EP2484838A1 - Excavator method - Google Patents

Abstract

The method of removing sandy and/or silt deposits on a bottom surface of water using hydropneumatic methods such as water injection and suction dredging, comprises exposing the force reducing the viscosity of the deposit on the bottom surface before the application of hydropneumatic removal process, where the force acting on the deposit surface causes vibration and shear stress on the deposit, converting the treated deposit in a fluid density layer using a water-injection process, removing the deposit by a suction dredge method, and partially separating the removed material. The method of removing sandy and/or silt deposits on a bottom surface of water using hydropneumatic methods such as water injection and suction dredging, comprises exposing the force reducing the viscosity of the deposit on the bottom surface before the application of hydropneumatic removal process, where the force acting on the deposit surface causes vibration and shear stress on the deposit, converting the treated deposit in a fluid density layer using a water-injection process, removing the deposit by a suction dredge method, partially separating the removed material from the aspirated water, and recycling the separated water by suction hopper dredging. The sand/silt deposit exhibits thixotropic properties and a linear particle size distribution in the sand fraction, and comprises platelet-like particles. An independent claim is included for an apparatus for removing sandy/silty soil deposits on surfaces of water bodies.

Description

The invention relates to a method and an apparatus for removing sandy / silty deposits on ground surfaces of waters by means of hydropneumatic measures.

In many waters, in particular on busy streams, the navigation channels are to be recessed to more than 14 m asl due to the navigability of modern container ships. In connection with this, costly and expensive dredging work is also necessary in the adjacent ports in order to enable tide-independent shipping traffic.

It has long been preferred for deepening and maintenance dredging two hydropneumatic processes, which are relatively inexpensive and environmentally friendly, namely on the one hand water injection method and on the other hand suction dredger method.

In the water injection methods, water is injected under pressure into the surface layer of the waterbed to be removed, in order to reduce the viscosity of this layer without destroying it by fluidization. The layer thus treated (also referred to as a dense layer) can flow off over a suitable level difference at the bottom of the water. For example, a detailed description of water injection procedures is available Meyer-Nehls in "The Water Injection Method: Results from the Dredging Material Investigation Program", Issue 8, October 2000, FHH Hamburg, ISSN 0177-1191 , A recent publication that also deals with injection procedures is DE-10 2009 015 203 A1 , Injection methods are particularly suitable for removing silt and similar deposits.

Suction dredger methods are suitable for all types of deposits and are variously described above. Popular today are those methods in which the sucked mixture of solid and liquid components is partially separated, so that a portion of the sucked water can be returned to the water (Suction Hopper Dredging).

Dredging with the water injection device (WI method) and the hopper dredger reach the limits of their performance especially in sandy / low silty sediments, with a linear grain distribution (especially of the sand fraction). By "sandy / silty" in the context of this description is meant the presence of sand together with clay particles.

In principle, in both ("hydropneumatic") method, a rearrangement of the sediments from a partially stable position by water pressure or by water suction. In the water injection process, the sediment is released by means of water pressure of 1.5 to 3 bar via nozzles from the bottom and rearranged by naturally prevailing gradient or currents.
With the hopper dredger, the sediments with the surrounding water are pumped from the bottom into the ship's hold by pump suction. There, the transport water is largely separated from the sediments by sedimentation in the hull and returned to the water. The remaining sediments are transported by the dredger and either dumped at one point in the water or transferred to land on rinse fields.

While in silty (poorly sanded) sediments the rearrangement is almost effortless in terms of times of use, however, the time spent on special silty sands is large in terms of the effect and thus the cost is unduly high.

Such sediments with essentially linear grain distribution of silty fine sands often occur in waters because of the naturally occurring longitudinal classification. They are difficult to mobilize with the known hydropneumatic process mentioned above.

For example, in the case of dredging in the port of Cuxhaven, it was found that a sediment thickness of 10 cm could only be relocated in the areas mentioned with the WI method after 17 times very slow driving. Due to the high time required high costs. These can reach between 700.00 € / h and 1.200,00 € / h.
Due to the longer processing times more suspended matter is generated from the density streams of the transported sediments, which should be avoided for ecological reasons.
In addition, the shipping traffic is hampered more than necessary by the dredging, which statistically leads to a greater risk of accidents.

Against this background, it is an object of the invention to provide a method and an apparatus by means of which difficult-to-evacuate sediments can be removed faster, safer and more ecologically without the disadvantages of the known methods.

The solution of these and other objects is achieved by the inventive method according to the appended independent patent claims, and the inventive device according to the appended independent device patent claim.

The subclaims define advantageous and preferred embodiments of the invention.

