Abstract To understand the mechanical characteristics of a multi-arch tunnel support structure in loess, the pres? sure on the surrounding rock, the axial force of the anchor bolt, the internal force of the steel arch and the force on the secondary lining are tested using steel-wire transducers. The test results indicate that: 1) the pressure of the surrounding rock fluctuates a lot at the juncture between the top of the mid-wall and the arch and the joint between the bottom of the wall and the invert, with maximum pressures of 195 kPa and 115 kPa, respectively. The pressure of the tunnel invert center at a rock transition section is relatively large, with a maximum pressure of 267 kPa and shaped like a large heaving floor, with the pressure of the rock mass distributing in a "double-saddle" shape; 2) the measured vertical pressure of a rock mass at a deep buried depth is close to the result calculated based on a half span of a multiple-arch tunnel specified in the“Code for Road Tunnels.”The pressures on rock masses calculated by different formulas are larger than the ones measured at the shallow-buried section, while the pressures obtained by the Terzaghi formula are relatively close to the measured ones; 3) the proportions of load sharing between the initial support and the secondary lining of this loess tunnel are 47.66% and 52.34%, which shows the secondary lining is in a load-bearing state; 4) the axial force of an anchor bolt is relatively small and distributed in a“fish-maw” shape, with the load largely borne by the steel arch and the anchor bolt playing a limited function due to the strong support of the steel arch; and 5) it proves that there is a longitudinal effect on the loess tunnel because of the existence of middle wall torque, and attention should be paid to this during construction and design.
Abstract：
To understand the mechanical characteristics of a multi-arch tunnel support structure in loess, the pres? sure on the surrounding rock, the axial force of the anchor bolt, the internal force of the steel arch and the force on the secondary lining are tested using steel-wire transducers. The test results indicate that: 1) the pressure of the surrounding rock fluctuates a lot at the juncture between the top of the mid-wall and the arch and the joint between the bottom of the wall and the invert, with maximum pressures of 195 kPa and 115 kPa, respectively. The pressure of the tunnel invert center at a rock transition section is relatively large, with a maximum pressure of 267 kPa and shaped like a large heaving floor, with the pressure of the rock mass distributing in a "double-saddle" shape; 2) the measured vertical pressure of a rock mass at a deep buried depth is close to the result calculated based on a half span of a multiple-arch tunnel specified in the“Code for Road Tunnels.”The pressures on rock masses calculated by different formulas are larger than the ones measured at the shallow-buried section, while the pressures obtained by the Terzaghi formula are relatively close to the measured ones; 3) the proportions of load sharing between the initial support and the secondary lining of this loess tunnel are 47.66% and 52.34%, which shows the secondary lining is in a load-bearing state; 4) the axial force of an anchor bolt is relatively small and distributed in a“fish-maw” shape, with the load largely borne by the steel arch and the anchor bolt playing a limited function due to the strong support of the steel arch; and 5) it proves that there is a longitudinal effect on the loess tunnel because of the existence of middle wall torque, and attention should be paid to this during construction and design.
2017, Vol. 54 