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A geotechnical monitoring campaign and a site investigation have been recently planned and undertaken aiming at the preservation and protection of the “Palazzone” Etruscan necropolis, an archaeological site dated back to Hellenistic period located 4 km from the city of Perugia, along the southeastern margin of the hill where the town is settled. The site includes some beautiful and monumental cavities, among them, the Volumni Hypogeum. The majority of the graves are underground cavities excavated in partially saturated alluvial soil deposits. Their inspection reveals the geological features and the depositional structures. The groundwater table is located about 35 m below the ground surface. Due to the difficulties of soil-sampling inside the ancient cavities, only limited portions of the material were retrieved for conventional laboratory tests, although not enough for a geotechnical characterization. On the other hand, XRD analyses and MIP tests were performed. The obtained results allowed to recognize the relevant contribution of soil suction to the stability conditions of the lateral walls and the ceiling of the cavities, which is complementary to the weak cementation characterizing the soil mass. This important information supports the conservation strategy of the monument, which has as its primary tool the monitoring of environmental conditions, aimed at maintaining the unsaturated conditions of the soil mass.

The paper focuses on the assessment of the seismic performance of Menta Dam, a bituminous faced-rockfill dam located in Southern Italy. The dam was designed in the ‘70s and a comprehensive assessment of hydraulic and seismic vulnerability has been recently performed according to most recent Italian dam regulations. The present work aims at predicting the displacement capacity of the embankment as an indicator to assess the overall seismic vulnerability of the system. To this aim, different displacement-based methods, which can be classified in the framework of simplified dynamic analyses, have been applied. The results of empirical approaches and of Newmark’s type dynamic analyses are compared to the ones obtained by a novel application of Direct Displacement-Based Assessment (DDBA) method for embankment structures. The latter approach seems to be promising, since it is capable to furnish the maximum displacement experienced by the dam crest for progressively increasing seismic actions, and its probability of exceedance; hence, the likelihood of reaching a threshold damaged condition can be deduced and usefully plotted in terms of fragility curves.

Several methods are available for the evaluation of the horizontal capacity of piles in cohesionless (c′ = 0) or in purely cohesive (su > 0 and ϕu = 0) soils. In this paper, the well-known theory by Broms (1964a, 1964b) is extended to soils possessing both cohesion and friction (c-ϕ soils). A simple profile of the ultimate soil pressure (plim) with depth is assumed, accounting for soil cohesion and pile embedment and encompassing Broms’ profile for drained loading. By considering translational and rotational equilibrium, equations for the different mechanisms of failure – short, intermediate and long piles - are given. The results are also presented in the form of non-dimensional graphs, allowing for an expeditious evaluation of the horizontal capacity of piles and the maximum bending moment. For most cases, it is found that giving consideration to the soil’s effective cohesion (c′) can lead to significant advantages in terms of increased pile capacity and the consequent reduction in pile dimensions and costs. A comparison of the proposed solution with some documented field cases allows for the first validation of the study.

Menta Embankment Dam has been selected as Theme B of the International Benchmark Workshop of the International Committee on Large Dams held in Milan in September 2019. The static and seismic behaviour of the dam under seismic input has been evaluated by 13 groups of Contributors coming all around the world. The Menta Dam is a rockfill dam with upstream bituminous facing located in the South of Italy. The major challenge faced by the Contributors was the simulation of the complex dynamic behaviour of rockfill material in order to predict the stress-strain behaviour of the embankment under seismic conditions. Despite the different modeling assumptions proposed by the Contributors, the numerical analyses showed a satisfactorily dynamic performance of the embankment under the proposed seismic input.

Volumni Hypogeum is part of the Palazzone Etruscan necropolis, an archaeological site dated back to Hellenistic period (V sec B.C.). The Hypogeum is a large underground cavity excavated in a partially saturated alluvial soil deposit located in the outskirts of Perugia city. Stability conditions and safety requirements of the vault and the lateral walls are analysed based on the available field results. The physical properties of the material in which the Hypogeum was excavated, such as, natural water content, soil suction, relative humidity of the rooms, temperature, as well as the groundwater conditions undoubtedly influence the state of conservation of the site itself. The variations of these properties may significantly affect the mechanical behaviour of the soil-materials and, in turn, the stability conditions of the ceiling/walls. Moreover, the site is daily exposed to road/rail traffic-induced vibrations. If also considering seismic actions, this site is extremely vulnerable. A multi-scale approach methodology has been recently undertaken aiming at the preservation and protection of the soil/monument system. The present study focuses on a very recent investigation of the microstructural features of the in situ materials. Preliminary numerical analyses of the cave have been performed in order to investigate on the stability conditions.

