Study On Slurry Penetration And Stability Of Slurry Shield Tunnel Face Based On Interaction Of "Cutter-Soil"

In recent years,more and more river-crossing and sea-crossing underwater tunnels have become the first choice for the construction of large channels in regions with developed river system.Relying on its superior pressure control mode and high security,slurry shield is used widely in the construction of underwater tunnels with large crosssections.However,the underwater geological environment is complex,and in the sandy soil layer,the self-stability is poor and the water permeability is strong.At the same time,the mutual disturbance between the cutter head of shield machine and the soil of the stratum reconstructs the slurry pressure transmission mechanism.Therefore,the support efficiency of excavation face significantly decreases,and instability accidents such as collapse and water inrush are prone to occur during shield tunneling.In view of the above key problems,this thesis systematically studied the mechanism of slurry infiltration filter cake formation on the excavation face of slurry shield under the cuttersoil interaction and the stability of the excavation face through the combination of model test,numerical simulation and theoretical analysis.It revealed the influence of the cutting effect of shield cutter head on the characteristics and mechanism of filter cake formation and the stability of excavation face,obtained the evolutionary law of the progressive instability of tunnel excavation face under the cutter-soil interaction,and proposed a calculation method for limit support pressure conforming to the deformation characteristics of excavation face under the cutter-soil interaction.The main contents and research results are as follows:(1)A set of testing device for slurry infiltration filter cake formation was developed based on the cutter-soil-slurry interaction,and slurry infiltration filter cake formation tests were carried out under different cutter structures,different cutter arrangements,and different cutter head speeds.The infiltration capacity of slurry infiltration filter cake formation,the conversion rate of effective pressure,and the change rule of soil conductivity with cutter head speed were obtained.The characteristics of filter cake formation under different cutter structures and different cutter arrangements were also obtained.The test results showed that the characteristics of filter cake formation based on the cutter-soil interaction were significantly different from those without considering the tool cutting effect,that is,under the influence of tool cutting,the volume of leachate in unit time increased significantly compared with that under the static state of cutter head,the effective pressure conversion rate of slurry decreased,and the maximum penetration distance of slurry increased.The rotating speed of cutter head and the number of cutters on the same path were the main control factors affecting the filter cake characteristics and the pressure transmission mechanism.Under the static state of cutter head,filter cake was not disturbed by the cutting tool,and it could be considered that a single slurry pressure transmission mechanism was formed on the excavation face.However,considering the cutter-soil interaction,the slurry pressure transmission on the excavation face was often a composite slurry pressure transmission,and two or more slurry pressure transmission mechanisms coexisted.(2)Based on the stability test and numerical simulation study on the excavation face of slurry shield under the cutter-soil interaction,the pore water pressure of excavation face and the periodic change law of surface deformation were obtained under different cutter head speeds,different water head heights and different cutter structures.The characteristics of surface deformation and filter cake distribution were also obtained under the cutter-soil interaction.In addition,the progressive spatiotemporal evolution process and instability mechanism of the active instability of tunnel excavation face were revealed.The research results showed that under the influence of the cutter-soil interaction,the excavation face started to crack from the cutting position and expanded downward and upward at the same time.When the cutter head rotated,due to the loosening effect of soil disturbance caused by the cutter head,the deformation of the excavation face was like a logarithmic spiral.When the rotating speed of the cutter head increased,the deformation of the soil above the logarithmic spiral extended to the front and back of the excavation face,until a kind of logarithmic spiral-pyramid-shaped overall instability was formed.The limit effective pressure of the excavation face increased continuously with the increase of the cutter head speed,and at each speed it was significantly larger than that at the standstill of the cutter head.(3)Based on the cutter-soil interaction,a theoretical model of active instable failure of the logarithmic spiral-pyramid excavation face was established.Heterogeneous pressure transmission(HPT)model was used to characterize the slurry pressure transmission mechanism in the instable region.The validity of the model was verified by the comparison of the calculation results with model test and numerical simulation.The research results showed that the effective pressure conversion rate of slurry decreased with the increase of the cutter head speed,the total number of cutters,and the number of cutters on the same path,and the effective pressure conversion rate of slurry could be elevated via properly increasing the effective pressure of slurry.(4)The influencing factors of the limit support force of the tunnel excavation face under the cutter-soil interaction were studied,and the influencing laws of the effective weight of soil,internal friction angle,shield diameter,thickness-span ratio,cutter head speed,and the number of cutters on the same path on the limit support pressure of the excavation face were proved.The results showed that the limit support force of slurry on the excavation face increased with the increase of the effective weight of soil,shield diameter,thickness-span ratio,cutter head speed and the number of cutters on the same path,and decreased with the increase of the internal friction angle of soil.Moreover,combined with project cases,the stability control strategy of the excavation face of slurry shield in the sandy soil layer was put forward,which is "optimization of types,observation of cuts,slow speed of revolution,slight increase of pressure".This thesis contains 106 figures,14 tables and 225 references.