November 2009 Reducing Wall Deflection Session 4 How to reduce wall deflection Time Session Topic p 09:00 – 10:30 1 Overview Coffee Break 10:30 – 11:00 11:00 – 12:30 2 Design (Part 1) 12:30 - 01:30 01:30 – 03:00 3 Mohr-Coulomb Soil Model & Design (Part 2) Coffee Break 03:00 – 03:30 03:30 – 05:00 4 How to reduce wall deflection Reducing Wall Deflection How to reduce wall deflection? Reducing Wall Deflection Wong Kai Sin 1 Options: 1. Change to circular shape 2. Increase wall stiffness 3. Increase 3 c ease no. o of o struts s us 4. Increase preloads 5. Increase wall penetration 6. Install cross-walls 7. Ground improvement • JGP - Jet grouting • DCM - Deep cement mixing 8. Improved soil slab with tension piles 2 1 November 2009 Reducing Wall Deflection Ring Beam System Central at Clarke Quay in Clarke Quay in Singapore Reducing Wall Deflection 3 The Sail at Marina Bay in Singapore Reducing Wall Deflection Wong Kai Sin 4 2 November 2009 Reducing Wall Deflection Effect of Penetration & Wall Stiffness Sheetpile Wall Diaphragm Wall Reducing Wall Deflection 5 Effect of Number of Level Struts 2 3 struts struts Diaphragm Wall Reducing Wall Deflection Wong Kai Sin 4 4 5 struts struts struts Sheetpile Wall 6 3 November 2009 Reducing Wall Deflection Diaphragm Wall with Cross-Wall Cross-wall Sand Cross-wall Marine Clay Diaphragm wall Old Alluvium Diaphragm wall Reducing Wall Deflection 7 TERS Design with Cross‐Walls DW DW Cross‐Wall Cross‐Wall Reducing Wall Deflection Wong Kai Sin 8 4 November 2009 Reducing Wall Deflection Main applications of JGP in deep excavation are: 1. To reduce wall deflection & ground settlement 2. To minimize effect on adjacent structures 3. To improve basal heave stability 4. To improve toe kick‐in stability 5. To control seepage Reducing Wall Deflection 9 JGP – Jet Grouted Piles Ground Level Ground Water Table FILL FILL MARINE MARINE CLAY CLAY FLUVIAL CLAY FLUVIAL CLAY JGP MARINE MARINE CLAY CLAY D/WALL D/WALL Reducing Wall Deflection OLD ALLUVIUM Completed JGP Slabs prior to Excavation 10 Slide 10 Wong Kai Sin 5 November 2009 Reducing Wall Deflection How does it work? It acts as a compression member to reduce wall deflection deflection. In addition, it can also act as an anchored slab to minimize bottom heave minimize bottom heave. Reducing Wall Deflection 11 No JGP/DCM δH,max = 361 mm 3m JGP/DCM δH,max = 141 mm 3m JGP/DCM with tension piles δH,max = 37 mm Reducing Wall Deflection Wong Kai Sin 12 6 November 2009 Reducing Wall Deflection Full Penetration Wall Floating Wall 1.2mD W 1.2mD W 5m JGP 5m JGP δmax = 90 mm Tmax = 1600 kN/m Mmax = 350 kNm/m Reducing Wall Deflection No Sacrificial JGP 1.2mD W 5m JGP δmax = 90 mm Tmax = 1600 kN/m Mmax = 350 kNm/m Reducing Wall Deflection Wong Kai Sin δmax = 101 mm Tmax = 1580 kN/m Mmax = 439 kNm/m 13 2m Sacrificial JGP 2m JGP 1.2mD W 5m JGP δmax = 58 mm Tmax = 1590 kN/m Mmax = 371 kNm/m 14 7 November 2009 Reducing Wall Deflection No Piles 7 Piles 2m JGP 1.2mD W 5m JGP δmax = 58 mm Tmax = 1590 kN/m Mmax = 371 kNm/m Reducing Wall Deflection 1.2mD W 2m JGP 5m JGP δmax = 442 mm Tmax = n.a. Mmax = n.a. 15 Factor of safety without JGP = 0.45 to 0.6 Clark