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HomeMy WebLinkAboutHARMONY TECHNOLOGY PARK SECOND - Filed SER-SUBSURFACE EXPLORATION REPORT -GEOTECHNICAL ENGINEERING REPORT HARMONY TECHNOLOGY CENTER BUILDINGS C AND E, ASSOCIATED PARKING AREAS TECHNOLOGY PARKWAY AND STREETS A AND B SOUTH OF HARMONY ROAD, EAST OF CELESTICA FORT COLLINS, COLORADO TERRACON PROJECT NO. 20005198 MARCH 21, 2001 Prepared for. MICHAEL BARBER ARCHITECTURE 303 16T" STREET — SUITE 300 DENVER, COLORADO 80202-5657 ATTN: MR. DENNIS ARMSTRONG Prepared by: Terracon 301 North Howes Street Fort Collins, Colorado 80521 1rerracon Geotechnical Engineering Report Irerracon Harmony Technology Center — Buildings C and E Consulting Engineers & Scientists Terracon Project No. 20005198 301 North Howes Fort Collins, Colorado 80521 through 12, at approximate depths of 14 to 29 feet below existing site grades. A bedrock corAQW6 MP8WM9 developed for this portion of the site and is presented in Appendix A as Figure 2. Fax 970,484.0454 www.terracon.com Groundwater was encountered in the majority of the test borings at approximate depths of 7 to 12 feet below existing site grades when checked 1 to 5 days after drilling. In the area of the proposed detention pond, groundwater was encountered in Test Boring Nos. 17A, 17B, and 18 at approximate depths of 10 to 12 feet below existing site grades. A groundwater contour map of the general area of the detention pond was developed and is presented in Appendix A as Figure 3. The results of our field exploration and laboratory testing completed for this study indicate that the overburden soils at the site have a low to moderate expansive potential and low bearing characteristics. The bedrock stratum is weathered, moderately hard to hard with increased depths and exhibits moderate swell potential and moderate load bearing capabilities. Based on the subsurface soils and bedrock, conditions encountered, the type of construction proposed, and the anticipated maximum loads for the buildings, it is recommended the structures be supported on a grade beam and straight shaft pier/caisson foundation system. Conventional slab -on -grade construction is feasible for each of the proposed buildings, provided the recommendations contained in this report are followed. Other design and construction recommendations for the detention pond, pavement sections and other related areas, 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 Prepared by: 1 David A. Richer, Pt Department Manager/Geotechnical Engineer Reviewed by: William J. Attwooll, P.E. Office Manager Copies to: Addressee (5) JR Engineering — Mr. Robert Almiral (2) bha design — Mr. Bruce Hendee and Mr. Roger Sherman (2) Hewlett Packard — Mr. Michael Bello (1) i J I I Delivering Success for Clients and Employees Since 1965 More Than 95 Offices Nationwide 11 Geotechnical Engineering Report Harmony Technology Center — Buildings C and E Terracon Project No. 20005198 TABLE OF CONTENTS Page No. Letterof Transmittal...............................................................................................i INTRODUCTION...................................................................................................................1 PREVIOUS EXPLORATIONS ................................................................................ 2 PROPOSEDCONSTRUCTION............................................................................................ 2 SITEEXPLORATION ........................................... ................................................................ 2 Field Exploration ................ 3 LaboratoryTesting...........;.......................................................................................... 4 SITECONDITIONS............................................................................................................... 5 J SUBSURFACECONDITIONS.............................................................................................. 5 Geology....................................................................................................................... 5 Soil and Bedrock Conditions ................................................................. 6 Field and Laboratory Test Results...............................................................................6 GroundwaterConditions.............................................................................................. ENGINEERING ANALYSES AND RECOMMENDATIONS...................................................8 Geotechnical Considerations....................................................................................... 8 Foundation Systems — Drilled Piers/Caissons.............................................................8 Lateral Earth Pressures............................................................................................. 11 Seismic Considerations `•••••••••••• 12 RetainingWall Drainage............................................................................................ 12 Floor Slab Design and Construction..........................................................................12 Pavement Design and Construction.......................................................................... 13 y General Considerations.................................................................................... 19 19 Site Preparation ................................................................................ Subgrade Preparation...................................................................................... 20 PlacementFillMaterialsand ............................................................................ 20 Shrinkage ....................... ...................................................... 21 Slopes.............................................................. 22 Trench Construction............................................................... 22 Excavation and 23 Additional Design and Construction Considerations.................................................. Exterior Slab Design and Construction...............................•....................