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Home My WebLink AboutPARKING AT 620 S. LEMAY AVE. - MJA/FDP - FDP150009 - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTTerracon Consultants, Inc. 1901 Sharp Point Drive, Suite C Fort Collins, Colorado 80525 P [970] 484 0359 F [970] 484 0454 terracon.com March 9, 2015 CS Design, Inc. 2519 South Shields Street, #129 Fort Collins, Colorado 80526 Attn: Ms. Cara Scohy, RLA, ASLA P: (970) 420-9462 E: cara@csdesigncorp.com Re: Geotechnical Engineering Report New Parking Lot at Existing Concentra Facility 620 South Lemay Avenue Fort Collins, Colorado Terracon Project No. 20155014 Dear Ms. Scohy: Previously, Terracon Consultants, Inc. (Terracon) prepared a Geotechnical Engineering Report (Project No. 20005056; report dated April 11, 2000) for the existing Concentra facility referenced above. We understand a new parking lot is planned to the east of this existing facility. We were requested to review the geotechnical data obtained during the initial study at this facility and provide recommendations for the new parking lot based on assumptions made for anticipated subsurface conditions. This report presents our findings and geotechnical engineering recommendations for the new parking lot. Project Information Terracon was provided with a conceptual Site Plan for the project prepared by CS Design, Inc. The Site Plan indicated the new parking lot will include access drives and approximately 37 parking spaces. We anticipate the parking lot will be either asphalt or concrete with curb and gutter surrounding the lot and some landscape islands. We understand the traffic loading will consist primarily of passenger vehicles with minor amounts of light-duty truck traffic. Site Conditions We made a site visit to observe current conditions of the new parking lot site. The site is covered with native grasses and weeds as well as a moderate coverage of willow trees. In general, the site is relatively flat sloping gently from the south down to the north towards the Cache la Poudre River. Very moist soil conditions could be present below this site as is evident by the type and density of vegetation observed at the site. Geotechnical Engineering Report New Parking Lot at Existing Concentra Facility ■ Fort Collins, Colorado March 9, 2015 ■ Terracon Project No. 20155014 Responsive ■ Resourceful ■ Reliable 2 Subsurface Conditions We have reviewed the typical subsurface conditions encountered in the borings completed as part of the initial subsurface exploration completed back in 2000. In general, subsurface conditions consisted of approximately 6 inches of topsoil over interlayered sandy lean clay and clayey to silty sand and gravel. Claystone/siltstone bedrock was encountered in two borings at depths of about 12 feet below site grades at the time of the initial field exploration. In general, the lean clay and clayey sand soils are low swelling to non-expansive and the silty sand and gravel are judged non-expansive. At the time of our initial study, groundwater was encountered in only one of the test borings at a depth of about 11½ feet below site grades. Groundwater levels can be expected to fluctuate with varying seasonal and weather conditions as well as water levels in the Cache la Poudre River. In addition, we believe groundwater could be shallower than encountered prior to site development. Typically, groundwater levels rise following site development due to watering of landscaping, covering of the site with impervious materials (i.e. asphalt parking lots, building envelopes, etc.) and other factors. Earthwork Recommendations Considering the amount of vegetation currently covering the site, stripping and tree removal will be extensive and should be completed properly prior to constructing the proposed parking lot. Recommendations for earthwork including site preparation, subgrade preparation, fill materials and placement, and excavation are presented in the initial geotechnical report referenced above. It is possible unstable conditions could be encountered following initial site preparation. Terracon is available to assist with subgrade stabilization recommendations if these type of conditions are encountered. Pavement Recommendations Our recommendations for pavements at the new parking lot are based on assumptions of subsurface conditions below the site. Subsurface exploration for this site was not completed. Terracon should be contacted during construction of the new parking lot to confirm subsurface conditions by observing shallow test pits. Terracon should also be retained to provide construction materials testing during construction. Recommendations for pavements presented in our initial report are generally acceptable for the new parking lot provided subsurface conditions exposed at pavement subgrade levels are consistent with those described in the initial geotechnical report. However, the pavement recommendations included certain items that have been