AWA~ -D OF EXCELLENCE Category: Buildings

GOLDER ASSOCIATES

Library of Parliament Excavation Using mining techniques and careful sequencing, engineers excavated below one of Canada's most important heritage buildings in Ottawa.

T he Library of Parliament in Ottawa is the only re­maining part of the original Centre Block and the most prestigious structure on Parliament Hill. Com­pleted in 1876, the building was acclaimed both in

Canada and abroad for its beauty and grandeur. Planning studies for a comprehensive conservation, reha­

bilitation and upgrade program for the building were launch­ed in 1995 and a three-year construction phase began in 2002. Renovations were required all the way from the weathervane on the pinnacle of the roof, down to the heating, ventilating and air-conditioning (HVAC) system in the sub-basement.

To provide proper indoor environmental conditions, a much larger space was required for the mechanical systems and ducts. A new, visible, above-ground expansion of the Li­brary building was unacceptable, since any new structure would affect existing aesthetics and the national heritage en­vironment of Parliament Hill.

Excavation risks Substantial technical risk was involved in undertaking ex­cavations close to and under the rings of heavily loaded, masonry walls. Any work had to avoid damaging the build­ing's dome and roof, its leaded windows and its mas0nry support walls and flying buttresses.

Golder Associates, as geotechnical subconsultant to the architects, had to tackle the geotechnical risks of creating the required space underground in a cost-effective manner, while maintaining the integrity of the heritage building.

The company developed innovative rock engineering solutions and used a staged excavation sequence to allow the rock to be safely removed while preserving and im­proving the strength and integrity of the fissured , bed­ded sedimentary limestone bedrock.

The level of technical risk associated with the rock ex­cavations beneath the Library is comparable with other

EAST TOWER ~ I i I i

WEST TOWER ~ !

CENTRE BLOCK ( BEYOND)

EXISTING FILLED-' VENTILATION TUNNELC4

NEW MECHANICAL ROOM

NEW ELEVATOR SHAFT

44 www.canadianconsultingengineer.com October/November 2004

Left: excavations are close to the 1867 building. Centre: layout of HVAC showing required ducts; many computer models were used to develop the support structure and appropriate sequencing. Right tunnel.

world class heritage rehabilitation projects, such as the un­derpinning of the mediaeval towers of York Minster or the recent remediation of the Leaning Tower of Pisa.

Design approach Golder set stringent design requirements: (a) that rock mass excavation would be by mechanical methods only, (b) that vibrations would be maintained below critical threshold peak particle vibration (PPV) and frequency limits, (c) close perimeter line drilling would be used, and (d) an elaborate array of pre-support and rock reinforcement, plus grQuting of prominent fissures would be specified.

Control of the rock excavation sequencing and near real-time monitoring of the movements of both the rock and the foundation zones were critical. Various analytical and two- and three-dimensional numerical modelling methods were used to optimize the excavation geometries and formulate rock support layouts. Similarly, models were developed to time the pre-support installation and to de­velop appropriate sequencing for the staged excavation.

Based on the modelling, discrete areas of rock mass overstress or building impact were identified either for concentrated rock reinforcement, or to rearrange the ex­cavation layouts to mitigate any stability problems.

Areas identified as requiring additional support were the abutment zones to the intersection of the Link Tunnel with the Main Mechanical Room, and also its intersection with other discrete excavations, such as the Elevator Shaft. In these areas the rock mass could have lost confinement due to the effects of stress interaction. Also, because of increased degrees of free­dom created by re-entrant (indent) excavation geometries, wedges or blocks might be freed to slide or rotate on pre-exist­ing discontinuities and along newly created tensile fractures.

For rock mass zones where general de-stressing had the potential to extend into the crowns or side walls of the ex­cavations, the engineers developed patterned reinforce­ment layouts to keep the total movements below levels that might affect the overlying masonry structure.

Because access to the heritage structure was limited, the use of typical large-scale civil engineering equipment was con-

strained. Golder decided that mining approaches, more usu­ally used for ventilation and ore pass construction, would work better for the complex HVAC system duct work requirements.

Golder proposed that it would be best not to use the exist­ing historic openings through the masonry walls, but instead to create an external access shaft and tunnel under the existing foundations, thereby allowing more rapid excavation progress.

The project used a mix of conventional construction methods such as hoe-ramming to remove rock and per­cussion drilling for the anchor installations, along with ad­vanced techniques such as: • sawing and precision line drilling; • continuous perimeter controlled coring for very tight tol­erance areas; • specialized installation of extensive steel and fibreglass pre-support; • application of hydraulic rock splitting technology; • use of a raise bore drill for construction of vent ducts; • installation of needle beams and concrete packing for underpinning the masonry walls.

During the excavation, arrays of high-precision instru­ments were used to monitor displacements of the rock mass (dilation, tilt, settlement, shear), and of the masonry ring walls

continued on page 46

Name of project: Excavation for Renovation of Library of Parliament, Ottawa Award-winningfirm: Golder Associates, Mississauga and Ottawa (Dr. Trevor G. Carter, P.Eng., Gerry S. Webb, P.Eng., Philip de Graaf, P.Eng., Mark] Telesnicki, P.Eng., Daryl Miller) Owner: Public Works and Government Services Canada Client: Ogilvie and Hogg, Desnoyers Mercure & associes, Spencer R. Higgins and Lundholm Associates, architects in joint venture Other key players: Adjeleian Allen Rubeli (structural engineering); Pageau, Morel & associes (mechanical & electrical engineering); Thomas Fuller Construction (general contractor); Dibco Underground (excavation); JS. Redpath (raise bores); GeoFoundations (grouting); Fondex (instrumentation) Suppliers: Marathon Drilling (drilling); Multicrete Systems (Shotcrete ); Roctest (instrumentation)

October/November 2004 Canadian Consulting Engineer 45

continued from page 45

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(deflection, tilt, settlement) , as well as potential groundwater level changes. The state-of-the-art geotechnical instru­mentation included multi-point and sonic probe borehole extensometers, joint meters, piezometers, tilt beams, strain gauges, as well as convergence and inclinometer arrays.

The rock engineering aspects of the Library project met the approved budgets and schedule for the design phase. All major rock excavation and associated monitoring was completed on schedule by December 2003. The project was completed without dam­aging the heritage structure, and with­out disrupting the operations of Par­liament or public events such as the Changing of the Guard ceremony.

The Parliamentary Precinct, in­cluding the Library of Parliament, is a National Historic Site, designated as one of only three heritage cultur­al landscapes in Canada, and a major tourist attraction. The protection of the building's heritage status and the guaranteed operation of essential building systems is key to preserving this heritage treasure as a national trust for future generations. CCE

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- Ground Engineering

<I and Environmental Services ~ Golder :Associates

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46 www.canadianconsultingengineer.com October/November 2004

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