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Home My WebLink AboutHARVEST PARK - 1 OF 3 REPORTS SUBGRADE INVESTIGATION HARVEST PARK ROCK CREEK DRIVE, CORBETT DRIVE, CORNER STONE DRIVE, CORNER STONE LANE, AND SPRING HARVEST LANE FORT COLLINS, COLORADO APPROVED L' : C DATE: l GCC) • City of Fort Collins tti gineering Department =` / r 1 11g h Cam[.4-I-(o (191v CTL/THOMPSON , INC . CONSULTING ENGINEERS L J SUBGRADE INVESTIGATION HARVEST PARK ROCK CREEK DRIVE, CORBETT DRIVE, CORNER STONE DRIVE, CORNER STONE LANE, AND SPRING HARVEST LANE FORT COLLINS, COLORADO Prepared For: THE WRITER CORPORATION Northern Colorado Division 5200 Hahns Peak Drive Suite 160 Loveland, Colorado 80538 Attention: Mr. Jim Burczyk Job No. FC-1667 December 1, 2000 L -aLij Appendix B. Pavement design alternatives are summarized in Table A. TABLE A PAVEMENT DESIGN ALTERNATIVES Full-Depth Asphalt (HBP) + Hot Bituminous Minimum Location Asphalt Aggregate Base Pavement (HBP) + Structural (HBP) on Course (ABC) Plant Mix Number Subgrade* Bituminous Base (PMBB) + Aggregate Base Course (ABC) Corbett Drive 7" HBP 5.5" HBP+ 6"ABC 3" HBP + 3.5" 3.08 (residential or 5" HBP + 8" PMBB + 6"ABC collector, ABC EDLA=70) Corner Stone Drive 7" HBP 5.5" HBP + 6"ABC 3" HBP + 3.5" 3.08 (residential or 5" HBP+ 8" PMBB + 6"ABC collector, ABC EDLA=35) Rock Creek Drive 7" HBP 5.5" HBP + 6"ABC 3" HBP + 3" 2.97 (residential or 5" HBP+ 7" PMBB + 6"ABC collector, ABC EDLA=30) Corner Stone Lane 5" HBP 3.5" HBP+ 6"ABC -- 2.20 and Spring Harvest Lane (residential serving less than 50 dwelling units) *Full depth asphalt sections may not be acceptable to the City of Fort Collins and would require special review. PAVEMENT SELECTION We have provided three pavement design alternatives for the streets included in this investigation, including asphalt (hot bituminous pavement) over a prepared subgrade, asphalt (hot bituminous pavement) on aggregate base course, and hot bituminous pavement and plant mix bituminous base on aggregate base course. Asphalt over a prepared subgrade is restricted by the City of Fort Collins regulations. If this is the preferred pavement alternative for the remaining streets, special review and approval by the City will be needed. We believe a flexible pavement will perform well at this site. Our experience THE WRITER CORPORATION HARVEST PARK SUBGRADE INVESTIGATION AND PAVEMENT DESIGN CTUT JOB NO.FC-1667 7 L J indicates that asphalt concrete over a prepared subgrade should perform well in areas of low to moderate swell, such as this site. The asphalt concrete provides a stiff, stable pavement to withstand heavy loading and provide good fatigue- resistance, while the aggregate base course provides a flexible layer to help distribute potential swell of the subgrade. For this alternative, embrittlement of the asphalt and moisture in the subgrade are likely to be the primary causes of distress. This alternative retains a higher risk of distress due to moisture in the subgrade than other alternatives. Ground water was not encountered in the subgrade borings for this site. Ground water was encountered at depths of 8 to 17 feet in exploratory borings in the Harvest Park Subdivision adjacent to these streets, and ground water has been encountered in some utility excavations at the site. The use of a geotextile fabric such as Mirafi 500X or equivalent to separate the subgrade from the aggregate base course is optional. Our experience has shown that such fabrics are effective in reducing the co-mingling of materials that occurs over time between base course and clay soils. We do not recommend Portland cement concrete due to the swelling soils. Although the swell potential of the site soils is low, the variability of the soils may result in differential movement of larger concrete slabs. Concrete pavements do not have sufficient weight to counteract the swelling soils and will likely result in differential movement of the slab, creating rough ride characteristics, increased maintenance and a decreased service life. To reduce the swell potential of the clay soils encountered in the street subgrade,the upper 12 inches of the subgrade should be scarified, moisture treated to between optimum and 3 percent above optimum moisture content, and compacted to at least 95 percent of standard Proctor dry density (ASTM D 698). The contractor should anticipate some difficult construction conditions, including soft, yielding subgrade for areas with moisture content above optimum moisture content. Achieving stability for a passing proof roll test will prove difficult at higher moisture contents. If extensive soft, yielding areas are encountered, chemical stabilization such as fly ash, lime, kiln dust or a combination may be more cost-effective than extensive mechanical stabilization techniques. If chemical stabilization is desired for workability,the pavement section alternatives presented in Table A would remain THE WRITER CORPORATION HARVEST PARK SUBGRADE INVESTIGATION AND PAVEMENT DESIGN 8 CTL/T JOB NO.FC-1667 L as shown since no credit is currently allowed by the City of Fort Collins in the pavement design for chemical stabilization. If chemical stabilization is desired, we would be pleased to provide a proposal for mix designs and construction services. The pavement design methodology is based on subgrade properties including soil support characteristics and swell potential, estimated traffic loads, and local experience. The data and analyses indicate the sections recommended will perform adequately for the anticipated support and traffic conditions. SOLUBLE SULFATES Water soluble sulfates were measured for 5 samples of the near-surface clays. The measured soluble sulfates ranged from 0.004 to 0.028 percent. Measured soluble sulfates from the Harvest Park Subdivision Soils and Foundation Investigations for Block 7 and Block 9 adjacent to the streets included in this investigation ranged from 0.001 to 0.02 percent for samples at depths of 2 and 4 feet. The purpose of the tests was to determine the risk of increased swelling if stabilization is required for the subgrade and the likelihood of sulfate attack on Portland cement concrete. The low values found at this site indicate a negligible potential for sulfate attack on concrete (e.g. curb and gutter) and little risk of increased swelling if stabilization is required. The American Concrete Institute (ACI) indicates Type I or Type II cement can be used for concrete which comes into contact with the subsoils. MATERIALS AND CONSTRUCTION The performance of a pavement system is determined by the quality of the paving materials and construction practices. Material properties and construction practice guidelines are presented in Appendix C. During construction, careful attention should be paid to the following details: • Maintaining subgrade moisture content as close to optimum moisture content as practical. • Placement and compaction of trench backfill. THE WRITER CORPORATION HARVEST PARK SUBGRADE INVESTIGATION AND PAVEMENT DESIGN CTLIT JOB NO.FC-1667 9 No other warranty, express or implied, is made. If we can be of further service in discussing the contents of this report, or in the analyses of the proposed pavement systems fro, -a-geo echnical point of view, please call. �p,0 Fi E GIST O• .:,N �p� CT .IPSON, O oczc !2 3 9 Marilyn . .'PIm Geotechnic -Engineer Revie '�oA.ECis��c (\‘? k \384 Thomas'? ^Gh p i :6* PE Project 1 MWP:TAC:cem (4 copies sent) THE WRITER CORPORATION HARVEST PARK SUBGRADE INVESTIGATION AND PAVEMENT DESIGN CTL/T JOB NO.FC-1667 1