Piezocone Penetration Tests CPTU

Transcription

1 Piezocone Penetration Tests CPTU Fernando Schnaid Universidade Federal do Rio Grande do Sul, Brazil

2 CPTU Standards Equipment & Procedures Measurements & Corrections Interpretation methods New devices Cone-pressuremeter Seismic-cone Environmental cone

3 CPTU Advantages - Fast penetration (20mm/s); - Continuous measurements; - Resolution & repeatability; - Robustness; - Flexibility on pushing equipments Limitations - No sampling; - Good workmanship - Penetration in hard soils and soft rocks

4 Standard 1930: CPT development in the Netherlands; 1950: Brazil / 1979 Standard 1977/1989: ISSMFE; 1979: ASTM; 1994: Eurocode 7

5 Onshore and offshore

6 Onshore and offshore

7 Onshore and offshore

8 Equipment v s f s u 2 u 1 q t

9 Equipment

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11 New Equipment Flow penetrometers (Randolph, 2000s)

12 Measurements & corrections Pore pressure u1 tip; u2 base; u3 shaft; Tip resistance q t = q c + ( 1 a). u 2 qt = corrected tip resistance qc = measured tip resistance a = area ratio (=AN/AT),

13 Measurements & corrections Shaft resistance u A u A A 2 sb 3 ft = fs + Al ft = corrected shaft resistance fs = measured shaft resistance Asb, Ast = areas Al = shaft area l st Poro pressure parameter Friction ratio B q = u ( q ( 2 t uo) σ ) vo R = f f q s c

14 Typical CPTU profile Penetration rate: 20 ± 5mm/s Tip 60 o angle and roughness of less than 1μm Slope sensor 50 o change in inclination over 1m Dissipation tests: monitoring the dacay in pore pressure after stopping test at given depth Saturation of the porous stone for accurate measurements

15 Typical CPTU profile BR101 Santa Catarina

16 Breakwater, Brazil

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20 Soil Classification Pore pressure- u Tip resistance - qt Shaft friction - ft Classification charts (Douglas & Olsen, 1981; Senneset & Janbu, 1985; Robertson e outros, 1986; Robertson, 1990; Jefferies & Davies, 1991).

21 CLASSIFICAÇÃO DO SOLO Douglas & Olsen (1981)

22 CLASSIFICAÇÃO DO SOLO Q t = q t σ σ, vo vo F r = q t f s σ vo *100% Jefferies & Davies, 1991

23 CLASSIFICAÇÃO DO SOLO Robertson et al (1986)

24 Interpretation methods An example of octahedral and shear induced pore pressures during penetration Distribution of pore water pressure Baligh (1980s)

25 Soil properties Cohesive soils Su OCR Ko Go Ch Granular soils ψ φ Dr Go Silty soils U V Cemented geomaterials Go Undrained shear strength Stress history Geostatic stresses Stiffness Coefficient of consolidation State parameter Friction angle Relative density Stiffness Partial consolidation Soil stiffness

26 Interpretation methods Soil parameters References Soil classification Douglas & Olsen (1981); Senneset & Janbu (1985); Robertson et al (1986), Robertson (1990) In situ stresses (K 0 ) Mitchell & Masood (1994); Kulhawy et al (1985); Mayne & Kulhawy (1990); Brown & Mayne (1993) Internal friction angle (φ ) Senneset & Janbu (1984); Sandven (1990); Kulhawy & Mayne (1990) Modulo Constrained (D) Kulhawy & Mayne (1990) Shear modulus (G max ) Rix & Stoke (1992); Mayne & Rix (1993); Tanaka et al (1994); Simonini & Cola (2000); Powell & Butcher (2004); Watabe et al (2004); Schnaid (2005) Stress history (σ p, OCR) Schmertmann (1978) ; Sennesset et al (1982); Jamiolkowski et al (1985) ; Konrad (1987); Larsson & Mulabdic (1991) ; Mayne (1991; 1992); Chen & Mayne (1994) Sensitivity (S t ) Robertson & Campanella (1988) Undrained shear strength (S u ) Hydraulic conductivity (K) Robertson et al. (1992) Consolidation coefficient (C h ) Soil specific density (γ) Larsson & Mulabdic (1991) Cohesion intercept (c ) Senneset et al. (1989) Vésic (1975); Aas et al. (1986); Konrad & Law (1987); Teh & Houlsby (1991); Yu et al (2000); Su & Liao (2002) Torstensson (1977); Baligh (1985); Baligh & Levadoux (1986); Teh & Houlsby (1991); Robertson et al (1992)

