# Optimisation of Synchronous Grouting Mix Ratio for Shield Tunnels
## 3 Results and Discussion  
### Single Factor Test  
Figure 1 shows the effect of the water-reducing agent dosage on slurry fluidity, segregation rate, and bleeding rate. As shown in Figure 1a, the water-reducing agent significantly affected the fluidity of the slurry. As the water-reducing agent dosage increased, the fluidity of the grouting slurry increased significantly. This is because the water-reducing agent can destroy the floc structure formed by cement hydration, release the free water in the mortar [36], and reduce the friction between the slurry particles [37]. As shown in Figure 1b,c, the addition of a water-reducing agent causes the segregation rate and bleeding rate of the slurry to decrease first and then increase with the increase in dosage. This is because the addition of a water-reducing agent can release the free water in the mortar and allow it to further participate in the hydration reaction [36], improving the water retention of the slurry [12], which subsequently reduces both the segregation rate and bleeding rate of the slurry. However, as the dosage of the water-reducing agent continues to increase, more and more flocculation structures are destroyed [38], and it can also inhibit the hydration reaction [39], thereby reducing the stability of the mortar [40]. This ultimately leads to an increase in the segregation rate and bleeding rate of the slurry.  
Figure 1: Influence of water reducer dosage on (**a**) fluidity, (**b**) segregation rate, and (**c**) bleeding rate of synchronous grouting slurry in shield tunnels.  
When the water-reducing agent dosage was 1.46 kg/m3, the segregation rate was low and the fluidity was 255 mm, which meets the performance index requirements of Type 2 mortar as stipulated in the gelatin-type dry-mixed mortar for shield-driving grouting (Q/ZTJHN1-2019) [41]. Therefore, the water-reducing agent dosage was determined to be 1.46 kg/m3.  
As shown in Figure 2a, with the increase in latex powder content, the fluidity of the slurry first increases and then decreases. This is because the water-soluble protective colloidal coating of redispersible latex powder particles can prevent aggregation between particles, and latex powder has air entrainment properties, which can introduce a large number of tiny bubbles, allowing polymer particles and tiny bubbles to produce a \"ball-bearing effect\" in the cement slurry [42; 43]. Therefore, the addition of latex powder increases the fluidity of the slurry [44; 45]. However, as the latex powder content further increases, the fluidity of the slurry decreases. This is because the dissolved latex powder becomes more viscous, increasing the viscosity of the mortar [46] and the internal friction of the slurry [47], resulting in a decrease in slurry fluidity. As shown in Figure 2b, with the increase in latex powder content, the segregation rate of the slurry generally shows a downward trend. This is because the incorporation of latex powder can increase the water retention of the slurry [48], enhance the hydration within the slurry, as well as cohesion and adhesion [49; 50], thereby improving mortar stability [40] and reducing the segregation rate. However, when the content exceeds 0.37 kg/m3, the segregation rate increases slightly. This is because when the latex powder content is too high, it can adhere to the surface of cement particles, impeding the contact between cement and water and weakening the hydration reaction [51], which in turn increases the slurry segregation rate.  
Figure 2: Influence of latex powder dosage on (**a**) fluidity, (**b**) segregation rate, and (**c**) bleeding rate of synchronous grouting slurry in shield tunnels.