EVALUATION OF LIQUEFACTION POTENTIAL INTERMS OF SURFACE WAVE METHODYU Shizhou*

Supervisor:

TAMURA, Masahito**
HAYASHI, Koichi***

MEE06023
ABSTRACT

Soil liquefaction had been observed as a kind of ground failure after strong earthquake. Now, in many
countries, judgment of liquefaction potential is considered in seismic code, and the standard penetration
tests (SPT) is usually performed for the soil liquefaction potential situation. But, according to the cost,limited time, unsuitable site condition, traditional method often couldn’t meet the user’s demands. As anattempt, an alternate method in terms of Surface Wave Method (SWM) has been used in recent years. In
this paper, based on the Noto-Hanto earthquake (M6.9, March 25, 2007) and the Niigata Chuetsu-Oki
earthquake (M6.8, July 16, 2007), SWM method and further comparison with active method had been
carried out for the valuation of liquefaction potential.
Keywords: Liquefaction, Earthquake, Valuation, SWM method

INTRODUCTION
SWM method is based on the analysis of the dispersion of surface waves. And the vertical distribution ofthe dynamic shear modulus in the subsoil can be obtained by this method. Main steps for this method areestimating the dispersive characteristics of a site by means of acquisition and processing of seismic data,
further inverting the data for estimate of the subsoil properties. At last, the vertical profile of the shear
wave velocity is obtained. In order to recognize the various propagation characteristics of the seismic
wave field, Multi–channel analysis of surface waves (MASW) method (Park et al., 1999a; Xia et al., 1999;
Miller et al., 1999) is utilized, which employs multiple receivers equally placed along a linear survey linewith seismic waves generated by an impulsive source. Hayashi and Suzuki (2004) proposed Common
Mid-Point (CMP) cross-correlation analysis of multi–channel surface wave method to give accurate phasevelocity curves, and enable us to reconstruct 2D (two dimensional) velocity structures with high resolution.
For the judgment of soil liquefaction potential, a simplified procedure is the judgment of soilliquefaction potential based on the Standard Penetration Test (SPT). And the cyclic stress ratio (CSR) is
used to represent the seismic load on the soil. This method had been developed several times after 1971
(Seed 1979; Seed and Idriss 1982; Seed at al 1983; Seed at al 1985). Now, comparing with SPT method,some simple, easy methods are carried out, such as the Cone Penetration Test (CPT) and small strain shear
wave velocity Vs measurement, which had been reviewed by the National Research Council (NRC, 1995)
and Youd and Idriss (1997). Especially, the liquefaction evaluation method based on Vs had been
recommended by Dobry et al. 1981, Seed et al. 1983, Stoke et al. 1988, Tokimatsu and Uchida 1990.
According to feasibility, easy and simple operation, non-destructiveness, it had been developed very fast.
* Institute of Engineering Mechanics (IEM), China Earthquake Administration (CEA), ** Building
Research Institute (BRI), International Institute of Seismology and Earthquake Engineering (IISEE), ***OYO Technology and Engineering Center, OYO Corporation.

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LIQUEFACTION JUDGMENT BY SURFACE WAVE METHOD
In field studies, survey lines were performed to construct
the shear wave velocity profile down to 20 m of the siteusing MASW technique. And then the factor of safety
against liquefaction could be calculated by shear wave
velocity (Vs).
Test method and procedure
Figure 2 Diagram of data acquisition
system for MASW method
Source= -0.5m
0Time (msec)
100

200

300

400

500

60002468Distance (m)Surface wave measurement
Based on the MASW method, the data had been acquired.
The schematic view of a surface wave method is shown in
Figure 2, and the equipment for this survey (Figure 2) iscomposed from:z Data logger: OYO McSEIS-SXWz Seismometers: geophones with 4.5 Hz frequency
z Source: Sledgehammer
In this figure, Twenty four geo-phones of 4.5 Hz resonant
frequency are deployed at 1 m spacing along a survey linewith receivers connected to multi-channel recording device.
10 kg sledgehammer is used as the active source placedwith 1 to 2 m intervals.

