GB2237591A

GB2237591A - Foundation for shaft tubbing means

Info

Publication number: GB2237591A
Application number: GB9021881A
Authority: GB
Inventors: Andreas Schmitz; Klaus-Frieder Weibezahn; Karl-Josef Maab
Original assignee: Heitkamp E GmbH
Current assignee: Heitkamp E GmbH
Priority date: 1989-10-09
Filing date: 1990-10-09
Publication date: 1991-05-08
Anticipated expiration: 2010-10-09
Also published as: GB2237591B; DE3933692C2; GB9021881D0; RU2005183C1; DE3933692A1

Abstract

The invention provides for a foundation 1 for the footings 2 of a shaft tubbing arrangement or system 3 with a support cylinder 4, which is bonded to a steel sealing liner 11 arranged in the footings 2. The section of the support cylinder 4 which underpins the lower edge of the footings 2 is bonded, in a watertight manner, to a massive steel ring 5 which forms the supports contact surface 10, and by way of the steel sealing liner 11 of the footings 2 forms an annular space 15 with the inner walling 13 of the shaft excavation 14 which is filled with a yielding material such as bitumen, asphaltic sand 16 or similar material. A yielding joint the thickness D is thus formed which is greater than the maximum possible displacement of rock strata into the yielding joint 15 to be taken into consideration as a consequence of the effect of extraction. <IMAGE>

Description

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FOUNDATION FOR SHAFT TUBBING MEANS DESCRIPTION

The present invention relates to a foundation for shaft tubbing means and in particular, but not exclusively, for the footings of such means having a support cylinder which is connected to a sealing steel liner disposed in the footings.

A known foundation is disclosed in German published patent 35 24 253 but is disadvantageous due to the considerable expense of setting up the enlarged borehole into which the footings are concreted. The employment of an enlarged borehole is avoided in two older unpublished proposals by the present applicant, in accordance with the German patent applications P 39 13 927.1-23 (see Figure 5 in the latter) and P 39 16 475.6-24 (see Figure 10 in the latter), but the lower end of the respective footings is provided with backfilling material. Rock strata can be displaced relative to each other in this backfilled area under the effects of extraction and no available support is able to withstand the forces generated in this way. In fact, the support shears and the steel sealing liner is destroyed. If the packing cracks at the lower end of the footings and the foundations which surround them are made of backfilling concrete, a new seal to prevent the penetration of water is very difficult and almost impossible to achieve.

In the above-mentioned patent applications an inclined support surface on the rock is provided. As a rule, a yielding shaft tubbing arrangement or system must be designed for a specified minimum radius of curvature, which is to be understood as a substitute stress for the effects of shaft extraction. As a consequence of the inclined support surf ace, a large resultant horizontal f orce is produced when a radius of curvature is applied to the lower edge of the footings. Calculations have revealed that the horizontal displacements produced in this way can also cause a disadvantageous larger displacement in the shaft column.

Starting from the disadvantageous features of the prior art, the present invention, whilst retaining the advantages of known foundations, seeks to improve the latter so as to overcome at least some of the disadvantages.

According to the present invention there is provided a foundation for the footings of a shaft tubbing arrangement f or a shaft excavation, the arrangement having a support cylinder which is connected to a sealing steel liner arranged in the footings, wherein part of the support cylinder which underpins the lower edge of the footings is provided, connected in a watertight manner, with an annular member forming a contact surface for the footings and in which the sealing steel liner for the footings forms an annular space with the inner walling of the shaft excavation which provides a yielding joint for receiving a yielding material, the thickness of which annular space is grater than the maximum displacement of rock strata to be taken into consideration in the yielding joint as a consequence of the effect of extraction or excavation.

As such, the foundation can be provided on a rock shoulder without the necessity f or an enlarged borehole so that the maximum displacements caused by the action of rock strata to be taken into account down to the lower edge of the footings do not influence the latter.

Accordingly, the area of the support cylinder which underpins the lower edge of the footings is connected in a WI watertight manner to the annular member, f or example a massive steel ring, which forms the contact surface of the latter. The sealing steel liner of the footings forms an annular space with the inner walling of the shaft excavation which is then filled with yielding material such as bitumen, asphaltic sand or the like as a yielding joint. The thickness of which annular space is greater than the maximum displacement of rock strata into the sliding joint to be taken into consideration as a consequence of the effects of extraction. Thus the steel ring itself acts as a,yielding support" right down to its lower edge. The yielding joint filled with a yielding material can absorb horizontal displacements by rock strata without the support being subjected to stress. The thickness of this yielding joint is thus also dependent on the magnitude of the horizontal displacements occurring in the rock strata as well as on engineering aspects determined by the manufacturing process.

