Experimental Study On Deformation And Failure Characteristics Of Carbon Mudstone At CFG Pile End Under Dynamic Loading

Carbon mudstone is easy to disintegrate and soften when it meets water,which brings great harm to the later operation of high speed railway with extremely high standard of subsidence control.In recent years,some domestic scholars have gradually realized the impact of its engineering characteristics on engineering and started relevant research.Taking the subgrade settlement regulation project of Guilin West Railway Station as the research object,this paper studies the engineering characteristics and dynamic properties of carbon mudstone at pile end under dynamic load,the reason of subgrade settlement in Guilin West Railway Station is analyzed,and the treatment measures are put forward.It provides theoretical basis for the design and construction of traffic engineering under construction and proposed construction under similar geological condition.The main conclusions are as follows:(1)The engineering properties of carbon mudstone were studied by physical,water physical and mechanical properties tests combined with SEM microscopic test results.Analysis shows: The carbon mudstone granules in Guilin West Station are mainly polygonal and flaky,and their structures are significantly affected by water;After being exposed to water,it has obvious expansion deformation and extremely poor water stability.The mechanical properties of carbon mudstone are significantly affected by water,The cohesive forces before and after water immersion and softening are 112.7 kPa and 4.5 kPa,the internal friction angle are29.9°and 8.1°,the average compression modulus is 14 MPa and 4 MPa,and the average compressive deformation is 0.52 mm and 10.19 mm.The difference before and after water softening was significant(2)The dynamic deformation of carbon mudstone was studied by dynamic model test.Analysis of the results shows: Both water and train dynamic load have important influence on the sedimentation of carbon mudstone,but the influence of water on carbon mudstone is much greater than that of dynamic load.The settlement of carbon mudstone before and after softening is more obvious under the same load.The settlement caused by water immersion softening is more than 2 times settlement after constructiont value.After softening in water,the stiffness,strength and viscosity of carbon mudstone decrease;With the increase of vibration times,the degree of damage of carbon mudstone is gradually the same before and after water softening.(3)Based on data analysis from three aspects of survey,design and construction,combined with engineering properties and dynamic load model test results before and after softening of carbon mudstone,the comprehensive analysis shows that the excessive settlement of roadbed of guilin west railway station is caused by the softening of carbon mudstone soaked in water at pile end and the thinning of roof of karst cave.After the subgrade construction is completed,the surcharge preloading can be carried out,and the compression deformation of the carbonaceous mudstone at the pile end after softening is completed in advance through the preloading load;Or adopt non-buried or shallow-buried pile-plank structure span.