1012141618202224

sxom8030.sg2

Figure 3 Survey line and obtained data

Data processing
In this step, the CMP cross-correlations analysis will be applied to multi-channel and multi-shot surface
wave data. Based on nonlinear least squares inversion, a 2D surface wave velocity profile is reconstructed.
The procedure of the CMP cross-correlations analysis is summarized in the following points.
z For every pair of traces, cross-correlations are calculated in each shot gather.
z The correlation traces with a common mid-point are gathered, and those traces having equal
spacing are stacked in the time domain. The resultant cross-correlation gathers resemble shot
gathers and are referred to as CMP cross–correlation gathers.
z For calculating phase velocities of surface waves, a multi–channel analysis is applied to theCMP cross–correlation gathers.
z By non-linear least squares inversion, a 2D S–wave velocity profile is reconstructed.
Frequency (Hz)
500.0

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0(m)40.0

S-velocity

0.0

450.0
400.0

Depth

Phase-velocity (m/s)

Toge A Line

350.0
300.0
250.0

500.00280.00160.00100.00
40.00

4.0
8.0

200.0

12.0

150.0

0.0

100.0

10.0

20.0

50.0
0.0

Distance

Dispersion curve :Figure 4 Dispersion curve and Vs structure of one survey line230.0(m)(m/sec)Calculation of liquefaction potential
Safety factor (Fs)
For the judgment of liquefaction potential based on Shear wave velocity (Vs), the safety factor againstliquefaction of a soil at a particular depth in a soil deposit is defined as follows.

Fs =CRR;
CSR(1)Where, CRR is the resistance of the soil, which is expressed as the cyclic resistance ratio (CRR).
And CSR is the loading induced by an earthquake which is expressed as the cyclic stress ratio (CSR). Ifthe Fs is less than 1, the occurrence of liquefaction is predicted.
For CSR is generally expressed as follows (Seed and Idriss 1971).

CSR = 0.65

σ υ ⎛ a max ⎞ rd⎟⋅;⋅⎜σ υ/ ⎜⎝ g ⎟⎠ MSF(2)

Where, σ υ is total overburden stress at the depth in question, [kN/m2]; σ υ is initial effective/overburden stress at the same depth, [kn/m2]; amax is peak horizontal ground surface acceleration, [gal];

g is acceleration of gravity, [980cm/s2]; rd is shear stress reduction factor to adjust for flexibility of thesoil profile. The value rd at the depth of z can be calculated using the following equation (Liao et al. 1988;
Robertson and Wride, 1998).
rd = 1 − 0.00765 z

forz ≤ 9.15m;

rd = 1.174 − 0.0267 z

for9.15m ≤ z ≤ 23m;

rd = 0.744 − 0.008 z

for23m ≤ z ≤ 30m;

(3)

As a characteristic of the ground shaking intensity, amax is defined as the peak value in a horizontal
ground acceleration record. Peak acceleration is commonly estimated using empirical attenuation
relationships of amax, as a function of earthquake magnitude, distance from the energy source, and local
site conditions. And the densities of the various soil layers and characteristics of the ground water (unit,σ'σmeter) would be used in the calculation of ν and ν . The magnitude of earthquake is used in thecalculation of MSF which can be expressed by the following equation.
n⎛M ⎞MSF = ⎜ w ⎟ ;⎝ 7.5 ⎠(4)

Where: Mw moment magnitude of the earthquake. The lower bound for the range of magnitudescaling factor recommended by the 1996 NCEER workshop is defined with 2.56 (Idriss personalcommunication to T.L.Youd, 1995) for earthquakes with magnitude ≤7.5. The upper bound of therecommended range is defined with 3.3 Andrus and stokoe, 1997) for earthquakes with magnitude ≤7.5.
For earthquakes with magnitude >7.5, the recommended factors are defined with 2.56.

3The CRR expressed as the cyclic resistance is generally established by separating liquefied cases
from non liquefied cases. The following empirical equation defined by Andrus et al. (1999).

