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Home My WebLink AboutSHERWOOD STREET ALLEYWAY - Filed SEPD-SURFACE EXPLORATION/PAVEMENT DESIGN REPORT - 2017-12-14Geotechnical Subsurface Exploration and Pavement Design Report 317-321 Sherwood Street Alleyway Pavements Fort Collins, Colorado Soilogic # 17-1053 2 FIELD EXPLORATION To develop subsurface information for use in the pavement design, two (2) soil borings were advanced within the alleyway alignment to a depth of approximately ten (10) feet below alleyway subgrade level in accordance with the Larimer County Urban Area Street Standards (LCUASS). The boring locations were established in the field by Soilogic personnel by pacing and estimating angles and distances from identifiable site references. The boring locations should be considered accurate only to the degree implied by the methods used to make the field measurements. A diagram indicating the approximate boring locations is included with this report. Graphic logs of the auger borings are also included. The test holes were advanced using 4-inch diameter continuous-flight auger powered by a truck-mounted CME-45 drill rig. Samples of the subsurface materials were obtained at regular intervals using California barrel sampling procedures in general accordance with ASTM specification D-1586. As part of the D-1586 sampling procedure, standard sampling barrels are driven into the substrata using a 140-pound hammer falling a distance of 30 inches. The number of blows required to advance the samplers a distance of 12 inches is recorded and helpful in estimating the consistency or relative density of the soils encountered. In the California barrel sampling procedure, lesser disturbed samples are obtained in removable brass liners. Samples of the subsurface materials obtained in the field were sealed and returned to the laboratory for further evaluation, classification and testing. LABORATORY TESTING The samples collected were tested in the laboratory to measure natural moisture content and visually and/or manually classified in accordance with the Unified Soil Classification System (USCS). The USCS group symbols are indicated on the attached boring logs. An outline of the USCS classification system is included with this report. As part of the laboratory testing, a calibrated hand penetrometer (CHP) was used to estimate the unconfined compressive strength of essentially cohesive specimens. The CHP also provides a more reliable estimate of soil consistency than tactual observation Geotechnical Subsurface Exploration and Pavement Design Report 317-321 Sherwood Street Alleyway Pavements Fort Collins, Colorado Soilogic # 17-1053 3 alone. Dry density, Atterberg limits, -200 wash and swell/consolidation tests were completed on selected samples to help establish specific soil characteristics. Atterberg limits tests are used to determine soil plasticity. The percent passing the #200 size sieve (-200 wash test) is used to determine the percentage of fine grained materials (clay and silt) in a sample. Swell/consolidation tests are performed to evaluate soil volume change potential with variation in moisture content. Swell/consolidation tests completed on samples obtained at a depth of approximately 2 feet below ground surface were inundated with water at a 150 psf confining pressure. As part of the completed laboratory testing, one (1) resistance value (R-value) test was completed on a representative subgrade sample for use in pavement design. The results of the completed laboratory tests are outlined on the attached boring logs and swell/consolidation summary sheets. SUBSURFACE CONDITIONS The subsurface materials encountered in the completed site borings can be summarized as follows. Approximately 6 inches of recycled asphalt pavement (RAP) was encountered at the surface at the boring locations. At the location of boring B-2, the RAP was underlain by apparent fill/utility backfill consisting