Small Craft Facilities

Riggs was retained by Small Craft Harbours to redesign and supervise the reconstruction of both the outer and inner legs of the Batchawana Bay wharf. This structure is on the shoreline of Lake Superior at Batchawana Bay, approximately 72km north of Sault Ste. Marie, Ontario.

The original outer leg consisted of timber decking supported on timber stringers, pile caps and piles with bracing between the piles for lateral restraint. The inner leg consisted of timber decking supported on stringers, pile caps, piles and continuous closed face timber piles. The outer leg had suffered severe deterioration.

Riggs redesigned the wharf with vertical steel H-piles, steel sheet piling and a timber superstructure. Finite element analysis was used to design each structural component of the wharf. The initial design of the new wharf included battered piles; however since they produce large uplift forces from ice impact, the design was changed to vertical piles. Since vertical piles do not provide sufficient lateral restraint, an additional pile cap was introduced which runs perpendicular to the frame. Moment connections were designed at all pile cap locations. This system provided better lateral restraint and smaller uplift forces. The H-piles were driven to stiff, silty clay to provide sufficient bearing so that settlement of the structure, due to live load, does not occur and to acquire adequate skin resistance to prevent uplift.

Riggs undertook a condition survey of the popular timber boardwalk wharf in Tobermory (which is located at the northern tip of the Bruce Peninsula) in 2007-08. The timber wharf suffered from deterioration of the crib timbers, basal instability related to inadequate bearing capacity and possibly scouring at the lake bed. As well, the timber deck had numerous trip hazards due to the deterioration of the timber stringers.

The solution involved demolition of the timber work to the low water line and reconstruction with precast concrete elements. The stability of the cribs as well as the precast concrete elements was analyzed using classical limit equilibrium methods. The precast concrete elements were simulated using finite element software as shell elements and both the shape and reinforcing steel were optimized. The stability of the cribs was enhanced by employing helical pier anchors in 2010.

Riggs was engaged by Ontario Northland to propose and design temporary floating docks for the ferry Niska, which provides service to Moose Factory Island and design a marine railway and ferry cradle for winter storage of the ferry at the Moosonee terminal.

The designs included 3-D hydrodynamic modeling of 50 km of the Moose River and a sediment re-suspension study taking into account peak tidal currents with and without boat/ferry motion. A design of underwater structures to withstand ice scouring and impacts was also undertaken, as well as soundings of the Moose River between Moosonee and Moose Factory Island.

Riggs provided the following services:

• Detailed design of the floating docks, marine railway and ferry cradle.
• Plans and specifications for all three contracts.
• Contract administration and residential site services.

Riggs was retained by Fisheries and Oceans Canada to investigate the condition of the existing piers in the commercial fishing basin in the Rondeau Harbour, at Erieau, Ontario (located on the north shore of Lake Erie).

The investigation determined that the timber on the existing timber laminate composite deck was deteriorated and the timber piles caps were showing sign of rot and vessel impact damage.

Riggs designed and supervised the rehabilitation. The project included the following:

• Replacement of the deteriorating timber laminate composite deck and timber pile caps.
• Demolition of the existing deck down to the top of the existing timber piles. These piles were preserved for re-use.
• New tightly-fit high density polyethylene pipes were placed over the existing pipe and the annular space filled with grout. The existing timber pile caps were replaced with new steel hollow structural steel sections and pinned to the top of the piles.
• Rehabilitation required a deck system and pile caps not exceed the mass of the existing system. Mass was reduced by using precast hollow core slabs with a bonded concrete topping.