Laboratory study of soil-nail interaction in loose, completely decomposed granite

The technique of soil nailing is seldom used in stabilizing loose fill slopes because there is a lack of understanding of the interaction behaviour of nails in loose fills. A large-scale laboratory apparatus has been built to study the soil-nail interaction in loose fill materials. Pullout tests were performed in a displacement-rate-controlled manner on steel bars embedded in loose, completely decomposed granitic soils. The load-displacement curves have distinct peak values followed by a sharp decrease in the pullout force. The test results also show that the normal stress acting on the nail changes because of the volume-change tendency and arching effect of the soil being sheared around the nail. The post-peak decrease in the pullout force is mainly due to the reduction in the normal stress caused by the arching effect of soil around the nail. The conventional method of analysis tends to give a low interface friction angle and high interface adhesion. The correct interface parameters can be determined by taking the changes in the normal stress acting on the nail into account.