TRUNK SEWER RELOCATIONS AT 900 ALBERT STREET SERVICING, CONSTRUCTABILITY AND MAINTENANCE REPORT

Transcription

1 P a g e 0 Prepared for: Trinity Development Group, Inc. TRUNK SEWER RELOCATIONS AT 900 ALBERT STREET SERVICING, CONSTRUCTABILITY AND MAINTENANCE REPORT OTTAWA, ON November 2016

2 P a g e 1 TABLE OF CONTENTS 1 PROJECT OVERVIEW SITE SERVICING CONSTRUCTION SEQUENCING GENERAL SANITARY SEWER WNC STORM SEWER NBST CONSTRUCTABILITY ISSUES MM HPTM ALBERT STREET MH5A MH MH MUP AND O-TRAIN STATION CYCLING ROUTES O-TRAIN TRANSITWAY EASEMENTS UTILITY RELOCATIONS TREE REMOVALS SEWER MAINTENANCE SITE ACCESS ANTICIPATED CONSTRUCTION SCHEDULE...11

3 P a g e 1 1 PROJECT OVERVIEW Trinity Development Group Inc. (Trinity) is proposing a mixed use development on the lands located at 900 Albert Street, which is a currently vacant property located on the south side of Albert Street between the O-Train tracks and City Centre Avenue. This development will consist of three 50+ storey residential towers over top of various levels of retail, commercial and parking. The City of Ottawa currently has three trunk sewers which pass through the 900 Albert Street property. The West Nepean Collector (WNC) is a 1650x1650 sanitary sewer which runs east-west across the property. The Mooney s Bay Collector (MBC) is a 1050mm diameter sanitary sewer which runs northsouth across the property, flowing into the WNC at its downstream end. The Nepean Bay Storm Trunk (NBST) is a 1800mm diameter submerged storm sewer which runs north-south across the property. The sewers will need to be relocated to the west and south boundaries to facilitate building construction. Drawing No. GEN1 provides a site plan location and general location of major infrastructure existing and proposed. 2 SITE SERVICING The existing WNC is a 1650x1650 sanitary sewer with an approximate slope of 0.08%. The proposed relocated WNC will be a 1950mm diameter sanitary sewer with an approximate slope of 0.06%. The relocated WNC will include four additional bends and approximately 62 additional metres of pipe. High level hydraulic modeling of the new WNC was previously completed by IBI Group; WSP MMM is currently conducting more thorough hydraulic modeling of the relocated WNC. Those hydraulic modeling results will be provided to the City of Ottawa when they become available. The MBC will be diverted into the new WNC near the south end of the site. The MBC will be abandoned north of this point. An existing flow monitoring station located on the section of the MBC to be abandoned will be removed. The existing NBST is an 1800mm diameter storm sewer. As the NBST lies below the Ottawa River level throughout the site, it is in a permanently submerged condition. The slope on the existing NBST ranges from 2.50% at the upstream end of the site to 0.15% at the downstream end. The relocated NBST will include two additional bends and approximately 55 additional metres of pipe. As with the WNC, high level hydraulic modeling of the new NBST was previously completed by IBI Group. The IBI modeling recommended upsizing the storm sewer from 1800mm diameter to 2400mm diameter, which represents an 82% increase in cross sectional area. WSP MMM is currently conducting more thorough hydraulic modeling of the relocated NBST to confirm this increase in pipe size. Those hydraulic modeling results will be provided to the City of Ottawa when they become available. Examination of the original design drawings of the NBST from 1962 revealed that the existing NBST narrowly passed underneath a now abandoned 1050mm trunk sewer and a now abandoned 1200mm watermain on what is now Albert Street. It is unknown what state or condition they were left. The clearance between the existing NBST and these pipes is as little as 300mm. The consequences of the microtunnel boring machine striking those pipes deep under Albert Street, which is a major transit corridor, are very severe. Therefore, WSP MMM is recommending that the section of the storm sewer

