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Home My WebLink About07 Geotechnical Report for Headwaters Academy 2020_01_14 GEOTECHNICAL REPORT FOR: Headwaters Academy Bozeman, Montana January 2020 Project 19-024 Civil Engineering ● Geotechnical Engineering ● Land Surveying ● Construction Services ALLIED ENGINEERING 32 Discovery Dr. Bozeman, MT 59718 Ph: (406) 582-0221 www.alliedengineering.com January 14, 2020 Headwaters Academy, Inc. c/o Kira Ogle Legends Studio 3805 Valley Commons Drive, Suite 11 Bozeman, MT 59718 email: kira@legendsstudio.com Re: Geotechnical Report for Headwaters Academy - Bozeman, Montana Dear Ms. Ogle: Enclosed please find an electronic PDF of the geotechnical report for the above referenced project. Hard copies of the report can be provided at your request. As per the scope of work, this report presents Allied Engineering’s geotechnical assessment of the project site and provides recommendations pertaining to site design and construction, earthwork, foundations, slabs, walls, fill materials, asphalt pavement, and surface and subsurface drainage. This report was prepared for use by all associated parties during the planning, design, and construction phases of this site development project. It is important that all Contractors involved with the site grading, foundation earthwork, underground utility installation, and road/parking lot construction are provided with copies of the report, such that they are informed of the site conditions and the construction recommendations. If you have any questions regarding this report, please call. Thank you. Sincerely, Allied Engineering Services, Inc. Craig R. Madson, PE Principal Geotechnical Engineer enc: Final Geotechnical Report The Headwaters Academy, Inc Headwaters Academy Geotechnical Report January 14, 2020 Bozeman, Montana Allied Engineering Services, Inc. ● 32 Discovery Drive. Bozeman, Montana 59718 ● Ph: (406) 582-0221 Page 1 TABLE OF CONTENTS INTRODUCTION ............................................................................................................................... 3 DESCRIPTION OF THE PROPERTY .................................................................................................... 3 SCOPE OF WORK ............................................................................................................................. 3 PROPOSED IMPROVEMENTS .......................................................................................................... 4 EXPLORATIONS AND SUBSURFACE CONDITIONS ........................................................................... 4 Subsurface Explorations .............................................................................................................. 4 Subsurface Conditions ................................................................................................................. 4 Groundwater Conditions ............................................................................................................. 5 FOUNDATION, SLAB, AND DRAINAGE RECOMMENDATIONS......................................................... 5 Seismic Design Factors ................................................................................................................ 5 Foundation Design ...................................................................................................................... 5 Lateral Earth Pressures................................................................................................................ 6 Foundation Wall Backfill.............................................................................................................. 7 Interior Concrete Slabs ................................................................................................................ 7 Subsurface Drainage and Damp-Proofing ................................................................................... 7 Vapor Barrier Under Interior Concrete Slab ............................................................................... 7 Exterior Concrete Slabs ............................................................................................................... 8 Surface Drainage Recommendations .......................................................................................... 8 FOUNDATION-RELATED FILL MATERIAL RECOMMENDATIONS ..................................................... 8 Excavated Foundation Soils ......................................................................................................... 9 Sandy (pitrun) Gravel .................................................................................................................. 9 Crushed (road mix) Gravel .......................................................................................................... 9 Clean Crushed Rock ..................................................................................................................... 9 FILL PLACEMENT AND COMPACTION ........................................................................................... 10 ASPHALT PAVEMENT RECOMMENDATIONS ................................................................................ 10 Pavement Section Design .......................................................................................................... 10 Pavement Section Materials, Placement, and Compaction ...................................................... 11 The Headwaters Academy, Inc Headwaters Academy Geotechnical Report January 14, 2020 Bozeman, Montana Allied Engineering Services, Inc. ● 32 Discovery Drive. Bozeman, Montana 59718 ● Ph: (406) 582-0221 Page 2 UNDERGROUND UTILITY RECOMMENDATIONS ........................................................................... 12 Foundation Support of Utility Lines .......................................................................................... 