Experimental Study And Representation Of Constitutive Model On Time-Dependent Characteristicst Of Over-Consolidated Soil

With the implementation of the 12 th five-year plan,the highway and the high-speed railway construction of China has been in the period of rapid development,and the operating kilometre locates in the forefront all over the world.In addition,it will gradually extend from the East to the Southwest and Midwest quickly where the terrain conditions are more complex with extremely common high filling,deep excavation,semi-filling,semi-excavation and other high embankments.Thus,it puts forward strict requirements on the control of the long-term deformation of subgrade soil,in which establishing the rate-dependent constitutive model which can reflect the rheological properties of soil is considered to be an effective way to solve this problem.Based on this,the main works are as follows:To study the over-consolidation stress history of clay in a high-filled embankment during hierarchical compaction,indoor compaction and one-dimensional consolidation tests are performed on roadbed backfill clay.Two homemade compaction devices are used to drill into standard heavy compacted clay to prepare compacted clay samples and subsequently investigate the influence of compaction work,compaction impulse,water content,and compaction degree on over-consolidation stress history.Results provide an experimental basis to determine the parameters of an over-consolidated constitutive model.To investigate the effects of overconsolidation ratio,strain rate,confining pressure on strength-deformation characteristic,pore water pressure and stress path of over-consolidated remoulded clay,undrained triaxial shear compression test is performed on saturated remoulded clay with consolidation ratio OCR of 16,8,4,2,1 and three strain rates of 0.5625%/min,0.0375%/min,0.0025%/min.The evolutions of normalized undrained shear strength,normalized pore water pressure and effective stress ratio under the influence of OCR and strain rate in stress-strain curve and stress path are summarized.In order to research on the time-dependent deformation characteristics of unsaturated subgrade compacted clay of high-filled embankment,CD triaxial tests of the unsaturated compacted clay with compacting degrees of 90%,93%,96% and cell pressures of 50 kPa,100kPa,200 kPa were carried out under loading rates of 0.01mm/min,0.1mm/min,and the shear strength index under different working condition was investigated.The means of the volume change measurement of unsaturated compacted clay is put forward,indirectly obtained by the cell pressure controller of GDS saturated static triaxial system.Five types of overstress functions were discussesd,it turned out that the over-stress function should adopt the exponential type or power type,with the overconsolidated ratio degenerate function r of subloading surface,a brand new practical elasto-viscoplastic constitutive model is proposed,meanwhile two material parameters c₀ and m? about the rate sensitivity are added into the new model.Prediction results show that the modified over-stress viscoelasto-plastic constitutive model can reasonably characterize the rate sensitivity,strain softening,dilatancy and other deformation characteristics of saturated and unsaturated over-consolidated soil,which lays a foundation for the application of the high-level model into engineering.Based on the suggested over-consolidated soil elasto-viscoplasticity constitutive model,the dam-embankment engineering under complex boundary condition of Lanzhou to Shiwan K50+650^K50+860 highway was numerically analysised with the aid of ABAQUS,by combining with field observation,the long-term settlement of high-filling embankment was predicted effectively,which provided a guidance for controlling post-construction settlement,meanwhile the correctness of constitutive model was verified.