Experimental study on grouting in underconsolidated soil to control excessive settlement

The underconsolidated soils in reclaimed land have low strength and high compressibility, resulting in susceptibility to excessive settlement and associated negative effects, which can be controlled by grouting. However, there is little research on the mechanism of grouting in underconsolidated soil, compared with the normally consolidated or overconsolidated soil. In this study, we present a series of laboratory grouting tests to investigate the grouting mechanism and the effect of degree of consolidation, soil type, load increment ratio and initial overlying load on the grouting performance. The results showed that the influence of grouting on primary consolidation settlement for underconsolidated soil included the heave effect, the additional settlement due to the dissipation of excess pore water pressure induced by grouting and the reduced settlement due to the increased modulus induced by grouting. However, grouting in underconsolidated soil had no influence on the secondary consolidation settlement. Grouting in underconsolidated soil with low degree of consolidation could obtain a shorter time of primary consolidation and a higher final grouting efficiency in primary consolidation stage. The final grouting efficiency in primary consolidation stage increased linearly with increasing load increment ratio, but decreased with increasing initial overlying load. As the overconsolidation ratio increased, the final grouting efficiency in primary consolidation stage decreased for underconsolidated soil, dropping to the lowest value for normally consolidated soil and then increased for the overconsolidated soil, reaching a limit. Moreover, the peak grouting pressure was proportional to the vertical effective stress at the beginning of grouting.