Paolo Perazzelli Pini Swiss Engineers, Zurich Bolt reinforcement of the tunnel face

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1 Paolo Perazzelli Pini Swiss Engineers, Zurich Bolt reinforcement of the tunnel face Kolloquium Bauhilfsmassnahmen im Tunnelbau ETH Zürich

2 Outline Introduction Analysis method On the effect of the design parameters grounds above the water table grounds below the water table (drained and undrained) Conclusions

3 Introduction General overview Ground reinforcement using bolts is a very effective measure for stabilizing the face in conventional tunnelling

4 Introduction General overview A pipes umbrella 9.8 m 12 m Detail 1 face bolt 1.25 m excavation round A installation interval (l) 16 total length of the bolt (L) A-A bolting density (n) Detail 1 diameter of the borehole (d) ground shotcrete and steel sets face bolt grout diameter of the bolt (d b ) bolt

5 Introduction Research at the ETH Zurich Anagnostou, G., Serafeimidis, K., The dimensioning of tunnel face reinforcement. World Tunnel Congress 2007 (Prague) Serafeimidis, K., Ramoni, M., and Anagnostou, G. (2007). Analysing the stability of reinforced tunnel faces. Europ. Conf. on Soil Mech. and Geotech. Eng. (Rotterdam) Perazzelli, P., Anagnostou, G., Stress analysis of reinforced tunnel faces and comparison with the limit equilibrium method. Tunnel. Undergr. Space Techn. 38, Anagnostou, G., Perazzelli, P., Analysis method and design charts for bolt reinforcement of the tunnel face in cohesive-frictional soils. Tunnel. Undergr Space Techn. 47, Perazzelli, P., Anagnostou, G., Analysis method and design charts for bolt reinforcement of the tunnel face in purely cohesive soils. Journal of geotechnical and geoenvironmental engineering, 143 (9), American Society of Civil Engineers. Perazzelli, P., Cimbali, G., Anagnostou, G., Stability under seepage flow conditions of a tunnel face reinforced by bolts. EUROCK 2017 (Ostrava)

6 Introduction Relevant design parameters Surface load Unit weight of the ground Level of the water table Overburden Shape and dimension of the tunnel Unsupported span Load Strength of the ground (c,, s u ) Bond strength of bolt/grout and grout/ground Tensile resistance of the bolt Bolting density Bolting type (diameter, with/without plate, ) Bolting length and installation interval Resistance

7 Introduction Relevant design parameters Surface load Unit weight of the ground Level of the water table Overburden Shape and dimension of the tunnel Unsupported span Load Strength of the ground (c,, s u ) Bond strength of bolt/grout and grout/ground Tensile resistance of the bolt Bolting density Bolting type (diameter, with/without plate, ) Bolting length and installation interval Resistance

8 Introduction Relevant design parameters (a) Large installation interval Total lenght L = 12 m

9 Introduction Relevant design parameters (a) Large installation interval Total lenght L = 12 m Installation interval l = 8 m

10 Introduction Relevant design parameters (a) Large installation interval Total lenght L = 12 m New bolts Installation interval l = 8 m Overlapping L = 4 m

11 Introduction Relevant design parameters (a) Large installation interval Total lenght L = 12 m New bolts Installation interval l = 8 m Overlapping L = 4 m (b) Small installation interval Total lenght L = 12 m New bolts Installation interval l = 3 m Overlapping L1 = 3 m, L2 = 6 m, L3 = 9 m

12 Analysis method General concept - Failure mechanism Ground above the water table Ground below the water table drained Ground below the water table undrained

13 Analysis method General concept - Failure mechanism Limit equilibrium condition Trapdoor load V trap = Bearing capacity of wedge V res 1 H V trap 2 3 B Depth of cover (h)

14 Analysis method General concept - Failure mechanism Ground above the water table Ground below the water table drained Ground below the water table undrained

