Project Description
Bridge No. 05491 carries Bailiwick Road over Byram River in the Town of Greenwich (Town), Connecticut. The 33 foot long single span concrete deck arch bridge with masonry fascias was built in 1970 and is located approximately fifty-five feet west of the intersection of Bailiwick Road and Riversville Road. The bridge carries one lane of traffic in the eastbound and westbound directions over a roadway with a 26.1 foot curb-curb width. According to information made available by Connecticut Department of Transportation (ConnDOT), the bridge has an inventory load rating capacity of 34 Tons based on engineering judgment.
The project consists of the replacement of the bridge due to damage sustained during a major storm event that took place on April 15, 2007. Because the bridge is hydraulically deficient, the Byram River overtopped the bridge resulting in the detachment of the north parapet and rail system from the bridge structure and washing out of the bituminous concrete pavement. Significant damages were also reported by abutting property owners as a result of the flooding. Subsequent to the storm event, the Town was able to reopen the bridge with the installation of a temporary concrete barrier and a new wearing surface. The Town has recently replaced the storm damaged parapet with funding from the Federal Emergency Management Agency (FEMA). Apart from the storm damage, the arch structure also exhibits spalled, scaled and cracked concrete. Since the performed repairs are temporary in nature and the bridge provides the only official access to the neighborhood of approximately 200 residents, the bridge is eligible for replacement under ConnDOT’s Federal Local Bridge Program. During the overtopping of the 2007 storm event, the Town was successful in obtaining permission from Bailiwick Club to use their private roadway (an extension of Duncan Drive) for accessing Angelis Drive and provide for a temporary detour. The hydraulic capacity of the bridge is an important design consideration. This bridge is not considered to be historic and proposed replacement is not anticipated to affect the state’s historic and archeological resources.
A scope of services has been developed to perform a Preliminary Engineering Study to determine feasible alternatives to replace the existing structure and increase the hydraulic opening under the bridge. Any increase in the hydraulic opening will need to be carefully evaluated due to potential impacts downstream of the bridge. Dewberry-Goodkind Inc. supported by sub-consultants, John
Paul Garcia and Associates (Surveyors & DBE) and William Kenny and Associates (Soil Scientists), will prepare a Preliminary Engineering Study Report summarizing the evaluation of feasible design alternatives and make recommendations to the Town for the selection of the best alternative. The Preliminary Engineering Study will be performed in accordance with all applicable FHWA, AASHTO and ConnDOT guidelines and specifications and prepared in English units.
1. Survey: Topographic and planimetric survey will be performed to an A-2 accuracy to provide horizontal and vertical controls in the vicinity of the bridge. The survey will be performed in accordance with ConnDOT Location Survey Manual. The horizontal control for surveying and mapping of the project will be on the Connecticut Coordinate Grid System (CGS) and the vertical control will be based on National Geodetic Vertical Datum of 1929 (NGVD). Mapping shall be developed at a scale of 1 inch equal 20 feet. A Digital Terrain Model (DTM) will be provided along with digital MicroStation CAD (ver. XM or V8) files. A digital copy in AutoCAD shall be provided to the Town for filing. One hard copy of the survey at the specified scale will also be required.
Field survey and mapping will be performed to locate significant features including existing roadway, bridge, utility appurtenances, drainage structure data, fences, signs, and limits of wooded areas. Tree sizes within 20 feet of the edge of pavement will be shown to the nearest 4 inches. Ornamental trees less than 4 inches in diameter will be shown to the nearest 3/8 inch. Survey limits will extend 500 feet from the westerly abutment of the bridge in the westerly direction along Bailiwick Road and up to the eastern edge of Riversville Road in the easterly direction. Within these limits, survey coverage will extend to 100 feet on each side from the edge of the roadway. Federal and State wetland area limits identified and marked by a Soils Scientist will be located by field survey and mapped. Existing utilities and adjacent landowner’s property will be researched and mapped. All monuments, iron pins, or other property markers found during survey shall be tied so that they can be reestablished, if disturbed, during construction. The topographic survey shall be plotted with 2-foot contour intervals and spot elevations as appropriate.
Twelve (12) stream cross sections will be taken in the immediate vicinity of the bridge at each bridge face and 30 feet, 60 feet, 100 feet, 150 feet, and 200 feet from each bridge face. The stream cross sections will be surveyed to the western edge of Riversville Road pavement in the easterly direction and 100 feet past the top of bank in the westerly direction. The Byram River will be profiled to the limits of the river cross sections.
2. Review Existing Information: A site reconnaissance will be performed to observe items such as sight distances and roadside safety features, potential utility conflicts, critical controls and environmental conditions. Existing documents including the ConnDOT Inspection Reports and original Design Plans will be reviewed. An inspection of the existing bridge will not be performed since rehabilitation of the existing structure will not be studied as a potential design alternative.
3. Environmental Review: Wetlands and watercourses within the project area will be examined and delineated by a certified Soils Scientist in accordance with current State and Federal guidelines. There are no known populations of state or federal endangered or threatened species present within the project site according to a memorandum issued by ConnDOT Office of Environmental Planning dated September 18, 2007. The proposed bridge replacement alternatives will adhere to the requirements specified by the Inland Fisheries Division of the Connecticut Department of Environmental Protection (Conn DEP) in their letter dated January 25, 2008.
4. Hydrology: The existing peak flows listed for the Byram River’s Conrail crossing in the 1999 FEMA Flood Insurance Study, Page 8 (FIS) for the Town of Greenwich will be used for this project. The FIS lists flows for the 10-, 50-, 100-, and 500-year storm events. A Hydrology Report will be prepared and submitted to ConnDOT’s Consultant Liaison Engineer (CLE) for review and approval prior to performing a hydraulic analysis. The development of a hydrologic model or the computation of peak discharges for use in the hydraulic model is not included in this scope of work.
