GEOTECHNICAL GORDON ENGINEERING, INC. LETTER REPORT
G
GORDON GEOTECHNICAL ENGINEERING, INC.
2
LETTER REPORT GEOTECHNICAL PAVEMENT DESIGN STUDY ROADWAY OVERLAYS AND FULL-DEPTH REPLACEMENTS FOR FORT DOUGLAS BOULEVARD AND CONNOR ROAD UNIVERSITY OF UTAH SALT LAKE CITY, UTAH
October 23, 2015 Job No. 278-002-15
Prepared for: NV5 5217 South State Street, Suite 200 Murray, Utah 84107
John Staheli 04/26/2016
GEOLOGICAL ENGINEERING
Prepared by: Gordon Geotechnical Engineering, Inc. 4426 South Century Drive, Suite 100 Salt Lake City, Utah 84123 Tel: 801-327-9600 Fax: 801-327-9601 www.gordongeotech.com
GEOTECHNICAL ENGINEERING
ENVIRONMENTAL SERVICES
G
2
GORDON GEOTECHNICAL ENGINEERING, INC.
October 23, 2015 Job No. 278-002-15 NV5 5217 South State Street, Suite 200 Murray, Utah 84107 Attention:
Mr. Brandon Preece
Ladies and Gentlemen: Re:
Letter Report Geotechnical Pavement Design Study Roadway Overlays and Full-Depth Replacements for Fort Douglas Boulevard and Connor Road University of Utah Salt Lake City, Utah
1.
INTRODUCTION
1.1
GENERAL
This letter report presents the results of our geotechnical pavement design study performed at the site of the proposed roadway overlays and full-depth replacement at Fort Douglas Boulevard and Connor Road located at the University of Utah in Salt Lake City, Utah. The general location of the site with respect to major topographic features and existing facilities, as of 1998, is presented on Figure 1, Vicinity Map. A more detailed layout of the site showing the proposed construction as well as existing roadways and structures is presented on Figures 2 through 4, Site Plans. 1.2
OBJECTIVES AND SCOPE
The objectives and scope of our study were planned in discussions between Mr. Brandon Preece of NV5, and Mr. Patrick Emery of Gordon Geotechnical Engineering, Inc. (G2).
Gordon Geotechnical Engineering, Inc. 4426 South Century Drive, Suite 100 Salt Lake City, Utah 84123
GEOLOGICAL ENGINEERING
Tel: 801-327-9600 Fax: 801-327-9601 www.gordongeotech.com
GEOTECHNICAL ENGINEERING
ENVIRONMENTAL SERVICES
NV5 Job No. 278-002-15 Geotechnical Pavement Design Study October 23, 2015
G
2
GORDON GEOTECHNICAL ENGINEERING, INC.
In general, the objectives of this study were to: 1.
Provide appropriate earthwork and preliminary pavement recommendations to be utilized in the design and construction of the proposed pavement section.
In accomplishing these objectives, our scope has included the following:
1.3
1.
A field program consisting of a site visit to observe existing conditions.
2.
An office program consisting of the correlation of available data, engineering analyses, and the preparation of this summary report.
AUTHORIZATION
Authorization was provided verbally by Mr. Brandon Preece of NV5 for our Professional Services Agreement No. 15-0110-rev2 dated September 24, 2015 followed by a NV5 Professional Services Subconsultant Agreement dated October 5, 2015. 1.4
PROFESSIONAL STATEMENTS
Supporting data upon which our recommendations are based are presented in subsequent sections of this report. Recommendations presented herein are governed by the layout and design data discussed in Section 2., Proposed Construction, of this report. If subsurface conditions other than those described in this report are encountered and/or if design and layout changes are implemented, G2 must be informed so that our recommendations can be reviewed and amended, if necessary. Our professional services have been performed, our findings developed, and our recommendations prepared in accordance with generally accepted engineering principles and practices in this area at this time. 2.
PROPOSED CONSTRUCTION
The project is to consist of rehabilitating a distance of approximately 2,700 feet along Fort Douglas Boulevard and approximately 300 feet along Connor Road. The pavement rehabilitation will consist of an overlay of the majority of the Douglas Boulevard pavement section. All of the designated portion of Connor Road and a portion of Fort Douglas Boulevard will get a full-depth pavement replacement. The areas of the overlay and full-depth replacement are shown on Figures 2 through 4. A detailed traffic study was beyond the scope of this project. G2 developed a ‘rough estimate’ of the projected daily traffic based on 18,000 pound equivalent single-axle loads (ESALs). This
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Job No. 278-002-15 Geotechnical Pavement Design Study October 23, 2015
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GORDON GEOTECHNICAL ENGINEERING, INC.
traffic is projected through the year 2035. A tabulation of the projected traffic and associated ESALs is presented in the following table: Traffic Type
Number per day ESALs
Automobiles
2000/day
Light Trucks
100/day
Buses
up to 100/day
Delivery Trucks
up to 50/day
Total approximate ESALs per day - 75
Cuts and fills associated with the proposed pavements are not anticipated to exceed one to two feet. 3.
