Giuseppe Modoni

Analysis of Foundations Reinforced with Jet Grouting

AbstractThe use of jet grouting columns to increase the bearing capacity and reduce the settlements of foundations is dealt with, the aim being to formulate a complete design procedure where theoretical analyses and site observations are combined. The study is based on experimental results reported in the literature, which show that jet grouting columns are able to transfer high vertical loads to the surrounding soil but also that structural collapse may locally occur because of a sudden narrowing of their cross sections and/or poor soil cementation. Noticeable attention has been then given to these aspects by interpreting the results of full-scale tests specifically performed to investigate the characteristics of jet grouting columns and their mechanical interaction with the surrounding soil. The results of this analysis form the basis of a numerical method developed to simulate the response of vertically loaded rafts supported by arrays of columns. The nonlinear load-settlement response of axially loade...

EVALUATION OF GRAVEL STIFFNESS BY PULSE WAVE TRANSMISSION TESTS

Laboratory techniques for the measurements of very small strain stiffness parameters of coarse-grained materials include: (a) static tests using local strain transducers and (b) wave propagation measurements performed using bender elements, shear plates, and so on. The former method has been employed for most kinds of soil, while the use of wave propagation methods has been restricted to small specimens of sand and clay. At the University of Naples Federico II, a simple device, to generate and monitor compressional and shear waves directly inside a specimen, was designed to be used in large-scale triaxial apparatuses. The testing device was first used on densely compacted gravel specimens in a large triaxial apparatus in Naples and, after some further improvement, also in another large triaxial cell in Tokyo. In the tests carried out in Tokyo, dynamic and static measurements were performed simultaneously on single gravel specimens. In this paper, the details of the new system are presented and the results are discussed. The comparison between stiffness moduli evaluated by dynamic and static measurements shows that density, stress state, and strain history effects are similar, but that the dynamically measured stiffness values are consistently larger, about two times, than the statically determined ones. Since the stiffness of gravels has proven to be strain rate independent, possible reasons for this difference are addressed.

Design of jet grouted excavation bottom plugs

AbstractA methodology for cost-effective design of jet grouted water-sealing bottom plugs is presented in this paper. These massive barriers, made of partially overlapping jet grouted columns, are required to ensure temporary waterproofing to excavation areas and adequate uplift resistance against water loads. Therefore, the proposed calculation procedure simultaneously focuses on the structural performance and continuity of the plug. The design may be optimized by considering the possibility of reducing column length, performing injections only in the lower part of the plug, and leaving the upper part of the plug untreated. The reduction in column length may then result in a very slender slab, and a structural check has to be performed to avoid tension fracturing or overall structural collapse. Additionally, in spite of strict controls, jet grouted columns are never perfectly cylindrical or exactly aligned along their prescribed position, and thus the plug may present imperfections. Statistical evaluatio...

New geological data on the Cassino intermontane basin, central Apennines, Italy

This paper presents the outcome of photogeological analysis, field survey as well as borehole correlation, to add new data concerning the intermontane Cassino basin and define facies and thickness of its Quaternary deposits. The investigated area is located in the end sector of the Latina Valley, Southern Lazio and belongs to the Lazio–Abruzzi domain. With a maximum extension of 250 km2 and a NW–SE trend, this paleo-lake was created by lava flows from the Roccamonfina volcano, which barred the Latina Valley. The lacustrine facies were described during the 1960s but available bibliographic data about its spatial distribution and its relationship with the Mesozoic–Cenozoic bedrock are scarce. The thickness of Quaternary deposits has been deeply influenced by inherited paleo-morphologies. Indeed the geological reconstruction of the basin has outlined the presence of an underlying horst and graben structure. This latter obscured the contractional tectonics originated by the orogenetic deformation, even if new structures have been recognized at the foot of Montecassino Hill. We infer that a key role has been performed by the Roveto Valley–Atina–Caserta fault, between Atina and San Pietro Infine.

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.

Upgrading equipment and procedures for stress path triaxial testing of coarse grained materials

Advanced laboratory testing is often the only way to gain an insight into the mechanical behavior of soils in the whole range from small strains to failure, which in some cases is required for the engineering modeling of complex structures. When such structures are rockfill dams, the use of a large apparatus in-laboratory is virtually unavoidable because of particle size, even though testing becomes far more difficult than usual. This paper presents problems arising from the upgrading of an existing large triaxial cell in order to provide fully automated stress-path control. Because of the large dimensions of the apparatus, implementation of both stress rate and strain rate controls posed a number of unusual problems. Even though the control had to be carefully tuned in order to consider strain-softening behavior, the adopted procedure proved successful. The new cell produced good results for different kinds of stress paths, with satisfactory control in all stages.

