Diego Carlo Lo Presti

Characterization of Soil Deposits for Seismic Response Analysis

The paper critically reviews in situ and laboratory testing methods used to characterize soil deposits for seismic response analyses. Cyclic loading triaxial tests (CLTX), Cyclic loading torsional shear tests (CLTST) and Resonant column tests (RCT) are considered. As for the in situ testing, geophysical seismic tests and dynamic penetration tests are discussed. Influence of ground conditions on seismic response analyses in a number of real cases is shown. The database made available by the Regional Government of Tuscany (RT) has been used.

DP Test in Geotechnical Characterization of Shallow Landslides Source Area: Results and Perspectives

Aiming at improving the knowledge on the source areas of shallow landslides, this research deals with the geotechnical characterization of the debris slope cover of arenaceous formations, by means of low cost dynamic penetration tests (Dynamic Probing – DP).

Learning from the observation of failures

The Medicean Aqueduct of Pisa (Tuscany, Italy), is a relevant historical infrastructure built at the end of the XVI century, composed of 954 masonry arches over a total length of 6 km. Many of the arches are affected with several decay phenomena, which occurred during the years, due to ordinary and extraordinary causes. These have changed the original static arrangement, so that several arches are collapsed or degraded. It is worthwhile to point out that originally the foundation was supported by wooden piles that probably have been totally or partially deteriorated with time. A research activity is undergoing in order to understand the causes that induced the alteration of the original static model and to design necessary countermeasures. Anyway, the present paper illustrates the possible use of such a case history as educational material related to: durability, maintenance and preservation of historical heritage. The multidisciplinary nature of the case history is also pointed out. As for the research project the following activities have already been carried out by the research team, which consists of structural, geotechnical engineering and geophysicists: · analysis of the historic documentation; · accurate survey of the geometric characteristics of most of the structure above ground (the typology of the building materials and the decay phenomena were carefully catalogued); · geotechnical investigations (along the structure) consisting of boreholes, laboratory testing, piezocone testing and geophysical testing. On the contrary, it was not yet possible to assess the foundation geometry. Direct investigations are not possible for safety problems. Indirect investigations by means of geo-radar are planned at the end of the dry season. Since the masonry behaves according to a set of specific macro-elements, namely of rigid-bodies, the structural analysis mainly concerns the identification of these macro-elements and the related failure mechanisms activated by specific actions, such as the settlement of foundation or earthquakes. The structure has been studied with various types of analysis. Since the various aspects of the structural behaviour are captured by different methods, comprehensive answers are obtained only through a combined approach.

An example of teaching slope stability from true case hisrories: Three year experience

Part of the information summarized in this paper has already been published (Lo Presti 2013). The context (Study Course, Subject) within which the case history has been used and the case history itself has already been described. Such details are reported for a full understanding. Anyway the present paper mainly evaluates the effectiveness of using such a case history after an experience of three years. The use of case histories in classroom mainly involves an inductive teaching approach. This paper discusses the intrinsic advantages and possible drawbacks of such an inductive approach in the light of three year experience. More specifically, the paper illustrates an example of teaching the class of “slope stability” based on such methodology. The experience took place at the University of Pisa in the second tier degree of Civil Engineering of Infrastructures in 2010 and covered three academic years. The inductive teaching approach is very popular in the British/American Higher Education system. On the contrary it is not so popular in Latin countries like Italy. In order to make more clear the comprehension of this paper to the potential readers, information on the Higher Education system in Europe and specifically in Italy is also given.

A Monitoring System to Study Seepage Through River Embankments.

The results of stability analyses of river embankments under unsteady flow conditions are uncertain for the limited knowledge of the initial conditions and the lack of a detailed geotechnical characterization of both the embankment and the foundation soil. This paper illustrates a monitoring system of a real scale embankment to realistically evaluate hydraulic and saturation conditions during different periods of the embankment life (dry season and flood events). The aims of the proposed monitoring system are calibration of stability analyses under unsteady flow conditions and evaluation of the effectiveness of a plastic diaphragm that have been realized using a quite innovative technique. This paper illustrates the monitoring system and the geotechnical characterization of the study embankment. Another companion paper (submitted to this Conference) shows the preliminary results of the monitoring system and comments on the low–pressure dry deep mixing technology that have been adopted to realize the plastic diaphragm.

An Innovative Method to Evaluate Degree of Compaction of River Embankments

The paper illustrates an innovative method to evaluate the degree of compaction of both existing and new river embankments after their completion. A tip resistance target—profile is inferred from laboratory tests in a mini calibration chamber (CC) using a mini CPT (cone penetration test). The “laboratory” tip resistance (qcLAB) is expressed as a function of the expected density and of the vertical—horizontal stress components. Such a dependence of qcLAB is obtained carrying out a number of repeated tests in the CC at given density and different consolidation stresses. In situ stresses are inferred by combining DMT (Marchetti Dilatomer) results and an estimate of the vertical stress component. A comparison between the qcLAB profile, from CC testing, and the qc, as inferred from in situ CPT, gives the possibility of assessing the density of existing embankments, while, for new embankments, the method defines the expected in situ qc for a given target density.

Use of Plastic Diaphragms to Improve the Resistance of River Embankments Against Hydraulic Failures

Failure of (floodplain) river embankments is mainly due to internal erosion phenomena, hydraulic heave, mechanical instability triggered by seepage forces. In order to minimize the risk of internal erosion (piping) or hydraulic heave, the use of plastic diaphragm or sheet piles is recommended. The main advantage of sheet piles is the structural resistance of this type of barrier which contributes to the mechanical resistance of the embankment and provides a hydraulic barrier even in the case that overtopping of the embankment has caused the erosion of the bank itself on the country side. On the other hand, sheet piles are very expensive and subject to possible corrosion or thickness reduction because of aggressive water and parasite currents into the soil. Plastic diaphragms are less expensive than sheet piles and can be installed quickly without compromising the serviceability of the embankment. This last advantage is also typical of sheet piles. The (dry) deep—mixing technology for the construction of plastic diaphragms is shortly illustrated and the advantages of such a method are pointed out. Eventually the effectiveness of a trial diaphragm, that have been constructed inside an existing (floodplain) river embankment at the Bottacci site (Province of Lucca, Northern Tuscany, Italy), is shown after the occurrence of repeated floods. Direct controls of the diaphragm and the information obtained by a monitoring system installed inside the embankment have been used for such a purpose. The geotechnical characterization of the embankment and the monitoring system are illustrated in a companion paper.

Liquefaction Potential Assessment Of Silty And Silty‐Sand Deposits: A Case Study

The paper shows a case study concerning the liquefaction potential assessment of deposits which mainly consist of non plastic silts and sands (FC>35 %,Ip<10%, CF negligible). The site under study has been characterized by means of in situ tests (CPTU, SPT and DPSH), boreholes and laboratory tests on undisturbed and remolded samples. More specifically, classification tests, cyclic undrained stress‐controlled triaxial tests and resonant column tests have been performed. Liquefaction susceptibility has been evaluated by means of several procedures prescribed by codes or available in technical literature. The evaluation of liquefaction potential has been carried out by means of three different procedure based on in situ and laboratory tests.