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Home My WebLink AboutTIMBER LARK SINGLE-FAMILY DEVELOPMENT - FDP220008 - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTPRELIMINARY SUBSURFACE EXPLORATION SOUTH TIMBERLINE DEVELOPMENT NORTH OF TRILBY ROAD and WEST OF TIMBERLINE ROAD FORT COLLINS, COLORADO EEC PROJECT NO. 1202034 Prepared for: AADT Land Holdings, LLC 13005 Lowell Boulevard Broomfield, Colorado 80020 Attn: Mr. Alex Aigner, c/o Steve Schroyer (schroyer@haydenoutdoors.com) Prepared by: Earth Engineering Consultants, LLC 4396 Greenfield Drive Windsor, Colorado 80550 4396 GREENFIELD DRIVE W INDSOR, COLORADO 80550 (970) 545-3908 FAX (970) 663-0282 June 2, 2020 AADT Land Holdings, LLC 13005 Lowell Boulevard Broomfield, Colorado 80020 Attn: Mr. Alex Aigner, c/o Steve Schroyer (schroyer@haydenoutdoors.com) Re: Preliminary Subsurface Exploration Report South Timberline Development North of Trilby Road and West of Timberline Road Fort Collins, Colorado EEC Project No. 1202034 Mr. Aigner: Enclosed, herewith, are the results of the preliminary subsurface exploration completed by Earth Engineering Consultants, LLC personnel for the referenced project in Fort Collins, Colorado. For this project, five (5) preliminary soil borings were drilled at the approximate locations as indicated on the enclosed Boring Location Diagram included with this report. The borings were extended to depths of approximately 20 to 35 feet below existing site grades. Individual boring logs, including groundwater observations, depth to bedrock where encountered, and results of laboratory testing are included as a part of the attached report. This exploration was completed in general accordance with our proposal dated March 25, 2020. In summary, the subsurface soils encountered in the preliminary test borings generally consisted of lean clay with varying amounts of sand soils, which extended to the depths explored or to the bedrock formation below. The lean clay soils were generally very stiff to medium stiff and exhibited low to very high swell potential at current moisture and density conditions. The lean clay soils extended to the depths explored at approximately 20 feet in borings B-2 and B-4 and to the underlying bedrock at depths of approximately 19 to 28 feet below the ground surface in the remaining borings. Claystone bedrock was encountered underlying the lean clay soils in a majority of the borings. The claystone bedrock was highly weathered becoming moderately hard with depth, exhibited moderate swell potential and extended to the depths explored, approximately 40 feet below the ground surface. Groundwater was observed in Borings B-1, B-3 and B-5 at depths of approximately 15 to 33 feet below existing site grades at the time of drilling. PRELIMINARY SUBSURFACE EXPLORATION SOUTH TIMBERLINE DEVELOPMENT NORTH OF TRILBY ROAD and WEST OF TIMBERLINE ROAD FORT COLLINS, COLORADO EEC PROJECT NO. 1202034 June 2, 2020 INTRODUCTION The preliminary subsurface exploration for the South Timberline Residential Development located north of Trilby Road and west of Timberline Road in Fort Collins, Colorado has been completed. For this preliminary exploration, five (5) soil borings were drilled and four (4) hand/field slotted groundwater piezometers were installed on May 13, 2020 at the approximate locations as indicated on the enclosed Boring Location Diagram included with this report. The preliminary soil borings were advanced to depths of approximately 20 to 35 feet below existing site grades to obtain general information on existing subsurface and groundwater conditions. The individual boring logs and a site diagram indicating the approximate boring locations are included with this report. The property, as we understand will most likely be developed for residential use with potential full- depth basements including associated interior roadways and infrastructure. Foundation loads for the proposed residential structures are anticipated to be light with continuous wall loads less than 3 kips per lineal foot and individual column loads less than 50 kips. Floor loads are expected to be light. We anticipate maximum cuts and fills on the order of 5 feet (+/-) will be completed to develop the site grades. Overall site development will include construction of interior roadways designed in general accordance with the typical Larimer County Pavement Design Criteria. The purpose of this report is to describe the subsurface conditions encountered in the preliminary borings, analyze and evaluate the test data and provide supplementary/updated geotechnical recommendations concerning site development including foundations, floor slabs, an area underdrain system, and pavement sections. EXPLORATION AND TESTING PROCEDURES The boring locations were established in the field by a representative of Earth Engineering Consultants, LLC (EEC) by pacing and estimating angles from identifiable site features. Those locations should be considered accurate only to the degree implied by the methods used to make the Earth Engineering Consultants, LLC EEC Project No. 1202034 June 2, 2020 Page 2 field measurements. Photographs of the site taken at the time of drilling are provided with this report. The preliminary borings were performed using a truck-mounted CME 55 drill rig equipped with a hydraulic head employed in drilling and sampling operations. The boreholes were advanced using 4- inch diameter continuous flight augers. Samples of the subsurface materials encountered were obtained using split-barrel and California barrel sampling procedures in general accordance with ASTM Specifications D1586 and D3550, respectively. In the split-barrel and California barrel sampling procedures, standard sampling spoons are driven into the ground by means of a 140-pound hammer falling a distance of 30 inches. The number of blows required to advance the samplers is recorded and is used to estimate the in-situ relative density of cohesionless soils and, to a lesser degree of accuracy, the consistency of cohesive soils and hardness of weathered bedrock. In the California barrel sampling procedure, relatively undisturbed samples are obtained in brass liners. All samples