Experimental Study On Durability Of Cement-modified Loess Subgrade Structure Under Rainfall-evaporation Cycle

The dry and wet effect is an important factor affecting the durability of the roadbed structure,the subgrade is exposed to the natural environment,the repeated effects of atmospheric rainfall infiltration and evaporation make seasonal changes in the water content of the subgrade,specific performance in the rainfall season of subgrade soil water volume expansion,the dry season soil water loss shrinkage,this reciprocating effect on the physical and mechanical properties of subgrade soil degradation,and then lead to a variety of roadbed diseases,such as roadbed sinking,fog mud,slope collapse,slope erosion,etc,not only threaten the safe operation of the railway,but also to the railway maintenance and repair difficult to overcome the difficulties.However,under the influence of rainfall-evaporation cycle,the durability of roadbed structure is unavoidable,and it also has strong concealment,in the short term,the weakening of the durability of the roadbed structure is not easily found without affecting the safe operation of the railway,with the extension of time,when it is perceived that the durability of the weakening of its functional and structural damage,has delayed the timing of governance,resulting in greater losses.Therefore,this paper studies the weakening law of the durability of subgrade structure under rainfall-evaporation cycle,and hopes to provide theoretical reference for roadbed disease prevention and control and even operation and maintenance.In order to study the influence of rainfall evaporation cycle effect on the durability of high-speed railway subgrade structure of loess area,adopting the research method of reduced model size test,by filling the roadbed model with cement improved loess in the indoor,using self-designed rainfall and evaporator to simulate rainfall and evaporation in the natural environment,to observe the state of the roadbed slope during the test and check the durability weakening index,such as weighing erosion,sampling test subgrade soil density and unconfined compressive strength and determination of subgrade bearing capacity,after analyzing the law of change,the main conclusions are as follows:(1)For roadbed models filled with cement improved soil,the cement content in a certain range of,with the increase of cement proportion,the improved effect is more obvious,the subgrade soil density,the higher the strength model of bearing capacity is strong,the structure is more stable;(2)Different cement content of the subgrade model due to the basic properties of different parameters,by the dry and wet effects in the details of a slight difference,but the overall trend is the same.The weakening effect of wetting drying cycles on durability of subgrade structure is a long process,as the cycle continues to advance,the erosion amount of subgrade model gradually increased.In addition,the smaller the cement content of the subgrade model erosion faster.When the cement incorporation ratio of 3%,5% and 7% of the modified soil subgrade structure,after N=78 cycles,the erosion amount of the subgrade model is 1.26 kg,1.01 kg and 0.87 kg respectively;(3)In the early stage of rainfall evaporation cycle,the density of subgrade soil decreased with a large amplitude,with the increase of cycle number,attenuation amplitude decreases gradually and tends to be smooth,in addition,the subgrade model with smaller cement mixing ratio,the greater the slope of the decay curve.When the cement incorporation ratio of 3%,5% and 7% of the modified soil subgrade structure,after N=78 cycles,the density of subgrade model is reduced by 7.74%,7.49% and 7.06% respectively;(4)The improved loess roadbed model with different cement incorporation ratio under the influence of rainfall-evaporation cycle,the unconfined compressive strength of soil has a decreasing law,and the attenuation rate decreases,finally showing a steady trend.When the cement incorporation ratio of 3%,5% and 7% of the modified soil subgrade structure,after N=78 cycles,unconfined compressive strength of subgrade model is reduced by 17.98%,14.13% and 12.00%;(5)Under the influence of rainfall-evaporation cycle,the bearing capacity of subgrade model has the decreasing rule,and the bearing capacity of the early model decreased significantly,the late attenuation decreased and tended to be stable.When the cement incorporation ratio of 3%,5% and 7% of the modified soil subgrade structure,after N=78 cycles,the bearing capacity of the subgrade model is reduced by 7.19%,6.83% and 6.56%,respectively.