HomeMy WebLinkAboutB11-0188 B12-0042 Concert Hall Geo Report 379 Indian Road, Grand Junction, CO 81501 Phone (970) 242 -4300 Fax (970) 242 -4301 www.groundeng.com Office Locations: Englewood Commerce City Loveland Granby Gypsum Grand Junction Casper Subsurface Exploration Program and Geotechnical Recommendations Proposed Concert Hall Plaza Addition Vail , Colorado Prepared For: Town of Vail 75 S. Frontage Road Vail, Colorado 81657 Atten tion: Mr. Tom Kass m el Job Number: 11 -6024 December 14 , 2011
Proposed Concert Hall Plaza Addition 610 W. Lionshead Circle Vail, Colorado TABLE OF CONTENTS Page Purpose and Scope of Study ..................................................................................... 1 Proposed Construction .............................................................................................. 1 Site Conditions .......................................................................................................... 1 Regional and Project Site Geology ............................................................................. 2 Seismic Classification ................................................................................................ 2 Subsurface Exploration ............................................................................................. 3 Laboratory Testing .................................................................................................... 3 Subsurface Conditions .............................................................................................. 4 Geotechnical Considerations For Design ...................................................................... 5 Foundation Systems ...................................................................................................... 5 Floor Systems ............................................................................................................... 8 Exterior Flatwork ..................................................................................................... 10 Water Sol uble Sulfates .............................................................................................. 13 Soil Corrosivity .......................................................................................................... 14 Project Earthwork ..................................................................................................... 16 E xc avation Considerations ...................................................................................... 20 Bus Transit Plaza ........................................................................................................ 20 Surface Drainage .................................................................................................... 25 Foundation Walls ........................................................................................................ 27 Closure ..................................................................................................................... 28 Locations of Test Holes ................................................................................... Figure 1 Log of Test Hole ............................................................................................. Figure 2 Legend and Notes ........................................................................................... Fig ure 3 Consoli dation Test Results .............................................................................. Fig ure 4
Proposed Concert Hall Plaza Addition 610 W. Lionshead Circle Vail, Colorado Summary of Laboratory Test Results .............................................................. Table 1
PURPOSE AND SCOPE OF STUDY This report presents the results of a subsurface exploration program performed by GROUND Engineering Consultants, Inc. (GROUND) to develop geotechnical recommendations for th e proposed concert hall plaza addition located north west of the existing building located at 610 W. Lionshead Circle , Va il , Colorado. Our study was conducted in general accordanc e with GROUND‟s Proposal No. 1110 -1592 , dated November 3 , 2011. A field exploration program was conducted to obtain information on subsurface conditions at the site. Material samples obtained during the subsurface exploration were tested in our laboratory to provide data on the classification and engineering characteristics of the on -site soils . The results of the field exploration and laboratory testing are presented herein. This report has been prepared to summarize the data obtained and to present our conclusions and recommendations based on the proposed construction and the subsurface conditions encountered. Design parameters and a discussion of geotechnical engineering considerations rel ated to construction are included herein. PROPOSED CONSTRUCTION We understand that proposed con struction is preliminary, but likely will consist of a one -story addition at the north west corner of the existing buildin g for addition of a mechanical/boiler ro om . We understand a below grade level may be included in construction. L oads are anticipated to be light to moderate, typical of this type of construction. If the proposed construction differs significantly from that described above, GROUND should be no tified to re -evaluate the recommendations contained herein. SITE CONDITIONS T he existing concert hall is a single -story structure with a below grade basement level . The building is located just north and east fr om the bus station „transit plaza‟ east of W est Lionshead Circle . (S ee Figure 1 .) The surrounding area has been developed for commercial use with restaurants and shopping areas with areas of landscaped grass, bushes, and trees. The general topography at the site is gently to moderately sloping with an overall slope of approximately 10 percent descending towards the southwest.
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 4 of 32 REGIONAL, PROJECT SITE GEOLOGY AND POTENTIAL HAZARDS The proje ct area is located near the northern tip of the north -trending Sawatch Range anticlinal uplift , a geo logic structure that developed during the Laramide orogeny (about 40 to 80 million years ago), and east of the Colorado evaporate region and Burns Syncline . Surficial deposits at the project site are mapped as outwash sands and gravels (Qg) associated wit h the Pinedale Glaciation which overlie the Pennsylvanian Age Minturn Formation. The closest geologically young faults exhibiting movement in the last 15,000 years that are considered capable of generating large earthquakes are located in the northern se ction of the Williams For k Mountains fault zone, about 20 miles north of the project site. Although rockfall, landslide, and avalanche hazards do occur in the area, In our opinion, we consider the possibility of such a geologic hazard affecting the project site to be low compared to areas of closer proximity to surrounding hillsides . SEISMIC CLASSIFICATION Utilizing the USGS‟s Earthquake Ground Motion Tool v.5.1.0 and site approximate latitude/l ongitude coordinates [of 39.6438 and –106.3903 (obt ained from Google Earth) respectively], the project site is indicated to be subject to an SD S value of 0.285 g and an SD 1 value of 0.068 g. Compared with other regions of the Western United States, recorded earthquake frequency in the project vicinity is re latively low. In the absence of actual shear wave velocity testing/analysis or deep drilling, GROUND estimates that a Seismic Site Class D according to the 2006/2009 IBC classification (Table 1613.5.2) is applicable to the site . In the event t hat the o wner desires to utilize Site Class C for design, according to the 2006/2009 IBC, actual downhole seismic shear wave velocity testing and/or exploration to subsurface depths of at least 100 feet, should be performed . Based on available data, we consider th e likelihood of realizing a Site Class C to be low. SUBSURFACE EXPLORATION
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 5 of 32 The subsurface exploration for the project site was conducted on November 11 , 2011. One test hole was located in an area north west of the existing building within the proposed footprint of the proposed construction. A second test hole was located in the bus turnaround area southwest of the Concert Hall Plaza. The test ho le depths were 18½ and 6 feet below existing surface grad e for the concert hall plaza addition and bus tur naround area, respectively. Test holes were advanced using a conventional, track -mounte d, drilling rig to evaluate the subsurface conditions, as well as to retrieve soil samples for laboratory testing and analysis. A GROUND engineer directed the subsurf ace exploration, logged the test holes in the field, and prepared the soil samples fo r transport to our laboratory. Samples of the subs urface materials were retrieved with a 2 -inch I.D. “California ” -type liner sampler and a 1⅜-inch I.D. Standard Penetrati on Test (“split spoon”) sampler. The samplers were driven into the substrata with blows from a 140 -pound hammer falling 30 inches. This procedure is similar to the Standard Penetration Test described by ASTM Method D1586. Penetration resistance values, when properly evaluated, indicate the relative density or consistency of soils. Depths at which the samples were obtained and associated penetration resistance values are shown on the test hole logs. The approximate locations of the test holes are shown i n Figure 1. Logs of the exploratory test holes are presented in Figure 2. Explanatory notes and a legend are provided in Figure 3 . To locate the test holes, GRO UND utilized the site plan provided by The Town of Vail indicating existing features. LABORATORY TESTING Samples retrieved from our test holes were examined and visually classified in the laboratory by the project engine er. Laboratory testing of soil samples obtained from the subject site included standard property tests, such as natural m oisture contents, dry uni t weights, grain size analyses , and liquid and plastic limits. Swell -consolidation, w ater -soluble sulfate and corrosivity tests were performed on selected samples of the soils as well. Laboratory tests were performed in general a ccordance with applicable ASTM and AASHTO protocols. Results of the laboratory testing program are summarized on Tables 1 .