27 Soil properties Cohesive soils Critical state soil mechanics S σ u ' vo = M 2 OCR r Λ Λ, r, M = state parametes Empirical and theoretical approches q c = N S + σ Nc= cone fator c u o a) Bearing capacity theory (BCT), b) Cavity expansion theory (CET), c) Strain path method (SPM), a) Finite element method (FEM).

28 Soil properties N c Penetration model Reference 7.0 to 9.94 BCT Caquot & Kerisel (1956) Beer (1977) lnI r CET Vesic (1975) 12+lnI r CET Baligh (1975) I r.67 + r c ( 1+ ln I ) + 2.4λ 0.2λ 1. Δ 1 s SPM+ FEM Teh & Houlsby (1991) FEM Yu et al (2000) ln λ 1. 83Δ I r 1+ Ar 1 A ln I r A 3 r lnI r -2.1Δ r + R A r 1+ 2A r A 1/8 r (1 + A r) 2Δ CET+ FEM CET+ FEM Su & Liao (2002) Abu-Farsakh et al (2003) (e.g. Yu and Mitchell, 1998; Yu, 2004)

29 Soil properties Undrained shear strength q t = N kt S u + σ vo Nkt = empirical factor σvo = vertical stress

30 Soil properties Undrained shear strength S u = ( q u2 ) t N ke Senneset et al (1982) S u = u ( 2 o ) Battaglio et al (1981) N u Δu Argila Porto Alegre

31 Soil properties Limites para o fator N Randolph (2004)

32 Soil properties Stress history [ S [ S u u / σ ' / σ ' vo vo ] ] nc = OCR Λ (Schofield & Wroth, 1962; Ladd e outros., 1977) Λ= state parameter Su σ ' vo = 023, OCR 08, (Jamiolkowski at al., 1985) S u = 0,22σ ' m (Mesri, 1975)

33 Soil properties Stress history Andresen et al, 1979

34 Soil properties Stress history Cavity expansion + critical state soil mechanics Mayne (1991) 1 OCR = M q c u ' σ vo 1 q = 2 c u OCR ' 1.95M + 1 σvo 1 2 1/ Λ 1/ Λ Pre-consolidation pressure M=1.2 (corresponding to φ =30) Λ=0.75 (Mayne, 2000) u2 = poro pressão shoulder u1 = poro pressão point Chen & Mayne, 1996 ' σ p = 0.305( qt σ vo ) Ip = plasticity index σ ' p = 0.65( qt σ vo )( I p ) 0.23

35 Soil properties Stress history (Mayne, 2000)

36 Soil properties Stress state K 0 σ ' = σ ' h v Normally consolidated Jacky, (1944) K 0 = 1 sen φ' Pre-consolidated Mayne & Kulhawy, (1982) K = ( sen φ') OCR 0 1 sen φ ' K 0 qt σ = 0,1 σ ' v0 v0 Porto Alegre research site

37 Soil properties Correlation between φ and IP for NA clays

38 Soil properties Soil stiffness Hardin (1978), Lo Presti (1982) among others identified the various factors affecting G G = f (σ v, eo, OCR, Sr, C, K, T) σ v = effective stress eo= initial void ratio Sr = degree of saturation C = grain properties K = soil structure T = temperature

39 Soil properties Soil stiffness G o = SF ( e)( σ σ ) ' v ' h n p (1 2n ) a S,n = empirical constants F(e) = void ratio fucntion (1/e), (1+e) ou (2.17-e)2/(1+e) G o = 1 ' 0.5 k 625 ( p ) ( ) 2 o OCR kpa ( e ) o Hardin (1978) G o 1.43 ' 0.22 ' (0.22) = 480( e) ( σ v ) ( σ h ) ( pa ) Jamiolkowski et al (1995)

40 Soil properties Soil stiffness G o 2.4 ' 0.5 = 24000(1 + e ) ( σ ) ( kpa) Shybuya et al (1997) o v Preliminary design G o = 406qc eo Mayne & Rix (1993) G = 50( σ vo ) Watabe et al (2004) o q t

