The Experiment Study On Mud Pumping Mechanism In Road Subgrade Under Cyclic Loading

In recent years,with the development of economic,the road traffic volume increased rapidly,which has aggravated varies of subgrade disasters and posing a great threat to the personal and property safety of people and affecting the harmonious development of the economy and society,mud pumping is one of the most common phenomena among road base disasters,and it is attracting more attention.Mud pumping is a phenomenon that subgrade soil wetted by water forms slurry and runs out of the subgrade surface from the gap of ballast and track-bed under the effect of traffic loading Mud pumping causes pollution of road ballast and destroys structure of subgrade,which may result in the decrease of mechanical properties of road subgrade and reduces road service life,so the research about mud pumping is necessaryThis paper mainly discusses the development laws and occurrence mechanism of mud pumping under different loading conditions and soil characteristics,and propose a criterion of mud pumping in a further step.On the other hand,the pore water pressure and displacement are calculated based on consolidation theory to make a contrast with the experiment results,in order to describe the development rule of mud pumping.The following are the work and achieved results carried out in this article(1).In this paper,a self-made apparatus is designed and manufactured firstly.The apparatus consists of four parts:the test barrel,servo loading system,water pressure control system and Data collection system.The subbase and subgrade are simulated with graded ballast and silty-clay respectively.A series of mud pumping tests had been conducted to investigate the development law and occurrence condition of mud pumping under different fine content and void ratio through the measurement of pore water pressure and deformation,and a criterion is proposed in a further step.The experiment results show that the pore water pressure accumulates under the cyclic loading,when the effective stress turns negative,the soil liquification and mud pumping will happen in the subgrade;on the other hand,the fine content and void ratio are important parameters to mud pumping in silt clay foundation,the development of mud pumping can be aggravated by the increase of the fine content and the void ratio;furthermore,a criterion including plastic index(IP)and void ratio(e)has been proposed to distinguish whether the soil is prone to mud pumping.When the coordinate point of sample is above the criterion,the soil is prone to mud pumping.(2).By this self-made apparatus,a series of mud pumping tests on the saturated soft soil foundation are conducted to investigate the mechanism and rule of mud pumping under different loading amplitudes,and its influence on the mechanical properties of subgrade is also investigated.The experimental results show that the cyclic loading amplitude to trigger the mud pumping in the silty clay has a critical value.When the cyclic loading amplitude is below the critical value,the road base keeps stable and only the ballast particle penetration into the subgrade happens.While as the cyclic loading amplitude reaches the critical value,the pore water pressure in subgrade layer accumulates and leads to soil liquefaction finally,which triggers mud pumping from the subgrade to the road base.As the consequence of mud pumping,the inner structure of the road base fillings changes,following by the resilient modulus and the increase of damping ratio.(3).Neglecting the fine loss caused by mud pumping,the pore water pressure and accumulated displacement under different loading amplitude are ca lculated based on large strain consolidation of soft clay theory,the results are compared with the experimental results to verify the feasibility.On the basis of calculation results,the mud pumping zones in subgrade is investigated in a further step.The following are achieved results carried out in this part:because of the limitation of consolidation theory,the mud pumping model have similar trend o/in the procedure of pore water pressure dissipation.For deep soil layers of subgrade,the calculation results fit well with the experimental results,but in superficial layers,the deviation exists because of the structural failure of subgrade.As for the displacement development of road base,the calculation results do well in group qcyc=70 kPa and group qcyc=90 kPa,but have deviation in group qcyc=50kPa.The mud pumping ratio was also calculated in different specimens,at the beginning of loading,the mud pumping ratio is low which indicates the mud pumping happens severely in specimen,as loading time increases,the subgrade tends to be steady.High loading amplitude can aggravate mud pumping in deep layers in short term loading,but have slight influence in long term loading.