CA1127855A - Trenching apparatus - Google Patents

Abstract

ABSTRACT OF THE INVENTION An apparatus for trenching beneath an elongated member lying on the bottom of a body of water has a movable frame member, at least one cutting assembly, an assembly support means connected to the frame member for supporting each cutting assembly and for moving each cutting assembly at least in a laterally directed plane, and a spoil removal system. Each cutting assembly comprises at least two actuatable cutting tools which are driven for cutting movement relative to cutting tool axes. The cutting tool axes, for each cutting assembly, define an assembly cutting plane and means are provided for rotating the assembly cutting plane relative to the laterally directed plane, thereby, varying the cutting swath of the associated cutting assembly. Each cutting assembly has a rotatable bifurcated cutting tool support arm for supporting two generally upright, downwardly directed rotatable cutting tools and means actuatable to rotate said tools about respective tool rotating axes.

Description

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TRENCHIN~, APPARATUS

The invention relates to apparatus for use in underwater environments and more particularly, to apparatus forburyingor entrenching an elongated member lying on the bottom of a body of water.

BACKGROUND OF THE INVENTION

It is common, after placing a pipeline, a submarine cable, or othex elongated member, at the bottom of a body of water, to bury or entrench the elongated member to avoid .
the effects of, for example, ocean or other water currents, passing vessels, and other hazards of the sea. Various techni~ues for entrenching an elongated member have been suggested and used. By far the most common is the "jetting"
method by which fluids are propelled at high velocities against the subsea surface to dislodge and otherwise remove debris and other ground materials from beneath the elongated membert so that the member will fall into the resulting trench and thereby be safely situated beneath the water hottom.
Despite its versatilityr as compared to other methods of trenching thus far used, the "jetting" method nevertheless has its shortcomings. For example, the jetting method has a high operating cost and a slow rate of progress, is uneconomical for deeper waters, and is relatively inefficient in certain kinds of soil composition.

AS the demand for oil and gas resources has increased, those exploring offshore for these natural resources have ventured into deeper waters and more severe environments.
In order to extend the trenching capahility to these deeper waters, considerable effort has been devoted to the development

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of other trenching techniques. As a result, equipment utilizing mechanical cutters has been discussed in the literature, and various versions of such equipment have been developed, all using the same basic trenching technique. They differ from each other primarily only in certain relatively minor details. Gernerally, these devices are also relatively inflexible and cannot easily be adapted to different trenching applications.
It is therefore an object of the invention to provide an apparatus for trenching the bottom of a body of water which operates at depths up to and exceeding 3000 feet, which has a relatively low operating cost, and which has a relatively high rate of progress.
Further objects of this invention are to provide a novel cutting assembly which is capable of varying the width of the cutting swath, which flexibly varies the depth and angle of the cutting assembly, and which provides mechanical cutting means to trench from a side to a position beneath an elongated member.
Other objects of the invention include providing a trenching apparatus which can be operated by either remote control or by an operator on board the apparatus, which provides reliable and safe access to the operating control module or chamber, and which is particularly useful for trenching beneath a prelaid pipeline.

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SU~ARY OF THE INVENTION

An apparatus for trenching beneath an elongated member lying on the bottom of a body of water, according to the invention, features a movable frame member for movement relative to the elongated member, at least one cutting assembly, and assembly support means connected to the Erame member for supporting each cutting assembly and for moving each cutting assembly at least in a laterally directed plane substantially normal to a longitudinal axis of the frame member. Each cutting assembly has a rotatable bifurcated cutting tool support arm for supporting two downwardly directed rotatable cutting tools.
The tool support arm is preferably connected to and movable by the assembly support means, and means are provided for rotating the tool support arm and an assembly cutting plane about an assembly longitudinal axis ~or varying the cutting width of the cutting assembly, the assembly axis being substantially parallel to both the assembly cutting plane and the laterally directed plane. Each actuatable cutting tool has a mechanical cutting means secured thereto for cutting movement, and drive means actuatable for driving, relative to a cutting tool axisl the cutting means in the direction of cutting movement. The cutting tool axes for each assembly are substantially aligned in and define the assembly cutting plane. -~ ~7~5iS

