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European Journal of Applied Sciences – Vol. 12, No. 4
Publication Date: August 25, 2024
DOI:10.14738/aivp.124.17430.
Oboshenure, K. K., George, G. C., & Keme, P. (2024). Investigating Soil Instability and Subsidence Risks Using an Integrated ERT
and MASW Analysis. European Journal of Applied Sciences, Vol - 12(4). 310-326.
Services for Science and Education – United Kingdom
Investigating Soil Instability and Subsidence Risks Using an
Integrated ERT and MASW Analysis
Oboshenure, K. K.
Department of Physics, Niger Delta University,
Wilberforce Island Bayelsa State
George Godwin C
Department of Physics, Covenant University,
Ota Ogun State
Keme, P.
Department of Physics, Niger Delta University,
Wilberforce Island Bayelsa State
ABSTRACT
Subsidence is a major structural concern, particularly in deltaic areas with soft,
compressible soils. This study looks into the subsurface conditions at Niger Delta
University, Amassoma, using a combination of Electrical Resistivity Tomography
(ERT), Multichannel Analysis of Surface Waves (MASW), and Standard Penetration
Tests. Analysis of five ERT profiles identified three stratigraphic layers having
resistivity values that ranged from 0.453 Ωm to 145 Ωm, indicating different soil
compositions and moisture levels. MASW measurements also confirmed these
findings, with shear wave velocities ranging from 207 m/s in the topmost layer
characterised with moisture to 824 m/s in the deepest probed layer. The
computed Standard Penetration Test (N-value) findings revealed a significant
variance in soil strength, with N-values ranging from 8.3 in the topmost layer to
459 in the deepest layer probed. This complex profile suggests that the softer
upper layer, which is insufficiently secure for normal foundations, overlies stiffer
layers. The study emphasises the importance of deep foundation techniques and
soil stabilisation in reducing subsidence risks and ensuring the structural
integrity of facilities. These findings provide critical insights into geotechnical
engineering techniques in deltaic regions, emphasising the significance of
thorough subsurface investigations in anticipating and dealing with structural
stability issues.
INTRODUCTION
Subsidence, or the progressive sinking of ground or buildings, poses substantial problems to
structural stability and lifespan, especially in deltaic areas like Nigeria's Niger Delta. Because
of its unique geographical and geological location, Niger Delta University in Amassoma,
Southern Ijaw, Bayelsa State, serves as an excellent case study for exploring these
geotechnical challenges [1, 2, 3, 4]. Deltaic environments are distinguished by soft,
compressible soils that are frequently wet with water and prone to subsidence under the
weight of erected structures [5, 6]. In these situations, typical foundation design approaches
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Oboshenure, K. K., George, G. C., & Keme, P. (2024). Investigating Soil Instability and Subsidence Risks Using an Integrated ERT and MASW
Analysis. European Journal of Applied Sciences, Vol - 12(4). 310-326.
URL: http://dx.doi.org/10.14738/aivp.124.17430
frequently fail to offer long-term stability, necessitating in-depth subsurface investigations to
determine acceptable engineering solutions [7, 8, 9].
Recent research has demonstrated the efficiency of combining geophysical approaches such
as Electrical Resistivity Tomography (ERT) and Multichannel Analysis of Surface Waves
(MASW) in analysing subsurface conditions. ERT gives precise resistivity profiles that aid in
identifying different soil layers and their moisture content, whereas MASW monitors shear
wave velocities to determine soil stiffness [10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23,
24, 25, 26]. Despite the popularity of geotechnical studies in diverse infrastructure contexts,
not much research has focused on the combination of ERT and MASW in understanding
subsidence on university campuses in deltaic environments. This gap highlights the need for
targeted research that uses these integrated geophysical tools to better predict and manage
subsidence risks [27, 28, 29, 30, 31, 32, 33, 34].
Furthermore, evaluating soil bearing capacity by Standard Penetration Tests (SPT) or N-value
measurements is critical for monitoring potential subsidence and building appropriate
foundations. The substantial variation in N-values across layers indicates a complicated
subsurface profile that may pose a challenge to typical foundation techniques [35, 36, 37, 38,
39].
The importance of this study resides not just in its applicability to Niger Delta University, but
also in its broader implications for structures in geologically equivalent places. This study
intends to help build more effective construction and mitigation measures by providing a
complete understanding of subsurface conditions and their impact on structure stability.
This study is also consistent with global efforts to gain insight and adapt to the geotechnical
challenges faced by climate change and rising sea levels, which can worsen subsidence issues
in coastal and deltaic locations. Thus, the findings of this study are predicted to have broad
impacts on urban planning, civil engineering, and environmental policy. This research
addresses a pressing need for extensive subsurface investigations utilising cutting-edge
geophysical techniques to advise safer and more sustainable building practices in susceptible
places such as the Niger Delta. The insights gathered here will assist bridge large gaps in the
literature and offer a platform for future study in this critical field of geotechnical engineering.
GEOLOGY OF THE STUDY AREA
The study location Niger Delta University is in Amassoma, a town in the Southern Ijaw Local
Government area in Bayelsa State, Nigeria, and is part of the Niger Delta region, a huge
sedimentary basin recognized for its complex geology and geomorphological features [40].
This region is part of the wider Niger Delta Province, which includes one of the world's largest
deltas, produced by millions of years of sediment deposition. The Niger Delta is underlain by a
thick succession of Tertiary to Quaternary sedimentary rocks, primarily clastic deposits
deposited in a fluvio-deltaic setting [41]. The stratigraphy of the Niger Delta is often classified
into three formations: Akata, Agbada, and Benin. The Akata Formation, the deepest of the
three, is mostly made up of marine shales and is notable for its over pressured shale bodies.
Above the Akata Formation is the Agbada Formation, which is made up of a diverse mix of
sands and shales deposited in both marine and river environments [42, 43], this formation is
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European Journal of Applied Sciences (EJAS) Vol. 12, Issue 4, August-2024
critical to comprehending the petroleum system in addition to the geotechnical features that
are vital to construction. The topmost formation, the Benin Formation, is composed primarily
of continental sands with some shale intercalations and was formed in a river to deltaic
environment. The Benin Formation is where much of the Niger Delta's urban and
infrastructure development is concentrated [44, 45]. The depositional history and lithology of
the Benin Formation influence the geotechnical properties of Amassoma's soils. The region is
distinguished by soft, compressible soils with high moisture content, such as silts, clays, and
sandy clays, which present substantial obstacles to construction and urban development. The
high groundwater table and frequent flooding exacerbate geotechnical conditions,
compromising soil stability and building foundation integrity [46, 47, 48].
This study's inquiry into Amassoma's underlying conditions is especially important given the
region's complicated geological framework. Understanding the relationship between
lithological composition, soil qualities, and groundwater dynamics is critical for assessing
geotechnical risks associated with construction and developing mitigation solutions for
probable building collapses.
Fig 1: Map of Bayelsa state showing southern ijaw LGA.
MATERIALS AND METHOD
Geophysical Investigation (Electrical Resistivity Imaging)
The use of integrated geophysical techniques such as 2-D Electrical Resistivity Imaging (ERI),
Vertical Electrical Sounding (VES) and Multichannel Analysis of Surface Waves (MASW) could
provide useful information about the geotechnical properties of subsoil layers underlying a
proposed engineering site. [47]. This research was carried out around the Newsite Campus of
the Niger Delta University situated in a sinking building using the electrical resistivity imaging
(ERI) method and Multi-Channel Surface Wave (MASW) technique of seismic refraction. The
survey divided into 100 m by 60 m square grid pattern and Pasi Earth Resistivity metre