US20050129467A1

US20050129467A1 - Drop mass compaction of soil

Info

Publication number: US20050129467A1
Application number: US11/019,902
Authority: US
Inventors: Eric Cook
Original assignee: Compaction Technology Soil Ltd
Current assignee: Compaction Technology Soil Ltd
Priority date: 2002-07-01
Filing date: 2004-12-22
Publication date: 2005-06-16

Abstract

A soil compaction apparatus includes a drop mass soil compactor having a mass and a lift assembly that repeatedly raises the mass above a soil surface and then drops it to apply impacts to the soil surface. The apparatus also has a sensor arranged to provide periodic indications of one or more instantaneous properties of the soil. The apparatus also includes a controller that received a signal from the sensor and controls the lift assembly to attain desired, pre-programmed soil properties based on a number of impacts, energy imparted to the soil at each impact or frequency if impacts of the mass.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No. PCT/IB2003/002578, filed Jul. 1, 2003, which was published in the English language on Jan. 8, 2004, under International Publication No. WO 2004/003301 A1, and the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to methods and apparatus for achieving drop mass soil compaction and for monitoring soil properties.
There are numerous applications where it is necessary to compact a relatively small area of soil but where the use of conventional soil compaction machinery, typically employing rollers of one type or another, is inappropriate. One important example is in the compaction of soil adjacent bridge abutments, where limited space makes it impossible to compact with conventional large rollers or other machines. Another example is in the compaction of soil in relatively narrow trenches for pipes, strip foundations or the like. Yet another example is in road maintenance where local failure of a section of a road may have taken place in a relatively small area.
Although small vibratory rollers and impactors are available and are widely used in such applications, the level of soil compaction and the depth of compaction influence which can be achieved with such devices is limited. The result is often that undue settlement and or structural failure can take place after a relatively short period of time.
It has been proposed to use drop mass soil compaction to achieve compaction of soil in the kind of situations envisaged above. In drop mass compaction, a substantial mass is repeatedly raised and dropped to apply impacts to the soil surface for the purposes of compacting it. For more detail about one known drop mass soil compactor, reference may for instance be made to International Patent Application Publication No. WO 00/28154 A1 (Cook, et al.).
Although the principles of drop mass soil compaction are sound, it is felt that greater control over the compaction process is required to enable this type of compaction technology to achieve its full potential.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided a method of compacting soil. The method includes repeatedly raising a mass above the soil surface and then dropping the mass to apply impacts to the soil surface, from the impacts on the soil surface periodically deriving indications of one or more instantaneous properties of the soil, and controlling the number of subsequent impacts and/or the energy imparted to the soil at each impact and/or the frequency of the impacts, in accordance with the indicated property or properties, in order to achieve in the soil one or more predetermined properties.
The instantaneous properties for indications are periodically derived may include, for instance, mechanical properties such as the stiffness or strength of the soil or the bearing capacity thereof. Alternatively, indications may periodically be derived for a property such as total or incremental soil settlement.
Preferably, a controller is used to vary one or more of the above parameters automatically to achieve the predetermined mechanical property or properties. The controller may include a programmable logic controller (PLC) which is pre-programmed with one or more predetermined mechanical properties to be attained.
In a preferred embodiment of the method, a sensor is associated with the mass to provide the necessary indications. The output of the sensor is fed to the controller. This sensor may be, for instance, an accelerometer which is arranged to monitor the deceleration of the mass at each impact and which is arranged to output signals related to, for instance, the instantaneous stiffness of the soil to the controller.
According to another aspect of the invention, there is provided a soil compaction apparatus that includes a drop mass soil compactor. The drop mass soil compactor has a mass and a lift assembly that repeatedly raises the mass above the soil surface and then drops the mass to apply impacts to the soil surface. The apparatus also includes a sensor arranged to provide periodic indications of one or more instantaneous properties of the soil, and a controller responsive to the indications provided by the sensor in order to control the number of subsequent impacts and/or the energy imparted to the soil at each impact and/or the frequency of the impacts, thereby to achieve in the soil one or more predetermined soil properties.
