A method for filling a ring area between the outer surface of a tunnel section ring and a foundation of a tunnel structure surrounding it by introducing a construction material mixture, wherein: a) a liquid basic component for producing the construction material mixture is transported from a remote supply point to a tunnel boring machine through a pipeline, wherein the liquid basic component is a mixture containing at least one clay mineral phyllosilicate, at least one hydraulic and/or latent-hydraulic binder and water, contains only small-grained particles with a diameter of less than approximately 5 mm and either does not cure automatically or has a curing time that is delayed by more than 24 hours, preferably more than 72 hours, b) an activator component is admixed to the basic component at the site of the tunnel boring machine in such a way that the mixture being produced reaches a gel consistency after a brief reaction time of less than 5 minutes, preferably less than 3 minutes, particularly less than 1 minute, c) a tenside component is admixed to the basic component and/or the activator component and/or the mixture produced thereof, d) the mixture consisting of basic component, activator component and tenside component is conveyed through a tubular flow chamber of a foam generator, which is realized in the form of a gas treatment section, wherein air is admixed to the mixture through a gas-permeable porous wall of the gas treatment section by supplying compressed air to a pressure chamber of the foam generator, which at least partially encloses the tubular flow chamber, such that a mixture containing foam is produced, and e) the mixture containing foam is introduced into the ring area, wherein the mixture reaches the gel consistency in the ring area after a brief reaction time and subsequently hardens, wherein the pressure of the compressed air in the pressure chamber is adjusted in dependence on the pore size of the porous wall of the gas treatment section and in dependence on the pressure, with which the mixture containing the foam is filled into the ring area, in such a way that a predefined foam quantity with a predefined distribution of air bubble sizes is introduced into the mixture consisting of basic component, activator component and tenside component. a) a liquid basic component for producing the construction material mixture is transported from a remote supply point to a tunnel boring machine through a pipeline, wherein the liquid basic component is a mixture containing at least one clay mineral phyllosilicate, at least one hydraulic and/or latent-hydraulic binder and water, contains only small-grained particles with a diameter of less than approximately 5 mm and either does not cure automatically or has a curing time that is delayed by more than 24 hours, preferably more than 72 hours, b) an activator component is admixed to the basic component at the site of the tunnel boring machine in such a way that the mixture being produced reaches a gel consistency after a brief reaction time of less than 5 minutes, preferably less than 3 minutes, particularly less than 1 minute, c) a tenside component is admixed to the basic component and/or the activator component and/or the mixture produced thereof, d) the mixture consisting of basic component, activator component and tenside component is conveyed through a tubular flow chamber of a foam generator, which is realized in the form of a gas treatment section, wherein air is admixed to the mixture through a gas-permeable porous wall of the gas treatment section by supplying compressed air to a pressure chamber of the foam generator, which at least partially encloses the tubular flow chamber, such that a mixture containing foam is produced, and e) the mixture containing foam is introduced into the ring area, wherein the mixture reaches the gel consistency in the ring area after a brief reaction time and subsequently hardens,