Geotechnical issues around ballasted track and slab track in Japan. Railway Technical Research Institute Yoshitsugu Momoya

Transcription

1 1 Geotechnical issues around ballasted track and slab track in Japan Yoshitsugu Momoya

2 2 Contents Introduction Ballasted tracks in existing line Asphalt roadbed in design standard Slab track on earth structure

3 3 Ballasted track and slab track Ballasted track Periodical maintenance work is necessary. Easy to correct track irregularity. Construction cost is relatively low. Slab track Low maintenance work. Difficult to correct track irregularity. Construction cost is relatively high.

4 4 Requirement for ballasted track Supporting sleepers stably and uniformly. Distribute train load applied on roadbed. Wheel load of train Ballast Roadbed 10% 20% 40% 20% 10% Subgrade

5 5 Requirement for ballasted track Easy to correct track irregularity by tamping. Good drainage.

6 6 Requirement for ballasted track Lateral resistance against lateral train load and rail buckling. Apply adequate elasticity on track (especially on bridge or viaduct)

7 7 Requirement for slab track Maintenance free. Not high construction cost.

8 8 Difficult circumstance for railway track in Japan Soft ground. Alluvial clays are deposited at plains. Geological ages are young. (younger than 6000 years) Mud pumping on soft ground Tokyo Present coast line Coast line 6000 years ago

9 9 Difficult circumstance for railway track in Japan Heavy rain. Rain fall in September (average) Typhoon China Japan Ballasted track after rain

10 10 Contents Introduction Ballasted tracks in existing line Asphalt roadbed in design standard Slab track on earth structure

11 11 Existing line and newly constructed line Existing line Constructed before 1960 s Design standard was not regulated. Newly constructed line Constructed after 1970 s Design standard was established in 1978 Most of railway lines in Japan were constructed before 1950 s

12 12 Roadbed and subgrade in existing line No specific roadbed layer Material is not regulated Insufficient drainage Low stiffness subgrade Penetration of ballast into roadbed Mud pumping Large dynamic deformation Increase of maintenance work

13 Depth (cm) Depth (cm) 13 Penetration of ballast into roadbed Ballast layer SPT test N-value Ballast penetration layer SPT test N-value Roadbed Subgrade Subgrade Existing line Newly constructed line

14 道床バラスト貫入層の深さ Depth of ballast penetration layer (cm) (cm) 14 Depth of ballast penetration layer Log e h=-0.019k K 地盤の K 30 値 (MN/m 3 30 value of plate loading test (MN/m ) 3 )

15 15 Vertical stress in roadbed and subgrade Ballasted track Ballast Roadbed Vertical stress in roadbed and subgrade Subgrade 3.0m

16 Amplitude of roadbed displacement (mm) 16 Stiffness of roadbed and track irregularity Settlement of ballasted tracks and track irregularity strongly depends on the stiffness of roadbed and subgrade. Track irregularity mm/10,000 ton

17 17 Roadbed improvement Most of the roadbeds constructed before 1960 s do not have sufficient stiffness. Without improvement Roadbed improvement Large settlement Less settlement Roadbed improvement Settlement of ballasted track becomes less after roadbed improvement.

18 18 Conventional roadbed improvement Conventional roadbed improvement method: Crushed stone, steel slag, cement treated material. Sufficient compaction work was necessary.

19 19 New roadbed improvement method Reusing degraded ballast mixed with cement grout. Pump Liquid A Slag cement Setting accelerator Water Grout Plastic pipe Pump Liquid B Hardening agent Water 発生バラストの投入 Degraded Contaminated ballast (Mixed ballast ( バラストwith by + 硅砂 sand) ) グラウトの注入 Grout

20 20 Cyclic loading test Cyclic loading 5Hz, ΔP=80kN Sleeper Ballast Roadbed

21 Settlement of sleeper (mm) 21 Cyclic loading test results 0-5 Grouted deteriorated ballast Grouted new ballast Sand roadbed Water pouring Water pouring Number of cycles (x1000)

22 Settlement of sleeper (mm) 22 Cyclic loading test results 0.0 Settlement after 750,000 cycles Groudted degraded ballast Grouted new ballast Sand roadbed Number of cycles (x1000)

23 Application at site Before roadbed improvement Excavation of ballasted track Degraded ballast Grout material Preparation of grout Liquid A Degraded ballast Liquid B 23

