WO1999063164A1 - Procede et appareil pour consolider des lits sedimentaires - Google Patents

Procede et appareil pour consolider des lits sedimentaires Download PDF

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Publication number
WO1999063164A1
WO1999063164A1 PCT/GB1999/001727 GB9901727W WO9963164A1 WO 1999063164 A1 WO1999063164 A1 WO 1999063164A1 GB 9901727 W GB9901727 W GB 9901727W WO 9963164 A1 WO9963164 A1 WO 9963164A1
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WO
WIPO (PCT)
Prior art keywords
bed
layer
water
low permeability
sedimentary
Prior art date
Application number
PCT/GB1999/001727
Other languages
English (en)
Inventor
Gilliane Christine Sills
Original Assignee
Isis Innovation Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Isis Innovation Limited filed Critical Isis Innovation Limited
Publication of WO1999063164A1 publication Critical patent/WO1999063164A1/fr

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Classifications

    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D3/00—Improving or preserving soil or rock, e.g. preserving permafrost soil
    • E02D3/02—Improving by compacting
    • E02D3/10—Improving by compacting by watering, draining, de-aerating or blasting, e.g. by installing sand or wick drains
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D2300/00—Materials
    • E02D2300/0004—Synthetics
    • E02D2300/0006—Plastics
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D2300/00—Materials
    • E02D2300/0085—Geotextiles
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D2300/00—Materials
    • E02D2300/0085—Geotextiles
    • E02D2300/0089—Geotextiles non-woven

