TITLE:
Soil Subgrade’s Characterization and Classification of Thies (Senegal, West Africa) on a Radius of 2.5 Kilometers along Five Roads
AUTHORS:
E.H.B.M. Niakhate, Séni Tamba, Makhaly Ba, Adama Dione, Issa Ndoye
KEYWORDS:
Subgrade Soil, Mechanistic Pavement Design, Arc GIS, AASHTO, CBR, Resilient Modulus
JOURNAL NAME:
Geomaterials,
Vol.6 No.1,
December
24,
2015
ABSTRACT: This article explains the
results of a study conducted on the characterizations of subgrade soils in the
region of Thies. The road platforms are mainly composed of a background soil,
which is generally overlapped by a surface layer that plays two roles. Firstly,
it protects the soil structure, ensures the leveling, and facilitates the
movement of vehicles. Secondly, it brings harmony in the mechanistic
characteristics of the materials that compose the soil while improving the
long-term life force. The methodology consisted in taking samples of subgrade
soil along the roads all over the region of Thies in a 5 km diameter span. The
identification tests allowed the Thies-Tivaoune, Thies-Khombole and Thies-Noto
axes are characterized by tight sands, poorly graded size. While Thies
Pout-axis is characteristic of severe solid particle size and spread well
graded and serious to spread and well graded particle size. Finally the
Thies-Montrolland axis is characterized by severe to very tight particle size
and graduated to spread and serious and well graded particle size. The specific
gravity values found Proctor test shows the presence of sand, sandy laterite
and laterite. In the target area, polished soils of the A-3 type according to
the AASHTO classification system are the most represented with 60%, followed by
the A-2-6 type 25%, and the A-2-4 type with 9%, which are typical of gravel,
clay, and silty sands. Soils of the A-1-b type (2%) typical of roc fragments,
sands and clay are also represented. Polished sands of the A-3 type have a
better efficiency on road infrastructures than other types of soil listed
above. Finally, we’ve also noted the presence of soils of the A-2-7 and A-4
types with the low percentage of 2%. Subgrade soils of class S4 are the most
represented with 58%, followed by those of class S5 with 42%. Samples of the
Thies-Montrolland road have a claylike plasticity (CL or CH group), while those
of the Thies-Pout road belong to the ML or OL and CL or OL groups with a
tendency mostly directed to the CL or OL group. All these results confirm the
very nature of soils on the two roads and put the light on the presence of
lateritic materials with certain plasticity.