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 6 of 32 SUBSURFACE CONDITIONS The subsurface conditions encountered in the addition test hol e generally consisted of about 8 feet of undoc umented fill material s over sands and gravels . Dense sandy gravels and cobbles were encountered below 16 feet and practical drilling r efusal occurred at a depth of 18½ feet below surface grade. The pavement test hole encountered approximately 3½ feet of fill below 6¼ inches of asphalt over 10 inches of base course. Native soils below 3½ feet consisted of silty sands with gravels. Groundwater was not encountered in the test ho les a t the time of drilling and the test hole caved at 5 feet . Fill The fill soils encountered consisted of fine to coarse sands with gravel, clay, silt and scattered cobbles and possible boulders . Fill material was loose to very dense, moist , and dark brown in color. Sand and Gravels with Cobbles and possible boulders. The natural soils encountered were stratified layers of clean sand and sandy gravels with scattered cobbles . Very dense cobbles and possible boulders were encountered below 16 feet. Soils generally consisted of medium to coarse sands, angu lar to sub -rounded gravels, medium dense, moist, and light brown to brown in color. It should be noted that it is not possible to characterize coarse gravel -, cobble - and boulder -sized materials in small diameter test holes. Therefore, those relying on this report should a nticipate that coarser materials than recognized herein may be present in the soils at this site . Swell -Consolidation Testing suggested a potential for consolidation in the sands and gravels when wetted under various surcharge loads. Tests performed on samples of sandy silty gravel at Test Hole 1 indicated a potential for consolidation up to 3.7 percent. A sample of silty sand at Test Hole 2 indicated a potential for consolidation up to 4.0 percent. Groundwater was not encountered in the test hole s at the time of drilling to the depths explored , however, f luctuations in ground water levels may occur and the water table may be significantly higher during spring and summer seasons .
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 7 of 32 GEOTECHNICAL CONSIDERATIONS FOR DESIGN The fill and native sandy gravels and sand s encountered at shallow to moderate depths across much of the site to depths of 16 feet or more have the potential for vertical movement upon wetting . GROUND recommends a deep foundatio n system extending into d en se gravels would provide the least risk of post construction movement . Micro -piles may be the most cost -efficient deep foundation system for the area. It should be noted that somewhat greater strains commonly are required for this type of foundation system to mobilize their strength relative to drilled piers or driven H -piles . Therefore, apparent settlements upon imposition of structural loads may be u p to 1 inch. A micro -pile system is designed and installed by a specialty supplier / contractor and we anticipate that the subsurface information provided in this report is sufficient for designs of a micro -pile system to be developed. Subsurface sands a nd gravels became denser at 16 feet below surface grade and drilling refusal was encountered at 18½ feet. I t may be necessary to advance micro -piles 10 feet below this dense layer, however, actual penetration depths should be developed by the micropile co ntractor . As a higher risk alternative, the addition can be supported on spread footings provided that surface moisture is carefully controlled and a section of properly compacted soil is construct ed beneath the addition . Therefore, geotechnical paramete rs for a shallow foundation are provided below. Parameters for a non -proprietary deep foundation system can be provided upon request. Supporting a shallow foundation system and a slab -on -grade floor directly on the local soils, could experience likely tota l and differential vertical movements on the order of 5 or more inches. If constructed o n a properly prepared fill section as described below, likely building foundation movements of approximately 1 to 2 inches with differential move ments of 1 inch over a span of 3 0 feet are estimated. FOUNDATION SYSTEMS The design and construction criteria presented below may be observed for a spread footing foundation system. The construction details can be considered when preparing project documents. The precautions and recommendations provided below will not prevent movement of the footings if the underlying materials are allowed to become wet. However, the recommended measures will tend to make the mo vement more uniform, and reduce resultant damage if such movement occurs.
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 8 of 32 1. Fo otings should bear on at least 4 feet of properly moisture -conditioned and compacted fill soils. The existing soils should be excavated from beneath the building footprin t to a dep th of 4 feet or more below the lowest foundation element, thoroughly mixed, moisture conditioned and replaced as properly compacted fill. Excavation and replacement to the full, recommende d depth should extend at least 4 feet beyond the building perimete r. The contractor should provide surveyed elevations of the bottoms of the excavations beneath the building verifying that the remedial excavation was advanced to a sufficient depth. Recommendations for fill placement and compaction are provided in the P roject Earthwork section of this report. The Contractor should take care to construct a fill layer of uniform composition to reduce differential post -construction building, slab and flatwork movements. In addition, scarification and re -compaction of the underlying 8 to 12 inches of material at the base of the excavated section should be performed and compacted to the density requirements specified in the Project Earthwork section of this geotechnical report. 2. Footings bearing on at least 4 feet of properl y compacted fill may be designed for an allowable soil bearing pressure (Q a ) of 1 ,500 psf for a footing width up to 4 feet in minimum , lateral dimension. A geotechnical engineer should be retained to provided bearing pressures where larger footings are us ed. These values may be increased by 1 /3 for transient loads such as wind or seismic loading. Based on these recomme nded allowable bearing pressure , we anticipate post -construction settlements from direct compression of the fo undation soils to be on the order of 1 inch . 3. In order to reduce differential settlements between footings or along continuous footings, footing loads should be as uniform as possible. Differentially loaded footings will settle differentially. 4. Connections to the structures of all types must be flexible and/or adjustable to accommodate the potential, post -construction movements.