In one aspect of the apparatus of the invention, two cutting assemblies are provided, a first forward cutting assembly and a second rearward cutting assembly, the assemblies having, respectively, first and second laterally directed planes, the planes being spaced apart along the longitudinal axis of the frame~ Thus, the assemblies are offset mounted on the frame member in a spaced apart relationship both laterally and longitudinally with respect to the center of frame member.
According to a preferred embodiment of the invention, each cutting assembly is supported by a cutting depth control assembly which is part of the assembly support means and which varies the position of the associated cutting assembly along the cutting assembly longitudinal axis. The assembly support means also includes a cutting angle control assembly for varying the angular orientation of the longitudinal axis of an associated cutting assembly in the laterally directed plane.
In a particularly preferred embodiment of the invention, adjacent cutting tools of each assembly rotate in opposite directions about their respective tool rotating axes.

DESCR~P'rION OF I~IE DRAWINGS

Other objects, features, and advantages of the invention will appear from the following description ~f preferred particula r embodiments taken together with the drawings in which:
¦ Fig. l is a top perspective view of an apparatus constructed according to the invention positioned on the botto~ of a body of water; -Fig. 2 is a bottom perspective view of an apparatus ~ constructed according to the invention showing in particular I the cutting assemblies and the frame member;
¦¦ Fig. 3 is a top plane view of the apparatus of Figs. l and 2;
Fig. 4 is a side elevation view of the apparatus of Figs.
l and 2;
1 Fig. 5 is an elevation vie~ detailing the cutting assembly ¦l and a portion of the means ~sed to support the cutting assembly;
', Fig. 6 is a cross-sectional view taken along lines 6-6 ,~ of Fig. 5;
'I Fig, 7 is a cross-sectional view taken along lines 7-7 of ~ Fig. 6 with some guide members omitted and with a portion of the 1l! spoil removal means rotated 90 for clarity;
j; Fig. 8 is a side elevation view of a particular e~bodiment ~ according to the invention showing an alternate ;
¦ sp3il removal system;
, Fig. 9 is a schematic representation of an alternate apparatus and method according to the invention for trenching beneath an elongated member; and Fig. lO is a simplified cross section of the apparatus of F s. 1-7 in operation.

5~ , DESCRIPTION OF PARTICUL.AR PREFERRED EIIBODIMENTS

General ~escription Referring to Figs. 1 and 2, an appara~us 10 for trenching the bottom of a body of water has a movable frame member 12, at least one and preferably t~o cutting asse~blies 14a, 14b, assembly support means 16a, 16b, and spoil removal means 18a, 18b. The assembly support means ls connected to the frame member and supports each cuttir.g a~ssembly. The assembly support means also is connected to move each cutting assembly at least in a laterally directed plane substantially normal to a longitudinal axis 20 of the frame member.
Each cutting assembly, of which there are two in the illustrated embodiment, comprises at least two actuatable cutting tools 22a, 22b and 22c, 22d and tool support-means 24a, 24b.
Each cutting tool 22a, 22b, 22c, 22d has mechanical cutting means 26a, 26b, 26c, 26d secured thereto for a cutting movement, and drive means 28a~ 28b, 28c, 28d actuatable for driving the cutting means, relative to cutting tool axes 30a, 30b, 30c 9 30d, respectively, in the direction of cut~in~ movement. The cutting tool axes 30a, 30b and 30c, 30d, corresponding to the cutting tools of each cutting assembly, are substantiallyaligned in and define a cutting assembly cutting plane.
The cutting tools are supported by the tool support means 24a, 24b in a generally downwardly extending direction for cutting movement relative to their respective cutting tool axes 30. The tool support means 24a, 24b are connected to and movable by the assembly support means 16a, 16b respectively. Each tool support means can also be rotated about an assembly longitud'nal axis ~, . . . . .

I llZ7B55 32a, 32b for varying the width of the cutting swath of the cutting assembly. Each assembly longitudinal axis is substan-tially parallel to both the associated assembly cutting plane and the associated laterally directed plane of the frame member, and the assembly cutting plane is rotated about the assembly longitudinal axis as the associated tool support means is rotated about that axis.
The trenching apparatus 10 is lowered from a surface vessel (not shown) into an operational relationshlp to an elongated I member, for example a pipeline 34 lying on the bottom 33 of a body of water. The apparatus may thereafter be either pulled along by a surface vessel or may be self-propelled employing fluid and/or electrical power provided over a power umbilical

