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HomeMy WebLinkAboutCity of San Luis Obispo Transit Yard Pavement Rehabilitation Report PAVEMENT REHABILITATION REPORT CITY OF SAN LUIS OBISPO – TRANSIT YARD PAVEMENT REHABILITATION SAN LUIS OBISPO, CALIFORNIA May 30, 2025 Prepared for Ms. Emma Laplante City of San Luis Obispo Prepared by Earth Systems Pacific 4378 Old Santa Fe Road San Luis Obispo, CA 93401 Copyright © 2025 ii May 30, 2025 File No.: 307146-001 Ms. Emma Laplante City of San Luis Obispo 919 Palm Street San Luis Obispo, CA 93401 PROJECT: CITY OF SAN LUIS OBISPO – TRANSIT YARD PAVEMENT REHABILITATION SAN LUIS OBISPO, CALIFORNIA SUBJECT: Pavement Rehabilitation Report REF: Proposal for Pavement Exploration and Rehabilitation Recommendations, City of San Luis Obispo – Transit Yard Parking Lot Rehabilitation, San Luis Obispo, California, by Earth Systems Pacific, dated March 25, 2025, Doc. No. SLO-2503-051.PRP Dear Ms. Laplante: Per your authorization of the above-referenced proposal, this pavement rehabilitation report has been prepared for use in the development of plans and specifications for the pavement rehabilitation project located at the Transit Yard Parking Lot in San Luis Obispo, California. Preliminary geotechnical engineering recommendations for pavement reconstruction/rehabilitation are presented herein. An electronic copy of this report has been furnished for your use. We appreciate the opportunity to have provided professional services for this project and look forward to working with you again in the future. If there are any questions concerning this report, please do not hesitate to contact the undersigned. Sincerely, Earth Systems Pacific Robert Down, PE Robert Kompsie Sydney Johnson Principal Engineer Engineering Intern Project Manager Doc. No.: 2505-083.RPT/pm 307146-001 1 2505-083.RPT TABLE OF CONTENTS Page 1.0 SCOPE OF SERVICES ..................................................................................................... 1 2.0 EXISTING CONDITIONS ................................................................................................ 1 3.0 FIELD INVESTIGATION AND LABORATORY ANALYSIS ................................................... 1 4.0 SURFACE AND SUBSURFACE CONDITIONS .................................................................. 2 5.0 ANALYSIS AND RECOMMENDATIONS .......................................................................... 2 6.0 CLOSURE...................................................................................................................... 5 TECHNICAL REFERENCE LIST .................................................................................................... 6 APPENDICES APPENDIX A Figure 1 – Site Vicinity Map Figure 2 to 4 – Exploration Location Maps Boring Log Legend Boring Logs APPENDIX B Laboratory Test Results SLO Transit Yard – Pavement Rehabilitation May 30, 2025 San Luis Obispo, California 307146-001 1 2505-083.RPT 1.0 SCOPE OF SERVICES Our scope of services for this project was to perform subsurface exploration in the existing parking lot, measure the existing asphalt concrete (AC) and base sections and identify and sample the subgrade for the purpose of providing pavement rehabilitation recommendations. Asphalt concrete (AC) and aggregate base (AB) thicknesses were recorded and are reported herein. One subgrade sample was submitted to our laboratory for R-value testing, or resistance to deformation under repeated loading (ASTM D2844/D2844-13). Field reconnaissance and laboratory test data were then analyzed for the development of geotechnical recommendations for the project, including pavement section recommendations for reconstruction. 2.0 EXISTING CONDITIONS The site is the parking lot at the City of SLO Transit Yard, located off Prado Road and adjacent to Highway 101. The parking lot is entirely surfaced with AC and has an approximate area of 10,000 square feet. There are visible utility trenches and pavement patches that are identifiable by pavement joints and variable pavement surfaces and conditions. The pavement condition of the SLO Transit Yard parking lot is primarily characterized by oxidation, identified by lack of fines in the pavement surface, and alligator cracking which indicates base failure. Most of the parking lot is confined by an asphalt concrete (AC) dike. In the area behind the bus wash building, pavement repairs appeared to have been performed within the bus traffic wheel tracks. 