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Home My WebLink AboutLINCOLN PARK (FORMERLY LINCOLN MIXED-USE PDP), 1110 E. LINCOLN - PDP - 40-94G - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTGeotechnical Engineering Report lferracon Proposed Lincoln Avenue Townhome Development Project Fort Collins, Colorado Project No. 20045173 To satisfy forces in the horizontal direction, piers may be design for lateral loads using a modulus of 75 tons per square foot for the portion of the pier in clays, weathered siltstone/claystone bedrock and/or engineered fill., and 400 tsf in competent bedrock for a pier diameter of 12 inches. The coefficient of subgrad.e reaction for varying pier diameters is as follows: Coefficient ofbgra eteachon (.topyw ns/fit, j Pierlfl iaineter (Jnches,) " Engrneere'� Fi it or tiff Clays �IB rock Ira'r1.8n+raria�raamlme.a+..+w,aastutvrr ,m..i%n +u+cv1 k x� rxiirfzem.,amk.'.. ,awY+.ewNvxieFu'�+'dr. R,.'4P 12 75 400 18 50 267 24 38. 200 30 30 160 The soil modulus and coefficient of subgrade reaction are ultimate values; therefore, appropriate factors of safety should be applied in the pier design. To reduce potential uplift forces on piers, use of long grade beam spans to increase individual pier loading, and small diameter piers are recommended. For this project, use of a minimum pier diameter of 12-inches is recommended. A minimum 6-inch void space should be provided beneath grade beams between piers.'The void material should be of suitable strength to support the weight of fresh concrete used in grade beam construction, and to avoid collapse when foundation backfill is placed. Drilling -caissons should be possible with conventional single flight power augers within the weathered portions of the underlying bedrock formation. Areas of well -cemented sandstone bedrock were encountered throughout the site where specialized drilling equipment and/or rock augers may be required. Excavation penetrating the well -cemented sandstone bedrock may require the use of specialized heavy-duty equipment, together with rock augers and/or core barrels. Consideration should be given to obtaining a unit price for difficult caisson excavation in the contract documents for the project. Shafts will probably remain open without stabilizing measures. However, pier concrete should be placed soon after completion of drilling and cleaning. Groundwater was encountered during the drilling exploration; therefore, temporary casing will be required. Groundwater should be removed - - from each pier -hole- prior -to concrete placement.-- A--maximum--3=inch depth- of groundwater- is— - - acceptable in each pier prior to concrete placement. If pier concrete cannot be placed in dry conditions, a tremie should be used for concrete placement. Due. to potential sloughing and raveling, foundation concrete quantities may exceed calculated geometric volumes. Pier concrete with slump in the range of 6 to 8 inches is recommended. If casing is used for pier construction, it should be withdrawn in a slow continuous manner maintaining a sufficient head of concrete to prevent infiltration of water or the creation of voids in 7 Geotechnical Engineering Report Proposed Lincoln Avenue Townhome Development Project Fort Collins, Colorado Project No. 20045173 1rerraron 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 10-feet of foundation walls. Landscaped irrigation adjacent to the foundation system should be minimized or eliminated. 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. The analysis and recommendations presented in this report are based upon the data obtained from the, borings performed at the indicated locations and from other information discussed in this report. This report does not reflect variations that may occur between borings, 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. _ ..... _..... _. _. _.....- _ . - . 19 Geotechnical Engineering Report Proposed Lincoln Avenue Townhome Development Project Fort Collins, Colorado Project No. 20045173 -1 Additional Design and Construction Considerations Exterior Slab Design and Construction lferracon Exterior slabs -on -grade, exterior architectural features and utilities founded onor in backfill may experience some, movement due to the volume change of the backfill. Potential movement could be reduced by: • minimizing moisture increases in the backfill • controlling moisture -density during placement of backfill • using designs which allow vertical movement between the exterior features and adjoining structural elements • placing effective control joints on relatively close centers • Underground Utility Systems All piping should be adequately bedded for proper load distribution. It is suggested that clean, graded gravel compacted to 75 percent of Relative Density ASTM D4253 be used -'as bedding. Where utilities are excavated below groundwater, temporary dewatering will be -required during excavation, pipe placement and backfilling operations for proper construction. utility trenches should be excavated on safe and stable slopes in accordance with OSHA regulations as discussed above. Backfill should consist of the on - site soils or imported material approved by the geotechnical engineer. The pipe backfill should be compacted to a minimum of 95 percent of Standard Proctor Density ASTM D698. Surface Drainage Positive drainage should be provided during construction and maintained throughout the life of the proposed project. Infiltration of water into utility or foundation excavations must be prevented during construction. Planters and other surface features, which could retain water in areas adjacent to the building or pavements, should be sealed! or eliminated. 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 footings, 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. 