WO2011137507A1

WO2011137507A1 - Method and apparatus for ground improvement using compacted aggregate columns

Info

Publication number: WO2011137507A1
Application number: PCT/CA2011/000484
Authority: WO
Inventors: Gary Hamata; Charles Forcier; Barry Macgregor
Original assignee: North American Pile Driving Inc.
Priority date: 2010-05-01
Filing date: 2011-05-02
Publication date: 2011-11-10
Also published as: CA2839784A1

Abstract

An apparatus and method for forming compact aggregate columns. The apparatus includes an aggregate materials hopper; a hollow mandrel adapted to be driven into the ground, and having an enlarged diameter bottom section; between 4 and 8 rubber bearing isolators disposed between the mandrel and the hopper for reducing transmission of vibratory energy between the mandrel and the hopper, and a rubber seal encircling and moulded to the outer circumference of the mandrel for preventing aggregate leakage from the hopper; a stone gate convertible between an open position and a closed position for controlling aggregate flow, one or more collars encircling the mandrel disposed along the length of the mandrel, each collar having an outer circumference greater than the mandrel circumference; a vibratory hammer attached to a vehicle for inserting and removing the mandrel into the ground; and a monitoring and control system in the cab of the vehicle.

Description

METHOD AND APPARATUS FOR GROUND IMPROVEMENT

USING COMPACTED AGGREGATE COLUMNS

TECHNICAL FIELD OF THE INVENTION

The present invention relates to ground improvement. In particular, the present invention relates to methods and apparatus for ground improvement using compacted aggregate columns.

BACKGROUND OF THE INVENTION

It is known to provide methods and apparatus for forming compact aggregate columns for ground improvement. There are a variety of methods and equipment in common use which use compacted gravel as a means of improving the density and strengths of soils commonly called "ground improvement". One of these methods is the use of driven gravel columns using the expanded base (Franki Pile) method, vibroflotation with or without air or water, and with or without the introduction of aggregate.

It would be desirable to improve such systems by improving the control of the aggregate flow through the tube, increasing the efficiency of the system by managing vibratory energy more efficiently, and improving the densification of the surrounding soil. The present invention meets all of these objectives.

SUMMARY OF THE INVENTION

There is provided an apparatus for forming compact aggregate columns, the apparatus comprising a materials hopper having a top opening and a bottom opening; a hollow mandrel adapted to be driven into the ground, its upper end passing through the bottom opening in the hopper, and having an enlarged diameter bottom section and an aggregate receiving opening; connection means between the hopper and the mandrel; flow control means near the upper end of the mandrel, for controlling the flow of aggregate from the hopper into the mandrel; soil densification means disposed along the length of the mandrel; a vibratory hammer for inserting and removing the mandrel into the ground; and monitoring and control means.

The connection means may be one or more rubber bearing isolators disposed between the mandrel and the hopper, and a rubber seal between the mandrel and the hopper. Preferably, there are 4 to 8 rubber bearing isolators which reduce vibratory energy transmission between the mandrel and the hopper. The rubber seal may encircle the mandrel and is moulded to the mandrel.

The flow control means may be a stone gate convertible between an open position to allow aggregate flow from the hopper to the mandrel, and a closed position to prevent aggregate flow from the hopper to the mandrel.

The soil densification means may be one or more collars encircling the mandrel, each collar having an outer circumference greater than the mandrel circumference. As the mandrel is driven into the ground, the collars increase the densification of the soil in their vicinity. The collars may be spaced at intervals along the length of the mandrel, preferably at 5 foot intervals.

The vibratory hammer used to drive and retract the mandrel may be attached to a vehicle, and the system may be monitored and controlled from monitors and controls located in the cab of the vehicle.

There is also provided a method for forming compact aggregate columns, the method comprising the steps of filling a hollow mandrel with aggregate from a hopper above the mandrel through an opening in the side of the mandrel; closing a stone gate near the upper end of the mandrel to prevent aggregate from rising in the mandrel; driving the mandrel into the ground with a vibratory hammer, wherein ariving the apparatus into the ground displaces the soil outwardly and downwardly from the mandrel to create a hole extending downwardly from the ground surface, and compacts aggregate present in the hole into an aggregate column; withdrawing the mandrel, thereby allowing aggregate to exit the mandrel into the hole; opening the stone gate to allow more aggregate to fill the mandrel; and repeating the above steps until a compacted aggregate column of a desired length is achieved.