3.0 FIELD INVESTIGATION AND LABORATORY ANALYSIS The subsurface investigation consisted of six exploratory borings drilled at the site on April 14, 2025. The borings were drilled to depths between 2.0-5.0 feet below the existing ground surface (bgs) with a truck-mounted Simco SP200 drill rig equipped with a 6-inch diameter solid-stem auger. As the borings were drilled, bulk soil samples were obtained from the auger cuttings. The approximate locations of the borings are shown on Figure 2 – Exploration Location Map in Appendix A. Soils encountered in the borings were categorized and logged in general accordance with the Unified Soil Classification System and ASTM D 2488-17. Logs of the borings are presented in Appendix A, along with a Boring Log Legend. In reviewing the boring logs and legend, the reader should recognize that the legend is intended as a guideline only, and there are a number of SLO Transit Yard – Pavement Rehabilitation May 30, 2025 San Luis Obispo, California 307146-001 2 2406-049.RPT conditions that may influence the characteristics observed during drilling. These include, but are not limited to, the presence of cobbles or boulders, cementation, variations in soil moisture, presence of groundwater, and other factors. Consequently, the logger must exercise judgment in interpreting soil characteristics, possibly resulting in soil descriptions that vary from the legend. One subgrade sample was tested for R-value (ASTM D 2844/D 2844M-18); the test result yielded an R-value of 9. The results of the laboratory test are presented in Appendix B. 4.0 SURFACE AND SUBSURFACE CONDITIONS Table 1 presents the pavement structural sections and subgrade conditions encountered in our borings. Table 1: Existing Pavement Structural Sections Boring No. Asphalt Concrete (inches) Aggregate Base (inches) Subgrade Soil or Rock Type 1 3.00 12.0 Sandy Lean Clay 2 3.00 12.0 Sandy Lean Clay 3A 3.00 12.0 Sandy Lean Clay 3B 5.00 0.0 Poorly Graded Sand 4 3.00 15.0 Sandy Fat Clay 5 3.00 15.0 Sandy Fat Clay† † R-value at B5: 9 Beneath the pavement structural sections, the borings generally encountered native soils, logged as alluvium. Native soils consisted of stiff to medium stiff sandy lean and fat clays. The boring logs in Appendix A contain a more complete description of the subsurface conditions encountered at the site. 5.0 ANALYSIS AND RECOMMENDATIONS Based upon the conditions encountered and our observations, the pavement failure of the roadway surface appears to be due to an inadequate structural section for the traffic loading and subsurface materials, and weathering and aging. The following recommendations for the parking lot at the SLO Transit Yard should be used to guide project plans and design. SLO Transit Yard – Pavement Rehabilitation May 30, 2025 San Luis Obispo, California 307146-001 3 2406-049.RPT The approximate AC pavement thicknesses range from about 3.0 to 5.0 inches. Aggregate base thicknesses ranged from 0.0 to 15.0 inches. While the roadway section thicknesses in some repaired areas, namely the wheel track repairs behind the bus wash, may be adequate for the current traffic loads, the pavement does not have the adequate structural section to support the current traffic loading. As the existing parking lot pavement has failed, our recommendation is to reconstruct the parking lot with conventional reconstruction. Reconstruction has numerous advantages, including addressing the underlying subgrade failures and providing the opportunity to correct grading and drainage problems. Pavement rehabilitation techniques such as full depth reclamation with chemical treatment were evaluated, but due to the size of the project, it is our opinion that this would not be a cost-effective recommendation. One R-value test was performed on subgrade material; the R-value test result was 9. We have included traditional reconstruction sections below in Table 2. These sections are based upon an R-value of 9 and a variety of traffic indices (T.I.s) ranging from 4.5 to 10.0. It should be noted that the