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CC - Drainage Report
6/3/25 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 31 August 2016 Page # 2 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. TABLE OF CONTENTS INTRODUCTION ............................................................................................................................................................... 3 Project Description ................................................................................................................................................. 3 Authorization .......................................................................................................................................................... 3 Purpose ................................................................................................................................................................... 3 Scope of Investigation ............................................................................................................................................ 3 Warranty and Limiting Conditions ......................................................................................................................... 4 SITE DESCRIPTION .......................................................................................................................................................... 5 Site Access .............................................................................................................................................................. 5 Regional Geology ................................................................................................................................................... 5 General Site Characteristics .................................................................................................................................... 5 Regional Site Climatology and Geochemistry ........................................................................................................ 6 SOILS EXPLORATION ...................................................................................................................................................... 6 Exploration and Sampling Procedures .................................................................................................................... 6 Laboratory Testing Program ................................................................................................................................... 6 Soil and Sediment Profile ....................................................................................................................................... 7 Volatile Organic Scan ............................................................................................................................................. 7 SITE HYDROLOGY........................................................................................................................................................... 7 Groundwater ........................................................................................................................................................... 7 Soil Infiltration Rates .............................................................................................................................................. 8 PAVEMENT DISCUSSION AND RECOMMENDATIONS ........................................................................................................ 8 Recommended Pavement Sections ......................................................................................................................... 8 Flexible Pavement Section ..................................................................................................................................... 9 Common Pavement Section Construction Issues ................................................................................................... 9 CONSTRUCTION CONSIDERATIONS ............................................................................................................................... 10 Earthwork ............................................................................................................................................................. 10 Dry Weather ......................................................................................................................................................... 11 Wet Weather ......................................................................................................................................................... 11 Soft Subgrade Soils .............................................................................................................................................. 11 Frozen Subgrade Soils .......................................................................................................................................... 