Behavior of Reinforced Embankment on Soft Ground with and without Jet Grouted Soil-Cement Piles

Transcription

1 Behavior of Reinforced Embankment on Soft Ground with and without Jet Grouted Soil-Cement Piles by 1 Dennes T. Bergado and 2 Glen A. Lorenzo 1 Professor and 2 Doctoral Candidate, respectively Geotechnical Engineering Program Asian Institute of Technology, Bangkok, THAILAND 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 1

2 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 2

3 Soil Profile along Bangkok-Chonburi SOFT CLAY MEDIUM CLAY STIFF CLAY 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 3

4 Failure of Embankment on Soft Ground 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 4

5 Problem of Bridge Approach on Subsiding Ground 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 5

6 Basal Reinforced Piled Embankments Transition between non-piled and piled foundations 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 6

7 Some Applications of Soil-Cement Piles (DJM Research Group, 1984) Prevent slope failures and settlement of embankment and structure Increase stability of slopes Increase horizontal resistance of structures Reduce settlement and prevent slope failures of bridge s abutments 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 7

8 Advantages of Soil-Cement Stabilization It can significantly increase the strength and reduce the compressibility of soil. Soil improvement can be attained at optimum period of only 1 month. Cement is abundant and cheaper in Asia. Cement is effective than lime. 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 8

9 Full-Scale Embankment on DMM Piles (Jet grouting) THE SITE 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 9

10 Soil Profile at the Site (Jet grouted piles) 0 Unit weight (kn/m 3 ) Clay backfill Weathered clay 3 Depth (m) Soft clay Medium stiff clay Unit weight G s PL w N LL P' o P' max G s PL, w N, LL Corrected S u (kpa) from Vane Sheat Test P' o and P' max (kpa) 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 10

11 Jet Grouting Machine Jet pressure = 20 MPa 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 11

12 Sequence of Soil-Cement Piles Installation (1) Positioning (2) Penetration (Remolding) (3) Completion of (4) Feeding of penetration cementing agent (withdrawal) (5) Completion 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 12

13 Plan View and Layout of DMM Piles 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 13

14 Front Elevation and DMM Pile Penetration 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 14

15 Section thru Center Line 17m 6 m 6 m 6m 14.5m 2m 1.5m 4 m 3m PIEZOMETERS REFERENCE 6m HEXAGONAL WIRE MESH REINFORCEMENT VERTICAL PRE-CAST CONCRETE FACING 9 m 6 m PIEZOMETER BOARD 3 m 3 m P1-P5 P1-P5 S5/S1 S6/S2 S7/S3 S8/S4 P6 P7 P8 DS1 DS2 DS3 P6 P7 P8 DS6 DS7 DS8 DUMMY REINFORCEMENT FOR FIELD PULL-OUT TEST EXTENSOMETER WIRES WELL COMPACTED AYUTHAYA SAND BACKFILL EXTENSOMETER SUPPORT 1.5m CLAY BACKFILL 1m WEATHERED CRUST SOFT CLAY SETTLEMENT REFERENCE 8m P1-P5 P6 P7 P8 NOTE: PLEASE SEE THE PLAN VIEW FOR DETAILS OF THE LOCATION OF OTHER INTRUMENTATION POINTS 15 m depth 1.5m = 9m 2m 1m 0.6 m DIAMETER SOIL- CEMENT PILES AT 1.5 m SPACING IN SQUARE PATTERN MEDIUM STIFF CLAY 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 15

16 Instrumentations and Laying of Reinforcements 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 16

17 Reinforcement Connection 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 17

18 Hexagonal Wire Mesh Width Length Basic hexagonal wire mesh reinforcement geometry Steel core wire Zinc Coating Steel core wire PVC Coating Zinc Coating Cross section of different types of hexagonal wire mesh reinforcement 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 18

19 Deformation and Necking Phenomenon of Hexagonal Wire Mesh Reinforcement during Pullout (Conventional pullout test) Hexagonal cell in the centerline of the reinforcement Hexagonal cell at the edge of the reinforcement 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 19

