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HomeMy WebLinkAboutFRONT RANGE COMMUNITY COLLEGE SOUTH PARKING LOT EXPANSION - SPAR - SPA130004 - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTSubsurface Exploration Program Geotechnical and Pavement Recommendations Front Range Community College New South Parking Lot Ft. Collins, Colorado Prepared for: Adolfson & Peterson Construction 797 Ventura Street Aurora, CO 80011 Attention: Mr. Charles Zachemsky Job Number 13-0024A October 11, 2013 TABLE OF CONTENTS Page Purpose and Scope of Study ..................................................................................... 1 Proposed Construction .............................................................................................. 1 Site Conditions .......................................................................................................... 2 Subsurface Exploration ............................................................................................. 2 Laboratory Testing ...................................................................................................... 3 Subsurface Conditions .............................................................................................. 3 Exterior Flatwork ....................................................................................................... 4 Water Soluble Sulfates ............................................................................................... 5 Project Earthworks .................................................................................................... 6 Utility Pipe Installation and Backfilling ........................................................................ 9 Pavement Recommendations ................................................................................. 12 Closure and Limitations ........................................................................................... 17 Locations of Test Holes ................................................................................... Figure 1 Logs of Test Holes ......................................................................................... Figure 2 Legend and Notes ........................................................................................... Figure 3 Summary of Laboratory Test Results .............................................................. Table 1 Summary of Soil Corrosion Test Results ......................................................... Table 2 Pavement Section Calculations ................................................................. Appendix A Front Range Community College: South Parking Lot Ft. Collins, Colorado Job No. 13-0024A Ground Engineering Consultants, Inc. Page 1 of 19 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsurface exploration program performed by GROUND Engineering Consultants, Inc. (GROUND) to provide geotechnical recommendations for the proposed South Parking Lot at the Front Range Community College in Fort Collins, Colorado. The project site is located at 4616 South Shields Street. Our study was conducted in general accordance with GROUND’s Proposal No. 1302-0235, dated July 2, 2013. Field and office studies provided information regarding surface and subsurface conditions, including existing site vicinity improvements. Material samples retrieved during the subsurface exploration were tested in our laboratory to assess the engineering characteristics of the site earth materials, and assist in the development of our geotechnical recommendations. Results of the field, office, and laboratory studies are presented below. This report has been prepared to summarize the data obtained and to present our conclusions and recommendations based on the proposed construction and the subsurface conditions encountered. Design parameters and a discussion of engineering considerations related to construction of the proposed facility are included herein. PROPOSED CONSTRUCTION We understand the proposed construction is to include a new parking lot on the south end of the campus. Site grading plans were not available at the time of this report preparation. Based on existing topography, it appears that fills ranging up to 4 feet may be required to facilitate proper drainage. Development will likely include installation of underground utilities to service the proposed parking lot. If proposed construction, including the anticipated site grading, differ from those described above, or changes subsequently, GROUND should be notified to re-evaluate our recommendations in this report. Front Range Community College: South Parking Lot Ft. Collins, Colorado Job No. 13-0024A Ground Engineering Consultants, Inc. Page 2 of 19 SITE CONDITIONS At the time of our exploration, the site generally consisted of an open field with grasses and weeds. The general topography across the site was rolling with a slope ranging from approximately 2 to 4 percent descending generally to the north-northwest. The project site is bordered by the Harmony Library parking lot to the north, Shields Street to the west, an irrigation ditch to the north, and residential housing to the east. SUBSURFACE EXPLORATION The subsurface exploration for the project was conducted on February 22nd, 2013. A total of five (5) test holes were drilled with a truck-mounted, continuous flight power auger rig to evaluate the subsurface conditions as well as to retrieve soil samples for laboratory testing and analysis. A representative of GROUND directed the subsurface Front Range Community College: South Parking Lot Ft. Collins, Colorado Job No. 13-0024A Ground Engineering Consultants, Inc. Page 3 of 19 exploration, logged the test holes in the field, and prepared the soil samples for transport to our laboratory. Samples of the subsurface materials were retrieved with a 2-inch I.D. California liner sampler. The California sampler was driven into the substrata with blows from a 140- pound hammer falling 30 inches. This procedure is similar to the Standard Penetration Test described by ASTM Method D1586. Penetration resistance values, when properly evaluated, indicate the relative density or consistency of materials. Depths at which the samples were obtained and associated penetration resistance values are shown