•• 23 Underground Utility Systems............................................................................ 23 iii if Geotechnical Engineering Report Harmony Technology Center — Buildings C and E Terracon Project No. 20005198 CorrosionProtection......................................................................................... 23 Surface Drainage ....... 24 GENERALCOMMENTS..................................................................................................... 25 APPENDIX A Site Plans — Figures 1, 2, and 3 Logs of Borings APPENDIX B Laboratory Test Results APPENDIX C General Notes Pavement Notes w " 4, GEOTECHNICAL ENGINEERING REPORT HARMONY TECHNOLOGY CENTER BUILDINGS C AND E, ASSOCIATED PARKING AREAS TECHNOLOGY PARKWAY AND STREETS A AND B SOUTH OF HARMONY ROAD, EAST OF CELESTICA FORT COLLINS, COLORADO TERRACON PROJECT NO. 20005198 MARCH 19, 2001 INTRODUCTION This report contains the results of our geotechnical engineering exploration for a portion of the Harmony Technology Center Development situated on the south side of Harmony Road and east of the adjacent Celestica facility in southeast Fort Collins, Colorado. This report specifically provides geotechnical engineering recommendations for Buildings C and E and their associated parking areas, Technology Parkway, Streets A and B, the utility installation along Cambridge Drive, and the detention pond along the southern portion of the property. The site is located in the Northwest '/4 of Section 4, Township 6 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 detention pond 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. Geotechnical Engineering Report Harmony Technology Center — Buildings C and E Terracon Project No. 20005198 PREVIOUS EXPLORATIONS Terracon performed a preliminary geotechnical engineering exploration for the proposed site encompassing the entire Northwest '/4 of Section 4, Township 6 North, Range 68 West, in September of 1996. In August of 1997, we performed a detailed geotechnical engineering exploration/evaluation for the Celestica facility. We also prepared a site specific preliminary geotechnical engineering report in October of 2000, in which 3 additional test borings were drilled and incorporated into our original preliminary findings. For further information and findings thereof, please refer to our reports titled "Preliminary Geotechnical Engineering Report" dated September 18, 1996, Project No. 20965104, our "Geotechnical Engineering Report" dated September 11, 1997, Project No. 20975066 for the Celestica facility, and our Preliminary Geotechnical Engineering Report" dated October 11, 2000, Project No. 20005198. PROPOSED CONSTRUCTION " Based on information provided by the design team, the proposed structures will be single -story to multi -story office/technology buildings, similar in complexity to the existing Hewlett Packard HP) Campus located on the north side of Harmony Road, directly across from the subject property. The proposed buildings are expected to exhibit heavy concentrated loads. Technology Parkway, a north to south directional roadway, is to be constructed along the western boundary of the site, east of the Celestica facility. Two other roadways are also to be constructed, which at this time are being identified as Streets A and B. A new water line is to be installed for the site, which is to be located along the existing alignment of Cambridge Drive along the eastern boundary of the property. A large detention pond is also planned for the site, and is to be situated in the southeast portion of the site. The proposed buildings will be surrounded by paved parking and landscaped areas. Although final site grading plans were not available at the time of the field exploration, ground floor levels are anticipated to be at or slightly above existing site elevations. 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. E ae otechnical Engineering Report iarmony Technology Center— Buildings C and E rracon Project No. 20005198 Meld Exploration A total of 30 test borings were drilled at the site on March 2, 5, and 7, 2001, to approximate depths of 10 to 30 feet below existing site grades at the locations shown on the Site Plan, Figure 1. All of the test borings were advanced with a truck -mounted drilling rig, utilizing 4-inch diameter solid stem augers. Twelve (12) test borings were located within the footprints of Buildings C and E, and drilled to approximate depths 30 feet, 4 test borings were located within the associated parking areas adjacent to Buildings C and E, and drilled to approximate depths of 10 feet, 3 test borings were located within the proposed water line alignment along Cambridge Drive and drilled to approximate depths of 15 feet, and 3 test borings were located within the proposed detention pond area and drilled to approximate depths of 15 feet. After drilling the test borings within the proposed detention pond area; these borings were converted to groundwater monitoring/piezometers in an effort to evaluate groundwater fluctuations. The piezometers consisted of a 2-inch diameter, flush -jointed, PVC pipe with a 5-foot slotted screen at each of the three locations. The slotted screens were backfilled with silica sand to 2 feet above the slotted portion with an approximate 2-foot bentonite seal placed above the screened sections. The remaining annulus of each piezometer was backfilled with auger cuttings. The piezometer cross -sectional details are shown on the boring logs in Appendix A. The 8 remaining test borings were located within the proposed City of Fort Collins roadway alignments, which included Technology Parkway, and Streets A and B. These test borings were drilled to approximate depths of 10 feet below site grades. These borings were drilled at this time to provide preliminary pavement thickness recommendations for construction bid purposes. It is our understanding these roadways will be dedicated City of Fort Collins' streets. Therefore, in accordance with the City of Fort Collins' Engineering Department Pavement Design Criteria, additional test borings will be required when all roadway utilities have been installed and the subgrade has been prepared to "rough" final subgrade elevations. L' The additional geotechnical engineering exploration for the roadways, in accordance with the Pavement Design Criteria will be performed and completed in 2 phases. After the utilities have been installed and final subgrade has been achieved additional test borings, located on approximate 500-foot intervals within the proposed roadway alignments will be drilled. The results of the field exploration and the associated laboratory tests will then be included in a Phase 1 report and submitted to the City of Fort Collins for their review. The City of Fort L Collins then provides the design 18-kip ESAL values and the final Phase 2 Pavement Thickness Report is prepared. 