GEOTECHNICAL CHARACTERIZATION OF ALLUVIAL SOIL AS AN ALTERNATIVE ROADWAY CONSTRUCTION MATERIAL
Keywords:Alluvial soil,, Road foundation, CBR, Direct shear strength, Morphology
The rapid infrastructure development in the Philippines over the past years poses problem on construction cost due to the limited supply of suitable road foundation materials within economic haul distances. An economic and sustainable solution is to use locally available but suitable materials. This study utilized the naturally-occurring alluvial soil along the Angat Riverbanks as a potential road foundation material. Geotechnical characterization of the alluvial soil was performed including direct shear and California bearing ratio (CBR) tests. The findings of the index properties showed that the alluvial soil is 92% sand, non-plastic, and was classified as poorly-graded sand. A CBR of 41% makes the river sand a suitable subbase course material. However, the sample failed on the gradation requirement for subbase application due to lacking of coarse aggregates. From the direct shear tests, the soil showed brittle failure that yields peak shear stress and dilative volume change behavior. The critical state friction angles for dry and saturated conditions are 37.52° and 36.61°, respectively. Morphological analyses were also performed to further evaluate the material composition of the alluvial soil. The sedimentological analysis found that the sample is both texturally and compositionally immature. Sediments are angular to subrounded and moderately sorted. Correspondingly, the SEM-EDX revealed flocculation with flakey particles and small inter granular voids that justifies the shear strength of the sand. It is recommended to blend coarse aggregates with the alluvial soil to meet the gradation requirements and possibly increase its bearing strength for base course applications.