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Home My WebLink AboutUNIVERSITY CENTER FOR THE ARTS - SITE PLAN ADVISORY REVIEW - 34-02 - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTAN .�wr/.A'��i 1M i I g Blau �vihor �zila66� ih Pewtu. �5 kproIr.�-�l� IxAnf�+�'� 281 NvalAeAbGm7G• FIGURE 1: SITE PLAN �p ll� COLORADO STATE UNIVERSITY UNIVERSITY CENTER FOR THE ARTS FORT COLLINS, COLORADO LEGEND Pmject Mrgr. ProjectNa. APPROX. TEST BORING LOCATION DAR Ir'orracon Designed By: Scale' 301 N. Howes Street Checked By. DAR Dar . ApWoved By. Dr By. Fort COBIns, Colorado 80521 DAR DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES. FlIaName: 25131FIGt F No. Geotechnical Engineering Report Proposed Center for the Arts Expansion Old Fort Collins High School Project No. 20025131 GENERAL COMMENTS lerracon 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 assessment of the site or identification of contaminated or hazardous materials or conditions. If the owner is concerned about the potential for such contamination, 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. 16 ' Geotechnical Engineering Report lrerracon Proposed Center for the Arts Expansion Old Fort Collins High School ' Project No. 20025131 • 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. Corrosion Protection Results of soluble sulfate testing indicate that ASTM Type I Portland cement is suitable for all concrete on and below grade. However, if there is no, or minimal cost differential, ' use of ASTM Type II Portland cement is recommended for additional sulfate resistance of construction concrete. Foundation concrete should be designed in accordance with ' the provisions of the ACI Design Manual, Section 318, Chapter 4. Surface Drainage Positive drainage should be provided during construction and maintained throughout the life of the proposed project. 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 5 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. ' 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. Landscaped irrigation adjacent to the foundation system should be minimized or eliminated. ' 15 1 Geotechnical Engineering Report lferracon Proposed Center for the Arts Expansion Old Fort Collins High School ' Project No. 20025131 ' Aggregate base (beneath slabs)............................................................95 On -site clay for backfill or grading purposes should be compacted within a moisture content range of 2 percent below, to 2 percent above optimum. Imported or on -site 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 may encounter caving soils and groundwater, depending upon the final depth of excavation. 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. 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. ' Additional Design and Construction Considerations Exterior Slab Design and Construction ' Exterior slabs -on -grade, exterior architectural features and utilities founded on or 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 14 I Geotechnical Engineering Report Proposed Center for the Arts Expansion Old Fort Collins High School Project No. 20025131 lferracon Depending upon depth of excavation and seasonal conditions, groundwater may be encountered in excavations on the site. Pumping from sumps may be utilized to control water within excavations. Well points may be required for significant groundwater flow, or where excavations penetrate groundwater to a significant depth. Subgrade Preparation ' Subgrade soils beneath interior and exterior slabs, and beneath pavements should be scarified; moisture conditioned and compacted to a minimum depth of 8 inches. The moisture content and compaction of subgrade soils should be maintained until slab or ' pavement construction. Fill Materials and Placement Clean on -site soils or 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........................................................................................30-80 No. 200 Sieve...............................................................................50 (max) • Liquid Limit.......................................................................30 (max) • Plasticity Index..................................................................15 (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. Recommended compaction criteria for engineered fill materials are as follows: Material Minimum Percent (ASTM D698) Scarified subgrade soils.........................................................................95 On -site and imported fill soils: ' Beneath foundations...................................................................95 Beneathslabs.............................................................................95 Beneath pavements....................................................................95 13 J ' Geotechnical Engineering Report lerracon Proposed Center for the Arts Expansion Old Fort Collins High School Project No. 20025131 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 preparation, foundation bearing soils, and other geotechnical conditions exposed during the construction of the project. It is recommended the existing on -site fill material within foundation portions of the site ' be removed to the native soils and stockpiled for reuse. The on -site fill material is suitable for reuse provided the recommendations contained within this section of the ' report are followed. The fill material should be moisture conditioned, placed in uniform 8 to 