A new system for viewing and real time analysis of ground movement has been developed by piling and Ground Engineering contractor Kvaerner Cementation Foundations.
The Surpoint+ system was originally created for construction of a seven-storey basement on a major contract in Knightsbridge, London. Kvaerner Cementation says that it allows the observational method to be used, so that the most appropriate solutions can be chosen at each stage of construction.
Work involved installation of a 30m deep diaphragm wall, large diameter piling, mini piling, compensation grouting and extensive structural and ground instrumentation and monitoring.A shaft was also sunk from inside an existing building to the same level as the basement, with the two eventually being connected with a tunnel.
The project was a catalyst for developing the system, explains project manager Martin Kenwr ight .
'It was something that was needed to do the job properly, but we had an idea it would transfer to other projects.'
Sites in London are becoming more congested and confined, he says. 'Clients and owners of adjacent buildings were becoming increasingly concerned about the effects of excavations.'
The firm was already using six different packages to collect and process site data, 'an excessive number of packages to be working with, 'says Kenwright.
'We decided the only realistic option was to bring them all together in one new system.'
A CAD package was added to the data processing software.Business and information systems undergraduate Andrew Mothersele was given the task of developing the new software.
On the Knightsbridge contract, Surpoint+ was used to collect data from more than 2,500 instruments including precise level points, electrolevel beams, inclinometers, water levels, 3D survey targets and base traverse stations.
Monitoring frequencies for these varied from every 15 minutes for automatic real-time monitoring to once a week for manual instrumentation. On average 35,000 readings were recorded and analysed each week.
The firm says that because Surpoint+ records and inputs all measurements taken on site, the number of surveyors and engineers needed on site are reduced and human error minimised. A built-in error trapping facility means recorded values differing greatly from previous readings are identified for verification before they are entered on to the database.
Readings are taken and processed 24 hours a day. If Surpoint+ records a measurement change above a pre-determined level, it sends comprehensive details to engineers' pagers.All pager holders have access to the site computer system from home and can ensure movements are not significant - or take immediate action at any time of day or night.
'Basically, Surpoint+ records all the data on movement and displacement and puts it in a simple, sensible format which is flexible and easy to use, 'says Kvaerner Cementation project engineer Rob Dickson, who is in charge of monitoring on the Knightsbridge contract.
Based around a CAD drawing of the site, the system allows users to zoom in or pan out and focus on a particular area of the job. Userfriendly menus also let engineers filter data by instrument type, date, location, elevation, or a pre-defined instrument group.Reporting tools enable easily-understood tabular summaries and interpretative plots of critical data to be produced.
Surpoint+ showed its potential almost immediately in London where real-time readings revealed movement in the sevenstorey basement and its surrounding buildings was minimal. This allowed a change in programme with fewer supporting floors being installed during excavation, shaving 15 weeks off construction and producing savings of about £250,000.
The system has now been transferred to a smaller contract at Plantation House in the central London, where a hard-hard secant piled wall is being installed to depths of 35m inside existing retaining walls for a new office complex.
Busy roads, the District Line underground, the Docklands Light Railway, a small but ancient church, an office block and the usual mass of services surround the site.
Readings are being taken from 180 precise levelling points, electrolevel beams, in-place inclinometers, three-dimensional survey targets and boreholes.
Kenwright believes that the system provides a complete Ground Engineering and ground movement monitoring package, ideally suited to major excavation work in congested cities.