for later use. However, in areas where trees are/were present, deeper excavation depths should be anticipated. Stripping depths should be adjusted in the field to assure that the entire root zone or disturbed zone or topsoil are removed prior to placement and compaction of structural fill materials. Exact removal depths should be determined during grading operations by MTI personnel, and should be based upon subgrade soil type, composition, and firmness or soil stability. If underground storage tanks, underground utilities, wells, or septic systems are discovered during construction activities, they must be decommissioned then removed or abandoned in accordance with governing Federal, State, and local agencies. Excavations developed as the result of such removal must be backfilled with structural fill materials as defined in the Structural Fill section. 5 June 2019 Page # 14 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection MTI should oversee subgrade conditions (i.e., moisture content) as well as placement and compaction of new fill (if required) after native soils are excavated to design grade. Recommendations for structural fill presented in this report can be used to minimize volume changes and differential settlements that are detrimental to the behavior of footings, pavements, and floor slabs. Sufficient density tests should be performed to properly monitor compaction. For structural fill beneath building structures, one in-place density test per lift for every 5,000 square feet is recommended. In parking and driveway areas, this can be decreased to one test per lift for every 10,000 square feet. Dry Weather If construction is to be conducted during dry seasonal conditions, many problems associated with soft soils may be avoided. However, some rutting of subgrade soils may be induced by shallow groundwater conditions related to springtime runoff or irrigation activities during late summer through early fall. Solutions to problems associated with soft subgrade soils are outlined in the Soft Subgrade Soils section. Problems may also arise because of lack of moisture in native and fill soils at time of placement. This will require the addition of water to achieve near-optimum moisture levels. Low-cohesion soils exposed in excavations may become friable, increasing chances of sloughing or caving. Measures to control excessive dust should be considered as part of the overall health and safety management plan. Wet Weather If construction is to be conducted during wet seasonal conditions (commonly from mid-November through May), problems associated with soft soils must be considered as part of the construction plan. During this time of year, fine-grained soils such as silts and clays will become unstable with increased moisture content, and eventually deform or rut. Additionally, constant low temperatures reduce the possibility of drying soils to near optimum conditions. Soft Subgrade Soils Shallow fine-grained subgrade soils that are high in moisture content should be expected to pump and rut under construction traffic. During periods of wet weather, construction may become very difficult if not impossible. The following recommendations and options have been included for dealing with soft subgrade conditions: • Track-mounted vehicles should be used to strip the subgrade of root matter and other deleterious debris. Heavy rubber-tired equipment should be prohibited from operating directly on the native subgrade and areas in which structural fill materials have been placed. Construction traffic should be restricted to designated roadways that do not cross, or cross on a limited basis, proposed roadway or parking areas. • Soft areas can be over-excavated and replaced with granular structural fill. • Construction roadways on soft subgrade soils should consist of a minimum 2-foot thickness of large cobbles of 4 to 6 inches in diameter with sufficient sand and fines to fill voids. Construction entrances should consist of a 6-inch thickness of clean, 2-inch minimum, angular drain-rock and must be a minimum of 10 feet wide and 30 to 50 feet long. During the construction process, top dressing of the entrance may be required for maintenance. 