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GEOTECHNICAL REPORT - 22-00284 - Teton River Lofts - 24 Units - Bldg 3
GEOTECHNICAL INVESTIGATION TETON RIVER LOFTS 320 East 7th North Rexburg, ID PREPARED FOR: Ms. Shalynn Lister Leatham Development PO Box 429 Rexburg, ID 83440 PREPARED BY: Atlas Technical Consultants, LLC 1778 East Precision Drive Idaho Falls, ID 83401 February 21, 2022 E220171g Page | 1 1778 East Precision Drive Idaho Falls, ID 83401 (208) 529-8242 | oneatlas.com February 21, 2022 Atlas No. E220171g Ms. Shalynn Lister Leatham Development PO Box 429 Rexburg, ID 83440 Subject: Geotechnical Investigation Teton River Lofts 320 East 7th North Rexburg, ID Dear Ms. Lister: In compliance with your instructions, Atlas has conducted a soils exploration and foundation evaluation for the above referenced development. Fieldwork for this investigation was conducted on February 1, 2022. Data have been analyzed to evaluate pertinent geotechnical conditions. Results of this investigation, together with our recommendations, are to be found in the following report. We have provided a PDF copy for your review and distribution. Often, questions arise concerning soil conditions because of design and construction details that occur on a project. Atlas would be pleased to continue our role as geotechnical engineers during project implementation. If you have any questions, please call us at (208) 529-8242. Respectfully submitted, Ethan Salove, PE Elizabeth Brown, PE Geotechnical Engineer Geotechnical Services Manager Distribution: Bron Leatham, Leatham Development (PDF Copy). Atlas No. E220171g Page | i Copyright © 2022 Atlas Technical Consultants CONTENTS 1. INTRODUCTION ................................................................................................................. 1 1.1 Project Description ..................................................................................................... 1 1.2 Authorization .............................................................................................................. 1 1.3 Scope of Investigation ................................................................................................ 1 2. SITE DESCRIPTION ........................................................................................................... 2 2.1 Site Access ................................................................................................................ 2 2.2 Regional Geology ....................................................................................................... 2 2.3 General Site Characteristics ....................................................................................... 2 2.4 Regional Site Climatology and Geochemistry ............................................................. 3 3. SEISMIC SITE EVALUATION ............................................................................................ 3 3.1 Geoseismic Setting .................................................................................................... 3 3.2 Seismic Design Parameter Values ............................................................................. 3 4. SOILS EXPLORATION ....................................................................................................... 4 4.1 Exploration and Sampling Procedures........................................................................ 4 4.2 Laboratory Testing Program ....................................................................................... 4 4.3 Soil and Sediment Profile ........................................................................................... 5 4.4 Volatile Organic Scan ................................................................................................. 5 5. SITE HYDROLOGY ............................................................................................................ 5 5.1 Groundwater .............................................................................................................. 5 5.2 Soil Infiltration Rates .................................................................................................. 6 6. FOUNDATION AND SLAB DISCUSSION AND RECOMMENDATIONS............................ 7 6.1 Foundation Design Recommendations ....................................................................... 7 6.2 Floor Slab-on-Grade ................................................................................................... 8 7. PAVEMENT DISCUSSION AND RECOMMENDATIONS ................................................... 9 7.1 Flexible Pavement Sections ....................................................................................... 9 7.2 Pavement Subgrade Preparation ..............................................................................10 7.3 Common Pavement Section Construction Issues ......................................................10 8. CONSTRUCTION CONSIDERATIONS .............................................................................10 8.1 Earthwork ..................................................................................................................11 8.2 Dry Weather ..............................................................................................................11 8.3 Wet Weather .............................................................................................................12 8.4 Soft Subgrade Soils...................................................................................................12 8.5 Frozen Subgrade Soils ..............................................................................................12 8.6 Structural Fill .............................................................................................................13 8.7 Backfill of Walls .........................................................................................................14 8.8 Excavations ...............................................................................................................14 8.9 Groundwater Control .................................................................................................15 Atlas No. E220171g Page | ii Copyright © 2022 Atlas Technical Consultants 9. GENERAL COMMENTS ....................................................................................................15 10. REFERENCES.................................................................................................................16 TABLES Table 1 – Seismic Design Values ................................................................................................ 