INVESTIGATIONS
3.1
FIELD PROGRAM
Due to State Historic Preservation Office (SHPO) restrictions, it has been requested that exploration borings be omitted from our scope of work. Therefore, a field program was not performed in conjunction with this study. Conservative pavement recommendations will be provided based on our past experience with nearby projects, including soil types and projected strength parameters. G2 has requested information on the existing pavement sections in the area. understanding that information on the existing construction is unavailable. 3.2
It is our
SITE VISIT
On October 19, 2015, a site visit was performed at Fort Douglas Boulevard and Connor Road. Although, a formal traffic study was not performed, numerous automobiles were counted on both roads during the site visit as well as multiple shuttle buses. It should be noted that, due to the axle configuration, buses can contribute significantly to the projected ESALs the roads will experience. The existing asphalt concrete roadways were observed and photographed. Pictures of the existing Fort Douglas Boulevard and Connor Road are presented on the attached figures, Photographs. It should be noted that areas of patching, cracking (spider and longitudinal), and subgrade failure were observed. Pictures of these specific pavement failures are also
Page 3
NV5 Job No. 278-002-15 Geotechnical Pavement Design Study October 23, 2015
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2
GORDON GEOTECHNICAL ENGINEERING, INC.
presented on Photographs. In general, it should be noted Fort Douglas Boulevard is in better condition than Connor Road. 3.3
SUBSURFACE SOIL AND GROUNDWATER
G2 has performed numerous geotechnical studies in the area. The soil conditions varied from silty clay with some sand to clayey sand and gravel. Conservative fine-grained soils are projected as the subsurface soils. Due to the lack of subsurface information, conservative soil strength parameters have been utilized. In general, groundwater tends to be deeper in this area. However, there is a potential for “perched” groundwater layers and artesian conditions. 4.
DISCUSSIONS AND RECOMMENDATIONS
4.1
SUMMARY OF FINDINGS
It is difficult to determine the cause of the roadway failure without knowing the existing pavement section and underlying subgrade soils. G2 projects that the roadway may not have been properly designed for the heavy bus traffic it is currently experiencing. During construction it is essential that a thorough investigation of the existing pavement section and subsurface conditions be performed to determine the cause of failure. When more detailed subsurface conditions information becomes available, we can rerun our analysis and update our recommendations accordingly. In the following sections, detailed discussions pertaining to pavements and earthwork are provided. 4.2
OVERLAY SECTIONS
G2 recommends that three options be considered for the pavement rehabilitation in the areas of the pavement overlays. Each option will need to be evaluated based on the conditions of the existing pavement and desired final grade of the finished pavement. In some locations, and for the desired final grade, it may be necessary to rebuild the pavement section in its entirety. They are: 1.
In areas that contain thick layers of asphalt concrete in good condition, rotomill the existing asphalt concrete pavements to the required depth, perforate, and evaluate the existing asphalt concrete prior to placing the new pavement overlay. Perforating the existing asphalt concrete will improve drainage.
2.
In areas that contain thick layers of asphalt concrete in poor condition, rotomill the existing asphalt concrete pavements to the required depth, place one inch of
Page 4
NV5
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Job No. 278-002-15 Geotechnical Pavement Design Study October 23, 2015
2
GORDON GEOTECHNICAL ENGINEERING, INC.
leveling course, and install a Glasgrid Pavement Reinforcement System prior to placing the new pavement overlay. 3.
In areas that contain thin layers of asphalt concrete in poor condition, rotomill the existing asphalt concrete pavements to the required depth and place a new pavement overlay, ensuring that there is a minimum of 6.0 inches of asphalt concrete overlying 8.0 inches of base course and 12.0 inches of granular subbase. If the existing asphalt concrete pavements are completely removed, the exposed road base or subbase must be proofrolled in order to identify soft spots.
