EP1078147B1

EP1078147B1 - Method for boring a tunnel in soft ground or rock with a boring equipment having a boring head

Info

Publication number: EP1078147B1
Application number: EP99922647A
Authority: EP
Inventors: Robert Hendrikus Cornelius Van Berkel; Michiel Adriaan Van De Griendt
Original assignee: Hollandsche Beton Groep NV
Current assignee: Hollandsche Beton Groep NV
Priority date: 1998-05-14
Filing date: 1999-05-11
Publication date: 2004-03-03
Anticipated expiration: 2019-05-11
Also published as: NL1009166C2; WO1999058818A1; DE69915279D1; DE69915279T2; AU3959799A; EP1078147A1

Description

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 28.

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 hardenable material that hardens to give a compact block and in that the hardened compact block 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 hardened contact block.

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 for setting. There is no question of replacement of soft ground by a hardenable material.

Further DE 974458 discloses a method for boring a tunnel in soft ground with the aid of boring equipment with a cutting head. At the starting part of the tunnel to be bored soft ground surrounding the boring equipment is replaced by little coherent sand or gravel or other soil material. In the tube shaped boring equipment a natural stable slope is formed. The material replacing the original soft ground is not hardenable and a rigid compact block is not formed.

If soft ground or rock is replaced by said hardenable 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 hardenable 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 hardened 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 hardenable 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 hardenable material and a tunnel section is bored by the boring equipment through at least part of the cross-section of the hardened material.

US A 2107671 discloses a method of tunneling through porous material beneath a body of water comprising: excavating a trench in the porous material, filling the trench with yielding and impermeable material such as clay, and advancing the tunnel through the yielding material. The yielding material is not hardenable and does not form a compact rigid block.

If soft ground or rock is replaced by said hardenable 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 and at least part of the said adjoining tunnel tubes to be produced is surrounded, at least some of the earth or rock in the space within the sheet piling wall is replaced by said hardenable material, such that at least part of the transverse link tube to be produced is located in the hardenable material, the sheet piling wall is removed after the said material has hardened, 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 hardenable material previously poured, is produced, starting from at least one of the tunnel tubes.

It is also possible for the hardenable 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 hardenable material.

The fresh hardenable material which still has to harden 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 dimeasion". "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 dernixing 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 hardened material where the permeability coefficient is less than 10^-7 m/s, in accordance with the Darcy method of determination.

The hardened material has a density of between 1000 and 2400 kg/m³, preferably of between 1500 and 1800 kg/m³, and a compressive strength of between 0.1 and 15 MPa, preferably of between 0.5 and 5 MPa.

An embodiment of 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 I 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 tunnel 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 hardenable material, allowing said material to harden 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 10 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 hardenable material that is given the time to harden to a compact block 11. The tunnel section is then bored through the hardened 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 hardened matearial, 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 hardened compact block is not too low and not too high (that is to say between 1000 and 2400 kg/m³, preferably between 1500 and 1800 kg/m³) and the compressive strength of the hardened 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 hardenable material from which

compact block

7, 11 is made is a cernent-bonded material, the preference is then for a material for the fresh material which has still to harden 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 hardenable material with which the permeability coefficient is less than 10^-7 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 hard 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 1a and 1b 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 1a, 1b, before said tubes have reached the desired position for a transverse link tube 12, a transverse compact block 13 of hardenable material is produced between the tunnel tubes 1a, 1b 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 hardenable material, allowing said material to harden, filling the space above the formed transverse compact block 13 with earth and removing the sheet piling walls. After boring of the tunnel tubes 1a, 1b 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

Method for boring a tunnel (1) in soft ground or rock with the aid of boring equipment (8) with a cutting head (9), characterised in that at least over part of the length of the tunnel to be bored soft ground or rock is replaced by a hardenable material that hardens to give a compact block (7; 13), and in that the hardened compact block (7; 13) has been bored through with said boring equipment (8) in such a way that the tunnel (1) extends at least through part of the cross-section of the hardened compact block (7).
Method according to Claim 1, characterised in that soft ground or rock is replaced by said hardenable material in the location of the initial stretch and end stretch of the tunnel to be bored, wherein three sheet piling walls (3, 4, 5) 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 (3, 4) is excavated, earth or rock in the space between the second and third sheet piling walls (4, 5) is replaced by said hardenable material, a hole is made in the second sheet piling wall (4) to allow the passage of the boring equipment (8), a tunnel section is bored through the hardened compact block (7), and the boring equipment is fed further into the ground after either the third sheet piling wall (5) 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 (5).
Method according to Claim 1, characterised in that a trench is dredged immediately beneath a waterway, said trench is filled with hardenable material and the boring equipment bores a tunnel section through at least part of the cross-section of the hardened material.
Method according to Claim 1, characterised in that soft ground or rock is replaced by said hardenable material at the location of at least one transverse tube link (13) in a tunnel system to be bored, consisting of at least two tunnel tubes (1a; 1b) running parallel, between which at least one transverse link tube (12) is projected, wherein sheet piling walls (14, 15) 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 (12) to be produced and at least part of the said adjoining tunnel tubes to be produced is surrounded, at least some of the earth or rock in the space within the sheet piling walls (14, 15) is replaced by said hardenable material, such that at least part of the transverse link tube (12) to be produced is located in the hardenable material, the sheet piling walls (14, 15) are removed after the said material has hardened, the parallel tunnel tubes (1a, 1b) are produced, during which operation part of the said material is bored through at the location of a transverse link tube (12) to be produced, after which a transverse link tube, passing through at least part of the hardenable material previously poured, is produced, starting from at least one of the tunnel tubes (1a, 1b).
Method according to one of the preceding claims, characterised in that the ground-replacing hardenable material at least consists of a mixture of sand, cement, water and clay.
Method according to Claim 5, characterised in that the clay component of the hardenable material is bentonite.
Method according to one of the preceding claims, characterised in that the hardenable material has a density of between 1000 and 2400 kg/m³.
Method according to Claim 7, characterised in that the hardenable material has a density of between 1500 and 1800 kg/m³.
Method according to one of the preceding claims, characterised in that the hardenable material has a compressive strength of between 0.1 and 15 MPa.
Method according to Claim 9, characterised in that the hardenable material has a compressive strength of between 0.5 and 5 MPa.
Method according to one of the preceding claims, characterised in that the flow dimension of the fresh hardenable material which still has to harden is between a diameter of 300 and 1200 millimetres.
Method according to one of the preceding claims, characterised in that the bleeding of the fresh hardenable material which still has to harden is less than 5 percent by volume.
Method according to Claim 12, characterised in that the bleeding of the fresh hardenable material which still has to harden is less than 2 percent by volume.
Method according to one of the preceding claims, wherein the fluid permeability of the hardened material has a permeability coefficient which is less than 10^-7 m/s.
Method according to one of the preceding claims, characterised in that the hardenable material is introduced in adjoining vertically oriented segments positioned alongside one another, wherein the segments have different material characteristics.
Method according to one of the preceding claims, characterised in that, between two essentially parallel tunnel tubes, a transverse contact block (transverse compact block) is produced beforehand between said tunnel tubes and a tube is produced between said tunnel tubes (1a, I b) through at least part of the contact block (13).