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Numerical Investigation into the Effects of Controlled Tunnel Blast on Dynamic Responses of the Transmission Tower

Numerical Investigation into the Effects of Controlled Tunnel Blast on Dynamic Responses of the... Hindawi Advances in Civil Engineering Volume 2023, Article ID 6021465, 12 pages https://doi.org/10.1155/2023/6021465 Research Article Numerical Investigation into the Effects of Controlled Tunnel Blast on Dynamic Responses of the Transmission Tower 1 2 3 4 Feng Wang, Gaohai Zhang, Wenwen Li , and Hongwei Nie China Railway 18th Bureau Group Co., Ltd., Tianjian, China China Railway Construction Investment Co., Ltd., Beijing, China Changshu Institute of Technology, Suzhou, China Soochow University, Suzhou, China Correspondence should be addressed to Wenwen Li; lwwgeo@hotmail.com Received 9 February 2022; Revised 23 April 2022; Accepted 20 April 2023; Published 3 May 2023 Academic Editor: Andre´ Furtado Copyright © 2023 Feng Wang et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. At present, the drill-and-blast method is still one of the main construction means in the road tunnel excavation process. When the tunnel penetrates underneath sensitive structures such as high-voltage transmission towers, the blasting and supporting pa- rameters must be strictly controlled to ensure the stability and safety of the surface structures. In this paper, numerical simulations based on a large-section shallow buried tunnel project in Zhuhai are conducted to study the efect of controlled tunnel blast on the dynamic response of transmission towers. Te numerical simulation results indicate that the blast vibration velocity of the rock generated by controlled blasting decreases rapidly along the tunnel excavation direction. Te blast vibration velocity of the high- voltage transmission tower and its pile foundation gradually increases with the propagation of the blast waves, and the maximum vibration velocity is about 1.24 cm/s. Te results indicate that the controlled blasting design of this project can efectively restrain the vibration velocity induced by the blasting load and could ensure the stability and safety of the transmission tower. by researchers [4–7]. Te site test can objectively refect the 1. Introduction infuence of blasting vibration on the rock mass structure. With the rapid development of highways in China, large- However, due to the nonhomogeneity and the defects of the section tunnels are widely used in highway construction internal structure in the rock mass, the experimental con- because of their ability to signifcantly reduce road mileage ditions are difcult to control. Compared with the site tests, and improve transport efciency. Te tunnels would the numerical calculation can simulate the dynamic re- sometimes inevitably penetrate beneath sensitive structures, sponse problem in the complicated geological conditions, such as transmission towers and other existing structures, thus the numerical simulation method is widely used to analyze the blasting vibration response. Some studies [8–10] which poses challenges for the design and construction of large-section tunnels. evaluated the vibration damage to transmission towers based on the fnite element method. Luo et al. [11] analyzed the At present, the drill-and-blast method is still one of the main construction methods in the road tunnel excavation dynamic characteristic of the tunnel for surface explosion of process [1–3]. When the tunnel penetrates underneath 100 and 300 kg TNT charge, respectively. Duan et al. [12] sensitive structures such as high-voltage transmission investigated the vibration characteristic of high-voltage towers, the blasting and support parameters need to be tower under the infuence of adjacent tunnel blasting ex- strictly controlled to ensure the stability and safety of the cavation. Beside the study on the infuence of vibration surface structures. To study the infuence of vibration caused induced by controlled blasting on transmission tower, more by controlled blasting on rock mass and sensitive structures, research focuses on the dynamic responses of adjacent site test and numerical simulation methods are widely used structures. Zhao et al. [13] used feld monitoring 2 Advances in Civil Engineering experiments and numerical simulation to study the efect of blast-induced vibration from adjacent tunnel on existing tunnel. Jiang et al. [14] investigate the efect of excavation blasting vibration on adjacent buried gas pipeline in a metro tunnel. However, the dynamic responses of the transmission 1.92 m tower system remain one of the most challenging tasks in the civil engineering as a complex, continuous, and mechanical system. Based on a large-section shallow buried tunnel project in Zhuhai, China, this paper studies the efects of controlled Tunnel tunnel blasting on the dynamic responses of high-voltage 2.96 m transmission towers. Tree-dimensional numerical analyses 220 KV high voltage were conducted in the fnite diference program FLAC3D, transmission tower and the dynamic responses of the tunnel surrounding rock and high-voltage transmission towers under the blast loading were studied. Te vibration velocity, deformation responses of surrounding rock and high-voltage trans- Figure 1: Schematic view of the locations of the tunnel and mission towers were predicted to provide scientifc basis and transmission tower. reference for relevant construction optimization and decision-making. and width of the model are selected as 100 m and 52 m, 2. Overview of the Project respectively, which could efectively reduce the boundary efect. Te axis used in the numerical model is defned as Te Black and White General Hill tunnel is a large-section follows: X axis is along the direction of tunnel excavation; Y shallow buried tunnel under construction in Zhuhai, China, axis is along the cross-section of the tunnel; and Z axis is which is built to enhance the transportation links between along the gravity direction. Te numerical model mainly diferent districts in Zhuhai. Te exit section of the tunnel consisted of the tunnel, surrounding rocks, transmission penetrates directly underneath a high-voltage transmission tower, and its fle foundation. It is noted that the trans- tower. A schematic view of the locations of the tunnel and mission tower and its pile foundation are modelled using the transmission tower is shown in Figure 1. Te transmission structure elements implanted in FLAC3D to reduce model tower is a 2F-SJ2 type tower with a total height of 41.5 m, complexity and increase calculation speed. Te total number supported by four piles with a diameter of 2.1 m and a length of zones in the 3D numerical model is 112,400, and the total of 12 m. Te vertical distance from the top of the tunnel to number of nodes is 12033. the pile toe is about 7.5 m, and the smallest horizontal