These options will also depend on the quality of asphalt concrete that is exposed after rotomilling. If the exposed asphalt concrete is in poor condition, the asphalt concrete may need to be removed. 4.3
FULL REPLACEMENT SECTIONS
Based upon projected traffic and recommendations are presented below:
subsurface
conditions,
the
pavement
section
Roadways (Moderate to Moderately High Volume of Automobiles and Light Trucks, Light to Moderate Volume of Medium-Weight Vehicles, and Occasional to Low Volume of Heavy-Weight Trucks) [75 equivalent 18-kip axle loads per day] Flexible Pavement: (Asphalt Concrete)
*
6.0 inches
Asphalt concrete
6.0 inches
Aggregate base course
12.0 inches
Granular subbase*
Over
Properly prepared subgrade structural site grading fill
and/or
Granular subbase should consist of low plastic granular soils with a minimum CBR value of 20 percent.
The above pavement design recommendations are based on a calculated 75 ESALs per day for the two-lane roadway over a design life of 20 years. If more definitive traffic information
Page 5
NV5 Job No. 278-002-15 Geotechnical Pavement Design Study October 23, 2015
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2
GORDON GEOTECHNICAL ENGINEERING, INC.
becomes available, G2 must be notified to amend our recommendations as necessary. Additionally, once earthwork operations commence, G2 should be notified to observe the existing pavement and subsurface soil conditions at the site. 4.4
EARTHWORK
4.4.1
Site Preparation
Site preparation for the full replacement sections shall consist of the complete removal of all surface vegetation, topsoil, root bulbs, sod, rubbish, non-engineered fill, and any other deleterious materials from an area extending at least two feet beyond the perimeter of the proposed pavements areas. Vegetation and other deleterious materials should be removed from the site. Stripped topsoil will be unsuitable for structural fill but may be stockpiled for subsequent landscaping purposes. Subsequent to the above operations and prior to the placement of structural site grading fill, the exposed natural subgrade must be proofrolled by passing moderate-weight rubber tire-mounted construction equipment over the surface at least twice. In pavement areas, unsuitable soils encountered during recompaction and proofrolling must be removed to a maximum depth of two feet and replaced with compacted granular structural fill. All subgrade must be designed to provide positive drainage. This will increase the performance and lifetime of the new pavements. 4.4.2
Structural Fill
Structural fill is defined as all fill which will ultimately be subjected to structural loadings, such as imposed by pavements, etc. Structural fill will be required as backfill over utilities, as site grading fill. All structural fill must be free of sod, rubbish, topsoil, frozen soil, and other deleterious materials. Structural site grading fill is defined as fill placed over fairly large open areas to raise the overall site grade. For structural site grading fill, the maximum particle size should generally not exceed four inches; although, occasional larger particles, not exceeding six inches in diameter may be incorporated if placed randomly in a manner such that “honeycombing” does not occur and the desired degree of compaction can be achieved. The maximum particle size within structural fill placed within confined areas should generally be restricted to two inches. Only granular soils are recommended as structural fill in confined areas, such as within utility trenches.
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NV5 Job No. 278-002-15 Geotechnical Pavement Design Study October 23, 2015
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GORDON GEOTECHNICAL ENGINEERING, INC.
To stabilize soft subgrade conditions or where structural fill is required to be placed below a level one foot above the water table at the time of construction, a mixture of coarse gravels and cobbles and/or one and one-half- to two-inch gravel (stabilizing fill) should be utilized. Non-structural site grading fill is defined as all fill material not designated as structural fill and may consist of any cohesive or granular soils not containing excessive amounts of degradable material. 4.4.3
Fill Placement and Compaction
All structural fill should be placed in lifts not exceeding eight inches in loose thickness. Structural fills placed below the pavement section less than 5 feet thick, should be compacted to at least 95 percent of the maximum dry density as determined by the AASHTO1 T-180 (ASTM2 D-1557) compaction criteria. Structural fills greater than 5 feet thick, placed below the pavement section, should be compacted to at least 92 percent of the above-defined criteria. Structural fills greater than 10 feet thick are not anticipated at the site. Structural fills associated with the pavement section (base course and subbase) should be compacted to 96 percent and 95 percent, respectively, of the above-defined criteria. Coarse gravel and cobble mixtures (stabilizing fill), if utilized, shall be end-dumped, spread to a maximum loose lift thickness of 15 inches, and compacted by dropping a backhoe bucket onto the surface continuously at least twice. As an alternative, the fill may be compacted by passing moderately heavy construction equipment or large self-propelled compaction equipment at least twice. Subsequent fill material placed over the coarse gravels and cobbles shall be adequately placed so that the “fines” are “worked into” the voids in the underlying coarser gravels and cobbles. Non-structural fill may be placed in lifts not exceeding 12 inches in loose thickness and compacted by passing construction, spreading, or hauling equipment over the surface at least twice. 4.4.4
Utility Trenches
All utility trench backfill material below structurally loaded facilities (roads, etc.) should be placed at the same density requirements established for structural fill. If the surface of the backfill becomes disturbed during the course of construction, the backfill should be proofrolled and/or properly compacted prior to the construction of any exterior flatwork over a backfilled trench. Proofrolling may be performed by passing moderately loaded rubber tire-mounted construction equipment uniformly over the surface at least twice. If excessively loose or soft areas are 1 2
American Association of State Highway and Transportation Officials American Society for Testing and Materials Page 7
NV5
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~~~~~~~~~~~~~~~~~~~ ~ ·GORDON Job No. 278-002-15 Geotechnical Pavement Design Study October 23, 2015
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GEOTECHNICAL ENGINEERING, INC.
