STUDY ON THE TUNNEL SECONDARY LINING CONCRETE CRACKING PERFORMANCE DURING SERVICE PERIOD OF WU- GUANG PASSENGER DEDICATED LINE

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1 STUDY ON THE TUNNEL SECONDARY LINING CONCRETE CRACKING PERFORMANCE DURING SERVICE PERIOD OF WU- GUANG PASSENGER DEDICATED LINE Yan Liu (1) Xian Liu (2) Lei Huang (3) Guoping Liu (3) (1) School of Material Science and Engineering, Tongji University, Shanghai , China; (2) Department of Geotechnical Engineering; Tongji University; Shanghai ; China (3) Shanghai Royang Innovative Material Technologies Co., Ltd, Shanghai ; China ABSTRACT This paper is based on the research on the cracking control of the tunnel secondary lining of Wu-Guang passenger dedicated line (Wu-Guang PDL) during service period and provides a new method for evaluating the concrete cracking performance of the tunnel secondary lining during service period. Firstly, research and modeling of the load-bearing mechanism of tunnel secondary lining are made. Then the secondary lining concrete permeability under cyclic loading is tested and the crack extension of the micro crack in concrete of tunnel secondary lining is shown by air permeability coefficient. The test shows that cellulose fibers can improve the anti-cracking performance of tunnel secondary lining concrete during service period. PREFACE The tunnels of Wu-Guang Passenger Dedicated Line use the structure of shotcrete First Lining + PVC waterproof board + concrete secondary lining. The speed of PDL can reach the velocity of 350Km/h.Considering the air pressure and track vibration influence on the tunnel secondary lining during service period and the similar projects in Germany, reinforcement mat is generally used to control the crack of secondary lining. But that will cause the cost rising and construction difficulty and reinforcement mat can not solve the problem of concrete early age plastic cracking. the tunnel secondary lining of Wu-Guang passenger dedicated line adopt the cellulose fiber concrete plan and use cellulose fibers as the reinforced material. The anti-cracking performance is characterized by the concrete early age cracking and shrinkage. There is no standard method to test and characterize the anti-cracking performance on concrete during service period. This paper is based on the tunnel secondary lining project of Wu-Guang PDL and research on the concrete cracking performance during service period. 785

2 1. MODELING OF WU-GUANG PDL TUNNEL SECONDARY LINING DURING SERVICE PERIOD Firstly, this paper analyzes the load-bearing mechanism of Wu-Guang PDL tunnel secondary lining and certified the influence factors and index of the secondary lining concrete. Then, modeling and tests are made to characterize the anti-cracking performance of secondary lining concrete. 1.1 Study on the load-bearing mechanism of Wu-Guang PDL tunnel secondary lining It is shown that the problems of tunnel lining were usually caused by track vibration, foundation changes and durability of construction material in some paper [1-3]. As for the PDL, its features are: (1) When the train pass the tunnel with high speed (350Km/h), the air flow in the tunnel will be influenced which will cause the change of air pressure and may damage the tunnel lining structure; (2) Track vibration caused by high speed train passing may damage the tunnel lining structure; (3) The foundation changes caused by vibration may damage the tunnel lining structure Analysis of finite element analysis model on the concrete structure of Wu-Guang PDL tunnel secondary lining According to the report of geological investigation of Wu-Guang PDL tunnel, the physical and mechanical parameters of geo-material in the Dynamic Analysis are resulted by weighted sums of several earth layers. As the Table 1 shows; Table 2 shows the material parameters of tunnel secondary lining concrete. Table 1 the Physical and Mechanical Parameters of Geo-material density 3 ( Kg / m ) elastic modulus ( Pa ) Poisson ratio - cohesion ( Pa ) friction angle ( o ) expansion angle ( o ) Table 2 Material Parameters of Tunnel Secondary Lining Concrete depth ( m ) diameter ( m ) thickness ( m ) elastic modulus ( Pa ) Poisson ratio - density 3 Kg / m In this paper, the horizontal and vertical calculating area of tunnel is 54 m (10 times the tunnel radius) and 200 m long along the tunnel. The depth above and under the tunnel are 11.5 m and 45 m (10 times the tunnel radius). According to the calculating modelling, the tunnel uses four nodes isoparametric element and concrete lining uses two nodes beam element. Rock mass use elastoplastic DP constitutive model and lining uses elastic constitutive model. The tunnel calculating modelling and detail enlarging figure are shown as Fig1. 786

3 Figure 1: The tunnel calculate modelling and detail enlarge figure To reduce vibration reflection, the damping ratio is 0.45 in the calculating area and the other material parameters keep constant. Outside the high damp material, the horizontal displacement is restricted by four vertical sides and all degrees of freedom are fixed by bottom nodes. Setting the load of the train on the bottom of the tunnel (modelling), we can get the dynamic response of the tunnel structure by using Newmark step integration method. Fig.2 shows dynamic response figure of tunnel cross section (t=0.35 s, L=0 m). It shows that displacement of tunnel dynamic response is mainly at tunnel bottom which is 3-6 times the displacements of side and top. It is because that the load of the train causes the tunnel bottom vibration firstly, then the other parts. The vibration was reduced with the distance grows. Fig.3 shows the static load response displacement of tunnel. The displacement caused by Dynamic load is higher than static load of same load. Figure 2: Dynamic response figure of tunnel cross section Figure 3: The static load response displacement of tunnel Fig.4 shows deformation time-history of the top and bottom of the tunnel lining at L=700m tunnel cross section and it is supposed that the train arrives this cross section at t=3.5s. The vibration changed from weak to strong and came to the top point when the train reached this 787