4 Table 2 – Groundwater Data ....................................................................................................... 6 Table 3 – Soil Bearing Capacity .................................................................................................. 7 Table 4 – AASHTO Flexible Pavement Specifications................................................................. 9 APPENDICES Warranty and Limiting Conditions Vicinity Map Site Map Geotechnical Investigation Test Pit Log Geotechnical General Notes AASHTO Pavement Design Important Information About This Geotechnical Engineering Report Atlas No. E220171g Page | 1 Copyright © 2022 Atlas Technical Consultants 1. INTRODUCTION This report presents results of a geotechnical investigation and analysis in support of data utilized in design of structures as defined in the 2018 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. 1.1 Project Description The proposed development is in the northeastern portion of the City of Rexburg, Madison County, ID, and occupies a portion of the NW¼NW¼ of Section 20, Township 6 North, Range 40 East, Boise Meridian. This project will consist of construction of an unknown number of 3-story condominium structures to be developed on approximately 10.05 acres. Total settlements are limited to 1 inch. Loads of up to 5,000 pounds per lineal foot for wall footings, and column loads of up to 100,000 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. Atlas has not been informed of the proposed grading plan. 1.2 Authorization Authorization to perform this exploration and analysis was given in the form of a written authorization to proceed from Bron Leatham of Leatham Development to Clinton Wyllie of Atlas Technical Consultants (Atlas), on January 20, 2022. Said authorization is subject to terms, conditions, and limitations described in the Professional Services Contract entered into between Leatham Development and Atlas. Our scope of services for the proposed development has been provided in our proposal dated January 18, 2022 and repeated below. 1.3 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. The scope of work did not include design recommendations specific to individual structures. Atlas No. E220171g Page | 2 Copyright © 2022 Atlas Technical Consultants 2. SITE DESCRIPTION 2.1 Site Access Access to the site may be gained via Highway 20 to the Rexburg Main Street exit. Proceed east on Main Street approximately 1.7 miles to its intersection with North 2nd East. From this intersection, proceed north on North 2nd East 1.0 mile to East 7th North. Continue east on East 7th North for 0.25 mile to its intersection with Lorene Street. The site occupies the southwest corner of this intersection. The location is depicted on site maps included in the Appendix. 2.2 Regional Geology The site is located in the city of Rexburg in an area known as the Eastern Snake River Plain. Sediments deposited here are derived from Middle Pleistocene Granites and Upper Pleistocene Rhyolitic Volcanics (Alt and Hyndman, 1998), which outcrop immediately south-southeast of Rexburg, and compose the bedrock throughout the region. Sediments were deposited during the Pleistocene Period (0.6 to 1.8 million years ago) and have been mapped as outwash fanglomerate and terrace gravels, and consist of medium to coarse-grained river deposits (Bond, 1978). These sediments were deposited in a variety of geologic environments, which existed along the northeastern margin of the ancestral Eastern Snake River Plain. Since their deposition, these formations have gradually been eroded away from the Rexburg Foothills. 2.3 General Site Characteristics The site to be developed is approximately 10.05 acres in size and consists of relatively flat and level undeveloped agricultural land. Vegetation on the site consists primarily of agricultural crop remnants. To the west of the site are existing commercial properties. To the north and east of the project site, existing residential developments are in place. To the south of the site, further undeveloped land is present. The northern property boundary is bordered by East 7th North. The southern and eastern property boundaries are bordered by Lorene Street. Regional drainage is south and west toward the South Teton 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 drainage from off-site sources. Stormwater drainage collection and retention systems are not in place on the project site and do not currently exist within the vicinity of the project site. However, some of the adjacent roadways have curb and gutter installed. Atlas No. E220171g Page | 3 Copyright © 2022 Atlas Technical Consultants 2.4 Regional Site Climatology and Geochemistry According to the Western Regional Climate Center, the average precipitation for the Southeastern Snake River Plain, Madison County is on the order of 13 inches per year, with an annual snowfall of approximately 49 inches. The monthly mean daily temperatures range from 13°F to 83°F, with daily extremes ranging from -25°F to 111°F. Winds are generally from the southwest with an annual average wind speed of approximately 12 miles per hour. 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 5.6 to 7.0 (USGS). 3. SEISMIC SITE EVALUATION 3.1 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 7-16. 