GB2132667A

GB2132667A - Method of installing precast concrete piles

Info

Publication number: GB2132667A
Application number: GB08236424A
Authority: GB
Inventors: Eimatsu Kaito; Sadao Nishikawa
Original assignee: SHEKISAN KOGYO CO Ltd
Current assignee: SHEKISAN KOGYO CO Ltd
Priority date: 1982-12-22
Filing date: 1982-12-22
Publication date: 1984-07-11
Also published as: GB2132667B

Abstract

A pile hole 1 is dug substantially equal in diameter to the external diameter of a cast concrete pile 9. Mud soil removed is stirred and is applied onto the wall side of the hole 1 under pressure supplied by mud compacting means 7 on an earth auger, so that the wall side is compactly consolidated with mud soil. The pile 9 is inserted into the hole 1 filled with water mud soil after the digging operation. After the pile 9 reaches the bottom, it is rotated so that holding metal means 10 fixed to the bottom of the pile are forced into the bottom soil. <IMAGE>

Description

SPECIFICATION Method of installing precast concrete piles The present invention relates generally to civil engineering technology and more particularly to a method that can be applied to the installation of precast concrete piles through the ground on the site, whereby the precast concrete pile is sunk to a depth into a preformed vertical hole and fixed in position on the bottom. For installing concrete piles through the ground on the site where they are to be installed, whether they are precast concrete piles of cast-in-place concrete piles, several different methods are known and have practically been employed.For example, those methods include the method of driving a precast concrete pile into the ground by means of the pile driver such as the drop hammer and similar impact means, the method that uses vibration or percussion to drive a concrete pile into the ground the method whereby a hole is previously formed in the ground and then concrete is poured into the hole to be formed into a concrete pile (the case applies to the cast-in-place concrete pile), and the method in which a hole is formed into the ground and a precast concrete pile is then inserted into the hole and fixed in position on the bottom. The present invention pertains to improvements in and to the last-mentioned method, which is a technology whereby a pile hole is formed in the ground and a precast concrete pile is inserted into the hole and fixed in position on the bottom.

Among the various conventional methods as mentioned above for applying to the concrete pile installation or placement, the method whereby a pile hole is first formed in the ground on the site where a precast concrete pile is to be placed and the pile is inserted into the hole and fixed in position produces waste soil during the process of the excavation for the precast concrete pile. In putting the method into practice, the resulting waste soil must totally be removed for disposal, which requires considerable human labor, time and expenses for the transportation of the waste soil. There are sometimes situations in which the site where precast concrete piles are to be installed present a soft soil. in those situations, pile holes formed according to the above conventional method have walls which are easy to collapse due to the soft soil.For this reason, the precast concrete piles that have thus been installed in the holes have the stability that is greatly influenced by the nature of the soil which is soft or firm. According to the same method, a bentonite is used for making the sides of the holes firm and therefore the problem arises with the post-disposition of the bentonite. There is also a problem in tightening the precast conrete pile to the underground soil, which remains yet to be solved according to the above method. The subsequent treatment or disposition of the mud containing water or the bentonite used has the accompanying environmental pollution. Since the stability of the installed precast concrete pile is adversely influenced by the soil when it is soft, the reliability in holding up the pile firmly tends to be lowered.

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 ot the present invention includes the process of applying the mud that is produced during the excavation of a pile hole onto the hole wall sides under pressure. In 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 sunk 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 produced by the excavation 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 disposal of the waste soil. The precast concrete pile to be used for the purpose of the present invention is equipped with a holding metal means at the end that firmly holds the pile to the supporting soil at the bottom.As such, with the bottom end of the precast concrete pile reaching the bottom of the hole, the pile is rotated on its axis to an amount enough to force the holding metal means on the end of the pile to enter the supporting bottom soil so that the pile can be firmly held up in position.

In practising the method according to the present invention, a pile hole is previously formed to any desired depth in the ground on the site where a precast concrete pile is to be installed, the hole having an internal diameter substantially equal to the external diameter of the precast concrete pile. The excavating rod to be employed for the purpose of forming the pile hole is made of a vertical rotary member which is driven for axial rotation and has a bit in the form of a blade at the bottom end thereof. The rotary member also includes mud compacting or consolidating means for applying mud around the hole wall sides under pressure, and individual stirring blades arranged stepwise in a staggered manner along the axial length of the member and extending radially as a whole as viewed from the plane traversing the axis.The excavating rod is operated under control of the tower-mounted truck so that it can be forced into the ground while it is being driven for rotation. As it is progressively falling down, the rotary rod is digging the ground by means of its bit, forming a hole which has a diameter equal to the bit diameter. The soil or mud in the hole resulting from the digging process is consolidated or compacted into the hole wall sides by means of the compacting means of the rod. It is usual that the soil skin exposed by forming the hole is rough surfaced, but the compacting means provides the function of applying the mud onto the rough surfaced wall sides under pressure, consolidating the wall sides with the mud and thus making them more compact ànd smooth surfaces. This has the resulting effect of preventing the hole wall from collapsing.Furthermore, no extra or particular precautions or provisions are required for the disposal of the waste soil that is produced by the digging operation, because the waste soil can effectively be used for the compaction of consolidation done by the compacting means.