41 Soil properties Leroueil & Hight (2003) have shown the effect of anisotropy Ghv/Ghh ou Gvh/Ghh versus s v /s h.

42 Soil properties Ghh and qt relationship Powell & Butcher (2004)

43 Soil properties Operational modulus Eu = n Su M = 8,25 (qt - σv0) Duncan & Buchignani, (1976)

44 Soil properties Coefficient of consolidation T * = R c 2 h t I r R = radius of the piezocone t = time for 50% dissipation Ir = rigidity index (= G/Su) G = shear modulus C h = T R 2 t I r Degree of consolidatio Filter position (%) Cone face (u 1 ) Cone shoulder (u 2 ) Five radii above cone shoulder Ten radii above cone shoulder T* (Houlsby & Teh, 1988)

45 Soil properties Coefficient of consolidation Typical example to calculate Ch

46 Soil properties Theoretical and experimental pore pressure curves u2 (soft clay)

47 Soil properties Coefficient of consolidation C h RR ( NA) = CR C Piezocone h( ) RR/CR (0,13 e 0,15) C = v k k v h C h Nature of clay No macrofabric, or slightly developed macrofibric, essentially homogeneous deposits From fairly well to well-developed macrofabric, e.g. sedimentary clays with discontinuous lenses and layers of permeable material Varved clays and other deposits containing embedded and more or less continuous permeable layers k h / k v 1 to to to 15 Jamiolkowski et al. (1985)

48 Soil properties Coefficient of consolidation Champlain Site, Canada Leroueil et al (1992) Robertson et al. (1992)

49 New Salgado Filho Tempo de recalques Airport Porto Alegre, RS 1. Introdução Curva Teórica e Experimental de dissipação, poro pressões u2 (solo argiloso)

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51 Settlement prediction Tempo (dias) Recalque (cm) Projeto PLACA 19 PLACA 22 PLACA 27 PLACA 28

52 Soil properties: granular Characterization Schnaid & Yu (2005) q c1 = q p c a pa σ v G o = α q σ 3 ' a v p a α = entre 110 e 280

53 Soil properties Uncemented unaged sands (after Eslaamizaad & Robertson, 1997 Western Australia sands (after Schnaid et al,2004)

54 Soil properties Ensaios Centrifuga Gaudin et et al al (2005) Liquefação Wride et et al al (2000)

55 Soil properties Granular soils N q q = c ' σ = vo exp(7.63tanφ') φ ' = arctan + [ log( / )] ' q σ t vo Mayne, 2006

56 Soil properties Granular soils Relative density D r = log 10 ( σ q c, vo ) 0,5 Jamiolkowski et al., 1985; 2003; Houlsby, Friction ratio [ D ( Q p ) R] ' ln ' ' φ φ = m Bolton, 1986 p cv r

57 Soil properties Granular soils (Robertson & Campanella, 1983) Previsão de densidade relativa através de qc (Lancellotta,1985)

58 Soil properties Granular soils Schnaid et al, 2004 G = 3 σ v q c pa Cimented G = 3 σ v q c pa Uncemented Jamiolkowiski et al, 1986

59 Houlsby (1998) Calibration chamber tests (clean sands): scatter

60 Soil properties State parameter ψ p e + λ ln p = ' 1 ' Γ λ, Γ = critical state parameters p 1 = mean stresses Wroth & Basset (1965) & Jefferies (1985)

61 New techniques Cone Pressuremeter

62 Conepressuremeter φ ps = 14.7 qc ln I ψ s l ξ o = qc ln ψ l CPT & SBPM + cavity expansion Yu, Schnaid & Collins, 1996

63 Seismic - cone V s 2 G o = ρ Vs u 2 u 1 q t

64 NOVOS EQUIPAMENTOS Cone Sísmico Medidas do Ensaio

65 Oscilloscope Crosshole Testing ASTM 4428 Pump Δt Shear Wave Velocity: V s = Δx/Δt Test Depth Downhole Hammer (Source) packer Note: Verticality of casing must be established by slope inclinometers to correct distances Δx with depth. PVC-cased Borehole Slope Inclinometer Δx PVC-cased Borehole Velocity Transducer (Geophone Receiver) Slope Inclinometer

