This invention relates to a method for building a wall or a part thereof in the ground, a system for carrying out the method, and a wall building device for use in the method and system.
Known tunnel wall building devices are e.g. described in the xe2x80x9cHandbook of Mining and Tunnel Machineryxe2x80x9d, Barbara Stack, 1982, published by John Wiley and Sons, pages 415-417. These known tunnel wall building devices comprise a cutting face at the front of a cylindrical shield. The tunnel wall building device is pushed in the direction of the advance of the shield by hydraulic cylinders acting between the rear side of the shield and the constructed tunnel wall.
A first drawback of the use of such tunnel wall building devices is the criticality of the control over the stabilization of the ground in front of the cutting face. Too much excavation will cause local collapse of the ground, while too great a push force will cause undesirable settlements of the ground.
A second drawback is the required axial support of the tunnel wall building device on the tunnel wall. In case of the use of prefabricated elements the axial support force might be a governing load case.
In other methods the tunnel wall is made of extruded concrete. In this respect reference is made here to EP-A-0 354 335 describing axially supporting a boring shield by the extruded concrete tunnel wall through formwork elements used for forming the inner side of the tunnel wall. The tunnel wall building method according to this publication is discontinuous, taking away formwork elements where the concrete has hardened, and adding the formwork elements, after cleaning thereof, directly behind the boring shield. This method is expensive and time-consuming as a result of the use of the formwork elements, which need to be handled behind the boring shield, and can only be removed when the concrete they are supporting has hardened sufficiently, which may take considerable time.
EP-A-0 483 445 describes a continuous tunnel wall building method, extruding concrete to form a tunnel wall, and using a sliding formwork arrangement requiring additional means to transfer the axial boring forces to the hardened part of the tunnel wall and to facilitate continuity.
In all previous methods the management of the ground water level during the fabrication of the tunnel wall may present serious problems.
The object of the present invention is to provide a method, system, and device for building a wall or a part thereof in general, and a tunnel wall in particular which avoid the risk of collapse or undesirable settlement of the ground in front of the wall building area.
Another object of the present invention is to provide a wall building method, system, and device which do not rely on the wall for providing an axial support for the wall building activities.
Yet another object of the present invention is to provide a wall building method, system, and device which can be continuous and do not use formwork elements.
A further object of the present invention is to provide a wall building method, system, and device which are virtually unaffected by the ground water level.
To reach the above objects, in the method according to the invention a wall building device having cross-sectional dimensions which are substantially equal to the dimensions of at least a part of the cross-section of the wall is pulled through the ground, at least a part of the wall being formed by injecting a hardenable material behind the wall building device. In the process of making the wall, the wall is supported on all sides by the ground surrounding the wall (and, in the case of a tunnel wall, by the ground filling the tunnel wall). Consequently, the wall requires no direct strength, and can e.g. be made from fiber concrete with a normal hardening time. The excavation of the ground at one side of the wall can be done after the completion of the tunnel wall, and the stability of the excavation presents no problem at all. Different shapes of wall cross-sections are possible, but not limited to: (semi-)circular, elliptical, rectangular, triangular, flat. Since the wall building device is advanced by pulling, no reaction force is applied on the constructed wall. The advance of the wall building device is therefore independent from the structural strength of the wall at any given moment.
In a preferred embodiment of the wall building method according to the invention, the following steps are performed: drilling one or more holes in the ground, on or parallel to the projected path of the wall, each of the one or more holes being drilled by means of a drill string; connecting one end of each drill string at the end of the drilling operation to the wall building device; and pulling the wall building device through the ground by retracting the one or more drill strings. Alternatively, the wall building method may comprise the steps of: drilling one or more holes in the ground, on or parallel to the projected path of the wall, each of the one or more holes being drilled by means of a drill string; connecting one end of each drill string at the end of the drilling operation to one end of a casing string; pulling each casing string through the ground by retracting the drill string connected thereto; disconnecting each casing string from the corresponding drill string; connecting one end of each casing string to the wall building device; and pulling the wall building device through the ground by retracting the one or more casing strings. Accordingly, depending on the kind of wall to be built, in particular its cross-sectional area and its length, one or more drill strings and or one or more casing strings are used to pull the wall building device through the ground, using standard directional drilling techniques to bring the drill and casing strings into the ground. The directional drilling techniques are capable of very accurately following the projected path of the wall. The accuracy of the paths of the casing strings can be further improved by using a single drill string and by means of a connecting assembly connecting the ends of several casing strings to one end of the drill string and transversely spaced therefrom, which drill string is then pulled through the ground at the other end thereof.
