Effects of tunnel construction on nearby pile foundations 5

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Journal of Geotechnical and Geoenvironmental engineering, September issue, pp. 764-774. 332 E.2 Geology and ground conditions From the soil investigation carried out, the structure is generally founded on the Old Alluvium with the degree of weathering varying with depth. The Old Alluvium is an alluvial deposit that has been variably cemented and has the strength of weak rock (LTA, 2001). The Old Alluvium which composed of silty sandy clay can be classified into five classes, i.e. OA1 to OA5 which are defined by the SPT-N of 100 respectively. However, the 7m of soil below the basement consists of mixed layers of fluvial sand (F1) and clay (F2), marine clay (M) and fill material, typically the Kallang Formation (Fig. E.2). Ground water is close to the original ground level. The piles are generally founded on the dense Old Alluvium material (i.e. OA5). Material of OA3 to OA5 was encountered during the north bound tunnel advancement whereas the south bound tunnel encountered only OA5 material. E.3 Construction sequence The tunnels were driven by two earth pressure balance machine (EPBM) manufactured by Herrenknecht and has an outer diameter of 6.58m and length of 8m. When the EPBM were under the building, good soil condition was encountered, therefore leading to good advance rate (i.e. approximately 50mm/min) and progress rate (up to 10 rings/day). A face pressure of 150kPa was maintained in the chamber to provide face stability although it is realised that the material encountered is generally stable and has a considerable stand-up time even without the pressure. The first EPBM (for North bound tunnel) was launched from Millenia Station on the 22 January 2003 and advance towards the Convention Centre Station. This is followed by the second EPBM (for South bound tunnel) which was launched two months later from the same launching shaft. The construction of the tunnels were scheduled such that the lower tunnel was bored first and followed by the upper tunnel to minimise the effect on the structure. Initially the tunnels started 347 off in a horizontally parallel position for length of approximately 230m (Figure E.3a). However, the tunnels were then gradually shifted into a vertically stacked alignment when reaching the link structure due to space constraint from the pile foundation (Figure E.3b). Pan Pacific Hotel ** Marina Square ** Raffles Boulevard SB tunnel NB tunnel (a) Pan Pacific Hotel ** Pedestrian Link Link structure Marina Square ** Road Car park Link NB tunnel SB tunnel SB tunnel NB tunnel *Not to scale ** Foundation not illustrated (b) Figure E.3 Alignment of tunnels (a) before reaching structure (b) under structure 348 TOWARDS MILLENIA STATION 8500 CL OF TUNNEL PG1 8600 8500 10600 P2 P1 P3 P4a P4b PG15 P5 P6 PG2 PG16 PG11 8600 PG7 P7 8600 PG4 PG9 PG17 PG12 PG18 8600 PG13 PG5 PG19 PG10 8600 PAN PACIFIC HOTEL PG8 MARINA SQUARE Tunnelling direction PG3 P8 P9 PG14 P10 P11 P12 P13 PG6 P14 PG20 TOWARDS CONVENTION CENTRE STATION 8500 10600 8500 LEGEND EXISTING PILE EXISTING PILE TO BE CUT-OFF Figure E.4 Foundation layout of the link structure 349 Figure E.4 shows the foundation layout of the building and the tunnel location. One of the main challenges in this section was the intersection of three numbers of piles with the upper tunnel (Figure E.5). Two piles were encountered at the front wall and one pile at the rear wall of the structure. Initially, only two piles were expected. However, an unexpected H-pile of 375mm x 375mm was encountered exactly adjacent to one of the piles to be expected during tunnelling. Approximately 3m length of each pile was to be removed to allow the tunnel machine to pass through. The EPBM was stopped allowing the piles to be cut-off manually. To avoid loading on the tunnel lining, polystyrene foam block was attached to the base of the pile (Figure E.6). Figure E.7 shows the view inside the chamber during pile removal and Figure E.8 shows the scrap piles 441mm BASEMENT LEVEL 98.916 EXISTING PILE TO CUT TO 300mm ABOVE PROPOSED