The foresight that originally led Dywidag-Systems International to expand the use of tensioned bars in concrete superstructures to foundations and ground support systems is still influencing business growth.
Just over 50 years ago, Dywidag-Systems International (DSI) was enjoying immense success in pre stressed concrete bridge design, using post-tensioned rods to achieve record spans.
dublin nia micro piles
The resourceful minds that headed up the firm realised then that similar success could be achieved in different media – soil or rock – or in different types of structure such as piled foundations and embankments. In 1967, its 16mm threaded bar was marketed for use in ground and rock anchors and, in 1969, in piles, under the name “Gewi Piles”. Soon, DSI was known for more than just its products, but entire systems as well – to solve bigger problems.
The company, which was started in Germany in 1865 has continued its interest in understanding the synergies between bridge design and ground strengthening and is still expanding its products and services to meet changing customer needs. The firm’s recent restructuring has brought the company together to make better use of knowledge and experience gained worldwide, although it still aims to deliver solutions region by region.
“DSI has come up with many great solutions across the world,” says DSI Geotechnics global president Mike Kelley. “We are now better at understanding the global need for these solutions and can work closely with designers and contractors at a local level to deliver projects in a co-ordinated way.”
The firm’s main geotechnical areas of interest are in anchor and pile systems, which are used in projects involving slope stabilisation, excavation, dam and marine structures and tunnel portals.
Its bar product has been continually improved to perform better. “Double corrosion protection” of the bar, achieved by surrounding it in a plastic corrugated wrapping and grouting the annulus with cement, for example, sets the highest standard for durability for a 100 year-plus design life.
Complementing the bar product is a range of add-ons that improve productivity and safety on site.
“Superlatch”, for example, offers a safer method of connecting pile cages, where an approaching reinforcement cage activates a spring device pre-fitted onto the receiving cage in the shaft.
This enables the two to latch together automatically. The “hands-free” system has been used in the Battersea Power Station redevelopment site.
pic 3 superlatch brochure
The direction the firm is now taking goes beyond building new and into the realm of extending the life of existing structures. Alerted to customer concerns regarding the condition of ageing assets, DSI now offers a full monitoring package – to verify the as-built condition of its products using sensors and the ability to inspect and monitor them in the longer term. This then informs future repairs and maintenance so that more costly replacement is avoided for as long as possible. Although monitoring for tensile strength or ground movement has been carried out on past projects using its Dyna Force sensors (see box), the firm’s recent acquisitions allow it to offer inspection and monitoring as a more comprehensive service.
“Infrastructure is ageing and governments and asset owners are investing heavily in extending the life of their assets,” says DSI chief operating office Matti Kuivalainen.
Acquisition of Alpin Technik und Ingenieurservice in March this year enables the firm to use robots to inspect structures and infrastructure using photographic imaging, while acquisition of Datum Group in October means it can monitor the long-term health of structures.
Signs of deterioration in structures can be the result of nearby ground issues, continues Kuivalainen, so while a railway embankment is being monitored for movement, adjacent land and buildings should be monitored too to work out the relationship between them all. In the UK, where new infrastructure projects, such as HS2, will be built near existing railway infrastructure and historic structures, and in densely built-up areas, monitoring can add enormous value.
DSI intends to work with major infrastructure clients and developers to establish long-term monitoring programmes which can help manage these high-risk environments. Bridge owners in the US are already taking up the option of monitoring regularly beyond the construction or initial repair phase and it is expected that the ground engineering community will follow.
“Robots are commonly used to inspect cables on bridges. Repeating the activity periodically paints a picture of how it is deteriorating, which helps the bridge-owner make decisions on the future of the asset,” continues Kuivalainen.
“Eventually, the data will be valuable in predicting how other similar structures will age.”
Driven by safety, it will become common practice, Kuivalainen says, to inspect and monitor and predict and maintain to extend the life of new structures and infrastructure.
“Sensor technology has improved, so monitoring is more economically viable to the point where asset owners will soon be asking themselves, ‘Why wouldn’t I want to monitor the condition of my asset?’”
Equipment in action
The 50-year-old spillway of Boundary Dam near Estevan in the Canadian province of Saskatchewan had suffered frost damage. Built over rock, post-tensioned anchors were going to be installed as part of the repair programme.
To determine how stress was distributed along the anchor bond zone, test anchors were installed in the ground with Dyna Force sensors. Results revealed that load was transferred to the first half of the bonded length, resulting in shorter anchors being feasible for the fi nal solution. This led to material, programme and cost savings.
Deep excavations for new reactors at Hinkley Point C nuclear power station were monitored using Dyna Force sensors to understand changes in stress in the ground. The sensors acted as an early warning system to alert engineers of ground movement and high stress. The sensors worked in conjunction with some 14,000 Gewi soil nails of 25mm to 40mm diameter, installed to depths of up to 13.5m to support excavations. Ground movement was expected because some excavations were known to cross fault zones.
When sensors indicated ground movement, additional bolts or anchors were installed before the excavation advanced. Sensors were also used to verify that heavy machinery operating near the excavation were not exacerbating the situation. Continuous slope monitoring, with readings analysed remotely, ensured that ground movements were kept under control. Although sensors were only used to monitor the ground during the construction phase, the owner has the option to use the equipment to monitor for a further 50 years.
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