Structural remodelling of existing wall to function as anchored retaining wall - design case study

G. Belton, C.M. Merrifield, N. Garside

In the proceedings of: GEO2011: 64th Canadian Geotechnical Conference, 14th Pan-American Conference on Soil Mechanics and Geotechnical Engineering, 5th Pan-American Conference on Teaching and Learning of Geotechnical Engineering

Session: Retaining Walls

ABSTRACT: As part of the development of an inner city site including several pre-existing buildings, it was necessary to demolish a three storey municipal building, the rear wall of which was integrated into a reinforced concrete retaining structure. This paper describes processes followed to provide an economic and safe design for the reinforced concrete retaining wall. The iterative nature of the wall support design approach incorporated support from ground anchors; the locations, working loads and inclinations of which were optimized to avoid distress to the wall. Wall displacements were monitored during the demolition of the building, anchor installation and stressing. These show clearly the wall response to removal of support and subsequent application of anchor working loads. Based on the wall response it was concluded that the design approach was appropriate. Rigorous anchor testing demonstrated that the design anchor free and fixed lengths were appropriate.

RÉSUMÉ: Comme la partie du développement d'un site de ville intérieur y compris plusieurs bâtiments préexistants, c'était nécessaire de démolir un trois étage bâtiment municipal, le mur postérieur que dont a été intégré dans un béton renforcé qui retient la structure. Ce papier décrit des processus pour fournir une conception économique et sûre pour le mur de soutènement. La nature itérative de l'approche de conception de soutien de mur incorporée le soutien des ancres de sol; les emplacements, travaillant des chargements et des inclinations qu'a été optimisé dont éviter la détresse au mur. Les déplacements de mur ont été contrôlés pendant la démolition du bâtiment, d'installation d'ancre et d'accentuer. Ceux-ci montrent clairement la réponse du mur à l'enlèvement de soutien et l'application subséquente de chargements de fonctionnement d'ancre. La réponse du mur indique que l'approche de conception était appropriée. L'essai rigoureux d'ancre a démontré que les longueurs libères et fixés étaient approprié. 1. CONTEXT AND BRIEF As part of the redevelopment of a derelict site in central Huddersfield (West Yorkshire, UK) for the construction of a new further education campus, advance preparatory engineering works were required. The most significant item was to demolish an existing municipal building, West Riding House (WRH), along with other associated smaller buildings obstructing development. The building was situated adjacent to and appeared to form part of a retaining wall supporting a road (Manchester Road) at its crest. The challenge lay in the development of a support system for the wall to replace that provided by the building. 2. OBJECTIVES OF PAPER The paper presents, as a case study, two contiguous processes: (i) the investigation and analysis undertaken to assess how the retaining wall would behave with the building support removed and (ii) the development of a dynamic design to ensure the long term stability of the free standing wall to retain its function for an extended design life. The main objective of the paper is to present, as a case study, a design process able to respond to the phased discovery of the nature and behavior of an initially propped wall to ensure its long term stability as a free standing wall and to continue to function as a retaining structure with a live roadway at its crest. 3. EXISTING DATA ON CONDITION OF WALL AND WEST RIDING HOUSE The original wall was constructed circa 1968 along with the construction of WRH (Arup, 2006). Movement joints were visible within the wall stem immediately to the east and to the west of WRH. Either side of these joints were freestanding cantilever reinforced concrete retaining walls. Figure 1 shows WRH with the retaining wall directly behind it in the background. From the previous studies and investigations at the site (Arup, 2006 and 2009), there was no historical documented information available on the construction of the wall or of WRH. Limited structural investigations had been carried out previously while the building was still occupied, during which several cores through the floor slab and the walls were drilled (Arup, 2009).

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