3 I ' Geotechnical Engineering Report Harmony Technology Center— Buildings C and E Terracon Project No. 20005198 The borings were located in the field by measuring from property lines and/or existing site features. Ground surface elevations were estimated at each boring location by interpolation from the topographic contour map prepared by JR Engineering, the project's civil engineer. The accuracy of boring locations and elevations should only be assumed to the level implied by the methods used. Continuous lithologic logs of each boring were recorded by the engineer 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. Composite bulk samples were obtained at various pavement boring locations for subgrade strength determination characteristics. Penetration resistance measurements were obtained by driving the split -spoon and/or 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. Groundwater conditions were evaluated in each boring at the time of site exploration, and 1 to 5 days after drilling. Slug tests were performed in each of the detention pond piezometers to evaluate aquifer characteristics. The results were recorded by an electronic data -logger using a pressure transducer set near the bottom of the piezometer. The groundwater levels in the piezometers were recorded at the time of the tests and at the times of other site visits. 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 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 ASTM, local or other accepted standards. 2 Geotechnical Engineering Report Harmony Technology Center — Buildings C and E j Terracon Protect No. 20005198 Selected soil and bedrock samples were tested for the following engineering properties: Water Content Plasticity Index Dry Density • Water Soluble Sulfate Content Swell -Consolidation • Resistivity Characteristics Compressive Strength • R-Value (Hveem Stabilometer) Expansion SITE CONDITIONS The Celestica facility presently occupies the northwest portion of the overall site area. The remaining portion of the quarter section consists of an irrigated cornfield. The Harmony School building is located on the north side of the Celestica facility. The property is relatively flat and has minor drainage to the east and south. The site is bordered on the north by Harmony Road, to the west by County Road 9, (Ziegler Road), to the east by Cambridge Lane, which runs south from Harmony Road approximately two-thirds of the eastern boundary, and to the south by additional farmland. Irrigation laterals are located throughout the site. SUBSURFACE CONDITIONS Geology The proposed area 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 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 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 13'/2 to 21'/2 feet below the surface. The bedrock is overlain by residual and alluvial soils of Pleistocene and/or Recent Age. 5 Geotechnical Engineering Report Harmony Technology Center — Buildings C and E Terracon Project No. 20005198 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 geological 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 "Moderate Swell Potential." Potentially expansive materials mapped in this area include bedrock, weathered bedrock and colluvium (surficial units). Soil and Bedrock Conditions The subsurface soils at the site generally consist of sandy lean clay and/or clayey sand, underlain by silty sand and silty sand with gravel extending to the depths explored and/or to the bedrock below. Siltstone/claystone bedrock was encountered in the deep foundation related borings, Test Boring Nos. 1 through 12, at approximate depths of 14 to 29 feet below existing site grades. The upper 4 to 6 feet is weathered, however the underlying siltstone/claystone is moderately hard to hard with increased depth. A bedrock contour map was developed for this portion of the site and is presented in Appendix A as Figure 2. Field and Laboratory Test Results Field and laboratory test results indicate the overburden clay soils are soft to medium stiff in consistency, slightly to moderately plastic and exhibit low to moderate swell potential and low bearing characteristics. The silty sand and coarse granular strata are medium dense in relative density, exhibit a non -swell potential and moderate bearing capabilities. The siltstone/claystone bedrock exhibits moderate swell potential and moderate bearing characteristics. The results of the slug tests were used to evaluate the permeability of the sand layer encountered beneath the upper clay soils. The resulting permeabilities are as follows: Piezometer No. i Piezometer No. 17A Piezometer No. 17B Piezometer No. 18 Average and/or Design Value Permeability, cm/sec Slug -Out Test - 6.0 x 10 a 1.1 x 10- 2.5 x 10- 1.4 x 10- W ' Hart, Stephen S., 1972, Potentially Swelling Soil and Rock in the Front Range Urban Corridor, Colorado, Colorado Geological Survey, Environmental Geology No. 7. 