Quay Station Entrance (Shirlaw et al., 2005) This is one occasion where modeling of piles is a must. Reducing Wall Deflection Wong Kai Sin 16 8 November 2009 Reducing Wall Deflection d = 1.5 m d = 3 m d = 6 m Effect of Grout Layer Thickness Reducing Wall Deflection 17 Presence of JGP slab can reduce the number of strut levels. Reducing Wall Deflection Wong Kai Sin 18 9 November 2009 Reducing Wall Deflection JGP Jet Grouted Piles 19 Jet Grouting Reducing Wall Deflection Construction of Jet Grout Slab Reducing Wall Deflection Wong Kai Sin 20 10 November 2009 Wong Kai Sin Reducing Wall Deflection Reducing Wall Deflection 21 Reducing Wall Deflection 22 11 November 2009 Reducing Wall Deflection Jet grouting on land Jet grouting over a canal Reducing Wall Deflection 23 Bulk density of JGP 2 1.9 Bulk Density (Mg/m3) 1.8 1.7 1.6 1.5 1.4 1.3 Triple Tube 1.2 Double Tube 1.1 1 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Unconfined Compressive Strength qu (kPa) Reducing Wall Deflection Wong Kai Sin 24 12 November 2009 Reducing Wall Deflection JGP Strength & Density (Shirlaw et al., 2000) qu = 2 cu Reducing Wall Deflection 25 JGP strength (14 days) Design qu (kPa) Mean Measured qu (kPa) Singapore River Double tube 500 1225 Chia & Tan (1993) Geylang River Single tube 500 1843 Liang et al. (1993) Clarke Quay MRT Station - 600 2520 Shirlaw et al. (2000) Tunnel at Race Course Rd - 600 2024 Shirlaw et al. (2000) Tunnel at Race Course Rd - 600 1290 Wen (2005) C824 – Nicoll Highway Double tube 900 5826 This study C824 – Nicoll Highway Triple tube 900 3584 This study Reducing Wall Deflection Wong Kai Sin Source JGP Method Project 26 13 November 2009 Reducing Wall Deflection JGP strength from C824 at Types C to M3 8 7 Specification: qu = 0.9 MPa No. of Samples 6 5 4 3 2 1 0 <0.9 0.9-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 Unconfined Compressive Strength of JGP (MPa) Reducing Wall Deflection 27 JGP Modulus 1400 Eu / qu ~ 100 Eu/qu ~ 100 Eu / c / cuEu/Cu ~ 200 200 ~ 200 1200 Modulus (MPa) 1000 800 600 400 Triple Tube 200 Double Tube 0 0 2000 4000 6000 8000 10000 12000 14000 Unconfined Compressive Strength (kPa) Reducing Wall Deflection Wong Kai Sin 28 14 November 2009 Reducing Wall Deflection Deep Cement Mixing ‐‐ DCM Reducing Wall Deflection 29 Deep Cement Mixing Reducing Wall Deflection Wong Kai Sin 30 15 November 2009 Reducing Wall Deflection Strength & Modulus of DCM samples in Marine Clay External measurements Reducing Wall Deflection 31 σ−ε curves from local and external strain measurements (Tan et al., 2002) Reducing Wall Deflection Wong Kai Sin 32 16 November 2009 Reducing Wall Deflection Modulus and Strength of DCM Samples in Marine Clay (Tan et al., 2002) External Measurements Local Measurements Reducing Wall Deflection 33 Curing Time of DCM Samples in Marine Clay (Tan et al., 2002) Reducing Wall Deflection Wong Kai Sin 34 17 November 2009 Reducing Wall Deflection Adverse Effects of Jet Grouting Double Tube Method 1. It pushes the wall outward away from excavation area away from excavation area. 2. It causes ground heave. Esplanade by the Bay I-5D I-6D I-12D I-9D I-10D Reducing Wall Deflection 35 How to model JGP slab in FEA? 1. Wall and JGP slab are wished‐in‐place. 