GB2148968A

GB2148968A - Recoverable ground anchor

Info

Publication number: GB2148968A
Application number: GB08329605A
Authority: GB
Inventors: Hsi Huan Lu
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-11-05
Filing date: 1983-11-05
Publication date: 1985-06-05
Also published as: GB8329605D0

Abstract

The anchor comprises an anchor head having a central post (1) and a plurality of radially disposed pivotal arms (2), which when folded up define a hollow cylinder surrounding a length of the central post. The head may be extended by any number of hollow tubes (3) and extension rods (7). Water can flow through the interspace between the extension tubes and extension rod and flow out of the anchor head. The extension members and rods can be recovered after the operation is finished. <IMAGE>

Description

SPECIFICATION Recoverable ground anchor This invention relates to a recoverable gound anchor.

A construction can structurally divided into a upper aboveground part and lower underground part (generally referred to as "base ment"). The damages occurring in the former are generally easier to repair, but the damages of the latter always present many problems to civil engineers, and repairing is often extremely costly. In the construction basement, retaining engineering plays an important role to prevent the soil mass from shifting or collapsing. As shown in Fig. 7, the commonest method is by far the ground anchorage method, in which steel pipe is driven into the soil and concrete grout is pumped through the pipe into the soil and concrete grout is pumped through the pipe into the soil to form a global root at the tip end of the pipe to frictionally anchor the retaining structure in the soil.High tensile bars which are buried in the soil in advance are thus casted integrally with the global root and exert a strong tension on the latter thereby achieving the purpose of anchorage. Recently, the steel pipe is superceded by prepack grouting piles. The only difference consists in that the internal grouting of the steel pipe is substituted by external grouting of the steel pipe. However, with their respective drawbacks, both methods are not altogether satisfactory, because of the following points: 1. The anchorage is achieved by the friction of the concrete mass of the fixed end (root) and its ambient soil. This necessitates a deep boring, therefore increasing the difficulties, and also the expense of the operation.

2. The prestressed steel tendon cannot be recovered after the construction is completed, thus entailing extra cost of material. If any construction is to be carried out on the abutting land in the future, the tendons, which previously "invaded" into the underground territory of its neighbor, will hamper the operation of the basement construction.

3. The fixed end (root) is a cylindrical body by grouting around the prestressed tendons.

In operation, the subsequent steps must be halted until the grout hardens.

4. The cost is relatively high.

5. It takes a long duration of operation.

since grouting is required and a period have to be waited for the solidification of the grout.

Quarrels of the owners of adjacent lands often rise as a result of the underground invasion. Since the concrete column of the invading "root" contains steel reinforcement.

which is very difficult to break so as to excavate a land for basement construction, a large, powerful power shovel is required.

It is the chief object of this invention to provide a recoverable ground anchor whereby the aforesaid drawbacks are satisfactorily obviated or mitigated.

Numerous other features and advantages will become apparent when read in connection with the accompanying drawing, wherein: Figure 1 is a perspective view of this invention; Figure 2 is a fragmentary view of this invention; Figure 3 is a detailed view of the extension member of this invention; Figure 4 is an embodiment of this invention; Figure 5 is a graphical representation of two typical conventional concrete root ground anchors.

Referring to Figs. 1 and 2, this invention comprises a head member having a central post (1), and a plurality of (in this preferred embodiment, four) like pivotal arms, which when swung inwardly, may define a cylinder encircling the substantial length of the central post. Central post (1) has a thickening head of which the tip is provided with toothing structure, the crest of the toothing being at the same radial extent as the other untoothed portion of the thickening head. Central post is centrally provided with a tunnel (5), through which water may pass.Above the thickening head, there are four pivotal seats, each pivotally mounting a pivotal arm (2), which, when folded up, along with the other pivotal arms, defines a hollow cylinder of which the interior dimension snugly fits the contour of the thinner portion of central post, and the outer dimesnion of which just coincides with the thickening head (See Fig. 3), or slightly smaller than the latter, but still far greater than the thinner portion. Tunnel (5) can communicate to the vicinity of the pivotal arms (2) so that water can flow out therefrom. When the head member is driven into the earth, the arms (2) are forced to fold up by the resistance of the soil, so as to facilitate the advancing of the anchor to the disired position.Yet when slightly pulled backward, the arms are forced to open to define a claw, because the external dimension cylinder defined by the four arms is much greater than the rear thinner portion of the head member, thus is may be firmly anchored in the ground. Note the end face of a pivotal arm dips inwardly when the arm is folded up. This helps to open the arms. The head member can be extended to any desired length by using desired number of extension tube (3), preferably by mating thread means.