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 9 of 32 5. Spread footings should have a minimum footing lateral dimension of 16 or more inches for linear strip footings and a minimum lateral dimension of 24 or more inches for isolated pad or drilled footings. Actual footing dimensions, however, should be determined by the structural engineer, based on the design loads. 6. Footings should bear at an el evation 4 or more feet below the lowest adjacent exterior finish gra des to have adequate soil cover above their bearing elevation for frost protection. 7. Continuous foundation walls should be reinforced top and bottom to span an unsupported length of at least 10 feet. 8. The lateral resistance of spread footings will be devel oped as sliding resistance of the footing bottoms on the onsite soil. Sliding friction at the bottom of footings may be taken as 0.4 0 times the vertical dead load. 9. The addition should be isolated, structurally, from the existing building. Finishes that s pan the joints between building and addition should be tolerant of differential movement and/or readily replaced. 10. Compacted fill placed against the sides of the footings should be compacted to at least 95 percent relative compaction in accordance with the recommendations in Project Earthwork section of this report. 11. Care should be taken when excavating the foundation to avoid disturbing the supporting materials . 12. Footing excavation bottoms may expose organics, debris, loos e, wet or otherwise unsuitable materi als which should be excavated and replaced with properly compacted fill. FLOOR SYSTEMS Constructing the building floors as structural floors, supported on deep foundations in the same manner as the building, is the most effective way of limiting post -construction floor movements. We r ecommend providing the addition with structural floors to minimize floor movements. Detailed recommendations for struc
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 10 of 32 Slab -on -Grade Concrete Floor We understand that conventional slab -on -grade floors are generally acceptable in the project area. However, such a system would represent a higher risk alternative to a structural floor. We estimate that post -construction floor movements of approximately 2 inches are likely, with similar differential movements over span s of about 30 feet. The criteria below may be followed if a slab -on -grade floor is selected. 1. T he floor system should bear on a section of properly compacted fill at least 8 feet in thickness . We estimate likely post -construction movement of a slab c onstructed o n 8 feet of fill to be about 1 inch. The thickness of the fill section should be taken from the bottom of the slab + gravel layer system. If the gravel layer is not installed, the fill section should be correspondingly thickened. Screened rock (coarser than ¾-inch) may be used a t the base of the fill to facilitate drainage during times of high water table. If screened rock is used, a layer of filter fabric should be placed on the screened rock, beneath the common fill . The contractor should su rvey the excavations beneath the building verifying that the remedial excavations were advanced to a sufficient depth and extent. The contractor should ta ke care to construct a fill section of uniform depth and composition to reduce differential post -const ruction addition , slab and flatwork movements. A differential fill beneath the addition will tend to increase differential movements. Organics, or l oose, soft or otherwise unsuitable materials exposed on the prepared surface on which a floor slab will be cast should be excavated and replaced with properly compacted fill. 2. Concrete slabs -on -grade should be constructed and cured in accordance with applicable industry standards and slab design specifications.
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 11 of 32 3. An allowable vertical modulus of subgrade reaction (K v ) of 60 tcf may be used for design of concrete slabs bearing o n a properly prepared fill section. 4. The floor slabs should be separated from all bearing walls and columns with slip joints, which allow unrestrained vertical movement. Joints should be obser ved periodically by the owner, particularly during the first several years after construction. Slab movement can cause previously free -slipping joints to bind. Measures should be taken to assure that slab isolation is maintained in order to reduce the li kelihood of damage to walls and other interior improvements, including door frames, plumbing fixtures, etc. 5. Interior partitions resting on floor slabs should be provided with slip joints or tracks so that if the slabs move, the movement cannot be transmitt ed to the upper structure. This detail is also important for wallboards and doorframes. Slip join ts, which will allow at least 2 or more inches of vertical movement, should be considered. 6. Concrete slab -on -grade floors should be provided with properly des igned and constructed control joints. ACI, AASHTO and other industry groups provide guidelines for proper design and construction of concrete slabs -on -grade, and associated jointing. The design and construction of such joints should account for cracking resulting from concrete shrinkage, curling, tension and applied loads, as well as other factors related to the proposed slab use. Joint layout based on slab design may require more frequent, additional or deeper joints than typical industry minimums, and should reflect the configuration and proposed use of the slab. Particular attention in slab joint design should be given to areas where slabs exhibit interior corners or curves, e.g., at column block -outs or reentrant corners, and slabs with high length t o width ratios, significant slopes, thickness transitions, high traffic loads, or other unique features. The improper placement or construction of control joints will increase the potential for slab cracking. 7. A floor slab should be adequately reinforced. Recommendations based on structural considerations for slab thickness, jointing, and steel reinforcement in floor slabs should be developed by a structural engineer. 8. Moisture can be introduced into a slab subgrade during construction and additional mois ture will be released from the slab concrete as it cures. GROUND
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 12 of 32 recommends placement of a properly compacted layer of free -draining gravel, 8 or more inches in thickness, beneath the slabs. This layer will help distribute floor slab loadings, ease const ruction, reduce capillary moisture rise, and aid in drainage. The free -draining gravel should contain less than 5 percent material passing the No. 200 Sieve, more than 50 percent retained on the No. 4 Sieve, and a maximum particle size of 2 inches. The capillary break and the drainage space provided by the gravel layer also may reduce the potential for excessive water vapor fluxes from the slab after construction as mix water is released from the concrete. We understand, however, that professional exp erience and opinion differ with regard to inclusion of a free -draining gravel layer beneath slab -on -grade floors. If these issues are understood by the owner and appropriate measures are implemented to address potential concerns including slab curling and moisture fluxes, then the gravel layer may be deleted. EXTERIOR FLATWORK Proper design, drainage, construction and maintenance of th e areas surrounding the proposed building and parking/driveway areas are critical to the satisfactory performance of the project. Sidewalks, entranceway slabs and roofs, fountains, raised planters and other highly visible improvements commonly are installed within these zones, and distr ess in or near these improvements is com mon. Often , soil preparation in these areas receives little attention because they fall between the building and pavement (which are typically built with heavy equipment). Subsequent landscaping and hardscape insta llation often is performed by multiple sub -contractors with light or hand equipment, and over -excavation / soil processing is not performed. Therefore, GROUND recommends that the design team, contractor, and pertinent subcontractors take particular care w ith regard to proper subgrade preparation around the structure exteriors. Similar to slab -on -grade floors, exterior flatwork and other hardscaping placed on the soils encountered on -site may experience post -construction movements due to volume change of the subsurface soils and the relatively light loads that they impose. Both vertical and lateral soil movements can be anticipated as the soils expe rience volume
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 13 of 32 change as the moisture content varies. Distress to rigid hardscaping likely will result. The following measures will help to reduc e damages to these improvements: 1. Ideally, subgrade soils beneath project sidewalks, paved entryways and patios , masonry planters and short, decorative walls, and other hardscaping should be placed on native sand and gravel material, or undocumented fill should be removed and replaced with proper ly compacted fill. To perform like a slab -on -grade floor, hardscaping should bear on a similar fill section as those discussed for an (alternative) slab -on -grade floor . 2. Excavating to native gravels may not be feasible in all areas. Provided the owner understands the risks id entified above, the subgrade under exterior flat work or other (n on -building) site improvements sh ould be underlain by a section of properly compacted fill at least 3 feet in thickness . This should occur prior to placing any additional fill required to achieve finished design grades. We estimate potent ial settlements on the order of 2 + inches with t his processing depth . 3. Increasing the processing depth may improve performance. The excavated soil should be replaced as properly moisture -conditioned and compacted fill as outlined in the Project Earthwor k section of this report. As stated above, greater depths of moisture -density conditioning of the subgrade soils beyond the above minimum such as discussed may improve hardscape performance. Movement will occur, some of which could be significant, especi ally if sufficient surface drainage is not maintained. 4. Prior to placement of flatwork, a proof roll should be performed to identify areas that exhibit instability and deflection. The soils in these areas should be removed and replaced with properly comp acted fill or stabilized. 5. Flatwork should be provided with effective control joints. Increasing the frequency of joints may improve performance. ACI recommendations should be followed regarding construction and/or control joints. 6. In no case should exterior flatwork extend to under any portion of the building where there is less than two inches of clearance between the flatwork and any
