COLLOQUIUM ON GROUND IMPROVEMENT. ZÜRICH 24 October 2013

Transcription

1 ETH ZÜRICH COLLOQUIUM ON GROUND IMPROVEMENT ZÜRICH 24 October 2013 TC-211 ISSMGE Concept & Geotechnical parameters for the Design and Control of major ground improvement works around the world Serge VARAKSIN Chairman T.C. Ground Improvement (TC 211) 1

2 Thursday 31 May & Friday 1 June - International Symposium : Publications 4 Volumes >1600 pages VOL I : 7 general reports 2 specialty lectures VOL II-III-IV = >140 papers Contribution WTCB-CSTC - Edition of the 4 Volumes (N. Denies & N. Huybrechts) - Vol I :General report Deep mixing 40 p. summary of 30 papers - Vol III : 4 publications with regard to BBRI soil mix research (54 p.) cgo@bbri.be 2

3 Parameters related to ground improvement : Differents types of in situ tests Vane test (VT) Static Cone Penetration Test (CPT) Dynamic Penetration Test (SPT) Pressuremeter (PMT) 3

4 State of the Art Report 4

5 Category Method Principle A1. Dynamic compaction Densification of granular soil by dropping a heavy weight from air onto ground. A. Ground A2. Vibrocompaction Densification of granular soil using a vibratory probe inserted into ground. improvement A3. Explosive compaction Shock waves and vibrations are generated by blasting to cause granular soil ground without to settle through liquefaction or compaction. admixtures in non-cohesive A4. Electric pulse compaction Densification of granular soil using the shock waves and energy generated by electric soils or fill pulse under ultra-high voltage. materials A5. Surface compaction (including rapid Compaction of fill or ground at the surface or shallow depth using a variety of B. Ground improvement without admixtures in cohesive soils impact compaction). B1. Replacement/displacement (including load reduction using light weight materials) compaction machines. Remove bad soil by excavation or displacement and replace it by good soil or rocks. Some light weight materials may be used as backfill to reduce the load or earth pressure. B2. Preloading using fill (including the use of Fill is applied and removed to pre-consolidate compressible soil so that its vertical drains) compressibility will be much reduced when future loads are applied. B3. Preloading using vacuum (including Vacuum pressure of up to 90 kpa is used to pre-consolidate compressible soil so that combined fill and vacuum) its compressibility will be much reduced when future loads are applied. B4. Dynamic consolidation with enhanced Similar to dynamic compaction except vertical or horizontal drains (or together with drainage (including the use of vacuum) vacuum) are used to dissipate pore pressures generated in soil during compaction. B5. Electro-osmosis or electro-kinetic DC current causes water in soil or solutions to flow from anodes to cathodes which consolidation are installed in soil. B6. Thermal stabilisation using heating or Change the physical or mechanical properties of soil permanently or temporarily by freezing heating or freezing the soil. B7. Hydro-blasting compaction Collapsible soil (loess) is compacted by a combined wetting and deep explosion action along a borehole. 5

6 C. Ground improvement with admixtures or inclusions C1. Vibro replacement or stone columns Hole jetted into soft, fine-grained soil and back filled with densely compacted gravel or sand to form columns. C2. Dynamic replacement Aggregates are driven into soil by high energy dynamic impact to form columns. The backfill can be either sand, gravel, stones or demolition debris. C3. Sand compaction piles Sand is fed into ground through a casing pipe and compacted by either vibration, dynamic impact, or static excitation to form columns. C4. Geotextile confined columns Sand is fed into a closed bottom geotextile lined cylindrical hole to form a column. C5. Rigid inclusions (or composite Use of piles, rigid or semi-rigid bodies or columns which are either premade or formed foundation, also see Table 5) in-situ to strengthen soft ground. C6. Geosynthetic reinforced column or pile Use of piles, rigid or semi-rigid columns/inclusions and geosynthetic girds to enhance supported embankment the stability and reduce the settlement of embankments. C7. Microbial methods Use of microbial materials to modify soil to increase its strength or reduce its permeability. C8 Other methods Unconventional methods, such as formation of sand piles using blasting and the use of bamboo, timber and other natural products. 6

7 D. Ground improvement with grouting type admixtures E. Earth reinforcement g D2. Chemical grouting Solutions of two or more chemicals react in soil pores to form a gel or a solid precipitate to either increase the strength or reduce the permeability of soil or ground. D3. Mixing methods (including premixing or Treat the weak soil by mixing it with cement, lime, or other binders in-situ using a deep mixing) mixing machine or before placement D4. Jet grouting High speed jets at depth erode the soil and inject grout to form columns or panels D5. Compaction grouting Very stiff, mortar-like grout is injected into discrete soil zones and remains in a homogenous mass so as to densify loose soil or lift settled ground. D6. Compensation grouting Medium to high viscosity particulate suspensions is injected into the ground between a subsurface excavation and a structure in order to negate or reduce settlement of the structure due to ongoing excavation. E1. Geosynthetics or mechanically stabilised Use of the tensile strength of various steel or geosynthetic materials to enhance the earth (MSE) shear strength of soil and stability of roads, foundations, embankments, slopes, or retaining walls. E2. Ground anchors or soil nails Use of the tensile strength of embedded nails or anchors to enhance the stability of slopes or retaining walls. E3. Biological methods using vegetation Use of the roots of vegetation for stability of slopes. 7

