It was a turning point of the increasing speed ofthe sf1when the controlling displacement sconwasequal to 2.5 mm. It was because at this momentthe scope of the extruded concrete reached theadjacent rib and the developing speed becameslower. When sconreached 4.5 mm and it was justhalf of the clear distance of the two adjacent ribs.At last, the frictional resistant force sf1becamestable.