obtained in the field were sealed and returned to the laboratory for further examination, classification and testing. After completing the drilling and sampling, and prior to removal of the flight augers, a hand/field slotted 1-inch diameter PVC casing was installed in four (4) of the borings. Laboratory moisture content tests were performed on each of the recovered samples. In addition, selected samples were tested for fines content and plasticity by washed sieve analysis and Atterberg limits tests. Swell/consolidation tests were completed on selected samples to evaluate the subgrade materials’ tendency to change volume with variation in moisture content and load. The quantity of water-soluble sulfates was determined on select samples to evaluate the risk of sulfate attack on site concrete. As a part of the testing program, all samples were examined in the laboratory and classified in general accordance with the attached General Notes and the Unified Soil Classification System, based on the sample's texture and plasticity. The estimated group symbol for the Unified Soil Classification System is shown on the boring logs and a brief description of that classification system is included with this report. Classification of the bedrock was based on visual and tactual observation of disturbed samples and auger cuttings. Coring and/or petrographic analysis may reveal other rock types. Earth Engineering Consultants, LLC EEC Project No. 1202034 June 2, 2020 Page 3 SITE AND SUBSURFACE CONDITIONS The development property is located north of Trilby Road in Fort Collins, Colorado. The project site is generally undeveloped with vegetation and topsoil at the surface of the borings. Surface water drainage across the site is generally to the east. Estimated relief across the site from northwest or southeast is approximately 20 to 35 feet (±). An EEC field engineer was on-site during drilling to direct the drilling activities and evaluate the subsurface materials encountered. Field descriptions of the materials encountered were based on visual and tactual observation of disturbed samples and auger cuttings. The boring logs included with this report may contain modifications to the field logs based on results of laboratory testing and engineering evaluation. Based on results of field and laboratory evaluation, subsurface conditions can be generalized as follows. Vegetation and topsoil were encountered at the surface of the borings. The topsoil and vegetation layers were underlain by lean clay with varying amounts of sand soils. The lean clay soils were generally very stiff to medium stiff and exhibited low to very high swell potential at current moisture and density conditions. The lean clay soils extended to the depths explored at approximately 20 feet in borings B-2 and B-4 and to the underlying bedrock at depths of approximately 19 to 28 feet below the ground surface in the remaining borings. Claystone bedrock was encountered underlying the lean clay soils in a majority of the borings. The claystone bedrock was highly weathered becoming moderately hard with depth, exhibited moderate swell potential and extended to the depths explored, approximately 35 feet below the ground surface. The stratification boundaries indicated on the boring logs represent the approximate locations of changes in soil and rock types; in-situ, the transition of materials may be gradual and indistinct. GROUNDWATER OBSERVATIONS Observations were made while drilling and on May 18, 2020, within the temporary piezometers to detect the presence and level of groundwater. At the time of drilling and on May 18, groundwater was observed in Borings B-1, B-3 and B-5 at depths ranging from approximately 15 to 33 feet below existing site grades. The measured depths to groundwater are recorded near the upper right-hand corner of each boring log included with this report. The groundwater measurements provided with Earth Engineering Consultants, LLC EEC Project No. 1202034 June 2, 2020 Page 4 this report are indicative of groundwater levels at the location and at the time the measurements were completed. Perched and/or trapped water may be encountered in more permeable zones in the subgrade soils at times throughout the year. Perched water is commonly encountered in soils immediately overlying less permeable bedrock materials. Fluctuations in ground water levels and in the location and amount of perched water may occur over time depending on variations in hydrologic conditions, irrigation activities on surrounding properties and other conditions not apparent at the time of this report. ANALYSIS AND RECOMMENDATIONS Swell/Consolidation Test Results Swell/consolidation testing is performed to evaluate the swell or collapse potential of soil or bedrock to assist in determining/evaluating foundation, floor slab and/or pavement design criteria. In the swell/consolidation test, relatively undisturbed samples obtained directly from the California barrel sampler are placed in a laboratory apparatus and inundated with water under a pre-established load. The swell-index is the resulting amount of swell or collapse under the initial loading condition expressed as a percent of the sample’s initial thickness. After the inundation period, additional incremental loads are applied to evaluate swell pressure and/or consolidation. For this assessment, we conducted seven (7) swell-consolidation tests on relatively undisturbed soil samples obtained at various intervals/depths on the site. The swell index values for the in-situ soil samples analyzed revealed low swell characteristics and a tendency to consolidate upon loading as well as moderate to very high swell potential characteristics as indicated on the attached swell test summaries. The (+) test results indicate the soil materials swell potential characteristics while the (-) test results indicate the soils materials collapse/consolidation potential characteristics when inundated with water. Results of the laboratory swell tests are indicated in Table I below as well as on attached boring logs and the enclosed summary sheets. Earth Engineering Consultants, LLC EEC Project No. 1202034 June 2, 2020 Page 5 Table I – Laboratory Swell-Consolidation Test Results No of Samples Tested Pre-Load / Inundation Pressure, PSF Description of Material In-Situ Characteristics Range of Swell – Index Test Results Range of Moisture Contents, % Range of Dry Densities, PCF Low End, % High End, % Low End, PCF High End, PCF Low End (+/-) % High End, (+/-) % 3 150 Sandy Lean Clay 7.9 9.1 98.3 116.1 (+) 4.5 (+) 12.7 4 500 Lean Clay with Sand 9.5 19.7 110.4 126.8 (+) 1.9 (+) 5.9 The Colorado Association of Geotechnical Engineers (CAGE) uses the following information to provide uniformity in terminology between geotechnical engineers to provide a relative correlation risk performance to measured swell. “The representative percent swell values are not necessarily measured values; rather, they are a judgment of the swell of the soil and/or bedrock profile likely to influence slab performance.” Geotechnical engineers use this information to also evaluate the swell potential risks for foundation performance based on the risk categories. TABLE II: Recommended Representative Swell Potential Descriptions and Corresponding Slab Performance Risk Categories Slab Performance Risk Category Representative Percent Swell (500 psf Surcharge) Representative Percent Swell (1000 psf Surcharge) Low 0 to < 3 0 < 2 Moderate 3 to < 5 2 to < 4 High 5 to < 8 4 to < 6 Very High > 8 > 6 Based on the laboratory test results, the samples of overburden soils analyzed exhibited generally low to very high swell potential conditions within the lean clay and compressible conditions nearing the ground table. The swell potential for the samples taken at depths of approximately 2 feet below the ground surface generally exhibited swell potential greater than the maximum allowable 2% for pavement design, therefore a swell mitigation procedure will likely be necessary for pavement subgrades. General Considerations General guidelines are provided below for the site subgrade preparation. However, it should be noted that for possible residential development areas, compaction and moisture requirements vary Earth Engineering Consultants, LLC EEC Project No. 1202034 June 2, 2020 Page 6 between home builders and, consequently, between geotechnical engineering companies. If the residential development lots will be marketed to a target group of builders, fill placement criteria should be obtained from those builders and/or their geotechnical engineering consultants prior to beginning earthwork activities on the site. Representatives from those entities should verify that the fill is being placed consistent with the home builders’ guidelines. The upper lean clay soils that exhibited moderate to very high swell potential would be of concern for support of building foundations, exterior flatwork, and pavements. If the near surface lean clay soils were to become wetted subsequent to construction of overlying improvements, heaving and/or differential heaving caused by soils/underlying bedrock could result in significant total and differential movement of foundations, pavements, exterior flatwork, and floor slabs. To reduce the risk of potential movement for building foundations consideration could be given to the use of drilled pier foundations for in the areas with moderately to highly expansive lean clay as described in this report. Consideration could also be given to completing over excavation procedures below spread footing foundations, floor slabs, exterior flatwork, and pavements as described herein. If lower level construction or full-depth basements are being considered for the site, we would suggest that the lower level subgrade(s) be placed a minimum of 3 feet above the maximum anticipated rise in groundwater levels. Site Preparation All existing vegetation and/or topsoil should be removed from beneath site fills, roadways or building subgrade areas. Stripping depths should be expected to vary, depending, in part, on past agricultural activities. In addition, any soft/loose native soils or any existing fill materials without documentation of controlled fill placement should be removed from improvement and/or new fill areas. After stripping and completing all cuts, and prior to placement of any fill, floor slabs or pavements, we recommend the exposed soils be scarified to a minimum depth of 9 inches, adjusted in moisture content and compacted to at least 95% of the material's maximum dry density as determined in accordance with ASTM Specification D698, the standard Proctor procedure. The moisture content of the scarified materials should be adjusted to be within a range of 2% of standard Proctor optimum moisture at the time of compaction. Earth Engineering Consultants, LLC EEC Project No. 1202034 June 2, 2020 Page 7 We expect mitigation for moderate to very high swell cohesive soils will be required in foundation, flatwork, floor slab (non-basement), and pavement areas in portions of the site. That mitigation would commonly include removal of dry and hard materials, increasing the moisture in the clay soils and replacing the moisture conditioned soils as controlled density fill. Mitigation could be done on an individual residence/roadway basis; however, care should be taken during overlot grading to avoid placing fill above the dry, dense soils which would require future removal and reworking. In general, fill materials required to develop the building areas or site pavement subgrades should consist of approved, low-volume change materials which are free from organic matter and debris. The near surface lean clay, and/or approved imported structural fill could be used as fill in these areas. If granular imported structural fill is used, it should be similar to CDOT Class 5, 6 or 7 base course material with sufficient fines to prevent ponding of water in the fill. We recommend the fill soils be placed in loose lifts not to exceed 9 inches thick, adjusted in moisture content and compacted to at least 95% of the material’s maximum dry density as determined in accordance with the standard Proctor procedure. The moisture content of cohesive soils should be adjusted to be within the range of ±2% of optimum moisture content at the time of placement. Granular soil should be adjusted to a