PSI - Issue 62

Stefano Stacul et al. / Procedia Structural Integrity 62 (2024) 185–192 Stefano Stacul and Nunziante Squeglia / Structural Integrity Procedia 00 (2019) 000 – 000

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Keywords: existing bridge; shallow foundation depth; deep foundation depth; non-destructive tests; parallel seismic test; electrical resistivity tomography

1. Introduction The new multi-level and multi-risk approach for assessing the safety of existing bridges issued by the Italian Ministry for Sustainable Infrastructure and Mobility (MIMS, 2022) is aimed, in the first stage of its application, to classify bridges based on interfering risks, such as structural, seismic, and hydrogeological. The Level 0 and Level 1, in the new Guidelines multi-level approach, consist in collecting all the available information of the bridge under consideration and in carrying out a visual inspection. For the first time, the structural engineer performing the inspection is also supported by hydraulic, geological, and geotechnical experts to better define hydraulic and landslide hazards. In the Level 2, instead, the so-called Class of Attention (5 classes: low, low-medium, medium, medium-high, high) for each risk and the overall Class of Attention is assigned to the bridge under examination. One of the main issues encountered in the application of the first three levels (0, 1 and 2) of the new Guidelines was the identification of the foundation system (type, geometry, material) of existing bridges. This contribution is oriented towards reporting in an organized manner the available techniques (showing main capabilities, limitations, and field of application) for identifying existing bridge foundation systems with special attention to deep foundations. 2. Nondestructive testing methods for deep foundations: stress wave methods Based on the historical reconstruction of Nondestructive Testing methods (NDT) provided in Hertlein and Davis (2007), despite the scientific principles on which are founded most of the recent techniques date back to the end of 19 th Century and the earliest research was carried out by Glanville et al. (1938), their use began in the last two-three decades. Pioneering works on NDT were realized by the teams at Case Western Reserve University and at The Netherlands Organization, in USA and Holland, respectively, in the 50s. Obviously, due the level of technology at those dates, the application of these methods in practice was limited. Only starting from the end of 70s and the beginning of 80s thanks to the introduction of personal computer and the growth of electronic industry, the use of NDT became a possible option to be implemented in the field. Then the Federal Highway Administration report on drilled shafts for bridge foundations (Baker et al., 1993) definitively established the recognition of these “ new ” investigation methodologies. NDT for deep foundations were developed to solve two issues: • the assessment of the foundation integrity • the assessment of pile capacity/performance (reducing the excessive costs of static loading tests) and can be divided in two main classes: High-strain and Low-strain methods. For the special purpose of investigating existing bridge foundations Low-strain methods are of course the best option. Among these we can mention the most attractive which are: • Impulse Echo or Sonic Echo • Impulse Response or Sonic Mobility • Cross-hole Sonic Logging • Parallel Seismic Test All these NDT were developed in the 60s based on the experiences of the research group of the CEBTP coordinated by Jean Paquet (Paquet, 1968). Impulse Echo (IE) and Impulse Response (IR) methods consist of record and analyze the pile head response (in terms of acceleration or velocity) as a result of a strike applied at the head with a hammer. Cross-hole Sonic Logging (CSL) and Parallel Seismic (PS) methods, instead, consist of record and analyze the signal