12-inch lifts, and mechanically compacted to at least 95% of Standard Proctor Density ASTM D698. A minimum 2-foot layer of the existing on -site fill material should be removed, re -conditioned and re -compacted beneath all slab on grade and future pavement construction areas. ' Site Preparation Strip and remove existing fill, debris, and other deleterious materials from proposed ' building and pavement 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 proposed building structures. ' All exposed areas which will receive fill, once properly cleared where necessary, should be scarified to a minimum depth of eight inches, conditioned to near optimum moisture ' content, and compacted. Demolition of any existing structures should include removal of all foundation systems ' within the proposed construction area. This should include removal of any loose backfill found adjacent to existing foundations. All materials derived from the demolition of existing structures and pavements should not be allowed for use in any on -site fills. ' It is anticipated that excavations for the proposed construction can be accomplished with conventional earthmoving equipment. 12 ' Geotechnical Engineering Report lrerracon Proposed Center for the Arts Expansion Old Fort Collins High School Project No. 20025131 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, a soil profile type Sc should be used for the design of structures for the proposed project (1997 Uniform Building Code, Table No. 16-J). ' Floor Slab Design and Construction 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. ' 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 cohesive subsoils and ' 200 pci if placed on the coarse granular stratum. Additional floor slab design and construction recommendations are as follows: 'a Positive separations and/or isolation joints should be provided between slabs and all foundations, columns or utility lines to allow independent movement. '0 Control joints should be provided in slabs to control the location and extent of cracking. '0 Interior trench backfill placed beneath slabs should be compacted in ' accordance with recommended specifications outlined below. • A minimum 8-inch layer of free -draining gravel should be placed beneath lower ' level floor slabs in conjunction with the underslab drainage system. • In areas subjected to normal loading, a minimum 4-inch layer of clean -graded gravel should be placed beneath interior slabs. For heavy loading, reevaluation of slab and/or base course thickness may be required. ' 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. ' 11 ' Geotechnical Engineering Report lrerracon Proposed Center for the Arts Expansion Old Fort Collins High School Project No. 20025131 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. ' The dewatering system should, at a minimum, include an underslab gravel drainage layer sloped to an interior perimeter drainage system. ' 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).........................................45 psf/ft Cohesionless soil backfill (on -site sand).................................35 psf/ft ' On -site bedrock materials .......................... not recommended for use • Passive: ' Cohesive soil backfill (on -site clay).......................................250 psf/ft Cohesionless soil backfill (on -site sand)...............................350 psf/ft Undisturbed bedrock............................................................400 psf/ft t L Where the design includes restrained elements, the following equivalent fluid pressures are recommended: • At rest: Cohesive soil backfill (on -site clay).........................................60 psf/ft Cohesionless soil backfill (on -site sand).................................50 psf/ft On -site bedrock materials .......................... not recommended for use 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. 10 I ' Geotechnical Engineering Report lerracon Proposed Center for the Arts Expansion Old Fort Collins High School Project No. 20025131 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 24-inches is recommended. ' Drilling to design depths should be possible with conventional single flight power augers on the majority of the site. However, lenses of very hard well -cemented sandstone may be encountered where specialized drilling equipment may be required. Based on the groundwater conditions encountered during drilling exploration, it appears casing may be required. Pier concrete should be placed immediately after completion of drilling and cleaning. If pier concrete ' cannot be placed in less than 3 inches of water, a tremie should be used for concrete placement to a maximum of 6 inches of water. Due to potential sloughing and raveling, foundation concrete quantities may exceed calculated geometric volumes. Pier concrete with ' slump in the range of 5 to 8 inches is recommended. To provide increased resistance to potential uplift forces, the sides of each pier should be ' mechanically roughened in the bearing strata. 