DGF møde, 29.10.2015 i Øst, DTU, Kgs. Lyngby Geoteknikerens hverdag Multi anchored sheet pile wall in soft clay standing on rock by Kristoffer Lauridsen, COWI Carsten S. Sørensen, COWI Søren Juel Christensen, Aarsleff Ole Møller, Aarsleff NOM Oct 2015 1
Scope 1. To compare design approaches (DAs) and partial coefficients of the Nordic countries (on the agenda for NMGEC7 meeting in Reykjavik on 21-22 nd August 2015) 2. To evaluate different modelling and effect of prestress of anchors NOM Oct 2015 2
Agenda ULS analysis with LEM fixed support elastic support without pre-stress elastic support with pre-stress ULS analysis with FEM with pre-stress SLS analysis with FEM with pre-stress NOM Oct 2015 3
Comparison of DAs and partial coefficients Parameters for LEM analysis Fill: rough wall / = 18/10 kn/m 3 = 35 Soft clay: smooth wall = 6 kn/m 3 c u = 7 kn/m 2 + 1,2 kn/m 2 x z = 0 Till: rough wall / = 10 kn/m 3 = 38 Hydrostatic water pressure NOM Oct 2015 4
Comparison of DAs and partial coefficients NMGEC7 - meeting Reykjavik 2015 Encl. 1 Retaining wall ULS - LEM earth pressure calculation DA3 DK NA, LC4 Soil parameters, M Actions, F Parameter c' cu G Q Partial coefficient 1,2 1,2 1,8 1,0 1,5 Id Soil level depth, z ' ' k ' d rough Earth pressure coefficients [m] [m] [kn/m 3 ] [ ] [ ] k K (k) K p (k) K c (k) 1 Fill 0,0 0,0 18-35 -30,3 1,0 0,26 0,27 1,25 1 Fill -2,0 2,0 18-35 -30,3 1,0 0,26 0,27 1,25 2 Soft clay -2,0 2,0 6 0 0,0 0,0 1,00 1,00 2,00 2 Soft clay -9,0 9,0 6 0 0,0 0,0 1,00 1,00 2,00 3 Till -9,0 9,0 10-38 -33,1 1,0 0,23 0,24 1,17 3 Till -10,0 10,0 10-38 -33,1 1,0 0,23 0,24 1,17 NOM Oct 2015 5
Comparison of DAs and partial coefficients NMGEC7 - meeting Reykjavik 2015 Retaining wall ULS - LEM earth pressure calculation C:\Users\nom\Desktop\NMGEC7\[Nordic LEM earth pressure.xlsx]dk DA3 LC4 DA3 DK NA, LC4 Soil parameters, M Actions, F Parameter c' cu G Q surface load, p k = 10 kn/m 2 Partial coefficient 1,2 1,2 1,8 1,0 1,5 Id Soil level depth, z ' ' k ' d c' k c' d c uk c ud u s' vd p d e d e d + u [m] [m] [kn/m 3 ] [ ] [ ] [kn/m 2 ] [kn/m 2 ] [kn/m 2 ] [kn/m 2 ] [kn/m 2 ] [kn/m 2 ] [kn/m 2 ] [kn/m 2 ] [kn/m 2 ] 1 Fill 0,0 0,0 18-35 -30,3 0 0,0 0 0 15 4,05 4,05 1 Fill -2,0 2,0 18-35 -30,3 0 0,0 0 0 36 15 13,52 13,52 2 Soft clay -2,0 2,0 6 0 0,0 0 0,0 7,0 3,9 0 36 15 43,22 43,22 2 Soft clay -9,0 9,0 6 0 0,0 0 0,0 15,4 8,6 70 78 15 75,89 145,89 3 Till -9,0 9,0 10-38 -33,1 10 8,3 0 70 78 15 11,83 81,83 3 Till -10,0 10,0 10-38 -33,1 10 8,3 0 80 88 15 14,14 94,14 NOM Oct 2015 6
Comparison of DAs and partial coefficients 0,0-1,0-2,0-3,0-4,0-5,0-6,0-7,0-8,0-9,0 LEM earth + water pressure -10,0 0 50 100 150 200 [kn/m 2 ] Total earth- and water pressure = 767 kn/m by DK NA, LC 4 NOM Oct 2015 7