12 Trench Backfill ........................................................................................................................... 12 STORM DRAINAGE PONDS ............................................................................................................ 12 CONSTRUCTION RECOMMENDATIONS ........................................................................................ 12 COLD/WINTER WEATHER CONSTRUCTION .................................................................................. 12 AESI INVOLVEMENT DURING DESIGN AND CONSTRUCTION ....................................................... 13 LIMITATIONS ................................................................................................................................. 13 REFERENCES .................................................................................................................................. 14 SUPPLEMENTAL INFORMATION o List of Tables • Table 1 – Compaction Recommendations (Application vs. Percent Compaction) • Table 2 – Pavement Section Components and Required Compacted Thickness o List of Figures • Figure 1 – Vicinity Map • Figure 2 – Quadrangle Map • Figure 3 – Test Pit Location Map • Figure 4 – Geology Map o List of Appendices • Appendix A – Test Pit Logs • Appendix B – Laboratory Testing Results • Appendix C – Limitations of Your Geotechnical Report The Headwaters Academy, Inc Headwaters Academy Geotechnical Report January 14, 2020 Bozeman, Montana Allied Engineering Services, Inc. ● 32 Discovery Drive. Bozeman, Montana 59718 ● Ph: (406) 582-0221 Page 3 INTRODUCTION This report and attachments provide geotechnical recommendations for the proposed classroom building at Headwaters Academy in Bozeman, Montana. The information contained herein is based on an investigation of the property’s topographical and subsurface conditions, a review of geologic maps and literature for the project area, and experience with similar developments in the area. The purpose of this report is to provide a description of the site’s soil and groundwater conditions as well as recommendations for the design and construction of the proposed development. DESCRIPTION OF THE PROPERTY The 3.021-acre property is legally described in Warranty Deed #2643833, and is located in the Southeast One-Quarter of Section 1, Township 2 South, Range 5 East, Principal Meridian Montana, City of Bozeman, Gallatin County, Montana. See Figures 1 and 2 for site location maps. The property slopes gently to the north and consists of an existing paved driveway, house, greenhouse, cabin, garage, and sidewalks. There are several stands of bushes and trees around the property, a pond on the north side of the lot, and a large, maintained lawn. The western property line is neighbored by Mandeville Creek (and associated wetland grasses and plants) which flows in a northerly direction. The site sets atop alluvial deposits of sand and gravel overlain by fine-grained flood deposits of silt and clay. Groundwater was not encountered during the subsurface investigation but signs of potential high groundwater (increased moisture with depth) were observed. For this reason, a groundwater monitor was placed on the property for periodic monitoring. SCOPE OF WORK The Scope of Services for this project included: • Excavation of three test pits within the proposed development site. The location of each test pit is shown in Figure 3. • Installation of one groundwater monitor. • Laboratory testing of select samples from the test pits. • Providing allowable bearing capacity criteria. • Surface and subsurface drainage recommendations. • Backfill material and compaction recommendations. • Asphalt pavement section materials and design thickness. • Site earthwork and construction recommendations. The Headwaters Academy, Inc Headwaters Academy Geotechnical Report January 14, 2020 Bozeman, Montana Allied Engineering Services, Inc. ● 32 Discovery Drive. Bozeman, Montana 59718 ● Ph: (406) 582-0221 Page 4 PROPOSED IMPROVEMENTS The proposed improvements include removing the existing greenhouse, cabin, and portion of the garage and constructing a single-story classroom building. Based on information provided by the architect, the foundation system will be a slab-on-grade. Recommendations in this report are based on plans for a slab-on-grade foundation. Additional site improvements will include parking/access roads, storm detention pond, and underground utilities. EXPLORATIONS AND SUBSURFACE CONDITIONS Subsurface Explorations Soil investigations were conducted on December 19, 2019 under the direction of Erik Schnaderbeck, a Geotechnical Engineer with Allied Engineering Services, Inc. (AESI). Three test pits were dug using a Hitachi 35U mini-excavator provided and operated by Townsend Excavation. The approximate location of the test pits is shown on the base map (Figure 3). Test pit logs from the site investigation are provided in the attached Appendix A. During the explorations, soil and groundwater conditions were characterized, measured, and logged. The relative densities of the exposed soils were estimated based on the ease or difficulty of digging, probing of the test pit walls, pocket penetrometer readings, and overall stability of the completed excavations. The logs provide assorted field information, such as soil depths and descriptions, groundwater conditions, relative density data, and a sketch of the soil stratigraphy. Please be aware that the detail provided in the logs cannot be summarized in a paragraph; therefore, it is important to review the logs in conjunction with this report. Select soil samples were brought back to the laboratory for further testing and classification. Laboratory testing results are provided in Appendix B. Subsurface Conditions Soil conditions were similar in all three test