DEVELOPMENT SERVICES COMMITTEE
	TO:	Mayor and Members of Council
	FROM:	Alan Brown, Director of Engineering
	PREPARED BY:	Simon Hung, Development Engineer
	DATE OF MEETING:	September 23, 2003
	SUBJECT:	Markham Centre Shoring Encroachment Agreement

RECOMMENDATION:

That the September 23, 2003 report entitled “Markham Centre, Shoring Encroachment Agreement”, be received,

That the encroachment of shoring into public right-of-way for development with underground structures be authorized subject to conditions satisfactory to the Town.

And that Mayor and Clerk to be authorized to execute the Shoring Encroachment Agreements to the satisfaction of the Town Solicitor and Director of Engineering.

PURPOSE:

This purpose of this report is:

• To establish a policy and conditions for the encroachment of shoring into public right-of-way to facilitate construction of underground structures.
• To authorize the Mayor and Clerk to execute encroachment agreement to the satisfaction of Senior Management.

EXECUTIVE SUMMARY:

The Tridel Circa development is the first significant residential development in the Markham downtown area with high rise buildings and two levels of underground parking located adjacent to the street line (exterior wall is approximately 1.0 metre from the public right of way in most cases). This requires special construction techniques for the excavation of the underground structure being in close proximity to the public right-of-way. An efficient and safe construction method with minimum impact to the public right-of-way, acceptable to the Town, is therefore required. Staff have reviewed this matter not only as it relates to the Tridel application but future development of underground structures in Markham Centre and other potential areas.

An anchor/tie-back system illustrated in Fig. 1 is commonly used in other municipalities in the GTA such as Toronto and Mississauga. Although the anchors will encroach into the public right of way, they will be well below the utilities, sewers and watermain infrastructure with sufficient clearance. Once the underground structure is constructed, the anchors become redundant and can be removed if required. It is recommended that the anchor system be approved with the following conditions.

• That an encroachment agreement must be executed prior to the installation of the shoring system or excavation
• That approval from all the impacted utility providers must be obtained
• That monitoring of movements along the perimeter of the excavation be provided to the Town’s satisfaction at specified time intervals, before, during and after the excavation
• That all excavation must stop when movements are considered excessive by the Town. Excavation may be resumed only at the instruction of the Town after satisfactory remediation is performed
• That any damage to the utilities, municipal sidewalk, boulevard or public properties must be restored to the satisfaction of the Town at the sole cost of the Owner
• That steel piles encroaching into the public right of way must be cut down sufficiently deep to clear all utilities, watermain or other services as specified by the Town
• That hoarding to protect the public be erected along the perimeter of the excavation, to the satisfaction of the Town
• That the Owner shall indemnify and save harmless the Town from any action, claim, damage or loss whatsoever arising from the granting of permission to excavate and install permanent anchors within the public right of way
• That the Owner shall provide insurance (minimum $10,000,000.00) and guarantee as required by the Town
• That the Owner be responsible for the removal of the piles or anchors when deemed necessary by the Town
• That the Owner be responsible for all costs for peer review of application and staff costs to process the application and agreement
• That the Owner shall provide sufficient Letter of Credit as determine by the Director of Engineering
• That the works shall be certified by a Professional Engineer during and after the construction

BACKGROUND:

The goal to provide a pedestrian friendly environment in the downtown setting of Markham Centre encourages buildings to be closer to the public road allowance with minimal setback. One challenge that emerges from this concept is that very little space is available for the excavation of underground structures with proper sloping. Vertical support during excavation to prevent lateral earth movement is therefore inevitable in order to construct the underground structure while protecting the public right of way. The proposed Tridel Circa development has two levels of underground parking structure which will be 10 metres below existing ground. An engineering solution is therefore necessary to support the earth on the public road allowances during the excavation so that the existing boulevard with sidewalk, utilities or other infrastructure may continue to function.

OPTIONS/DISCUSSION:

Anchor/Tie-back System

The anchor/tie-back system is being proposed for the Tridel Development (refer to Fig. 1 and Fig. 2 for details). Prior to excavation, vertical steel piles are installed along the perimeter of the excavation at pre-determined intervals and to depths below the base of the excavation. Excavation will then proceed to the first anchor level while horizontal timber laggings are installed between steel piles to support the earth. Inclined holes are drilled into the right-of-way behind the steel piles in which concrete is poured to form the anchors. Steel cables connecting the concrete anchors and the steel piles are stressed to provide resistance to the earth pressure from the un-excavated side. After the anchors are installed, excavation will proceed to the next anchor level (if more than one layer of anchors is required, the process will be repeated) or to the base of the excavation.

The anchor system is the technique of choice by the construction industry and the accepted choice by most municipalities for the following reasons.

· Better control of excavation movements by adjusting the tension in the anchors and the number of anchors.

· The area to be excavated is totally un-obstructed, thus allow uninterrupted earth removal and expeditious construction of the permanent structure. This offers significant saving in cost and time.

· Once the underground structure is completed, lateral support will be provided by the permanent structure and hence renders the anchors redundant.

· The anchors are located sufficiently deep to clear all existing and future utilities and services. In rare occasions, removal of the anchors may be necessary when they conflict with other installations. Removal can be achieved by simply cutting through the anchors. Otherwise, the anchors may be left in place permanently.

Encroachment Agreement

The principles of the encroachment agreement shall include all the conditions outlined on page 2 and the following additional requirements.

· Movement of the shoring system shall be monitored by the consulting engineer throughout the entire construction process and work shall be stopped once a 12mm horizontal displacement is reached .

· Piles that encroach into the public right-of-way shall be cut down to depths as specified to provide clearance for utility installation (within 0.3m from the street line, pile shall be cut down 1.5m; more than 0.3m from the street line, pile shall be cut down 2.5m)

· The Owner shall obtain permission from all the utility companies prior to the construction

· The Town may at any time, at its sole discretion, terminate the Agreement upon delivery of Notice to the Owner.

· The encroachment agreement shall be registered on title.

The Encroachment Agreement shall be finalized to the satisfaction of the Senior Management. A sample agreement from the City of Toronto is attached for reference.

FINANCIAL CONSIDERATIONS:

The Owner is responsible for all the costs for processing the application.

Although it is not anticipated that the piles or anchors will conflict with existing or future infrastructure, individual assessments may be necessary to determine if financial compensation is required.

ENVIRONMENTAL CONSIDERATIONS:

It is not expected that there would be environmental implications.

BUSINESS UNITS CONSULTED AND AFFECTED:

The Street Services Department have been involved in the analysis and concur with the recommendations.

The Legal Department and Street Services Department will provide input into a standard encroachment agreement.

ATTACHMENTS:

Fig. 1 Typical cross section with anchors

Fig. 2 Photographs of excavation with anchors

Sample “Tie-back Piling and Shoring Agreement” from City of Toronto

Alan Brown, C.E.T. Director of Engineering

Jim Baird, M.C.I.P., R.P.P. Commissioner of Development Services

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