of brown clayey sand and gravel. The RAP encountered at the location of boring B-3 and apparent fill encountered at the location of boring B-2 was underlain by light reddish brown to brown silty lean clay. The silty lean clay varied from soft to stiff in terms of consistency, exhibited low swell potential at in-situ moisture and density conditions and extended to depths ranging from approximately 7 to 8 feet below ground surface where it transitioned to tan to light reddish brown sandy lean to fat clay. The lean to fat clay was stiff in consistency and extended to the bottom of both borings at a depth of approximately 10 feet below present site grades. The stratigraphy indicated on the included boring logs represents the approximate location of changes in soil types. Actual changes may be more gradual than those indicated. Groundwater was not encountered in either of the completed site borings at the time of drilling. Groundwater levels will vary seasonally and over time based on weather conditions, site development, irrigation practices and other hydrologic conditions. Geotechnical Subsurface Exploration and Pavement Design Report 317-321 Sherwood Street Alleyway Pavements Fort Collins, Colorado Soilogic # 17-1053 4 Perched and/or trapped groundwater conditions may also be encountered at times throughout the year. Perched water is commonly encountered in soils overlying less permeable soil layers and/or bedrock. Trapped water is typically encountered within more permeable zones of layered soil and bedrock systems. The location and amount of perched and/or trapped water can also vary over time. ANALYSIS AND RECOMMENDATIONS Roadway Subgrade Development The lean clay subgrade soils encountered in the completed site borings exhibited low swell potential at in-situ moisture and density conditions. The clayey sand and gravel encountered near surface at boring location B-2 would be expected to be non-expansive or possess low swell potential based on the materials physical properties and engineering characteristics. Based on results of the completed field and laboratory testing, it is our opinion the clayey sand and gravel and silty lean clay could be used for direct support of the alleyway pavements. Immediately prior to paving, we recommend the exposed subgrade soils be scarified to a depth of 9 inches, adjusted in moisture content and compacted to at least 95% of the materials standard Proctor maximum dry density. The moisture content of the scarified subgrade soils should be adjusted to be within the range of ±2% of standard Proctor optimum moisture content at the time of compaction. If fly ash stabilization of the pavement subgrade soils will be completed, reconditioning of the subgrade soils prior to fly ash treatment would not be required. Care should be taken to avoid disturbing the developed subgrade soils prior to paving. In addition, efforts to maintain the proper moisture content in the subgrade soils should be made. If subgrade soils are disturbed by the construction activities or allowed to dry out or become elevated in moisture content, those materials should be reworked in place or removed and replaced prior to surfacing. Proof-rolling of the alleyway subgrade soils should be completed prior to paving to help identify any areas of soft/unstable soils. Those areas identified as unstable would need to be mended prior to paving. Isolated areas of instability can be mended on a case by case basis. If more extensive areas of subgrade instability are encountered and depending on Geotechnical Subsurface Exploration and Pavement Design Report 317-321 Sherwood Street Alleyway Pavements Fort Collins, Colorado Soilogic # 17-1053 5 the time of year when construction occurs and other hydrologic conditions, stabilization of the subgrade soils may become necessary to develop a suitable paving platform. Based on the materials encountered in the completed site borings and results of