on the test hole logs. The approximate locations of the test holes are shown in Figure 1. Logs of the exploratory test holes are presented in Figure 2. Explanatory notes and a legend are provided in Figure 3. Elevations indicated on the test hole logs for test holes TH-1 through TH-3 were surveyed by a representative of the client. LABORATORY TESTING Samples retrieved from our test holes were examined and visually classified in the laboratory by the project engineer. Laboratory testing of soil samples obtained from the subject site included standard property tests, such as natural moisture contents, dry unit weights, grain size analyses, and liquid and plastic limits. Water-soluble sulfate and corrosivity tests were completed on selected samples of the materials as well. Laboratory tests were performed in general accordance with applicable ASTM and AASHTO protocols. Results of the laboratory testing program are summarized on Table 1. SUBSURFACE CONDITIONS The subsurface conditions encountered in the test holes generally consisted of a thin veneer of topsoil, approximately 6 inches thick, underlain by clay materials that extended to depths of approximately 4 to 10 feet below existing grades. Sandstone was encountered below the clay and extended to the test hole termination depths of approximately 20 to 40 feet below existing grade. Material descriptions of the subsurface materials are summarized on Figure 3 (Legend and Notes). Front Range Community College: South Parking Lot Ft. Collins, Colorado Job No. 13-0024A Ground Engineering Consultants, Inc. Page 4 of 19 Swell-Consolidation Testing results ranged from approximately 0.6 to 4.4 percent upon wetting against various surcharge loads (See Table 1). Groundwater was encountered in the foundation test holes at depths ranging from approximately 6 ½ to 9 ½ feet below existing grades when measured 8 days after drilling. Groundwater levels can be expected to fluctuate, however, in response to annual and longer-term cycles of precipitation, irrigation, surface drainage, land use, and the development of transient, perched water conditions. Man-made fill was not obviously encountered in our tests holes. The exact extents, limits, and composition of any man-made fill were not determined as part of the scope of work addressed by this study, and should be expected to exist at varying depths and locations across the site. EXTERIOR FLATWORK Proper design, drainage, construction and maintenance of the areas between parking/driveway areas are critical to the satisfactory performance of the project. Sidewalks, entranceway slabs and roofs, fountains, raised planters and other highly visible improvements commonly are installed within these zones, and distress in or near these improvements is common. Commonly, soil preparation in these areas receives little attention because they fall between the building and pavement (which are typically built with heavy equipment). Subsequent landscaping and hardscape installation often is performed by multiple sub-contractors with light or hand equipment, and over- excavation / soil processing is not performed. Therefore, GROUND recommends that the design team, contractor, and pertinent subcontractors take particular care with regard to proper subgrade preparation around the structure exteriors. Exterior flatwork and other hardscaping placed on the soils encountered on-site may experience post-construction movements due to volume change of the subsurface soils and the relatively light loads that they impose. Both vertical and lateral soil movements can be anticipated as the soils experience volume change as the moisture content varies. Distress to rigid hardscaping likely will result, some of which may be significant. The following measures will help to reduce, but not eliminate damages to these improvements. Front Range Community College: South Parking Lot Ft. Collins, Colorado Job No. 13-0024A Ground Engineering Consultants, Inc. Page 5 of 19 Provided the owner understands the risks identified above, we believe that subgrade under exterior flatwork or other (non-building) site improvements could be excavated and/or scarified to a minimum depth of 12 or more inches. The excavated soil should be replaced as properly moisture-conditioned and compacted fill as outlined in the Project Earthwork section of this report. As stated above, greater depths of moisture-density conditioning of the subgrade soils beyond the above minimum will improve hardscape performance, however should be based on acceptable risk. Prior to placement of flatwork, a proof roll should be performed to identify areas that exhibit instability and deflection. The soils in these areas should be removed and replaced with properly compacted fill or stabilized. Flatwork should be provided with effective control joints. Increasing the frequency of joints may improve performance. ACI recommendations should be followed regarding construction and/or control joints. As discussed in the Surface Drainage section of this report, proper drainage also should be maintained after completion of the project, and re-established as necessary. In no case should water be allowed to pond on or near any of the site improvements or a reduction in performance should be anticipated. WATER-SOLUBLE SULFATES The concentrations of water-soluble sulfates measured in a selected sample retrieved from the test hole TH-1 was approximately 0.01 percent by weight. (See Table 2.) Such concentrations of water-soluble sulfates represent a negligible degree of sulfate attack on concrete exposed to these materials. Degrees of attack are based on the scale of 'negligible,' 'moderate,' 'severe' and 'very severe' as described in the “Design and Control of Concrete Mixtures,” published by the Portland Cement Association (PCA). The Colorado Department of Transportation (CDOT) utilizes a corresponding scale with 4 classes of severity of sulfate exposure (Class 0 to Class 3) as described in the published table below. Front Range Community College: South Parking Lot Ft. Collins, Colorado Job No. 13-0024A Ground Engineering Consultants, Inc. Page 6 of 19 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 (%) Sulfate (SO4) In Water (ppm) Water Cementitious Ratio (maximum) Cementitious Material Requirements Class 0 