encountered during proofrolling, they should be removed to a maximum depth of two feet below design finish grade and replaced with structural fill . Most utility companies and City-County governments are now requiring that Type A-1 or A-1-a (AASHTO Designation - basically granular soils with limited fines) soils be used as backfill over utilities. These organizations are also requiring that in public roadways the backfill over major utilities be compacted over the full depth of fill to at least 96 percent of the maximum dry density as determined by the AASHTO T -180 (ASTM 0-1557) method of compaction. We recommend that as the major utilities continue onto the site that these compaction specifications are followed. The natural fine-grained cohesive soils (if encountered) are not recommended for use as trench backfill. Some of the natural granular soils may be suitable for use as trench backfill (if encountered). 4.5
SITE VISITS
During construction G 2 must return to the site to observe the existing pavement sections and underlying subgrade soils so that we can adjust our recommendations, if necessary.
We appreciate the opportunity of providing this service for you. If you have any questions or require additional information, please do not hesitate to contact us. Respectfully submitted, Gordon Geotechnical Engineering, Inc.
f Utah No. 6252902
Patrick R. Emery, State of Uta --..;..,;;-=--Senior Engineer
JMW/PRE:sn
Encl.
Figure 1, Vicinity Map Figures 2 through 4, Site Plans Photographs
Addressee (1 + email)
Page 8
NV5 JOB NO. 278-002-15
CONNER ROAD
FORT DOUGLAS BOULEVARD
1000
SCALE IN FEET 0 1000
2000
REFERENCE: USGS 7.5 MINUTE TOPOGRAPHIC QUADRANGLE MAPS TITLED “FORT DOUGLAS, UTAH”, AND “SUGAR HOUSE, UTAH”, BOTH DATED 1998
FIGURE 1 VICINITY MAP
NV5 JOB NO. 278-002-15
KEY
S
LA
UG
DO
Connor Road (area of full-depth replacement)
RT
Fort Douglas Boulevard (area of full-depth replacement))
FO
Fort Douglas Boulevard (area of overlay)
D
AR
VE UL
BO
ER
NN
CO AD
RO
REFERENCE: ADAPTED FROM AERIAL PHOTOGRAPH DOWNLOADED FROM 2015 GOOGLE EARTH IMAGERY DATED JUNE 16, 2015
SCALE:
feet km
FIGURE 2 SITE PLAN 1
4000
NV5 JOB NO. 278-002-15
FORT DOUGLAS BOULEVARD KEY Fort Douglas Boulevard (area of overlay) Fort Douglas Boulevard (area of full-depth replacement)
FORT DOUGLAS BOULEVARD
REFERENCE: ADAPTED FROM DRAWING ENTITLED “FORT DOUGLAS BOULEVARD, UNIVERSITY OF UTAH ROADWAY OVERALL”, SHEET NO. C-201 BY NV5, DATED JUNE 2015
FIGURE 3
NV5 JOB NO. 278-002-15
CONNER ROAD KEY Conner Road (area of full-depth replacement)
CONNER ROAD
REFERENCE: ADAPTED FROM DRAWING ENTITLED “CONNER STREET, UNIVERSITY OF UTAH ROADWAY SITE PLAN”, SHEET NO. C-201 BY NV5, DATED SEPTEMBER 2015
FIGURE 4
NV5 JOB NO. 278-002-15
FORT DOUGLAS BOULEVARD PHOTOGRAPHS
NV5 JOB NO. 278-002-15
CONNER ROAD PHOTOGRAPHS
GORDON GEOTECHNICAL ENGINEERING, INC.