20 Modified Pullout Test Set Up (In-soil Pullout Test) Boundary of Large Scale Pullout Box Apparatus Pullout Direction Outer Clamps Steel Rods In-soil Clamps 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 20

21 Pullout Test Apparatus (Maccaferri, 1997) 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 21

22 70 Maximum Pullout Resistance in Various Pullout Test Programs Maximum pullout load (kn/m) Tult = 44.8 kn/m (in-air tensile test) Maccaferri (1997) Kongkitkul (2001), L = 0.70 m Kabiling (1997), L = 1.10 m Kabiling (1997), L = 0.90 m Kabiling (1997), L = 0.70 m Applied normal pressure (kpa) 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 22

23 The Finished 6m High Reinforced Embankment 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 23

24 Surface Settlement (hollow symbol= on clay ; solid = on pile ) Fill height (m) Settlement (mm) Time (Days) /1/24 Behavior of Reinforced Embankment on Soft Ground S1 S5 S10 S14 S2 S6 S11 S15 S p (ave.) =325mm (improved ground) S p =1200mm (Untreated ground)

25 Differential Settlement between Soil and Pile (hollow symbol= on clay ; solid = on pile ) Settlement (mm) Time (Days) S1 S5 S10 S14 S2 S6 S11 S15 click 25mm 60mm 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 25

26 Horizontal Inclinometer H1 (on pile) Distance (m) Settlement (mm) Started on Jan 28 Ended on Feb Jan 05.Feb 09.Feb 12.Feb 13.Feb 15.Feb 23.Feb 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 26

27 Horizontal Inclinometer H2 (on clay) Distance (m) Settlement (mm) Jan 05.Feb 09.Feb 12.Feb 13.Feb 15.Feb 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 27

28 Predicted vs. Measured Settlement Fill ht. (m) Settlement (mm) Time (days) Field monitoring, [S2 at the Center], on pile Field monitoring, [S6 at the Center], on ground Untreated ground (1D method) Lorenzo and Bergado (2003), on pile Lorenzo and Bergado (2003), on clay Asaoka's method on clay 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 28

29 Steel-Grid Reinforced Embankment on Unimproved Ground Soil Profile at the Site 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 29

30 Steel-Grid MSE Embankment on Unimproved Soft Foundation 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 30

31 Front Elevation (unimproved foundation) 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 31

32 Section View (unimproved foundation) 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 32

33 Pullout Friction Resistance of Steel Grid 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 33

34 Pullout Bearing Resistance of Steel Grid 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 34

35 Comparison of Lateral Displacement Profiles (with and without jet grouted piles) Wall face Depth (m) Lateral movement (mm) Backfill/ Weathered clay Soft clay Medium to Stiff Clay With jet grouted piles (TE2), after construction With jet grouted piles (TE2), 7 months after const'n No improvement (TE1), after construction No improvement (TE1), 7 months after const'n 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 35

36 Comparison of Surface Settlements (with and without jet grouted piles) Surface settlement (mm) FACE EMBANKMENT TOE With jet grouted piles (TE2), after construction With jet grouted piles (TE2), 1 year after const'n No improvement (TE1), after construction No improvement (TE1), 1 year after const'n Horizontal distance (m) 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 36

37 Settlement Reduction and Rate of Settlement Settlement (m) Finite element Finite element SS6 Untreated, 1-D conventional Sp =1200mm (Untreated ground) Time (Days) Click to location of SS6 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 37

38 Excess pore pressure (kpa) Faster Rate of Consolidation of Improved Ground Outside the improved ground (35% dissipated) p1/6 p2/6 p3/6 p4/6 p5/6 p6/6 p7/6 p8/ Time (days) OARD click 3 m 3 m P1-P5 P1-P5 P1-P5 S5/S1 S6/S2 S7/S3 S8/S4 P6 P7 P8 DS1 DS2 DS3 P6 P7 P8 DS6 DS7 DS8 P6 P7 P8 Within the improved ground (55% dissipated) Excess Pore Pressure in Clay at 6m Depth Height (m) 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 38

