OLD SCHOOL, BUT EFFECTIVE CONSTRUCTION OF THE SEMPLE AVENUE TRUNK SEWER UTILIZING TWO-PASS TUNNELLING

Minneapolis, Minnesota

OLD SCHOOL, BUT EFFECTIVE:

Construction of the Semple Avenue Trunk Sewer Utilizing Two-Pass Tunnelling Methods

Jordan Thompson, AECOM, Winnipeg, Manitoba, Canada Marvin McDonald, AECOM, Winnipeg, Manitoba, Canada Jurgen Friesen, City of Winnipeg, Winnipeg, Manitoba, Canada Kas Zurek, City of Winnipeg, Winnipeg, Manitoba, Canada

ABSTRACT

The Semple Avenue Trunk Sewer was constructed to provide combined sewer relief for the Jefferson East Combined Sewer District in Winnipeg, Manitoba, Canada. The land drainage sewer (LDS) trunk relieves hydraulic load on the combined sewer system, reducing risk of basement flooding and combined sewer overflows to the nearby Red River. The trunk is the launch point for future sewer separation contracts in the district.

Construction included approximately 400 m (1,312') of 1,800 mm (72") LDS and 1,140 m (3,740') of 2,100 mm (84") LDS, associated lateral sewer stubs, catch basins, and manholes. The project is located in a densely treed, mature residential neighbourhood.

The subsurface stratigraphy along the alignment generally comprises of mixed upper complex soils (sand, silt and clay) overlying glacio-lacustrine clay, and glacial till deposits. A geotechnical investigation was undertaken during the design phase and a Geotechnical Baseline Report (GBR) was produced to set clear baselines for conditions that were anticipated to be encountered during construction.

The project specifications stipulated long drive tunnels to minimize disruption of the neighbourhood. Two trenchless construction methods were tendered competitively, including single-pass tunnelling with pipe jacking, and two-pass tunnelling with a grouted in place carrier pipe. The successful proponent utilized a two-pass TBM tunnelling method with rib and lagging primary support and a Centrifugally Cast, Fiberglass-Reinforced, Polymer Mortar Pipe (CCFRPMP) carrier. The tunnel was constructed in a single drive of approximately 1,540 m (5,052") over the course of approximately five months.

INTRODUCTION

The Jefferson East Combined Sewer District represents an area of 475 hectares (1175 acres) of predominantly residential area in a mature neighbourhood in Winnipeg, Manitoba, Canada. AECOM developed the conceptual basement flooding relief and pollution abatement plan in 2009 and has been engaged in the implementation of the program since 2011.

The scope of construction work was segmented into ten (10) separate construction contracts; each providing relief to various catchments within the Jefferson East Combined Sewer District. Contracts one (1) through three (3) provided relief to catchments east of Main Street. Contracts four (4) through ten (10) will provide complete separation of the combined sewer system west of Main Street. An overview of contracts four (4) through ten (10) is shown in Figure 1.

The Semple Avenue Trunk Sewer was predominantly constructed under Contract 5, shown in orange above, to provide combined sewer relief to the Jefferson East Combined Sewer District. The new land drainage sewer (LDS) trunk relieves hydraulic load on the combined sewer system, reducing risk of basement flooding and combined sewer overflows to the nearby Red River. The trunk is the launch point for future sewer separation contracts in the district.

Construction included approximately 400 m (1,312') of 1,800 mm (72") LDS and 1,140 m (3,740') of 2,100 mm (84") LDS, associated lateral sewer stubs, catch basins, and manholes.