2
LETTER REPORT GEOTECHNICAL PAVEMENT DESIGN STUDY ROADWAY OVERLAYS AND FULL-DEPTH REPLACEMENTS FOR FORT DOUGLAS BOULEVARD AND CONNOR ROAD UNIVERSITY OF UTAH SALT LAKE CITY, UTAH
October 23, 2015 Job No. 278-002-15
Prepared for: NV5 5217 South State Street, Suite 200 Murray, Utah 84107
John Staheli 04/26/2016
GEOLOGICAL ENGINEERING
Prepared by: Gordon Geotechnical Engineering, Inc. 4426 South Century Drive, Suite 100 Salt Lake City, Utah 84123 Tel: 801-327-9600 Fax: 801-327-9601 www.gordongeotech.com
GEOTECHNICAL ENGINEERING
ENVIRONMENTAL SERVICES
G
2
GORDON GEOTECHNICAL ENGINEERING, INC.
October 23, 2015 Job No. 278-002-15 NV5 5217 South State Street, Suite 200 Murray, Utah 84107 Attention:
Mr. Brandon Preece
Ladies and Gentlemen: Re:
Letter Report Geotechnical Pavement Design Study Roadway Overlays and Full-Depth Replacements for Fort Douglas Boulevard and Connor Road University of Utah Salt Lake City, Utah
1.
INTRODUCTION
1.1
GENERAL
This letter report presents the results of our geotechnical pavement design study performed at the site of the proposed roadway overlays and full-depth replacement at Fort Douglas Boulevard and Connor Road located at the University of Utah in Salt Lake City, Utah. The general location of the site with respect to major topographic features and existing facilities, as of 1998, is presented on Figure 1, Vicinity Map. A more detailed layout of the site showing the proposed construction as well as existing roadways and structures is presented on Figures 2 through 4, Site Plans. 1.2
OBJECTIVES AND SCOPE
The objectives and scope of our study were planned in discussions between Mr. Brandon Preece of NV5, and Mr. Patrick Emery of Gordon Geotechnical Engineering, Inc. (G2).
Gordon Geotechnical Engineering, Inc. 4426 South Century Drive, Suite 100 Salt Lake City, Utah 84123
GEOLOGICAL ENGINEERING
Tel: 801-327-9600 Fax: 801-327-9601 www.gordongeotech.com
GEOTECHNICAL ENGINEERING
ENVIRONMENTAL SERVICES
NV5 Job No. 278-002-15 Geotechnical Pavement Design Study October 23, 2015
G
2
GORDON GEOTECHNICAL ENGINEERING, INC.
In general, the objectives of this study were to: 1.
Provide appropriate earthwork and preliminary pavement recommendations to be utilized in the design and construction of the proposed pavement section.
In accomplishing these objectives, our scope has included the following:
1.3
1.
A field program consisting of a site visit to observe existing conditions.
2.
An office program consisting of the correlation of available data, engineering analyses, and the preparation of this summary report.
AUTHORIZATION
Authorization was provided verbally by Mr. Brandon Preece of NV5 for our Professional Services Agreement No. 15-0110-rev2 dated September 24, 2015 followed by a NV5 Professional Services Subconsultant Agreement dated October 5, 2015. 1.4
PROFESSIONAL STATEMENTS
Supporting data upon which our recommendations are based are presented in subsequent sections of this report. Recommendations presented herein are governed by the layout and design data discussed in Section 2., Proposed Construction, of this report. If subsurface conditions other than those described in this report are encountered and/or if design and layout changes are implemented, G2 must be informed so that our recommendations can be reviewed and amended, if necessary. Our professional services have been performed, our findings developed, and our recommendations prepared in accordance with generally accepted engineering principles and practices in this area at this time. 2.
PROPOSED CONSTRUCTION
The project is to consist of rehabilitating a distance of approximately 2,700 feet along Fort Douglas Boulevard and approximately 300 feet along Connor Road. The pavement rehabilitation will consist of an overlay of the majority of the Douglas Boulevard pavement section. All of the designated portion of Connor Road and a portion of Fort Douglas Boulevard will get a full-depth pavement replacement. The areas of the overlay and full-depth replacement are shown on Figures 2 through 4. A detailed traffic study was beyond the scope of this project. G2 developed a ‘rough estimate’ of the projected daily traffic based on 18,000 pound equivalent single-axle loads (ESALs). This
Page 2
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Job No. 278-002-15 Geotechnical Pavement Design Study October 23, 2015
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GORDON GEOTECHNICAL ENGINEERING, INC.
traffic is projected through the year 2035. A tabulation of the projected traffic and associated ESALs is presented in the following table: Traffic Type
Number per day ESALs
Automobiles
2000/day
Light Trucks
100/day
Buses
up to 100/day
Delivery Trucks
up to 50/day
Total approximate ESALs per day - 75
Cuts and fills associated with the proposed pavements are not anticipated to exceed one to two feet. 3.