0.00 to 0.10 0 to 150 0.45 Class 0 Class 1 0.11 to 0.20 151 to 1500 0.45 Class 1 Class 2 0.21 to 2.00 1501 to 10,000 0.45 Class 2 Class 3 2.01 or greater 10,001 or greater 0.40 Class 3 Based on these data GROUND, makes no recommendation for use of a special, sulfate- resistant cement in project concrete. PROJECT EARTHWORKS Based existing topography, it appears that fills ranging up to 4 feet will be required to facilitate proposed construction. Site grading should be planned carefully to provide positive surface drainage away from all buildings, pavements, utility alignments, and flatwork. Surface diversion features should be provided around paved areas to prevent surface runoff from flowing across the paved surfaces. General Considerations: Site grading should be performed as early as possible in the construction sequence to allow settlement of fills and surcharged ground to be realized to the greatest extent prior to subsequent construction. Prior to earthwork construction, existing structures, vegetation and other deleterious materials should be removed and disposed of off-site. Relic underground utilities should be abandoned in accordance with applicable regulations, removed as necessary, and properly capped. Topsoil present on-site should not be incorporated into ordinary fills. Instead, topsoil should be stockpiled during initial grading operations for placement in areas to be landscaped or for other approved uses. Use of Existing Native Soils: Overburden soils that are free of trash, organic material, construction debris, and other deleterious materials are suitable, in general, for Front Range Community College: South Parking Lot Ft. Collins, Colorado Job No. 13-0024A Ground Engineering Consultants, Inc. Page 7 of 19 placement as compacted fill. Organic materials should not be incorporated into project fills. Fragments of rock, cobbles, and inert construction debris (e.g., concrete or asphalt) larger than 3 inches in maximum dimension will require special handling and/or placement to be incorporated into project fills. In general, such materials should be placed as deeply as possible in the project fills. A Geotechnical Engineer should be consulted regarding appropriate recommendations for usage of such materials on a case-by-case basis when such materials have been identified during earthwork. Standard recommendations that likely will be generally applicable can be found in Section 203 of the current CDOT Standard Specifications for Road and Bridge Construction. Imported Fill Materials: If it is necessary to import material to the site, the imported soils should be free of organic material, and other deleterious materials. Imported material should consist of relatively impervious soils that have less than 50 percent passing the No. 200 Sieve and should have a plasticity index of less than 15. Representative samples of the materials proposed for import should be tested and approved prior to transport to the site. Fill Platform Preparation: Prior to filling, the top 12 inches of in-place materials on which fill soils will be placed should be scarified, moisture conditioned and properly compacted in accordance with the recommendations below to provide a uniform base for fill placement. If over-excavation is to be performed, then these recommendations for subgrade preparation are for the subgrade below the bottom of the specified over- excavation depth. If surfaces to receive fill expose loose, wet, soft or otherwise deleterious material, additional material should be excavated, or other measures taken to establish a firm platform for filling. The surfaces to receive fill must be effectively stable prior to placement of fill. Fill Placement: Fill materials should be thoroughly mixed to achieve a uniform moisture content, placed in uniform lifts not exceeding 8 inches in loose thickness, and properly compacted. Front Range Community College: South Parking Lot Ft. Collins, Colorado Job No. 13-0024A Ground Engineering Consultants, Inc. Page 8 of 19 Soils that classify as GP, GW, GM, GC, SP, SW, SM, or SC in accordance with the USCS classification system (granular materials) should be compacted to 95 or more percent of the maximum standard Proctor dry density at moisture contents within 2 percent of optimum moisture content as determined by ASTM D698. Site soils that classify as ML or CL should be compacted to 95 percent of the maximum standard Proctor density at moisture contents from 1 percent below to 3 percent above the optimum moisture content as determined by ASTM D698. It may be necessary to rework the fill materials more than once by adjusting moisture and replacing the materials, in order to achieve the recommended compaction and moisture criteria. No fill materials should be placed, worked, rolled while they are frozen, thawing, or during poor/inclement weather conditions. Care should be taken with regard to achieving and maintaining proper moisture contents during placement and compaction. Materials that are not properly moisture conditioned may exhibit significant pumping, rutting, and deflection at moisture contents near optimum and above. The Contractor should be prepared to handle soils of this type, including the use of chemical stabilization, if necessary. Compaction areas should be kept separate, and no lift should be covered by another until relative compaction and moisture content within the recommended ranges are obtained. Use of Squeegee: Relatively uniformly graded fine gravel or coarse sand, i.e., “squeegee,” or similar materials commonly are proposed for backfilling foundation excavations, utility trenches (excluding approved pipe bedding), and other areas where employing compaction equipment is difficult. In general, GROUND does not recommend this procedure for the following reasons: Although commonly considered “self compacting,” uniformly graded granular materials require densification after placement, typically by vibration. The equipment to densify these materials is not available on many job-sites. Even when properly densified, uniformly graded granular materials are permeable and allow water to reach and collect in the lower portions of the excavations backfilled with Front Range Community College: South Parking Lot Ft. Collins, Colorado Job No. 13-0024A Ground