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Home My WebLink AboutMONTAVA - PHASE G & IRRIGATION POND - BDR210013 - SUBMITTAL DOCUMENTS - ROUND 5 - GEOTECHNICAL (SOILS) REPORTSUBSURFACE EXPLORATION REPORT MONTAVA DEVELOPMENT – TRACT G – BOARDWALK STRUCTURES NORTHWEST CORNER OT TIMBERLINE ROAD AND MOUNTAIN VISTA DRIVE FORT COLLINS, COLORADO EEC PROJECT NO. 1172058 Prepared for: Montava Development, LLC 430 N College Avenue, Suite 410 Fort Collins, Colorado 80524 Attn: Mr. Max Moss (Max@hf2m.com), and Mr. Forrest Hancock (forrest@montava.com) Prepared by: Earth Engineering Consultants, LLC 4396 Greenfield Drive Windsor, Colorado 80550 4396 GREENFIELD D RIVE W INDSOR, COLORADO 80550 (970) 545-3908 FAX (970) 663-0282 www.earth-engineering.com March 23, 2023 Montava Development, LLC 430 N College Avenue, Suite 410 Fort Collins, Colorado 80524 Attn: Mr. Max Moss (Max@hf2m.com), and Mr. Forrest Hancock (forrest@montava.com) Re: Geotechnical Engineering Subsurface Exploration Report Montava Development- Tract G – Boardwalk Structures Northwest Corner of Timberline Road and Mountain Vista Drive Fort Collins, Colorado EEC Project No. 1172058 Mr. Moss and Mr. Hancock: Enclosed, herewith, are the results of the geotechnical subsurface exploration completed by Earth Engineering Consultants, LLC (EEC) personnel for the proposed boardwalk structures planned for design and construction within Tract G of the Montava Development project situated at the northwest corner of Timberline Road and Mountain Vista Drive in Fort Collins, Colorado. For this phase of the project EEC personnel completed two (2) preliminary borings in close proximity to the planned boardwalk structures in August of 2018, (please refer to our borings B- 2 and B-5 completed for EEC Project No. 1172058) along with four (4) supplemental preliminary borings for the Tract G phase (please refer to our Supplemental Borings S-6, S-7, S- 8, and S-9) recently completed in March 2023. In general, this project involves the design and construction of six (6) boardwalk structures/grade level crossings as depicted on the enclosed site diagram, which also illustrates the close proximity of the borings previously mentioned. This exploration was completed in general accordance with our proposal dated February 15, 2023. In summary, subsurface conditions observed in the nearby boardwalk borings, generally consisted of lean clay with sand overburden subsoils which extended to the depths explored of approximately 15 to 25 feet below existing site grades or to the underlying coarse granular sand and gravel strata encountered in boring B-5 at an approximate depth of 39-feet below site grades. The lean clay with sand subsoils were generally medium stiff to stiff to very stiff in consistency, exhibited low to moderate swell potential characteristics, and low to moderate bearing capacity characteristics. The underlying course granular sand and gravel strata was medium dense to dense in relative density and exhibited nil swell potential and moderate bearing characteristics. SUBSURFACE EXPLORATION REPORT MONTAVA DEVELOPMENT – TRACT G – BOARDWALK STRUCTURES NORTHWEST CORNER OT TIMBERLINE ROAD AND MOUNTAIN VISTA DRIVE FORT COLLINS, COLORADO EEC PROJECT NO. 1172058 March 23, 2023 INTRODUCTION The subsurface exploration for the six (6) proposed boardwalk structures planned for design and construction within the Montava Development Tract G phase situated at the northwest corner of Timberline Road and Mountain Vista Drive in Fort Collins, Colorado has been completed. For this phase of the project EEC personnel completed two (2) preliminary borings in close proximity to the planned boardwalk structures in August of 2018, (please refer to our borings B-2 and B-5 completed for EEC Project No. 1172058) along with four (4) supplemental preliminary borings for the Tract G preliminary phase (please refer to our Supplemental Borings S-6, S-7, S-8, and S-9) recently completed in March 2023. In general, this project involves the design and construction of six (6) boardwalk structures/grade level crossings as depicted on the enclosed site diagram, which also illustrates the close proximity of the borings previously mentioned. Individual boring logs and a site diagram indicating the approximate boring locations are included with this report. We understand this project involves the construction of six (6) ground level boardwalk/crossing structures as depicted on the enclosed site diagram. The boardwalk structures are expected to be single span wood framed structures exhibiting relatively light foundation loads. Anticipated cuts and fills across the various boardwalk structure could range on the order of (+/-) 5-feet. A general conceptual idea of the planned boardwalk structures is depicted below. We have been requested to provide a geotechnical engineering report to assist the civil and structural engineers in the appropriate foundation type and design parameters for the project. Earth Engineering Consultants, LLC EEC Project No. 1172058 March 23, 2023 Page 2 The current plan concept includes spread footings; however, these boardwalk structures will be constructed in areas also having rain gardens, thus the subsoils may become saturated and not suitable for support. Alternative foundation types to consider would be a deeper foundation system consisting drilled friction piers, micro- piers or helical piers. The concern of a deeper foundation system is that the subsurface profile generally consists of approximately 35 feet (+/-) of cohesive