A method for constructing an underground structure comprising the realization of successive underground floors (PN, PN-1) by descending from a supporting floor, while digging the subsoil as the realization of the floors (PN, PN-1) progresses from top to bottom, each underground floor (PN, PN-1) being realized by pouring a building material in a formwork suspended on at least one higher-level floor by means of suspension devices, said method being characterized in that it comprises the following steps: - providing several suspension devices, each comprising: • a suspension bar on which are mounted at least two, preferably at least three, abutment members (31, 32, 33) adjustable in position along said bar; • at least two removable wedges (41, 42) each presenting an upper bearing surface for the abutment members (31, 32, 33); • an actuator comprising a movable portion driven in translation between several positions and presenting a support for a wedge; - suspending the formwork on at least one floor called upper floor by means of the suspension devices, each bar presenting a lower end fastened on the formwork, and each bar passing through the concerned upper floor by presenting an upper portion protruding from said upper floor and on which are mounted two abutment members (31, 32), each bar being supported by the concerned upper floor by means of one of the two abutment members bearing on one of the wedges, called the lower wedge, placée on said upper floor around the bar; - pouring a building material in the suspended formwork in order to realize a floor called lower floor (PN-1), letting it dry, and digging the subsoil under the formwork; - positioning each actuator on the upper floor next to the corresponding bar and, for each actuator, positioning the other of the wedges, called upper wedge, on the support of its movable portion and around said bar, the other of the two abutment members being positioned, beforehand above said upper wedge; - descending the formwork by descending the bars by successive bearings by acting both on the positions of the abutment members (31, 32, 33) and on the positions of the movable portions of the actuators. - providing several suspension devices, each comprising: • a suspension bar on which are mounted at least two, preferably at least three, abutment members (31, 32, 33) adjustable in position along said bar; • at least two removable wedges (41, 42) each presenting an upper bearing surface for the abutment members (31, 32, 33); • an actuator comprising a movable portion driven in translation between several positions and presenting a support for a wedge; • a suspension bar on which are mounted at least two, preferably at least three, abutment members (31, 32, 33) adjustable in position along said bar; • at least two removable wedges (41, 42) each presenting an upper bearing surface for the abutment members (31, 32, 33); • an actuator comprising a movable portion driven in translation between several positions and presenting a support for a wedge; - suspending the formwork on at least one floor called upper floor by means of the suspension devices, each bar presenting a lower end fastened on the formwork, and each bar passing through the concerned upper floor by presenting an upper portion protruding from said upper floor and on which are mounted two abutment members (31, 32), each bar being supported by the concerned upper floor by means of one of the two abutment members bearing on one of the wedges, called the lower wedge, placée on said upper floor around the bar; - pouring a building material in the suspended formwork in order to realize a floor called lower floor (PN-1), letting it dry, and digging the subsoil under the formwork; - positioning each actuator on the upper floor next to the corresponding bar and, for each actuator, positioning the other of the wedges, called upper wedge, on the support of its movable portion and around said bar, the other of the two abutment members being positioned, beforehand above said upper wedge; - descending the formwork by descending the bars by successive bearings by acting both on the positions of the abutment members (31, 32, 33) and on the positions of the movable portions of the actuators.