4 P a g e 2 across Albert Street be sized as 1800mm, matching the existing, in order to avoid potential conflicts with the abandoned infrastructure in Albert Street. WSP MMM is currently conducting detailed hydraulic modeling to prove that using an 1800mm pipe across Albert Street will not negatively affect the Hydraulic Grade Line (HGL) in the relocation storm sewer. Site servicing for the buildings will be completed by David Schaeffer Engineering Ltd. (DSEL) under separate cover. WSP MMM has coordinated the site servicing with DSEL to ensure that there are no conflicts between the local infrastructure and the relocated trunk sewers. It is anticipated that there will be local sanitary connections to the WNC at MH 1A, MH 3A, and MH 4A. Those connections will be made to the manholes on the trunk sewer using OPSD external drop structures. The local storm connections will occur at MH 1 and MH 3. The proposed site servicing on the relocated trunk sewers is illustrated on Drawing No. GEN1. Planprofile drawings of the proposed trunk relocations are included in Drawing No. PP1 thru PP5. 3 CONSTRUCTION SEQUENCING 3.1 GENERAL The sanitary sewer is located at a lower elevation than the storm sewer and along the south property boundary. This condition necessitates that it be constructed first. Having the new sanitary sewer in place and operational prior to the storm sewer provides a readily accessible discharge point for stormwater bypasses. These bypasses, if required, would be short duration and covered by a discharge permit with the City. Although the contractor may choose their own means and methods of installing the new sewers, the following sequencing represents the designers expectations. Deviations from these expectations will be reviewed by the design team, and where it impacts City infrastructure or operations the City will be consulted. 3.2 SANITARY SEWER WNC Generally, contractors prefer to install sewers from the low point to the high point. This aids in ground water control. MH5A will consist of a doghouse style precast unit placed over the existing 1650 x 1650 WNC. This precast unit will have an opening for the new sanitary sewer pipe. Once the chamber is installed and all existing and new pipes sealed into chamber, the excavation will be backfilled and the shoring system will be removed and sewer installation will proceed upstream while the sanitary flows in the existing sanitary sewer remain uninterrupted. Pipe sections and chambers from MH5A to MH4A to MH3A to MH2A will be installed using open cut excavation and trench box, as necessary. Rock removal by hoe ram will be required periodically to maintain the necessary slope on the pipe. The trench will backfilled as pipe installation proceeds to mitigate groundwater issues and not impact site traffic. The section of sanitary sewer between MH3A and MH2A passes under the existing NBST. This existing section of storm sewer pipe will be supported while the new sanitary pipe is installed beneath it. The Contractor will be required to submit shop drawings for the support system that have been signed and

5 P a g e 3 stamped by a Professional Engineer prior to construction. Bypassing and draining this section of the NBST while the sanitary sewer is being installed will be considered. This reduces the weight of the pipe being supported and eliminates the risk of a pipe rupture. MH2A will be the new connection point for the MBC into the WNC. MH2A is located offline from the existing MBC, so it will be constructed in the dry while the MBC is still active. A doghouse manhole, MH 6A will be constructed a few metres to the south on the existing MBC. A short section of 1050mm sewer will then be constructed to convey MBC flows into MH 2A. The new WNC will then be made live between MH 2A and MH 5A. This will allow for MBC flows to be diverted to the new WNC, which will allow for the existing MBC to be removed between MH 2A and MH 1A, where the existing pipe will be in conflict with the new WNC. The process for making the new WNC live between MH 2A and MH 5A is as follows: 1. City to minimize sanitary flows in the WNC through up upstream operational diversions thus reducing bypass pumping requirement. 2. Contractor to have several pumper trucks on site to pump sewage from the WNC manholes if it starts to surcharge. 3. Install plug in WNC manhole upstream on MH 5A. 4. At this point the existing WNC will start to surcharge. 5. Break into existing WNC at MH 5A and connect new WNC to existing WNC. 6. Remove plug on existing WNC manhole upstream of MH 5A. This will stop the surcharging in the WNC. 7. Remove plug on new MBC at MH 6A. 8. Install plug on existing MBC at MH 6A. MH1A is very similar to MH5A in configuration. The chamber will have opening for the upstream and downstream 66 x 66 WNC as well as the downstream section of new sanitary sewer. There is sufficient open space around this connection point so as not to require a shoring system. The existing sewers and new sewer pipe will be grouted into the chamber and a plug will be installed in the new pipe. At this point all new chambers and pipe are in place. The existing WNC is still flowing normally. The following sequence is suggested as a viable cross over procedure. 9. City to minimize sanitary flows in the WNC through up upstream operational diversions thus reducing bypass pumping requirement. 10. Contractor to have several pumper trucks on site to pump sewage from the WNC manholes if it starts to surcharge. WNC is now flowing in original pipe but connected to new piping at MH5A. MBC is now flowing through new system.

