Geotechnical Characterization of Subsurface Using Seismic and Resistivity Geophysical Methods: A Case Study of Mikinduri, Meru County, Kenya
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Date
2024-01
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Kenyatta University
Abstract
This study was undertaken at Mikinduri town the headquater of Tigania central sub county in M eru county which lies 23km from Meru town on the North. The town is rapidly growing due to its strategic location, increasing population and administrative functions. However, the Mikinduri area has been experiencing landslides during heavy downpours, accompanied by structural failure leading to loss of property and life. The study aimed at establishing the causes of landslides, thick alluvium deposits, subsurface fractures/faults and ground subsidence. Electrical resistivity and seismic refraction geophysical techniques were employed in this investigation. The subsurface was characterised in terms hosting/bearing capabilities. Geo-electric, acoustic layers, and subsurface structures were delineated and determined. Geological reports and borehole logs were used to constrain the models. Sounding curves, travel time curves, 2D geo electric sections, and 2D seismic models revealed 3-5 lithologic units to a depth of 30- 250 m. The study established thick loose alluvium deposits mixed with clay to a depth of 0.3- 15m on an impermeable sub-basement as the possible major trigger of the landslides witnessed during rainy seasons. Fractured and saturated zones ( aquifer) was established to far northwest with resistivity values of 10 -100 𝛺𝑚 to a depth of between 65-100 m. Resistivity values ≥ 1000 𝛺𝑚 represented hard zones or solid basaltic rock basement to a depth of between 2 m to 38 m in the southwest. Three acoustic layers were delineated with p-wave velocities of 250-450m/s, 500-650m/s, and 700-3300m/s for the first, second, and third layers respectively. Loose alluvium and clay soils have poor foundation bearing capabilities, while compacted gravel and hard basaltic rock basement have good foundation bearing capabilities. Piling among other engineering techniques are recommended for structures to rest on a direct competent basement also the northeast area of Mikinduri is recommended for underground water harvesting, construction of car parks, playfields, and shallow foundation structures. Landslide mitigation measures such as slope reinforcement,erosion control measures, revegetation and reforestation, slope monitoring and instrumentation among others should be implemented. Further research on slope inclination at mikinduri are recommended.
Description
A Thesis Submitted in Partial Fulfillment of the Requirements for the Award of the Degree of Master of Science (Physics) in the School of Pure and Applied Sciences of Kenyatta University, January 2024.
Supervisor
1. Willis. J. Ambusso
2. Githiri John Gitonga