Get all the hottest headlines on the whole network in one web
Yang Wenbo Zhang Hang Luo Chunyu Kang Haibo Du Mingyang Lin Lin He Chuan Liu Zijing. Based on this, combined with three-dimensional numerical simulation analysis, the excavation methods of different tunnels and the tunnel aftershock dynamic response rules at different constructio
Yang Wenbo Zhang Hang Luo Chunyu Kang Haibo Du Mingyang Lin Lin He Chuan Liu Zijing
Key Laboratory of Ministry of Education of the Ministry of Education of Southwest Jiaotong University Civil Engineering School of Southwest Jiaotong University Sichuan Highway Bridge Construction Group Co., Ltd. Highway Tunnel Branch
Abstract: Relying on a typical soft rock tunnel in a complex stress environment in a strong earthquake zone, through on-site actual data, the structural mechanics characteristics of tunnel during static excavation were first analyzed; based on this basis, combined with three-dimensional numerical simulation analysis, the excavation methods of different tunnels and the dynamic response laws of tunnel aftershocks at different construction stages were further studied. The research results show that under different excavation methods of the tunnel, by comparing the tunnel displacement difference, the acceleration response of the tunnel structure and surrounding rock, the plastic zone and the minimum main stress of the initial support caused by the aftershock, it was found that the tunnel excavation method had little impact on the dynamic response law of the tunnel aftershock; in different stages of tunnel excavation, that is, the initial branch acts separately and the initial branch second lining, the application of second lining reduced the tunnel displacement difference by 17.44%, and the initial support compressive stress decreased by 16.13%, indicating that the application of the second lining is conducive to reducing the adverse effects of aftershocks on the tunnel. Comprehensive research results show that when a soft rock tunnel is constructed in a complex stress environment encounters aftershock effects, the palm surface in front of the tunnel is prone to shear damage, and the tunnel structure is under relatively weak stress at the arch shoulders and arch feet, and should be the focus of observation after the aftershock.
Keywords: Highway tunnel; Soft rock tunnel in strong earthquake zone; Aftershock; Structural mechanical properties; Dynamic time range analysis;
Received date: 2021-04-08
Received date: 2021-04-08
Fund: National Natural Science Foundation Project, Project number 51678499;
"5·12" Wenchuan earthquake , aftershocks occurred in western my country. Tunnels have become an important choice for the construction of lines in the western region because of their good seismic resistance. However, in the construction of highways and railways in the western mountainous areas, it is inevitable to cross the Longmenshan fault zone between Chengdu Plain and Qinghai-Tibet Plateau , and a large number of layered soft rocks represented by Qianmei Rocks are distributed in this fault zone. The metamorphic rock type with tin woven luster is often a fine-grained scale metamorphic structure. The Qianmei Rock tunnel is affected by the complex stress environment and its own rock mass characteristics. A large number of engineering problems have occurred during construction, such as the instability of the palm surface, deformation of the support structure, and distortion of the arch frame during construction [1,2,3]. Zhong Yujian et al. [4] compared and analyzed on-site monitoring and numerical simulation, and the results showed that the waist of the arch-right arch was relatively unfavorable. Guo Xiaolong et al. [5] obtained the reasonable time for the two-linear fabrication of different deformation levels in the tunnel based on the long-term monitoring results of tunnel deformation. Layered soft rocks represented by
k rocks are more likely to be damaged than other rock bodies under strong earthquakes, which further increases the construction difficulty [5]. Therefore, it is of practical significance to ensure that aftershocks are frequently occurring, and there are currently certain research results. Zhang Jing et al. [7] investigated the tunnel collapse during the construction period of Guanggan Expressway, and used the finite difference method to explore the influence of the hollow on its dynamic response law under the aftershock. Zhao Wei [8] took the Dujiashan Tunnel as an example and obtained their respective response characteristics for the three stages during the construction period (naked hole, initial branching, and second linering). Ling Yao [9] took the Dujiashan Tunnel on the Guanggan Expressway as an example, and studied the impact of aftershock effects on surrounding rock and its second lining after the second lining is completed, and proposed measures to deal with cracks in the second lining of the tunnel. Lai Jiongcheng [10] considers the physical characteristics of the rock mass of the fractured rock mass and the role of groundwater after the earthquake, and reduces the mechanical parameters of the material, and studies the influence of the initial support and the combined action of the primary support and the primary support second lining on its dynamic response law. Xu Jinhua [11] conducted a systematic study on the instability failure mode, cause mechanism, catastrophic characteristics and instability mechanism under the influence of aftershocks in soft rock tunnels in the cracked rock mass area.