To maintain the pressure per unit of area in the steel ring and in the rock strata at the lowest possible value, the contact surface for the footings on the steel ring is designed to be larger than the supporting surface for the steel ring. Moreover the greater vertical presence of the asphalt increases the influence of an even distribution of axial stress compared with an uneven one in the presence of a curvature in the shaft column.

In accordance with the first alternative embodiment the steel ring and the support cylinder are formed integrally as a single part, which. although it may be'more expensive to manufacture, has the advantage of including a stable, namely material, connection between the steel ring and the support cylinder.

In a second embodiment, the steel ring and the support cylinder each comprise a separate or several parts. In this arrangement the steel ring and the support cylinder may be welded together or, in the case of a positive-locking connection, may be joined together in a rigid and/or shearresistant manner. The steel ring and the support cylinder must in all circumstances be impermeable to water under pressure up to the support surface of the steel ring.

To guarantee that the yielding joint is filled with a yielding material between the footings and the inner walling of the shaft excavation on the one hand and between the external circumferential surface of the steel ring and the inner walling of the shaft excavation on the other, the steel ring includes a formation or device on its external circumferential surface for flushing concrete away in its yielding joint and the yielding joint of the footings.

To produce reliable foundations, it is necessary to ensure that all the loads propagated by the shaft tubbing are transferred via the steel ring, as a foundation, and to the rock shoulder. As such, the support cylinder is unable to absorb any vertical loads. For this reason, it is advantageously fitted with a yielding layer on its outer casing, e.g. a bitumen coating. In this way, after its external circumferential surface has been backfilled with concrete it is unable to bond with the latter but rather will slide along it if settlement takes place in the vertical direction. Thus the support cylinder provides the function of a collecting safety device for horizontal forces from the rock strata so that deepening can take place in stable rock under protection of the safety device.

According to an advantageous further development of the invention, a plain bearing may be disposed between the underside of the steel ring and its contact surface with a rock shouldeiZ, whereby the plain bearing is either seated directly on the rock shoulder or a compensation layer is inserted between the bearing and the rock shoulder. This measure, which is taken from the previous proposal, in 1 accordance with German patent application P 39 13 927.1-24, ensures that all the forces absorbed by the steel ring are transferred vertically on to the surface of the shoulder of rock to the surrounding rock strata. In such a case, the plain bearing, which consists of a bearing ring and which can be installed together with the footings of the shaft tubbing column and the steel ring attached to it with support cylinder, is either seated directly on the rock shoulder or is embedded in the compensation layer which is to be backfilled. The bearing ring should preferably consist of a pressure-resistant plastic such a PTFE, an elastomer or a metal such as bronze or lead.

The angle between the outer casing of the support cylinder and the underside of the steel ring may be formed approximately at 900. This design is particularly suited to shaft tubbing which is produced using the known, but very expensive, freezing process.

However, the angle between the outer casing of the support cylinder and underside of the steel ring may be greater than 900 and particularly advantageously between 1050 and 1200.

To achieve a separation between the yielding support and the foundation structure, a separating coating or an intermediate layer is disposed between the contact surfaces of the footings and the steel ring up to the weld seam, which connection between the steel sealing liner and the steel ring is impermeable to water under pressure. This reduces stresses from the statically undefined position of the shaft tubbing column on the new foundations. Transverse forces and crimping moments caused by different deformations in the steel structure and the footings are also reduced in this way.

Accordingly, the present invention, whilst retaining the advantages of foundations in accordance with the preamble.

-6 improves the latter so that the foundations can be provided on a rock shoulder without an enlarged bore and so that the maximum displacements that is possible, by way of the action of rock strata, up to the lower edge of the footings, are unable to act on the latter.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings in which:

Fig. 1 is a cross-section through a foundation according to one embodiment of the present invention; Fig. 2 is a cross-section through a foundation according to another embodiment of the present invention; Fig. 3 shows an enlargement of the section marked III in Fig. 2; Fig. 4 is a cross-sectional view of a foundation according to a further embodiment of the present invention; and fig. 5 is an enlargement of the section marked V in Fig.