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. 3.2 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 0.233 is appropriate for the project site based on a Site Class D. 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 2018 IBC. Design spectral response acceleration parameters as presented in the 2018 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). Atlas No. E220171g Page | 4 Copyright © 2022 Atlas Technical Consultants Table 1 – Seismic Design Values Seismic Design Parameter Design Value Site Class D “Stiff Soil” Ss 0.370 (g) S1 0.143 (g) Fa 1.504 Fv 2.313 SMS 0.556 SM1 0.332 SDS 0.371 SD1 0.221 4. SOILS EXPLORATION 4.1 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 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. Atlas recommends that these logs not be used to estimate fill material quantities. 4.2 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 in the Appendix. The laboratory testing program for this report included: Atterberg Limits Testing – ASTM D4318 and Grain Size Analysis – ASTM C117/C136. Atlas No. E220171g Page | 5 Copyright © 2022 Atlas Technical Consultants 4.3 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. Sandy lean clay soils were encountered at ground surface. These soils were brown, dry, very stiff to hard, with fine-grained sand. Many of these firmer soil horizons contained some degree of calcium carbonate cementation (hardpan). Organic materials and disturbed materials as a result of plowing activities usually reach a depth of 1.5 feet. At depth, poorly graded gravel with sand sediments were exposed. Poorly graded gravels were light brown, dry, and medium dense to dense. Fine to coarse-grained sand, fine to coarse gravels, and 4-inch minus cobbles were noted throughout. 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. 4.4 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. No groundwater was encountered. 5. 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. 5.1 Groundwater During this field investigation, groundwater was not encountered in test pits advanced to a maximum depth of 14.0 feet bgs. Soil moistures in the test pits were generally dry throughout. In the vicinity of the project site, groundwater levels are controlled in large part by the stage and flow of the South Fork of the Teton River. Maximum groundwater elevations likely occur during late spring to early summer runoff season. Atlas has previously performed 5 geotechnical investigations within 0.50 mile of the project site. Information from these investigations has been provided in the table below. Atlas No. E220171g Page | 6 Copyright © 2022 Atlas Technical Consultants Table 2 – Groundwater Data Date Approximate Distance from Site (mile) Direction from Site Groundwater Depth (feet bgs) December 2014 0.06 East Not Encountered to 14.0 January 2014 0.14 West Not Encountered to 13.0 October 2018 0.17 Southwest Not Encountered to 12.0 November 2019 0.38 Southeast Not Encountered to 11.7 August 2018 0.35 West 10.7 to 18.2 Furthermore, according to Idaho Department of Water Resources (IDWR) well data within approximately ½-mile of the project site, groundwater was measured at depths ranging between 10 and 20 feet bgs. Based on evidence of this investigation and background knowledge of the area, Atlas estimates groundwater depths to remain greater than approximately 10 feet bgs throughout the year. However, as the site is heavily influenced by the Teton River, flooding or near flooding conditions will result in temporarily higher groundwater elevations. 5.2 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, sandy lean clay soils will commonly exhibit infiltration rates of less than 2 inches per hour; though calcium carbonate cementation may reduce this value 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 se diments because of their free-draining nature. It is recommended that infiltration facilities constructed on the site be extended into native poorly graded gravel with sand sediments. Excavation depths of approximately 4 to 9 feet bgs should be anticipated to expose these poorly graded gravel with sand sediments. Because of the high soil permeability, ASTM C33 filter sand, or equivalent, should be incorporated into design of infiltration facilities. An infiltration rate of 8 inches per hour should be used in design. Actual infiltration rates should be confirmed at the time of construction. Atlas No. E220171g Page | 7 Copyright © 2022 Atlas Technical Consultants 6. FOUNDATION AND SLAB DISCUSSION AND RECOMMENDATIONS Various foundation types have been considered for support of the proposed structures. 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 structure 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, multiple structures are 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. 6.1 Foundation Design Recommendations Based on data obtained from the site and test results from various laboratory tests performed, Atlas recommends the following guidelines for the net allowable soil bearing capacity: Table 3 – Soil Bearing Capacity Footing Depth ASTM D1557 Subgrade Compaction Net Allowable Soil Bearing Capacity Footings must bear on competent, undisturbed, native sandy lean clay soils, poorly graded gravel sediments, or compacted structural fill. Existing organic materials and plow zone materials must be completely removed from below foundation elements.1 Excavation depths ranging from roughly 1 to 2 feet bgs should be anticipated to expose proper bearing soils.2 Not Required for Native Soil 95% for Structural Fill 2,000 lbs/ft2 Footings must bear on at least 12 inches of compacted structural fill placed on competent, undisturbed, native sandy lean clay soils or poorly graded gravel sediments. Existing organic materials and plow zone materials must be completely removed from below foundation elements.1 Excavation depths ranging from roughly 1 to 2 feet bgs should be anticipated to expose proper bearing soils.2 Not Required for Native Soil 95% for