Climb Height and Overflow of Grout in Shaft Base Grouting

Based on the assumptions of exponential fluid and narrow plate model, formulas for calculating the climb height of grout in shaft base post grouting was deduced. It is shown that the climb height of grout is mainly related to the grouting pressure, the shaft length, the shaft diameter and the mudcake thickness. With the theoretic analysis and case study, it is indicated that thicker mudcake, higher grouting pressure and shorter shaft length would lead to larger climb height and larger risk of overflow. The overflow of grout would be prevented by reducing the grouting pressure, the mudcake thickness and debris thickness. The overflow of grout can also be prevented by increasing the strength of mudcake. For the overflow shafts, intermission grouting would be employed. Compared with the ordinary shafts, the former has higher bearing capacity than the latter, resulting from the grout upwards along the shaft soil interface.