18 Geotechnical Engineering Report Proposed Lincoln Avenue Townhome Development Project Fort Collins, Colorado Project No. 20045173 lrerracon The soils to be penetrated by the proposed excavations may vary significantly across the site. The preliminary soil classifications are based solely on the materials encountered in widely spaced exploratory test borings. The contractor should verify that similar conditions exist throughout the proposed area of excavation. If different subsurface conditions are encountered at the time of construction, the actual conditions should be evaluated to determine any excavation modifications necessary to maintain safe conditions. As a safety measure, it is recommended that all vehicles and soil piles be kept to a minimum lateral distance from the crest of the slope equal to no less than the slope height. The exposed slope face should be protected against the elements. Detention Ponds, (if required) Based on our understanding, a large detention pond is planned along the western -portion of the site. Soil conditions, as depicted by our Boring No. 5, generally consist of an approximate 3-foot layer of sandy lean clay, underlain by well -graded sand with silt and gravel to depths explored. Groundwater was encountered at approximate depths of 6-feet below existing site grades. The detention pond is to collect surface water and/or roof runoff for the project as a temporary "holding basin" over time .and. eventually discharge the water into the storm sewer drainage system. Depending upon the final design depth of the detention pond, and due to the potential for groundwater fluctuations to become elevated and enter the pond, consideration could be given to lining the pond bottom of the ponds with the on -site clay soils or approved imported cohesive materials, to prevent groundwater intrusion from entering the pond. It is suggested to maintain a separation of 2 to 3-feet between maximum anticipated rise in groundwater and the bottom of the each pond. It is anticipated that excavation of the detention ponds. could be accomplished by conventional type excavation equipment. The pond should be excavated on slopes of 2:1 or flatter and any associated berms should be constructed on 2:1 slopes. The berms surrounding the ponds should be lined the cohesive type soils, and/or imported clay materials approved by the Geotechnical Engineer. The cohesive type soils should be moisture conditioned to plus or minus 2 percent of optimum moisture content, placed in uniform lifts and mechanically compacted to at least 95 percent of Standard Proctor Density ASTM D698. After site configurations and detention pond elevations have been more defined we can provide additional geotechnical exploration activities, laboratory testing and lining recommendations upon request. 17 Geotechnical Engineering Report lferracan Proposed Lincoln Avenue Townhome Development Project Fort Collins, Colorado Project No. 20045173 Fill Materials and Placement Approved imported materials may be used as fill material and are suitable for use as compacted fill beneath interior or exterior floor slabs. Imported soils (if required) should conform to the following: Gradation Percent finer by weight (ASTM C136) 3"......................................................................................................... 100 No. 4 Sieve.................................................................7................... 50-100 . No. 200 Sieve.............................................................................. 35 (max). • Liquid Limit...................................................................:............... 30 (max) • Plasticity Index.......................................................................:...... 15 (max) • Group Index................................................................................. 10 (max) Engineered fill should be placed and compacted in horizontal lifts, using equipment and procedures that will produce recommended moisture contents and densities throughout the lift. it is recommended ail fill material to placed on the site be compacted to at least 95 percent.of Standard Proctor Density ASTM D698. Crn-site clay soils- should be compacted within a moisture content range of 1 percent below, to 3 percent above optimum. Imported granular soils should be compacted within a moisture range of 3 percent below to 3 percent above optimum unless modified by the project geotechnical engineer. Excavation and Trench Construction Excavations into the on -site soils will encounter a variety of conditions. Excavations into the clays can be expected to stand on relatively steep temporary slopes during - --- -- - - -"- - coris ruction.—-oweVe�, caving soils and groundwater may also be encountered. The individual contractor(s) should be made responsible for designing and constructing stable, temporary excavations as required to maintain stability of both the excavation sides and bottom. All excavations should be sloped or shored in the interest of safety following local and federal regulations, including current OSHA excavation and trench safety standards. 16 I Geotechnical Engineering Report lrerracon Proposed Lincoln Avenue Townhome Development Project Fort Collins, Colorado Project No. 20045173 preparation, foundation bearing soils, and other geotechnical conditions exposed during the construction of the project. Site Preparation Strip and remove any existing debris or other deleterious materials from proposed building areas. All exposed surfaces should be free of mounds and depressions that could prevent uniform compaction. The site should be initially graded to create a relatively level surface to receive fill, and to provide for a relatively uniform thickness of fill beneath fill areas. All exposed areas which will receive fill, once properly cleared and benched where necessary, should be scarified to.a minimum depth of 12-inches and conditioned to the moisture contents outlined under the "Fill Materials and Placement' section of this report. It is anticipated that excavations for the proposed construction can be accomplished with conventional earthmoving equipment. Based upon the subsurface conditions determined from. the geotechnical exploration, the majority of the underlying subgrade soils exposed during construction are anticipated to be relatively stable; however soft compressible and/or unstable areas may be encountered during construction, especially in close proximity to the groundwater. The stability of the subgrade may be affected by precipitation, repetitive construction traffic or other factors. If unstable conditions develop, workability may be improved by scarifying and drying. Overexcavation of wet zones and replacement with granular materials may be necessary. Use of lime, fly ash, kiln dust, cement or geotextiles could also be considered as a stabilization technique. Laboratory evaluation is recommended to determine the effect of chemical stabilization on subgrade soils prior to construction. Lightweight excavation equipment may be required to reduce subgrade pumping. 