12 Structural Fill ........................................................................................................................................................ 12 Excavations ........................................................................................................................................................... 13 Groundwater Control ............................................................................................................................................ 13 GENERAL COMMENTS .................................................................................................................................................. 14 REFERENCES ................................................................................................................................................................. 15 APPENDICES ................................................................................................................................................................. 16 Acronym List ........................................................................................................................................................ 16 Geotechnical General Notes ................................................................................................................................. 17 Geotechnical Investigation Test Pit Log ............................................................................................................... 18 Gravel Equivalent Method Pavement Thickness Design Procedures ................................................................ 23 R-Value Laboratory Test Data .............................................................................................................................. 24 Plate 1: Vicinity Map ............................................................................................................................................ 25 Plate 2: Site Map ................................................................................................................................................... 26 31 August 2016 Page # 3 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. INTRODUCTION This report presents results of a geotechnical investigation and analysis in support of data utilized in design of pavements as defined in the Idaho Standard for Public Works Construction. 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 northwest of the City of Meridian, Ada County, ID, and occupies a portion of the SE¼SW¼ and SW¼SE¼ of Section 21, Township 4 North, Range 1 West, Boise Meridian. This project will consist of relocating a portion of Pollard Lane to align with Levi Lane on the south side of Chinden Boulevard. The proposed roadway section will be roughly 0.35 mile in length. At this time, barrow ditches are planned for the sides of the rural roadway. 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. Jon Wardle of Brighton Corporation to Monica Saculles of Materials Testing and Inspection, Inc. (MTI), on 10 August 2016. Said authorization is subject to terms, conditions, and limitations described in the Professional Services Contract entered into between Brighton Corporation and MTI. Our scope of services for the proposed development has been provided in our proposal dated 10 August 2016 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 site drainage designs Indicating issues pertaining to earthwork construction Preparing rural roadway pavement section design requirements 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 pavement materials. Our scope of work did not include foundation recommendations. 31 August 2016 Page # 4 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. 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 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 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. 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. 31 August 2016 Page # 5 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. 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 4.7 miles to its intersection with Highway 20/26. From this intersection, proceed west 1.7 miles to its intersection with Pollard Lane. The site occupies the northeast corner of this intersection. Presently the site exists as an agricultural field. 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 dimentary 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 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. General Site Characteristics This proposed development consists of an approximately 0.35 mile length of proposed roadway that is relatively flat and level terrain. Throughout the majority of the site, surficial soils consist of fine-grained silt soils. Vegetation primarily consists of onions at the time of the investigation. An irrigation ditch runs through the southern boundary of the project site. 31 August 2016 Page # 6 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. Regional drainage is north and west 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 and were not noted within the vicinity of the project site. 