Evaluation of volcanic ash along Maai Mahiu-Narok road and its effect on road stability after long rains

Abstract
Volcanic soils are widely distributed group of soils, which cover significant parts of the world's
surface including areas occupied by urban settlements, structures and infrastructure, and may
create geo-engineering problems. These soils exhibit a distinctive behavior that is a consequence
of their formation history, mineralogy and structure. Some part of the subsoil of a large area
along Maai Mahiu - Narok Road in Kenya mainly consists of volcaniclastic deposits. This paper
presents the results of the part of a research programme aiming at geotechnically characterizing
the uppermost layer of this volcaniclastic sequence, particularly focusing on its collapse
potential, shear behavior and the influence of microstructure on these behaviours. In addition, its
main features were investigated and the stability of sub-vertical cuts in this soil was also
assessed. The experimental investigation mainly consisted of index and classification tests,
consolidation and direct shear box tests to assess the collapse potential and shear behaviour of
the soil, respectively. Matric suction of the samples was also determined for preliminary
evaluation of the influence of suction on collapse and shear behaviors of the soil. In addition,
thin-section studies, X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis
were also conducted to determine mineralogical and microstructural features and to evaluate
their influences on the mechanical behavior of the volcanic soil.

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