workable moisture content. Specific explorations should be completed for each building/individual residential lot to develop recommendations specific to the proposed structure and owner/builder and for specific pavement sections. Care should be taken after preparation of the subgrades to avoid disturbing the subgrade materials. Positive drainage should be developed away from structures and across and away from pavement edges to avoid wetting of subgrade materials. Subgrade materials allowed to become wetted subsequent to construction of the residences and/or pavements can result in unacceptable performance of those improvements. Areas of greater fills overlying areas with loose/compressible subsoils, especially within the deeper utility alignments, may experience settlement due to the loose/compressible subsoils below and within the zone of placed fill materials. Settlement on the order of 1-inch or more per each 10 feet of fill depth would be estimated. The rate of settlement will be dependent on the type of fill material placed and construction methods. Granular soils will consolidate essentially immediately upon placement of overlying loads. Cohesive soils will consolidate at a slower rate. Preloading and/or Earth Engineering Consultants, LLC EEC Project No. 1202034 June 2, 2020 Page 8 surcharging the fill areas could be considered to induce additional settlement in these areas prior to construction of improvements in or on the fills. Unless positive steps are taken to pre-consolidate the fill materials and/or underlying loose/compressible subgrades, special care will be needed for construction of improvements supported on or within these areas. Foundation Systems – General Considerations The cohesive subsoils will require particular attention in the design and construction to reduce the amount of movement due to moderate to very high swell potential. The following preliminary foundation systems were evaluated for use on the site for the proposed residential buildings.  Footing foundations on a zone of over excavated and replaced subsoils with an approved engineered controlled fill material  Straight shaft drilled piers bearing into the underlying bedrock formation Other alternative foundation systems could be considered, and we would be pleased to provide additional alternatives upon request. Preliminary Spread Footing Foundation Recommendations We anticipate use of conventional footing foundations could be considered for lightly loaded structures at this site. We expect footing foundations would be supported on newly placed and compacted fills. The near surface lean clay with dry and dense conditions exhibiting moderate to very high swell potential would be of concern for the support of foundations. After completing a site-specific/lot-specific geotechnical exploration study, a thorough “open- hole/foundation excavation” observation should be performed prior to foundation formwork placement to determine/confirm the extent of any possible over excavation and replacement procedures. In general, the over excavation area would extend 8 inches laterally beyond the building perimeter for every 12 inches of over excavation depth. Backfill materials should be placed as described in the section Site Preparation. Earth Engineering Consultants, LLC EEC Project No. 1202034 June 2, 2020 Page 9 For design of footing foundations bearing on properly placed and compacted fill materials as outlined above, maximum net allowable total load soil bearing pressures on the order of 1,500 to 2,500 psf could be considered depending upon the specific backfill material used. The net bearing pressure refers to the pressure at foundation bearing level in excess of the minimum surrounding overburden pressure. Total load would include full dead and live loads. Exterior foundations and foundations in unheated areas are typically located at least 30 inches below adjacent exterior grade to provide frost protection. Formed continuous footings would have minimum widths of 12 to 16 inches and isolated column foundations would have a minimum width of 24 to 30 inches. Care should be taken to avoid placement of structures partly on native soils and partly on newly placed fill materials to avoid differential settlement. In these areas, mitigation approaches could include surcharging of the fill materials or overexcavation of the native soils. Mitigation approaches may vary between structures depending, in part, on the extent and depth of new fill placement. Specific approaches could be established at the time of exploration for the individual structures. Care should be taken on the site to fully document the horizontal and vertical extent of fill placement on the site, including benching the fill into native slopes. Preliminary Drilled Piers/Caissons Foundation Recommendations Based on the subsurface conditions and relatively shallow depth to bedrock across a majority of the site, as well as the anticipated foundation loads, we believe site structures could also be supported on a grade beam and straight shaft drilled pier/caisson foundation systems extending into the underlying bedrock formation. For axial compression loads, we estimate a design maximum end-bearing pressure in the range of 20,000 pounds per square foot (psf) to 30,000 psf, along with an estimated skin-friction in the range of 2,000 psf to 3,000 psf for the portion of the pier extended into the underlying firm and/or harder bedrock formation. Specific explorations should be made for each building and/or individual residential lot to determine actual design end-bearing and skin friction values. Additional recommendations for the design of straight shaft piers can be made at the time the lot-specific subsurface explorations. Earth Engineering Consultants, LLC EEC Project No. 1202034 June 2, 2020 Page 10 Drilling caissons to design depth should be possible with conventional heavy-duty single flight power augers equipped with rock teeth on the majority of the site. However, areas of well-cemented sandstone bedrock lenses may be encountered throughout the site at various depths where specialized drilling equipment and/or rock excavating equipment may be required. Excavation