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. 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 pits were located in the field by a represen device was used to obtain longitude and latitude of test pit sites and are reportedly accurate to within ten 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. 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, Grain Size Analysis ASTM C117/C136, and Resistance Value (R-value) and Expansion Pressure of Compacted Soils Idaho T-8. 31 August 2016 Page # 7 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. 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. Surficial soils were predominately silt with sand and sandy silt soils. Silts with sand and sandy silts were dark brown to brown, dry to slightly moist, stiff to hard, and contained fine-grained sand. In test pit 5, silty sand with gravel fills were encountered at ground surface. Silty sand with gravel fills were light brown to brown, dry, medium dense to dense, and contained fine to coarse-grained sand. Plow zones/disturbed zones should be expected throughout the length of the roadway. Actual depths of these zones are unknown at this time since test pits were kept to the edges of the crops. Underlying the silts with sand and sandy silts were silty sand sediments. Silty sands were brown to light brown, dry to slightly moist, dense to very dense, and contained fine to medium-grained sand and varying degrees of calcium carbonate cementation and induration. At depth in all the test pits were poorly graded gravel with sand sediments. Poorly graded gravels were light brown, dry to saturated, medium dense to dense, and contained fine to coarse-grained sand, fine to coarse gravel, and 6-inch-minus cobbles. Competency of test pit walls 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. 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 pit 5 at a depth of 15.2 feet bgs. Soil moistures in the test pits were generally dry to slightly moist within surficial soils. Within the poorly graded gravels, soil moistures graded from dry to saturated as the water table was approached and penetrated. 31 August 2016 Page # 8 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. In the vicinity of the project site, groundwater levels are controlled in large part by residential and aggricultural irrigation activity and leakage from nearby irrigation ditches and canals. Maximum groundwater elevations likely occur during the later portion of the irrigation season. During previous investigations performed in September 2011 and May 2013 within approximately ½-mile to the east and northeast of the project site, no evidence of groundwater was noted within test pits advanced to depths as great as 13.5 to 15.0 feet bgs. Furthermore, according to United States Geological Survey (USGS) monitoring well data within approximately ½-mile of the project site, groundwater was measured at depths ranging between 20 and 30 feet bgs. Based on evidence of this investigation and background knowledge of the area, MTI estimates groundwater depths to remain greater than approximately 13 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, silt with sand 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 and silty sand sediments usually display rates of 4 to 8 inches per hour; though calcium carbonate cementation and induration may reduce these values to near zero. Poorly graded gravel sediments typically exhibit infiltration values in excess of 12 inches per hour. Infiltration testing is generally not required within these sediments because of their free-draining nature. PAVEMENT DISCUSSION AND RECOMMENDATIONS Recommended Pavement Sections As required by Ada County Highway District (ACHD), MTI has used a traffic index of 6 to determine the necessary pavement cross-section for the site. MTI has made assumptions for traffic loading variables based on the character of the proposed construction. The Client should review these assumptions to make sure they reflect intended use and loading of pavements both now and in the future. MTI collected a sample of near- surface soils for Resistance Value (R-value) testing representative of soils to depths of 2 feet below existing ground surface. This sample, consisting of sandy silt collected from test pit 4, yielded a R-value of 12. 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. Results of the test are graphically depicted in the Appendix. 