Structural Fill 2,500 lbs/ft2 1It will be required for Atlas 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. Atlas No. E220171g Page | 8 Copyright © 2022 Atlas Technical Consultants The following sliding frictional coefficient values should be used: 1) 0.35 for footings bearing on native sandy lean clay soils and 2) 0.45 for footings bearing on granular structural fill. A passive lateral earth pressure of 330 pounds per square foot per foot (psf/ft) should be used for sandy lean clay soils. For compacted sandy gravel fill, a passive lateral earth pressure of 496 psf/ft should be used. Footings should be proportioned to meet either the stated soil bearing capacity or the 2018 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, Atlas recommends continuous footings be suitably reinforced to make them as rigid as possible. For frost protection, the bottom of external footings should be 36 inches below finished grade. Based on the soil types encountered onsite, foundation drains are not needed. 6.2 Floor Slab-on-Grade Plow zones with organic materials were encountered in portions of the site. Atlas recommends that the organic materials be removed. If plow zones remain after organic materials have been removed, the exposed subgrade must be compacted to at least 95 percent of the maximum dry density as determined by ASTM D1557. Atlas personnel must be present during excavation to identify these materials. 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 should be provided below slabs-on-grade to provide drainage and a uniform and stable bearing surface. 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, Atlas can provide further consultation regarding installation. Atlas No. E220171g Page | 9 Copyright © 2022 Atlas Technical Consultants 7. PAVEMENT DISCUSSION AND RECOMMENDATIONS Atlas 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 sandy lean clay 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. 7.1 Flexible Pavement Sections The American Association of State Highway and Transportation Officials (AASHTO) design method has been used to calculate the following pavement sections. Calculation sheets provided in the Appendix indicate the soils constant, traffic loading, traffic projections, and material constants used to calculate the pavement sections. Atlas 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. Table 4 – AASHTO Flexible Pavement Specifications Pavement Section Component Driveways and Parking Light Duty Driveways and Parking Moderate Duty Asphaltic Concrete 2.5 Inches 3.0 Inches Crushed Aggregate Base 4.0 Inches 4.0 Inches Structural Subbase 10.0 Inches 10.0 Inches Compacted Subgrade See Pavement Subgrade Preparation Section See Pavement Subgrade Preparation Section 1It will be required for Atlas personnel to verify subgrade competency at the time of construction. • Asphaltic Concrete: Asphalt mix design shall meet the requirements of ISPWC, Section 810. 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. Atlas No. E220171g Page | 10 Copyright © 2022 Atlas Technical Consultants 7.2 Pavement Subgrade Preparation Plow zones with organic materials were encountered in portions of the site. Atlas recommends that the organic materials be removed. If plow zones remain after organic materials have been removed, the exposed subgrade must be compacted to at least 95 percent of the maximum dry density as determined by ASTM D698. Atlas personnel must be present during excavation to identify these materials. 7.3 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 Atlas 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. Atlas anticipated that pavement areas will be subjected to moderate traffic. Subgrade clayey soils 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 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. Atlas 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 (see Floor Slab-on-Grade section), and should be reinforced with welded wire fabric. Control joints must be on 12-foot centers or less. 8. CONSTRUCTION CONSIDERATIONS Recommendations in this report are based upon structural elements of the project being founded on competent, native sandy lean clay soils or compacted structural fill. Structural areas should be stripped to an elevation that exposes these soil types. Atlas No. E220171g Page | 11 Copyright © 2022 Atlas Technical Consultants 8.1 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 crop remnants 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 Atlas 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. Atlas 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. 8.2 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. Atlas No. E220171g Page | 12 Copyright © 2022 Atlas Technical Consultants 8.3 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. 8.4 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. • 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. Atlas is available to provide recommendations and guidelines at your request. 8.5 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. Atlas No. E220171g Page | 13 Copyright © 2022 Atlas Technical Consultants The onsite, shallow clayey 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. Atlas is available to provide further guidance/assistance upon request. 8.6 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. 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. Atlas No. E220171g Page | 14 Copyright © 2022 Atlas Technical Consultants 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. 8.7 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. 8.8 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. During the subsurface exploration, test pit sidewalls generally exhibited little indication of collapse; however, sloughing of native granular sediments from test pit sidewalls was observed. 