lean clay with sand materials and bedrock was not encountered to a depth of approximately 40-feet. Even though bedrock was not encountered in the borings presented herein, variations may exist across the site. A drilled friction pier or helical pier system may be a feasible option. The purpose of this report is to describe the subsurface conditions encountered in the nearby boardwalk related test borings, analyze and evaluate the developed data on site subsurface conditions and provide geotechnical recommendations concerning design and construction of foundations for the proposed structure. EXPLORATION AND TESTING PROCEDURES The test borings associated with the proposed boardwalk structures were established in the field by Earth Engineering Consultants, LLC (EEC) personnel by pacing and estimating angles from identifiable site features. The approximate boring locations are indicated on the attached boring location diagram. The locations of the borings should be considered accurate only to the degree implied by the methods used to make the field measurements. The borings were completed 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 nominal 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 split-barrel and California barrel samplers is recorded and is used to Earth Engineering Consultants, LLC EEC Project No. 1172058 March 23, 2023 Page 3 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 intact samples are obtained in removable brass sampling sleeves. All samples obtained in the field were sealed and returned to our laboratory for further examination, classification and testing. Laboratory moisture content tests were completed on each of the recovered samples with dry density tests completed on appropriate California barrel samples. The unconfined strength of appropriate samples was estimated using a calibrated hand penetrometer. Atterberg limits and washed sieve analysis tests were completed on selected samples to determine the plasticity and quantity of fines in the subgrade materials, respectfully. Swell/consolidation tests were completed on selected samples to evaluate the tendency of the subgrade materials to change volume with variation in moisture content and load. Soluble sulfate tests were performed to help evaluate possible sulfate attack on site cast concrete. Results of the outlined tests are indicated on the attached boring logs, summary sheets and/or herein. 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 soil'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. SITE AND SUBSURFACE CONDITIONS The proposed six (6) boardwalks will be constructed at the approximate locations indicated on the attached boring location diagram. The proposed boardwalk structures will be crossings designed within drainages and/or within rain garden areas as previously mentioned, predominantly in cut areas. Based on results of the field borings and laboratory testing, subsurface conditions encountered within the boardwalk related borings presented herein can be generalized as follows. In summary, subsurface conditions observed in the nearby boardwalk borings, generally consisted of lean clay with sand overburden subsoils which extended to the depths explored of approximately 15 to 25 feet below existing site grades or to the underlying coarse granular sand and gravel strata encountered in boring B-5 at an approximate depth of 39-feet below site grades. The lean clay with sand subsoils Earth Engineering Consultants, LLC EEC Project No. 1172058 March 23, 2023 Page 4 were generally medium stiff to stiff to very stiff in consistency, exhibited low to moderate swell potential characteristics, and low to moderate bearing capacity characteristics. The underlying course granular sand and gravel strata was medium dense to dense in relative density and exhibited nil swell potential and moderate bearing characteristics. 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 CONDITIONS Observations were made while drilling and after the completion of the borings to detect the presence and depth to the hydrostatic groundwater table. Groundwater was only observed in the deeper preliminary boring B-5 completed in August 2018 at an approximate depth of 29 feet below existing site grades. No groundwater was encountered in the remaining borings completed to depths of 15 to 25 feet below site grades; however, variations may exist across the site. The depth to the observed groundwater table is indicated in the upper right-hand corner of the boring logs. The boreholes were backfilled after completion of drilling and additional groundwater measurements were not obtained. Water level measurements provided with this report are indicative of water levels at the locations and at the time the borings/water level measurements were completed. Fluctuations in groundwater levels can occur over time depending on variations in hydrologic conditions and other conditions not apparent at the time of this report. In addition, zones of perched and/or trapped water can be encountered in more permeable zones in the subgrade soils or in fractured or higher permeability zones interbedded within the underlying bedrock formation. Perched water is commonly encountered in soils immediately above a lower permeability bedrock. The location and amount of perched/trapped water can also vary over time depending on variations in hydrologic conditions and other conditions not apparent at the time of this report. ANALYSIS AND RECOMMENDATIONS Swell – Consolidation Test Results The swell-consolidation