Given the relatively high land and property values in London (and its outer suburbs), basement construction has become increasingly popular in recent years. Several local authorities have recognised that the construction of basements has the potential to impact on flooding, groundwater, land stability and the structural stability of adjoining/neighbouring properties.
Therefore, a number of London Boroughs, notably Camden, Westminster, Kensington & Chelsea require a specific Basement Impact Assessment (BIA) at the planning stage to assess the hydrogeological, hydrological and geotechnical impact of a basement construction on neighbouring properties.
In 2009, the London Borough of Kensington and Chelsea produced their own planning guidance document entitled “Subterranean Development”. The London Borough of Camden adopted a similar approach for their use in planning applications involving basements (Camden development policy DP27). The Camden Basement Development document (CPG4) presents a structured approach which identifies the potential risks in a five-stage Basement Impact Assessment (BIA) process. The overall process has now also being adopted by a number of other London Boroughs as a template for their own assessment of basement construction applications.
Southern Testing has produced a significant number of Basement Impact Assessments (BIA) in the last few years to comply with local authority planning requirements. Our clients have included individual householders, architects, structural engineers and specialist basement design and construction companies. We can provide Geotechnical, Hydrogeological and Hydrological Basement Impact Reports to support planning submissions. As now required by many London Boroughs, our experienced geological, geotechnical and hydrogeological specialists have the relevant Chartered Engineering, Geologist and Environmental qualifications to act as signatories.
Our Basement Impact Assessment (BIA) services include:
Stage 1 and 2 – Screening and Scoping Reports; Risk based reports to assess the potential impact on factors such as surface flow and flooding, local groundwater flow, potential ground movement and the structural stability of adjoining/neighbouring properties.
Stage 3 – Ground Investigation Reports; We can specify and carry out the ground investigation to establish soil and groundwater conditions. We operate a variety of drilling equipment to enable ground investigation in restricted access site environments such as within existing basements, light-wells, buildings, low headroom areas, rear gardens and on steep slopes, where conventional equipment cannot be mobilised.
Stage 4 – Impact analysis; We carry out detailed analyses (if required) on the effects of the basement construction in terms of ground movements and damage category assessment of neighbouring structures and adjacent buildings, slope stability and groundwater flows using specialist analytical software such as Pdisp, Xdisp, SlopeW and ModFlow (three-dimensional finite-difference groundwater modelling).
Close liaison with the Clients’ Architect and Structural Engineer at all stages is essential.