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HomeMy WebLinkAboutB11-0188 B12-0042 Geo ReportDecember 15, 2011 KCE Job No. 11-052 TABLE OF CONTENTS SCOPE 1  PROPOSED CONSTRUCTION 1  SITE CONDITIONS 2  SUBSURFACE EXPLORATION 2  SUBSURFACE CONDITIONS 3  EXCAVATIONS 3  SEISMICITY 4  FOUNDATIONS 4  SLABS-ON-GRADE 6  SURFACE DRAINAGE 7  COMPACTED FILL 7  LIMITATIONS 9   VICINITY MAP Fig. 1 LOCATIONS OF EXPLORATORY BORINGS Fig. 2 LOGS OF EXPLORATORY BORINGS Fig. 3 LEGEND OF EXPLORATORY BORINGS Fig. 4 GRADATION TEST RESULTS Fig. 5 December 15, 2011 KCE Job No. 11-052 1 SCOPE This report presents the results of a subsurface exploration for the reconstruction of the East Mall Plaza shelter in Vail, Colo rado. The approximate s ite location is shown on the Vicinity Map, Fig. 1. The purpose of th is subsurface exploration was to evaluate the subsurface conditions at the site and to provide geotechnical recommendations for the proposed construction. This report includes descriptions of subsoil and ground water conditions encountered in the exploratory borings, r ecommended foundation syst ems, allowable soil bearing pressure, slabs-on-grade and reco mmended foundation design and construction criteria. This report was prepared from data developed during our field exploration, our laboratory testing, and our experience with similar projects and subsurface conditions in the area. The recommendations presented in this report are based on the proposed building being constructed. PROPOSED CONSTRUCTION We understand that an open shelter will be constructed on the subject site. We anticipate the proposed structure will be one st ory in height with no below grade level. We anticipate that the proposed structure will be of cast-in-place c oncrete, stone veneer and wood and steel-frame construc tion. We anticipated structural loads will be relatively light. December 15, 2011 KCE Job No. 11-052 2 SITE CONDITIONS The East Mall Plaza shelter to be recons tructed is located a pproximately 400 feet south of the intersection of East Lionshead Circle and the I-70 South Frontage Road. The site is bordered to the north by East Lions head Circle. The area has been developed for commercial use with the East Lionshead Parking Structure located to the northeast. Vegetation to the sides and within the existing islands of the existing bus stop consists of grass and trees. SUBSURFACE EXPLORATION Subsurface conditions were explored at this site on June 13, 2011 by drilling two shallow borings with a 4-inch diameter conti nuous flight power auger attached to a truck drill rig at the locations shown on the Locations of Exploratory Borings, Fig. 2. A representative from our office was on site to supervise the drilling of the borings and visually classify and document the subs urface soils and ground water conditions. Our personnel also obtained represen tative samples of the soils within the borings to be examined in our laboratory. A description of the subsurface soils encountered in the borings and a summary of laboratory test re sults are shown on the Logs of Exploratory Borings, Fig. 3; and on the Legend of Exploratory Borings, Fig. 4. Laboratory testing included visual classi fication by the project engineer and testing of the samples for moisture content, Atterberg limits, and gradation analysis properties. Results of the la boratory tests are presented on the Logs of Exploratory Borings, Fig. 3, and on the Gradation Test Results, Fig. 5. December 15, 2011 KCE Job No. 11-052 3 SUBSURFACE CONDITIONS Subsurface conditions encountered in the borings (P-1 and P-2) were generally similar. The subsurface conditions consisted of two feet of sand with gravel and silt. Observation of the drilling indicated the material was likely medium dense. Below two feet, the material became more gravelly and appeared dens er, based on drilling observations. This material extended to the maximum depth explored of 5 feet. At the time of drilling, ground water wa s not encountered in either of the borings to the maximum depth explored of 5 feet. EXCAVATIONS We anticipate that relatively shallow excavations will be required for the construction of the proposed structure. Base d on the subsurface conditions encountered at the site, we anticipate that