2. Step‐by‐step simulation of p y p excavation sequence qu = ? Eu = ? Reducing Wall Deflection Wong Kai Sin 36 18 November 2009 Reducing Wall Deflection Deep Excavation Shallow Excavation H H JGP strength not critical JGP strength critical Reducing Wall Deflection 37 qu (core) = qu (mass) ? 3D view of core sample Plan view of JGP slab Reducing Wall Deflection Wong Kai Sin 38 19 November 2009 Reducing Wall Deflection Eu (core) = Eu (mass) ? 3D view of core sample Plan view of JGP slab Reducing Wall Deflection 39 Other Issues: (1) Initial Stresses in JGP σ1 – σ3 Initial state of stress ε Assumptions commonly adopted in practice: (1) JGP slab is wished in‐place. (2) φu = 0 Æ Ko = 1.0 Æ (σ1 – σ3) = 0 Reducing Wall Deflection Wong Kai Sin 40 20 November 2009 Reducing Wall Deflection Other Issues: (1) Initial Stresses in JGP σ1 – σ3 Initial state of stress ε Actual condition in field: σ1 >> σ3 Æ (σ ( 1 – σ3) > 0 ) 0 What Ko value should we use in analysis? Reducing Wall Deflection 41 Other Issues: (2) Field Construction Sequence 1. Construction of DW panels • Reduction in σh 2. Installation of JGP slab • Increase in σ Increase in σh • Rotation of principal stress direction p = ? Reducing Wall Deflection Wong Kai Sin 42 21 November 2009 Reducing Wall Deflection Other Issues: (2) Field Construction Sequence 3. Step‐by‐step excavation • Reduction in σh Each soil element goes through a different stress path Each soil element goes through a different stress path. Can the soil model produce the correct response at each element? Reducing Wall Deflection 43 Other Issues: (3) Wall Deflection Profile Wall Deflection at I104 105 RL (m) Fill E Fill E 90 UMC UMC 85 F2 upper F2 upper 100 95 80 85.4 LMC LMC 75 LMC 70 69.4 65 60 63.7 61 2 61.2 59.2 55 50 0 50 100 150 200 250 300 350 400 F2 lower OA N = 20 OA N = 30 OA N = 70 F2 F2 lower OA N = 20 OA N = 30 OA N = 70 72.1 66. 864.7 60 0 60.0 OA N = 100 55.0 WallDeflection(mm) 1. Are these deflection profiles correct? 2. Can they be used to determine the wall bending moments? Reducing Wall Deflection Wong Kai Sin 44 22 November 2009 Reducing Wall Deflection Other Issues: (3) Wall Deflection Profile Where is the reference line? Profile A (Initial) Profile A Profile B (After JG) Profile D Profile C Using Profile A as reference line. Using Profile B as reference line. Reducing Wall Deflection 45 Profile B Profile A Profile A Measured wall deflection of an excavation in Taiwan (Lin & Lin, 2008) P fil D Profile D Profile C Reducing Wall Deflection Wong Kai Sin 46 23 November 2009 Reducing Wall Deflection Case 17 Case 3 With simulation of jet grouting Without simulation of jet grouting δHmax = 14 mm δHmax = 71 mm Reducing Wall Deflection δHmax = 90 mm 47 Case 17 With simulation of jet grouting Relative Shear Case 3 Without simulation of jet grouting Reducing Wall Deflection Wong Kai Sin 48 24 November 2009 Reducing Wall Deflection Profile B is the more rational choice as reference line. It gives the true deflection profile. Profile A (Initial) Profile A Profile B (After JG) Profile D Profile C Using Profile