POSTER PAPER PROCEEDINGS

Transcription

1 ITA - AITES WORLD TUNNEL CONGRESS April 2018 Dubai International Convention & Exhibition Centre, UAE POSTER PAPER PROCEEDINGS

2 Study on quick excavation and support method of Expressway Tunnel with 8 lanes in limestone formation Wu Jie1, Zhang Junru2, Feng Jimeng3, Chen Wenyin4, Zeng Sicong5, Yu Cheng6 1 Postgraduate, Key Laboratory of Transportation Tunnel Engineering, Ministry of Education, School of Civil Engineering, Southwest Jiaotong University, Chengdu , PR China, @qq.com 2 Associate professor, Key Laboratory of Transportation Tunnel Engineering, Ministry of Education, School of Civil Engineering, Southwest Jiaotong University, Chengdu , PR China, zhangjunru_swjtu@sina.com 3 Ph. D., Key Laboratory of Transportation Tunnel Engineering, Ministry of Education, School of Civil Engineering, Southwest Jiaotong University, Chengdu , PR China, @qq.com 4 Senior engineer, China Tiesiju Civil Engineering Group Co.,LTD, Anhui , PR China, @qq.com 5 Postgraduate, Key Laboratory of Transportation Tunnel Engineering, Ministry of Education, School of Civil Engineering, Southwest Jiaotong University, Chengdu , PR China, @qq.com 6 Engineer, China Tiesiju Civil Engineering Group Co.,LTD, Anhui , PR China, @qq.com ABSTRACT Jiangshuiquan tunnel, which is 8 lane tunnel with double holes, approximately 3100m in length, 170 to 207 square meters in excavation area, and 80km/h in the design speed, is located in Beijing-shanghai high-speed expressway. In consideration of large scale and tight schedule, a new excavation method named as steel-rock wall combined supporting method is proposed, which is on the basis of CD method and median septum step method, supported temporarily by steel frame and rock wall by which mid-partition in lower bench of the CD method replaced. The three construction methods: CD method, median septum step method and steel-rock wall combined supporting method are compared through numerical analysis, and the result shows that security of the steel-rock wall combined supporting method is sufficient. In addition, the internal force in-situ monitoring of primary support and lining with the method shows that the safety is also satisfied. The steel-rock wall combined supporting method has been applied to Jiangshuiquan tunnel and achieved better results, hoping to provide reference for other similar projects. Key Words: Four lane highway tunnel; Steel-rock wall combined supporting method; Quick construct; Monitoring structure; Safety evaluation 1. INTRODACTION The first segment of Jinan connecting line in Beijing-Shanghai Expressway is 5.38 km, the overall situation shown in Figure 1. Jiangshuiquan tunnel is a full-scale vital project with a length of 3101m and the largest excavation section in the cave is 220m². It is currently the longest bidirectional eight-lane mountain highway tunnel in China. 1

3 Figure 1. The location of Tunnel With the rapid development of China's expressway, a large number of super-large with 4 lane section tunnels have been produced, as shown in Table 1. From the situation shown in the table, the overall cross-sectional area of more than 200 square meters, and some even up to 400 square meters, but the length is generally small, such as the length of Jiangshuiquan Tunnel has not been reported. Table 1. Some cases of large section tunnel in China Lianyungang - Huoerguosi expressway reconstruction and expansion project of Xiaowu(three) Single-hole, 4 lanes. 2

4 A large number of studies have been conducted on the construction methods and safety of large section tunnels. Sasaki R(2004)[1] found that the safe excavation was required while keeping the settlement of the railway track below an allowable level when he studied a 14-m-diameter water tunnel was constructed in unconsolidated ground in an urban area of Kobe. Jiang S P(2005)[2] suggested that a curved section with 3 main content of circles to apply in poor geological condition with thin cover over the tunnel, the net width of the inner contour of the tunnel is 18.65m, net height 9.16m with height-width ratio 0.48 and headroom area of the tunnel m2. Chao Z(2007)[3] indicated that, to some extent, each countermeasure can decrease the displacements of the tunnel support and all these countermeasures will also reduce plastic area in surrounding rock and increase structure safety to a certain extent. Zhou D(2011)[4] indicated that during the construction, the excavation of the lower bench in the left drift and the bench in the core rock significantly affected the deformation and stress of the support structure. The longitudinal range of influence of the excavation of the tunnel is about 1 to 1.5 times of the drift span, from 8 to 12 m ahead of the work face. Xiong S(2015)[5]showed that the surrounding rock displacement and stress variation under different excavation sequences are analysed and compared by numerical simulation of the excavation process for a tunnel constructed using the CRD method. Li Y(2016)[6] pointed out that deformations and stress distributions in large tunnel intersection areas are more complicated than those in common tunnels. Barla G(2016)[7] studied the full-face excavation of large tunnels in difficult conditions. Luo Y(2017)[8] did a lot of work in a large cross-section shallow tunnel excavated by centre cross diagram method (CRD) was constructed on a site with weak surrounding rock. The current research mainly lies in the safety and stability of the traditional construction methods, and few studies on the new construction methods. 2. Construction status of large section tunnel From the situation exposed by the excavation surface, the surrounding rock where the design adopts CD method is good. If strictly in accordance with the CD method of construction, there are a lot of problem such as large interference of various branches of the construction organization, the complexity of removing the temporary support system, slow construction progress, high costs. For the surrounding rock, different tunnel excavation methods bring different stress changes and different paths, which also change the strength parameters of the soil. In general, the disturbances of excavation will change the structure of the soil, resulting in the change of the grain position of the soil and the fracturing of the cement between the soil particles, which will reduce the cohesion and the internal friction angle and the self-bearing capacity surrounding rock. So the load of the support structure will increase. To ensure the construction safety during the excavation process, super-large section tunnels often adopt the step method, ring excavation stay core soil method and the both side drift method, whose difference are in Table 2. According to the table, with the increase of excavation division, the safety of the tunnel is increasing, but the construction difficulty, the construction procedure, the construction period and the investment are increasing. How to reduce the division and construction procedures and ensure the speed and safety of construction is a critical challenge for the construction of tunnels that require tight construction schedules. 3