conventional construction equipment will be capable of completing the necessary excavations. Care needs to be exercised during cons truction so that the excavation slopes remain stable. In our opinion, th e granular materials encountered at this site classify as Type C soils in accordance with OSHA classifications. The contractor’s designated competent person should evaluate the soils during cutting to a ssess the appropriate classification at the time of construction. OSHA regulations should be followed in any excavations or cuts. December 15, 2011 KCE Job No. 11-052 4 SEISMICITY The subsurface soil and ground water conditions encountered at the site indicate that the soil profile classifies as a very de nse soil and soft rock profile. Based on this classification and the International Building C ode (IBC), it is our opinion that the subject site has a seismic site classification of Site Class C. FOUNDATIONS We anticipate that the subsurface conditi ons at the foundation elevation for the proposed shelter will consist of silty sand and gravel with nil to low potential swell. It is our opinion that the proposed shelter may be constructed using a spread footing foundation system constructe d on the silty sand and gravel or properly moisture conditioned and compacted, non-expansive, struct ural fill with a low risk of movement. Since the borings for this project were not comp leted within the foot print of the structure, we must be contacted to observe the completed excavation and determine if the design criteria are valid. We recommend that spread footings be designed and constructed to meet the following criteria: 1. Footings should be constructed on th e silty sand and gravel, or properly moisture conditioned and compacted, non-expansive structural fill, as described below in Items 2, 8, and 9. 2. Any topsoil or existing fill encount ered beneath foundations must be removed in order to expose the natu ral sand and gravel. If necessary, properly moisture conditioned and compacted structural fill may be placed beneath the proposed foundations. Refer to the COMPACTED FILL section of this report for backfill requirements. December 15, 2011 KCE Job No. 11-052 5 3. Spread footings constructed on the silty sand and gravel, or properly moisture treated and compacted structural fill may be designed for a maximum allowable soil bearin g pressure of 3,500 psf. 4. Spread footings constructed on the silty sand and gravel, or properly moisture conditioned and compacted structural fill should experience less than 1.0-inch of differential move ment between foundation elements. 5. Foundation systems should be designed to span a distance of at least 10 feet in order to account fo r anomalies in the soil. 6. The base of the exterior footings should be established at a minimum depth below the exterior ground surface, as required by the local building code. We believe that the depth for frost protection in the local building code in this area is 4 feet. 7. Column footings should have a minimu m dimension of 24 inches square and continuous wall footings should have a minimum width of 16 inches. Footing widths may be greater to ac commodate structural design loads. 8. Pockets or layers of loose or soft so ils or fill may be encountered in the bottom of the completed footing excav ations. These materials should be removed to expose the undisturbed natural, sand and gravel. The foundations should be c onstructed on the natura l sand and gravel; or properly moisture conditioned and compacted structural fill. Refer to the COMPACTED FILL section of this report for backfill requirements. 9. Fill should be placed and compacted as outlined in the COMPACTED FILL section of this report. We re commend that a representative of our office observe and test the compaction of structural fill used in foundation construction during the placement process. It has been our experience that without engineering quality control, inappropriate cons truction techniques occur which result in unsatis factory foundation performance. 