Structural analysis of wall and anchors ULS analysis with LEM fixed support elastic support without pre-stress elastic support with pre-stress AZ 50 I = 121.060 cm 4 /m, g = 253 kg/m 2 W el = 5015 cm 3 /m W pl = 5816 cm 3 /m AZ 19-700 I = 39.380 cm 4 /m, g = 114 kg/m 2 W el = 1870 cm 3 /m W pl = 2206 cm 3 /m NOM Oct 2015 8
Structural analysis of wall and anchors Spring constant of anchors: s E N A E L L N EA L L per anchor per meter horizontal Id Level c Ø0,62" A EA v L EA/L EA/L/c EA/L/c x cos(v) Unit [m] [m] n [mm 2 ] [kn] [ ] [m] [kn/mm] [kn/mm/m] [kn/mm/m] Upper -1,0 3,5 6 900 189.000 45 12,73 14,85 4,24 3,00 Mid -3,5 3,5 6 900 189.000 45 9,19 20,56 5,87 4,15 Lower -7,0 2,4 7 1050 220.500 45 4,24 51,97 21,66 15,31 Note c n horizontal distance between anchors number of Ø0,62" strands, each with 150 mm 2 cross sectional area E = 210.000 N/mm 2 v inclination to horizontal L axial length from anchor point at sheet pile wall down to top of rock at level -10 NOM Oct 2015 9
Structural analysis of wall and anchors Capacity of anchors and max. proof load P p Max possible Proof load P p axial per axial per horizontal Id Level c Ø0,62" N yk N uk anchor meter per meter Unit [m] [m] n [kn] [kn] [kn] [kn/m] [kn/m] Upper -1,0 3,5 6 1494 1674 1339 383 271 Mid -3,5 3,5 6 1494 1674 1339 383 271 Lower -7,0 2,4 7 1743 1953 1562 651 460 Note f yk 1660 MPa yield stress f uk 1860 MPa tensile strength P p proof load min {0,8 f uk ; 0,95 f yk ) x A Structural strength Characteristic NOM Oct 2015 10
LEM: a) stiff support mm -40 Deflection -35-30 -25-20 -15 a) AZ50, stiff support -10-5 0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0 0 5 10 NOM Oct 2015 11
LEM: a) stiff support knm/m 350 Bending moment 300 250 200 150 100 a) Stiff support 50 0 0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0-50 -100-150 NOM Oct 2015 12
LEM: b) elastic support, AZ50, no pre-stress mm -40 Deflection -35-30 -25-20 -15 a) AZ50, stiff support b) AZ50 no PS -10-5 0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0 0 5 10 NOM Oct 2015 13
LEM: b) elastic support, AZ50, no pre-stress knm/m 350 Bending moment 300 250 200 150 100 a) Stiff support b) AZ50 no PS 50 0 0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0-50 -100-150 NOM Oct 2015 14
LEM: c1) Finish pre-stress, AZ50 mm -40 Deflection -35-30 -25-20 -15 a) AZ50, stiff support b) AZ50 no PS c1) AZ50 Fin PS -10-5 0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0 0 5 10 NOM Oct 2015 15
LEM: c1) Finish pre-stress, AZ50 knm/m 350 Bending moment 300 250 200 150 100 50 a) Stiff support b) AZ50 no PS c1) AZ50 Fin PS 0 0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0-50 -100-150 NOM Oct 2015 16
LEM: c2) Finish pre-stress, AZ19-700 mm -40 Deflection -35-30 -25-20 -15-10 a) AZ50, stiff support b) AZ50 no PS c1) AZ50 Fin PS c2) AZ19 FIn PS -5 0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0 0 5 10 NOM Oct 2015 17