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 14 of 32 element of the building. Exterior flatwork in contact with brick, rock facades, or any other elem ent of the building can cause damage to the structure if the flatwork experiences movements. 7. As discussed in the Surface Drainage section of this report, proper drainage also should be maintained after completion of the project, and re -established as nece ssary. In no case should water be allowed to pond on or near any of the site improvements or a reduction in performance should be anticipated. Concrete Scaling Climatic conditions in the project area including relatively low humidity, large temperature ch anges and repeated freeze – thaw cycles, make it likely that project sidewalks and other exterior concrete will experience surficial scaling or spalling. The likelihood of concrete scaling can be increased by poor workmanship during construction, such as „over -finishing‟ the surfaces. In addition, the use of de -icing salts on exterior concrete flatwork, particularly during the first winter after construction, will increase the likelihood of scaling. Even use of de -icing salts on nearby roadways, from whe re vehicle traffic can transfer them to newly placed concrete, can be sufficient to induce scaling. Typical quality control / quality assurance tests that are performed during construction for concrete strength, air content, etc., do not provide informati on with regard to the properties and conditions that give rise to scaling. We understand that some municipalities require removal and replacement of concrete that exhibits scaling, even if the material was within specification and placed correctly. The contractor should be aware of the local requirements and be prepared to take measures to reduce the potential for scaling and/or replace concrete that scales. In GROUND‟s experience the measures below can be beneficial for reducing the likelihood of con crete scaling. It must be understood, however, that because of the other factors involved, including weather conditions and workmanship, surface damage to concrete can develop, even where all of these measures were followed. 1) Maintaining a maximum water/cement ratio of 0.45 by weight for exterior concrete mixes. 2) Include Type F fly ash in exterior concrete mixes as 20 percent of the cementitious material.
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 15 of 32 3) Specify a minimum, 28 -day, compressive strength of 4,500 psi for all exterior concrete. 4) Include „fib ermesh‟ in the concrete mix also may be beneficial for reducing surficial scaling. 5) Cure the concrete effectively at uniform temperature and humidity. This commonly will require fogging, blanketing and/or tenting, depending on the weather conditions. As long as 3 to 4 weeks of curing may be required, and possibly more. 6) Avoid placement of concrete during cold weather so that it is not exposed to freeze -thaw cycling before it is fully cured. 7) Avoid the use of de -icing salts on given reaches of flatwork th rough the first winter after construction. We understand that commonly it may not be practical to implement some of these measures for reducing scaling due to safety considerations, project scheduling, etc. In such cases, additional costs for flatwork maintenance or reconstruction should be incorporated into project budgets. WATER -SOLUBLE SULFATES The concentrations of water -soluble sulfates measured in selected sample retrieved from the test holes was less than approximately 0.01 percent by weight . (Se e Table 1 .) Such concentrations of water -soluble sulfates represent a negligible degree of sulfate attack on concrete exposed to these materials. Degrees of attack are based on the scale of 'negligible,' 'moderate,' 'severe' and 'very severe' as described in the “Design and Control of Concrete Mixtures,” published by the Portland Cement Association (PCA). Based on these data GROUND, makes no recommendation for use of a special, sulfate -resistant cement in project concrete.
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 16 of 32 SOIL CORROSIVITY The degree of risk for corrosion of metals in soils commonly is considered to be in two categories: corrosion in undisturbed soils and corrosion in disturbed soils. The potential for corrosion in undisturbed soil is generally low, regardless of soil types and condition s, because it is limited by the amount of oxygen that is available to create an electrolytic cell. In disturbed soils, the potential for corrosion typically is higher, but is strongly affected by soil conditions for a variety of reasons but primarily soil chemistry. A corrosivity analysis was performed to provide a general assessment of the potential for corrosion of ferrous metals installed in contact with earth materials at the site, based on the conditions existing at the time of GROUND‟s evaluation. S oil chemistry and physical property data including pH, oxidation -reduction (redox) potential, sulfides, and moisture content were obtained. Test results are summarized on Table 1 . Reduction -Oxidation Reduction and oxidation testing indicated negative potential: -72 millivolts. Such a low potentials typically creates a more corrosive environment. Sulfide Reactivity Sulfide reactivity testing for the presence of sulfides indicated a “trace ” result in the on -sit e soils. The presence of sulfides suggests a more corrosive environment. pH Where pH is less than 4.0, soil serves as an electrolyte; the pH range of about 6.5 to 7.5 indicates soil conditions that are optimum for sulfate reduction. In the pH range abov e 8.5, soils are generally high in dissolved salts, yielding a low soil resistivity 1 . Testing indicated a pH value of approximately 8.1 in the local earth materials. Soil Resistivity In order to assess the “worst case” for mitigation planning, samples of materials retrieved from the test holes were tested for resistivity in the laboratory, after being saturated with water, rather than in the field. Resistivity also varies inversely with temperature. Measurements of electrical resistivity indicated a va lue of approximately 4,327 ohm -centimeters in a sample of the site earth materials. The American Water Works Association (AWWA) has developed a point system scale used to predict corrosivity. The scale is intended for protection of ductile iron pipe but is 1 ,3 American Water Works Association ANSI/AWWA C105/A21.5 -05 Standard
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 17 of 32 valuable for project steel selection. When the scale equals 10 points or higher, protective measures for ductile iron pipe are recommended. The AWWA scale is presented below. The soil characteristics refer to the conditions at and above pipe install ation depth. T ABLE A.1 S OIL -TEST E VALUATION 2 Soil Characteristic / Value Points Resistivity <1,500 ohm -cm ................................................................................................. 10 1,500 to 1,800 ohm -cm ....................................................................................... 8 1,800 to 2,100 ohm -cm ....................................................................................... 5 2,100 to 2,500 ohm -cm ....................................................................................... 2 2,500 to 3,000 ohm -cm ....................................................................................... 1 >3,000 ohm -cm ........................................................................................ 0 pH 0 to 2.0 ............................................................................................................ 5 2.0 to 4.0 ......................................................................................................... 3 4.0 to 6.5 ......................................................................................................... 0 6.5 to 7.5 ...................................................................................................... 0 * 7.5 to 8.5 ......................................................................................................... 0 >8.5 .......................................................................................................... 3 Redox Potential < 0 (negative values) . ...................................................................................... 5 0 to +50 mV ..................................................................................................... 4 +50 to +100 mV .................................................................................… ....... 3½ > +100 mV . .............................................................................................. 0 Sulfide Content Positive .... ..................................................................................................... 3½ Trace ...........… .................................................................................................. 2 Negative .......…. ................................................................................................ 0 Moisture Poor drainage, continuously wet......................................…. ............................ 2 Fair drainage, generally moist ......................… ............................................. 1 Good drainage, generally dry ......................................... .............................. 0 * If sulfides are present and low or negative redox -potential results (< 50 mV) are obtained, add three points for this range. We anticipate tha t drainage at the site after construction will be good. Based on the values obtained for the soil parameters, the site soils appear to comprise a low corrosive environment for metals (7 points).