The above study mainly considers the two stages in tunnel construction, namely the joint action of the initial branch and the initial branch two lining, but the impact of the specific excavation method on the dynamic response of the soft rock tunnel under the aftershock effect was not considered, and the impact of the extrusion effect of the soil in front of the palm on the aftershock response was not considered, and the project based on it was relatively single. Based on this, this article relies on the Lanjiayan Tunnel, which crosses a large number of Qianmei Rock formations, which has the characteristics of high ground stress and weak surrounding rocks. The frequent aftershocks in the tunnel site will make the tunnel surrounding rock-support system in a more unfavorable state. This paper studies the internal force and surrounding rock-support dynamic response laws of the tunnel structure during the Lanjiayan Tunnel under the high ground stress state in the strong earthquake zone through on-site measurement and numerical calculation methods, analyzes the stability of the surrounding rock-support system under the action of aftershocks, and provides reference for the proposal of scientific and reasonable design and construction plans for similar projects.
1 Project Overview
Lanjiayan Tunnel is located in Maoxian County, Aba Prefecture. It is a key control project of the Mianzhu-Maoxian highway. The tunnel area is located in the back mountain fault zone of the Longmenshan push-over tectonic belt. It is a strongly affected area of the "5.12" Wenchuan earthquake. On May 12, 2008, after the 8.0-magnitude earthquake in Wenchuan, there were constant aftershocks in the tunnel area, and there were still strong aftershock activities occasionally. The positional relationship between Lanjiayan Tunnel and Longmenshan Fault Zone is shown in Figure 1.
Figure 1 Schematic of the location of the Mian (Zhu) Mao (County) Highway and Longmenshan Fault Zone
Tunnel is mostly Qianmei rocks, which have the characteristics of soft lithology, easy to soften when exposed to water, and joint fracture development. Especially under the influence of strong earthquake dynamics, it is more likely to cause rubbing damage and crack loosening than other rocks, thus increasing the difficulty of building tunnels in this type of rock.
This paper selects the soft rock section of the highland stress field of Lanjiayan Tunnel as the research object. The section is shown in Figure 2, and the support parameters used in the tunnel are shown in Table 1.
2 Analysis of the mechanical characteristics of the two-lined structure of Lanjiayan Tunnel based on actual measured data
The tunnels passing through Qianmeiyan strata are mostly in high ground stress environments, so local damage caused by the extrusion deformation of the surrounding rock often occurs in projects, which may lead to serious consequences. In order to observe the stress of the second lining during tunnel construction, the second lining strain of the Lanjiayan Tunnel was monitored to study the mechanical characteristics of the second lining structure during the construction of such high-ground stress soft rock tunnels to ensure the smooth progress of on-site construction.
Figure 2 Lanjiayan Tunnel Section
Unit: cm
Table 1 Support parameters of the stress soft rock section of the Lanjiayan Tunnel Highland Stressed Structure
system anchor (length/spacing (vertical × ring))/m
jet C20 concrete thickness degrees/cm
steel frame (type/spacing)
8
.0/1.5×1.2
0
I18/80 (full ring)
C30 concrete soil/50*
5
html l20
2.1 monitoring plan determines that
To understand the stress status of the secondary lining of Lanjiayan tunnel, test the rationality of the secondary lining design, and judge the reliability and safety of the long-term use of the secondary lining support structure, 8 pairs (16) concrete strain gauge were buried symmetrically at each measurement section, which were arranged at the tunnel arch top, left and right shoulders, left and right arch waist, left and right arch feet, and bottom. The concrete strain gauge needs to be buried in pairs, and the two concrete strain gauges are located on the inner and outer sides of the second lining concrete, thereby calculating the axial force and bending moment in the cross-section of the secondary lining. The schematic diagram of the cross-sectional burial of components and the on-site photos are shown in Figures 3 and 4 respectively.
