Subgrade stabilization strategies effect on pavement thickness according to AASHTO pavement design method. (Review)

Abstract

There are a variety of techniques and materials that have been lately developed and employed for stabilizing weak subgrade soils in pavement construction. Some of these techniques and materials are becoming more common due to their comparative cost-effectiveness, practicality and efficiency. Hence, it is quite agreed that there is a necessity for evaluating and assessing the comparative performance of these pavement subgrade stabilizing methods and treatments. The current research aims to review some relative efficiency of several mechanical and chemical stabilizing mechanisms that have been currently examined by several researchers independently. Ten recent studies that have used different stabilizing mechanisms for stabilizing the strength capacity of different subgrade soils used as pavement foundations. The studied soil types involved Fine grained silt (ML), poorly graded sand (SP), soft sand, Sandy-Clay (CH), Salty sand, clay and soft clay. The laboratory and field California bearing ratio (CBR) test has been chosen as the quantitative basis for comparison. AASHTO (1998) for highway pavement design procedure has been adopted for computing the reduction in pavement thickness due the increase in CBR-value resulting from the adopted stabilizing mechanism for each study. The weakest soil type is silty clay located in India with CBR equal to 1%, while the higher strength soil was clay also located in India with CBR equal to 6.64%. The best reduction achieved by physical additives was from Asphalt emulsion added by 12% that increased CBR from 4.6% to 20.6%. The best reduction achieved by chemical additives was from gypsum added by 25% that increased CBR from 1% to 22%, this result is the best at all. Using geogrids increased CBR from 2.14% to 12.84% whereas no effective reduction was obtained by adding 4% polymers.