TUNNEL LINING 416mm 391mm 365mm EXISTING PILE TUNNEL IT SHALL BE THE RESPONSIBILITY OF THE CONTRACTOR TO FURNISH STEEL SHELLS OF SUFFICIENT STRENGTH AND THICKNESS TO ENABLE THEM TO BE DRIVEN TO THE REQUIRED PENETRATION OR RESISTANCE WITHOUT DAMAGE DUE TO IN-PLACE SOIL PRESSURES. THE SHELL FOR THE LOWER 1/3 OF THE PILE SHALL BE AT LEAST 14 CAGE 19mm (3/4") THICK CLOSURE PLATE SECURELY WELDED TO PIPE 3658 (12'0") SECTIONS AS REQUIRED 340mm LENGTH AS REQUIRED CONCRETE FILL SHALL BE NORMAL WEIGHT AND HAVE A MINIMUM 28 DAY COMPRESSIVE CUBE STRENGTH OF 4.3 N/mm (6250 PSI) ROAD LEVEL 103.15 750 (TYPICAL) after removal. Figure E.5 Detailed of Raymond step-tapered pile 350 PIPE PILE STEEL H-PILE PIPE PILE STEEL H-PILE POLYFOAM BLOCK 0.4m 3m UPPER TUNNEL (NB) CL (a) UPPER TUNNEL (NB) CL (b) Figure E.6 Pile cut-off at one of the wall section (a) before (b) after Raymond Step-taper pile Figure E.7 A view inside the chamber during pile removal 351 Raymond Step-Taper pile (a) Steel H-pile (b) Figure E.8 Scrap of removed piles (a) Raymond Step-Taper pile (b) Steel H-pile 352 E.4 Monitoring scheme and results As part of the stringent requirement laid by the Land Transport Authority (LTA), the building was fully instrumented. Settlement markers were installed in almost all the columns at the basement level of the structure. In addition, tilt meters and tape extensometers were also installed in some of the columns and walls. During the advancement of the SB tunnel, the maximum column settlement recorded is only up to 3mm. Subsequently, after the NB tunnel has advanced, the maximum accumulated settlement is up to 7mm. Figure E.9 plots all the columns settlements in three-dimensional visualisation for cases when the face of the second EPBM (for NB tunnel) was (a) at the front wall of structure (b) at the rear wall of structure (c) at a distance of 10 times tunnel diameter away from the rear wall. With relatively good ground conditions and well controlled tunnelling procedure, the maximum and differential measured settlements were kept small. 353 PAN PACIFIC HOTEL MARINA SQUARE POSITION OF EPBM MAX. 2mm OCT 2003 (a) PAN PACIFIC HOTEL MARINA SQUARE MAX. 4.4mm 20 OCT 2003 (b) PAN PACIFIC HOTEL POSITION OF EPBM MARINA SQUARE MAX. 7mm 11 NOV 2003 (c) Figure E.9 Measured building settlement for NB tunnel advancement (a) EPBM at front wall (b) EPBM at rear wall (c) EPBM leaving the structure 354 APPENDIX F PLANE STRAIN FE ANALYSIS OF CENTRIFUGE TESTS Three centrifuge tests were carried out by Loganathan (1999) to study the response of pile foundation due to tunnelling. All the magnitudes reported herein are based on the prototype value. The only difference between each test was the tunnel depth i.e. 15m (Test 1), 18m (Test 2) and 21m (Test 3). The pile diameter and length was 0.8m and 18m respectively. A single pile and 2x2 pile group were arranged on each side of the tunnel. The distance between tunnel axis and the centre of single pile was 5.5m. The same distance was also arranged between tunnel axis and centre of the front pile of 2x2 pile group. Piles in the pile group were spaced at a distance of 2.5m which is equivalent to three times pile diameter. Pre-tunnelling loading of 1340kN and 4550kN were applied to the single pile and pile group respectively. A schematic diagram of the tests set-up is shown in Figure F.1. All the tests were carried out in stiff Kaolin clay with undrained shear strength typically varied from 25kPa at the surface to 100kPa at the 25m.b.g.l. Volume loss was simulated by removing the silicone oil in the model uniformly and therefore represents a plane strain tunnel. Pile cap thickness = 1m Cap-soil gap = 0.1m 4m Ground surface Test : Y1 = 15m Test : Y1 = 18m Test : Y1 = 21m Y1 Lp = 18m 30m Dp = 0.8m 2.1m Test Test Test 2.5m D = 6m 32.5m 32.5m Figure F.1 Schematic diagram showing the position and dimension of tunnel and piles in the centrifuge tests (prototype dimension) 355 FE analysis was carried out on two tests, i.e. Tests and 3. Dimension of the mesh followed exactly the dimension of centrifuge strongbox in prototype scale. Exploiting the plane of symmetry at