Figure 3 Schematic of component section burial
Figure 4 Component installation
2.2 Analysis of on-site monitoring results
2.2.1 Two lining internal force
Figure 5 and 6 are the tense curves of the measured axial force and bending moment of the secondary lining in Lanjiayan respectively. From Figures 5 and 6, we can see that after the secondary lining is applied, the axial force and bending moment change rapidly in the first 30 days, and the growth rate gradually slows down from 30 to 60 days until the secondary lining is gradually stabilized after 60 days.
Figure 5 Axial force time course curve of secondary lining
Figure 6 Bending moment time course curve of secondary lining
It can be seen from Figure 5 that the axial force of secondary lining at each position is negative, indicating that the two linings at each monitoring position are compressed. From the perspective of axial force, the maximum axial force of tunnel excavation is located at the waist of the right arch, which is 3 360.82 kN, and the minimum axial force at the bottom of the arch is 1 226.73 kN. From the perspective of the second lining bending moment, the arch top and the bottom of the arch are subjected to positive bending moment (inner tension), and the rest of the parts are subjected to negative bending moment (outer tension), with the maximum positive bending moment located at the bottom of the arch, which is 38.37 kN·m, and the maximum negative bending moment is located at the left arch foot, which is -107.58 kN·m.
2.2.2 Secondary lining safety factor
Based on the actual measurement results of the axial force and bending moment of secondary lining of soft rock fracture in Lanjiayan Tunnel, according to the "Highway Tunnel Design Code Volume 1 Civil Engineering" [12], the tense curve of the second lining safety factor at this section is calculated, as shown in Figure 7. From Figure 7, the tunnel safety factor is similar to the internal force change of the tunnel second lining. In the first 30 days, the safety factor decreases sharply due to the increase in the internal force of the tunnel second lining, and then gradually slows down and eventually stabilizes. The safety factor of Lanjiayan Tunnel is greater than the specified value, and the safety factor at the waist and foot of the arch is low, with a minimum value of 3.37.
Figure 7 Time course curve of secondary lining safety coefficient
3 Research on the dynamic response of surrounding rock-structured during the construction period of Lanjiayan tunnel based on numerical simulation
Aftershocks in the Lanjiayan tunnel area will make the surrounding rock-support system of highland stress soft rock tunnel in a more unfavorable state. Based on this, this paper uses numerical simulation to study the dynamic response characteristics of surrounding rock-structured under the aftershock during the construction period of Lanjiayan tunnel. The main calculation steps are: first calculate the initial stress based on the results of the geostress inversion of Lanjiayan tunnel; then perform tunnel excavation and support; finally apply seismic wave at the bottom of the model to perform dynamic solutions.
3.1 Model parameters and input seismic wave
This paper uses the finite difference software FALC 3DDD 3DD (length × width × height). The upper surface of the model is a free boundary and constrains the normal displacement of the sides and bottom surfaces. Moore-Cullun constitutive model was selected, solid units were used to simulate surrounding rocks, and advanced reinforcement was simulated by improving the surrounding rock parameters in the reinforcement area [13]; initial support was used for solid units, and steel arch frames were considered through equivalent stiffness [14]; secondary lining was used for shell units (shell). The specific physical parameters are shown in Table 2. In order to simulate the actual buried depth of the on-site tunnel, a tectonic stress field was applied based on the geostress inversion result of Lanjiayan tunnel [15].
