Emergency Re-Construction of Sawmill Brook Culvert on Monument Street

Town Contact:

Justin Richardson, Assistant Town Engineer, 978-318-3213, jrichardson@concordma.gov

General Contractor:

MIG Corporation, Inc.

Engineering Consultant:

Wright-Pierce

Project Schedule:

Work began Monday, June 28, 2021 and is now complete. 

Traffic Implications:

Roadway is fully open to traffic.

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Project Overview:

Background:

On April 29, 2021, Concord Public Works (CPW) responded to a report of unusually high water in Sawmill Brook in the vicinity of 1061 Monument Street. While attempting to remove a suspected beaver dam believed to be blocking the inlet of the culvert, rushing backwater created a sinkhole close to edge of the roadway. CPW and its subcontract stopped the follow of water with sandbags which prevented the road from further washout.

Monument Street is a major arterial route for the Town and Minuteman National Park. A road washout at this location would have directly compromised a 12” water main and service to approximately 150 households, isolate those homes from emergency services as well as potentially impact the agricultural land downstream. There is also a natural gas main in the roadway and a utility pole located immediately over the culvert and adjacent to the sink hole.

CPW prepared and implemented an emergency response that involved a large pumping operation that at first deployed three large pumps to bring the water level down to an elevation that no longer threatened that roadway and utilities. The pumping operation has been reduced to now only running one pump with another pump asking as backup until a permanent solution can be implemented.

Repair:

Through emergency funding approved at Town Meeting CPW has executed a contract with MIG Corporation, Inc. to repair the culvert and its headwalls. Additionally, an engineering firm, Wright-Pierce of Andover, MA with significant experience in culvert design was brought in to evaluate the situation and recommend a remedy.   The permanent repair will involve the installation of five precast concrete box culvert segments matching the existing stone box dimensions to replace the existing, compromised, corrugated metal pipe on the inlet side of the culvert and to extend the culvert downstream for a safer road embankment slope. The design plan can be seen below.

SMB Reconst Design Plan

Construction Updates:

Updates will be provided weekly on the contractor’s progress.

June 28, 2021- July 2, 2021: – MIG Corporation, Inc. has mobilized and has set up jersey barriers and temporary traffic signals to close one travel lane to provide a work area adjacent to the Sawmill Brook Culvert. They have also installed erosion control devices and cleared/grubbed the area where the cofferdam and crane pad will be installed.

July 5, 2021- July 9, 2021: – MIG Corporation, Inc. installed pad to support cofferdam installation equipment and re-established erosion controls in the area of the pad. Sheeting for the cofferdam was brought to the site and stockpiled. A major rainstorm even occurred on Friday (July 9, 2021) and site preparation for the storm was implemented.

July 12, 2021- July 16, 2021: – MIG Corporation, Inc. has installed the northerly side of the cofferdam and is in the process of installing the westerly and southerly side of the cofferdam

July 19, 2021- July 23, 2021: – MIG Corporation, Inc. has installed the three sides of the cofferdam and has been working on attaching the structural supports to the cofferdam. They have also installed the wooden matting on the Easterly/Downstream section of the culvert to reduce the damage from construction equipment, and allow access to the downstream section of culvert.

July 26, 2021- July 30, 2021: – MIG Corporation, Inc. completed the installation of the cofferdam supports and have excavated the material from inside the cofferdam. They have excavated down to the existing stone culvert that they will be attaching the new sections of concrete box culvert to.

August 2, 2021- August 6, 2021: – MIG Corporation, Inc. has completely uncovered the upstream end of the stone box culvert that the proposed concrete culvert will be connected to. The connection location is being discussed by MIG and the design Engineer to ensure that the existing stone culvert and the concrete culvert connect without restricting water flow. One section of culvert was installed on the downstream end of the culvert and forming is being done for the concrete collar that will connect the existing stone culvert to the proposed concrete culvert.

August 9, 2021- August 13, 2021: – MIG Corporation, Inc. has completed the formwork for the concrete collar and headwall footing for the downstream end of the culvert. They have also installed lagging and a second roadway plate for soil stabilization so that they may continue to excavate to the extent required on the upstream end of the culvert. 

August 16, 2021- August 20, 2021: – MIG Corporation, Inc. has completed the installation of the two downstream sections of concrete culvert and have been working on the concrete formwork for the headwall.  Due to weather and unforeseen circumstances, there has been a delay in the installation of the upstream sections of concrete culvert.  A solution to address the new issues has been developed and if all goes as planned will be implemented next week.

August 23, 2021- August 27, 2021: – MIG Corporation, Inc. has completed pouring of the downstream headwall.  They have installed one section of upstream concrete culvert and have started pouring the upstream collar that will connect to concrete culvert to the existing stone culvert.

August 30, 2021- September 3, 2021: – MIG Corporation, Inc. prepped the site for the large rain event that was predicted.  They completed the pour of the upstream concrete collar and installed an additional concrete box culvert section and started backfilling over the collar and box culvert.

September 6, 2021- September 10, 2021: – MIG Corporation, Inc. Installed the third section of the concrete box culvert on the upstream section and continued to back fill the area. They then constructed the upstream headwall footing forms and poured the upstream headwall footing. 

September 13, 2021- September 17, 2021: – MIG Corporation, Inc. installed the last section of concrete box culvert on the upstream side of the culvert. They then formed and poured the upstream headwall.  The compensatory storage excavation was completed and filling over both upstream and downstream sections of culverts was completed. 

September 20, 2021- September 24, 2021: – MIG Corporation, Inc. opened the cofferdam allowing water to flow unobstructed through the culvert for the first time since the collapse occurred.  They continued to remove the cofferdam, pumps and the excavator pad that was temporarily constructed. 

September 27, 2021- October 8, 2021: – MIG Corporation, Inc. restored the embankments on both the upstream and downstream sides, reinstalled guardrails, and started cleanup and demobilizing equipment.

October 11, 2021- October 15, 2021: – MIG Corporation, Inc. repaired street pavement and asphalt berms, removed jersey barriers and temporary traffic lights and opened roadway fully to vehicular traffic.

Construction Look Ahead:

In the coming weeks in October/November, 2021, MIG is expected to address punch list items. Minor traffic interruptions are anticipated.