Reed Place, Harpenden - Excavation Monitoring

The planned construction of a five-storey apartment building incorporating a basement and lower ground floor in leafy Harpenden, England was not straightforward. The building site, which would incorporate an underground car park and require foundation and excavation works on uneven and complex ground, was bordered by two adjacent residential properties and a Grade II Listed historic wall.

Due to the configuration and characteristics of the complex building site, as well as the need to protect the developer against any potential future liability, and most importantly to ensure no damage to the two adjacent properties in this densely populated residential street, RSK Environmental and MKMT Associates needed a monitoring solution.

RSK had used Senceive’s precise and accurate monitoring solutions on other successful construction projects. They wanted to offer MKMT a full monitoring solution and asked us to provide them with a kit for movement monitoring on the two adjacent homes as well as the historic wall.

14 triaxial tilt sensors – each attached to tilt beams - were installed on the exterior of the two homes facing the building site as well as two solar powered gateways – one on each house. An additional 8 tilt sensors on tilt beams were installed on the Listed retaining wall.

The sensors monitored for rotational stability (and implicitly structural stability) of the external building walls and historic wall. The decision to deploy tilt sensor nodes fixed to beams rather than directly onto the masonry walls was made in order to assess movement over a wider zone and therefore provide a more comprehensive assessment.

All 22 tilt nodes were configured to both gateways. This meant that, in the unlikely event of a gateway failure, the monitoring system would have a backup gateway.

The sensors and gateways were installed in just a few hours to provide a wire and mains-power free solution. The mesh network formed by the sensors was able to relay data from the sensors to the gateways and onto WebMonitor™, Senceive’s data visualisation software which can be fully customised to set up alert levels.

The system was configured to upload data automatically every 20 minutes throughout the course of the works. Authorised users were given access to the data using any device (computer, tablet or phone). The system was set up to send automated alerts by SMS and email in the event of any movement beyond the established threshold values.

An accurate and fail-safe monitoring system was compulsory to ensure a safe excavation process. The homeowners of the two adjacent homes were very satisfied and reassured by the solution.