GROUND IMPROVEMENT WORKSHOP JUNE 2010 PERTH, AUSTRALIA. CHAIRMAN OF T.C. Ground Improvement

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1 GROUND IMPROVEMENT WORKSHOP JUNE 2010 PERTH, AUSTRALIA GROUND IMPROVEMENT IN EXTREME GROUND CONDITIONS Presented by Serge VARAKSIN CHAIRMAN OF T.C. Ground Improvement

2 EPEC Bang Bo: Works Procedure Gulf of Thailand Construction ti of a 2-km road embankment, 1.33m thick 2

3 Ground Conditions Layer 1: Weathered crust (OC clay) ~ 1-2m thick Layer 2: Soft Bangkok clay (NC clay) ~ 20m thick Layer 3: Firm / stiff clay (overlying alt. sand layers) > 25m 3

4 Engineering Properties Layer 1 C u /σ = 0.2 Layer 2 C u /σ = 0.3 Soft layer 1: 0 10m highly plastic very soft Bangkok clay (av. C r ~ 0.35; av. C v ~ m 2 /y) Soft layer 2: 10 20m soft to medium firm clay 4

5 Potential Problems Final embankment height = 1.33m Fill to compensate settlement = 3m Total fill to be placed = 4.33m 2m Surcharge? Layer 1 (0 10m) C u ~ 4 10 kpa Contract t period of 12 months including consolidation and pavement works. 5

6 Criteria / Concerns LONG TERM CRITERIA Post construction performance ( t = 25 years ): Differential settlement < 1:750 Residual settlement < 40cm Stability : Factor of safety > 1.5 SHORT TERM CONCERNS Stability during construction (most critical) Handover date for turbine & other heavy structures (time constraint) Inadequate local source of fill materials and high price (reduce or eliminate surcharge?) 6

7 Preparation of Working Platform Encounter slip failures and lateral flows! 7

Vacuum depressurization at 60 kpa for 7 months Primary

8 Design Scheme & Field Implementation Double drain grid design for layer 1 and layer 2 soft clay. Vacuum depressurization at 60 kpa for 7 months Primary Grid : 1 drain per m 2 ISOTROPIC CONSOLIDATION Secondary Grid :1 drain per 2m 2 8

9 Initial Conditions 9

10 Pre Engineering Tests 10

11 Horizontal Drains Connection 11

12 Installation of Geotechnical Instruments 12

13 Initial Depressurization Initial depressurization of 0.3 bar (30 kpa) achieved in 3-5 days. Then, proceed with embankment construction. 13

14 Advanced Stage of Consolidation 14

15 Settlement Results Settlement: Mean (40) = 2.63m Most critical was embankment remained STABLE! vacuum pumping δs/δt < 0.5mm/day 15

16 Post Treatment Strength After Before Design 16

17 Another Proven Record Before Menard Vacuum 1m fill : FS < 1 During Menard Vacuum 4m fill : FS >

18 1 st Successful Vacuum Project in Thailand Client: EPEC / Consultant: SEATEC / M.Contractor: ABB Alstom 18

19 1 st Successful Vacuum Project in Thailand Total area treated t by MV: 30, m2 Drains: Total length of drains: Equipment: Working time: 600,000 m (V+H drains) 4rigs+2vibro 3 months Vacuum: Pumping equipment: Pumping duration: Average total settlement: 15 pumps 7 months 2.65 m Total working time: 10 months 19

20 Soil Profile 21

21 Future Caisson Stability Analysis 22

22 Exhibited Design 23

23 As built conditions 24

24 Proposed solution Layer I 15% rock (φ = 45 ) + 85% clay (C u = 50 kpa) Layer II 25

25 Shear strength mobilised in exhibited design The upper layer I consists of compacted sand fill of 1.3m thick (ϕ = 35 o ; C = 0) and the lower layer II consists of natural undisturbed clay of 1.5m thick (ϕ = 0 o ; C = 250 kn/m 2 ). Assuming an overburden effective stress (σ ) of 275 kn/m 2, we have the following: Layer I: τ = C + σ tan φ = 275 * tan(35 o ) = 192kN / m 2 Layer II: τ = C + σ tan φ = 250kN / m 2 26

26 Shear strength mobilised for proposed solution The upper layer I consists of compacted rock mat of 1.3m thick with 30% of rock size 150mm to 200mm and 70% of rock size 200mm to 300mm (ϕ = 45 o ; C = 0) and the lower layer II consists of composite rock-clay soil layer of 1.5m thick with an area replacement ratio m = 15%. The rock inclusions with similar grading as above has ϕ r = 45 o (C r = 0) and the surrounding clay soil has C s = 50 kn/m 2 (ϕ s = 0 o ). Taking the same overburden effective stress (σ ) of 275 kn/m 2, we have the following: Case 1: Without considering consolidation effect with no gain in shear strength Layer I: ϕ = 45 o ; C = 0 Layer II: Computation for composite ϕ and C Using equation (7): C = C ( m) + C (1 m) = 50(1 0.15) 42.5kN / m r s = 2 Using equation (10): σ r σ s o tan φ = m tan φ r + (1 m) tan φs = 0.15(2.04) tan σ σ tan φ = ϕ = 17 o (for σ s /σ = 2.04 see calculation on page 8 below) Layer I: Layer II: o τ = C + σ tan φ = 275* tan(45 ) = 275kN / m τ = C + σ tan φ = tan17 o 2 = 127kN / m 2 27

