Temporary Strand Anchors Stabilize Slurry Wall at the New S8 Express Road

During the last few years, road infrastructure development has become one of the main objectives of Poland’s government. Ever since Poland and Ukraine were selected to host the European Football Championship Euro 2012, it has become very hard to find a place in Poland where people are not busy building a new road.

Context

On the west side of Warsaw, the new S8 express road is currently being built. The connection of the planned A2 motorway west of Warsaw to the existing Armii Krajower route will become a part of the northern Warsaw ring road. The S8 budget is approximately 500 Mio. Euros. Work started in February 2008 and was finished at the end of 2010.

The new 10.4km long road section along the S8 will have three 3.5m wide lanes per driving direction. In addition, the road will have 2.5m wide emergency lanes in each direction as well as a 4m wide median strip. Three segments of the road with a total length of 2.6km will be built below ground water level, which is why they have to be stabilized by slurry walls with bottom slabs.

Due to the high ground water level, the non-cohesive soils, the depth of the concrete slab and the slurry wall span, a horizontal diaphragm had to be built before the excavation was carried out. This “plug” was made of 1.6m diameter jet-grouted plugs with an overlap of 0.25m. Depending on excavation depths, plug thickness ranged from 1 to 4m, and they were positioned at depths of up to 17m. Additionally, the excavations were divided into smaller segments, which were closed with jet-grouted facing walls. The palisades used had diameters of 80cm and maximum lengths of 10m.

Solution

Until the concrete slabs are in place and can decrease the bending force in the slurry walls, additional temporary support is necessary to withstand the loads during the excavation phase.

DSI Poland supplied a total of 1,730 Temporary Strand Anchors (140mm2 Type SUSPA-Systems 6-5 GR1570/1770) in total lengths of approximately 21m and with bond lengths of approximately 8-9m. Three injection pipes were installed on every anchor for the grouting process. The anchors fulfilled all the requirements of European Standard EN 1537 in terms of corrosion protection for temporary anchors.

DSI Poland also supplied two complete stressing units with ultra light CFK Hollow-Piston Jacks, 1,175kN – 25kg. Every anchor was stressed and checked according to test method No. 3 of EN 1537. In this method, creep is measured between the 3rd and the 15th minute with constant loads of 0.9Pt0.1k – 955kN. Seven days after completion of the concrete bottom slab, the anchors were cut off and the holes in the slurry walls were filled with cement grout.

Supplytechnical assistance

AARSLEFF Sp. z o.o., Warsaw, Poland

Joint venture consisting of TPF PLANEGE – Consultores de Engenharia e Gestão S.A., Lisbon, Portugal and E&L Architects Sp. z o.o.,Warsaw, Poland