laboratory testing, it is our opinion fly ash stabilization of the pavement subgrades could be completed to develop a suitable paving platform. With the increase in support strength developed by the stabilization procedures, it is our opinion the zone of stabilized subgrade could be included in the pavement section design, slightly reducing the required thickness of overlying aggregate base course. Pavement section design options incorporating some structural credit for the fly ash stabilized subgrade soils are outlined below in Table I. Fly ash stabilization can eliminate some of the uncertainty associated with attempting to pave during periods of inclement weather. For half credit and if fly ash stabilization will be completed, we recommend the addition of 12% class ‘C’ fly ash based on component dry unit weights. A 12-inch thick stabilized zone should be constructed by thoroughly blending the fly ash with the in-place subgrade soils. Some “fluffing” of the finish subgrade level should be expected with the stabilization procedures. The blended materials should be adjusted to within ±2% of standard Proctor optimum moisture content and compacted to at least 95% of the material’s standard Proctor maximum dry density within two (2) hours of fly ash addition. Pavement Design Site pavement could be supported directly on stable reconditioned subgrade soils or fly ash treated subgrade soils developed as outlined above. The pavement subgrade soils are expected to consist of reconditioned silty lean clay and clayey sand and gravel. The silty lean clay soils classify as A-6 soils in accordance with The American Association of State Highway and Transportation Officials (AASHTO) classification system and would be expected to exhibit low remolded shear strength. An R-value of less than 5 was determined on a representative subgrade sample obtained from the borings and used in pavement section design. Design ESAL’s were provided by City of Fort Collins personnel. Serviceability loss and reliability were obtained from the current LCUASS. Outlined below in Table I. are pavement section design options for the project alleyway. Geotechnical Subsurface Exploration and Pavement Design Report 317-321 Sherwood Street Alleyway Pavements Fort Collins, Colorado Soilogic # 17-1053 6 TABLE 1 – PAVEMENT SECTION DESIGN Roadway Classification ESAL’s Reliability % Loss Resilient Modulus (Mr) Design Structural Number Option A – Composite Surface Asphalt (Grading S or SX) Aggregate Base (Class 5 or 6) (Structural Number) Option B – Composite on Fly Ash Asphalt (Grading S or SX) Aggregate Base (Class 5 or 6) Fly Ash Treated Subgrade (Structural Number) 317-321 Sherwood Street Alleyway Alley/Local Residential 73,000 80% 2.5% 3025 (2.83) 5” (0.44/inch) 6” (0.11/inch) (2.86) 4” (0.44/inch) 5” (0.11/inch) 12” (10 @ .05/inch) (2.81) Asphaltic concrete should consist of a bituminous plant mix composed of a mixture of aggregate, filler, binders and additives if required meeting the design requirements of the City of Fort Collins (LCUASS). Aggregate used in the asphaltic concrete for local residential roadways should meet specific gradation requirements for Colorado Department of Transportation (CDOT) grading S (3/4 inch minus) or SX (1/2 inch minus) mixes. Hot mix asphalt designed using “Superpave” criteria should be compacted to within 92 to 96% of the materials Maximum Theoretical Density. Aggregate base should be consistent with CDOT requirements for Class 5 or 6 aggregate base, placed in loose lifts not to exceed 9 inches thick and compacted to at least 95% of the materials standard Proctor maximum dry density. The proposed pavement section design does not include an allowance for excessive loading conditions imposed by heavy construction vehicles or equipment. The recommended pavement sections are minimums and periodic maintenance efforts should be expected. A preventative maintenance program can help increase the service