A Method for Calculating Soil Deformation Induced by Shielded Tunneling in Ground Stratum with Cavities

Abstract

The existence of cavities in shallow ground strata is one of the important causes of urban road collapse under the disturbance of tunnel excavation. Thus, this paper discusses the convergent deformation mode of ellipsoidal cavities. To this end, the convergent deformation of a cavity and the overall displacement of a tunnel were comprehensively examined. A three-dimensional symmetrical calculation model of the soil deformation under the combined action of the tunnel and the cavity was also established. Moreover, three-dimensional formulas for calculating the soil deformation and the surface settlement of the upper part of the tunnel and the cavity were derived. The influence of the different positions of the cavity on the surface settlement of the upper part of the tunnel was also examined. Further, the change in the soil settlement with the direction of the tunnel excavation and the depth of burial of the cavity was analyzed. The results show that the calculated settlement curves are consistent with the ones reported in the related literature. The cavity can also aggravate the surface settlement and deformation of the soil caused by the tunnel excavation. When the cavity is directly above the tunnel, the surface settlement curve is symmetrically distributed. As the position of the cavity changes, the overall settlement curve shifts to the direction of the cavity, showing asymmetry. Additionally, along the x-axis direction of the shielded tunnel, the surface settlement gradually increases to a limit value with a decrease in x and slowly declines to zero as x rises. Finally, along the depth of burial of the cavity, the settlement of the soil continues to enlarge; also, the growth rate of the soil settlement continues to increase further at positions closer to the cavity and the tunnel until it reaches a critical maximum.

Model Test on the Influence of Surcharge, Unloading and Excavation of Soft Clay Soils on Shield Tunnels

“…In view of this engineering problem, local and international scholars have done a lot of research. The research methods of the influence of surcharge, unloading and excavation on shield tunnel of adjacent subway are mainly divided into field measurement method [3][4][5][6], theoretical analysis method [7][8][9][10][11][12][13][14][15][16][17], numerical analysis method [18][19][20][21][22] and model test method [23][24][25][26][27][28][29], among which the cost of model test method is controllable and the obtained test results are relatively reliable, which is a better method to study the influence of surcharge, unloading and excavation on the shield tunnel of an adjacent subway. Xian Liu et al [23] conducted a full-scale experimental study on the bearing capacity of the shield tunnel structure under overload conditions.…”