US3664142A

US3664142A - Method of burying an object in the soil

Info

Publication number: US3664142A
Application number: US69236A
Authority: US
Inventors: Joost Werner Jansz
Original assignee: NEDERLANDSE OFFSHORE CO
Current assignee: MICRODRY Inc A CORP OF KENTUCKY; NEDERLANDSE OFFSHORE CO; Nederlandse Voor Werken Buitengaats Netherlands Offshore Co Nv Mij
Priority date: 1970-09-03
Filing date: 1970-09-03
Publication date: 1972-05-23
Anticipated expiration: 1989-05-23

Abstract

A method of burying objects, for example pipelines and cables in the bottom of the sea includes loosening the soil, laying the object in the loosened soil and compacting the soil placed on top of the object laid by means of vibrators.

Description

United States Patent Jansz [54] METHOD OF BURYING AN OBJECT IN THE SOIL Inventor: Joost Werner Jansz, Rijswijk, Netherlands Assignee: Nederlandse Maatschappij voor Werken Buitengaats (Netherlands Offshore Company) N.V., The Hague, Netherlands Filed: Sept. 3, 1970 Appl. No.: 69,236

US. Cl ..6l/72.4, 61/35 Int. Cl. ..Fl6l 1/00, E02f 5/12 Field ofSearch ..6l/72.4, 72.1, 72.3, 36

[ 1 May23, 1972 [56] References Cited UNITED STATES PATENTS 3,195,314 7/1950 Degen ..61/50 3,540,226 II/ 1970 Sherrod .61/72.4

FOREIGN PATENTS 0R APPLICATIONS 1,428,155 0/1966 France ..6l/72.4

Primary E.xaminerJacob Shapiro Attorney-Holcombe, Wethen'll & Brisebois ABSTRACT A method of burying objects, for example pipelines and cables in the bottom of the sea includes loosening the soil, laying the object in the loosened soil and compacting the soil placed on top of the object laid by means of vibrators.

3 Claims, 1 Drawing Figure METHOD OF BURYING AN OBJECT IN THE SOIL This invention relates to a method of burying an object, for example pipelines, cable or the like, in the bottom of the sea (which word is used herein to include rivers and other water areas).

Objects that are buried in soil under the so called phreatic surface have a tendency to float up when the specific gravity of the object is less than the specific gravity of the soil in loosened conditions. Usually an object is lowered into a ditch or trench by imposing a load on it. This ballast prevents the object from floating up. In many cases the load is removed as soon as the object is covered by soil, which consequently has a loose structure. When for some reason this loose soil which covers the object starts to settle and some internal flowing leads to a spontaneous liquification, this soil will temporarily behave like a heavy liquid with a specific gravity that can exceed that of the object. The object may then float up in this heavy liquid, displacing the soil which immediately settles in a more dense structure than it was before the internal flowing occurred.

In order to prevent an object that is buried under the phreatic surface in the soil from floating up in its surrounding soil as a result of the internal flowing patterns, the method of this invention consists in deliberately vibrating the loose soil on top of the object in order to force the soil to settle quickly in a more dense structure while the imposed load on top of the object is still acting on it. This ensures that no internal flowing can occur, and the imposed load can safely be removed.

An example of the application of the method of this invention to burying a pipeline in the sea bed will now be described. To bury an offshore gas pipeline which, for instance, has a specific gravity when immersed of 1.3 in a sandy seabottom, a normal practice is to loosen the soil by means of strong jet streams which cause the sand to come into a fluidized state. By the weight of the trenching machine working on the pipe, the latter will be lowered in to this fluidized sand until it reaches the unloosened sand. Due to the stiffness of the pipe, the downward force of the trenching machine will keep the pipe in its lowered position even at some distance behind the trencher where the sand deposits over the pipe in a loose condition. By applying vibrations to the sand in the said area, the loose sand particles are forced to settle into a denser structure caused by its spontaneous internal flow, and the floating up of the pipe is prevented. When the trenching machine moves forward, the pipeline left behind is buried and covered by a sufficiently compact sand layer of such a dense structure that it will be kept in position in spite of its relatively low specific gravity.

A preferred embodiment of the invention will now be described with reference to the accompanying drawing which shows a schematic sectional view through the sea bed illustrating the laying ofa pipeline.

Referring to the drawing, there is shown a pipeline 1 which has been initially laid on the seabed 2 as indicated at 3. A trenching apparatus, indicated diagrammatically at 4 by dotted lines, and which may be of the type described in copending patent applications Ser. No. 18538/69 and No.

36650/69, has moved along a part of the pipeline in the direction of the arrow 4a and loosened the soil around the pipeline by means including jet streams of water to form a trench-like region, thereby enabling the part of the pipeline along which it has moved to sink through the said region to the level shown at 5. The loosened soil mixed with water is conveyed to the rear of the apparatus 4 and the soil is placed on top of the pipeline lying at the level 5. The surface of the soil being placed on top of the pipeline in the trench falls away naturally from a peak towards the apparatus 4 and on this sloping surface behind the apparatus 4 there is arranged a plurality of torpedo shaped vibrators 6, 7 and 8, of known design and suitable for underwater working, which are hydraulically operated via connecting lines 9, 10 and 11 from the apparatus 4. The connecting lines 9,10 and 11 also include means for hauling the vibrators 6, 7 and 8 behind the trenching apparatus as the apparatus 4 moves along the pipeline. it will be noted that the vibrator 6, which is at the lowest level, precedes the vibrators at a higher level, in order to compact the soil nearest to the pipeline first. The degree of the compacting of the soil in the trench-like region is represented on the drawing and indicates that the soil at 12 is more densely compacted than that at 13 and that at 13 is more densely compacted than that at 14 because the soil at 12 has been compacted by the vibrators 6, 7 and 8 and that at 13 by the vibrators 6 and 7, while the soil at 14 has only been compacted by the vibrator 6 passing over it. The number and spacing of the vibrators, in a row next to each other, depends upon the width of the loosened soil. Of course, if necessary, more than one train of vibrators may be employed. The vibrators may be operated by other means, for example pneumatically, and it will be understood that their power and the frequency at which they vibrate will be chosen to ensure sufiicient compacting of the soil at the particular speed of movement to prevent the pipeline from rising from the level 5.

While a particular embodiment has been described it will be understood that various modifications can be made without departing from the scope of the invention, For example, in certain circumstances it is necessary to use only one vibrator and the vibrator or vibrators may be hauled by means other than the trenching apparatus.

I claim:

1. A method of burying a pipeline, cable or the like in the bottom of the sea (as herein defined) which includes the step of loosening the soil in a region of the sea bottom by means of a trenching apparatus which is movable along the pipeline, lowering the object into the region in which the soil has been loosened and hauling one or more vibrators attached to the trenching apparatus behind the apparatus as it moves along the pipeline in order to vibrate and compact the soil on top of the pipeline.

2. A method according to claim 1 including the step of positioning the vibrators at different levels above the pipeline.

3. A method according to claim 2 wherein the vibrators at a low level precede those at a higher level.