5. Hydraulics: Hydrologic and hydraulic data will be collected from the project site and the floodplain characteristics will be evaluated. A backwater analysis (HEC-RAS model) for the structure will be developed for the natural, existing and proposed conditions. A summary memorandum of preliminary hydraulic findings will be prepared for inclusion in the Preliminary Engineering Report. The development of a detailed hydraulic report in accordance with ConnDOT procedures is not included in this scope of work.
It is anticipated that, because of existing conditions and hydraulic limitations of the site, the proposed structure may not be able to pass the 100-year storm. This scope includes the study of a maximum of the following three (3) proposed roadway/bridge configurations:
· New bridge structure with span length similar to existing and raise bridge low chord/roadway profile,
· New bridge structure with a longer clear span, and
· Combination of the above concepts.
The development of a downstream impact analysis or a hydraulic model of the Byram River beyond 200 feet upstream or downstream of the Bailiwick Road Bridge is not included in this scope of work. The development of a temporary conditions hydraulic model is also not included in this scope of work.
6. Scour Analysis: Due to the presence of bedrock near the streambed, it is anticipated that the structure will be founded on rock. Therefore, no scour countermeasures should be necessary, and the quantitative computation of anticipated scour depths as outlined in HEC-18 and the ConnDOT Drainage Manual are not included in this scope of work. However, a qualitative scour evaluation will be performed. The scour potential for each of the three alternatives described above will be briefly discussed in a in the Preliminary Engineering Report. The design of scour protection (riprap, sheeting, gabions, pavers, etc.) is not included in this scope of work.
7. Soils and Foundation Investigation: A soils investigation program will be developed to include field borings and a Preliminary Geotechnical Report. This preliminary report will include recommendations on allowable bearing capacity of native soils and/or bedrock for evaluation of subsurface conditions. The report will also include preliminary design guidelines for new abutment and wingwall foundations and roadway embankments, scour protection, and general construction recommendations. The provided services will include:
· Site visit to identify soil types and rock outcrops and review available existing soils data.
· Develop a subsurface investigation and soil sampling program. A total of two (2) borings are anticipated, with one (1) boring performed at each of the proposed abutment locations to determine the depth, condition and suitability of the in situ soil and bedrock strata.
· Prepare bid documents and specifications and solicit bids from drillers in accordance with ConnDOT Geotechnical Manual and award a contract to the lowest qualified bidder.
· Provide technical monitoring of the driller’s field operations.
· Review and evaluate boring logs and prepare Preliminary Geotechnical Report.
Additional borings will be taken during the Final Design phase after the proposed bridge geometry is finalized and a Final Geotechnical Report will be prepared.
8. Structure Type Study: Based on the results of the hydraulic and geotechnical analyses, one (1) design alternative will be considered for the proposed bridge. Rehabilitation of the existing arch structure will not be considered as an alternative. Number of spans, span lengths, structure and material type will be some of the parameters considered for evaluation. General details, sketches and cost estimates will be provided for the studied structure type. Life-cycle cost comparisons, constructability challenges and maintenance requirements will be summarized in a Structure Type Study Report and a bridge type recommendation to the Town will be made. Structural evaluation will be performed in accordance with the AASHTO LRFD Bridge Design Specifications and ConnDOT’s Bridge Design Manual.
9. Preliminary Highway Engineering: A conceptual horizontal and vertical geometric layout of the proposed alignment will be developed to detail the desired improvement, assess ROW and environmental impacts and determine conceptual construction costs. Two critical cross sections, one on each side of the bridge, will be developed to examine the potential alignment. A preliminary Design Statement will be prepared summarizing existing conditions, design assumptions and proposed project elements and identify possible design exceptions.
10. Maintenance and Protection of Traffic (MPT): Based on the selected structure type, potential MPT alternatives to accomplish the construction will be evaluated. Detouring traffic and staging of construction, the two potential alternatives, will be carefully studied considering the concerns of the resident community. Consideration of a traffic detour will require permission from the Bailiwick Club. The traffic count data provided by the Town will be utilized to study the impacts from the potential detour.
11. Preliminary Engineering Report: A Preliminary Engineering Report will be prepared summarizing the results of the environmental review, hydraulics & scour investigations, soils and foundation analysis, highway engineering, MPT, traffic analysis and bridge replacement options.
12. Coordination and Meetings: Coordination will be required with the Town to ensure smooth progress in project design. An update of the project will be provided to the Town prior to internal monthly meeting. Dewberry will attend up to one (1) meeting with Town and/or CLE for project review and coordination.
13. Public Participation – Project Website: A project web page will be created (Website www.bailwickbridge.com). The website will facilitate continuous coordination between the town offices, the design team and the residents, as well as other interested parties and key stakeholders. The website will be created at the start of the project and will be maintained monthly for the duration of the project.
It is anticipated that (at a minimum) the following information will be available on the site:
- Contact information for the whole project team including the town’s Project Manager
- Project description including photos gathered during site visits
- Project Schedule and status of activities (upcoming and past)
- Meeting minutes, design reports and permits
- Links to other sites such as Town of Greenwich, Dewberry, FEMA, etc.
- Frequently asked questions (FAQ’s), and a
- Comment section
14. Public Meetings: Dewberry will prepare visual aids and make a presentation of the Preliminary Engineering Study to the Town of Greenwich citizenry through one Public Information Meeting to be arranged by the Town. Additionally, early and during the study process, one (1) preliminary meeting with neighboring residents is anticipated to gather design input from the community and apprise them of the proposed study.