Surface Settlement of Shallow Shield Tunneling: Face Pressure, Tail-Void Grouting Pressure, and Grout Volume

Abstract

Surface settlement caused by shallow shield tunneling can occur frequently. Machine variables such as face pressure, tail-void grouting pressure, and grout volume play an essential role in the settlement control of earth pressure balance (EPB) tunnel boring machines (TBMs). Combined with literature review, theoretical derivation, case verification, and numerical simulation, methods were established for adjusting the key parameters, including the face pressure in the plenum chamber, the advance speed of the shield machine, and the rotational speed of the screw conveyor. The grouting volume required to backfill the tail void was calculated according to shield kinematics, a physical model test under high pressure and soil states during excavation,. From the mechanical properties of soil, the function between surface settlement and tail-void grouting pressure based on the Peck formula, stochastic medium theory, and Terzaghi soil arching theory was deduced for the first time. With the increase in grouting pressure, the soil was compressed after the formation of the soil arch, and the process from original settlement to upheaval was also expressed by numerical simulations. In addition, the proposed methods could control the surface settlement effectively and result in more accurate predictions. By comparing the predicted surface settlement to measured data from the Harbin Metro Line 2 project, the adaptability of the proposed methods for the face pressure, tail-void grouting pressure, and grout volume was verified.