Dynamic Characteristics and Mechanism of the Saturated Compacted Loess under Freeze-Thaw Cycles

Qian Wang,Zhongnan Gao,Xiumei Zhong,Fuqiang Liu,Yuxin Liang,Shouyun Liang,Zhongqiong Zhang

doi:10.1155/2021/6296578

Qian Wang, Zhongnan Gao + Show 5 more

Open Access

https://doi.org/10.1155/2021/6296578

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Journal: Geofluids	Publication Date: Oct 8, 2021
Citations: 1	License type: CC BY 4.0

Affiliation: China Earthquake Administration, Lanzhou University

Abstract

To study the dynamic characteristics and mechanism of saturated loess after freeze-thaw cycles, a series of laboratory tests including freeze-thaw cycle tests, dynamic triaxial tests, and scanning electron microscope tests of the saturated remolded loess was conducted. The characteristics of the dynamic parameters of the saturated loess after different freeze-thaw cycles were discussed. The characteristics of the microstructure parameters changes were analyzed. The evolution process and mechanism of the microstructure of the remolded loess under freeze-thaw cycles were proposed. The results show that after different freeze-thaw cycles, the dynamic stress-dynamic strain curves of the saturated remolded loess conform to the hyperbolic model; however, the freeze-thaw cycle has a significant effect on the model parameter b . With the increase of freeze-thaw cycles, the dynamic shear modulus of saturated remolded loess first decreases and then increases, while the damping ratio is opposite. When saturated remolded loess experiences freeze-thaw cycles greater than four, its dynamic stability is better than that of saturated soil without freeze-thaw cycles. The dynamic stability reaches its peak after seven freeze-thaw cycles and is equivalent to that of saturated soil without freeze-thaw cycles after forty cycles. Combined with the results of the quantitative analysis of microstructure images, with the increase of the freeze-thaw cycles, the number of large and medium particles in the soil reduces, and the number of micros and small particles increases. The particle size tends to be uniform. The apparent porosity increases rapidly and then decreases sharply and tends to be stable after 4 freeze-thaw cycles. The pore and particle fractal dimensions continue to decrease. The probability of entropy increases first and then decreases. It is illustrated that the saturated loess has mainly experienced three steps under freeze-thaw cycles: (1) fracture and expansion of original skeleton cementation, (2) damage, crushing and aggregation of the particle, and (3) compaction and reorganization of soil structure. Besides, the saturation condition significantly accelerates the evolution process of the internal structure of the soil under freeze-thaw cycles. These lead to the strengthening effect of soil dynamic stiffness under long-term freeze-thaw cycles.

Highlights

Loess is a kind of special soil formed in an arid climate, which is widely distributed in seasonal frozen areas of Middle and Western China
The interaction of confining pressure, freezing temperature, and freeze-thaw cycles has a significant impact on the strength of silty soil [7,8,9,10,11,12], as well as the nonlinear dynamic parameters and characteristics of seismic engineering [13, 14]
In the process of freezing, the surface layer of the soil is first frozen by cold, the binding water film has frozen cracks, the temperature gradient and electric field gradient are generated inside, and the water migration force reacts on the soil structure, which causes further damage

Summary

Introduction

Loess is a kind of special soil formed in an arid climate, which is widely distributed in seasonal frozen areas of Middle and Western China. The freeze-thaw cycle as a special strong weathering effect can significantly change the structure and physical and mechanical properties of soil, which is easy to lead to strength deterioration of soil and causes the destruction of various engineering infrastructure [4,5,6]. The physical and mechanical properties and structural behaviors of the soil change due to cryogenic actions in the freeze-thaw cycle. The interaction of confining pressure, freezing temperature, and freeze-thaw cycles has a significant impact on the strength of silty soil [7,8,9,10,11,12], as well as the nonlinear dynamic parameters and characteristics of seismic engineering [13, 14]. The main reason that causes the variation of the Geofluids static and kinetic behaviors of the soil during the freezingthaw cycle is the changes in microstructure. The structural damage of the soil trends to stable with the increase of the freezing-thaw cycles [15,16,17,18,19]

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Discussion

Conclusion