test is performed to evaluate the swell or collapse potential of soils to help determine foundation, floor slab and pavement design criteria. In this test, relatively undisturbed samples obtained directly from the California sampler are placed in a laboratory apparatus and Earth Engineering Consultants, LLC EEC Project No. 1172058 March 23, 2023 Page 5 inundated with water under a predetermined load. The swell-index is the resulting amount of swell or collapse after the inundation period expressed as a percent of the sample’s preload/initial thickness. After the inundation period, additional incremental loads are applied to evaluate the swell pressure and/or consolidation. For this assessment, we conducted six (6) swell-consolidation tests on relatively undisturbed soil samples obtained at various intervals/depths on the site. The (+) test results indicate the soil materials swell potential characteristics while the (-) test results, if applicable, indicate the soils materials collapse/consolidation potential characteristics when inundated with water. The following table summarizes the swell-consolidation laboratory test results for samples obtained during our field explorations for the subject site. Table I – Laboratory Swell-Consolidation Test Results Boring No. Depth, FT. Pre-Load / Inundation Pressure, PSF Description of Material In-Situ Characteristics Swell – Index Test Results Moisture Contents, % Dry Densities, PCF Swell Pressure, PSF Swell Index, % (+/-) 6 4 500 Lean Clay with Sand (CL) 11.5 118.0 8000 (+) 4.8 7 4 500 Lean Clay with Sand (CL) 6.3 111.3 2500 (+) 3.1 7 14 1000 Lean Clay with Sand (CL) 7.8 112.1 4000 (+) 3.1 8 9 500 Lean Clay with Sand (CL) 8.8 102.0 1400 (+) 1.3 9 2 150 Lean Clay with Sand (CL) 10.8 115.9 2000 (+) 5.1 9 9 500 Lean Clay with Sand (CL) 10.7 118.1 4000 (+) 3.3 Colorado Association of Geotechnical Engineers (CAGE) uses the following information to provide uniformity in terminology between geotechnical engineers to provide a relative correlation of slab performance risk 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 Earth Engineering Consultants, LLC EEC Project No. 1172058 March 23, 2023 Page 6 Based on the laboratory test results, the in-situ overburden subsoil samples analyzed for this project were within the low to moderate range. In our opinion, these subsoils when over-excavated, moisture conditioned and properly placed and compacted as engineered/controlled fill material would most likely reveal low swell potential characteristics as long as the moisture content of the subgrades are maintained near placement levels. The concern we have with an over-excavation and replacement approach with on-site subsoils, is in the rain garden areas in which the subsoils may become inundated with surface water runoff and become soft/compressible to create settlement of the boardwalk structures. General Considerations The overburden soils along the boardwalk alignments generally consists of approximately 15 to 20 feet of lean clay with varying amounts of sand subsoils. Low to moderate swell potential was exhibited by the near surface samples extending to depths of about 9 feet; in our opinion this is likely due to the dry and very stiff conditions of the lean clay soils. In general, clay soils tend to swell when inundated with water when in-situ moisture contents are less than -2% dry of optimum moisture content. Typical optimum moisture contents for clay soils range from approximately 15 to 20%. The moisture contents observed in the borings, were approximately 4 to 10% less than that range. Additionally, the lean clay soils appeared to be very stiff. When moisture conditioned and re-compacted to near optimum moisture and density conditions, the swell potential of clay soils can be significantly reduced. The Site Preparation section of this report includes recommendations for an over excavation moisture treatment, and re-compaction procedure to reduce the risk of movement for the soils underlying the proposed site improvements. Even if these procedures are followed, some movement and at least minor cracking in the structures should be anticipated. The severity of cracking and other cosmetic damage such as uneven floor slabs will probably increase if any modification of the site results in excessive wetting or drying of the site’s subsoils. Eliminating the risk of movement and cosmetic distress may not be feasible, but it may be possible to further reduce the risk of movement if significantly more extensive/expensive measures are used during construction. Some of these options, such as over-excavating and replacing site materials with an imported granular material and/or the use of a deep foundation system are discussed in this report. Earth Engineering Consultants, LLC EEC Project No. 1172058 March 23, 2023 Page 7 Site Preparation All existing topsoil/vegetation and apparent fill materials should be removed from the site improvement areas. After removal of all topsoil/vegetation within the planned development areas, as well as removal of unacceptable or unsuitable subsoils, removal of any previous fill material, and after all cuts, and prior to placement of fill and/or site improvements, the exposed soils should be scarified to a depth of 9 inches, adjusted in moisture content to within (+/-) 2% of standard Proctor optimum moisture content and compacted to at least 95% of the material's standard Proctor maximum dry density as determined in accordance with ASTM Specification D698. Fill materials used to replace any