CHARACTERISTICS OF SUB-GRADE SOIL & ITS EFFECTS ON THE STRUCTURE OF PAVEMENT

Abstract

The importance of Sub-grade soil strength to road pavement plays a great role in design optimization of overlying structural layers. Sub-grade soil strength is major factor in the design, construction and performance of road pavements. An accurate determination of the characteristic sub-grade materials is essential for successful analysis intended to support structural design. The main objective of this study is to study sub-grade soil properties and their effects on the structure of road pavement layers employing Laboratory and field tests to estimate physical and engineering properties of the soil. Also is to estimate a moisture adjustment factor to simulate field condition then present comparative analysis between laboratory tests results with field results. The field investigation for sub grade soils consisted of excavation of test pits along the centerline of the roads alignment and DCP field tests approximately one meter below ground surface. Laboratory and field tests were performed on samples taken randomly from Streets in Khartoum City (Al-Giraffe west Street), Khartoum Bahari City ( Mara bee Al-Sharif, Zaim Al-Azharry, Almoulead and Bahari Alshabia Street ) and Omdurman City (Sook AL- Shabby Streets). The analysis process in this study was carried out by the using Microsoft Excel Spread Sheet and UKDCP3.1 program for the analysis and drawing graphics of the test results. The main findings of the study concluded that the sub grade soil strength and moisture content affects road pavement structural layers This research recommends processing the top of foundation preparation of sub grade soil to achieve the maximum density in roads and the control of moisture content.