10. A representative of our office must observe the completed foundation excavation. Variations from the conditions described in this report, which were not indicated by our borings, can occur. The representative can observe the excavation to evaluate the exposed subsurface conditions and make the necessary recommendations. December 15, 2011 KCE Job No. 11-052 6 SLABS-ON-GRADE We anticipate that the subsurface conditi ons at the approximate slab-on-grade elevation will consist of silty and gravelly sand, or new struct ural fill with a low risk of movement. Any topsoil or existing fill beneath slabs-on-grade must be removed and if necessary, replaced with properly moistu re treated and compacted, non-expansive structural fill. We recommend that slabs-on-grade be designed and constructed to meet the following criteria: 1. Slabs-on-grade may be constructed on the natural sand and gravel, or properly compacted non-expansive fill, as described below in Items 2 and 6. 2. Any topsoil or existing fill below th e slabs-on-grade should be removed and if necessary, replaced with properly compacted and moisture treated, non-expansive structural fill. Refer to the COMPACTED FILL section of this report for backfill requirements. 3. Slabs-on-grade constructed on structural fill or the existing granular materials may be designed using a modulus of subgrade reaction of 150 pci. 4. Slabs-on-grade should be separated fro m the building. These slabs should be reinforced to function as indepe ndent units. Movement of these slabs should not be transmitted directly to the foundations or walls of the structure. 5. Frequent control joints should be pr ovided in all slabs to reduce problems associated with shrinka ge of the concrete. 6. Structural fill beneath slabs-on-grade may consist of the existing on-site soils free of all organics and delete rious materials, or approved imported, non-expansive fill. Structural fill should be placed and compacted as outlined in the COMPACTED FILL section of this report. We recommend that a representative of our office observe and test the placement and compaction of each lift of structur al fill used in slab-on-grade construction. It has been our experi ence that without engineering quality control, inappropriate construction techniques can occur which result in unsatisfactory slab performance. December 15, 2011 KCE Job No. 11-052 7 SURFACE DRAINAGE Reducing the wetting of structural soils can be achieved by carefully planned and maintained surface drainage. We recommend the following precautions be observed during construction and maintained at all time s after the proposed c onstruction has been completed. 1. Wetting or drying of the open excav ations should be minimized during construction. 2. All surface water should be directed away from the top and sides of the excavation during construction. 3. The ground surface surrounding the exte rior of the proposed structure should be sloped to drain away from th e structure in all directions. We recommend a slope of at least 12 inches in the first 10 feet in landscaped areas. 4. Hardscape (concrete and asphalt) shoul d be sloped to drain away from the structure. We recommend a slope of at least 2 percent for all hardscape within 10 feet of the structure. 5. Backfill, especially around foundati on walls, should be placed and compacted as recommended in the COMPACTED FILL section of this report. 6. Roof drains should discharge at l east 10 feet away from foundation walls with drainage directed away from the structure. 7. Surface drainage for this site should be designed by a Professional Civil Engineer. COMPACTED FILL Structural fill for this project may consist of on-site, natural, granular materials, or approved imported, non-expansive structural f ill. Any topsoil or existing fill should be December 15, 2011 KCE Job No. 11-052 8 removed prior to construction. T opsoil with organics or other deleterious mate rial may be used in landscaped areas. The imported fill ma y consist of non-expansive silty or clayey sands or gravels with up to 10 percent passing the No. 200 sieve with a maximum plasticity index of 10. No gravel or cobbles la rger than 6 inches should be placed in fill areas. Fill areas should be stripped of all vege tation, topsoil, and existing fill, and then scarified. Fill should be placed and compacted in thin loose lifts, moisture conditioned and compacted to the recommended compaction shown in the following table. The recommended compaction varies