6 Geotechnical Engineering Report Harmony Technology Center — Buildings C and E Terracon Project No. 20005198 If there is a necessity to install an underdrain system beneath the proposed detention pond, using the average and/or design in -situ permeability value for the soils at or near groundwaterelevationswithinthedetentionpondarea, as well as the ranges of draw down anticipated for a possible underdrain system, we estimate the radius of influence to be approximately 500-feet depending on the area drain configuration. A composite sample was obtained from the detention pond area from a backhoe test pit excavated by Connell Resources on February 28, 2001. A Standard Proctor Density, ASTM D698 test was performed on this sample to determine its maximum dry density and optimum moisture content characteristics, results of which are enclosed with this report. A Falling Head Permeability test was conducted to estimate the coefficient of permeability and the suitability for reuse as a liner material. The sample was remolded to approximately 95 percent of its Standard Proctor Density at or near Optimum Moisture content, and inundated. The measured coefficient of permeability was 7.5 x10-' cm/sec. Therefore, based on the laboratory test results and our experience with similar type soils, it is our opinion this material is suitable foruseasthedetentionpondlinerifdesignspecificationsrequirethewettedperimetertobelined. Groundwater Conditions Groundwater was generally encountered throughout the site at approximate depths of 8 to 12 feet below existing site grades when checked 1 to 5 days after drilling. These observationsLrepresentgroundwaterconditionsatthetimeofthefieldexploration, and may not be indicative of other times, or at other locations. Groundwater levels can be expected to fluctuate with L' varying seasonal and weather conditions. Existing groundwater levels have probably been effected by irrigation of the site. When irrigation is permanently sopped, water levels may lower at the site depending on future landscaping and lawn irrigation of the site. In Lcomparison, the current groundwater levels in the general vicinity of the detention pond appear to be approximately 2 to 4 feet lower in elevation then when measured during the 1996 site exploration and may be close to long term groundwater levels. The possibility of groundwater fluctuations should be considered when developing design and construction plans for the project. Fluctuations in groundwater levels can best be determinedL by implementationlementation of a groundwater -monitoring plan. Such a plan would include installation of groundwater monitoring wells, and periodic measurement of groundwater levels over a sufficient period of time. As previously stated, Terracon installed 3 groundwater piezometers in the area of the proposed detention pond in an effort to monitor the groundwater fluctuations 7 Geotechnical Engineering Report Harmony Technology Center — Buildings C and E Terracon Proiect No. 20005198 over a period of time. This will enable an evaluation of an appropriate design bottom depth elevation for the proposed detention pond. The following table provides the ground surface elevations and the groundwater levels obtained from Piezometer Nos. 17A, 1713, and 18, when measured on March 7, 2001. Groundwater V Es#irtiated ``gym ,A Piezometer No. Approximate Ground Measurement from Groundwater, , Surface Elevation Ground Surface, ft. 1 Elevation., 17A 4910.7 12.1 4898.6 17B 4908.3 9.0 4899.3 18 4908.5 11.6 4896.9 The estimated piezometric surface was developed for the proposed detention pond area based on the piezometric data collected on March 7, 2001. The groundwater contour map for this area is illustrated on Figure 3 included in Appendix A of this report. The piezometric surface was estimated using linear interpolations between piezometers and was based upon groundwater elevations in each piezometer. As illustrated on the contour map, the groundwater flow was estimated to be in the south to slightly southeast direction. ENGINEERING ANALYSES AND RECOMMENDATIONS Geotechnical Considerations The site appears suitable for the proposed construction from a geotechnical engineering point of view. The following foundation systems were evaluated for use on the site: grade beams and straight shaft piers/caisson drilled into the bedrock. Foundation Systems — Drilled Piers/Caissons Due to the anticipated maximum concentrated column loads, the type of proposed construction, a grade beam and drilled pier foundation system is recommended for support of the proposed buildings. Straight shaft piers, drilled a minimum of 10 feet into the moderately hard to hard siltstone/claystone bedrock, with a minimum shaft length of 20 feet are recommended. M Geotechnical Engineering Report Harmony Technology Center — Buildings C and E Terracon Project No. 20005198 For axial compression loads, piers may be design for a maximum end -bearing pressure of 15,000 pounds per square foot (psf), for the first 10 feet, and 20,000 psf for additional penetration. The piers may also be designed using a skin friction of 1,500 psf for the first 10 feet into the bedrock and 2,000 psf for the remaining portion of the pier in firm or hard bedrock. 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. 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 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 design for lateral loads using a modulus of 75 tons per square foot for the portion of the pier in sands and/or engineered fill, and 200 tsf in bedrock for a pier diameter of 12 inches. The coefficient of subgrade reaction for varying pier diameters is as follows: LPier Diameter (inches) Coefficient of Subgrade-Reaction(tons/ft3) Engineered Fill or Stiff Clays Bedrock 12 75 200 18 50 133 24 38 100 10 30 80 36 25 67 we L L Geotechnical Engineering Report Harmony Technology Center— Buildings C and E Terracon Project No. 20005198 The soil modulus and coefficient of subgrade reaction are ultimate values; therefore, appropriate factors of safety should be applied in the pier design. 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. Terracon recommends the "stiff clay with no water" condition be used. The following parameters may be used for the design of laterally loaded piers, using the L-Pile (COM 624) computer program: Parameters Compacted Existing Fh rVl&f &l Bedrock` Structural Fill and on -site Clay Soils Unit Weight of Soil (pcf) 130 115111 125(') Cohesion (psf) 0 1000 5000 Angle of Internal Friction 0 35 23 0 degrees) Strain Corresponding to '/2 Max. 0.02 0.015 Principal Stress Difference e50 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. 