Experimental Study of the Formation Mechanism of a Grouting Filter Cake at the Shield Tail of a Saturated Fine Sand Layer under the Effect of Seepage

An equation for the filter cake growth rate for shield tail grouting in water-rich fine sand was established with the water–cement ratio and grouting pressure, and the average acceleration of filter cake growth ar was defined. A filter cake formation test device and shield tail grouting similarity model test system were developed, and the model was verified for different water–cement ratios and grouting pressures. Under certain conditions, the greater the grouting pressure was, the greater the filter cake growth rate and thickness, the shorter the filter cake growth duration, and the smaller the surface settlement. Under other conditions, the greater the water–cement ratio was, the smaller the filter cake growth rate and thickness, the longer the filter cake growth duration, and the smaller the surface settlement. The grouting pressure should be increased and the water–cement ratio of the grout should be reduced to ensure that the filter cake has a certain thickness, forms rapidly, and reduces surface settlement. The recommended water–cement ratio of grout for grouting at 0.4 MPa in water-rich silty fine sand with a porosity of 0.36 is 0.8–0.85. These results are relevant to shield tail grouting in water-rich fine sand layers.