5 June 2019 Page # 15 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection • Scarification and aeration of subgrade soils can be employed to reduce the moisture content of wet subgrade soils. After stripping is complete, the exposed subgrade should be ripped or disked to a depth of 1½ feet and allowed to air dry for 2 to 4 weeks. Further disking should be performed on a weekly basis to aid the aeration process. • Alternative soil stabilization methods include use of geotextiles, lime, and cement stabilization. MTI is available to provide recommendations and guidelines at your request. Frozen Subgrade Soils Prior to placement of structural fill materials or foundation elements, frozen subgrade soils must either be allowed to thaw or be stripped to depths that expose non-frozen soils and wasted or stockpiled for later use. Stockpiled materials must be allowed to thaw and return to near-optimal conditions prior to use as structural fill. The onsite, shallow lean clay and silty soils are susceptible to frost heave during freezing temperatures. For exterior flatwork and other structural elements, adequate drainage away from subgrades is critical. Compaction and use of structural fill will also help to mitigate the potential for frost heave. Complete removal of frost susceptible soils for the full frost depth, followed by replacement with a non-frost susceptible structural fill, can also be used to mitigate the potential for frost heave. MTI is available to provide further guidance/assistance upon request. Structural Fill Soils recommended for use as structural fill are those classified as GW, GP, SW, and SP in accordance with the Unified Soil Classification System (USCS) (ASTM D2487). Use of silty soils (USCS designation of GM, SM, and ML) as structural fill may be acceptable. However, use of silty soils (GM, SM, and ML) as structural fill below footings is prohibited. These materials require very high moisture contents for compaction and require a long time to dry out if natural moisture contents are too high and may also be susceptible to frost heave under certain conditions. Therefore, these materials can be quite difficult to work with as moisture content, lift thickness, and compactive effort becomes difficult to control. If silty soil is used for structural fill, lift thicknesses should not exceed 6 inches (loose), and fill material moisture must be closely monitored at both the working elevation and the elevations of materials already placed. Following placement, silty soils must be protected from degradation resulting from construction traffic or subsequent construction. Recommended granular structural fill materials, those classified as GW, GP, SW, and SP, should consist of a 6-inch minus select, clean, granular soil with no more than 50 percent oversize (greater than ¾-inch) material and no more than 12 percent fines (passing No. 200 sieve). These fill materials should be placed in layers not to exceed 12 inches in loose thickness. Prior to placement of structural fill materials, surfaces must be prepared as outlined in the Construction Considerations section. Structural fill material should be moisture-conditioned to achieve optimum moisture content prior to compaction. For structural fill below footings, areas of compacted backfill must extend outside the perimeter of the footings for a distance equal to the thickness of fill between the bottom of foundation and underlying soils, or 5 feet, whichever is less. All fill materials must be monitored during placement and tested to confirm compaction requirements, outlined below, have been achieved. 5 June 2019 Page # 16 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection Each layer of structural fill must be compacted, as outlined below: • Below Structures and Rigid Pavements: A minimum of 95 percent of the maximum dry density as determined by ASTM D1557. • Below Flexible Pavements: A minimum of 92 percent of the maximum dry density as determined by ASTM D1557 or 95 percent of the maximum dry density as determined by ASTM D698. The ASTM D1557 test method must be used for samples containing up to 40 percent oversize (greater than ¾- inch) particles. If material contains more than 40 percent but less than 50 percent oversize particles, compaction of fill must