HomeMy WebLinkAboutAtt 5B_Alternatives Analysis - Weir Road Bridge
Weir Road Culvert
Yarmouth, MA
Alternatives Analysis Report
Friends of Bass River
June 2024
Revised October 202 4
ALTERNATIVES ANALYSIS REPORT Tighe&Bond
Table of Contents
Table of Contents ....................................................................................................... 1
Introduction .............................................................................................................. 2
Existing Conditions and Constraints .............................................................................. 3
Survey & Site Review ............................................................................................... 3
Roadway Conditions ................................................................................................. 3
Hamblins Brook ....................................................................................................... 5
Hydrologic and Hydraulic (H&H) Analysis .................................................................... 5
Geotechnical Analysis ............................................................................................... 7
Permitting .............................................................................................................. 7
Traffic Management ............................................................................................... 10
Alternatives Analysis and Recommendations ................................................................ 11
Alternative 1: 24-foot Span Precast Concrete Arch..................................................... 12
Alternative 2: 24-foot Span Precast Concrete Arch with Raised Road ........................... 13
Alternative 3: 24-foot Span Precast Concrete Rigid Frame .......................................... 14
Alternative 4: 24-foot Span Prestressed Concrete Beams ........................................... 15
Summary and Opinion of Probable Construction Cost ................................................. 16
Recommendations ................................................................................................. 16
Appendix A: Conceptual Drawings (2024)
Appendix B: Field Report with Photograph Documentation (2020)
Appendix C: Hydrologic and Hydraulic Report (2024)
Appendix D: Geotechnical Report (2024)
Appendix E: Opinions of Probable Construction Cost (2024)
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Introduction
This report describes an evaluation of alternatives for replacement of the Weir Road Culvert
over Hamblins Brook in Yarmouth, Massachusetts as part of the Bass River Restoration
Project. Friends of Bass River (FOBR) obtained grant funding from the Division of Ecological
Restoration, and in turn requested that Tighe & Bond perform this conceptual study , thus
refining a previous version prepared in July 2021 which was funded through the Southeast
New England Program (SNEP) Watersheds Grant . The Yarmouth Community Preservation
Committee awarded grant funding to FOBR for preliminary design. A NOAA Coastal Zone
Habitat and Restoration Grant was announced, which will fund final design and construction.
The existing culvert carries Weir Road over Hamblins Brook flowing southwest to northeast.
The culvert length overall is approximately 36’-3” perpendicular to the roadway and consists
of stone slabs and piled stone walls. The approximate culvert opening varies between 1’-6”
wide with a rise of 2’-0” at the inlet and 3-feet wide with a rise of 2’-2” at the outlet. The
structure does not have a designated MassDOT culvert ID number.
The culvert is believed to have been constructed in the late 1800’s or early 1900’s. Drawings
for the existing structure are not available.
Proposed replacement of the Weir Road culvert is intended to be part of a larger project to
restore the Bass River, which includes upsizing the river crossing at North Dennis Road,
improving nutrient flushing of Mill Pond, and restoring wetlands along Hamblins Brook
between Miss Thatchers Pond and Mill Pond. The wetlands in this area consist of abandoned
cranberry bogs and a network of small streams. Restoration is intended to consolidate flows
to provide a continuous river. The purpose of the river restoration project is to provide
environmental improvements for the wetlands and waterway. R eplacing the existing structure
is required to maintain continuity of the stream under Weir Road.
Since the existing culvert is insufficient for required flows, is unsuitable for aquatic organism
passage, and is in overall poor condition, it was determined that rehabilitation of the existing
structure is not an option. The replacement structure on Weir Road will satisfy Massachusetts
River and Stream Crossing Standards (MARSCS) and accommodate proposed flows of the
restored river, as designed by Inter-Fluve, Inc.
The purpose of this Alternatives Analysis Report is to outline existing conditions that need to
be considered for a replacement structure, identify general replacement structure
alternatives, and provide conceptual costs for each alternative. This report describes site
conditions and constraints, including:
• A survey and site review
• Existing roadway conditions
• An analysis of hydrologic and hydraulic conditions
• A geotechnical analysis
• A discussion of permitting and environmental considerations
• Traffic management
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Existing Conditions and Constraints
Survey & Site Review
Survey data was collected by Inter-Fluve in October/November 2020. Survey data in the
vicinity of the culvert includes the road, culvert, guardrails, other surface features, edge of
water, and existing contours. Survey data is depicted on conceptual drawings included in
Appendix A.
