Case Study: Blaenavon

A designated World Heritage site, Blaenavon was one of the first large scale centres of iron production. The latest phase of conservation of this historical industrial site involves work to stabilise and conserve retaining walls built into the hillside behind the site’s five furnaces.

Sub-contractor, Ascend Rope Access (Cymru) has recently completed the ifrst stage to consolidate the southern section (Area 2) of an original Gas Tunnel which runs behind five furnaces. Welsh Consulting Engineers, Veryards Ltd specified the Cintec system, manufactures by Cintec International. Veryards, term engineers to Cadw, (Welsh Historic Monuments), are Project Managers for the current works on behalf of the client, Cadw. Thyssen Construction Ltd is the main contractor. Cintec anchors feature a patented encapsulating sleeve or ‘sock’, which is injected with cementitious grout to provide a continuous bond into the masonry. A variety of Cintec anchors are also being used for current work to stabilise and consolidate further sections of stone masonry retaining walls in Area 3, behind the position once occupied by the middle furnace.

Conservation of the Blaenavon Ironworks began as long ago as 1974, when the site passed into the public sector and the ownership of Cadw. The Cintec system has been successfully used over the last decade for the conservation of furnaces and other masonry structures on the site.

Tunnel Conservation

The cylindrical bricks gas tunnel in Work Area 2 runs behind the furnace bank wall at a height of about 10 meters from the ground. An old collapse of a section of the wall has left the broken remains of part of the tunnel in a precarious state of the steep slope. The tunnel was originally supported on iron plates and cylindrical bars spanning onto stone masonry walls. Much of the outer support wall is now missing, leaving the tunnel remains with little obvious support and unsafe to access from below.

The first stage of conservation has involved the installation of Cintec anchors through the brickwork of the tunnel into stone masonry and the embankment behind, to support the weight of the tunnel. The anchoring operation will allow safe access to be achieved from below, for the rebuilding of support masonry. The instability of the remains precluded access from above was the specified method of installation.

Riddled with Voids

The exact composition of the tunnel remnants and interfacing wall structures was unknown. Initial drilling of cores for the anchors confirmed that the 200+ year old structures were riddles with voids and inconsistent mix of stone masonry, clay and coal. The fully encapsulated design of the Cintec system offered an efficient way of stabilising these wall conditions. By containing the grout, the Cintec sock ensures none is lost and there is no undesirable migration into other parts of the structure. An optimum amount of grout is taken into the sock in achieving a sound, continuously embedded structural solution in the wall regardless of voids.

David Dunstan, Project Engineer at Veryards, says: “The expanding sock of the Cintec system keys into all materials along its length, including poor quality masonry. This effectively binds together all of the various materials penetrated, resulting in good cohesion and consolidation, particularly in the masonry walls undergoing stabilisation in Areas 2 and 3.”

A total of 29 deformed round bar stainless steel Cintec anchors, measuring 20mm diameter and 4m long, were used in Area 2. A combination of 8m long consolidating stitching anchors, 30mm by 30mm by 3mm SHS (square hollow section), and ground anchors approximately 11m long, were used in Area 3.

Speed and convenience of installation were also factors in Veryard’s specification of the Cintec system. Installation is simple, self-contained and requires the minimum of intervention, an important benefit to heritage work. Neil Black, Project Manager for the installers, Ascend, said: “The Cintec sock definitely saved us time and material, and gave us some control and predictability in dealing with unknown and therefore difficult wall conditions.”

Cintec anchors were selected for their sensitivity to other important aspects of the conservation of historic monuments. The grout used, known as Presstec, is based on Portland cement, and provides natural compatibility with the original stone and brick materials found in historic structures. The anchors can also be installed without visible impact on the surface of the structure.

David Dunstan of Veryard’s says: “The Cintec system allows effective anchoring without the need for external plates and capping details. The anchor can be terminated within the wall, and the masonry core reset in position, leaving minimal visual impact.”

The Cintec system is approved by The National Trust, English Heritage and CADW for the restoration of all types of listed and protected structures.