penetrating the well-cemented sandstone bedrock may require the use of specialized heavy-duty equipment, together with rock augers and/or core barrels. Consideration should be given to obtaining a unit price for difficult caisson excavation in the contract documents for the project. We expect temporary casings may be required to maintain open boreholes within areas. Preliminary Basement Design and Construction Groundwater was encountered across the site within the preliminary soil borings at approximate depths of 15 to 33 feet below existing site grades. If lower level construction for either garden-level or full-depth basements is being considered for the site, as well as any slab-on-grade (no basement) construction within very shallow groundwater areas we would suggest that the lower level subgrade(s) be placed a minimum of 3 feet above maximum anticipated rise in groundwater levels, or a combination exterior and interior perimeter drainage system(s) be installed in areas with shallow groundwater. Recommendations for a drainage system can be provided upon request. Preliminary Floor Slab/Exterior Flatwork Subgrades Based on the observed subsurface conditions, we believe properly placed engineered/controlled fill material could be used for direct support of floor slabs. Floor slab and exterior flatwork subgrades should be prepared as outlined in the section Site Preparation. Preliminary Pavement Subgrades Based on the current subsurface conditions, we believe a swell mitigation plan will be required for pavements, this would likely consist of moisture conditioning and reworking a zone of the dry near surface clay material. Pavement subgrades should be prepared as described in the section site preparation. After completion of the pavement subgrades, care should be taken to prevent disturbance of those materials prior to placement of the overlying pavements. Soils which are disturbed by construction Earth Engineering Consultants, LLC EEC Project No. 1202034 June 2, 2020 Page 11 activities should be reworked in-place or, if necessary, removed and replaced prior to placement of overlying fill or pavements. Depending on final site grading and/or weather conditions at the time of pavement construction, stabilization of a portion of the site pavement subgrades may be required to develop suitable pavement subgrades. The site clay soils could be subject to instability at higher moisture contents. Stabilization could also be considered as part of the pavement design, although prior to finalizing those sections, a stabilization mix design would be required. Preliminary Site Pavements Pavement sections are based on traffic volumes and subgrade strength characteristics. An assumed R-Value of 10 was used for the preliminary pavement design. Suggested preliminary pavement sections for the local residential and minor collector roadways are provided below in Table III. Thicker pavement sections may be required for roadways classified as major collectors. A final pavement design thickness evaluation will be determined when a pavement design exploration is completed (after subgrades are developed to ± 6 inches of design and wet utilities installed in the roadways). The projected traffic may vary from the traffic assumed from the roadway classification based on a site-specific traffic study. TABLE III – PRELIMINARY PAVEMENT SECTIONS Local Residential Roadways Minor Collectors Roadways EDLA – assume local residential roadways Reliability Resilient Modulus PSI Loss – (Initial 4.5, Terminal 2.0 and 2.5 respectively) 10 80% 3562 2.5 25 80% 3562 2.2 Design Structure Number 2.67 3.11 Composite Section without Fly Ash – Alternative A Hot Mix Asphalt (HMA) Grading S (75) PG 58-28 Aggregate Base Course ABC – CDOT Class 5 or 6 Design Structure Number 4ʺ 9ʺ (2.75) 5ʺ 9ʺ (3.19) Composite Section with Fly Ash – Alternative B Hot Mix Asphalt (HMA) Grading S (75) PG 58-28 Aggregate Base Course ABC – CDOT Class 5 or 6 Fly Ash Treated Subgrade Design Structure Number 4ʺ 6 ʺ 12″ (2.92) 4ʺ 7ʺ 12ʺ (3.04) PCC (Non-reinforced) – placed on an approved subgrade 6″ 6½″ Earth Engineering Consultants, LLC EEC Project No. 1202034 June 2, 2020 Page 12 Asphalt surfacing should consist of grading S-75 or SX-75 hot bituminous pavement with PG 64-22 or PG 58-28 binder in accordance with Larimer County requirements. Aggregate base should be consistent with CDOT requirements for Class 5 or Class 6 aggregate base. As previously mentioned, a final subgrade investigation and pavement design should be performed in general accordance with the Larimer County Pavement Design Criteria prior to placement of any pavement sections, to determine the required pavement section after design configurations, roadway utilities have been installed and roadway have been prepared to “rough” subgrade elevations have been completed. Underground Utility Systems All piping should be adequately bedded for proper load distribution. It is suggested that clean, graded gravel compacted to 70 percent of Relative Density ASTM D4253 be used as bedding. Where utilities are excavated below groundwater, temporary dewatering will be required during excavation, pipe placement and backfilling operations for proper construction. Utility trenches should be excavated on safe and stable slopes in accordance with OSHA regulations as further discussed herein. Backfill should consist of the on-site soils or approved imported materials. The pipe backfill should be compacted to a minimum of 95 percent of Standard Proctor Density ASTM D698. Other Considerations and Recommendations Although evidence of fills or underground facilities such as septic tanks, cesspools, basements, and utilities was not observed during the site reconnaissance, such features could be encountered during construction. If unexpected fills or underground facilities are encountered, such features should be removed, and the excavation thoroughly cleaned prior to backfill placement and/or construction. Excavations into the on-site soils will encounter a variety of conditions. Excavations into the essentially cohesive soils can be expected to stand on relatively steep temporary slopes during construction. The individual