Figure 8 Dynamic calculation model and marginal conditions
Table 2 Surrounding rock and support structure Physical mechanics Parameters
Surrounding rock category
severe γkN⋅m−3severe γkΝ⋅m-3
severe γkN⋅m−3severe γkΝ⋅m-3
elastic modulus E/GPa
concentration c/kPa
Inner friction angle φ/(°)
Poisson's ratio
彩海
1.5
0
6
.36
Reinforcement area surrounding rock
4.0
4.0html l15
2
00
0
.28
Early support
2.0
5.69
-
-
-
-
.2
Secondary lining
5.0
8.0
8.0
--
html l1--
.2
MechanicsDamping uses Rayleigh damping commonly used in engineering, because the rock mass is a weak surrounding rock, and the bottom of the boundary condition model uses a viscous boundary, which converts the velocity time range into a stress form input, and is surrounded by a free field boundary. Because there is no direct measured aftershock wave, the main seismic seismic wave in the tunnel area (Wenchuan Qingping seismic wave) is selected as the earthquake input in reference [11]. Generally speaking, the obtained seismic wave record is an acceleration time course curve. This time, the amplitude of the seismic wave is taken to be 0.33 g, as shown in Figure 9. The integration is converted into the speed time, and then the stress is converted into the bottom of the model by using formulas (1) and (2).
σn=-2( ρ·CP)vn)vn) (1)
σs=-2( ρ·CS)vs)vs (2)
where: σn is normal stress; σs is shear stress ; ρ is media density; CP is media density; CP is media html of the html of the medium 2P wave velocity; CS is the S wave velocity of the medium; vn is the particle velocity in the vertical direction; vs is the particle velocity in the horizontal direction.
Figure 9 Input seismic wave acceleration time course curve
3.2 Consider the working conditions and monitoring scheme
First consider three excavation methods: up and down step method, up and down step reserve core soil method, and three-step method to explore the impact of the excavation method on the dynamic response under the aftershock, and consider the extrusion effect of the soil in front of the palm, among which the upper step excavation reached 43.5 m, as shown in Figure 10. In view of the actual construction method of tunnels - the core soil method of reserved on the upper and lower steps, considering two processes during the construction process: the initial support construction completion and the secondary lining construction completion, to compare the seismic effects, surrounding rock-support dynamic response and structural safety encountered at different stages of construction. During the aftershock process, 8 positions at the initial support and secondary lining of the 10 m section were monitored, and the measurement points at different heights of the soil were monitored, as shown in Figure 11, where S1~S8 is the tunnel monitoring points and T1~T9 is the soil monitoring points.
4 Numerical calculation results and analysis
4.1 Surrounding rock-support dynamic response characteristics under different excavation methods
4.1.1 Displacement characteristics analysis
The displacement difference of adjacent parts of the structure is an important basis for judging structural earthquake response. During the earthquake, the displacement of 8 measurement points at 10 m sections around the cave was monitored. The results showed that it generated the largest displacement difference between the tunnel arch and the center of the arch, and the displacement difference time course curve of different excavation methods was drawn, as shown in Figure 12. The change curves of the periphery of the tunnel tunnel under different excavation methods are similar, and the maximum displacement difference is close to 12.35 s (the peak point of positive acceleration of seismic waves). The maximum displacement difference between the three methods of the upper and lower step method, the core soil method of the upper and lower step reserve, and the three-step method is 1.00 cm, 0.86 cm, 1.04 cm, indicating that under the action of aftershock, the overall displacement difference of the tunnel is small, and the displacement difference of the three methods is not large, and the displacement difference shows a trend of the three-step method to reserve core soil methods for up and down steps.
4.1.2 Acceleration Characteristic Analysis
Monitor the X direction acceleration in the tunnel during earthquake, and extract the acceleration time course curve of the tunnel arch and soil body at the same height, as shown in Figure 13. It can be seen from Figure 13 that the acceleration time course curve of the tunnel arch is almost the same as the surrounding rock at the same height, and is similar to the input acceleration time course curve, indicating that the implementation of the tunnel structure has little impact on the seismic dynamic response of the surrounding rock, which is the same as the conclusion obtained by Lai Jiongcheng [10], that is, the tunnel structure has obvious followings the response to the stratigraphic acceleration.