Te high-voltage transmission tower is built upon a hill distance from the tunnel to the transmission tower is about which the tunnel penetrates through. Te curved surface of 1.9 m. the hill needs to be considered in the numerical model to Te surrounding rocks at the tunnel exit consisted of obtain a correct initial stress condition in the surrounding medium strongly weathered quartz amphibolite. Te arches rocks. Te curved surface is generated in SketchUp by and sidewalls of the tunnel exit are of poor stability, which importing the contour lines of the hill. Ten, the 3D hill could lead to rock collapse and drops at drill-and-blast surface is exported to FLAC3D, and it connects with the excavation. Te uneven weathering of the surrounding tunnel model built in FLAC3D to form the 3D numerical rocks has an impact on the stability of the tunnel portal and model. Te process of model generation is shown in Fig- the side slopes. Tese geological conditions would pose ure 3. Te soil layer distribution is generated based on the a threat to the stability of the transmission tower. geological data using the curved surface import method. According to the geological survey, the soil stratum from top to bottom within the exploration depth is divided into clay, fully weathered, strongly weathered, medium weath- 3.2. Constitutive Model and Material Parameters. Te ered, and slightly weathered quartz amphibolite. Based on Mohr–Coulomb model is selected as the constitutive model the results of the wave velocity test and other geotechnical for the soil and rock in this project. Te parameters of tests, the physical properties of the soil and rock are shown density, cohesion, and friction angle are adopted directly in Table 1. from the geological survey data, which is shown in Table 1. Te transmission tower is modelled with the beam element implemented in FLAC3D, which is a two-noded, straight, 3. Numerical Investigation fnite element with six degrees of freedom per node. Te 3.1.NumericalModel. A 100 m range of tunnel exit (mileage beam element has three material parameters, density, elastic YK4 + 820–YK4 + 920) is selected as the modelling area, with modulus, and Poisson’s ratio, which are set to be 7850 kg/m , the tunnel and transmission tower included. Te numerical 200 GPa, and 0.3, respectively. Te pile foundation of the model built in FLAC3D is shown in Figure 2. Considering transmission tower is modelled using the pile element, which the infuence of tunnel depth and blasting, the total length could efectively simulate the normal-directed Advances in Civil Engineering 3 Table 1: Property parameters of the soil. Friction angle Elastic modulus Soil layer Name Density (kN/m ) Cohesion (kPa) Poisson’s ratio ( ) (MPa) 1 Clay 19.8 25 20 20 0.38 2 Fully weathered quartz amphibolite 23.0 26 28 48 0.35 3 Strongly weathered quartz amphibolite 27.7 28 30 70 0.32 3 4 4 Medium weathered quartz amphibolite 28.9 5.5 ×10 41 4.0 ×10 0.30 3 4 5 Slightly weathered quartz amphibolite 30.0 7.0 ×10 42 6.5 ×10 0.23 Zone Group Slot soil layer W1 rock W2 rock W3 rock W4 rock silt clay X Y Figure 2: 3D numerical model. (perpendicular to the pile axis) and shear-directed (parallel load generated by millisecond delay blasting needs to be with the pile axis) frictional interaction between the pile and applied at the tunnel. the soil. Te soil-pile interaction is considered by the shear In the process of blasting, the interaction of stress waves and normal coupling springs. Te coupling springs are generated by blasting will make cracks spread along the nonlinear, spring-slider connectors that transfer forces and connecting line of adjacent blastholes. With the growth of motion between the pile and the grid at the pile nodes. Te the blast induced crack and interpenetration throughout the shear behavior of the pile-grid interface is cohesive and rock, a new free surface will be created along the blasthole frictional in nature. Te lining and anchors used as tunnel line, which is the designed blasting excavation boundary. supporting are simulated with the liner element and cable Terefore, the blasting excavation boundary is taken as the element, respectively. Te parameters of the structure ele- inner boundary of the numerical model. Tus, the full scale ment (pile, liner, and cable) adopted in this paper are shown blastholes are not included in this model, and the blasting in Tables 2–4. pressure is applied equivalently to the excavation boundary, which avoids tremendous model meshing and computa- tional work due to detonations of too many tiny blastholes. In this paper, an equivalent pulse load of the multihole 3.3. Blasting Load. Due the short distance from the tunnel and the sensitivity of the transmission tower, the controlled blasts is applied at the blasting excavation boundary of the tunnel. Tis simplifed equivalent load method certainly blast and double-sided guide-pit method are adopted in the excavation and initial support of tunnel exit to ensure the causes some deviation in the immediate vicinity of blast- holes. However, this study is to investigate the dynamic stability of the transmission tower. Te detailed blast-hole distribution and blasting sequences for the double-sided responses of the transmission tower and surrounding rocks outside the blasting boundary rather than the explosion- guide-pit method are shown in Figure 4. Tere are about 330 blast-holes in each blast section, distributed in a cross- induced rock fracture and fragmentation process around blastholes. Terefore, this equivalent pulse load simplifca- sectional area of 305 m . Te unit explosive consumption is about 0.9 kg/m for the controlled blast design. In order to tion is acceptable to a certain degree. Following the pro- cedure used by Yang et al. [15, 16], the equivalent pulse load study the efect of controlled blast on the dynamic responses applied in this paper is shown in Figure 5. of the transmission tower and surrounding rock, the blast 4 Advances in Civil Engineering Figure 3: Process of 3D surface model generation. 