tunnel axis, dimension of mesh was reduced to 32.5m x 30m in horizontal and vertical axis respectively. The type of element and node are similar as used in all the studies described above. Besides, same soil model was also adopted. A normalised soil stiffness, Gmax/p’ of 500 was assigned. The analysis was carried out in three steps:- • Step 1: Generating the initial stress in soil • Step 2: Pile foundation is wished-in-place and loaded • Step 3: Tunnel is allowed to deform under convergence confinement method to the required volume loss of 1% (undrained) Following are the required parameters to determine the modification factor from calibration charts:- • Pile foundation configuration = Single pile and 2x2 pile group • Loading condition = With pre-tunnelling loading (1340kN for single pile and 4550kN for pile group) • Pile diameter, Dpile = 0.8m • Pile length to tunnel depth ratio, Lp/Htun = 1.2 (Test 1) & 0.86 (Test 3) • Pile-tunnel distance, Xpile = 5.5m (or Xpile/Dtun = 0.92) • Pile stiffness, Epile = 200GPa • Tunnel diameter, Dtun = 6m (single tunnel) • Tunnel volume loss, VL = 1% • Normalised soil shear stiffness, Gmax/p’ = 500 According to the above parameters, the tests fall into Condition (single pile with pre-tunnelling loading) and Condition (pile group with pre-tunnelling loading). As described in Section 6.6.4, 356 the conditions coupled with Lp/Htun of 1.0 or less not allow convergence between 2-D and 3-D analyses. A set of Ewall(2D) was assumed as sensitivity studies. Figures F.2a, b and c show the predicted and measured greenfield surface settlement, lateral soil movement and soil settlement of Test respectively. No pile was yet included in the analysis so that the greenfield model can be first compared. Very good match was obtained for both magnitude and trend despite the simple model adopted. Figures F.3a and b show the single pile lateral deflection and pile head settlement of Test respectively. Five analyses were carried out with varying pile stiffness modification factor, i.e. 0.33, 0.46, 0.63, 1.0 and 1.5 which were computed from the equivalent pile stiffness method. To be noted, the modification factor has no influence on the pile response. This agrees with the calibration charts in Section 6.6.2 where no convergence was observed for the similar condition. However, both the pile lateral deflection and settlement were well predicted with the model. In the analysis of pile group of Test 1, the lateral deflection of front pile and pile head settlement are shown in Figures F.4a and b respectively. In this situation, the predicted profile of lateral deflection was off track from the measured. The lateral deflection is higher at the pile head instead of the pile tip. This is likely to be the restraint from pile length below tunnel springline and the inability of soil flow above the tunnel which causes large displacement on the upper length of piles. Besides, the 2-D analysis over-predicts pile head settlement by approximately two times (Figure F.4b). For Test 3, the predicted and measured greenfield soil movement are shown in Figure F.5. Again, all the predicted trend and magnitude match very well with the measured. However, for the single pile response, FE analysis could not resemble the trend of measured lateral deflection profile 357 (Figure F.6a). But the predicted maximum deflection is very close to the measured. Furthermore, the pile head settlement is over-predicted by about 2.6 times (Figure F.6b). The pile group prediction for Test is also notably off sight from the measurement. Figures F.7a and b show the lateral deflection of front pile and pile head settlement respectively. A more flexible profile of deflection was observed in the FE analysis whereas the measurement shows the pile to move in a rigid form by translation. Besides, the pile settlement is highly over-predicted by four to five times (Figure F.7b). Even a high increment of pile stiffness (i.e. modification factor of 3.0) could not arrest the large settlement. 