contractor(s) should be made responsible for designing and constructing stable, temporary excavations as required to maintain stability of both the excavation sides and bottom. All excavations should be sloped or shored in the interest of safety following local and federal regulations, including current OSHA excavation and trench safety standards. Earth Engineering Consultants, LLC EEC Project No. 1202034 June 2, 2020 Page 13 GENERAL COMMENTS The analysis and recommendations presented in this report are based upon the data obtained from the soil borings performed at the indicated locations and from any other information discussed in this report. This report does not reflect any variations which may occur across the site. The nature and extent of such variations may not become evident until construction. If variations appear evident, it will be necessary to re-evaluate the recommendations of this report. Site specific explorations will be necessary for the proposed site buildings. It is recommended that the geotechnical engineer be retained to review the plans and specifications so that comments can be made regarding the interpretation and implementation of our geotechnical recommendations in the design and specifications. It is further recommended that the geotechnical engineer be retained for testing and observations during earthwork and foundation construction phases to help determine that the design requirements are fulfilled. This report has been prepared for the exclusive use of AADT Land Holdings, LLC for specific application to the project discussed and has been prepared in accordance with generally accepted geotechnical engineering practices. No warranty, express or implied, is made. In the event that any changes in the nature, design or location of the project as outlined in this report are planned, the conclusions and recommendations contained in this report shall not be considered valid unless the changes are reviewed, and the conclusions of this report modified or verified in writing by the geotechnical engineer. Earth Engineering Consultants, LLC DRILLING AND EXPLORATION DRILLING & SAMPLING SYMBOLS: SS: Split Spoon ‐ 13/8" I.D., 2" O.D., unless otherwise noted PS: Piston Sample ST: Thin‐Walled Tube ‐ 2" O.D., unless otherwise noted WS: Wash Sample R: Ring Barrel Sampler ‐ 2.42" I.D., 3" O.D. unless otherwise noted PA: Power Auger FT: Fish Tail Bit HA: Hand Auger RB: Rock Bit DB: Diamond Bit = 4", N, B BS: Bulk Sample AS: Auger Sample PM: Pressure Meter HS: Hollow Stem Auger WB: Wash Bore Standard "N" Penetration: Blows per foot of a 140 pound hammer falling 30 inches on a 2‐inch O.D. split spoon, except where noted. WATER LEVEL MEASUREMENT SYMBOLS: WL : Water Level WS : While Sampling WCI: Wet Cave in WD : While Drilling DCI: Dry Cave in BCR: Before Casing Removal AB : After Boring ACR: After Casting Removal Water levels indicated on the boring logs are the levels measured in the borings at the time indicated. In pervious soils, the indicated levels may reflect the location of ground water. In low permeability soils, the accurate determination of ground water levels is not possible with only short term observations. DESCRIPTIVE SOIL CLASSIFICATION Soil Classification is based on the Unified Soil Classification system and the ASTM Designations D‐2488. Coarse Grained Soils have move than 50% of their dry weight retained on a #200 sieve; they are described as: boulders, cobbles, gravel or sand. Fine Grained Soils have less than 50% of their dry weight retained on a #200 sieve; they are described as : clays, if they are plastic, and silts if they are slightly plastic or non‐plastic. Major constituents may be added as modifiers and minor constituents may be added according to the relative proportions based on grain size. In addition to gradation, coarse grained soils are defined on the basis of their relative in‐ place density and fine grained soils on the basis of their consistency. Example: Lean clay with sand, trace gravel, stiff (CL); silty sand, trace gravel, medium dense (SM). CONSISTENCY OF FINE‐GRAINED SOILS Unconfined Compressive Strength, Qu, psf Consistency < 500 Very Soft 500 ‐ 1,000 Soft 1,001 ‐ 2,000 Medium 2,001 ‐ 4,000 Stiff 4,001 ‐ 8,000 Very Stiff 8,001 ‐ 16,000 Very Hard RELATIVE DENSITY OF COARSE‐GRAINED SOILS: N‐Blows/ft Relative Density 0‐3 Very Loose 4‐9 Loose 10‐29 Medium Dense 30‐49 Dense 50‐80 Very Dense 80 + Extremely Dense PHYSICAL PROPERTIES OF BEDROCK DEGREE OF WEATHERING: Slight Slight decomposition of parent material on joints. May be color change. Moderate Some decomposition and color change throughout. High Rock highly decomposed, may be extremely broken. HARDNESS AND DEGREE OF CEMENTATION: Limestone and Dolomite: Hard Difficult to scratch with knife. Moderately Can be scratched easily with knife. Hard Cannot be scratched with fingernail. Soft Can be scratched with fingernail. Shale, Siltstone and Claystone: Hard Can be scratched easily with knife, cannot be scratched with fingernail. Moderately Can be scratched with fingernail. Hard Soft Can be easily dented but not molded with fingers. Sandstone and Conglomerate: Well Capable of scratching a knife blade. Cemented Cemented Can be scratched with knife. Poorly Can be broken apart easily with fingers. Cemented Group Symbol Group Name Cu≥4 and 1<Cc≤3E GW Well-graded gravel F Cu<4 and/or 1>Cc>3E GP Poorly-graded gravel F Fines classify as ML or MH GM Silty gravel G,H Fines Classify as CL or CH GC Clayey Gravel F,G,H Cu≥6 and 1<Cc≤3E SW Well-graded sand I Cu<6 and/or 1>Cc>3E SP Poorly-graded sand I Fines classify as ML or MH SM Silty sand G,H,I Fines classify as CL or CH SC Clayey sand G,H,I inorganic PI>7 and plots on or above "A" Line CL Lean clay K,L,M PI<4 or plots below "A" Line ML Silt K,L,M organic Liquid Limit - oven dried Organic clay K,L,M,N Liquid Limit - not dried Organic silt K,L,M,O inorganic PI plots on or above "A" Line CH Fat clay K,L,M PI plots below "A" Line MH Elastic Silt K,L,M organic Liquid Limit - oven dried Organic clay K,L,M,P Liquid Limit - not dried Organic silt K,L,M,O Highly organic soils PT Peat (D30)2 D10 x D60 GW-GM well graded gravel with silt NPI≥4 and plots on or above "A" line. GW-GC