In a preferred embodiment each casing string comprises an inner string and an outer string enclosing the inner string, the inner string being adapted to transfer the pulling force required by the wall building device, and the outer string being adapted to provide low friction forces when moving the inner string relative to the outer string. The outer string serves as a guide for the inner string when pulling the wall building device through the ground by the inner string. The friction forces between the inner string and the outer string can be still further reduced by supplying a fluid to the space between the inner string and the outer string.
Preferably, the inner string of the casing string is made of steel providing the strength needed, while the outer string is made of plastics, e.g. polyethylene providing an excellent low cost and low friction separation wall between the inner string and the ground.
When moving the wall building device through the ground, a hardenable material is injected behind it to form the wall. The wall material preferably is supplied to the wall building device through at least one of the one or more drill strings/casing strings used for pulling the wall building device through the ground. Additionally, at least one of the one or more drill strings/casing strings may contain at least one line for supplying energy, at least one line for controlling and/or monitoring the wall building device, at least one duct for supplying a drilling fluid to the wall building device, and/or at least one duct for discharging ground removed by the wall building device. Alternatively, or in addition thereto, the wall material and the drilling fluid may be supplied to the wall building device through ducts extruded in the wall. Such ducts can also be used for accommodating lines for supplying energy to the wall building device, or for controlling and/or monitoring the wall building device. Further, such ducts can be used for discharging ground removed by the wall building device.
For an improved positioning accuracy of different wall parts relative to each other, preferably the wall building device is adapted to build a wall or wall part provided with wall guide means, the or a further wall building device being provided with means for engaging the wall guide means. In this way the latter wall building device is allowed to exactly follow the path of the wall or wall part already in place in the ground. The wall guide means preferably comprise a guide slit, which may have an essentially L-shaped cross-section. More generally, in a preferred embodiment at least one guide member is provided in the ground, the wall building device is adapted to be guided along the guide member through the ground.
When a wall building device is used in a multi-pass mode, i.e. for subsequently passing through the ground along adjacent paths for building a wall from a plurality of separately built wall sections, preferably the wall building device is adapted to be connected to the leading end of a pulling string for pulling the pulling string into the ground simultaneously with pulling the wall building device through the ground. The pulling string is used for pulling the or a further wall building device through the ground in a next passage. For this purpose, the wall building device preferably has an essentially Z-shaped cross-section.
An essentially flat wall can be built in the ground by at least two wall building devices which at at least one side thereof are adapted to be coupled to another, which wall building devices further are adapted to be pulled through the ground in a forward direction, and in a direction at an angle to the forward direction.
For improving the quality of the wall, the wall material preferably is injected between one or more membranes defining one or more sides of the wall or wall part formed by the wall building device. The membrane or membranes can be stored in the wall building device in a folded or rolled-up form, and be unfolded or unrolled when injecting the wall material.
The friction between the wall building device and the surrounding ground, and the resistance the ground offers to the wall building device when pulling the wall building device through the ground is preferably reduced by vibrating, lubrication, jetting and/or removing the ground area adjacent to the front part of the wall building device.
The claims and advantages will be more readily appreciated as the same becomes better understood by reference to the following detailed description and considered in connection with the accompanying drawings in which like reference symbols relate to the same parts or parts having the same function. Arrows without reference numerals indicate normal directions of movement.