4 cross section and then the vibration changed from being strong to weak. The vibration shape of the lining top is mainly the same as the bottom and the amplitude is 1/4-1/2 times the lining bottom and there is 0.05s time late than the bottom. The acceleration time history shows the same feature as fig.5. It is shown that the testing curve is more complex than the calculating figure curve. It is because that the realistic topographies were made by several earth layers and vibration energy passing the soil interface will generate new wave source because of the transmission and reflection and it will result in the distortion of the vibration wave and it is complex to analyze the vibration stacking caused by wheels of the train. Figure 4: Deformation time-history of the top Figure 5: The acceleration time history and bottom of the tunnel lining Conclusion on the analysis of the load-bearing mechanism of tunnel secondary lining of Wu-Guang PDL (1) The vibration load influence on the tunnel lining dynamic response is mainly concentrated at tunnel inverted arch, arch foot and sidewall and has relatively small influence on the part of arch waist and the arch top. (2) The dynamic response problem under dynamic load of high speed train is in essence a concrete tunnel lining fatigue property problem. (3)the vibration frequency transported to the tunnel lining is comparatively low and mainly at the scope of 5 40 Hz. 1.2 The research modeling of tunnel secondary lining during service period Based on the analysis of the load-bearing mechanism of tunnel secondary lining, it is concluded that the dynamic response problem under dynamic load of high speed train is in essence a concrete tunnel lining fatigue property problem. The research takes the lining concrete under fatigue load as the test modeling and simulates the control concrete and cellulose fiber concrete structure under cycling load during service period, then further research concrete anti-cracking performance of the tunnel secondary lining. 2. TESTING STUDY ON SECONDARY LINING CONCRETE PERFORMANCE OF ANTI-CRACK DURING SERVICE PERIOD The permeability of concrete mainly depends on existence and extension of tiny cracks within concrete [4-6]. Thus, anti-permeability of concrete can character existence and 788

5 extension when under load of tiny cracks within concrete. In this test, anti-permeability of concrete after repetitive fatigue load is introduced and used in token of the high PDL tunnel secondary lining concrete performance of anti-cracking when during service period. 2.1 Testing mixing ratio Wu-Guang PDL tunnel secondary lining concrete mixing ratio is adopted in test, as shown in table 3. Ultra Fiber 500 is used in the test, which is Cellulose fiber and produced by Buckeye Technologies Inc. According to the standard trial method, 28d compressive strength of concrete is tested by the sample size of 150 mm 150 mm 150 mm, as shown in table 4. Table 3: mixing ratio(kg/m 3 ) composition group C S Plain concrete Cellulose fiber concrete G 5~10mm 10~20mm 16~31.5mm W F A Fiber Table 4: 28d compressive strength (MPa) group Sample 1 Sample 2 Sample 3 Average Plain concrete Cellulose fiber concrete Wu-Guang PDL Secondary lining concrete loading test Sample preparation Fatigue loading is used in this test, and purpose of this method is to bring the samples recurrent load and give the samples moderate damnification but not destroy. According to test equipments, the size of loading test samples is determined as 2100mm 400 mm 500 mm, as shown in fig.6. Figure 6: loading test size 789

6 2.2.2 Testing method In order to make comparison of different sample damnification due to different group, the bending fatigue load testing apparatus is designed as fig.7. Figure 7: testing apparatus sketch This bending fatigue load test use the method of same extent sine wave load. Parameters are assumed according to trial standard. (1) Level of fatigue load It can be concluded that the utmost tensile strength is about 2 MPa. As a result, the utmost load M is shown as Eq.(1). cr 1 2 M cr = σ ch b = 33. 3kN m (Eq.1) 6 Where σ c is utmost tensile strength; h is sample height (500mm); b is sample width (400mm); According to sample size and pensile point, pensile load M is calculated as Eq.(2) ql1 L2 ql1 L1 M = = 0. 92kN m (Eq.2) Where q is concrete average weight of per meter (25 kn/m); L1 is sample length (2.1m);L2 is the distance of pensile point (1.4 m). According to the service condition, we assume that upper limit load M is 15% and 30% of M cr, and actual load F is calculated as Eq.(3), as shown in table 5. F L0 ql1 L1 F ql1 L0 M = + + (Eq.3) Where F is actual load( kn ); L 0 is the distance of underprop point (1.8 m). Table 5: testing load Load plan M ( kn m ) F(kN ) Plan Plan

