RURAL ROAD PAVEMENT SUBGRADE AND SUBBASE IMPROVEMENT USING LIME, FLY ASH AND GEOSYNTHETICS IN SOUTH GUJARAT REGION

Abstract

South Gujarat region comprises of Narmada, Surat, Tapi, Navsari, Valsad and Dang districts. The majority of the region has soil type varying from clayey to clay loam type soil. Also, the average annual rainfall is more than 1500 mm in the region. Some parts of Surat, Navsari and Valsad districts are in coastal region and have soft and compressible clayey soil. Under this environmental scenario of soil, climate and increasing traffic, it is observed that most of the roads suffer from premature failure in terms of heavy deformation, cracking, rutting and stripping, and raveling causing very high maintenance cost for these roads. Therefore, it was felt appropriate to treat the low strength subgrade soil and also to provide locally available subbase material treated with non-conventional materials while designing the flexible pavements. This is necessary in order to achieve both the objectives of durability and economy of pavement construction and maintenance. Accordingly, in the present study, total thirteen rural road sections are selected for subgrade and subbase stabilization with the use of lime, lime-fly-ash mix, lime-fly ash-sand mix and geo-synthetics. The optimum proportion of lime is found in the range of 3 to 5% and that of fly ash is 15%. In case of stabilization with lime and fly ash, it is observed that the field soaked CBR is found to increase from 2–3% to 12–23%, whereas FSI values are reduced by 50%. Also, the cost effective evaluation is also carried out for analyzing the economic benefits of treating subgrade and subbase materials. From this analysis, the construction cost is observed to be cut down to 10–12% by adoption of stabilization technique in case of highly expansive CH soil and compressible soil subgrade. Required subbase of 300 mm is provided in two layers of lower subbase of soil treated with 5% lime and 18% fly ash; and upper subbase of GSB; each of 150 mm thickness. Saving of  424 per cum of subbase is achieved through the adopted stabilization technique. Overall, the cost saving in subbase construction was found to be 5%. The present paper also provides detail discussion of practical challenges in the execution works of road widening with the use of lime and lime-fly ash in remote areas in addition to quality monitoring strategy adopted during construction works as well as post construction assessment of pavement layer properties. Keywords: Fly ash, geosynthetics, geotextile, geogrid, subgrade.