Characterization Of Cohesive Pavement Subgrade Soils

Abstract

Geotechnical engineering has been critical to highway construction since engineers realized that successful civil works depended on the strength and integrity of the foundation material. Road design and construction over different types of soil, especially over highly expansive soil and soft marine deposits are interesting engineering challenges to engineers especially at the Roads. Many geotechnical options are available for engineers’ consideration. Embankment design of road needs to satisfy two important requirements among others; the stability and settlement. The short term stability for embankment over soil is always more critical than long term simply because the subsoil consolidates with time under loading and the strength increases. In design, it is very important to check the stability of the embankment with consideration for different potential failure surfaces namely circular and noncircular. It is also necessary to evaluate both the magnitude and rate of settlement of the subsoil supporting the embankment when designing the embankment so that the settlement in the long term will not influence the serviceability and safety of the embankment. 2 Very often, the non-circular failure is more critical than circular slip failure for layered soil especially with very soft subsoil at top few meters. Long term stability of embankment is usually not an issue of embankment over soft marine deposits because the subsoil would gain strength with time after the excess pore water pressure in the subsoil dissipates during consolidation. When the analyses based on subsoil and thickness of embankment indicate multistage construction is required, the construction of the embankment usually takes substantially longer time especially when the cohesive subsoil does not have sand lenses. However, geometry change requires wide road reserve due to flatter slope and stabilizing berms. It has been shown that geotechnical design can be innovative solutions for highway construction problems. Nowadays in Sudan, there are so many constructions of highways. Since highways also involve foundation, these mean geotechnical aspects are also important in the highway construction. Shear strength parameters are always associated with the bearing capacity of the soil. However for highway engineers, they always prefer to use CBR test to determine the suitable strength of designing road pavement. This research is to find the correlation between CBR, DCP and Vane Shear Strength (VSS) of subgrade soils .It can provide better understanding between highway and geotechnical engineer.