1. Creating a Conference Poster
The Application of MASW for Geotechnical Investigation (Site Characterization): Strengths and Limitations
Abdullah Alhaj*, Neil Anderson, and Evgeniy Torgashov
Department of Geosciences and Geological and Petroleum Engineering, Missouri University of Science and Technology, Rolla, MO 65409, USA
Creating a Conference Poster
Authors or Reserachers
Department or Organization
Introduction
Results and Discussions
Objective:
Multichannel analysis of surface wave (MASW) method is a nondestructive seismic method, which is widely used for geotechnical investigations; including but not limited to engineering properties of soil, variable depth to bedrock, or as a supportive geophysical method with other geophysical methods such as ERT, SCPT, borehole, etc. MASW is a rapid and cost-effective method to calculate 1D shear wave velocity profile of subsurface. However, this technique has some limitations that can affect its utility such as the short depth of investigation, invisible thin layers, and lateral and vertical averaging of the acquired field data. An overview about MASW is addressed including its strengths and limitations.
Introduction :
Multichannel analysis of surface waves (MASW) method is one of the seismic survey methods which is utilized to evaluate the elastic condition (stiffness) of the subsurface for geotechnical engineering purposes. MASW first analyzes seismic surface waves generated from various types of seismic sources such as sledge hammer to determine the phase velocities of these surface waves, and then finally, calculate the shear-wave velocity (Vs) variations of the subsurface. Under most circumstances, Vs is a direct indicator of the ground strength (stiffness) and therefore commonly used to derive load-bearing capacity. After a relatively simple procedure, final Vs information is provided in 1-D, 2-D, and 3-D formats that can provide us with the geotechnical characteristics of the subsurface material [1].
MASW advantages:
1-Rapid and cost-effective technique.
2-Reiable method for site characterization and determining shear wave velocity.
3-Simplicity on analyzing and interpreting the results.
MASW disadvantages:
1- Sometimes, it requires integrated geophysical techniques to increase the reliability of interpreted data and reduce results ambiguity.
2-Invisible thin layers.
3-Short depth of investigation.
4-Laterial and vertical averaging of acquired data.
Figure 1: Active MASW data acquisition [2]
Conclusion
The overview of MASW method discussed its applicability and understanding its strengths and limitations for better applying this technique for geotechnical investigations. The main advantages of this method are the cost effectiveness , rapidness and simplicity on analyzing and interpreting the results. however, there are some disadvantage such as short depth of investigation , invisible thin layers, and averaging of acquired data of the subsurface.
Figure 2: Principle of MASW [2]
Acknowledgements
Dr. Neil Anderson and Dr. Evgeniy Torgashov faculty members of geological engineering program at Missouri S&T.
Hadhramout Establishment for Human Development (HEHD).  
Figure 5: 2D Vs map from an Multiple 1D shear wave profiles . (Kansas Geological Survey)
Methodology
The simplicity of using MASW makes it a straightforward method for geotechnical application. The seismograph records the wave velocity (V) of the subsurface interfaces as Rayleigh (VR) by vertical polarized motion detectors. By knowing the two-way travel time (ΔT) of the signal and the depth (Z) of which the signal reflected as expressed in the equation below:
V=2Z/ΔT
The first step is to acquire the data as a form of seismic profile (figure 3) then convert it to a dispersion curve (figure 4) and finally generate the shear velocity profile Vs (figure 5). Multiple 1-D Vs profile generate a 2D Vs (figure 6), to understand the geology of the subsurface by knowing shear velocity variations with depth (figure7).
Figure 3: Dispersion curve (phase shear velocity vs frequency)
References
Figure 4: 1D Shear velocity profile
[1]
[2]Kansas Geological Survey
[3] Cox, Brady (2010)
Contact
Abdullah Al-haj
M.Sc. Candidate
Dept. of Geosciences and Geological and Petroleum Engineering, Missouri University of Science and Technology
Figure 6: Site Classification by Shear Velocity [3]