Stabilized Lithomargic Soil Subgrades for Low Volume Road Design Using Industrial Wastes

Lithomargic soil is considered a major group of “residual soil” which is identified as a problematic soil in the coastline region of Karnataka state of India. Previous studies reveal that the soil will cause several serious pavement deterioration problems when used as a pavement material. The present study focuses on the stabilization of this problematic shedi soil to make it suitable as a pavement subgrade material using fly ash (FA) and copper slag (CS) additives as stabilizers. In this investigation, various geotechnical properties were investigated to study the improvements in the mechanical soil properties with different percentages of FA and CS additions. For this investigation, relevant Indian standard (IS) codal guidelines were used. Initially, the effect of CS is studied by adding the various trial dosages of the CS from 0 to 50% (by weight) to the soil. The unconfined compressive strength (UCS) test revealed that the soil sample with 25% of CS has shown satisfactory results. Further, by maintaining the 25% CS dosage as constant, the FA dosage was introduced at an increment interval of 2% (by weight). The IS light compaction and UCS results revealed that a 6% dosage of FA had led to maximum strength gain. The improved mechanical performance includes an improvement in standard maximum proctor density from 15.22 to 18.16 kN/m 3 , soaked CBR value from 2.40 to 10.51%, and UCS value from 93 to 312 kPa. Further, the developments in the UCS and california bearing ratio (CBR) were studied by subjecting the virgin and modified soil to sustained desiccator curing at different intervals up to 56 days, the corresponding results indicated a strength gain of about 22% for the modified lithomargic soil. The durability tests were performed by subjecting the UCS specimens to alternate wetting–drying conditions and alternate freezing–thawing cycles. The test results were compared with that of the un-modified shedi soil. The test results were satisfactory for the application as the pavement subgrade material. The pavement design for the low-volume roads has been carried out using IRC: SP-72 guidelines and the pavement analysis is carried out using KENPAVE software. The results indicate that the use of 25% of CS along with 6% of FA in lithomargic soil could lead to a reduction of 46.15% of design pavement thickness and a reduced maximum deflection value upon stabilization.