8 Laboratory Engineering Properties Why Soil improvement? To increase bearing capacity and stability (avoid failure) To reduce post construction settlements To reduce liquefaction risk (sismic area) Advantages / classical solutions avoid deep foundation (price reduction also on structure work like slab on pile) avoid soil replacement save time Avoid to change site Save money! 8

9 Soil Improvement Techniques Cohesive soil Peat, clay Soil with friction Sand, fill Without added materials 1 Drainage 2 VAcuum 3 Dynamic consolidation 4 Vibroflottation With added materials 4 Dynamic replacement 5 Stone columns 6 CMC 7 Jet Grouting 8 Cement Mixing 9

10 Parameters For Concept -Soil caracteristics -cohesive or non cohesive - blocks? - Water content, water table position - Organic materials -Soil thickness -Structure to support -Isolated or uniform load -Deformability -Site environment -Close to existing structure -Height constraints -Time available to build 10

11 Preloading with vertical drains high fines contents soils σ=σ +u 11

12 Radial and Vertical consolidation 12

13 Vertical drains: material High fines contents soils Flat drain circular drain 5 cm, PVC vertical drain + geotextile 13

14 Vertical Drains 14

15 Vacuum Consolidation (high fines contents soils) VACUUM (J.M. COGNON PATENT) 15

16 Case history EADS Airbus Plant, Hamburg 16

17 Case history EADS Airbus Plant, Hamburg General overview of Airbus site 17

18 Basic design and alternate concept of Moebius Menard Temporary sheet pile wall in 5 month dyke construction in 3 years Settlement 2,0 5,5 m Settlement 2,0 5,5 m Dyke construction to +6.5 in 8.5 month and to in 16 month Columns GCC Settlement 0, m Dyke construction to +6.5 in 8.5 month and to in 16 month Columns GCC Settlement 0, m 18

19 Subsoil characteristics 19

20 Case history EADS Airbus Plant, Hamburg How to move on the mud! 20

21 Case history EADS Airbus Plant, Hamburg 21

22 Case history EADS Airbus Plant, Hamburg 22

23 Stress path for Vacuum Process Surcharge p = 2/3 σ 1 K o = 0.5 Deviation Deviatoric Stress (q ) (q) Vacuum p = σ 1 ; K o = 1 Isotropic σ 1 = 80kPa σ 3 = 80kPa σ 2 = 40kPa K f (failure line) σ 1 = 80kPa σ 2 = 80kPa σ 3 = 40kPa Active Zone ε h < 0 Surcharge K o (ε h = 0) Passive Zone ε h > 0 Vacuum Consolidation Mean Stress (p ) 23

24 Case history : Kimhae (Korea)

25 Soil Improvement Techniques Cohesive soil Peat, clay Soil with friction Sand, fill Without added materials 1 Drainage 2 VAcuum 3 Dynamic consolidation 4 Vibroflottation With added materials 4 Dynamic replacement 5 Stone columns 6 CMC 7 Jet Grouting 8 Cement Mixing 25

26 Nice airport runway consolidation Granular soil Case History Very high energy (200 t, 24 m) 26

27 KAUST PROJECT Concept and application of ground improvement for a 2,600,000 m² 27

28 Discovering the Habitants 28

29 Areas to be treated AREAS TO BE TREATED AL KHODARI ( m2) BIN LADIN ( m2) SCHEDULE 8 month 29

30 Dynamic Consolidation Shock waves during dynamic consolidation upper part of figure after R.D. Woods (1968). 30

31 Concept Depth of footing = 0.8m Below G.L. Engineered fill Working platform (gravelly sand) 150 TONS σ z = 200 kn/m² 2 meters arching layer Compressible layer from loose sand to very soft sabkah 0 to 9 meters 31

32 Specifications ELEVATION (meters) TYPICAL SITE CROSS SECTION OF UPPER DEPOSITS SITE 1,5 km LAGOON FILLED BY SABKAH RED SEA CORAL BARRIER LAYER USC w % % fines N 1 - SABKAH SM + ML ,2-4 0,4-1,9 avr LOOSE SILTY SAND SM ,5-1,2 2, CORAL ,1-7, LOOSE TO MED DENSE SAND SM ,5-1, Qc BARS F R % P L BARS E P BARS 32