Tighe & Bond conducted a visual field review of the site in April and November 2020 to
document existing conditions and verify general site conditions identified in the survey. A field
report containing photos with descriptions of findings is included in Appendix B.
The culvert is in poor condition overall with numerous deficiencies, including collapsed roof -
stones in the stream within the culvert, debris buildup, and settlement. The downstream
headwall is 8-feet tall with cracked or missing mortar, has missing stones with loss of backfill
material, and is heaving forward. Roadway fill material is degrading and eroding into the
stream through areas of missing stones or large gaps between stones. It is not possible to
review the interior of the culvert because stones ha ve collapsed into the waterway at both
ends, blocking visual access and the flow of water.
Portions of the culvert have already failed, and due to the lack of access to the interior, the
risk of full failure is unknown. However, if subject to high flows, further significant degradation
is likely.
Maintenance options for this partially collapsed structure are limited. Backfilling can be
performed to replace roadway materials that have eroded into the stream. The collapsed
stones prevent proper maintenance to the interior of the culvert.
Streamflows currently have found alternate paths around the stones but continue to erode
soils and the collapsed stones prevent aquatic and terrestrial organism passage.
Roadway Conditions
Weir Road is a Town-accepted road in the Town of Yarmouth, MA. It is classified as an urban
collector or rural minor collector by MassDOT. It provides an east-west connection between
Route 6A in the Yarmouth Port section of Yarmouth to North Dennis Road. According to the
Cape Cod Metropolitan Planning Organization (MPO), the average daily traffic (ADT) is 1,465
vehicles per day as of June 2009. The traffic volume is seasonal to an extent, with higher
traffic volumes during the summer vacation season.
Weir Road crosses Hamblins Brook between the junctions of Seminole Drive and Lexington
Lane. The horizontal alignment of the road at the culvert location is on a curve that is
superelevated. There is no speed limit posted, but for purposes of sight distance analysis,
30mph was assumed to be consistent in character to other nearby roads with posted speed
limits of 30mph. The existing roadway alignment does not provide the minimum horizontal
radius of 371 feet for the design speed as specified in AASHTO: A Policy on Geometric Design
of Highways and Streets.
The existing road is a two-lane road at the culvert location with a guardrail-to-guardrail width
of approximately 24’-0”. Each travel lane is approximately 10 feet wide and does not include
a striped shoulder. The travel lanes meet the minimum design criteria for travel lanes of a
collector classification, according to the 2006 MassDOT Project Development & Design Guide.
There are no pedestrian or bicycle accommodations on or nearby the existing structure. The
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pavement is in satisfactory condition. Notable intersections along Weir Road in the vicinity of
the culvert include:
• Seminole Drive, approx. 300 feet northwest of the culvert
• Private Driveway for 72 Seminole Drive, approx. 200 feet northwest of the culvert
• Private Driveway for 3 Lexington Lane, approx. 40 feet southeast of the culvert
• Private Driveway for 142 Weir Road, approx. 160 feet southeast of the culvert
• Lexington Lane, approx. 200 feet southeast of the culvert
Utilities at the site were identified by survey, dig-safe, and verified by the Town and include:
• Overhead electric- [Eversource Energy]
• Communications– [Cox]
• Underground Gas – [National Grid]
• Drainage Structures –Town of Yarmouth
• Water Main – Town of Yarmouth
A utility pole is located approximately 12 feet northwest of the upstream invert of the culvert
and therefore will need to be permanently relocated for all alternatives evaluated.
Additionally, the 2-inch gas main will need to be temporarily relocated during construction.
Based on discussions with the Water Superintendent, the water main can be taken offline
during construction which will avoid a temporary bypass and reconstructed as part of the new
structure. The gas and water main will need to be protected, and considerations for frost,
loads, and exposure to potential damage will need to be considered. Sewer lines are not
present at the site. The current alternatives make no accommodations for future sewer
retrofit.