LEM: c2) Finish pre-stress, AZ19-700 knm/m 350 Bending moment 300 250 200 150 100 50 a) Stiff support b) AZ50 no PS c1) AZ50 Fin PS c2) AZ19 FIn PS 0 0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0-50 -100-150 NOM Oct 2015 18
LEM: d) DK pre-stress, AZ19-700 mm -40 Deflection -35-30 -25-20 -15-10 a) AZ50, stiff support b) AZ50 no PS c1) AZ50 Fin PS c2) AZ19 FIn PS d) AZ19 DK PS -5 0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0 0 5 10 NOM Oct 2015 19
LEM: d) DK pre-stress, AZ19-700 knm/m 350 Bending moment 300 250 200 150 100 50 a) Stiff support b) AZ50 no PS c1) AZ50 Fin PS c2) AZ19 FIn PS d) AZ19 DK PS 0 0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0-50 -100-150 NOM Oct 2015 20
LEM: Anchor loads, horizontal Anchor / support A1 A2 A3 Rock bolt Total Level -1,0-3,5-7,0-10,0 Unit kn/m kn/m kn/m kn/m kn/m a) stiff, F ULS,d 17 206 422 123 768 b) AZ50, no PS, F ULS,d 107 135 305 220 767 c1) AZ50, Fin PS, P 0 81 101 162 344 c1) AZ50, Fin PS, F ULS,d 99 145 308 215 767 c1) AZ50, Fin PS, F ULS,d /P 0 1,22 1,44 1,90 c2) AZ19, Fin PS, P 0 81 101 162 344 c2) AZ19, Fin PS, F ULS,d 76 149 369 174 768 c2) AZ19, Fin PS, F ULS,d / P 0 0,94 1,48 2,28 d) AZ19, DK PS, P 0 60 100 100 260 d) AZ19, DK PS, F ULS,d 71 165 350 182 768 d) AZ19, DK PS, F ULS,d / P 0 1,18 1,65 3,50 Max P p (horizontal) 271 271 460 R GEO,d = Max P p / 1,3 = 208 208 354 NOM Oct 2015 21
LEM: Anchor loads, horizontal Final load on anchors and rock bolts 0 100 200 300 400 500 kn/m a) stiff, FULS,d b) AZ50, no PS, FULS,d c1) AZ50, Fin PS, FULS,d A1 (-1,0) A2 (-3,5) A3 (-7,0) Rock bolts (-10,0) c2) AZ19, Fin PS, FULS,d d) AZ19, DK PS, FULS,d NOM Oct 2015 22
LEM: Anchor loads, axial + rock bolt Anchor / support A1 A2 A3 Rock bolt Level -1,0-3,5-7,0-10,0 c-c (m) 3,5 3,5 2,4 1,0 Inclination, v ( ) 45,0 45,0 45,0 0,0 Unit kn kn kn kn a) stiff, F ULS,d 84 1020 1432 123 b) AZ50, no PS, F ULS,d 530 668 1035 220 c1) AZ50, Fin PS, P 0 401 500 550 c1) AZ50, Fin PS, F ULS,d 490 718 1045 215 c1) AZ50, Fin PS, F ULS,d /P 0 1,22 1,44 1,90 c2) AZ19, Fin PS, P 0 401 500 550 c2) AZ19, Fin PS, F ULS,d 376 738 1252 174 c2) AZ19, Fin PS, F ULS,d / P 0 0,94 1,48 2,28 d) AZ19, DK PS, P 0 297 495 339 d) AZ19, DK PS, F ULS,d 351 817 1188 182 d) AZ19, DK PS, F ULS,d / P 0 1,18 1,65 3,50 Max P p 1339 1339 1562 R GEO,d = Max P p / 1,3 = 1030 1030 1202 NOM Oct 2015 23
LEM: Anchor loads, axial Final load on anchors and rock bolts 0 200 400 600 800 1000 1200 1400 1600 kn a) stiff, FULS,d b) AZ50, no PS, FULS,d c1) AZ50, Fin PS, FULS,d A1 (-1,0) A2 (-3,5) A3 (-7,0) Rock bolts (-10,0) c2) AZ19, Fin PS, FULS,d d) AZ19, DK PS, FULS,d NOM Oct 2015 24
