Field performance of residual stresses in jacked PHC pipe piles in layered ground

The residual stress along piles after unloading at pile tip is significant during installation. The full-scale tests are conducted on 5 piles inserted with quasi distributed FBG optical fiber sensors jacked into stratified soils. The post-installation residual stress in opened PHC pipe piles during installation, the variations in residual stress during 17 d after installation and the effect on static load tests are elaborated. The results indicate that the distribution of residual stresses and average residual shaft friction in opened PHC pipe piles during installation resemble a folded line, and the ratio of neutral point depth to pile penetration is between 0.66 and 0.92, which is positively related with the bearing stratum compactness at pile tip and residual point resistance. The plugging effect becomes one of the main factors to restrict the residual point resistance in opened PHC pipe piles, and it is different from that of other pile types. The residual stresses tend to decay to a stable value gradually after installation, and the reduction of residual stress in neutral point is between 3.2% and 29.88%, while that of the residual point resistance is between 10.78 % and 32.39%. It will overestimate the side friction above neutral point by about 53.46%, and underestimate the side friction below neutral point by about 53.46% and the tip resistance by 10% separately without regard to the post-installation residual stresses during the static load tests. The research results can provide the basis for the post-installation residual stresses in opened PHC pipe piles further.