THE IMPACT OF EARTHQUAKES ON THE TUNNEL FROM HANOI METRO SYSTEM WHEN THE TUNNEL HAS A HORSESHOE SHAPE CROSS-SECTION

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 10, Issue 02, February 2019, pp , Article ID: IJCIET_10_02_010 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed THE IMPACT OF EARTHQUAKES ON THE TUNNEL FROM HANOI METRO SYSTEM WHEN THE TUNNEL HAS A HORSESHOE SHAPE CROSS-SECTION Gospodarikov Alexandr Saint Petersburg Mining University, Saint Petersburg, Russia Federation Thanh Nguyen Chi Saint Petersburg Mining University, Saint Petersburg, Russia Federation Hanoi University of Mining and Geology, Hanoi, Vietnam ABSTRACT Hanoi is capital Viet Nam. Currently, the metro system is being constructed in Hanoi. This paper uses the 2D numerical method with Abaqus software to set up the tunnel model that has a horseshoe shape cross-section of the Hanoi metro system, passing through the Hanoi center. On the basis of the data about the strongest earthquake that could occur in Hanoi center, the paper calculated the impact of this strongest earthquake to the tunnel in two case: the first case with the soil environment surrounding the tunnel that has been studied is elastic, uniform and isotropic, the second case with the soil environment surrounding the tunnel is elastic perfectlyplastic according to Mohr-Coulomb failure criterion and has a damping ratio is 5%. On the basis of the results obtained, the paper assessed and given results about the impact of the strongest earthquake that could occur the Hanoi area to the stability of the tunnel that has a horseshoe shape cross-section from the Hanoi metro system. Key words: horseshoe tunnel, earthquake, impact, model, soil. Cite this Article: Gospodarikov Alexandr and Thanh Nguyen Chi, The Impact of Earthquakes on the Tunnel from Hanoi Metro System when the Tunnel has a Horseshoe Shape Cross-Section, International Journal of Civil Engineering and Technology (IJCIET) 10(2), 2019, pp INTRODUCTION Hanoi is located in North Vietnam, near Song La-Dien Bien fault and Red River fault with the strongest earthquake that has magnitude M w = 6.5 Richter that may occur in the North Vietnam and effect to Hanoi [4, 5, 6]. With the geological and hydro-geological conditions of Hanoi center and the parameters of the strongest earthquake, that may occur in the Hanoi area, this paper studied and evaluate the impact of the strongest earthquake on the tunnel lining that 79 editor@iaeme.com

2 The Impact of Earthquakes on the Tunnel from Hanoi Metro System when the Tunnel has a Horseshoe Shape Cross-Section has a horseshoe shape cross-section from to Hanoi metro system. At present, there are not many methods of calculating and evaluating the effects of earthquakes on tunnels that have a horseshoe shape cross-section. Some analytical methods can be used to calculate the effects of earthquakes on tunnels such as those of Wang (2003) [12], Penzien (2008) [10], Oreste et al., (2007) [8] or Wood (2004, 2005) [13, 14]... However, these methods only apply to tunnels with the circular cross-section and the rectangular cross-sections. This paper has used the 2D numerical method with ABAQUS software on calculating and evaluating the effects of the strongest earthquake that may occur to Hanoi center on the tunnel that has a horseshoe shape cross-section from the Hanoi metro system. 2. THE HYDROGEOLOGICAL, GEOLOGICAL CONDITIONS AND PARAMETERS OF TUNNEL IN HANOI CENTER The groundwater level in Hanoi center that is three meters below the surface. In Hanoi center it has usually six layers of soils distributed from the ground surface to the bedrock at a depth of 48 m. All parameters of soil layers at Hanoi center in Table 1 and in Figure 1. Soil Layer 1 - Backfill - thickness 4.6 m Soil Layer 2 - Soft clay - thickness 1.1 m 20 m R=2.95 m Soil Layer 3 - Stiff lean clay-thickness 11.8 m h=2.95 m Tunnel Soil Layer 4 - Dense clay sand - thickness 12.5 m Soil Layer 5 - Very dense clay sand - thickness 11.0 m Soil Layer 6 - Coarse sand with Gravel - thickness 7.0 m Bed rock Figure 1 Layers soils surrounding the tunnel The tunnel is located at a depth of 20 m from the surface ground. The tunnel has got a horseshoe shape cross-section with the radius of the dome R and the height of the columnwall h, R=h=2.95 m, the tunnel lining is made reinforced concrete. The design parameters of the tunnel lining are listed below [4, 6, 7]: - Young s modulus E l = MPa; - Poisson s ratio ν l = 0.15; - Lining thickness t l = 0.3 m. Parameters of the strongest earthquake that can occur in the Hanoi center are [3, 4]: - The earthquake with a maximum magnitude M w = 6.5 Richter; - Distance from the epicenter of the earthquake to Hanoi is 20 to 50 km and peak ground acceleration a max = 0.2 g editor@iaeme.com