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 Terracon should inspect the bearing surface and pier configuration. ' 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 ' masonry walls is recommended. Foundation excavations should be observed by Terracon. If the soil conditions encountered differ significantly from those presented in this report, supplemental recommendations will be required. ' Lower Level/Below Grade Construction Groundwater was encountered at the site at approximate depths of 20-1/2 to 22-1/2 feet below site grades when checked on July 11, 2002. Therefore, any below grade construction is considered feasible provided a dewatering system is in -place.. ■ To reduce the potential for groundwater fluctuations and/or surface water infiltration from entering any lower level/below grade construction, installation of a dewatering system is ' recommended. The drainage system should be constructed around the exterior perimeter of the below -grade 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 properly sized 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 9 1 I L' 1 1 F Geotechnical Engineering Report Proposed Center for the Arts Expansion Old Fort Collins High School Project No. 20025131 The coefficient of subgrade reaction for varying pier diameters is as follows: lrerracon sFs a p'at. a tih ".r n r: a h F.'r+ - ..x ivtd.�'_3 a r Coefficient of Subgrade l3eaction;(tons/ft) } . �,. zPier Diameter (inches) r max,, ��, s� gineeiel FIII Stiff Clays Bedrock or 12 75 400 18 50 267 24 38 200 30 30 160 36 25 133 All piers should be reinforced full depth for the applied axial, lateral and uplift stresses imposed. The amount of reinforcing steel for the tensile force should determine expansion created by the uplift force on each pier, with allowance for dead load. Minimum reinforcement of at least one- half percent of the cross -sectional area of each pier should be specified. When the lateral capacity of drilled piers is evaluated by the L-Pile (COM 624) computer program, we recommend that internally generated load -deformation (P-Y) curves be used. The following parameters may be used for the design of laterally loaded piers, using the L-Pile (COM 624) computer program: Compacted Existing Fill Material and Parameters Bedrock Strucfural Fill on -site ClaySoils Unit Weight of Soil (pcf) 130 115(') 125(1� Cohesion (pso 1 0 1 1500 1 5000 Angle of Internal Friction 0 35 25 I 20 (degrees) Strain Corresponding to '/z Max. --- I 0.02 I 0.015 � Principal Stress Difference E 'Notes: 1) Use of 65 PCF below the water table 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. Minimum reinforcement of at least one-half percent of the cross -sectional area of each pier should be specified. ' Geotechnical Engineering Report lferracon Proposed Center for the Arts Expansion Old Fort Collins High School ' Project No. 20025131 Foundation Systems — Drilled Piers/Caissons ' Due to the type of proposed construction and the anticipated maximum wall and column loads, a grade beam and drilled pier foundation system is recommended for support of the proposed University Center of Arts additions. Straight shaft piers, drilled a minimum of 10-feet into firm or harder bedrock, with a minimum shaft length of 25 feet are recommended. ' For axial compression loads, piers may be design for a maximum end -bearing pressure of 30,000 pounds per square foot (psf), and skin friction of 3,000 psf for the portion of the pier in ' firm or harder bedrock. All piers should be designed for a minimum dead load of 7,500 psf based upon pier end area. ' A minimum practical horizontal spacing between piers of at least three diameters should be maintained, and adjacent piers should bear at the same elevation. Piers should be considered to work in-group action if the horizontal spacing is -less than three pier diameters. The capacity of individual piers may need to be reduced when considering the effects of group . action. Capacity reduction is a function of pier spacing and the number of piers within a group. If group action analyses are necessary, capacity reduction factors can be provided for the analyses. ' All piers require sufficient dead load and additional penetration into the bearing strata to resist the potential uplift of the expansive materials. ' 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: ' UP=20xD Where: Up = the uplift force in kips, and D = the pier diameter in feet 1 1 L. Uplift forces on piers should be resisted by a combination of dead load and pier penetration below a depth of 7 feet and in the bearing strata. To satisfy forces in the horizontal direction, piers may be designed for lateral loads using a modulus of 75 tons per square foot for the portion of the pier in clays and/or engineered fill, and 400 tsf in bedrock for a pier diameter of 12 inches. 7 t I 1 Geotechnical Engineering Report Proposed Center for the Arts Expansion Old Fort Collins High School Project No. 20025131 1rerracon '` Test Bonng No ''; A 'rozimate Surf ice, Elevation , , Estimated` Ground water,Elevation 1 99.5 77.0 2 98.5 77.0 3 98.0 76.5 4 99.5 77.0 5 99.5 77.0 6 99.0 78.5 7 99.0 77.5 The estimated piezometric surface was developed based on the initial groundwater measurement data collected on July 11, 2002 after the initial drilling operations. The groundwater contour map for the site based on the piezometric data is included with this report as Figure 3. The piezometric surface was estimated using linear interpolations between piezometers and was based upon groundwater elevations in each test boring during the initial site exploration. As illustrated from Figure 3, the groundwater flow was estimated to be in the northeasterly direction. Actual conditions may vary depending upon various conditions. ENGINEERING ANALYSES AND RECOMMENDATIONS Geotechnical Considerations The site appears suitable for the proposed construction from a geotechnical engineering point of