Mechanism of micro-deterioration of soft and hard interbedded rock mass under the influence of freeze-thaw cycle
To solve the engineering safety problem of geological disasters such as local landslides,col-lapses,peeling,and falling blocks that are easily caused by freeze-thaw action on soft and hard interlay-ered rock slopes in cold regions,and to better reveal their stability and damage mechanisms,this study was based on the geological prototype of sandstone and mudstone interlayers in northern Shaanxi.Simi-lar materials were used to make soft and hard rock interlayered rock samples,and different initial satu-rations(0％,30％,70％,100％)were tested on rock samples with different cycles(0,5,10,15,20,25)of interlayered soft and hard rocks to obtain the degradation law of freeze-thaw damage.Electron microscopy(SEM)and nuclear magnetic resonance(NMR)experiments were employed to analyze the changes in internal pore structure.Additionally,uniaxial compression tests were conducted to reveal the damage and degradation mechanisms of layered rock formations under freeze-thaw cycles.Through the above research,the damage and deterioration mechanism of soft hard interlayered rock masses under freeze-thaw cycles was revealed at the macro and micro levels.Results indicate that the T2 spectrum distribution relaxation time of layered rock specimens is mainly concentrated between 0.01 and 1ms,with pore sizes primarily distributed in the range of 1 to 10 µm.As the number of freeze-thaw cycles in-creases,the peak value of the T2 spectrum gradually increases.Pores in the range of 0 to 0.5μm gradu-ally disappear after the 5th cycle,while micropores and small pores decrease,and medium and large pores increase.Uniaxial compressive strength and elastic modulus gradually decrease.In partially satu-rated conditions(0％,30％and 70％),the changes in pore structure are small,resulting in lower lev-els of freeze-thaw damage.In fully saturated conditions(100％),significant changes in T2 spectrum and pore size distribution occur,with large pores(10～10 000 μm)present only under complete saturation,indicating more pronounced damage and degradation.The freeze-thaw damage to layered rock speci-mens originates from two sources:firstly,in the saturated state,internal pores of soft rock expand due to freeze-thaw cycles,leading to the initiation of tiny cracks;secondly,at the interface between soft and hard rocks,unfrozen water in pore spaces initiates crack formation and propagation under freeze-thaw forces,ultimately leading to fracture.This study holds significant theoretical and practical value for dis-aster prevention and control in the construction of layered rock slopes in cold regions.
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