over-excavated zone and establish grades for the proposed boardwalk structures and flatwork areas, after the initial zone has been prepared as recommended above, should consist of approved on-site lean clay with various amounts of sand subsoils or approved structural fill material which is free from organic matter and debris. If on-site cohesive subsoils are used as engineered fill, they should be placed in maximum 9-inch loose lifts, and be moisture conditioned and compacted as recommended for the scarified subgrade soils. If structural fill materials are used, they should be graded similarly to a CDOT Class 5, 6 or 7 aggregate base with sufficient fines to prevent ponding of water within the fill. Structural fill material should be placed in loose lifts not to exceed 9 inches thick, adjusted to a workable moisture content and compacted to at least 95% of standard Proctor maximum dry density as determined by ASTM Specification D698. Care should be exercised after preparation of the subgrades to avoid disturbing the subgrade materials. Positive drainage should be developed away from the structures and pavements to avoid wetting of subgrade materials. Subgrade materials becoming wet subsequent to construction of the site improvements can result in unacceptable performance. Boardwalk Foundations General The subsurface soils observed in the general areas of the six (6) proposed boardwalk structures were generally medium stiff to stiff cohesive subsoils. However, after grading operations and installation of various rain gardens these areas may exhibit soft compressible conditions due to designed surface Earth Engineering Consultants, LLC EEC Project No. 1172058 March 23, 2023 Page 8 water infiltration. Therefore, soft compressible soils in these areas may become prevalent requiring a different/deeper foundation system than the typical conventional spread footing approach. We believe supporting the boardwalk structures on a deeper foundation system such as drilled friction piers or helical piers into the underlying granular subsurface materials, could be considered to provide adequate foundation support. Recommendations are provided below for drilled friction pier foundations or helical pier foundations extending into the underlying coarse granular subsoils. Drilled Friction Pier Foundations An alternative foundation system for supporting the six (6) proposed boardwalk structures, (as opposed to conventional spread footings), would be a drilled friction pier foundation extending into the underlying sand and gravel strata, or if loads are allowable and designs can be accommodated, possibly end bearing in the cohesive subsoils as long as the skin friction developed. Recommended allowable design parameters, assuming overburden cohesive subsoils to an approximate depth of 35 feet (+/-) with the sand and gravel zone below, along with anticipated groundwater level at an approximate depth of 29 feet, (basically we modeled the drilled friction using the soil profile encountered in our initial preliminary boring B-5 completed in August of 2018), are provided below in Table III for varying design depths. These values are provided herein with an applied factor of safety of 3. Values between those provided can be interpolated linearly except that friction for the top 3 feet should be ignored. Table III – Allowable Design Values – Drilled Friction Piers Depth (ft.) Allowable End Bearing (psf) Skin Friction – Vertical & Uplift, psf Lateral, psf/ft 0 0 0 0 5 1070 65 525 10 2135 130 1050 15 3200 190 1580 20 4275 255 2100 25 5340 320 2630 30 6300 375 3100 35 6850 410 3375 40 9500 460 3800 Earth Engineering Consultants, LLC EEC Project No. 1172058 March 23, 2023 Page 9 Groundwater was encountered at an approximate depth of 29 feet below existing site grades in the vicinity of boring B-5 and was not encountered in the remaining borings to maximum depths drilled of 15 to 25 feet. The values provided in the table above reflect the presence of groundwater at an approximate depth of 29-feet. The effect of groundwater should be taken into account in the design of friction piers and may vary across the site. Temporary casing may be required to adequately/properly drill and clean piers prior to concrete placement. Groundwater should be removed from each pier hole prior to concrete placement. Pier concrete should be placed immediately after completion of drilling and cleaning. A maximum 3-inch depth of groundwater is acceptable in each pier prior to concrete placement. If pier concrete cannot be placed in dry conditions, a tremie should be used for concrete placement. Due to potential sloughing and raveling, foundation concrete quantities may exceed calculated geometric volumes. Pier concrete with slump in the range of 6 to 8 inches is recommended. Casing used for pier construction should be withdrawn in a slow continuous manner maintaining a sufficient head of concrete to prevent infiltration of water or the creation of voids in pier concrete. Foundation excavations should be observed by the geotechnical engineer. A representative of the geotechnical engineer should inspect the bearing surface and pier configuration. If the soil conditions encountered differ significantly from those presented in this report, supplemental recommendations will be required. Helical Pier Foundations Another deep foundation system to consider would be to support the six (6) proposed boardwalk structures on a helical pier foundation system. In general accordance with the International Building Code (IBC) 2009 