3.4. Analysis Procedures and Boundary Condition. Te focus propagating waves back into the model and do not allow the of the research in this paper is to investigate the dynamic necessary energy radiation. Terefore, the fxed boundary responses of the transmission tower under tunnel blasting to condition is converted into a viscous boundary by using ensure the stability and functionality of the transmission independent dashpots in the normal and shear directions at tower. Terefore, the numerical study chooses the condition the model boundaries in the dynamic loading stage. where the tunnel has been excavated directly underneath the transmission tower, and the initial support and cables have 4. Results and Discussions been installed in the excavated part of the tunnel, which is shown in Figure 6. Te blast load generated by the frst section 4.1. Responses of the Surrounding Rock. To ensure the sta- of the tunnel (as shown in Figure 4) beneath the transmission bility of the transmission tower, the dynamic responses of tower is applied at the numerical model, when the infuence of the surrounding rock are analyzed frst. Figure 7 shows the the blast on the transmission tower is the most obvious. time histories of blast velocities measured at diferent dis- Before the blast loading is applied, the boundary of the tances from the blast surface. Te maximum blast velocities numerical model is set to be fxed in their normal direction along X, Y, and Z axis caused by controlled blasting of to calculate the initial stress condition. In static analysis, section 1 are about 9 cm/s, 0.58 cm/s, and 3 cm/s, re- fxed boundaries applied here are realistic since the model spectively. It can be concluded that the control blasting of size is large enough and the boundary is placed at some section 1 of the tunnel generates main vibration of sur- distance from the region of interest. However, such rounding rock in the tunnel excavation direction, while the boundary conditions cause the refection of outward Y and Z axis component is relatively small. Advances in Civil Engineering 5 Table 2: Parameters of pile elements. 3 2 Type Density (kg/m ) Elastic modulus (GPa) Poisson’s ratio Cross-sectional area (m ) Coupling stifness (GPa) Coupling friction angle Coupling cohesion (kPa) Pile 2400 80 0.3 3.464 13 25 25 80 6 Advances in Civil Engineering Table 3: Parameters of liner elements. Elastic modulus Normal coupling Shear coupling Type Density (kg/m ) Tickness (m) Poisson’s ratio (GPa) stifness (GPa) stifness (GPa) Liner 2000 1 30 0.25 9.77 9.77 Table 4: Parameters of cable elements. Cross-sectional area Elastic modulus Grout cohesion Grout friction Type Density (kg/m ) (cm ) (GPa) (kPa) angle Cable 2000 5.9 100 50 35 13# 11# 100 5 9# 7# 1# 5# 3# 1# 3 5# 1 3 9# 9# 7# 106 7# # # 5 5 9# 40 40 # 3# # 3 # # 90 # # 1# 3 1# 9 9 3 1 7# 11# 7# 1 70 70 13# # 9 9 1# 1# 1# 3# 3 11# 11# 90 90 5# 5# 5# 11# 11# 9# 90 9# 7# 7# 7# 11# 11# 13# Figure 4: Blasting sequences of the double sidewall guide pit method. 0 2468 Time (ms) Figure 5: Time history of the equivalent pulse load. Blast load (MPa) 100 100 100 100 60 Advances in Civil Engineering 7 Cable Group of Element Geometry=cable1 Anchors Liner Group of Element Default=Liner 1 Zone Group Slot soil layer W1 rock W2 rock W3 rock W4 rock silt clay Lining Figure 6: Initial support and cables of the tunnel. 4 0.6 0.5 0.4 0.3 0.2 -2 0.1 -4 -0.1 -6 -0.2 -8 -0.3 -10 -0.4 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 Time (s) Time (s) 10 m distance from the blast surface 10 m distance from the blast surface 20 m distance from the blast surface 20 m distance from the blast surface 30 m distance from the blast surface 30 m distance from the blast surface 40 m distance from the blast surface 40 m distance from the blast surface (a) (b) 2.5 1.5 0.5 -0.5 -1 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 Time (s) 10 m distance from the blast surface 20 m distance from the blast surface 30 m distance from the blast surface 40 m distance from the blast surface (c) Figure 7: Time histories of blast velocities. Blast velocity along X-axis V (cm/s) Blast velocity along Z-axis V (cm/s) Blast velocity along Y-axis V (cm/s) y 8 Advances in Civil Engineering 10 15 20 25 30 35 40 Distance from blast surface (m) Velocity along X axis-V Velocity along Y axis-V Velocity along Z axis-V Figure 8: Te maximum blast velocity distribution. −1 5.38×10 −1 1.84×10 −1 5.00×10 −1 −1 1.80×10 4.50×10 −1 −1 1.60×10 4.00×10 −1 −1 1.40×10 3.50×10 −1 −1 1.20×10 3.00×10 −1 −1 2.50×10 1.00×10 −1 −2 2.00×10 8.00×10 −1 1.50×10 −2 6.00×10 −1 1.00×10 −2 4.00×10 −2 5.00×10 −2 2.00×10 −11 6.65×10 −9 1.38×10 0.003 s 0.012 s −2 5.10×10 −2 5.00×10 −2 4.50×10 −2 4.45×10 −2 4.00×10 −2 4.00×10 −2 3.50×10 −2 3.50×10 −2 3.00×10 −2 3.00×10 −2 2.50×10 −2 2.50×10 −2 2.00×10 −2 2.00×10 −2 1.50×10 −2 −2 1.50×10 1.00×10 −3 −3 5.00×10 5.00×10 −9 −8 7.69×10 1.34×10 Unit:m/s 0.021 s 0.03 s Figure 9: Blast velocity contour of the rock mass. Figure 8 shows the decay curves of the maximum blast disturbance gradually expands, but its peak size decreases rapidly. After 0.02 s from the start of blasting, the blast velocity along the tunnel excavation direction caused by controlled blasting in section 1, where the red, blue, and velocity around the tunnel has basically decayed to zero, green curves are the velocity components in X, Y, and Z while the vibration velocity above the tunnel is the largest direction, respectively. As shown in the fgure, the magni- part of the rock mass at this time. Terefore, the controlled tude of blast velocity components in the three axes decreases blasting design of this project can efectively control the rapidly in the range from 10 m to 20 m from the blast blasting vibration velocity of the rock around the tunnel, surface. Beyond that distance, the maximum blast velocity which meets the safety requirements of the specifcation and basically remains constant. can efectively ensure the safety and stability of tunnel Figure 9 shows the blast velocity contour of the rock blasting. mass due to controlled blasting in section 1. Te four Figure 10 shows the maximum dynamic stress induced contour graphs are captured at 0.003 s, 0.012 s, 0.021 s, and by the controlled blast, which is measured at 3 ms. As shown in the fgure, the maximum dynamic stress occurred at the 0.03 s after blasting. It can be seen that at 0.003 s after blasting, the rock disturbance caused by controlled blasting surrounding rock located near the blast section, with a value of section 1 is basically concentrated within 4 m of the tunnel about 10 MPa. Te dynamic stress decreases dramatically perimeter. With the increase of time, the range of rock with the increase of distance from the blast section, with an Maximum blast velocity V (cm/s) max Advances in Civil Engineering 9 Zone Total Measure Stress Calculated by: Volumetric Averaging 9.90×10 9.75×10 9.00×10 8.25×10 7.50×10 6.75×10 6.00×10 5.25×10 4.50×10 3.75×10 3.00×10 2.25×10 1.50×10 7.50×10 1.46×10 Units: Pa Figure 10: Te maximum dynamic stress measured at the blasting surface. 