| Judging from the application of shields at home and abroad,the application of large-diameter slurry shields has been widely used.However,when large-diameter slurry shields pass through complex layers such as clay layers,silty clay layers and argillaceous siltstones,they will often face the problem of cake mud.With regarding to the problem of shield cutter plate mud,many researchers have studied the cause of sludge formation and prevention and control measures.However,most previous studies used empirical methods to systematically study the mechanism of specific sludge formation.The causes of blockage of the cutterhead of the shield include: large diameter,geological reasons,design defects of the cutterhead,cutter,and flushing system,construction control factors,etc,this paper analyzes the problem of shield cutter head mud from the fluid point of view and proposes a method for studying the mud problem by researching the flow field of the fluid in the mud silo.The main research contents are as follows:(1)This article relies on the large-diameter muddy water pressure balance shield tunnelling project of the Wuhan Sanyang Road Tunnel,with a focus on the fluid characteristics and effects of the high-density mud near the cutterhead excavation surface,using the fluid calculation software CFX for the shield mud silo.The fluid was subjected to numerical simulation analysis.Based on the results of the lateral comparison of fluid flow conditions in the vicinity of the excavation surface,the following conclusions were drawn: Relative to the flow velocity of the surrounding area,the fluid velocity in the middle region near the excavation surface was extremely low,and the flow was disordered.The formation of vortices,resulting in energy loss,in this case,can be qualitatively judged that the center of the cutter head is prone to mud cake problems.(2)Taking the Φ15.76 m Herrenknecht Slurry Balanced Shield as the prototype,a scale model with a scale of 1:10 is planned to be constructed,and the muddy water movement morphology test is carried out according to the actual construction site conditions.In this paper,the experimental model and boundary conditions are designed based on the principle of dynamic similarity.The flow field demonstration scheme and the particle image velocity measurement(PIV)experimental scheme are proposed to carry out experiments.The specific test equipment and equipment are described in detail and formulated.Reasonable test arrangements.(3)Based on the numerical simulation of the fluid in the mud storage chamber of the second chapter of the large-diameter slurry balance shield,it is considered that the problem of the size of the mud in the cutterhead is related to the fluid velocity.It is proposed that the cutterhead center can be accelerated by changing the distribution of the fluid flow field in the mud silo.The principle of regional fluid velocity,developed two improvements: change the cutter head flushing system and optimized cutters.According to the shield type selection and actual construction condition of Sanyang Road Tunnel,the scheme of increasing the flow distribution system is adopted to reconstruct the position,size and flow distribution of the scour hole on the cutterhead,and three modification conditions are proposed.After the numerical simulation analysis of these three working conditions,the three results are compared with the numerical simulation results in the actual conditions of the shield,and the working condition with the maximum fluid flow velocity in the center of the cutter head is selected as the optimum working condition.In the process,the position of the flushing hole and the flow distribution are designed with the best working conditions.In this paper,after analyzing the function of the cutter(hob)used in the center of the large-diameter mud-water shield cutterhead,two types of cutting function are designed,which are not only cutting and stirring mud,but also have the function of transporting muddy water from the center of the cutterhead to the center.The new tools,and introduced in detail the design of the two new types of tools and configuration programs. |
