A capping of Made Ground was noted to overlie the superficial River Terrace Deposits within both boreholes; however, there were significant changes between both boreholes, summarised below.

Based on the results of the site investigation and findings from laboratory geotechnical testing, the following possible causes for subsidence were noted:

• At both TP1 and TP2, the exposed foundations were both marginally below the minimum required foundation depth for medium volume change potential soils (0.90m bgl)
• Given the medium volume change potential of the soils encountered, and the varied moisture content profiles, the soils underlying foundations may be susceptible to shrink and swell cycles, possibly causing subsidence
• Given the soft spots and deeper Made Ground in WS1, when compared to WS2, an element of contrast might have been introduced, with a potential for a possible differential settlement regime
• Whilst fresh roots were only proven to 0.50m bgl, dense vegetation was noted at the wall location
• It was considered that groundwater was too deep to effect the existing foundations of the wall; however, should any leaking drainage or perched water be encountered, differential movements may be exacerbated.

After discussions with the structural engineer, it was considered that the cracks close to WS1/TP1 were from structural reasons, rather than geotechnical reasons, given the cracks were localised to the top of the wall and no red flags were noted at WS1/TP1 following the site investigation. WS2/TP2 however was considered to be from geotechnical reasons and was required to be remediated.

The reporting, finalised within less than a month from the conclusion of site works, provided details to the client in order to finalise its design.