3~ from a surface vessel. (The hydraulic and electrical inter-¦ connections have been omitted in the ~igures to provide clearer ¦ views oE the apparatus.) Prior to moving the apparatus forward, I the cutting assemblies 14, which in the illustrated embodiment !' are both longitudinally and laterally offset from the center of !! the trenching apparatus and its frame, are moved to a position Il whereby they successively and simultaneously trench beneath the elongated member and preferably wherein the resulting trenches ¦~ 3~a, 38b overlap to provide a single trench into which the I elongated member 34 falls (Fig 10). The spoil and debris ¦i generated as a result of the trenching step is removed by the ¦¦ spoil removal means 18 which, in this particular embodiment~
¦¦ employs a suction creating source such as frame mounted center-less pumps 40a, 40b, which create a suction at the bottom end of the respective eductor cylindrical tubular members 42a, 42b.
il This suction causes the spoil to be drawn into the tubular 30 1l members and discharged in a direction away from the apparatus 10 I at eductor discharge open ngs 44a, 44b.

-~ 5 5 The Frame Member Frame member 12 comprises a plurality of tubular structural members 50 interconnected, for example, by welding, to provide a rigid structural support for the assembly support means, the spoil rem~val means, the cutting assemblies, and other associatec equipment (to be described below) required to properly operate the trenching apparatus. The tubular members 50 may be inter-connected to form a fluid-tight buoyancy control system for controlling, in part, the buoyancy of the frame 12~ In the illustrated embodiment, the frame member l2 supports a pair of crawler members 52a, 52b, one on each side of the frame. In other embodiments, more than one crawler member may be provided on each side of the frame. Each crawler consists of an endless chain of linked tracks 54 and each crawler is powered or driven by a separate hydraulic power drive unit 56a, 56b. While the apparatus can have many different effective operating configura-tions, in the illustrated embodiments, the trenching apparatus 10 is self-propelIed having hydraulic motors 56 driving the caterpiller type crawlers 52 in a forward or reverse direction.
In other embodîments of the invention, the crawlers may be replaced by, for example pontoons, whereby the apparatus would be pulled for example by a surface vessel throu~h a tow line connected between the vessel and the trenching apparatus.
The frame member further supports a plurality of pressure stabilized tanks 58 for housing the electro-hydraulic power and control elements which provide the drive power to (a) propel the apparatus, (b) operate the assembly support means, (c) drive the cutting assemblies~ (d) operate the spoil removal system, and (e) provide power to other auxiliaries. Tanks 58 can also vary :

--the buoyancy of the apparatus Power umbilical 36 ~arries electricai power and acoustic signals to operate the electrical monitoring and control systems on the trenching apparatus as described below. An umbilical tower (not shown) can be provided to keep the umbilical 36 away from other components of the apparatus. .
The illustrated frame member further supports a pressure stabilized control chamber 62 in which an operator may be safely . housed to control all operations of the apparatus. The apparatus 10 Il may also be controlled remotely by duplicating all of the control s li on a surface vessel and connecting the surface vessel to the apparatus through ~mbilical 36. Alth~ugh oth~r chamber conflgurations can be used, the illustrated control chamber has a substantially spherically shaped outer shell which is able to withstand the hydrostatic pressures at 3000 or more feet. The l outer shell of the control chamber has a cylindrical portion 64 ¦
¦l at its upper end; and cylindrical portion 64 is designed to releasably couple, in a standard manner, with a corresponding Il portion of a transfer module 66 which enables personnel to ¦
, transfer between the control chamber 62 and a surface vessel (not shown). The transfer module 66 and the control chamber 62 are preferably connected by a guide line 68 which is used to .
"winch down" or "winch up" the transfer module 66 to and from the control chamber 62. The winch, not shown, is provided on .frame 12. Pressure stabiliæed control chamber 62, as well as the ~.
¦ transfe. module, are each maintained at substantially one atmosphere pressure to provide a suitable env;ronment for the control operator.