The digging operation progresses into a prescribed depth, and after the pile hole is completed, the excavating rod is lifted away from the hole. Then, a precast concrete pile is inserted into the hole. During this operation, the precast concrete pile is allowed to fall by its own weight into the hole which is filled with the watercontained mud. Therefore, this sinking of the pile can be accomplished easily and smoothly. Upon reaching the bottom of the pile hole, the pile is driven for the required amount of rotation, forcing the holding metal member secured to the bottom end of the pile to enter the bottom soil of the hole.

This has the action of engaging the holding metal member with the internal soil, thus firmly holding the pile to its supporting soil. It should be noted that the mud compacting means for use in practising the present invention can be constructed in various forms other than those shown and described herein, which are cited simply for aiding in understanding the features of the present invention and are therefore nonlimitative.

As described above, the excavating rod includes a rotation-driven member having the tip blade, mud compacting members and stirring members, whose individual constructional features are later to be described in detail. It should be understood, however, that the structural shapes and arrangements of those members shown are nonlimitative but may be varied in any other shapes and arrangements. Similarly, the structural shapes and constructions of the precast concrete piles which are later to be described should be understood not to be limited to those presented as preferred embodiments of the present invention. Instead, the present invention provides variations that may be made depending upon the usage requirements of the precast concrete piles to be installed.

Brief description of the drawings Fig. 1 is a side elevation of the equipment including a tower which is used to handle the associated members in practising the various preferred embodiments of the present invention; Fig. 2 through 5 are sectional views illustrating the sequential steps of the operation to be performed according to the present invention, in which Fig. 2 indicates the step of the excavation work under way with the excavating rod progressing down into the ground, Fig. 3 indicates the state in which a complete pile hole has been achieved and the excavating rod is now being lifted, Fig. 4 indicates that a precast concrete pile is being lowered (sunk) into the hole, and Fig. 5 indicates that the precast conrete pile is firmly held to its supporting soil at the bottom with the holding metal member engaging the supporting soil, after the pile has reached the bottom and then rotated sufficiently to cause the holding metal member to enter the soil, Fig. 6 is an enlarged view showing how the excavating rod is digging the ground with a forced rotation and a pile hole is being formed; Fig. 7 is an enlarged cross-sectional view of the mud compacting member provided on the excavating rod shown in Fig. 6; Fig. 8 is an enlarged view of a varied form of the excavating rod which has two mud compacting members, an upper one and a lower one; Fig. 9 is a cross-sectional plan view of the upper compacting member; Fig. 10 is a cross-sectional plan view of the lower compacting member;; Fig. 11 is a front view of part of a varied form of the excavating rod, which has a plurality of crook-ended members arranged in a staggered disposition along the axial length and which act as both the compacting members and stirring members; Fig. 12 is a partly sectional front view showing, on an enlarged scale, the structure of an example of the precast concrete pile for use in putting the method into practice; Fig. 13 is an enlarged bottom view of the pile shown in Fig. 12; Fig. 14 is a partly sectional front view showing the structure of another example of the precast concrete pile; Fig. 1 5 is a bottom view of the pile shown in Fig. 14; Fig. 1 6 is a partly sectional front view showing, on an enlarged scale, a varied structure of the precast concrete pile having a saw-toothed bottom end; ; Fig. 1 7 is an elarged bottom view of the pile shown in Fig. 16; Fig. 1 8 is a partly front view of a variation of the precast concrete pile which has metal blades extending radially from the center at the bottom end; Fig. 19 is a bottom view of the pile shown in Fig. 18; Fig. 20 is a partly front view of a varied form of the precast concrete pile having angle metals at the bottom end arranged in square configuration as viewed from the plane perpendicular to the axial direction, the angle metals being mounted on the thick wall circumference of the pile and each including a pointed top and sides which form a valley between the sides of the adjoining angle metals; Fig. 21 is a bottom view of the pile shown in Fig. 20;; Fig. 22 is a partly front view of a further variation of the precast concrete pile having individual angle metals at the bottom end each disposed such that it extends from the inner diameter wall tangently thereto toward the outer diameter wall, as viewed from the plane; Fig. 23 is a bottom view of the pile shown in Fig. 22; Fig. 24 is a partly front view of another variation of the precast concrete pile having individual mountain-like metal members at the bottom end, each individual member being mounted on the thick wall between the inner and outer diameters; Fig. 25 is a bottom view of the pile shown in Fig. 24;; Fig. 26 is a partly front view of still another variation of the precast concrete pile having three metal blades supported by an apertured base plate at the bottom end and configured such that the blades are arranged at equal angular intervals and extend from the center aperture radially toward the outer periphery of the pile; Fig. 27 is a bottom view of the pile shown in Fig. 26; Fig. 28 is a partly front view of a variation of the precast concrete pile of Fig. 26 with the outer aperture closed at the bottom end; Fig. 29 is a bottom view of the pile shown in Fig. 28; Fig. 30 is a partly front view of another variation of the precast concrete pile of Fig. 26 in which the base plate carries three apertures each between the adjacent metal blades, and Fig. 31 is a bottom view of the pile shown in Fig. 30.

