1- Introduction

2- Field investigation and analysis of tunnel damage through fault zone

3- Design idea of sectional tunnel lining with flexible joints through fault

4- Experimental method and apparatus

5- Model test results and discussion

6- Conclusions

References

Abstract

Tunnels often suffered severe seismic damage when passing through the active fault in high intensity earthquake area. The fault movement might be divided into fault movement and seismic motion under the strong earthquake action, and both of them could have the significant influence on the stability of tunnel structure. To improve the seismic performance of the mountain tunnel through fault, a design idea or method of the between sectional tunnel structures with the flexible joint were put forward to run through the active fault and verified or analyzed by using the shaking table test. Firstly, the typical seismic damage characteristics of the tunnel passing through the fault were analyzed after Wenchuan earthquake; secondly, the sectional tunnel linings with the flexible joint were designed in the active fault zone under the strong seismic motion, and the basic theory of this design method was presented in detail. Thirdly, the scaled model shaking table test was carried out to study the seismic performance of flexible joints of tunnels under the normal fault action, and some key parameters of the test was designed, including similarity relationship, boundary condition, sensor layout, input earthquake wave and flexible joint design. The test results showed that the joints between sectional linings could make structure localize damage rather than global damage, and compared to seismic motion, the fault movement suffered more serious damage for the tunnel structure. The tunnel lining at hanging wall was more susceptible to damage or destroy than that at the footwall under the normal fault action, and the flexible joint could adapt to the differential deformation of fault during the strong earthquake. Lastly, the dynamic response of the tunnel lining demonstrated that the upper-structure of the tunnel mainly suffered the severe seismic load, while the lower-structure might experiences the imposed deformation of fault movement under strong earthquake motion. So the design method of the sectional tunnel lining with the flexible joint would be applied to tunnel structure design to improve the adaptive deformation ability of tunnel structure through active fault.

Introduction

For a long time, the underground structure has been generally considered to suffer a lower level of damage in comparison with the surface structure during an earthquake (Asakura et al., 2007). The tunnel engineering project will be prior to be recommended due to the advantages of shortening lines, smoothing the curve of traffic lines and resisting geological hazards and earthquake disaster (Yan et al., 2020a, 2020b). However, tunnels located in the active fault area are easily vulnerable to damage by shear deformation under strong ground motion (Kun and Onargan, 2013). A lot of tunnels are designed or constructed in China Western and inevitably cross through active fault zones in mountainous area with some disasters. Therefore, the damage mechanism of the tunnel through fracture zone should be firstly demonstrated under the strong ground motion, and some seismic design method need to be studied to improve the seismic performance of the tunnel running through fault zone in the high intensity earthquake area. A number of related researches have been carried out to investigate the damage mechanism and seismic design method for tunnels crossing the fault section including numerical simulation (Anastasopoulos et al., 2008; Wang and Zhang, 2013), theoretical analysis (Zhang et al., 2018) and model tests (Su et al., 2019; Wang et al., 2019a, 2019b). Researches have shown that the most severe earthquake damage occurs in fault fracture zones, followed by tunnel entrances and public road sections (Lai et al., 2017; Yu et al., 2016).

