Study On Stability Of Coarse Grain Frozen Soil Slope In Bangda Section Of Sichuan-tibet Railway

The proposed Bunda area of the Sichuan-Tibet Railway will pass through a large number of seasonal coarse-grained frozen land zones.The seasonal coarse-grained frozen soil slopes will be frosted in winter,and the slope stability will drop sharply under the action of spring snow and ice and summer rainstorm.Most of the slopes surveyed in the field were destroyed to varying degrees.The main forms of damage were: slumping,surface slippery,hot melt slump,and slope flushing.In this paper,the damage of the gravel soil slope under the action of dry-wet cycle and frost heaving cycle is studied by means of indoor model test.The failure mechanism of the gravel soil slope in Bangda area is studied by numerical simulation.In the dry-wet cycle model test,the 60° and 45° gravel soil slopes were studied under the same conditions.The 45° slope was stable and the slope did not change significantly.The 60° slope occurred and the slope decreased continuously.After the body is destroyed,the slope surface usually has three angles from top to bottom.The closer to the slope foot,the smaller the angle.When the upper and lower slope angles of the slope body are reduced to 43°,the angle is gradually stable,and the angle of the pile body at the foot of the slope tends to be stable at 24°.The dry and wet cycle causes the slope to lose water and produce cracks.The slope cracks during rainfall are favorable for rainwater intrusion,which leads to widening of cracks in the slope and threatens the stability of the slope.It is found that the slope of the slope is larger,and the lower water content may initiate the slope damage.The water content of the 60° gravel soil slope is about 39.4%,and the 45° degree gravel soil slope is watery.No signs of slipping under the rate.In the freeze-thaw cycle model test,for the stable slope angle of dry-wet cycle,the slope with different water content of 45° slope was selected as the research object,and the freezethaw of the 45° slope with 18% moisture content and 22% moisture content was respectively carried out.cycle.The study found that the greater the water content of the slope,the greater the amount of frost heave under the same frost heave conditions.The frost heave amount of the slope top is the largest,and the frost heave amount from the top of the slope to the slope is gradually reduced.The deformation of the slope is proportional to the amount of frost heaving.The deformation of the upper part of the slope is the largest and the damage is easy to occur.During the frost heaving process,the fine particles in the slope will be precipitated first,and the icing will be coral-like.The coarse-grained gravel will be under the coral-like fine particles.When the melting,the fine particles on the slope cannot be completely restored,and the pores between the coarse particles become larger.Gradually become loose and prone to damage.After frost heaving,the loose surface layer is washed away under rainfall conditions.Under the action of frost heaving circulation and dry-wet cycle,the slope surface is destroyed layer by layer,gradually receding and the slope is reduced.Comprehensive rainfall and frost heave effects,combined with numerical simulation verification,found that the combined effects of dry and wet cycles and frost heaving cycles are the causes of seasonal coarse-grained frozen soil slope failure in Bangda area.After freezing and thawing,the slope density decreases,and the slope is destroyed under external force disturbance(such as rainfall).The degree of slope failure is related to the original slope.When the slope of the gravel soil slope is greater than 43°,the slope of the rainfall is easy to slide after frost heave,and the steeper the original slope,the greater the change of the slope angle after the final stability;the gravel soil slope When the slope is less than 43°,the slope surface is mostly destroyed,and the slope angle is not changed much.