pits. The upper 1.25 to 1.5 feet consisted of organic topsoil that was soft, moist, and predominantly silty in nature. The topsoil layer was underlain by fine-grained deposits to a depth of four to five feet below the ground surface. The fine-grained deposits were classified as a stiff to very stiff; slightly moist to moist; sandy silt/clay. The fine- grain deposits set atop alluvial deposits of dense sandy gravel with rounded cobbles that was moist to very moist. The alluvial gravel deposits were determined to be suitable bearing material. Foundation support recommendations provided later in this report are based on excavation to the native gravels. The Headwaters Academy, Inc Headwaters Academy Geotechnical Report January 14, 2020 Bozeman, Montana Allied Engineering Services, Inc. ● 32 Discovery Drive. Bozeman, Montana 59718 ● Ph: (406) 582-0221 Page 5 During future site work, test pits completed as part of the explorations that are located within the footprint of the building (or under exterior hardscapes) should be dug out and replaced with compacted granular structural fill. The backfill was only lightly compacted when filling the explorations back in following work and could be subject to undesirable settlements. Groundwater Conditions During the subsurface investigation, groundwater was not encountered in any of the three test pits. However, an increase in moisture content was observed starting at eight feet below the ground surface. Very moist soils near the bottom of the test pit indicate that groundwater is nearby. Groundwater levels are expected to rise between the spring and summer months due to runoff and snowmelt. To monitor changes in groundwater levels, AESI installed a groundwater monitoring well in Test Pit #2 and will implement a monthly groundwater monitoring program beginning March 1, 2020 and continuing through peak groundwater. The results will be provided to the Client upon completion. FOUNDATION, SLAB, AND DRAINAGE RECOMMENDATIONS Seismic Design Factors This area lies in an area that can be subject to earthquakes. Therefore, the improvements will need to be designed according to the appropriate earthquake loading parameters. A requirement of the Structural Engineer will be a determination of the site class since this is a basis for the seismic analysis. Based on the on-site explorations and knowledge of the area’s geology, the site class for the project site is Site Class D (as per criteria presented in the 2012 IBC). Foundation Design The fine-grain topsoil, silt, and clay found at the site are prone to excessive settlement (over an inch) under anticipated foundation loads. For this reason, over-excavating to the native sandy gravel (found at depths of four to five feet) and bearing all footings on this material or granular structural fill that is founded on this material is recommended. Native gravels may be wet and could be saturated depending on the time of year the excavation is completed. Utilizing non-moisture sensitive clean, crushed rock as structural fill to bring the excavation above the water table (if needed) is allowable provided there is no more than 6 inches of water at the bottom of the excavation. If standing water is greater than 6 inches, some dewatering may be necessary to install structural fill. Based on the depth to native gravels, excavating along the footing lines may be the most cost- effective foundation excavation method. In the areas where structural fill bears on the native gravel, the width of the excavation (in order to ensure load transfer occurs in the structural fill) is the width of the footing plus the depth from the bottom of the footing to target bearing The Headwaters Academy, Inc Headwaters Academy Geotechnical Report January 14, 2020 Bozeman, Montana Allied Engineering Services, Inc. ● 32 Discovery Drive. Bozeman, Montana 59718 ● Ph: (406) 582-0221 Page 6 (essentially a 0.5H:1V slope extending downward from the edge of footings). For example, if the width of the footing is two feet and the depth to native gravels below the bottom of the footing is one foot, the necessary trench width is three feet (assuming the footing is centered on the trench). In areas where footings bear directly in the native gravels without the need for structural fill, the subgrade should be proof-rolled to an unyielding condition. Any soft or overly moist areas should be removed and replaced with compacted structural fill placed in lifts as discussed later in this report. Lightly loaded interior concrete slabs should bear on a minimum of 12 inches of granular structural fill and six inches of crushed rock directly under the slab supported on the native non- organic sandy silt/clay compacted to an unyielding condition. An appropriate bearing capacity for design assuming conventional spread and continuous footings is 3,000 pounds per square foot (psf). Total settlements are estimated to be under 0.75 inches with minimal differential settlements. Allowable bearing pressures during earthquakes may be increased by 50 percent. Lateral Earth Pressures All foundation walls that will be fixed at the top prior to the placement of backfill should be designed for an “at rest” equivalent fluid pressure of 60 pounds per cubic foot (pcf). In contrast, cantilevered retaining walls may be designed for a lower, “active” equivalent fluid pressure of 45 pcf, provided either some slight outward rotation of the wall is acceptable upon backfilling or the wall is constructed in such a way that accommodates the expected rotation. The “at rest” and “active” design values are only applicable for walls that will have backfill slopes of less than ten percent and will not be externally loaded by surface pressures applied above and/or behind the wall. These lateral earth pressures also assume proper subsurface drainage provisions are installed to prevent the development