Introduction

Structural control systems can be used in modern engineering practice to protect structures from destructive effects of earthquakes. Structural control systems are mainly categorized as passive, active, semi-active, and hybrid systems. The basic concept of passive control systems is to lower the effective earthquake forces by elongating the fundamental period of the structure, thereby, lowering both the floor accelerations and the inter-story drift ratios to keep them within desired limits. The main challenge that such systems face is the large displacement requirements of the isolation system in case of nearfault earthquakes [1], which may exceed practical and economical limits [2]. Such large base displacements may even exceed the seismic gap, thus, posing serious risks [3]. Providing high passive isolation damping may be of help but such a solution may cause increase in floor accelerations and inter-story drifts depending on the earthquake characteristics [4]. Various other studies [1,5–7] also revealed that additional damping that is necessary for controlling base displacement may not guarantee good performance in structural response under the near-fault earthquakes, which would be a problem for missioncritical buildings such as hospitals that house vibration-sensitive contents [2,8]. Thus, active or semi-active isolation systems that can adapt to earthquake excitations of different frequency contents are necessary. Although active control systems are effective, they require very high power to operate [9,10]. Moreover, adding mechanical energy actively to the building may cause stability problems to the structure [11–13]. These drawbacks increase the interest in semi-active control systems, which can provide the proper amount of damping without causing any stability problems. Also, they need much less power to operate than the active control systems [12,13]. Symans et al. [14] showed that both isolation displacement and superstructure response can be limited by such adaptive base isolation systems. Likewise, [15–17] confirmed that the safety performance of a seismic isolation system that is equipped with semi-active dampers are quite high and it is effective in simultaneously limiting both base displacement and superstructure responses. On the other hand, it is known that the mechanical properties of isolators can vary due to the variation in temperature, ageing, contamination, or scragging [18–20]. Likewise, the mechanical properties semi-active control devices can vary. Researchers [18,19,21] have evaluated the effect of variability in passive isolation system parameters on the response of superstructure. The results emphasized the significance of variability of these parameters on the response of isolated buildings. At this point, it can be said that probabilistic seismic risk analysis, which takes such uncertainties into account, is the best method for determining the realistic seismic performance of seismically isolated buildings equipped with semi-active control systems. Due to the difficulty of describing the probabilistic characteristic of the whole problem analytically, the Monte-Carlo Simulation technique can be used as a convenient alternative. It is an accurate method for conducting safety and reliability analysis [22] that is based on mathematical modeling and recursive computer analysis in which the uncertainty is taken into account by defining random variables to follow certain probabilistic distributions.

1- Introduction

2- Tectonic division and geological setting

3- Archean meta-volcanic and intrusive rocks (Art)

4- Paleoproterozoic and Columbia tectonic event (Pt1t)

5- Neoproterozoic metamorphic basement and Rodinia tectonic event (Pt3t)

6- Sinian to Paleozoic passive continental margin (Pzt)

7- Mesozoic composite tectonics (Mzt)

8- The Cenozoic orogenic plateau superimposing (Kzt)

9- Discussion

10- Conclusions

References

Abstract

The Longmenshan Tectonic Complex (LSTC), along the eastern margin of the Tibetan Plateau, the site of devastating earthquakes such as the magnitude 8.0 (Wenchuan) earthquake on 12 May 2008, preserves an exceptionally complete history of the tectonic evolution of the Yangtze block and its relations to adjacent tectonic units. Due to sequential tectonic superposition and tectonic reactivation, the tectonic nature of the LSTC, and in particularly the older history, has been profoundly debated and many different tectonic models have been proposed. Herein we summarize the current understandings of the major tectonic events that have shaped this important tectonic complex, highlighting problems left to be solved by future work, including: (1) The nature and constraints for at least 6 regional tectonic events, i.e., building of the metamorphic basement (Art), the Columbia/Nuna supercontinent (Pt1t), the Rodinia supercontinent (Pt3t), the Paleozoic passive continental margin (Pzt), the Paleotethys orogeny (Mzt) and the Neotethys orogeny (Kzt); (2) Metamorphic basement exposures and their tectonic implications, including rock types and geochronological constraints for the Archean, Paleoproterozoic and Neoproterozoic basements; (3) Nature of the present LSTC and its affinity with adjacent tectonic units; (4) Consideration of the NE-striking Longmenshan thrust belt and arcuate-shape Yanyuan-Muli thrust belt as parts of a single tectonic feature; (5) Mountain-basin coupled systems recording past tectonic eposides. We draw the following conclusions and tectonic models based on published research combined with our own recent studies: (1) The well preserved Archean Yudongzi gneiss group in the LSTC has a genetic affinity with the Kongling group, and thus belongs to the Yangtze block; (2) The Paleoproterozoic Hejiayan group, juxtaposed adjacent to the Archean Yudongzi group, may represent a 2000–1800 Ma orogenic belt, which corresponds to the supercontinent Nuna/Columbia amalgamation event; (3) A Neoproterozoic trench-arc-basin system, which is reconstructed based on identification of a Neoproterozoic ophiolite complex, arc-type magmatic rock assemblages and volcaniclastic basinal deposits along the western margin of the Yangtze block and the LSTC, may represent the record of eastward subduction of the Neoproterozoic Mozambique oceanic lithosphere beneath the Yangtze block during the assembly of the Rodinia supercontinent; (4) A complete bidirectional Wilson cycle was reconstructed by the formation of the late Permian to the middle-late Triassic back-arc Ganze-Litang rift and ocean following the early Paleozoic Mianlue continental rift and ocean, and subsequent closure of the ocean basin by simultaneous bidirectional northward and southwestward subduction and later collision. This relatively uncommon bidirectional Wilson cycle might be attributed to the formation of the three-armed rift system in the eastern Paleotethys associated with the late Permian Eemeishan Large Igneous Province in the LSTC; (5) A three-stage tectonic sequence of, in-sequence imbricate thrust in the LSTC during India-Eurasian collisional orogeny at 55–15 Ma, extrusion from 15 to 5 Ma and the plateau uplift since ∼5 Ma resulting from lower crustal channel flow, is proposed for the formation of the present LSTC.

