Soil Dynamics and Earthquake Engineering 117 (2019) 300–311 Contents lists available at ScienceDirect Soil Dynamics and Earthquake Engineering journal homepage: www.elsevier.com/locate/soildyn Reliability of FTA general vibration assessment model in prediction of T subway induced ground borne vibrations ⁎ Javad Sadeghi , M. Hassan Esmaeili, Masoud Akbari Iran University of Science and Technology, Tehran, Iran ARTICLE INFO ABSTRACT Keywords: One of the main factors in the design of subways is the level of subway-induced vibrations. The ground borne Subway vibrations are usually estimated by prediction models among which the FTA (Federal Transportation Ground-borne vibration Association) general vibration assessment model is the most popular one. Although FTA approach/model is Slab track vastly used in the design and operation of underground railway systems, its reliability has not been sufficiently FTA evaluated in the available literatures. This is addressed in this research. For this purpose, a comprehensive General vibration assessment model experimental investigation (both in the time and frequency domains) was conducted in three newly constructed subway lines in the Iranian underground railway (subway) network. The track and soil characteristics as well as ground borne vibrations were measured. The reliability and accuracy of the FTA model was assessed through comparisons of the experimental results obtained here with the FTA predictions. Contrary to the current belief, considerable underestimations of subway ground borne vibrations in the FTA model predictions were shown in this research. The results obtained indicate up to 20 dB differences between the experimental results and those of FTA predictions. Based on the field measurements obtained here and the theoretical background, the FTAmodel was improved/optimized, leading to increase the reliability of FTA model predictions in subway systems. 1. Introduction cross-section. The model was based on a three-dimensional analytical solution of thin cylindrical shell surrounded by soil of infinite radial A massive growth in subway construction has been observed around extent. It was used for predicting vibration levels in the frequency do- the world since 1970s [1]. The urban residents can enjoy the con- main. This model is not applicable in real engineering problems because venience of subway systems, because they provide residents with access of the complications in the geometry and material properties of the to a cheap transportation, reduce their dependence on cars, and ease subway structures. Moreover, the vibration is only predicted at the sprawl. However, they expose people to subway induced noise and ground level and the effect of the receiver is not considered inthe vibrations, which may affect their comfort. This has been one ofthe model. Similar analytical models have been also developed by Melke main concerns in the development of subways/underground railway [3] and Trochides [4]. systems in cosmopolitan cities. As subways are expanded, research Using the high performance computing systems, various numerical works related to the railway noise and vibrations are increased. The models have been developed based on finite element, boundary ele- frequency of the works published during 2000–2017 are illustrated in ment, and hybrid methods for the prediction of subway induced vi- Fig. 1, indicating considerable increase in recent years (i.e., the im- brations. Due to the complexity of the problem, these models are portance of the issue). usually composed of three independent sub models to simulate: (1) the One of the main challenges in the railway vibration field is the ac- source (wheel/rail interaction), (2) the path (track/tunnel and sur- curacy of the subway induced vibrations predictions. A review of the rounding media), and (3) the receiver (building and its interaction with literature indicates that several prediction models have been developed the ground). For instance, Zhou [5] presented a two-and-a-half-di- to estimate the level of subway induced vibrations [2–10]. There are mensional (2.5-D) boundary element model in a pyroclastic half-space. three approaches for the prediction of railway vibrations: analytical, Similar works (models) have been reported in [6–9] and [10]. The main numerical and semi-empirical methods. concern in these models is the differences between the theoretical Forest and Hunt [2] developed an analytical model to predict vi- predictions and those of measurements, particularly when the models bration levels in a deep underground railway tunnel with a circular underestimate the vibrations. For instance, comparisons between field ⁎ Corresponding author. E-mail addresses: [email protected] (J. Sadeghi), [email protected] (M.H. Esmaeili), [email protected] (M. Akbari). https://doi.org/10.1016/j.soildyn.2018.11.002 Received 4 July 2018; Received in revised form 19 October 2018; Accepted 6 November 2018 0267-7261/ © 2018 Elsevier Ltd. All rights reserved. J. Sadeghi et al. Soil