5 Table 2. The comprehensive comparison of different methods 3. Steel-rock wall combined supporting method According to the characteristics of the surrounding rock of Jinshuiquan Tunnel, based on the CD method and Median septum step method, using the characteristics of strong bearing capacity of the surrounding rock of the basement, the middle wall of the upper terrace and the part of the dikes reserved by the lower terrace are used to form temporary vertical support system, forming Steel-rock wall combined supporting method. The concrete construction process is as follows: the tunnel section is divided into two steps of upper and lower terrace and five steps of excavation, using steel frame as temporary support and staggered left and right for the upper terrace to reduce the excavation span each time; as for the lower terrace, the left and right sides of the wall is excavated step by step, anchor bolts and timely support ensuring the stability of the side wall after the wall steel frame landed, and then the whole excavation and support system is formed through the combined support composed by the interim retaining dikes and the temporary steel frame to effectively control the tunnel deformation. Finally remove the temporary steel frame support and the interim retaining dikes, complete closing the primary support. The dikes are reserved to retain the width of the car as a road for the construction of the upper terrace to ensure that five steps will construct rapidly at the same time. The cross-sectional layout of constriction method is shown in Figure 2, the step of the construction is shown in Figure 3. Figure 2. The section of steel-rock wall combined supporting method Figure 3. Construction schematic diagram of steel-rock wall combined supporting method 4

6 4. Contrast analysis of the safety of construction method The safety analysis of construction method is mainly carried out by means of numerical simulation. FLAC3D is used to model and calculate on the base of the actual situation of Jangshuiquan Tunnel Calculation parameters The selection of the calculated parameters is based on the measured values of Jiangshuiquan Tunnel and the recommended values provided by the relevant specifications. The buried depth is 40m. The parameter of surrounding rock and concrete is shown in Table 3 and table 4. Table 3. Calculation parameter table of surrounding rock 4.2. Calculation condition According to the difference of excavation method, three construction methods are selected, namely, the CD method, median septum step method and steel-rock wall combined supporting method, as shown in Figure 4. (a) CD method (b) Median septum step method supporting method (c) Steel-rock wall combined 4.3. Analysis of calculation results Analysis of displacement Figure 4. Three methods The displacement data mainly collected the deformation of the surrounding rock of the vault and side wall. As shown in Figure 5 and Figure 6, respectively. 5

7 Figure 5. The displacement of vault (unit: m) Figure 6. The displacement of side wall (unit: m) From Figure 6 to Figure 7 we can get the following rules: (1) The overall deformation of the tunnel is not large, and the deformation of each method is not very different. (2) The amount of deformation of steel-rock wall combined supporting method is between the CD method and median septum step method, and the CD method is the smallest. (3) The process of dismantling and supporting will cause sudden increase of the deformation of the side wall, but the deformation is limited Analysis of stress The stress data mainly chooses the vertical stress of the surrounding rock vault and horizontal stress of the side wall, as shown in Figure.7 and Figure.8. 6

8 Figure 7. Vertical stress curve of surrounding rock of each method (unit: Pa) Figure 8. Horizontal stress curve of surrounding rock of each working method (unit: Pa) From Figure 8 and Figure 9 we can get the following rules (1)Surrounding rock stress values of the vault and side wall change more frequently with the excavation process, but the overall value is small (2)The vertical stress of surrounding rock of CD method is the largest, followed by the steel-rock wall combined supporting method, and the minimum of median septum step method. (3)Surrounding rock horizontal stress in each method difference is not very different Primary support deformation and stress data analysis The primary support will bear the main load during the construction, so its deformation has a crucial influence on the overall safety of the tunnel structure. As shown from Figure 9 to Figure 11. 7

