The subgrade soil reaction can be determined by several experimental methods, in site and in laboratory.
In this paper, the value of subgrade soil reaction Ks was measured and calculated by using the oedometer
test. In addition, the variations of K
s in function of void ratio, applied pressure and time were studied.
Three types of normal consolidated clay soil were tested by using odeometer test. The results show that the
variation of subgrade soil reaction in function of void ratio decreases at the beginning of the test until a
determined value, and then this value increases continuously. This phenomenon can be explained by the
fact that while the applied pressure are near the cohesion strength of the soil, the deformation will be
negligible and the value of Ks is very high, then it decreases until a determined value, and after that this
value increases continuously because the sample can not be deformed any more in the oedometer cell.
The value of subgrade soil reaction is variable in function of void ratio, applied pressure, and settlement
and it decreases in function of plasticity.
For an applied pressure, the value of subgrade soil reaction varies in function of time, where it takes a
very high value at the beginning of loading, and then it decreases gradually in function of time until it
stabilizes at the end of the test.