Engineering Consultants, Inc. Page 9 of 19 those materials. This leads to wetting of the underlying soils and resultant potential loss of bearing support as well as increased local heave or settlement. GROUND recommends that wherever possible, excavations be backfilled with approved, on-site soils placed as properly compacted fill. Where this is not feasible, use of “Controlled Low Strength Material” (CLSM), i.e., a lean, sand-cement slurry (“flowable fill”) or a similar material for backfilling should be considered. Where “squeegee” or similar materials are proposed for use by the Contractor, the design team should be notified by means of a Request for Information (RFI), so that the proposed use can be considered on a case-by-case basis. Where “squeegee” meets the project requirements for pipe bedding material, however, it is acceptable for that use. Settlements: Settlements will occur in filled ground, typically on the order of 1 to 2 percent of the fill depth. If fill placement is performed properly and is tightly controlled, in GROUND’s experience the majority (on the order of 60 to 80 percent) of that settlement will typically take place during earthwork construction, provided the contractor achieves the compaction levels recommended herein. The remaining potential settlements likely will take several months or longer to be realized, and may be exacerbated if these fills are subjected to changes in moisture content. Cut and Filled Slopes: Permanent site slopes supported by on-site soils up to 10 feet in height may be constructed no steeper than 3:1 (horizontal : vertical). Minor raveling or surficial sloughing should be anticipated on slopes cut at this angle until vegetation is well re-established. Surface drainage should be designed to direct water away from slope faces. UTILITY PIPE INSTALLATION AND BACKFILLING Pipe Support: The bearing capacity of the site soils appeared adequate, in general, for support of buried utilities. The utilities, typically, are less dense than the soils which will be displaced for installation. Therefore, GROUND anticipates no significant pipe settlements in these materials where properly bedded. Excavation bottoms may expose soft, loose or otherwise deleterious materials, including debris. Firm materials may be disturbed by the excavation process. All such unsuitable Front Range Community College: South Parking Lot Ft. Collins, Colorado Job No. 13-0024A Ground Engineering Consultants, Inc. Page 10 of 19 materials should be excavated and replaced with properly compacted fill. Areas allowed to pond water will require excavation and replacement with properly compacted fill. The contractor should take particular care to ensure adequate support near pipe joints which are less tolerant of extensional strains. Trench Backfilling: Some settlement of compacted soil trench backfill materials should be anticipated, even where all the backfill is placed and compacted correctly. Typical settlements are on the order of 1 to 2 percent of fill thickness. However, the need to compact to the lowest portion of the backfill must be balanced against the need to protect the pipe from damage from the compaction process. Some thickness of backfill may need to be placed at compaction levels lower than recommended or specified (or smaller compaction equipment used together with thinner lifts) to avoid damaging the pipe. Protecting the pipe in this manner can result in somewhat greater surface settlements. Therefore, although other alternatives may be available, the following options are presented for consideration: Controlled Low Strength Material: Because of these limitations, we recommend backfilling the entire depth of the trench (both bedding and common backfill zones) with “controlled low strength material” (CLSM), i.e., a lean, sand-cement slurry, “flowable fill,” or similar material along all trench alignment reaches with low tolerances for surface settlements. We recommend that CLSM used as pipe bedding and trench backfill exhibit a 28-day unconfined compressive strength between 50 to 200 psi so that re-excavation is not unusually difficult. Placement of the CLSM in several lifts or other measures likely will be necessary to avoid ‘floating’ the pipe. Measures also should be taken to maintain pipe alignment during CLSM placement. Compacted Soil Backfilling: Where compacted soil backfilling is employed, using the site soils or similar materials as backfill, the risk of backfill settlements entailed in the selection of this higher risk alternative must be anticipated and accepted by the Client/Owner. Front Range Community College: South Parking Lot Ft. Collins, Colorado Job No. 13-0024A Ground Engineering Consultants, Inc. Page 11 of 19 We anticipate that the on-site soils excavated from trenches will be suitable, in general, for use as common trench backfill within the above-described limitations. Backfill soils should be free of vegetation, organic debris and other deleterious materials. Fragments of rock, cobbles, and inert construction debris (e.g., concrete or asphalt) coarser than 3 inches in maximum dimension should not be incorporated into trench backfills. If it is necessary to import material for use as backfill, the imported soils should be free of vegetation, organic debris, and other deleterious materials. Imported material should consist of relatively impervious soils that have less than 60 percent passing the No. 200 Sieve and should have a plasticity index of less than 15. Representative samples of the materials proposed for import should be tested and approved prior to transport to the site. Soils placed for compaction as trench backfill should be conditioned to a relatively uniform moisture content, placed and compacted in accordance with the recommendations in the Project Earthwork section of this report. Pipe Bedding: Pipe bedding materials, placement and compaction should meet the specifications of the pipe manufacturer and applicable municipal standards. Bedding should be brought up uniformly on both sides of the pipe to reduce differential loadings. As discussed above, we recommend the use of CLSM or similar material in lieu of granular bedding and compacted soil backfill where the tolerance for surface settlement is low. (Placement of CLSM as bedding to at least 