Effects of Excavation Gap Filling of Under-1 Crossing Tunnel on Pipelines

Excavation gap filling is an important means to control the strata movement in tunneling. In practice, synchronous grouting or secondary replenishment of the gap is usually used to control the settlement, instead of filling the excavation clearance. In fact, the diameter of the cutterhead is usually slightly larger than that of the shield, and the front shield is also larger than its back. As a result, there will be an annular gap (i.e., an excavation clearance) between the tunnel soil layer and the shield. Thus, effectively filling the gap contributes to controlling the formation displacement. In this paper, the Wei Lai Da Dao to Feng Tai Nan Lu section of Zhengzhou Metro Line 3 is selected as the study object. Based on the three-dimensional finite element method, the influence of an under-crossing shield tunnel sewage pipes on strata movement under complicated conditions is analyzed. Field tests also show that the movement and development trend are similar to the simulated results, which further indicates that, under similar geological conditions, numerical simulation results can be used to guide the filling of excavation clearance in EPB. It is found that the excavation gap filling can effectively reduce the surface settlement rate and make the surface settlement stabilize faster and the curve shape of “settlement trough” changes from “narrow and deep” to “shallow and wide.” However, the grout used in this method should be with the properties of short hardening time, large elastic modulus, and low shear strength. Besides, the excavation gap filling can also reduce the extrusion deformation of sewage pipe and inhibit the horizontal and vertical displacement of sewage pipes. Therefore, it is considered that excavation clearance filling is an effective method to reduce stratum movement and tunnel deformation, which is of great significance for future research and practical engineering.

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