39 One-Dimensional and Unconfined Compression of Cement-Admixed Clay of Higher Water Content 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 39

40 Properties of the Base Clay Bangkok Clay 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 40

41 Definition of higher water content clay: A clay that has a natural water content equal to or greater than its liquid limit (LL), or a clay that has been remolded to water content equal to or greater than its LL. 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 41

42 Conceptual Diagram of Cement Stabilized Clay at Higher Water Content Prolong curing Better dispersion of cementing agents/ions within the pores. It is expected to yield higher strength. Higher permeability and good drainage ability. 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 42

43 Laboratory Test Remolding the base clay at clay water contents from liquid limit (LL) to 2LL. Water/cement ratio of slurry of 0.6. Curing the specimens directly in the oedometer rings for oedometer tests, and in the PVC mold for UC tests. Curing the specimen in the humid room within 7, 14 and 28 days; only 28 days for oedometer tests. 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 43

44 Void ratio, e Remolding Symbol water content (%) Undisturbed Intrinsic Generated post yield compression line Void ratio, e Effective stress, σ v ' (kpa) a) 5% Cement content; 130% to 200% remolding water content Effective stress, σ v ' (kpa) b) 10% Cement content; 100% to 250% remolding water content Post-Yield Compression Lines (5% and 10% cement) (measured values vs. predicted values) 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 44

45 Void ratio, e Remolding ymbol water content (%) Undisturbed Intrinsic Generated post yield compression line Effective stress, σ v ' (kpa) c) 15% Cement content; 100% to 200% remolding water content Post-Yield Compression Lines (15% cement) (measured values vs. predicted values) 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 45

46 Modified void index, I vnc Symbol Cement content 15% 10% 8% 5% 3% Intrinsic Fitting curve Effective stress, σ v ' (kpa) Normalized Post-Yield Compression Curves Normalizing parameter I vnc = (e t -e t,1600 )/C * ct where: e t = void ratio of treated sample at certain effective stress, σ v ; e t1600 = void ratio of treated sample at effective stress of 1600 kpa for certain cement content; C * ct = mean slope of the postyield compression line for certain cement content. Fitted curve I vnc = -0.06(logσ' v ) (logσ' v ) (logσ v ) ; in similar form of ICL of Burland (1990). 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 46

47 Schematic Diagram for Predicting Compression Line of Cement Treated Clay (curing time: at least one month) Void ratio, e e ot,1 e ot,2 σ vy,1 σ vy,2 Post-yield compression line for particular cement content Effective stress, σ v ' (kpa) Void ratio after curing, e ot e ot = initial void ratio after curing; σ vy = predicted vertical yield stress. Swelling index Increasing A w 20% 15% 10% 5% Cement content, A w Vertical yield stress, σ vy (kpa) 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 47

48 Coefficient of Permeability from Oedometer Test of Untreated and Cement-Treated Soft Bangkok Clay Void ratio, e Symbol Cement content 15% 10% 8% 5% Intrinsic Undisturbed C=2.5 e = 1.2Log(k) e = 1.2Log(k) + C Note: k x m/s C= Permeability, k v (x10-10 m/s) 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 48

49 Unconfined Compression Tests UC strength, q u (kpa) days curing Note: * = remolding water content + = cement content Base clay UC strength, q u (kpa) days curing Axial strain (%) Axial strain (%) 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 49

50 Unconfined Compression Tests (cont d) UC strength, q u (kpa) Curing 28 days 14 days 7 days UC strength, q u (kpa) q = u B A wc/ A w Curing 28 days 14 days 7 days Clay water/cement content ratio, wc/a w Clay water/cement content ratio, wc/a w q = u B A wc/ A w A = f (time, clay type, etc.) = intercept B = f (clay type, etc.) = slope 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 50