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 18 of 32 Corrosive conditions can be addressed by use of materials not vulnerable to corrosion, heavier gauge materials with longer design lives, polyethylene encasement, or cathodic protection systems. If additional information or recommendations are needed regar ding soil corrosivity, GROUND recommends contacting the American Water Works Association or a Corrosion Engineer. It should be noted, however, that changes to the site conditions during construction, such as the import of other soils, or the intended or u nintended introduction of off -site water, may alter corr osion potentials significantly. PROJECT EARTHWORK T he project site has undergone previous grading for the existing building construction and surrounding pedestrian walkways. We anticipate cuts up to 8 feet to construct the addition and 2 feet for concrete walkway areas depending on the earthwork selected . The following information is for private improvements; public roadways or utilities should be constructed in accordance with applicable municipal / agency standards. General Considerations Site grading should be performed as early as possible in the construction sequence to allow settlement of fills and surcharged ground to be realized to the greatest extent prior to subsequent construction. Prior to earthwork construction, vegetation and other deleterious materials should be removed and disposed of off -site. Relic underground utilities should be abandoned in accordance with applicable regulations, removed as necessary, and properly capped. Topsoil present on -site should not be incorporated into ordinary fills. Instead, topsoil should be stockpiled during initial grading operations for placement in areas to be landscaped or for other approved uses. Existing Fill Soils Actual contents an d co mposition of the fill materials on -site generally classified as clayey sand with gravels. S ome of the excavated fill materials may not be suitable for replacement as backfill. A geotechnical engineer should be retained during site excavations to observe t he excavated fill materials and provide recommendations for its suitability for reuse.
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 19 of 32 Use of Existing Native Soils Native soils that are free of trash, organic material, construction debris, and other deleterious materials are suitable, in general, for p lacement as compacted fill. Organic materials should not be incorporated into project fills. Fragments of rock, cobbles, and inert construction debris (e.g., concrete or asphalt) larger than 3 inches in maximum dimension will require special handling and/o r placement to be incorporated into project fills. In general, such materials should be placed as deeply as possible in the project fills. A geotechnical engineer should be consulted regarding appropriate recommendations for usage of such materials on a case -by -case basis when such materials have been identified during earthwork. Standard recommendations that likely will be generally applicable can be found in Section 203 of the current CDOT Standard Specifications for Road and Bridge Construction. Imp orted Fill Materials If it is necessary to import material to any of the sites, the imported soils should be fre e of organic material and other deleterious materials. Imported material for use as common fill should consist of soils that have less than 30 percent passing the No. 200 Sieve and should have a plasticity index of less than 1 0. Representative samples of the materials proposed for import should be tested and approved prior to transport to the site. “Pit run” material for use as common fill sho uld be approved prior to use. Fill Platform Preparation Prior to filling, the top 8 to 12 inches of in -place materials on which fill soils will be placed should be scarified, moisture conditioned and properly compacted in accordance with the recommendation s below to provide a uniform base for fill placement. Where over -excavation is performed, these measures for subgrade preparation apply to the subgrade surface at the base of the over -excavation depth. If surfaces to receive fill expose loose, wet, soft o r otherwise deleterious material, additional material should be excavated, or other measures taken to establish a firm platform for filling. The surfaces to receive fill must be effectively stable prior to placement of fill.
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 20 of 32 Fill Placement Fill materials should be thoroughly mixed to achieve a uniform moisture content, placed in uniform lifts not exceeding 8 inches in loose thickness, and properly compacted. All soils should be compacted to 95 or more percent of the maximum dry density at moisture contents within 2 percent of the optimum moisture content as determined by ASTM D1557, the “modified Proctor.” No fill materials should be placed, worked, rolled while they are frozen, thawing, or during poor/inclement weather conditions. Car e should be taken with regard to achieving and maintaining proper fill soil moisture contents during placement and compaction. Soils with excessive moisture may exhibit pumping, rutting, and deflection, and not compact effectively. The contractor should be prepared to handle soils of this type, including using chemical stabilization, where necessary. Compaction areas should be kept separate, and no lift should be covered by another until relative compaction and moisture content within the recommended rang es are obtained. Where soils supporting building floors or on which floors will be placed are exposed to freezing temperatures or repeated freeze – thaw cycling during construction (commonly due to water ponding on project soils) bearing capacity typical ly is reduced and/or settlements increased due to the loss of density in the supporting soils. After periods of freezing conditions, the contractor should re -work areas affected by the formation of ice to re -establish adequate bearing support. Use of Sque egee Relatively uniformly graded fine gravel or coarse sand, i.e., “squeegee,” or similar materials commonly are proposed for backfilling foundation excavations, utility trenches (excluding approved pipe bedding), and other areas where employing compaction equipment is difficult. In general, GROUND does not recommend this procedure for the following reasons: 1. Although commonly considered “self compacting,” uniformly graded granular materials require densification after placement, typically by vibration. Th e equipment to densify these materials is not available on many job -sites.