12 inches above the pipe can protect the pipe and assist construction of a well-compacted conventional backfill, although possibly at an increased cost relative to the use of conventional bedding.) If a granular bedding material is specified, GROUND recommends that with regard to potential migration of fines into the pipe bedding, design and installation follow ASTM D2321. If the granular bedding does not meet filter criteria for the enclosing soils, then non-woven filter fabric (e.g., Mirafi® 140N, or the equivalent) should be placed around the bedding to reduce migration of fines into the bedding which can result in severe, local surface settlements. Where this protection is not provided, settlements can develop/continue several months or years after completion of the project. In addition, clay or concrete cut-off walls should be installed to interrupt the granular bedding section Front Range Community College: South Parking Lot Ft. Collins, Colorado Job No. 13-0024A Ground Engineering Consultants, Inc. Page 12 of 19 to reduce the rates and volumes of water transmitted along the utility alignment which can contribute to migration of fines. If granular bedding is specified, the contractor should anticipate that significant volumes of on-site soils may not be suitable for that use. Materials proposed for use as pipe bedding should be tested by a geotechnical engineer for suitability prior to use. Imported materials should be tested and approved by a geotechnical engineer prior to transport to the site. PAVEMENT RECOMMENDATIONS A pavement section is a layered system designed to distribute concentrated traffic loads to the subgrade. Performance of the pavement structure is directly related to the physical properties of the subgrade soils and traffic loadings. The standard care of practice in pavement design describes the recommended flexible pavement section as a “20-year” design pavement: however, most flexible pavements will not remain in satisfactory condition without routine maintenance and rehabilitation procedures performed throughout the life of the pavement. Pavement designs for the private pavements were developed in general accordance with the design guidelines and procedures of the American Association of State Highway and Transportation Officials (AASHTO). Subgrade Materials Based on the results of our field exploration and laboratory testing, the potential pavement subgrade materials classify as A-6 to A-7-6 soils in accordance with the American Association of State Highway and Transportation Officials (AASHTO) classification system. Based on our experience at similar sites, an assumed resilient modulus value of 3,025 psi was estimated for the on-site materials. It is important to note that significant decreases in soil support have been observed as the moisture content increases above the optimum. Pavements that are not properly drained may experience a loss of the soil support and subsequent reduction in pavement life. Front Range Community College: South Parking Lot Ft. Collins, Colorado Job No. 13-0024A Ground Engineering Consultants, Inc. Page 13 of 19 Anticipated Traffic Based on our experience with similar projects equivalent 18-kip daily load application (EDLA) values of 4 and 8 were assumed for the general parking areas and drive lanes areas, respectively. The EDLA values of 4 and 8 were converted to equivalent 18-kip single axle load (ESAL) values of 29,200 and 58,400, respectively for a 20-year design life. If anticipated traffic loadings differ significantly from these assumed values, GROUND should be notified to re-evaluate the pavement recommendations below Pavement Recommendations The soil resilient modulus and the ESAL values were used to determine the required design structural number for the project pavements. The required structural number was then used to develop recommended pavement sections. Pavement sections were based on the DARWin™ computer program that solves the 1993 AASHTO pavement design equations. A Reliability Level of 85 percent and a terminal serviceability of 2.0 were utilized for the pavement sections. A structural coefficient of 0.40 was used for hot bituminous asphalt and 0.10 was used for aggregate base course. The minimum pavement sections recommended by GROUND for a 20-year design are tabulated below. Recommended Minimum Pavement Sections Location Full Depth Flexible Pavement Section (inches Asphalt) Composite Flexible Pavement Section (inches Asphalt / inches Aggregate Base) Rigid Pavement Section (inches Concrete / inches Aggregate Base) General Parking 6.5 4.5 / 8.0 - High Traffic 7.5 5.0 / 10.0 6.0 / 6.0 Additionally, trash collection areas, loading docks, as well as other pavement areas subjected to high turning stresses or heavy truck traffic be provided with rigid pavements consisting of Portland cement concrete (see table above). Additionally, the owner should consider reinforced concrete in these areas. Concrete sections should be underlain by 6 inches of properly compacted aggregate base. Front Range Community College: South Parking Lot Ft. Collins, Colorado Job No. 13-0024A Ground Engineering Consultants, Inc. Page 14 of 19 Asphalt pavement should consist of a bituminous plant mix composed of a mixture of aggregate and bituminous material. Asphalt mixture(s) should meet the requirements of a job-mix formula established by a qualified Engineer. Concrete pavements should consist of a plant mix composed of a mixture of aggregate, Portland cement and appropriate admixtures meeting the requirements of a job-mix formula established by a qualified engineer. Concrete should have a minimum modulus of rupture of third point loading of 650 psi. Normally, concrete with a 28-day compressive strength of 4,000 psi should develop this modulus of rupture value. The concrete should be air-entrained with approximately 6 percent air and should have a minimum cement content of 6 sacks per cubic yard. Maximum allowable slump should be 4 inches. In areas of repeated turning stresses we recommend that the concrete pavement joints be fully tied or doweled. We suggest that civil design consider joint layout in accordance with CDOT’s M Standards. Standard plans for placement of ties and dowels, etc., (CDOT M Standards) for concrete pavements can be found at the