Multi anchored sheet pile wall in soft clay standing on rock

Transcription

1 DGF møde, 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

2 Scope 1. To compare design approaches (DAs) and partial coefficients of the Nordic countries (on the agenda for NMGEC7 meeting in Reykjavik on nd August 2015) 2. To evaluate different modelling and effect of prestress of anchors NOM Oct

3 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

4 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

5 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, ,3 1,0 0,26 0,27 1,25 1 Fill -2,0 2, ,3 1,0 0,26 0,27 1,25 2 Soft clay -2,0 2, ,0 0,0 1,00 1,00 2,00 2 Soft clay -9,0 9, ,0 0,0 1,00 1,00 2,00 3 Till -9,0 9, ,1 1,0 0,23 0,24 1,17 3 Till -10,0 10, ,1 1,0 0,23 0,24 1,17 NOM Oct

6 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, ,3 0 0, ,05 4,05 1 Fill -2,0 2, ,3 0 0, ,52 13,52 2 Soft clay -2,0 2, ,0 0 0,0 7,0 3, ,22 43,22 2 Soft clay -9,0 9, ,0 0 0,0 15,4 8, ,89 145,89 3 Till -9,0 9, ,1 10 8, ,83 81,83 3 Till -10,0 10, ,1 10 8, ,14 94,14 NOM Oct

7 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, [kn/m 2 ] Total earth- and water pressure = 767 kn/m by DK NA, LC 4 NOM Oct

8 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 = cm 4 /m, g = 253 kg/m 2 W el = 5015 cm 3 /m W pl = 5816 cm 3 /m AZ I = cm 4 /m, g = 114 kg/m 2 W el = 1870 cm 3 /m W pl = 2206 cm 3 /m NOM Oct

9 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, ,73 14,85 4,24 3,00 Mid -3,5 3, ,19 20,56 5,87 4,15 Lower -7,0 2, ,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 = 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

10 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, Mid -3,5 3, Lower -7,0 2, 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

11 LEM: a) stiff support mm -40 Deflection a) AZ50, stiff support ,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10, NOM Oct

12 LEM: a) stiff support knm/m 350 Bending moment a) Stiff support ,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10, NOM Oct

13 LEM: b) elastic support, AZ50, no pre-stress mm -40 Deflection a) AZ50, stiff support b) AZ50 no PS ,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10, NOM Oct

14 LEM: b) elastic support, AZ50, no pre-stress knm/m 350 Bending moment a) Stiff support b) AZ50 no PS ,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10, NOM Oct

15 LEM: c1) Finish pre-stress, AZ50 mm -40 Deflection a) AZ50, stiff support b) AZ50 no PS c1) AZ50 Fin PS ,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10, NOM Oct

16 LEM: c1) Finish pre-stress, AZ50 knm/m 350 Bending moment 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, NOM Oct

17 LEM: c2) Finish pre-stress, AZ mm -40 Deflection 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, NOM Oct

18 LEM: c2) Finish pre-stress, AZ knm/m 350 Bending moment 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, NOM Oct

19 LEM: d) DK pre-stress, AZ mm -40 Deflection 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, NOM Oct

20 LEM: d) DK pre-stress, AZ knm/m 350 Bending moment 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, NOM Oct

21 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 b) AZ50, no PS, F ULS,d c1) AZ50, Fin PS, P c1) AZ50, Fin PS, F ULS,d c1) AZ50, Fin PS, F ULS,d /P 0 1,22 1,44 1,90 c2) AZ19, Fin PS, P c2) AZ19, Fin PS, F ULS,d c2) AZ19, Fin PS, F ULS,d / P 0 0,94 1,48 2,28 d) AZ19, DK PS, P d) AZ19, DK PS, F ULS,d d) AZ19, DK PS, F ULS,d / P 0 1,18 1,65 3,50 Max P p (horizontal) R GEO,d = Max P p / 1,3 = NOM Oct

22 LEM: Anchor loads, horizontal Final load on anchors and rock bolts 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

23 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 b) AZ50, no PS, F ULS,d c1) AZ50, Fin PS, P c1) AZ50, Fin PS, F ULS,d c1) AZ50, Fin PS, F ULS,d /P 0 1,22 1,44 1,90 c2) AZ19, Fin PS, P c2) AZ19, Fin PS, F ULS,d c2) AZ19, Fin PS, F ULS,d / P 0 0,94 1,48 2,28 d) AZ19, DK PS, P d) AZ19, DK PS, F ULS,d d) AZ19, DK PS, F ULS,d / P 0 1,18 1,65 3,50 Max P p R GEO,d = Max P p / 1,3 = NOM Oct

24 LEM: Anchor loads, axial Final load on anchors and rock bolts 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

25 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

26 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

27 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

28 FEM The calculation phases: NOM Oct

29 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

30 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

31 FEM ULS Bending moment during excavation BENDING MOMENT [KNM/M] -4 DEPTH [M] excav 2. excav 3. excav Final excavation NOM Oct

32 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 A A A Final Anchor Loads Pa LEM ULS FEM ULS FEM SLS A A A Rockbolt 0 kn/m 0 kn/m 0 kn/m Rockbolt 215 kn/m 433 kn/m 319 kn/m NOM Oct

33 Comparison between LEM and FEM results Bending moment at the final stage (AZ50 with Finish pre-stress) [knm/m] Depth [m] FEM ULS LEM ULS SLS FEM NOM Oct

34 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] excav 2. excav 3. excav Final excav NOM Oct

35 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