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. Atlas No. E220171g Page | 15 Copyright © 2022 Atlas Technical Consultants 8.9 Groundwater Control Groundwater was not encountered during the investigation and is anticipated to be below the depth of most construction. Should the scope of the proposed project change, Atlas 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. 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. 9. 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 development, consultation with Atlas must be arranged as supplementary recommendations may be required. Suitability of subgrade soils and compaction of structural fill materials must be verified by Atlas 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. Atlas No. E220171g Page | 16 Copyright © 2022 Atlas Technical Consultants 10. REFERENCES Alt, D.D. and Hyndman, D.W., (1998). Roadside Geology of Idaho. Missoula, MT: Mountain Press Publishing Company. 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 (2021). ASCE 7 Hazards Tool: Web Interface [Online] Available: <https://asce7hazardtool.online/> (2021). American Society of Civil Engineers (ASCE) (2013). Minimum Design Loads for Buildings and Other Structures: ASCE/SEI 7-16. Reston, VA: ASCE. American Society for Testing and Materials (ASTM) (2017). 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) (2017). 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) (2017). 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. Bond, J.G., (1978). Geologic Map of Idaho: Idaho Department of Lands, Bureau of Mines and Geology with Contributions from United States Geological Survey, scale 1: 500,000. Moscow, ID. Desert Research Institute. Western Regional Climate Center. [Online] Available: <http://www.wrcc.dri.edu/> (2021). Idaho Department of Water Resources. [Online] Well Construction & Drilling, Find a Well Mapping Tool. <http://www.idwr.idaho.gov/wells/find-a-well.html> (2021). International Building Code Council (2018). International Building Code, 2018. Country Club Hills, IL: Author. Atlas No. E220171g Page | 17 Copyright © 2022 Atlas Technical Consultants Local Highway Technical Assistance Council (LHTAC) (2017). Idaho Standards for Public Works Construction, 2017. Boise, ID: Author. 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> (2021). Atlas No. E220171g Page | 18 Copyright © 2022 Atlas Technical Consultants WARRANTY AND LIMITING CONDITIONS Atlas 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 Atlas Technical Consultants (“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, Atlas 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 Atlas should be retained to observe actual subsurface conditions during earthwork construction activities to provide additional construction recommendations as needed. Atlas No. E220171g Page | 19 Copyright © 2022 Atlas Technical Consultants 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 Atlas 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, Atlas can provide, via a separate contract, those personnel who are trained to investigate and delineate soil and water contamination. V i c i n i t y M a p F i g u r e 1 M A P N O T E S : L E G E N D A p p r o x i m a t e S i t e L o c a t i o n D e l o r m e S t r e e t A t l a s N o t t o S c a l e S i t e L o c a t i o n T e t o n R i v e r L o f t s 3 2 0 E a s t 7 t h N o r t h R e x b u r g , I D M o d i f i e d f r o m D e L o r m e b y : C C W F e b r u a r y 9 , 2 0 2 2 D r a w i n g : E 2 2 0 1 7 1 g P h o n e : ( 2 0 8 ) 5 2 9 - 8 2 4 2 F a x : ( 2 0 8 ) 5 2 9 - 6 9 1 1 W e b : o n e a t l a s . c o m 1 2 3 0 N . S k y l i n e D r , S u i t e C I d a h o F a l l s , I D 8 3 4 0 2 N S i t e M a p N O T E S : L E G E N D F i g u r e 2 A p p r o x i m a t e S i t e B o u n d a r y A p p r o x i m a t e A t l a s T e s t P i t L o c a t i o n N o t t o S c a l e T e t o n R i v e r L o f t s 3 2 0 E a s t 7 t h N o r t h R e x b u r g , I D D r a w n b y : C C W F e b r u a r y 9 , 2 0 2 2 D r a w i n g : E 2 2 0 1 7 1 g P h o n e : ( 2 0 8 ) 2 3 3 - 9 5 0 0 F a x : ( 2 0 8 ) 2 3 3 - 9 9 0 0 W e b : o n e a t l a s . c o m 1 2 3 0 N . S k y l i n e D r , S u i t e C I d a h o F a l l s , I D 8 3 4 0 2 N T P - 2 T P - 3 T P - 5 T P - 4 T P - 1 E A S T 7 T H N O R T H LORENE STREET LORENE STREET Atlas No. E220171g Page | 22 Copyright © 2022 Atlas Technical Consultants GEOTECHNICAL INVESTIGATION TEST PIT LOG Test Pit Log #: TP-1 Date Advanced: February 1, 2022 Excavated by: Hill and Sons Excavating Logged by: Robert Jenson, EI Latitude: 43.840095 Longitude: -111.775596 Depth to Water Table: Not Encountered Total Depth: 14.0 feet bgs Depth (feet bgs) Field Description and USCS Soil and Sediment Classification Sample Type Sample Depth (feet bgs) Qp Lab Test ID 0.0-9.0 Sandy Lean Clay (CL): Brown, dry, very stiff , with fine-grained sand. --Frozen to 0.7 foot bgs --Organic material and plow zones noted to 1.5 feet bgs. 3.5-4.0 9.0-14.0 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. --Iron staining noted at 12.0 feet bgs. --Test pit side walls readily caved. Notes: See Site Map for test pit location. Atlas No. E220171g Page | 23 Copyright © 2022 Atlas Technical Consultants GEOTECHNICAL INVESTIGATION TEST PIT LOG Test Pit Log #: TP-2 Date Advanced: February 1, 2022 Excavated by: Hill and Sons Excavating Logged by: Robert Jenson, EI Latitude: 43.840122 Longitude: -111.773702 Depth to Water Table: Not Encountered Total Depth: 13.5 feet bgs Depth (feet bgs) Field Description and USCS Soil and Sediment Classification Sample Type Sample Depth (feet bgs) Qp Lab Test ID 0.0-4.0 Sandy Lean Clay (CL): Brown, dry, very stiff , with fine-grained sand. --Frozen to 0.7 foot bgs --Organic material and plow zones noted to 1.5 feet bgs. 3.5-4.0 4.0-13.5 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. --Test pit side walls readily caved. Notes: See Site Map for test pit location. Atlas No. E220171g Page | 24 Copyright © 2022 Atlas Technical Consultants GEOTECHNICAL INVESTIGATION TEST PIT LOG Test Pit Log #: TP-3 Date Advanced: February 1, 2022 Excavated by: Hill and Sons Excavating Logged by: Robert