view. For the interior renovations within the gymnasium portions of the existing structure where new walls are to be constructed and/or where new foundations will be required, use a spread footing foundation system may be utilized. However, additional studies will be required after the interior bearing strata has been exposed and prior to placement of foundation concrete. It is our understanding the existing classroom and gymnasium structures are supported by a spread footing foundation system. Empire Laboratories, Inc., Terracon's predecessor, conducted geotechnical engineering site explorations for the additions constructed in 1970 and 1982. For further information and findings thereof, please refer to the reports dated May 8, 1970, Project 688-70 and May 21, 1982, Project No. 4757-82. The following foundation system was evaluated for use on the site for the proposed additions: ' • Grade beams and straight shaft piers/caisson drilled into the bedrock ' Slab -on -grade construction is considered acceptable for use, provided that design and construction recommendations are followed and an exterior perimeter drainage system is installed around any below grade construction. 1 6 n ' Geotechnical Engineering Report lrerracon Proposed Center for the Arts Expansion Old Fort Collins High School ' Project No. 20025131 Soil Conditions ' The subsurface conditions encountered beneath the existing pavement and topsoil/landscaping fill material consisted of sandy lean clay and lean clay with sand extending to approximate ' depths of 12 to 22-feet below existing site grades. Underlying the cohesive overburden soils were layers of well -graded sand with silt and gravel, silty sand with gravel, silty clayey sand with gravel and silty clayey sand extending to the bedrock below. Siltstone/sandstone bedrock was ' encountered at approximate depths of 24-1/2 to 28-feet below existing site grades and extended to the maximum depths explored, approximately 39-feet. Based on the surface ' elevation obtained at each test boring and the approximate depth at which bedrock was encountered in each boring, we have included in Appendix A, a bedrock contour map, Figure 2, illustrating the bedrock profile. The stratification boundaries shown on the enclosed boring logs represent the approximate locations of changes in soil types; in -situ, the transition of materials may be gradual. The soil ' profile for this portion of the site is generally consistent with the soil conditions presented in our previous subsurface exploration report. ' Field and Laboratory Test Results Field and laboratory test results indicate that the clay soils at the site are soft to medium stiff ' in consistency and the granular soils are loose to medium dense to dense in relative density. The siltstone/sandstone is cemented to well cemented with increase depths and exhibits ' moderate to high bearing characteristics. Very hard, well -cemented sandstone lenses were encountered with greater depths. It is not known whether the on -site fill material was properly placed or uniformly compacted. Therefore, the fill material, in its in -situ condition is not ' suitable for supporting the proposed foundations and/or slabs unless supporting documentation is presented to indicate otherwise. The fill is suitable for reuse as fill and/or backfill provided the recommendations contained in the "Earthwork" section are followed. Groundwater Conditions tGroundwater was encountered at the site at approximate depths of 20-1/2 to 22-1/2 feet below site grades when checked on July 11, 2002. 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. ' The following table provides the estimated ground surface elevation and the measured groundwater levels obtained in each test boring during the initial site exploration phases on July ' 11, 2002. 5 Geotechnical Engineering Report Proposed Center for the Arts Expansion Old Fort Collins High School Project No. 20025131 SITE CONDITIONS lrerracon The project site is located at the southeast corner of Pitkin Street and Remington Avenue in Fort Collins, Colorado. The existing historic Fort Collins High School facility occupies the southeastern portion of the site. Existing asphalt pavement is adjacent to the structure on the north and northwest portions of the site and the remainder of the site is covered with landscaping, grass and trees. East of the site are several buildings and an asphalt -paved parking lot presently being used by Colorado State University personnel. Another asphalt paved parking lot lies to the northeast. The site appears to exhibit positive surface drainage away from the existing structure. An Aerial Photograph, Figure No. 4 in Appendix A of this report depicts the present site conditions. SUBURFACE CONDITIONS Geology The proposed site is located within the Colorado Piedmont section of the Great Plains physiographic province. The Colorado Piedmont, formed during Late Tertiary and Early quaternary time (approximately two million (2,000,000) years ago), is a broad, erosional trench, which separates the Southern Rocky Mountains from the High Plains. Structurally, the site lies along the western flank of the Denver Basin. During the Late Mesozoic and Early Cenozoic Periods (approximately seventy million (70,000,000) years ago), intense tectonic activity occurred, causing the uplifting of the Front Range and associated downwarping of the Denver Basin to the east. Relatively flat uplands and broad valleys characterize the