following sections for conventional construction include 8 inches of subgrade processing and compaction to 95 percent relative compaction below the aggregate base section. Table 2: Traditional Roadway Reconstruction Sections (R-value of 9) Traffic Index (TI) HMA* (inches) Class 2 AB** (inches) 5.0 2.75 10.00 5.5 3.00 11.50 6.0 3.25 12.50 6.5 3.75 13.50 7.0 4.00 14.50 8.0 4.50 17.50 9.0 5.25 20.00 10.0 6.00 22.50 *Per Caltrans Section 39 **Per Caltrans Section 26 SLO Transit Yard – Pavement Rehabilitation May 30, 2025 San Luis Obispo, California 307146-001 4 2406-049.RPT Consideration could be given to constructing the parking lot with two different roadway sections: one for areas that will receive bus traffic and one for areas that will not. Further consideration could be given to using existing aggregate base and asphalt grindings as an aggregate subbase to provide potential cost savings. If this strategy is used, we recommend having the existing aggregate base/grindings blend tested for R-value during construction to verify that the structural section will meet the desired project outcomes. A minimum of 6 inches of fresh aggregate base should be constructed atop the subbase. The combined depth of the aggregate base and subbase should be planned to be 4 inches greater than the aggregate base depth recommended in Table 2. Additionally, we recommend increasing the minimum compaction specification to 92% relative compaction and specifying that hot mix asphalt contains liquid antistrip (LAS). General Pavement Recommendations 1.Wherever a new subgrade is established, the subgrade should be scarified a minimum of 8 inches, moisture conditioned to optimum or just above optimum moisture content, and compacted. The subgrade and all aggregate base should be compacted to a minimum of 95 percent of maximum dry density. Subgrade and aggregate base should be firm and unyielding when proof rolled with heavy, rubber-tire grading equipment prior to continuing construction. 2.Finished pavement surfaces should be sloped to freely drain toward appropriate drainage facilities. Water should not be allowed to stand or pond on or adjacent to pavement or other improvements as it could infiltrate into the aggregate base and/or subgrade, causing premature pavement deterioration. 3.To reduce migration of surface drainage into the subgrade, maintenance of pavement areas is critical. Any cracks that develop in the pavement should be promptly sealed. 4.A program of slurry sealing of the new pavement should be established based upon the City’s maintenance program. Typically, approximate 5-year increments are considered to be appropriate for application of slurry seals. 5.Where pavement edges are not constrained, asphalt or concrete curbs are recommended to be installed along the edge of the roadway. Curbs should be deepened to maintain a minimum setback distance of 5 feet from the outermost face of the curb to the face of any existing descending slope. SLO Transit Yard – Pavement Rehabilitation May 30, 2025 San Luis Obispo, California 307146-001 5 2406-049.RPT 6.To reduce potential for undermining of pavement sections, rodent activity should be aggressively controlled. 6.0 CLOSURE Our intent was to perform the investigation in a manner consistent with the level of care and skill ordinarily exercised by members of the profession currently practicing in the locality of this project and under similar conditions. No representation, warranty, or guarantee is either expressed or implied. This report is intended for the exclusive use by the client as discussed in the “Scope of Services” section. Application beyond the stated intent is strictly at the user's risk. This report is valid for conditions as they exist at this time for the type of project described herein. The conclusions and recommendations contained in this report could be rendered invalid, either in whole or in part, due to changes in building codes, regulations, standards of geotechnical or construction practice, changes in physical conditions, or the broadening of knowledge. If Earth Systems Pacific is not retained to provide construction observation and testing services, it shall not be responsible for the interpretation of the information by others or any consequences