The present invention is now described in detail by referring to the accompanying drawings showing the various preferred embodiments of the invention. In Fig. 1, an excavating equipment is schematically shown, which consists of an operator control truck 3 and a tower 4. In digging a vertical hole 1 into the ground on the site where a precast concrete pile is to be installed, an excavating rod 2, which is held up by means of the tower 4 and is driven for axial rotation, is progressively digging the ground to a depth. The excavating rod 2 is equipped with a bit 5 in the form of a blade at the bottom end thereof, which is breaking the ground into a hole 1 whilst the rod 2 is going down with a forced axial rotation. The excavating rod 2 is made of a hollow pipe, through which a pressurized fluid (such as water) is delivered intd the hole 1.A nozzle 6 is provided at the bottom end of the hollow pipe 2, from which the pressurized water is jetted. The excavating rod 2 has a plurality of mud compacting members 7 and a plurality of stirring blades 8, 8 on the outer wall along the axial length of the rod 2. The mud compacting members 7 are fixed to the rod 2 at intervals of about 5 m along the length of the rod, whose action is later to be expiained. The individual stirring blades 8, 8 are also fixed to the rod 2 and arranged in a stepwise, staggered configuration, each of the stirring blades extending in radial direction. As the excavation rod 2 is progressively advancing into the ground with a forced rotation, its tip blade 5 breaks the ground, leaving a hole 1 behind it.The muddy soil removed by the blade 5, which contains water fed from the pipe 2, has a stirring action by the stirring blades 8, 8, forming a water-contained mud soil. Part of the mud soil is coated under pressure by means of the mud compacting members 7 onto the inner wall sides of the hole 1. In this case, the inner diameter of the hole 1 is determined by the external diameter of the compacting member 7, so that much mud soil can be applied under pressure onto the hole wall sides, thus making the hole wall compactly consolidated. The excavating rod 2 progresses further into the ground in this manner, until it finally forms a hole to a prescribed depth, and then the rod 2 is removed from the completely formed hole 1. After the removal, a precast concrete pile 9, which is held up by the tower 4, is placed in the hole and is then left to sink into the hole by its own weight.The sinking is done smoothly and easily through the water-contained mud in the hole until the concrete pile reaches the bottom of the hole. Then, the concrete pile 9 still held up by the tower is driven for axial rotation to such an extent that it causes the holding metal member 10 at the tip to be forced into the bottom soil. As a result, the holding metal member and bottom soil engage each other, combining both together and thus holding the concrete pile firmly to the bottom soil. As previously described, the precast concrete pile is hollow, having a central aperture through it. As such, the mud soil as well as water contained in the mud is filling the central aperture of the pile as it is going down into the mud. When the concrete pile is completely installed on the bottom, the mud soil is almost totally contained in the hollow concrete pile.

The shape, number and relative positions of the mud compacting member 7 are not limited to the above described embodiment, but may be varied depending upon the requirements for the concrete pile installation.

