The Effect of Soil Improvements under Road Pavement along Diyala Governorate Highways

Abstract

ABSTRACT Pavement failures correlated to subgrade soils defects are quite common in local highways. This may represent the major cause of excessive maintenance work if not the reconstruction process required to keep these highways serviceable. This could be attributed to many reasons, the most important of which are the types of soils and their characteristics in addition to the presence of a high level of groundwater. Accordingly; it was deemed reasonable to investigate the subsurface soils in the vicinity of Baquba City, which is taken as a case study, to come up with the most applicable improvement procedures through the application of several additives and scale their impact on the natural soils and consequently on the highway pavement performance. Five additives were selected for the stabilization trials each with different percentages, these additives are; 3%,5%,7% and 9% quicklime,5%,10%,15% and 20% class F fly ash activated by 5% Portland cement,10%,15%,20% and 25% rock powder,5%,10% and 15% crushed waste concrete, and 2%,4%,6% and 8% crumb rubber of tires. All the percentages are by dry weight of soil. II The test program in this study included the UCS and un-soaked CBR tests which were conducted on each one of the controlled types of soil samples with the addition of about four different percentages of each of the five additives that may require some 60 UCS tests and 60 un-soaked CBR tests. The test results revealed that the optimum percentages of each stabilizer, in descending order of the additives preferability, were (25%) rock powder, (15%) crushed waste concrete, (15%) class F fly ash activated by cement, (9%) quicklime, and (4%) crumb rubber of tires. The - strain curves from the UCS test for the three soils using the whole used five additives' percentages. The best stabilizer according to the UCS test and unsoaked CBR test is the rock powder which raised the UCS by 904% for soil A and it raised unsoaked CBR by 570% for soil A too. Both of those increments were at 25% rock powder. These optimum additive percentages admixtures choose to subject to the soaked CBR test for the three controlled soil types, hence conducting 18 soaked CBR tests which reveal a different priority in their results. The optimum enhancement to the natural soil is in this order; for the weakest soil type A, the optimum enhancement achieves by the addition of 15% of fly ash activated by cement, which increases the original CBRS about eight times from 3.8% to 31%. For soil type B, the optimum additive is 25% of RP which increases the CBRS a little shy five times from 3.95% of the natural soil to 19%. For soil type C, it finds that the optimum addition is 15% of CWC that increases the natural CBRS value about three times from 4% to 11.5%. Finally; the CBR structural design method for flexible pavement was consulted to scale the impact of the previously mentioned enhancements on local soils surrounding Baquba City. The results of this design method showed that; the stabilization to type A soil with 9% of quicklime will reduce the required pavement by 67%, from 54cm to 18cm, while the addition of 15% crushed waste concrete to soil III type B will reduce the required pavement thickness by 45% of the original thickness, from 54cm to 24cm, while the addition of the same percentage as in type C which is 15% of crushed waste concrete will reduce the pavement thickness by 40% from 53cm to 32cm. Thus; the addition of the determinant additives to the local soils as distributed geographically is very well justified.