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 18-inches is recommended. Drilling to design depths should be possible with conventional single flight power augers. Groundwater conditions indicate that temporary steel casing will be required to properly drill and clean piers prior to concrete placement. Groundwater should be removed from each pier hole prior to concrete placement. 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 10 Geotechnical Engineering Report Harmony Technology Center — Buildings C and E Terracon Project No. 20005198 potential sloughing and raveling, foundation concrete quantities may exceed calculated geometric volumes. Casing 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 pier concrete. Pier concrete should have a relatively high fluidity when placed in cased pier holes or through a tremie. Pier concrete with slump in the range of 5 to 8 inches is recommended. Free -fall concrete placement in piers will only be acceptable if provisions are taken to avoid striking the concrete on the sides of the hole or reinforcing steel. The use of a bottom -dump hopper, or an elephant's trunk discharging near the bottom of the hole where concrete segregation will be minimized, 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 the geotechnical engineer should inspect the bearing surface and pier configuration. 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 clays) ...................................... 45 psf/ft Cohesionless soil backfill (on -site or imported sand) ............. 35 psf/ft Passive: Cohesive soil backfill (on -site clays) .................................... 250 psf/ft Cohesionless soil backfill (on -site or imported sand)........... 350 psf/ft Adhesion at base of footing....................................................500 psf Where the design includes restrained elements, the following equivalent fluid pressures are recommended: At rest: Cohesive soil backfill (on -site clays) ...................................... 60 psf/ft 11 7 Geotechnical Engineering Report Harmony Technology Center — Buildings C and E Terracon Proiect No. 20005198 Cohesionless soil backfill (on -site or imported sand) ............. 50 psf/ft Fill against grade beams and retaining walls should be compacted to densities specified in Earthwork. High plasticity clay soils should not be used as backfill against retaining walls. 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. 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 S, should be used for the design of structures for the proposed project (1997 Uniform Building Code, cable No. 16-J). Retaining Wall Drainage To reduce hydrostatic loading on retaining walls, a subsurface drain system should be placed behind the wall. The drain system should consist of free -draining granular soils containing less than five percent fines (by weight) passing a No. 200 sieve placed adjacent to the wall. The free -draining granular material should be graded to prevent the intrusion of fines or encapsulated in a suitable filter fabric. A drainage system consisting of either weep holes or perforated drain lines (placed near the base of the wall) should be used to intercept and discharge water, which would tend to saturate the backfill. Where used, drain lines should be embedded in a uniformly graded filter material and provided with adequate clean -outs for periodic maintenance. An impervious soil should be used in the upper layer of backfill to reduce the potential for water infiltration. As an alternative, a prefabricated drainage structure, such as geocomposite, may be used as a substitute for the granular backfill adjacent to the wall. Floor Slab Design and Construction It is anticipated non -expansive or low -swelling natural soils or engineered fill will support the floor slab. 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 or engineered fill 12 L_ L Geotechnical Engineering Report Harmony Technology Center — Buildings C and E Terracon Project No. 20005198 consisting of on -site soils. A modulus of 200 pci may be used for floors supported on at least 2 feet of non -expansive imported fill meeting the specifications outlined below. Additional floor slab design and construction recommendations are as follows: LPositive 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. Interior trench backfill placed beneath slabs should be compacted in accordance with recommended specifications outlined below. In areas subjected to normal loading, a minimum 6-inch layer of sand, clean - graded gravel or aggregate base course 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 are recommended. Pavement Design and Construction Design of pavements for the project have been based on the procedures outlined in the 1993 Guideline for Design of Pavement Structures by the American Association of State Highway and Transportation Officials (AASHTO) and in general accordance with the City of Fort Collins Engineering Department Pavement Design Criteria. As previously stated, we are providing the minimum pavement thicknesses for the proposed City of Fort Collins' jurisdictional roadways based on preliminary findings for construction bid purposes only. We anticipate performing a project specific pavement evaluation after roadway utilities have been installed and the subgrade has been completed to "rough" final -grade. Local drainage characteristics of proposed parking and roadway 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 13 Geotechnical Engineering Report Harmony Technology Center — Buildings C and E Terracon Project No. 20005198 characteristics, coupled with the approximate duration of saturated subgrade conditions, results in a design drainage coefficient of 1.0 when applying the AASHTO criteria for design. For flexible pavement design, the following data were used in accordance with the City of Fort Collins and Larimer County Urban Growth Pavement Design Criteria. Traffic Calculated Street Name Classification ESAL Reliability, % Initial Servicea Terminal Serviceability singtural Technology Industrial / 730,000 85 4.5 2.3 3.19 Parkway Commercial Streets A and Major 365,000. 