be confirmed by proof rolling each lift with a 10-ton vibratory roller (or equivalent) until the maximum density has been achieved. Density testing must be performed after each proof rolling pass until the in-place density test results indicate a drop (or no increase) in the dry density, defined as maximum density or “break over” point. The number of required passes should be used as the requirements on the remainder of fill placement. Material should contain sufficient fines to fill void spaces, and must not contain more than 50 percent oversize particles. Backfill of Walls Backfill materials must conform to the requirements of structural fill, as defined in this report. For wall heights greater than 2.5 feet, the maximum material size should not exceed 4 inches in diameter. Placing oversized material against rigid surfaces interferes with proper compaction, and can induce excessive point loads on walls. Backfill shall not commence until the wall has gained sufficient strength to resist placement and compaction forces. Further, retaining walls above 2.5 feet in height shall be backfilled in a manner that will limit the potential for damage from compaction methods and/or equipment. It is recommended that only small hand- operated compaction equipment be used for compaction of backfill within a horizontal distance equal to the height of the wall, measured from the back face of the wall. Backfill should be compacted in accordance with the specifications for structural fill, except in those areas where it is determined that future settlement is not a concern, such as planter areas. In nonstructural areas, backfill must be compacted to a firm and unyielding condition. Excavations Shallow excavations that do not exceed 4 feet in depth may be constructed with side slopes approaching vertical. Below this depth, it is recommended that slopes be constructed in accordance with Occupational Safety and Health Administration (OSHA) regulations, Section 1926, Subpart P. Based on these regulations, on-site soils are classified as type “C” soil, and as such, excavations within these soils should be constructed at a maximum slope of 1½ feet horizontal to 1 foot vertical (1½:1) for excavations up to 20 feet in height. Excavations in excess of 20 feet will require additional analysis. Note that these slope angles are considered stable for short- term conditions only, and will not be stable for long-term conditions. 5 June 2019 Page # 17 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection During the subsurface exploration, test pit sidewalls generally exhibited little indication of collapse; however, sloughing of fill materials and native granular sediments from test pit sidewalls was observed, particularly after penetration of the water table. For deep excavations, native granular sediments cannot be expected to remain in position. These materials are prone to failure and may collapse, thereby undermining upper soil layers. This is especially true when excavations approach depths near the water table. Care must be taken to ensure that excavations are properly backfilled in accordance with procedures outlined in this report. Groundwater Control Groundwater was encountered during the investigation but is anticipated to be below the depth of most construction. Excavations below the water table will require a dewatering program. Dewatering will be required prior to placement of fill materials. Placement of concrete can be accomplished through water by the use of a treme. It may be possible to discharge dewatering effluent to remote portions of the site, to a sump, or to a pit. This will essentially recycle effluent, thus eliminating the need to enter into agreements with local drainage authorities. Should the scope of the proposed project change, MTI should be contacted to provide more detailed groundwater control measures. Special precautions may be required for control of surface runoff and subsurface seepage. It is recommended that runoff be directed away from open excavations. Silty and clayey soils may become soft and pump if subjected to excessive traffic during time of surface runoff. Ponded water in construction areas should be drained through methods such as trenching, sloping, crowning