A as reference line. Using Profile B as reference line. Reducing Wall Deflection 49 Other Issues: (4) JGP Slab Thickness Design • Reasonable to assume uniform thickness • Need to conduct sensitivity study eed to co duct se s t ty study Back‐Analysis • Need to know variations of JGP thickness Reducing Wall Deflection Wong Kai Sin 50 25 November 2009 Reducing Wall Deflection Other Issues: (5) JGP Post‐Failure Behaviour σ σ σ3 = 0 kPa σ3 = 500 kPa ε Unconfined compression test ε Confined compression test Reducing Wall Deflection 51 stress‐strain curves of clay‐cement mix under different confining pressures Reducing Wall Deflection Wong Kai Sin 52 26 November 2009 Reducing Wall Deflection Modelling of JGP Post‐Failure Behaviour σ σ σ3 = 0 kPa ε σ3 = 500 kPa ε σ1 – σ3 FE simulation using Mohr‐ Coulomb Model ε Reducing Wall Deflection 53 Cross‐section & soil profile adopted in the analysis Reducing Wall Deflection Wong Kai Sin 54 27 November 2009 Reducing Wall Deflection Plastic points showing extensive yielding in JGP slab and surrounding soils at 7th strut level JGP1 Sacrificial JGP layer Reducing Wall Deflection 55 Modelling of JGP Post‐Failure Behaviour σ σ σ 50% ε ε ε (A) (B) (C) no softening 50% reduction 80% reduction Reducing Wall Deflection Wong Kai Sin 80% 56 28 November 2009 Reducing Wall Deflection Maximum wall deflections computed by Analyses A, B and C at 10th level Analysis Strain Softening Maximum Wall Deflection ((mm)) South Wall North Wall A None 263 191 B 50% reduction 318 220 C 80% reduction 380 225 325 181 Measured Reducing Wall Deflection 57 Deflection profiles at the south wall at different stages of excavation 105 Level 3 100 Level 4 100 100 100 90 90 Level e e 5 Level 6 95 Level 7 90 Level 9 75 70 Reduced Level (m) Reduced Level (m) Reduced Level (m) 80 Level 1 Level 2 Level 10 85 80 70 Level 3 Reduced Level (m) Level 8 90 80 70 Level 4 80 Level 5 Level 6 Level 7 70 Level 8 Level 9 65 Level 10 60 60 60 60 55 0 50 100 150 200 250 300 350 400 Wall Deflection (mm) Measured (326 mm) Reducing Wall Deflection Wong Kai Sin -100 50 50 50 50 100 300 Wall deflection (mm) 500 -100 0 100 200 300 400 Wall deflection (mm) -100 0 100 200 300 400 Wall deflection (m m ) (A) (B) (C) no softening 50% reduction 80% reduction (263 mm) (318 mm) (380 mm) 58 29 November 2009 Reducing Wall Deflection Deflection profiles at the north wall at different stages of excavation 105 100 100 100 100 90 90 90 95 90 Level 1 75 70 80 70 Level 1 Level 2 Level 3 Level 4 Level 5 Level 6 Level 7 Level 8 Level 9 Level 10 65 60 55 50 0 20 40 60 80 100 120 140 160 180 200 220 240 Level 3 Reduced Level (m) Reduced Level (m) Reduced Level (m) 80 Reduced Level (m) Level 2 85 80 70 Level 4 80 Level 5 Level 6 Level 7 Level 8 70 Level 9 Level 10 60 60 50 -40 0 40 Wall Deflection (mm) 80 60 50 -40 0 120 160 200 240 280 40 Measured 80 50 -40 0 120 160 200 240 280 Wall deflection ((mm)) Wall deflection ((mm)) 40 80 120 160 200 240 280 Wall a de deflection ect o ((m m)) (A) (B) (C) no softening 50% reduction 80% reduction (191 mm) (220 mm) (225 mm) (181 mm) Reducing Wall Deflection 59 Comparison of Computed and Measured Strut Forces 100 