E. Sakellariadi

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.

Numerical modelling for clays with internal discontinuity surfaces

A numerical model capable of performing deformation analysis of a medium containing discontinuity surfaces is presented. The discontinuity can be either a crack, which can be open or closed, or a shear band. The model consists of two separate numerical algorithms, which are coupled together by means of the principle of superposition. In particular, an integral equation scheme based on the theory of dislocations is adopted for modelling the discontinuity, while a finite element discretization is used for the continuous medium. In this paper the discontinuity modelling is illustrated in detail, together with the specific formulation of the principle of superposition adopted, and some simple examples of application are presented. The well-known modelling approach based on Fracture Mechanics theory is also briefly discussed. The two models are compared and some advantages and drawbacks of each are pointed out, comments are made regarding their applicability in the specific case of soil mechanics, and conclusions are drawn as regards the conditions under which one or the other is appropriate. Finally, a full-scale example of deformation analysis using the proposed model is presented.

Small-Strain Stiffness Values for a Reconstituted Soil from Southern Italy

In numerical modelling of soil response it is often required to define an accurate value for the stiffness at small strains (G0). Such values are usually obtained from tables or charts available in the literature, rather than being directly measured in tests. These will however be sufficiently accurate only if a similar soil has already been studied and described. In the present paper, the results of a series of laboratory tests conducted on a soil from southern Italy are reported. In these tests, a well-established empirical relationship linking small-strain stiffness values to state parameters was calibrated, allowing the determination of accurate G0 values for the specific soil, and contributing to the collection of data in the literature. The bender element technique, in conjunction with standard triaxial testing on reconstituted soil samples, was employed. A series of isotropic compression tests was used for the calibration, and the resulting power law was then checked through shear testing. The proposed equation compares well with results reported in the literature for different types of soils. On approaching failure a change in behaviour is evident; this is in accordance with observations already reported in the literature for a variety of soils and is subject to several interpretations, but does not substantially interfere with the general validity of the proposed correlation, which can therefore be adopted as a useful empirical equation for determining G0 values for this soil.