Abstract: The standard of deformation stability and the design of stepwise loading are the key factors affecting the efficiency and accuracy of K30 test, and closely related to deformation time-effect state of the filling in the loading process. To get time history curve and deformation data, three small plate loading tests of unit structure filling models are carried out in optimal water rate at compaction coefficient (K) of 0.90, 0.95 and 1.00. The change of the deformation state of the soil during the loading process of K30 test and the influence of the loading stability time are discussed. The results indicate that, the deformation of well compacted silty clay filler in the process of K30 test is mainly elastic, and almost in state of slow convergence. With the increasing of load, the ratio of plastic deformation gradually develops, and the evolution trend of deformation state is presented from weak to strong. When accumulated to 1.25 mm, the deformation is in the sub-state of weak in slow convergence. The standard of “0.01 mm/min”, step-loading time of which shows accelerating growth pattern, can apparently reduce test time with acceptable test error. On the principle that the deformation state should be in apparent state during loading process, and deformation should exceed 1.25 mm, for loading system of five steps and 0.04 MPa load increment, it is suggested that the K30 value in the detection of compaction quality of fine grained soil filler should be between 60-160 MPa/m.

Key words: railway subgrade, silt clay, K30 test, time effect, deformation state