6 P a g e Low flow period (after evening peak) plug WNC and MBC upstream of site to completely stop sanitary flow into site. City will determine window of time that surcharging is allowable. Time can be supplemented with tanker trucks pumping from surcharged manholes. 12. Complete removals, permanent plugging and benching in MH1A and MH5A 13. Remove plug from WNC and MBC upstream of site. 14. Sanitary sewers bisecting site can now be removed. 15. City to reinstall MBC flow monitoring equipment upstream of site. This process eliminates the need for bypass pumping on the trunk sewers, which substantially reduces risks. During the construction phase the contractor will provide a detailed schedule and plan for each task for review by the engineers and City Operations Staff. 3.3 STORM SEWER NBST The new storm sewer consists of two distinct sections. They are the open cut portion between MH1 to MH3 and the micro-tunnelled portion under Albert Street between MH3 and MH4. Construction of MH4 will be a long duration element (>1 month) due to the type of construction and limited access. Once the shoring system (possibly sinking caisson) is in place around the NBST north of Albert Street, the contractor will install a very limited shoring system on the Albert Street embankment north of the proposed MH3, which is the launch pit for the micro-tunneling operation. The actual tunneling and sewer installation will take only a few days. The shoring will have penetration cut for the tunnelling machine. Once the tunneling and pipe installation is complete the contractor will install MH4 while leaving the existing sewer completely intact and operational. The new pipe will be permanently connected to the new chamber. MH3 will be installed and sewer installation to MH2 and then to MH1 will continue. MH1 will be installed as a doghouse over the NBST. The Hydraulic Grade Line (HGL) for the NBST is above the obvert of the pipe and during high flow events it can rise above ground levels at some upstream locations. This condition means that plugging the pipe and using the fill time to complete the connection work is not a viable approach. Also, the sewer is below the Ottawa River water level meaning that dewatering the pipe will require a downstream plug to prevent river water intrusion. The recommended process is as follows: 1. Install bypass pumping equipment and pipe plug on downstream pipe at manhole immediately upstream of MH1. 2. Install plug in manhole downstream of MH4. 3. Bypass pump stormwater to sanitary manhole MH3A.

7 P a g e 5 This will be done during dry weather (summer) conditions and when the City has diverted sanitary flows out of the WNC as they did during the sanitary switch over. 4. Dewater NBST storm sewer from MH1 to MH4. 5. Complete sewer connections at MH1 and MH4. 6. Remove plugs and discontinue bypass pumping 7. Remove abandoned pipes crossing the site 8. New sewer pipes which have insufficient frost protection cover in this temporary condition will be insulated 4 CONSTRUCTABILITY ISSUES MM HPTM The watermain located along the south boundary of the site carries a significant portion of the entire water supply for the City of Ottawa. This condition makes it s protection of very high importance during the sewer relocation construction. The City has provided the designers with specific constraints related to construction activities proximate to the watermain. They are as follows: Vibration and settlement monitoring No shut down between May 1 st and October 1 st. No stockpiling of material or running of equipment over top of pipe The construction of the new storm sewer between MH2 and MH3 presents the closest interaction the relocation project will have with the watermain. The sewer will be installed using conventional open-cut excavation with a trench box. The storm sewer excavation is quite shallow (depth to invert is about 5 metres), so vertical trenching using a trench box will be feasible. This will result in the limit of all excavations being at least 3 metres clear of the existing HPTM. It has been confirmed that the watermain is concrete encased. There is no need for the watermain to be shut down. Due to the size of MH1 and MH2 and their proximity to the watermain, temporary excavation shoring may be used to provide added protection to the HPTM. The contactor will be required to install settlement and vibration monitors along the watermain for the duration of the sewer construction work.

