GB2132668A - Concrete pile installing method - Google Patents

Abstract

A precast concrete pile 1 with a central aperture is set in position on the site where it is to be installed, together with a digging device 3 inserted through the pile. The digging device 3 gradually digs the ground with forced rotation to form a pile hole 9 substantially equal in diameter to the pile 1. Mud soil produced is stirred and is applied to the side of the hole 9 under pressure. The pile 1 is gradually inserted concurrently with formation of the hole 9. When the prescribed depth is reached, the digging device 3 is removed. When the pile 1 reaches the bottom, it is rotated to force a metal holding member 11 into the bottom ground. <IMAGE>

Description

SPECIFICATION Concrete pile installing method The present invention relates generally to civil engineering technology, and more particularly to a method for installing a precast concrete pile into a hole preformed to a depth in the ground. For installing concrete piles through the ground, there are known various methods that have practically been employed, including the precast concrete pile driving method in which the concrete pile is driven into the ground by means of a drop hammer or the like, the vibration or percussion driving method whereby the precast concrete pile is driven under the applied vibration, the cast-in-situ method whereby a pile hole is formed in the ground on the site and concrete is poured into the hole and is then allowed to harden, and the method whereby a pile hole is formed through ground on the site and a precast concrete pile is sunk into the hole and fixed in position. The present invention pertains to the last-mentioned method technology whereby the precast concrete pile is installed in the preformed hole.

In using the conventional method whereby a pile hole is formed through ground on the site and a precast concrete pile is placed into the hole, the waste soil produced by forming the hole must almost totally be removed from the hole for disposal. The disposal of the waste soil requires a great deal of human labor, time and expenses for the transportation. There are sometimes situations in which the site where precast concrete piles are to be installed presents a soft soil. In those situations, the wall side of the formed hole is easy to collapse, and whether the concrete pile can firmly be held up or not depends largely upon the nature of the soil which is soft or firm. The disposal of the waste soil or the bentonite used on the site also causes an environmental pollution problem.The above conventional method has a problem that the ability to support the concrete pile is likely to be affected by the fact that it is not firmly held up to the bottom ground.

The present invention provides an improved method which eliminates completely the problems and disadvantages that are inherent in the conventional method mentioned in the preceding description. For this purpose, the method according to the present invention includes the process.of applying the mud that is produced during the formation of a pile hole onto the hole wall sides under pressure. During this process, the mud is compactly consolidated into the hole wall soil, thus strengthening the hole wall sides. As required, water is poured into the hole, and the mud in the hole is stirred or mixed together with the water to form a watery mud. Then, a precast concrete pile is inserted into the hole containing the watery mud, and is allowed to be sink into the watery mud, falling down by its own weight until it reaches the bottom of the hole.Thus, the method according to the present invention eliminates the need of removing the waste soil from the hole for the disposal of the same, and is therefore economical in terms of the time, human labor and expenses that would otherwise be required for the disposal of the waste soil. In installing a precast concrete pile which is usually hollow and is held up by means of a digging truck tower, an excavating rod with a bit at the bottom tip, which is also held up by means of the tower, is inserted through the precast concrete pile and is driven for axial rotation so that it can dig the ground, forming a vertical hole substantially equal in diameter to the external diameter of the concrete pile.As the excavating rod progresses deeper into the ground, the mud produced by breaking the ground into the hole is applied under pressure onto the hole wall sides, thus strengthening the hole wall, and then the concrete pile is gradually lowered into the hole. This procedure proceeds until a desired depth is reached. Since the hole being gradually formed is thus consolidated with the mud, even in the case of the soft soil on the site, the pile installation work can be continued smoothly and effectively, without any accompanying risk of the work delay that may occur due to the otherwise possible collapse of the hole wall sides. The precast concrete pile is equipped at the bottom end with a holding metal member which holds the pile firmly to the bottom ground.As such, upon reaching the bottom of the completed hole, the precast concrete pile is driven for the required amount of axial rotation, causing its holding member to enter the ground so that the pile can be firmly held up to the ground. This ensures the reliable support of the pile.

The specific features of the present invention are as follows. Those features can be obtained by the process of the method that is specific to the present invention as described below. First, a pile hole is gradually formed in the ground on the site where a hollow precast concrete pile is to be installed, by means of the digging device or earth auger which has the form of a bit-tipped rod and is inserted through the concrete pile. The hole is being formed to a diameter substantially equal to the external diameter of the pile and to a desired depth. During the gradual formation of the pile hole, the produced waste mud is stirred or mixed with water if required and part of the mud is applied under pressure onto the hole wall sides so that it can be compactly consolidated into the wall, thus strengthening the wall sides.As the digging rod progresses deeper into the ground, the concrete pile is left to be sunk by its own weight.