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. 15 Geotechnical Engineering Report Proposed Lincoln Avenue Townhome Development Project Fort Collins, Colorado Project No. 20045173 lrerracon • Seal all landscaped areas in, or adjacent to pavements to minimize or prevent moisture migration to subgrade soils; Placing compacted, low permeability backfill against the exterior side of curb and gutter; and, • Placing curb, gutter and/or sidewalk directly on subgrade soils without the use of base course materials. 1 Preventive maintenance should be planned and provided for through an on -going pavement management program. Preventive maintenance activities are intended to slow the rate of pavement deterioration, and to preserve the pavement investment. , Preventive maintenance consists of both localized maintenance (e.g. crack and joint sealing and patching) and global maintenance (e.g. surface sealing). Preventive maintenance is usually the first priority when implementing a planned pavement maintenance program and provides the highest return on investment for pavements. Prior to implementing any maintenance, additional engineering observation is recommended to determine the type and extent of preventive maintenance. Site grading is generally accomplished early in the construction phase. However as construction proceeds, the subgrade may be disturbed due to utility excavations, construction traffic, desiccation, or rainfall. As a result, the pavement subgrade may not be suitable for pavement construction and corrective action will be required. The subgrade should be carefully evaluated at the time of pavement construction for signs of disturbance or excessive rutting. If disturbance has occurred, pavement subgrade areas should be reworked, moisture conditioned,. and properly compacted to the recommendations in this report immediately prior to paving. Please note that if during or after placement of the stabilization 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 • General Considerations The following presents recommendations for site preparation, excavation, subgrade preparation and placement of engineered fills on the project. All earthwork on the project should be observed and evaluated by Terracon. The evaluation of earthwork should include observation and testing of engineered fill, subgrade 14 Geotechnical Engineering Report 1rerracon Proposed Lincoln Avenue Townhome Development Project Fort Collins, Colorado Project No. 20045173 (3) Alternative A assumes a minimum of 12-inches of overexcavated/scarification and moisture conditioned/processed subgrade material is prepared beneath the planned paved sections, and an approved proof -roll has been completed. Each alternative should be investigated with respect to current material availability and economic conditions. 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 hot 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 submitted prior to construction to verify their adequacy. Asphalt material should be placed in maximum 37inch lifts and should be compacted to a within a range of 92 to 96 % of Maximum Theoretical Density. For areas subject to concentrated and repetitive loading conditions such as dumpster pads, truck delivery docks and ingress/egress aprons, we recommend using a Portland cement concrete pavement with a thickness of at least 7 inches underlain by at least 4 inches of aggregate road base material. Prior to placement of the aggregate road base material, the areas should be thoroughly proofrolled. For dumpster pads, the concrete pavement area should be large enough to support the container and tipping axle of the refuse truck. Long term pavement performance will be dependent upon several factors, including maintaining subgrade moisture levels and providing for preventive maintenance. The following recommendations should be considered the minimum: • Site grading at a minimum 2% grade away from the pavements; • The subgrade and the pavement surface have a minimum % inch per foot slope to promote proper surface drainage. • . Consider appropriate edge drainage and pavement under drain systems, • Install pavement drainage surrounding areas anticipated for frequent wetting (e.g. garden centers, wash racks) • Install joint sealant and seal cracks immediately, 13 Geotechnical Engineering Report 1rerracon Proposed Lincoln Avenue Townhome Development Project Fort Collins, Colorado Project No. 20045173 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 each traffic area, are as follows: S.f �RECOMMENDEYM/NIMUM,PA;VEMENT,uTH/CKNESSR-!WCHESWAiMF % W ^ 22.11 �TraffcaAreaa: %' ��'L�.=koat?i^+h'', Alternatives_ » ,n Ki,-a�fu.��;, n.rPJrtaav v, �da„l �0r I-tlPygi+, µ - +Goncreteurface ,. Ott, t=_ air tz„,>,,�t�^'a�S�Gradmg er::`. r. ilmn ,'�.,..y w.*.. rGun:,. �4 phalt�``'Tri'a5�-" " �w, GorcreSe ,p ®;iSurfamce`u, SG. n , .a.x....x.: a ''�au.t�.'�',3lll.'w't'� �A99regateBase v d� - u Course ,Class 5 .5:,tinrrr�a s+ •w'��'�"w,. *^�ut�` a.....„ ew hI wlzlY Fly7reated�g ; t x. SubeBase 4r^z'�'"1d �aE.`r ,.m�1115�illr r +P•ui F y a�� ' hinnx .x�Sq Portland t. Cement ;'q y' .W �..� t M1Ydea"!- ,. �7otal .�:�. . ^i tk.i3gGr P) A 3.5. 