METHOD FOR BORING A TUNNEL IN SOFT GROUND OR ROCK WITH A BORING EQUIPMENT HAVING A BORING HEAD

Abstract: A tunnel is bored in soft ground or rock with the aid of boring equipment with a cutting head. In order to prevent collapse or breaking away of earth or rock and subsidence of the boring equipment at the location of high-risk sections of the tunnel, especially in the start or end section and in sections which run just below a traffic way, soft ground or rock is replaced, at least over a section of the length of the tunnel to be bored, by a settable material that sets to produce a solid compact block. The said boring equipment is used to bore through the set compact block in such a way that the tunnel extends at least through part of the cross section of the set compact block.

Description: Method for bori ng a tunnel in soft ground or rock with a boring equi pment having a bori ng head The invention relates to a method for boring a tunnel in soft ground or rock with the aid of boring equipment with a cutting head. Such a method is disclosed in "De Ingenieur" no. 18, 8 November 1995, pp. 26 to 29. Soft ground or rock is understood to be a material which gives way at the bore front during boring if no propping measures are taken. One problem when boring in soft ground or rock is that the ground around the bored hole can collapse and/or break away. In this case the bentonite suspension frequently used when boring could drain away and the boring equipment could subside. This problem can arise in particular just below ground level at the start and the end of the tunnel to be bored and also in the case of a short distance below a waterway. The aim of the invention is to solve this problem and to this end the method mentioned in the preamble is characterised in that at least over part of the length of the tunnel to be bored soft ground or rock is replaced by a settable material that sets to give a solid body and in that the set body has been bored through with said boring equipment in such a way that the tunnel extends at least through part of the cross-section of the set body. It is pointed out that German Patent 3 605 221 discloses an installation and method for boring a tunnel in soft ground with the aid of boring equipment, wherein the soft ground is rendered more coherent by means of a fluid that is injected via a hole bored centrally in front of the cutting head by the latter. This method is not suitable for preventing the breaking away of ground material when boring the start or end section of a tunnel because the boring equipment is provided with no or inadequate support in this stretch. Moreover, an exceptionally expensive facility is needed on the boring equipment and the method takes a great deal of time because of always having to wait lor setting. There is no question of replacement of soft ground by a settable material. If soft ground or rock is replaced by said settable material in the location of the initial stretch of the tunnel to be bored, three sheet piling walls are placed successively, seen in the longitudinal direction of the tunnel to be bored, in the soft ground or rock one after the other, together with the linking sheet piling, the space between the first and the second sheet piling wall is excavated, earth or rock in the space between the second and third sheet piling walls is replaced by said settable material, a hole is made in the second sheet piling wall to allow the passage of the boring equipment, a tunnel section is bored through the set material, the third sheet piling wall is removed or a hole is made in the third sheet piling wall and the boring equipment is fed further into the ground. In the end stretch the construction of settable material and sheet piling walls is mirrored with respect to the initial path. If a tunnel section has to run beneath a waterway, a trench is dredged at this location, said trench is filled with settable material and a tunnel section is bored by the boring equipment through at least part of the cross-section of the set material. If soft ground or rock is replaced by said settable material at the location of at least one transverse tube link in a tunnel system to be bored, consisting of at least two tunnel tubes running parallel, between which at least one transverse link tube is projected, a sheet piling wall having a virtually rectangular cross-section is installed from ground level or from the bed of a stretch of water and specifically is installed in such a way that the space for the transverse link tube to be produced is surrounded and at least part of the said adjoining tunnel tubes to be produced, at least some of the earth or rock in the space within the sheet piling wall is replaced by said settable material, such that at least part of the transverse link tube to be produced is located in the settable material, the sheet piling wall is removed after the said material has set, the parallel tunnel tubes are produced, during which operation part of the said material is bored through at the location of a transverse link tube to be produced, after which a transverse link tube, passing through the set settable material previously poured, is produced, starting from at least one of the tunnel tubes. It is also possible for the settable material to have been made up of vertically oriented segments having different material characteristics located alongside one another. By this means it is, for example, possible to have the requisite greater strength and thus greater hardness only in specific regions and to make the speed of boring as high as possible compared with the case where all of the material would be of the greater strength. Preferably, use is made of a mixture of sand, cement, water and clay, in which the clay component is preferably bentonite, as the ground-replacing settable material. The fresh settable material which still has to set preferably has a "flow dimension" which is between a diameter of 300 and 1200 millimetres. Moreover, the percentage by volume of the "bleeding" must be less than 5 %, preferably less than 2 %. In this context the flow dimension is the diameter of a quantity of fresh mixture that has flowed out onto a horizontal flat surface, the said quantity corresponding to the capacity of a truncated conical vessel and prepared in accordance with Netherlands standard NEN 5957, as in the case of the method for the determination of the "bulk dimension". "Bleeding" is understood to be the percentage by volume of fluid which is produced at the top of a test sample of the fresh mixture after a certain length