D. Segato

Excavation works in stiff jointed clay material: examples from the Trubi formation, southern Italy

The construction work of the DG22 mega lot, an 11-km segment of the new Jonica national road (southern Italy), mainly involves the Pliocene deposits belonging to the Trubi stiff jointed formation. This paper focuses on the geotechnical studies carried out to explain the kinematics of the instability processes which were observed during excavation work. Two different cases are presented. The first one refers to the movements caused by a 20-m-high slope excavated for a cut and cover tunnel. The second one describes the kinematics of the failure of a shallow tunnel which caused the subsidence of a widely extended area. In both cases, the response of the soil mass to the excavation was governed by the system of discontinuities that characterizes the Trubi clay formation. The influence of the structural features, beyond the knowledge of the mechanical behavior of the soil at the scale of the laboratory sample, was an essential ingredient to find a convincing explanation for both phenomena observed.

Slope Instability Problems in the Jonica Highway Construction

During the construction of the south portal of the tunnel Baldaia I along the SS106 motorway in Calabria, unexpectedly large and continuous displacements of the earth retaining structures occurred leading to a precautionary suspension of the excavation works. To study the kinematics of the observed instability phenomenon, inclinometer probes were used together with the topographic monitoring of the portal structures; it was found that the unstable mechanism was deep-seated, block-type and extending over the entire slope. In this paper the site investigation activities carried out to understand the origin of the instability process are presented. The interpretation of the observed behaviour is then given together with the description of the remedial measures suggested to safely complete the construction of the tunnel. The link between the time evolution of the instability and the sequence of the excavation works, which turned out to be an important issue in the process, is also discussed in some detail.

Sheet Pile Quay Wall Safety: Investigation of Posttensioned Anchor Failures

This paper examines the collapse of an important port structure and analyzes the causes of failure. In particular, a length of newly constructed anchored sheet pile wall exhibited very large displacements at the crest, which clearly indicated that a failure condition had been reached within the retained ground. On removal of the failing soil and inspection of the structure, all the barrel/wedge anchors were found to be devoid of the strands they should have been holding. Observations and testing on such components led to the conclusion that sliding of the wedge system within the barrel had actually been inhibited by two main causes: on one hand, corrosion of the metal surfaces, which is in part predictable in a marine environment and, on the other, the presence of cement mortar which blocked the wedge components in place.