of hydrostatic pressures. Lateral forces from wind, earthquakes, and earth pressures on the opposite side of the structure will be resisted by passive earth pressure against the buried portion of the foundation wall and by friction at the bottom of the footing. Passive earth pressures in compacted backfill should be assumed to have an equivalent fluid pressure of 280 pcf; while a coefficient of friction of 0.4 should be used between cast-in-place concrete and the native gravels or granular structural fill. Actual footing loads (not factored or allowable loads) should be used for calculating frictional resistance to sliding along the base of the footing. Please be aware that the friction coefficient has no built-in factor of safety; therefore, an appropriate safety factor should be selected and used in all subsequent calculations for each load case. The lateral earth pressures summarized above are for static conditions and should be factored for seismic (earthquake) conditions. The Headwaters Academy, Inc Headwaters Academy Geotechnical Report January 14, 2020 Bozeman, Montana Allied Engineering Services, Inc. ● 32 Discovery Drive. Bozeman, Montana 59718 ● Ph: (406) 582-0221 Page 7 Foundation Wall Backfill Exterior wall backfill can consist of any excavated foundation soil, other than topsoil, if it is not overly moist, highly plastic, or too rocky in composition. All select backfill materials should be placed in multiple lifts and properly compacted to 95 percent of their Standard Proctor density. To prevent damaging foundation walls during the backfilling process, only hand-operated, compaction equipment is recommended within three feet of walls that are not buried on both sides. The level of care (with respect to the selection of dry backfill materials and the compactive effort that is used) should be increased significantly in those areas along the foundation wall that will either receive concrete/asphalt surfacing or that will support a retaining wall to minimize the potential for future settlement problems. Finally, the re-use of topsoil as backfill should be limited to the uppermost four to six inches in landscape areas. Some drying of the fine-grain soils may be necessary in order to re-use as foundation wall backfill. Interior Concrete Slabs As discussed earlier, lightly loaded interior concrete slabs should be supported on a minimum of 12 inches of granular structural fill and six inches of compacted crushed rock. The structural fill may be supported on either native, non-organic fine-grain soils that have been compacted to an unyielding condition or embankment fill. If soft spots are encountered in the subgrade, these areas should be stripped out and replaced with structural fill. Any fill required to bring the subgrade up to the bottom of the structural fill should be compacted in lifts as specified in a later section. Subsurface Drainage and Damp-Proofing Assuming the foundation system will consist of a slab-on-grade with frost walls and footings, a footing drain is not necessary. Buried foundation walls should be damp-proofed with an acceptable commercial product as per the requirements of the International Building Code (IBC 2012). Vapor Barrier Under Interior Concrete Slab The addition of a Stego 15-mil vapor barrier directly under interior concrete slabs is recommended. The purpose of the vapor barrier is to limit rising water vapor which can accumulate under non-pervious flooring materials and affect the floor adhesives. The vapor barrier should be placed directly on top of the crushed rock in conjunction with the use of proper concrete mixes that will limit the possibility of curling at the edges. Burying the vapor barrier under a blotter course of crushed rock is done to avoid curling of the slab, but it also adds the risk of trapping moisture between the vapor barrier and the bottom of the slab. For this reason, placing the vapor barrier on top of the crushed rock and directly under the slab is suggested. The Headwaters Academy, Inc Headwaters Academy Geotechnical Report January 14, 2020 Bozeman, Montana Allied Engineering Services, Inc. ● 32 Discovery Drive. Bozeman, Montana 59718 ● Ph: (406) 582-0221 Page 8 Exterior Concrete Slabs Depending on site grading, exterior concrete slabs can either be supported on non-organic, native soils or on embankment fill material that is placed above the stripped subgrade surface to raise design elevations. Traffic loaded exterior slabs should be underlain by a minimum of six inches of clean crushed rock and 12 inches of granular structural fill. A woven geotextile fabric (Mirafi RS280i) may be added if the subgrade is wet or soft. Thickening the crushed rock layer to greater than six inches will improve the drainage capacity under the slab as well as provide additional separation from the underlying soils. Consequently, the frost heave potential of the slab should be reduced. Critical exterior slab areas which cannot undergo any heaving should be underlain by additional crushed rock and two inches or more of below-grade insulation extending outward two feet from the edge of the slab to limit frost penetration. Prior to placing any embankment fill or structural fill, both of which must be adequately compacted, the subgrade surface should be proof-rolled to confirm its stability. If soft or wet areas are identified, they should be over-excavated and replaced with suitable, compacted structural fill. Surface Drainage Recommendations Final site grading must establish and promote positive surface water drainage away from the foundation footprint in all directions. No water should be allowed to accumulate against or flow along any exposed walls. Concrete or asphalt surfacing that abut the foundation should be designed with a minimum grade of two percent; while adjacent landscaped areas should have a slope of at least five percent