66 Downhole Testing

67 Oscilloscope Pump Downhole Testing Horizontal Plank with normal load Δt z 1 z 2 Hammer x packer Test Depth Interval Shear Wave Velocity: V s = ΔR/Δt R 1 2 = z x 2 R 2 2 = z x 2 Horizontal Velocity Transducers (Geophone Receivers) Cased Borehole

68 Cabo Strain Gauges da Célula de Carga de Atrito Lateral Sensor de Temperatura Trandutor de Poro-Pressão Filtro de Material Plástico Acelerômetro Inclinômetro Luva de Atrito (Area de 150cm 2 ) Strain Gages da Célula de Carga de Resistência de Ponta Cone de 60 o diâmetro de 35.68mm V s = (L 1 -L 2 ) / (t 2 - t 1 ) G max γ = ρ V = g 2 2 s V s

69 Shear waves Downhole Left hand side blow Amplitude Time (ms) Δt Right hand side blow Vs med = ΔS Δt 2 Go Vs ( med = ρ )

70 Typical signal from SCPTU (Giacheti) Volts 0,500 0,375 0,250 0,125 0,500 8m de profundidade 0,000 0,00 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,09 0,10 0,11 0,12 0,13 0,14 0,15 0,16 0,17 0,18 0,19 0,20 9m de profundidade Δt V s ΔS 1m = = Δt Δt 0,375 Volts 0,250 0,125 0,000 0,00 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,09 0,10 0,11 0,12 0,13 0,14 0,15 0,16 0,17 0,18 0,19 0,20 0, m de profundidade Δt 0,3125 Volts 0,2500 0,1875 0,1250 0,00 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,09 0,10 0,11 0,12 0,13 0,14 0,15 0,16 0,17 0,18 0,19 0,20 Tempo (ms)

71 Giacheti (2001)

72 SCPTU desenvolvimento de sistema Heraldo L. Giacheti / FE-Unesp / EESC-USP

73 Computador registro solicitação Piezocone em câmara Pressão de água Aplicação Notebook registro piezocone

74 Seismic cone + = c o a q G p p ln ln ' χ α ψ β Cavity expansion + shear modulus Schnaid & Yu, 2005 Cavity expansion + shear modulus Schnaid & Yu, 2005

75 Fountanebleau Canlex, Wride Sand centrifuge et et al al (2000) tests Gaudin et et al al (2005)

76 Poland Seismic events Tailing dams

77 Brazilian experience on iron ore, gold and alumina storages Alumina tailings Upstream dikes Upstream tailings main dike Initial deposition

78 Upstream dikes Vertical drains Initial dike Side channel Liquefaction potential in sandy and silty tailings

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80 profundidade (m) ψ 0 0,25 0,5 0,75 1 PZC 1 PZC 2 PZC 3 PZC 4 PZC 5 PZC 6 PZC 7 PZC 8 Costa Filho &Bedin (2008)

81 Soil properties Silty soils

82 Soil properties Schnaid et al (2004)

83 Soil properties Schnaid et al (2006)

84 Soil properties Experimental (Blight 1968) Experimental (Randolph & Hope 2004) Numerical (Schnaid, 2005) Dimnsionless velocity V M. Randolph (2004) V = v d C v v = penetration vlocity d = cone diameter Cv =coefficient of consolidation Degree of drainage - U U = ( q q ) t ( q q ) t dr qtñ = undrained tip resistance qtdr = drained tip resistance qt = tip resistance tñ tñ

85 Soil properties

86 Soil properties RESÍDUOS DE MINERAÇÃO 1,4 1,2 1,0 Ouro (CPTU) Ouro (Palheta) Bauxita (CPTU) Argila (CPTU) Fertilizante (Palheta) Grau de drenagem (U) 0,8 0,6 0,4 0,2 0,0 1,0E-02 1,0E-01 1,0E+00 1,0E+01 1,0E+02 1,0E+03 1,0E+04 Velocidade (V)

87 Remarks Dedicated team with good workmanship The one test for soft clay Cam Clay type of materials (theoretical + empirical experience) Possibility of developing new interpretation methods in non-text book materials Silty soils need to change penetration velocity to avoid partial saturation during penetration