33 Typical surface conditions 33

34 ANALYSIS OF (PL-Po) IMPROVEMENT AS FUNCTION OF ENERGY AND FINES K.A.U.S.T. Saudi Arabia P L -P o (MPa) % DC DOMAIN SPEC DR I = 8 SI = 4,7 20% I = 6,25 SI = 2,3 30% DR DOMAIN SPEC DC I = 5,5 SI = 1,5 40% 50% I = 3,1 SI = 0, I = 3 SI = 0,56 Energy (kj/m 3 ) BASIS 60 grainsize tests 180 PMT tests PARAMETERS P L P o = pressuremeter limit pressure kj/m 3 = Energy per m 3 (E) % = % passing n 200 sieve I = improvement factor P P S.I : energy specific improvement factor LEGEND Average pre-treatment values Average values between phases Average post-treatment values LF Li SPEC DC : P L P o 0.75 MPa SPEC DR : PL Po 0.18 MPa I 100 E 34

35 35

36 VIBROFLOTS Amplitude 28 48mm 36

37 PORT BOTANY EXPANSION PROJECT GENERAL ARRAGEMENT COUNTERFORTS INCLUDING RECLAMATION 37

38 Soil Improvement Techniques Cohesive soil Peat, clay Granular soil Sand, fill Without added materials 1 Drainage 2 VAcuum 3 Dynamic consolidation 4 Vibroflottation With added materials 4 Dynamic replacement 5 Stone columns 6 CMC 7 Jet Grouting 8 Cement Mixing 38

39 Dynamic Replacement CONCEPT PARAMETERS -Very soft to stiff soils -Unsaturated soft clays -Thickness of less than 6 meters -Arching layer available -C,, µ, E y of soil, column and arching layers, grid -or P L, E P, µ of soil, column and arching layers, grid 39

40 Stone Columns Bottom Feed Vibrator penetration Material feeding Vibration of material during extraction Principle of the technology - bottom feed with air tank 40

41 Stone Columns Bottom Feed Stone Columns bottom feed to 22 m depth 41

42 Construction principles and equipment Wet soil-cement column systems SMET Tubular Soil Mix (TSM ) system Denies et al. Soil Mix walls as retaining structures Belgian practice. IS-GI 2012 Typical characteristics: Water/Cement weight ratio (W/C): 0.6 to 1.2 (-) Amount of cement: 200 to 450 kg/m3 Spoil return: up to 30% 42

43 Construction principles and equipment Cutter Soil Mixing (CSM ) system for soil mix panels Gerressen and Vohs. CSM-Cutter Soil Mixing Worldwide experiences of a young soil mixing method in challenging soil conditions. IS-GI 2012 Several case histories in the proceedings of the IS-GI 2012 Typical characteristics in Belgium: Water/Cement weight ratio (W/C): 0.6 to 1.2 (-) Amount of cement: 200 to 400 kg/m3 Spoil return: up to 30% 43

44 Deep mixing EN (CEN TC 288) : field of application 44

45 Field of applications and case histories Barrier against liquefaction and post-liquefaction damages 3D arrangement of Geomix caissons Benhamou and Mathieu. Geomix Caissons against liquefaction. IS-GI

46 Soil Improvement Techniques Cohesive soil Peat, clay Granular soil Sand, fill Without added materials 1 Drainage 2 VAcuum 3 Dynamic consolidation 4 Vibroflottation With added materials 4 Dynamic replacement 5 Stone columns 6 CMC 7 Jet Grouting 8 Cement Mixing 46

47 RIGID INCLUSIONS - PARAMETERS SOIL -C,, E y, µ, γ, ϕ INCLUSION -E y, µ, γ, D (non porous medium) -K v, K h if consolidation is considered 47

48 CMC Execution Fleet of specilized equipment Displacement auger => quasi no spoil High torque and pull down Fully integrated grout flow control Grout flow Soft soil 48

49 CMC Principle Create a composite material Soil + Rigid Inclusion (CMC) with: Increased bearing capacity Increased elastic modulus Transfer the load from structure to CMC network with a transition layer Transition layer Stress concentration CMC Residual stress Arch effect between the columns CMC 49

50 CMC Design Specific case of non vertical loading Calculation principle 1/ Estimation of the vertical stress in the column (% of the embankment load), 2/ Thus maximum momentum so that M / N D / 8 (no traction in the mortar), 3/ Thus maximum shear force taken by the includion (similar to a pile to which a displacement is applied), 4/ Modeling of the CMC as nails working in compression + imposed shear force under TALREN software (or equivalent). R i δ Ti 50

51 Future Caisson Stability Analysis 51

52 As built conditions 52

53 Proposed solution Layer I 15% rock (φ = 45 ) + 85% clay (C u = 50 kpa) Layer II 53

54 View of pounder construction 54

55 View of pounder ready to work 55

56 General SFT up 56

57 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 57

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