4.

A foundation 1 in accordance with the invention for associated footings 2 of a shaft tubbing arrangement or system 3 in accordance with the embodiments of Fig. 1 to 3, comprises a support cylinder 3, a steel ring 5, a plain bearing 6 and a yielding layer 7 on an external casing 8 of a support cylinder 4.

The support cylinder 4 is bonded, in a watertight manner, via a portion which underpins a lower edge 9, 18 of the footings 2, by way of a massive steel king 5 which forms its contact surface 20 for the lower edge 9. The watertight bond is provided by a welding seam 12 to a steel sealing liner 11, which envelops the external circumference of the footings 2 by way of the weld seam 12 to the contact surface 10 of the steel ring 5.

The annular space 15 f ormed between the steel sealing J.

liner 11 which forms the outer casing of the footings 2 and the inner walling of the shaft excavation 14 serves as a yielding joint and is filled with a yielding material such as bitumen, asphaltic sand 16 or similar material. The thickness D of the yielding joint 15 is determined so that it is greater than the maximum displacement of rock strata into the yielding joint 15, which is to be taken into consideration due to the effects of extraction. As a consequence of the latter, the thickness D can be from 15 to 25cm, or more, depending on the diameter of the shaft excavation 14. The maximum displacement to be taken into consideration, is considered as a substitute load, in which the longitudinal axis 17 of the shaft tubbing 3 is subjected to a circular curvature e.g. with a radius of 3000m, from the lower end of the footings 2 over a distance of 100m. Considerable bending stresses are exerted on the footings 2 in the presence of a load of this kind. If this footing is clamped tightly in the above-described foundations as in the prior art, a load situation can occur in which the footings 2 shear off transverse to the longitudinal axis 17 of the shaft 14. In this load situation, if the foundation 1 in accordance with the invention is used, the footings 2 can yield in all directions of their circular cross-section within the yielding joint 15 because the annular space 15 is filled with the yielding material such as asphaltic sand 16. The remaining annular space between the outer casing 19 of the shaft tubbing 3 and inner all 13 of the shaft excavation 14 is in any case filled with bitumen 2d which is also a yielding material.

Advantageously, the outer circumferential surface 22 of the steel ring 5 also forms a yielding joint 23 with the inner walling 13 of the shaft excavation 14, which joint 23 is also filled with a yielding material, such as bitumen, asphaltic sand 16 or similar material.

In all the illustrated embodiments, the steel ring 5 and the support cylinder 4 are provided as a single part. However, it is also possible for the steel ring 5 and the support cylinder 4 to be produced as separate or indeed several parts and for these two or more parts to be welded or bonded together in a rigid and/or shear-resistant manner.

The plain bearing 6, which is either seated directly on the rock shoulder 26 or is embedded in a backfilled layer 27 located between the bearing 6 and the shoulder of rock 26 is situated between the underside 24 of the steel ring 5 and its contact surface 25 on the rock shoulder 26.

In Fig. 2, the plain bearing 6 rests directly on the rock shoulder 26.

In the enlargement of the section of Fig. 2 shown in Fig. 3, a formation or device 28 is present on the external circumferential surface 22 of the steel ring 5 to flush concrete out of the yielding joint 15 of the footings 2 and into the yielding joint 23 of the ring 5. This is necessary when forming the backfilled compensation layer 27 using flushing for adjusting the level of the concrete. The device 28, for flushing, consists of a pipeline, which leads to the mouth of" the borehole (not shown) which can admit water which them emerges advantageously in a tangential direction f rom, the external circumferential surface 22 of the steel ring 5.

In the embodiments according to Figs. 1 to 3, the angle (a) between the outer casing 8 of the support cylinder 4 and the underside 24 of the steel ring 5 is designed so that it is larger than 90 and is preferably between 1050 and 120. This embodiment is particularly suitable for the provision of a yielding support in a drilled shaft.