0.14 0.12 0.1 0.08 0.06 0.04 0.02 -0.02 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 Time (s) Corner 1 of the tower base Corner 2 of the tower base Figure 11: Vibration speed time histories at the tower base. 0.40 0.37 Blasting surface 0.35 Node 3 Node 2 0.30 0.25 Node 4 0.25 Node 1 0.20 0.16 0.15 0.14 0.10 0.05 0.00 1 234 Bottom nodes of the transmission tower Figure 12: Vertical displacement measured at the tower base. 80% reduction in the peak value at the location with a dis- 4.2. Responses of the Transmission Tower. Figure 11 shows tance of two times the largest dimension of the blast section the time histories of blasting velocity in Z direction at the from the blast center. corners of the base of the high-voltage tower. During the Vibration speed V (cm/s) Vertical displacement (mm) z 10 Advances in Civil Engineering −2 1.24×10 −4 −2 1.20×10 2.13×10 −2 −4 1.10×10 2.00×10 −2 −4 1.00×10 1.80×10 −3 −4 9.00×10 1.60×10 −3 8.00×10 −4 1.40×10 −3 7.00×10 −4 1.20×10 −3 6.00×10 −4 1.00×10 −3 5.00×10 −5 8.00×10 −3 4.00×10 −5 −3 6.00×10 3.00×10 −5 −3 4.00×10 2.00×10 −5 −3 2.00×10 1.00×10 −5 −6 2.10×10 2.46×10 12 ms 3 ms −2 −2 1.18×10 1.11×10 −2 −2 1.10×10 1.10×10 −2 −2 1.00×10 1.00×10 −3 −3 9.00×10 9.00×10 −3 −3 8.00×10 8.00×10 −3 −3 7.00×10 7.00×10 −3 −3 6.00×10 6.00×10 −3 −3 5.00×10 5.00×10 −3 −3 4.00×10 4.00×10 −3 −3 3.00×10 3.00×10 −3 −3 2.00×10 2.00×10 −3 −3 1.00×10 1.00×10 −5 −4 2.26×10 7.27×10 30 ms 21 ms Units:m/s Figure 13: Vibration speed contour of the transmission tower. controlled blasting of tunnel section 1, the blasting vibration of the tower base are measured at the end of blast loading. in Z direction frst increases and then decreases, with a peak Figure 12 presents the vertical displacement at the four value of about 0.12 cm/s. Te blasting vibration velocity Vz corner nodes of the tower base and their relative position to in the Z-axis direction decreases to zero at about 0.2 s after the blasting surface. Te maximum and minimum vertical the blasting. Terefore, the magnitude of velocity measured displacements of the tower base are about 0.37 and 0.14 mm, at the base of the transmission tower is relatively small and respectively, which would result in a diferential settlement will not pose a threat to the stability of the transmission of 0.23 mm. It can be concluded that the diferential set- tower, which demonstrates the validity of the controlled tlement would only cause a neglectable tilt angle and would blasting design. not threaten the stability of the transmission tower. Te diferential settlement of the transmission tower is Figure 13 shows contour of vibration speed of the a key factor to monitor in practice to ensure the stability of transmission tower generated by controlled blasting. As can the transmission tower. Terefore, the vertical displacements be seen, the maximum vibration speed of the transmission Advances in Civil Engineering 11 Bending moment (N·m) 0 200 400 600 800 1000 Figure 14: Maximum bending moment of the pile foundation. tower and its pile foundation is about 0.02 cm/s at 0.003 s disturbance range gradually expands, but its peak after the controlled blasting. As the blast wave in the rock size decays rapidly propagates to the surface, the vibration speed of the (3) As the blast wave in the rock mass propagates to the transmission tower and its pile foundation gradually in- ground surface, the vibration speed of the trans- creases and its maximum vibration velocity is about 1.24 cm/ mission tower and its pile foundation gradually s, which occurs at the location of the tower base 0.012 s after increases with a maximum vibration velocity of the blasting. Ten, the vibration speed gradually decreases. It about 1.24 cm/s can be concluded that the design of controlled blasting of (4) Te controlled blasting design of this project can this project can ensure that the vibration speed of the efectively restrain the vibration velocity of the transmission tower is below the safe vibration speed of surrounding rock and the transmission tower, which 3.5 cm/s in the Chinese specifcation. could ensure the stability and safety of the Due to the short distance between the pile foundation transmission tower. and the undercrossing tunnel, the dynamic responses of the pile foundation would also afect the stability of the trans- Data Availability mission tower. Terefore, the maximum bending moment of the pile is measured during the controlled blasting, which is Te data come partly from the project site and engineering shown in Figure 14. Te peak value of the bending moment survey and partly from numerical simulations. All the data developed in the pile is about 920 N·m, which is developed at used to support the fndings of this study are available from 7 m below the pile top. Terefore, the blasting wave gen- the corresponding author upon request. erated by controlled blast would not signifcantly afect the internal force in the pile. Tis result indicates that the pile Conflicts of Interest foundation and the transmission tower remained stable during the blasting construction. Te authors declare that they have no conficts of interest. 5. Conclusions Acknowledgments Tis paper investigates the dynamic efects of controlled Te research was supported by <Research on Key Tech- tunnel blasting on surrounding rock and high transmission nologies for Construction of Large-Section Shallow Buried tower. A three-dimensional numerical analysis of a large Tunnels under Sensitive Structures in Jiangjunshan Tunnel>. section shallow buried tunnel under a transmission tower was conducted. Te dynamic responses of the surrounding References rock and the high transmission tower were analyzed in detail. Te main conclusions can be drawn as follows: [1] B. Duan, W. Gong, G. Ta, X. Yang, and X. Zhang, “Infuence of small, clear distance cross-tunnel blasting excavation on (1) Te vibration speed generated by controlled blasting existing tunnel below,” Advances in Civil Engineering, decays rapidly along the tunnel excavation direction vol. 2019, Article ID 4970269, 16 pages, 2019. (2) At 0.003 s after the start of blasting, the rock dis- [2] X. Xia, H. B. Li, J. C. Li, B. Liu, and C. Yu, “A case study on turbance caused by controlled blasting of section 1 is rock damage prediction and control method for underground basically concentrated within 4 m of the tunnel pe- tunnels subjected to adjacent excavation blasting,” Tunnelling rimeter, and with the increase of time, the rock and Underground Space Technology, vol. 35, pp. 1–7, 2013. Pile length (m) 12 Advances in Civil Engineering [3] Q. Liang, J. Li, D. Li, and E. Ou, “Efect of blast-induced vibration from new railway tunnel on existing adjacent railway tunnel in Xinjiang, China,” Rock Mechanics and Rock Engineering, vol. 46, no. 1, pp. 19–39, 2013. [4] N. Jiang and C. Zhou, “Blasting vibration safety criterion for a tunnel liner structure,” Tunnelling and Underground Space Technology, vol. 32, pp. 52–57, 2012. [5] M. Mohamadnejad, R. Gholami, and M. Ataei, “Comparison of intelligence science techniques and empirical methods for prediction of blasting vibrations,” Tunnelling and Un- derground Space Technology, vol. 28, pp. 238–244, 2012. [6] J.-H. Shin, H.-G. Moon, and S.