100 100 95 90 85 95 90 85 80 80 0 500 1000 1500 2000 Maximum strut load (kN/m) (A) no Softening Reducing Wall Deflection 95 90 85 80 75 75 Wong Kai Sin Reduced Level (m ) 105 Reduced Level (m ) 105 Redu ced L evel (m ) 105 75 0 500 1000 1500 2000 0 500 1000 1500 2000 M i Maximum strut t t load l d (kN/m) (kN/ ) Maximum strut load (kN/m) (B) 50% reduction (C) 80% reduction 60 30 November 2009 Reducing Wall Deflection Other Issues: (6) Adhesion between JGP and Pile h JGP How can we determine ca between JGP and pile? Reducing Wall Deflection 61 Mixing of clay & cement Roughen the surface Completed specimens Specimen and moulds Reducing Wall Deflection Wong Kai Sin 62 31 November 2009 Reducing Wall Deflection Compressive strength of specimen at different curing time (Goh, 2005) 1600 Compressive Strength (kPa) 1400 1200 28 days 1000 14 days 800 7 days 600 400 200 0 0 10 20 30 40 Water added (%) Reducing Wall Deflection 63 Adhesion between concrete with clay‐cement mixture (Goh, 2005) 700 y = 0.448x + 444.82 600 20%[email protected] Shear Strength (kPa) 500 30%[email protected] y = 0.3348x + 369.64 400 20%[email protected] 300 30%[email protected] y = 0.7408x 200 y = 0.6273x 100 0 0 50 100 150 200 250 300 350 400 450 500 Normal Stress (kPa) Reducing Wall Deflection Wong Kai Sin 64 32 November 2009 Reducing Wall Deflection PreliminaryTest Pile TP2 Max load 1750 Tonnes 1m diameter Rod extensometers (damaged on installation) SPT Blows per mm penetration Shear Transfer at maximum load GL (7) Sandy Made Ground Pile Load Test at KPE Typical <10/300 Pile head settlement at maximum load =23mm Residual settlement =4mm 10m (Shirlaw et al., 2005) (Shirlaw et al., 2005) Marine Clay (83) Jet Grout Slab (754) 20m (197) (52) Measured adhesion = 754 kPa Adhesion at failure >>754 kPa 30m Marine Clay 65.5m 40m (126) Fluvial Sand 50m Old Alluvium 46/300 25/300 (72) 44/300 55/300 100/220 100/260 (106) (15) 100/280 100/220 60m 100/220 0 Reducing Wall Deflection 500 Shear transfer (kN/m2) 1000 65 Other Issues: (7) How to model the adhesion in FEA? d Qs on piles in field = ( π d h / s ) ca Qs on piles in FEA = 2 h c il i FEA 2 h a,FEA ca,FEA = (π d ca) / (2 s) s h Reducing Wall Deflection Wong Kai Sin JGP Pile p g Spacing 2.5 d 3.0 d 3.5 d 4.0 d ca,FEA 0.63 ca 0.52 ca 0.45 ca 0.39 ca 66 33 November 2009 Reducing Wall Deflection Conclusions 1. Many uncertainties involving JGP: • Strength • Modulus • Initial stress • Slab thickness • Post‐failure behaviour 2. Shallow excavations Æ JGP strength may not be important. 3. Deep excavations Æ JGP strength becomes critical. Proper modeling of post‐failure behaviour becomes important. 4. Use qu=600 kPa and Eu=150 MPa as reference case Reducing Wall Deflection 67 5. Conduct sensitivity studies on ‐ Modulus ‐ Strength ‐ Slab thickness ‐ Post‐failure softening 6. Do not zero the inclinometer readings at the start of excavation. Always base on the initial readings. 7. Exercise stringent quality control during jet grouting. 8 M it 8. Monitor performance closely during construction. f l l d i t ti Reducing Wall Deflection Wong Kai Sin 68 34

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