within ten feet of the wall. To further reduce the potential for moisture infiltration along foundation walls, backfill materials should be well compacted, and in landscaped areas, capped by four to six inches of low permeability topsoil. Apart from the locations that will be surfaced by concrete or asphalt, finished grades (next to foundation walls) should be set no less than six inches below the top of slab or the bottom of the sill plate for framed floors. FOUNDATION-RELATED FILL MATERIAL RECOMMENDATIONS Provided below are recommendations for the foundation-related fill materials that may be used during construction. These include on-site excavated soils, sandy (pitrun) gravel, crushed (road mix) gravel, and clean crushed rock. Placement and compaction criteria follow the specifications for these materials. The Headwaters Academy, Inc Headwaters Academy Geotechnical Report January 14, 2020 Bozeman, Montana Allied Engineering Services, Inc. ● 32 Discovery Drive. Bozeman, Montana 59718 ● Ph: (406) 582-0221 Page 9 Excavated Foundation Soils A variety of soils will be excavated during foundation earthwork including topsoil, silt, clay, and potentially some sandy gravel with cobbles and boulders. All topsoil and organic materials should be stripped and stockpiled for re-use during site reclamation. On-site soils suitable for re-use as embankment fill should be separated from wet, rocky, or otherwise unsuitable soils during excavation. The suitability of the non-organic excavated soils will depend on their rocky condition, plasticity, natural moisture content, and ability to be re-compacted. The driest soils containing an even mixture of soil matrix and smaller rock fragments should be selected for use as compacted fill, while the wettest and rockiest soils should either be hauled off-site or used for general site grading in non-critical locations. Depending on the time of year, some of the native soil that is excavated may be wet of optimum and will require drying prior to re-use. This may necessitate the import of easily compacted fill material if work is conducted during the wet or winter season when drying is not an option. Sandy (pitrun) Gravel Sandy (pitrun) gravel is a granular structural fill alternative for placement under and/or behind footings, slabs, and walls. This material shall be a non-plastic, well-graded, mixture of clean sand and gravel with 100 percent of its fragments passing a four-inch screen and less than 10 percent of its particles (by weight) finer than the No. 200 sieve. In addition to these material and gradation recommendations, it should meet all other applicable specifications as presented in Section 02234 of the Montana Public Works Standard Specifications (MPWSS) for uncrushed, sub-base course gravel. Crushed (road mix) Gravel Crushed (road mix) gravel is another granular structural fill alternative for placement under and/or behind footings, slabs, and walls. This material shall be a non-plastic, well-graded, mixture of clean sand and gravel that is processed (crushed) such that 100 percent of its fragments pass a 1-1/2-inch screen and less than 10 percent of its particles (by weight) are finer than the No. 200 sieve. It should also meet all other specifications as presented in Section 02235 of the MPWSS for crushed, base course gravel. Clean Crushed Rock The primary uses for clean crushed rock include placement under concrete slabs and behind foundation and retaining walls for drainage-related purposes. Crushed rock shall consist of a clean assortment of angular fragments with 100 percent passing a one-inch screen and less than 1 percent (by weight) finer than the No. 100 sieve. This aggregate product needs to be manufactured by a crushing process and over 50 percent of its particles must The Headwaters Academy, Inc Headwaters Academy Geotechnical Report January 14, 2020 Bozeman, Montana Allied Engineering Services, Inc. ● 32 Discovery Drive. Bozeman, Montana 59718 ● Ph: (406) 582-0221 Page 10 have fractured faces. It is not acceptable to use rock that contains abundant rounded particles for foundation-related applications. FILL PLACEMENT AND COMPACTION All fill materials should be placed in uniform, horizontal lifts, and compacted to an unyielding condition. This includes clean crushed rock, which can be compacted and/or consolidated by vibratory means. The maximum “loose lift thickness” for all fill materials (prior to compaction) should be limited to about 12 inches for large self-propelled rollers, 8 inches for remote- controlled, dual drum rollers, and 6 inches for walk-behind plate or jumping jack compactors. The moisture content of any material to be compacted should be within approximately two percent (+/-) of its optimum value for maximum compaction. Special attention must be paid to the proper compaction of structural fill materials along the edges and in the corners of the foundation excavation. These areas often cannot be adequately accessed and compacted with large equipment. In those cases, either small compactors must be used, or the limits of the excavation must be increased such that compaction of the entire minimum structural fill width can be achieved with the larger equipment. Table 1 details compaction recommendations for foundation-related applications. These recommendations are presented as a percentage of the maximum dry density of the fill material is defined in ASTM D-698. Table 1. Compaction Recommendations (Application vs. Percent Compaction) APPLICATION % COMPACTION Granular Structural Fill Under Footings and Interior Slabs: 98 Embankment Fill Under Exterior Slabs: 95 Backfill Behind Foundation: 95 Clean Crushed Rock Under Slabs: N/A (Vibration Required) Sub-base and Base Course Materials for Asphalt Pavement: 95 ASPHALT PAVEMENT RECOMMENDATIONS Pavement Section Design Table 2 presents the recommended pavement section