INVESTIGATIONS
3.1
FIELD PROGRAM
Due to State Historic Preservation Office (SHPO) restrictions, it has been requested that exploration borings be omitted from our scope of work. Therefore, a field program was not performed in conjunction with this study. Conservative pavement recommendations will be provided based on our past experience with nearby projects, including soil types and projected strength parameters. G2 has requested information on the existing pavement sections in the area. understanding that information on the existing construction is unavailable. 3.2
It is our
SITE VISIT
On October 19, 2015, a site visit was performed at Fort Douglas Boulevard and Connor Road. Although, a formal traffic study was not performed, numerous automobiles were counted on both roads during the site visit as well as multiple shuttle buses. It should be noted that, due to the axle configuration, buses can contribute significantly to the projected ESALs the roads will experience. The existing asphalt concrete roadways were observed and photographed. Pictures of the existing Fort Douglas Boulevard and Connor Road are presented on the attached figures, Photographs. It should be noted that areas of patching, cracking (spider and longitudinal), and subgrade failure were observed. Pictures of these specific pavement failures are also
Page 3
NV5 Job No. 278-002-15 Geotechnical Pavement Design Study October 23, 2015
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2
GORDON GEOTECHNICAL ENGINEERING, INC.
presented on Photographs. In general, it should be noted Fort Douglas Boulevard is in better condition than Connor Road. 3.3
SUBSURFACE SOIL AND GROUNDWATER
G2 has performed numerous geotechnical studies in the area. The soil conditions varied from silty clay with some sand to clayey sand and gravel. Conservative fine-grained soils are projected as the subsurface soils. Due to the lack of subsurface information, conservative soil strength parameters have been utilized. In general, groundwater tends to be deeper in this area. However, there is a potential for “perched” groundwater layers and artesian conditions. 4.
DISCUSSIONS AND RECOMMENDATIONS
4.1
SUMMARY OF FINDINGS
It is difficult to determine the cause of the roadway failure without knowing the existing pavement section and underlying subgrade soils. G2 projects that the roadway may not have been properly designed for the heavy bus traffic it is currently experiencing. During construction it is essential that a thorough investigation of the existing pavement section and subsurface conditions be performed to determine the cause of failure. When more detailed subsurface conditions information becomes available, we can rerun our analysis and update our recommendations accordingly. In the following sections, detailed discussions pertaining to pavements and earthwork are provided. 4.2
OVERLAY SECTIONS
G2 recommends that three options be considered for the pavement rehabilitation in the areas of the pavement overlays. Each option will need to be evaluated based on the conditions of the existing pavement and desired final grade of the finished pavement. In some locations, and for the desired final grade, it may be necessary to rebuild the pavement section in its entirety. They are: 1.
In areas that contain thick layers of asphalt concrete in good condition, rotomill the existing asphalt concrete pavements to the required depth, perforate, and evaluate the existing asphalt concrete prior to placing the new pavement overlay. Perforating the existing asphalt concrete will improve drainage.
2.
In areas that contain thick layers of asphalt concrete in poor condition, rotomill the existing asphalt concrete pavements to the required depth, place one inch of
Page 4
NV5
G
Job No. 278-002-15 Geotechnical Pavement Design Study October 23, 2015
2
GORDON GEOTECHNICAL ENGINEERING, INC.
leveling course, and install a Glasgrid Pavement Reinforcement System prior to placing the new pavement overlay. 3.
In areas that contain thin layers of asphalt concrete in poor condition, rotomill the existing asphalt concrete pavements to the required depth and place a new pavement overlay, ensuring that there is a minimum of 6.0 inches of asphalt concrete overlying 8.0 inches of base course and 12.0 inches of granular subbase. If the existing asphalt concrete pavements are completely removed, the exposed road base or subbase must be proofrolled in order to identify soft spots.