Figure 10 Schematic of excavation method
Figure 11 Monitoring point layout
Figure 12 Tunnel displacement difference time course curve under different excavation methods
Figure 13 Direction acceleration time curve of the initial branch and surrounding rock under different excavation methods
is to compare the peak response of acceleration of different elevations in surrounding rocks. Under the action of aftershock, the peak acceleration of the X direction at the soil monitoring point at different locations is recorded, as shown in Figure 14. It can be seen from Figure 14 that as the distance from the bottom of the soil (the position of seismic wave application), the acceleration response gradually increases. Different excavation methods have little impact on the peak of the acceleration response, indicating that the soil acceleration response is mainly affected by the incident seismic wave and the rock body itself.
Figure 14 The distribution of the plastic zone after the aftershock of the excavation method is shown in Figure 15. It can be seen from Figure 15 that the damage caused by rock mass is mainly shear failure, and the soil in front of the palm is damaged in large quantities. The plastic area of different excavation methods shows a tendency to reserve core soil method three steps for upper and lower steps, but the overall difference is not large.
Figure 15 Plastic zones of different excavation methods
4.1.4 Initial support stress distribution
Aftershock, the initial support stress mainly bears compressive stress. During the process, the main stress at the 8 measurement points of the initial support was monitored to extract its minimum main stress, as shown in Figure 16. It can be seen from Figure 16 that under different excavation methods, the initial support stress distribution is similar, and the initial support compression stress is relatively large at the arch shoulder and foot. Among them, the maximum initial support stress of the upper and lower steps method, the core soil method of the upper and lower steps reserved at the arch foot method and the three-step method are 34.29 MPa, 33.53 MPa, and 33.35 MPa respectively. This shows that the excavation method has little impact on the initial support under the action of aftershocks, but it exceeds the compressive strength of concrete , which means that under the action of earthquake, the initial support is in a relatively unfavorable stress state, and concrete may fall.
Figure 16 Initial support stress distribution under different excavation methods
4.2 Characteristics of surrounding rock-support dynamics in different construction stages
4.2.1 Displacement and acceleration characteristics analysis
Draw a time chart of the displacement difference of tunnels in different construction stages, as shown in Figure 17. The change curves of the displacement difference of the tunnel periphery under different construction stages are similar. The maximum displacement difference between the initial support and the initial secondary lining are 0.86 cm and 0.61 cm respectively. The application of the secondary lining reduces the tunnel displacement difference by 17.44%, indicating that the application of the secondary lining is conducive to reducing the displacement difference caused by earthquake effects around the tunnel.
Figure 17 Time course curve of tunnel displacement difference in different construction stages
is the same as excavation method. The peak acceleration in the direction of different positions of the surrounding rock X (see Figure 11 for the surrounding rock measurement points), as shown in Table 3. It can be seen from Table 3 that the application of the second lining has little effect on the acceleration response of the surrounding rock, indicating that the application of the tunnel structure has no effect on the acceleration response of the surrounding rock, which is the same as the conclusion drawn in the previous article.
4.2.2 Analysis of initial support stress
From the previous article, it can be seen that under the action of an earthquake, the initial support is mainly under pressure, and the initial support compressive stress takes the maximum value at the arch foot. Therefore, the minimum main stress time curve of the initial support left arch foot is drawn in different construction stages, as shown in Figure 18.It can be seen from Figure 18 that the initial support compressive stress changes in different stages of construction are similar. The maximum compressive stress of the first support left arch foot under the combined action of the initial support and the initial support second lining are 33.53 MPa and 28.12 MPa respectively. The application of secondary lining reduces the initial support stress by 16.13%, indicating that the second lining is conducive to sharing the stress of the initial support.