for the parking lot and road improvements. This section is designed for a 20-year service life and is based on the site’s shallow subsurface conditions, the anticipated traffic loading associated with the academy, laboratory testing of the native soils, and previous experience in the area. If there is slight rutting during subgrade preparation, a woven-geotextile can be added to enhance subgrade strength as shown in Table 2 below. The Headwaters Academy, Inc Headwaters Academy Geotechnical Report January 14, 2020 Bozeman, Montana Allied Engineering Services, Inc. ● 32 Discovery Drive. Bozeman, Montana 59718 ● Ph: (406) 582-0221 Page 11 Table 2. Pavement Section Components and Required Compacted Thickness COMPONENT COMPACTED THICKNESS (IN) Asphalt Concrete: 3 Base Course - Crushed (road mix) Gravel: 6 Sub-Base Course - Uncrushed Sandy (pitrun): 9 Woven Geotextile (Mirafi RS280i): As Needed Stable Subgrade Soils (Less Topsoil): Compacted to 95% TOTAL SECTION THICKNESS: 18 Important Note: The design pavement section is suitable provided the subgrade soils are dry, stable, and can be compacted to 95 percent of ASTM D-698 prior to the placement of sub-base gravel. If widespread unstable subgrade conditions are an issue (i.e., significant deep rutting of over an inch), either the overly moist soils will need to be scarified and dried or the sub-base component of the pavement section will have to be thickened to bridge the inferior soils. Depending on the level of severity of the soft subgrade conditions, additional sub-base gravel thickness could range from 6 to 12 inches. A woven stabilizer fabric (Mirafi RS280i) may also be used to reinforced soft subgrade conditions if needed. A bid item within the contract documents is recommended for import structural fill and woven stabilizer fabric to be used if widespread unstable conditions are encountered. Pavement Section Materials, Placement, and Compaction The sub-base and base course materials that comprise the granular parts of the pavement section shall consist of 4-inch minus uncrushed sandy (pitrun) gravel and 1-1/2-inch minus crushed (road mix) gravel, respectively. Both gravel courses shall meet the material and gradation specifications as presented in the MPWSS, Sections 02234 and 02235. Under normal circumstances, these gravel products shall be placed in loose lifts not exceeding 12 inches in thickness and compacted to at least 95 percent of the maximum dry density as defined in ASTM D-698. However, wherever subgrade soils are overly soft, and a woven geotextile fabric is used, a full, 15 to 24-inch section of sub-base course gravel is recommended to be placed and compacted in one single lift to prevent damaging and tearing the fabric with the construction equipment. Prior to the placement of the pavement section components (see Table 2), all organic topsoil should be stripped and the excavated subgrade surface re-compacted. If subgrade elevations need to be raised, any on-site excavated soil, other than topsoil or wetland soil, can be used for embankment fill provided its moisture content is near optimum for compaction and it can be compacted to an unyielding condition. Following the re-compaction of the subgrade surface, it should be proof-rolled with a heavy piece of construction equipment, such as a loaded dump The Headwaters Academy, Inc Headwaters Academy Geotechnical Report January 14, 2020 Bozeman, Montana Allied Engineering Services, Inc. ● 32 Discovery Drive. Bozeman, Montana 59718 ● Ph: (406) 582-0221 Page 12 truck, to determine its stability. If any isolated soft spots are observed, they should be sub- excavated and replaced with suitable compacted fill on an individual basis. However, if it is found that widespread, unstable conditions exist (ie. the subgrade surface is overly soft, prone to rutting or pumping, and cannot be compacted to 95 percent of ASTM D-698) the subgrade soils will either need to be dried via scarification, the sub-base gravel component of the section increased, and/or woven fabric be added as described above. The use of geogrid is also an option if wide spread subgrade pumping is apparent. UNDERGROUND UTILITY RECOMMENDATIONS Foundation Support of Utility Lines Utility lines (water, sewer, and dry utilities) will likely be supported in the native gravels. These materials will provide suitable support for the utility lines. Proper bedding of these utilities following the specifications found in the Montana Public Works Standard Specifications is suggested. Note that depending on the time of year, some dewatering may be necessary in order to install the utilities. Trench Backfill Trench backfill may consist of any native material (except materials containing significant organics) that is not overly wet. Trench backfill should be compacted to a minimum of 95 percent of ASTM D-698 under pavement/slab areas and 92 percent in landscaped areas. STORM DRAINAGE PONDS The use of stormwater retention ponds is not recommended at this site. Rather, all stormwater ponds (detention ponds) should have a controlled outlet. CONSTRUCTION RECOMMENDATIONS Recognizing that elevated groundwater levels may be encountered at the site, careful construction planning and sequencing is recommended to complete the foundation preparation in the most expedient manner possible. If work is completed in the late spring and summer when groundwater levels are highest, site-wide groundwater de-watering may be required. If the work is completed in the late fall and winter, there is a possibility that significant de-watering costs may be avoided. AESI is happy to work with the Design Team and the Contractor regarding appropriate construction measures to successfully develop the site. COLD/WINTER WEATHER CONSTRUCTION If foundation construction will occur during the cold/winter weather season, the Contractor should take all necessary