85 4.5 2.3 2.87 B Collectors Heavy Volume Drive or Truck and/or Drive 73,000 75 4.5 2.3 2.10 Access Areas Areas Automobile Parking 51,100 75 4.5 2.0 1.98 Parking Areas 1) Traffic ESAL values were derived from the Design Traffic Information obtained in the Larimer County Urban Growth Area Flexible Pavement Design Criteria Manual as default values for either major or minor collectors. 2) The calculated Structural Nos. were derived using a subgrade strength R-Value of 10 and was calculated using the standard Larimer County's soil resilient modulus formula. Using the correlated design R-value of 10 for the interior infrastructure roadways, appropriate ESAL/day, environmental criteria and other factors, the above structural numbers (SN) of the pavement sections were determined on the basis of the 1993 AASHTO design equation. 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 600 psi (working stress 450 psi) was used for pavement concrete. The rigid 14 Geotechnical Engineering Report Harmony Technology Center — Buildings C and E Terracon Proiect No. 20005198 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: Traffic Area Alternatives Recomrhehtletl ll lfp(titUlfal I aVeinent Thickness - inches Asphalt Concrete Suif2lCe GradnvS' Asphalt Concrete Surface Grading S 1 or SG Aggregate Sase Course - CIaSs 5 or,6 Fly Ash Treated Sub Base a Portland Cement Concrete Total 2) A 3 3 6 12 Technology 3) B 3 4.5 7.5 Parkway - Industrial Commercial 4) C 3 3 6 12 24 Collector 5) D 3 3 12 18 6) E 8 8 2) A 2 3 7 12 3) B 3 4 7 Streets A and B Major Collectors 4) C 2 3 6 12 23 5) D - 2 3 12 17 6) E 7 7 2) A 3.5 6 9.5 3) B 2 3 5 Heavy Volume and/ or Truck C 1.5 3 4 12 20.5 Access Areas s) D 1.5 3 12 16.5 6) E 6 6 2) A 3 6' 9 3) B 1.5 3 4.5 Automobile Parking Areas 4) C 1.5 3 4 12 20.5 5) D 1.5 3 12 16.5 t6) E 5 5 1) In areas where flyash is to be used and is to be considered as part of the strength coefficient equation, it is recommended that the upper 12-inches of the subgrade be treated with flyash. Terracon used a strength coefficient value of 0.10 for the required minimum thickness of 12-inches, which results in a total strength value of 1.2 in the pavement thickness formula. Using a minimum thickness of 12-inches of flyash treated subgrade will reduce the required asphalt thickness by approximately 2-3/4-inches. 15 Geotechnical Engineering Report Harmony Technology Center — Buildings C and E Terracon Project No. 20005198 However, in most cases the required minimum asphalt pavement thickness in accordance with Larimer County's Pavement Design Criteria, takes precedent in the pavement thickness sections. Therefore no reduction is provided and the use of flyash may not be economical, unless needed for subgrade stabilization. Fyyash, where utilized, should be placed in general accordance with the standard of industry for placement procedures. Terracon is available to provide the required laboratory soil and flyash mix design as well as placement recommendations upon request. 2) Alternative A: Provides the minimum pavement thicknesses for use of asphalt concrete surface material, Grading S, SX and SG, underlain by Class 5 or 6 aggregate road base material. 3) Alternative B: Provides the minimum pavement thicknesses for use of full -depth asphalt concrete surface material, Grading S or SX, underlain by asphalt concrete surface material, Grading SG. 4) Alternative C: Provides the minimum pavement thicknesses for use of asphalt concrete surface material, Grading S, SX and SG, underlain by a minimum of 6-inches of Class 5 or 6 aggregate road base material, and a minimum of 12-inches of flyash treated subgrade. 5) Alternative D: Provides the minimum pavement thicknesses for use of full -depth asphalt concrete surface material, Grading S, SX and SG, underlain by a minimum of 12-inches of flyash treated subgrade. 6) Alternative E: Provides the minimum required pavement thicknesses for use of Portland Cement Concrete pavement. 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 not exceeding six inches and should be compacted to a minimum of 95% Standard Proctor Density (ASTM D698). Asphalt concrete and/or plant -mixed bituminous base course should be composed of a mixture of aggregate, filler and additives, if required, and approved bituminous material. The bituminous base and/or asphalt concrete should conform to approved mix designs stating the Hveem properties, optimum asphalt content, job mix formula and recommended mixing and placing temperatures. Aggregate used in plant -mixed bituminous base course and/or asphalt concrete should meet particular gradations. Material meeting Colorado Department of Transportation Grading S, SX or SG specification is recommended for asphalt concrete. Mix 16 Geotechnical Engineering Report Harmony Technology Center — Buildings C and E Terracon Proiect No. 20005198 designs should be submitted prior to construction to verify their adequacy. Asphalt material should be placed in maximum 3-inch lifts and should be compacted to a minimum of 92 to 96 of Maximum Theoretical Density. Where rigid pavements are used, the concrete should be obtained from an approved mix design with the following minimum properties: Modulus of Rupture @ 28 days...............................................600 psi minimum Strength Requirements.................................................................... ASTM C94 Minimum Cement Content.......................................................6.0 sacks/cu. yd. CementType............................................................................. Type I Portland Entrained Air Contenf::%......................................................................... 4 to 8% Concrete Aggregate ......................... ........... ASTM C33 and CDOT Section 703 Aggregate Size.........................................................................1 inch maximum Maximum Water Content .................................................... 0.49 lb/lb of cement Maximum Allowable Slump................................................................... 