6.0 9.5 Automobile B 3.5 6.0 12.0 21.5 Parking Areas C - 1 6.0 6.0 C-2 12.0 5.5 17.5 (3) A 1.5 2.5 8.0 12.0 Heavy B 1.5 2.0 6.0 12.0 21.5 Duty/Truck TrafFc Areas C - 1 7.0 7.0 C-2 12.0 6.0 18.0 (1) If the asphalt surface course is to consist of Grading S, then the required minimum lift/thickness placed should be 2-inches. If the asphalt surface course is to consist of Grading SX, the required minimum lift/thickness placed should be 1-1/2-inches. (2) If fly ash is utilized for the on -site ,pavement improvement areas to mitigate the unstable nature of the subgrade materials, it is recommended that at least the upper 12-inches of the prepared subgrade be treated with fly ash. Using a minimum thickness of 12-inches of fly ash - - -------treated - subgrade-will- reduce - the-- required asphalt-thickness-by-approximately-1-to 1-1/2-- inches. However, in most cases the required minimum asphalt pavement thicknesses take precedent in the pavement thickness sections. Therefore no reduction.is provided and the use of fly ash is incorporated into the pavement design and construction procedures to mitigate the swell potential of the subgrade soils only.. Terracon is available to provide the I equired laboratory soil and fly ash mix design as well as placement recommendations upon request. 12 Geotechnical Engineering Report 1rerracon Proposed Lincoln Avenue Townhome Development Project Fort Collins, Colorado Project No. 20045173 Proofrolling and recompacting the subgrade is recommended immediately prior to placement of the aggregate road base section. Soft or weak areas delineated by the proofrolling operations should be.undercut or stabilized in -place to achieve the appropriate subgrade support. Asphalt concrete underlain by crushed aggregate base course with or without a fly ash treated subgrade, and non -reinforced concrete pavement are feasible alternatives for the proposed on - site paved sections. Based on the subsurface conditions encountered at the site, and the laboratory test results, it is recommended the on -site private drives and parking areas be designed using a minimum R-value of 10. Pavement design methods are intended to provide structural sections with adequate thickness over a particular subgrade such that wheel loads are reduced to a level the subgrade can support. The support characteristics of the subgrade for pavement design do not account for shrink/swell movements of the existing subgrade soils encountered on this project. Thus, the pavement may be adequate from a structural standpoint, yet still experience cracking and deformation due to shrink/swell related movement of the subgrade. .It is, therefore, important to minimize moisture changes in the subgrade to reduce shrink/swell movements. Design of pavements for the project have been based on the procedures outlinedin 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 10 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. 11 Geotechnical Engineering Report lferracon Proposed Lincoln Avenue Townhome Development Project Fort Collins, Colorado Project No. 20045173 these options, such as the use of structural floors or overexcavating and replacing expansive materials are discussed in this report. We would be pleased to discuss other construction alternatives with you upon request. . Additional floor slab design and construction recommendations for floor slabs are as follow: • Positive separations and/or isolation joints should be provided between slabs and all foundations, columns or utility lines to allow independent movement. • Control joints should be provided in slabs to control the location and extent of cracking. 49 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. • In areas subjected to normal loading, a minimum 4-inch layer of clean -graded gravel or.aggregate base course should be placed beneath upper level interior slabs. In areas of heavier floor loading conditions, considerations should be given to increasing the amount of underslab gravel to a minimum of 6-inches. • Floor slabs should not be constructed on frozen subgrade. • Other design and construction considerations, as outlined in the ACI Design Manual, Section 302.1 R are recommended. Pavement Design and Construction Based on -the subsurface conditions encountered during the site exploration, it is our opinion the proposed on -site pavement areas are feasible provided the following recommendations are implemented. The shallow subsoils encountered throughout the site are generally non -plastic, cohesionless sand type soils exhibiting low to moderate subgrade strength characteristics and non -to low swell/expansive potential. 10 Geotechnical Engineering Report lrerracon Proposed Lincoln Avenue Townhome Development Project Fort Collins, Colorado �. Project No. 20045173 The lateral earth pressures herein do not include any factor of safety and are not applicable for submerged soils/hydrostatic loading. Additional recommendations may be necessary if submerged conditions are to be included in the design. . Fill against grade beams and retaining walls should be compacted to densities specified in Earthwork. Compaction of each lift adjacent to walls should be accomplished with hand -operated tampers or other lightweight compactors. Overcompaction may cause excessive lateral earth pressures, which could result in wall movement. ai Seismic Considerations The project site is located in Seismic Risk Zone I of the Seismic Zone Map of the United States as indicated by the 1997 Uniform Building Code. Based upon the nature of the subsurface materials, Soil Profile Type "Sc" should be used for the design of structures for the proposed project (1997 Uniform Building Code, Table No. 16-J). A site classification "C" should be used for the design of structures for the proposed project (2000 International Building Code, Table No. 1615A .1). Floor Slab Design and Construction It is anticipated non -to -low expansive natural soils or approved engineered fill material will support the proposed floor slabs. For conventional -type slab on grade construction, differential slab movement on the order of 1-inch or more is possible should the underlying subsoils increase in moisture content. Therefore, positive drainage away from the building footprints to reduce the potential for surface water infiltration from impacting the underlying slab subgrade material should be implemented during and after construction activities. For structural design of concrete slabs -on -grade, a modulus of subgrade reaction of 100 pounds per cubic