Stabilising the foundations – underpinning works at Woodford Green 

The Maybank Building at Latchett Hall, Woodford Green had been subject to subsidence over the years, which had come to light through visible cracking in the walls. Church Growth Trust (CGT) worked alongside a consulting Structural Engineer to determine the cause of the issues and possible remediations. 

A ground investigation was carried out which included the digging of trial holes to check on the make-up of the existing ground, and the foundations were exposed to check their depth and dimensions. 

The existing foundations were found to be quite shallow, with some notable voids within the surrounding ground. The mature trees in the vicinity of the Maybank Building meant shrinkage was likely to be a contributing factor. Shrinkage occurs when nearby tree roots extract most of the moisture from the ground during the warm, dry summer months. The subsequent lack of water in the ground causes the clay to shrink and, in turn, causes the foundations to shift. 

Work on these mature trees including the lopping, reduction, and removal of existing tree stumps, was a vital part of the remedial solution. This work required an application to the Local Planning Authority given that the trees had Tree Protection Orders (TPOs). 

Underpinning was then required to prevent the voids underneath the foundations from causing slippage and further cracking to the walls. There were options to carry out the underpinning via either traditional mass concrete infill (in essence to excavate under the foundations and pump in a depth of concrete to support them from below) or via geopolymer injection. 

To keep costs down and minimise disruption to the church, it was decided that rather than opting for traditional concrete infill, they would carry out the underpinning via geopolymer injection. The first step was to check the condition of the existing drains followed by an underground trace to check the area was clear of underground services. Holes were then drilled into the ground with several thin tubes fed into them. The geopolymer material was then pumped in, filling the voids, and stabilising the ground below. 

CGT is delighted to say that the works were all completed in a tidy, timely fashion and within budget. We hope and pray that these works will ensure the stability of the foundations of the Maybank Building, allowing the church to focus on their future ministry and outreach work.