4 inches Concrete should be deposited by truck mixers or agitators and placed a maximum of 90 y minutes from the time the water is added to the mix. Other specifications outlined by the Colorado Department of Transportation should be followed. y Longitudinal and transverse joints should be provided as needed in concrete pavements for expansion/contraction and isolation. The location and extent of joints should be based upon the final pavement geometry and should be placed (in feet) at roughly twice the slab thickness in inches) on center in either direction. Sawed joints should be cut within 24-hours of concrete placement, and should be a minimum of 25% of slab thickness plus 1/4 inch. All joints should be sealed to prevent entry of foreign material and dowelled where necessary for load transfer. Preventative maintenance should be planned and provided for through an on -going pavement management program in order to enhance future pavement performance. Preventative maintenance activities are intended to slow the rate of pavement deterioration, and to preserve the pavement investment. Preventative maintenance consists of both localized maintenance (e.g. crack sealing and patching) and global maintenance (e.g. surface sealing). Preventative maintenance is usually 17 L L Geotechnical Engineering Report Harmony Technology Center - Buildings C and E Terracon Project No. 20005198 L y the first priority when implementing a planned pavement maintenance program and providesPYP9PPP9 1 the highest return on investment for pavements. Recommended preventative maintenance policies for asphalt and jointed concrete pavements, based upon type and severity of distress, are provided. Prior to implementing anyLmaintenance, additional engineering observation is recommended to determine the type and extent of preventative maintenance. LDetention Pond - Design and Construction Recommendations Test Boring Nos. 17A, 17B and 18 were drilled within the detention pond area and were converted to groundwater piezometers in an effort to monitor the groundwater fluctuations within the pond configuration as well as assist in evaluating a design pond bottom elevation. Based on the previously mentioned depth to groundwater levels, anticipated fluctuations, and the groundwater contours developed from the field exploration and presented on Figure 3, it is our opinion an underdrain system may not be necessary if the detention pond floor is constructed at an elevation of 4900 or higher. If the owner needs to increase the depth of the pond and is willing to allow groundwater seepage in the northern portion of the pond with infiltration in the southern portion, the pond could be constructed at an elevation of 4899 without installing an underdrain system. If the pond is to be constructed with an impervious clay liner and designed not to allow for groundwater fluctuations to impact the bottom, an underdrain system would be required for the pond if extended deeper than the approximate elevation of 4899. Terracon is prepared to provide an underdrain design for the proposed detention pond depending upon site -specific design concepts. After the owner reviews the above -mentioned bottom design elevation concepts, additional information with regards to an underdrain system will be prepared, if necessary. Depending upon the actual design bottom, and in view of the depth to groundwater encountered in the general vicinity of the pond, the bottom may be at or near existing groundwater. Temporary dewatering may be required during construction to adequately construct the detention pond. Lining of the pond may be required to separate detention water from the groundwater. If required, the pond should be lined with a minimum of 12-inch layer of the on -site clay materials. A typical design criteria is to provide an approximate 12 to 18-inch compacted clay liner around the wetted perimeter of a detention pond having an equivalent coefficient of permeability on the order of 1x10- 6 cm/sec. The upper 8 to 12 inches of the wetted perimeter of the pond including the bottom of the pond and cut slopes of the pond should be scarified and recompacted plus or minus 2 percent of optimum moisture to a minimum of 95 percent of Standard Proctor Density ASTM D698. Embankments constructed to form the pond should consist of the on -site clays compacted in uniform 6 to 8 inch lifts and 18 Geotechnical Engineering Report Harmony Technology Center — Buildings C and E Terracon Project No. 20005198 mechanically compacted to the required moisture and density. Detention pond cut and fill slopes should be constructed on grades of 3:1 or flatter. The ponds should be designed to maintain a minimum amount of water to resist hydrostatic uplift, or the bottom pond elevation should be raised to protect the pond lining should water levels rise at the site. Consideration may be given to use of a synthetic liner and pressure relief valves to protect the pond from high groundwater. 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. Site Preparation Strip and remove existing uncontrolled fill (if encountered during construction), vegetation, debris, and other deleterious materials from proposed building and pavement areas. All exposed surfaces should be free of mounds and depressions, which 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 pavements and building structures. All exposed areas which will receive fill, once properly cleared and benched where necessary, should be scarified to a minimum depth of eight inches, conditioned to near optimum moisture content, and compacted. It is anticipated that excavations for the proposed construction can be accomplished with conventional earthmoving equipment. However, interbedded densely cemented sandstone lenses were locally encountered at increased depth within the bedrock formation that may require blasting. Depending upon depth of excavation and 19 Geotechnical Engineering Report Harmony Technology Center — Buildings C and E Terracon Project No. 20005198 seasonal conditions, groundwater may be encountered in excavations on the site. Pumping from sumps may be utilized to control water within excavations. Based upon the subsurface conditions determined from the geotechnical exploration, subgrade soils exposed during construction are anticipated to be relatively stable. However, 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 eight 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 and/or approved imported materials may be used as fill and/or as backfill material. On -site bedrock is not suitable for use as fill and/or backfill. Imported soils (if required) should conform to the following: Percent fines by weight Gradation (ASTM C136) 6"........................................................................................... 