Experimental study on pore structure characteristics and strength properties of red soil subjected to dry-wet cycles
[Objective]Periodical rise and drawdown of reservoir water level cause the soils along riparian zones of the Three Gorges Reservoir to experience repeated dry-wet cycles,leading to irreversible changes in the pore structure and strength proper-ties.[Methods]Taking a red soil from a landslide in Three Gorges Reservoir as an example,triaxial tests,scanning electron microscopy and nuclear magnetic resonance tests under dry-wet cycles were performed to analyze the influence of dry-wet cycles on the microstructure and strength properties of the soil sample.The evolution and correlation of soil pore structure and strength properties are addressed.[Results]The results show that applying dry-wet cycles leads to a significant deterioration of shear strength.With increase of dry-wet cycles,the shear strength decreases and tends to a stable level.Under the influence of dry-wet cycles,pore structure expands and the distance between the soil particle enlarges.Aggregate disintegration with fracture develop-ment produces a smaller size aggregate and improves the pore connectivity.The microstructure transmits into a new steady state of pore structure.[Conclusion]A double fractal distribution of pore structure is observed,and the cohesion and internal friction angle are closely related to the fractal dimension of bigger pores.The dry-wet cycles reduce the complexity of big pore size distri-bution,loosen the pore structure and weaken intergranular occlusion,Resulting in a decrease of cohesion and internal friction angle.
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