Where SBMAs reduce costs
SBMAs achieve significantly higher working loads than conventional anchors installed in soils and weak rocks. By doubling the achievable loads, the number of anchors required for a particular structure can be effectively halved.
Such dramatic reductions in the number of required anchors means:
- Less drilling rig set ups
- Fewer drilled holes
- Lower grout usage
- Minimized stressing operations
This results in significant savings on any given project where SBMAs can be used in place of conventional anchors.
The following is an illustration of cost savings on a real SBMA project:
€10M saving on Austrian Autobahn
The failure of a steeply sloping embankment carrying an Alpine section of the A2 Autobahn in Austria was on the cards without effective stabilisation.
A 330m stretch set above a steep dam at Degendamm had long been regarded as a particularly dangerous slope. Stabilisation had originally been carried out on the 55m high slope when the four-lane carriageway was built in 1985, when 400 permanent anchors, each with a working load of 1000kN, were installed.
Further work was carried out in 2004-05, which included 6.4m diameter concrete wells being installed at the bottom of the slope.
But these measures were not sufficient to create stable conditions.
The embankment had seen 40-50mm of movement over the past five years and this slope would have failed without an effective stabilisation programme.
Inspection of the the existing anchor heads revealed signs of corrosion and that many prestressing strands had suffered extension of the the peripheral wires and depression of the king wires, suggesting overloading.
Replacement of the anchors looked to be a prohibitively expensive option. The original anchors could not be re-stressed as they were designed to accommodate a working load of 1000kN and in many cases would have failed if additional loads were applied. So it was decided that new anchors should be installed around the existing ones.
At Degendamm, working loads were effectively doubled by using SBMAs, thereby halving the number of anchors required.
Austria’s motorway operator ASFINAG initially planned to install 400 replacement anchors, each with a working load of 1,900kN to prevent the high risk slope from failing.
The total cost of using conventional anchors was estimated at €40M.
The SBMA system was proposed as an innovative and economical alternative. Working loads on the project were double the estimated loads of the proposed conventional anchors and the total number of required anchors halved.
The original solution was based on each of the 400 conventional anchors having a 1,900kN working load resulting in a total of 40,000 linear metres of drilling.
Using SBMAs at Degendamm shaved an enormous €10M (£9.1M, $14.5M) from the original estimated project costs.
The use of the SBMA system meant that the total linear meters drilled was reduced to just 17,000m.
The Degendamm project was completed in significantly less time than an equivalent conventional anchor project would have taken and well ahead of schedule.
It has been estimated that a conventional anchor project would have taken in excess of 50% more time to completion due to the mobilisation required to drill additional lengths.
Using SBMAs at Degendamm shaved an enormous €10M (£9.1M, $14.5M) from the original estimated project costs.