3 Acceleration, g Gospodarikov Alexandr and Thanh Nguyen Chi Number of soil layers Elastic module, E, MPa Table 1 Parameters of layers soil in Hanoi center [3] Poisson s ratio, Thickness of layer (h), m Depths of soil layers, m Density of the soil, ρ, g/cm Ground water level, m SET UP THE TUNNEL MODEL BY 2D NUMERICAL Using ABAQUS software to establish a tunnel model that has a horseshoe shape cross-section and this tunnel model has been influenced by the strongest earthquake, which can affect the Hanoi center. The tunnel model and lining are set up with the parameters that were described in Section 2. The soil environment surrounding the tunnel is also established along with the tunnel model with the properties of the soil environment these are represented by a single soil layer. The soil environment has properties equivalent to 6 actual soil layers, this is done to ensure the accuracy of the model when this model is operating. There are two cases of operating given in this model. The first case, the soil environment surrounding the tunnel is elastic, uniform and isotropic. The second case is that the soil environment surrounding the tunnel is elastic perfectly-plastic, according to Mohr-Coulomb failure criterion and has a damping factor is 5%. In both cases, the tunnel lining is elastic. Note: In this study, using data of El Centro earthquake (with characteristics of the El Centro earthquake almost identical to characteristics of the strongest earthquake that can occur in the Hanoi) M w = 6.5 Richter and be showed in Figure 2 [4, 8, 11]. The numerical analysis has been performed regardless of the effect of gravity and groundwater conditions and all case of being the calculation for case no-slip at the soil tunnel lining. The tunnel lining is continuous Figure 2 Data of El Centro earthquake [3, 7] In this 2D numerical model, 6 soil layers are replaced with a single soil layer with equivalent parameters [6, 7]: Young s modulus, E = MPa; - Poisson s ratio, 0.34; Time, s 81 editor@iaeme.com

4 The Impact of Earthquakes on the Tunnel from Hanoi Metro System when the Tunnel has a Horseshoe Shape Cross-Section - Damping ratio is 5%. Size of the 2D numerical model: 180 m wide in the x-direction, 80 m in the z-direction. Phases of the construction process of the tunnel model and soil layer surrounding the tunnel in this study [1, 3, 7]: - Phase 1 (model setup): The tunnel model and soil layer surrounding the tunnel have been set up, assignment of the plane strain boundary conditions, there is no reflection wave at the boundary of the model and regardless the influence of the gravity and groundwater. The model has two parts, the first part contains the tunnel and the soil layer surrounding the tunnel, the second part is the area that using infinite elements so that the model has not to wave reflection phenomenon when be affected by the earthquake; - Phase 2: Construction of the tunnel model and tunnel lining with parameters of soil layer surrounding and tunnel lining, assigning the tunnel lining with layer soil surrounding link conditions (the tunnel lining is continuous). Setting up the stress over the whole tunnel boundary on both the tunnel lining and model's boundary, assign to the peak ground acceleration of the earthquake to the tunnel model; - Phase 3: The results obtained of the model (see Figures 4, 5, 6, 7, 8, 9): Figure 3 The model of tunnel and soil layer surrounding [7] 4. RESULTS AND DISCUSSION Figure 4 Result calculation in case of the soil layer surrounding tunnel is elastic [7] 82 editor@iaeme.com

5 Gospodarikov Alexandr and Thanh Nguyen Chi Figure 5 State stress on the tunnel lining in case of the soil layer surrounding tunnel is elastic Figure 6 Strain of the tunnel lining in case of the soil layer surrounding tunnel is elastic Figure 7 Result calculation in case of the soil layer surrounding tunnel is elastic perfectly-plastic, damping ratio = 5% 83 editor@iaeme.com

6 The Impact of Earthquakes on the Tunnel from Hanoi Metro System when the Tunnel has a Horseshoe Shape Cross-Section Figure 8 State stress on the tunnel lining in case of the soil layer surround tunnel is elastic perfectlyplastic, damping ratio = 5% Figure 9 Strain of the tunnel lining in case of the soil layer surround tunnel is elastic perfectly-plastic, damping ratio = 5% Table 2 Analysis results of the different cases for the horseshoe tunnel Сase studies The maximum stresses, (MPa) max Difference (%) 1 Elastic (reference case) Elastic perfectly-plastic, damping ratio = 5% Based on the results obtained in two cases: The first case, the soil layer surrounding the tunnel is elastic, homogeneous and isotropic. In this case, the maximum stresses obtained in the tunnel lining is of great value, reaching MPa. In case of the soil layer surrounding the tunnel working according to the Mohr-Coulomb failure criterion, it is an elastic perfectlyplastic constitutive model and has a damping ratio is 5%, maximum stress on the lining when under the influence of the earthquake with a value of MPa-the difference with the stress value in case the soil environment surrounding the tunnel is elastic, uniform and isotropic given is %. These differences are very large. It can be seen that the impact of the damping ratio of the soil environment surrounds the tunnel to the maximum stress value 84 editor@iaeme.com

