Analysis of borehole data Luis Fabian Bonilla Universite Paris-Est, - PowerPoint PPT Presentation

Analysis of borehole data Luis Fabian Bonilla Universite Paris-Est, IFSTTAR, France 1

Outline • Advantages of borehole data • Difficulties of working with these data • Understanding linear and nonlinear modeling • Working proposition? 2

1. Advantages of borehole data Garner Valley - USA (Borehole Obs.) Wave propagation from bedrock to surface 3

PGA distribution (KiK-net) Field data observation of soil nonlinearity onset? Statistical analysis with respect to magnitude and Vs30 4

Calibration of soil models Stress computation from Waveform modeling deformation data 5

Revealing nonlinear response after Bonilla et al. (2011) • 2011 Tohoku earthquake data • Predominant frequency more affected than fundamental • Affected frequency increases as Vs30 increases 6

Port Island, Kobe / Kushiro Port Loose sand => liquefaction Dense sand => cyclic mobility - Lowpass filtering - High frequency peaks - Deamplification - Amplification Velocity model is not always enough! 7

2. Difficulties of borehole data Downgoing wavefield Site response (outcrop response) is not the same as borehole response 8

Vs30 uncertainty (lack of knowledge of the medium) • Variability within each soil class is important • This variability is even larger at depths greater than 30 m • Is Vs30 enough? • Not always core sampling, thus no dynamic soil parameters 9

Analysis of KiK-net boreholes • Similar Vs30 (between 350 and 450 m/s) • Different velocity distribution at depth • Different site response • Is Vs30 enough? After Regnier et al. (2010) 10

Vs30 = 400 +/- 5 m/s Vs (m/s) 500 1000 1500 2000 2500 3000 0 After Regnier et al. (2010) 20 40 60 Depth(m) 80 100 120 140 "+>&'+"( 160 No comments! The data speak alone 11

3. We need to know well the linear response (example of the CORSSA array, Greece) 1. H/V spectral ratio (noise data) 2. H/V spectral ratio (earthquake data) 3. Standard spectral ratio (borehole response) 4. Borehole response inversion (velocity, thickness, and Q profiles) 12

1832 T. Satoh, T. Sate, and H. Kawase Table 3 Soil Properties Obtained from the Identification Method for S-Wave Velocities and Damping Factors S-Wave Velocity (m/see) Damping-Factor (%) Thickness Kanagawa Kanagawa No. (m) Mainshock Foreshock Aftershock Earthquake Mainshock Foreshock Aftershock Earthquake 1 7.0 53.8(63.8) 60.7 59.1 64.4 7.0(6.3) 3.4 3.9 5.0 2 5.0 158.8(168.8) 165.7 165.8 169.4 3 16.0 690.0* 4 48.0 340.0 5 6.0 750.0* 2.8 6 12.0 340.0 7 3.6 700.0* 8 -- 800.0* In the first and second layers, the values in parentheses are identified from the part just after the main parts of the mainshock records, and the values Inverting for nonlinear soil properties without parentheses are identified from the main parts. Asterisks indicate S-wave velocities based on the logging results, i.e., not identified here. in the main part and the part just after the main part of the strong motion, vertically propagating S waves are dominant (a) (b) Sand and gravel Clay in the period range from 0.1 to 2.0 sec, while in the later Identified Equivalent linear part, horizontally propagating waves are dominant in the pe- 1 1 11 3, 5, 9 10 4 1 2 PI = 200% the main part of the foreshock record A riod range longer than 0.7 sec, and vertically propagating S ~t 8 0. 8 0. 8 the main part of the mainshock record O waves are still dominant in the shorter period range. For the G/G max G/G max just after the main part of the mainshock record m weak motion, only the main part can be examined because 0. 6 0. 6 PI = 0% of the small signal-to-noise ratios in other parts. In the main 7 1.0 20 0. 4 0. 4 part of the weak motion, vertically propagating S waves are 0.8 6 16 I lllllll IIIIIIII also dominant. Inversion - sand Inversion - clay 0. 2 0. 2 ..q 0.6 Inversion - gravel Vucetic and 12 IIIlllll IIIitll Based on these results, we decided to analyze these three Seed and Idriss (1970b) Dorby (1991) ~7 > 0.4 8 0 0 S-wave dominant time segments, that is, the main part of the IIIIIIll I LtlI_'. - 10 -6 10 -5 10 -3 10 -2 10 -6 10 -5 10 -4 10 -4 10 -3 10 -2 0.2 '--FI-fl-flff- I IIIIIll 4 strong motion, the part just after the main part of the strong γ γ motion, and the main part of the weak motions, based on 1D 0.0 10-4 De Martin et al. (2010) 100 0 10- 3 10- 2 10- 1 '-n wave propagation theory for vertically propagating S waves. >. o (a) First layer The observed spectral ratio between KD2 and KS2 for the 1.0 ,q (a) (b) 20 Surface Layer Intermediate Layer o main part of the strong motion shows a longer peak period t ll,,Jl,,I ,,,lll,Jt I < 0.8 16 with lower amplitude at the peak around 0.5 sec compared 1.4 1.4 0,6 041j r Empirical 12 to the corresponding peak for the weak motions. The shift Relationship 1.2 1.2 8 Empirical I IIIIIJl lJ l-- llrllll I of the peak period can be clearly seen in the Fourier spectra 120 Relationship 02 o.of-FFIll-Itff-Tlflllltl I IIIIIIII I IIIIIIII 4 140 of the KS2 records. To quantify this period and amplitude 1.0 1.0 80 70 0 shift, the S-wave velocities and the damping factors are iden- 60 10 -4 10-3 10- 2 10-1 100 60 0.8 0.8 50 100 tified by minimizing the residual between the observed spec- SHEAR STRAIN (%) 50 80 tral ratio and the theoretical amplification factor calculated 0.6 0.6 (b) Second layer 90 70 40 140 from the 1D wave propagation theory. The S-wave velocity 0.4 0.4 Figure 15. Relationships between the effective and the damping factor in the surface alluvial layer identified Fujisawa Sand Disturbed Samples 40 Pioneering work by T. shear strain and the shear modulus reduction ratio or for the main part of the strong motion are about 10% smaller Undisturbed 0.2 0.2 Samples the damping factor for (a) the first layer and (b) the and 50% greater, respectively, than those identified for the : void ratio Satoh since the 90’s second layer are estimated by two methods. Solid 0 0 main part of the weak motions. The relationships between 10 -2 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 symbols shows the values based on linear 1D theory 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 the effective shear strain and the shear modulus reduction with the S-wave velocities and the damping factors Strain Strain estimated by the identification method. Open symbols ratios or damping factors estimated by the identification Mogi et al. (2010) show the values based on the equivalent linear 1D method agrees with the laboratory test results. We corrob- theory in which the S-wave velocities and the damp- • Use of vertical arrays orate that the main part of the strong motion, whose maxi- ing factor for the main part of the foreshock are used mum acceleration at the surface station KS2 is 220 cm/sec 2 as initial values for iteration. The shear modulus re- duction ratio for the foreshock are assumed to be unity and whose duration is 3 sec, has the potential of making the • Inversion of G/Gmax only and the damping factor to be 3.4% at the effective surface soil nonlinear at an effective shear strain on the order shear strain of 10-4%. Solid and dashed curves rep- of 0.1%. resent the shear modulus reduction ratios and the The S-wave velocities in the alluvial layers identified damping factors as a function of the effective shear strain given by JESG (1991) from laboratory tests. from the part just after the main part of the strong motion 13

