Loading...
HomeMy WebLinkAbout2300 W. ELIZABETH, EBERL / SIMPSON - PDP - 22-04 - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTLimited Geotechnical Engineering Report Proposed 2-Story with Garden -Level Duplex Unit 2300 W. Elizabeth Street Fort Collins, Co Project No. 20045075 Page 7 Terracon The analysis and recommendations presented in this report are based upon the limited field data obtained from the test pit observations and from other information discussed in this report. This report does not reflect variations that may occur between test pits, across the site, or due to the modifying effects of weather. The nature and extent of such variations may not become evident until during or after construction. If variations appear, we should be immediately notified so that further evaluation and supplemental recommendations can be provided. The scope of services for this project does not include either specifically or by implication any environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or identification or prevention of pollutants, hazardous materials or conditions. If the owner is concerned about the potential for such contamination or pollution, other studies should be undertaken.' This report has been prepared for the exclusive use of our client for specific application to the project discussed and has been prepared in accordance with generally accepted geotechnical engineering practices. No warranties, either express or implied, are intended or made. Site safety, excavation support, and dewatering requirements are the responsibility of others. In the event that 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 Terracon reviews the changes and either verifies or modifies the conclusions of this report in writing. We appreciate being of service to you in the geotechnical engineering phase of this project, and are prepared to assist you during the construction phases as well. If you have any questions concerning this report or any of our testing, inspection, design and consulting services please do not hesitate to contact us. SIncGFeiV. --- RRACON L. Wilson, P.E. oilact�nica4 Enoineer Copies to: (3) Addressee ��D RE��T A. • 277 �oF .• � c David A. Rich , r-.•••'�G��` Geotechnical E Manager Limited Geotechnical Engineering Report Proposed 2-Story with Garden -Level Duplex Unit 2300 W. Elizabeth Street Fort Collins, Co Project No. 20045075 Page 6 Terracon submitted prior to construction to verify their adequacy. Asphalt material should be placed in maximum 3-inch lifts and should be compacted to a within a range of 92 to 96 % of Maximum Theoretical Density. Preventative maintenance should be planned and provided for through an on -going pavement management program in order to enhance future pavement performance. Preventative maintenance activities are intended to slow the rate of pavement deterioration, and to preserve the pavement investment. Preventative maintenance consists of both localized maintenance (e.g. crack sealing and patching) and global maintenance (e.g. surface sealing). Preventative maintenance is usually the first priority when implementing a planned pavement maintenance program and provides the highest return on investment for pavements. Recommended preventative maintenance policies for asphalt and jointed concrete pavements, based upon type and severity of distress, are provided. Prior to implementing any maintenance, additional engineering observation is recommended to determine the type and extent of preventative maintenance. Please note that if during or after placement of the stabilization and/or initial lift of pavement, the area is observed to be yielding under vehicle traffic or construction equipment, it is recommended that Terracon be contacted for additional alternative methods of stabilization, or a change in the pavement section. Earthwork Subgrade Preparation Subgrade soils beneath interior and exterior slabs, and beneath pavements should be scarified, moisture conditioned and compacted to a minimum depth of 12-inches below proposed controlled fill material. The moisture content and compaction of subgrade soils should be maintained until slab or pavement construction. GENERAL COMMENTS Terracon should be retained to review the final design plans and specifications so comments can be made regarding interpretation and implementation of our geotechnical recommendations in the design and specifications. Terracon also should be retained to provide testing and observation during excavation, grading, foundation and construction phases of the project. Limited Geotechnical Engineering Report Proposed 2-Story with Garden -Level Duplex Unit 2300 W. Elizabeth Street Fort Collins, Co Project No. 20045075 Page 5 Terracon In addition to the flexible pavement design analyses, a rigid pavement design analysis was completed, based upon AASHTO design procedures. Rigid pavement design is based on an evaluation of the Modulus of Subgrade Reaction of the soils (K-value), the Modulus of Rupture of the concrete, and other factors previously outlined. The design K-value of 100 for the subgrade soil was determined by correlation to the laboratory tests results. A modulus of rupture of 650 psi (working stress 488 psi) was used for pavement concrete. The rigid pavement thicknesses for each traffic category were determined on the basis of the AASHTO design equation. Recommended alternatives for flexible and rigid pavements, summarized for parking areas, are as follows: RECOMMENDED MINIMUM PAVEMENT THICKNESS — INCHES Asphalt Asphalt Portland Traffic Area Alternatives Concrete Concrete Aggregate Base Course — Cement Total Surface Grading Surface Class 5 or 6 Concrete S or SX Grading SG Automobile A 4.0 6.0 10.0 Parking Areas (2) B 5.5 5.5 (1) Alternative A: Provides the minimum pavement thicknesses for use of asphalt concrete surface material, Grading S, SX and SG, underlain by Class 5 or 6 aggregate road base material. (2) Alternative B: Provides the minimum required pavement thicknesses for use of Portland Cement Concrete pavement. Due to the properties of the existing cohesive on -site soils, full depth asphalt pavement is not recommended. Each alternative should be investigated with respect to current material availability and economic conditions. Rigid concrete pavement, a minimum of 6-inches in thickness, is recommended at the location of dumpsters where trash trucks park and load. 