Introduction

The Longmenshan Tectonic Complex (LSTC) along the eastern margin of the Tibetan Plateau is composed of the NE-striking Longmenshan thrust belt in the north and the arcuate-shaped Yanyuan-Muli thrust belt in the south (Figs. 1 and 2). The LSTC, which is bounded by the Triassic south Qinling-Dabie orogenic belt to the north, the Cenozoic eastern Tibet Plateau and the Triassic Songpan-Ganze terrane to the west, and the Yangtze block (including the western Sichuan foreland basin) to the east, extends ~800 km from northeast to southwest (Figs. 1 and 2). Active tectonics within the LSTC has been widely documented and is characterized by SE to SSE vergent overthrusting with repeated thrusting and denudation since 20 Ma (Arne et al., 1997; Ali et al., 2004), manifests recently by the devastating magnitude 8.0 Ms (Wenchuan) earthquake on 12 May 2008, the 7.0 Ms Lushan earthquake on 20 April 2013, and the 7.0 Ms Jiuzhaigou earthquake on 8 August 2017 (Burchfiel et al., 2008; Lu et al., 2008; Parsons et al., 2008; Hubbard and Shaw, 2009; Jia et al., 2010; Jin et al., 2010; Xu et al., 2016). Marking the present eastern margin of the Tibetan Plateau, the LSTC includes both the pre-collisional Longmenshan orogenic belt with defined tectonic domains of the hinterland belt, the foreland thrust belt and western Sichuan foreland basin (Xu et al., 1992), and the Cenozoic orogenic belt produced by the on-going collision between the Indian and Eurasian continents and associated gravitational relaxation (c.f., Arne et al., 1997; Clark and Royden, 2000; Meng et al., 2005; Lai et al., 2007; Burchfiel et al., 2008; Parsons et al., 2008). The LSTC has experienced a rich and protracted tectonic history and many aspects of the history continue to be debated.

1- Introduction

2- Fault-crossing bridges damaged in past earthquakes

3- Bridges crossing potentially active fault rupture zones

4- Experimental studies

5- Analytical and numerical studies

6- Seismic design provisions and recommendations

7- Summary, concluding remarks, and future directions

References

Abstract

Several earthquakes over the past two decades have demonstrated that bridges crossing fault rupture zones may suffer significant damage due to the combined effects of ground shaking and surface rupture. Although it is widely recommended to avoid building a bridge across a fault, it is not always possible to achieve this objective, especially in regions with a dense network of active faults. This review begins by compiling two databases: one of fault-crossing bridges damaged in past earthquakes and another of bridges crossing potentially active fault rupture zones. The article then continues to review findings of experimental, analytical and numerical studies, and to summarize seismic design provisions and recommendations related to fault-crossing bridges. The review ends with suggestions for future research directions in this area.