BRIEF DESCRIPTION OF THE DRAWINGS A detailed description of the preferred embodiments is provided by way of example only and with reference to the following drawings, in which:

Fig. 1 is a plan view of the apparatus of the present invention; Fig. 2 is a plan view of the lower end of the mandrel of the assembly, according to one embodiment of the invention;

Fig. 3 is a plan view of the lower end of the mandrel of the assembly, according to another embodiment of the invention; Fig. 4 is a front view of the hopper of the assembly, according to the invention;

Fig. 5 is a side view of the hopper of the assembly, according to the invention;

Fig. 6 is a top view of the hopper of the assembly, according to the invention;

Fig. 7 is a side view of the assembly below the hopper depicting the connection between the hopper and the mandrel, and the stone gate; Fig. 8 is a top view of the stone gate in an open position;

Fig. 9 is a cross sectional view of the stone gate in an open position;

Fig. 10 is a top view of the stone gate in a closed position;

Fig. 11 is an end view of the stone gate in a closed position; and

Fig. 12 is a cross sectional view of the stone gate in a closed position. In the drawings, one embodiment of the invention is illustrated by way of example. It is to be expressly understood that the description and drawings are only for the purpose of illustration and as an aid to understanding, which are not intended as a definition of the limits of the invention.

DETAILED DESCRIPTION OF THE INVENTION The applicant has developed a method and equipment for the introduction of gravel into the ground with compaction to produce a compacted gravel column.

The method involves the use of a mandrel 2 with an enlarged bottom 4, a stone gate 6 to control the flow of gravel and a hopper 8 to introduce the gravel into the mandrel. This assembly is attached to a vibratory hammer (not shown) which is suspended, guided and powered by a track machine base with an adjustable leader at the front of the machine.

According to one embodiment, the apparatus of the present invention comprises a hopper, a mandrel extending downwardly from an opening 10 in the hopper; connection means between the hopper and the mandrel; flow control means at the upper end of the mandrel; soil densification means along the mandrel of the present invention, monitoring and control means; and mandrel insertion and removal means.

The mandrel insertion and removal means preferably comprises a base machine which can be moved into a desired position for driving the mandrel and with capacity to elevate a vibrohammer used to vibrate the mandrel as it is driven into and withdrawn from the soil.

The hopper of the present invention preferably is fiUable using a long reach loader.

The connection means for connecting the hopper and the mandrel preferably comprise a rubber bearing isolator 12 which surrounds the mandrel and is disposed between the mandrel and the hopper to reduce the transmission of vibrations from the mandrel to the hopper. The connection means also includes a rubber seal 14 disposed between the hopper and the mandrel to prevent aggregate leakage from the mandrel and further reduces the transmission of energy between the hopper and the mandrel.

The soil densification means comprises a plurality of collars 16 welded at regular intervals along the length of the mandrel. Vibration energy is transmitted outwardly from each of these collars into the surrounding soil to increase densification of the surrounding soil.

According to one embodiment, the bottom enlarged section of mandrel may be approximately 8 inches long, as depicted in Fig. 2. According to another embodiment depicted in Fig. 3, the bottom enlarged section of the mandrel may be six feet in length. Other lengths are also within the scope of the invention. The flow control means of the apparatus of the present invention comprises a stone gate movable between an open position to allow aggregate flow from the hopper into the mandrel, and a closed position to prevent aggregate flow from the hopper into the mandrel. Fig. 7 depicts a closed stone gate 18, The monitoring and control means of the present invention comprises hydraulic systems controlled and monitored from the cab of the base machine.

According to the preferred embodiment of the method of the present invention, ground improvement using the present invention is achieved by the following process: First, the mandrel is driven down using the vibrohammer and base machine. The mandrel displaces the soil by a volume equal to the volume of the mandrel as it is driven into the soil, thereby increasing soil density. Vibration of the soil by the mandrel as it is being driven down densities the soil. This is further enhanced by the addition of collars which have been welded to the outside of the mandrel at regular intervals. Once the mandrel has been driven to its intended depth, the stone gate is opened which allows gravel to flow from the hopper into the mandrel and down to the tip of the mandrel. As the mandrel is extracted upwards the gravel flows out of the bottom into the cavity produced by the extraction of the mandrel. The mandrel is extracted a short distance, preferably 3 to 5 inches, then driven back down a distance of preferably 2 to 4 feet into the previously deposited gravel. This redriving of the mandrel impacts the gravel and forces it outward to produce a gravel column which is larger in diameter than the mandrel diameter. The distance the mandrel is redriven down is a function of the energy required to do so, which is measured by hydraulic flow and pressure which is registered and controlled in the operator's cab.

The process of extraction and redriving is continued until the mandrel is completely withdrawn from the ground. Filling of the gravel hopper with a long reach loader takes place as the mandrel is driven and extracted. A gravel column approximately 2 feet in diameter is produced. Other column diameters can be produced by using larger mandrel diameters and larger hammers.

The apparatus of the present invention improves upon the prior art technology in a variety of ways. The mandrel of the present invention includes collars welded to the mandrel at regular five foot intervals, which improves the soil densification as the mandrel is vibrated up and down.

