Study On The Grouts Diffusion Mechanism Of Shield Tunnel Back-filled Grouts

Backfill grouting as a key process of shield method, has been paid much attention byresearchers and scholars for a long period of time Mainly because improper constructionmethods may cause engineering problems such as settlement, uplift, segment rupture, and blotcut. Most previous studies focused on properties of grout and grouting effects throughnumerical simulations, field measurements and model testing. However few studies havetaken consideration of grout diffusion mechanism. Combined with the features of shieldmethod, this paper divids the grout diffusion process into four types, filling diffusion,penetration diffusion, compaction diffusion, and splitting diffusion. Furthermore, The papertheoretically studies the diffusion mechanism for each model respectively.The paper establishes a the single plasma grout annular and fan-shaped filling diffusionmodel, derived single plasma grout filling pressure distribution formula by using Newtonianfluid model and Bingham fluid model. The formulas are then validated by an engineeringexample. Comparative analysis of the links and differences between the two calculationformulas are carried out. The results shows that both annular and fan-shaped filling diffusionmodels can reflect the grout pressure attenuation law.This paper sstablishes a spherical and a cylindrical diffusion model considering the grouttime-varying characteristics， andderivs grout diffusion scope calculation formula and groutpressure for segment calculation formula. Analysis relevant parameters effect for grouting.The results show that, of the two diffusion models are suitable for the single plasma groutgrouting calculation where use shield method in sandy soil.And this paper also establishes two theoretical models when the grout is hemisphericalcompression of surrounding soil and grout is cylindrical compression of surrounding soil, andanalysis an engineering example. Derived surface deformation caused by grouting calculationformula by using mirror image method. From the perspective of control deformation andstress of segment put forward a critical grouting pressure calculation method for backfillgrouting.Finally, make a brief discussion of existing problem and research direction of backfillgrouting.