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Geotechnical software: Computer controlled construction

Remediation of a former quarry for a residential development is demonstrating the capability of geotechnical software to feed essential data into construction software. 

Show homes at a new David Wilson Homes (DWH) development on a former basalt quarry in Doseley near Telford are set to open their doors to prospective buyers in April. However it is unlikely viewers will know how essential geotechnical software has proven itself to be in efficiently taking data for scheme from site investigation and planning through to remediation and earthworks.

The “garden city” influence that DWH uses to describe the finished development of Doseley Park is a far cry from the site’s origins as a quarry and concrete products site. Over the last four years consultant Wardell Armstrong (WA) has used specialist software to use geotechnical data to its full advantage to reclaim the 28ha former quarry.

“The quarry, which operated two canals for the import of equipment and export of aggregates, closed in 1961,” says WA associate director Tim Cawood. “During quarrying, waste from the operation was used to partially backfill the quarry and a number of landfills later raised site levels further.”

This approach to backfilling meant that the material was highly variable and poorly engineered – not ideal for redevelopment.

“We collated all the site investigation records within Keynetix’s Holebase SI program to incorporate old datasets migrated from Holebase 3.1 using AGS files and new investigation data,” explains WA associate director Chris Smith. “This provided in excess of 130 boreholes and trial pits across the site.”

Using the ability to add web map services (WMS) links within Holebase, WA was able to check the investigation data against BGS and Coal Authority datasets and prepare a rapid assessment of the geology beneath the site.

“Having all site investigation data available in an easily accessible electronic format, with the ability to quickly visualise the ground conditions in 3D, made it possible to interrogate and remove rogue records from the data and correct errors before they became embedded into the engineering design,” says Smith.

WA then imported the ground investigation data into Autodesk’s Civil3D auto CAD software, using the Keynetix Keyhole plugin, to generate a 3D ground model. This model defined the extent and thickness of multiple types of made ground and the underlying natural strata.

“The 3D model was supplemented with accurate topographical survey data and drainage survey records to form a complete picture of the site,” adds Smith. “This allowed volumetric calculations to consider the cut and fill required within each of the made ground types, and to design the best earthworks strategy to avoid key drainage infrastructure.

“Site design levels were then iteratively adjusted to achieve a crude earthworks balance, considering the potential for bulking and reduction factors within each of the material type during earthworks processing, while providing adequate cover levels to the indicative site drainage strategy.”

According to Cawood, the overall rationale for the works design is to excavate and re-compact the on-site fill materials with sufficient control to allow the houses to be built on reinforced strip foundations.

“This represents a significant cost and programme saving compared to the alternatives, but increases the importance of earthworks performance and its validation,” he says.

Design and build contractor McAuliffe Civil Engineering developed a cut and fill model based on the initial WA design to allow the earthworks to be undertaken using machine control. A Topcon-equipped 3D GPS-controlled dozer and excavator were used to take the design from the model and into reality.

As well as using 3D GPS to create the earthworks, the system also creates a highly accurate model of the as-built earthworks, providing a high level of confidence for the client. The GPS equipment was also used by WA to record the locations of the in-situ testing and sampling that allowed the results to be incorporated back into Holebase, along with the AGS-formatted lab analysis.

“This permits rapid assessment of not only the results themselves but also their spatial context,” says Cawood.

“This project is an excellent example of how software, such as Holebase, can be used to fully integrate the collection, processing and transfer of geotechnical information.”

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