关键词: 砂卵石土, 长期强度, 黏弹塑性, 剪切流变模型

Abstract:

Sandy pebble soil has been widely used in engineering applications，such as railway subgrade，high earth-rock dams，bridge piers due to its excellent compaction performance and strong water permeability.At present，the research on the mechanical properties of sandy pebble soil at home and abroad mainly focuses on： （1）The dynamic deformation strength characteristics under complex stress state； （2）The effects of different density and water content on the mechanical parameters； （3）The simulation software to reflect the mechanical failure phenomenon of sandy pebble soil and calculate the mechanical parameters.The instability of rock mass is mainly caused by the slippage of rock mass along the failure surface under shear stress，but there was no research on shear rheological properties of sandy pebble soil at home and abroad.Shear rheological tests on sandy pebble soil under different normal stresses was carried out，and mechanical analysis and shear rheological model research were conducted based on experimental data to provide scientific analysis for the stability of sandy pebble soil engineering，thus ensuring long-term safety of sandy pebble soil engineering operations.The specific process of the test was to carry out the shear rheological test of the sandy pebble soil by the stepwise incremental loading method the normal stress of 0.025 MPa and 0.0375 MPa were applied to the two sets of samples，when the stability was stable for more than 24 h.Then the shear stress was applied from the low to the high grading time.When the displacement of the rheology within 24 h was not more than 0.001 mm，the deformation was considered to be relatively stable，and the next-stage shear stress can be applied. Did this until the test piece breaks. The RYL-600 rock shear rheometer recorded the rheological data for the entire process. Some classical viscoelastic models were used to simulate and compare the rheological curves before the accelerated rheology under 0.025 MPa normal stress and 0.203 MPa shear stress. It was known that the five-element viscoelastic model has an accurate simulation on stage before accelerated rheological transformation of sandy pebble soil. Because the accelerated rheological phase highlights the plastic properties of the rock，a new model obtained by connecting the five-element viscoelastic model and the VR viscoplastic model in series was used to fit the accelerated rheological results of the sandy pebble soil. Based on experimental data and analytical simulations，the following conclusions can be drawn： （1）Under the action of low shear stress，sandy pebble soil undergone instantaneous elastic deformation，initial rheological phase with decreasing speed，and constant steady rheological phase.When the shear stress of the sandy pebble soil exceeded its long-term strength，the rheology will continue to develop into an accelerated rheological failure stage. The magnitude of long-term shear strength increased with increasing normal stress.The reason was that the greater the normal stress，the higher the frictional force on the failure surface. （2）Through simulation comparison and analysis，it was found that the viscoelastic-plastic model obtained by connecting the five-element viscoelastic model and the VR viscoplastic model in series had a good fitting effect on the whole process rheological curve of sandy pebble soil.And the instantaneous elastic modulus tended to decrease linearly with the increase of shear stress. Although the viscoelastic shear modulus fluctuated，it was stable within the range of 1~5 MPa/mm. （3）The discrete nature of the particles and the randomness of the geometric distribution of the pebble also had a certain influence on the mechanical properties of the sandy pebble soil. In the future research，new numerical processing methods and simulation software should be adopted to characterize these important parameters，and analyze the specific effects of these parameters on the mechanical properties of sandy pebble soil.

Key words: sandy pebble soil, long-term strength, viscoelastic-plasticity, shear rheological model