LEM vs FEM LEM: Limit Equilibrium Method Influence of ration of stiffness between wall and anchors (no stiff support) No soil-structure interaction, constant plastic earth pressure FEM: Finite Element Method compatibility between strains and stresses in the soil elasto-plastic soil structure interaction Plaxis vs. NovaPoint Geocalc? MC model? modelling of rock bolt support ULS with pre-stress? AZ50 vs. AZ19-700? SLS with pre-stress? Final anchor loads (F Serv;k vs. F ULS;d c.f. new Ch. 8) NOM Oct 2015 25
FEM The FEM model: Finland uses NovaPoint Geocalc computer programme s v' M m s a s a 1 n OCR k (1 n ) NOM Oct 2015 26
FEM The FEM model: In the Plaxis model a Mohr-coulomb material model was utilized, with a depth(stress) depended stiffness and strength. NOM Oct 2015 27
FEM The calculation phases: NOM Oct 2015 28
FEM Modelling of the rock bolt: Several approaches where tested: best approach: to applied a fixity at the foot of the sheet pile wall NOM Oct 2015 29
FEM ULS Calculated ULS LK4 anchor forces: c1) AZ50 with Finish prestress A1: 910kN/anchor A2: N/A A3: N/A A1: 901kN/anchor A2: 675kN/anchor A3: N/A A1: 861kN/anchor A2: 598 kn/anchor A3: 545 kn/anchor NOM Oct 2015 30
FEM ULS Bending moment during excavation 0-100 0 100 200 300 400 500 600 700-2 BENDING MOMENT [KNM/M] -4 DEPTH [M] -6-8 1. excav 2. excav 3. excav Final excavation -10-12 NOM Oct 2015 31
Comparison between LEM and FEM results AZ 50 with Finish prestress, final stage axial anchor loads horizontal (shear) force on rock bolt Pre-stress P0 LEM ULS FEM ULS FEM SLS A1 401 400 400 A2 500 500 500 A3 550 550 550 Final Anchor Loads Pa LEM ULS FEM ULS FEM SLS A1 490 861 663 A2 718 598 620 A3 1045 545 562 Rockbolt 0 kn/m 0 kn/m 0 kn/m Rockbolt 215 kn/m 433 kn/m 319 kn/m NOM Oct 2015 32
Comparison between LEM and FEM results Bending moment at the final stage (AZ50 with Finish pre-stress) 0-2 0 100 200 300 400 500 600 [knm/m] Depth [m] -4-6 -8 FEM ULS LEM ULS SLS FEM -10-12 NOM Oct 2015 33
FEM Deformations during excavation 0 0,00 0,01 0,02 0,03 0,04 0,05 0,06 0,07 Displacement [m] -2 Depth [m] -4-6 -8 1. excav 2. excav 3. excav Final excav -10-12 NOM Oct 2015 34
Findings Big effect of pre-stress on deformation by LEM, not by FEM Effects of very soft clay, near failure during excavations by FEM Bending moments by FEM twice the moments by LEM Adverse tendency of anchor loads by LEM compared to FEM Max at the bottom by LEM. Max at the top by FEM. The reason for this is: in spite of the relatively stiff (short) lower anchors, the effect of staged construction by FEM and the wall rotating (~ rigid) around the foot (fixed by the rock bolt) leads to bigger upper anchor loads and the LEM is only carried out for the final stage with no superposed section forces (pre bending) from previous stages. FEM: SLS anchor loads > ULS anchor loads for mid and lower anchors NOM Oct 2015 35