The restoration of San Paolo Church in Pisa: Geotechnical aspects

San Paolo a Riva d'Arno is an important medieval church located in Pisa, on the south bank of the Arno river. Its existence is documented before 1032, most probably around 925: its actual configuration, however, was reached only at the end of 14th century. Structural diseases, following damages by bombing during World War II, have affected the church over the last decades; cracks in the perimeter walls and problems to the wooden frames of the roof are progressively appearing. After recent earthquakes the evolution of the statical situation has forced the authorities to close the church to the public. A comprehensive investigation on both the subsoil and the structure has been carried out with the aim of conceiving, designing and implementing suitable remedial works. Particular attention has been given to the collection of quantitative data about the foundation: layout, depth, thickness and state of conservation of the masonry. Geophysical techniques, such as electric tomography and ground penetrating radar, have been attempted with doubtful results; a special technique, consisting in small diameter holes drilled through the masonry with an instrumented drilling machine, was eventually developed. To investigate earthquake effects, a thorough analysis of local amplification of seismic action has been performed. Local seismic response of the subsoil has been analysed by different techniques applied to two different subsoil models; the results obtained evidence of significant differences among the different analyses and in comparison with the prescriptions of the Italian Seismic Code

Liquefaction Potential Assessment of Silty and Silty-Sand Deposits: A Case Study

he 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

Laterally loaded single pile response considering the influence of suction and non-linear behaviour of reinforced concrete sections

A hybrid BEM-p-y curves approach was developed for the single pile analysis with free/fixed head restraint conditions. The method considers the soil non-linear behaviour by means of p-y curves in series to a multi-layered elastic half-space. The non-linearity of reinforced concrete pile sections, also considering the influence of tension-stiffening, has been considered. The model reproduces the influence of suction by increasing the stress state and hence the stiffness of shallow soil-layers. Suction is modeled using the Modified-Kovacs model. The hybrid BEM-py curves method was validated by comparing results from data of 22 load tests on single piles. In addition, a detailed comparison is presented between measured and computed data on a large-diameter reinforced concrete bored single pile

Importance of full scale tests for the design of levees

This paper illustrates a case history, based on full-scale tests (trial embankment). More specifically, the settlements of a full-scale trial embankment on a very compressible soil (organic clay) for a period of 5 years are reported. The observed settlements are compared with those obtained from an A type prediction, as well as a B type prediction. The analysis results suggest the importance of an appropriate modelling of secondary settlements of organic soils. The difficulties in obtaining good quality undisturbed samples of organic clay and the peculiar creep behaviour point out the importance of full-scale tests

General Report - Session 3

This General Report summarizes the 84 papers accepted for the Session 3 focused on: - 3a. Case Histories on Failure and Remediation of Slopes, Dams, Embankments and Landfills (53 papers), - 3b. Case Histories on Failure and Remediation of Retaining Structures, Slurry Walls, and Deep Excavations, Dewatering, Stability (27 papers), - 3c. Improving the Stability and Maintenance of Monuments (4 papers). The papers originate from 26 countries (11 European countries, 3 American countries, 11 Asian countries and 1 African country). The papers cover a number of relevant topics divided into three different sub - sessions. As for the two papers included in Session 3c, only one deals with maintenance and retrofit of historical monuments. Indeed paper 3.03c is more pertinent to session 3b. On the other hand some papers included in Session 3a could also be considered in Session 3b and vice versa

Geotechnical Characterization of the Flood Plain Embankments of the Serchio River (Tuscany, Italy)

The flood plain embankments of the Serchio river have been constructed since the XVIII century and construction details are not known. These embankments have experienced failures several times during their life (last in December 2009). After the last event a detailed geotechnical investigation has been carried out. This paper discusses the necessary criteria for a cost – effective campaign considering the total length of the embankments (30 km) and the requested level of detail. In fact levee failure, although it is of limited extension, causes the achievement of the ultimate limit state of the entire embankment system. The campaign, in addition to laboratory tests, included boreholes, CPTu, permeability tests, 2D geo-electric tomography and 15 tests performed by the use of the continuous core drilling system. This last has proved to be a very useful tool for obtaining the more accurate evaluation of the in situ soil density (as confirmed by CPTu results). CPTu test, economical and expeditious, has proved to be an indispensable tool for delineating soil stratigraphy. In fact, their results combined with the borehole logs and laboratory testing provide extensive information. Geo-electric investigations can be very useful to highlight anomalies and heterogeneities in the cross section. Eventually, it is worthwhile to stress that embankments have generally a height of less than 4 m and a width between 1.2 and 3 m. This has restricted the investigation tools that could be used in this peculiar case

Stability Analysis of the Serchio River Flood Plain Embankments (Tuscany, Italy)