arising therefrom. If changes with respect to project type or location become necessary, if items not addressed in this report are incorporated into plans, or if any of the assumptions used in the preparation of this report are not correct, this firm shall be notified for modifications to this report. Any items not specifically addressed in this report should comply with the CBC (CBSC, 2022) and the requirements of the governing jurisdiction. The preliminary recommendations of this geotechnical report are based upon the geotechnical conditions encountered at the site and may be augmented by additional requirements of the architect/engineer, or by additional recommendations provided by the geotechnical engineer based on conditions exposed at the time of construction. This document, the data, conclusions, and recommendations contained herein are the property of Earth Systems Pacific. This report shall be used in its entirety, with no individual sections reproduced or used out of context. Copies may be made only by Earth Systems Pacific, the client, and the client’s authorized agents for use exclusively on the subject project. Any other use is subject to federal copyright laws and the written approval of Earth Systems Pacific. Thank you for this opportunity to have been of service. If you have any questions, please feel free to contact this office at your convenience. End of Text. SLO Transit Yard – Pavement Rehabilitation May 30, 2025 San Luis Obispo, California 307146-001 6 2406-049.RPT TECHNICAL REFERENCE LIST California Department of Transportation (Caltrans). 2023. "Standard Specifications." California Department of Transportation (Caltrans). 2018. “Flexible Pavement, Chapter 630.” Highway Design Manual. Google Earth. 2025. Google Earth [website], retrieved from: www.google.com/earth/index.html APPENDIX A Figure 1 – Site Vicinity Map Figure 2 to 4 – Exploration Location Maps Boring Log Legend Boring Logs Earth Systems Pacific4378 Old Santa Fe Road, San Luis Obispo, CA 93401www.earthsystems.com(805) 544-3276 Fax (805) 544-1786DateApril 2025Project No.307146-001Figure 1 of 2SITE VICINITY MAPCity of SLO Transit Yard - Parking Lot Rehabilitation29 Prado Road San Luis Obispo, CaliforniaNOT TO SCALEBASE MAP PROVIDED BY: Google Earth (2025)SITE Earth Systems Pacific4378 Old Santa Fe Road, San Luis Obispo, CA 93401www.earthsystems.com(805) 544-3276 Fax (805) 544-1786DateApril 2025Project No.307146-001Figure 2 of 2EXPLORATION LOCATION MAPCity of SLO Transit Yard - Parking Lot Rehabilitation29 Prado Road San Luis Obispo, CaliforniaNOT TO SCALEBASE MAP PROVIDED BY: Google Earth (2025)B1AB1Boring Location (Approx.)LegendB2B3B1BB4B5 drafting/masters/Boring Log Legend 062719.dwgUNIFIED SOIL CLASSIFICATION SYSTEM (ASTM D 2487) OBSERVED MOISTURE CONDITION DRY SLIGHTLY MOIST MOIST VERY MOIST WET (SATURATED) TYPICAL BEDROCK HARDNESS TYPICAL BEDROCK WEATHERING GRAIN SIZES CONSISTENCY DEPTH(feet)USCS CLASSSYMBOLINTERVAL(feet)SAMPLETYPEDRY DENSITY(pcf)MOISTURE(%)BLOWSPER 6 IN.SAMPLE DATA SOIL DESCRIPTION Earth Systems Pacific LEGEND: Ring Sample Grab Sample Shelby Tube Sample SPT NOTE: This log of subsurface conditions is a simplification of actual conditions encountered. It applies at the location and time of drilling. Subsurface conditions may differ at other locations and times. AUGER TYPE: 6" Solid Stem DRILL RIG: SIMCO EP200 with Automatic Hammer LOGGED BY: R. Kompsie 3.0" ASPHALT CONCRETE / 12.0" AGGREGATE BASE End of Boring @ 5.0' No subsurface water encountered PAGE 1 OF 1 Boring No. 1A JOB NO.: 307146-001 DATE: 04/14/2025 LEAN CLAY: dark brown, soft, slightly moist 2.0 - 3.0 City of SLO Transit Yard - Parking Lot Rehab 29 Prado Road San Luis Obispo, California CL FAT CLAY: dark grayish brown, firm, moistCH DEPTH(feet)USCS CLASSSYMBOLINTERVAL(feet)SAMPLETYPEDRY DENSITY(pcf)MOISTURE(%)BLOWSPER 6 IN.SAMPLE DATA SOIL DESCRIPTION Earth Systems Pacific LEGEND: Ring Sample Grab Sample Shelby Tube Sample SPT NOTE: This log of subsurface conditions is a simplification of actual conditions encountered. It applies at the location and time of drilling. Subsurface conditions may differ at other locations and times. AUGER TYPE: 6" Solid Stem DRILL RIG: SIMCO EP200 with Automatic Hammer LOGGED BY: R. Kompsie 5.0" ASPHALT