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The Cutting Assembly Support Means The two cutting assembly support means 16a, 16b of the illustrated embodiment operate in an identical manner and are of identical construction. Therefore, only support means 16a will be described in detail. However, corresponding parts of the two illustrated support means 16 are labelled with corresponding ¦ reference numbers (differing in the letter suffix~.
¦ The cutting asslembly support means, in the preferred embodiment, is supported by frame member 12 for pivotal movement about a pivot axis 76 (FigsD 3 and 4) extending parallel to the longitudinal axis of the frame member. The cutting assembly support means is supported by the frame member at bearing suppor members 78,80 on each side of the support means, which allow the pivoting movement of the assembly support means 16, and hence the cutting assembly 14, in the :laterally directed plane substantially normal to the longitudinal axis of the frame membe~ .
The degree of pivotal movement is controlled by a cutting angle control assembly, here a linear actuator, such as a hydraulicall~
operated cylinder 8~, having an extend;ng rod 84 which is connected between tubular structural members 50 and a longi-tudinally stationary portion of the assembly support means 16.
The connections of the rod and actuator assembly to the frame member and support means each provide for pivotal movement of the actuator rod in the laterally directed plane. That movement accommodates for the rotational movement of the rod to support assembly connection relative to the positionally fixed cylinder to frame connection.

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Refe~ring now to Figs. 5, 6, and 7, the support means has cylindrical protrusions 90 connected to a support means main frame 92 by support members 94. Protrusions 90 are supported ¦ for movement in bearing support members 78, 80 connected to the frame member 12, as described above, the supporting structure I allowing the support means to pivot around pivot axis 76.
Support members 94 may, for example, be weided to structural tubul~r members 96, 98 of the support means. The primary support structure of illustrated support means 16, the main 1¦ frame 92, has a plurality of vertically disposed tubular members 96 arranged in a substantially square cross-sectional configura-i tion interconnected around the square periphery by substantially j' horizontally disposed short tubular members 98.
!~ Arranged within the primary structure defined by tubular ¦'l members 96, 98 is a cutting depth control assembly for varyingthe position of the associated cutting assembly along the assembl longitudinal axis The illustrated assembly includes a tele-¦¦ scoping cutting assembly support member 100, which is controllabl ~I translated in the direction of the assembly longitudinal axis ,, 32 for moving the cutting assembly 14 pa~allel to longitudinalaxis 32. ~The illustrated cylindrical tubular member 4~ is substantially coaxial with telescoping cutting assembly support ¦i member lOO and can be moved independently of support member 100 in 2 direction parallel to the longitudinal axis 32 of the cutting assembly.) The telescoping cutting assembly support member, in the illustrated embodiment, has a plurality of flat, elongated struc-tural members 104 assembled to form a telescoping hollow cylinder hsvine a square cro5s section. The telescopins cylinder is I I ' reinforced at its corners by right-angled structural strip members 108 having secured thereto a plurality of flat strip guide members 110. A plurality of cam members, here rollers 1129¦
are supported for rotational movement about roller axes 114.
¦ Rollers 112 contact the telescoping cutter assembly support ¦ member at the flat strip guide members 110 to provide guiding alignment to all sides of the telescoping cylinder. The rollers 112 are supported for rotation by roller support members 116 ~¦ which a`re each secured, for example by weldingg to horizontal Il tubular members 98.
I; The translational movement of telescoping cutting assembly support member 100 along assembly longitudinal axis 32 can be ¦ controlled by hydraulically actuated cylinders 120a and 120b having extending piston rods 122a and 122b, as illustrated, or alternatively, by for example, a rack and pinion type device (not shown). Cylinders 120 are secured in the illustrated embodiment to the tubular members 98 of the cutting assembly ! support means 16, for example by brackets 124 welded to the ¦~, tubular members g8, Each piston rod 122 is connected to the tI ~elescoping support member 100, and in particular to the tele-¦~ scoping cylinder, at a pivotal connecting point 126. Thus, as I~ the hydrauiically controlled and actuated cylinders 120 vary ~he ¦I position of the piston rods 122, the telescoping support member II 100 translates parallel to the longitudinal axis of the cutting assembly~ l The cylindrical tubular member 42 is supported for telescop-¦
Il ing movement within and is preferably coaxial with the support Ij member 100. A plurality of camming members 130 are spaced around I the outer periphery of tubular member 42. In the preferred I embodiment, the camming members 130 are rollers mounted for Il - 13 -' I .

