Widening of the M1: Great Britain’s Largest Soil Nailing Project
The M1 motorway in Great Britain links London with the North of the country. The motorway, which was built in the 1950’s, is one of the most important connections in the country and is heavily overburdened.
Consequently, the motorway is now being widened north of London between interchanges 10 and 13, between Luton and Milton Keynes. Construction work is being carried out on the hard shoulders so that they can be used as additional lanes during peak hours.
For stabilizing the motorway embankments, DSI supplied 17,000 Type R38 DYWI® Drill Hollow Bar Soil Nails in lengths of 6-10m and with a total length of 150,000m as well as Ø 25mm GEWI® Soil Nails for the clay areas. All the soil nails are top bar galvanized with formed bearing plates and domed nuts for angle compensation.
The engineer chose to use hollow bars because they allow simultaneous drilling and grouting and ensure that grout is placed at all points within the ground as drilling is advanced.
DSI worked closely with the drilling contractor in order to design the most suitable drilling equipment that could reach over the embankments.
Furthermore, DSI consulted with the contractor on the selection of rotary percussive top hammers (drifters) to ensure correct rotation speeds (120 RPM) and blow rates of the hammer (400-600 BPM).
DSI also tested the soil nails and worked up a testing method for the hollow bars with the designers. In this method, which has become known as the long and short nail testing method, tests are applied to sacrificial soil nails, and the resulting design load is calculated by taking the load of the short nail away from that of the long nail. Thanks to this method, bond stress in the stable zone can be quantified.
Construction work was carried out from February 2010 to September 2011 on only one lane at a time in order not to cause any disruptions to traffic in the area.