Abstract: It is important to determine the stability of underground projects which are driven in soft rock masses or buried in deep site. Restraining the floor heave of the chamber adjoining with soft rock masses is an effective approach to control its stability and ensure its service period. The flexible inverted arch with composite structures is designed mainly to reduce the floor heave, and its operating mechanism is also studied. The time effects of the flexible inverted arch with composite structures to control the floor heave of the chamber adjoining soft rock masses will include the initial stage with negative floor heave, flexible support stage to absorb deformation energy, and rigid support stage to prolong its service period. The flexible support effect has steadily ensured a longer service period of the chamber. The practices indicate that the time effects of negative floor heave under test conditions last a period of 63 days, the controlling period of flexible structure to the floor heave may be up to 158 days, and the service period of 140 days of the testing roadway is prolonged by the rigid structure of inverted arch to restrain the floor heave. Therefore, the testing roadway may dispense with rebuilding work in one year, particularly in the floor heave. Although the flexible inverted arch with composite structures has distinct effects to control the floor heave, the overall stability of the chamber can not simply depend on the only factor. The relatively weak boundary part of the supporting system will become the main cause of the destruction of the chamber adjoining soft rock masses.