Definitions

  • the present invention relates to the consolidation of sedimentary beds, in other words to the production of a consolidated layer of sediment, e.g. soil, from a suspension of sediment in water.
  • Consolidation in a sediment bed is achieved by an increase in the effective stress ⁇ ' v , which is defined as the difference between the total stress ⁇ v applied to the bed and the pore water pressure u.
  • the effective stress can be increased by an increase in the total stress (e.g. by laying sand or gravel over the bed) or a decrease in the pore water pressure, or both.
  • the effect of these can be understood by simple analogy if one imagines squeezing a bag of crisps between the hands. The total stress is the pressure applied by the hands. When the bag is sealed the stress is resisted by the increased air pressure in the bag rather than the crisps, so the crisps are under relatively little stress (they can still rattle around inside the bag) . But if one puts a pinhole in the bag to let the air leak out, so that the air pressure gradually becomes less than the applied stress (equivalent to letting the water drain out of the bed) , gradually the crisps will be stressed and squeezed together.
  • Figure 1(a) illustrates the situation where there is no base drainage.
  • the pore water pressure which is just the hydrostatic pressure, increases as a straight line with depth.
  • the stress also increases with depth because of the weight (actually the buoyant weight) of the sediment, but in a slight curve because the density of the sediment increases towards the bottom of the bed. It can be seen that the distance between the two curves, which is the effective stress on the sediment, increases with depth.
  • Figure 1(b) illustrates the situation with base drainage. Because the base is open the water pressure there is reduced giving an increased difference between the two curves and thus an increased effective stress and increased consolidation.
  • the effective stress can be further increased by reducing still further the pore water pressure at the base as shown in Figure 1 (c) .
  • This can be achieved by applying a negative head P' to the bottom of the bed, e.g. by pumping out the water.
  • the present invention achieves this by adding a permeable layer on the top of the consolidating sediment, with this permeable layer having a permeability which is low by comparison with that of the sediment bed. A considerable part of the head loss that occurs between the bottom of the overlying water and the base of the sediment bed will occur through the low permeability layer. Thus, at the surface of the sediment, the pore water pressure will be considerably less than hydrostatic, and the effective stress considerably greater than zero. The bed surface will therefore consolidate and the effective stress gradient through the bed will be reduced.
  • a method of consolidating a water-containing sedimentary bed comprising the steps: applying over the surface of the bed to be consolidated a low permeability layer, and removing water from below the bed to be consolidated.
  • the method includes the step of maintaining a layer of water overlying the low permeability layer, though the depth of this water layer need not be constant.
  • the permeability of the low permeability layer is preferably significantly lower than that of the sediment, more preferably two to three orders of magnitude lower.
  • the permeability of the low permeability layer is selected to be such that a significant proportion of the pressure drop from the bottom of the overlying water to the base of the sedimentary bed occurs in the low permeability layer, typically 20 to 60%, more preferably 20-40%.
  • the low permeability layer is a sheet material, for instance of textile (woven or non-woven) or a permeable plastics sheet.
  • the method may include the step of pumping water from the base of the sedimentary layer. Water may be pumped onto the top of the low permeability layer to increase the water pressure thereon.
  • the method may further include as a preliminary step the laying down of a drainage layer of sand and/or gravel and/or textile onto which the sedimentary layer is deposited. This can facilitate the removal of water from the bed.
  • the low permeability layer may be removed and the bed further compacted using compaction equipment.
  • the invention also provides a sheet material for use in the above method, and having a permeability selected according to the nature of the bed to be consolidated.
  • Figure 1(a) to (c) illustrate the pressure and stress in a sedimentary bed after consolidation according to three prior art methods
  • Figure 2 (a) is a schematic diagram of the present invention.
  • Figure 2 (b) illustrates the pressure and stress in a sedimentary bed after consolidation according to the present invention.
  • Figure 2(a) illustrates an embodiment of the invention in which a sedimentary layer 1 has overlying it a low permeability layer 3, in this case of thick canvas, and a layer of water 5. It should be noted that Figure 2 illustrates the situation after considerable consolidation has taken place. It should also be noted that, although not illustrated, arrangements are made to remove water from the bottom of the bed, either by pumping or by free drainage.
  • Figure 2(b) illustrates the pore water pressure u w and the total stress ⁇ in the bed with the low permeability layer of the invention. Because the permeability of the layer 3 is less than that of the sediment 1 a significant pressure drop occurs as the water moves downwards through the low permeability layer. This can be seen in the sharp deviation of the pressure curve marked 7. Thus at the bottom of the low permeability layer (which is the top of the sediment) the pressure is considerably less than it would be without the layer 3 and thus much less than it is in the prior art of Figure 1(c) . This means that the effective stress, and thus the soil consolidation, is much greater than zero - there is a large difference between the curves of u and ⁇ at point 9 in Figure 2 (b) . It can be seen that the pressure drop through the low permeability layer is about 30% of the total drop from the bottom of the water 5 to the base of the sediment bed 1.
  • the low permeability layer other materials than canvas can be used; the requirement is for a material with the desired permeability - two to three orders of magnitude less than that of the sediment.
  • the permeability of sediments has a large range - five to six orders of magnitude.
  • the range of sediment permeability is from 1 x 10 "4 m/s for very soft river mud to 1 x 10 "10 m/s for oilsands fine tailings.
  • the material for the layer 3 must be selected having regard to the application. It is useful, though, to provide a range of materials which can be chosen for typical applications.
  • the invention can be applied to sites for disposal of dredging waste or similar material.
  • a drainage layer of sand and/or gravel is laid to facilitate water removal, before the waste is deposited and the low permeability layer 3 is subsequently laid over the top when the bed of waste is partly or wholly consolidated.
  • the invention is applied by first preparing the site to receive the material to be consolidated. This may involve laying down a drainage layer as mentioned, and/or arranging for pumping of water in and out of the site. Arranging for controlled ingress or egress of water from a nearly river or sea can also be used in some situations. Then the waste material (soil slurry) is pumped into the side for as long as desired. When the desired amount has been pumped in, the low permeability layer 3 is laid over the site. The material for the layer is chosen, as described above, by reference to the permeability of the sediment.

Abstract

L'invention concerne un procédé permettant de consolider un lit sédimentaire contenant de l'eau, ce procédé consistant notamment à ajouter une couche perméable (3) au sommet du lit sédimentaire de consolidation (1), cette couche (3) présentant une faible perméabilité par rapport à celle dudit lit sédimentaire (1). Une grande partie des pertes de charge se produisant entre le fond de l'eau sus-jacente (5) et la base du lit sédimentaire survient à travers la couche de faible perméabilité. Aussi, à la surface du lit sédimentaire (1), la pression de l'eau interstitielle est largement moins qu'hydrostatique, et la contrainte effective amplement supérieure à zéro. La surface du lit peut donc être consolidée, réduisant ainsi le gradient de la contrainte effective à travers ce lit.
PCT/GB1999/001727 1998-06-02 1999-06-02 Procede et appareil pour consolider des lits sedimentaires WO1999063164A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9811872A GB2338006A (en) 1998-06-02 1998-06-02 Consolidation of sedimentary beds
GB9811872.2 1998-06-02