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 21 of 32 2. Even when properly densified, uniformly graded granular materials are permeable and allow water to reach and collect in the lower portions of the excavations backfilled with those materials. This leads to wetting of the underlying soils and resultant potential loss of bearing support as well as increased local heave or settlement. GROUND recommends that wherever possible, excavations be backfilled with approved, on -site soils place d as properly compacted fill. Where this is not feasible, use of “Controlled Low Strength Material” (CLSM), i.e., a lean, sand -cement slurry (“flowable fill”) or a similar material for backfilling should be considered. Where “squeegee” or similar material s are proposed for use by the contractor, the design team should be notified by means of a Request for Information (RFI), so that the proposed use can be considered on a case -by -case basis. Where “squeegee” meets the project requirements for pipe bedding material, however, it is acceptable for that use. Settlements Settlements will occur in filled ground, typically on the order of 1 to 2 percent of the fill depth. If fill placement is performed properly and is tightly controlled, in GROUND‟s experience th e majority (on the order of 60 to 80 percent) of that settlement will typically take place during earthwork construction, provided the contractor achieves the compaction levels recommended herein. The remaining potential settlements likely will take sever al months or longer to be realized, and may be exacerbated if these fills are subjected to changes in moisture content. Cut and Filled Slopes Permanent site slopes supported by on -site soils up to 4 feet in height may be constructed no steeper than 2½:1 (horizontal : vertical). Minor raveling or surficial sloughing should be anticipated on slopes cut at this angle until vegetation is well re -established. Surface drainage should be designed to dire ct water away from slope faces. EXCAVATION CONSIDERATIONS The test holes for the subsurface exploration were excavated to the depths indicated by means of tra ck -mounted, flight auger drilling equipment. We anticipate no significant
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 22 of 32 excavation difficulties in the majority of the site with conventional heavy -duty excavation equipment in good working condition. We recommend that temporary, un -s hored excavation slopes up to 8 feet in height be cut no steeper than 1½:1 (horizontal : vertical) in the site soils in the absence of seepage. Sloughing on the slope face s should be anticipated at this angle. Local conditions encountered during construction, such as groundwater seepage and loose sand, will require flatter slopes. Stockpiling of materials should not be permitted closer to the tops of temporary slopes than 5 feet or a distance equal to the depth of the excavation, which ever is greater. Should site constraints prohibit the use of the recommended slope angles, temporary shoring should be used. The shoring should be designed to resist the lateral earth pressu re exerted by building, traffic, equipment, and stockpiles. GROUND can provide shoring design upon request. Good surface drainage should be provided around temporary excavation slopes to direct surface runoff away from the slope faces. A properly desig ned drainage swale should be provided at the top of the excavations. In no case should water be allowed to pond at the site. Slopes should also be protected against erosion. Erosion along the slopes will result in sloughing and could lead to a slope fai lure. Excavations in which personnel will be working must comply with all OSHA Standards and Regulations. The contractor‟s “responsible person” should evaluate the soil exposed in the excavations as part of the contractor‟s safety procedures. GROUND has provid ed the information above solely as a service to The Town of Vail , and is not assuming responsibility for construction site safety or the Contractor‟s activities. BUS TRANSIT PLAZA A pavement section is a layered system designed to distribute concentrated traffic loads to the subgrade. Performance of the pavement structure is directly related to the physical properties of the subgrade soils and traffic loadings. Bec ause the project pavements will be maintained by the city , the recommended pavement sectio ns were developed in general accordance with town specifications , the Colorado Department of Transportation (CDOT) and local construction practice.
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 23 of 32 Subgrade Materials Based on the results of our field and laboratory studies, the subgrade soils in the are a proposed for the bus transit station consis ted predominantly of non -plastic sands and gravels . These materials were classified typically as A -1 -B soils in accordance with the AASHTO classification system , with Group Index value of 0 . Pavement Section We recommend that the bus route or other portions of the potential areas for bus parking be provided with rigid pavements consisting of 6½ or more inches of portland cement concrete. For superior performance, the concrete should be underlain by 6 or more inches of properly compacted CDOT Class 6 Aggregate Base Course. (A numerically equival ent composite section would be 6 ½ inches of asphalt over 11 inches of aggregat e base, but that section would not perform as well as a rigid section under heavy vehicle traffic and turning stresses.) Pavement Materials Concrete pavements should consist of a plant mix composed of a mixture of aggregate, portland cement and appropriat e admixtures meeting the requirements of a job -mix formula established by a qualified engineer as well as applicable municipal design requirements. Concrete should have a minimum modulus of rupture of third point loading of 650 psi. Normally, concrete wi th a 28 -day compressive strength of 4,200 psi should develop this modulus of rupture value. The concrete should be air -entrained with approximately 6 percent air and should have a minimum cement content of 7 sacks per cubic yard. Maximum allowable slump should be 4 inches. Concrete pavements should contain sawed or formed joints. CDOT and various industry groups provide guidelines for proper design and concrete construction and associated jointing. In areas of repeated turning stresses we recommend tha t the concrete pavement joints be fully tied and doweled. We suggest that civil design consider joint layout in accordance with CDOT‟s M standards, found at the CDOT website: http://www.dot.state.co.us/DesignSupport/. These concrete mix design criteria should be coordinated with other project requirements including the criteria for sulfate resistance presented in the Water -Soluble Sulfates section of this report. To reduce surficial spalling result ing from freeze -thaw cycling, we suggest that pavement concrete meet the requirements of CDOT Class P concrete. In addition, the use of de -icing salts on concrete pavements during the first winter after construction will increase the likelihood of the dev elopment of scaling. Placement of flatwork concrete during cold weather so that it is exposed to freeze -thaw cycling before it is fully cured also increases its vulnerability to scaling. Concrete placing during cold weather conditions should be blanketed or tented to allow full curing.