8 P a g e ALBERT STREET Albert Street is presently operating as the Transitway route through the western downtown. As such the constraints on lane closures and pedestrian route interruptions are very severe. The sewer relocation plan approaches Albert Street in three critical locations, namely: MH5A, MH3 and MH MH5A The downstream terminal manhole for the sanitary sewer relocation, MH5A, is located west of the intersection of Albert Street and City Centre Avenue. The precast manhole will need to be placed over the existing sewer with cut outs for the existing pipe and the new connection. To install this precast manhole shoring will be installed south of the sidewalk and still north of the existing sewer with suitable working space for the new installation. The shoring installation and removal will be done from the south side of the sidewalk during the night or on the weekend to minimize any impacts on the pedestrian traffic. During the sheet pile installation, pedestrian traffic will need to be detoured through the Bayview Station pathways. Disruptions to the south sidewalk and south curb lane will be restricted to just the installation and removal of the shoring. The installation of the shoring is anticipated to be a short term duration event that can be completed on an evening or weekend. The Contractor will be required to coordinate with the City of Ottawa to confirm an appropriate time to complete the shoring installation. Once the temporary shoring has been installed, there will be no further disruptions to pedestrian or vehicular traffic on Albert Street. The excavation for MH 5A and the installation of MH 5A will be completed from within the 900 Albert Street property on the south side of the shoring.

9 P a g e MH3 Similar to MH5A, MH3 is located south of the south side sidewalk on Albert Street. This chamber will be the launching pit for the micro-tunnelling work to cross under Albert Street. The excavation will be into the side of the Albert Street embankment and the shoring will be installed only on the north side just south of the sidewalk. Again the shoring installation and removal will occur at night or on weekends to minimize any impacts on the pedestrian traffic. During the sheet pile installation, pedestrian traffic will need to be detoured through the Bayview Station pathways. Wayfinding signage will be installed at the bus transit and O-train stations.

10 P a g e MH4 MH4 is the downstream terminal manhole for the storm sewer relocation. This section of pipe under Albert Street will be installed using micro-tunneling excavation methods and as such will involve a tunneling machine which will advance from MH3 to MH4. This chamber is offset to the final chamber to allow for removal of the tunnelling machine while the existing sewer is still operational. Similar to MH 5A, the new precast chamber will set over the existing pipe with cut outs for the existing pipe and the new connection. The chamber is located such that the final alignment of the sewer is with city property and not on NCC lands. NCC lands will be used for construction staging and construction access. In this location the shoring system will be a cast-in-place chamber that will be alternately poured and sunk into the ground overtop of the existing sewer. A temporary construction access permit will be required from the NCC to access this site. The shoring chamber will be constructed partially on the NCC property to provide sufficient construction access. The section of the chamber located on NCC property will be removed after the permanent manhole construction is complete. The circular shoring system will be approximately 8 meters from the edge of pavement. No impacts are anticipated to vehicular, bicycle or pedestrian traffic.

11 P a g e MUP AND O-TRAIN STATION The temporary east-west MUP located on the property is subject of an easement granted by Trinity to the City of Ottawa. The sewer relocation project is far enough removed from the MUP and the toe of slope to not pose an issue. The MUP does interfere with the building construction and this interference will be dealt with through removal of the MUP in the fall of The north-south MUP located west of MH 1A will not be impacted by construction activities. 4.4 CYCLING ROUTES The east west MUP on the north side of Albert Street will be preserved throughout the construction. During construction of MH4 the hording or fencing around the construction site will be 7 to 8 m from the curb on Albert Street allowing sufficient space for pedestrian and cyclists. The north-south MUP located west of MH 1A will not be impacted by construction activities. 4.5 O-TRAIN Construction activities along the west boundary of the site are more than 30 m from the O-Train. The contractor will engage the O-Train operation group and their maintenance contractor, Rail Term, to determine what, if any, permits or assistance such as flag men, will be required during our sewer relocation project. This will include compliance with any Provincial or Federal regulations respecting our work near the rail line. Construction activities are not anticipated to disrupt O-Train operations in any capacity.