life of the roadway pavement. Geotechnical Subsurface Exploration and Pavement Design Report 317-321 Sherwood Street Alleyway Pavements Fort Collins, Colorado Soilogic # 17-1053 7 Drainage Positive drainage is imperative for long term performance of the alleyway pavements. Water which is allowed to pond adjacent to alleyway pavements can result in a loss of subgrade support and premature failure of the overlying pavement section. LIMITATIONS This report was prepared based upon the data obtained from the completed site exploration, laboratory testing, engineering analysis and any other information discussed. The completed borings provide an indication of subsurface conditions at the boring locations only. Variations in subsurface conditions can occur in relatively short distances away from the borings. This report does not reflect any variations which may occur across the site or away from the borings. If variations in the subsurface conditions anticipated become evident, the geotechnical engineer should be notified immediately so that further evaluation and supplemental recommendations can be provided. The scope of services for this project does not include either specifically or by implication any biological or environmental assessment of the site or identification or prevention of pollutants or hazardous materials or conditions. Other studies should be completed if concerns over the potential of such contamination or pollution exist. The geotechnical engineer should be retained to review the plans and specifications so that comments can be made regarding the interpretation and implementation of our geotechnical recommendations in the design and specifications. The geotechnical engineer should also be retained to provide testing and observation services during construction to help determine that the design requirements are fulfilled. 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 the generally accepted standard of care for the profession. No warranties express or implied, are made. The conclusions and recommendations contained in this report should not be considered valid in the event that any changes in the nature, design or location of the project as outlined in Geotechnical Subsurface Exploration and Pavement Design Report 317-321 Sherwood Street Alleyway Pavements Fort Collins, Colorado Soilogic # 17-1053 8 this report are planned, unless those changes are reviewed and the conclusions of this report modified and verified in writing by the geotechnical engineer. We appreciate the opportunity to be of service to you on this project. If you have any questions concerning the enclosed information or if we can be of further assistance to you in any way, please do not hesitate to contact us. Very Truly Yours, Soilogic, Inc. Reviewed by: Wolf von Carlowitz, P.E. Darrel DiCarlo, P.E. Principal Engineer Senior Project Engineer 36746 44271 LOG OF BORING B-2 1/1 CME 45 4" CFA Automatic CP/ZG Estimated Swell % Passing SOIL DESCRIPTION Depth "N" MC DD qu % Swell @ Pressure # 200 Sieve (ft) (%) (pcf) (psf) 500 psf (psf) LL PI (%) 6" RECYCLED ASPHALT PAVEMENT - SC-GC FILL - CLAYEY SAND AND GRAVEL 1 brown - 2 - 3 CS 11 18.9 108.2 9000+ 0.4% - - - - CL SILTY LEAN CLAY - light reddish brown 4 soft to stiff - 5 CS 5 19.6 96.3 6000 - - 34 15 80.3% - 6 - 7 - 8 CL-CH SANDY LEAN TO FAT CLAY - tan to light reddish brown 9 stiff - 10 CS 14 19.7 107.3 7000 - - - - - BOTTOM OF BORING 10' - 11 - 12 - 13 - 14 - 15 - 16 - 17 - 18 - 19 - 20 - 21 - 22 - 23 - 24 - 25 Sheet Drilling Rig: Water Depth Information 317-321 SHERWOOD STREET ALLEYWAY PAVEMENTS LOG OF BORING B-3 1/1 CME 45 4" CFA Automatic CP/ZG Estimated Swell % Passing SOIL DESCRIPTION Depth "N" MC DD qu % Swell @ Pressure # 200 Sieve (ft) (%) (pcf) (psf) 500 psf (psf) LL PI (%) 6" RECYCLED ASPHALT PAVEMENT - 1 - CL SILTY LEAN CLAY 2 brown - medium stiff 3 CS 8 17.6 110.8 9000+ 0.6% - - - - - 4 - 5 CS 7 18.5 100.3 9000+ - - - - - - 6 - 7 - CL-CH