inch (pci) may be used for floors supported on existing on -site soils. A modulus of 200 pci may be used for floors supported on non -expansive imported fill meeting the specifications outlined below. -- --This-report provides -recommendations -to -help mitigate the effects of -soil -movement- However; even if these procedures are followed, some movement and at least minor cracking in the structure's foundation system and floor slab should be anticipated. The severity of cracking and other cosmetic damage such as uneven floor slabs will probably increase if any modification of the site results in excessive wetting or drying of the expansive materials. Eliminating the risk of movement and cosmetic distress may not be feasible, but it may be possible to further reduce the .risk of movement if significantly more expensive measures are used during construction. Some of 9 Geotechnical Engineering Report Proposed Lincoln Avenue Townhome Development Project Fort Collins, Colorado Project No. 20045173 lrerracon pier concrete. Pier concrete should have relatively high fluidity when placed in cased pier holes or through a tremie. To provide increased resistance to. potential uplift forces, the sides of each pier should be mechanically roughened in the bearing strata below a depth of 10-feet. This should be accomplished by a roughening tooth placed on the auger. Pier bearing surfaces must be cleaned prior to concrete placement. A representative of the geotechnical engineer should inspect the bearing surface and pier configuration. Foundation excavations should be observed by the geotechnical engineer. A representative of the geotechnical engineer should inspect the bearing surface and pier configuration. If the soil conditions encountered differ significantly from those presented .in this report, supplemental recommendations will be required. Lateral Earth Pressures For soils above any, free water surface, recommended equivalent fluid pressures for unrestrained foundation elements are: • Active: Cohesive soil backfill (on -site clay) ............................................... 50 psf/ft Cohesionless soil backfill (imported granular material) ................. 35 psf/ft On -site bedrock materials..................................not recommended for use • Passive: Cohesive soil backfill (on -site clay)..............................................250 psf/ft Cohesionless soil backfill (imported granular material) ................350 psf/ft 'Undisturbed bedrock....................................................................450 psf/ft Where the design includes restrained elements, the following equivalent fluid pressures are recommended: - - t rest:---- ------------ ------- — --- ---- ------ - Cohesive soil backfill (on -site clay) ................................................ 65 psf/ft Cohesionless soil backfill (imported granular material) ................. 50 psf/ft On -site bedrock materials .................................. not recommended for use M. i iGeotechnical Engineering Report lrerracan Proposed Lincoln Avenue Townhome Development Project Fort Collins, Colorado Project No. 20045173 movement -resulting from the assumed structural loads is estimated to be on the order of 1-inch or less. 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 ,o construction. Foundation Systems — Drilled Piers/Caissons If maximum concentrated loads exceed those presented herein, then a grade beam and drilled pier/caisson foundation system should be used to support the structure. Straight shaft piers, drilled a minimum of 8-feet into competent or harder bedrock, with minimum shaft lengths of 20- feet are recommended. For axial compression loads, piers may be design for a net allowable end -bearing pressure of 20,000 pounds per square foot (psf), and skin friction of 2,000 psf for the portion of the pier in firm or harder bedrock. Piers should be designed for a minimum dead -load pressure of 5,000 psf, based upon pier end.area. All piers should be reinforced full depth for the applied axial, lateral and uplift stresses imposed. The amount of reinforcing steel for expansion should be determined by the tensile force created by the uplift force on each pier, with allowance for dead load. To reduce potential uplift forces on piers, use of long grade beam spans to increase individual pier loading, and small diameter piers are recommended. For this project, use of a minimum pier diameter of 12-inches is recommended. A minimum 4-inch or greater void space should be provided beneath grade beams between piers. The void material should be of suitable strength to support the weight of fresh concrete used in grade beam construction, and to avoid collapse when foundation backfill is placed. Required pier penetration should be balanced against potential uplift forces due to expansion of the subsoils and bedrock on the site. For design purposes, the uplift force on each pier can be determined on the basis of the following equation: Where: UP = the uplift force in kips, and D = the pier diameter in feet Uplift forces on piers should be resisted by a combination of dead load and pier penetration below a depth of 1 O feet and in the bearing strata. Geotechnical Engineering Report 1(erracon Proposed Lincoln Avenue Townhome Development Project Fort Collins, Colorado Project No. 20045173 • If maximum concentrated loads exceed those presented herein, grade beams and straight shaft piers/caisson drilled into the bedrock. Conventional type slab on grade construction is feasible for the site provided all slabs are placed a minimum of 4-feet above the groundwater table. Foundations and masonry 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 masonry walls is recommended. Foundation excavations should be observed by the geotechnical engineer: If the soil conditions encountered differ significantly from . those presented in this report, supplemental recommendations will be required. Foundation Systems — Conventional Spread Footings Spread footing foundations placed a minimum of 3-feet above the maximum anticipated rise in groundwater and bearing on the native undisturbed subsoils or engineered