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 24 of 32 Depending on the weather conditions, this may result in 3 to 4 weeks of curing, and possibly more. T he aggregate base material should meet the criteria of CDOT Class 6 aggregate base course. Base course should be placed a nd compacted as recommended in the Project Earthwork section of this report . Subgrade Preparation Although subgrade preparation to a depth of 8 to 12 inches is typical in the project area, pavement performance commonly can be improved by a greater depth of moisture -density conditioning of the soils. Remedial Earthwork GROUND recommends that shortly before p aving, the pavement subgrade be excavated and/or scarified to a depth of at least 2 feet , moisture -conditione d and properly re -compacted. Recommendations for fill placement and compaction are provided in the Project Earthwork section of this report . The contractor should be prepared either to dry the subgrade materials or moisten them, as needed, prior to compaction. Subgrade preparation should extend the full width of the pavement from back -of -curb to back -of -curb. The subgrade for sidewalks and other p roject hardscaping also should be prepared in the same manner. Where adequate drainage cannot be achieved or maintained, a greater depth of excavation and replacement is recommended, in addition to the edge drains recommended below . Proof Rolling Immediat ely prior to paving, the subgrade should be proof rolled with a heavily loaded, pneumatic tired vehicle. Areas where water that show excessive deflection during proof rolling should be excavated and replaced and stabilized. Areas allowed to pond prior to paving will require significant re -working prior to proof -rolling. Passing proof -rolling is an additional requirement for pavement subgrade soils; it may be possible for soils to be compacted within the limits indicated in the Project Earthwork section o f this report and fail proof rolling, particularly in the upper range of recommended moisture contents. Subgrade Stabilization Because of the sandy nature of some of the site soils, they may “pump” or deflect during compaction and proof -rolling if moistur e levels are not carefully controlled and achieving a stable platform for paving may be difficult. Chemical
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 25 of 32 stabilization of the pavement subgrade may be necessary. Because of the water -soluble sulfates in the site soils, stabilization with lime does not appear feasible. We anticipate, however, that stabilization with portland cement would be effective. It is not possible to assess subgrade stability reliably on the basis of information during geotechnical exploration or subsequent laboratory testing. It is often our experience that where an existing pavement is removed, the underlying subgrade exhibits instability when subjected to construction and/or traffic loading, even where testing suggests otherwise acceptable moisture contents and density. Ther efore, it may be necessary to stabilize the majority of the existing subgrade prior to repaving. This may require reprocessing or chemical stabilization of existing soils or removal and replacement with other site materials or imported soil. Our office s hould be retained to observe the subgrade condition and stability during the removal process. If additional or more specific information is required, then we suggest additional exploration be performed along the proposed roadway. Drainage and Maintenance The collection and diversion of surface drainage away from paved areas is extremely important to satisfactory performance of the pavement. The subsurface and surface drainage systems should be carefully designed to ensure removal of the water from paved areas and subgrade soils. Where topography, site constraints or other factors limit or preclude adequate surface drainage, pavements should be provided with edge drains to reduce loss of subgrade support. The long -term performance of the pavement also can be improved greatly by proper backfilling and compaction behind curb, gutter, and sidewalk. Unless the interceptor drain and edge drains (where included) are installed properly and maintained, and site drainage in general is well maintained, there is an increased risk of poor pavement performance at this site due to the expansive subgrade materials and the local introduction of off -site irrigation water. Landscape irrigation in planters adjacent to pavements and in “island” planters within paved areas should be carefully controlled or differential settlement and/or rutting of the nearby pavements will result. Drip irrigation systems are recommended for such planters to reduce over -spray and water infiltration beyond the planters. Enclosing the soil in the planters with plastic liners and providing them with positive drainage also will reduce differential moisture increases in the surrounding subgrade soils. In our experience, infiltration from planters adjacent to pavements is a principal source of mo isture increase beneath those pavements. This wetting of the subgrade soils from
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 26 of 32 infiltrating irrigation commonly leads to loss of subgrade support for the pavement with resultant accelerating distress, loss of pavement life and increased maintenance cost s. This is particularly the case in the later stages of project construction after landscaping has been emplaced but heavy construction traffic has not ended. Heavy vehicle traffic over wetted subgrade commonly results in rutting and pushing of flexible pavements, and cracking of rigid pavements. In relatively flat areas where design drainage gradients necessarily are small, subgrade settlement can obstruct proper drainage and yield increased infiltration, exaggerated distress, etc. (These consideration s apply to project flatwork, as well.) Also, GROUND‟s experience indicates that longitudinal cracking is common in asphalt -pavements generally parallel to the interface between the asphalt and concrete structures such as curbs, gutters or drain pans. This of this type is likely to occur even where the subgrade has been prepared properly and the asphalt has been compacted properly. The anticipated traffic loading does not include excess loading conditions imposed by heavy construction vehicles. Consequen tly, heavily loaded concrete, lumber, and building material trucks can have a detrimental effect on the pavement. In areas where the maintenance traffic is turning, concrete pavement is recommended. As noted above, the standard care of practice in pavem ent design describes the recommended flexible pavement section as a “20 -year” design pavement; however, most pavements will not remain in satisfactory condition without regular maintenance and rehabilitation procedures performed throughout the life of the pavement. Maintenance and rehabilitation measures preserve, rather than improve, the structural capacity of the pavement structure. Therefore, GROUND recommends that an effective program of regular maintenance be developed and implemented to seal cracks , repair distressed areas. The greatest benefit of pavement overlaying will be achieved by overlaying sound pavements that exhibit little or no distress. Crack sealing should be performed at least annually. After approximately 8 to 10 yea rs after constru ction, patching and additional crack sealing may be required. Prior to overlays, it is important that all cracks be sealed with a flexible, rubberized crack sealant in order to reduce the potential for propagation of the crack through the overlay. If act ual traffic loadings exceed the values used for development of the pavement sections, however, pavement maintenance measures will be needed on a n accelerated schedule.
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 27 of 32 SURFACE DRAINAGE The following drainage measures are recommended for design, construct ion, and should be maintained at all times after the project has been completed: 1) Wetting or drying of foundation and underslab areas should be avoided. Permitting increases/variations in moisture to the adjacent or supporting soils may result in a decrease in bearing capacity and an increase in volume change of the underlying soils and/or differential movement. 2) Positive surface drainage measures should be provided and maintained to reduce water infiltration into foundation soils. The ground surface surrounding the exterior of the building should be sloped to drain away from the foundation in all directions. We recommend a minimu m slope of 12 inches in the first 10 feet in areas not covered with pavement or concrete slabs, or a minimum 3 percent in the first 10 feet in the areas covered with pavement or concrete slabs. Reducing the slopes to comply with ADA requirements may be ne cessary but may result in an increased potential for moisture infiltration and subsequent volume change of the underlying soils. In no case should water be allowed to pond near or adjacent to foundation elements. However, if positive surface drainage is implemented and maintained directing moisture away from the building, lesser slopes can be utilized if the risk of incrementally greater settlements is accepted . In no case should water be allowed to pond near or adjacent to foundation elements, or on sid ewalks, hardscaping, or other improvements as well as utility trench alignments, which ar e likely to be adversely affect ed by moisture -volume changes in the underlying soils or flow of infiltrating water. Drainage measures also should be included in projec t design to direct water away from sidewalks and other hardscaping as well as utility trench alignments which are likely to be adversely affected by moisture -volume changes in the underlying soils or flow of infiltrating water. Routine maintenance of site drainage should be undertaken throughout the design life of the project. In GROUND‟s experience, it is common during construction that in areas of partially completed paving or hardscaping, bare soil behind curbs and gutters, and utility trenches, water i s allowed to pond after rain or snow -melt events.
