지표면 표면파 시험

지표면 표면파 시험 

 

영신컨설턴트 (02) 529 8803 ystcha@naver.com 2021 3

 

내진설계를 위해 현장시험 (콘관입시험 CPT, 표준관입시험 SPT, 다운홀, 연약지반 SCPT Vs)을 하고 실내시험으로 공진주 시험, 비틂 시험, bender element, 삼축 미소변형 시험합니다.

 

현장 다운홀 시험은 천공 후 지반과 센서의 접촉을 위해 케이싱 외부 그라우팅이 필요합니다. downhole 시험은 해머 타격으로 심도 30m이내 적합합니다.

 

지표면 표면파 시험은 상시 미동(passive)과 헴머 타격(active)시험으로 구분할 수 있고 상시미동 (passive method) 를 이용하면 시추공 없이 깊은 심도 전단파 속도를 알 수 있다.

 

 

ASTM D7400 08 Standard Test Methods for Down hole Seismic Testing Borehole Preparation: Acceptable Grouting Techniques Schematic

 

다운 홀 시험 시 케이싱 외부 그라우팅 

 

전단파 실내 현장시험 종류

 

지표면 표면파 시험

 

 

active method 헤머 타격

 

SASW, spectral analysis of surface waves ( Nazarian and Stokoe, 1984)

 

MASW, multichannel analysis of surface waves (Park et al., 1999)

 

상시 미동

 

SPAC, spatial autocorrelation Aki, 1957);

 

ESAC, extended spatial autocorrelation (Ohori et al., 2002);

 

Re-Mi TM, Refraction Microtemor TM (Louie, 2001);

 

SSAP, statistical self-alignment property (Mulargia and Castellaro, 2013).

 

 

 

표면파 Vs, 굴절법 Vp 시험기

 

 

표면파 분산곡선 dispersion curve

 

 

파장이 작고 주파수 큰 파는 지표면에 가깝고 속도가 느리고 파장이 크고 주파수 작은

 

파는 깊은 심도로 전파되고 속도가 빠르다. 이것을 분산곡선이라 한다.

 

short (high frequency) waves travelling close to the surface and with generally low velocity, long (low frequency) waves shaking also deep layers and propagating with the larger velocity characteristic of deeper layers. This property is called dispersion.

 

 

속도 The velocity of propagation of surface waves ?

 

?= ?x ?

 

? the wavelength 파장 , wave frequency ?주파수

분산곡선 주파수와 속도

 

 

표면파는 파장의 1/2 심도에서 대부분의 변위가 발생한다.

위 분산 그래프에서 5Hz (x축) 120m/sec (y)

파장 ?= 120m/sec / 5Hz = 24m

대부분 변위를 발생하는 심도 z 는 z =24/2 =12m

active method (hammer 타격) SASW, MASW

 

SASW

the source to near-receiver spacing (d1) = the receiver spacing (d2)

 

VR = f * d2 / (Δφ/360°),

 

 

 

위상각 Δφ, 지오폰 거리 d2, 파장 ?관계 Δφ / 360° = d2 / ? VR = ? x ?

 

 

Cross-correlation 2 지오폰 신호 시간 차 time lag ? 비교

 

Rayleigh wave phase velocity spectra from a MASW survey. The color scale indicates the amplitude of the correlation function for each tested velocity and frequency (high correlation in red, low correlation in blue).

 

Wavefield transform of MASW data

 

One advantage of the MASW technique is that the wave field transformation may not only identify the fundamental mode but also higher modes of surface waves.

At some sites, particularly those with large velocity inversions, higher surface wave modes may contain more energy than the fundamental mode.

 

 

 

상시미동 표면파 측정 Passive Surface Wave Techniques

 

 

 

array microtremor and refraction microtremor (REMI) techniques.

 

Passive surface wave techniques measure noise; surface waves from ocean wave activity, traffic, factories, wind, etc. These techniques include the array microtremor and refraction microtremor (REMI) techniques.

The array microtremor technique typically uses 7 or more 4.5- or 1-Hz geophones arranged in a two-dimensional array.

 

spatial autocorrelation (SPAC)

 

A technique called spatial autocorrelation (SPAC) is used to obtain the Rayleigh wave dispersion curve. For a particular frequency the phase velocity is equal to that which best fits a first order Bessel function to the SPAC function.

 

The image shown is phase velocity versus frequency showing the degree of fitness of the Bessel function to the SPAC function for a wide velocity and frequency range. The dispersion curve, is the peak (best fit), as shown in the figure below.

 

 

refraction microtremor (REMI)

 

The refraction microtremor (REMI) technique uses a field layout similar to the seismic refraction method (hence its name). Twenty-four, 4.5 Hz geophones are laid out in a linear array with a spacing of 6 to 8m and fifteen to twenty 30-second noise records are acquired.

 

Surface wave dispersion curve, VS models and PS suspension log from Dolphin Park,

Carson, California.

 

 

The 2000 International Building Code (IBC)

 

Class A – hard rock – VS30 > 1500 m/s (UBC) or VS100 > 5,000 ft/s (IBC)

Class B – rock – 760 < VS30 ≤ 1500 m/s (UBC) or 2,500 < VS100 ≤ 5,000 ft/s (IBC)

Class C – very dense soil and soft rock – 360 < VS30 ≤ 760 m/s (UBC)

          or 1,200 < VS100 ≤ 2,500 ft/s (IBC)

Class D – stiff soil – 180 < VS30 ≤ 360 m/s (UBC) or 600 < VS100 ≤ 1,200 ft/s (IBC)

Class E – soft soil – VS30 ≤ 180 m/s (UBC) or VS100 ≤ 600 ft/s (IBC)

Class F – soils requiring site-specific evaluation