Jenson, EI Latitude: 43.839597 Longitude: -111.774624 Depth to Water Table: Not Encountered Total Depth: 12.4 feet bgs Depth (feet bgs) Field Description and USCS Soil and Sediment Classification Sample Type Sample Depth (feet bgs) Qp Lab Test ID 0.0-3.9 Sandy Lean Clay (CL): Brown, dry, very stiff, with fine-grained sand. --Frozen to 0.7 foot bgs --Organic material and plow zones noted to 1.5 feet bgs. --Weak calcium carbonate cementation noted from 1.5 to 3.9 feet bgs. GS 2.0-2.5 3.5-4.0 A 3.9-12.4 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. --Test pit side walls readily caved. Notes: See Site Map for test pit location. Lab Test ID Moisture (%) LL PI Sieve Analysis (% Passing) #4 #10 #40 #100 #200 A 13.7 37 18 100 99 92 78 67.5 Atlas No. E220171g Page | 25 Copyright © 2022 Atlas Technical Consultants GEOTECHNICAL INVESTIGATION TEST PIT LOG Test Pit Log #: TP-4 Date Advanced: February 1, 2022 Excavated by: Hill and Sons Excavating Logged by: Robert Jenson, EI Latitude: 43.838926 Longitude: -111.775571 Depth to Water Table: Not Encountered Total Depth: 12.9 feet bgs Depth (feet bgs) Field Description and USCS Soil and Sediment Classification Sample Type Sample Depth (feet bgs) Qp Lab Test ID 0.0-5.7 Sandy Lean Clay (CL): Brown, dry, very stiff , with fine-grained sand. --Frozen to 0.7 foot bgs --Organic material and plow zones noted to 1.5 feet bgs. --Weak calcium carbonate cementation noted from 1.5 to 5.7 feet bgs. 3.5-4.0 5.7-12.9 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. --Test pit side walls readily caved. Notes: See Site Map for test pit location. Atlas No. E220171g Page | 26 Copyright © 2022 Atlas Technical Consultants GEOTECHNICAL INVESTIGATION TEST PIT LOG Test Pit Log #: TP-5 Date Advanced: February 1, 2022 Excavated by: Hill and Sons Excavating Logged by: Robert Jenson, EI Latitude: 43.838921 Longitude: -111.773528 Depth to Water Table: Not Encountered Total Depth: 13.2 feet bgs Depth (feet bgs) Field Description and USCS Soil and Sediment Classification Sample Type Sample Depth (feet bgs) Qp Lab Test ID 0.0-5.4 Sandy Lean Clay (CL): Brown, dry, very stiff, with fine-grained sand. --Frozen to 1.0 foot bgs. --Organic material and plow zones noted to 1.5 feet bgs. --Weak calcium carbonate cementation noted from 1.5 to 5.4 feet bgs. GS 2.5-3.0 3.5-4.0 B 5.4-13.2 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. --Test pit side walls readily caved. Notes: See Site Map for test pit location. Lab Test ID Moisture (%) LL PI Sieve Analysis (% Passing) #4 #10 #40 #100 #200 B 7.7 30 13 100 99 95 79 60.7 Atlas No. E220171g Page | 27 Copyright © 2022 Atlas Technical Consultants GEOTECHNICAL GENERAL NOTES 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 Relative Density and Consistency Classification Moisture Content and Cementation Classification Coarse-Grained Soils SPT Blow Counts (N) Description Field Test Very Loose: < 4 Dry Absence of moisture, dry to touch Loose: 4-10 Slightly Moist Damp, but no visible moisture Medium Dense: 10-30 Moist Visible moisture Dense: 30-50 Wet Visible free water Very Dense: > 50 Saturated Soil is usually below water table Fine-Grained Soils SPT Blow Counts (N) Description Field Test Very Soft: < 2 Weak Crumbles or breaks with handling or slight finger pressure Soft: 2-4 Medium Stiff: 4-8 Moderate Crumbles or breaks with considerable finger pressure Stiff: 8-15 Very Stiff: 15-30 Strong Will not crumble or break with finger pressure Hard: > 30 Particle Size Acronym List Boulders: > 12 in. GS grab sample Cobbles: 12 to 3 in. LL Liquid Limit Gravel: 3 in. to 5 mm M moisture content Coarse-Grained Sand: 5 to 0.6 mm NP non-plastic Medium-Grained Sand: 0.6 to 0.2 mm PI Plasticity Index Fine-Grained Sand: 0.2 to 0.075 mm Qp penetrometer value, unconfined compressive strength, tsf Silts: 0.075 to 0.005 mm Clays: < 0.005 mm V vane value, ultimate shearing strength, tsf Atlas No. E220171g Page | 28 Copyright © 2022 Atlas Technical Consultants AASHTO PAVEMENT DESIGN Pavement Section Design Location:Teton River Lofts - Light Duty Average Daily Traffic Count:400 All Lanes & Both Directions Design Life:20 Years Percent of Traffic in Design Lane:50% Terminal 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:156 2.0%0.0008 1,107 Buses:0 2.0%0.6806 0 Panel & Pickup Trucks:40 2.0%0.0122 4,328 2-Axle, 6-Tire Trucks:3 2.0%0.1890 5,028 Emergency Vehicles: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:200 Total Design Life 18-kip ESALs:50,194 Actual Log (ESALs):4.701 Trial SN:2.50 Trial Log (ESALs):4.749 Pavement Section Design SN:2.61 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-Treated Base:0.00 0.17 n/a Crushed Aggregate Base:4.00 0.14 1.0 Subbase:10.00 0.10 1.0 Special Aggregate Subgrade:0.00 0.09 0.9 Atlas No. E220171g Page | 29 Copyright © 2022 Atlas Technical Consultants AASHTO PAVEMENT DESIGN Pavement Section Design Location:Teton River Lofts - Moderate Duty Average Daily Traffic Count:400 All Lanes & Both Directions Design Life:20 Years Percent of Traffic in Design Lane:50% Terminal 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:140 2.0%0.0008 993 Buses:3 2.0%0.6806 18,108 Panel & Pickup Trucks:46 2.0%0.0122 4,977 2-Axle, 6-Tire Trucks:10 2.0%0.1890 16,762 Emergency Vehicles: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:200 Total Design Life 18-kip ESALs:80,571 Actual Log (ESALs):4.906 Trial SN:2.80 Trial Log (ESALs):5.045 Pavement Section Design SN:2.82 Design Depth Structural Drainage Inches Coefficient Coefficient Asphaltic Concrete:3.00 0.42 n/a Asphalt-Treated Base:0.00 0.25 n/a Cement-Treated Base:0.00 0.17 n/a Crushed Aggregate Base:4.00 0.14 1.0 Subbase:10.00 0.10 1.0 Special Aggregate Subgrade:0.00 0.09 0.9 Geotechnical-Engineering Report Important Information about This Subsurface problems are a principal cause of construction delays, cost overruns, claims, and disputes. While you cannot eliminate all such risks, you can manage them. The following information is provided to help. The Geoprofessional