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 base course. Aggregate base course should be placed in lifts not exceeding six inches and should be compacted to a minimum of 95% Standard Proctor Density (ASTM D698). Asphalt concrete pavement should be composed of a mixture of aggregate, filler, binders, and additives, if required, and approved bituminous material in accordance with the LCUASS Pavement Design Criteria. The asphalt concrete should conform to an approved mix design stating the Hveem and/or Superpave properties, optimum asphalt content, job mix formula and recommended mixing and placing temperatures. Aggregate used in the asphalt concrete should meet particular gradations, such as the Colorado Department of Transportation Grading S, SX or SG specifications. Mix designs should be Limited Geotechnical Engineering Report Proposed 2-Story with Garden -Level Duplex Unit 2300 W. Elizabeth Street Fort Collins, Co Project No. 20045075 Page 4 Terracon The exterior drainage system should consist of a properly sized perforated pipe, embedded in free - draining gravel, and 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 system should be underlain with a polyethylene moisture barrier, sealed to the foundation walls, and extending at least to the edge of the backfill zone. The gravel should be covered with drainage fabric prior to placement of foundation backfill. Pavement Design and Construction Based on the subsurface conditions encountered during the limited site exploration, it is our opinion the proposed on -site pavement areas are feasible provided the following recommendations are implemented. However, it is recommended a more detailed study be performed for the pavement subgrade soils to provide "site specific" design criteria. Asphalt concrete underlain by crushed aggregate base course and non -reinforced concrete pavement are feasible alternatives for the proposed on -site paved sections. Based on the subsurface conditions encountered at the site, it is recommended the on -site private drives and parking areas be designed using a assumed minimum R-value of 7. Design of pavements for the project have been based on the procedures outlined in the 1993 Guideline for Design of Pavement Structures by the American Association of State Highway and Transportation Officials (AASHTO). Areas within proposed pavements on the site will be divided into two categories based upon anticipated traffic and usage. Traffic criteria provided for pavement thickness designs are estimated by Terracon based on similar projects and are to include single 18-kip equivalent single axle loads (ESAL's) of 51,100 for automobile parking, and 146,000 for heavy volume and/or truck access areas. Local drainage characteristics of proposed pavement areas are considered to vary from fair to good depending upon location on the site. For purposes of this design analysis, fair drainage characteristics are considered to control the design. These characteristics, coupled with the approximate duration of saturated subgrade conditions, result in a design drainage coefficient of 1.0 when applying the AASHTO criteria for design. For flexible pavement design, a terminal serviceability index of 2.0 was utilized along with an inherent reliability of 70%, and a design life of 20 years. Using an estimated design R-value estimated at 7 based on the group index/soil classification values, appropriate ESAL/day, environmental criteria and other factors, the structural numbers (SN) of the pavement sections were determined on the basis of the 1993 AASHTO design equation. Limited Geotechnical Engineering Report Proposed 2-Story with Garden -Level Duplex Unit 2300 W. Elizabeth Street Fort Collins, Co Project No. 20045075 Page 3 Terracon • Control joints should be provided in slabs to control the location and extent of cracking. • A minimum 2-inch void space should be constructed above, or below non -bearing partition walls placed on the floor slab. Special framing details should be provided at doorjambs and frames within partition walls to avoid potential distortion. Partition walls should be isolated from suspended ceilings. • Interior trench backfill placed beneath slabs should be compacted in accordance with recommended specifications outlined below. • A minimum 4-inch layer of free -draining gravel should be placed beneath floor slabs exhibiting normal floor loading. Consideration should be given to placing 6-inches of underslab gravel in areas where heavy loading is anticipated. It is also recommended in areas where heavy loading is to occur, that a minimum 6-inches of wire and/or fiber mesh reinforced concrete be placed. • A minimum 8-inch layer of free -draining gravel should be placed beneath basement floor slabs in conjunction with the underslab drainage system. • Floor slabs should not be constructed on frozen subgrade. • Other design and construction considerations, as outlined in the ACI Design Manual, Section 302.1 are recommended. Lower Level Construction Groundwater was not encountered