CONCRETE / 0.0" AGGREGATE BASE End of Boring @ 2.0' No subsurface water encountered PAGE 1 OF 1 Boring No. 1B JOB NO.: 307146-001 DATE: 04/14/2025 WELL GRADED SAND: light grayish brown, loose, slightly moist (Fill) City of SLO Transit Yard - Parking Lot Rehab 29 Prado Road San Luis Obispo, California SW DEPTH(feet)USCS CLASSSYMBOLINTERVAL(feet)SAMPLETYPEDRY DENSITY(pcf)MOISTURE(%)BLOWSPER 6 IN.SAMPLE DATA SOIL DESCRIPTION Earth Systems Pacific LEGEND: Ring Sample Grab Sample Shelby Tube Sample SPT NOTE: This log of subsurface conditions is a simplification of actual conditions encountered. It applies at the location and time of drilling. Subsurface conditions may differ at other locations and times. AUGER TYPE: 6" Solid Stem DRILL RIG: SIMCO EP200 with Automatic Hammer LOGGED BY: R. Kompsie 3.0" ASPHALT CONCRETE / 12.0" AGGREGATE BASE End of Boring @ 5.0' No subsurface water encountered PAGE 1 OF 1 Boring No. 2 JOB NO.: 307146-001 DATE: 04/14/2025 LEAN CLAY: grayish dark brown, soft, moist City of SLO Transit Yard - Parking Lot Rehab 29 Prado Road San Luis Obispo, California CL firm, some gravel DEPTH(feet)USCS CLASSSYMBOLINTERVAL(feet)SAMPLETYPEDRY DENSITY(pcf)MOISTURE(%)BLOWSPER 6 IN.SAMPLE DATA SOIL DESCRIPTION Earth Systems Pacific LEGEND: Ring Sample Grab Sample Shelby Tube Sample SPT NOTE: This log of subsurface conditions is a simplification of actual conditions encountered. It applies at the location and time of drilling. Subsurface conditions may differ at other locations and times. AUGER TYPE: 6" Solid Stem DRILL RIG: SIMCO EP200 with Automatic Hammer LOGGED BY: R. Kompsie 3.0" ASPHALT CONCRETE / 12.0" AGGREGATE BASE End of Boring @ 5.0' No subsurface water encountered PAGE 1 OF 1 Boring No. 3 JOB NO.: 307146-001 DATE: 04/14/2025 LEAN CLAY: dark grayish brown, stiff, slightly moist City of SLO Transit Yard - Parking Lot Rehab 29 Prado Road San Luis Obispo, California CL moist DEPTH(feet)USCS CLASSSYMBOLINTERVAL(feet)SAMPLETYPEDRY DENSITY(pcf)MOISTURE(%)BLOWSPER 6 IN.SAMPLE DATA SOIL DESCRIPTION Earth Systems Pacific LEGEND: Ring Sample Grab Sample Shelby Tube Sample SPT NOTE: This log of subsurface conditions is a simplification of actual conditions encountered. It applies at the location and time of drilling. Subsurface conditions may differ at other locations and times. AUGER TYPE: 6" Solid Stem DRILL RIG: SIMCO EP200 with Automatic Hammer LOGGED BY: R. Kompsie 3.0" ASPHALT CONCRETE / 15.0" AGGREGATE BASE End of Boring @ 5.0' No subsurface water encountered PAGE 1 OF 1 Boring No. 4 JOB NO.: 307146-001 DATE: 04/14/2025 FAT CLAY: grayish dark brown, soft, slightly moist, some gravel 2.0 - 3.0 City of SLO Transit Yard - Parking Lot Rehab 29 Prado Road San Luis Obispo, California CH stiff DEPTH(feet)USCS CLASSSYMBOLINTERVAL(feet)SAMPLETYPEDRY DENSITY(pcf)MOISTURE(%)BLOWSPER 6 IN.SAMPLE DATA SOIL DESCRIPTION Earth Systems Pacific LEGEND: Ring Sample Grab Sample Shelby Tube Sample SPT NOTE: This log of subsurface conditions is a simplification of actual conditions encountered. It applies at the location and time of drilling. Subsurface conditions may differ at other locations and times. AUGER TYPE: 6" Solid Stem DRILL RIG: SIMCO EP200 with Automatic Hammer LOGGED BY: R. Kompsie 3.0" ASPHALT CONCRETE / 15.0" AGGREGATE BASE End of Boring @ 5.0' No subsurface water encountered PAGE 1 OF 1 Boring No. 5 JOB NO.: 307146-001 DATE: 04/14/2025 FAT CLAY: grayish dark brown, firm, slightly moist 2.0 - 3.0 City of SLO Transit Yard - Parking Lot Rehab 29 Prado Road San Luis Obispo, California CH some gravels 3.5 - 5.0LEAN CLAY: grayish dark brown, stiff, moistCL APPENDIX B Laboratory Test Results City of San Luis Obispo 307146-001 Transit Yard Parking Lot RESISTANCE 'R ' VALUE AND EXPANSION PRESSURE ASTM D 2844-18 May 29, 2025 Boring #5 @ 2.0 - 3.0'Dry Density @ 300 psi Exudation Pressure: 107.7-pcf Dark Brown Sandy Fat Clay (CH)% Moisture @ 300 psi Exudation Pressure: 24.2% R-Value - Exudation Pressure: 9 R-Value - Expansion Pressure: N/A R-Value @ Equilibrium: 9 0 10 20 0100200300400500R-VALUEEXUDATION PRESSURE, psi EXUDATION PRESSURE CHART 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0COVER THICKNESS BY EXUDATION PRESSURE, ftCOVER THICKNESS BY EXPANSION PRESSURE, ft EXPANSION PRESSURE CHART