| The microwave assisted mechanical rock breaking technology has become a hot topic in the research of hard rock tunnel excavation.After being irradiated by microwave,damage occurs inside the rock,reducing its compressive strength,tensile strength,and wear resistance,effectively improving construction efficiency and saving construction costs.During TBM excavation of hard rock tunnels,the rock mass of the tunnel face is located in a complex stress environment.In order to study the influence of complex stress states on the effect of microwave irradiation on rock,COMSOL was used to establish two-dimensional and three-dimensional numerical models of three types of rock samples under different stress states,as well as threedimensional numerical models of tunnel face excavation and microwave irradiation on the rock mass of the tunnel face after excavation.From the electromagnetic field,temperature field The stress field,plastic zone,and other aspects were analyzed;The influence of indoor experimental loading conditions and stress environment on the effect of microwave irradiation on rocks was explored.The main conclusions are as follows:(1)The stress state of the rock mass on the tunnel face was analyzed.Rock blocks at 16 positions on the face were selected,and nine paths in three directions were selected to analyze the stress state and distribution characteristics of rock blocks at different positions on the face.The distribution pattern of the first principal stress in the rock mass at different positions on the excavation face was summarized.The medium pressure stress of the first principal stress significantly increased at the excavation boundary of the face,and the peak value was located at a certain distance within the face,where the pressure was significant.The rock block located in the center of the palm face has compressive stress located directly behind the palm face.The first principal stress on the entire palm surface is approximately 0 in tensile stress,and the compressive stress increases at a certain distance behind the palm surface.The first principal stress exhibits an axisymmetric trend with respect to the palm surface.After analyzing the first principal stress change curve in three directions,provide a basis for applying the stress state of the rock mass on the face of the tunnel under microwave irradiation for different stress states.(2)By establishing the model of microwave irradiation analysis for three common rocks,the irradiation effect of the same microwave power under the condition of different pressure coefficient on different sides was studied,and the electromagnetic field,temperature field,stress field and plastic zone of the sample were analyzed.Research has found that after microwave irradiation,the electric field intensity of three common rock samples does not change significantly with the increase of lateral pressure coefficient,and is symmetrically distributed.Limestone is the largest,followed by granite,and basalt is the smallest;The temperature and temperature gradient do not change with the change of lateral pressure coefficient,but both increase with the increase of irradiation time.Basalt is the largest,limestone is the second,and granite is the smallest;The confining pressure is a compressive stress,while COMSOL stipulates positive tension and negative pressure,and the first principal stress decreases with the increase of lateral pressure coefficient;The plastic zone irradiated by microwave is caused by the tensile failure of rock sample,so the plastic zone decreases with the increase of lateral pressure coefficient,and increases with the increase of irradiation time.Basalt is more sensitive to microwaves,with a larger proportion of absorbing minerals,while granite has the highest content of transmitting minerals and the lowest sensitivity to microwaves.Therefore,the plastic zone generated under the same irradiation time,power,and confining pressure is the smallest.Under the same lateral pressure coefficient,the area of plastic zone is the largest for basalt,followed by limestone,and the smallest for granite.The initiation time of plastic zone is delayed with the increase of lateral pressure coefficient.The greater the lateral pressure coefficient is,the later the plastic zone is generated.The confining pressure has an inhibitory effect on the expansion of plastic zone.(3)By establishing a model of microwave irradiation on rocks after excavation of the tunnel face,and utilizing the stress states of 16 rock blocks taken after excavation of the tunnel face in Chapter 2,microwave irradiation studies were conducted on the rock masses of three different rock types in the tunnel face.Research has found that there is no significant change in the electric field intensity,temperature,and temperature gradient of rock blocks in different parts of the palm face after microwave irradiation,and these three factors do not change with the changes in the position of the palm face rock mass;But it has a significant impact on the first principal stress value and plastic zone after microwave irradiation.After irradiation,the tensile stress of the rock increases significantly.The closer the rock block is to the center of the palm face,the better the irradiation effect,and the closer the rock block is to the edge,the worse the irradiation effect.The reason is that the rock blocks at the boundary of the palm face have greater compressive stress,which suppresses the generation and expansion of plastic zones,thereby reducing the effect of microwave irradiation.However,the rock blocks at the center of the palm face have smaller compressive stress,resulting in a larger volume of plastic zones under the same irradiation time and power conditions,which has a better microwave irradiation effect.For the plastic zone volume generated by the irradiation effect of the tunnel face with three different lithologies,basalt is the largest,followed by limestone,and granite is the smallest.This is related to the rock dielectric constant and internal mineral composition of the three lithologies. |
