Research and evaluation on Water-dispersion resistance of synchronous grouting slurry in shield tunnel

When the shield tunnel passes through the watered stratum with high permeability, as the shield tail interspace prone to be filled with groundwater, resulting in the segregation and loss of ordinary grout slurry during synchronous grouting, then critically affect the physical and mechanical properties as well as the durability of the curing grouting ring. Hence, it is necessary to optimize the performance of the existing ordinary grouting slurry to improve its water-dispersion resistance on the premise of ensuring the original performance. By means of theoretical analysis and indoor tests, this paper systematically investigates the mechanism of water-dispersion resistance of synchronous grouting slurry in water-rich stratum with high permeability, establishing a set of testing process and detection method for water-dispersion resistance of synchronous grouting. Moreover, the influences of different flocculants with corresponding contents on the performance of synchronous grouting slurry have been revealed, and the evaluation criterion of water-dispersion resistance of synchronous grouting slurry in shield tunnel is also clarified. The results show that: 1) Turbidity has notable responses to the change of flocculant content, which could better reflect the clarity of water samples. So, the turbidity is considered as a main evaluation index of water-dispersion resistance of synchronous grouting; 2) On the other hand, pH and water-land strength ratio also demonstrates the acid-base changes of groundwater and the loss of cementitious materials respectively during grouting. Thus, the two indexes are applied as auxiliary evaluation indexes for water-dispersion resistance of synchronous grouting; 3) For the above evaluation indexes, corresponding critical values to satisfy the water-dispersion resistance of synchronous grouting slurry are ensured: turbidity < 100NTU, pH < 10, and water–air strength ratio at different curing ages greater than 80%.