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Buried plates prop Victorian wall

Forming retreats for slow-worms proved just one of a number of unusual requests for contractor Phi Group on a recent soil nailing contract in Worcester

Movements and partial collapse of a 130 year old brick retaining wall at Landsdowne Crescent in Worcester had led to partial closure of the road. Previous attempts to prop the wall had failed and in places the wall appeared to be moving away from the stationary buttresses.

Conservation requirements added significantly to the technical challenges of the task of stabilisation.

First step was partial clearance of existing trees and shrubs in a small strip of woodland which ran along the toe of the wall.

Some trees had to be left in place and where rig access was restricted, contractor Phi Group adopted hand drilling using Ischebeck Titan self drilling hollow core nails.

A more unusual conservation issue came from slowworms migrating from nearby allotments into the woodland strip where they habitually hibernate for the winter. With remedial work taking place during the worms' migration period, there was ecological concern over the slow-worms' chances of surviving the journey.

The conflict was resolved after consultation with wildlife specialists who recommended creating mounds of soft earth into which the worms would preferentially hibernate - safely away from the hazardous site equipment.

Given the age and aesthetic value of the wall, the client wanted to avoid defacing its Victorian charm by fixing nails and bearing plates on the face. Phi Group overcame this by coring out the wall at each of the 420 nail positions to a depth of 250mm, fixing the nail plates and replacing the core.

Phi assessed the bearing pressure of each plate position and improved areas of poor quality mortar by pressure grouting before fixing the nail plates.

With the nails in place, Phi replaced the circular brick cores, and by selecting a mortar to match the original lime-based product, produced a repair that is invisible at a distance Structural work, including rebuilding another section of wall and localised repointing, was completed in eight weeks.

The company will plant replacement trees, once the slowworms have returned to their allotments in the spring.

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