Introduction

The vulnerability of bridges crossing active fault rupture zones (called “fault-crossing bridges” in this study) has received increasing attention from earthquake engineers over the past two decades. The impetus was provided by the devastating effects of the 1999 Mw 7.4 Kocaeli, 1999 Mw 7.6 Chi-Chi, and 1999 Mw 7.2 Duzce earthquakes on bridge structures traversed by fault rupture zones. Although it is widely recommended to avoid building a bridge across a fault, it is not always possible to achieve this objective, especially in regions with a dense network of active faults. Active faults that break through the ground surface and have the potential to generate significant fault offset in the event of an earthquake have the capacity to impose a severe combination of ground shaking and surface rupture on fault-crossing bridges. In general, the fault offset may vary from a few centimeters to several meters depending on the earthquake magnitude (e.g., [133]). Similar to nonfault-crossing bridges located in the vicinity of a fault, fault-crossing bridges are subjected to near-fault-pulse-like ground motions affected by forward directivity and permanent translation (fling) (e.g., [81]), but now these ground motions vary across the fault rupture. According to Slemmons and dePolo [111], there are three main types of surface rupture associated with faulting (Fig. 1): (1) primary rupture, which occurs along the primary fault where most of the seismic energy is released; (2) secondary rupture, which occurs along a secondary (or branch) fault subordinate to the primary fault; and (3) sympathetic (or triggered) rupture, which occurs along another nearby fault that is disturbed by the strain release along the primary fault or the vibratory ground motion. It is noted that a surface fault rupture should not be viewed as a fault line, but rather as a fault zone with a finite width subjected to ground distortion. In this study, a faultcrossing bridge is defined as a bridge structure traversed by a surface fault rupture zone (primary, secondary or sympathetic) passing beneath any portion of the bridge (span, pier, abutment or approach road) (Fig. 1).

With the increase of complexity in industrial processes, it is necessary to ensure process safety and efficiency so that fault detection and diagnosis (FDD) plays an important role in process system. However, the characteristics of process data (high dimension and significant correlations) bring a lot of difficulties in FDD, because fault information is buried in the huge historical data. Hence, data-driven methods [1] [2] [3] are developed rapidly in this field. Generally, data-driven methods [4] such as principal component analysis (PCA) [5], partial least squares (PLS) [6] and fisher discriminant analysis (FDA) [7] can transform the highly correlated data into a low-dimensional subspace. With the evolution of data-driven methods, more and more machine learning algorithms have been introduced in FDD research area. Indeed, those algorithms exhibit improved performance in dealing with a large scale industrial process data. Among machine learning algorithms, Bayesian network classifier (BNC) [8] is famous for its capacity of causal analysis under system uncertainty. The Bayesian network (BN) [9] is a type of graphical model and able to model probabilistic influence, which based on a strong mathematical theory, named Bayesian Theorem. The application of BNC for FDD achieves some successes. Parteepasen [10] demonstrates the ability to combine signals from acoustic emission and vibration sensors for tool wear monitoring. Sylvain Verron [11] applied the Bayesian network in multivariate process for fault diagnosis. However, classical BNC only takes static distribution of fault data into consideration to complete the classification task in fault diagnosis, while ignores the importance of dynamic nature in fault data. The dynamic nature in fault data is reflected in temporal behaviors of process data. Therefore, the information extracted from this aspect is called dynamic information, which explicitly depicts some meaningful underlying fault characteristics [12]. More deeply, dynamic information and static information carry the different fault information, analogous to the concepts of position and velocity in physics, respectively. In terms of complex industrial process, there is usually a phenomenon where some faults are unable to be well classified by classifiers when they are put together. These faults are termed as inseparable faults. The reason of this phenomenon is various, such as co-linearity and the similar position distribution. Fortunately, extracting the dynamic information, as an alternative method, can tackle this problem. Because each fault has its own dynamic nature, the dynamic information can be used to divide the inseparable faults into different classifiers in order to achieve a better classification accuracy. One of the methods to extract dynamic information is slow feature analysis (SFA). The SFA [13] is a promising dimension reduction methodology that extracts slow varying features from temporal data. From 2002, SFA has received increasing attention in image recognition [14] and human action recognition [15]. Until 2015, it was found to be used in fault detection by Shang [16]. He has defined two new indices to detect anomalies in process dynamics through the SFA.