SITE CONTRAINTS AND CHALLENGES

The area for construction of the new trunk sewer is a largely residential, mature neighbourhood located in north Winnipeg. The trunk spans approximately 1,540 m (5,052") along Semple Avenue and crosses eight intersections including Main Street. Several constraints and challenges were identified during the detailed design phase including: • Impact on Existing Mature Trees • Utility Density (Buried and Overhead) • Noise • Vibration • Construction Footprint • Traffic Disruption • Close Vertical Proximity of Existing

Combined Sewer Trunks (less than 150 millimetres) Given the compact and well-established nature of the neighbourhood, minimizing the impact on homeowners was the top priority when reviewing potential construction technologies, monitoring requirements and mitigation measures. Trenchless construction methods were identified early in the design phase as the only acceptable method of construction that would be suitable to the area. The Semple Avenue right of way includes a large canopy of mature elm trees

Figure 1: Jefferson East Combined Sewer Relief – Contracts 4 through 10.

(shown in Figure 2) that are highly valued by the neighbourhood and the City of Winnipeg. Trenchless construction would allow work to occur without the need to remove trees. In addition to the tree lined boulevards, overhead power lines (shown in Figure 3) and extensive buried utilities precluded traditional open cut construction methods in the Semple Avenue right of way.

The impact of noise caused by construction was also evaluated. The City of Winnipeg Neighbourhood Liveability By-law places restrictions on noise associated with construction projects. Construction projects in Winnipeg must adhere to the requirements of the bylaw, which includes limiting construction activities to regular working day hours. Given the nature of trenchless construction and the desire to allow for the possibility of 24-hour construction, the City of Winnipeg granted exemptions to the by-law for activities deemed critical and necessary to tunnelling operations. Additional restrictions were placed on activities undertaken outside of the time periods allowed for in the by-law to ensure that the impact of noise on the neighbourhood was minimized. The restrictions included: • Only equipment deemed critical for tunnelling operations would be allowed to operate outside of regular working hours, • Equipment must meet stringent noise output requirements, and • Sound attenuation barriers and devices would be required if the equipment did not satisfy the noise output requirements. Baseline sound measurements of the neighbourhood were to be recorded and acoustic monitoring of construction would be implemented to confirm conformance with the specified maximum noise levels.

Construction methods that are likely to impart major vibrations, including but not limited to driving sheet piles, would not be suitable to the area due to the proximity of homes and other infrastructure. The proposed construction schedule also overlapped with the coldest months of winter, which meant that frozen ground would exacerbate the potential for large vibrations. A Vibration Monitoring Plan was to be undertaken by the contractor to document the impact of potential vibrations caused by construction. The plan included: • Pre-construction surveys of nearby buildings and structures,

Figure 2: Semple Avenue – Tree Canopy.

Figure 3: Semple Avenue – Overhead Utilities.

Figure 4: Extent of Geotechnical Test Holes along Semple Avenue between McKenzie Street and Scotia Street.

• The supply and installation of vibration monitoring systems, • Daily vibration monitoring reports, and • Post-construction surveys of affected buildings and structures, as required. Semple Avenue spans approximately 1.5 km (0.9 mi) intersecting eight roads in the project area including Main Street, the primary arterial link between downtown Winnipeg and north Winnipeg. Several of the intersecting streets serve as public transit and school bus routes. Semple Avenue is a narrow two-lane street with limited space for lay-down areas. Block to block distances are approximately 200 m (656') on center, therefore minimum tunnelling drive lengths of 200 m (656') were required to minimize mid-block construction during tunnelling activities and to minimize the impact on traffic in the area.

The alignment of the proposed trunk crosses under several active sewer and water utilities including watermains and combined sewers. While the new pipe is generally much deeper than the surrounding utilities (5.5 m (18') to obvert), clearance for several deeper combined sewers ranged from 0 mm (0") to 500 mm (19.7") depending on TBM size and amount of overcut required. Utilities deemed close enough to be obstacles would require temporary relocation or bypass pumping, whereas utilities not deemed to be obstacles but at risk of damage due to subsidence of the tunnel below would require monitoring. A surface and subsurface monitoring plan was included in the contract that required that all major combined sewers and watermains along the alignment be monitored for settlement by means of surface and subsurface monitoring points.

