An anti-fault study of basalt fiber reinforced concrete in tunnels crossing a stick-slip fault

https://doi.org/10.1016/j.soildyn.2021.106687Get rights and content

Highlights

  • The LongMenShan Fault dislocation was analyzed by a large-scale plate thrust model.

  • The crack morphology of the plain concrete tunnel structure was revealed after subjecting to LongMenShan Fault dislocation.

  • The optimal volume content of basalt reinforced fiber concrete was determined through SEM test and mechanical tests.

  • The anti-fault performance of the articulated tunnel constructed by 5% basalt reinforced fiber concrete was estimated.

Abstract

Crossing active faults has proven to cause significant damage in tunnels. In this study, a large–scale plate thrust model stimulating the LongMenShan Fault (LMSF) dislocation was established numerically. The characteristic dislocation curve of the fault generated at the stick-slip incidence was derived. Furthermore, a soil-structure FE model was established with a tunnel structure crossing the LMSF Zone, in which the hanging wall and footwall moved according to the abovementioned dislocation curve. To cope with the serious damage of tunnel caused by fault dislocation, the articulated design was adopted. For discovering an appropriate material to construct the articulated sections and enhance the flexibility of tunnel structure, basalt fiber reinforced concrete (BFRC) was studied by SEM test and mechanical tests. The results showed that basalt fiber could increase the tensile capacity and tenacity of concrete and the 0.5% BFRC was selected as the optimal fiber volume content. By applying the 0.5% BFRC articulated design, the length and width of tunnel cracks generated by fault dislocation decreased by 33.45% and 38.11%, respectively. This study could serve as a reference in the design of fault-crossing tunnel projects.

Introduction

An earthquake is a common engineering geological hazard caused by tectonic shifts. Researchers have reported that an earthquake is triggered by the brittle rift and dislocation that occur abruptly inside the crust. During the process, a large amount of energy is released, which causes the stick-slip behavior of causative faults [1].

In practice, crossing faults are inevitable in a tunnel project because of geological and circuit constraints [2,3]. Several studies have demonstrated that tunnel crossing faults can cause severe damage. During the Izu M7.0 earthquake in Japan which occurred in 1930, the Dana tunnel, affected by fault slip, was damaged. Furthermore, during the M7.0 earthquake in Izumi Island, Japan, which occurred in 1978, the central section of the Inatori tunnel was destroyed, and the tunnel lining on both sides of the fault was staggered by approximately 50 cm [4]. During the Düzce earthquake in Turkey in 1999, both the Tuzla tunnel and Bolu tunnel that were constructed in the fault zone were severely damaged. The Bolu tunnel experienced a 400–m collapse of the primary support of structures and simultaneous collapse in one portal caused by thrusting of the surrounding rock [5]. Due to the action of the Tyrrhenian sea and faults, the entire Apennine peninsula is still in the process of continuous uplift resulting in serious earthquake damage at several parts of the Paloncelli tunnel across faults [6]. During the Wenchuan M8.0 earthquake in China in 2008, 75% of the lining structures of the Longxi tunnel, Longdongzi tunnel, and Zipingpu tunnel in the LongMenShan Fault (LMSF) zone was damaged. Particularly, in the Longxi tunnel that is located between the Yingxiu Fault and Longxi Fault, the relative displacement along the vertical orientation reached nearly 100 cm, and the lining arch collapsed resulting in a complete loss of functionality [7].

Several researchers have studied the influencing mechanism of fault dislocation in underground structures through various numerical simulations and model tests. One of the major challenges in imitating the stick-slip fault is the ways of stimulating the fault dislocation. Wang Z.Z [8]. arranged the fault movement of 20 cm to the stratum in a numerical model. Liu X.Z [9]. assumed that the lifting height of the stratum was 100 mm (with a loading procedure of 1 mm/min) in a model test to simulate the stick-slip fault. Wang D.Y [10]. conducted large–scale model tests on anti-seismic and damping measures for dislocation of the stick-slip fault, and dislocation of 5 cm was adopted in the tests to stimulate a realistic dislocation of 1.5 m. Using numerical simulation, Zhao K [11]. studied a typical large-diameter transmission water tunnel crossing a fault zone with a stick-slip rate of 1.0–3.3 mm/a (average value of 2.2 mm/a). The aforementioned studies adapted a given size of the fault dislocation to simulate the stick-slip fault, which neglected the time–response variation of the stratum displacement. Hence, to reveal the authentic tunnel response to the fault stick-slip, the fault dislocation features generated by conformance to the causal mechanism of fault must be studied.

