Abstract
In the process of the underground tunnel excavation, a kind of geological condition Necking Region is often encountered. The ground surface inclines very fast, which also leads to the increase of Earth pressure on the excavation face. The determination of the excavation face support pressure is essential to solve the active Earth pressure when the shield passes through the Necking Region. In this paper, based on Horn’s wedge model, considering the influence of surface dip angle on excavation face support pressure, the traditional wedge model was improved. The analytical solution of the ultimate support pressure for the active failure of shield excavation face was derived. To evaluate the quality of the model, the theoretical model was compared with the ultimate bearing pressure of the horizontal surface test. The influence of the ultimate support pressure on the parameters of Nc, Nγ, and Nq was consistent with the results of finite element simulation and existing theories, which verified the rationality of the model. The stability of the excavation face of the Heyan road river crossing tunnel was analyzed by using the improved wedge model. The results show that the mud support pressure considering the slope angle was 36 kPa higher than that without considering the slope angle.
Highlights
In the process of the underground tunnel excavation, a kind of geological condition Necking Region is often encountered. e ground surface inclines very fast, which leads to the increase of Earth pressure on the excavation face. e determination of the excavation face support pressure is essential to solve the active Earth pressure when the shield passes through the Necking Region
To evaluate the quality of the model, the theoretical model was compared with the ultimate bearing pressure of the horizontal surface test. e influence of the ultimate support pressure on the parameters of Nc, Nc, and Nq was consistent with the results of finite element simulation and existing theories, which verified the rationality of the model. e stability of the excavation face of the Heyan road river crossing tunnel was analyzed by using the improved wedge model. e results show that the mud support pressure considering the slope angle was 36 kPa higher than that without considering the slope angle
E stability analysis of excavation face based on wedge instability model is the most common method for tunnel excavation under the horizontal surface. e wedge model proposed by Horn [9] is the earliest and most widely used excavation face support pressure solution mode, which is based on the equilibrium method. e essence of the theory is to use Coulomb’s static equilibrium theory for reference, assume the sliding surface of the tunneling surface, establish the mechanical balance equation of the excavation face based on Janssen’s [10] silo theory, and solve the excavation face support pressure
Summary
In the purpose of verifying the rationality of the theoretical analysis, it is essential to obtain the influence of the above coefficients on the ultimate support pressure. If the active Earth pressure coefficient could be expressed by cohesion and internal friction angle, an extreme value of cohesion could be obtained It could be seen from the first two groups of figures that the influence of cohesion on the support pressure of the excavation face is similar to that of gravity. As the friction angle was less than 25°, the increased slope of active Earth pressure was obviously higher than that of friction angle greater than 25°, and the increase of active Earth pressure had a rapidly increasing trend It showed that the closer the surface dip angle is to the formation friction angle, the greater the ultimate pressure of the tunneling surface and the greater the support difficulty. When the formation density was the same, with the increase of cohesion, the finite element simulation results and the improved theoretical analysis results showed a trend of first increase and decrease, which showed that
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