The proposed roadway for the culvert replacement includes two 11-foot lanes with varying
minimum width shoulders to provide a total minimum roadway width of 25-feet. Although
sidewalks are not anticipated along each roadway approach, a sidewalk is included in the
proposed stream crossing, resulting in a 33’-9” wide structure. The sidewalk will provide
protection to buried utilities (i.e. gas and water).
The horizontal alignment of the roadway is proposed to remain in the existing location. This
is proposed to limit environmental impacts to the wetlands and stream as well as impacts to
private property and utilities. Since the horizontal alignment does not meet the design
requirements for the design speed, an advisory speed limit is suggested to warn drivers of
the sharp curve. Additionally, new guidelines in the MassDOT 2023 Project Development and
Design Guide provide allowance for consideration of a target speed in design of horizontal
geometry. The Town of Yarmouth has noted that residents complain about the high speeds of
vehicles and would prefer to implement an advisory speed limit around this curve.
These dimensions are in accordance with A Policy on Geometric Design of Highways and
Streets, 7th Edition. A roadway plan is included in Appendix A and an overview of the site is
shown below, in Figure 1.
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Figure 1- Overview of the Project Site (taken from google.com)
Hamblins Brook
Hamblins Brook flows from the southwest (upstream) to the northeast (downstream) at Weir
Road. The Brook was historically part of the Bass River and allowed free-flowing tide waters
from the Atlantic Ocean through Bass River and Mill Pond in the 1800’s. This allowed for an
ecosystem which thrived on the tidal influence that reached Weir Road and beyond, and it
included a large Herring population. In the early 1900’s, the wetlands area upstream of Mill
Pond was dammed and modified for cranberry farming. Flows are channelized through various
farming channels with control structures along Hamblins Brook. A goal of the Bass River
Restoration Project is to restore historic free-flowing hydraulic connectivity to Bass River to
restore the ecosystem and nutrient levels. The bankfull width of the Brook in the vicinity of
the culvert is 14 feet according to Inter-Fluve’s report included in Appendix C.
Hydrologic and Hydraulic (H&H) Analysis
Various Hydrologic and Hydraulic Analyses have been performed to support this project to
understand the tidal influence, the restoration of the wetland, and the upsizing of the culvert
structure. The H&H work completed to date includes the following:
• 2021 – Woods Hole Group Upper Bass River Restoration: Mill Pond & Crab Creek (Tidal
Flushing Analysis)
• 2021 – Inter-Fluve Bass River Headwaters Restoration Design Report
• 2021 – Tighe & Bond Preliminary H&H Modeling for Bridge Structure
• 2022 – Woods Hole Group Upper Bass River Restoration: Model Expansion &
Inundation Mapping
• 2024 – Woods Hole Group Upper Bass River Restoration, Hydraulic & Hydrologic Study
(Coastal H&H)
• 2024 – Tighe & Bond Upper Bass River Restoration, Hydraulic & Hydrologic Study
(Bridge Structure H&H)
Tighe & Bond’s Hydrologic and Hydraulic Analysis Report dated June 2024, and revised
September 2024, for the existing and proposed conditions at the Weir Road Culvert is included
Weir Road Culvert
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in Appendix C. The analysis built upon the evaluation performed by Inter-Fluve as part of the
Bass River Restoration Project and the coastal modeling performed by Woods Hole Group
(WHG) for the Bass River.
It is anticipated that the Bass River Restoration Project will include the removal of berms and
hydraulic barriers, resulting in tidally influenced saltwater flows at the culvert which will,
therefore, need to be designed for exposure to salt water. Furthermore, the widening of
structures downstream of Weir Road, including the proposed widening of North Dennis Road
culvert, will result in additional tidal flows that are anticipated at the Weir Road culvert. WHG’s
coastal analysis conservatively assumed that all of the downstream stream crossing
restrictions (Route 28, Highbank Road, CCRT, Route 6, and North Dennis Road) would be
upsized such that the proposed Weir Road structure can accommodate future conditions.
The proposed structure was evaluated for storm events in accordance with MassDOT LRFD
Bridge Manual standards for hydraulic design. These include 10% Average Exceedance
Probability (AEP) event for capacity with 2 feet of freeboard, a 4% AEP storm for scour design,
and a 2% AEP storm for scour check.