design manual, Chapter 18, section 1802, a helical pier is defined as “a manufactured steel deep foundation element consisting of a central shaft and one or more helical bearing plates. A helical pile is installed by rotating it into the ground. Each helical bearing plate is formed into a screw thread with a uniform defined pitch.” Based upon review of the soil, underlying granular strata, and groundwater conditions at the site, it is our opinion a helical pier foundation system could be considered as a foundation alternative to drilled friction piers. However, an experienced helical pier contractor should be consulted to review the log of borings included herein. Groundwater, and variable depths to the underlying granular stratum and/or possibly weathered/soft to moderately hard to competent/hard to very hard Earth Engineering Consultants, LLC EEC Project No. 1172058 March 23, 2023 Page 10 sandstone/siltstone/claystone bedrock encountered at the site could result in pile installation difficulties. The helical pier contractor working in conjunction with the project’s structural engineer, should be capable of designing a helical pier foundation system to accommodate the necessary loads for the project based on the structural engineer's load design calculations as well as a pile cap/foundation wall system where necessary. The helical piers may vary in depth and generally follow the underlying coarse granular stratum or the bedrock contours. However, bedrock was not encountered to maximum depths of exploration, thus the helical should be designed with the appropriate flight/helix configuration to end bear in the overburden subsoils. The helical piers should extend into the underlying subsurface strata sufficiently to achieve the design torque to support the anticipated loading parameters. A helical pier is installed to a design torque and not necessarily a required depth of penetration into the bedrock. As long as the required torque is achieved the helical pier install is then terminated. Typically, depending upon the design loads as well as the design torque, a helical pier may only extend a few feet into the underlying granular strata, and/or possibly the bedrock formation if encountered. The helical pier contractor and/or structural engineer should be capable of designing the helical pier system with the necessary shaft and helix configuration to accommodate the project. Helical piers should be considered to work in-group action if the horizontal spacing is less than 3 pile diameters from outside of flight to outside of flight distance. A minimum practical horizontal spacing between piles of at least 3 diameters should be maintained, and adjacent piles should bear at or near the same elevation. The capacity of individual piles must be reduced when considering the effects of group action. Capacity reduction is a function of pile spacing and the number of piles within a group. If group action analyses are necessary, capacity reduction factors can be provided for the analyses. A representative of the geotechnical engineering consulting firm should be present to observe helical pier installation to verify that proper bearing materials been encountered, and the design torque has been achieved during installation procedures. Conventional Type Spread Footing Foundations If a deep foundation system is cost prohibited and the ownership group is willing to accept a potential greater risk of movement, consideration could be given to supporting the boardwalk Earth Engineering Consultants, LLC EEC Project No. 1172058 March 23, 2023 Page 11 structures by the use of conventional spread footings bearing on a minimum 2-foot zone of placed and compacted imported structural fill material. To reduce the potential for post-construction movement of the footings, subsequent to construction, we recommend the in-place soils be removed/over-excavated to allow for at least 2 feet of imported structural fill below all foundation bearing elements. The over-excavated zone could be backfilled with an approved imported structural fill material placed and compacted as described in the General Considerations and Site Preparation section of this report. Prior to placement and compaction of the engineered fill material and/or approved structural fill an open hole/foundation excavation observation should be performed to observe the existing subsoils below the fill zone to determine if additional over-excavation is necessary. Footings bearing on a zone of at least 2-feet of approved structural fill material placed and compacted as described in the General Considerations and Site Preparation section of this report could be designed for a maximum net allowable total load soil bearing pressure of 2,000 psf. A minimum dead load pressure would not be required. The net bearing pressure refers to the pressure at foundation bearing level in excess of the minimum surrounding overburden pressure. Total load includes full dead load and live load conditions. Footings should be placed on similar like subsoils to minimize the potential for differential movement of dissimilar material. We estimate the total long-term settlement of footings designed as outlined above could be in the range of about ¾ to 2-inches, depending on the severity of surface water infiltration. After placement of the fill materials for foundation support, care should be taken to avoid wetting or drying of those materials. Bearing materials, which are loosened or disturbed by the construction activities or materials which become dry