present-day topography of the Colorado Piedmont in this region. The site is underlain by the Cretaceous Pierre formation. The Pierre shale underlies the site at approximate depths of 24-1/2 to 28-feet below the surface. The Pierre shale is overlain by alluvial sands and clays of Pleistocene and/or Recent Age. ' Due to the relatively flat nature of the site, geologic hazards at the site are anticipated to be low. Seismic activity in the area is anticipated to be low; and from a structural standpoint, the ' property should be relatively stable. With proper site grading around proposed structures, erosional problems at the site should be minimal. ' Mapping completed by the Colorado Geological Survey ('Hart, 1972), indicates the site in an area of "Low to Moderate Swell Potential'. Potentially expansive materials mapped in this area include bedrock, weathered bedrock and colluvium (surficial units). ' 'Hart, Stephen S., 1972, Potentially Swelling Soil and Rock in the Front Range Urban Corridor, Colorado, Colorado Geological Survey, Environmental Geology No. 7. 4 Geotechnical Engineering Report Proposed Center for the Arts Expansion Old Fort Collins High School Project No. 20025131 1rerracon 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 samplers. Penetration resistance measurements were obtained by driving the split -spoon sampler 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. Groundwater conditions were evaluated in the test borings during initial drilling operations and follow-up measurements were obtained on July 11, 2002. The test borings were backfilled on July 11, 2002 for safety purposes; therefore additional groundwater measurements are not obtainable. Laboratory Testing All samples retrieved during the field exploration were returned to the laboratory for observation by the project geotechnical engineer and were classified in accordance with the Unified Soil Classification System described in Appendix C. Samples of bedrock were classified in 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 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 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 ASTM, local or other accepted standards. ' Selected soil and bedrock samples were tested for the following engineering properties: • Water Content . Plasticity Index • Dry Density • Grain Size Distribution • Swell - Consolidation • Compressive Strength • Water Soluble Sulfates 3 ' Geotechnical Engineering Report lerracon Proposed Center for the Arts Expansion Old Fort Collins High School ' Project No. 20025131 additions including the gymnasium addition in 1952, several small additions in 1971, the infill between the original facility and the 1952 gymnasium in 1980 and a 2-story classroom addition in 1982. The proposed renovation activities are to include, but not be limited to the following: the original gymnasium is to modified and used as the Dance Convertible area, the existing ' auditorium is to modified and used as a recital hall, and the 1952 gymnasium area is to be converted into small theaters, and rehearsal and support areas, and a small mezzanine in the southeast area of the gymnasium for the Metal/Welding Shop is also planned. The expansion and/or additions are to include a Dance Studio, a Performance Hall Addition, an Instrumental Rehearsal Addition and a Back of House Addition. ' The majority of the renovation and/or new construction is to be consist of reinforced concrete masonry walls with brick veneer and long span open web steel joists with steel roof decking. ' The walls range from 8 to 12-inches in width and heights from 18 to 72-feet in height, resulting in anticipated wall loads on the order of approximately 2 to 15 kips per linear foot, (klf). Based on the complexity of the project and the anticipated and/or reported heavy concentrated wall ' and column loads for the expansion areas, these additions should be supported by a drilled pier/caisson foundation system. For the interior renovations within the gymnasium portions of the existing structure where new walls are to be constructed, use a spread footing foundation ' system may be utilized. However, additional studies may be required after the interior bearing strata has been exposed and prior to placement of foundation concrete. It is our understanding ' the existing classroom and gymnasium structures are supported by a spread footing foundation system. ' SITE EXPLORATION The scope of the services performed for this project included a site reconnaissance by an ' engineering geologist, a subsurface exploration program, laboratory testing and engineering analyses. ' Field Exploration A total of 7 test borings were drilled at the site on July 10, 2002, to approximate depths of 25- ' 1/2 to 39-feet below existing site grades at the locations shown on the Site Plan, Figure 1. The test borings drilled at the site were advanced with a truck -mounted drilling rig, utilizing 4-inch diameter solid -stem augers. ' The borings were located in the field by Terracon by pacing from existing site features and/or ' property lines. Surface elevations were obtained by use of an engineer's level and referenced to a temporary benchmark (TBM) consisting of the finished floor elevation of the existing facility, as shown on the Site Plan, Figure 1. The accuracy of boring locations and elevations should ' only be assumed to the level implied by the methods used to determine each. 2 ' GEOTECHNICAL ENGINEERING REPORT PROPOSED COLORADO STATE