during initial site observations. Therefore, lower level construction is feasible. Perched groundwater and/or surface water infiltration may occur at times since the subsurface soils are relatively impermeable and tend to trap water. Completion of site development, including installation of landscaping and irrigation systems, may lead to perched groundwater development. To intercept the potential for surface water infiltration from impacting the foundation bearing stratum and entering the lower level in areas, an exterior perimeter drainage is recommended. The exterior 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. Limited Geotechnical Engineering Report Terracon Proposed 2-Story with Garden -Level Duplex Unit 2300 W. Elizabeth Street Fort Collins, Co Project No. 20045075 Page 2 ENGINEERING RECOMMENDATIONS Foundation Systems Due to the presence of non- to low -swelling soils and bedrock on the site, spread footings bearing upon undisturbed subsoils, sandstone/claystone/siltstone bedrock, and/or engineered fill are recommended for support of the proposed structure. The footings bearing on undisturbed or engineered fill material should be designed for a net allowable bearing pressure of 2,000 psf. The footings should also be designed to maintain a minimum dead load pressure of 500 psf. The design bearing pressure applies to dead loads plus design live load conditions. Exterior footings should be placed a minimum of 30 inches below finished grade for frost protection and to provide confinement for the bearing soils. Finished grade is the lowest adjacent grade for perimeter footings. Footings should be proportioned to reduce differential foundation movement. Proportioning on the basis of equal total settlement is recommended; however, proportioning to relative constant dead -load pressure will also reduce differential settlement between adjacent footings. Total settlement resulting from the assumed structural loads is estimated to be on the order of 1-inch or less. Differential settlement should be on the order of 1/2 to 3/4 of the estimated total settlement. Additional foundation movements could occur if water from any source infiltrates the foundation soils; therefore, proper drainage should be provided in the final design and during construction. Footings and foundation walls should be reinforced as necessary to reduce the potential for distress caused by differential foundation movement. The use of joints at openings or other discontinuities in walls is recommended. The geotechnical engineer should observe foundation excavations. If the soil conditions encountered differ significantly from those presented in this report, supplemental recommendations will be required. Floor Slab Design and Construction It is anticipated low -swelling soils or engineered fill will support the floor slab of the proposed structure. Some differential movement of a slab -on -grade floor system is possible should the subgrade soils become elevated in moisture content. To reduce potential slab movements, the subgrade soils should be prepared as outlined in the earthwork section of this report. Additional floor slab design and construction recommendations are as follows: • Positive separations and/or isolation joints should be provided between slabs and all foundations, columns or utility lines to allow independent movement. June 8, 2004 Ebcon Development Company 8101 Islander Court Fort Collins. Colorado 80528 Attn: Mr. Jim Simpson Re: Limited Geotechnical Engineering Report Proposed 2-Story with Garden -Level Duplex Unit 2300 West Elizabeth Street Fort Collins, Colorado Terracon Project No. 20045075 Irerracon 301 N. Howes • P.O. Box 503 Fort Collins, Colorado 80521-0503 (970)484-0359 Fax .(970)484-0454 A representative from Terracon was on -site on June 2, 2004, to perform a limited subsurface investigation by observing (3) backhoe test pits excavated by the contractor and located within the proposed parking lot and building footprint areas south and north of the existing residence. Based on our observations from the backhoe test pits, the areas observed within the proposed parking lot and building footprint consisted of approximately 6-inches of topsoil underlain by lean clay with sand, silty clayey sand and silty sand with gravel and sandstone/claystone/siltstone bedrock which was encountered at an approximate depth of 6-feet below the existing site grades in Test Pit No. 1. A "grab" sample of the bedrock was obtained and a laboratory "free -swell" analysis test was performed on the sample to determine the swell potential. The test results indicate a low swell potential for the bedrock sample within Test Pit No. 1. Groundwater was not encountered in the test pits during the initial site observation. The Backhoe Test Pit Logs are shown below. BACKHOE TEST PIT LOGS Location Description Comments Test Pit No. 1 12' N. & 12' E. of SW Cor. of Existing Building 0.0-0.5' Topsoil 0.5-1.5' Lean Clay w/ Sand, trace gravel 1.5-3.0' Silty Clayey Sand w/ Gravel 3.0-6.0' Silty Sand w/ Gravel 6.0-7.0' Sandstone/Claystone/Siltstone Bedrock Swell Pressure=430 psf Test Pit No. 2 33' N. & 10' E. of NW Car. of Existing Building 0.0-0.5' Topsoil 0.5-2.0' Lean Clay w/ Sand, trace gravel 2.0-4.5' Silty Clayey Sand, trace gravel 4.5-7.0' Silty Sand w/ Gravel Test Pit No. 3 63' N. & 20' E. of NW Cor. of Existing Building 0.0-0.5' Topsoil 0.5-3.0' Lean Clay w/ Sand 3.0-8.0' Silty Clayey Sand, trace gravel 8.0-8.5' Silty Sand, trace gravel Arizona ■ Arkansas ■ Colorado ■ Idaho ■ Illinois ■ Iowa ■ Kansas ■ Minnesota ■ Missouri ■ Montana Nebraska ■ Nevada ■ New Mexico ■ North Dakota ■ Oklahoma ■ Tennessee ■ Texas ■ Utah ■ Wisconsin ■ Wyoming Quality Engineering Since 1965