The quality of road pavement is affected mostly by the type of sub-grade which is acting as road foundation. The roads degradation is related to many factors especially the climatic conditions, the quality, and the thickness of the base materials. The thickness of this layer depends on its California Bearing Ratio (CBR) test value which by its turn is highly affected by the quantity of water infiltrated under the road after heavy rain. The capacity of the base material to drain out its water is predominant factor because any change in moisture content causes change in sub-grade strength. This paper studies the effect of the soaking period of soil especially clay on its CBR value. For this reason, we collected many clayey samples and on each soil, two groups of experiments were performed: main tests consisting of Proctor and CBR test from one side and from other side identification tests consisting of other tests such as Atterberg limits tests. Each soil sample was first subjected to Proctor test in order to find its optimum moisture content which will be used to perform the CBR test. Four CBR tests were performed on each soil with different soaking period. The first CBR was done without soaking the soil sample; the second one with two days soaking, the third one with four days soaking period and the last one was done under eight days soaking. By comparing the results of CBR tests performed with different soaking time, a more detailed understanding was given to the role of the water in reducing the CBR of soil. In fact, by extending the soaking period, the CBR was found to be reduced quickly the first two days and slower after. A precise reduction factor of the CBR in relation with soaking period was found at the end of this paper.
The quality of pavement is affected mostly by the type of subgrade soil and in many countries the subgrade soil is weak. One way to measure the strength of the subgrade soil is the California Bearing Ratio test which is a penetration test under continuous uniform loading. But the real traffic surcharge on roads is simulated to be more cyclic load than uniform load. Our objective is to perform the CBR test on different clayey soil samples under cyclic load. This will be done by loading the soil sample to a penetration of 0.in. then to stop the loading for a while. After it, the CBR plunger will penetrate again the soil. This cycle of loadingunloadingreloading will be repeated two times in order to study the effect of the cyclic load on the CBR values. After this, the same procedure will be repeated on the other sample of the same soil but under 0.2in. penetration. Moreover, one normal CBR test under continuous loading will be performed on the same soil in order to compare the results. To achieve our objective, we collected six clayey samples from different Lebanese zones. Proctor test was done first on each soil in order to find the optimum moisture content OMC which will be used to compact the soil for CBR test. The comparison of different tests performed on the same soil appears to be very fruitful. In fact, the loadingunloadingreloading cycle applied to clay tends to enhance the CBR values.
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