24 Application at site Laying degraded ballast Injection of grout Injection of grout After roadbed improvement 24

25 Track 高低変位 irregularity (mm) (mm) 25 Track irregularity after the roadbed improvement Roadbed 路盤改良範囲 improvement ヵ月後 After 6 months 未対策 11 ヵ月後 After 11 months Before improvement Position 位置 (m) (mm) (m)

26 26 Issues around transition zone Concrete structure Structural transition zone Embankment Embankment Concrete structure Structural transition General section Floating sleeper large settlement No floating sleeper

27 27 Moving loading test Multi-actuator moving loading test apparatus Loading actuators Track model Scale: 1/5 Load cells Concrete structure model Embankment model

28 Load 28 Multi-actuator moving loading test apparatus Actuator No.1 No.2 No.3 No.4 No.5 No.6 No.7 No.8 Posoition of virtual axial load Load by each actuator No.1+No.2 No.2+No.3 No.3+No.4 No.4+No.5 No.5+No.6 No.6+No.7 No.7+No.8 Virtual axial load (combined actuator load) vehicle vehicle Unit: m

29 Actuator load (kn) Sleeper load (kn) Actuator load (kn) Sleeper displacement (mm) 29 Multi-actuator moving loading test apparatus Actuator load Actuator load Time (sec) Time (sec) Sleeper load Sleeper settlement Time (sec) Time (sec)

30 Settlement of sleeper (mm) Sleeper load (kn) 30 Moving loading test results Train load Concrete Embankment 4 3 Sleeper load 4000cycles Concrete structure Embankment Sleeper settlement 10 trains 50 trains 100 trains 200 trains Sleeper position (mm) Those sleepers are not supporting wheel load (Floating sleeper) Accelerate local settlement Position of sleeper (mm)

31 31 Moving loading test results Approach block (Design standard) Approach block Concrete approach slab Low stiffness roadbed Concrete slab Low stiffness mat

32 Settlement of sleeper (mm) 32 Moving loading test results Concrete Embankment Approach block Concrete approace slab Low stiffness roadbed Without counter measure Position (mm)

33 33 Contents Introduction Ballasted tracks in existing line Asphalt roadbed in design standard Slab track on earth structure

34 34 Asphalt roadbed for newly constructed lines Asphalt roadbed became standard structure in Japan after 1978 Asphalt concrete Subgrade: K 30 70MN/m 3 Well graded crushed stone Sufficient bearing capacity. No ballast penetration. Good drainage.

35 35 Design of asphalt roadbed Road Railway Sleepers Rail Wheel Asphalt concrete layer Tensile strain Ballast Asphalt concrete layer Tensile strain Subgrade Subgrade Multi-layered elastic analysis FEM analysis

36 36 Design of asphalt roadbed Sleeper Ballast Displacement at the surface of roadbed Asphalt concrete Well graded crushed stone Subgrade Rail Asphalt concrete Well graded crushed stone Subgrade 1/4 symmetric model Tensile strain at the bottom of asphalt concrete

37 Displacement of asphalt roadbed surface (mm) Strain at the bottom of asphalt concrete ) ( 37 Design of asphalt roadbed Settlement Wheel load 80 kn (bogie axle) Strain Wheel load 80 kn (bogie axle) Thickness of crushed stone layer: 15cm 30cm 60cm Beneath sleeper: Tensile strain Thickness of crushed stone layer 15cm 30cm 60cm Position (cm) -40 Between sleeper: Compressive strain Position (cm) Asphalt concrete Well graded crushed stone Subgrade

38 38 Design of asphalt roadbed Tensile strain at the bottom of asphalt concrete ε t Allowable number of cyclic loading for Fatigue failure N A = C e t E A Where N A :Allowable number of cyclic loading for Fatigue failure e t :Tensile strain E A :Young s modulus (MN/m 2 ) V v :void ratio V b : asphalt volume C = 10 M M = 4.84 (V b / (V v +V b ) ) Vertical displacement at the surface of asphalt roadbed Less than 2.5mm considering impact load