According to the invention, a method is defined for better mobilization of fine-grained, sandy and / or silty sediments in bodies of water during the rearrangement, which makes use of the thixotropic properties of such sediments.

In soil science, thixotropy refers to a state in fine-grained, mostly sandy / clayey sediments in which reversible viscosity differences occur due to mechanical stress. Typical is a change from solid to liquid by vibration with subsequent return to the solid state. Crucial for these properties are grain size composition and type of sediment forming substances. Mostly it is platelet-shaped clay minerals, which - against a microscopic scale - are initially supported against each other in all spatial directions. When shocked, the structure collapses like a house of cards, the mineral platelets are paralleled and begin to slip past each other under the influence of gravity due to the lack of internal adhesive forces. Thixotropy has also been observed with aqueous fine sands (quicksand).

A significant influence on the reduction of the viscosity, in particular with clay-containing sands, has been shown in the comparative laboratory experiment to be the linear grain distribution of the fine sands. The friction within the grain packets is reduced by induced water.
Essentially, there is a dependency on the Reynolds number, which is defined by the quotient of acceleration work and friction work in liquids: $$\mathrm{acceleration\; work}\mathrm{/}\mathrm{friction\; work}\mathrm{=}\mathrm{0}\mathrm{.}\mathrm{5}{\mathrm{x\; \delta \; x\; V\; xv}}^{\mathrm{2}}\mathrm{:}\left(\mathrm{F\; x\; \eta \; x\; L\; x\; dv}\mathrm{/}\mathrm{dz}\right)\mathrm{=}\mathrm{vx\; \delta \; x\; X}\mathrm{:}\mathrm{\eta }\mathrm{=}\mathrm{vx\; X}\mathrm{:}\mathrm{\upsilon }\left[\mathrm{1}\right]$$

The Reynolds number provides information about the flow state. Physically important is the boundary layer analysis of the solid-liquid phase. Within longitudinally flown walls (particle walls), strong frictional forces act in a very thin layer, the boundary layer or the friction layer. $${\mathrm{K}}_{\mathrm{R}}\mathrm{=}\mathrm{\eta \; x\; F\; x\; dv}\mathrm{/}\mathrm{dz}\left[\mathrm{N}\right]$$

The boundary layer thickness is essential for the frictional forces that must be expended when transporting the sediments. Due to the nature of the mechanical influence on the thixotropic state of the sediments, according to the invention, the K _{R is} at times substantially reduced in size.

The layer thickness is calculated as follows: $${\mathrm{D}}_{\mathrm{x}}\mathrm{=}\mathrm{3}\mathrm{.}\mathrm{02}\mathrm{xx}\mathrm{:}\left({\mathrm{re}}_{\mathrm{x}}\right)\mathrm{½}\left[\mathrm{m}\right]\mathrm{;}\mathrm{1}\mathrm{=}\mathrm{3}\mathrm{.}\mathrm{02}{\left(\mathrm{\eta \; x\; X}\mathrm{:}\left\{\mathrm{\rho \; x\; \upsilon }\right\}\right)}^{\mathrm{0}\mathrm{.}\mathrm{5}}\mathrm{=}\mathrm{3}\mathrm{.}\mathrm{02}\mathrm{xx}\mathrm{:}{\left(\mathrm{re}\right)}^{\mathrm{0}\mathrm{.}\mathrm{5}}\left[\mathrm{m}\right]$$

Since the pressure drops occurring at the boundary layers of the sediment particles reduce the friction, the time-limited thixotropic flow behavior is favored. This reduces the pressure required for the sediments to be mobilized. $$\mathrm{Ap}\mathrm{=}\mathrm{\lambda \; x\; L}\mathrm{/}\mathrm{dx}\mathrm{0}\mathrm{.}\mathrm{5}{\mathrm{x\; \rho \; xv}}^{\mathrm{2}}\left[\mathrm{N}\mathrm{/}{\mathrm{m}}^{\mathrm{2}}\right]$$

In principle, the kinematic and dynamic viscosity of the semi-stable sediment is significantly reduced in the short term by targeted mechanical forces acting on the thixotropic medium before the hydropneumatic action by the aforementioned dredging method on the sediment.
The mechanical force is preferably applied by shearing and shaking on the sediment surface. In order to optimize the use of energy, a resonance is sought in the relocated sediments. The optimal parameters can be easily determined by preliminary tests.
When shaking the pore water in the sediment during the transmission of power into the depth of the sediment layer with.
The frequently occurring stabilizing corrugation of the sediment surface is dissolved and the moment of inertia of the recumbent is minimized.