and desiccated or wet and softened, should be removed and replaced or reworked in place prior to construction of the overlying improvements. Foundations should be located at least 30 inches below adjacent exterior grade to provide frost protection. Seismic Conditions The site soil conditions consist of approximately 40 feet of overburden soils overlying soft to moderately hard to hard bedrock. For those site conditions, the 2015 International Building Code indicates a Seismic Site Classification of D. Earth Engineering Consultants, LLC EEC Project No. 1172058 March 23, 2023 Page 12 Lateral Earth Pressures Passive lateral earth pressures may help resist the driving forces for any retaining wall/wing wall or other similar site structures. Active lateral earth pressures could be used for design of structures where some movement of the structure is anticipated, such as retaining walls. The total deflection of structures for design with active earth pressure is estimated to be on the order of one half of one percent of the height of the down slope side of the structure. We recommend at-rest pressures be used for design of structures where rotation of the walls is restrained. Passive pressures and friction between the footing and bearing soils could be used for design of resistance to movement of retaining walls. Coefficient values for backfill with anticipated types of soils for calculation of active, at rest and passive earth pressures are provided in the table below. Those coefficient values are based on horizontal backfill with backfill soils consisting of on-site lean clay with varying amounts of sand subsoils with friction angles of 25 degrees and structural fill with friction angles of 35 degrees. Equivalent fluid pressure is equal to the appropriate coefficient times the appropriate soil unit weight. Care will be needed to account for buoyant soil weights and hydrostatic loading conditions as appropriate. For the at-rest and active earth pressures, slopes down and away from the structure would result in reduced driving forces with slopes up and away from the structures resulting in greater forces on the walls. The passive resistance would be reduced with slopes away from the wall. The top 30 inches of soil on the passive resistance side of walls could be used as a surcharge load; however, the top 30 inches of soil should not be used as part of the passive resistance value. Frictional resistance is equal to the tangent of the friction angle times the normal force. Surcharge loads or point loads placed in the backfill can also create additional loads on below grade walls. Those situations should be designed on an individual basis. Earth Engineering Consultants, LLC EEC Project No. 1172058 March 23, 2023 Page 13 Table IV – Lateral Earth Pressure Coefficients Soil Type On-Site Cohesive Subsoils Imported Medium Dense Granular Wet Unit Weight (pcf) 115 135 Saturated Unit Weight (pcf) 135 140 Friction Angle (φ) – (assumed) 25° 35° Active Pressure Coefficient 0.40 0.27 At-rest Pressure Coefficient 0.58 0.43 Passive Pressure Coefficient 2.46 3.70 The outlined values do not include factors of safety nor allowances for hydrostatic loads and are based on assumed friction angles and should be verified prior to construction. Care should be taken to develop appropriate systems in conjunction with below grade walls to eliminate potential for hydrostatic loads developing on the walls and/or design the walls to accommodate hydrostatic load conditions. Water Soluble Sulfates – (SO4) The water-soluble sulfate (SO4) testing of the on-site soils taken during our subsurface exploration at random locations and intervals are provided below. Based on reported sulfate contents test results this report includes a recommendation for the CLASS of cement for use for contact in association with the on-site subsoils. Table V - Water Soluble Sulfate Test Results Sample Location Description Soluble Sulfate Content (mg/kg) Soluble Sulfate Content (%) S-7, S-4 at 4' Lean Clay with Sand (CL) 110 0.01 S-9, S-1 at 2’ Lean Clay with Sand (CL) 340 0.03 Based on the results as presented above, ACI 318, Section 4.2 indicates the site soils have a low risk of sulfate attack on Portland cement concrete. Therefore, Class 0 and/or Type I/II cement could be used for concrete on and below site grades. Additional testing should be conducted to determine if different Classes and/or Types of cement can be used in other areas. Foundation concrete should be designed in accordance with the provisions of the ACI Design Manual, Section 318, Chapter 4. These results are being compared to the following table. Earth Engineering Consultants, LLC EEC Project No. 1172058 March 23, 2023 Page 14 Table VI - Requirements to Protect Against Damage to Concrete by Sulfate Attack from External Sources of Sulfate Severity of Sulfate exposure Water-soluble sulfate (SO4) in dry soil, percent Water-cement ratio, maximum Cementitious material Requirements Class 0 0.00 to 0.10% 0.45 Class 0 Class 1 0.11 to 0.20% 0.45 Class 1 Class 2 0.21 to 2.00% 0.45 Class 2 Class 3 2.01 of greater 0.45 Class 3 Other Considerations and Recommendations Excavations into the on-site soils will encounter a variety of conditions. Excavations into the clays can be expected to stand on relatively steep temporary slopes during construction. Groundwater seepage should also be anticipated for deeper utility excavations. Pumping from sumps may be utilized to control water within the excavations. Well points may be required for significant groundwater flow, or where excavations penetrate groundwater to a significant depth. 