precautions to prevent the earthwork from freezing and/or from being The Headwaters Academy, Inc Headwaters Academy Geotechnical Report January 14, 2020 Bozeman, Montana Allied Engineering Services, Inc. ● 32 Discovery Drive. Bozeman, Montana 59718 ● Ph: (406) 582-0221 Page 13 contaminated with snow. Exposed subgrade and fill materials (under footings, slabs, and walls) should be covered with concrete insulation blankets to prevent frost penetration and to protect them from snow. All soils that are used for fill under or around foundation components should be relatively dry, free of intermixed snow and frozen clods, and must not be placed when it is snowing. No fill materials (or footings) should be placed over frozen soils, which may be in a “frost-heaved condition”, or on layers of snow. AESI INVOLVEMENT DURING DESIGN AND CONSTRUCTION AESI recommends their retention during the design of the improvements to assure the recommendations as discussed in this report are implemented. AESI further recommends they be retained during the construction process to verify adequate bearing has been achieved and to observe road/parking lot subgrade conditions. LIMITATIONS This report provides AESI’s geotechnical-related recommendations for the proposed construction of the Headwaters Academy classroom building in Bozeman, Montana. Please be advised that this report is only applicable for the above-referenced property and shall not be used for other nearby project sites. The recommendations presented herein are primarily based on observation and evaluation of the site’s surface and subsurface conditions, along with review and interpretation of geologic maps, and previous engineering experience within the project area. If during earthwork construction, soil and groundwater conditions are found to be inconsistent with those described in the report, Allied Engineering should be advised immediately so the situation can be analyzed, and recommendations can be modified as needed. All individuals associated with this project should consult this report during the planning, design, and construction of the site improvements. It should be made available to other parties for information on factual data only and not as a warranty of actual subsurface conditions such as those interpreted herein. The opportunity to perform geotechnical services and provide recommendations is greatly appreciated. If you have any questions, please call. Sincerely, Allied Engineering Services, Inc. Craig R. Madson, PE Principal Geotechnical Engineer Sumner A. LaValley Staff Engineer Sumner LaValley The Headwaters Academy, Inc Headwaters Academy Geotechnical Report January 14, 2020 Bozeman, Montana Allied Engineering Services, Inc. ● 32 Discovery Drive. Bozeman, Montana 59718 ● Ph: (406) 582-0221 Page 14 REFERENCES 1. International Code Council, 2012. “2012 International Building Code”. 2. Montana Contractors’ Association, April 2010. “Montana Public Works Standard Specifications”, Sixth Edition. 3. Lonn, J. and English, A (2002). “Preliminary Geologic Map of the Eastern Part of the Gallatin Valley Montana”, MBMG Open-File Report 457. qa/qc: EGS P:\2019\19-024 Headwaters Academy Site Plan\05 Design\Geotech\Report\19-024 Geotech Report.docx LIST OF FIGURES FFiigguurree 11 –– VViicciinniittyy MMaapp FFiigguurree 22 –– QQuuaaddrraannggllee MMaapp FFiigguurree 33 –– TTeesstt PPiitt LLooccaattiioonn MMaapp FFiigguurree 44 –– GGeeoollooggyy MMaapp FIGURECivil Engineering Geotechnical Engineering Land Surveying 32 DISCOVERY DRIVE . BOZEMAN, MT 59718 PHONE (406) 582-0221 . FAX (406) 582-5770 www.alliedengineering.com HEADWATERS ACADEMY VICINITY MAP BOZEMAN, MONTANA 1 N FIGURECivil Engineering Geotechnical Engineering Land Surveying 32 DISCOVERY DRIVE . BOZEMAN, MT 59718 PHONE (406) 582-0221 . FAX (406) 582-5770 www.alliedengineering.com HEADWATERS ACADEMY QUADRANGLE MAP BOZEMAN, MONTANA 2 N FIGURECivil Engineering Geotechnical Engineering Land Surveying 32 DISCOVERY DRIVE . BOZEMAN, MT 59718 PHONE (406) 582-0221 . FAX (406) 582-5770 www.alliedengineering.com HEADWATERS ACADEMY TEST PIT LOCATION MAP BOZEMAN, MONTANA 3 N TP# TP-1 TP-2 TP-3 FIGURECivil Engineering Geotechnical Engineering Land Surveying 32 DISCOVERY DRIVE . BOZEMAN, MT 59718 PHONE (406) 582-0221 . FAX (406) 582-5770 www.alliedengineering.com HEADWATERS ACADEMY GEOLOGY MAP BOZEMAN, MONTANA 4 N APPENDIX A TTeesstt PPiitt LLooggss APPENDIX B LLaabboorraattoorryy TTeessttiinngg RReessuullttss MOISTURE CONTENT DETERMINATION (ASTM D-2216) Project: Headwaters AcademyProject Number: 19-024 Sample Identification: Varies Soil Classification: Varies Date Sampled: 12/19/2019 Date Tested: 12/19/2019 Tested By: EGS Sample Identification:S1-A S1-B S2-A S3-A S3-B Exploration Location:TP-1 TP-1 TP-2 TP-3 TP-3 Sample Depth (ft):3.0 8.5 2.5 3.5 7.0 Container Number:EE M O R GG Weight of Container:49.24 50.59 49.09 50.59 48.29 Container + Wet Soil:241.91 310.84 283.80 298.02 301.87 Container + Dry Soil:214.14 298.46 251.83 261.74 289.39 Weight of Water:27.77 12.38 31.97 36.28 12.48 Weight of Dry Soil:164.90 247.87 202.74 211.15 241.10 Moisture Content:16.8%5.0%15.8%17.2%5.2% Sample Identification: Exploration Location: Sample Depth (ft): Container Number: Weight of Container: Container + Wet Soil: Container + Dry Soil: Weight of Water: Weight of Dry Soil: Moisture Content: Reviewed By: 32 Discovery DriveBozeman, MT 59718Phone (406) 582-0221 Fax (406) 582-5770 Moisture Content Determinations APPENDIX C LLiimmiittaattiioonnss ooff YYoouurr GGeeootteecchhnniiccaall RReeppoorrtt LIMITATIONS OF YOUR GEOTECHNICAL REPORT GEOTECHNICAL REPORTS ARE PROJECT AND CLIENT SPECIFIC Geotechnical investigations, analyses, and recommendations are project and client specific. Each project and each client have individual criterion for risk, purpose, and cost of evaluation that are considered in the development