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Siena stone @ ShermanSlope. Hamilton, Ontario – A successful Collaboration


Shop Design:  Risi Stone Systems

Prime Consultant: AMEC

Block Supplier:

Owner: City of Hamilton

Wall Installation:
Rankin Construction

Geotechnical Engineer: Peto MacCallum Ltd

In the summer of 2011, a spectacular slope failure along the heavily traveled Sherman Access Roadway forced the City ofHamiltonto close this major municipal artery as a public safety precaution. As the major emergency access to St. Joseph’s Hospital, located atop Hamilton Mountain, the City had to act quickly to stabilize the slope, and the roadway above.

Consultants retained by the City immediately carried out a detailed Geotechnical Investigation and Slope Stability Analysis.  The study largely concluded the result of the pavement shoulder cracking (tension cracks) and slope failure was due to impeded drainage through underlying fissured bed rock. The report provided 2 possible solutions for long term slope stability.  Option 1 was a Caisson/Lagging wall and Option 2 was a Mechanically Stabilized Earth Retaining wall.

Due to the economic constraints, high performance requirements, and urgency to finish construction, Option 2, the MSE wall with a modular block facing option, was selected by the Consultant.  Unilock, supplier of the Siena Stone System, and Risi Stone Systems, licensor of the system, were contacted immediately to meet on site and discuss the options going forward.

At just over 225 kg per unit, the Siena Stone System was chosen for its large size and Engineering performance, fast rate of machine installation (over 1000 sq.ft per day typically), and Unilock’s ability to quickly supply this substantial amount of material.

Due to the urgency of the project, Risi Stone Systems produced a detailed Siena Stone MSE wall design within a couple of days.  In situations where slope stability and groundwater are major factors, the Design ends up being a collaboration between the Wall Design Engineer (Risi) and the Geotechnical Consultant (Peto MacCallum Ltd).  While the Wall Design looked specifically at the Internal and External stability of the MSE Wall, the Geotechnical Consultant provided input on the overall Global Stability (general wall/slope stability) and drainage provisions due to high groundwater levels.  Ultimately, the Design dealt with the obvious slope stability issues with sufficient geogrid length, and multiple internal and external drainage systems to deal with the groundwater.

Within a week of the failure, the Contractor had mobilized on site and began excavating the roadway down to bed rock.  At a total height of 4 metres, including substantial embedment for Global Stability, combined total face area of 200 square metres, the Contractor was able to install the Siena Stone Wall in just under six weeks.  Under the ongoing supervision of the Site Geotechnical Engineer, the resulting Structure was delivered to the City of Hamilton without delay, and the Sherman Access was reopened again to the relief of all.

This is a great example of cooperation between all parties, a smooth flow of information, the responsiveness of the Risi Stone design team, and the speed of construction and performance of the Siena Stone System.

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