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. Positive drainage should be developed away from the structures and pavement areas with a minimum slope of 1 inch per foot for the first 10 feet away from the improvements in landscape areas. Care should be taken in planning of landscaping (if required) adjacent to the buildings to avoid features which would pond water adjacent to the foundations or stemwalls. Placement of plants which require irrigation systems or could result in fluctuations of the moisture content of the subgrade material should be avoided adjacent to site improvements. Irrigation systems should not be placed within 5 feet of the perimeter of the buildings and parking areas. Spray heads should be designed not to spray water on or immediately adjacent to the structures or site pavements. Roof drains should be designed to discharge at least 5 feet away from the structures and away from the pavement areas. 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 between borings or across the Earth Engineering Consultants, LLC EEC Project No. 1172058 March 23, 2023 Page 15 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; we suggest those explorations be completed by individual builders, if possible, prior to completing any site work. 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 the infrastructure construction phases to help determine that the design requirements are fulfilled. The builders should direct the testing of individual lot development. This report has been prepared for the exclusive use of Montava Development, 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. S-6 S-7 B-2 S-8 S-9 B-5 EARTH ENGINEERING CONSULTANTS, LLC Legend Boring Location Diagram Montava Development - Tract G Boardwalks Fort Collins, Colorado EEC Project #: 1172058 Date: March 2023 B-2 and B-5 Appro[ Locations oI Preliminar\ Borings, AXgXst 2018 S- ThroXgh S- Appro[ Locations oI SXpplemental Borings, March 2023 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 DISKED FIELD _ _ 1 SANDY LEAN CLAY (CL)_ _ brown 2 stiff to very stiff _ _ with calcareous deposits 3 _ _ 4 _ _ CS 5 12 9000+13.3 115.2 27 15 56.2 1300 psf 0.7% _ _ 6 _ _ 7 _ _ 8 _ _ 9 _ _ SS 10 8 8500 14.0 _ _ 11 _ _ 12 _ _ 13 _ _ 14 _ _ with gypsum crystals CS 15 18 8500 16.9 111.9 _ _ 16 _ _ 17 _ _ 18 _ _ 19 _ _ SS 20 20 9000+16.6 _ _ 21 _ _ 22 _ _ 23 _ _ 24 _ _ CS 25 12 7500 19.9 106.7 Continued on Sheet 2 of 2 _ _ Earth Engineering Consultants, LLC A-LIMITS SWELL SURFACE ELEV N/A 24 HOUR N/A FINISH DATE 8/7/2018 AFTER DRILLING N/A SHEET 1 OF 2 WATER DEPTH START DATE 8/7/2018 WHILE DRILLING None 40-ACRE PARCEL W OF 800-ACRE MIXED USE DEVELOPMENT FOR PSD FORT COLLINS, COLORADO PROJECT NO: 1172058B LOG OF BORING B-2 AUGUST 2018 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 _ _ very stiff 28 _ _ 29 _ _ SS 30 17 6000 16.2 _ _ BOTTOM OF BORING DEPTH 30.5'31 _ _ 32 _ _ 33 _ _ 34 _ _ 35 _ _ 36 _ _ 37 _ _ 38 _ _ 39 _ _ 40 _ _ 41 _ _ 42 _ _ 43 _ _ 44 _ _ 45 _ _ 46 _ _ 47 _ _ 48 _ _ 49 _ _ 50 _ _ Earth Engineering Consultants, LLC A-LIMITS SWELL N/A 8/7/2018 AFTER DRILLING N/A SURFACE ELEV 24 HOUR N/A FINISH DATE SHEET 2 OF 2 WATER DEPTH START DATE 8/7/2018 WHILE DRILLING None 40-ACRE PARCEL W OF 800-ACRE MIXED USE DEVELOPMENT FOR PSD FORT COLLINS, COLORADO PROJECT NO: 1172058B LOG OF BORING B-2 AUGUST 2018 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 / WEEDS _ _ 1 CLAYEY SAND / SANDY LEAN CLAY (SC / CL)_ _ brown 2 medium dense / very stiff to stiff _ _% @ 150 psf CS 3 17 9000+9.2 111.0 30 20 48.2 1200 psf 3.9% _ _ 4 with calcareous deposits _ _ SS 5 12 9000+11.5 _ _ 6 _ _ 7 _ _ 8 _ _ 9 _ _ CS 10 8 9000+11.3 112.3 _ _ 11 _ _ 12 _ _ 13 _ _ 14 with gypsum crystals _ _ SS 15 11 4500 17.8 _ _ 16 _ _ 17 _ _ 18 _ _ 19 _ _ CS 20 9 3500 20.1 106.9 _ _ 21 _ _ 22 _ _ 23 _ _ 24 brown / red / gray _ _ SS 25 15 6000 24.2 Continued on Sheet 2 of 2 _ _ Earth Engineering Consultants, LLC A-LIMITS SWELL SURFACE ELEV N/A 8/8/2018 24.9' FINISH DATE 8/7/2018 AFTER DRILLING N/A SHEET 1 OF 2 WATER DEPTH START DATE 8/7/2018 WHILE DRILLING 29' 40-ACRE PARCEL W OF 800-ACRE MIXED USE DEVELOPMENT FOR PSD FORT COLLINS, COLORADO PROJECT NO: 1172058B LOG OF BORING B-5 AUGUST 2018 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 _ _ CLAYEY SAND / SANDY LEAN CLAY (SC / CL)27 brown / red _ _ medium dense / stiff 28 with trace gravel _ _ 29 _ _ CS 30 15 6000 19.2 _ _ 31 _ _ 32 _ _ 33 _ _ 34 with intermittent sand & gravel seams _ _ SS 35 11 --21.4 _ _ 36 _ _ 37 _ _ 38 _ _ 39 SAND & GRAVEL (SP/GP)_ _ brown, medium dense SS 40 11 --16.2 with trace clay zones _ _ BOTTOM OF BORING DEPTH 40.5'41 _ _ 42 _ _ 43 _ _ 44 _ _ 45 _ _ 46 _ _ 47 _ _ 48 _ _ 49 _ _ 50 _ _ Earth Engineering Consultants, LLC A-LIMITS SWELL N/A 8/7/2018 AFTER DRILLING N/A SURFACE ELEV 8/8/2018 24.9' FINISH DATE SHEET 2 OF 2 WATER DEPTH START DATE 8/7/2018 WHILE DRILLING 29' 40-ACRE PARCEL W OF 800-ACRE MIXED USE DEVELOPMENT FOR PSD FORT COLLINS, COLORADO PROJECT NO: 1172058B LOG OF BORING B-5 AUGUST 2018 DATE: RIG TYPE: CME55 FOREMAN: AK 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 _ _ 1 _ _ LEAN CLAY with (CL)2 brown _ _ very stiff to stiff 3 with calcareous deposits _ _ 4 _ _ CS 5 27 9000+11.5 117.8 35 20 74.2 8000 (+) 4.8% _ _ 6 _ _ 7 _ _ 8 _ _ 9 _ _ SS 10 10 9000+26.7 _ _ 11 _ _ 12 _ _ 13 _ _ 14 _ _ CS 15 17 9000+15.2 115.7 BOTTOM OF BORING DEPTH 15'_ _ 16 _ _ 17 _ _ 18 _ _ 19 _ _ 20 _ _ 21 _ _ 22 _ _ 23 _ _ 24 _ _ 25 _ _ Earth Engineering Consultants, LLC