358 Distance from tunnel axis (m) 10 15 20 25 30 35 Surface settlement (mm) -5 Surface settlement -10 -15 TUNNEL 2-D FE analysis Measure data (Test 1, Greenfield, VL = 1%) -20 (a) Lateral soil movement at 5.5m from tunnel axis (mm) -2 -4 -6 Soil settlement on tunnel axis (mm) -8 10 10 15 Depth (m.b.g.l.) Depth (m.b.g.l.) 15 Tunnel springline -10 -20 -40 Tunnel springline Horizontal soil movement at 5.5m from tunnel axis Settlement along tunnel axis 20 20 -30 TUNNEL TUNNEL 2-D FE analysis 25 5.5m Measured data (Test 1, Greenfield, VL=1%) (b) 2-D FE analysis 25 Measured data (Test 1, Greenfield, VL=1%) (c) Figure F.2 Comparison between predicted and measured greenfield soil movement of Test (a) Surface settlement (b) Subsurface lateral soil movement (c) Subsurface soil settlement 359 Pile lateral deflection (mm) -2 -3 -4 -1 -5 -6 -10 Test - Single pile -9 1340KN TEST -8 Pile head settlement (mm) Depth (m.b.g.l.) TUNNEL 10 15 Tunnel springline Measured -7 -6 -5 -4 -3 -2 20 -1 2-D factor = 0.330 2-D factor = 1.000 2-D factor = 1.500 2-D factor = 0.460 2-D factor = 0.628 Measured data (Test 1, Single pile) 25 0.33 0.46 0.63 1.00 1.50 Pile stiffness modification factor (a) (b) Figure F.3 Comparison between predicted and measured single pile response of Test (a) Pile lateral deflection (b) Pile head settlement Pile lateral deflection (mm) -5 -10 -20 -15 Test (Pile group) - Front pile Rear pile -18 -16 10 15 Tunnel springline Tunnel Rear Front Sym 20 Pile head settlement (mm) Depth (m.b.g.l.) -14 -12 -10 Measured -8 -6 -4 -2 2.1m 25 2-D factor = 1.000 2-D factor = 0.196 2-D factor = 1.500 Measured data (Test 1, 2x2 pile group, Front) 0.196 1.000 1.500 Pile stiffness modification factor (a) (b) Figure F.4 Comparison between predicted and measured pile group response of Test (a) Pile lateral deflection (b) Pile head settlement 360 Distance from tunnel axis (m) 10 15 20 25 30 35 Surface settlement (mm) -5 Surface settlement -10 TUNNEL 2-D FE analysis Measure data (Test 3, Greenfield, VL = 1%) -15 (a) Soil settlement on tunnel axis (mm) Lateral soil movement at 5.5m from tunnel axis (mm) -1 -2 -3 -4 -5 -6 -5 -10 -15 -20 -25 Horizontal soil movement at 5.5m from tunnel axis Settlement along tunnel axis TUNNEL TUNNEL 10 10 Depth (m.b.g.l.) Depth (m.b.g.l.) 5.5m 15 20 15 20 Tunnel springline Tunnel springline 25 25 2-D FE analysis 2-D FE analysis 30 Measured data (Test 3, Greenfield, VL=1%) (b) 30 Measured data (Test 3, Greenfield, VL=1%) (c) Figure F.5 Comparison between predicted and measured greenfield soil movement of Test (a) Surface settlement (b) Subsurface lateral soil movement (c) Subsurface soil settlement 361 Pile lateral deflection (mm) -2 -4 -25 -6 Test - Single pile -20 Pile head settlement (mm) Depth (m.b.g.l.) 10 1340KN TEST 15 -15 Measured -10 20 -5 Tunnel springline TUNNEL 25 2-D factor = 1.000 2-D factor = 0.460 2-D factor = 3.000 2-D factor = 0.152 Measured data (Test 3, Single pile) 30 0.15 0.46 1.00 3.00 Pile stiffness modification factor (a) (b) Figure F.6 Comparison between predicted and measured single pile response of Test (a) Pile lateral deflection (b) Pile head settlement Pile lateral deflection (mm) -2 -4 -6 -8 -10 -40 -12 Test (Pile group) - Front pile Rear pile -35 Sym 2.1m Depth (m.b.g.l.) 10 15 20 -30 Pile head settlement (mm) Tunnel Rear Front -25 -20 -15 Measured -10 Tunnel springline -5 25 30 2-D factor = 0.065 2-D factor = 0.196 2-D factor = 1.000 2-D factor = 3.000 Measured data (Test 3, 2x2 pile group, Front) 0.065 0.196 1.000 3.000 Pile stiffness modification factor (a) (b) Figure F.7 Comparison between predicted and measured pile group response of Test (a) Pile lateral deflection (b) Pile head settlement 362 [...]... Single pile (Single tunnel) Single pile (Twin tunnel) 1-row pile (Single tunnel) 1-row pile (Twin tunnel) D pile = 1.2m, E pile = 28GPa 300 250 G max /P' = 800, V L = 1.81% Tunnel- pile dist = 5. 45m Pile lateral deflection 200 150 2D response = 3D single pile response 50 0.16 100 0.08 Response of 2D to 3D analysis (%) 350 0 0.0 0.1 0.2 0.3 0.4 0 .5 Pile stiffness ratio, Ewall(2D) / Epile(3D) (a) Single pile. .. Single pile (Single tunnel) Single pile (Twin tunnel) 1-row pile group (Single tunnel) 1-row pile group (Twin tunnel) D pile = 1.2m, E pile = 28GPa 300 250 G max /P' = 800, V L = 1.81% Tunnel- pile dist = 5. 