GB2160562A

GB2160562A - Ground-freezing method

Info

Publication number: GB2160562A
Application number: GB08416031A
Authority: GB
Inventors: William Millington Wild; Walter Griffiths Deacon; William Henry Bradley; John Sidney Harris; Stephen John Harvey
Original assignee: FORAKY Ltd
Current assignee: FORAKY Ltd
Priority date: 1984-06-22
Filing date: 1984-06-22
Publication date: 1985-12-24
Also published as: GB2160562B; GB8416031D0

Abstract

Ground-freezing is used to permit sinking of a shaft in unstable or wet ground. The method relates to freezing a lower unstable region (10) without freezing a stable upper region. One or more main bore holes (A1 to A4) are drilled through the upper region and, from the or each main bore hole, a plurality of freezeholes (H1 to H3) are formed in the lower region (10) by directional-drilling. Refrigerant is supplied to the freezeholes to freeze and stabilise the lower region. <IMAGE>

Description

SPECIFICATION Ground freezing method This invention relates to a ground-freezing method for freezing, for example, unstable and/or watersaturated strata to permit sinking of a shaft without risk of collapse of the shaft walls and/or flooding of the shaft being sunk.

It is known to drill freezeholes at spaced intervals around the region in which a shaft is to be sunk, to insert tubes into the freezeholes and to freeze the surrounding region by means of a refrigerant passed through the tubes.

It is not usual for the upper strata to be relatively stable and the troublesome strata to be those lower down, so it is wasteful and expensive to freeze the upper strata. This has been avoided by first forming the freezeholes and sinking the tubes, then forming the upper part of the shaft in the stable strata, forming an enlarged chamber at the base of the upper part of the shaft to permit access to the freezehole tubes and connecting up refrigerant supply apparatus to the tubes in the chamber, so as to freeze only the lower strata before the lower part of the shaft is sunk. The holes above the chamber are then filled.

The present invention provides a further improvement in the method which further reduces the costs where only the lower strata need to be frozen.

In accordance with this invention, there is provided a groundfreezing method for freezing a lower region without freezing an upper region, comprising forming at least one main hole through the upper region, directionally-drilling a plurality of freezeholes in the lower region from said main hole or holes, the freezeholes being arranged around an area to be excavated, and supplying refrigerant to the freezeholes to freeze the ground around said area.

Using this method, the cost savings made by the prior art method, where only the lower region is frozen, are again made here, but, in addition, further considerable cost savings are made, since far fewer holes need be drilled in the upper region.

Reference is now made to the accompanying drawings wherein: Figure 1 is a side elevation of a shaft and drilled holes illustrating a first ground-freezing method according to the invention; Figure 2 is a diagrammatic plan view of the shaft and drilled holes of Figure 1; Figure 3 diagrammatically illustrates in elevation the first ground-freezing method and two alternative embodiments of the invention; Figure 4 illustrates, in plan view, the second alternative method; and Figure 5 illustrates, in plan view, the third alternative method.

Referring to Figures 1 and 2, the ground-freezing method comprises initially forming four main bore holes Al to A4 in the stable upper strata around an area to be formed, by excavation, with a shaft 11.

These holes are equi-angularly spaced around the location for the shaft 11.

Each hole, such as Al, is continued down into and through an unstable and/or wet lower stratum 10 in a straight line to form a hole H1 and the lower part of this hole is provided with a freezetube F2, the tube extending a short way up into the more stable upper strata. From the hole H1 further holes H2 and H3 are formed by directional-drilling (a known technique per se). These holes extend diagonally from the bottom of the main hole Al and then change direction to lie parallel to the hole H1.

The parallel lower parts of these holes extend through the unstable lower stratum 10 and are provided with freeze-tubes F1 and F3.

Each of the holes A2 to A4 is similarly provided with three spaced parallel branches having freezetubes F4 to F12. The freeze-tubes are all substantially equi-angularly spaced in a ring around the area to be formed with the shaft 11.

The shaft 11 is initially excavated through only the stable upper strata to a level 12, where a circumferential chamber 13 is formed to provide access to the freeze-tubes F1 to F12 for connection of the tubes to a refrigerant supply apparatus.

After freezing of the lower stratum 10, the shaft is further excavated through this stratum.

This method is further illustrated as alternative '1' in Figure 3. Another alternative '2' shows the initial drill holes being further spaced from the area to be excavated with the branch holes extending diagonally downwardly towards this area before forming the parallel freezeholes close to the area to be excavated.

This second alternative is also shown in Figure 4, where on the left is shown a main drill hole A10 and three branch holes H10 to H12 leading to freezeholes with freeze-tubes F10 to F12. On the right is shown a modification with four branches from the main drill hole All.

Two other modifications of this second alternative are also shown in Figure 4. At the top of the Figure, a main hole A12 is shown extending through the upper strata. From this main hole, an extension A12' leads to branches H13 to H16 and freezeholes F13 to F16. At the bottom of Figure 4, a similar arrangement, but different configuration is shown the main hole being labelled A13.

A third alternative is shown in Figure 5 and is marked '3' in Figure 3. In this method, a single main hole A20 is drilled at the centre of the area to be excavated and branches H20 et al radiate from this hole to form the parallel freezeholes with freeze-tubes F20 et al. Only some of the branches and freeze-tubes are illustrated. It is envisaged that more than one main hole may be provided in the area to be excavated.

It is possible to avoid the excavation of the circumferential chamber 13. Freezetubes can be arranged extending from the surface through the main hole, or holes, and the branches to the freezeholes and refrigerant can be supplied through these tubes from the surface. The upper parts of the freezeholes can be encircled by material with good heat-insulating properties to minimise the freezing effect in the upper strata.

Claims

1. A ground-freezing method for freezing a lower region without freezing an upper region, comprising forming at least one main hole through the upper region, directionally- drilling a plurality of freezeholes in the lower region from said main hole or holes, the freezeholes being arranged around an area to be excavated, and supplying refrigerant to the freezeholes to freeze the ground around said area.

2. A ground-freezing method according to Claim 1, wherein after forming of the freezeholes, a shaft is excavated in the upper region, a circumferential chamber is formed in the shaft to provide access to the freezeholes, refrigerant is supplied to freeze-tubes inserted in the freezeholes to freeze the ground in the lower region, and the shaft is further excavated into the lower region.

3. A ground-freezing method according to Claim 1, wherein a plurality of main holes are formed around the area to be excavated, a plurality of freezeholes formed from each main hole, freezetubes are inserted in the freezeholes and the main holes and refrigerant is supplied to the freezeholes through the main holes.

4. A ground-freezing method according to Claim 3, wherein heat-insulating material is positioned around the main holes.

5. A ground-freezing method according to Claim 1, wherein the or each main hole is provided in the area to be excavated and the freezeholes are formed by directionally-drilling outwardly into the peripheral margin of the area to be excavated.