grades, nightly smooth drum rolling, or installing a French drain system. Additionally, temporary or permanent driveway sections should be constructed if extended wet weather is forecasted. GENERAL COMMENTS Based on the subsurface conditions encountered during this investigation and available information regarding the proposed development, the site is adequate for the planned construction. When plans and specifications are complete, and if significant changes are made in the character or location of the proposed structure, consultation with MTI must be arranged as supplementary recommendations may be required. Suitability of subgrade soils and compaction of structural fill materials must be verified by MTI personnel prior to placement of structural elements. Additionally, monitoring and testing should be performed to verify that suitable materials are used for structural fill and that proper placement and compaction techniques are utilized. 5 June 2019 Page # 18 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection REFERENCES American Association of State Highway and Transportation Officials (AASHTO) (1993). AASHTO Guide for Design of Pavement Structures 1993. Washington D.C.: AASHTO. American Concrete Institute (ACI) (2015). Guide for Concrete Floor and Slab Construction: ACI 302.1R. Farmington Hills, MI: ACI. American Society of Civil Engineers (ASCE) (2013). Minimum Design Loads for Buildings and Other Structures: ASCE/SEI 7-10. Reston, VA: ASCE. American Society for Testing and Materials (ASTM) (2013). Standard Test Method for Materials Finer than 75-μm (No. 200) Sieve in Mineral Aggregates by Washing: ASTM C117. West Conshohocken, PA: ASTM. American Society for Testing and Materials (ASTM) (2014). Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates: ASTM C136. West Conshohocken, PA: ASTM. American Society for Testing and Materials (ASTM) (2012). Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort: ASTM D698. West Conshohocken, PA: ASTM. American Society for Testing and Materials (ASTM) (2012). Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort: ASTM D1557. West Conshohocken, PA: ASTM. American Society for Testing and Materials (ASTM) (2011). Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System): ASTM D2487. West Conshohocken, PA: ASTM. American Society for Testing and Materials (ASTM) (2010). Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils: ASTM D4318. West Conshohocken, PA: ASTM. American Society for Testing and Materials (ASTM) (2011). Standard Specification for Plastic Water Vapor Retarders Used in Contact with Soil or Granular Fill Under Concrete Slabs: ASTM E1745. West Conshohocken, PA: ASTM. Desert Research Institute. Western Regional Climate Center. [Online] Available: <http://www.wrcc.dri.edu/> (2019). International Building Code Council (2015). International Building Code, 2015. Country Club Hills, IL: Author. Local Highway Technical Assistance Council (LHTAC) (2017). Idaho Standards for Public Works Construction, 2017. Boise, ID: Author. Othberg, K. L. and Stanford, L. A., Idaho Geologic Society (1992). Geologic Map of the Boise Valley and Adjoining Area, Western Snake River Plain, Idaho. (scale 1:100,000). Boise, ID: Joslyn and Morris. U.S. Department of Labor, Occupational Safety and Health Administration. CFR 29, Part 1926, Subpart P: Safety and Health Regulations for Construction, Excavations (1986). [Online] Available: <www.osha.gov> (2019). U.S. Geological Survey (2019). National Water Information System: Web Interface. [Online] Available: <http://waterdata.usgs.gov/nwis> (2019). U.S. Geological Survey. (2011). U.S. Seismic Design Maps: Web Interface. [Online] Available: <https://earthquake.usgs.gov/designmaps/us/application.php> (2019). 