39 Fatigue life of asphalt concrete (year) Displacement of asphalt roadbed (mm) 39 Design of asphalt roadbed 1000 Fatigue life 4 Displacement years mm 10 Subgrade: K 30 = 70 MN/m 3 Subgrade: K 30 = 110 MN/m Thickness of crushed stone layer (cm) 1 Subgrade: K 30 = 70 MN/m 3 Subgrade: K 30 = 110 MN/m Thickness of crushed stone layer (cm) Subgrade K 30 = 70 MN/m 3 K 30 = 110 MN/m 3 Thickness of crushed stone layer for high speed line 60 cm (Settlement) 40 cm (Fatigue life)

40 40 Contents Introduction Ballasted tracks in existing line Asphalt roadbed in design standard Slab track on earth structure

41 Slab track Rail Fastener Rail Circular stopper Slab Concrete trackbed Cement asphalt mortar 鉄道総研 RRR 堀池

42 42 History of slab track Tokaido Shinkansen (1964): Ballasted track on embankment Bearing capacity of embankment was not very high. (using clay, compaction control etc) Settlement of ballasted track became very large after the start of train operation. Sanyo Shinkansen Okayama-Hakata (1975): Slab track on viaduct. Sanyo Hokuriku Hokuriku Shinkansen Takasaki-Nagano (1997): Slab track on high quality embankment Tokaido

43 Total cost 43 Cost of slab track Annual tonnage 1.2 million ton / year 9 years Year Life cycle cost of slab track is lower than that of ballasted track.

44 割合 (%) バラスト軌道スラブ軌道等東海道新幹線 ( 東京 新大阪 ) 山陽新幹線 ( 新大阪 岡山 ) 山陽新幹線 ( 岡山 博多 ) 上越新幹線 ( 大宮 新潟 ) 東北新幹線 ( 東京 盛岡 ) 北陸新幹線 ( 高崎 長野 ) 東北新幹線 ( 盛岡 新青森 ) 九州新幹線 ( 博多 鹿児島中央 ) 北陸新幹線 ( 長野 金沢 ) 北海道新幹線 ( 新青森 新函館 ) 九州新幹線 ( 武雄温泉 諫早 ) Ballasted track Slab track Tokaido shinkansen Sanyo shinkansen Jyoetsu shinkansen Tohoku shinkansen Hokuriku shinkansen Kyusyu shinkansen Hokkaido shinkansen Kyusyu shinkansen Hokuriku shinkansen Tohoku shinkansen Sanyo shinkansen Percentage (%) Percentage of slab track in Shinkansen 44

45 45 Slab track on earth structure Required specification for subgrade Stiffness: K MN/m 3 Density: Higher than 95% of maximum dry density Material for embankment: Gravel, Sandy gravel, Gravelly sand, sand

46 Depth for 改良深さ improvement (m) (m) 46 Subgrade improvement for slab track Subgrade of natural ground should be improved to satisfy K 30 value. h p Improved layer 路床改良層 Subgrade 原地盤 a E 1,μ 1 E 2,μ K 原地盤のK 30 値 (MN/m 3 30 value of natural ground (MN/m ) 3 ) Multi-layered elastic analysis

47 47 Numerical analysis for the design Rail レール Slab 軌道スラブ Rail 軌道パッド pad 鉄筋コンクリート版 CA CAモルタル mortar Reinforced concrete Slab 軌道スラブ Subgrade Train 列車輪重 load Rail レール軌道パッド Rail pad CA mortar CAモルタル鉄筋コンクリート版 Reinforced 路床 concrete Subgrade 路床 Train load Subgrade Train load Rail 列車輪重 レール Slab Rail pad 仮想部材 ( 軌道パッド ) 軌道スラブ仮想部材 (CAモルタル) (a) Parallel to rail direction CA mortar 鉄筋コンクリート版 Reinforced 路床 concrete Subgrade 3 200mm Slab CA mortar 軌道スラブ仮想部材 (CAモルタル) 鉄筋コンクリート版 Reinforced 路床 concrete (b) Perpendicular to rail direction

48 Subgrade (embankment) Concrete roadbed Track Cross section of slab track on earth structure Slab Filling layer (CA mortar) Reinforced concrete Slab track on earth structure (Cutting) Subgrade Well graded crushed stone Slab CA mortar Concrete roadbed Slab Reinforced concrete Prime coat Well graded crushed stone Drainage Layer Subgrade Railway Technical (Groundwork Research Institute or cutting) 48

49 49 Subgrade with N value less than 4 Standard RC roadbed Slab track Reinforced concrete Subgrade (K MN/m 3 ) Well-graded crushed stone If N value of subgarad by SPT test is less than 4, ground improvement is required.