Inverting for nonlinear soil properties Assimaki et al. (2010) Inverting for G/Gmax and damping ratio 14

An insight of nonlinear soil response out ts a a/ 2 ff P o.A P o.B P o.C Gandomzadeh (2011) 1 a 2 Foundation length 3 sb Soil-structure interaction model 0 Soil profile 1 − 5 Soil profile 2 ρ 1 = 1930 kg/m 3 Soil profile 3 10 m − 10 V s 1 = 220 m/s − 15 ρ 2 = 1980 kg/m 3 − 20 Depth (m) 20 m V s 2 = 400 m/s − 25 − 30 − 35 ρ 3 = 2040 kg/m 3 20 m V s 3 = 550 m/s − 40 − 45 ρ = 2100 kg/m 3 − 50 0 200 400 600 800 1000 V s = 800 m/s Shear Modulus (MPa) (a) Low-strain shear moduli of the profiles (b) Soil profile (#2) Confining pressure dependency 15

An insight of nonlinear soil response out ts a a/ 2 ff P o.A P o.B P o.C 1 a 2 Foundation length (a) Dissipated energy (b01 and soil profile #2) (b) Dissipated energy (b02 and soil profile #2) 3 sb 0. 2.5 .5 3. 1. 3.5 1.5 4. I soil = 1 � � σ ( x, t ) : d � ( x, t ) dV 2. 4.5 Ω 2.5 5. Ω t (d) Legend: ( J/m 3 ) (c) Dissipated energy (b03 and soil profile #2) 0.2g 0.7g 0 0 0 0 free field Po.A − 5 − 5 − 5 Po.B − 5 Po.C − 10 − 10 − 10 − 10 Dissipated energy is − 15 − 15 − 15 − 15 higher at interfaces − 20 − 20 − 20 − 20 and close to the free Depth Depth Depth Depth − 25 − 25 − 25 − 25 surface − 30 − 30 − 30 − 30 − 35 − 35 − 35 − 35 − 40 − 40 − 40 − 40 free field free field free field − 45 Po.A − 45 Po.A − 45 − 45 Po.A Po.B Po.B Po.B Po.C Po.C Po.C − 50 − 50 − 50 − 50 0 0.2 0.4 0 2 4 6 0 50 100 0 0.02 0.04 0.06 I soil (J/m 3 ) I soil (J/m 3 ) Shear strain (%) − 3 Shear strain (%) x 10 Gandomzadeh (2011) (a) Dissipated energy (b) Maximum shear strain (c) Dissipated energy (d) Maximum shear strain 16