Abstract: Based on the engineering case of a pipe-jacking working shaft sunk with the aid of caisson jacks in soft clay, the construction technology is presented and the effects on surrounding environment are studied. According to analysis of the soil mass and pipeline monitoring data during the jacked sinking process, some conclusions are drawn as follows. The jacked open caisson construction method can control the attitude of the open caisson and stabilize the sinking speed effectively; but it also squeezes the soil. At the preliminary stage of open caisson sinking, the compacting effect is significant and the excavation effect becomes more notable as the open caisson sinking deeper. The subsurface horizontal displacements and surface settlements grow along with the increase of the sinking depth H. The ground surface settlement profile is of spandrel type with an influence zone of 1.7H. Among layered settlements the unit settlement of the soft silty clay is the largest. The pipeline settlements are controlled in the millimeter level. Based on data fitting of the dimensionless surface settlements, an empirical method either in the form of exponential function or bilinear curve to predict the ground surface settlement caused by jacked open caisson construction is proposed, which is verified through two case studies.

Key words: jacked open caisson, settlement, pipeline, field measurement, environmental impact control