SANDY LEAN TO FAT CLAY 8 reddish brown - stiff 9 - 10 CS 16 18.6 111.3 9000+ - - - - - BOTTOM OF BORING 10' - 11 - 12 - 13 - 14 - 15 - 16 - 17 - 18 - 19 - 20 - 21 - 22 - 23 - 24 - 25 Sheet Drilling Rig: Water Depth Information 317-321 SHERWOOD STREET ALLEYWAY PAVEMENTS Liquid Limit - Plasticity Index - % Passing #200 - Dry Density (pcf) 108.2 317-321 SHERWOOD STREET ALLEYWAY PAVEMENTS FORT COLLINS, COLORADO Project # 17-1053 March 2017 SWELL/CONSOLIDATION TEST SUMMARY Sample ID: B-2 @ 2 Sample Description: (Swell Only) Initial Moisture 18.9% Final Moisture 19.5% % Swell @ 500 psf 0.4% Swell Pressure (psf) - -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 10 100 1000 10000 100000 --------- Applied Load (psf) Liquid Limit - Plasticity Index - % Passing #200 - Dry Density (pcf) 110.8 SWELL/CONSOLIDATION TEST SUMMARY 317-321 SHERWOOD STREET ALLEYWAY PAVEMENTS FORT COLLINS, COLORADO Project # 17-1053 March 2017 Initial Moisture 17.6% Sample ID: B-3 @ 2 Sample Description: (Swell Only) Final Moisture 19.1% % Swell @ 500 psf 0.6% Swell Pressure (psf) - -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 10 100 1000 10000 100000 --------- Applied Load (psf) UNIFIED SOIL CLASSIFICATION SYSTEM Criteria for Assigning Group Symbols and Group Names Using Laboratory TestsA Soil Classification Group Symbol Group NameB Clean Gravels Cu ! 4 and 1 " Cc " 3E GW Well graded gravelF Less than 5% finesC Cu < 4 and/or 1 > Cc > 3E GP Poorly graded gravelF Fines classify as ML or MH GM Silty gravelF,G, H Coarse Grained Soils More than 50% retained on No. 200 sieve Gravels More than 50% of coarse fraction retained on No. 4 sieve Gravels with Fines More than 12% finesC Fines classify as CL or CH GC Clayey gravelF,G,H Clean Sands Cu ! 6 and 1 " Cc " 3E SW Well graded sandI Less than 5% finesD Cu < 6 and/or 1 > Cc > 3E SP Poorly graded sandI Fines classify as ML or MH SM Silty sandG,H,I Sands 50% or more of coarse fraction passes No. 4 sieve Sands with Fines More than 12% finesD Fines classify as CL or CH SC Clayey sandG,H,I Silts and Clays PI > 7 and plots on or above “A” lineJ CL Lean clayK,L,M Liquid limit less than 50 Inorganic PI < 4 or plots below “A” lineJ ML SiltK,L,M Liquid limit - oven dried Organic clayK,L,M,N Fine-Grained Soils 50% or more passes the No. 200 sieve Organic Liquid limit - not dried < 0.75 OL Organic siltK,L,M,O Inorganic PI plots on or above “A” line CH Fat clayK,L,M Silts and Clays Liquid limit 50 or more PI plots below “A” line MH Elastic siltK,L,M Organic Liquid limit - oven dried Organic clayK,L,M,P Liquid limit - not dried < 0.75 OH Organic siltK,L,M,Q Highly organic soils Primarily organic matter, dark in color, and organic odor PT Peat A Based on the material passing the 3-in. (75-mm) sieve B If field sample contained cobbles or boulders, or both, add “with cobbles or boulders, or both” to group name. C Gravels with 5 to 12% fines require dual symbols: GW-GM well graded gravel with silt, GW-GC well graded gravel with clay, GP-GM poorly graded gravel with silt, GP-GC poorly graded gravel with clay. D Sands with 5 to 12% fines require dual symbols: SW-SM well graded sand with silt, SW-SC well graded sand with clay, SP-SM poorly graded sand with silt, SP-SC poorly graded sand with clay E Cu = D60/D10 Cc = GENERAL NOTES DRILLING & SAMPLING SYMBOLS: SS: Split Spoon - 1⅜" I.D., 2" O.D., unless otherwise noted HS: Hollow Stem Auger ST: Thin-Walled Tube – 2.5" O.D., unless otherwise noted PA: Power Auger RS: Ring Sampler - 2.42" I.D., 3" O.D., unless otherwise noted HA: Hand Auger CS: California Barrel - 1.92" I.D., 2.5" O.D., unless otherwise noted RB: Rock Bit BS: Bulk Sample or Auger Sample WB: Wash Boring or Mud Rotary The number of blows required to advance a standard 2-inch O.D. split-spoon sampler (SS) the last 12 inches of the total 18-inch penetration with a 140-pound hammer falling 30 inches is considered the “Standard Penetration” or “N-value”. For 2.5” O.D. California