fill material, may be used to support the proposed townhome structures for at the site. Footings bearing on the native undisturbed granular soils or on approved engineered fill material, should be designed for a net allowable bearing pressure of 2,000 psf. If actual design loads are heavier than those presented herein, then a drilled pier foundation system should be utilized. If foundation systems are placed on imported fill material, which may be necessary to achieve final grades, a minimum 2-foot. layer of imported granular structural fill material should be placed and compacted beneath the foundation systems. The fill material should extend horizontally 5- feet beyond the edge of the footprint of the structure and should be moisture conditioned to near optimum moisture content, placed in uniform 8 to 12-inch lifts and mechanically compacted to 98 percent of Standard Proctor Density (SPD) ASTM D698. Prior to placement of the imported fill section, the native subsoils, stripped of topsoil and any miscellaneous debris, encountered below the fill material zone should be scarified; moisture conditioned to near optimum moisture content and compacted to at least 95 percent of SPD ASTM D698. 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 movement is recommended; however, proportioning to relative constant dead-loadpressure will also reduce differential movement between adjacent footings. Total 5 1 Geotechnical Engineering Report lrerracon Proposed Lincoln Avenue Townhome Development Project Fort Collins, Colorado Project No. 20045173 graded silty sand with gravel was encountered beneath the cohesive. layer and extended to the depths explored and/or to the bedrock below. Siltstone/claystone bedrock was encountered in Test Boring Nos. 1 and 4 at an approximate depth of 22-feet below site grades and extended to the depths explored, 24-1/2-feet. Field and Laboratory Test Results Field and laboratory test results indicate the native :cohesive soils are medium stiff to stiff in consistency and exhibit low swell expansive potential and low to moderate bearing characteristics. The fine to coarse granular strata are medium dense to dense in relative density and exhibit low to moderate bearing characteristics. The bedrock stratum varies from moderately hard to hard with increasing depths and exhibits a low to moderate swell potential and moderate to high bearing characteristics with increased depths. Groundwater Conditions Groundwater was encountered in each test boring at an approximate depth. of 6-feet below existing site grades. Due to the granular nature of the underlying subsoils, when the follow up measurements were made, the borings had caved in. Therefore, stabilized groundwater measurements were not obtained. These observations represent groundwater conditions at the time of the field exploration, and may not be indicative of other times, or at other locations. Groundwater levels can be expected to fluctuate with varying seasonal and weather conditions. Zones of perched and/or trapped groundwater may occur at times in the subsurface soils overlying bedrock, on top of the bedrock surface or within permeable fractures in the bedrock materials. The location and amount of perched water is dependent upon several factors, including hydrologic conditions, type of site development, irrigation_ demands on or adjacent to the site, fluctuations in water features, seasonal and weather conditions. ■ ENGINEERING ANALYSES AND RECOMMENDATIONS Geotechnical Considerations The site appears suitable for the proposed construction from a geotechnical engineering point of view. The following foundation system was evaluated for use on the site for the proposed structures: • Conventional type spread footings bearing upon the undisturbed subsoils, or engineered fill material and placed a minimum of 3-feet above the maximum anticipated rise in groundwater; and 4 I Geotechnical Engineering Report Proposed Lincoln Avenue Townhome Development Project Fort Collins, Colorado . Project No. 20045173 lrerracon formulated to determine engineering properties of the subsurface materials. Boring logs were prepared and are presented in Appendix A. Laboratory tests were conducted on selected soil and bedrock samples and are presented in Appendix B. The test results were used for the geotechnical engineering analyses, and the development of foundation and earthwork recommendations. All laboratory tests were performed in general accordance with the applicable local or other accepted standards. Selected soil and bedrock samples were tested for the following engineering properties: • Water Content • Dry Density • Swell -Consolidation • Atterberg Limits/Soil Classifications . • Grain -Size Distribution SITE CONDITIONS The area for the proposed Lincoln Avenue Townhomes is located North of Lincoln Avenue and east of Lemay Avenue directly north and east of the Bank of Colorado facility currently under construction. The area consists of an abandoned farmhouse, two masonry block silos, several outbuildings and horse corrals. The site is subdivided into several parcels by barbwire and split rail fences and is presently being utilized as pasture/grazing land. Several tall deciduous trees are scattered throughout the site and predominantly line the western boundary. A drainage ditch/swale parallels Lincoln Avenue on the south side of the property, with Lincoln Avenue elevated slightly above the site. The area is relatively flat and exhibits poor surface drainage, predominantly in the southeast direct. North of the site a vacant strip of land with single-family residences and several outbuildings located beyond. East of the site is a vacant pasture land with commercial/office buildings located beyond. Lemay Avenue borders the site to the west and Lincoln Avenue borders the site to the south. SUBSURFACE CONDITIONS Soil and Bedrock Conditions An approximate o-inch layer of silty, topsoil containing organic matter and root growth was encountered at the surface of each test boring. Underlying the surface material was a thin layer, (i.e. approximate''/z to 5-feet) of sandy lean clay, which extended to the granular stratum