Horizontal extension by normal faulting often results in arrays of fault-bounded blocks that have rotated about horizontal axes as their bounding faults slip (so-called ‘domino’ or ‘bookshelf’ faulting) (e.g. Gilbert, 1928; Proffett, 1977; Morton and Black, 1975; Jackson and McKenzie, 1983). However, questions remain over what controls whether faults positioned across-strike from each other are active simultaneously or sequentially, and how this may vary between different extensional settings (e.g. Jackson et al., 1982; Dart et al., 1995). Additionally, in cases where the location of dominant slip activity migrates across-strike between faults, it is not known whether this transition is sudden or gradual, or what controls the direction of migration (e.g. Goldsworthy and Jackson, 2001). Addressing these questions will reveal important information about the mechanics and behaviour of faults, and will also highlight whether multiple faults in arrays of parallel structures need to be considered as sources of earthquake hazard. In addition, understanding the behaviour of arrays of faults will allow us to probe the properties of the underlying ductile layer. Specifically, we can address the controversy of whether strain accumulation at faults is governed by flow in a laterally-homogeneous viscoelastic material (e.g. Meade et al., 2013), or whether lateral contrasts in effective viscosity are the dominant control (e.g. Yamasaki et al., 2014). We address these questions by making new observations of Holocene fault slip on the Kenchreai Fault on the south side of the Gulf of Corinth in central Greece. The Kenchreai Fault bounds the south side of the isthmus between the Gulf of Corinth and the Saronic Gulf (Fig. 1). The northern, hangingwall, side of the fault is occupied by the Corinth Terraces – a series of marine terraces, dating from ∼0.5 Ma to the present, that have been uplifted by motion on the Heraion (also known as Xylokastro) and Pisia faults to the north (e.g. Armijo et al., 1996). This northern fault system ruptured in Mw 6.7 and 6.4 earthquakes in 1981 (e.g. Jackson et al., 1982). The uplift of the Corinth Terraces relative to the sea-level highstands at which they formed (e.g. Armijo et al., 1996) shows that the Heraion and Pisia faults have been more active over the last ∼400 kyr than the Kenchreai and Loutraki Faults, motion on which would produce hangingwall subsidence in the region of the terraces. It is likely that the Kenchreai Fault was the most active fault in the region in the early/mid Pleistocene, because the sediments currently exposed in the cutting of the Corinth Canal (Fig. 1; Collier and Dart, 1991) represent a series of climatically-controlled sea  level cycles superimposed upon tectonic subsidence, of which the Kenchreai Fault is thought to be the cause (e.g. Mack et al., 2009; Charalampakis et al., 2014). The rate of activity on the Kenchreai Fault therefore seems to have reduced since the mid Pleistocene, but questions remain as to whether it has been active at all in the latest Quaternary.

