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Home My WebLink About708 Keenesburg Ct - Special Inspections/Engineering - 08/14/2003August 14, 2003 Melody Homes 11031 Sheridan Blvd. Westminster, Colorado 80020 Attn: Mr. Corey Weaver Re: Geotechnical Engineering Report Ridgewood Hills 3rd Filing — Phase 7 Lot 300 708 Keensburg Court Fort Collins, Colorado Terracon Project No. 20005162 Irerracon 301 N. Howes • P.O. Box 503 Fort Collins, Colorado 80521-0503 (970) 484-0359 Fax: (970) 484-0454 B0401043 Terracon has completed a geotechnical engineering exploration for a proposed single family residence to be located on the above referenced lot within the Ridgewood Hills 3rd Filing — Phase 7 residential development project located in south Fort Collins, Colorado. The purpose of these services is to provide geotechnical-engineering recommendations for design of foundations, slab on grade, and perimeter drainage systems. Terracon performed a geotechnical engineering exploration for the 3rd Filing of Ridgewood Hills in October of 1997, which encompassed the above -referenced lot. For further information and additional geotechnical engineering recommendations please refer to our "Geotechnical Engineering Report" for the Ridgewood Hills 3rd Filing Residential Development revised January 16, 2001, Project No. 20975149. The additional site exploration, conducted on August 6, 2003, included one test boring drilled near the center of the lot as requested. A swell -consolidation test was performed on a relatively undisturbed sample obtained at a depth of 3-feet. The Log of Boring describing the soil and groundwater profile conditions along with the laboratory test results are attached with this letter. The materials tested on the above mentioned lot, based on the swell -consolidation index, are classified as low swelling according to the Colorado Association of Geotechnical Engineers (CAGE) criteria. The subsurface soils encountered on this lot consisted of sandy lean clay with sandstone fragments overlot grading fill material which extended to the bedrock below. Siltstone/sandstone bedrock was encountered at an approximate depth of 3-feet below existing site grades and extended to depths explored, approximately 14-feet. Intermittent well -cemented sandstone lenses were encountered with depth at increased depths within the bedrock formation. Excavations penetrating the well -cemented sandstone bedrock may require the use of specialized heavy-duty equipment, together with drilling and/or blasting to facilitate rock break-up and removal. It is our understanding the proposed residence will be constructed having a full depth basement. Therefore, based on the properties of the soils and bedrock present on this lot, Terracon recommends the proposed structure be supported by conventional type spread footings. Conventional type slab on grade construction procedures are feasible for the above -referenced lot. Arizona ■ Arkansas ■ Colorado ■ Georgia ■ Idaho ■ Illinois ■ Iowa ■ Kansas ■ Kentucky ■ Minnesota ■ Missouri Montana ■ Nebraska ■ Nevada ■ New Mexico ■ Oklahoma ■ Tennessee ■ Texas ■ Utah ■ Wisconsin ■ Wyoming Quality Engineering Since 1965 Geotechnical Engineering Report Melody Homes — Ridgewood Hills 3ro Filing Phase 8 Fort Collins, Colorado Terracon Project No. 20005162 FOUNDATION RECOMMENDATIONS Conventional Spread Footing Foundation Systems The proposed residence should be supported by conventional -type spread footing foundations bearing upon the undisturbed bedrock formation. All footings should be extended to the undisturbed bedrock formation to minimize the potential differential movement and should be designed for a net allowable bearing pressure of 2,500 psf. In addition, the footings should be sized to maintain a minimum dead - load pressure of 750 psf. The design bearing pressure applies to dead loads plus %Z of design live load conditions. If excavations are to be extended into the well -cemented sandstone bedrock lenses, the use of specialized heavy-duty equipment may be required. If a controlled blasting operation is necessary to facilitate basement construction, footings should bear upon a minimum of 2-feet of over -excavated and replaced fill material using a net allowable bearing pressure of 2,500 psf, also with a minimum dead load pressure of 750 psf. Basement Construction Groundwater was not