-E. Chae, “Efect of blast- induced vibration on existing tunnels in soft rocks,” Tun- nelling and Underground Space Technology, vol. 26, no. 1, pp. 51–61, 2011. [7] M. Monjezi, M. Ghafurikalajahi, and A. Bahrami, “Prediction of blast-induced ground vibration using artifcial neural networks,” Tunnelling and Underground Space Technology, vol. 26, no. 1, pp. 46–50, 2011. [8] L. Tian, H. Li, and G. Liu, “Seismic response of power transmission tower-line system subjected to spatially varying ground motions,” Mathematical Problems in Engineering, vol. 2010, Article ID 587317, 20 pages, 2010. [9] F. Wang, Z. Su, Q. Li, and J. Yang, “Response analysis of cathead transmission tower seismic performance based on Open Sees,” in Proceedings of the 2014 Fifth International Conference on Intelligent Systems Design and Engineering Applications, pp. 893–896, IEEE, Hunan, China, June 2014. [10] H.-N. Li, W.-L. Shi, G.-X. Wang, and L.-G. Jia, “Simplifed models and experimental verifcation for coupled trans- mission tower–line system to seismic excitations,” Journal of Sound and Vibration, vol. 286, no. 3, pp. 569–585, 2005. [11] K. Luo, Y. Wang, Y. Zhang, and L. Huang, “Numerical simulation of section subway tunnel under surface explosion,” Journal of PLA University of Science and Technology (Natural Science Edition), vol. 6, 2007. [12] L. Duan, W. Lin, J. Lai, P. Zhang, and Y. Luo, “Vibration characteristic of high-voltage tower infuenced by adjacent tunnel blasting construction,” Shock and Vibration, vol. 2019, Article ID 8520564, 16 pages, 2019. [13] H. Zhao, Y. Long, X. Li, and L. Lu, “Experimental and nu- merical investigation of the efect of blast-induced vibration from adjacent tunnel on existing tunnel,” KSCE Journal of Civil Engineering, vol. 20, no. 1, pp. 431–439, 2016. [14] N. Jiang, T. Gao, C. Zhou, and X. Luo, “Efect of excavation blasting vibration on adjacent buried gas pipeline in a metro tunnel,” Tunnelling and Underground Space Technology, vol. 81, pp. 590–601, 2018. [15] C. Z. Yang, Z. J. Yu, and S. F. 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Numerical Investigation into the Effects of Controlled Tunnel Blast on Dynamic Responses of the Transmission Tower

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Publisher
Hindawi Publishing Corporation
ISSN
1687-8086
eISSN
1687-8094
DOI
10.1155/2023/6021465
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Abstract

Hindawi Advances in Civil Engineering Volume 2023, Article ID 6021465, 12 pages https://doi.org/10.1155/2023/6021465 Research Article Numerical Investigation into the Effects of Controlled Tunnel Blast on Dynamic Responses of the Transmission Tower 1 2 3 4 Feng Wang, Gaohai Zhang, Wenwen Li , and Hongwei Nie China Railway 18th Bureau Group Co., Ltd., Tianjian, China China Railway Construction Investment Co., Ltd., Beijing, China Changshu Institute of Technology, Suzhou, China Soochow University, Suzhou, China Correspondence should be addressed to Wenwen Li; lwwgeo@hotmail.com Received 9 February 2022; Revised 23 April 2022; Accepted 20 April 2023; Published 3 May 2023 Academic Editor: Andre´ Furtado Copyright © 2023 Feng Wang et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. At present, the drill-and-blast method is still one of the main construction means in the road tunnel excavation process. When the tunnel penetrates underneath sensitive structures such as high-voltage transmission towers, the blasting and supporting pa- rameters must be strictly controlled to ensure the stability and safety of the surface structures. In this paper, numerical simulations based on a large-section shallow buried tunnel project in Zhuhai are conducted to study the efect of controlled tunnel blast on the dynamic response of transmission towers. Te numerical simulation results indicate that the blast vibration velocity of the rock generated by controlled blasting decreases rapidly along the tunnel excavation direction. Te blast vibration velocity of the high- voltage transmission tower and its pile foundation gradually increases with the propagation of the blast waves, and the maximum vibration velocity is about 1.24 cm/s. Te results indicate that the controlled blasting design of this project can efectively restrain the vibration velocity induced by the blasting load and could ensure the stability and safety of the transmission tower. by researchers [4–7]. Te site test can objectively refect the 1. Introduction infuence of blasting vibration on the rock mass structure. With the rapid development of highways in China, large- However, due to the nonhomogeneity and the defects of the section tunnels are widely used in highway construction internal structure in the rock mass, the experimental con- because of their ability to signifcantly reduce road mileage ditions are difcult to control. Compared with the site tests, and improve transport efciency. Te tunnels would the numerical calculation can simulate the dynamic re- sometimes inevitably penetrate beneath sensitive structures, sponse problem in the complicated geological conditions, such as transmission towers and other existing structures, thus the numerical simulation method is widely used to analyze the blasting vibration response. Some studies [8–10] which poses challenges for the design and construction of large-section tunnels. evaluated the vibration damage to transmission towers based on the fnite element method. Luo et al. [11] analyzed the At present, the drill-and-blast method is still one of the main construction methods in the road tunnel excavation dynamic characteristic of the tunnel for surface explosion of process [1–3]. When the tunnel penetrates underneath 100 and 300 kg TNT charge, respectively. Duan et al. [12] sensitive structures such as high-voltage transmission investigated the vibration characteristic of high-voltage towers, the blasting and support parameters need to be tower under the infuence of adjacent tunnel blasting ex- strictly controlled to ensure the stability and safety of the cavation. Beside the study on the infuence of vibration surface structures. To study the infuence of vibration caused induced by controlled blasting on transmission tower, more by controlled blasting on rock mass and sensitive structures, research focuses on the dynamic responses of adjacent site test and numerical simulation methods are widely used structures. Zhao et al. [13] used feld monitoring 2 Advances in Civil Engineering experiments and numerical simulation to study the efect of blast-induced vibration from adjacent tunnel on existing tunnel. Jiang et al. [14] investigate the efect of excavation blasting vibration on adjacent buried gas pipeline in a metro tunnel. However, the dynamic responses of the transmission 1.92 m tower system remain one of the most challenging tasks in the civil engineering as a complex, continuous, and mechanical system. Based on a large-section shallow buried tunnel project in Zhuhai, China, this paper studies the efects of controlled Tunnel tunnel blasting on the dynamic responses of high-voltage 2.96 m transmission towers. Tree-dimensional numerical analyses 220 KV high voltage were conducted in the fnite diference program FLAC3D, transmission tower and the dynamic responses