Problems which occured during the opening of a deep cutting for a new express highway are described. Due to changes in the gradient the cutting is 20 m deeper than originally planned. Stability problems of the cutting slopes occured from the start. These were caused by a disadvantageous joint set which was not known from the exploration works. The stability problems forced the highway authorities to change the concept of supporting the slopes. In addition to the planned weathering protection of the slope surfaces (40000 m2 of plantable revetment walls) around 2500 heavy prestressed rock anchors were necessary. The geotechnical situation in the cutting, the stability considerations, and the execution of construction are described. Some observations concerning the relaxation behaviour of the rock slopes are discussed.
Des problèmes qui sont survenus pendant le creusement de deux deblais pour une autoroute nouvelle sont decrits. Par des modifications de la planification du trace les deblais sont devenus 20 m plus profonds que projete d'abord. Pendant le debut des travaux de terrassement des problèmes de stabilite des escarpements sont survenus. Ils ont ete causes par une bande des fissures très desavantageux qui n'ont pas ete decouvrôs pendant les travaux d'exploration. Les problèmes ont oblige le maître d'oeuvre à changer la methode de stabilisation des falaises. Environ 2500 ancres precontraints ont ete necessaires pour stabiliser les falaises. A l'origine seulement une protection contre la desagregation (environ 40000 m2 des murs de revêtement plantables) a ete prevu. La situation geotechnique dans la coupure, les considerations sur la stabilite et la realisation de la construction sont decrits. Quelques observations concernant Le deplacement de la surface du rocher sont decrits.
Es wird ueber die Schwierigkeiten berichtet, die sich wahrend der Herstellung eines tiefen Einschnitts fuer eine neue Autobahn ergaben. Durch Änderung der Gradiente wahrend der Planung wurde Qer Einschnitt 20 m tiefer als urspruenglich vorgesehen. Bereits zu Beginn der Aushubarbeiten ergaben sich Standsicherheitsprobleme bei den Böschungen. Sie wurden durch eine in bezug zur Böschungsoberflache sehr unguenstig verlaufende Kluftschar hervorgerufen, die aus den Erkundungsbohrungen nicht bekannt war. Die Standsicherheitsprobleme zwangen den Bauherrn, das Konzept der Böschungssicherung zu andern. Zusatzlich zum vorgesehenen Verwitterungsschutz (ca. 40000 m2 begruenbare Futtermauern) wurde der Einbau von rd. 2500 schweren Felsankern erforderlich. Die geotechnische Situation im Einschnitt, die Stabilitatsbetrachtungen und die Ausfuehrung der Bauarbeiten werden beschrieben. Einige Beobachtungen ueber das Entspannungsverhalten der Felsböschungen werden mitgeteilt.
The new section of the federal express highway A 7 between the cities of Ulm and Wuerzburg will close a gap in the second long-distance highway connection between Scandinavia and the mediterranean countries. It ascends the escarpment of the Schwabische Alb, which is around 190 m high, in two parallel tunnels and two cuttings. The cuttings, which are the subject of this report, are 55 m and 40 m deep. They are divided by a 50 m high rockfill dam. The shallower cutting has a length of 850 m and the deeper one is 1050 m long. In the early planning stages it was proposed to keep a constant gradient of 4 % in the tunnels and the cuttings. New findings about the accident risks in descending high way tunnels caused the planners to decrease the gradient in the tunnels to 3 %. This had the consequence that the following cuttings became much deeper than it had been originally planned. Fig. 1 shows a view of the deeper (northern) cutting which made the problems described in this report.
The escarpment of the Schwabische Alb is the most remarkable scarp in the South West German landscape. It consists of the limestone and marlstone series of the Upper Jurassic (Malm, "White" Jurassic), which are in general much more resistant to weathering processes than the subjacent claystones and marls of the Middle and Lower Jurassic (Dogger, Lias). The good resistance to weathering, especially of the limestones which form the main part of the strata, is the reason for the existence of the escarpment. On the other hand its calcareous rocks have undergone karstification processes, and karst caves of different sizes can be found, mainly in the Malm β and Malm δ series. The highway cuts through the whole stratigraphic sequence of the Upper Jurassic. In fig. 1 the sequence of bedding relative to the highway can be seen. The dip of stratum is, in general, nearly horizontal, but may be locally 10° to 20° due to scattered fossile coral reefs.