Publications (1)

Publication Number Publication Date
WO1999063164A1 true WO1999063164A1 (fr) 1999-12-09

Family

ID=10833095

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1999/001727 WO1999063164A1 (fr) 1998-06-02 1999-06-02 Procede et appareil pour consolider des lits sedimentaires

Country Status (2)

Country Link
GB (1) GB2338006A (fr)
WO (1) WO1999063164A1 (fr)

Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1456363A (en) * 1972-06-14 1976-11-24 Larsen O J F Method of protecting against erosion of the seabed
EP0097098A1 (fr) * 1982-06-11 1983-12-28 Marcel Matière Procédé pour retenir les terres après excavation d'un sol en pente, notamment pour le passage d'une conduite en tranchée
EP0108269A2 (fr) * 1982-10-08 1984-05-16 Danmarks Geotekniske Institut Procédé pour provoquer la sédimentation de matériaux solides sédimenteux, transportés dans une masse d'eau, tel qu'un lac, une mer ou un océan
US4714376A (en) * 1984-12-31 1987-12-22 Jenab S Abdollah Hillslope landslide stability drain
EP0329500A1 (fr) * 1988-02-15 1989-08-23 MENARD-SOLTRAITEMENT (Société Anonyme) Procédé et dispositif de consolidation de terrains
FR2653463A1 (fr) * 1989-10-25 1991-04-26 Setec Geotechnique Procede de consolidation acceleree de vases molles draguees et deversees en remblais sur des aires munies de moyens de drainage.
EP0445788A1 (fr) * 1990-03-06 1991-09-11 NAUE-FASERTECHNIK GMBH & CO. KG Tapis d'étanchéité imperméable mis en fonction comme barrière contre l'eau et l'huile
EP0490529A1 (fr) * 1990-12-11 1992-06-17 James Clem Corporation Revêtement en argile pour pentes raides
EP0775512A1 (fr) * 1995-11-23 1997-05-28 Hollandsche Beton Groep N.V. Procédé pour enlever un liquide d'un mélange

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB663142A (en) * 1949-09-16 1951-12-19 Walter Kjellman Method for the consolidation and/or the stabilisation of soils

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1456363A (en) * 1972-06-14 1976-11-24 Larsen O J F Method of protecting against erosion of the seabed
EP0097098A1 (fr) * 1982-06-11 1983-12-28 Marcel Matière Procédé pour retenir les terres après excavation d'un sol en pente, notamment pour le passage d'une conduite en tranchée
EP0108269A2 (fr) * 1982-10-08 1984-05-16 Danmarks Geotekniske Institut Procédé pour provoquer la sédimentation de matériaux solides sédimenteux, transportés dans une masse d'eau, tel qu'un lac, une mer ou un océan
US4714376A (en) * 1984-12-31 1987-12-22 Jenab S Abdollah Hillslope landslide stability drain
EP0329500A1 (fr) * 1988-02-15 1989-08-23 MENARD-SOLTRAITEMENT (Société Anonyme) Procédé et dispositif de consolidation de terrains
FR2653463A1 (fr) * 1989-10-25 1991-04-26 Setec Geotechnique Procede de consolidation acceleree de vases molles draguees et deversees en remblais sur des aires munies de moyens de drainage.
EP0445788A1 (fr) * 1990-03-06 1991-09-11 NAUE-FASERTECHNIK GMBH & CO. KG Tapis d'étanchéité imperméable mis en fonction comme barrière contre l'eau et l'huile
EP0490529A1 (fr) * 1990-12-11 1992-06-17 James Clem Corporation Revêtement en argile pour pentes raides
EP0775512A1 (fr) * 1995-11-23 1997-05-28 Hollandsche Beton Groep N.V. Procédé pour enlever un liquide d'un mélange

Also Published As

Publication number Publication date
GB2338006A (en) 1999-12-08
GB9811872D0 (en) 1998-07-29

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