31 August 2016 Page # 9 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. Flexible Pavement Section The Gravel Equivalent Method, as defined in Section 500 of the State of Idaho Department of Transportation (ITD) Materials Manual, was used to develop the pavement sections. ACHD parameters for traffic index and substitution ratios, which were obtained from the ACHD Policy Manual, were also used in the design. Calculation sheet provided in the Appendix indicate the soils constant, traffic loading, traffic projections, and material constants used to calculate the pavement sections. MTI recommends that materials used in the construction of asphaltic concrete pavements meet the 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. Gravel Equivalent Method Flexible Pavement Specifications Pavement Section Component1 Roadway Section Asphaltic Concrete 2.5 Inches Crushed Aggregate Base 4.0 Inches Structural Subbase 12.0 Inches Compacted Subgrade2 Not Required for Native Soils 12.0 Inches to 95% of ASTM D698 for Existing Fill Materials/Plow Zones 1It will be required for MTI personnel to verify subgrade competency 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. 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: Material complying with requirements for granular structural fill (uncrushed) as defined in ISPWC. 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. MTI does not anticipate pumping material to become evident during compaction, but subgrade clays and silts near and above optimum moisture contents may tend to pump. Pumping or soft areas must be removed and replaced with structural fill. 31 August 2016 Page # 10 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. Fill material and aggregates 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. MTI recommends that rigid concrete pavement be provided for heavy garbage receptacles. This will eliminate damage caused by the considerable loading transferred through the small steel wheels onto asphaltic concrete. Rigid concrete pavement should consist of Portland Cement Concrete Pavement (PCCP) generally adhering to ITD specifications for Urban Concrete. PCCP should be 6 inches thick on a 4-inch drainage fill course and should be reinforced with welded wire fabric. The 4-inch drainage 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. A moisture-retarder should be placed beneath floor slabs to minimize potential ground moisture effects on moisture-sensitive floor coverings. The granular mat should be compacted to no less than 95 percent of the maximum dry density as determined by ASTM D1557. Upon request, MTI can provide further consultation regarding installation. Control joints must be on 12-foot centers or less. CONSTRUCTION CONSIDERATIONS Recommendations in this report are based upon pavement sections of the project being founded on competent silt soils with sand soils, sandy 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. Agricultural crops with associated root systems were noted at the time of our investigation. It is recommended that organic or disturbed soils, if encountered, be removed to depths of 1 foot (minimum), and wasted or stockpiled for later use. Stripping depths should be adjusted in the field to assure that the entire root zone or disturbed zone (plow depths) 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. 31 August 2016 Page # 11 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. 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 parking and driveway areas, one in- place density test per lift for every 10,000 square feet is recommended. 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. 31 August 2016 Page # 12 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. 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 silt 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. 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. All fill materials must be monitored during placement and tested to confirm compaction requirements, outlined below, have been achieved. 31 August 2016 Page # 13 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. 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 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. 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 ted 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. 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. 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. 31 August 2016 Page # 14 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. GENERAL COMMENTS When plans and specifications are complete, or if significant changes are made in the character or location of the proposed roadway, consultation with MTI should 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. 31 August 2016 Page # 15 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. REFERENCES Ada County Highway District (ACHD) (2013). Ada County Highway District Policy Manual (October 2015). [Online] Available: <http://www.achdidaho.org/AboutACHD/PolicyManual.aspx> (2016). American Society for Testing and Materials (ASTM) (2013). Standard Test Method for Materials Finer than 75-m (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) (2013). Standard Test Methods for Resistance Value (R-Value) and Expansion Pressure of Compacted Soils: ASTM D2844. 