CDOT website: http://www.dot.state.co.us/DesignSupport/ If composite flexible sections are placed, the aggregate base material should meet the criteria of CDOT Class 6 aggregate base course. Base course should be placed in uniform lifts not exceeding 8 inches in loose thickness and compacted to at least 95 percent of the maximum dry density a uniform moisture contents within 3 percent of the optimum as determined by ASTM D1557 / AASHTO T-180, the “modified Proctor.” Subgrade Preparation Prior to the placement of pavement, including aggregate base, the exposed subgrade soils should be over excavated to a depth of at least 2 feet, mixed to achieve a uniform moisture content and then re-compacted in accordance with the recommendations provided in the Project Earthworks section of this report. Subgrade preparation should extend the full width of the pavement from back-of-curb to back-of-curb. The Contractor should be prepared either to dry the subgrade materials or moisten them, as needed, prior to compaction. It may be difficult for the contractor to achieve and maintain compaction in some on-site soils encountered without careful control of water contents. Likewise, some site soils likely will “pump” or deflect during compaction if moisture levels are not carefully controlled. The Contractor should be prepared to Front Range Community College: South Parking Lot Ft. Collins, Colorado Job No. 13-0024A Ground Engineering Consultants, Inc. Page 15 of 19 process and compact such soils to establish a stable platform for paving, including use of chemical stabilization, if necessary. Immediately prior to paving, the subgrade should be proof rolled with a heavily loaded, pneumatic tired vehicle. Areas that show excessive deflection during proof rolling should be excavated and replaced and/or stabilized. Areas allowed to pond prior to paving will require significant re-working prior to proof-rolling. Passing a proof roll is an additional requirement, beyond placement and compaction of the subgrade soils in accordance with the recommendations in this report. Some soils that are compacted in accordance with the recommendations herein may not be stable under a proof roll, particularly at moisture contents in the upper portion of the acceptable range. Additional Observations The collection and diversion of surface drainage away from paved areas is extremely important to the satisfactory performance of the pavements. The subsurface and surface drainage systems should be carefully designed to ensure removal of the water from paved areas and subgrade soils. Allowing surface waters to pond on pavements will cause premature pavement deterioration. Where topography, site constraints, or other factors limit or preclude adequate surface drainage, pavements should be provided with edge drains to reduce loss of subgrade support. The long-term performance of the pavement also can be improved greatly by proper backfilling and compaction behind curbs, gutters, and sidewalks so that ponding is not permitted and water infiltration is reduced. Landscape irrigation in planters adjacent to pavements and in “island” planters within paved areas should be carefully controlled or differential heave and/or rutting of the nearby pavements will result. Drip irrigation systems are recommended for such planters to reduce over-spray and water infiltration beyond the planters. Enclosing the soil in the planters with plastic liners and providing them with positive drainage also will reduce differential moisture increases in the surrounding subgrade soils. In our experience, infiltration from planters adjacent to pavements is a principal source of moisture increase beneath those pavements. This wetting of the subgrade soils from infiltrating irrigation commonly leads to loss of subgrade support for the pavement with resultant accelerating distress, loss of pavement life and increased maintenance costs. This is particularly the case in the later stages of project construction after landscaping has been emplaced but heavy construction traffic has not ended. Heavy vehicle traffic Front Range Community College: South Parking Lot Ft. Collins, Colorado Job No. 13-0024A Ground Engineering Consultants, Inc. Page 16 of 19 over wetted subgrade commonly results in rutting and pushing of flexible pavements, and cracking of rigid pavements. In relatively flat areas where design drainage gradients necessarily are small, subgrade settlement can obstruct proper drainage and yield increased infiltration, exaggerated distress, etc. (These considerations apply to project flatwork, as well.) As noted above, the standard care of practice in pavement design describes the recommended flexible pavement section as a “20-year” design pavement; however, most pavements will not remain in satisfactory condition without routine, preventive maintenance and rehabilitation procedures performed throughout the life of the pavement. Preventive pavement treatments are surface rehabilitation and operations applied to improve or extend the functional life of a pavement. These treatments preserve, rather than improve, the structural capacity of the pavement structure. In the event the existing pavement is not structurally sound, the preventive maintenance will have no long-lasting effect. Therefore, a routine maintenance program to seal cracks, repair distressed areas, and perform thin overlays throughout the life of the pavement is recommended. A crack sealing and fog seal/chip seal program should be performed on the pavements every 3 to 4 years. After approximately 8 to 10 years, patching, additional crack sealing, and asphalt overlay may be required. Prior to future overlays, it is important that all transverse and longitudinal cracks be sealed with a flexible, rubberized crack sealant in order to reduce the potential for propagation of the crack through the overlay. Traffic volumes that exceed the values utilized by this report will likely necessitate the need of pavement maintenance practices on a schedule of shorter timeframe than that stated above. The greatest benefit of preventive maintenance is achieved by placing the treatments on sound pavements that have little or no distress. GROUND’s experience indicates that longitudinal cracking is common in asphalt- pavements generally