15 Analysis method Ground above the water table Trapdoor load Limit equilibrium of slices (silo theory) Ground surface c,, dry dn dts x = p y dn dt dt V trap Bearing capacity of wedge Limit equilibrium of slices x = w y c,, dry

16 Analysis method Ground above the water table Comparison with experimental results and other methods Ground surface c =0, h s [kpa] s D p = w = 1 [ ]

17 Analysis method General concept - Failure mechanism Ground above the water table Ground below the water table drained Ground below the water table undrained

18 Analysis method Ground below the water table drained Trapdoor load Limit equilibrium of slices (silo theory) Ground surface c,, dn dts x = p y dn dt dt V trap df y Bearing capacity of wedge Limit equilibrium of slices x = w y c,, df x

19 Analysis method General concept - Failure mechanism Ground above the water table Ground below the water table drained Ground below the water table undrained

20 Analysis method Ground below the water table undrained Trapdoor load Upper bound approach s u, sat Bearing capacity of wedge Limit equilibrium of the entire wedge s u, sat

21 Analysis method Ground below the water table undrained Comparison with experimental results and other methods Ground surface s u h s D

22 Analysis method Support pressure given by the bolts

23 Analysis method Support pressure given by the bolts s = n*min [F t, max(min(d m, d b g ) a, F p ), min(d m, d b g ) a(l -a)] Bearing capacity of the bolt plate Tensile resistance of the bolt Bolting density

24 Analysis method Support pressure given by the bolts s = n*min [F t, max(min(d m, d b g ) a, F p ), min(d m, d b g ) a(l -a)] Pull-out resistance inside the sliding wedge a Pull-out resistance outside the sliding wedge L -a m m d b overlapping length L

25 Analysis method Support pressure given by the bolts z 2 z s [kpa] L-l=3m n=1 bolt/m 2 L=12 m l=9 m

26 Analysis method Support pressure given by the bolts z 2 35 z s [kpa] L-l=3m n=1 bolt/m 2 L=12 m l=9 m

27 Analysis method Support pressure given by the bolts z 2 z s [kpa] L-l=3m n=1 bolt/m 2 L=12 m l=9 m L-2l=3m L-l=7.5m n=1 bolt/m 2 L=12 m l=4.5 m

28 Analysis method Computation of the minimum required number of bolts

29 Analysis method Computation of the minimum required number of bolts - For fixed failure mechanism i, required density of bolts n i is such that limit equilibrium condition fulfilled - Minimum required number of bolts n cr = max (n i ) V trap s (n)

Analysis method Computation of the minimum required number of bolts For the special case of a homogeneous ground with uniform face reinforcement Limit

30 Analysis method Computation of the minimum required number of bolts For the special case of a homogeneous ground with uniform face reinforcement Limit equilibrium condition c =0, c,, z n = n( z f ) (closed form solution) z f n cr = max [n( z f )] n (bolts / m 2 ) simple optimization problem (one-variable)

Analysis method Computation of the minimum required number of bolts For the most general case of heterogeneous ground and arbitrary bolt distribution c =0, N = min n k A k c 3, 3, 3 V res

31 Analysis method Computation of the minimum required number of bolts For the most general case of heterogeneous ground and arbitrary bolt distribution c =0, N = min n k A k c 3, 3, 3 V res ( z f ) V trap ( z f ) V( z f, z i ) 0 n 2 z z i c 2, 2, 2 complex optimization problem (multi-variable): numerical solution based on the simplex method n 1 z f c 1, 1, 2 n (bolts / m 2 )

32 Analysis method Design tools For the special case of a homogeneous ground with uniform face reinforcement Design charts

33 Analysis method Design tools For the special case of a homogeneous ground with uniform face reinforcement Tunnel+ (free App for smartphones) Tunnel+

34 Analysis method Design tools For the most general case of heterogeneous ground and arbitrary bolt distribution Standalone computer application with Graphical User Interface