well-graded gravel with clay OPI≤4 or plots below "A" line. GP-GM poorly-graded gravel with silt PPI plots on or above "A" line. GP-GC poorly-graded gravel with clay QPI plots below "A" line. SW-SM well-graded sand with silt SW-SC well-graded sand with clay SP-SM poorly graded sand with silt SP-SC poorly graded sand with clay Earth Engineering Consultants, LLC IIf soil contains >15% gravel, add "with gravel" to group name JIf Atterberg limits plots shaded area, soil is a CL- ML, Silty clay Unified Soil Classification System Soil Classification Criteria for Assigning Group Symbols and Group Names Using Laboratory Tests Sands 50% or more coarse fraction passes No. 4 sieve Fine-Grained Soils 50% or more passes the No. 200 sieve <0.75 OL Gravels with Fines more than 12% fines Clean Sands Less than 5% fines Sands with Fines more than 12% fines Clean Gravels Less than 5% fines Gravels more than 50% of coarse fraction retained on No. 4 sieve Coarse - Grained Soils more than 50% retained on No. 200 sieve CGravels with 5 to 12% fines required dual symbols: Kif soil contains 15 to 29% plus No. 200, add "with sand" or "with gravel", whichever is predominant. <0.75 OH Primarily organic matter, dark in color, and organic odor ABased on the material passing the 3-in. (75-mm) sieve ECu=D60/D10 Cc= HIf fines are organic, add "with organic fines" to group name LIf soil contains ≥ 30% plus No. 200 predominantly sand, add "sandy" to group name. MIf soil contains ≥30% plus No. 200 predominantly gravel, add "gravelly" to group name. DSands with 5 to 12% fines require dual symbols: BIf field sample contained cobbles or boulders, or both, add "with cobbles or boulders, or both" to group name.FIf soil contains ≥15% sand, add "with sand" to GIf fines classify as CL-ML, use dual symbol GC- CM, or SC-SM. Silts and Clays Liquid Limit less than 50 Silts and Clays Liquid Limit 50 or more 0 10 20 30 40 50 60 0 10 20 30 40 50 60 70 80 90 100 110PLASTICITY INDEX (PI) LIQUID LIMIT (LL) ML OR OL MH OR OH For Classification of fine-grained soils and fine-grained fraction of coarse-grained soils. Equation of "A"-line Horizontal at PI=4 to LL=25.5 then PI-0.73 (LL-20) Equation of "U"-line Vertical at LL=16 to PI-7, then PI=0.9 (LL-8) CL-ML SOUTH TIMBERLINE DEVELOPMENT FORT COLLINS, COLORADO EEC PROJECT NO. 1202034 MAY 2020 B-3B-2B-4B-1B-512Proposed Boring Location DiagramSouth Timberline Mixed-UseFort Collins, ColoradoMarch 2020EARTH ENGINEERING CONSULTANTS, LLCApproximate BoringLocations1LegendSite PhotosPhotos taNen in approximatelocation, in direction oI arroZ DATE: RIG TYPE: CME55 FOREMAN: DG AUGER TYPE: 4" CFA SPT HAMMER: AUTOMATIC SOIL DESCRIPTION D N QU MC DD -200 TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % @ 500 PSF SPARSE VEGETATION _ _ 1 SANDY LEAN CLAY (CL) _ _ brown 2 stiff to medium stiff _ _ with calcareous deposits 3 _ _ 4 _ _ CS 5 12 9000+ 9.6 99.2 35 24 62.1 8000 psf 5.5% _ _ 6 _ _ 7 _ _ 8 _ _ 9 _ _ SS 10 14 9000+ 12.4 _ _ 11 _ _ 12 _ _ 13 _ _ 14 _ _ CS 15 8 4500 25.0 96.9 _ _ 16 _ _ 17 _ _ 18 _ _ 19 _ _ CLAYSTONE SS 20 21 3500 23.2 brown / gray / rust _ _ highly weathered 21 _ _ 22 _ _ 23 _ _ 24 _ _ CS 25 42 9000+ 19.7 109.5 64 48 94.1 8000 psf 5.9% Continued on Sheet 2 of 2 _ _ Earth Engineering Consultants, LLC SOUTH TIMBERLINE DEVELOPMENT FORT COLLINS, COLORADO LOG OF BORING B-1PROJECT NO: 1202034 MAY 2020 SHEET 1 OF 1 WATER DEPTH START DATE 5/13/2020 WHILE DRILLING None FINISH DATE 5/13/2020 5/18/2020 33.3' A-LIMITS SWELL DATE: RIG TYPE: CME55 FOREMAN: DG AUGER TYPE: 4" CFA SPT HAMMER: AUTOMATIC SOIL DESCRIPTION D N QU MC DD -200 TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % @ 500 PSF Continued from Sheet 1 of 2 26 _ _ CLAYSTONE 27 brown / gray / rust _ _ highly weathered to moderately hard 28 with calcareous deposits and gypsum crystals _ _ 29 _ _ CS 30 59 9000 17.6 _ _ 31 _ _ 32 _ _ 33 _ _ 34 _ _ SS 35 50/9.5" 9000+ 17.7 113.7 _ _ BOTTOM OF BORING DEPTH 35.5' 36 _ _ 37 _ _ 38 _ _ 39 _ _ 40 _ _ 41 _ _ 42 _ _ 43 _ _ 44 _ _ 45 _ _ 46 _ _ 47 _ _ 48 _ _ 49 _ _ 50 _ _ Earth Engineering Consultants, LLC SOUTH TIMBERLINE DEVELOPMENT FORT COLLINS, COLORADO LOG OF BORING B-1 MAY 2020PROJECT NO: 1202034 SHEET 2 OF 2 WATER DEPTH START DATE 5/13/2020 WHILE DRILLING None 5/13/2020 5/18/2020 33.3'FINISH DATE A-LIMITS SWELL DATE: RIG TYPE: CME55 FOREMAN: DG AUGER TYPE: 4" CFA SPT HAMMER: AUTOMATIC SOIL DESCRIPTION D N QU MC DD -200 TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % @ 500 PSF VEGETATION & TOPSOIL _ _ 1 SANDY LEAN CLAY (CL) _ _ brown 2 very stiff to soft _ _% @ 150 psf with calcareous deposits CS 3 22 9000+ 7.9 850 psf 4.5% _ _ 4 _ _ SS 5 14 9000+ 4.9 _ _ 6 _ _ 7 _ _ 8 _ _ 9 _ _ CS 10 15 9000+ 10.3 117.0 _ _ 11 _ _ 12 _ _ 13 _ _ 14 _ _ SS 15 8 8000 14.7 _ _ 16 _ _ 17 _ _ 18 _ _ 19 _ _ CS 20 5 500 24.8 97.5 BOTTOM OF BORING DEPTH 20.0' _ _ 21 _ _ 22 _ _ 23 _ _ 24 _ _ 25 _ _ Earth Engineering Consultants, LLC SOUTH TIMBERLINE DEVELOPMENT FORT COLLINS, COLORADO PROJECT NO: 1202034 LOG OF BORING B-2 MAY 2020 SHEET 1 OF 1 WATER DEPTH START DATE 5/13/2020 WHILE DRILLING None FINISH DATE 5/13/2020 5/18/2020 None A-LIMITS SWELL DATE: RIG TYPE: CME55 FOREMAN: DG AUGER TYPE: 4" CFA SPT HAMMER: AUTOMATIC SOIL DESCRIPTION D N QU MC DD -200 TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % @ 500 PSF SPARSE VEGETATION _ _ 1 SANDY LEAN CLAY (CL) _ _ brown 2 very stiff to medium stiff _ _ with calcareous deposits 3 _ _ 4 _ _ CS 5 28 8000 8.2 _ _ 6 _ _ 7 _ _ 8 _ _ 9 _ _ CS 10 16 9000+ 9.5 110.5 31 21 65.1 2000 psf 1.9% _ _ 11 _ _ 12 _ _ 13 _ _ 14 _ _ SS 15 11 5000 11.8 _ _ 16 _ _ 17 _ _ 18 _ _ 19 _ _ CS 20 16 9000+ 16.4 113.6 _ _ 21 _ _ 22 _ _ 23 _ _ 24 _ _ SS 25 16 Continued on Sheet 2 of 2 _ _ Earth Engineering Consultants, LLC SOUTH TIMBERLINE DEVELOPMENT FORT COLLINS, COLORADO PROJECT NO: 1202034 LOG OF BORING B-3 MAY 2020 SHEET 1 OF 1 WATER DEPTH START DATE 5/13/2020 WHILE DRILLING 33.0' 5/18/2020 27.2' FINISH DATE 5/13/2020 20 HOURS 31.5' A-LIMITS SWELL DATE: RIG TYPE: CME55 FOREMAN: DG AUGER TYPE: 4" CFA SPT HAMMER: AUTOMATIC SOIL DESCRIPTION D N QU MC DD -200 TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % @ 500 PSF Continued from Sheet 1 of 2 26 _ _ SANDY LEAN CLAY (CL) 27 