Business Association (GBA) has prepared this advisory to help you – assumedly a client representative – interpret and apply this geotechnical-engineering report as effectively as SRVVLEOH,QWKDWZD\\RXFDQEHQH¿WIURPDORZHUHG exposure to problems associated with subsurface conditions at project sites and development of them that, for decades, have been a principal cause of construction delays, cost overruns, claims, and disputes. If you have questions or want more information about any of the issues discussed herein, contact your GBA-member geotechnical engineer. Active engagement in GBA exposes geotechnical engineers to a wide array of risk-confrontation WHFKQLTXHVWKDWFDQEHRIJHQXLQHEHQH¿WIRU everyone involved with a construction project. Understand the Geotechnical-Engineering Services Provided for this Report Geotechnical-engineering services typically include the planning, collection, interpretation, and analysis of exploratory data from widely spaced borings and/or test pits. Field data are combined with results from laboratory tests of soil and rock samples obtained from field exploration (if applicable), observations made during site reconnaissance, and historical information to form one or more models of the expected subsurface conditions beneath the site. Local geology and alterations of the site surface and subsurface by previous and proposed construction are also important considerations. Geotechnical engineers apply their engineering training, experience, and judgment to adapt the requirements of the prospective project to the subsurface model(s). Estimates are made of the subsurface conditions that will likely be exposed during construction as well as the expected performance of foundations and other structures being planned and/or affected by construction activities. The culmination of these geotechnical-engineering services is typically a geotechnical-engineering report providing the data obtained, a discussion of the subsurface model(s), the engineering and geologic engineering assessments and analyses made, and the recommendations developed to satisfy the given requirements of the project. These reports may be titled investigations, explorations, studies, assessments, or evaluations. Regardless of the title used, the geotechnical-engineering report is an engineering interpretation of the subsurface conditions within the context of the project and does not represent a close examination, systematic inquiry, or thorough investigation of all site and subsurface conditions. Geotechnical-Engineering Services are Performed IRU6SHFL¿F3XUSRVHV3HUVRQVDQG3URMHFWV DQG$W6SHFL¿F7LPHV Geotechnical engineers structure their services to meet the specific needs, goals, and risk management preferences of their clients. A geotechnical-engineering study conducted for a given civil engineer will not likely meet the needs of a civil-works constructor or even a different civil engineer. Because each geotechnical-engineering study is unique, each geotechnical-engineering report is unique, prepared solely for the client. Likewise, geotechnical-engineering services are performed for a specific project and purpose. For example, it is unlikely that a geotechnical- engineering study for a refrigerated warehouse will be the same as one prepared for a parking garage; and a few borings drilled during a preliminary study to evaluate site feasibility will not be adequate to develop geotechnical design recommendations for the project. Do not rely on this report if your geotechnical engineer prepared it: • for a different client; • for a different project or purpose; • for a different site (that may or may not include all or a portion of the original site); or • before important events occurred at the site or adjacent to it; e.g., man-made events like construction or environmental remediation, or natural events like floods, droughts, earthquakes, or groundwater fluctuations. Note, too, the reliability of a geotechnical-engineering report can be affected by the passage of time, because of factors like changed subsurface conditions; new or modified codes, standards, or regulations; or new techniques or tools. If you are the least bit uncertain about the continued reliability of this report, contact your geotechnical engineer before applying the recommendations in it. A minor amount of additional testing or analysis after the passage of time – if any is required at all – could prevent major problems. Read this Report in Full Costly problems have occurred because those relying on a geotechnical- engineering report did not read the report in its entirety. Do not rely on an executive summary. Do not read selective elements only. Read and refer to the report in full. You Need to Inform Your Geotechnical Engineer About Change Your geotechnical engineer considered unique, project-specific factors when developing the scope of study behind this report and developing the confirmation-dependent recommendations the report conveys. Typical changes that could erode the reliability of this report include those that affect: • the site’s size or shape; • the elevation, configuration, location, orientation, function or weight of the proposed structure and the desired performance criteria; • the composition of the design team; or • project ownership. As a general rule, always inform your geotechnical engineer of project or site changes – even minor ones – and request an assessment of their impact. The geotechnical engineer who prepared this report cannot accept responsibility or liability for problems that arise because the geotechnical engineer was not informed about developments the engineer otherwise would have considered. Most of the “Findings” Related in This Report Are Professional Opinions Before construction begins, geotechnical engineers explore a site’s subsurface using various sampling and testing procedures. Geotechnical engineers can observe actual subsurface conditions only at those specific locations where sampling