UNIVERSITY UNIVERSITY CENTER FOR THE ARTS EXPANSION TO THE OLD FORT COLLINS HIGH SCHOOL SOUTHEAST CORNER OF PITKIN STREET AND REMINGTON STREET FORT COLLINS, COLORADO TERRACON PROJECT NO. 20025131 JULY 18, 2002 INTRODUCTION This report contains the results of our geotechnical engineering exploration for the proposed Colorado State University's University Center for the Arts expansion to the existing facility, formerly known as the Old Fort Collins High School, located at the southeast corner of Pitkin ' Street and Remington Street in Fort Collins, Colorado. The site is located in the Southwest 1/4 of Section 13, Township 7 North, Range 69 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 ' • 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 ' Based on information provided to us by Slaterpaull Architects, with supplemental information ' provided by Anderson & Hastings Consulting Engineers, Inc., it is our understanding the proposed additions are to be situated on the north and northwest portions of the existing historic Fort Collins High School building constructed in 1924. Interior renovations of the existing ' structure are also planned. The existing building was constructed in 1924 and has had several 1 ' Geotechnical Engineering Report Proposed Center for the Arts Expansion Old Fort Collins High School Project No. 20025131 APPENDIX A ' Site Plan/Boring Location Diagram — Figure No. 1 Bedrock Contour Map — Figure No. 2 Groundwater Contour Map — Figure No. 3 ' Aerial Photograph — Figure No. 4 Logs of Test Boring Nos. 1 through 7 APPENDIX B ' Laboratory Test Results APPENDIX C ' General Notes Bedrock Notes iv 1rerracon I TABLE OF CONTENTS Page No. ' Letter of Transmittal......................................................................................................... .........i ' INTRODUCTION.................................................................................................................1 PROPOSEDCONSTRUCTION..........................................................................................1 ' SITE EXPLORATION..........................................................................................................2 FieldExploration............................................'.......................................................... 2 ' Laboratory Testing........................................:.......................................................... 3 SITECONDITIONS.............................................................................................................4 ' Geology................................................................................................................... SoilConditions.........................................................................................................5 4 Field and Laboratory Test Results........................................................................... 5 ' Groundwater Conditions.......................................................................................... 5 ENGINEERING ANALYSES AND RECOMMENDATIONS..................................................6 ' Geotechnical Considerations................................................................................... Foundation Systems — Drilled Piers/Caissons.......................................................... 6 7 Lower Level/Below Grade Construction...................................................................9 Lateral Earth Pressures...........................................................................................10 tSeismic Considerations...........................................................................................11 Floor Slab Design and Construction........................................................................11 Earthwork................................................................................................................12 ' General Considerations................................................................................12 SitePreparation...........................................................................................12 Subgrade Preparation..................................................................................13 Fill Materials and Placement........................................................................13 Excavation and Trench Construction............................................................14 Additional Design and Construction Considerations.................................................14 Exterior Slab Design and Construction.........................................................14 Underground Utility Systems........................................................................15 Corrosion Protection.....................................................................................15 ' Surface Drainage.........................................................................................15 GENERALCOMMENTS.....................................................................................................16 11 Geotechnical Engineering Report lrerracon Proposed Center for the Arts Expansion ' Old Fort Collins High School Project No. 20025131 exposed and prior to placement of foundation concrete. It is our understanding the existing ' classroom and gymnasium structures are supported by a spread footing foundation system. The results of our engineering study, including the boring location diagram, laboratory test results, ' test