45m Pile head settlement 200 150 2D response = 3D single pile response 100 0 0.0 0.1 0. 25 50 0.12 Response of 2D to 3D analysis (%) 350 0.2 0.3 0.4 0 .5 Pile stiffness ratio, Ewall(2D) / Epile(3D) (b) Figure... foundation configuration = Single pile and 2x2 pile group • Loading condition = With pre-tunnelling loading (1340kN for single pile and 455 0kN for pile group) • Pile diameter, Dpile = 0.8m • Pile length to tunnel depth ratio, Lp/Htun = 1.2 (Test 1) & 0.86 (Test 3) • Pile -tunnel distance, Xpile = 5. 5m (or Xpile/Dtun = 0.92) • Pile stiffness, Epile = 200GPa • Tunnel diameter, Dtun = 6m (single tunnel) • Tunnel. .. CONVENTION CENTRE STATION 850 0 10600 850 0 LEGEND EXISTING PILE EXISTING PILE TO BE CUT-OFF Figure E.4 Foundation layout of the link structure 349 Figure E.4 shows the foundation layout of the building and the tunnel location One of the main challenges in this section was the intersection of three numbers of piles with the upper tunnel (Figure E .5) Two piles were encountered at the front wall and one... Figure E .5 Detailed of Raymond step-tapered pile 350 PIPE PILE STEEL H -PILE PIPE PILE STEEL H -PILE POLYFOAM BLOCK 0.4m 3m UPPER TUNNEL (NB) CL (a) UPPER TUNNEL (NB) CL (b) Figure E.6 Pile cut-off at one of the wall section (a) before (b) after Raymond Step-taper pile Figure E.7 A view inside the chamber during pile removal 351 Raymond Step-Taper pile (a) Steel H -pile (b) Figure E.8 Scrap of removed piles... stages to be built (Yong & Pang, 2004b) In the contract, four stations namely the Dhoby Ghaut Station, Museum Station, Convention Centre Station and Millenia Station are to be built The contract also includes the construction of twin tunnels of 1.5km long All the constructions are located in the densely populated civic and business district centre of Singapore Inevitably, the construction has to be carried... (Non linear) 0.1 0.2 0.3 0.4 0 .5 Pile stiffness ratio, Ewall(2D) / Epile(3D) Figure D.1 Influence of soil model on pile stiffness modification factor Pile max horiz defl (NE, Ko=1.0) Pile max horiz defl (NE, Ko=1 .5) Pile head sett (NE, Ko=1.0) Pile head sett (NE, Ko=1 .5) 200 150 2D response = 3D single pile response 100 0 0.0 0.12 50 0.07 Response of 2D to 3D analysis (%) 250 0.1 0.2 0.3 0.4 0 .5 Pile. .. modification factors in both the pile horizontal deflection and pile head settlement However, it should be noted that the influence of Ko parameter is highly dependent on the type of soil model adopted 350 300 Pile max horiz defl (Mohr Coulomb) 250 Pile head sett (Non linear) Pile head sett (Mohr Coulomb) 200 150 2D response = 3D single pile response 50 0 0.0 0. 15 100 0.07 Response of 2D to 3D analysis (%) Pile. .. -10 0 - 15 10 20 20 Tunnel Tunnel springline 50 70 30 3-D tunnel adv (WL+tunnelling) Plane strain tunnel (WL+tunnelling) 3-D tunnel adv (WL) Plane strain tunnel (WL) With WL, Gmax/p'=800, V L=1%, Lp/Htun=3.0, Xpile/Dtun=1.0 (a) - 15 Tunnel 30 40 40 50 40 60 Depth (m) Depth (m) Depth (m) Tunnel springline 30 -10 10 20 Tunnel -5 0 0 10 -5 50 60 60 3-D tunnel adv (WL+tunnelling) 70 3-D tunnel adv (WL+tunnelling)... on the modification factor Two cases were simulated; single pile and one-row pile group Figures E.3a and b show respectively the typical 3D and 2-D mesh adopted for simulation of the twin tunnels which are located on each side of the single pile Equal distance between tunnel and pile was modelled on each side of the pile (i.e Xpile =5. 45m) Other tunnel- pile configuration and dimension remained the same . (20 05) . Dutch research on the impact of shield tunnelling on pile foundations. 5 th International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground, 15- 17 June 20 05, . Zanardo G (20 05) . The effects of tunneling on piled structures on the CTRL. 5 th International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground, 15- 17 June 20 05, Amsterdam,. Poulos H G (20 05) . Analysis of effects of tunnelling on single piles. 5 th International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground, 15- 17 June 20 05, Amsterdam,