Height of Highway Embankment for Tolerable Residual Settlement of Loose Cohesionless Subsoil

Abstract

Residual settlement of highway embankment is studied for different strengthof underlyingcohesionlesssubsoil. A vast volume of parametric study is carried out for different value of ESAL factorand for different height of embankment. The sum of elastic settlementsof cohesionless subsoil due to axle load and due to self-weight of pavement layers is considered as the residual settlement whichare to be occurred after construction of road pavement. The values of residual settlement (S_r) for different heights of road embankment (H_e) are obtained and presented graphically for different SPT Value (N₆₀) and ESALfactor. For rigid pavement and flexible pavementin approach to bridge or culvert,the tolerable limit of residual settlement is 0.1m. This limit is taken as 0.2m for flexible pavement in general sections of highway except approach to bridge or culvert.A comprehensive and completedesign guideline is developed for design of highway embankment underlain by very loose to loosecohesionless subsoil for limitingvalue of the residual settlement. In the current parametric studyconsidered rangesfor both ofESALfactorandSPT value N₆₀is 1-10. Theground improvement is not required if the average SPT value (N₆₀) within very loose subsoil underlying highway embankment is 5 or more for ESALfactor?10 and H_e ?1.5m.Allowable minimum values of the embankment height are obtained to satisfy tolerable or limiting level of the residual settlement of subsoil for different N₆₀ and ESAL factorwhich are termed as H_e,0.1 and H_e,0.2. Tables and charts are developed to identify H_e,0.1 and H_e,0.2 to keep the residual settlement within the mentioned tolerable limit.The developed guideline may be used to assess the necessity of ground improvement in case of cohesionless subsoil underlying highway embankment to avoid exceedance of tolerable settlement limit. The ground improvement only to be necessary when the residual settlement of subsoil is more than mentioned tolerable limit or H_e is less than H_e,0.1 or H_e,0.2  in corresponding type of road sections.