27 Total shear strength for exhibited design and proposed solution 28

28 Criteria retained for pounder design A - 35 tons submerged - 175X meter DR section B Design a stabilisation part that will rest on the side of print and guarantee penetration until stabilising part hits the crater side C Final design with final objective, -penetrating part 1.7 x 1.7 -length of penetration 1.7 m -stabilising part 2.4 x 2.4 m -ironing i i or compaction by turning over the pounder 29

29 View of pounder construction 33

30 Caisson construction yard 34

31 Pontoon PMT Testing 35

32 View of pounder ready to work 36

33 GPS Positionning system and grids 37

34 Quality control screen Liebherr

35 Depth of penetration versus number of blows Penetration Vs Blows 2 Penetratio on, m 1.5 Q2 P3 O4 Q4 Q3 P4 1 O6 Q6 Q5 P6 O5 P5 0.5 O Blows 39

36 Danger of offshore pounding V max of pounder measured by radar 8 m/sec V effective reached after 6 m drop 6 m/sec Weight below water 35 tons V = 2gh 36 = 20 h Equivalent drop height 2 m Equivalent Energy: 70 Tm Compaction Depth According to Classical Formula D = 83m 8,3 If δ = 0,5 D = 4,15 m!!! 40

37 General Set up 43

38 Testing pontoon 44

39 View on staff system 45

40 Self bored slotted tube : first experiment of Menard RETROJET SYSTEM S 46

41 Actual staff systems 47

42 Staff dulling equipment 48

43 Sequences of self boring staff system 49

44 Actual method for drilling PMT in rock mound (100 mm 300 mm) 51

45 Empirical determination of friction angle by PMT (Yee & Varaksin method) * = = C P C P m L m L l l φ φ φ φ * 2 2 φ P = * 2 φ P L 2 log log = m C P C L φ l φ = 4 40 * φ P L = * 2 P L 52

46 Reminder of technical solution SITE CONDITION SITE CONDITION Compacted sand fill Compacted ϕ = 35 ο sand fill ϕ = 35 ο undisturbed soil Variance 15% rock thickness (φ = 45 ) soften + soil 15% rock (φ = 45 ) + undisturbed soil Variance 85% 15% clay (C rock thickness u = (C50 u (φ = kpa) 50= soften kpa) 45 ) soil 85% + 15% clay rock (C u (φ = 50= kpa) 45 ) + 85% clay (C u = (C 50 u = kpa) 50 kpa) 85% clay (C u = 50 kpa) Natural undisturbed soil Natural undisturbed soil Natural undisturbed soil Natural undisturbed soil Natural undisturbed soil Natural undisturbed soil Layer I Layer II 53

47 Preliminary concept Original rock surface before compaction 1.3m φ=45 degree, Ar=15%, C=0kPa, Column Diameter=1.7m 15m 1.5m Cu=50kPa Cu=50kPa Cu=250kPa 54

48 After compaction actual results Original rock surface before compaction 0.2m 1.3m 1.3m φ=48 degree Ar=22% C=0kPa Column Dia=2.4m φ=40 degree φ=48 degree φ=40 degree Ar=22% Cu=50kPa C=0kPa Column Dia=2.4m Cu=50kPa φ=48 degree Ar=22% C=0kPa Column Dia=2.4m Cu=250kPa 55

49 Strength of layer I In summary, layer I and layer II shall have the following characteristics. o Layer I : ϕ = 49 o (harmonic mean value); C = 0, m=0.22 (22% of total area) For column Layer I: ϕ = 40 o ; C = 0, m=0.78 (78% of total t area) For in-between bt columns assuming lowest internal friction angle of 40 o. Layer I: Computation for composite ϕ and C C=0 tanφ comp = m tanφ c + (1 m) tanφ oc = 0.22 tan 49 o tan 40 φ comp =

50 Strength of layer II and total share strength Layer II: Computation for composite ϕ and C C = C ( m ) + C (1 m ) = 50(1 0.22) 39 kn / m r s = 2 σ r σ s o tan φ = m tanφr + (1 m) tanφs = 0.22(1.88) tan σ σ tan φ = 0.48 ϕ = 25.4 o (for σ s /σ = 1.88) Hence, layer I and layer II shall have the shear strength as below: Layer I: τ = C + σ tanφ = concept =275kN/m 2 ) 275* tan(42.2 o ) = 249kN / m 2 (compared with proposed Layer II: τ = C + σ tanφ = tan concept = 127kN/m 2 ) o = 170kN / m 2 (compared with proposed 57

51 Layout of CPT in sand area 59

52 Results of CPT in sand fill after DC Before Dynamic Compaction After Dynamic Compaction 60

53 GROUND IMPROVEMENT WORKSHOP JUNE 2010 PERTH, AUSTRALIA

BRASIL MAY 2010

BRASIL MAY 2010 ISSMGE TC - 17 221 BRASIL 22-23 MAY 2010 Symposium on New Techniques for Design and Construction in Soft Clays. Vacuum consolidation The environmental friendly consolidation of very soft poluted mud at