|Alternative Title||Influence of creep on plastic yield stress of frozen soil|
|Thesis Advisor||张豫川 ; 慕青松|
|Place of Conferral||兰州|
|Keyword||冻土 蠕变 塑性屈服应力 模型参数 有限元模拟|
There will be extrusion of water and air and corresponding movement of soil particles under sustained load as for thawed soil, which process is the consolidation of thawed soil. The consolidation process often accompanied by the change of the internal structure of the soil. The maximum consolidation pressure in the history of soil consolidation is called the pre consolidation pressure, which of essence is the macroscopic response of soil internal structure. Similar to the thawed soil, different forms of internal structure also exist in frozen soil, similar index like the preconsolidation should exist in frozen soils, the scholars called "quasi preconsolidation pressure", which of essence is the plastic yield stress for frozen soil. There is not consolidation process like thawed soil under the load because the permeability coefficient of the frozen soil is much smaller than that of the soil. However, under the action of load there exist creep for frozen soil which can lead to internal structure strengthening or weakening.It can be expected that the plastic yield stress, which represents the structural characteristics of frozen soil, should be changed accordingly under the continuous load.
In order to explore the influence of creep on frozen soil plastic yield stress, this paper first introduces several typical frozen soil creep theory, and their respective applicability, and then employed an isotache model. In order to verify the applicability of the model in describing the creep of frozen soil, creep experiment for different durations at different tempreture was conducted at first and then step loadings under K0 condition were applied. By comparing the theoretical calculation and the experiment, it shows that the model can well describe the creep process of frozen soil, and it has fewer parameters, both geometric and clear physical meaning, and also the creep process of frozen soil and plastic yield stress linked advantages. Finally, it is concluded that plastic yield stress is a function of initial plastic yield stress, compression and unloading index and the logarithm of plastic yield stress is linearly related with creep strain (time).
One of the most obvious differences among many difference in mechanical properties and behavior between frozen soil and thawed soil is the temperature sensitivity for frozen soil. Since the isotache model is developed from the thawed soil, it does not take into account the effect of temperature, in order to use the model to describe the creep process of frozen soil more accurately and reasonably, it is necessary to modify the model parameters into temperature correlation function and it can be seen from the experiment that the three main parameters of the model— compression index, unloading index and creep rate are all temperature correlation. The results show that the modified model can well predict the creep tendency of frozen soil, and the model parameters can be determined directly when the frozen soil temperature is known which make the model more simple , convenient and accurate.
Finally, in this paper, the creep settlement of U-shape crushed-rock embankment in 15 years is simulated. The results showed that the upper soil layer had larger creep and the creep process come into the third creep stage after thirteenth years’ creep. The results also showed that the lower soil layer of the subgrade has less creep settlement and the creep process just at the second stage. At the same time, there is a large horizontal displacement in the upper soil layer, which is due to the instability of the U-shape peripheral slope. To solve these problems this paper proposes setting geotextiles at every layer to restrict displacement on both sides of embankment when layered filling in subgrade construction which can make the whole embankment more stable.
|乔响平. 蠕变对冻土塑性屈服应力的影响研究[D]. 兰州. 兰州大学,2017.|
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