In-situ tests on ground surface settlement and additional strain of shaft linings

More than 100 shafts have ruptured in China during the past three decades. The vertical additional force is regarded as the mechanism of the rupture. Grouting of the surrounding soil to reduce the additional stress is found to be an effective method to cure the shafts. During the grouting period, the ground surface around the shafts upheaves, and the additional stress decreases. During the non-grouting period, the ground surface subsides, and the additional stress increases. The strain of shaft linings and the settlement are highly consistent. The additional force can be obtained from the settlement of the ground surface for the shafts without stress state monitoring system.