The Time-Dependent Grout Buoyancy Behavior Based on Cement Hydration Mechanism

The grout buoyancy has a great influence on the segment during synchronous grouting of shield tunnel. Traditionally, the large buoyancy leads to certain types of tunnel distresses, such as convergence deformation, differential settlement, cracks, and water leakage. This paper made a detailed study on the time-dependent grout buoyancy behavior. The hydration heat test and LF-NMR test were carried out. Then the four periods of hydration rate curve were revealed, and the evolution rules of gel water, capillary water and free water were also obtained. The time-dependent grout buoyancy was tested by self-designed equipment, and the theoretical formula of grout buoyancy considering w/c ratio and time was proposed. The indoor test results were compared with the theoretical solution. The theoretical formulas could effectively predict the size and variation rules of buoyancy. The indoor test results showed that variation trend of cement grout buoyancy is consistent with the hydration rules. The buoyancy mainly exists in the initial period and the induction period, and decreases sharply to zero before the acceleration period. The initial setting moment is the one in which hydration rate is the largest.