Through studying the experimental results on reinforcing soft foundation by vacuum preloading on an airdrome runway in Shanghai City

surface settlement and its calculation method

dissipation of excessive pore water pressure

and reinforcing effects on test zone are discussed. The testing data indicate that the setdement in test zone

from large to small

is observed in center

margin

and corner of site and this reflects the effects of vacuumpreloading method.When vacuum degree changes

the distribution of suction pressure with depth in drained body of test zone is almost equal.The range of suction pressure is 58-65 kPa

i.e.

68%-76%of vacuum degree under seal membrane. Furthermore

the analysis show that the estimation of surface settlement of soft foundation may be carried out through combining vertical equivalent penetration co-efficient

Terzaaghi's one dimensional-consolidation theory

and layerwise summation method.