The causal mechanism of fault has been highlighted among several researchers. Through rock friction tests, Brace and Byerle [12] first proposed that earthquakes are probably caused by frictional instability between plates. Subsequently, many scholars orientated their research towards the friction problem of focal faults. Using friction tests, Dietrich [13] established that the stick-slip process of focal fault is accompanied by noticeable stress drop, which is proportional to the logarithm of time. Scholz et al. [14]. concluded that the friction coefficient is inversely proportional to the logarithm of the sliding rate. A more authentic connection investigating the rock friction property was launched by Ruina [15], who used the rate–state dependent criterion. In that criterion, Ruina expressed that the friction coefficient decreases as the slide rate increases, causing instability on the fault face. Thereafter, with the increasing sliding displacement reaching the critical sliding weakening distance, the release of elastic strain energy ends, and the friction coefficient increased gradually, and the fault face returned to be bonded and locked, waiting for the next stick-slip incident. In the aspect of the earthquake mechanism caused by fault instability, most scholars used friction constitutive models to simulate the source vibrant process and recur the earthquake process. David et al.[16]. used the rate-state dependent criterion to simulate the earthquake preparation process based on the granular discrete element theory. Kato [17] studied the effect of far-field loading rate on the nucleation size and seismic intensity. Cao Y.Y [18]. quantitatively studied the damage evolution and crack development of rock during the stick-slip process by combining numerical simulation and friction tests.

Based on the aforementioned studies of causal mechanisms of faults, a large-scale plate strain numerical model can be established to derive the characteristic dislocation of stick-slip faults. Subjected to this dislocation, the rather authentic tunnel damages due to the incongruous deformation between the stratum and tunnel structure could be detected. In order to alleviate the damages, given that a moderately flexible structure could adapt to the stratum movement, researchers considered introducing flexible sections in a tunnel to enhance its flexibility. This anti-fault measure is commonly termed as the articulated design. For relieving the influence from the North Anatolian fault zone, the articulated design was adopted in the Bolu tunnel in Turkey, which allowed the tunnel structure to deform within 25 cm [19]. Using model tests, Liu X.Z [20]. Established that under the fault dislocation, the tunnel adopting articulated design showed trivial damage in the main structure with concentrated damage in the deformed joints. Furthermore, Li L [4]. Established a soil-structure model and applied low–stiffness sections in the tunnel lining. After stimulation using earthquake loads, the internal force in the fault-crossing tunnel structure tended to decay. Zhao K. et al. [21]. Demonstrated by conducting a numerical model where the flexible segments introduced in tunnel could efficiently absorb the fault dislocation and decrease the internal force in the structure.

The articulated design has not been adequately applied or studied, and a suitable material that could be used as flexible segments has not yet been found. Fiber concrete, however, is expected to be appropriate for the fabrication of flexible segments due to its excellent tensile capacity, tenacity, and ability of resisting impact and fatigue dynamic load [21,22]. Gong et al. (2017) [23] compared the seismic behavior of tunnel joints made of SFRC with those made of normal-weight concrete. The results revealed that SFRC improved the structural performances of the tunnel segmental joints, and it could partially replace the reinforcements in the joints. Avanaki et al. (2018) [24] investigated the seismic vulnerability of different composites of Steel FRC, in which the results showed that steel fibers concrete displays better seismic performance over conventional steel rebar in reinforced concrete linings. Based on the immersed tunnels in the Hong Kong-Zhuhai-Macau megaproject, Li Z.X. et al. (2019) [25] tested the properties of hybrid fiber reinforced concrete, in which the shear keys with steel and basalt fibers improved the ultimate load-carrying capacity, energy, dissipation capacity, and ductility of the shear keys by 44.6%, 229%, and 53.1%, respectively. Xin C.L. et al. (2019) [26] conducted a series of shaking table tests on scaled tunnel models, which showed that Polypropylene fiber allows tunnel lining to generate smaller deformations and strains to resist deformations of surrounding rock and gives tunnel with superior aseismic performance in soft rock. Based on the subway tunnel in F2-3 section of Jiujiawan fault, Cui G.Y. et al. (2020) [27] carried out an anti-breaking model test of the fiber-reinforced concrete lining in the active fault zone. The result showed that the fiber-reinforced concrete lining could increase the minimum value of the structural safety factor by 4–5 times.

