Stabilization measures of a slope affected by the North Pyrenean fault along the northern autoroute. (Medidas de estabilizacion de un talud afectado por la Falla Norpirenaica en la autovia del norte.)

Near the provinces border between Navara and GuipCzcoa, near the town of Leitza, the North Pyrenean Fault affects the Northern Autoroute (Pamplona - San Sebastian). The freeway in this area has been built by excavation with 40 metre slopes on the right-hand side, and 6-7 metres ones on the left. Briefly, the geological structure consists in an overlap of chalco-dolomite rocks from the Jurassic era over a series of cretaceous limonite and limestone across the prop level of the Keuper clays. The tectonic structure is transversal to the path of the freeway with which it forms a 45 angle and slopes southwards. Basically, the slope was excavated with a 1H: 1V inclinations in the lower half corresponding to the section of Triassic clays, and 1H: 2V in the upper half corresponding to the Jurassic Dolomites. Between both slopes, an intermediary 4-metre wide hard shoulder has been built. Following a first series of tests which failed with regards to the stabilization measures with agunite base, bolts, downspouts, berm ditches, light surfacing, etc., the final stabilization process was done by reconstructing a slope similar to the initial slope, and by providing environmental restoration with an implantation of green gunite using the Fibrater system. (A)