Santucci De Magistris Filippo

The stability in liquefied soils is one of the main problems affecting the design of buried structures. Moreover, the stability is even more important considering a malfunction of lifeline systems which extended for long stretches and are essential in human life and in economic development or when liquefaction affects pipelines in which dangerous substances are transported. To investigate the behavior of pipelines when the liquefaction phenomenon occurs, laboratory tests or numerical analyses have to be performed. While experimental tests contribute significantly toward understanding the mechanism, they are costly to perform compared to numerical analysis. On the other hand, numerical analyses are difficult to execute, because of the complexity of soil behavior in case of liquefaction occurrence and, despite numerous attempts, there are still many limitations and open questions. The applications, the results and the limitations of numerical analyses are an open research topic, with particular attention to the development of excess pore water pressures and the floatation of buried structures.
Furthermore, the seismic vulnerability of buried gas and liquid pipelines can be analysed from a large number of damage data to pipelines collected from post-earthquake reconnaissance reports.
Seismic fragility formulations and threshold values for the earthquake intensity with respect to the release of content from different types of pipelines could be derived, aiming at detecting novel seismic assessment tool which is able to cover the needs of industrial risk assessment procedures and land use planning requirements.

Mitigation measures for the stability of pipelines in liquefiable soils

Displacements of a buried pipeline in case of liquefaction can be due to the buoyancy effect of the hydraulic thrust when the pipe is under the water table level and the deepening or the floating due to earthquake forces. The effects of displacement on a pipe could be remarkable, because of the potential associated damage. One of the problems in mitigation techniques for these systems is their lack of standardization, because of the variable soil characteristics at site along the longitudinal development of the pipelines, which are often dislocated over wide areas. The proposal of new techniques needs a complete state of the art framework to generalize the solutions, as well as possible improving their applicability. New perspectives in mitigation measures constitute a matter that need to be investigated.

Prediction of the number of equivalent cycles for earthquake motion

Prediction models for computing the number of equivalent cycles in liquefaction analyses is a research topic that need to be investigated. The selection of the main synthetic parameters, usually adopted for the characterization of earthquakes, which help in calculating the number of cycles and on the correlation between this variable and the magnitude of the events need to be known. It appears that the number of cycles of an earthquake can be best estimated based on the knowledge of the five following parameters: peak ground acceleration; epicentral distance; Arias intensity; mean period; and frequency of the zero crossings. However, good estimation of the number of cycles can be obtained by knowing the first three parameters only. Moreover, the lack of correlation between magnitude and cycles numbers need to be further clarified.

Proper selection of the seismic motion in geotechnical earthquake engineering: case studies

The appropriate selection of seismic motion is one of the key points in performance-based design approach. This statement is quite trivial, being the behaviour of geotechnical systems under seismic loading strictly dependent not only from the peak acceleration, PGA, but also from the frequency content and signal length (i.e., the number of loading cycles) of the input motion.
In spite of this, the input motion for design is usually selected to match a design response spectrum, following indication reported in codes and guidelines that are usually too generic in defining how the records selection should be done. This means that, in the conventional practice, the search of a spectrum compatible accelerograms set takes into account the PGA, the magnitude and the epicentral distance expected to give the major contribute to the seismicity of the specific site. In some cases, the same site condition (site class and topographic factors) are adopted but, usually, the selection does not account for focal mechanism requirements. Therefore, specific researches are needed to analysing how the focal mechanism, apart from the couple magnitude-distance, might influence the characteristics of the seismic motion and to predict of the number of equivalent cycles for ground motions.

Lessons learned from case-histories of seismic microzonation

The prediction of the variability of the seismic ground motion in a given built-up area is considered an effective tool to plan appropriate urban development, to undertake actions on seismic risk mitigation, to understand the damage pattern caused by a strong-motion event. The procedures for studying the seismic response and the seismic microzonation of an urban area are well-established, nevertheless some controversial points still exists. Still are needed to understand the selection of a reference input motion, the construction of a subsoil model, and the seismic response analysis procedures need to be studied in detail, based on the lessons obtained by in case-histories.

Lessons learned from recent earthquakes

The April 25, 2015 Gorkha earthquake (MW 7.8) affected central Nepal and neighboring areas. Kathmandu valley witnessed severe damage in terms of structural collapse and casualties. Apart from this, soil liquefaction in the form of sand blows and lateral spreading were observed in 12 locations. Soil liquefaction in Kathmandu valley during 1934 (MW 8.1) earthquake was believed to be one of the major cause of damage in structures and lifelines but detail records are not available. To fulfill the gap of documentation in case of strong earthquake events like the Gorkha earthquake, field reconnaissance and collection of samples from each sand blow location need to be carried out. In addition to this, numerical analyses based on geotechnical investigation records for seven locations that manifested sand blows need to be performed.
Furthermore, Two main earthquakes occurred in the last 7 years in the central part of Italy: L’Aquila Earthquake in 2009 and the Amatrice sequence from 24th August 2016. Comparisons on earthquakes characteristics, ground motion recordings and produced damages are considered an interesting research field.