As indicated previously, the controller may include a PLC which is pre-programmed with one or more predetermined soil properties which it is desired to achieve and which is arranged to control one or more of the variable parameters listed above.
The apparatus of the invention may also include a position monitor, typically a global positioning system (GPS), which is interfaced with the controller to enable the controller to exercise control over the compaction of soil in accordance with a geographical plan.
The apparatus of the invention may be vehicle mounted and may be movable from a transportation orientation in which it is carried on the vehicle to an operative position in which it is located alongside the vehicle.
According to yet another aspect of the invention, there is provided a method of measuring one or more physical soil properties on a site. The method includes providing on the site a drop mass soil compactor that has a mass and a lift assembly that raises the mass above the soil surface and then drops the mass to apply an impact to the soil surface. The method also includes measuring one or more instantaneous physical properties of the soil from the impact applied to the soil surface by the mass.
Still further, the invention provides an apparatus that measures one or more physical soil properties on a site. The apparatus includes a drop mass soil compactor that has a mass and lift assembly that raises the mass above the soil surface and then drops the mass to apply an impact to the soil surface. The apparatus also includes a sensor that measures from the impact applied by the mass, one or more instantaneous physical properties of the soil.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
In the drawings:
FIG. 1 shows a side elevational view of a vehicle mounted drop mass soil compaction apparatus according to this invention, the apparatus being at an operative orientation; and
FIG. 2 shows a perspective view of the apparatus of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The drawings illustrate a drop mass soil compaction apparatus 10 according to this invention. In this embodiment, the apparatus 10 is mounted on the chassis 12 of a truck 14, but it will be understood that the apparatus could equally well be mounted on a wheeled trailer chassis drawn by a truck or tractor, or on a track-type self-driven vehicle or trailer.
The apparatus 10 includes a lift assembly 23 that raises and drops a compaction mass 28. The lift assembly 23 includes a frame 16 mounted for side to side traversing movement on a laterally extending traverse beam 18 which is pivoted to the rear end of the truck 14 at a pivot point 20. The frame 16 includes a pair of upright support members 22 supporting a rearwardly directed suspension member 26. The rearward end of the member 26 is located vertically above the compaction mass 28 and a hydraulic cylinder 30 acts between the suspension member 26 and the mass as illustrated. Extending vertically from the mass 28 are guide rods 32 which slide in guide cylinders 34 connected to the members 22 by inclined braces 35.
A bracket 36 connected to the support members 22 is engaged in slidable manner with the traverse beam 18 in order to achieve the side to side traversing movement of the frame as mentioned above. The apparatus 10 includes a drive (not shown) for driving the frame 16 from side to side. The drive could take any one of a number of conventional forms. It may, for instance, be a chain and sprocket drive, at least some components of which are mounted within the bracket 36, and/or the traverse beam 18.
The drop mass soil compactor apparatus 10 is shown at an operative orientation with the mass 28 resting on the ground. The compactor apparatus 10 will operate at this orientation during soil compaction activities. When the compactor apparatus 10 is to be transported from one location to another, hydraulic cylinders 38 acting between lugs 40 extending from the traverse beam 18 and the chassis 12 are contracted to pivot the frame 16 to a prone, generally horizontal orientation on the chassis 12.
In use, soil beneath the mass 28 is compacted by the lift assembly 23 repeatedly lifting the mass 28, by contracting the cylinder 30, and then dropping the mass 28 to apply impacts to the soil surface.
Attached to the mass 28 is a sensor 42 or specifically an accelerometer 42, the output of which is fed to a controller such as a programmable logic controller (PLC) 44. The PLC 44 is shown diagrammatically in FIG. 1 as a remote component, but it will be understood that in practice the PLC 44 and other ancillary equipment will form an integral part of the apparatus 10 itself. The controller or PLC 44 may include other ancillary control circuitry without departing from the invention.
As the mass 28 impacts on the soil, the deceleration which the mass 28 undergoes, as measured by the accelerometer 42, provides an indication of the instantaneous stiffness of the soil, and this in turn provides a reliable, real time indication of the level of compaction of the soil. In this example, the PLC 44 is pre-programmed for the apparatus 10 to achieve in the soil a predetermined level of soil stiffness. The PLC 44, in turn, automatically controls various parameters of the compaction operation. For instance, the PLC 44 may control the impact energy applied to the soil at each impact. This is achieved by varying the height to which the mass 28 is raised prior to each blow, and accordingly, the potential energy which is stored and which is available for delivery to the soil, by controlling the hydraulic operation of the cylinder 30 and/or by means of appropriate mass position sensors to sense the position of the mass.