Now, the construction of the earth auger for use in installing precast concrete piles according to the present invention is described. The structural arrangement includes a hollow pipe 2 which is capable of axial rotation, a plurality of stirring blade members 8, 8 spaced at regular invervals along the axial length of the rotary pipe and arranged in such a staggered configuration that the individual blade members extend radially and are oriented in different directions, a number of mud compacting members 7 fixed to the pipe at appropriate positions, and a bit 5 in the form of a blade mounted to the tip of the pipe. As example of the mud compacting member 7, it may be an assembly that consists of a drum 11 and radially (crosswise) extending internal arm plates 1 2 which hold the drum and secure it to the pipe, as shown in Fig. 7.Alternatively, it may be an assembly that includes two arch-shaped plates 13 and crosswise arm plates 14 which hold the plates 1 3 firmly to the pipe 2, as shown in Fig. 9. The stirring blade construction may consist of a series of individual straight bars as shown in Fig. 8. As a variation, the stirring blade construction may be a series of brackets 15 each having a downwardly crooked end 16 as shown in Fig. 1 The holding metal member to be fixed to the bottom end of a precast concrete pile is primarily intended to allow the pile's bottom end to be forced into its supporting soil, and therefore should preferably have the construction like a screw, for example.For example it is advantageously possible to construct the holding metal member like those shown in Figs. 12 through 31, as indicated by 18, 19, 20, 21, 22, 23, 24, 33, 34, and 35 in the respective figures.

In the preceding embodiments, the precast concrete pile is driven for rotation in the direction of arrows 26,27, 28,29, 30, 31,32,36,37, and 38, respectively, at its final stage of the installation. As there is little or no friction between the pile and the watery mud soil surrounding the pile when its rotation is driven, any possible twisting force upon the pile only occurs as a mechanical resistance between the holding metal member and the supporting soil at the bottom. Therefore, the pile is not adversely affected by the twisting force.

As clear from the preceding detailed description of the various embodiments of the present invention, the pile hole formed in the ground on the site where the precast concrete pile is to be installed contains mud soil which remains in the hole in the water mud state after the hole is completely formed. In installing the precast concrete pile, it can be left to sink to the depth of the hole by its own weight without any external resistance. Therefore, this sinking work can be accomplished without producing any noises or vibrations, which is advantageous from the standpoint of the preventive environmental considerations. Furthermore, the mud soil resulting from the hole excavation are for the most part compacted or consolidated into the hole wall sides. This eliminates the need of removing the mud soil from the hole, thus saving the time and human labor required for this removal.This also has the accompanying effect of solving the disposal problem of the mud soil for the environmental pollution prevention.

Compacting or consolidating the mud soil into the hole wall sides makes the hole wall stronger. In addition, the compacted or consolidated mud soil provides the resilient and friction action upon the pile, under which the pile can be firmly held just the same as the driven pile can be beld. As a result, the pile can be installed with improved stability. Another advantage of the present invention is the provision of the holding metal member at the bottom end of the precast concrete pile, which holds the pile firmly to its supporting soil at the bottom. As a result, the stability with which the pile is installed is further increased in combination with its side supporting stability. The combined holding action of the side wall and foot increases the supporting power for the pile. This supporting power can be maintained without any footing foundation that is necessary in practicing the conventional method for the driven concrete piles or poured concrete piles.

This reduces the total pile installation costs. The wall side of a hole being formed by the excavating rod is strengthened while the digging operation is under way, and the watery mud soil produced by the digging operation remains in the hole. This prevents the hole wall from collapsing and can consolidate it particularly when the soil surrounding the hole wall is soft. As water can be delivered as required into the hole during the digging operation, a required amount of waste soil can remain in the hole, so that it is possible to control the quantity of the soil to be wasted reasonably to a minimum rather than going to an excess.

Claims

1. A method for installing precast concrete piles, by means of an earth auger, into the ground on the site where the piles are to be installed, which comprises digging the ground to form a pile hole substantially equal in diameter to the external diameter of the precast concrete pile, stirring the mud soil removed by forming the hole, applying part of the stirred mud soil onto the wall side of the hole under the pressure supplied by the mud compacting means in the earth auger so that the wall side can be compactly consolidated with the mud soil, inserting a precast concrete pile into the hole filled with the watery mud soil after the digging operation is completed to a desired depth, and causing the precast concrete pile to be drive for axial rotation after the bottom end of the pile reaches the bottom of the hole so that the holding metal means fixed to the bottom end of the pile can be forced into the bottom soil until the holding metal means engages the bottom soil, thereby holding the pile firmly to the bottom ground of the hole.

2. A method as defined in Claim 1, wherein a jet of water is delivered as required into the hole from the nozzle provided at the tip of the earth auger while the hole is being formed.

3. A method as defined in Claim 1, wherein a precast concrete pile is allowed to sink by its own weight into the hole.