GEOTECHNICAL CONSIDERATIONS

Winnipeg is located beneath what was once glacial Lake Agassiz and lies in a flood plain at the confluence of the Red and Assiniboine rivers, which influences both the geotechnical and hydrological characteristics of the region. The shallow bedrock geology of the Winnipeg area generally comprises of carbonate rock of the Selkirk and Fort Garry Members belonging to the Red River Formation. The Red River Formation consists of alternating layers of limestome and dolomite with basal shale layers. The overlaying surficial soils generally comprise of upper complex deposits, glacio-lacustrine clays, and glacial till soils of varying thickness and compositions. The glacial till soils were laid down by the advancing and retreating glacial ice masses. The glacio-lacustrine soils are a product of fine materials deposited through suspension within the glacial lakes.

Geotechnical Investigation

Geotechnical investigations completed under the previous construction contracts provided initial geotechnical information for the project. A new geotechnical investigation was undertaken in 2019 along the length of the Semple Avenue Trunk Sewer to supplement the existing information and determine the subsurface conditions.

A hydro excavation investigation was completed at seventeen proposed test hole locations to a maximum depth of 3.1 m (10.2") to assess the presence of buried utilities or other obstructions. One proposed test hole was discarded due to the presence of underground and aboveground utilities. The 16 remaining test holes were drilled adjacent to the alignment of the trunk. Six test holes were drilled into the deeper glacial till and ten shallower test holes were drilled into the overlaying surficial soils. Samples collection from the drilling program were tested to determine moisture contents, grain size distribution, Atterberg limits, undrained shear strength, bulk unit weight, permeability, consolidation, swell, and electrochemical properties. An overview of the test hole program is shown in Figure 4.

A Geotechnical Data Report (GDR) was prepared to summarize the results of the geotechnical investigation. A Geotechnical Baseline Report (GBR) was prepared to detail baseline conditions for the proposed tunnelling and shaft construction work. The GDR and GBR were intended to be used in parallel to provide the contractor with: • Clear baselines for subsurface conditions anticipated to the encountered during construction, • A single contractual interpretation for bidders to utilize when preparing bids, and • To assist in evaluating the requirements for excavation, temporary support, groundwater control, and ground movement for the shaft and tunnel construction. Any claims related to a change of subsurface conditions during construction would be reviewed and evaluated against the baselines established in the GBR.

Historic Waterways

Winnipeg was once home to approximately 16 major streams and twenty small creeks that existed prior to the arrival of the first European settlers in the area. Many of these waterways have been drained, filled, entombed, or re-routed over time to allow for construction of infrastructure, roadways, neighbourhoods and buildings as the city

grew and developed over the 20th century. While detailed records of these waterways are scarce; a review of historical maps, articles and geological information revealed the presence of a historic waterway in the project area named Inkster’s Creek that appeared to cross the alignment of the proposed trunk between Main Street and Scotia Street. The presence of Inkster’s Creek was verified by survey, as there was an approximate 2.5 m (8.2") change in the roadway elevation and topographic contours in the area follow the shape of a likely former waterway. Houses were constructed the former creek in the early 1950s, indicating that the creek has been backfilled for at least 70 years. The location of the former creek is shown in Figure 5.

Particular attention was paid to collecting additional geotechnical information in this area to determine if there were any changes in subsurface conditions that would differ from the relatively consistent material overserved along the majority of the trunk, such as alluvial soils deposits that could impact the selection of tunnelling methods. Further, the change in ground elevation reduced the overburden thickness above the proposed trunk, which would need to be considered during design and construction. The geotechnical investigation revealed that there were no significant anomalies in subsurface conditions that would negatively impact tunnel construction.

TRENCHLESS CONSTRUCTION TECHNOLOGIES

Two trenchless construction technologies were selected as viable options for the project: • Single-Pass Tunnelling with Pipe Jacking • Two-Pass Tunnelling with Grouted in

Place Carrier Pipe The selection of these technologies was based on a balance of cost, technical requirements of the contract, and the ability to minimize disruption to the neighbourhood. It also allowed for a wide range of proponents located locally and from across Canada to pre-qualify and bid on the project.