At 12:03 am local time, on November 14th, 2016, a moment magnitude (Mw) 7.8 (USGS) earthquake struck the Kaikoura ¯ region of South Island, New Zealand. The earthquake occurred at a complicated portion of the Australian–Pacific plate boundary, where the motion between the two plates decreases southwestward, and the azimuth changes from trench-normal to trench-parallel along the 3000 km southward-developing subduction system (Litchfield et al., 2014) (Fig. 1 inset). The epicenter of the earthquake (Fig. 1a and inset) is located at the southern end of the subducting system (Barker et al., 2009; Eberhart-Phillips and Bannister, 2010; Williams et al., 2013). The 2016 Kaikoura ¯ earthquake was not unexpected, given its plate boundary location and the historical seismicity, yet it exhibited exceptional complexity. This complexity was initially reflected by the significant non-double-couple centroid moment tensor (CMT) solutions from the USGS (USGS, 2016) and GCMT (Ekstrom et al., 2012) (Fig. 1). Subsequently, field and aerial observations and satellite radar images acquired immediately after the earthquake showed that the quake produced one of the most complex surface ruptures ever recorded (Clark et al., 2017; Litchfield et al., 2017; Stirling et al., 2017). Although the epicenter is ∼50 km inland from the coast, the accompanying tsunami caused up to 5 m of run-ups at Goose Bay, on the Bank Peninsula, to the south of the epicenter and was well recorded by  many tide gauges located along the east coast of New Zealand (Lane et al., 2017; Power et al., 2017) (Fig. S1). The seismic and tsunami hazard due to such a complex rupture cannot be faithfully characterized based on a more typical single-fault rupture scenario (Hamling et al., 2017; Shi et al., 2017). Dense geodetic measurements and strong motion seismometers onshore provided valuable near-field observations to study slip partitioning in the up-dip portion of the subduction system, as the coastline is particularly close to the trench (<50 km). Preliminary seismological analysis shows that the mechanism of the mainshock was oblique thrust (Kaiser et al., 2017). Hamling et al. (2017) derived a static slip model with more than 10 fault segments using GPS and InSAR data. The surface displacement can be fitted reasonably well from their preferred model with most of the slip occurred on crustal faults, yet they have difficulties in simulating the observed tsunami waveforms. This is partially because they did not use a fault segment for the Papatea fault as they considered the associated deformation was inelastic and they could not fit it. Hollingsworth et al. (2017) used optical satellite imagery and teleseismic data to analyze the earthquake rupture process. Their rupture model, which was derived with only seismic data assuming a two-segment fault geometry, shows a source duration of ∼100 s with unilateral rupture to the northeast and most of the slip occurring on the subduction interface. Their model is similar to the result of multiple-point source models derived from the long-period teleseismic data (Duputel and Rivera, 2017), and the result from the back-projection analysis (Zhang et al., 2017).

There are various analytical methods to evaluate the seismic demands of different types of structures for design purposes and other practices. In spite of the ongoing developments in new complicated analytical approaches (e.g., adaptive pushover analysis, incremental dynamic analysis and time-endurance analysis methods) which offer more precise estimations for the seismic response of structures, the conventional static procedures are currently the most frequent approaches for analyzing and designing building new structures (ASCE 07-10; Iranian seismic design code) as well as the seismic assessment of existing structures (FEMA 356; ASCE 41-13). This is due to the simplicity and applicability of these methods in modeling, analyzing and processing the results. For this reason, the improvement in static procedures’ accuracy is a necessity for the structural engineering community. According to the Iranian code for seismic design of structures, the application of static analysis method is valid for a wide range of structures which satisfy the regularity requirements and some other limiting specifications. In this method, the design base shear is calculated based on the dynamic behavior characteristics of equivalent single-degree-of-freedom system. The base shear is then distributed along the height of structure in the form of pseudolateral forces. Seismic response quantities are then calculated using the static analysis methods. Therefore, the pattern of lateral force distribution over the height of structure as well as the estimation of base shear demand significantly influences the seismic response evaluations. The primary criteria for design of steel frames, especially mid- and high-rise frames, are limiting the story drift ratio (IDR) demands to prescribed values. According to the fourth edition of Iranian seismic design code for structures with 5 stories or less, the maximum IDR of all stories considering the second-order geometric nonlinearity must be limited to the 0.025. This limit is 0.02 for buildings with more than five stories. Besides the limiting lateral displacements to prescribed values, the strength capacity of the elements must sufficiently satisfy the capacity design specifications to ensure the stability of individual members. In other words, each structural member must be designed to resist internal force/moment actions.