of the tunnel surrounding rock and high-voltage transmission towers under the blast loading were studied. Te vibration velocity, deformation responses of surrounding rock and high-voltage trans- Figure 1: Schematic view of the locations of the tunnel and mission towers were predicted to provide scientifc basis and transmission tower. reference for relevant construction optimization and decision-making. and width of the model are selected as 100 m and 52 m, 2. Overview of the Project respectively, which could efectively reduce the boundary efect. Te axis used in the numerical model is defned as Te Black and White General Hill tunnel is a large-section follows: X axis is along the direction of tunnel excavation; Y shallow buried tunnel under construction in Zhuhai, China, axis is along the cross-section of the tunnel; and Z axis is which is built to enhance the transportation links between along the gravity direction. Te numerical model mainly diferent districts in Zhuhai. Te exit section of the tunnel consisted of the tunnel, surrounding rocks, transmission penetrates directly underneath a high-voltage transmission tower, and its fle foundation. It is noted that the trans- tower. A schematic view of the locations of the tunnel and mission tower and its pile foundation are modelled using the transmission tower is shown in Figure 1. Te transmission structure elements implanted in FLAC3D to reduce model tower is a 2F-SJ2 type tower with a total height of 41.5 m, complexity and increase calculation speed. Te total number supported by four piles with a diameter of 2.1 m and a length of zones in the 3D numerical model is 112,400, and the total of 12 m. Te vertical distance from the top of the tunnel to number of nodes is 12033. the pile toe is about 7.5 m, and the smallest horizontal Te high-voltage transmission tower is built upon a hill distance from the tunnel to the transmission tower is about which the tunnel penetrates through. Te curved surface of 1.9 m. the hill needs to be considered in the numerical model to Te surrounding rocks at the tunnel exit consisted of obtain a correct initial stress condition in the surrounding medium strongly weathered quartz amphibolite. Te arches rocks. Te curved surface is generated in SketchUp by and sidewalls of the tunnel exit are of poor stability, which importing the contour lines of the hill. Ten, the 3D hill could lead to rock collapse and drops at drill-and-blast surface is exported to FLAC3D, and it connects with the excavation. Te uneven weathering of the surrounding tunnel model built in FLAC3D to form the 3D numerical rocks has an impact on the stability of the tunnel portal and model. Te process of model generation is shown in Fig- the side slopes. Tese geological conditions would pose ure 3. Te soil layer distribution is generated based on the a threat to the stability of the transmission tower. geological data using the curved surface import method. According to the geological survey, the soil stratum from top to bottom within the exploration depth is divided into clay, fully weathered, strongly weathered, medium weath- 3.2. Constitutive Model and Material Parameters. Te ered, and slightly weathered quartz amphibolite. Based on Mohr–Coulomb model is selected as the constitutive model the results of the wave velocity test and other geotechnical for the soil and rock in this project. Te parameters of tests, the physical properties of the soil and rock are shown density, cohesion, and friction angle are adopted directly in Table 1. from the geological survey data, which is shown in Table 1. Te transmission tower is modelled with the beam element implemented in FLAC3D, which is a two-noded, straight, 3. Numerical Investigation fnite element with six degrees of freedom per node. Te 3.1.NumericalModel. A 100 m range of tunnel exit (mileage beam element has three material parameters, density, elastic YK4 + 820–YK4 + 920) is selected as the modelling area, with modulus, and Poisson’s ratio, which are set to be 7850 kg/m , the tunnel and transmission tower included. Te numerical 200 GPa, and 0.3, respectively. Te pile foundation of the model built in FLAC3D is shown in Figure 2. Considering transmission tower is modelled using the pile element, which the infuence of tunnel depth and blasting, the total length could efectively simulate the normal-directed Advances in Civil Engineering 3 Table 1: Property parameters of the soil. Friction angle Elastic modulus Soil layer Name Density (kN/m ) Cohesion (kPa) Poisson’s ratio ( ) (MPa) 1 Clay 19.8 25 20 20 0.38 2 Fully weathered quartz amphibolite 23.0 26 28 48 0.35 3 Strongly weathered quartz amphibolite 27.7 28 30 70 0.32 3 4 4 Medium weathered quartz amphibolite 28.9 5.5 ×10 41 4.0 ×10 0.30 3 4 5 Slightly weathered quartz amphibolite 30.0 7.0 ×10 42 6.5 ×10 0.23 Zone Group Slot soil layer W1 rock W2 rock W3 rock W4 rock silt clay X Y Figure 2: 3D numerical model. (perpendicular to the pile axis) and shear-directed (parallel load generated by millisecond delay blasting needs to be with the pile axis) frictional interaction between the pile and applied at the tunnel. the soil. Te soil-pile interaction is considered by the shear In the process of blasting, the interaction of stress waves and normal coupling springs. Te coupling springs are generated by blasting will make cracks spread along the nonlinear, spring-slider connectors that transfer forces and connecting line of adjacent blastholes. With the growth of motion between the pile and the grid at the pile nodes. Te the blast induced crack and interpenetration throughout the shear behavior of the pile-grid interface is cohesive and rock, a new free surface will be created along the blasthole frictional in nature. Te lining and anchors used as tunnel line, which is the designed blasting excavation boundary. supporting are simulated with the liner element and cable Terefore, the blasting excavation boundary is taken as the element, respectively. Te parameters of the structure ele- inner boundary of the numerical model. Tus, the full scale ment (pile, liner, and cable) adopted in this paper are shown blastholes are not included in this model, and the blasting in Tables 2–4. pressure is applied equivalently to the excavation boundary, which avoids tremendous model meshing and computa- tional work due to detonations of too many tiny blastholes. In this paper, an equivalent pulse load of the multihole 3.3. Blasting Load. Due the short distance from the tunnel and the sensitivity of the transmission tower, the controlled blasts is applied at the blasting excavation boundary of the tunnel. Tis simplifed equivalent load method certainly blast and double-sided guide-pit method are adopted in the excavation and initial support of tunnel exit to ensure the causes some deviation in the immediate vicinity of blast- holes. However, this study is to investigate the dynamic stability of the transmission tower. Te detailed blast-hole distribution and blasting sequences for the double-sided responses of the transmission tower and surrounding rocks outside the blasting boundary rather than the explosion- guide-pit method are shown in Figure 4. Tere are about 330 blast-holes in each blast section, distributed in a cross- induced rock fracture and fragmentation process around blastholes. Terefore, this equivalent pulse load simplifca- sectional area of 305 m . Te unit explosive consumption is about 0.9 kg/m for the controlled blast design. In order to tion is acceptable to a certain degree. Following the pro- cedure used by Yang et al. [15, 16], the equivalent pulse load study the efect of controlled blast on the dynamic responses applied in this paper is shown in Figure 5. of the transmission tower and surrounding rock, the blast 4 Advances in Civil Engineering Figure 3: Process of 3D surface model generation. 