sasw
TRANSCRIPT
SPECTRAL ANALYSIS OF SURFACE WAVES (SASW)
GROUP 3 :CHONG WAI LOON A141938
MUHAMMAD SYAHIR BIN NOTZIR A141551AMIRAH BINTI AHMAD SALEHIN A141161
What is SASW ?
In situ method and non-destructive measurement that is rapid and cost effective.
This method has been introduced since 1980’
Spectral analysis surface wave (SASW) technique will be applied to characterize dispersion curve material profile by varying the frequency via surface wave testing system.
Surface wave
Rayleigh wave , VR Love wave
- causing the ground to shake in an
elliptical motion, with no transverse, or
perpendicular, motion.
- cause horizontal shifting of the
Earth during an earthquake
Setting Up SASW
Apparatus1. Geophones
2. Measuring tape
Apparatus3. Sledge Hammer
4. Control Unit
Apparatus5. Battery or Generator
6. Computer
Procedure1. Set the inter-receiver spacing, and set up
geophones.
Procedure2. Strike the ground at distance of d1 from
Receiver R1.
Procedure3. Repeat the process with farther source
distance with the interval of d1.
Procedure4. Transfer recorded data to computer for analysis.
Application of SASW
Determination of pavement system profiles including the surface layer, subgrade materials.
Determination of abutment depths of bridges.
Condition assessment of concrete liners in tunnels, slabs, and other concrete members.
Determination of pavement system
Determination of pavement system
Determination of abutment depths of bridges
Determination of abutment depths of bridges
Condition assessment of concrete
Interpretation of data
• The phase shift of the cross power spectrum between two receivers is used to determine the experimental dispersion curve. The dispersion curves are as follows:• t(f)=φXY(f)/360*f•Vr(f)=D/t(f)• λr(f)=Vr(f)/f
Data collection
Typical phase of the cross spectrum and coherence function recorded during SASW test.
The figure shows dispersion curves determined from SASW. The measurement also shows the thickness of the surface layer
generated by grapher.
Advantages of SASW
It does readily images low velocity zone as refraction method cannot see.
It is a non-invasive method.
It is cost effective.
Disadvantages of SASW
It is not nearly as resolved as a seismic collection done in wellbore.
There are also possibility for non-unique solution to dispersion curves. (several sets of parameters can yield the same dispersion curve).