The invention relates to a method and device for carrying out essentially-parallelepiped-shaped excavations. The inventive method comprises the following steps consisting in: a) excavating the vertical end wall of the excavation using a mobile arm that is equipped with mobile buckets; b) lowering the corresponding sheet dampproofing to the excavated areas; c) fixing the dampproofing by concreting the area at the bottom adjacent to the end wall; d) continuing the excavation by moving the bucket-equipped arm, such as to excavate a bottom area and side walls adjacent to the existing wall; e) positioning the corresponding dampproofing at the newly-excavated area; and f) concreting the newly-excavated bottom and the side walls. The invention also relates to the device that is used to perform said method.