35 On the effect of the design parameters Grounds above the water table

36 On the effect of the design parameters Grounds above the water table Overburden and shape of the face n n 2 cr [bolts/m 2 ] ] = 25 A 8 m A B C c =0, = 25 4 m c = var 8 m = 20 kn/m 3 8 m 8 m 4 m h = var 0.8 h (m) = z B C 8 4 n (bolts / m 2 ) L = 12 m l = 9 m, m = 150 kpa, d = 114 mm c [kpa]

37 On the effect of the design parameters Grounds above the water table Overburden and shape of the face 53 bolts = = 22 n n 2 cr [bolts/m 2 ] ] = 25 A 8 m A B C 4 m 8 m 8 m 8 m 4 m c =0, = 25 c = 5 kpa = 20 kn/m 3 h = 0.8 h (m) = z B C 8 4 n (bolts / m 2 ) L = 12 m l = 9 m, m = 150 kpa, d = 114 mm c [kpa]

38 On the effect of the design parameters Grounds above the water table Installation interval n cr [bolts/m 2 ] = 25 8 m 8 m c =0, = 25 c = var = 20 kn/m 3 h = 0.8 L = 12m l = 9m z L = 12m l = 4.5m n (bolts / m 2 ) L = 12 m l = var, m = 150 kpa, d = 114 mm c [kpa]

39 On the effect of the design parameters Grounds above the water table Installation interval meters of bolts installed per linear meter of tunnel m/m n cr [bolts/m 2 ] = 25 8 m 8 m c =0, = 25 c = var = 20 kn/m 3 h = 0.8 L = 12m l = 9m z m/m L = 12m l = 4.5m n (bolts / m 2 ) L = 12 m l = var, m = 150 kpa, d = 114 mm c [kpa]

40 On the effect of the design parameters Grounds above the water table Spatial bolt distribution 108 m 8 m 10 m z H 3H/4 H/2 H/ z H 2H/3 H/ z H H/2 c =0, = 25 c = 10 kpa = 20 kn/m e= 1 m z h = 30 m L = 12 m l = 6 m, m = 150 kpa, d = 114 mm n (bolts / m 2 ) n (bolts / m 2 ) n (bolts / m 2 ) n (bolts / m 2 ) 28 bolts 29 bolts 34 bolts 35 bolts

41 On the effect of the design parameters Grounds below the water table - drained

42 On the effect of the design parameters Grounds below the water table - drained Drainage boreholes 8 m 88 m c =0, = var c = var t = 0 = 12 kn/m 3 h = 8 m z h 0 = 2H L = 16 m l = 8 m, m = 150 kpa, d = 114 mm Without advance drainage With advance drainage n (bolts / m 2 ) 35 bolts

43 On the effect of the design parameters Grounds below the water table - undrained

44 On the effect of the design parameters Grounds below the water table - undrained Over-consolidation ratio

45 On the effect of the design parameters Grounds below the water table - undrained Overburden OCR = 1.0

46 On the effect of the design parameters Grounds below the water table - undrained Overlapping length OCR = 1.0

47 Conclusions Experience and predictions prove that ground reinforcement using bolts is a very effective measure for stabilizing the tunnel face Excavation method and installation interval of the bolts affect significantly the required quantity of bolts (Top heading and Bench excavation method and small installation intervals allow to reduce the quantity of bolts) Big overlapping length are required in undrained soils Drainage boreholes are required in soils below the water table under drained conditions The uniform distribution is not the optimal one. A computational method was developed for the optimization of the face reinforcement

48 Paolo Perazzelli Pini Swiss Engineers, Zurich Thank you for the attention!

"The dimensioning of tunnel face reinforcement"

The dimensioning of tunnel face reinforcement Institute for Geotechnical Engineering Tunnelling and Rock Engineering Group Georg Anagnostou & Konstantinos Serafeimidis Institute for Geotechnical Engineering, ETH Zurich, Switzerland "The dimensioning