This study is primarily based on a fault-crossing tunnel built in the LMSF zone in China to reveal the seismic response of the tunnel and verify the anti-fault capacity of the BFRC articulated design. Initially, a spatial large–scale plate thrust model of 300 × 100 km2 area corresponding to the authentic stratum properties of the LMSF zone was established numerically. Thereafter, a characteristic dislocation curve of stratum generated by the stick-slip fault was derived through the model. Furthermore, this characteristic dislocation curve was input in a soil-structure FE model, serving as the movement of stratum, to derive the authentic dynamic damage occurring in the tunnel. The calculating sequences indicated that cracks of 14.65 m in length and 21.7 cm in width were generated in the tunnel structure after the tunnel was subjected to the stick-slip fault. Therefore, to mitigate the tunnel damages and identify an appropriate material used for the articulated segments, BFRC with five different fiber volume contents was tested. By comparing the mechanical properties of all the five cases, the optimal volume content was selected as 0.5% BFRC. Thus the 0.5% BFRC articulated design was proven to be efficient owing to its distinctive reduction of the cracks and damages in the fault-crossing tunnel. The results of this study could assume a reference role in the design of the fault-crossing tunnel project.

Section snippets

Stick-slip dislocation of LMSF zone and the characteristic dislocation curve of stratum

For investigating the dynamic response of tunnel based on a fault-crossing tunnel project built in the LMSF zone, it is imperative to study the stick-slip dislocation characteristics of LMSF. Accordingly, the characteristic dislocation curve could be derived through the time history of the stratum. Consequently, by penetrating this time–response dislocation into a soil-structure model including a fault-crossing tunnel, the rather authentic damage morphology of the tunnel structure could be

Soil-structure model with fault-crossing tunnel

A three–dimensional finite element model of a highway tunnel crossing the LMSF zone was established with a fault inclination angle of 60° (Fig. 6). The size of the model was 200 × 100 × 100 m3, and the tunnel clearance was 12.5 × 9.6 m2 with a 50–cm lining thickness.

The Mohr–Coulomb elastoplastic constitutive model was adopted, and the material parameters of surrounding rock were consistent with those mentioned in section 2.2. The properties of concrete were set conforming to the Code for

Basalt fiber

Basalt fiber is a type of hi-tech fiber developed by the former Soviet Union through more than 40 years ago [51]. Basalt fiber is proved to possess superior tensile strength (1.5–2 times higher than plain concrete) and integrated failure mode [52]. Numerous studies show that the properties of basalt fiber reinforced concrete (BFRC) have a strong association with the volume content of fiber. T. Ayub [53] tested the mechanical properties of BFRC and determined that the compressive strength of

Parameter determination of BFRC articulated design

To verify the superiority of the BFRC used to improve the anti-fault capacity of tunnel, the continuous lining with plain concrete in the soil-structure model mentioned in section 3.1 was changed into an articulated design structure with 0.5% BFRC flexible sections. In an articulated design, the rational length of articulated sections and proper protection range are significant in enhancing the tunnel anti-fault capacity within a limited cost, which are primarily determined based on the

Conclusion

This study initially established a spatial large–scale plate thrust model of 300 × 100 km2 corresponding to the authentic stratum properties of the LMSF zone. Consecutively, the characteristic dislocation curve of the stratum generated by the stick-slip fault was derived by the established model. Further, this dislocation curve was input in a soil-structure model for the movement of the stratum. The calculating sequences indicated the occurrence of substantial damage in the tunnel lining after

CRediT author contribution statement

Guanxiong Zeng: Methodology, Software, Writing – original draft, Writing – review & editing, Test Design and Conduction. Xiangyu Guo: Conceptualization, Supervision, Software. Peisong Li: Writing – original draft, Test Conduction. Qi Wang: Supervision, Test Design and Conduction. Ti Ding: Software. Ping Geng: Conceptualization, Methodology, Funding acquisition, Writing – review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The authors appreciate the support of the National Natural Science Foundation of China (No. 51878566); Key R & D Project in Sichuan Province (No. 2020YFS0294); Science and Thechnology Department of Sichuan Province (No. 2019YFG0001).

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