Critical dynamic stress and shakedown limit criterion of coarse-grained subgrade soil

Physical modeling of long-term dynamic characteristics of the subgrade for medium–low-speed maglevs

“…When the dynamic stress is greater than a certain limit, the internal structure of the soil is damaged by cyclic loading, the bearing capacity of the soil decreases rapidly, and the deformation of the soil increases sharply with a small number of load cycles; namely, macroscopic damage to the soil is observed. When the applied dynamic stress is less than this limit, cyclic loading results in the pore volume of the soil being continuously compressed until its compression is stable, and this limit value is the critical dynamic stress [34]. Therefore, the critical dynamic stress is the key parameter used to evaluate the long-term dynamic stability of the subgrade, and the method used to obtain it is mainly triaxial testing in the laboratory.…”

Evaluation of Critical Dynamic Stress and Accumulative Plastic Strain of an Unbound Granular Material Based on Cyclic Triaxial Tests

“… ε p — N relationship of saturation specimens: ( a ) σ 3 = 15 kPa; ( b ) σ 3 = 30 kPa; ( c ) σ 3 = 60 kPa [ 16 ]. …”

“…Subgrades of railways accumulate permanent settlement under dynamic traffic loading, and excessive accumulative surface settlement typically causes problems, such as vehicle turbulence in transition sections [ 7 , 8 ], uneven settlement [ 9 , 10 , 11 ], and lateral expansion of embankment shoulders [ 12 , 13 , 14 ]. One of the most effective ways to control the accumulative deformation of subgrades is maintaining the traffic-induced dynamic stress to be less than a critical value (i.e., the σ cri ), under which the development rate of ε p gradually decreases and can ultimately cease with an increase in the dynamic loading cycles [ 5 , 15 , 16 ]. Furthermore, the rapid development of high-speed transport and heavy-haul freight demands the subgrades beneath track structures must satisfy strict requirements on accumulative permanent settlements [ 17 , 18 , 19 ].…”

“…Recently, a few empirical models were developed to predict the σ cri ; Zhang et al [ 28 ] developed a regression model for predicting the σ cri based on the fuzzy linear regression theory and structural element method. Xu et al [ 6 ] presented an empirical method to predict the σ cri by introducing the concept of critical stress ratio; Zhai et al [ 16 ] predicted the σ cri of UGMs as a function of confining pressure based on results of cyclic triaxial tests of specimens with optimal moisture content. Most existing studies on σ cri were qualitative investigations.…”

“…The existing methods generally predict the ε p well within small loading cycles. However, they may overestimate the ε p of UGMs under large loading cycles because most of them demonstrate a monotonic increasing relationship between ε p and N , which is contrary to the fact that the rate of ε p of stable specimens gradually declines and finally ceases when the material enters a shakedown state [ 4 , 16 , 41 ]. Moreover, comparing with predicting the development trend of ε p , it is more practical to evaluate the final accumulative deformation of the UGM layers in the design of a railway subgrade.…”