of scope of geotechnical investigations, analyses and recommendations. For example, slight changes to building types or use may alter the applicability of a particular foundation type, as can a particular client’s aversion or acceptance of risk. Also, additional risk is often created by scope‐of service limitations imposed by the client and a report prepared for a particular client (say a construction contractor) may not be applicable or adequate for another client (say an architect, owner, or developer for example), and vice‐versa. No one should apply a geotechnical report for any purpose other than that originally contemplated without first conferring with the consulting geotechnical engineer. Geotechnical reports should be made available to contractors and professionals for information on factual data only and not as a warranty of subsurface conditions, such as those interpreted in the exploration logs and discussed in the report. GEOTECHNICAL CONDITIONS CAN CHANGE Geotechnical conditions may be affected as a result of natural processes or human activity. Geotechnical reports are based on conditions that existed at the time of subsurface exploration. Construction operations such as cuts, fills, or drains in the vicinity of the site and natural events such as floods, earthquakes, or groundwater fluctuations may affect subsurface conditions and, thus, the continuing adequacy of a geotechnical report. GEOTECHNICAL ENGINEERING IS NOT AN EXACT SCIENCE The site exploration and sampling process interprets subsurface conditions using drill action, soil sampling, resistance to excavation, and other subjective observations at discrete points on the surface and in the subsurface. The data is then interpreted by the engineer, who applies professional judgment to render an opinion about over‐all subsurface conditions. Actual conditions in areas not sampled or observed may differ from those predicted in your report. Retaining your consultant to advise you during the design process, review plans and specifications, and then to observe subsurface construction operations can minimize the risks associated with the uncertainties associated with such interpretations. The conclusions described in your geotechnical report are preliminary because they must be based on the assumption that conditions revealed through selective exploration and sampling are indicative of actual Allied Engineering Services, Inc. ● 32 Discovery Drive. Bozeman, Montana 59718 ● Ph: (406) 582‐0221 Page 2 conditions throughout a site. A more complete view of subsurface conditions is often revealed during earthwork; therefore, you should retain your consultant to observe earthwork to confirm conditions and/or to provide revised recommendations if necessary. Allied Engineering cannot assume responsibility or liability for the adequacy of the report’s recommendations if another party is retained to observe construction. EXPLORATIONS LOGS SHOULD NOT BE SEPARATED FROM THE REPORT Final explorations logs developed by the consultant are based upon interpretation of field logs (assembled by site personnel), field test results, and laboratory and/or office evaluation of field samples and data. Only final exploration logs and data are customarily included in geotechnical reports. These final logs should not be redrawn for inclusion in Architectural or other design drawings, because drafters may commit errors or omissions in the transfer process. To reduce the likelihood of exploration log misinterpretation, contractors should be given ready access to the complete geotechnical report and should be advised of its limitations and purpose. While a contractor may gain important knowledge from a report prepared for another party, the contractor should discuss the report with Allied Engineering and perform the additional or alternative work believed necessary to obtain the data specifically appropriate for construction cost estimating purposes. OWNERSHIP OF RISK AND STANDARD OF CARE Because geotechnical engineering is much less exact than other design disciplines, there is more risk associated with geotechnical parameters than with most other design issues. Given the hidden and variable character of natural soils and geologic hazards, this risk is impossible to eliminate with any amount of study and exploration. Appropriate geotechnical exploration, analysis, and recommendations can identify and reduce these risks. However, assuming an appropriate geotechnical evaluation, the remaining risk of unknown soil conditions and other geo‐hazards typically belongs to the owner of a project unless specifically transferred to another party such as a contractor, insurance company, or engineer. The geotechnical engineer’s duty is to provide professional services in accordance with their stated scope and consistent with the standard of practice at the present time and in the subject geographic area. It is not to provide insurance against geo‐hazards or unanticipated soil conditions. The conclusions and recommendations expressed in this report are opinions based our professional judgment and the project parameters as relayed by the client. The conclusions and recommendations assume that site conditions are not substantially different than those exposed by the explorations. If during construction, subsurface conditions different from those encountered in the explorations are observed or appear to be present, Allied Engineering should be advised at once such that we may review those conditions and reconsider our recommendations where necessary. RETENTION OF SOIL SAMPLES Allied Engineering will typically retain soil samples for one month after issuing the geotechnical report. If you would like to hold the samples for a longer period of time, you should make specific arrangements to have the samples held longer or arrange to take charge of the samples yourself.