Study On Mechanical Effect Of Pea-Gravel Backfill Grouting Layer In TBM Tunnel Lining System

In the process of TBM construction,the strength of backfill layer often fails to meet the design requirements.There is a question:does the backfill layer need to reach the strength of the current design?In this paper,engineering data analysis,basic theory research,numerical model test,laboratory test and other methods are used to carry out research.Firstly,the process of backfilling and grouting of Pea-Gravel and the formation process of backfilling grout of Pea-Gravel are fully considered.Through laboratory tests,the relationship between strength and deformation of backfilling is studied,and the physical and mechanical parameters of backfilling under different strength conditions are determined;Then the function of backfill layer in the combined stress system is studied,and the mechanism of backfill layer is revealed.The effects of elastic modulus,thickness,Poisson's ratio of backfill layer and lateral pressure coefficient of in-situ stress on the stress magnitude and distribution on segments are studied;Finally,combining the research results with engineering application,the strength requirement of backfill layer in engineering is clarified,and The strength design suggestions of backfill of pressure tunnel and pressure tunnel are put forward,which can serve as a reference for future engineering design.The main achievements of this paper are as follows:?1?The uniaxial compression tests were carried out with field sampling and indoor prefabricated samples,and the relationship among elastic modulus,Poisson's ratio and strength of backfill layer was fitted.The conclusion was drawn that the elastic modulus increased and the Poisson's ratio decreased with the increase of backfill layer strength.?2?The influence of elastic modulus:There is a critical point on the curve between segment stress and E_b/E?Ratio of elastic modulus between backfill and surrounding rock?.The value of E_b corresponding to the critical point can be called the critical value,which is expressed by symbol E_K1.When E_b is less than the critical value E_K1,the segment stress increases with the increase of backfill layer strength;when E_b is greater than the critical value,the segment stress decreases with the increase of backfill layer strength.?3?The influence of Poisson's ratio:The influence of Poisson's ratio on segment stress is related to the elastic modulus of backfill layer,which has a critical value of E_K2.When the elastic modulus of backfill layer is less than E_K2,the segment stress increases with the increase of Poisson's ratio,and the smaller the elastic modulus,the more obvious the trend is.When the elastic modulus of backfill layer is greater than E_K2,the segment stress decreases with the increase of Poisson's ratio,and the greater the elastic modulus,the more obvious the trend is.?4?The influence of thickness:The influence of backfill thickness on segment stress is related to the elastic modulus of backfill.There is a critical value E_K3 for the elastic modulus.When the elastic modulus of backfill is less than E_K3,the segment stress increases with the increase of t₂/t₁?Ratio of backfill to segment thickness?value,and the smaller the elastic modulus,the more obvious the trend.When the elastic modulus of backfill is greater than E_K3,the segment stress decreases with the increase of t₂/t₁ value,and the greater the elastic modulus,the more obvious the trend.?5?The change of elastic modulus and Poisson's ratio of backfill layer has little effect on the stress distribution of segment,but the thickness of backfill layer and In-situ stress lateral pressure coefficient have greater influence.?6?For pressure-free tunnels,when the surrounding rock conditions are good,the strength of backfill layer should be reduced as far as possible under the condition that the backfill itself is not destroyed;and when the surrounding rock conditions are poor,high strength backfill layer should be used as far as possible.For pressure tunnel,high strength backfill layer should be used as far as possible.In engineering application,specific problems should be analyzed.