and testing is performed. The data derived from that sampling and testing were reviewed by your geotechnical engineer, who then applied professional judgement to form opinions about subsurface conditions throughout the site. Actual sitewide-subsurface conditions may differ – maybe significantly – from those indicated in this report. Confront that risk by retaining your geotechnical engineer to serve on the design team through project completion to obtain informed guidance quickly, whenever needed. This Report’s Recommendations Are &RQ¿UPDWLRQ'HSHQGHQW The recommendations included in this report – including any options or alternatives – are confirmation-dependent. In other words, they are not final, because the geotechnical engineer who developed them relied heavily on judgement and opinion to do so. Your geotechnical engineer can finalize the recommendations only after observing actual subsurface conditions exposed during construction. If through observation your geotechnical engineer confirms that the conditions assumed to exist actually do exist, the recommendations can be relied upon, assuming no other changes have occurred. The geotechnical engineer who prepared this report cannot assume responsibility or liability for confirmation-dependent recommendations if you fail to retain that engineer to perform construction observation. This Report Could Be Misinterpreted Other design professionals’ misinterpretation of geotechnical- engineering reports has resulted in costly problems. Confront that risk by having your geotechnical engineer serve as a continuing member of the design team, to: • confer with other design-team members; • help develop specifications; • review pertinent elements of other design professionals’ plans and specifications; and • be available whenever geotechnical-engineering guidance is needed. You should also confront the risk of constructors misinterpreting this report. Do so by retaining your geotechnical engineer to participate in prebid and preconstruction conferences and to perform construction- phase observations. Give Constructors a Complete Report and Guidance Some owners and design professionals mistakenly believe they can shift unanticipated-subsurface-conditions liability to constructors by limiting the information they provide for bid preparation. To help prevent the costly, contentious problems this practice has caused, include the complete geotechnical-engineering report, along with any attachments or appendices, with your contract documents, but be certain to note conspicuously that you’ve included the material for information purposes only. To avoid misunderstanding, you may also want to note that “informational purposes” means constructors have no right to rely on the interpretations, opinions, conclusions, or recommendations in the report. Be certain that constructors know they may learn about specific project requirements, including options selected from the report, only from the design drawings and specifications. Remind constructors that they may perform their own studies if they want to, and be sure to allow enough time to permit them to do so. Only then might you be in a position to give constructors the information available to you, while requiring them to at least share some of the financial responsibilities stemming from unanticipated conditions. Conducting prebid and preconstruction conferences can also be valuable in this respect. Read Responsibility Provisions Closely Some client representatives, design professionals, and constructors do not realize that geotechnical engineering is far less exact than other engineering disciplines. This happens in part because soil and rock on project sites are typically heterogeneous and not manufactured materials with well-defined engineering properties like steel and concrete. That lack of understanding has nurtured unrealistic expectations that have resulted in disappointments, delays, cost overruns, claims, and disputes. To confront that risk, geotechnical engineers commonly include explanatory provisions in their reports. Sometimes labeled “limitations,” many of these provisions indicate where geotechnical engineers’ responsibilities begin and end, to help others recognize their own responsibilities and risks. Read these provisions closely. Ask questions. Your geotechnical engineer should respond fully and frankly. Geoenvironmental Concerns Are Not Covered The personnel, equipment, and techniques used to perform an environmental study – e.g., a “phase-one” or “phase-two” environmental site assessment – differ significantly from those used to perform a geotechnical-engineering study. For that reason, a geotechnical-engineering report does not usually provide environmental findings, conclusions, or recommendations; e.g., about the likelihood of encountering underground storage tanks or regulated contaminants. Unanticipated subsurface environmental problems have led to project failures. If you have not obtained your own environmental information about the project site, ask your geotechnical consultant for a recommendation on how to find environmental risk-management guidance. 2EWDLQ3URIHVVLRQDO$VVLVWDQFHWR'HDOZLWK 0RLVWXUH,Q¿OWUDWLRQDQG0ROG While your geotechnical engineer may have addressed groundwater, water infiltration, or similar issues in this report, the engineer’s services were not designed, conducted, or intended to prevent migration of moisture – including water vapor – from the soil through building slabs and walls and into the building interior, where it can cause mold growth and material-performance deficiencies. Accordingly, proper implementation of the geotechnical engineer’s recommendations will not of itself be sufficient to prevent moisture infiltration. Confront the risk of moisture infiltration by including building-envelope or mold specialists on the design team. Geotechnical engineers are not building-envelope or mold specialists. 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