A bonding agent for solidification of geological formations including a mixture of A) a heterocondensate, obtainable by hydrolysis and condensation of at least one hydrolysable silicon compound selected from silicon compounds of the general formula R n SiX 4-n wherein the residues X are the same or different and represent hydroxy groups, hydrogen, halogen, alkoxy, isocyanato, aryloxy, alkaryloxy, acyloxy, alkylcarbonyl, NH 2, with alkyl, aryl and/or aralkyl mono- or disubstituted amino, amido, aldoxime, ketoxime groups, wherein two or three groups X can also be connected with each other, to form Si polyol complexes with glycol, glycerine or brenzcatechin, wherein the aforementioned groups can optionally include substituents, seleceted from halogen, hydroxyl or alkoxy, and n has the value 1, 2 or 3, wherein at least one residue R has a polymerisable group selected from epoxide, hydroxy, amino, monoalkylamino, dialkylamino, optionally substituted anilino, amide, carboxy, alkenyl, alkinyl, acryloyl, acryloyloxy, methacryloyl, methacryloyloxy, mercapto, cyano, isocyanato, aldehyde, ketone, alkylcarbonyl, acid anhydride and phosphoric acid, which is bonded to the silicon atom by way of a divalent bridging group, and, if present, the other residues R are the same or different and selected from alkyl, aryl, aralkyl, alkaryl, or cyclic C 3 -C 12 -alkyl, and at least one metal, phosphorous or boron compound, wherein the metal is selected from Al, Ge, Sn, Pb, Ti, Mg, Li, V, Nb, Ta, Zr and Hf, B) at least one organic polymerisable or polycondensable monomer or oligomer with one or more polymerisable groups selected from epoxide, hydroxy, amino, monoalkylamino, dialkylamino, optionally substituted anilino, amide, carboxy, alkenyl, alkinyl, acryloyl, acryloyloxy, methacryloyl, methacryloyloxy, mercapto, cyano, isocyanato, or acid anhydride, and C) at least one hydrolysable silicon compound, which includes a non-hydrolysable residue with at least one hydrophilic group, selected from a silicon compound of the general formula (IIIa) R' n SiX 4-n (IIIa) wherein the residues R' are the same or different and represent hydrolytically non-separable groups, wherein at least one residue R' has at least one hydrophilic group as a substituent, the residues X are the same or different and are as defined above for the general formula, and n has the value 1, 2 or 3, wherein the at least one hydrolytically non-separable residue R' with at least one hydrophilic group includes a divalent bridging group by means of which the hydrophilic group is connected to the silicon atom, wherein the hydrophilic group is selected from a glycidyloxy, amino, polyethylene glycol, polyethylene amine, carbaldehyde, epoxy, hydroxyl, carboxy, mercapto, acid anhydride, sulphonato and phosphonato group, and the silicon compound of the general formula (IIIa) in addition to the residue R' with a hydrophilic group can comprise one or two further non-hydrolysable residues R' without a hydrophilic group selected from alkyl, aryl, aralkyl, alkaryl, or cyclic C 3 -C 12 -alkyl. A) a heterocondensate, obtainable by hydrolysis and condensation of at least one hydrolysable silicon compound selected from silicon compounds of the general formula R n SiX 4-n wherein the residues X are the same or different and represent hydroxy groups, hydrogen, halogen, alkoxy, isocyanato, aryloxy, alkaryloxy, acyloxy, alkylcarbonyl, NH 2, with alkyl, aryl and/or aralkyl mono- or disubstituted amino, amido, aldoxime, ketoxime groups, wherein two or three groups X can also be connected with each other, to form Si polyol complexes with glycol, glycerine or brenzcatechin, wherein the aforementioned groups can optionally include substituents, seleceted from halogen, hydroxyl or alkoxy, and n has the value 1, 2 or 3, wherein at least one residue R has a polymerisable group selected from epoxide, hydroxy, amino, monoalkylamino, dialkylamino, optionally substituted anilino, amide, carboxy, alkenyl, alkinyl, acryloyl, acryloyloxy, methacryloyl, methacryloyloxy, mercapto, cyano, isocyanato, aldehyde, ketone, alkylcarbonyl, acid anhydride and phosphoric acid, which is bonded to the silicon atom by way of a divalent bridging group, and, if present, the other residues R are the same or different and selected from alkyl, aryl, aralkyl, alkaryl, or cyclic C 3 -C 12 -alkyl, and at least one metal, phosphorous or boron compound, wherein the metal is selected from Al, Ge, Sn, Pb, Ti, Mg, Li, V, Nb, Ta, Zr and Hf, B) at least one organic polymerisable or polycondensable monomer or oligomer with one or more polymerisable groups selected from epoxide, hydroxy, amino, monoalkylamino, dialkylamino, optionally substituted anilino, amide, carboxy, alkenyl, alkinyl, acryloyl, acryloyloxy, methacryloyl, methacryloyloxy, mercapto, cyano, isocyanato, or acid anhydride, and C) at least one hydrolysable silicon compound, which includes a non-hydrolysable residue with at least one hydrophilic group, selected from a silicon compound of the general formula (IIIa) R' n SiX 4-n (IIIa) wherein the residues R' are the same or different and represent hydrolytically non-separable groups, wherein at least one residue R' has at least one hydrophilic group as a substituent, the residues X are the same or different and are as defined above for the general formula, and n has the value 1, 2 or 3,