The hydrostatic pressure of the overlying water body, currents and influence of the physical boundary layers act in the reduction of the

Stability and persistence of the sediments to be relocated reduce the energy input.

In summary, shaking and shearing of thixotropic sediments temporarily and partially reduces their viscosity, thereby making it faster and more energy efficient to remove these deposits, which are difficult to remove by conventional excavator techniques.

While it is conceivable to form a device for the application of the invention as a separate device, the technical device for reducing the viscosity is preferably installed on water injection dredgers, hopper dredgers and tractors. It consists of, for example, a beam-like lowerable device, which is up to 12 m long and is carried across the direction of travel of the ships on the sediment base lying. Through this device, the mechanical energy is transmitted via vibrators, shaving heads, vibrators and eccentrics to the thixotropic sediment. The respective use of the aforementioned various devices depends on the sediment quality to be processed and is selected according to the best efficiency.

The device is z. B. in the water injection process in the machine direction, and approximately parallel to the water injection bar and reduces the viscosity. Hydrodynamics is used to transfer the sediment into a density stream via the following injection nozzles, which is then transferred to the flow or slope.
An advantage of this combination method is that, compared to the known WI and Hopper method, considerably more thixotropic sediment per unit time can be mobilized.

To comply with the legal requirement of the Water Framework Directive (EU level; WFD: Conservation of waters despite their use in good condition; the replacement measures) devices are preferably attached to the plant at the bottom to scare away the macroorganisms.

glossary

Impact number: term from physical chemistry; a mathematical formula by which the frequency of two or more chemical reactants can be calculated.

• p = Druck [N/m²]
• V = Volumen [m³]
• n = Anzahl [1]
• R = molare Gaskonstante [8,314426..J/mol ° K]
• T = Temperatur in ° Kelvin
• Re = Reynoldszahl [1]
• δ = Dichte [kg/m³]
• υ= kinematische Viskosität [m³/s]
• η = dynamische Viskosität [Ns/m²]
• v = Geschwindigkeit [m/s]
• X, L = maßgebliche Längen [m]
• λ= Strömungszustand [1]
• d = Durchmesser [m]

Mathematical formula symbols:

• p = pressure [N / m ² ]
• V = volume [m ³ ]
• n = number [1]
• R = molar gas constant [8.314426..J / mol ° K]
• T = temperature in ° Kelvin
• Re = Reynolds number [1]
• δ = density [kg / m ³ ]
• υ = kinematic viscosity [m ³ / s]
• η = dynamic viscosity [Ns / m ² ]
• v = speed [m / s]
• X, L = relevant lengths [m]
• λ = flow state [1]
• d = diameter [m]

Claims (14)

Method for removing sandy and / or silty deposits on ground surfaces of water bodies by means of hydro-pneumatic processes, in particular water injection, suction dredging or the like,
characterized in that subjecting the sandy / silty deposit to be removed, prior to application of the hydropneumatic removal process, to a force which reduces the viscosity of the deposit. A method according to claim 1, wherein the action of force over the deposition surface is effected by mechanical stressing of the deposit, in particular by shaking and shearing stress. The method of claim 1 or 2, wherein the force is applied in sufficiently short time interval, in particular immediately before the application of the hydropneumatic process. A method according to any one of claims 1-3, wherein the sandy / silty deposit has thixotropic properties. Method according to one of claims 1-4, wherein the sandy / silty deposit also comprises clays, in particular with platelet-shaped particles. Method according to one of claims 1-5, wherein the sandy / silty deposit has a substantially linear particle size distribution, in particular in the sand content. Method according to one of claims 1-6, wherein the deposit is treated in accordance with the claim and then converted by means of a water-injection process into a sufficiently flowable density layer. Method according to one of claims 1-6, wherein the deposit according to any one of claims 1-6 treated and then removed by means of a suction dredger method. The method of claim 8, wherein the removed material is at least partially separated from the aspirated water and the separated water is returned (suction hopper dredging). Device for removing sandy / silty deposits on the bottom surfaces of bodies of water, in particular according to one of claims 1 to 9, with means for the mechanical application of force to the surface of the deposit to be removed by hydropneumatic means. Apparatus according to claim 10, wherein the means comprise vibrators, shaving heads, vibrators, eccentrics and the like. Apparatus according to claim 10 or 11, which is designed as a watercraft, in particular as a ship, wherein the means for the action of force on the water bottom can be lowered. Apparatus according to claim 12, comprising a transversely extending, lowerable support to which the devices are attached. Apparatus according to any one of claims 10 to 13 further provided with means for applying a hydro-pneumatic removal process.