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. Desert Research Institute. Western Regional Climate Center. [Online] Available: <http://www.wrcc.dri.edu/> (2016). Local Highway Technical Assistance Council (LHTAC) (2010). Idaho Standards for Public Works Construction, 2010. 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> (2016). U.S. Geological Survey (2016). National Water Information System: Web Interface. [Online] Available: <http://waterdata.usgs.gov/nwis> (2016). 31 August 2016 Page # 16 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. 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 IDEQ Idaho Department of Environmental Quality 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 31 August 2016 Page # 17 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. 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 31 August 2016 Page # 18 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. GEOTECHNICAL INVESTIGATION TEST PIT LOG Test Pit Log #: TP-1 Date Advanced: 19 Aug 2016 Logged by: Jacob Schlador, E.I.T. Excavated by: Location: See Site Map Plates Latitude: 43.6639557 Longitude: -116.4682846 Depth to Water Table: Not Encountered Total Depth: 11.2 Feet bgs Depth (Feet bgs) Field Description and USCS Soil and Sediment Classification Sample Type Sample Depth (Feet bgs) Qp Lab Test ID 0.0-1.9 Silt with Sand (ML): Dark brown, slightly moist, stiff to very stiff, with fine-grained sand. --Organics to a depth of 0.8 foot bgs. 1.5-2.5 1.9-3.7 Silty Sand (SM): Brown, dry to slightly moist, dense to very dense, with fine to medium-grained sand. --A thin layer of weak calcium carbonate cementation encountered at 2.7 feet bgs. 3.7-11.2 Poorly Graded Gravel with Sand (GP): Light brown, dry to slightly moist, medium dense to dense, with fine to coarse-grained sand, fine to coarse gravel, and 4-inch-minus cobbles. 31 August 2016 Page # 19 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. GEOTECHNICAL INVESTIGATION TEST PIT LOG Test Pit Log #: TP-2 Date Advanced: 19 Aug 2016 Logged by: Jacob Schlador, E.I.T. Excavated by: Location: See Site Map Plates Latitude: 43.6665344 Longitude: -116.4682312 Depth to Water Table: Not Encountered Total Depth: 15.0 Feet bgs Notes: Piezometer installed to 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 0.0-4.3 Silt with Sand (ML): Dark brown to brown, slightly moist, stiff to hard, with fine-grained sand. --Organics to a depth of 0.9 foot bgs. 2.0-4.5 4.3-11.1 Silty Sand (SM): Brown, dry to slightly moist, dense to very dense, with fine to medium-grained sand. --Moderate to strong induration encountered from 4.3 to 7.1 feet bgs. --Moderate calcium carbonate cementation encountered from 7.1 to 9.1 feet bgs. 11.1-15.0 Poorly Graded Gravel with Sand (GP): Light brown, dry to slightly moist, medium dense to dense, with fine to coarse-grained sand, fine to coarse gravel, and 6-inch-minus cobbles. 31 August 2016 Page # 20 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. GEOTECHNICAL INVESTIGATION TEST PIT LOG Test Pit Log #: TP-3 Date Advanced: 19 Aug 2016 Logged by: Jacob Schlador, E.I.T. Excavated by: Location: See Site Map Plates Latitude: 43.6664276 Longitude: -116.4586716 Depth to Water Table: Not Encountered Total Depth: 8.1 Feet bgs Depth (Feet bgs) Field Description and USCS Soil and Sediment Classification Sample Type Sample Depth (Feet bgs) Qp Lab Test ID 0.0-3.4 Silt with Sand (ML): Dark brown, dry to slightly moist, very stiff, with fine-grained sand. --No organics noted within the test pit. 2.5-3.75 3.4-6.2 Silty Sand (SM): Brown to light brown, dry to slightly moist, dense to very dense, with fine to medium-grained sand. --Weak to moderate calcium carbonate cementation from 3.6 to 4.1 feet bgs. 6.2-8.1 Poorly Graded Gravel with Sand (GP): Light brown, dry, medium dense to dense, with fine to coarse-grained sand, fine to coarse gravel, and 5- inch-minus cobbles. 31 August 2016 Page # 21 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. GEOTECHNICAL INVESTIGATION TEST PIT LOG Test Pit Log #: TP-4 Date Advanced: 19 Aug 2016 Logged by: Jacob Schlador, E.I.T. Excavated by: Location: See Site Map Plates Latitude: 43.6635551 Longitude: -116.4601364 Depth to Water Table: Not Encountered Total Depth: 7.9 Feet bgs Depth (Feet bgs) Field Description and USCS Soil and Sediment Classification Sample Type Sample Depth (Feet bgs) Qp Lab Test ID 0.0-3.7 Sandy Silt (ML): Dark brown to brown, dry to slightly moist, stiff to very stiff, with fine-grained sand. --Organics to a depth of 0.8 foot bgs. Bulk 0.5-1.0 1.25-3.0 A/ R-Value 3.7-6.1 Silty Sand (SM): Brown, dry, dense to very dense, with fine to medium-grained sand. --Moderate calcium carbonate cementation encountered from 5.1 to 5.4 feet bgs. 