Abstract：In order to analyze the rheological properties of coarsely granular red sandstone soil in the highway embankment engineering，a series of rheological experiments were conducted on the rheological device that was developed by the authors. Through these rheological experiments，the rheological properties，the main factors affecting the coarsely granular red sandstone soil¢s rheological properties and a rheological model of the coarsely granular red sandstone soil were studied. The experimental results show that the principal stress was the main factor that affects the rheological strain action. According to these rheological tests data，creep curves under the low principal stress conditions(s ≤0.8 MPa) display the linear viscoelastic rheological properties；while creep curves under the high principal stress conditions(s＞0.8 MPa) show the nonlinear viscoelasto-plastic rheological properties. The linear viscoelastic rheological model(Burgers) can describe the linear rheological properties well. At the same time，Burgers rheological model parameters are identified by the modified least square algorithm with the test data. The test data show that the Burgers rheological model can describe the linear rheological properties，including the declining rheological phase and stable rheological phase as well，but can not describe the nonlinear rheological properties，especially the accelerating rheological phase. According to the nonlinear viscous elastoplastic rheological properties，a new viscoplastic rheological body(VPB) model based on hyperbolic function is put forward to describe the accelerating rheological phase of coarsely granular red sandstone soil under the high principal stress conditions. Then，a new 6-element nonlinear viscoelasto-plastic rheological body(VEPB) model is set up by putting the new viscoplastic rheological body model and the Burgers model. According to the rheological test data，the parameters of the VEPB are identified by the modified least square algorithm method. During the rheological tests，there is a good agreement between the creep test curves and the VEPB rheological model¢s creep curves，which is testified that the VEPB model is reasonable and the viscoelasto-plastic rheological Burges model could describe all rheological phases of coarsely granular red sandstone soil including the accelerating rheological phase.
