| As a highly integrated tunnel construction machine,the Tunnel Boring Machine has many advantages,such as high tunneling speed,small surrounding rock disturbance,safety and reliability.It is widely used in rock tunnel construction such as highway,railway,water conservancy and so on.However,when encountering high confining pressure,high abrasive hard rock and extremely hard rock,the rock breaking ability of the hob is seriously insufficient,resulting in a series of engineering problems,such as low penetration,abnormal damage of the cutter head,bearing fracture,etc.It seriously restricts the TBM tunneling efficiency.In order to improve the ability of cutting tools to break extremely hard rocks,the traditional implementation methods focus on developing stronger cutting tool materials and increasing the diameter of cutting tools.Although the rock breaking performance of TBM has been improved to a certain extent,it has not fundamentally solved the dilemma of extremely hard rock excavation.Therefore,a new generation of TBM concept based on high-pressure water jet-assisted rock breaking technology has been proposed,and it has quickly become a hot spot in the field of underground engineering at home and abroad.Abrasive water jet has been successfully applied in the processing of hard materials such as metals and alloys due to the addition of hard abrasive particles to the high-speed jet,which greatly enhances the cutting ability.In view of this,a new method of abrasive water jet-hob combined rock breaking is proposed in this paper.However the application of this method to TBM construction should solve the following problems:(1)Lack of understanding about the effect and mechanism of cutting extremely hard rock by abrasive water jet under the condition of high traverse speed of TBM,especially;(2)Lack of understanding of the combined rock-breaking effect and synergistic mechanism under different combination modes of abrasive water jet and hob;(3)Lack of design and optimization methods for abrasive waterjet TBMs.In view of the above problems,this paper has adopted the method of combining laboratory test,theoretical analysis and numerical analysis to carried out the research on the effect and mechanism of cutting extremely hard rock by high transverse velocity abrasive water jet,the effect and mechanism of breaking extremely hard rock by abrasive water jet and hob with the same and different trajectory,and the design optimization method of cutter head for breaking rock by abrasive water jet and hob.The effect of high transverse velocity abrasive water jet and abrasive water jet hob combined rock breaking is clarified.Moreover,the mechanism of high transverse velocity abrasive water jet and combined hob rock breaking is revealed,and the cutterhead design optimization method of abrasive water jet-hob combined rock breaking is constructed and realized.The main research work and results of this paper are as follows:(1)Study on the effect and mechanism of cutting very hard rock with high transverse velocity abrasive water jet.The dynamic process of rock cutting by abrasive water jet and the characteristics of kerf morphology were analyzed based on the cutting test.The rock cross section cut by high transverse velocity abrasive water jet and the characteristics of abrasive particle morphology were observed by electron microscope.It is revealed that the abrasive water jet breaking hard rock is the combined action of brittle fracture and plastic shear,and the removal mechanism of extremely hard rock is mainly plastic shear.Through the single factor cutting test,the influence rule between the transverse velocity,pump pressure,target distance,nozzle diameter,abrasive flow rate,cutting times and the depth of abrasive water jet cutting is clarified.The sensitivity of the process parameters to the target of the kerf depth is analyzed through multi factor experiments,and the prediction model of the kerf depth of extremely hard rock fractured by abrasive water jet is established.(2)Study on the rock breaking effect of abrasive water jet and hob with the same and different trajectory in extremely hard rock.Combined with the structure of abrasive water jet device and the arrangement characteristics of TBM cutter head hob,a combined rock breaking model of abrasive water jet and hob with the same and different trajectory is proposed.A full-scale abrasive water jet pre-kerf and hob combined rock-breaking test was carried out,and the relationship between the hob penetration,kerf spacing(knife spacing),kerf depth parameters and the hob’s rock-breaking force and rock-breaking specific energy was studied.And the applicable conditions and advantageous rock-breaking parameters of combined rock breaking with the same and different trajectory mode are defined.The results show that when the penetration of hob is less than the pre-kerf depth of abrasive water jet,the reducing effect of the same trajectory mode on the normal rock breaking force is better than that of the different trajectory mode.Otherwise,it is worse than the different trajectory mode.The optimal penetration,kerf spacing and kerf depth of broken extremely hard rock are 4.9mm,71mm,6mm and 3.8mm,78mm,6mm,under the same and different trajectory mode respectively.(3)Study on the mechanism and synergism of abrasive water jet and hob combined rock breaking.Based on the understanding of the characteristics of the combined rock breaking of abrasive water jet and hob,the mechanical model of the combined rock breaking with abrasive water jet pre-kerf hob is established.The fracture mechanics theory and discrete element numerical analysis method are used for analysis,it is found that the abrasive water jet pre-kerf reduces the rock crack resistance,induces the propagation direction of the intermediate crack and the lateral crack,promotes the tensile failure,and reduces the rock breaking force of the hob.Combined with the macro fracture model of the combined rock breaking test,the action mechanism of that the abrasive water jet pre-kerf hob combined rock-breaking promotes the tensile failure of the rock is revealed.(4)Design optimization and implementation method of abrasive water jet-hob combined rock-breaking cutter head.Considering the working characteristics of abrasive water jet breaking extremely hard rock,abrasive water jet-hob combined rock breaking and TBM cutter head,the design principle of combined rock breaking cutter head is established,and the design optimization method of abrasive water jet hob combined rock breaking cutterhead is formed.Taking a project cutter head as an example,the implementation and verification of the design optimization method of the combined rock-breaking cutterhead are carried out. |
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