Desk Study and Site Investigation, reveals massive variances in the integrity of the underlying chalk bedrock at Watford redevelopment.
Ground & Water’s client was a property developer working in Hertfordshire
Watford is situated on the ‘Upper Chalk’ of the Chiltern Crest. During phase 1 reporting, a chalk dissolution risk assessment was carried out and identified the site to be at a low risk from ground dissolution stability hazards owing to the geology of Winter Hill Gravel Member overlying the Seaford Chalk Formation and Newhaven Chalk Formation (Undifferentiated). This classification means that soluble rocks are present within the ground and that some dissolution features may be present. The site and surrounding environs were also identified as an area where sporadic underground mining of restricted extent may have occurred, although historical maps did not identify any associated features marked on-site or within 250m. LiDAR imagery was reviewed; however, due to the heavily built-up nature of the site and surrounding environs, no meaningful data could be gained due to interference and shadowing from surrounding structures. The Peter Brett Associates Database revealed no features recorded within 250m of the site; that said, three sinkholes and five solution pipes were recorded at two sites between 340 – 479m to the east of the site within the same geology.
The site was located within central Watford in an area characterised by a mixture of residential and commercial properties. The existing development consisted of a block of flats with associated car parking and soft landscaping. The proposed development comprised the demolition of the existing structure with the construction of a new direct replacement, like-for-like block of flats. Ground & Water was instructed to carry out a comprehensive site investigation, including the production of phase 1 and phase 2 reports.