Cosesimic liquefaction phenomena from DInSAR after the May 20, 2012 Emilia earthquake

In this paper, we have investigated the capability of Differential Interferometry Synthetic Aperture Radar (DInSAR) technique to detect the ground effects induced by liquefaction phenomena occurred during the May 20, 2012 Emilia earthquake. To this aim, a set of COSMO-SkyMed (CSK) SAR images covering the coseismic phase has been used. The detected surface effects have been related to liquefaction of deep sandy layers. Thanks to the geological/geotechnical data in the area and a liquefaction susceptibility analysis of the subsoil, it has been identified a sandy layer between 9 and 13 m in deep, which probably liquefied during the earthquake. The estimated vertical displacements due to liquefaction are comparable with the values measured by DInSAR.

GIS-Based Study of Land Subsidence in the City of Bologna

Geographic information systems (GIS) are very powerful tools capable of performing spatial analyses over large amounts of the territory representing large amounts of data. They consist of hardware, software, and human activities that facilitate collection, analysis, and storage of data, in different forms, related to the features of the territory. In the present chapter, the potential of the GIS tool is explored in a study of the effects of subsidence that occurred during the previous decades in the city of Bologna, where a valuable historic and cultural heritage made up of an intricate system of old masonry buildings, churches and monuments, is exposed and at risk. Data from previous geological, hydrogeological and geotechnical studies was collected and georeferenced. Then, topographical investigations and periodic records of the groundwater level in the network wells were superposed to establish a relation between causes and effects. The analysis reveals the spatial and temporal distribution of settlements in the city center and in the surrounding area. The evolution of the subsidence phenomenon has been possible, and the use of GIS has revealed the role of different factors and their mutual correlation. By combining all information, it can be seen that the area is severely affected by the distribution of total and differential settlements and that a particularly critical situation emerges in the city center. Additionally, the causes of the phenomenon could be established with great precision, enabling the identification of appropriate countermeasures.

A review of jet grouting practice and development

The jet grouting technique was originally initiated in the UK and progressively developed following the needs for larger geometries, ease of implementation, economic rationality, and better mechanical properties. This paper presents a comprehensive review of the development and practice of jet grouting through some fundamental concepts and relevant case studies. Subsequently, a laboratory testing program is performed to investigate the factors affecting the efficacy of the twin grouting system. The principal objective of this study is to define the suitable conditions for the jet grouting efficacy regarding economic rationality as well as quality control. For the first phase, a particular emphasis is placed on the properties of jet columns, site geological conditions, implementation methods, and the justification of each selected treatment option, while the second phase mainly focuses on the unconfined compressive strength (UCS) tests. It follows that the mono-fluid jet grouting system presents a valuable flexibility in dealing with complex configurations; yet, the double- and triple-fluid systems are more indicated for cases of mass treatments for which large portions of space must be treated and overlapping is fundamentally important for the reliability of the treatment. Furthermore, it was established that the efficacy of the twin-jet method primarily relies on the proper adequacy of some critical parameters, namely, the cement content, the water-cement ratio, and cement slurry-water glass ratio. In spite of some uncertainties inherently related to the technique, the UCS test represents the quintessential laboratory index for evaluating the mechanical properties of grouted elements, deriving jet grouting efficacy and the economics of jet grouts.

Geostatistical Analysis of Settlements Induced by Groundwater Extraction

One of the most important effects induced by the over-exploitation of aquifers is the land subsidence. This dangerous situation may reduce in relatively short time the functionality and safety of structures and infrastructures present on a territory and impair their efficiency and stability. The city of Bologna is one of the most sensational cases of Italy, especially for the amount of recorded settlements and the great historical and cultural value of exposed assets. This article analyses the spatial and temporal distribution of settlements over an area of about 270 km2 including the centre of the city. The topographical measurements, carried out starting from 1943 with a progressively increasing detail, highlight an articulated framework of settlements with maximum values exceeding 4 m. After a brief introduction of the phenomenon and its causes, a geostatistical analysis has been performed on a Geographical Information System. In order to validate the results, the potential damage on buildings present in the area has been evaluated. To this end, data were collected regarding the geometrical characteristics and the structural types of the buildings. The strain levels from the current configuration of the ground surface have been calculated for each of them. Finally, the expected damage levels have been assessed, following the classifications proposed in the literature that allow to assign a severity level for each building. These results were compared with damage observed by previous studies. This approach is a prerequisite to the planning of any vulnerability mitigation strategy.