Following the geotechnical characterization of 30 km long flood - plain embankments of the Serchio River (Tuscany – Italy), a number of numerical analyses have been carried out. The embankments have been constructed since the XVIII century and have experienced several failures in the years (the last in December 2009). The geotechnical characterization of the river embankments and the 2009 flood are described in a companion paper in this Conference. This paper shows the results of numerical analyses that have been carried out for various purposes. More specifically, the numerical analyses were carried out a) to clarify the causes of the December 2009 failures, b) to design appropriate repair of the failures and retrofit of the embankments in proximity of the failures (about 6 km) and c) to identify the most risk areas considering the whole extension of the embankments (30 km). The limit equilibrium method was used to assess the stability of the embankments under steady state flow conditions (areas close to the failures). For this analysis three different types of commercial software were used. The stability analyses were carried out using the Bishop simplified method with circular sliding surfaces. The different codes indicated very similar failure surfaces corresponding to the minimum (meaningful) values of the global safety factor. Some differences on the values of the global safety factor were observed by comparing the results obtained from the three codes. More specifically, the analyses results show that, for the selected cross sections, the safety factors are rather small and approaching to unity, if the seepage forces are not considered. In the case of steady state flow, safety factor drastically reduces becoming lower than one. This result apparently contradicts the fact that the considered embankments are standing up since centuries and failures occurred only in the occasion of floods. The FEM analysis (PLAXIS Flow) shows that the safety margins of the considered sections, in absence of filtration, are assigned to the partial saturation of the embankment. Unfortunately, an appropriate characterization of the material under conditions of partial saturation was not available. Therefore, the FEM analyses were also aimed at determining the necessary time to approach the steady state flow conditions. For the case under consideration it was estimated that 10 days are necessary to approach the steady state flow conditions. This time is apparently much longer than the duration of the longest flood event (few hours). From the above it is possible to conclude that the hypothesis of permanent flow is generally too cautious. Anyway for the failures under consideration, that have occurred with the concurrence of various adverse factors like the melting of the snow because of a sudden temperature increase and the contemporary long raining period (two consecutive floods), it is reasonable to assume that the permanent flow conditions were probably reached. In addition to the numerical analyses, evidences of the considered event and the susceptibility of the analyzed soil to piping phenomena have also been considered to find out all the possible causes and to design in an appropriate way both repair of the failures and retrofitting of the surrounding areas. Assessment of the most risky areas, considering the whole extension of the embankments (30 km), has been carried out following expeditious criteria which were based on the embankment geometry and the mechanical soil characteristics

Innovative Triaxial/Resonant Column Equipment

The present paper describes a new triaxial apparatus which allows the measurement of low strain stiffness by means of both bender elements and resonant column test. In a previous paper Squeglia et al. (2009) described the innovative use of bender elements as receivers for the measurement of shear wave velocity. The proposed technique is synthetically described with the further development of apparatus which allow to perform resonant column test during a triaxial test. Since the apparatus has not been designed as a resonant column device, some critical points have been dealt with. Some tests have been dedicated to solve the problem of apparatus calibration, in particular it was not clear which type of restraint was introduced by some mechanical details concerning the ram for application of axial load. After calibration, some results have been presented. Tests carried out with the new apparatus have been compared with results of tests carried out with a Drnevich type resonant column apparatus showing a good agreement

Il Battistero di San Giovanni in Pisa

In 2013, the movement of one of the blocks of northwestern arcs triggered the studies presented in this paper. Although the monuments of Piazza dei Miracoli appear, with the exception of the Tower, solid and stable in time, they reveal the need for continuous maintenance and restoring. In the case of the Baptistery of San Giovanni, the 2013 event provided the opportunity to deepen the knowledge of the monument. In order to obtain more information, a series of investigation activities have been initiated. At first, some information about history of construction has been collected. The information were accurate for the period covering the first 50 years of the construction. After this period the information became poor and in some cases not consistent. In addition to historical information, some investigation regarded the masonry of foundation, the subsoil and the geometry of the whole structure. About the foundation, a specially developed drilling machine has been used to obtain information about geometry of foundation (mainly foundation plan depth) and solidity of masonry. The instrumented perforation confirmed the presence of a sort of reclamation stratum as reported in some chronicles of that time. Investigation of geometry, carried out by means of laser scanner, provided a reliable support for further structural studies and provided some additional elements to clarify construction sequence. In fact, one of uncertainties concerns the construction of floor of first gallery. The measurement of difference in level of floor indicates that the construction of floor occurred after the completion of building. A two-year monitoring of structure allowed a better understanding of structure behaviour as a consequence of environmental conditions changing. Thermal effects seem to be dominant and some movements are not reversible. A specially designed instrumented drilling machine has been used for the investigation of the foundations. The instrumented drilling machine provided the definition of geometry of foundation masonry. It is finally outlined a program for the new surveys and measurements