By way of example, the impact energy which is applied may be controlled by the PLC 44 to have the same value for a number of impacts, then a different value for a succeeding series of impacts, and so on. Alternatively, the impact energy may be varied from impact to impact or the same energy level may be maintained throughout the compaction operation.
The PLC 44 may also control, in accordance with its program, the number of blows applied to the soil. As yet another possibility, the PLC 44 may control the frequency of the impacts, in this case by varying the duration of each impact cycle and/or by varying the time lapse between cycles. Although not specifically mentioned, other variable parameters may also be controlled instantaneously by the PLC 44.
In the drawings, the numeral 50 indicates a flexible cable tray which carries signal transmitting wiring and/or hydraulic hoses for the cylinder 30 and its ancillary equipment such as hydraulic pumps and so on. It will also be understood that in practice a hydraulic power pack (not illustrated) will be mounted on the chassis 12.
In practice, the soil compaction apparatus 10 described above may be used to compact soil at various locations on a site, or to compact the entire site. It will be understood that the vehicle 14 can be driven from one location to another on the site to enable the soil compaction apparatus to be used to compact different regions of the site. At each stationary location of the vehicle 14, the apparatus 10 can be used to compact a limited strip of soil, this being permitted by the ability of the frame 16 to traverse from side to side on the traverse beam 18 and the maneuverability of the vehicle 14.
The soil compaction apparatus 10 described above can also be interfaced with a positioning system, typically a global positioning system (GPS), so that indications of soil stiffness can be correlated with geographical position. This in turn enables a site plan to be derived which gives real time information related to the levels of soil compaction at different locations on the site. It will be understood that integrated information regarding geographical position and level of soil compaction can be stored digitally and/or represented graphically to provide a substantially complete analysis of the state of soil compaction across a site or selected regions thereof.
Although mention has been made of compacting soil regions over a site, the principles of the invention are equally applicable to compaction of single, small areas where a specific level of compaction is required. A typical example here would be soil compaction adjacent a fixed structure such as a bridge abutment or building.
Also, although specific mention has been made of monitoring soil stiffness and of varying the operating parameters to achieve a desired level of soil stiffness, it is within the scope of the invention for the apparatus 10 to monitor a variety of other soil properties and to control the operating parameters to achieve one or more specific, desired properties. The apparatus 10 could be arranged to monitor any one or more of a number of other mechanical soil properties other than stiffness, for instance soil strength and/or bearing capacity, and to control the operating parameters to achieve desired properties. Still further the apparatus could be arranged to monitor a soil property such as total soil settlement at each point in time or incremental soil settlement, i.e., the amount of soil settlement in a given period of time or as a result of one or more impact blows.
Instead of an accelerometer 42 to monitor any particular soil property, in the above example the soil stiffness, any other suitable form of sensor 42 could also be used. Other viable forms of sensor 42 include a velocity sensor to measure the velocity of the mass during impact, a displacement sensor such as a displacement transducer to measure soil settlement or a force or pressure transducer to measure the force or pressure applied to the soil surface by the mass at impact.
As mentioned previously, the principles of the invention can be used not only to achieve and control soil compaction, but also to measure instantaneous soil properties on a site. In this role, the apparatus 10 described above may be arranged to raise and drop the mass 28 only once at each location on the site where a measurement of instantaneous soil properties is required. The monitoring equipment, including the accelerometer 42 and/or additional transducers described above, are then arranged to provide, at each such location, a measurement of a selected soil property, such as stiffness, settlement and so on. As in the case of the apparatus described above, the apparatus in this role may be interfaced with a geographical positioning system such as a GPS, thereby to provide soil property measurements for different site locations. The information obtained in this way may, with appropriate signal processing equipment and associated software, be presented in the form of a map, contoured or otherwise, or in tabular form. This application may for instance be employed by soils engineers to assist them in performing site certification functions.
It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.

