Vacuum preloading technique without sand cushion layer has been successfully applied to the weak foundation reinforcement; but it is difficult to shorten construction period due to the low permeability of weak soil. Intermittent air injection is proposed to increase the drainage rate for vacuum drainage. The combined method of vacuum preloading and air injection is investigated for different conditions of the injecting positions and air pressures based on finite element simulation. Seepage velocity

drainage rate and seepage gradient are compared and analyzed before and after air injection. The simulation results show that the air injection can improve the efficiency of vacuum drainage

so as to enhance the foundation reinforcement and reduce preloading time of the vacuum loading. The efficiency of injecting air below the drain boards is better than that above the bottom ends of boards. And in the case of not breaking through the foundation in the air injection

the greater the air pressure is set

the better effect of reinforcement will be. The combined method of vacuum preloading and air injection could be widely used in the improvement practice of weak ground.