The stream configuration and bankfull width of 14 feet will generally not change as part of
Inter-Fluve’s bog restoration design in the vicinity of the culvert. MARSCS do not apply to
tidally-influenced streams, but were referenced as a basis of comparison between existing
conditions and proposed alternatives. Satisfying MARSCS would require a bridge span
greater than 16.8-feet to meet the 1.2 x bankfull requirement.
The improved stream could be relocated to a new alignment which in turn can help with
control of water during construction. However, a new stream alignment would negatively
impact existing driveways, utility poles, or right-of-way. Maintaining the existing alignment
was assumed for this report.
As part of the modeling performed by Woods Hole Group, coastal effects are considered as
part of the design alternatives. Effects include high tides, surges due to storms (i.e. tropical
storms and Nor’easters), and future Sea Level Rise (SLR). These consid erations are expected
to have increasing impacts as the restored river is reconnected to tidal flow at the location of
the bridge crossing.
A 24-foot span structure with a minimum low chord at 7.2 feet is determined to satisfy the
requirements of MassDOT to pass a 10% AEP frequency riverine storm event with an excess
of 2 feet of freeboard. However, it is not anticipated to provide adequate capacity to pass the
10% AEP coastal storm surge event without raising the low chord. Based on the Town's
desired level of service for the roadway, the low chord could be raised to 9.0 feet NAVD88 to
pass the 10% AEP coastal surge event with two feet of freeboard, but this would require
raising the roadway profile to an elevation of 12.2 feet NAVD88 to provide adequate headroom
for existing utilities, leading to additional environmental impacts that have not been
evaluated.
Scour was evaluated for the structure to inform the foundation depth and type. The scour
design storm (4% AEP storm) and the scour check storm (2% AEP storm) are anticipated to
be 1.8 feet and 3.3 feet, respectively. The bridge foundations will be constructed below the
anticipated design scour depths in accordance with MassDOT guidelines.
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Geotechnical Analysis
Tighe & Bond conducted a subsurface explorations program to evaluate the suitability of the
site’s subsurface conditions to support the proposed structure. Two borings (TB-1 and TB-2)
were drilled by New England Boring Contractors of Brockton, Massachusetts on October 19,
2020. Due to uncertainty in N-values in boring TB-1 and shallow completion depth of boring
TB-2, a supplemental geotechnical boring (TB-101) was drilled by Seaboard Drilling, LLC of
Chicopee, Massachusetts on June 12, 2023. Borings were advanced with 4-inch-diameter
flush-joint casing using drive-and-wash methods to depths of 54 feet, 11 feet, and 57 feet
below the existing ground surface. Split-spoon sampling and Standard Penetration Tests
(SPTs) were conducted continuously at depths of 9 to 19 feet, and at 5-foot intervals
elsewhere in boring TB-101.
Recovered soil samples were visually classified in the fiel d and eight mechanical particle size
analysis tests were performed in a laboratory. The Geotechnical Evaluation report is included
in Appendix D.
Subsurface conditions observed in the explorations generally consisted of 12 inches of asphalt
pavement, overlying approximately 4 to 9 feet of loose to medium dense existing fill, overlying
approximately 2 to 4 feet of very soft organic soils (fibrous peat), overlying loose to medium
dense, native sands, which were penetrated up to 48 feet before the explorations were
terminated.
Footings should bear a minimum of 4 feet below adjacent ground surface exposed to freezing
temperatures for frost protection, and the depth should consider scour depth. Shallow
foundations for the proposed bridge and wingwalls are anticipated to bear on native sands,
which are considered suitable bearing materials. Subgrades may be easily disturbed during
construction if they become wet; therefore, it is recommended that subgrades be over -
excavated by 6 to 12 inches to allow for placement of compacted Crushed Stone wrapped in
a nonwoven geotextile to provide a stable working subgrade.
