Model Test Study On Rock Breaking Efficiency By TBM Cutter Assisted With High Pressure Water Jet In Highly Abrasive Hard Rock

With the large-scale development of infrastructure construction in our country,the number of underground projects and tunnels is increasing,the geological environment encountered is becoming more and more complex,and the difficulty of TBM tunneling is increasing.When encountered with high abrasive hard rock,the tunneling problem is more prominent,which inevitably leads to serious wear of the cutter,such as tool ring cracking,cutter partial wear,bearing damage,jet ring rolling edge and so on,which will seriously affect the construction progress and cost control of TBM.In particular,the complex environmental conditions such as deep high confining pressure will further worsen the above problems.In order to further improve the driving efficiency of TBM in high abrasive hard rock strata,the new rock breaking technology is developing continuously,in which the high pressure water jet-TBM cutter hydraulic coupling rock breaking method has been applied to the TBM tunnel of Wananxi Water diversion Project in Longyan,Fujian Province.Based on the indoor cutter penetration model test of high abrasive hard rock samples,this paper focuses on the crushing process and rock breaking efficiency of TBM cutter under different confining pressure gradient and different geometric parameters of vertical cracks,and reveals the rock breaking law of TBM cutter assisted by high pressure water cutter.The main research contents are as follows:(1)The main results are as follows:(1)based on the basic physical and mechanical tests,such as rock uniaxial compression test,Brazilian splitting tensile test,rock abrasion test,mineral composition analysis test and so on,the physical and mechanical indexes of medium strength sandstone samples,hard granite samples and very hard granite samples were determined,mineral composition analysis and abrasion value were determined respectively.The test results show that the hard granite sample belongs to high abrasive superhard rock,which will seriously affect TBM tunneling.(2)based on the indoor model test of cutter penetration,combined with acoustic emission system and high-speed photographic image recognition technology,the whole failure process of intact and highly abrasive hard rock specimen is studied.The characteristic law of penetration load-penetration curve under different confining pressure is analyzed.The results show that under the condition of no pre-cutting joint,with the increase of confining pressure,the peak penetration load of rock samples increases,the number of penetration load-penetration curve increases,and the failure characteristics of samples change from brittle failure to ductile failure,and the difficulty of TBM tunneling in high strength and high abrasive strata without confining pressure is higher than that in conventional strength strata and high strength abrasive strata.The failure process of TBM cutter penetration into high strength and high abrasive granite samples can be divided into four stages: contact compaction stage(stage Ⅰ),microcrack initiation stage(stage Ⅱ),crack propagation-penetration damage stage(stage Ⅲ)and residual bearing capacity stage(stageⅣ).(3)based on the indoor model test of TBM cutter penetration assisted by high pressure water jet,the wedge fracture mechanism of water jet cutting high abrasion hard rock specimen under the condition of low confining pressure and different geometric parameters of water jet cutting crack is studied by using acoustic emission system and high speed photography image recognition technology,and the curve fluctuation characteristics of penetration load-penetration degree evolution curve and rock step breaking characteristics are revealed.The results show that under the condition of pre-cutting seam,the splitting mode failure occurs when the distance between the pre-cutting seam and the tool axis Lind0,and the peak penetration load of the rock sample is significantly less than that of L≠0 without confining pressure,and under the condition of confining pressure,the penetration corresponding to the peak penetration load of the rock sample is significantly larger than that of L≠0.Under the condition of pre-cutting seam,when the distance between pre-cutting seam and tool axis L≠0,the greater the pre-cutting seam depth H is,the higher the rock breaking efficiency is,and the larger high pressure water jet cutting depth H can reduce the cutter wear rate in TBM excavation of high strength and high erosion stratum.Under the condition of pre-cutting seam,when the pre-cutting depth H is constant,the peak penetration load and the corresponding penetration degree of rock samples under different L values increase with the increase of confining pressure,while when the L value is larger,to a certain extent,it is necessary to increase the driving thrust to achieve efficient rock breaking.(4)the whole process of water jet cutting high abrasive hard rock samples under medium and high confining pressure is studied,and the evolution law of penetration load-penetration and crushing characteristics under different confining pressure are analyzed.The results show that under the condition of high confining pressure,the penetration failure process of pre-slotted specimens roughly includes the following three stages: contact compaction stage(stage Ⅰ),microcrack initiation stage(stage Ⅱ),crack propagation-penetration damage stage(stage Ⅲ 1,stage Ⅲ 2).Among them,there is a great difference in the crack propagation-penetration damage stage stage between the pre-slotted and non-pre-slotted samples;in the Ⅲ1 stage,the crack under the cutting tool of the pre-slotted rock sample penetrates with the bottom of the pre-slotted seam,forming an effective rock breaking;in theⅢ2 stage,the penetration curve of the pre-slotted rock sample shows the characteristic of "double peak";when the confining pressure is greater than 15 MPa,with the increase of the confining pressure,the promoting effect of the pre-slotted rock sample on the rock breaking of TBM cutter is stronger.