6.1-7.9 Poorly Graded Gravel with Sand (GP): Light brown, dry, medium dense to dense, with fine to coarse-grained sand, fine to coarse gravel, and 4- inch-minus cobbles. Lab Test ID M LL PI Sieve Analysis (% passing) - % - - #4 #10 #40 #100 #200 A 18.1 28 5 98 96 87 69 61.0 31 August 2016 Page # 22 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. GEOTECHNICAL INVESTIGATION TEST PIT LOG Test Pit Log #: TP-5 Date Advanced: 19 Aug 2016 Logged by: Jacob Schlador, E.I.T. Excavated by: Location: See Site Map Plates Latitude: 43.6633445 Longitude: -116.4601364 Depth to Water Table: 15.2 Feet bgs Total Depth: 15.8 Feet bgs Notes: Piezometer installed to 15.8 feet bgs. Depth (Feet bgs) Field Description and USCS Soil and Sediment Classification Sample Type Sample Depth (Feet bgs) Qp Lab Test ID 0.0-2.3 Silty Sand with Gravel Fill (SM-FILL): Light brown to brown, dry, medium dense to dense, with fine to coarse-grained sand and fine to coarse gravel. 2.3-15.8 Poorly Graded Gravel with Sand (GP): Light brown, dry to saturated, medium dense to dense, with fine to coarse-grained sand, fine to coarse gravel, and 4-inch-minus cobbles. 31 August 2016 Page # 23 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. GRAVEL EQUIVALENT METHOD PAVEMENT THICKNESS DESIGN PROCEDURES Pavement Section Design Location:Pollard Lane Realignment, Rural Road Average Daily Traffic Count:300 All Lanes & Both Directions Design Life:20 Years Traffic Index:6.00 Climate Factor:1 R-Value of Subgrade:12.00 Subgrade CBR Value:5 Subgrade Mr:7,500 R-Value of Aggregate Base:80 R-Value of Granular Borrow:60 Subgrade R-Value:12 Expansion Pressure of Subgrade:0.19 Unit Weight of Base Materials:130 Total Design Life 18 kip ESAL's:33,131 ASPHALTIC CONCRETE: Gravel Equivalent, Calculated:0.384 Thickness:0.196923077 Use =2.5 Inches Gravel Equivalent, ACTUAL:0.41 CRUSHED AGGREGATE BASE: Gravel Equivalent (Ballast):0.768 Thickness:0.329 Use =4 Inches Gravel Equivalent, ACTUAL:0.773 SUBBASE: Gravel Equivalent (Ballast):1.690 Thickness:0.917 Use =12 Inches Gravel Equivalent, ACTUAL:1.773 TOTAL Thickness:1.542 Thickness Required by Exp. Pressure:0.210 Design ACHD Depth Substitution Inches Ratios Asphaltic Concrete (at least 2.5):2.50 1.95 Asphalt Treated Base (at least 4.2):0.00 Cement Treated Base (at least 4.2):0.00 Crushed Aggregate Base (at least 4.2):4.00 1.10 Subbase (at least 4.2):12.00 1.00 31 August 2016 Page # 24 of 26 b161073g_geotech.docx 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 © 2016 Materials Testing & Inspection, Inc. R-VALUE LABORATORY TEST DATA Source and Description: TP-4, 0.5-1.0 Sandy Silt Date Obtained: August 19, 2016 Sample ID: 16-7545 Sampling and Preparation: ASTM D75: AASHTO T2: X ASTM D421: AASHTO T87: X Test Standard: ASTM D2844: AASHTO T190: Idaho T8: X Sample A B C Dry Density (lb/ft3) 106.3 104.1 101.7 Moisture Content (%) 17.7 19.5 20.1 Expansion Pressure (psi) 0.51 0.24 0.12 Exudation Pressure (psi) 416 247 134 R-Value 16 13 10 R-Value @ 200 psi Exudation Pressure = 12 4 March 2019 Page # 1 of 6 b161073g_addendum#1-revised.docx 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 Mr. Kameron Nauahi Brighton Corporation 12601 West Explore Drive, Suite 200 Boise, ID 83713 208-378-4000 Re: Addendum #1 Pavement Recommendations Pollard Lane Realignment Pollard Lane & Chinden Boulevard Meridian, ID Dear Mr. Wardle: This addendum report presents recommendations not requested at the time of the previously issued MTI Geotechnical Engineering Report (B161073g). Descriptions of general site characteristics and the proposed project are available in the previous report. Unless otherwise noted in this addendum, all initial recommendations, limitations, and warranties expressed in the previous report must be adhered to. Recommended Pavement Sections As required by Ada County Highway District (ACHD), MTI has used a traffic index of 6 for local streets and 8 for collector and commercial streets to determine the necessary pavement cross-section for the site. MTI has made assumptions for traffic loading variables based on the character of the proposed construction. The Client should review these assumptions to make sure they reflect intended use and loading of pavements both now and in the future. MTI collected a sample of near-surface soils for Resistance Value (R-value) testing representative of soils to depths of 2 feet below existing ground surface. This sample, consisting of sandy silt collected from test pit 4, yielded a R-value of 12. 