Although the existing soils are considered suitable to support a shallow foundation system,
pile foundations are assumed for the purpose of this report for budgetary planning purposes
due to the organic and loose subsurface material that was encountered and low bearing
resistance to avoid settlement. The applied bearing pressure will be calculated during design
phase and suitability of spread footings will be reviewed, if viable. We assume that a deep
foundation system may be required to support the bridge. Technically feasible deep
foundation alternatives include driven pipe piles, driven taper piles, ductile iron pipe piles
(DIPs), and drilled micropiles (DMPs).
Due to the proximity of residences to the proposed replacement bridge, vibrations from
construction equipment will need to be carefully controlled and monitored. As such, micropiles
or DIPs are considered to be lower risk deep foundation alternatives as th ey can be installed
with minimal vibration compared to driven piles. If there are no “Made-in-America” provisions
associated with the project, DIPs are recommended as they are typically quicker and less
expensive to install than traditional micropiles with out producing drilling spoils.
Permitting
Proposed work for replacing the structure will require authorization under local, state, and
federal environmental regulations. Freshwater stream crossings are required to comply with
the Massachusetts Stream Crossing Standards to the maximum extent practicable, and are a
consideration for this site even though they are not required for tidally influenced stream
crossings.
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Wetland resource area boundaries were delineated by Tighe & Bond, Inc. on June 15, 2023
as part of this study in order to inform project design and support environmental permit
applications. For the purposes of identifying probable permits that will be required, t he
following types of wetlands are present at the site, but are not limited to:
• Bordering Vegetated Wetlands (BVW)
• Inland Bank/Mean Annual High Water
• Land Under Waterbodies and Waterways
• 200-foot Riverfront Area
• 100-foot Buffer Zone
Proposed work will occur within areas subject to protection and jurisdiction under local, state,
and federal regulatory programs. Based on the assumed wetland resources relative to the
proposed structure location, Table 1 below summarizes anticipated permit requirements. It is
likely that permits will be obtained jointly with the adjacent river restoration work, but the
following requirements are anticipated for the culvert replacement in and of itself.
TABLE 1
Summary of Anticipated Permits
Agency Permit, Review, or Approval
Local
Yarmouth Conservation Commission Order of Conditions under the Massachusetts Wetlands
Protection Act (MAWPA) and Yarmouth Wetlands
Regulations (Chapter 143)
State
Massachusetts Department of
Environmental Protection (MassDEP)
Superseding Order of Conditions (only required upon
appeal of local Order)
401 Water Quality Certification (if greater than 5,000 sf
of work, cumulatively, in Land Under Water, BVW and/or
IVW; or 100 cubic yards of dredging or more)
Chapter 91 Waterways License
Massachusetts Historical Commission
(MHC) & Massachusetts Board of
Underwater Archaeological Resources
(MABUAR)
Determination of No Adverse Effect (if filing Pre-
Construction Notification with the Corps)
Massachusetts Department of
Transportation (MassDOT)
Municipal Bridge Projects Massachusetts General Law
(MGL) Chapter 85 Section 35 Review Process
Federal
U.S. Army Corps of Engineers (Corps) Section 404 Self Verification (if less than 5,000 sf of work,
cumulatively, in land under water, BVW and/or IVW; or
other categorical triggers)
Section 404 Pre-Construction Notification (if greater than
5,000 sf of work, cumulatively, in land under water, BVW
and/or IVW; or other categorical triggers)
A Project Notification Form (PNF) will need to be prepared and submitted to the
Massachusetts Historical Commission (MHC), which serves as the State Historical Preservation
Office (SHPO), along with the geographically pertinent Tribal Historic Preservation Officers
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(THPOs) that have an interest in the area per the United States Army Corps of Engineers
(Corps) MA General Permit, and with the Massachusetts Board of Underwater Archaeological
Resources (MA BUAR).
A Chapter 91 Waterways License may also be required from MassDEP, as the replacement
structure may require licensing pursuant to 310 CMR 9.00.
A Notice of Intent (NOI) will be required for proposed work within jurisdictional resource
areas and the 100-foot Buffer Zone in accordance with the Massachusetts Wetlands Protection
Act (MAWPA) and Chapter 143. A site visit may be required as well as attendance at public
hearings with the Yarmouth Conservation Commission. The Order of Conditions (i.e., permit)
will need to be recorded at the Barnstable County Registry of Deeds.