MONTAVA DEVELOPMENT - PHASE G PROJECT NO: 1172058 LOG OF BORING S-6 MARCH 2023 FORT COLLINS, COLORADO SHEET 1 OF 1 WATER DEPTH START DATE 3/16/2023 WHILE DRILLING None SURFACE ELEV N/A 24 HOUR N/A FINISH DATE 3/16/2023 AFTER DRILLING N/A A-LIMITS SWELL DATE: RIG TYPE: CME55 FOREMAN: AK 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 _ _ 2 _ _ 3 _ _ 4 LEAN CLAY with SAND (CL)_ _ brown CS 5 13 9000+6.3 114.1 2500 (+) 3.1% stiff to medium stiff _ _ 6 _ _ 7 _ _ 8 _ _ 9 _ _ SS 10 14 9000+9.1 _ _ 11 _ _ 12 _ _ 13 _ _ 14 _ _@ 1000 PSF CS 15 20 9000+7.8 118.1 4000 (+) 3.1% _ _ 16 _ _ 17 _ _ 18 _ _ 19 _ _ SS 20 10 9000+10.2 _ _ 21 _ _ 22 _ _ 23 _ _ 24 _ _ CS 25 11 9000+20.3 104.6 BOTTOM OF BORING DEPTH 25'_ _ Earth Engineering Consultants, LLC MONTAVA DEVELOPMENT - PHASE G PROJECT NO: 1172058 LOG OF BORING S-7 MARCH 2023 FORT COLLINS, COLORADO SHEET 1 OF 1 WATER DEPTH START DATE 3/3/2023 WHILE DRILLING None SURFACE ELEV N/A 24 HOUR N/A FINISH DATE 3/3/2023 AFTER DRILLING N/A A-LIMITS SWELL DATE: RIG TYPE: CME55 FOREMAN: AK 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 DISCED FIELD _ _ 1 _ _ 2 LEAN CLAY with SAND (CL)_ _ brown CS 3 26 9000+9.1 118.8 very stiff, stiff to medium stiff _ _ 4 _ _ SS 5 15 _ _ 6 _ _ 7 _ _ 8 _ _ 9 _ _ CS 10 20 9000+8.8 113.8 29 13 76.6 1400 (+) 1.3% _ _ 11 _ _ 12 _ _ 13 _ _ 14 _ _ SS 15 11 9000+12.4 _ _ BOTTOM OF BORING DEPTH 15.5'16 _ _ 17 _ _ 18 _ _ 19 _ _ 20 _ _ 21 _ _ 22 _ _ 23 _ _ 24 _ _ 25 _ _ Earth Engineering Consultants, LLC MONTAVA DEVELOPMENT - PHASE G PROJECT NO: 1172058 LOG OF BORING S-8 MARCH 2023 FORT COLLINS, COLORADO SHEET 1 OF 1 WATER DEPTH START DATE 3/3/2023 WHILE DRILLING None SURFACE ELEV N/A 24 HOUR N/A FINISH DATE 3/3/2023 AFTER DRILLING N/A A-LIMITS SWELL DATE: RIG TYPE: CME55 FOREMAN: AK 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 DISCED FIELD _ _ 1 _ _ 2 LEAN CLAY with SAND (CL)_ _@ 150 PSF brown CS 3 18 9000+10.8 122.4 34 19 73.5 2000 (+) 5.1% stiff to medium stiff _ _ 4 _ _ SS 5 5 9000+11.6 _ _ 6 _ _ 7 _ _ 8 _ _ 9 _ _ CS 10 5 9000+10.7 116.5 4000 (+) 3.3% _ _ 11 _ _ 12 _ _ 13 _ _ 14 _ _ SS 15 11 9000+13.3 _ _ BOTTOM OF BORING DEPTH 15.5'16 _ _ 17 _ _ 18 _ _ 19 _ _ 20 _ _ 21 _ _ 22 _ _ 23 _ _ 24 _ _ 25 _ _ Earth Engineering Consultants, LLC MONTAVA DEVELOPMENT - PHASE G PROJECT NO: 1172058 LOG OF BORING S-9 MARCH 2023 FORT COLLINS, COLORADO SHEET 1 OF 1 WATER DEPTH START DATE 3/3/2023 WHILE DRILLING None SURFACE ELEV N/A 24 HOUR N/A FINISH DATE 3/3/2023 AFTER DRILLING N/A A-LIMITS SWELL Project: Location: Project #: Date: Montava Development - Tract G - Boardwalks Fort Collins, Colorado 1172058 March 2023 Beginning Moisture: 11.5%Dry Density: 118 pcf Ending Moisture: 16.6% Swell Pressure: 8000 psf % Swell @ 500:4.8% Sample Location:Boring 6, Sample 1, Depth 4' Liquid Limit: 35 Plasticity Index: 20 % Passing #200: 74.2% SWELL / CONSOLIDATION TEST RESULTS Material Description:Lean Clay with Sand (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)SwellConsolidationWater Added Project: Location: Project #: Date: Montava Development - Tract G - Boardwalks Fort Collins, Colorado 1172058 March 2023 Beginning Moisture: 6.3%Dry Density: 111.3 pcf Ending Moisture: 18.6% Swell Pressure: 2500 psf % Swell @ 500:3.1% Sample Location:Boring 7, Sample 1, Depth 4' Liquid Limit: - -Plasticity Index: - -% Passing #200: - - SWELL / CONSOLIDATION TEST RESULTS Material Description:Lean Clay with Sand (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)SwellConsolidationWater Added Project: Location: Project #: Date: Montava Development - Tract G - Boardwalks Fort Collins, Colorado 1172058 March 2023 Beginning Moisture: 7.8%Dry Density: 112.1 pcf Ending Moisture: 17.6% Swell Pressure: 4000 psf % Swell @ 1000:3.1% Sample Location:Boring 7, Sample 3, Depth 14' Liquid Limit: - -Plasticity Index: - -% Passing #200: - - SWELL / CONSOLIDATION TEST RESULTS Material Description:Lean Clay with Sand (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)SwellConsolidationWater Added Project: Location: Project #: Date: Montava Development - Tract G - Boardwalks Fort Collins, Colorado 1172058 March 2023 Beginning Moisture: 8.8%Dry Density: 102 pcf Ending Moisture: 20.6% Swell Pressure: 1400 psf % Swell @ 500:1.3% Sample Location:Boring 8, Sample 3, Depth 9' Liquid Limit: 29 Plasticity Index: 13 % Passing #200: 76.6% SWELL / CONSOLIDATION TEST RESULTS Material Description:Lean Clay with Sand (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)SwellConsolidationWater Added Project: Location: Project #: Date: Montava Development - Tract G - Boardwalks Fort Collins, Colorado 1172058 March 2023 Beginning Moisture: 10.8%Dry Density: 115.9 pcf Ending Moisture: 17.1% Swell Pressure: 2000 psf % Swell @ 150:5.1% Sample Location:Boring 9, Sample 1, Depth 2' Liquid Limit: 34 Plasticity Index: 19 % Passing #200: 73.5% SWELL / CONSOLIDATION TEST RESULTS Material Description:Lean Clay with Sand (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)SwellConsolidationWater Added Project: Location: Project #: Date: Montava Development - Tract G - Boardwalks Fort Collins, Colorado 1172058 March 2023 Beginning Moisture: 10.7%Dry Density: 118.1 pcf Ending Moisture: 15.4% Swell Pressure: 4000 psf % Swell @ 500:3.3% Sample Location:Boring 9, Sample 3, Depth 9' Liquid Limit: - -Plasticity Index: - -% Passing #200: - - SWELL / CONSOLIDATION TEST RESULTS Material Description:Lean Clay with Sand (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)SwellConsolidationWater Added 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