Despite limiting allowable tunnelling methods to two primary technologies, innovation and creativity were encouraged during the procurement process. The intent was to allow for a wide range of technical approaches to the means and methods including various laydown and working areas, shaft construction techniques, pipe materials, and drive lengths. Proponents were also permitted to upsize pipe diameters, should that be of benefit to the contractor’s means and methods.

PROCUREMENT Pre-Qualification

A Request for Qualifications (RFQ) was issued in November 2019 to identify experienced and capable proponents to successfully execute the work. To qualify, the proponents were required to address the following:

1) Project Understanding: • Demonstrate an understanding of project objectives, key issues, and risks. • Describe the propose approach for dealing with site constraints, access limitations and traffic movements. • Describe proposed methods of mitigating deviations in the

Neighbourhood Livability By-Law (working hours, noise, etc.).

2) Proposed Tunnelling Method: • Describe the proposed tunnelling method(s). • Describe the proposed number of drives, shafts, and any pipe upsizing. • Describe methods for dealing with potential obstructions. • Describe proposed method of shaft construction.

3) Proposed Tunnelling Equipment: • Tunnel boring machine (TBM). • Spoil removal equipment. • Slurry separation equipment (if required).

4) Past Project Experience (three examples per proponent, subcontractor, or key personnel): • Minimum drive lengths of 400 m (1,312"), • At least one drive length equal to or exceeding 600 m (1,969"), and • Include the installation of pipes with a minimum internal diameter of 1,800 mm (70.87"), with one example including pipes with a minimum internal diameter of 2,100 mm (82.68").

Six contractors were deemed pre-qualified to bid on the project for the single-pass method, and three contractors for the twopass method.

Construction Tender

The project was tendered in January 2020 and closed in February 2020. A total of responsive bids were received ranging from $17,971,800.00 to over $32,000,000. Bids received included construction methods of microtunnelling with pipe jacking, conventional open face TBM with pipe jacking, and two-pass tunnelling with GRP liner.

McNally Construction Ltd. (McNally) of Hamilton, Ontario, Canada was awarded the construction contract in May 2020. The proposed method was a two-pass tunnelling system.

CONSTRUCTION Mobilization:

Construction commenced in August 2020 with site mobilization and the installation of all surface, subsurface and utility monitoring points. The contractor arranged for direct connection to the local power grid, rather than using conventional diesel generators, to meet acceptable noise levels in accordance with the contract specifications and the City of Winnipeg Neighbourhood Livability By-Law.

Figure 5: Historical Location of Inkster’s Creek with Reference to the Trunk Sewer.

Hydrogeological Investigation:

A hydrogeological investigation was undertaken by the contractor prior to the commencement of shaft construction to assess the feasibility of bedrock depressurization as a means of relieving hydrostatic pressure from the underlying bedrock aquifer at the base of the excavation. A test well was drilled, and a pumping test was completed to determine the required pumping rates and predicted radius of influence of the pumping. It was concluded that due to the low hydraulic conductivity of the glacial till, an adequate factor of safety against basal heave was attainable without the need for depressurization of the bedrock aquifer.

Tunnelling Activities:

The means and methods of tunnelling proposed by the contractor consisted of the following: • Two-Pass Tunnelling with Grouted in

Place Carrier Pipe. • TBM: 112" Rotary Lovat TBM. • Primary Tunnel Support: Steel ribs and timber lagging. • Locomotive conveyed spoil removal system. • A single tunnel drive of 1,542 m (5,059"). The proposed extent of tunnelling is shown in Figure 6.

The tunnel launch shaft was constructed at the intersection of Semple Avenue and McKenzie Street. The shaft consisted of conventional steel soldier piles with timber lagging excavated to a depth of approximately 9 m (29.5"). The steel soldier piles were pre-drilled prior to installation to mitigate the potential for vibrations. Photos of the launch shaft are shown in Figure 7.

