Excavating – Ditcher – Condition responsive
Reexamination Certificate
2001-03-02
2002-05-14
Batson, Victor (Department: 3671)
Excavating
Ditcher
Condition responsive
C037S905000
Reexamination Certificate
active
06385868
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an excavating device using a jet liquid to break up and mix with the ground such that the mixture can be discharged.
2. Discussion of the Background
EP-A-0 890 708 describes an excavating device which has a plurality of jet excavating units adjoining one another. In the jet excavating unit a rotating jet device is provided which sprays high-pressure jet liquid onto the ground which is to be excavated, which as a result is broken down. While the jet excavating device is being pulled through the ground in the excavation direction, the channel behind the jet excavating unit, which is formed by the jet device, is filled with a hardenable material. In this way, a wall is formed in the ground. Any desired shape can be selected for the channel to be formed in the ground, by arranging a number of jet excavating units in a desired way with respect to one another.
The known excavating device provides considerable drawbacks in relation to the way in which the excavation is controlled. Because of the increase in earth pressure as the depth in the ground increases, the known excavating device, given a relatively homogeneous soil composition, tends to tilt forwards, since in an excavating device of this nature which extends over a depth, the lower part will be subject to a greater resistance from the soil to be excavated than the part being above it. Consequently, the displacement of the lower part tends to lag behind the displacement of the upper part.
The rotating jet device has the drawback of including a plurality of moving parts, for example a motor and bearings, which are susceptible to faults and wear. Moreover, while the wall is being formed, the jet excavating device is not accessible for maintenance or repair purposes. Consequently, the excavating device is unreliable. Another complication is that under natural conditions the soil composition almost always varies in the excavation direction and/or over the cross section of the channel to be excavated, in particular when excavating under a slope, where it is highly probable that it will be necessary to cut through various soil strata. The jet devices of one or various jet excavating units are then simultaneously cutting through different types of soil, for example clay and sand, which exhibit different cohesion properties and thus break down under different jetting conditions. The variations in the nature of the soil cannot be predicted accurately, not even if an extensive and detailed soil analysis is carried out. The resistance to which the plurality of mutually adjacent jet excavating units are exposed by different types of soil during excavation varies, for example as a result of a first jet excavating unit excavating the soil to be excavated in front of it more quickly and more easily than a second jet excavating unit of the same excavating device. Consequently, the first jet excavating unit may excavate too much soil, with the result that the stability of the excavation front is jeopardized. Moreover, settlement occurs, leading to subsidence at ground level.
Another drawback of the known excavating device with a plurality of mutually adjacent jet excavating units is that obstacles which are encountered during excavation (for example unexploded bombs or rocky objects which cannot be cut up) are difficult to remove. It is usually impossible to move the obstacle out of the path of the channel which is to be excavated, and consequently the excavation process has to be interrupted and the obstacle has to be dug out of the path of the channel to be excavated from ground level, since the excavation front in front of the excavating device is not accessible in any other way. This is time-consuming and expensive and also causes problems for the environment above ground level. In the particular case in which the obstacle is displaced out of the path of the channel to be excavated, this may entail high local forces which cause damage to the excavating device.
SUMMARY OF THE INVENTION
The present invention provides an excavating device which to a large extent eliminates the drawbacks outlined above.
Accordingly, the present invention advantageously provides an excavating device for forming a channel of predetermined cross section in the ground, in an excavation direction, comprising an assembly of jet excavating units, which together define the cross section of the channel and are each provided with at least one jet device which can be operated with jet liquid. The jet liquid, such as water, which flows out of the jet devices is directed at the relatively soft ground which is to be excavated and includes, for example, of clay, sand or peat or a combination thereof. As a result, the ground is broken up and mixed with the jet liquid, after which the mixture obtained can be discharged. The excavating device has at least one sensor which is connected to at least one of the jet excavating units, for measuring a force which is exerted on the at least one jet excavating unit by the ground substantially parallel to the excavation direction, and control means for controlling the excavation by the excavating device on the basis of the force measured by the at least one sensor.
The excavating device according to the invention has the advantage that the force from the jet excavating unit is transmitted to the particles of soil in part via water pressure and in part mechanically, rendering the use of an excavating liquid superfluous. This saves on costs for the liquid and facilities required therefor and also provides excavated soil which can be reused more easily.
Another advantage of the invention is that the excavation process carried out by a system of jet excavating units can be successfully managed and better control of the excavating device can be obtained. The excavation carried out by the individual jet excavating units can be activated separately on the basis of forces measured locally in the cross section of the channel, with the result that the excavating device can move along a desired path accurately and under control, for example in order to ensure that the assembly of jet excavating units run simultaneously.
It is also possible, in the event of variations in the nature of the soil which are already known, for example from soil analysis, for the level of force to be locally adjusted according to a specific nature of the soil.
Moreover, with the excavating device according to the invention there is no need to carry out the measurements of the flow rate and the concentration of the soil mixture to be discharged by each excavating unit, since a force measurement is carried out instead of having to keep up to date with the soil balance. The fact that it is no longer necessary to measure the concentration of the soil mixture in particular yields considerable economic and safety benefits.
Since the excavation by the jet devices of the excavating device according to the invention is adapted on a local basis, i.e. for each jet excavating unit or for each jet device, to the desired or possible advancement, the use of energy and jet liquid is minimized, resulting in economic and environmental advantages.
In a preferred embodiment of the excavating device according to the invention, the control means are adapted to set a flow rate of the jet liquid used in at least one of the jet devices. In this way, it is easy to set the excavation by the jet device. Preferably, the flow rate of the at least one jet device of the jet excavating unit connected to the at least one sensor is set. This makes the control means simple to implement, since there is no need to take into account the possibility of different jet excavating units influencing one another. Preferably, the control means are adapted to increase or reduce the flow rate of the jet liquid of the at least one jet device in the event of an increase or decrease, respectively, in the force measured by the at least one sensor. This has the advantage that the resistance which the excavating device is subjec
Koene Rogier Cristian
Koppert Frits-Jan
Van Den Bout Rokus
Van Zandwijk Cornelius
Batson Victor
Heerema Holding Construction Inc.
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