Table 3 Weiyan X
test point
T1
T2
T2
html ml1T3
T4
T5
T6
T6
T7
T8
T9
initial branch effect
.10
.06
.06
.83
.80
.72
.64
.61
.39
.04
initial branch two lining joint
.11
.11
.06
.83
.80
.73
.65 6
.62
.38
.04
Figure 18 The minimum main stress time curve of the first support left arch foot at different construction stages
4.3 Internal force response analysis of lining structure
Under the joint working condition of the initial support second liner of the tunnel, the peak of the internal force of the tunnel was extracted and the results of the internal force of the second liner excavated to this section were compared, as shown in Figures 19 and 20. From Figures 19 and 20, it can be seen that under the action of static power, the tunnel bending moment is symmetrically distributed along the tunnel axis, and the extreme value is obtained at the left and right arch feet; the axial force is symmetrically distributed along the 45° direction of the tunnel, and the extreme value is obtained at the left and right arch shoulders. Under the dynamic case, the maximum bending moment is 278.09 kN·m, and the maximum axial force is 4 129.73 kN. Under the action of power, the bending moment of the tunnel increases sharply, which is most obvious at the arch shoulder. The dynamic bending moment is 8.19-8.49 times the static bending moment. The remaining parts increase by 0-2 times, and the dynamic axial force growth value is less than 1 times, which is prone to large eccentricity and instability failure.
Figure 19 Two-lined bending moment peak
Unit: kN·m
Figure 20 Two-lined shaft force peak
Unit: kN
Unit: kN
Highlight the safety coefficient of each part of the second lining during the tunnel earthquake based on the internal force value of the second lining, and extract its minimum value, as shown in Figure 21. The tunnel safety factor is smaller at the right arch shoulder and the left arch foot, which is 2.83 and 2.80 respectively, both greater than the safety factor specified in the "Highway Tunnel Seismic Design Code" [16]. Compared with the static effect, the minimum safety factor is reduced by 16.91%, indicating that under the aftershock, the two-lined structure that has been constructed in the tunnel is safer, but seismic protection should be paid at the arch shoulder and arch foot.
Figure 21 Tunnel two-lined safety factor
5 Conclusion
This paper relies on the Lanjiayan Highland stress soft rock tunnel, firstly analyzes the internal force and safety of the tunnel's second-lined lining and its safety through on-site measured data, and then for different excavation methods: up and down step method, up and down step reserve core soil method, and three-step method, through numerical simulation, the impact of the tunnel excavation method on the surrounding rock-support dynamic response under the aftershock effect is studied, and the following conclusions are drawn.
(
) The internal force of the tunnel second lining is similar to its security coefficient. In the first 0 d tunnel second lining internal force increases rapidly, causing the safety coefficient of the tunnel second lining to decrease. The change rate of 0~60 d gradually slows down, and the internal force and safety coefficient of the second lining after 0 d after is stable. Under the aftershock, the overall displacement difference of the tunnel is small, and the displacement difference shows a trend of the three-step method to reserve core soil methods for the up and down steps. The acceleration response of the tunnel structure has obvious follow-up to the acceleration response of the formation. The acceleration response of the surrounding rock is mainly affected by the incident seismic wave and the properties of the soil, and has nothing to do with the excavation method and the implementation of the tunnel structure.
() The earthquake caused rock mass damage mainly by shear damage, and the soil in front of the palm is damaged in large quantities. The plastic area of different excavation methods shows a tendency to reserve core soil method three-step method up and down step methods, but the overall difference is not large. Under the action of an earthquake, the initial support is subjected to greater compressive stress, and concrete may fall.
(
) The combined effect of the first branch two linings is compared with the first branch alone. The tunnel displacement difference is reduced by
7.44
%, and the maximum compressive stress of the initial support is reduced by
6.13
%, indicating that the application of the second lining is conducive to reducing the displacement difference caused by earthquakes around the tunnel and sharing the initial support force. Under the aftershock of
(
) the tunnel bending moment increases sharply, which is most obvious at the shoulder. The dynamic bending moment is
.19~8.49 times of the static bending moment. The remaining parts increase by
~2 times, and the dynamic axial force growth value is within 1 times of
html, which is prone to large eccentricity and instability damage. Compared with static effects, aftershock effects reduce the minimum safety factor by
6.91
%. A smaller value is obtained at the right shoulder and the left foot of the arch, and attention should be paid to seismic protection.