Claims

1. A method of compacting soil comprising:

repeatedly raising a mass above the soil surface and then dropping the mass to apply impacts to the soil surface;

from the impacts on the soil surface periodically deriving indications of one or more instantaneous properties of the soil; and

controlling at least one of the number of subsequent impacts, energy imparted to the soil at each impact and frequency of the impacts, in accordance with the indicated property or properties, a sensor being associated with the mass to provide the periodic indications and an output of the sensor is fed to a controller including a programmable logic controller (PLC) that is pre-programmed with one or more predetermined soil properties to be attained,

the PLC operating automatically to vary at least one of the number of impacts, the energy imparted to the soil at each impact and the frequency of the impacts to achieve the predetermined soil property or properties.

2. The method according to claim 1, wherein indications are periodically derived of instantaneous mechanical or physical properties of the soil.

3. The method according to claim 2, wherein the mechanical properties of the soil include at least one of the stiffness of the soil, strength of the soil and the bearing capacity of the soil.

4. The method according to claim 1, wherein indications are periodically derived from at least one of total soil settlement and incremental soil settlement.

5. The method according to claim 1, wherein the sensor is an accelerometer associated with the mass and the accelerometer is configured to output signals related to the deceleration of the mass at each impact to the PLC.

6. A soil compaction apparatus comprising:

a drop mass soil compactor having a mass and means for repeatedly raising the mass above a soil surface and then dropping it to apply impacts to the soil surface; and

a control means having a programmable logic controller (PLC) which is pre-programmed with one or more predetermined soil properties to be attained and a sensor associated with the mass to provide periodic indications of one or more instantaneous properties of the soil, the PLC being arranged to respond to the indications provided by the sensor and to control at least one of a number of impacts, energy imparted to the soil at each impact and frequency of impacts of the mass, to thereby achieve in the soil the one or more predetermined soil properties.

7. The apparatus according to claim 6, further comprising:

a geographical position monitor which is interfaced with the PLC to enable the control means to exercise control over the compaction of soil in accordance with a geographical plan.

8. The apparatus according to claim 7, wherein the geographical position monitor is a global positioning system (GPS).

9. The apparatus according to claim 6, wherein the sensor is an accelerometer arranged to output signals related to the deceleration of the mass at each impact to the PLC.

10. The apparatus according to claim 6, wherein the apparatus is configured to be vehicle mounted.

11. The apparatus according to claim 10, wherein the apparatus is configured to be movable from a transportation orientation in which the apparatus is carried on the vehicle to an operative position in which the apparatus is located alongside the vehicle.

12. A soil compaction apparatus comprising:

a drop mass soil compactor having a compaction mass and a lift assembly, the lift assembly being coupled to the compaction mass and being configured to repeatedly raise the compaction mass above a soil surface and drop the compaction mass onto the soil surface;

a sensor having an output, the sensor detecting at least one of conditions of the mass and conditions of the soil; and

a controller that receives the output from the sensor and controls the lift assembly, the controller controlling at least one of a number of impacts, energy imparted on an impact and frequency of impacts of the compaction mass.