below. Poorly graded to well 3 I Geotechnical Engineering Report . Proposed Lincoln Avenue Townhome Development Project Fort Collins, Colorado Project No. 20045173 lferraron respectively. Although final site grading plans were not available at the time of the field exploration, it is assumed finished floor levels will be at or slightly above existing site grades. SITE EXPLORATION The scope of the services performed for thisproject included a site reconnaissance by an engineering geologist, a subsurface exploration program, laboratory testing and engineering analyses. Field Exploration A total of test borings were drilled on October 22, 2004, at the locations shown on the Test Boring Location Diagram, Figure No. 1. Four (4) test borings were located within the footprints of the proposed townhome structures, and one (1) was located within the planned detention pond located along the western portion of the site, and were drilled to approximate depths of 15 to 25- �, feet below existing site grades. The borings were advanced with a truck -mounted drilling rig, utilizing 4-inch diameter solid stem augers. The borings were located in the field by pacing from existing site features. Approximate ground surface elevations were determined at each boring location by means of an engineers level and referenced to a temporary benchmark (TBM) as shown on the enclosed site plan. The accuracy of boring locations and elevations should only be assumed to the level implied by the methods used. Lithologic logs of each boring were recorded by the engineering geologist during the drilling operations. At selected intervals, samples of the subsurface materials were taken. by means of pushing thin -walled Shelby tubes, or by driving split -spoon and ring barrel samplers. Penetration resistance measurements were obtained by driving the split -spoon and ring barrel into the subsurface materials with a 140-pound hammer falling 30 inches. The penetration resistance value is a useful index in estimating the consistency, relative density or hardness of the materials encountered. Laboratory Testing I All samples retrieved during the field exploration were returned to the laboratory for observation by the project geotechnical engineer and were classified in general accordance with the Unified Soil Classification System described in Appendix C. Samples of bedrock were classified in general accordance with the general notes for Bedrock Classification. At that time; the field descriptions were confirmed or modified as necessary and an applicable laboratory testing program was I2 GEOTECHNICAL ENGINEERING REPORT PROPOSED LINCOLN AVENUE TOWNHOME DEVELOPMENT PROJECT NORTHEAST CORNER OF LINCOLN AVENUE AND LEMAY AVENUE FORT COLLINS, COLORADO TERRACON PROJECT NO. 20046173 November 17, 2004 INTRODUCTION This report contains the.results of our supplemental geotechnical engineering exploration for the proposed Lincoln Avenue Townhome Development Project, to be located near the northeast corner of Lincoln Avenue and Lemay Avenue, north and east of the Bank of Colorado facility situated directly at the northeast corner of the intersection, in northeast Fort Collins, Colorado. The site is located in the Northeast 1/4 of Section 7, Township 7 North, Range 68 West of the 6th Principal Meridian, Larimer County, Colorado. The purpose of these services is to provide information and geotechnical engineering recommendations relative to: • subsurface soil and bedrock conditions • groundwater conditions • foundation design and construction • lateral earth pressures • floor slab design and construction • pavement design and construction • earthwork • drainage The recommendations contained in this report are based upon the results of field and laboratory testing, engineering analyses, and experience with similar soil conditions, structures and our understanding of the proposed project. PROPOSED CONSTRUCTION It is Terracon's understanding the project is to consist of a series of 2 ,to 3-story, 5 to 8 units/building townhome structures having slab on grade 'construction. Also included will be associated driveways, parking areas and a large detention pond located along the western portion of the site. Future planed office buildings are proposed along the southern portion of the site. The anticipated maximum wall and columns loads for the project are 1 to 4 klf and 10 to 75 kips, TABLE OF CONTENTS Page No. Letter of Transmittal..............................................................................:....................I INTRODUCTION.............................................................................................................................1 PROPOSED CONSTRUCTION ...... :....................................................................................... :....... 1 SITEEXPLORATION................................................................:.....................................................2 FieldExploration....................................................................................................................2 LaboratoryTesting..................:..............................................................................................2 SITE CONDITIONS.........................................................................................................................3 SUBSURFACE CONDITIONS......................................................................................................:.3 Soil and Bedrock Conditions.................................................................................................3 Field and Laboratory Test Results........................................................................................4 ENGINEERING ANALYSES AND RECOMMENDATIONS...........................................................4 Geotechnical Considerations.................................................................................................4 Foundation Systems - Conventional Spread Footings.........................................................5 Foundation Systems — Drilled Piers/Caissons......................................................................6 