7 (2) Loading frequency According to the theory analysis and the capacity of testing apparatus, loading frequency is chose as 5 Hz. Sample is offloaded after 500,000 times recurrent fatigue load. Fatigue loading test is shown as fig.8. Figure 8: fatigue loading test 2.3 Anti-cracking performance test of Wu-Guang PDL secondary lining concrete Because permeability of concrete has close relation with the existence and extension of tiny cracks within concrete, anti-permeability performance of concrete can show existence and extension of tiny cracks when under load within concrete. Special test method is introduced into this test, including test sample and test apparatus. Air permeability is used to be in token of Anti-crack performance Sample preparation After fatigue loading test, cylinder samples are drilled from the bending section of the beam in the width direction, which have diameter of 150 mm. and the testing samples are intercepted by the sample s thickness of 50 mm, as shown in fig.9. Fig.9 testing samples Air permeability testing apparatus According to the testing standard, oxygen is pressed into the bottom of samples with fixed pressure, and air permeability of concrete is deduced by testing air quantity in the top of the samples. Testing pressure is 0.7 MPa, and testing apparatus is shown as fig

8 Fig.10 air permeability testing apparatus 2.4Testing conclusion 2.4.1Calculation of permeability coefficient Permeability coefficient is calculated by Darcy law after modification when the air quantity over cross samples maintains stable. Permeability coefficient under all levels of pressure can be calculated as Eq.(4) 2Pa Qi Lµ ki = (Eq.4) 2 2 A( Pi Pa ) Where Pa is atmospheric pressure; Q i is the quantity of air bubble in unit time under i level pressure; L is height of samples; A is acreage of samples cross section; µ is dynamical sticky coefficient of air; P i is the pressure in i level Testing result In order to make comparison of air permeability in different level of recurrent load, Air permeability coefficient under different levels of pressure is calculated, as shown in table 6. From table 6, it can be concluded that when load level is 15% of utmost load, anti-air permeability under different pressure levels of cellulose fiber concrete is improved than plain concrete, but not obviously. When load level is 30% of utmost load, anti-air permeability under 0.2MPa and 0.3MPa levels of cellulose fiber concrete is obviously improved than plain concrete. Table 6 air permeability coefficient under different load levels and pressure levels Load level Pressure level (MPa) Plain concrete 6.57E E E E E E-16 cellulose fiber 5.57E E E E E E-16 concrete Improvement (%) % Result analysis From the test, it is concluded that: 792

9 (1) Air permeability coefficient increases with load level heightens, which means damnification within concrete is severer. (2) After experiencing the same recurrent fatigue load, concrete by adding cellulose fibers has less damnification inside than plain concrete. Because with same load level, air permeability coefficient under different pressure levels of cellulose fiber concrete is less than plain concrete. (3) The improvement effect on anti-permeability is more obvious by adding cellulose fiber into concrete when the fatigue load on concrete increases. Adding cellulose fibers (UF500) into concrete can improve the ability of crack control within concrete, and the improvement effect on anti-permeability is more obvious when the fatigue load on concrete increases. It is significant to add cellulose fibers into PDL tunnel secondary lining concrete, which suffered complex stress when in actual environment. It is also ensured that it s effective to improve the ability of in service concrete to resist crack by adding cellulose fibers into PDL tunnel secondary lining concrete. 3. CONCLUSIONS Based on the research on the cracking control of the tunnel secondary lining of Wu- Guang PDL during service period, a new method is mentioned in this paper to evaluate concrete anti-cracking performance; anti-permeability of concrete after recurrent fatigue load test can character existence and extension when under load of tiny cracks within concrete. After experiencing the same recurrent fatigue load, concrete by adding cellulose fiber (UF500) has less damnification inside than plain concrete, because with same load level, air permeability coefficient under different pressure levels of cellulose fiber concrete is less than plain concrete. The improvement effect on anti-permeability is more obvious by adding cellulose fibers (UF500) into concrete when the fatigue loading on concrete increases. It is significant to add cellulose fibers (UF500) into PDL tunnel secondary lining concrete, which suffered complex stress when in actual environment. REFERENCE [1] Jun S. Lee. Damage identification of a tunnel liner based on deformation data. Tunnelling and Underground Space Technology, 2005,(20) : [2] Yuanlin Z and Carbee DL. Strain rate effect on tensile strength of frozen silt. In: Proceedings of the 4 th International Symposium on Ground Freezing, Sapporo, Japan, August 1985, [3] Alkire BD and Morrison JA. Comparative response of soils to freeze-thaw and repeated loading. In: Proceedings of the 3rd International Symposium on Ground Freezing, Hanover, New Hampshire, June 1982, [4] Banthial, N. and Bhargava, A. Permeability of Stressed Concrete and Role of Fiber Reinforcement, UBC report, Canada, [5] Banthial, N. Permeability of concrete with fiber reinforcement and service life predictions. Materials and Structures, 2008, (41): [6] Hideto Mashimo, Nobuharu Isago and so on. Effect of fiber reinforced concrete on shrinkage crack of tunnel lining. Tunnelling and Underground Space Technology 2006, (21):