Giacomo Russo

JET-GROUTING PERFORMANCE IN TUNNELLING

The paper focuses on the role of jet grouting on tunnel support, although the influence of supplementary techniques is also considered. For this purpose, experience gained from two well documented case histories (highway tunnels in Italy) is presented. Reported observations and experimental data have been selected in order to help in the identification of proper design limit states. Jet grouting has proven to be quite effective, allowing tunneling in very difficult conditions, but some failures have also been recorded. Failure mechanisms can be classified according to three different modes: excavation face failure, canopy tip failure, provisional lining failure. With regard to the control of settlements, jet grouting has proven to be very effective but some ground uplift can be temporarily induced by soil treatment.

Interpretation of CPTU Tests with Statistical and Geostatistical Methods

In the paper statistical methods for the interpretation of CPT data for the definition of subsoil stratigraphy have been applied to a subsoil CPTU data set of the Italian Center of Aerospatial Research (CIRA) in Capua (Italy). Results obtained by following the method proposed by Wickremesinghe and Campanella (1991) have been compared with those obtained by a geostatistical method recently proposed by Spacagna (2014), based on the spatial variability analysis of CPTU data. The latter results showed a more detailed definition of the transitions between different subsoil layers along the investigated vertical axes.

Yielding Behaviour of an Alluvial Compacted Soil in Saturated and Unsaturated Conditions

In this paper some results of an experimental work on the yielding of compacted soils are reported. The yielding behaviour has been investigated by means of triaxial tests on saturated and unsaturated samples. As observed for natural samples, saturated and unsaturated compacted samples showed a nearly elliptical and inclined shape of the yield curve in the effective stress space. Two different analytical expressions for the yield surface were used to fit the experimental data.

Collapse upon Wetting of Lime Stabilised Pyroclastic Soils

Compacted soils are commonly used in the construction of geotechnical works such as road embankments and earth dams. Several investigators have highlighted the wetting-induced behaviour of compacted soils resulting in collapse of the soil skeleton with increase of volume strains. The addition of lime, with the subsequent physic-chemical reactions, generally reduces the collapse potential of the stabilised soil if compared to the not treated one. In the paper, soil collapse has been investigated by means of soaking tests under constant stress on reconstituted not treated and lime stabilised pyroclastic soils. The soil collapse has been analysed for stress levels corresponding to pre-yield, yield and post-yield condition. The experimental results show the relevant dependency of the collapsible behaviour on the initial state of the compacted samples (void ratio, water content), the treatment parameters (curing time) and the reference stress level.