Analysis of Tilted Primary Diaphragm Wall in Very Soft Clay

Diaphragm wall panels are constructed in alternating method (or Pilgrim) in Taiwan. Two adjacent primary panels are placed leaving out the secondary panel in between. Following the two primary panels, gaps are closed by the secondary panels. Primary panels have smaller width than secondary panels due to the use of end plates. Nylon sheets are bound along both sides of end plate to make a blocking screen, together with end plates, to prevent the tremie concrete from detouring into the evacuated trench. This paper studies history cases in which just-finished primary panels in very soft and thick clay deposit are tilted away from the adjacent secondary panel under tremie concreting. The force and moment equilibriums of tilting primary panels are analyzed by considering the resistant force from undrained shear strength of soft clay and driving force from the unset concrete in the secondary panel. The factors to cause this incident include panel thickness, panel width, concrete curing time of primary panel, concrete setting rate and concrete placing speed of secondary panel, and the roughness of trench wall. A checklist is established after this investigation to prevent this incident from happening again.