for the given use of the fill. Use of Fill Recommended Compaction Percentage of the Standard Proctor Maximum Dry Density (ASTM D 698) Percentage of the Modified Proctor Maximum Dry Density (ASTM D 1557) Below Structure Foundations 98 95 Below Slabs-on-Grade 95 90 Utility Trench Backfill 95 90 Backfill (Non-Structural) 90 90 Notes: 1. For granular soils, the moisture content should be –2 to +2 percent of the optimum moisture content. We recommend that a representative of our office observe and test the placement and compaction of each lift placed for structur al fill. Fill placed below foundations, slabs-on-grade, and behind retaining wa lls is considered structural. It has been our experience that without engineering quality control, in appropriate cons truction techniques can occur which result in unsatisfactory founda tion and slab-on-grade performance. December 15, 2011 KCE Job No. 11-052 9 LIMITATIONS The exploratory borings were originally located to obtain a reasonably accurate determination of conditions at the subject site for paving of the bus loop, with one boring relatively close to the proposed structure. Variations in the s ubsurface conditions are always possible. Any variations that exist beneath the site generally become evident during excavations for the proposed stru cture. A representative from our office must observe the completed excavation to confirm that the soils are as indicated by the exploratory borings and to verify our founda tion, slab-on-grade, a nd general design and construction recommendations. The placement and compaction of fill, as well as installation of foundations, shoul d also be observed and test ed. The design criteria and subsurface data presented in this report are valid for 3 years from the date of this report. We appreciate the opportunity to provide th is service. If we can be of further assistance in discussing the contents of this report or in analysis of the existing or proposed pavements from a geotechnical vi ewpoint, please c ontact our office. KOECHLEIN CONSULTING ENGINEERS, INC. Timothy A. Mitchell, P.E. Senior Engineer (4 copies sent) P-1 WC=2.3 -200=9.9 LL=NV PI=NP P-2 WC=3.0 -200=12 LL=NV PI=NP 0 2 4 6 8 10 12 14 16 Depth in Feet 0 2 4 6 8 10 12 14 16 Depth in Feet KOECHLEIN CONSULTING ENGINEERS, INC.Geotechnical and Materials Engineers LOGS OF EXPLORATORY BORINGS JOB NO. 11-052 Fig. 3 1. Borings were drilled on 6-13-11 using a 4-inch diameter continuous flight power auger mounted on a truck drill rig.2. Borings were originally drilled for East Lionshead Circle Bus Stop, KCE Job No. 11-025 3. No free ground water was encountered at the time of drilling in any of the pavement borings to the maximum depth explored of 5 feet.4. The Boring Logs are subject to the explanations, limitations, and conclusions as contained in this report.5. Laboratory Test Results: WC - Indicates natural moisture (%) -200 - Indicates percent passing the No. 200 sieve (%) LL - Indicates liquid limit (%) PI - Indicates plasticity index (%)Notes:SAND, Gravelly, Silty, Medium dense, Slightly moist,Brown SAND and GRAVEL, Silty, Dense, Slightly moist,Brown BULK SAMPLE. Obtained from auger cuttings.KOECHLEIN CONSULTING ENGINEERS, INC.Geotechnical and Material Engineers LEGEND:LEGEND OF EXPLORATORY BORINGS JOB NO. 11-052 Fig. 4 LIQUID LIMIT Sample of Job No.%PLASTICITY INDEX %LIQUID LIMIT %SILT & CLAY Elev./Depth Sample No.Source %SAND %GRAVEL Sample of %PLASTICITY INDEX %%SILT & CLAY Elev./Depth Sample No.Source %SAND %GRAVEL KOECHLEIN CONSULTING ENGINEERS 10 90 20 80 30 70 40 60 50 50 60 40 70 30 80 20 90 10 0 100 100 0 PERCENT PASSING PERCENT RETAINED 100 10 1 0.1 0.01 0.001 200 DIAMETER OF PARTICLE IN MM +75 MMGRAVELSAND SILTCLAY 6 in.3 in.2 in.1-1/2 in.1 in.3/4 in.1/2 in.3/8 in.#4 #10 #20 #30 #40 #60 #100 #140 #200 5 11-052 NP NV 10 0.5 to 5 Feet P-1 40 50 Poorly Graded GRAVEL with Silt and Sand (GP-GM)Fig.GRADATION TEST RESULTS 10 90 20 80 30 70 40 60 50 50 60 40 70 30 80 20 90 10 0 100 100 0 PERCENT PASSING PERCENT RETAINED 100 10 1 0.1 0.01 0.001 200 DIAMETER OF PARTICLE IN MM +75 MMGRAVELSAND SILTCLAY 6 in.3 in.2 in.1-1/2 in.1 in.3/4 in.1/2 in.3/8 in.#4 #10 #20 #30 #40 #60 #100 #140 #200 NP NV 12 0.5 to 5 Feet P-2 44 44 Poorly Graded SAND With Silt and Gravel (SP-SM)