The stone gate of the present apparatus is situated just below the hopper. The stone gate may be opened and closed to control the flow of gravel into the mandrel. One or more rubber bearing isolators are incorporated between the hopper and the mandrel to significantly reduce the amount of vibration transmitted to the hopper. When filled, the hopper is quite heavy, approximately 16,000 pounds, and if not isolated from the mandrel a significant amount of energy would be lost in vibrating the hopper, reducing the energy transmitted to the mandrel.

There is provided a very sturdy top of mandrel connection point for connection of the vibratory clamp. This is an improvement on the bolted plate connection known in the prior art.

There is provided a seal between the hopper and the mandrel which prevents the gravel from leaking out of the mandrel and is made of rubber molded to the outside of the mandrel, which reduces the energy transmission between the hopper and the mandrel.

The mandrel of the present invention does not contain any upward flow restrictor mechanism inside the bottom end of the mandrel to prevent gravel from upward movement into the mandrel during driving. The system of the present invention uses the sacrificial plate at the bottom of the mandrel widely known in the prior art, or relies on the stone gate at the upper end of the mandrel to prevent the upward flow if gravel during the driving process.

It will be appreciated by those skilled in the art that other variations of the preferred embodiment may also be practised without departing from the scope of the invention.

Claims

1. An apparatus for forming compact aggregate columns, the apparatus comprising: an aggregate materials hopper having a top opening and a bottom opening; a hollow mandrel adapted to be driven into the ground, its upper end passing through the bottom opening in the hopper, and having an enlarged diameter bottom section and an aggregate receiving opening; connection means between the hopper and the mandrel; flow control means near the upper end of the mandrel, for controlling the flow of aggregate from the hopper into the mandrel; soil densification means disposed along the length of the mandrel; a vibratory hammer for inserting and removing the mandrel into the ground; and monitoring and control means.

2. The apparatus of claim 1, wherein the connection means comprises one or more rubber bearing isolators disposed between the mandrel and the hopper, and a rubber seal between the mandrel and the hopper.

3. The apparatus of claim 2, wherein the one or more rubber bearing isolators comprise 4 isolators.

4. The apparatus of claim 2, wherein the one or more rubber bearing isolators comprise 8 isolators.

5. The apparatus of claim 2, wherein the rubber seal encircles and is moulded to the mandrel,

6. The apparatus of claim 1, wherein the flow control means comprises a stone gate convertible between an open position to allow aggregate flow from the hopper to the mandrel, and a closed position to prevent aggregate flow from the hopper to the mandrel.

7. The apparatus of claim 1, wherein the soil densification means comprise one or more collars encircling the mandrel, each collar having an outer circumference greater than the mandrel circumference.

8. The apparatus of claim 7, wherein the one or more collars are disposed at spaced intervals along the length of the mandrel.

9. The apparatus of claim 7, wherein the one or more collars are disposed at intervals of 5 feet along the length of the mandrel.

10. The apparatus of claim 1 , wherein the vibratory hammer is attached to a vehicle.

11. The apparatus of claim 10, wherein the monitoring and control means includes hydraulic systems monitored and controlled from the cab of the vehicle.

12. An apparatus for forming compact aggregate columns, the apparatus comprising: a materials hopper having a top opening and a bottom opening; a hollow mandrel adapted to be driven into the ground, its upper end passing through the bottom opening in the hopper, and having an enlarged diameter bottom section and an aggregate receiving opening; between 4 and 8 rubber bearing isolators disposed between the mandrel and the hopper, and a rubber seal encircling and moulded to the outer circumference of the mandrel; a stone gate convertible between an open position to allow aggregate flow from the hopper to the mandrel, and a closed position to prevent aggregate flow from the hopper to the mandrel; one or more collars encircling the mandrel disposed at spaced intervals along the length of the mandrel, each collar having an outer circumference greater than the mandrel circumference; a vibratory hammer attached to a vehicle for inserting and removing the mandrel into the ground; and a monitoring and control system in the cab of the vehicle.

13. A method for preparing compacted aggregate columns comprising the steps of: filling a hollow mandrel with aggregate from a hopper above the mandrel through an opening in the side of the mandrel; closing a stone gate near the upper end of the mandrel to prevent aggregate from rising in the mandrel; driving the mandrel into the ground with a vibratory hammer, wherein driving the apparatus into the ground displaces the soil outwardly and downwardly from the mandrel to create a hole extending downwardly from the ground surface, and compacts aggregate present in the hole into an aggregate column; withdrawing the mandrel, thereby allowing aggregate to exit the mandrel into the hole; opening the stone gate to allow more aggregate to fill the mandrel; and repeating the above steps until a compacted aggregate column of a desired length is achieved.