Vibration monitoring systems were installed prior to the construction of all shafts on the project. Baseline vibration measurements were recorded for one week prior to the commencement of excavation and were maintained for the duration of construction until shafts were backfilled, and shoring removed. While there was a noted increase in vibrations during certain activities such as the movement of larger equipment on site, the measured vibrations did not exceed the allowable thresholds. In instances where vibrations were approaching the thresholds, work was temporarily stopped on site to modify means and methods to reduce vibrations to an acceptable level.

Tunnelling commenced in November 2020. Production rates ranged from approximately 15–19 m (49.2–62.3") per day during peak production. Tunnelling continued through a cold Winnipeg winter, where temperatures dropped as low as -38.8°C (-37.8°F). Tunnelling was completed five months later in April 2021. Photos of the TBM during installation at the launch shaft, completed tunnel section, and TBM at breakthrough in the reception shaft are shown in Figure 8.

Carrier Pipe Installation:

The carrier pipe consisted of approximately 400 m (1,312') of 1,800 m (72") and 1,140 m (3,740') of 2,100 millimetre (84") CCFRPMP supplied by HOBAS. The pipe segments were installed using a rail mounted cantilever boom pipe carrier, shown in Figure 9.

An intermediate shaft was installed at the location of the size change at Andrews Street. Carrier pipe installation was completed in May 2021. The carrier pipe was grouted in place using cellular concrete grout in June 2021. Figure 10 includes photos of the grouted in place pipe at the launch shaft and the interior of the pipe.

Appurtenances and Restoration:

All existing on street drainage was connected to the new sewer trunk upon the completion of grouting activities. LDS stubs were trenchlessly installed at Andrews Street and McKenzie Street to push the

Figure 6: Extent of Tunneling on Semple Avenue from McKenzie Street to Scotia Street.

Figure 7: Tunnel Launch Shaft.

Figure 8: TBM install at the Launch Shaft, Completed Tunnel Section, and Breakthrough at the Reception Shaft.

Figure 9: Cross-Sectional View of Carrier Pipe Installation.

location connections under future contracts out of the Semple Avenue right-of-way and minimize future on-street excavations. 3,658 mm (12”) precast concrete box manholes were installed on the trunk at McKenzie Street, Andrews Street, and Scotia Street. Substantial Performance of the contract was achieved in October 2021. Restorations were largely complete by the end of October 2021.

SUMMARY

The Semple Trunk Sewer was constructed to provide combined sewer relief for the Jefferson East Combined Sewer District in Winnipeg, thereby reducing the risk of basement flooding and combined sewer overflows to the nearby Red River. Construction commenced in the Summer of 2020 and was successfully completed in the fall of 2021.

The successful proponent utilized a twopass TBM tunnelling method with rib and lagging primary support and a CCFRPMP carrier pipe. The tunnel was constructed in a single drive of approximately 1,540 m (5052") over the course of approximately five months.

The location of the project presented unique challenges in terms of executing a relatively large construction project in a compact residential neighbourhood. Project constraints, challenges, and potential impacts on the surrounding neighbourhood were identified early in the design process and mitigations were developed and included in the project specifications.

The mitigations put in place during construction included the requirement for long tunnel drive lengths, vibration monitoring, noise mitigation, and subsurface utility monitoring. These mitigations allowed construction to occur over a footprint of approximately 1.5 km (0.9 mi) with minimal disruption to the neighbourhood. Clear and consistent communication between AECOM, the contractor, the City of Winnipeg, as well as homeowners, schools, and businesses in the area was vital to ensuring that project objectives were met.

The procurement methods encouraged industry to be creative, utilize innovation and allowed for proponents to consider a variety of technical approaches in their means and methods to achieve the desired end result of a safe and successful sewer installation. The flexible approach in procurement resulted in a competitive, open market, and cost-effective means of tendering the project with a wide range of high-quality proponents. Bids ranged from approximately $17,400,000 to over $32,000,000. The project was successfully completed on budget.

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Figure 10: Carrier Pipe at Launch Shaft and Interior.

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