Barrel samplers (CB) the penetration value is reported as the number of blows required to advance the sampler 12 inches using a 140-pound hammer falling 30 inches, reported as “blows per inch,” and is not considered equivalent to the “Standard Penetration” or “N-value”. WATER LEVEL MEASUREMENT SYMBOLS: WL: Water Level WS: While Sampling WCI: Wet Cave in WD: While Drilling DCI: Dry Cave in BCR: Before Casing Removal AB: After Boring ACR: After Casing Removal Water levels indicated on the boring logs are the levels measured in the borings at the times indicated. Groundwater levels at other times and other locations across the site could vary. In pervious soils, the indicated levels may reflect the location of groundwater. In low permeability soils, the accurate determination of groundwater levels may not be possible with only short-term observations. DESCRIPTIVE SOIL CLASSIFICATION: Soil classification is based on the Unified Classification System. Coarse Grained Soils have more than 50% of their dry weight retained on a #200 sieve; their principal descriptors are: boulders, cobbles, gravel or sand. Fine Grained Soils have less than 50% of their dry weight retained on a #200 sieve; they are principally described as clays if they are plastic, and silts if they are slightly plastic or non-plastic. Major constituents may be added as modifiers and minor constituents may be added according to the relative proportions based on grain size. In addition to gradation, coarse-grained soils are defined on the basis of their in-place relative density and fine-grained soils on the basis of their consistency. FINE-GRAINED SOILS COARSE-GRAINED SOILS BEDROCK (CB) Blows/Ft. (SS) Blows/Ft. Consistency (CB) Blows/Ft. (SS) Blows/Ft. Relative Density (CB) Blows/Ft. (SS) Blows/Ft. Consistency < 3 0-2 Very Soft 0-5 < 3 Very Loose < 24 < 20 Weathered 3-5 3-4 Soft 6-14 4-9 Loose 24-35 20-29 Firm 6-10 5-8 Medium Stiff 15-46 10-29 Medium Dense 36-60 30-49 Medium Hard 11-18 9-15 Stiff 47-79 30-50 Dense 61-96 50-79 Hard 19-36 16-30 Very Stiff > 79 > 50 Very Dense > 96 > 79 Very Hard > 36 > 30 Hard RELATIVE PROPORTIONS OF SAND AND GRAVEL GRAIN SIZE TERMINOLOGY Descriptive Terms of Other Constituents Percent of Dry Weight Major Component of Sample Particle Size Trace < 15 Boulders Over 12 in. (300mm) With 15 – 29 Cobbles 12 in. to 3 in. (300mm to 75 mm) Modifier > 30 Gravel 3 in. to #4 sieve (75mm to 4.75 mm) Sand Silt or Clay #4 to #200 sieve (4.75mm to 0.075mm) Passing #200 Sieve (0.075mm) RELATIVE PROPORTIONS OF FINES PLASTICITY DESCRIPTION Descriptive Terms of Other Constituents Percent of Dry Weight Term Plasticity Index Trace With Modifiers < 5 5 – 12 > 12 Non-plastic Low Medium High 0 1-10 11-30 30+ F If soil contains ! 15% sand, add “with sand” to group name. G If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM. HIf fines are organic, add “with organic fines” to group name. I If soil contains ! 15% gravel, add “with gravel” to group name. J If Atterberg limits plot in shaded area, soil is a CL-ML, silty clay. K If soil contains 15 to 29% plus No. 200, add “with sand” or “with gravel,” whichever is predominant. L If soil contains ! 30% plus No. 200 predominantly sand, add “sandy” to group name. M If soil contains ! 30% plus No. 200, predominantly gravel, add “gravelly” to group name. N PI ! 4 and plots on or above “A” line. O PI < 4 or plots below “A” line. P PI plots on or above “A” line. Q PI plots below “A” line. FORT COLLINS, COLORADO Project # 17-1053 March 2017 USCS Sampler Atterberg Limits Start Date 3/6/2017 Auger Type: During Drilling None Finish Date 3/6/2017 Hammer Type: After Drilling None Surface Elev. - Field Personnel: 24 Hours After Drilling - FORT COLLINS, COLORADO Project # 17-1053 March 2017 USCS Sampler Atterberg Limits Start Date 3/6/2017 Auger Type: During Drilling None Finish Date 3/6/2017 Hammer Type: After Drilling None Surface Elev. - Field Personnel: 24 Hours After Drilling -