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 28 of 32 Wetting of the subgrade can result in loss of subgrade support and increased settlements / increase heave. By the time final grading has been completed, significant volumes of water can already have enter ed the subgrade, leading to subsequent distress and failures. The contractor should maintain effective site drainage throughout construction so that water is directed into appropriate drainage structures. 3) Roof downspouts and drains should discharge well b eyond the perimeter of the structure‟s foundation, or be provided with positive conveyance off -site for collected waters. Downspouts should not discharge into a building underdrain system. 4) Landscaping which requires watering should be located 10 or more f eet from the building perimeter. Irrigation sprinkler heads should be deployed so that applied water is not introduced into foundation soils. Landscape irrigation should be limited to the minimum quantities necessary to sustain healthy plant growth. Us e of drip irrigation systems can be beneficial for reducing over -spray beyond planters. Drip irrigation also can be beneficial for reducing the amounts of water introduced to building foundation soils, but only if the total volumes of applied water are co ntrolled with regard to limiting that introduction. Controlling rates of moisture increase beneath the foundations and floors should take higher priority than minimizing landscape plant losses. Where plantings are desired within 10 feet of the building, GROUND recommends that the plants be placed in water -tight planters, constructed either in -ground or above -grade, to reduce moisture infiltration in the surrounding subgrade soils. Planters should be provided with positive drainage and landscape underdrai ns. 5) We do not recommend the use of plastic membranes to cover the ground surface near the building without careful consideration of other components of project drainage. Plastic membranes can be beneficial to directing surface waters away from the build ing and toward drainage structures. However, they effectively preclude evaporation or transpiration of shallow soil moisture. Therefore, soil
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 29 of 32 moisture tends to increase beneath a continuous membrane. Where plastic membranes are used, additional shallow, subsurface drains should be installed. FOUNDATION WALLS Foundation walls that are laterally supported and can be expected to undergo only a limited amount of deflection, i.e., an “at -rest” condition, should be designed to resist lateral earth pressures co mputed on the basis of an equivalent fluid unit weight of 55 pcf if imported, select, granular, structural backfill (meeting the criteria presented below) is used to backfill the walls. The at -rest lateral earth pressures should be computed using an eq uivalent fluid unit weight of 65 pcf where on -site materials are used as backfill. The loads recommended above are for well -drained conditions with a horizontal upper backfill surface. The additional loading of an upward sloping backfill, hydrostatic lo ads if sufficient drainage is not provided, as well as loads from traffic, stockpiled materials, etc., should be included in foundation wall design. GROUND recommends use of structural backfill behind the walls to achieve lower lateral earth pressures. To realize the lower equivalent fluid unit weight, structural fill should be placed behind the wall to a minimum distance equal or greater than half of the wall height. Where structura l backfill is used, the upper 1 foot of the wall backfill should be a rel atively impermeable soil or otherwise protected to reduce surface water infiltration into the backfill. Backfill soils should be thoroughly mixed to achieve a uniform moisture content, placed in uniform lifts not exceeding 6 inches in loose thickness, and properly compacted in accordance with the recommendations in the Site Grading section of this report. The contractor should take care not to over -compact the backfills, which could result in excessive lateral pressures on the walls. Some settlement of wal l backfills will occur even where the material was placed correctly. This settlement likely will be differential, increasing with depth of fill. Where shallowly founded structures and pavements must be placed on backfilled zones, structural design, pipe connections, etc., should take into account backfill settlement, including differential movement and the associated risks are understood. A geotechnical engineer should be retained to provide recommendations for founding improvements in such areas.
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 30 of 32 CLOSURE Geotechnical Review T he author of this report should be retained to review project plans and specifications to evaluate whether they comply with the intent of the recommendations in this report. The review should be requested in writing. The geote chnical recommendations presented in this report are contingent upon observation and testing of project earthworks by representatives of GROUND. If another geotechnical consultant is selected to provide materials testing, then that consultant must assume all responsibility for the geotechnical aspects of the project by concurring in writing with the recommendations in this report, or by providing alternative recommendations. Materials Testing The Town of Vail should consider retaining a geotechnical e ngineer to perform materials testing during construction. The performance of such testing or lack thereof, in no way alleviates the burden of the contractor or subcontractor from constructing in a manner that conforms to applicable project documents and i ndus try standards. The contractor or pertinent subcontractor is ultimately responsible for managing the quality of their work; furthermore, testing by the geotechnical engineer does not preclude the contractor from obtaining or providing whatever services they deem necessary to complete the project in accordance with applicable documents. Limitations This report has been prepare d for The Town of Vail as it pertains to the proposed concert hall addition and „transit plaza‟ bus pull out as described herein . It may not contain sufficient information for other parties or other purposes. The owner or any prospective buyer relying upon this report must be made aware of and must agree to the terms, conditions, and liability limitations outlined in the proposal . In addition, GROUND has assumed that project construction will commence by Summer 2012. Any changes in project plans or schedule should be brought to the attention of a geotechnical e ngineer, in order that the geotechnical recommendations may be re -eval uated and, as necessary, modified. The geotechnical conclusions and recommendations in this report relied upon subsurface exploration at a limited number of exploration points, as shown in Figure 1, as well as the means and methods described herein. Subsu rface conditions were
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 31 of 32 interpolated between and extrapolated beyond these locations. It is not possible to guarantee the subsurface conditions are as indicated in this report. Actual conditions exposed during construction may differ from those encountered during site exploration. If during construction, surface, soil, bedrock, or groundwater conditions appear to be at variance with those described herein, a geotechnical engineer should be advised at once, so that re -evaluation of the recommendations may be made in a timely manner. In addition, a contractor who relies upon this report for development of his scope of work or cost estimates may find the geotechnical information in this report to be inadequate for his purposes or find the geotechnical condit ions described herein to be at variance with his experience in the greater project area. The contractor is responsible for obtaining the additional geotechnical information that is necessary to develop his workscope and cost estimates with sufficient prec ision. This includes current depths to groundwater, etc. The materials present on -site are stable at their natural moisture content, but may change volume or lose bearing capacity or stability with changes in moisture content. Performance of the proposed structure and pavement will depend on implementation of the recommendations in this report and on proper maintenance after construction is completed. Because water is a significant cause of volume change in soils and rock, allowing moisture infiltration may result in movements, some of which will exceed estimates provided herein and should therefore be expected by the owner. This report was prepared in accordance with generally accepted soil and foundation engineering practice in the project area at the d ate of preparation. GROUND makes no warranties, either expressed or implied, as to the professional data, opinions or recommendations contained herein. Because of numerous considerations that are beyond GROUND‟s control, the economic or technical perform ance of the project cannot be guaranteed in any respect.
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 32 of 32
Subsurface Exploration Program Proposed Bus / Vehicle Pull Out South Frontage Road East Vail, Colorado Job No. 11 -6024 GROUND Engineering Consultants, Inc . Page 33 of 32