1. Application and Innovation
of Geophysics in
Geotechnical Engineering
Presented by
Roshiya Fathima N, Gayathri Devi M N
National Conference on
Soils and Foundations SAF-2024
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2. INTRODUCTION
• Overview of near-surface geophysical
techniques in geotechnical challenges
• To assess the in-situ geo-mechanical properties
of the soil
• Types of subsurface information retrieval
procedures (Eslaamizaad et al., 1998).
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3. • There are two main types of subsurface
information retrieval procedures
1. Direct methods.
2. Indirect methods
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4. DIRECT TECHNIQUES
• Exploring in situ materials, man-made
structures, groundwater levels, and exploring
shafts
• Mapping subsurface structures using modern
geophysical techniques
• Extracting and analyzing representative
disturbed and/or undisturbed specimens of the
in situ materials from borings, test pits,
trenches, and shafts
• Conducting basic geotechnical field tests, like
the standard penetration test (SPT)
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5. INDIRECT METHODS
• Aerial photography
• The interpretation of topographic maps
• The examination of already published
geological reports, maps
• Soil surveys
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8. Electrical Resistivity Tomography
(ERT )
• Current is induced in the ground using two
current electrodes
• The electrical potential drop is then read using
two other electrodes.
• ERT can be used to map geologic variations
including:.
• Soil lithology, presence of ground water,
fracture zones, variations in soil saturation,
areas of increased salinity or, in some cases,
ground water contamination.(B. Butchibabu et
.al 2018) .
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9. • ERT is often the best option for mapping
cavities such as caves, karst and/or
evaporate dissolution sinkholes
Figure 1 Installation of ERT ( source ;google)
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10. Multichannel Analysis of Surface
Waves (MASW)
• Three steps typically make up the MASW
process:
• Obtaining multichannel field records, also
known as shot collects
• Deriving dispersion curves from each record
• Inverting these to get 1D (depth) VS profiles
(one profile from one curve), more dispersion
curves must be obtained.( Soupios et al 2007)
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11. Multichannel Analysis of Surface
Waves (MASW)
• The primary benefit of MASW is that can fully
account for the complex nature of seismic
waves, which are always accompanied by
noise waves including undesirable higher
modes of surface waves, body waves, scattered
waves, and traffic waves ( Choon B et al 2007)
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12. LIDAR, or light detection and ranging
• Ground-penetrating radar uses electromagnetic
waves to penetrate the soil and create an image
of the subsurface, allowing for the detection of
buried objects
• Seismic waves can provide information about
the subsurface by analyzing the energy waves
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13. LIDAR, or light detection and ranging
• LIDAR, or light detection and ranging, uses
laser beams to measure the time it takes for the
beam to reflect from an object and return to the
receiver.
• This technology can be used to create detailed
3D maps of the terrain or detect changes in
elevation.
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14. Depth to Bedrock determination
• Fractures in bedrock are commonly found in
competent rocks that are unable to adjust to the
stresses placed upon them.
• These fractures are characterized by moisture,
which makes them more electrically conductive
than non-fractured bedrock.
• Fractured regions in bedrock may be
topographically more depressed than the
surrounding unfractured bedrock.
• This can be observed and mapped using
geophysical methods.( Khiem T et al )
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15. Seepage zones mapping
• Anomalous seepages can occur through
fault/joint structures controlled by the
structural bedrock topography.
• By using geophysical methods, such as
electrical resistivity and seismic methods,
engineers can detect and map the pathways of
seepage, providing valuable information for
the design and maintenance of dams.
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16. Site subsoil competence
• High apparent resistivity zones are considered
to be more competent compared to regions
with relatively low resistivity values.
• Certain ranges of apparent resistivity values
can be correlated with lithological competence.
• Geophysical methods, such as electrical
resistivity, can be used to assess the apparent
resistivity values and determine the
competence of the materials underlying a site
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17. Excavation works revealed a disrupted part of the
marly limestone, filled with red clay. The location of
geotechnical inhomogeneity, coincides with
theresistivity anomaly determined by the
implementation ofgeophysical engineering methods
.( Soupios P M et al )
Figure 2
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18. Limitations
• Low-velocity layers and embedded cavities
pose challenges for seismic wave method
• Potential problems with design engineer and
earthworks contractors
• The inversion results from the real data show
some consistency with crosshole, SPT N-
value, and material log results, but there may
still be some scatter in the data
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19. Conclusion
• Helps in characterisation of subsurface
formations that can assist to direct site studies
• Anomalous areas can be defined by the results
of the geophysical surveys
• Helps to prepare construction bid documents
and estimate potential costs
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20. Reference
• Butchibabu .B, Prosanta Kumar Khan,.
Jha.P.C, Foundation evaluation of underground
metro rail station using geophysical and
geotechnical investigationsEngeo(2018),
https://doi.org/10.1016/j.enggeo.2018.12.001
• Choon. B Park, Richard D. Miller, Jianghai,
Julian, Multichannel analysis of surface waves
(MASW)—active and passive methods Kansas
Geological Survey, Lawrence, USA 2008
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21. Reference
• Anderson, L Neil ,Croxton, Neil, Rick, Phil
Geophysical Methods Commonly Employed
for Geotechnical Site Characterization
http://www.trb.org/Publications/Blurbs/160352
.aspx
• Khiem T. Tran, Dennis R. Hiltunen, Ariel
Sarno, Nick Hudyma Geophysical Testing of
Rock and Its Relationships to Physical
Properties
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22. Reference
• Eslaamizaad, S., and Robertson, P.K. 1997.
Evaluation of settlement of footings on sand
from seismic in-sity tests. In Proceedings of
the 50th Canadian Geotechnical Conference,
Ottawa, Ont 1997. BiTech Publishers,
Richmond, B.C. Vol. 2, pp. 755–764.
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