In the embodiment shown in Figs. 4 and 5, the angle (A) between the outer casing 8 of the support cylinder 4 and the underside 24 of the steel ring 5 is 90. This embodiment is particularly suitable for shaft tubbing which is to be r 1 1 disposed in a shaft excavation 14 produced by the freezing method. In the embodiment of Fig. 4 and 5, a plain bearing 6 is not necessary since the angle (A) between the outer casing 8 of the support cylinder 4 and the underside 24 of the steel ring 5 is 90 and therefore a vertical transference of force from the steel ring 5 to the correspondingly shaped rock shoulder 26 is ensured. In all the above described embodiments, the intermediate space between the yielding layer 7 on the outer casing 8 of the support cylinder 4 and the inner walling 28 of the smaller shaft excavation 29, below the steel ring 5, as shown in Fig. 5, is backfilled with concrete 30. The latter is not necessary when providing the tubbing in suitable geological conditions as then the smaller shaft excavation 29, under the steel ring 5, is filled by the flow of the rock strata as a consequence of the imposed load. However, greater settling does occur in this situation. Moreover a separating coating 31 or an intermediate layer is disposed between the contact surface 10 for the footings 2 and its support surface 21.

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Claims

1. A foundation for the footings of a shaft tubbing arrangement for a shaft excavation, the arrangement having a support cylinder which is connected to a sealing steel liner arranged in the footings, wherein the part of the support cylinder which underpins the lower edge of the footings is connected in a watertight manner with an annular member providing a contact surface for the footings, and wherein the sealing steel liner forms an annular space with the inner wall of the shaft excavation which provides a yielding joint for receiving a yielding material and wherein the thickness of which annular space is greater than the maximum displacement of rock strata to be taken into consideration in the yielding joint as in consequence of the effects of shaft working.

2. A foundation as claimed in claim 1, wherein the contact surface of the annular member is larger than the supporting surface of the footings.

3. A foundation as claimed in claim 1 or 2, wherein the outer circumferential surface of the annular member forms a further yielding joint with the inner walling of the shaft excavation, which further joint is arranged to receive a yielding material.

4. A foundation as claimed in claims 1, 2 or 3, wherein the annular member and the support cylinder are integrally formed as one member.

5. A foundation as claimed in any one of claims I to 3, wherein the annular member and the support cylinder comprise separate members.

6. A foundation as claimed in claim 5, wherein the annular member is connected to the support cylinder in a rigid and/or shear-resistant manner.

7. A foundation as claimed in any preceding claLn, wherein the annular member includes means formed on the external circumference thereof for providing flushing of the yielding joint thereof and/or the yielding joint of the footings.

8. A foundation as claimed in any preceding claim, wherein the support cylinder is provided with a yielding coating on its outer casing.

9. A foundation as claimed in claim 10, wherein the yielding coating comprises a bitumen coating.

10. A foundation as claimed in any preceding claim, wherein a plain bearing is disposed between the underside of the annular member and a contact surface on a rock shoulder, whereby the plain bearing is supported either directly on the rock should or a compensation layer is inserted between the plain bearing and the rock shoulder.

11. A foundation as claimed in claim 10, wherein the plain bearing comprises a bearing ring which can be located as required along with the footings of the tubbing column and the steel ring attached to the same by way of the support cylinder.

12. A foundation as claimed in claim 10 or 11, wherein the bearing ring consists of a pressure-resistant plastic such as PTFE, an elastomer or a metal such as bronze or lead.

13. A foundation as claimed in any preceding claim wherein the angle between the outer casing of the support cylinder and the underside of the annular member is substantially a right angle.

14. A foundation as claimed in any one of claims 1 to 12, wherein the angle between the outer casing of the support cylinder and the underside of the steel ring is greater than 90".

15. A foundation as claimed in any preceding claim, wherein a separating coating or an intermediate layer is disposed between the contact surface of the annular member and the support surface of the footings.

16. A foundation as claimed in any preceding claim, wherein the end of the steel sealing liner corresponding to the contact surface of the footings is welded on to the annular member so as to remain sealed to liquids under pressure.

17. A foundation as claimed in any preceding claim, wherein the annular member comprises a steel ring.

18. A foundation as claimed in any preceding claim, wherein the yielding material comprises bitumen, asphaltic sand or like material.

19. A foundation for the footings of a shaft tubbing arrangement substantially as hereinbefore described with reference to and as illustrated ih Fig. 1, Figs. 2 and 3 and Figs. 4 and 5 of the accompanying drawings.

Publ shed 1991 at 7be Patent Office. State House. 66/71 High Holborn. IA)ndonWCIR47P. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point, Cwimclinfach, Cross Keys, Newport. NP1 7RZ. Printed by Multiplex techniques ltd. St Mary Cray. Kent.

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