These options will also depend on the quality of asphalt concrete that is exposed after rotomilling. If the exposed asphalt concrete is in poor condition, the asphalt concrete may need to be removed. 4.3
FULL REPLACEMENT SECTIONS
Based upon projected traffic and recommendations are presented below:
subsurface
conditions,
the
pavement
section
Roadways (Moderate to Moderately High Volume of Automobiles and Light Trucks, Light to Moderate Volume of Medium-Weight Vehicles, and Occasional to Low Volume of Heavy-Weight Trucks) [75 equivalent 18-kip axle loads per day] Flexible Pavement: (Asphalt Concrete)
*
6.0 inches
Asphalt concrete
6.0 inches
Aggregate base course
12.0 inches
Granular subbase*
Over
Properly prepared subgrade structural site grading fill
and/or
Granular subbase should consist of low plastic granular soils with a minimum CBR value of 20 percent.
The above pavement design recommendations are based on a calculated 75 ESALs per day for the two-lane roadway over a design life of 20 years. If more definitive traffic information
Page 5
NV5 Job No. 278-002-15 Geotechnical Pavement Design Study October 23, 2015
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2
GORDON GEOTECHNICAL ENGINEERING, INC.
becomes available, G2 must be notified to amend our recommendations as necessary. Additionally, once earthwork operations commence, G2 should be notified to observe the existing pavement and subsurface soil conditions at the site. 4.4
EARTHWORK
4.4.1
Site Preparation
Site preparation for the full replacement sections shall consist of the complete removal of all surface vegetation, topsoil, root bulbs, sod, rubbish, non-engineered fill, and any other deleterious materials from an area extending at least two feet beyond the perimeter of the proposed pavements areas. Vegetation and other deleterious materials should be removed from the site. Stripped topsoil will be unsuitable for structural fill but may be stockpiled for subsequent landscaping purposes. Subsequent to the above operations and prior to the placement of structural site grading fill, the exposed natural subgrade must be proofrolled by passing moderate-weight rubber tire-mounted construction equipment over the surface at least twice. In pavement areas, unsuitable soils encountered during recompaction and proofrolling must be removed to a maximum depth of two feet and replaced with compacted granular structural fill. All subgrade must be designed to provide positive drainage. This will increase the performance and lifetime of the new pavements. 4.4.2
Structural Fill
Structural fill is defined as all fill which will ultimately be subjected to structural loadings, such as imposed by pavements, etc. Structural fill will be required as backfill over utilities, as site grading fill. All structural fill must be free of sod, rubbish, topsoil, frozen soil, and other deleterious materials. Structural site grading fill is defined as fill placed over fairly large open areas to raise the overall site grade. For structural site grading fill, the maximum particle size should generally not exceed four inches; although, occasional larger particles, not exceeding six inches in diameter may be incorporated if placed randomly in a manner such that “honeycombing” does not occur and the desired degree of compaction can be achieved. The maximum particle size within structural fill placed within confined areas should generally be restricted to two inches. Only granular soils are recommended as structural fill in confined areas, such as within utility trenches.
Page 6
NV5 Job No. 278-002-15 Geotechnical Pavement Design Study October 23, 2015
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2
GORDON GEOTECHNICAL ENGINEERING, INC.
To stabilize soft subgrade conditions or where structural fill is required to be placed below a level one foot above the water table at the time of construction, a mixture of coarse gravels and cobbles and/or one and one-half- to two-inch gravel (stabilizing fill) should be utilized. Non-structural site grading fill is defined as all fill material not designated as structural fill and may consist of any cohesive or granular soils not containing excessive amounts of degradable material. 4.4.3
Fill Placement and Compaction
All structural fill should be placed in lifts not exceeding eight inches in loose thickness. Structural fills placed below the pavement section less than 5 feet thick, should be compacted to at least 95 percent of the maximum dry density as determined by the AASHTO1 T-180 (ASTM2 D-1557) compaction criteria. Structural fills greater than 5 feet thick, placed below the pavement section, should be compacted to at least 92 percent of the above-defined criteria. Structural fills greater than 10 feet thick are not anticipated at the site. Structural fills associated with the pavement section (base course and subbase) should be compacted to 96 percent and 95 percent, respectively, of the above-defined criteria. Coarse gravel and cobble mixtures (stabilizing fill), if utilized, shall be end-dumped, spread to a maximum loose lift thickness of 15 inches, and compacted by dropping a backhoe bucket onto the surface continuously at least twice. As an alternative, the fill may be compacted by passing moderately heavy construction equipment or large self-propelled compaction equipment at least twice. Subsequent fill material placed over the coarse gravels and cobbles shall be adequately placed so that the “fines” are “worked into” the voids in the underlying coarser gravels and cobbles. Non-structural fill may be placed in lifts not exceeding 12 inches in loose thickness and compacted by passing construction, spreading, or hauling equipment over the surface at least twice. 4.4.4
Utility Trenches
All utility trench backfill material below structurally loaded facilities (roads, etc.) should be placed at the same density requirements established for structural fill. If the surface of the backfill becomes disturbed during the course of construction, the backfill should be proofrolled and/or properly compacted prior to the construction of any exterior flatwork over a backfilled trench. Proofrolling may be performed by passing moderately loaded rubber tire-mounted construction equipment uniformly over the surface at least twice. If excessively loose or soft areas are 1 2
American Association of State Highway and Transportation Officials American Society for Testing and Materials Page 7
NV5
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~~~~~~~~~~~~~~~~~~~ ~ ·GORDON Job No. 278-002-15 Geotechnical Pavement Design Study October 23, 2015
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GEOTECHNICAL ENGINEERING, INC.