of time, usually as a consequence of demixing of the sample. To keep leakage of groundwater into the bored tunnel as low as possible, the preference is for a fluid permeability of the set material where the permeability coefficient is less than 10 "7 m/s, in accordance with the Darcy method of determination. The set material has a density of between 1000 and 2400 kg/m , preferably of between 1500 and 1800 kg/m 3 , and a compressive strength of between 0.1 and 15 MPa, preferably of between 0.5 and 5 MPa. The invention will now be explained in more detail with reference to the figures. Figure 1 is a diagrammatic representation of a tunnel that has been bored beneath a waterway. Figure 2 shows a longitudinal section through the section II in Figure 1 after boring. Figure 3 shows a longitudinal section through the section III in Figure 1 during boring. Figure 4 shows a plan view of an embodiment with two parallel tunnel tubes and a link between them. Figure 5 shows a longitudinal section through the line V - V in Figure 4. Boring the tunnel shown by 1 in Figure 1 beneath a canal 2 can present problems especially at the location of the sections II, IV and III because soft ground or rock collapses or breaks away during boring. As can be seen from Figure 2, in the initial section of the mnnel to be bored the problem is solved by placing three sheet piling walls 3, 4 and 5 into the ground some distance after one another in the soft ground, removing the bulk of the soft ground between the sheet piling walls 3 and 4, replacing the soft ground between the sheet piling walls 4 and 5 by a settable material, allowing said material to set to form a compact block 7, cutting a passageway 6 for the boring equipment 8 in the sheet piling wall 4 using the cutting head 9, allowing said boring equipment to bore a hole in the compact block 7 via the open space between the sheet piling walls 3 and 4 and the opening 6 and continuing to bore the tunnel with the boring equipment after the sheet piling wall 5 has been withdrawn from the ground or a hole has been made in said sheet piling wall 5. The compact block 7 exerts resistance during the action of the boring equipment. The problem of the ground breaking away or collapsing has been solved. It can also be seen from Figure 2 that abutting tunnel lining rings 11 composed of segments are positioned around the bored hole during boring, the various features being as indicated in the abovementioned article in "De Ingenieur". If, as is shown in Figures 1 and 3, the tunnel runs just beneath a waterway and the expensive solution of making the vertical distance between the tunnel and the bed of the canal small or even negligible is not chosen, there is likewise a risk of the soft ground breaking away. In order to avoid this, a trench is dredged with the aid of a dredger vessel in the canal 2, which trench is filled with settable material that is given the time to set to a compact block 11. The tunnel section is then bored through the set compact block using the boring equipment. An additional advantage is that the entry and exit ramps for the tunnel do not have to be as long if section III is bored through a ground-replacing setting material, as a result of which the minimum depth of the tunnel close to the bed of canal 2 can be much smaller than without the ground-replacing material. A variant could be that in an urban area compact block 11 has been produced beneath a different type of traffic way, such as a road or a railway track. The trench required for the production of compact block 11 is then preferably excavated using excavation machines used in the dry. Provided the density of the set compact block is not too low and not too high (that is to say between 1000 and 2400 kg/m 3 , preferably between 1500 and 1800 kg/m 3 ) and the compressive strength of the set compact block does not fall below a minimum limit or exceed a maximum limit (0.1 and 15 MPa respectively, preferably 0.5 and 5 MPa respectively), various materials are possible, a mixture of bentonite, sand, cement and water however being preferred. A mixture of cement and pieces of limestone of low compressive strength is also possible. If the ground-replacing setting material from which compact block 7, 11 is made is a cement-bonded material, the preference is then for a material for the fresh material which has still to set with which the flow dimension is between a diameter of 300 and 1200 millimetres and the bleeding is no higher than 5 percent by volume, preferably no higher than 2 percent by volume. To keep groundwater leakage in the bored tunnel as low as possible, a fluid permeability of the set material with which the permeability coefficient is less than 10 " m/s is preferred. A variant for a compact block can be that the latter is made up of adjoining segments having different material characteristics produced alongside one another. Thus, it is possible to provide the segment where the distance from the top of the tunnel and ground level or the bed of a waterway is the smallest with higher strength characteristics and/or a higher specific mass. The essential aspect of the invention is that soft ground or rock is replaced by a compact block in high-risk sections of the tunnel stretch before the cutting head bores through said tunnel sections. Incidentally, it is not precluded that the boring equipment bores a hole of which, viewed in cross-section, the upper part runs through the compact block and the remaining part through earth or rock that has not been replaced. With the embodiments according to Figures 4 and 5, two parallel tunnel tubes la and lb are bored in the ground in the abovementioned manner. Said tunnel tubes are linked to one another at regular intervals by a transverse link tube 12. To produce such a transverse link tube 12, during the work on the tunnel tubes la, lb, before said tubes have reached the desired position for a transverse link tube 12, a transverse compact block 13 of settable material is produced between the tunnel tubes la, lb by installing two sheet piling walls 14, 15, removing the earth between said sheet piling walls, filling the lower section of the space between said sheet piling walls with settable material, allowing said material to set, filling the space above the formed transverse compact block 13 with earth and removing the sheet piling walls. After boring of the tunnel tubes la, lb has proceeded to beyond the transverse compact block 13, a transverse link tube 12 to the other tunnel tube is produced from one tunnel tube through the transverse compact block 13.