7 ~ ~ ~ ( rotational movement about respective rotation axes 132 and are supported by and secured to interior walls o'f the telescoping cylinder by roller support assemblies 133. The rollers i30 align and guide the tubular member 42 for teiescoping movement parallel to the longitudinal axis'32 of the cutting assembly.
In the illustrated embodiment, the support ~ember 100 and tubular member 42 are both supported coaxially with the longi-t~dinal axis 32 of the cutting assembly. The tubular member is supported by hydraulically controlled cylinders 134 positioned 180 apart and each having a pistonrod 136'for moving the cylinder 42. Cylinders 134 are each supported, in the illustrate embodiment, at their upper end by structural support means 138a, 138b, which may, for example, be welded to the interior walls 139a, 139b of the telescoping cylinder. Each cylinder 134 is vertically disposed and the piston rods, in the illustrated embodiment~ extend from the lower end of the cylinders 134 and Il are connected to tubular member 42 by structural supports 140a, 140b. Thus, actuation of hydraulically controlled cylinders 134 causes the'tubular member 42 to move with respect to the tele-scoping cylinder; however~ the tubular member 42 will, for afixed position of the cylinders 134 and rods 136, move or transla e with the support member 100 under control of cylinders 120 and rods 122. 'Each movable component is additionally provided with locking devices and supports (not shown).
The Cutting Assemblies Referring to Figs. 2 and 5, each cutting assembly 14a, 14b, includes two cutting tools 22a, 22b and 22c, 22d. Each pair of I tools 22 is mounted on a rotatable bifurcated support arm 146a, ~ 146b. Each cuttiny tool is preferably independently rotated by Il : .

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hydraulic drive means 28a, 28b, as is well known in the art;
the top housing 147a, 147b, of the drive means, e.g motors, being visible above the arms 146. In the illustrated embodiment, adjacent cutting tools rotate in opposite directions but in other embodiments of the invention adjacent tools may rotate in the same or opposite direction. -Each cutting tool includes a mechanical cutting means secure thereto ~or cutting movement. In the illustrated embodiment, the cutting means are a plurallty of replacèable cutting elements 148 mounted about the outside surface of supporting cylinders lS0 The cutting elements are rotated about the respective cutting tool axes 30; and for each cutting assembly, the cutting tool axes associated with the cutting tools of that assembly define a cutting plane in which each associated cutting tool axis sub-stantially lies. In other embodiments of the invention, the cutting means may be any other configuration used to provide mechanical cutting and may, for example, comprise a plurality of cutting elements which reciprocate in a direction parallel to the assembly longitudinal axis.
Continuing to refer to Figs. 2 and S, the bifurcated support arm 146 is connected to the telescoping cylinder through outwardl extending flange members 152 which are connected by bolts 154 and nuts 156. Prior to being lowered into the water, the cutting assembly can thus be rotated about the longi~udinal cutting assembly axis by rotating flanges 152 relative to each other, whereby the effective cutting swath of the cutting assembly is varied. Thus, the width of the cut may be varied, in the illustrated embodiment on board the surface vessel, by varying I
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the orientation of the assembly cutting plane relative to the assembly longitudinal axis 32. When the cutting plane is normal¦
to the longitudinal axis of the frame, the-~utting swath is greatest9 and when the cutting plane is parallel to the longi-tudinal axis of the frame, the cutting swath is at a minimumO
Be~ween these two extremes, the cutting swath may be varied substantially at will depending only upon the number of possible¦
positions of bolt holes in the flange ~embers 152 relative to l each other.
I Spoil Removal Means I
The spoil removal means of the embodiment illustrated in Figs. 1-7 is a suction based system and comprises the cylindrical tubular members 42 which are elongated hollow cylindrical ¦
structures supported as described above for movement in pla~nes substantially parallel to the laterally directed plane and a ¦
l suction creating source, here illustrated centerless pumps 40, fJIr i creating a suction at the bottom 158 o-F the t~bular members ¦
¦I whereby a fluid flow, which includes spoil material from operati~n ¦~ of the cuttin~ assembly, is created at the bottom 158 of member 20 1i 42 and is carried away from the cutting assembly through member ¦i 42. The fluid flow created by centerless pumps 40 is discharged, ! in the illustrated embodiment, through the eductor discharge ¦ openings 44 of tubular discharge members 160. T~e discharge ¦¦ openings can be directed in substantially any convenient directio ~
¦~ and are preferably directed away from both the trenching apparatu ~ ¦
¦l and the elongated ~ember beneath which the trench is being create ¦l at a rearward and lateral corner of the trenching apparatus.
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Referring to Fig. 8, in an alternate embodiment of the invention, the spoil removal means creates a suction at the bottom 158 of member 42 by what iS3 in essence, the momentum transfer effect~ An eductor type connection device 162 is used in place of the centerless pump. Suction flow into bottom 158 is created by forcing fluid under pressure through flexible line 164 into the device 162. There results a low-pressure or partia vacuum on the inlet side of device 162 (from tubular Tnember 42), thereby creating a suction at the bottom 158 of mem~er 42. The fluid flow into the eductor 162 continues through flexible discharge conduit 166 which provides a path-to discnarge opening 168 at a rearward and lateral corner of the trenching apparatus.
Fig. 8 also shows the manner in which flexible lines 164 and conduits 166 may vary in shape depending upon the position of member 42. The solid lines indicate the position of the various components when the members 42 are in a raised position9 and the phantom lines represent the tubular members 42 in a lowered position, for example during a trenching operation.
General Operation 20 ¦ In the apparatus of Figs. 1-7, in normal operation, the trenching apparatus lO is lowered from a surface vessel (not shown) using support lines 202 to an operational relationship wherein the crawler tracks straddle the elongated rnember 34.
~The support lines 202, while shown taut, as ~hey are during the vertical movement of the trenching apparatus, are left loosely hanging during norrnal operation and do not interfere with move-ment of the transfer module 66. As noted above, an umbilical tower can be used.) The cutting assemblies 14 can then be ~ 7~ ~t~
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¦ lowered into or can trench into a position ~herein each preferabl Y
has the bottom portion of at least one cutting tool beneath the elongated member (Fig. 10). -¦ As noted above, the cutting assemblies are offset both longitudinally and laterally of the center of apparatus lO
(Figs. 1-3)o Each cutting assembly may bè adjusted independently of the other to, within the mechanical limits of the assembly, ¦ any desired cutting swath, cutting depth, and angle of cut. The I¦ cutting swath is adjusted, as noted above, by rotating the ~¦ cutting assembly about its longitudinal axis (relative to tele-¦I scoping member 100) thereby changing the angle or orientation of ¦! the cutting plane relative to the longitudinal axis of the ¦I trenching apparatus. (While in the illustrated embodiment this i I¦ a manual operation whereby flanges 152 are rotated relative to ¦¦ one another, in other embodiments of the invention, rotation may be effected dynamicallv from a remote location.) The angle of cut, that is, the angle of the cutting asse~bly longitudinal axis relative to the horizontal plane, is adjusted by actuating , hydraulic cylinder 82 and thereby driving extending rod 84 to ~l pivot the cutting assembly 16 about pivot axis 76. The cutting ! depth is adjusted by actuation of hydraulically controlled I cylinder 120 thereby moving the associated piston rod 122 to vary the position of the telescoping cylinder relative to the j tr~nslationally fixed portion of thé cutting assembly support I¦ means 16, for example tubular members 96, 98.
~¦ In the illustrated apparatus 10, the operator housed in control module 62 has substantially complete control over movemen I