brown _ _ 28 _ _ 29 CLAYSTONE _ _ brown / gray / rust CS 30 26 9000+ 18.1 112.6 5.9% highly weathered to moderately hard _ _ 31 _ _ 32 _ _ 33 _ _ 34 _ _ SS 35 50/11" 8000 22.6 _ _ BOTTOM OF BORING DEPTH 35.5' 36 _ _ 37 _ _ 38 _ _ 39 _ _ 40 _ _ 41 _ _ 42 _ _ 43 _ _ 44 _ _ 45 _ _ 46 _ _ 47 _ _ 48 _ _ 49 _ _ 50 _ _ Earth Engineering Consultants, LLC SOUTH TIMBERLINE DEVELOPMENT FORT COLLINS, COLORADO PROJECT NO: 1202034 LOG OF BORING B-3 MAY 2020 SHEET 2 OF 2 WATER DEPTH START DATE 5/13/2020 WHILE DRILLING 33.0' 5/13/2020 20 HOURS 31.5' 5/18/2020 27.2' FINISH DATE A-LIMITS SWELL DATE: RIG TYPE: CME55 FOREMAN: DG AUGER TYPE: 4" CFA SPT HAMMER: AUTOMATIC SOIL DESCRIPTION D N QU MC DD -200 TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % @ 500 PSF VEGETATION & TOPSOIL _ _ 1 SANDY LEAN CLAY (CL) _ _ brown 2 very stiff to medium stiff _ _% @ 150 psf with calcareous deposits CS 3 28 9000+ 8.9 123.6 37 22 59.0 9.1% _ _ 4 _ _ SS 5 16 9000+ 8.6 _ _ 6 _ _ 7 _ _ 8 _ _ 9 _ _ CS 10 11 9000+ 13.5 118.7 _ _ 11 _ _ 12 _ _ 13 _ _ 14 _ _ SS 15 12 4500 20.1 _ _ 16 _ _ 17 _ _ 18 _ _ 19 _ _ CS 20 13 5500 24.2 102.4 BOTTOM OF BORING DEPTH 20.0' _ _ 21 _ _ 22 _ _ 23 _ _ 24 _ _ 25 _ _ Earth Engineering Consultants, LLC SOUTH TIMBERLINE DEVELOPMENT FORT COLLINS, COLORADO PROJECT NO: 1202034 LOG OF BORING B-4 MAY 2020 SHEET 1 OF 1 WATER DEPTH START DATE 5/13/2020 WHILE DRILLING None FINISH DATE 5/13/2020 A-LIMITS SWELL DATE: RIG TYPE: CME55 FOREMAN: DG AUGER TYPE: 4" CFA SPT HAMMER: AUTOMATIC SOIL DESCRIPTION D N QU MC DD -200 TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % @ 500 PSF VEGETATION & TOPSOIL _ _ 1 SANDY LEAN CLAY (CL) _ _ brown 2 very stiff to medium stiff _ _ with calcareous deposits 3 _ _ 4 _ _% @ 150 psf CS 5 49 9000+ 9.1 7000 psf 12.7% _ _ 6 _ _ 7 _ _ 8 _ _ 9 _ _ CS 10 25 5000 20.2 104.7 _ _ 11 _ _ 12 _ _ 13 _ _ 14 _ _ SS 15 12 500 26.6 _ _ 16 _ _ 17 _ _ 18 _ _ 19 CLAYSTONE _ _ brown / gray / rust, highly weathered CS 20 13 7500 22.0 105.1 BOTTOM OF BORING DEPTH 20.0' _ _ 21 _ _ 22 _ _ 23 _ _ 24 _ _ 25 _ _ Earth Engineering Consultants, LLC SOUTH TIMBERLINE DEVELOPMENT FORT COLLINS, COLORADO PROJECT NO: 1202034 LOG OF BORING B-5 MAY 2020 SHEET 1 OF 1 WATER DEPTH START DATE 5/13/2020 WHILE DRILLING None 5/18/2020 15.1' FINISH DATE 5/13/2020 20 HOURS 15.0' A-LIMITS SWELL Project: Location: Project #: Date: South Timberline Development Fort Collins, Colorado 1202034 May 2020 Beginning Moisture: 9.6% Dry Density: 126.8 pcf Ending Moisture: 13.9% Swell Pressure: 8000 psf % Swell @ 500: 5.5% Sample Location: Boring 1, Sample 1, Depth 4' Liquid Limit: 35 Plasticity Index: 24 % Passing #200: 62.1% SWELL / CONSOLIDATION TEST RESULTS Material Description: Brown Sandy Lean Clay (CL) -10.0 -8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0 6.0 8.0 10.0 0.01 0.1 1 10Percent MovementLoad (TSF)SwellConsolidatioWater Added Project: Location: Project #: Date: South Timberline Development Fort Collins, Colorado 1202034 May 2020 Beginning Moisture: 19.7% Dry Density: 110.4 pcf Ending Moisture: 22.5% Swell Pressure: 8000 psf % Swell @ 500: 5.9% Sample Location: Boring 1, Sample 5, Depth 24' Liquid Limit: 64 Plasticity Index: 48 % Passing #200: 94.1% SWELL / CONSOLIDATION TEST RESULTS Material Description: Brown / Gray / Rust Claystone - classified as FAT CLAY (CH) -10.0 -8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0 6.0 8.0 10.0 0.01 0.1 1 10Percent MovementLoad (TSF)SwellConsolidatioWater Added Project: Location: Project #: Date: SWELL / CONSOLIDATION TEST RESULTS Material Description: Brown Sandy Lean Clay (CL) Sample Location: Boring 2, Sample 1, Depth 2' Liquid Limit: - - Plasticity Index: - - % Passing #200: - - Beginning Moisture: 7.9% Dry Density: 98.3 pcf Ending Moisture: 23.8% Swell Pressure: 850 psf % Swell @ 150: 4.5% South Timberline Development Fort Collins, Colorado 1202034 May 2020 -10.0 -8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0 6.0 8.0 10.0 0.01 0.1 1 10Percent MovementLoad (TSF)SwellConsolidatioWater Added Project: Location: Project #: Date: SWELL / CONSOLIDATION TEST RESULTS Material Description: Brown Lean Clay with Sand (CL) Sample Location: Boring 3, Sample 2, Depth 9' Liquid Limit: 31 Plasticity Index: 21 % Passing #200: 65.1% Beginning Moisture: 9.5% Dry Density: 112.2 pcf Ending Moisture: 19.0% Swell Pressure: 2000 psf % Swell @ 500: 1.9% South Timberline Development Fort Collins, Colorado 1202034 May 2020 -10.0 -8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0 6.0 8.0 10.0 0.01 0.1 1 10Percent MovementLoad (TSF)SwellConsolidatioWater Added Project: Location: Project #: Date: SWELL / CONSOLIDATION TEST RESULTS Material Description: Brown / Gray / Rust Claystone Sample Location: Boring 3, Sample 6, Depth 29' Liquid Limit: - - Plasticity Index: - - % Passing #200: - - Beginning Moisture: 18.1% Dry Density: 113.9 pcf Ending Moisture: 20.8% Swell Pressure: ~8000 psf % Swell @ 500: 5.9% South Timberline Development Fort Collins, Colorado 1202034 May 2020 -10.0 -8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0 6.0 8.0 10.0 0.01 0.1 1 10Percent MovementLoad (TSF)SwellConsolidatioWater Added Project: Location: Project #: Date: SWELL / CONSOLIDATION TEST RESULTS Material Description: Brown Sandy Lean Clay (CL) Sample Location: Boring 4, Sample 1, Depth 2' Liquid Limit: 37 Plasticity Index: 22 % Passing #200: 59.0% Beginning Moisture: 8.9% Dry Density: 116.1 pcf Ending Moisture: 20.2% Swell Pressure: ~4000 psf % Swell @ 150: 9.1% South Timberline Development Fort Collins, Colorado 1202034 May 2020 -10.0 -8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0 6.0 8.0 10.0 0.01 0.1 1 10Percent MovementLoad (TSF)SwellConsolidatioWater Added Project: Location: Project #: Date: SWELL / CONSOLIDATION TEST RESULTS Material Description: Brown Sandy Lean Clay (CL) Sample Location: Boring 5, Sample 1, Depth 4' Liquid Limit: - - Plasticity Index: - - % Passing #200: - - Beginning Moisture: 9.1% Dry Density: 115 pcf Ending Moisture: 16.7% Swell Pressure: 7000 psf % Swell @ 150: 12.7% South Timberline Development Fort Collins, Colorado 1202034 May 2020 -7.0 -5.0 -3.0 -1.0 1.0 3.0 5.0 7.0 9.0 11.0 13.0 0.01 0.1 1 10Percent MovementLoad (TSF)SwellConsolidatioWater Added