Abstract. The rheologic action of the soft rock-soil could be accelerated by the dynamic load, which induces catastrophe instability failure and more geo-technical engineering accidents and geologic disasters. Marine deposit soft-soil in Xiamen region is taken as the test sample, of which the rheological dynamics characteristics are tested under the dynamic load by adopting the dynamic rheological tri-axial device; the failure process of the accelerating rheological catastrophe is analyzed based on the catastrophe theory. The research shows that such different changing stages as decelerating rheology, relatively stable rheology and accelerating rheology are manifested under the process of the different amplitude dynamic load, and the catastrophe way in the accelerating rheological process is the gradual failure instability. The research results is of important and theoretical significance in revealing the dynamic rheological characteristics of the soft rock-soil, exploring the accelerating rheological failure process and conditions of catastrophe instability; they are also of important and practical significance in improving and ameliorating the indicator-monitoring system and technical method for the geo-technical geological disaster, enhancing the forecast scientific and accuracy.

By analyzing problems of highway subgrade fill height in Xinjiang plain terrain, this paper subdivided plain terrain types and proposed corresponding height control measures of subgrade fill based on features of different subtypes, which provides useful reference to similar engineering in plain terrain.