The extension members are all centrally tunnelled so that the resulting assembly defines a channel leading throughout its length. Practically, one end of extension tube (3) is externally threaded, while the other end is internally threaded. In each extension tube (3) except the foremost one, there can be provided a further extension rod (7), of which the outer diameter is much smaller than the inner diameter of the extension member, so as to leave a tubular space in each section through which water may pass. To centralize the column formed by such extension rods (7), a frustal cap is mounted on the anterior end of the column and fitted in the tapering cavity of the tail end of the first extension tube.After the head member is driven into the ground, water is pumped through the tubular space into the earth and washes the mud, silt or sand in the vicinity of the anchor head outwardly (See Fig. 4). As shown in Fig. 4, the anchorage can be devided into two sections a front fixed section and a rear free section. The length of the grout column depends on the requirement of the construction. When the head member is driven to a suitable depth it is slightly pulled rearwardly so that the arm opens. The ambient sand is washed outwardly and forms an arrow-shaped mass around the anchor head. Then the anchor is further driven more deeply. At this time, the arms close again, and similar procedures are repeated. In so doing, a plurality of arrowshaped masses are formed in the earth.After the anchor head has reached the desired position, the extension tubes can be removed, while the column of extension rods are still left in the ground. Then cement is pumped along the tunnel around the column of extension rods. It is noteworthy that the direction of the thread of the first extension tube (3) is opposite to that of the other extension tube.

Thus the first extension tube (3) is first retracted to a removable position (i.e. to the free section), then starts the grouting. When the fixed section is filled up with grouting, the extension tube (3) are removed one by one.

After the construction is finished, the extension rod (7) can be removed one by one from the free section. The direction of the threading of the extension must be the same in the fixed section and in the free section. Because water flows out from the vicinity of the arms, the motion of the arm can be ensured without the risk of being hampered by sand or stones so that it cannot open. A plurality of water hole (6) can be provided around the frustal cap to allow water to pass into the first extension tube. These holes (6) can directly connected to a plurality of water supply so that the flow is not interrupted during the connection of extension tubes. An interruption of water flow may result the invasion of underground water which causes troubles in operation.

This invention has several advantages over conventional means. The pivotal arm largely reinforces the anchorage, so the length of fixed section can be reduced. There is no need to prepare so many extension tubes corresponding to the length of the desired grouting calumn. The operation can be performed easily and quickly, thus saving much labor, and therefore cost of construction. The members in the free section can be completely recovered after the operation is finished, thus the future underground operation will not be affected.

Claims

1. Means for underground anchorage comprising: a central post; a plurality of pivotal arms pivotably jointed to the vicinity of the front end of said post; said central post being so structured, and said pivotal arms being so pivoted that each arm can only rotate no more then 90 degrees from the state where it lies paralled to said central post with its free end pointing to the tail end of said central post: each said pivotal arms having the shape of a split fraction of a hollow cylinder, and together defining a full hollow cylinder surrounding a length of said central post when they are folded; the tail end of said post having engaging means; which can cooperate with a corresponding engaging means to form a joint that does not loosen under axial tension.

2. The ground anchorage means according to Claim 1, further comprising a plurality of elongate extension members; wherein: the front end of each of said extension member is provided with engaging means capable of engaging said tail end of said central post, and the rear end of said extension member is provided with engaging means capable of engaging the front end of another extension member.

3. The ground anchorage means according to Claim 1, wherein said engaging means are internal and external threads.

4. The ground anchorage means according to Claim 1 or 2, wherein said central post and said extension member are centrally tunneled and so structred that when they are connected in sequence to form an assembly central tunnel defines a channel through which water may flow from the rear end of the assembly through the length of the assembly and flow out from the vicinity of said pivotal arms.

5. The ground anchorage means according to Claim 1 further comprising a plurality interconnectable extension rod of which the diameter is much smaller than the inner diameter of said extension members, the length of an extension rod corresponding to the length of an extension member.