Lateral Earth Pressures.........................................................................................................8 SeismicConsiderations.........................................................................................................9 Floor Slab Design and Construction......................................................................................9 Pavement Design and Construction....................................................................................10 Earthwork.............................................................................................................................14 General Considerations....................................................................................:........14 SitePreparation..........................................................................................................15 Subgrade Preparation.................................................................................................15 Fill Materials and Placement.....................................................................................16 Excavation and Trench Construction........................................................................16 Additional Design and Construction Considerations...........................................................18 Exterior Slab Design and Construction.....................................................................18 Underground Utility Systems.....................................................................................18 SurfaceDrainage.......................................................................................................18 GENERALCOMMENTS ................................. .............. ................................................................. 19 APPENDIX A - - Test Boring Location Diagram --Figure No:1 Logs of Borings — Nos. 1 through 5 APPENDIX B Laboratory Test Results Photographs of the Site APPENDIX C General Notes I Geotechnical Engineering Report lrerracon Proposed Lincoln Avenue Townhome Development Project Fort Collins, Colorado Project No. 20045173 construction is feasible for the site provided the recommendations contained herein are followed. Other design and construction recommendations, based upon geotechnical conditions, are presented in the report. 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. Sincerely, TERRACON �Oi�L U Rf��sl A. F. David A. Ricfi�z��,.•,••• ��c ug J. ob , P.E. Geotechnic al Eri`f ent Manager Regional Manager Copies to: (5) Addressee November 17, 2004 Lagunitas-Lincoln, Inc. 3944 JFK Parkway Fort Collins, Colorado 80525 Attn: Mr. Jon Prouty Re: Geotechnical Engineering Report Proposed Lincoln Avenue Townhome Development Project Northeast Corner of Lincoln Avenue and Lemay Avenue Fort Collins, Colorado Terracon Project No. 20045173 Irerracon 301 North Howes • P.O. Box 503 Fort Collins, Colorado 80521-0503 (970) 484-0359 Fax: (970) 484-0454 Terracon has completed a geotechnical engineering exploration for the proposed Lincoln Avenue Townhome Development Project, to be located at near the northeast comer of Lincoln Avenue and Lemay Avenue, north and east of the Bank of Colorado facility situated directly at the northeast comer of the intersection, in northeast Fort Collins, Colorado. The project is to consist of a series of 2 to 3-story, 5 to 8 units/building townhome structures having slab on grade construction. Also included will be associated. driveways, parking areas and a large detention pond located along the western portion of the site. Future planned office buildings are proposed along the southern portion of the site. This study was completed in general accordance with our Proposal No. D2004362 dated October 8, 2004. The results of our engineering study, including the boring location diagram, laboratory test results, test boring records, and the geotechnical recommendations needed to aid in the design and construction of foundations, pavements and other earth connected phases of this project are attached. An approximate 6-inch layer of silty topsoil containing organic matter and root growth was encountered at the surface of each test boring. Underlying the surface material was a thin layer, (i.e. approximate'/2 to 5-feet) of sandy lean clay, which extended to the granular stratum below. Poorly graded to well graded silty sand with gravel was encountered beneath the cohesive layer and extended to the depths explored or to the bedrock below. Siltstone/claystone bedrockwas encountered in Test Boring Nos. 1 and 4 at an approximate depth of 22-feet below site grades and extended to the depths explored, 24-1/2-feet. Groundwater was encountered in each test boring at an approximate depth of 6-feet below existing site grades. Due to the granular nature of the underlying subsoils, when the follow up groundwater measurements were Made, all the borings had caved in. Therefore, stabilized groundwater measurements were not obtained. The results of field exploration and laboratory testing completed for this study indicate the soils at the site have low expansive potential and exhibit low to moderate load bearina capabilities. Based on the subsurface conditions encountered and the type on construction proposed, the townhome structures could be supported by conventional type spread footings provided placement is a minimum of 3-feet above the maximum anticipated rise of groundwater. Conventional slab on grade Arizona ■ Arkansas ■ California ■ Colorado ■ Georgia ■ Idaho ■ Illinois ■ Iowa ■ Kansas ■ Kentucky ■ Minnesota ■ Missouri Montana ■ Nebraska ■ Nevada ■ New Mexico ■ North Carolina ■ Oklahoma ■Tennessee ■Texas ■ Utah ■ Wisconsin ■ Wyoming Consulting Engineers & Scientists Since 1965 www.terracon.com GEOTECHNICAL ENGINEERING REPORT PROPOSED LINCOLN AVENUE TOWNHOME DEVELOPMENT PROJECT NORTHEAST CORNER OF LINCOLN AVENUE AND LEMAY AVENUE FORT COLLINS, COLORADO TERRACON PROJECT NO.20045173 November 17, 2004 Prepared for. LAGUNITAS-LINCOLN, INC. 3944 JFK PARKWAY FORT COLLINS, COLORADO 80525 ATTN: MR. JON PROUTY Prepared by. Terracon 301 North Howes Street Fort Collins, Colorado 80521 Marracon