7 Gospodarikov Alexandr and Thanh Nguyen Chi appearing on the tunnel under the impact of the earthquake that is very large. It is this damping ratio of the soil environment that causes the vibration of tunnel lining to decrease over time and causes the stress that appears on the lining of the tunnel to be greatly reduced compared to the case of that has not a damping ratio. 5. CONCLUSIONS Currently, the numerical method is one of the most commonly used methods for calculating and designing tunnels when these tunnels work under the influence of earthquakes. Some advantages of numerical methods: establishing a link between the tunnel and the surrounding environment, can use many different failure criterion models, can take into account the effect of damping ratio...this paper used ABAQUS software to create and set up a tunnel that has a horseshoe shape cross-section in the Hanoi metro system under the influence of the strongest earthquake that could occur to Hanoi area in two cases: In the first case the tunnel lining and soil environment surrounding the tunnel are elastic, homogeneous and isotropic, the second case is the soil environment surrounding the tunnel is elastic perfectly-plastic according to the Mohr-Coulomb failure criterion and has a damping ratio is 5%. Based on the results obtained and the above analysis, the following conclusions can be made: - In both cases, the tunnel is still stable and sustainable under the impact of the strongest earthquake that may occur the area where the tunnel is located. The maximum stress value that appears on the tunnel lining is smaller than the limited stress value of the tunnel lining material ( max < =22 Mpa); limit - The damping ratio of the soil environment surrounding the tunnel that has a big effect on the stress value appearing in the tunnel lining under the impact of the earthquakes. Because of this effect, the fluctuation and vibrating of the tunnel lining under the effect of the earthquakes will decrease, thereby causing the stress on the tunnel lining to decrease markedly. ACKNOWLEDGEMENTS This work was supported by the Saint Petersburg Mining University. We thank two anonymous reviewers for their comments that were very valuable for revising the manuscript. REFERENCES [1] A. A. Sankovskii, E. R. Koval skii, The analysis of the stress-and-strain state in vicinity of mining excavations. JOURNAL OF MINING INSTITUTE, 207, 2014, pp [2] Do, N. A., Dias, D., Oreste, P. P., & Djeran-Maigre, 2D tunnel numerical investigationthe influence of the simplified excavation method on tunnel behavior. Geotechnical and Geological Engineering, 32(1), 2014a, pp [3] Gospodarikov Alexandr, Thanh Nguyen Chi, Liquefaction possibility of soil layers during earthquake in Hanoi, International Journal of GEOMATE, 13(39), 2017, pp [4] Gospodarikov Alexandr, Thanh Nguyen Chi, The impact of earthquakes of tunnel linings: A case study from the Hanoi metro system, International Journal of GEOMATE, 14(41), 2018, pp [5] Gospodarikov Alexandr, Thanh Nguyen Chi, Behaviour of segmental tunnel linings under the impact of earthquakes: A case study from the tunnel of Hanoi metro system, International Journal of GEOMATE, 15(48), 2018b, pp editor@iaeme.com

8 The Impact of Earthquakes on the Tunnel from Hanoi Metro System when the Tunnel has a Horseshoe Shape Cross-Section [6] Gospodarikov Alexandr, Thanh Nguyen Chi, Different behaviour of circular and rectangular tunnels under the impact of earthquakes: A case study from the tunnel of Hanoi metro system, International Journal of GEOMATE, 15(51), 2018c, pp [7] Gospodarikov Alexandr, Thanh Nguyen Chi, The Reasonable Cross-Section shape for the Tunnel from Hanoi Metro System under the Impact of the Earthquakes, International Journal of Civil Engineering and Technology, 9(12), 2018e, pp [8] ITA. ITA guidelines for the design of tunnels. Tunnelling and Underground Space Technology, 3(3), 1998, pp [9] Oreste, P. P, A numerical approach to the hyperstatic reaction method for the dimenshioning of tunnel supports, Tunnelling and Underground space technology, 22, 2007, pp [10] Penzien J., Wu, C, Stresses in linings of bored tunnels, Journal of Earthquake Eng. Structural Dynamics, 27, 1998, pp [11] The Southern California Earthquake Data Center (SCEDC). Data of El Centro earthquake, [12] Wang J. N. Seismic design of tunnels: A state of the art approach, Parsons Brinkerhoff Quad & Douglas Inc., New York, NY, Monograph 7, [13] Wood, J.H., Earthquake design procedures for rectangular underground structures. Project Report to Earthquake Commission, EQC Project No 01/470, Rev B July /470. New Zealand, [14] Wood, J.H, Earthquake design of rectangular underground structures. NZSEE Conference, New Zealand, 2005, pp editor@iaeme.com