Section 404 of the Clean Water Act is administered by the Corps. We anticipate that the
project will qualify for a Pre-Construction Notification under General Permits 1
(maintenance) and 14 (temporary construction, access, and dewatering).
Additionally, as part of the adjacent bog restoration, a certificate of the Secretary of Energy
and Environmental Affairs on the Expanded Environmental Notification Form (EENF)
pursuant to the Massachusetts Environmental Policy Act (MEPA) has been obtained and
is dated March 3, 2023.
Massachusetts River and Stream Crossing Standards
Massachusetts River and Stream Crossing Standards (MARSCS) do not apply to tidally -
influenced streams such as this one, but were referenced as a basis of comparison between
existing conditions and proposed alternatives. The MARSCS would require the span length to
be at least 1.2 times the bankfull width of the stream. The top width of the proposed channel
is 14 feet according to Inter-Fluve’s Design Report, leading to a minimum culvert width of
approximately 16.8 feet to meet MARSCS.
MARSCS are summarized below and are intended to be met to the greatest extent practicable
on this project to provide sufficient aquatic organism passage.
General standards include:
• Structure Type: Open bottom span or Bridge
• Embedment: Open bottom span or 2-feet embedment
• Span: Minimum 1.2 x bankfull width
• Substrate: Match stream substrate
• Water depth / velocity: Match natural parameters over a range of flows
• Openness ratio / height: 0.82 (General Standard)
2.46 / 8 ft (if wildlife passage inhibited
1.64 / 6 ft (otherwise)
• Banks: Match existing on both sides & no wildlife hinderance
Based upon standards set forth in the MARSCS, an openness (cross-sectional area divided by
the crossing length parallel to stream) of 1.64 feet is preferred since conditions that
significantly inhibit wildlife passage are not present at the site.
MassDOT Chapter 85 Section 35 Review
In accordance with Massachusetts General Law Chater 85 Section 35 “No bridge on a public
highway having a span in excess of ten feet, except a bridge constructed under the provisions
of chapter one hundred and fifty-nine, shall be constructed or reconstructed by any county or
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town except in accordance with plans and specifications therefor approved by the
department.” As such, these proposed alternatives resulting in a bridge span of 24 feet will
be subject to review and approval by MassDOT.
Traffic Management
The roadway will be closed throughout the entire duration of construction of the replacement
structure and a detour will be required. The proposed detour is anticipated to be Route 6A,
Union Street, Station Ave, Whites Path, North Main Street, North Dennis Road, and W Great
Western Road for a total detour length of 5.7 miles. Alternatively, Setucket Road and North
Dennis Road could be used for a total detour length of 4.2 miles.
In lieu of a full roadway closure, other options could be considered. These may be cost
prohibitive for the site and trigger additional permitting requirements. Accelerated Bridge
Construction (ABC) could be used to mitigate the closure duration, however, ABC is extremely
costly and not warranted for this rural site. Staged construction could also be used with lane
shifts and alternating single lanes of traffic. However, the existing roadway is narrow and
maintaining a portion of the fill over the existing buried structure would be challenging and
costly. Additionally, the proposed lane configuration is relatively narrow and buried structure
options would be challenging to backfill using stag ed construction.
A temporary bridge could be constructed at the site to limit the roadway closure. But in
addition to increased design and construction costs, the temporary alignment would have
substantial environmental impacts. It would be difficult to permit and would also lead to
challenging right-of-way takings and impacts.
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Alternatives Analysis and Recommendations
In this section, alternative structural types for the proposed culvert replacement are described
and evaluated. Four structural types/configurations that were evaluated are:
• Alternative 1: 24-foot span Precast Concrete Arch
• Alternative 2: 24-foot span Precast Concrete Arch with Raised Road
• Alternative 3: 24-foot span Precast Concrete Rigid Frame
• Alternative 4: 24-foot span Precast Prestressed Concrete Beams
Each alternative considered structural requirements, geometric recommendations outlined
previously, cost, and durability. All bridge components would be designed to support HL-93
live loading in accordance with AASHTO Load and Resistance Factor (LRFD) design criteria.