51 Modulus of Elasticity versus UC Strength (Laboratory mix cement-treated Bangkok clay) Initial tangent modulus, E i Secant modulus, E 50 E i = 175q u R 2 = Modulus of deformation E i, E 50 (MPa) E 50 = 147q u R 2 = E i = 115q u Horpibulsok (2001) E i = 121q u Win (1997) E 50 = 114q u Win (1997) Unconfined compressive strength, q u (kpa) 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 51

52 Vertical Yield Stress σ vy versus UC Strength q u of Cement-Treated Bangkok Clay and Ariake Clay Vertical yield stress, σ vy ' (kpa) σ vy = 1.4q u (kpa) Bangkok clay, 28 days curing Bergado and Lorenzo (2002) σ vy = 1.55q u (kpa) Bangkok clay 14 and 28 days curing This study σ vy = 1.27q u (kpa) Kamon and Bergado (1991) Ariake clay Test data, 28 days Test data, 14 days Unconfined compressive strength, q u (kpa) 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 52

53 Optimum Mixing Clay Water Content Optimum mixing clay water content (w opt ) is hereinafter defined as the total clay water content (or mixing clay water content) of the clay-cement paste that would give the highest possible improvement in strength of cured cement-admixed clay. 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 53

54 Effect of Mixing Clay Water Content on Unconfined Compression (10% Cement Content) Unconfined compressive strength, q u (kpa) days curing Total clay water content 105% 135% 165% 80% Axial strain (%) 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 54

55 Effect of Mixing Clay Water Content on 1-Dimensional Compression (10% Cement) Void ratio, e Totalclay water content 165% 135% 105% 80% Effective stress, σ v ' (kpa) 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 55

56 Typical Strength Curve of Cement-Admixed Clay (to get the optimum mixing clay water content) Unconfined compression strength, q u (kpa) cw=ll cw=1.15ll Total clay water content, cw (%) 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 56

57 CONCLUSIONS 1) Two full-scale reinforced embankments were constructed on soft ground. The first embankment (TE1), 5.7m high and reinforced with steel-grids, was constructed on unimproved ground. The second embankment (TE2), 6.0m high reinforced with hexagonal wire reinforcement, was constructed on jet grouted soil-cement piles improved ground. 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 57

58 CONCLUSIONS (cont d) 2) After embankment construction, the maximum lateral movements in the unimproved soft foundation soil was 130mm, while that of improved foundation soil was only 5mm. Therefore, the installation of soil-cement piles has effected significant increase in the lateral resistance and the bearing capacity of the foundation soil. 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 58

59 CONCLUSIONS (cont d) 3) One year after embankment construction, the maximum surface settlement of TE1 was 1.0m while that of TE2 was only 0.325m. Therefore, the soil-cement pile installation in the soft foundation has also effectively reduced the settlement by at least 70%. 4) Also, one year after construction the unimproved foundation was far from its 90% consolidation, but the soil-cement piles improved ground was already close to its 90% consolidation. 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 59

60 CONCLUSIONS (cont d) 5) The maximum lateral movement of the reinforced embankment on soil-cement piles improved ground was lower than that of reinforced embankment on unimproved foundation. 6) The existence of optimum mixing clay water content (w opt ) has been proven from the results of UC tests and oedometer tests of cement-admixed clay. 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 60

61 CONCLUSIONS (cont d) 7) w opt was found to fall within liquid limit (LL) up to 1.15LL of the base clay. 8) At optimum mixing clay water content, only 10% cement content by weight is needed instead of 17% in the conventional method to obtain a UC strength of 650 kpa, with consequent 40% cost reduction. 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 61

62 Layout of Settlement Plates 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 62

63 Location of Piezometers EZOMETER OARD S5/S1 S6/S2 S7/S3 S8/S4 3 m 3 m P6 P7 P8 P1-P5 DS1 DS2 DS3 P6 P7 P8 P1-P5 DS6 DS7 DS8 P1-P5 THE AILS P6 P7 P8 1.5m = 9m 2m 1m 2004/1/24 Behavior of Reinforced Embankment on Soft Ground... 63