9 Figure 9. Primary support deformation figure of CD method (unit: cm) Figure 10. Primary support deformation figure of steel-rock wall combined supporting method (unit: cm) Figure 11. Primary support deformation figure of median septum step method (unit: cm) The primary support deformation of median septum step method is the largest, followed by the steel-rock wall combined supporting method, and the minimum of CD method. From the comparison of deformation and stress of the three methods, the deformation and stress of steel-rock wall combined supporting method are between the CD method and the median septum step method, and the safety can also be satisfied. 5. Field test analysis Selecting construction site of Jiangshuiquan tunnel using steel-rock wall combined supporting method to test primary support pressure, force and secondary lining internal force. The layout of the test is shown in Figure 13 and the test components are shown in Figure 12 (a)concrete strain instrument (b)steel strain instrument (c)pressure box (d)reinforced stress instrument Figure 12. The test components The test results are shown in Figure 13 and Figure 14. Outside the figure is pressure and the inside is tension. 8

10 Figure 13. Monitoring data of primary support (unit: MPa): (a)surrounding rock pressure, (b)spray concrete stress, (c)steel frame stress Figure 14. Monitoring data of secondary lining (unit: MPa): (a) Pressure between primary support and secondary lining, (b)concrete stress, (c) Reinforced stress From the field test results, the pressure of surrounding rock, primary support and the secondary lining are unsymmetrical pressure. This is related to digging the soil on the left first, but the overall pressure is not large; Sprayed concrete is mainly subjected to compression, the maximum stress is 9.02MPa, which is far from the ultimate strength of C25 shotcrete and still has greater safety; As for steel frame, internal force of the vault is tensioned, and the rest are under pressure, the maximum value of 33.13MPa, far below the design strength of HRB335 steel value; The internal force of the secondary lining concrete and the stress of the steel bar are generally small, and the safety can meet the requirements. At the same time, according to the statistics of the construction site, original design using the CD method can excavate 50m each month. After using steel-rock wall combined supporting method, we can excavate 63m each month. This greatly improved the tunnel excavation progress, and the cost decreased 48,000 yuan per 10 meters. According to the length of this segment (2170m), the construction time will be saved by about days and the cost will be saved by 10,416,000 yuan, which has achieved good economic benefits. 6. Conclusion Based on the actual situation of the Jiangishuiquan tunnel and the construction characteristics of the large section tunnel, this paper adjusts the construction method. Compared with the traditional CD method and the median septum step method, we formed steel-rock wall combined supporting method. After numerical analysis and field measurement research, the following conclusions are obtained(1)the steelrock wall combined supporting method effectively utilizes the characteristics of high bearing capacity of hard rock base and reduces the unfavourable factors such as more construction processes, large amount of temporary support dismantlement, slow construction speed and so on. It also accelerates the construction speed and reduces the project cost; 9

11 (2)By comparing the CD method and the median septum step method, the deformation and stress of the steel-rock wall combined supporting method are between these two methods. According to the surrounding rock conditions, we can immediately change to the CD method or the median septum step method; (3)According to the measured data from the scene, the steel-rock wall combined supporting method is safe enough, and the construction speed is fast. The economic and social benefits are obvious. References Sasaki R, Tsukada M, Kimura M, et al. Construction of a Water Tunnel of Large Cross Section in Unconsolidated Ground in an Urban Area(Frontir of Tunneling)[J]. Soil Mechanics & Foundation Engineering, 2002, 50: Jiang S P, Huang L H, Xue-Bin H U. Design and Study of Highway Tunnel with Super-large Cross Section[J]. Underground Space, Chao Z. STUDY ON ABNORMAL DEFORMATION CONTROLLING MEASURES FOR LARGE CROSS-SECTION SUBSEA TUNNEL[J]. Chinese Journal of Rock Mechanics & Engineering, 2007, 26(11): Zhou D. In-situ test and 3D-effect analysis of a tunnel lining structure of large cross section[j]. China Civil Engineering Journal, 2011, 44(2): Xiong S, Zhang J, Liu B. A Study of the Construction Sequences of a Large-Section Shallow-Buried Unsymmetrical Loading Tunnel by the CRD Method[J]. Modern Tunnelling Technology, 2015, 52(3): Li Y, Jin X, Lv Z, et al. Deformation and mechanical characteristics of tunnel lining in tunnel intersection between subway station tunnel and construction tunnel[j]. Tunnelling and Underground Space Technology incorporating Trenchless Technology Research, 2016, 56: Barla G. Full-face excavation of large tunnels in difficult conditions[j]. Journal of Rock Mechanics and Geotechnical Engineering, 2016, 8(3): Luo Y, Chen J, Huang P, et al. Deformation and mechanical model of temporary support sidewall in tunnel cutting partial section[j]. Tunnelling and Underground Space Technology, 2017, 61: Li JYu C, et al, Summary of Some Problems in Construction of Large Cross Section Tunnels [J]. West-china Exploration Engineering :

12 THANK YOU FOR VISITING ITA AITES