Abstract:
Highway flexible pavement should be capable of carrying traffic axle loads down to the
subgrade soil. In some circumstances, marginal materials may be found along proposed
routes, which extend to a depth well below the subgrade level. For instance, Black Cotton
(BC) soils are highly expansive clay soil grayish to blackish, resulting in deformation and
premature failure of road pavements. Ethiopia's large areas of highland and lowlands,
specifically Addis Ababa city, BC soil coverage is abundant. Some stabilizing agents have
been used with these types of soils in different parts of the world, including Ethiopia, but
the problems persist. California Bearing Ratio (CBR) test is widely used as an index test
to assess the strength characteristic of stabilized subgrade. Still, the test is laborious,
costly, time-consuming, and complex, subject to erroneous results. Hence, this study
focused on investigating the effect of CWD and MP on local soil properties and
developing a model for predicting the CBR value of stabilized material from simple
identification tests, i.e. (LL, PL, PI, OMC, and MDD). Laboratory tests were conducted
on natural BC soils and stabilized material, then developed a prediction model using the
ANN approach to estimate CBR value. The results revealed that CWD and MP could
effectively stabilize BC soils using index properties and CBR values as evaluation
criteria. The OAC indicated 8% and 18% for CWD and MP, respectively. On the other
hand, Multilayer Perceptrons (MLPs) ANN model was utilized to simulate CBR values of
modified black clay, and it performed satisfactorily. The mean absolute error (MAE), root
mean square error (RMSE), and R2
-value were used as yardsticks and criteria. In the
process of neural network development, NN 5-8-1 and NN 5-2-1 respectively for CBR of a
CWD- and MP modified BC soils that gave the lowest MSE value were used in the hidden
layer of the network's architecture and performed satisfactorily. Hence, the performance
of the simulated network was very good, having R-values of 0.9645 and 0.9457 for the
CBR of CWD- and MP-modified BC soils, respectively. These values met the criteria
conventionally recommended of 0.8 for strong correlation conditions. In addition, a
strong correlation was observed between the experimental CBR of a CWD and MP
modified black clay soils CBR values as obtained by laboratory tests and the predicted
values using ANN.
