The field and laboratory tests are carried out to research the plugging effect of jacked prestressed concrete pipe pile under two different geological conditions. The test show that a higher plug would be caused by the longer pile with thinner wall jacked into stiffer soil. Open-ended pile is prone to a plugged mode when the hard soil is over the soft soil; while the plug is prone to sliding when the soft soil is over the hard soil. The general development of cone tip resistance of cone penetration test (CPT) is similar with that of annulus resistance; and the ratio of two is independent on incremental filling ratio and penetration depth. The ratios of annulus resistance to cone tip resistance

closely related to geological condition

are approximately 0.59 and 0.81 for muddy clay and silt respectively. The observed soil layers distribution in the soil column are similar to the subsurface condition

except for the convex interface for plug. Soil is evidently compressed during the penetration into pile

whereas reduced cohesion is measured probably due to the disturbance. The direct shear test results indicate evident time-effect on shear strength of plug column. The active plug length appears to be approximately 5-6 times pile diameter in silt

which is 70 percent of total plug length; whereas this value should be larger than 4 times pile diameter in muddy clay. The results are close to existing observations.