boring records, and the geotechnical engineering recommendations needed to aid in the design and construction of foundations, drainage systems, and other earth connected phases of this project are attached. The subsurface conditions encountered beneath the existing pavement and topsoil/landscaping fill material consisted of sandy lean clay and lean clay with sand extending to approximate depths of 12 to 22-feet below existing site grades. Underlying the cohesive overburden soils were layers of well - graded sand with silt and gravel, silty sand with gravel, silty clayey sand with gravel and silty clayey sand extending to the bedrock below. Siltstone/sandstone bedrock was encountered at approximate depths of 24-1/2 to 28-feet below existing site grades and extended to the maximum depths explored, approximately 39-feet. Groundwater was encountered at the site at approximate depths of 20-1/2 to 22-1/2 feet below site grades when checked on July 11, 2002. Based on the type of construction proposed, and the anticipated maximum wall and column loads for the proposed additions, it is recommended a grade beam and straight shaft pier/caisson foundation system be utilized. Slab -on -grade construction is feasible provided the recommendations set forth in this report are followed. Further details are provided in this report. We appreciate the opportunity to be of service to you on this phase of your project. If you have any questions concerning this report, or if we may be of further service to you, please do not hesitate to contact us. Sincerely, TERRACON Daniel R. Lambert, E.I.T. Geotechnical Engineer Copies to: Addressee (2) Slaterpaull Architects (4): Mr. Brian J. Fagerstrom, AIA Anderson & Hastings — Consulting Engineers, Inc. (1): Mr. Ron Stevens Manager I ' July 18, 2002 ' Colorado State University Facilities Management Department Fort Collins, Colorado 80523-6030 Attn: Mr. Greg Smith 11 I 1 1 1 Irerracon 301 N. Howes • P.O. Box 503 Fort Collins, Colorado 80521-0503 (970) 484-0359 Fax: (970) 484-0454 Re: Geotechnical Engineering Report Proposed Colorado State University — University Center for the Arts Expansion Old Fort Collins High School Southeast Corner of Pitkin Street and Remington Street Fort Collins, Colorado Terracon Project No. 20025131 Terracon has completed a geotechnical engineering exploration for the proposed Colorado State University's University Center for the Arts expansion to the existing facility, formerly known as the Old Fort Collins High School, located at the southeast corner of Pitkin Street and Remington Street in Fort Collins, Colorado. This study was performed in general accordance with our Proposal No. D2002255 dated July 2, 2002. Based on information provided to us by Slaterpaull Architects, with supplemental information provided by Anderson & Hastings Consulting Engineers, Inc., it is our understanding the proposed additions are to be situated on the north and northwest portions of the existing historic Fort Collins High School building constructed in 1924. Interior renovations of the existing structure are also planned. The existing building was constructed in 1924 and has had several additions including the gymnasium addition in 1952, several small additions in 1971, the infill between the original facility and the 1952 gymnasium in 1980 and a 2-story classroom addition in 1982. The proposed renovation activities are to include, but not be limited to the following: the original gymnasium is to modified and used as the Dance Convertible area, the existing auditorium is to modified and used as a recital hall, and the 1952 gymnasium area is to be converted into small theaters, and rehearsal and support areas, and a small mezzanine in the southeast area of the gymnasium for the Metal/Welding Shop is also planned. The expansion and/or additions are to include a Dance Studio, a Performance Hall Addition, an Instrumental Rehearsal Addition and a Back of House Addition. The majority of the renovation and /or new construction is to be consist of reinforced concrete masonry walls with brick veneer and long span open web steel joists with steel roof decking. The walls range from 8 to 12-inches in width and heights from 18 to 72-feet in height. Based on the complexity of the project and the anticipated and/or reported heavy concentrated wall and column loads for the expansion areas, these additions should be supported by a drilled pier/caisson foundation system. For the interior renovations within the gymnasium portions of the existing structure where new walls are to be constructed use a spread footing foundation system may be utilized. However, additional studies may be required after the interior bearing strata has been Arizona Arkansas 0 California 0 Colorado 0 Georgia 0 Idaho ■ Illinois ■ Iowa 0 Kansas ■ Kentucky Minnesota 0 Missouri Montana ■ Nebraska ■ Nevada 0 New Mexico ■ Oklahoma ■ Tennessee 0 Texas 0 Utah ■ Wisconsin 0 Wyoming Consulting Engineers & Scientists Since 1965 www.terracon.com 1 1 1 1 1 1 1 1 1 1 GEOTECHNICAL ENGINEERING REPORT PROPOSED COLORADO STATE UNIVERSITY UNIVERSITY CENTER FOR THE ARTS EXPANSION TO THE OLD FORT COLLINS HIGH SCHOOL SOUTHEAST CORNER OF PITKIN STREET AND REMINGTON STREET FORT COLLINS, COLORADO TERRACON PROJECT NO. 20025131 JULY 18, 2002 Prepared for. COLORADO STATE UNIVERSITY FACILITIES MANAGEMENT DEPARTMENT FORT COLLINS, COLORADO 80523-6030 ATTN: MR. GREG SMITH Prepared by. Terracon 301 North Howes Street Fort Collins, Colorado 80521 lrerraco