MASW = Geotechnical Data
The object of this survey was to help direct a fuller geotechnical investigation. There is a strong relationship between Shear wave velocity (Vs) and soil stiffness. The correlations use the relationships in Euro Code 8, . The lower Vs means lower soil stiffness vice versa a high value stiffer material.
- A high value (above 800 m/sec) is rock or slightly weathered rock or concrete with possible strength over 1 MPa,
- Mid-range values from 360 to 800m sec is a stiff soil with strength greater than 250kpa. Values between 180 and 360 suggest a stiff soil with a strength between 70 and 250 Kpa.
- Values less than 180 m/sec Vs suggest a weaker soil. A low value below 50 m/sec is a very weak soil, less than 20 KPa stiffness.
This table below is extracted from he euro-code 8 standard (pp14) –this is the European standard for seismic design of buildings
MASW is a seismic method, is uses a controlled source ( hammer or weight dropper) and a line of standard geophones (4.5Hz). This project uses a geophone spacing of 0.5 and 1m and set shots along the spread. The survey uses a Geometrics 24 channel Geode for the data collection. It took a day to get 6 lines of data.
Collecting the MASW data
This is a geophysical Team Collecting MASW Data
Geophysical Team Collection MASW Seismic Data
This is an example of the an intermediate step in processing the Dispersion curve. This data give a the “relationship” of seismic signal frequency and seismic velocity. The interpreter picks a series of points along the peak of the dispersion curve to give a starting point for a model of the velocity to depth model
MASW Dispersion curve relating frequency of the seismic signal to seismic wave velocity
The next step is to convert all the data to make a cross-section that shows the seismic structure of the ground. This model takes all the dispersion curve data and makes a two dmesnional model along the seismic line The picture below shows the lower velocity (weaker) soils down to 4 meters. At 4 meters there a concrete footing. This shows clearly on the section.
MASW Cross section showing high velocity concrete footing (blue) at 4m deep
Groundsearch are managing programs from its International Bases to diverse locations such as Mongolia,
Cambodia and Africa. We will work with you to deliver the right solution wherever your project
- cost effective,
- results driven,
- Locally relevant.
- Adding Value
VALUE ADDING SOLUTIONS FOR INVESTIGATIONS
- Rock Base and Geotechnical data from MASW
- Mapping Rock head to 100m or more
- Determine soil stiffness and strength directly from Geophysical Data
- Liquefaction Potential
- Correlate with SPT /Drill Hole and other site information