In framed r.c. or steel structures it is common practice to connect spread footings and strip foundations by means of tie-beams. While such beams are often required to absorb axial forces deriving from horizontal relative displacements at the foundation level, their ability to distribute and reduce the bending moments transferred to the ground is typically neglected. The present work shows that a significant advantage – in terms of foundation size and cost – can be obtained by considering the ability of tie-beams to absorb part of the bending moments which are normally attributed to the foundations alone. To this aim, it is first demonstrated that the distribution of internal forces in the soil-foundation-beam system is exclusively governed by a dimensionless parameter representing the relative rotational stiffness of the system. A simple approach is then proposed to evaluate the actions on both foundation ground and tie-beams, using a numerical model or, alternatively, an approximate method based on the superposition of effects. Finally, some examples are given to point out the usefulness of the proposed approach in terms of reduction of load eccentricity at the foundation bearing level, leading to a sensible reduction of foundations cost.

The paper presents a methodology aimed at reducing—or even avoiding—the risk of heave and uplift failures of reinforced concrete diaphragm walls. The method is based on the simple concept of increasing the drainage capacity of the embedded portion of the retaining walls. The behaviour of a strutted excavation in a cohesionless soil below groundwater is examined by means of two distinct series of numerical analyses, respectively focused on the hydraulic and mechanical behaviour of the retaining system. It is shown that, for some frequent cases, such methodology is capable to improve the safety of the retaining system with respect to both hydraulic and geotechnical limit states.

This study examines plane failure analysis of rock slopes and discusses its effect on seismic actions in a non-dimensional form, incorporating external loads transferred by anchors and stability indicators such as the depth of tension cracks and the failure plane dip. The results of limit equilibrium analyses, in terms of attained level of safety, are summarized in stability charts which can be used for design and assessment. Following guidelines established by Eurocode EC7, the stability is assessed through the R/E ratio, i.e. the ratio of the resisting shear forces (R) acting on the sliding surface and those promoting sliding (E). The proposed stability charts can be applied to various common practical situations, in order to provide a preliminary - but quantitative - assessment of the rock slope stability. As an example of an application, the paper focuses on the stability of a rock mass located at the bottom of the southern slope of the “Sasso di Pale” mountain (Central Italy), at the outskirts of the village of Pale. As many other historical towns in Central Italy, due to their location close to rock masses, this site is particularly exposed to instability phenomena such as plane failure and rock wedge failure. The structural-geological survey allowed us to identify the main joint sets affecting the behavior of the rock mass and, accordingly, we examined the plane failure mechanism involving sliding along a single plane. Stability verifications in pseudostatic conditions have been performed by adopting the proposed charts, consistent with Eurocodes prescriptions.

The paper presents an application of the seismic design method named “Direct Displacement Based Design” (DDBD), first introduced in 1990s in the field of earthquake structural engineering, and gaining due attention in the recent years. The method can be applied to a wide range of structural types, including geotechnical structures. The fundamental philosophy behind DDBD is that structures should be designed to achieve a specified performance level under a certain seismic intensity. In the paper, DDBD is described with considerable discussion on its applicability to flexible earth retaining structures in coarse grained-soils. Particular attention is given to the evaluation of the equivalent damping ratio of the wall/soil system, since it sensibly affects the results of the procedure. A simplification of the design process is proposed in order to provide a seismic demand curve, in terms of active/passive thrust, which is dependent on the system ductility. A numerical example of application of the method is provided in the paper.

The Italian cultural heritage is one of the most noticeable in the world; an important part of it is subjected to natural hazard and risk conditions. Religious buildings, due to their location on impervious sites are particularly exposed to landslides. In this paper we study the hermitage of Cerbaiolo (Tuscany, central Italy). The hermitage, founded in the 8th century as a Benedictine monastery is now a Franciscan Women Institute seat. The buildings are on the edges of a limestone plate overlapped to a clayey formation. Falls, toppling and slides are present along the limits of the plate due to the geomechanics properties of the rock and to the contrast between the two lithological complexes. In order to identify the main joint sets affecting the rock mass a structural-geological survey was carried out and four sets are identified. The rock plate was classified according to Bieniawski, Barton and Geological Strength Index approaches. The outcomes confirm the predisposing factors to mass movements, corresponding to the intensity and characteristics of fracturing of the rock mass. With regard to the slope stability analysis, a failure mechanism involving sliding along a single plane (plane failure) was assumed on the first approximation. The analyses take into account the presence of tension cracks as an indicator factor for the instability phenomenon. The results of stability analyses, performed in static and seismic conditions, indicate a widespread instability condition. The dip slope direction, the properties and type of discontinuities and the local variation of composition influence the hazard assessment.

Based on a pseudo-static approach, finite difference (FDM) numerical analyses have been performed aimed at evaluating the seismic effects on the ultimate bearing capacity of shallow strip foundations. In the specialised literature, such seismic effects are usually divided in two components, namely, a structure inertia and a soil inertia, which can be either considered together, or separately addressed and then superposed. Both of these inertia effects are investigated in this work. The results of a comprehensive numerical study are presented in—and critically compared to—the wide framework of available analytical solutions proposed in the literature in the last 30 years. The good agreement found between the numerical and the analytical approaches is pointed out, thus providing further evidence of the reliability of some available and widespread solutions. The possibility of superposition of the two inertia effects is investigated. It is found that in some cases the soil inertia may play a significant role in the seismic capacity of the system, and that simple one-constant equations can be readily used in foundation design to estimate the reduction in bearing capacity (namely, factors e i , e k ) deriving from the two inertia effects.