100 311 70-100 No. 4 Sieve..................................................................................... 50-100 No. 200 Sieve.............................................................................. 50 (max) LiquidLimit.................................................................................. 30 (max) Plasticity Index............................................................................ 15 (max) R-Value........................................................................................ 10 (min) 20 Geotechnical Engineering Report Harmony Technology Center — Buildings C and E Terracon Project No. 20005198 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: Minimum Percent Material (ASTM D698) Scarified subgrade soils........................................................................ 95 On -site and imported fill soils: Beneath foundations.................................................................. 95 Beneathslabs; ........................................................................... 95 Beneathpavements................................................................... 95 Miscellaneous backfill (non-structural areas) ......................................... 90 On -site clay soils should be compacted within a moisture content range of 2 percent below, to 2 percent above optimum. Imported granular soils and/or on -site sands should be compacted within a moisture range of 3 percent below to 3 percent above optimum unless modified by the project geotechnical engineer. Shrinkage For balancing grading plans, estimated shrink or swell of soils and bedrock when used as compacted fill following recommendations in this report are as follows: Estimated Shrink(-) Swell (+) Material Based on ASTM D698 On -site soils: Clays............................................................................... 0 to -15% Siltysands.....................................................................- 5 to -15% On -site bedrock materials: Siltstone/claystone bedrock..........................................-5 to +10% 21 J Geotechnical Engineering Report Harmony Technology Center — Buildings C and E Ld Terracon Project No. 20005198 Slopes For permanent slopes in compacted fill areas, recommended maximum configurations for on -site materials are as follows: Maximum Slope Material Horizontal:Vertical LCohesive soils (clayey sands and/or clays) .......................................... 2:1 Cohesionless soils.................................................................... 3:1 Bedrock.................................................................................. 1 YX 1 If steeper slopes are required for site development, stability analyses should be x completed to design the grading plan. The face of all slopes should be compacted to the minimum specification for fill i embankments. Alternately, fill slopes can be over -built and trimmed to compacted material. If any slope in cut or fill will exceed 25 feet in height, the Id include mid -height benches to intercept surface drainagegradingdesignshouldgP999 and divert flow from the face of the embankment. Excavation and Trench Construction Excavations into the on -site soils will encounter a variety of conditions. Excavations into the clays and bedrock can be expected to stand on relatively steep temporary slopes during construction. However, caving soils and groundwater may also be encountered. The individual contractor(s) should be made responsible for designing y 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 22 L L Geotechnical Engineering Report Harmony Technology Center— Buildings C and E Terracon Project No. 20555198 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 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 23 Geotechnical Engineering Report Harmony Technology Center — Buildings C and E Terracon Project No. 20005198 resistance of construction concrete. Foundation concrete should be designed in accordance with the provisions of the ACI Design Manual, Section 318, Chapter 4. On -site soil samples were collected from Test Boring Nos. 27 and 29 at an approximate depth of 8-feet below existing site grades and were subjected to corrosive potential characteristics testing. Laboratory test results indicate that on -site soils in the alignment for the proposed water line along Cambridge Drive have resistivities ranging from 2,800 to 4,000 ohm -centimeters, pH values ranging from 7.6 to 7.8, oxidation- reduction potentials of (-) 60 to (-) 67 milli -volts, and sulfide contents of trace amounts. These values should be used to determine potential corrosive characteristics of the on - site soils with respect to contact with the various underground materials, which will be used for project construction. The following table provides the laboratory test results for each boring location. LABORATOFT11E5T RESULTS F DEPTH, FT. RESISTIVITY vsNOe 1 OHM=CM pH SULFIDE r 11riU 27 8.0 4000 7.6 TRACE 59.7 29 8.0 2800 1 7.8 TRACE 67.4 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 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. 24 Geotechnical Engineering Report Harmony Technology Center — Buildings C and E Terracon Project No. 20005198 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, which may occur between borings or across the site. The nature and extent of such variations may not become evident until construction. If variations appear, it will be necessary to reevaluate the recommendations of this report. 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. 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. 25