All alternatives satisfy MARSCS with open-bottom natural streambeds. It was assumed that
the existing horizontal and vertical alignments would remain, except for Alternative #2 which
includes a raised roadway profile.
All alternatives provide sufficient hydraulic capacity to pass a 10% AEP riverine event during
MHHW with over 2 feet of freeboard. However, the roadway would need to be raised to
accommodate raising the precast concrete arch structure to achieve 2 feet of freeboard during
a 10% AEP coastal storm event. Alternative 2 focuses on meeting this criterion.
The four alternatives are further described and evaluated below. A summary of conceptual
design Opinions of Probable Construction Cost and recommendations for further design
development are provided.
For reference, structure types that were considered but not further evaluated as part of this
analysis include:
• A series of pipe culverts: This would consist of numerous 2 to 6-foot diameter pipe
culverts in a series to convey flows. This option would not meet many of the MARSCS
and are not considered feasible due to environmental permitting requirements. This
alternative would also not be conducive to ecological improvements proposed for the
Bass River Restoration Project.
• Four-sided box culverts: Open bottom structures are preferred for MARSCS and a box
culvert would require deep embedment below the streambed. Box culverts are more
cost effective for spans under 10 feet and were not considered for the larger spans.
Each alternative includes precast concrete sections, which would be manufactured offsite in a
precast concrete plant and delivered to the site. Using precast components where possible
will reduce the construction schedule on -site by avoiding lengthy set up and cure times.
Precast concrete also provides a superior quality control compared to cast -in-place concrete
since it is fabricated in a facility with regulated climate and ideal casting conditions.
All of the structure types require minimal maintenance compared to larger bridges. Joints
may be avoided at the roadway level due to the short span with minimal thermal expansion
and contraction. Periodic cleaning and concrete sealing could be performed to extend the
service life. General repairs should be performed based on findings and recommendations
from DOT inspection reports.
Conceptual drawings for each alternative are included in Appendix A. Conceptual opinions of
probable construction cost are provided in Appendix E and are summarized in Table 2.
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Alternative 1: 24-foot Span Precast Concrete Arch
This alternative includes a precast concrete arch on pedestal footings to provide an open-
bottom natural streambed. This buried structure alternative utilizes fill to distribute the load
effects from trucks.
Deep foundations are anticipated due to the soil conditions and proposed loads. Piles would
be driven and pile caps would be constructed. The arch would be placed on the concrete pile
caps.
The arch would be backfilled with gravel. A minimum of 24 inches of cover over the top of the
concrete would be provided to prevent pavement deformations. Precast headwalls would be
placed on the upstream and downstream ends of the structure and bridge barrier would be
attached to the top of the headwalls.
Some utilities may be placed within the fill such as the gas and water mains. The utilities can
be protected from axle loads by placing below a future sidewalk, outside of the traveled way.
A precast arch shape is aesthetically attractive and provides opportunities for enhancement
through use of formliners and stonework. The shape is well -suited for this semi-rural Cape
Cod location.
This is the preferred alternative as selected by the Town. The increased impacts to wetlands,
private property, overhead utility clearance, and land under Article 97 restrictions to raise the
low chord as in Alternative 2 would result in substantial cost and schedule impacts. The Town’s
preference is to maintain the existing roadway elevation.
Figure 2 - Typical Precast Concrete Arch
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Alternative 2: 24-foot Span Precast Concrete Arch with
Raised Road
This alternative uses a precast concrete arch as described under Alternative 1, but with a
raised roadway profile. The road would be raised approximately two feet so the low chord
would be at 9.0 feet NAVD88. This would allow the arch to pass the 10% AEP coastal storm
event with 2-feet of freeboard, which the MassDOT Municipal Bridge Project MGL Chapter 85
Section 35 Review Process Design Requirements and Submittal for New Bridge and Full Bridge
Replacement Projects considers optimal. Without raising the road, the precast concrete arch
passes the 10% AEP coastal surge event, but without 2 feet of freeboard as discussed under
Alternative 1. An arch was used for this alternative for consistency with the refined coastal
inundation modeling.
While this alternative would increase the hydraulic performance compared to Alternative 1, it
would also increase costs and impacts to wetlands, private property, overhead utility
clearance, and land under Article 97 restrictions. Further review of these impacts would be
required. Appendix A details the approximate impact areas.