Hydraulic failure by heave is one of the most dangerous limit states in geotechnical engineering practice. Hence, the margins of safety associated to this failure mechanism have traditionally been quite high. Nowadays, with the advent of the Eurocodes, the approaches to verify heave failure have been substantially modified to take into account “partial” factors, as opposed to the traditional “global” safety factor. In the paper it is demonstrated that the two approaches given in the present version of Eurocode 7 do not provide a consistent evaluation of safety against failure by heave and may lead to both over-conservative and un-conservative design. An alternative approach is given to eliminate such inconsistencies, and to provide more reasonable levels of safety. Finally, two simple examples are presented to compare the different approaches and to highlight possible limitations in their use for design.

Slope vegetation is currently finding wide applications all over the world to mitigate erosive phenomena and improve slope stability. A natural technology for slope protection has been recently developed in Italy; this uses only natural perennial grass plants with thin, deep roots with high tensile strength. The technology appears promising with regard to shallow slope instability because both the mechanical and hydrological effects of such a kind of soil vegetation may enhance the equilibrium conditions in the superficial (1 ÷ 2 m) portion of the slope. This short communication deals primarily with the positive mechanical effect of the roots in a simple infinite slope stability problem. With regard to the hydrological effects of the roots, some preliminary results of a numerical analysis are presented; in particular, for the specific case study herein discussed, such analysis allows highlighting the different roles played by deep roots permeating a cohesionless soil.

The chemical engineering literature abounds with empirical and theoretical equations relating the sedimentation and fluidization velocities of a given solid—liquid system and its porosity. A geotechnical approach shows that for active clay particles the problem lies in the definition, and associated determination, of a coefficient of permeability of the system. A fluidization test is proposed to provide a direct permeability measurement of clay suspensions. The experimental results obtained on two clay mixtures indicate that the coefficient of permeability varies continuously over a wide range of porosities, encompassing soil conditions and suspended conditions, and that a two-constant power equation can be usefully employed to represent such variation. Les textes de génie chimique abondent en équations empiriques et théoriques qui experiment les vitesses de sédimentation et de fluidisation d'un système solide—liquide donné et sa porosité. Une approche géotechnique montre que, pour des particules actives d'argile, le problème consiste à définir un coefficient de perméabilité du système et à le calculer. Les auteurs proposent un essai de fluidisation qui permet de mesurer directement la perméabilité d'argiles en suspension. Les résultats expérimentaux obtenus dans le cas de deux mélanges d'argile indlquent que le coefficient de perméabilité vane continuellement sur un vaste éventail de porosités, pour diverses conditions de sol et de suspension, et qu'on pent utiliser une équation à deux constantes pour représenter cette variation.

The author presents evidence that very small hydraulic gradients should be used in laboratory permeability tests to minimize errors arising from seepage-induced consolidation. These errors will be carried forward to practice in significant ways. The gradients must be such that the seepage-induced effective stresses are substantially less than the maximum past effective stress. In cases of normally consolidated soils, there will always be induced errors: the softer the clay, the greater the errors. These errors seem to be compounded by conventional constant and falling head permeability tests, because of the high gradients involved, and can be readily minimized by the flow pump method. In addition, this test can be performed in substantially less time than either a constant or a falling head test. In using conventional tests one is faced with a paradox. The use of high gradients reduces the time of testing but introduces substantial errors in the test results. However, the use of low gradients extends the testing time to unacceptable limits. The flow pump test solves both these problems. If the clay is very soft and normally consolidated, even the lowest gradients can cause significant consolidation. It may well be that indirect measurements, using inversion techniques, will be required for these cases. The laboratory data presented are based on gross changes in sample thickness and thus on average void ratios. For a complete analysis consideration of the time-dependent void ratio distribution within the sample during the test is required. (Author/TRRL)

L’articolo riporta l’analisi sismica prestazionale di una diga in rockfill con manto in conglomerato bituminoso situata nel sud Italia. Dopo una breve descrizione sui principi dell’analisi sismica prestazionale con riferimento alle odierne normative nazionali, sono stati definiti gli obiettivi prestazionali secondo quanto riportato nella letteratura. L’analisi sismica della diga è stata condotta tramite la realizzazione di modelli numerici 2D e 3D, sollecitati con input sismici naturali spettrocompatibili. La risposta tenso-deformativa del materiale incoerente costituente il corpo diga è stata simulata con un modello isotropo perfettamente plastico con smorzamento isteretico, i cui parametri sono stati calibrati sulla base di prove triassiali monotoniche e cicliche. L’efficacia di tale modello è stata testata simulando i risultati sperimentali ottenuti da prove dinamiche in centrifuga realizzate su sezioni 2D della diga stessa. Infine e stata eseguita l’analisi della diga reale, focalizzando l’attenzione sull’effetto indotto dalle caratteristiche geometriche e meccaniche del rilevato sulle accelerazioni massime registrate, sulle amplificazioni spettrali e sugli spostamenti permanenti subiti.