since updated such as aggregate grading for asphalt materials. Our recommendations for new parking lot pavements are as follows: Geotechnical Engineering Report New Parking Lot at Existing Concentra Facility ■ Fort Collins, Colorado March 9, 2015 ■ Terracon Project No. 20155014 Responsive ■ Resourceful ■ Reliable 3 We recommend the pavement subgrade be thoroughly proofrolled with a loaded tandem-axle dump truck prior to final grading and paving. All pavement areas should be moisture conditioned and properly compacted to the recommendations in this report immediately prior to paving. Design of new privately-maintained pavements for the project has been based on the procedures described by the National Asphalt Pavement Associations (NAPA) and the American Concrete Institute (ACI). We assumed the following design parameters for NAPA flexible pavement thickness design:  Automobile Parking Areas  Class I - Parking stalls and parking lots for cars and pick-up trucks, with Equivalent Single Axle Load (ESAL) up to 7,000 over 20 years  Subgrade Soil Characteristics  USCS Classification – CL, classified by NAPA as poor We assumed the following design parameters for ACI rigid pavement thickness design based upon the average daily truck traffic (ADTT):  Automobile Parking Areas  ACI Category A: Automobile parking with an ADTT of 1 over 20 years  Subgrade Soil Characteristics  USCS Classification – CL  Concrete modulus of rupture value of 600 psi We should be contacted to confirm and/or modify the recommendations contained herein if actual traffic volumes differ from the assumed values shown above. Recommended alternatives for flexible and rigid pavements are summarized for each traffic area as follows: Traffic Area Alternative Recommended Pavement Thickness (Inches) Asphaltic Concrete Surface Aggregate Base Course Portland Cement Concrete Total Automobile Parking (NAPA Class I and ACI Category A) A 3 7 -- 10 B -- -- 5½ 5½ Aggregate base course (if used on the site) should consist of a blend of sand and gravel which meets strict specifications for quality and gradation. Use of materials meeting Colorado Department of Transportation (CDOT) Class 5 or 6 specifications is recommended for aggregate Geotechnical Engineering Report New Parking Lot at Existing Concentra Facility ■ Fort Collins, Colorado March 9, 2015 ■ Terracon Project No. 20155014 Responsive ■ Resourceful ■ Reliable 4 base course. Aggregate base course should be placed in lifts not exceeding 6 inches and compacted to a minimum of 95 percent of the maximum dry unit weight as determined by ASTM D698. Asphaltic concrete should be composed of a mixture of aggregate, filler and additives (if required) and approved bituminous material. The asphalt concrete should conform to approved mix designs stating the Superpave properties, optimum asphalt content, job mix formula and recommended mixing and placing temperatures. Aggregate used in asphalt concrete should meet particular gradations. Material meeting CDOT Grading S specifications or equivalent is recommended for asphalt concrete. Mix designs should be submitted prior to construction to verify their adequacy. Asphalt material should be placed in maximum 3-inch lifts and compacted within a range of 92 to 96 percent of the theoretical maximum (Rice) density (ASTM D2041). Where rigid pavements are used, the concrete should be produced from an approved mix design with the following minimum properties: Properties Value Compressive strength 4,000 psi Cement type Type I or II portland cement Entrained air content (%) 5 to 8 Concrete aggregate ASTM C33 and CDOT Section 703 Concrete should be deposited by truck mixers or agitators and placed a maximum of 90 minutes from the time the water is added to the mix. Longitudinal and transverse joints should be provided as needed in concrete pavements for expansion/contraction and isolation per ACI 325. The location and extent of joints should be based upon the final pavement geometry. Although not required for structural support, a minimum 4-inch thick aggregate base course layer is recommended for the PCC pavements to help reduce the potential for slab curl, shrinkage cracking, and subgrade “pumping” through joints. Proper joint spacing will also be required for PCC pavements to prevent excessive slab curling and shrinkage cracking. All joints should be sealed to prevent entry of foreign material and dowelled where necessary for load transfer. Pavement performance is affected by its surroundings. In addition to providing preventive maintenance, the civil engineer should consider the following recommendations in the design and layout of pavements:  Site grades should slope a minimum of 2 percent away from the pavements;  The subgrade and the pavement surface have a minimum 2 percent slope to promote proper surface drainage;  Consider appropriate edge drainage and pavement under drain systems;  Install pavement drainage surrounding areas anticipated for frequent wetting;