5 June 2019 Page # 19 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection APPENDICES ACRONYM LIST AASHTO: American Association of State Highway and Transportation Officials ACHD: Ada County Highway District ACI American Concrete Institute ASCE American Society of Civil Engineers ASTM: American Society for Testing and Materials bgs: below ground surface CBR: California Bearing Ratio D: natural dry unit weight, pcf ESAL Equivalent Single Axle Load GS: grab sample IBC: International Building Code ISPWC: Idaho Standards for Public Works Construction ITD: Idaho Transportation Department LL: Liquid Limit M: water content MSL: mean sea level N: Standard "N" penetration: blows per foot, Standard Penetration Test NP: nonplastic OSHA Occupational Safety and Health Administration PCCP: Portland Cement Concrete Pavement PERM: vapor permeability PI: Plasticity Index PID: photoionization detector PVC: polyvinyl chloride Qc: cone penetrometer value, unconfined compressive strength, psi Qp: Penetrometer value, unconfined compressive strength, tsf Qu: Unconfined compressive strength, tsf RMR Rock Mass Rating RQD Rock Quality Designation R-Value Resistance Value SPT: Standard Penetration Test (140:pound hammer falling 30 in. on a 2:in. split spoon) USCS: Unified Soil Classification System USDA: United States Department of Agriculture UST: underground storage tank V: vane value, ultimate shearing strength, tsf 5 June 2019 Page # 20 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection GEOTECHNICAL GENERAL NOTES RELATIVE DENSITY AND CONSISTENCY CLASSIFICATION Coarse-Grained Soils SPT Blow Counts (N) Fine-Grained Soils SPT Blow Counts (N) Very Loose: < 4 Very Soft: < 2 Loose: 4-10 Soft: 2-4 Medium Dense: 10-30 Medium Stiff: 4-8 Dense: 30-50 Stiff: 8-15 Very Dense: >50 Very Stiff: 15-30 Hard: >30 Moisture Content Cementation Description Field Test Description Field Test Dry Absence of moisture, dusty, dry to touch Weakly Crumbles or breaks with handling or slight finger pressure Moist Damp but not visible moisture Moderately Crumbles or beaks with considerable finger pressure Wet Visible free water, usually soil is below water table Strongly Will not crumble or break with finger pressure PARTICLE SIZE Boulders: >12 in. Coarse-Grained Sand: 5 to 0.6 mm Silts: 0.075 to 0.005 mm Cobbles: 12 to 3 in. Medium-Grained Sand: 0.6 to 0.2 mm Clays: <0.005 mm Gravel: 3 in. to 5 mm Fine-Grained Sand: 0.2 to 0.075 mm UNIFIED SOIL CLASSIFICATION SYSTEM Major Divisions Symbol Soil Descriptions Coarse-Grained Soils <50% passes No.200 sieve Gravel & Gravelly Soils <50% coarse fraction passes No.4 sieve GW Well-graded gravels; gravel/sand mixtures with little or no fines GP Poorly-graded gravels; gravel/sand mixtures with little or no fines GM Silty gravels; poorly-graded gravel/sand/silt mixtures GC Clayey gravels; poorly-graded gravel/sand/clay mixtures Sand & Sandy Soils >50% coarse fraction passes No.4 sieve SW Well-graded sands; gravelly sands with little or no fines SP Poorly-graded sands; gravelly sands with little or no fines SM Silty sands; poorly-graded sand/gravel/silt mixtures SC Clayey sands; poorly-graded sand/gravel/clay mixtures Fine Grained Soils >50% passes No.200 sieve Silts & Clays LL < 50 ML Inorganic silts; sandy, gravelly or clayey silts CL Lean clays; inorganic, gravelly, sandy, or silty, low to medium-plasticity clays OL Organic, low-plasticity clays and silts Silts & Clays LL > 50 MH Inorganic, elastic silts; sandy, gravelly or clayey elastic silts CH Fat clays; high-plasticity, inorganic clays OH Organic, medium to high-plasticity clays and silts Highly Organic Soils PT Peat, humus, hydric soils with high organic content 5 June 2019 Page # 21 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection GEOTECHNICAL INVESTIGATION TEST PIT LOG Test Pit Log #: TP-1 Date Advanced: 22 May 2019 Logged by: Maren Tanberg, E.I.T., G.I.T. Excavated by: Xtreme Xcavation Location: See Site Map Plates Latitude: 43.615577 Longitude: -116.432597 Depth to Water Table: 14.0 Feet bgs Total Depth: 15.0 Feet bgs Depth (Feet bgs) Field Description and USCS Soil and Sediment Classification Sample Type Sample Depth (Feet bgs) Qp Lab Test ID 0.0-1.4 Lean Clay (CL): Dark brown, slightly moist, medium stiff to stiff. --Organics noted throughout. 1.0-1.5 1.4-5.0 Sandy Silt (ML): Light brown, dry to slightly moist, very stiff, with fine to medium grained sand and intermittent coarse-grained sand. --Organics noted to 2.0 feet bgs. --Moderate to strong calcium carbonate cementation noted from 4.0 to 5.0 feet bgs. --Sand content increased with depth. 