Claims: Claims 1. Method for boring a tunnel in soft ground or rock with the aid of boring equipment with a cutting head, characterised in that at least over part of the length of the tunnel to be bored soft ground or rock is replaced by a settable material that sets to give a solid body and in that the set body has been bored through with said boring equipment in such a way that the tunnel extends at least through part of the cross-section of the set body. 2. Method according to Claim 1 , characterised in that soft ground or rock is replaced by said settable material in the location of the initial stretch and end stretch of the tunnel to be bored, wherein three sheet piling walls are placed successively, seen in the longitudinal direction of the tunnel to be bored, in the soft ground or rock one after the other, together with the linking sheet piling, the space between the first and second sheet piling walls is excavated, earth or rock in the space between the second and third sheet piling walls is replaced by said settable material, a hole is made in the second sheet piling wall to allow the passage of the boring equipment, a tunnel section is bored through the set material, and the boring equipment is fed further into the ground after either the third sheet piling wall has been withdrawn from the ground or a hole to allow the passage of the boring equipment has been made in the third sheet piling wall. 3. Method according to Claim 1, characterised in that a trench is dredged immediately beneath a waterway, said trench is filled with settable material and the boring equipment bores a tunnel section through at least part of the cross-section of the set material. 4. Method according to Claim 1, characterised in that soft ground or rock is replaced by said settable material at the location of at least one transverse tube link in a tunnel system to be bored, consisting of at least two tunnel tubes running parallel, between which at least one transverse link tube is projected, wherein a sheet piling wall having a virtually rectangular cross-section is installed from ground level or from the bed of a stretch of water and specifically is installed in such a way that the space for the transverse link tube to be produced is surrounded and at least part of the said adjoining tunnel tubes to be produced, at least some of the earth or rock in the space within the sheet piling wall is replaced by said settable material, such that at least part of the transverse link tube to be produced is located in the settable material, the sheet piling wall is removed after the said material has set, the parallel tunnel tubes are produced, during which operation part of the said material is bored through at the location of a transverse link tube to be produced, after which a transverse link tube, passing through at least part of the set settable material previously poured, is produced, starting from at least one of the tunnel tubes. 5. Method according to one of the preceding claims, characterised in that the ground- replacing settable material at least consists of a mixture of sand, cement, water and clay. 6. Method according to Claim 5, characterised in that the clay component of the settable material is bentonite. 7. Method according to one of the preceding claims, characterised in that the settable material has a density of between 1000 and 2400 kg/m . 8. Method according to Claim 7, characterised in that the settable material has a density of between 1500 and 1800 kg/m 3 . 9. Method according to one of the preceding claims, characterised in that the settable material has a compressive strength of between 0.1 and 15 MPa. 10. Method according to Claim 9, characterised in that the settable material has a compressive strength of between 0.5 and 5 MPa. 11. Method according to one of the preceding claims, characterised in that the flow dimension of the fresh settable material which still has to set is between a diameter of 300 and 1200 millimetres. 12. Method according to one of the preceding claims, characterised in that the bleeding of the fresh settable material which still has to set is less than 5 percent by volume. 13. Method according to Claim 12, characterised in that the bleeding of the fresh settable material which still has to set is less than 2 percent by volume. 14. Method according to one of the preceding claims, wherein the fluid permeability of the set material has a permeability coefficient which is less than 10 "7 m/s. 15. Method according to one of the preceding claims, characterised in that the settable material is introduced in adjoining vertically oriented segments positioned alongside one another, wherein the segments have different material characteristics. 16. Method according to one of the preceding claims, characterised in that, between two essentially parallel tunnel tubes, a transverse solid body (transverse compact block) is produced beforehand between said tunnel tubes and a tube is produced between said tunnel tubes (la, lb) through at least part of the solid body.

Inventors: VAN BERKEL ROBERT HENDRIKUS CO, VAN DE GRIENDT MICHIEL ADRIAAN, VAN BERKEL, ROBERT, HENDRIKUS, CORNELIUS, VAN DE GRIENDT, MICHIEL, ADRIAAN
Applicants: BERKEL ROBERT HENDRIKUS CORNEL, GRIENDT MICHIEL ADRIAAN VAN DE, HOLLANDSCHE BETONGROEP NV, HOLLANDSCHE BETON GROEP N.V., VAN BERKEL, ROBERT, HENDRIKUS, CORNELIUS, VAN DE GRIENDT, MICHIEL, ADRIAAN
Application year: 1999
Main classification: E21D9
IPC codes: E21D9