When the hole is finally completed and the bottom end of the pile reaches the bottom of the hole, then the digging rod is lifted through the concrete pile and removed away from the hole. After the removal, the concrete pile is driven for the required amount of axial rotation enough that the holding metal member at the bottom end of the pile can engage the bottom ground to hold the pile firmly to the ground. As clear from the above description, the successive steps of the process can be carried out without producing noises or vibrations. Furthermore, the waste mud soil produced by the hole formation needs no disposal, part of which can be used for strengthening the hole wall by means of consolidating the mud thereto under the applied pressure. This advantageously eliminates the need for the disposal of the waste soil.Because the sinking of the precast concrete pile occurs concurrently with the gradual formation of the hole, the hole wall can be prevented from collapse even in the case of the soft ground. The holding of the pile bottom firmly to the ground improves the pile holding reliability. The sides of the pile can be held under the pressure supplied by the surrounding hole wall mud that is consolidated and expands toward the pile, thus increasing the frictional supporting power between the pile and hole wails.

Among the above described features, one specific feature of the present invention is in permitting the sinking of a precast concrete pile to occur concurrently with the gradual formation of a pile hole, which is accomplished by the digging device passed through the central aperture through the pile. Anotherfeature of the present invention is to eliminate the need for disposing of the waste soil that is produced during the hole formation because the waste soil is almost totally used for strengthening the hole wall sides. This feature is advantageous from the standpoint of the environmental pollution prevention. Another feature of the present invention is tightening the bottom end of the pile to its supporting ground by means of the holding metal member at the bottom end of the pile.This can be achieved by causing the pile to rotate enough to enable the holding member to engage the ground.

Brief Description of the Drawings Fig. 1 is a schematic sectional view for a preferred embodiment of the present invention, illustrating how a pile hole is formed while a precast concrete pile is inserted following the gradual formation of the hole; Fig. 2 is a cross sectional view taken along the line A-A in Fig. 1; Fig. 3 is a partly omitted sectional view illustrating the completed pile hole after the removal of the earth auger in which the pile is going to sink into the remaining mud; Fig. 4 is a partly broken-away sectional view showing the installation of the pile has been completed; Fig. 5 is a bottom view of Fig. 4;; Fig. 6 through 8 are partly perspective views illustrating the different configurations of the holding metal member secured to the bottom end of the precast concrete pile according to the corresponding preferred embodiments of the present invention, the embodiment shown in Fig.

6 including four metal pieces each of the same width as the wall of the pile and having the rectangular cross section gradually increasing in thickness, the embodiment shown in Fig. 7 including four metal pieces each having the same configuration as those in Fig. 6 except for the triangular cross section, and the embodiment shown in Fig. 8 including four metal pieces each having the same configuration and cross section as those in Fig. 6 but gradually decreasing in width.

The present invention is now described by referring to the accompanying drawings showing the preferred embodiments of the invention. In Fig.

1, a vertical tower mounted to an operator truck (not shown) stands on the site where a precast concrete pile 1 is to be installed, and the pile 1 which is normally hollow and the digging device 3 such as earth auger inserted through the pile 1 are held up by means of the tower. The construction of the digging device 3 comprises a hollow tube 4 which is capable of axial rotation and is equipped with a bit 5 at the end thereof, and a mud stirring and compacting device 8 above the bit 5 which includes a plurality of arm members 6 arranged at regularly spaced intervals along the axial length of the tube 4 and extending radially as viewed from the plane traversing the axis in Fig. 2, each arm member 6 carrying a mud compacting plate 7 at the free end.The bit assembly 5 and each of the mud stirring and compacting arm members generally designated by 8 are capable of expanding themselves and closing. They are designed to expand when the hollow tube 4 is driven for a forward rotation, and close when the tube is driven for a reverse rotation. Then, the digging device 3 which is held up by means of the tower is operated so that it can dig the ground, forming a pile hole 9 substantially equal in diameter to the external diameter of the concrete pile 1 to be installed. The digging operation occurs by driving the hollow tube 4 for a forward rotation so that it can progress into the ground. That is, the forward rotation of the hollow tube 4 causes its bits assembly 5 to expand itself and progressively break the ground, deepening the pile hole 9.The waste mud soil which is produced during the digging operation is stirred by the stirring and compacting members 8 which are now expanded, and is partly applied onto the wall side of the formed hole 9 under the pressure supplied by the plates 7 of the members 8. The hole wall sides are thus compactly consolidated. The hollow tube 4 is also equipped with a nozzle 10 at the bottom end, from which an appropriate quantity of pressurized water may be jetted if the mud to be stirred contains little water.

