According to the analysis of creep mechanism of rockfill

it is concluded that the main factor causing the creep strain is the filling of pores among the rockfill with broken coarse materials under continuous compression. Some new results are obtained for the creep strain of rockfills. Basically

the rheological rules are the same with tri-axial rheological test and one-dimensional creep test corresponding to the stress state and time factor

but the rheological parameters could hardly be determined by test. Some rheological parameters are determined by back calculation of observation in site

in accordance with the creep relations with four parameters and the time variation in hardening rules of double yield surface elasto-plastic model. It shows that feed-back analysis is an effective method in study of the rheological parameters of rockfills.