encountered during proofrolling, they should be removed to a maximum depth of two feet below design finish grade and replaced with structural fill . Most utility companies and City-County governments are now requiring that Type A-1 or A-1-a (AASHTO Designation - basically granular soils with limited fines) soils be used as backfill over utilities. These organizations are also requiring that in public roadways the backfill over major utilities be compacted over the full depth of fill to at least 96 percent of the maximum dry density as determined by the AASHTO T -180 (ASTM 0-1557) method of compaction. We recommend that as the major utilities continue onto the site that these compaction specifications are followed. The natural fine-grained cohesive soils (if encountered) are not recommended for use as trench backfill. Some of the natural granular soils may be suitable for use as trench backfill (if encountered). 4.5
SITE VISITS
During construction G 2 must return to the site to observe the existing pavement sections and underlying subgrade soils so that we can adjust our recommendations, if necessary.
We appreciate the opportunity of providing this service for you. If you have any questions or require additional information, please do not hesitate to contact us. Respectfully submitted, Gordon Geotechnical Engineering, Inc.
f Utah No. 6252902
Patrick R. Emery, State of Uta --..;..,;;-=--Senior Engineer
JMW/PRE:sn
Encl.
Figure 1, Vicinity Map Figures 2 through 4, Site Plans Photographs
Addressee (1 + email)
Page 8
NV5 JOB NO. 278-002-15
CONNER ROAD
FORT DOUGLAS BOULEVARD
1000
SCALE IN FEET 0 1000
2000
REFERENCE: USGS 7.5 MINUTE TOPOGRAPHIC QUADRANGLE MAPS TITLED “FORT DOUGLAS, UTAH”, AND “SUGAR HOUSE, UTAH”, BOTH DATED 1998
FIGURE 1 VICINITY MAP
NV5 JOB NO. 278-002-15
KEY
S
LA
UG
DO
Connor Road (area of full-depth replacement)
RT
Fort Douglas Boulevard (area of full-depth replacement))
FO
Fort Douglas Boulevard (area of overlay)
D
AR
VE UL
BO
ER
NN
CO AD
RO
REFERENCE: ADAPTED FROM AERIAL PHOTOGRAPH DOWNLOADED FROM 2015 GOOGLE EARTH IMAGERY DATED JUNE 16, 2015
SCALE:
feet km
FIGURE 2 SITE PLAN 1
4000
NV5 JOB NO. 278-002-15
FORT DOUGLAS BOULEVARD KEY Fort Douglas Boulevard (area of overlay) Fort Douglas Boulevard (area of full-depth replacement)
FORT DOUGLAS BOULEVARD
REFERENCE: ADAPTED FROM DRAWING ENTITLED “FORT DOUGLAS BOULEVARD, UNIVERSITY OF UTAH ROADWAY OVERALL”, SHEET NO. C-201 BY NV5, DATED JUNE 2015
FIGURE 3
NV5 JOB NO. 278-002-15
CONNER ROAD KEY Conner Road (area of full-depth replacement)
CONNER ROAD
REFERENCE: ADAPTED FROM DRAWING ENTITLED “CONNER STREET, UNIVERSITY OF UTAH ROADWAY SITE PLAN”, SHEET NO. C-201 BY NV5, DATED SEPTEMBER 2015
FIGURE 4
NV5 JOB NO. 278-002-15
FORT DOUGLAS BOULEVARD PHOTOGRAPHS
NV5 JOB NO. 278-002-15
CONNER ROAD PHOTOGRAPHS
