Bentonite Mud Test And Analysis For Improvement Of Shield Muck

In shield construction of metro,when crossing different geological conditions,there are often a series of problems,such as cutter head caking,cutter head wear,screw earth conveyor spraying and so on.Therefore,muck improvement is the most critical link in shield construction.At present,there is no uniform standard requirement for the use of bentonite mud and the amount of bentonite mud commonly used in shield muck improver,which is arbitrary and needs to be further systematically studied.In this paper,based on some projects of Shenyang Metro Line 10,through bentonite mud test and muck improvement test,the correlation between the main performance indicators of mud was studied,and the reasonable performance indicators of mud improved muck were obtained.A new calcium-based bentonite mud was prepared based on the reasonable mud performance index of muck improvement test.Then,through the numerical simulation analysis of the influence of bentonite mud on the mechanical behavior of tunnel shield construction,the influence of mud on the settlement of soil around the tunnel and the stress of segments is studied.The following research results have been achieved:(1)Three kinds of sodium-based bentonite mud were prepared.Each mud has 7 kinds of proportions and 21 groups of mud.The mud viscosity,mud specific gravity,mud filtration vector,consistency coefficient,colloid ratio,acidity and alkalinity were taken as the research indexes.The correlations among the properties of different sodium-based bentonite mud were analyzed,and the correlations among the main indexes were obtained by fitting the experimental data.(2)Based on three kinds of sodium-based bentonite mud,clayey soil,coarse sand soil and sandy pebble soil were improved by muck.The fluidity,adhesiveness,permeability and friction of the improved muck were measured,and the reasonable ratio of sodium bentonite mud and mud index were obtained.(3)Combining with the reasonable index of sodium-based bentonite mud for different dregs,a new calcium-based bentonite mud with calcium-based bentonite as the main material,caustic soda,baking soda,carboxymethyl cellulose,xanthan gum and guar gum as the mud improvement additives was optimized by orthogonal test.(4)According to the change of shield tunneling parameters before and after the use of new calcium-based bentonite mud,the displacement stress in tunnel shield construction isanalyzed by numerical simulation.The results show that the new calcium-based bentonite mud can reduce the settlement of the vault,the uplift of the vault bottom and the maximum stress on the segment during the tunnel construction.