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Alternative 3: 24-foot Span Precast Concrete Rigid Frame
This alternative is similar to the precast concrete arch (Alternative 1). The key difference is
that the top of the frame would be flat rather than arched. This difference may result in a
thicker top-slab of the frame compared to an arch. Approach slabs can be avoided for arch
structures due to their rounded shape but are typically required for 3-sided frames, which
increases cost.
A possible conservative benefit with a three-sided concrete rigid frame is the additional
hydraulic capacity that can be provided with a rectangular shape compared to an arch during
infrequent storm events when the arch is at 100% capacity; however, increased hydraulic
capacity would need to be carefully reviewed for tidal inundation impacts. This type of
structure was evaluated as part of the project's initial hydraulic modeling, but was not
included with the refined modeling that considered coastal surges. The refined modeling was
performed for the arch (the preferred alternative).
Figure 3 - Typical Precast Concrete Rigid Frame
ALTERNATIVES ANALYSIS REPORT Tighe&Bond
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Alternative 4: 24-foot Span Prestressed Concrete Beams
This alternative includes precast prestressed concrete beams on abutments.
Deep foundations are anticipated due to the soil conditions and proposed loads. Piles would
be driven and pile caps would be constructed as abutments. The beams would be placed on
the concrete pile cap abutments.
Precast concrete voided slab beams are assumed for this span. The joints between abutting
beams would be grouted together and a concrete overlay would be provided to distribute
loads into the beams. Pavement would be provided over the concrete. Bridge rail or concrete
barrier would be attached at each curbline. Rubber bearings would be provided on the
abutments to resist deterioration.
A utility bay could be provided between the beams to accommodate the gas and water mains.
A utility bay could also be placed for future utilities such as sewer, underground electric,
telephone, cable, or fiberoptic.
Similar to Alternative 3, the increased hydraulic capacity would need to be carefully reviewed
for tidal inundation impacts. This type of structure was evaluated as part of the project's initial
hydraulic modeling, but was not included with the refined modeling that considered coastal
surges. The refined modeling was performed for the arch (the preferred alternative).
Figure 4 - Typical Bridge Comprised of Precast/Prestressed Concrete Voided Slab Beams
ALTERNATIVES ANALYSIS REPORT Tighe&Bond
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Summary and Opinion of Probable Construction Cost
Conceptual opinions of probable construction cost are presented below in Table 2 and detailed
breakdowns are included in Appendix E. The costs include a 30% Construction Contingency
and a 20% Material and Bidding Contingency.
TABLE 2
Summary of Opinions of Probable Construction Cost
Alternative Opinion of Probable
Construction Cost
1 – 24’ Precast Concrete Arch $2,200,000
2 – 24’ Precast Concrete Arch with Raised Road $2,330,000*
3 – 24’ Precast Concrete Rigid Frame $2,340,000
4 – 24’ Precast Prestressed Concrete Beams $2,440,000
*Further review would be needed to understand the full impacts of raising the roadway. This
cost does not include additional expenses which may be needed as a result of raising the
road, such as additional survey, right-of-way acquisition, utility impacts, restorative
landscaping on private property, wetland restoration and/or replication, or associated design.
Recommendations
This report provides an analysis of alternatives for replacement of a culvert carrying Weir
Road over Hamblins Brook in Yarmouth, Massachusetts. Of the alternatives evaluated, the
recommended alternative is the 24’ clear span precast concrete arch bridge, Alternative 1,
based on the Town's desired aesthetic, level of service for the roadway, and preference to
maintain the existing roadway elevation. The recommended alternative has the lowest
construction costs, provides adequate hydraulic capacity, and meets MARSCS. Furthermore,
it avoids raising the roadway to minimize impacts to overhead utilities, adjacent wetlands,
private property, and open space protected by Article 97. Since 2’ of freeboard will not be
provided for the preferred alternative, it is recommended that the structure be designed for
stream pressure which considers an appropriate drag coefficient for possible debris buildup.
Precast concrete arch bridges are durable with a long service life and require very little
maintenance. They are aesthetically attractive alternatives that can be designed and detailed
to fit well at the crossing site.
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