⎡ ⎛ V s1 ⎞ 2⎛ 1 ⎞ 1⎤⎟⎟ − ⎥;CRR = ⎢a⎜(5)⎟ + b⎜⎜
100c−Vc⎦⎝⎠⎝s1 ⎠⎣Where, a, b, c are curse fitting parameters ( a = 0.022, b = 2.8, c = 200 ~ 215 m ); V isss1
overburden stress corrected shear wave velocity (m/s), which is defined in the following equation.
⎛P ⎞Vs1 = Vs ⋅ ⎜⎜ a/ ⎟⎟⎝ συ ⎠0.25(6)

Where, Vs is the measured shear wave velocity, (m/s); Pa: reference stress (100kPa); σ υ is initialeffective overburden stress, (kPa). The parameter c in the Eq(6) represents the limiting upper value of Vs1for liquefaction occurrence.
/Liquefaction Index (PL)The liquefaction index is calculated using the following formula:20

PL = ∫ F ⋅ w( x ) dx0(7)Where, F < 1.0, F = 1 − F ; F ≥ 1.0, F = 0 , w( x ) is weighted function value, w( x ) = 10 − 0.5x
LLLand x is the depth from surface.
FIELD STUDY
During the two field studies, total 40 survey lines had been selected for surface wave method application.
According to the damage due to soil liquefaction, 12 and 28 MSAW data had been acquired separately in
Noto and Niigata area. As examples, some results are shown below.

Figure 5 Sketch map investigate and Vs structure & FL results of survey line 41, 42, 43 in Kariwa

4FL (sand & all type)FL (sand & all type)0120

3

SWS data 49

223244668

Depth (m)Depth (m)100

SWS data 48

1012810121414161618182020All type

All type

Sand

SandFigure 6 N value and FL results of SWS data 48, 49 in Kariwa, Niigata
From Figure 5 and 6, Vs structure can describe the soil profile more clear than conventional method.
Compared with the results of SWS data, SWM method can draw a similar conclusion. From the groundsurface to depths of 8 or 10 meters is covered by loose sandy layer which has very high potential ofliquefaction.

AD
Copyright problem

Copyright problem

BCFigure 7 Results and maps about survey line 51, 52 in Matsunami, Niigata
As another example shown in Figure 7, the red ellipse in part B marks severely damaged area.
Compared with part B, part C is an old map, it shows the coniferous forest and wet low land distributed in
the two sides of the red boundary line. From part D, the Vs structures describe the soil condition moreclearly. Around 50m from left side of line 51, the soil stiff is harder than that of the other part, and the FL
value also bigger. From part A, the FL values of SWS data 51, 52, 53 are so bigger than the results ofother data.

5CONCLUSIONSIn this paper, the surface wave method has been introduced to judge soil liquefaction potential fromsurface as a nondestructive test. The shear wave velocity can be obtained by the surface wave method andcomparing with existing data, such as borehole data and Swedish Weight Sounding data, the results
calculated based on surface wave method can be used as a new judgment method of liquefaction potential,and explain the damage due to soil liquefaction. The final conclusions are summarized as follows:z In order to verify the causes of damage due to soil liquefaction, the surface wave method was applied
to obtain the shear wave velocity, furthermore to judge liquefaction potential in two fields.
z For field study in Nodo area, without enough borehole data, a new judgment method of soil typebased on shear velocity and N value of SWS is carried out. The last results can take the place of thesoil profile determined by SWS method.
z For field study in Niigata area, comparison with borehole data, judgment of liquefaction potential had
been applied and the results found to be agreed with the data of traditional method very well.
z Comparing with SWS data, shear wave velocity is more accurate to describe the soil stiffness andconfirm the soil profile.
z Compared with active method, surface wave method can obtain more data due to economy, easy
control and nondestructive characteristic.
In order to reduce earthquake casualties and economic losses, safety evaluation of site is very
important. Compared to traditional method, the surface wave method is an easy, inexpensive andnondestructive method to evaluate liquefaction potential. For these advantages, it has vast vistas topopularize and utilize in the future.

ACKNOWLEDGEMENT
During my individual study, Dr. Hayashi from OYO Corporation my advisor, guided, inspired andsupported my work. Also, I would like to thank them and other staff working with me in the field tests forevery packed but meaningful day.

REFERENCES
Hayashi K., Suzuki H., 2004, CMP cross-correlation analysis of multi-channel surface wave data,
Exploration Geophysics 35, 7-13.
Jamts, A., 2006. Soil tests by surface wave method, master report.
Miller R.D., Xia J., Park C.B Ivanov J, 1999, Multichannel analysis of surface waves to map bedrock,
The Leading Edge, 18(12), 1392-1396.
Xia J., Miller R.D., Park C.B., 1999, Estimation of near-surface shear-wave velocity by inversion ofRayleigh waves, Geophysics, 64, 691-700.

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