Dynamics and Earthquake Engineering 117 (2019) 300–311 foundation with building floors, interior walls and secondary elements, the amplification due to resonances of various building elements), most of the recent researches have been focused on empirical or semi-em- pirical models developed based on field measurements [15]. For in- stance, Paneiro [16] presented an empirical model for prediction of ground borne vibrations induced by a railway train circulation in urban environments. He used the results obtained from field tests and devel- oped a multiple linear regression model for prediction of subway vi- bration levels. The model was verified using data from the same site. Connoly et. all. [17] used a large database obtained from measurements in the high-speed railway network across Europe to train a neural network model in which the train speed and soil characteristics were the input data and the PPV levels were the model output. In a similar work, Paneiro et al. [18] developed a neural network model, using vibration measurements made in the urban underground railway in Fig. 1. Frequency of railway noise and vibration studies during 2000–2017 Lisbon, Portugal. Kouroussis et. al developed a hybrid experimental- extracted from Google Scholar. numerical approach capable of vibrations prediction in the presence of transition zones, switches, crossings, and rail joints [19], localized wheel/rail defects [20,21], and various types of rolling stocks [22]. Table 1 These models are practical and reliable in the vibration prediction of a VdB versus distance relationship coefficients proposed by FTA and FRAand subway when the conditions of the subway is similar to those of the optimized by Connolly et al. field from which the model data-base has been created. Notethat Reference Application Correlation coefficients creating a new field test database is costly and sometimes impractical. A well-known semi-empirical model (called general vibration as- a b c sessment model) developed by FTA (Federal Transportation FRA [24] High-speed lines 1 0.002 123 Association) [23] and FRA (Federal Railroad Administration) [24] is FRA optimized [30] High-speed lines 1 0.0016 110 commonly used in practices for the prediction of railway ground vi- FTA [23] Subways 5 − 0.05 100 brations in conventional railways (FTA approach) and high-speed tracks (FRA approach). FTA and FRA have proposed a series of graphs for various conventional mass transit and high-speed systems by which measurements and predictions of FE models developed by Lopez et al. the vibration level can be derived as a function of distance from the [7], Costa et al. [11], Gupta et al. [12] and Hall et al. [13] indicate up to track. FTA and FRA take into account the influencing parameters such 180%, 30%, 600% and 400% underestimation in their predictions, re- as track type, vehicle speeds, type of building, and track/wheel con- spectively. Note that, according to the ISO standard, the models should ditions [17]. The FTA model is vastly used in practice particularly for present “worst case” in ground-borne vibrations predictions [14]. the design of subway systems. For instance, it has been used in the Due to the complications in the theoretical modeling of subway design of all Iranian metro lines adjacent to the historical buildings. system (such as coupling between soil and foundation, interaction of Fig. 2. Three test sites and their surrounding environment, a: Site 1 (Tehran), b: Site 2 (Isfahan) and c: Site 3 (Shiraz). 301 J. Sadeghi et al. Soil Dynamics and Earthquake Engineering 117 (2019) 300–311 Table 2 As discussed above, the investigations are limited to the reliability Characteristics and lengths of trains. of the FRA approach proposed for high-speed tracks [17,30,32]. That is, there is no serious study on the limitation or reliability of the FTA Site Car Car arrangement L1 (m) L2 (m) L3 (m) L4 (m) manufacturer model in prediction of subway-induced vibrations. Since the vibration characteristics of the metro structure are considerably different from 1 (Tehran) TWM TcMMsMsMMTc 25 17.5 7.5 2.5 those of the high-speed and at ground railway systems, there is a need 2 (Isfahan) Puzhen and TcMpMMp-Tc 19.32 12.6 6.92 2.1 3 (Shiraz) Dalian TcMpMMp-Tc 19.32 12.6 6.92 2.1 to investigate the applicability of the FTA approach in subway systems. This research is a response to this need. That is, the application and reliability of the FTA model in various types of subways were in- Table 3 vestigated through comparisons of the FTA predictions with those of a Technical characteristics and configurations of three slab in three test sites. compressive field tests carried out in this research. Using the results Parts Properties, Unit Site 1 Site 2 Site 3 obtained here, the FTA method was improved/optimized by developing and incorporating a correction/adjustment factor into the FTA model. Rail Flexural rigidity, Nm2 4,909,590 3,819,900 3,819,900 Mass per unit length, Kg/m 54.77 49.769 49.769 Fastening Fastening space, m 0.65 0.6 0.6 2.