50 50 Integrated RC roadbed Integrated RC roadbed Slab track Surface improvement Clay subgrade(n<4) Reinforced concrete Well-graded crushed stone Ground improvement is necessary in the standard design method Investigation was carried out to apply integrated RC roadbed on soft diluvial clay subgrade. Diluvial clay: Ageing effect, pre-loaded(cutting)

51 51 Ground investigation method Standard penetration test Electric cone penetration test

52 Depth from the surface of concrete roadbed (m) 52 Ground investigation result SPT N-value Surface improvement (Crushed stone) N-value must not be plotted in this area Gravel Clay Silt Clay Gravely clay Clay Silty sand Clayey sand Electric cone penetration test Point resitance q t (MN/m2 ) Pore water pressure u d (kn/m 2 ) Side surface friction f s (kn/m2 ) Silty sand N value Point resistance Pore water pressure Side friction

53 Deviator stress 1-3 (kn/m 2 ) Young's modulus E sec (MN/m 2 ) 53 Triaxial test Confining pressure 100 kn/m 2 Confining pressure 50 kn/m Confining pressure 100 kn/m 2 Confining pressure 50 kn/m 2 50 Confining pressure 20 kn/m 2 50 Confining pressure 20 kn/m Axial strain (%) 0 1E-5 1E-4 1E Axial strain

54 1,000 1,000 In-situ cyclic loading test Up line 2400 Down line Vibration machine Integrated RC roadbed 1,500 Vibration machine Base concrete (Thickness: 200mm) Reinforced concrete 1,500 (Thickness: 300mm) Crushed stone layer (150mm) Subgrade improvement(crushed stone) Subgrade (clay) Gauges Acceleration Pore water Earth pressure Steel stress 11,840 Unit(mm) Subgrade Test site Integrated RC roadbed 54

55 Reinforcing steel stress (N/mm 2 ) Subgrade vertical stress (kn/m 2 ) Acceleration (m/s 2 ) Displacement (mm) Loading test results 120kN, 20Hz, 2x10 6 times loading Acceleration Clay subgrade surface (Just beneath loading point) Concrete roadbed surface (Just beneath loading point) 0.5 2,700 mm distant from loading point Number of cycles (*1000) Displacement Concrete roadbed surface (Just beneath loading point) 2,700 mm distant from loading point Number of cycles (*1000) Reinforcing steel stress Edge of concrete base Just beneath loading point Subgrade vertical stress Surface of subgrade improvement 0.5 2,700 mm distant from loading point Number of cycles (*1000) 5 Clay subgrade surface Number of cycles (*1000) 55

56 RC roadbed displacement (mm) Reinforcing steel stress (N/mm 2 ) Vertical stress (kn/m 2 ) FEM to simulate the loading test Reinforced concrete (Integrated RC roadbed) Vibration machine Well graded crushed stone Clay subgrade Displacement Reinforcing steel stress Vertical stress Loading test FEM analysis Longitudinal direction of track (m) Loading test FEM analysis Transverse direction of track (m) Loading test FEM analysis Surface of subgrade improvement Surface of clay subgrade Depth from RC roadbed surface (m) 56

57 57 Deformation of RC roadbed Standard RC roadbed Integrated RC roadbed Wheel load 85kN Wheel load 85kN Integrated RC roadbed distributes train load widely.

58 58 Vertical stress on subgrade Standard RC roadbed Integrated RC roadbed Integrated RC roadbed reduces stress applied on subgrade.

59 59 Comparison between Standard RC roadbed and integrated RC roadbed Vertical displacement Reinforcing steel stress Subgrade surface stress Clay subgrade surface stress Integrated RC roadbed Standard RC roadbed Integrated / Standard 0.60 mm 0.71 mm MN/m MN/m kN/m kn/m kn/m kn/m

60 60 Summary Bearing capacity of roadbed and subgrade is important factor to reduce the maintenance work of ballasted track. To reduce the settlement of ballasted track at transition zone is an important issue. Asphalt roadbed is widely applied to ballasted track. Slab track is widely constructed on the earth structure in these 20 years. Integrated RC roadbed is a new method to apply slab track on relatively soft subgrade, such as aged diluvial clay.