Abstract: The embankment behind the bridge abutment of the high speed railway is different from the general railway in the aspects of padding, construction control and quality supervision. However, there is a little experimental research of the earth pressure behind abutment; and there are a lot of factors influencing the earth pressure also; and the distribution of the earth pressure is not exact predicted through actual earth pressure theories. Therefore, a long-time in-situ observation was practiced to gain the first materials. Based on the experiment results, the changing of the earth pressure with time and the height of embankment, the magnitude and distribution of earth pressures behind the abutment are given. Test results show, the earth pressure behind abutment is nonlinearity with the depth of abutment. To begin with, the earth pressure of abutment increased with the depth of abutment, later, it minished with the depth increasing of abutment. The comparison are made between formula presented with the experimental observations; the points of application of the resultant earth pressures have significantly difference; the height of actual action point of resultant earth pressure is 0.41 of the embankment height.

Key words: earth pressure, abutment, high speed railway, action point of resultant force