encountered on the lot to the maximum depths of exploration, 15-feet, during the initial site exploration. Therefore full -depth basement construction is considered acceptable. To reduce the potential for groundwater and/or surface water infiltration to enter the basement of the residence, installation of a dewatering system is recommended. The drainage system should be constructed around the exterior perimeter of the basement foundation, and sloped at a minimum 1/8 inch per foot to a suitable outlet, such as a sump and pump system. The drainage system should consist of a 4-inch diameter perforated pipe, embedded in free -draining gravel, placed in a trench at least 12 inches in width. Gravel should extend a minimum of 3 inches beneath the bottom of the pipe, and at least 1-foot above the bottom of the foundation wall. The gravel should be covered with drainage fabric prior to placement of foundation backfill. Backfill placed around the outside perimeter of the structure should be placed in uniform lifts; moisture conditioned to optimum moisture content and mechanically compacted to 95% of Standard Proctor Density ASTM 698. Floor Slab Design and Construction The variability of the existing soils at approximate slab subgrade elevation could result in differential movement of floor slab -on -grade should the subsurface soils increase in moisture content. Based on the CAGE criteria, the subsoils at the site have a slab performance risk category of 'low". Movement not likely to exceed up to 2 inches or more is estimated if the subsoils below slabs become wetted for a zone of approximately 10 feet below the basement. Slab -on -grade construction for the basement of 2 Geotechnical Engineering Report Melody Homes — Ridgewood Hills V Filing Phase 8 Fort Collins, Colorado Terracon Project No. 20005162 this residence should perform in accordance with the above criteria. The homeowner should be aware of the risk of this slab movement and should take this into account prior to purchasing the residence. To reduce potential slab movements, slabs should be constructed in accordance with the recommendations of the Geotechnical Engineering Report. Surface Drainage Positive drainage should be provided during construction and maintained throughout the life of the proposed residence. In areas where sidewalks or paving do not immediately adjoin the structure, we recommend that protective slopes be provided with a minimum grade of approximately 10 percent for at least 10 feet from perimeter walls. Backfill against foundations, exterior walls and in utility and sprinkler line trenches should be well compacted and free of all construction debris to reduce the possibility of moisture infiltration. Downspouts, roof drains or scuppers should discharge into splash blocks or extensions when the ground surface beneath such features is not protected by exterior slabs or paving. Sprinkler systems should not be installed within 5 feet of foundation walls. Construction Observation The following observations are recommended during construction: • Foundation Excavation; • Footing sizes and void form placement; • Foundation Wall Steel/Reinforcement; • Perimeter Drainage System; and • Floor Slab for Basement and Garage We appreciate the opportunity to be of service to you on this phase of your project. If you have any questions, or if we may be of further service to you, please feel free to contact us. Sincerely,0m TERRACO • • Q l / 1 w � t l w wee David A. Riche Geotechnical Engine , epartment Manager Copies to: Addressee (6) Enclosures: Log of Boring (1) 3 LOG OF BORING NO. 300 Page 1 of 1 CLIENT ARCHITECT/ENGINEER Melody Homes SITE Ridgewood Hills-3rd Filing PROJECT Fort Collins, Colorado Ridgewood Hills-3rd Filing SAMPLES TESTS C7 DESCRIPTION J m y o ° a wZ U a � i W > z(n F of w z � z� C7 W L)i 2 d LU OU H3 O ~Z r� 6a ow � � � Z � � aim QUO O �� SANDY LEAN CLAY Brown, moist, medium stiff 3 SILTSTONE/SANDSTONE Brown, light gray, moist, cemented SS 9 50/0.8 5 10 14.2 BOTTOM OF BORING 0 a ro O Z QO K K H a' c7 Uj w co a The stratification lines represent the approximate boundary lines between soil and rock types: in -situ, the transition may be gradual. g WATER LEVEL OBSERVATIONS, ft " DRY WD 1 BORING STARTED 8-6-03 Ui WL BORING COMPLETED 8-6-03 3 W L WIrerracon m WL INITIAL WATER LEVEL READING RIG CME-55 FOREMAN JJ APPROVED DAR JOB # 20005162