References
[1] Zhu Anlong. Large deformation mechanism of railway tunnels with high ground stress steep tilts of Qianzi Rock formations[J]. Modern Tunnel Technology, 2019, 56(S2):231-238.
[2]
Lai Hongpeng, Yang Wanjing, Xie Yongli. Deformation and loading characteristics of soft rock large deformation bias highway tunnel [J]. Journal of Central South University: Natural Science Edition, 2014, 45(6):1924-1931.
[3] Xu Guowen, He Chuan, Dai Cong, et al. Research on the mechanism and excavation method of soft rock tunnel under complex geological conditions [J]. Modern Tunnel Technology, 2017, 54(5):146-154.
[4] Zhong Yujian, Miaomiao, Wang Yadong, et al. Monitoring and finite element simulation of deformation law of Qianmei Rock Tunnel in large span shallow buried bias [J]. Highway, 2019, (6):277-283.
[5] Guo Xiaolong, Tan Zhongsheng, Li Lei et al. Research on the timing of secondary lining construction of Qianmei Rock Tunnel in highland stress [J]. Journal of China Highways, 2020, 33(12):249-261.
[6] Wang Bo, He Chuan, Zhou Yi, et al. Seismic fracture characteristics of weak rock mass in strong earthquake zones and their problems faced in tunnel construction [C]//Tunnel Engineering Branch of China Highway Society, Chongqing Municipal Transportation Committee. Proceedings of the National Highway Tunnel Academic Conference in 2013, 2013.
[7] Zhang Jing, He Chuan, Wang Bo, et al. Research on the aftershock dynamic response laws of tunnels under construction on the Guanggan Expressway [J]. Journal of Underground Space and Engineering, 2016, 12(1):268-274.
[8] Zhao Wei. Analysis of dynamic effects of thousands of rocks surrounding rocks in Dujiashan Tunnel [D]. Chengdu: Chengdu University of Science and Technology, 2012.
[9] Ling Yao. Research on the collapse mechanism and aftershock impact of soft rock tunnel in Guanggan Expressway [D]. Chengdu University of Science and Technology, 2012.
[10] Lai Jiongcheng. Research on the dynamic response characteristics and stability of earthquakes during the construction period of the cracked rock tunnel [D]. Chengdu; Southwest Jiaotong University, 2013.
[11] Xu Jinhua. Research on the instability mechanism and safety control measures of soft rock tunnels in the cracked rock tunnel area [D]. Chengdu: Southwest Jiaotong University, 2014.
[13] Niu Hongtao. Research on the technology of tunnel forming a complex surrounding rock tunnel in the loess-covered soil-rock contact zone [D]. Xi'an: Xi'an University of Technology, 2010.
[14] Huo Runke, Wang Yanbo, Song Zhanping, et al. Analysis of initial support performance of loess tunnels [J]. Geoscience Mechanics, 2009, 30(S2):287-290.
[15] Dai Cong. Research on excavation and support of soft rock tunnels in highland stress fields [D]. Xi'an: Southwest Jiaotong University, 2018.
[16] JTG/T 2232-01—2019 Seismic design specifications for highway tunnels [S].
"Internet celebrity" self-heating hot pot: dangerous and flammable! The explosion of lime plus water caused a fever and explosion that once blew up the eyes of an eight-year-old boy! There are no national and industry standards!
Is there a hot pot to eat in the primitive era? ! "Bears in the Original Age" Sichuan dialect version is released today, and more dialect versions are released simultaneously
During the National Day holiday, Xu Min and Du Xinzhi launched a big family competition to show their reunion separately, but the effects were very different.
Xunyi Court held a singing pk contest for "Welcome National Day, praise the new era, offer gifts to the 20th National Congress, and always follow the party"
