Cintec International Ltd were invited to devise a scheme in conjunction with the client’s structural engineers, for the stabilization of a magnificent Grade 2* listed building in 2023. 

Built between 1743 and 1764 the Neo-Palladian style building had been in commercial usage for many years and been subject to extensive alterations and modifications during that part of  its life. 

In addition to alterations the structure had suffered movement due to poor ground beneath old timber foundations which necessitated substantial underpinning. 

Major new modifications and alterations were now planned making the complete stabilization necessary before those works commenced. 

A further complication was the listed status of the building as a number of large new structural  openings would be formed at basement level requiring removal of long lengths of thick internal  structural walls at that level. 

Consequently the traditional support method of needling and propping the walls above new  openings was not possible as the internal walls needed to be preserved by the conservation  architects. 

Cintec International and their engineers MDHP were therefore tasked with the design of the  anchor support system which would be installed within the internal walls above all the new  openings, to carry the imposed loads which were up to 700kN/m. 

The blue shaded areas in the plan above indicate the intended location of the Cintec anchors within the  ground floor walls above the new openings in the basement. So a substantial proportion of the walls  would be removed which presented a huge structural challenge. 

The walls were up to 1200mm in thickness and consisted mostly of brickwork of varying ages and quality.

Preserving the Past for the Future

The first task was to install 12mm diameter Cintec consolidation anchors to all  areas of walls at ground  and basement levels which  would be affected by the  works to form openings. 

The nature of the walls  was variable and to ensure  their structural integrity, as  the imposed loads were so high being up to 700kN/m, the anchors were installed at approximately 500mm  horizontal vertical intervals  and at closer centers if  deemed necessary by the  engineer, and around  openings installed at  300mm centers. 

A further important task  was to provide lateral restraint to all internal and external walls which would  provide the necessary stability both during alterations and to ensure longevity in the future. This was accomplished by  installing threaded Cintec anchors to the perimeter of every floor and attaching  either an “Armlock” or “X Lock” fitted to the joists. 

This then used the floors as a diaphragm and created a  stable “box” structure within the building. A total in excess of 300 lateral restraint devices were  installed.

In conjunction with the client’s engineers the specification and methods of lateral restraint were agreed. The consolidation anchor and main reinforcement anchors were determined by MDHP’s calculations using the imposed load advised by the client’s engineers. 

The general layout and pattern were agreed along with the extent and scope of work. Longitudinal stitching anchors were agreed and shown on the construction drawings along with schedules for lateral restraint and consolidation. 

All agreed anchor locations were shown on the construction drawings subsequent to agreement by the project architects and conservation officer. The lines in red and blue indicate anchors.

Once the Cintec consolidation anchors had been installed the main anchors could be installed within the ground floor wall thicknesses to carry the imposed loads being up to 700kN/m. 

The anchors were Cintec GB24 in 65mm diameter core  drilled holes and up to 11.00 meters in length. As these anchors could not be drilled externally from the  building as access was restricted by either too much scaffolding or none at all, all the drilling had to be from within the door openings in each respective wall at ground floor level. This entailed making the anchors in 1500mm lengths and coupling them together whilst feeding them into each side of  the openings to the correct overall length. 

Grouting was then carried out in both directions. The restriction on drilling and installing increased the duration of the operation but additional teams of operatives were  used to carry out works concurrently. In excess of 600 meters of the GB24 anchors were installed. After the anchor installation was completed the ground floor  openings, from where the drilling was carried out, required  propping and strutting to resist compression forces when the  wall below was removed. 

This was only a temporary measure as reinforced concrete portals would be formed as permanent support for the new openings. As the imposed loads were of a high magnitude the engineers required temporary intermediate propping in the basement to reduce the unsupported span during the opening up  works to a maximum of 1250mm and each capable of carrying 325kN load. 

Additional 12mm stud anchors were installed into the sides of new openings to tie the new in-situ concrete portals to the  existing masonry. Finally, a total of more than 180 meters of Cintec 16mm diameter stitching anchors in 65mm diameter holes, up to 10 meters in length, were installed into the two end walls to provide additional restraint to the east façade and to stitch over  existing vertical cracks in both walls. 

Despite the working and access restrictions the structural stabilization works were completed on program and without  any issues being experienced when the openings up to  5.00m in width were formed at basement level.