3.5-4.0 5.0-9.0 Poorly Graded Sand (SP): Light brown, dry, loose to medium dense, with fine to coarse- grained sand. 9.0-11.6 Silty Sand (SM): Brown to reddish brown, moist, dense, with fine to coarse-grained sand. 11.6-15.0 Poorly Graded Sand with Gravel (GP): Brown, wet to saturated, medium dense to dense, with fine to coarse-grained sand and fine to coarse gravel. 5 June 2019 Page # 22 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection GEOTECHNICAL INVESTIGATION TEST PIT LOG Test Pit Log #: TP-2 Date Advanced: 22 May 2019 Logged by: Maren Tanberg, E.I.T., G.I.T. Excavated by: Xtreme Xcavation Location: See Site Map Plates Latitude: 43.615267 Longitude: -116.432136 Depth to Water Table: 14.5 Feet bgs Total Depth: 15.0 Feet bgs Depth (Feet bgs) Field Description and USCS Soil and Sediment Classification Sample Type Sample Depth (Feet bgs) Qp Lab Test ID 0.0-1.6 Lean Clay (CL): Dark brown, slightly moist, medium stiff to very stiff. --Organics noted throughout. 1.0-2.5 1.6-3.7 Silt (ML): Light brown, dry to slightly moist, stiff to very stiff. --Organics noted to 2.0 feet bgs. 2.0-4.0 3.7-6.4 Silt with Sand (ML): Brown, dry to slightly moist, very stiff, with fine to medium-grained sand. --Sand content increases with depth. 6.4-8.4 Poorly Graded Sand with Silt (SP-SM): Light brown, dry to slightly moist, medium dense, with fine to coarse-grained sand and intermittent coarse-grained sand. 8.4-12.6 Silty Sand (SM): Red brown, dry to moist, very dense, with fine to coarse-grained sand. --Calcium carbonate veining noted throughout. 12.6-15.0 Poorly Graded Sand with Gravel (SP): Brown, moist to saturated, medium dense, with fine to coarse-grained sand and fine to coarse-gravel. 5 June 2019 Page # 23 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection GEOTECHNICAL INVESTIGATION TEST PIT LOG Test Pit Log #: TP-3 Date Advanced: 22 May 2019 Logged by: Maren Tanberg, E.I.T., G.I.T. Excavated by: Xtreme Xcavation Location: See Site Map Plates Latitude: 43.615340 Longitude: -116.432756 Depth to Water Table: 13.9 Feet bgs Total Depth: 14.6 Feet bgs Depth (Feet bgs) Field Description and USCS Soil and Sediment Classification Sample Type Sample Depth (Feet bgs) Qp Lab Test ID 0.0-2.0 Lean Clay (CL): Dark brown, slightly moist, medium stiff to very stiff. --Organics noted to 1.4 feet bgs. 1.0-2.0 2.0-5.5 Silty Sand (SM): Light brown, dry to slightly moist, stiff to very stiff. --Sand content increases with depth. --Calcium carbonate veining noted from 4.0 to 5.5 feet bgs. GS 3.0-3.5 2.5-4.0 A 5.5-10.4 Sandy Silt (ML): Red brown, dry, hard, with fine to coarse-grained sand. --Moderate to strong calcium carbonate cementation noted from 6.4 to 10.4 feet bgs. 10.4-14.6 Poorly Graded Sand with Gravel (SP): Brown, moist to saturated, medium dense, with fine to coarse-grained sand and fine to coarse-gravel. Lab Test ID M LL PI Sieve Analysis (% passing) - % - - #4 #10 #40 #100 #200 A 23.2 NP NP 100 99 95 61 47.0 5 June 2019 Page # 24 of 26 b190906g_geotech Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections 2791 S Victory View Way Boise, ID 83709 (208) 376-4748 Fax (208) 322-6515 www.mti-id.com mti@mti-id.com Copyright © 2019 Materials Testing & Inspection AASHTO PAVEMENT THICKNESS DESIGN PROCEDURES Pavement Section Design Location:Proposed 4-Lot Subdivision, Residential Roadway Average Daily Traffic Count:200 All Lanes & Both Directions Design Life:20 Years Percent of Traffic in Design Lane:50% T erminal Seviceability Index (Pt):2.5 Level of Reliability:95 Subgrade CBR Value:4 Subgrade Mr:6,000 Calculation of Design-18 kip ESALs Daily Growth Load Design Traffic Rate Factors ESALs Passenger Cars:69 2.0%0.0008 490 Buses:0 2.0%0.6806 0 Panel & Pickup Trucks:30 2.0%0.0122 3,246 2-Axle, 6-Tire Trucks:0 2.0%0.1890 0 Emergency Vehicle:1.0 2.0%4.4800 39,731 Dump Trucks:0 2.0%3.6300 0 Tractor Semi Trailer Trucks:0 2.0%2.3719 0 Double Trailer Trucks 0 2.0%2.3187 0 Heavy Tractor Trailer Combo Trucks:0 2.0%2.9760 0 Average Daily Traffic in Design Lane:100 Total Design Life 18-kip ESALs:43,466 Actual Log (ESALs):4.638 T rial SN:2.40 Trial Log (ESALs):4.643 Pavement Section Design SN:2.41 Design Depth Structural Drainage Inches Coefficient Coefficient Asphaltic Concrete:2.50 0.42 n/a Asphalt-Treated Base:0.00 0.25 n/a Cement-T reated Base:0.00 0.17 n/a Crushed Aggregate Base:4.00 0.14 1.0 Subbase:8.00 0.10 1.0 Special Aggregate Subgrade:0.00 0.09 0.9