12 P a g e TRANSITWAY The blocking of any lanes on the Albert Street Transitway during operating hours will be strictly prohibited. The eastbound curb lane may need to be shut down overnight to install temporary shoring at MH 5A and at MH 3. The timing of this work will be coordinated with the City of Ottawa. 4.7 EASEMENTS A temporary working easement will be required on the NCC property during the construction of MH 4. No permanent structures will be left on the NCC property. No permanent easement will be required from the NCC. 4.8 UTILITY RELOCATIONS A flow monitoring station is currently situated on a section of the existing MBC that is to be abandoned. This flow monitoring station could be relocated to a MBC manhole upstream of the site if the City deems it operationally necessary. There are traffic and street light cables located in close proximity to the proposed shaft at MH 4. However, it is anticipated that construction at MH 4 will be able to proceed without any utility relocations. The Contractor will contact the City of Ottawa if it is determined that these cables need to be relocated to complete the shaft construction. There are fibre optic cables owned by telecommunication companies which may need to be relocated in the vicinity of MH 1. Trinity will coordinate these relocations with the utility companies affected. 4.9 TREE REMOVALS Several private trees located in the western portion of the 900 Albert Street site will need to be removed to facilitate sanitary sewer construction between MH 2A and MH 1A. Trinity will obtain all required tree removal approval required from the City for these removals, likely through this pipe relocation Site Plan Agreement. Some City trees between MH1A and MH2A may need to be removed. Trinity will obtain all required approvals and pay the requisite tree compensation fee. 5 SEWER MAINTENANCE 5.1 MAINTENANCE ACCESS Following construction, MH 4 on the north side of Albert Street can be accessed at all times by the MUP. MH 5A can be accessed from the south sidewalk of Albert Street. MH 3 and MH 2 are located within the drive aisle for the development. The drive aisle leads to an asphalt loading area along the southern portion of the site, from which MH 1, MH 3A, and MH 4A can be accessed. An asphalt path will be constructed from the south loading area to the north-south MUP adjacent to the O-Train tracks; from this asphalt path MH 1A, MH 2A, and MH 6A will be accessible.

13 P a g e 11 Between MH 2 and MH 3 the drive aisle will be covered. The drive aisle will have an overhead clearance of approximately 6 metres, which is high enough to allow for construction equipment to excavate the storm sewer in the future if necessary. However, in order to reduce the likelihood of future maintenance issues on the storm sewer between MH 2 and MH 3, it is proposed to concrete encase the storm sewer between MH 2 and MH 3. MH 1 on the storm sewer will be constructed with removable roof slabs which will allow for a clear opening of 3.0 metres x 3.0 metres. This will allow for the City of Ottawa to have enough space to insert large equipment into the storm sewer during sediment cleaning operations in the future. A gravel staging pad (12m x 15 m) is proposed to be located southwest of MH 1 to allow for the City to stage sediment removal operations. 6 ANTICIPATED CONSTRUCTION SCHEDULE Construction on the sewer relocation project is anticipated to commence in mid-march The anticipated duration of construction is approximately 8 months, with construction concluding in approximately October ACCESS/ENCROACHMENTS ONTO CITY PROPERTY Drawing PROP1 of this submission provides a graphical presentation of the various space requirement required for constructing the new sewers. Specifically, it indicates the various encroachments onto City and NCC property. Trinity has had meetings with Ellis Don related to the construction access for MH4. Ellis Don is the constructor of the OLRT Bayview Station and as such has control of the abutting NCC lands during OLRT construction. An agreement will be reached between Ellis Don, NCCC and Trinity to ensure construction access for MH4 is available.