Application of Dual Calcined Clays and Sisal Fibre for the Enhancement of Black Cotton Soil

ABSTRACT
Several studies have been conducted globally on the use of various agricultural and industrial
waste products in soil stabilization techniques. However, a review of existing literature reveals
that limited research has been carried out on the combined effect of dual calcined clays and natural
fibers on expansive tropical soils, particularly Black Cotton Soil (BCS). This study, therefore,
presents the results of a laboratory investigation aimed at assessing the influence of Calcined Marl
(CM), Calcined Bentonite (CB), and Sisal Fibre (SF) on the engineering properties of BCS. The
laboratory tests conducted on both the untreated and stabilized soil samples include Natural
Moisture Content, Specific Gravity, Particle Size Analysis, Atterberg Limits, Compaction
Characteristics, California Bearing Ratio (CBR), and Unconfined Compressive Strength (UCS).
The preliminary investigation of the black cotton soil collected from Ukatur, Benue State, shows
that it belongs to A-7-6(23) in AASHTO and CH in the Unified Soil Classification System
(USCS), respectively. Soil under these groups are usually very poor for engineering use which was
why it was treated with dual calcined clays and sisal fibre with mix proportions designed with L9
Taguchi Orthogonal Array. Compaction was carried out in accordance with section 3 of BS 1377
(1990) Part 4. The liquid limit, plastic limit and plasticity index of the 100% BC was observed to
be 53.24%, 29.53% and 23.71% respectively. Unconfined compressive strength (UCS) value of
66.49 kN/m2 was recorded for the natural soil were increased from 330.79 kN/m² at 1 day to 941.66
kN/m² at 28 days, representing an increment of 184.6% for Trial Mix 4 (15% CM, 10% CB, 0.7%
SF). CBR results demonstrated a substantial improvement in load-bearing capacity with
stabilization. Trial T8 (20% CM, 15% CB, 0.3% SF) exhibited the highest CBR value (97.82% at
2.5 mm penetration), representing a significant enhancement compared to the natural BCS. This
indicates that higher CM and CB contents significantly improve soil stability.
Based on these results, it can be concluded that calcined clays (metbentonite & calcined marl) and
sisal fibre gave satisfactory results in the stabilization of the soil.