CREEP EFFECT OF LOESS STRATA ON SURROUNDING ROCK PRESSURE OF TUNNELS

Based on a highway loess tunnel, the uniaxial creep tests of undisturbed Q₂ loess in the different moisture content were conducted to explore the creep properties, and the effect of long-term deformation on the evolution laws of surrounding rock pressure and convergence deformation were analyzed by numerical methods, finally, the distribution modes and calculation methods of surrounding rock pressure were put forward. The results showed that:1) in the course of long-term deformation development of loess strata, the surrounding rock pressure and vertical convergence deformation all showed a trend of increase. 10 years later, the surrounding rock pressure would keep it stable, and the distribution form would be in the "cat's ear" shape. The average magnifications of vertical and horizontal surrounding rock pressure were 1.61 and 1.33, the average vertical subsidence of the arch crown was magnified by 1.22 times and horizontal convergence deformation was reduced by 0.97 times respectively;2) with the increase of tunnel embedment, the ratios of surrounding rock pressure and convergence deformation generally increared, and increase of embedment, the magnified effects on stress and deformation were more obvious; 3) the greater the initial moisture content of the loess, the greater the surrounding rock pressure and convergence deformation, but the ratios of them tended to decrease;4)the surrounding rock pressure ratio was introduced into Terzaghi theory and XIE Jiaxiu's formula, the modified formula of surrounding rock pressure were put forward, and the long-term deformation effect of loess strata on the surrounding rock pressure could be considered.