3.4. Analysis Procedures and Boundary Condition. Te focus propagating waves back into the model and do not allow the of the research in this paper is to investigate the dynamic necessary energy radiation. Terefore, the fxed boundary responses of the transmission tower under tunnel blasting to condition is converted into a viscous boundary by using ensure the stability and functionality of the transmission independent dashpots in the normal and shear directions at tower. Terefore, the numerical study chooses the condition the model boundaries in the dynamic loading stage. where the tunnel has been excavated directly underneath the transmission tower, and the initial support and cables have 4. Results and Discussions been installed in the excavated part of the tunnel, which is shown in Figure 6. Te blast load generated by the frst section 4.1. Responses of the Surrounding Rock. To ensure the sta- of the tunnel (as shown in Figure 4) beneath the transmission bility of the transmission tower, the dynamic responses of tower is applied at the numerical model, when the infuence of the surrounding rock are analyzed frst. Figure 7 shows the the blast on the transmission tower is the most obvious. time histories of blast velocities measured at diferent dis- Before the blast loading is applied, the boundary of the tances from the blast surface. Te maximum blast velocities numerical model is set to be fxed in their normal direction along X, Y, and Z axis caused by controlled blasting of to calculate the initial stress condition. In static analysis, section 1 are about 9 cm/s, 0.58 cm/s, and 3 cm/s, re- fxed boundaries applied here are realistic since the model spectively. It can be concluded that the control blasting of size is large enough and the boundary is placed at some section 1 of the tunnel generates main vibration of sur- distance from the region of interest. However, such rounding rock in the tunnel excavation direction, while the boundary conditions cause the refection of outward Y and Z axis component is relatively small. Advances in Civil Engineering 5 Table 2: Parameters of pile elements. 3 2 Type Density (kg/m ) Elastic modulus (GPa) Poisson’s ratio Cross-sectional area (m ) Coupling stifness (GPa) Coupling friction angle Coupling cohesion (kPa) Pile 2400 80 0.3 3.464 13 25 25 80 6 Advances in Civil Engineering Table 3: Parameters of liner elements. Elastic modulus Normal coupling Shear coupling Type Density (kg/m ) Tickness (m) Poisson’s ratio (GPa) stifness (GPa) stifness (GPa) Liner 2000 1 30 0.25 9.77 9.77 Table 4: Parameters of cable elements. Cross-sectional area Elastic modulus Grout cohesion Grout friction Type Density (kg/m ) (cm ) (GPa) (kPa) angle Cable 2000 5.9 100 50 35 13# 11# 100 5 9# 7# 1# 5# 3# 1# 3 5# 1 3 9# 9# 7# 106 7# # # 5 5 9# 40 40 # 3# # 3 # # 90 # # 1# 3 1# 9 9 3 1 7# 11# 7# 1 70 70 13# # 9 9 1# 1# 1# 3# 3 11# 11# 90 90 5# 5# 5# 11# 11# 9# 90 9# 7# 7# 7# 11# 11# 13# Figure 4: Blasting sequences of the double sidewall guide pit method. 0 2468 Time (ms) Figure 5: Time history of the equivalent pulse load. Blast load (MPa) 100 100 100 100 60 Advances in Civil Engineering 7 Cable Group of Element Geometry=cable1 Anchors Liner Group of Element Default=Liner 1 Zone Group Slot soil layer W1 rock W2 rock W3 rock W4 rock silt clay Lining Figure 6: Initial support and cables of the tunnel. 4 0.6 0.5 0.4 0.3 0.2 -2 0.1 -4 -0.1 -6 -0.2 -8 -0.3 -10 -0.4 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 Time (s) Time (s) 10 m distance from the blast surface 10 m distance from the blast surface 20 m distance from the blast surface 20 m distance from the blast surface 30 m distance from the blast surface 30 m distance from the blast surface 40 m distance from the blast surface 40 m distance from the blast surface (a) (b) 2.5 1.5 0.5 -0.5 -1 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 Time (s) 10 m distance from the blast surface 20 m distance from the blast surface 30 m distance from the blast surface 40 m distance from the blast surface (c) Figure 7: Time histories of blast velocities. Blast velocity along X-axis V (cm/s) Blast velocity along Z-axis V (cm/s) Blast velocity along Y-axis V (cm/s) y 8 Advances in Civil Engineering 10 15 20 25 30 35 40 Distance from blast surface (m) Velocity along X axis-V Velocity along Y axis-V Velocity along Z axis-V Figure 8: Te maximum blast velocity distribution. −1 5.38×10 −1 1.84×10 −1 5.00×10 −1 −1 1.80×10 4.50×10 −1 −1 1.60×10 4.00×10 −1 −1 1.40×10 3.50×10 −1 −1 1.20×10 3.00×10 −1 −1 2.50×10 1.00×10 −1 −2 2.00×10 8.00×10 −1 1.50×10 −2 6.00×10 −1 1.00×10 −2 4.00×10 −2 5.00×10 −2 2.00×10 −11 6.65×10 −9 1.38×10 0.003 s 0.012 s −2 5.10×10 −2 5.00×10 −2 4.50×10 −2 4.45×10 −2 4.00×10 −2 4.00×10 −2 3.50×10 −2 3.50×10 −2 3.00×10 −2 3.00×10 −2 2.50×10 −2 2.50×10 −2 2.00×10 −2 2.00×10 −2 1.50×10 −2 −2 1.50×10 1.00×10 −3 −3 5.00×10 5.00×10 −9 −8 7.69×10 1.34×10 Unit:m/s 0.021 s 0.03 s Figure 9: Blast velocity contour of the rock mass. Figure 8 shows the decay curves of the maximum blast disturbance gradually expands, but its peak size decreases rapidly. After 0.02 s from the start of blasting, the blast velocity along the tunnel excavation direction caused by controlled blasting in section 1, where the red, blue, and velocity around the tunnel has basically decayed to zero, green curves are the velocity components in X, Y, and Z while the vibration velocity above the tunnel is the largest direction, respectively. As shown in the fgure, the magni- part of the rock mass at this time. Terefore, the controlled tude of blast velocity components in the three axes decreases blasting design of this project can efectively control the rapidly in the range from 10 m to 20 m from the blast blasting vibration velocity of the rock around the tunnel, surface. Beyond that distance, the maximum blast velocity which meets the safety requirements of the specifcation and basically remains constant. can efectively ensure