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 of the original report. Results of the test are graphically depicted in the Enclosures section. Flexible Pavement Sections The Gravel Equivalent Method, as defined in Section 500 of the State of Idaho Department of Transportation (ITD) Materials Manual, was used to develop the pavement sections. ACHD parameters for traffic index and substitution ratios, which were obtained from the ACHD Policy Manual, were also used in the design. Calculation sheets provided in the Enclosures section indicate the soils constant, traffic loading, traffic projections, and material constants used to calculate the pavement sections. MTI recommends that materials used in the construction of asphaltic concrete pavements meet the 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 Construction Considerations section of the original report. 4 March 2019 Page # 2 of 6 b161073g_addendum#1-revised.docx 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 Gravel Equivalent Method Flexible Pavement Specifications Pavement Section Component1 Local Roadway Section Collectors and Commercial Roadway Sections Asphaltic Concrete 2.5 Inches 3.25 Inches Crushed Aggregate Base 4.0 Inches 4.0 Inches Structural Subbase 12.0 Inches 17.0 Inches Compacted Subgrade Not Required for Native Soils 12.0 Inches to 95% of ASTM D698 for Existing Fill Materials/Plow Zones Not Required for Native Soils 12.0 Inches to 95% of ASTM D698 for Existing Fill Materials/Plow Zones 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: Material complying with requirements for granular structural fill (uncrushed) as defined in ISPWC. Common Pavement Section Construction Issues The subgrade upon which above pavement sections are to be constructed must be properly stripped, compacted (if indicated), 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. MTI does not anticipate pumping material to become evident during compaction, but subgrade clays and silts near and above optimum moisture contents may tend to pump. Pumping or soft areas must be removed and replaced with structural fill. Fill material and aggregates 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. 4 March 2019 Page # 4 of 6 b161073g_addendum#1-revised.docx 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 GRAVEL EQUIVALENT METHOD PAVEMENT THICKNESS DESIGN PROCEDURES Pavement Section Design Location:Pollard Subdivision, Local Roadways Average Daily Traffic Count:300 All Lanes & Both Directions Design Life:20 Years Traffic Index:6.00 Climate Factor:1 R-Value of Subgrade:12.00 Subgrade CBR Value:5 Subgrade Mr:7,500 R-Value of Aggregate Base:80 R-Value of Granular Borrow:60 Subgrade R-Value:12 Expansion Pressure of Subgrade:0.19 Unit Weight of Base Materials:130 Total Design Life 18 kip ESAL's:33,131 ASPHALTIC CONCRETE: Gravel Equivalent, Calculated:0.384 Thickness:0.196923077 Use = 2.5 Inches Gravel Equivalent, ACTUAL:0.41 CRUSHED AGGREGATE BASE: Gravel Equivalent (Ballast):0.768 Thickness:0.329 Use = 4 Inches Gravel Equivalent, ACTUAL:0.773 SUBBASE: Gravel Equivalent (Ballast):1.690 Thickness:0.917 Use = 12 Inches Gravel Equivalent, ACTUAL:1.773 TOTAL Thickness:1.542 Thickness Required by Exp. Pressure:0.210 Design ACHD Depth Substitution Inches Ratios Asphaltic Concrete (at least 2.5): 2.50 1.95 Asphalt Treated Base (at least 4.2): 0.00 Cement Treated Base (at least 4.2): 0.00 Crushed Aggregate Base (at least 4.2): 4.00 1.10 Subbase (at least 4.2): 12.00 1.00 4 March 2019 Page # 5 of 6 b161073g_addendum#1-revised.docx 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 GRAVEL EQUIVALENT METHOD PAVEMENT THICKNESS DESIGN PROCEDURES Pavement Section Design Location:Pollard Subdivision, Commercial and Collector Streets Average Daily Traffic Count:700 All Lanes & Both Directions Design Life:20 Years Traffic Index:8.00 Climate Factor:1 R-Value of Subgrade:12.00 Subgrade CBR Value:5 Subgrade Mr:7,500 R-Value of Aggregate Base:80 R-Value of Granular Borrow:60 Subgrade R-Value:12 Expansion Pressure of Subgrade:0.19 Unit Weight of Base Materials:130 Total Design Life 18 kip ESAL's:371,659 ASPHALTIC CONCRETE: Gravel Equivalent, Calculated:0.512 Thickness:0.262564103 Use =3.25 Inches Gravel Equivalent, ACTUAL:0.53 CRUSHED AGGREGATE BASE: Gravel Equivalent (Ballast):1.024 Thickness:0.451 Use =4 Inches Gravel Equivalent, ACTUAL:0.895 SUBBASE: Gravel Equivalent (Ballast):2.253 Thickness:1.358 Use =17 Inches Gravel Equivalent, ACTUAL:2.311 TOTAL Thickness:2.021 Thickness Required by Exp. Pressure:0.210 Design ACHD Depth Substitution Inches Ratios Asphaltic Concrete (at least 2.5):3.25 1.95 Asphalt Treated Base (at least 4.2):0.00 Cement Treated Base (at least 4.2):0.00 Crushed Aggregate Base (at least 4.2):4.00 1.10 Subbase (at least 4.2):17.00 1.00 4 March 2019 Page # 6 of 6 b161073g_addendum#1-revised.docx 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 R-VALUE LABORATORY TEST DATA Source and Description: TP-4, 0.5-1.0 Sandy Silt Date Obtained: August 19, 2016 Sample ID: 16-7545 Sampling and Preparation: ASTM D75: AASHTO T2: X ASTM D421: AASHTO T87: X Test Standard: ASTM D2844: AASHTO T190: Idaho T8: X Sample A B C Dry Density (lb/ft3) 106.3 104.1 101.7 Moisture Content (%) 17.7 19.5 20.1 Expansion Pressure (psi) 0.51 0.24 0.12 Exudation Pressure (psi) 416 247 134 R-Value 16 13 10 R-Value @ 200 psi Exudation Pressure = 12