Research on the influence of clay shock on inert slurry in shield-tunneling construction

Shield-out synchronous grouting is a new technology used to fill temporarily shield-out spaces between the strata and the shield when creating subterraneous tunnels. The grouting materials are called ‘clay shock’, which is soft, plastic, sticky and easily dispersed by using a pressurized jet. This study analyzes the mixing process of clay shock and backfill grouting material (inert slurry) and investigates the influence of clay shock on the inert slurry through laboratory testing. The findings show that the fluidity and bleeding rate of the inert slurry continuously decrease with the clay shock volume. The unconfined compressive strength and flexural strength of the inert slurry increase initially before decreasing with the clay shock volume ratio. The X-ray diffraction and scanning electron microscopy results reveal that the alkalinity of the clay shock initiates an alkali excitation reaction, which generates more gelling products and increases the strength of the inert slurry. Excessive clay shock causes the inert slurry to retain a loose and porous structure, which then decreases its strength. To ensure the effect of the inert slurry on settlement control, the grouting volume of the clay shock should not exceed one-fourth of the inert slurry volume.