the safety and stability of tunnel Figure 9 shows the blast velocity contour of the rock blasting. mass due to controlled blasting in section 1. Te four Figure 10 shows the maximum dynamic stress induced contour graphs are captured at 0.003 s, 0.012 s, 0.021 s, and by the controlled blast, which is measured at 3 ms. As shown in the fgure, the maximum dynamic stress occurred at the 0.03 s after blasting. It can be seen that at 0.003 s after blasting, the rock disturbance caused by controlled blasting surrounding rock located near the blast section, with a value of section 1 is basically concentrated within 4 m of the tunnel about 10 MPa. Te dynamic stress decreases dramatically perimeter. With the increase of time, the range of rock with the increase of distance from the blast section, with an Maximum blast velocity V (cm/s) max Advances in Civil Engineering 9 Zone Total Measure Stress Calculated by: Volumetric Averaging 9.90×10 9.75×10 9.00×10 8.25×10 7.50×10 6.75×10 6.00×10 5.25×10 4.50×10 3.75×10 3.00×10 2.25×10 1.50×10 7.50×10 1.46×10 Units: Pa Figure 10: Te maximum dynamic stress measured at the blasting surface. 0.14 0.12 0.1 0.08 0.06 0.04 0.02 -0.02 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 Time (s) Corner 1 of the tower base Corner 2 of the tower base Figure 11: Vibration speed time histories at the tower base. 0.40 0.37 Blasting surface 0.35 Node 3 Node 2 0.30 0.25 Node 4 0.25 Node 1 0.20 0.16 0.15 0.14 0.10 0.05 0.00 1 234 Bottom nodes of the transmission tower Figure 12: Vertical displacement measured at the tower base. 80% reduction in the peak value at the location with a dis- 4.2. Responses of the Transmission Tower. Figure 11 shows tance of two times the largest dimension of the blast section the time histories of blasting velocity in Z direction at the from the blast center. corners of the base of the high-voltage tower. During the Vibration speed V (cm/s) Vertical displacement (mm) z 10 Advances in Civil Engineering −2 1.24×10 −4 −2 1.20×10 2.13×10 −2 −4 1.10×10 2.00×10 −2 −4 1.00×10 1.80×10 −3 −4 9.00×10 1.60×10 −3 8.00×10 −4 1.40×10 −3 7.00×10 −4 1.20×10 −3 6.00×10 −4 1.00×10 −3 5.00×10 −5 8.00×10 −3 4.00×10 −5 −3 6.00×10 3.00×10 −5 −3 4.00×10 2.00×10 −5 −3 2.00×10 1.00×10 −5 −6 2.10×10 2.46×10 12 ms 3 ms −2 −2 1.18×10 1.11×10 −2 −2 1.10×10 1.10×10 −2 −2 1.00×10 1.00×10 −3 −3 9.00×10 9.00×10 −3 −3 8.00×10 8.00×10 −3 −3 7.00×10 7.00×10 −3 −3 6.00×10 6.00×10 −3 −3 5.00×10 5.00×10 −3 −3 4.00×10 4.00×10 −3 −3 3.00×10 3.00×10 −3 −3 2.00×10 2.00×10 −3 −3 1.00×10 1.00×10 −5 −4 2.26×10 7.27×10 30 ms 21 ms Units:m/s Figure 13: Vibration speed contour of the transmission tower. controlled blasting of tunnel section 1, the blasting vibration of the tower base are measured at the end of blast loading. in Z direction frst increases and then decreases, with a peak Figure 12 presents the vertical displacement at the four value of about 0.12 cm/s. Te blasting vibration velocity Vz corner nodes of the tower base and their relative position to in the Z-axis direction decreases to zero at about 0.2 s after the blasting surface. Te maximum and minimum vertical the blasting. Terefore, the magnitude of velocity measured displacements of the tower base are about 0.37 and 0.14 mm, at the base of the transmission tower is relatively small and respectively, which would result in a diferential settlement will not pose a threat to the stability of the transmission of 0.23 mm. It can be concluded that the diferential set- tower, which demonstrates the validity of the controlled tlement would only cause a neglectable tilt angle and would blasting design. not threaten the stability of the transmission tower. Te diferential settlement of the transmission tower is Figure 13 shows contour of vibration speed of the a key factor to monitor in practice to ensure the stability of transmission tower generated by controlled blasting. As can the transmission tower. Terefore, the vertical displacements be seen, the maximum vibration speed of the transmission Advances in Civil Engineering 11 Bending moment (N·m) 0 200 400 600 800 1000 Figure 14: Maximum bending moment of the pile foundation. tower and its pile foundation is about 0.02 cm/s at 0.003 s disturbance range gradually expands, but its peak after the controlled blasting. As the blast wave in the rock size decays rapidly propagates to the surface, the vibration speed of the (3) As the blast wave in the rock mass propagates to the transmission tower and its pile foundation gradually in- ground surface, the vibration speed of the trans- creases and its maximum vibration velocity is about 1.24 cm/ mission tower and its pile foundation gradually s, which occurs at the location of the tower base 0.012 s after increases with a maximum vibration velocity of the blasting. Ten, the vibration speed gradually decreases. It about 1.24 cm/s can be concluded that the design of controlled blasting of (4) Te controlled blasting design of this project can this project can ensure that the vibration speed of the efectively restrain the vibration velocity of the transmission tower is below the safe vibration speed of surrounding rock and the transmission tower, which 3.5 cm/s in the Chinese specifcation. could ensure the stability and safety of the Due to the short distance between the pile foundation transmission tower. and the undercrossing tunnel, the dynamic responses of the pile foundation would also afect the stability of the trans- Data Availability mission tower. Terefore, the maximum bending moment of the pile is measured during the controlled blasting, which is Te data come partly from the project site and engineering shown in Figure 14. Te peak value of the bending moment survey and partly from numerical simulations. All the data developed in the pile is about 920 N·m, which is developed at used to support the fndings of this study are available from 7 m below the pile top. Terefore, the blasting wave gen- the corresponding author upon request. erated by controlled blast would not signifcantly afect the internal force in the pile. Tis result indicates that the pile Conflicts of Interest foundation and the transmission tower remained stable during the blasting construction. Te authors declare that they have no conficts of interest. 5. Conclusions Acknowledgments Tis paper investigates the dynamic efects of controlled Te research was supported by <Research on Key Tech- tunnel blasting on surrounding rock and high transmission nologies for Construction of Large-Section Shallow Buried tower. A three-dimensional numerical analysis of a large Tunnels under Sensitive Structures in Jiangjunshan Tunnel>. section shallow buried tunnel under a transmission tower was conducted. 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Advances in Civil EngineeringHindawi Publishing Corporation

Published: May 3, 2023

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