Concurrently with the digging operation that is gradually breaking the ground into the pile hole 9, the precast concrete pile 1 is being sunk into the hole. As described earlier, the pile hole 9 is being formed to a diameter substantially equal to the external diameter of the pile 1.There.fore, the pile 1 can be left to fall down by its own weight into the hole 1, and so the pile need not be driven for the axial rotation, which might possibly damage the pile.

The digging operation by the digging device 3 proceeds in this manner until a hole 9 of a specified depth is finally formed. Then, the hollow tube 4 is driven for a reverse rotation, causing the bit assembly 5 and each of the stirring and compacting assemblies 8 to be closed. The digging device 3 is then lifted to be removed through the pile 1 away from the hole 9. After the removal, the pile 1 is further sunk until its bottom end reaches the bottom of the hole. Then, the pile 1 is rotated slightly enough to enable the holding metal member 11 mounted to the bottom end of the pile 1 to be forced into the ground and engage the same. The pile 1 and its supporting ground are thus tightly combined together.

For the axial rotation of the pile 1 as described above, the friction that may occur between the pile periphery and hole wall is nearly negligible, which means that only a small torque is required for causing the rotation of the pile. As a result, the pile can be protected against any damage or breakage due to the twist. It has been described that the waste mud soil that is produced as a result of the hole digging process need not be removed for the disposal. Part of the waste soil can be used for the consolidation of the wall side of the hole 9, which is done by applying the mud onto the hole wall under the pressure. Practically all remaining waste soil can enter the central aperture through the pile 1 when it is falling down.

The pile which has been installed is completely buried with the waste soil. As the pile can be held up to the ground by means of its holding metal member 11 that aids the bottom end of the pile in reaching into the firm ground layer, there is no need of the footing using cement or other materials. In the preceding embodiment shown in Fig. 6, the holding metal member includes four metal pieces 11 each configured to provide a rectangular cross section, a width substantially equal to the wall of the pile and a gradually decreasing thickness. This configuration is nonlimitative, but may be varied.For example, the configuration shown in Fig. 7 includes four metal pieces 1 2 of triangular cross section, and the configuration shown in Fig. 8 includes four metal pieces 1 3 each of which has a rectangular cross section and gradually decreasing width and thickness. All the configurations shown can be applied in practicing the method according to the present invention.

The various embodiments of the present invention have been described in detail. As it can readily be understood, the method according to the present invention provides various advantages over any of the conventional methods. The method according to the present invention comprises the process of gradually forming a vertical pile hole and strengthening the hole wall by consolidating the watery mud thereinto, allowing a hollow precast concrete pile gradually to sink into the hole by its own height concurrently with the formation of the hole, and, upon reaching the bottom ground of the hole, causing the precast concrete pile to rotate slightly enough to force its holding metal member into the bottom ground, thereby holding the bottom end of the pile firmly to the ground.As such, regardless of the nature of the soil on the site where precast concrete piles are to be installed, such as sand layer or layer containing underground water flow, successive vertical pile holes can be formed without any collapse and the piles can be sunk into the respective holes without difficulties. The action of securing the bottom end of the pile to the supporting ground, coupled with the reduction of the diametr of the pile hole which is caused by bringing the consolidated soil back toward the pile, provides the pile holding capability equivalent to that of the driven concrete pile.

Differently from the driven concrete pile, however, the method according to the present invention produces no noises or vibrations. The waste soil can almost totally remain in the hole, so that the disposal problem will not arise. Consequently, the present invention provokes no environmental pollution problem in any way.

Claims (4)

1. A method for installing precast concrete piles each having a central aperture through it, which comprises setting a precast concrete pile in position on the site where it is to be installed together with the digging device or earth auger inserted through the pile, causing the digging device gradually to dig the ground with forced rotation to form a pile hole substantially equal in diameter to the external diameter, stirring the mud soil produced by digging the ground and applying part of the stirred mud soil onto the wall side of the formed pile hole under pressure so that it can compactly be consolidated into the wall side, gradually inserting the precast concrete pile into the pile hole concurrently with the hole formation, lifting the digging device away from the hole when it has digged into a prescribed depth, and, upon reaching the bottom ground, causing the precast concrete pile to rotate slightly enough to force its holding metal member into the bottom ground so that the pile can be firmly held up to the ground.

2. A method as defined in Claim 1, wherein during the digging operation an appropriate quantity of a jet of water is supplied into the hole from the nozzle at the tip end of the digging device

3. A method as defined in Claim 1, wherein the applying of the mud soil onto the wall side of the hole under the pressure and the resultant consolidation of the mud soil into the wall side are done by means of the mud compacting means mounted to the digging device.

4. A method as defined in Claim 1, wherein the inserting of the precast concrete pile is done by allowing it gradually to be sunk into the hole by its own weight.