parallel to the interface between the asphalt and concrete structures such as curbs, gutters or drain pans. Distress of this type is likely to occur even where the subgrade has been prepared properly and the asphalt has been compacted properly. The use of thick base course or reinforced concrete pavement can reduce this. Our office should be contacted if these alternates are desired. The assumed traffic loading does not include excess loading conditions imposed by heavy construction vehicles. Consequently, heavily loaded concrete, lumber, and Front Range Community College: South Parking Lot Ft. Collins, Colorado Job No. 13-0024A Ground Engineering Consultants, Inc. Page 17 of 19 building material trucks can have a detrimental effect on the pavement. GROUND recommends that an effective program of regular maintenance be developed and implemented to seal cracks, repair distressed areas, and perform thin overlays throughout the life of the pavements. CLOSURE Geotechnical Review: The author of this report or a company principal should be retained to review project plans and specifications to evaluate whether they comply with the intent of the recommendations in this report. The review should be requested in writing. The geotechnical recommendations presented in this report are contingent upon observation and testing of project earthworks by representatives of GROUND. If another geotechnical consultant is selected to provide materials testing, then that consultant must assume all responsibility for the geotechnical aspects of the project by concurring in writing with the recommendations in this report, or by providing alternative recommendations. Materials Testing: The Client should consider retaining a Geotechnical Engineer to perform materials testing during construction. The performance of such testing or lack thereof, in no way alleviates the burden of the contractor or subcontractor from constructing in a manner that conforms to applicable project documents and industry standards. The contractor or pertinent subcontractor is ultimately responsible for managing the quality of their work; furthermore, testing by the geotechnical engineer does not preclude the contractor from obtaining or providing whatever services they deem necessary to complete the project in accordance with applicable documents. Limitations: This report has been prepared for the Adolfson and Peterson as it pertains to design of the proposed Front Range Community College; New South Parking Lot as described herein. It may not contain sufficient information for other parties or other purposes. This document, together with the concepts and recommendations presented herein, as an instrument of service, is intended only for the specific purpose and client for which it was prepared. Reuse of and/or improper reliance on this document without written authorization and adaption by GROUND Engineering Consultants, Inc. shall be without liability to GROUND Engineering Consultants, Inc. Front Range Community College: South Parking Lot Ft. Collins, Colorado Job No. 13-0024A Ground Engineering Consultants, Inc. Page 18 of 19 In addition, GROUND has assumed that project construction will commence by Spring 2014. Any changes in project plans or schedule should be brought to the attention of the Geotechnical Engineer, in order that the geotechnical recommendations may be re- evaluated and, as necessary, modified. The geotechnical conclusions and recommendations in this report relied upon subsurface exploration at a limited number of exploration points, as shown in Figure 1, as well as the means and methods described herein. Subsurface conditions were interpolated between and extrapolated beyond these locations. It is not possible to guarantee the subsurface conditions are as indicated in this report. Actual conditions exposed during construction may differ from those encountered during site exploration. If during construction, surface, soil, bedrock, or groundwater conditions appear to be at variance with those described herein, the Geotechnical Engineer should be advised at once, so that re-evaluation of the recommendations may be made in a timely manner. ALL DEVELOPMENT CONTAINS INHERENT RISKS. It is important that ALL aspects of this report, as well as the estimated performance (and limitations with any such estimations) of proposed project improvements are understood by Adolfson and Peterson Construction, the Owner, and properly conveyed to any future owner(s). Utilizing these recommendations for planning, design, and/or construction constitutes understanding and acceptance of the recommendations and other information provided herein, the potential risks, associated improvement performance, as well as the limitations inherent within such estimations. If any information referred to herein is not well understood, it is imperative for Adolfson and Peterson, or anyone using this report to contact the author or a GROUND principal immediately. We are available to meet to discuss the risks and remedial approaches presented in this report, as well as other potential approaches, upon request. This report was prepared in accordance with generally accepted soil and foundation engineering practice in the project area at the date of preparation. GROUND makes no warranties, either expressed or implied, as to the professional data, opinions or recommendations contained herein. Because of numerous considerations that are Front Range Community College: South Parking Lot Ft. Collins, Colorado Job No. 13-0024A Ground Engineering Consultants, Inc. Page 19 of 19 beyond GROUND’s control, the economic or technical performance of the project cannot be guaranteed in any respect. GROUND appreciates the opportunity to complete this portion of the project and welcomes the opportunity to provide the Owner with a cost proposal for construction observation and materials testing prior to construction commencement. Sincerely, GROUND Engineering Consultants, Inc. Kelsey Van Bemmel, P.E. Reviewed by Joseph Zorack, P.E Indicates test hole number and approximate location. (Not to Scale) LOCATION OF TEST HOLES CADFILE NAME: 0024SITE.DWG JOB NO.: 13-0024 FIGURE: 1 1 TH-1 TH-2 TH-3 P-1 P-2 Elevation - Feet Test Hole Test Hole Test Hole 5085 TH-1 TH-2 TH-3 JOB NO.: CADFILE NAME: 13-0024 FIGURE: 2 LOGS OF TEST HOLES 0024LOG.DWG 5080 5075 5070 5065 5060 5055 5050 5045 5040 Elev. 5082.5' Elev. 5079.3' Elev. 5079.4' 13/12 33/12 50/9 50/6 50/4 0 15/12 50/12 50/9 50/5 44/12 50/8 50/6 50/5 0 8 8 8 Test Hole Test Hole P-1 P-2 Elev. Unknown Elev. Unknown 12/12 14/12 JOB NO.: CADFILE NAME: FIGURE: LEGEND AND NOTES 13-0024 0024LEG.DWG 3 LEGEND: 7) The material descriptions on this legend are for general classification purposes only. See the full text of this report for related recommendations. Topsoil Clay: Sandstone Bedrock: Drive sample, 2-inch I.D. California liner sample Drive sample blow count, indicates 23 blows of a 140-pound hammer falling 30 inches were required to drive the sampler 12 inches. 23/12 Depth to water level and number of days after drilling that measurement was taken. 0 with 4-inch diameter continuous flight augers. 4) The test hole locations and elevations should be considered accurate only to the degree 3) Elevations of the test holes surveyed by a representative of the client and 2) Locations of test holes TH-1, TH-2, and TH-3 were surveyed by a representative of the client. P-1 and P-2 boundaries between material types and the transitions may be gradual. 5) The lines between materials shown on the test hole logs represent the approximate implied by the method used. were measured approximately by pacing from features shown on the site plan provided. 1) Test holes were drilled on 07/08/2013 the logs of the test holes are drawn to elevation. NOTES: indicated. Fluctuations in the water level may occur with time. 6) Groundwater level readings shown on the logs were made at the time and under the conditions Materials ranged from slightly sandy to sandy, were fine to medium grained, slightly moist to moist, medium to highly plastic, stiff to very stiff, light to dark brown with occasional iron staining. Fine to medium grained, dry to wet, non to low plasticity, medium to very hard, light brown to gray in color with iron staining. TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Sample Location Natural Natural Percent Atterberg Limits Percent USCS AASHTO Test Moisture Dry Passing Liquid Plasticity Swell Classifi- Classifi- Soil or Hole Depth Content Density No. 200 Limit Index (Surcharge cation cation Bedrock Type No. (feet) (%) (pcf) Sieve Pressure) (GI) TH-1 4 20.6 103.9 88 43 22 2.2 (500) CL A-7-6 (20) Slightly Sandy Clay TH-1 9 13.2 117.0 56 31 10 0.6(1000) CL A-4 (3) Sandy Clay TH-2 3 18.2 104.2 79 46 26 4.4 (500) CL A-7-6 (20) Sandy Clay TH-2 8 13.9 120.2 64 33 14 1.4 (1000) CL A-6 (7) Sandy Clay TH-3 4 9.4 129.5 28 NA NP - SM A-2-4 (0) Sand Stone TH-3 14 15.5 110.6 46 NA NP - SM A-4 (0) Sand Stone P-1 3 12.5 106.3 71 35 16 - CL A-6(10) Sandy Clay P-1 2 11.4 105.7 67 37 18 - CL A-6(10) Sandy Clay Job No. 13-0024 TABLE 2 SUMMARY OF SOIL CORROSION TEST RESULTS Sample Location Water Redox Sulfides USCS Test Soluble pH Potential Content Resistivity Classifi- Soil or Hole Depth Sulfates cation Bedrock Type No. (feet) (%) (mV) (ohm-cm) TH-1 4 0.01 6.1 -288 Trace 1,121 CL Slightly Sandy Clay Job No. 13-0024 APPENDIX A: Pavement Section Calculations Page 1 1993 AASHTO Pavement Design DARWin Pavement Design and Analysis System A Proprietary AASHTOWare Computer Software Product Network Administrator Flexible Structural Design Module Front Range Community College South Parking Lot Fort Collins, CO Driveways, Entrances, Exits Composite Section Flexible Structural Design 18-kip ESALs Over Initial Performance Period 58,400 Initial Serviceability 4.5 Terminal Serviceability 2 Reliability Level 85 % Overall Standard Deviation 0.44 Roadbed Soil Resilient Modulus 3,025 psi Stage Construction 1 Calculated Design Structural Number 2.81 in Specified Layer Design Layer Material Description Struct Coef. (Ai) Drain Coef. (Mi) Thickness (Di)(in) Width (ft) Calculated SN (in) 1 Hot Mix Asphalt 0.4 1 5 - 2.00 2 Aggregate Base Course 0.1 1 10 - 1.00 Total - - - 15.00 - 3.00 Page 1 1993 AASHTO Pavement Design DARWin Pavement Design and Analysis System A Proprietary AASHTOWare Computer Software Product Network Administrator Flexible Structural Design Module Front Range Community College South Parking Lot Parking Stalls Composite Section Flexible Structural Design 18-kip ESALs Over Initial Performance Period 29,200 Initial Serviceability 4.5 Terminal Serviceability 2 Reliability Level 85 % Overall Standard Deviation 0.44 Roadbed Soil Resilient Modulus 3,025 psi Stage Construction 1 Calculated Design Structural Number 2.54 in Specified Layer Design Layer Material Description Struct Coef. (Ai) Drain Coef. (Mi) Thickness (Di)(in) Width (ft) Calculated SN (in) 1 Hot Mix Asphalt 0.4 1 4.5 - 1.80 2 Aggregate Base Course 0.1 1 8 - 0.80 Total - - - 12.50 - 2.60 Page 1 1993 AASHTO Pavement Design DARWin Pavement Design and Analysis System A Proprietary AASHTOWare Computer Software Product Network Administrator Flexible Structural Design Module Front Range Community College South Parking Lot Fort Collins, CO Driveways, Entrances, Exits Full Depth Asphalt Section Flexible Structural Design 18-kip ESALs Over Initial Performance Period 58,400 Initial Serviceability 4.5 Terminal Serviceability 2 Reliability Level 85 % Overall Standard Deviation 0.44 Roadbed Soil Resilient Modulus 3,025 psi Stage Construction 1 Calculated Design Structural Number 2.81 in Specified Layer Design Layer Material Description Struct Coef. (Ai) Drain Coef. (Mi) Thickness (Di)(in) Width (ft) Calculated SN (in) 1 Hot Mix Asphalt 0.4 1 7.5 - 3.00 Total - - - 7.50 - 3.00 Page 1 1993 AASHTO Pavement Design DARWin Pavement Design and Analysis System A Proprietary AASHTOWare Computer Software Product Network Administrator Flexible Structural Design Module Front Range Community College South Parking Lot Fort Collins, CO Parking Stalls Full Depth Asphalt Section Flexible Structural Design 18-kip ESALs Over Initial Performance Period 29,200 Initial Serviceability 4.5 Terminal Serviceability 2 Reliability Level 85 % Overall Standard Deviation 0.44 Roadbed Soil Resilient Modulus 3,025 psi Stage Construction 1 Calculated Design Structural Number 2.54 in Specified Layer Design Layer Material Description Struct Coef. (Ai) Drain Coef. (Mi) Thickness (Di)(in) Width (ft) Calculated SN (in) 1 Hot Mix Asphalt 0.4 1 6.5 - 2.60 Total - - - 6.50 - 2.60