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of the apparatusn In order to properly track the elongated member, tracking means, not shown but well known in the art, are used to maintain a specific known operational relationship between the movement of the trenching apparatus 10 and the elongated member. This is true whether the apparatus straddles the elongated member or is off to one side (Fig. 9). Preferably, the operator has available, as the primary tracking system, at least one and preferably a plurality of sensing devices to independently measure the relationship of the apparatus to the elongated member. To that end, a re~otely operated sonar 204 and television 206 equipment (Figs. 9 and 10) may be installed at convenient locations on the apparatus to monitor, both visually and electronically, the operation of the apparatus.
An example of another suitable tracking means, which in the illustrated embodiment would be a secondary tracking system, is .. . . .. _ described in Perot, Jr., U.S. Patent No _~,751,927, issued August 14, 1973. Using the Perot, Jr. tracking system, positional movement of the apparatus may be substantially controlled by an automatic system; and as a result, the operator's duties would then normally be supervisory only.
In addition to the equipment thus far described, frame 12 may further support hydraulically or electrically operated thrusters 208 which are provided primarily to provide some maneuverability to the apparatus as it is being lowered to the sea bottom. The thrusters may also be used to offset small translational or rotational forces affecting operation o~
the apparatus, for example slowlv moving ocean currents. The thrusters may be operated either under manual control by the operator or under automatic control by a tracking system which maintains ~e apparatus in alignment with the elongated member.

,~ llZ7B55 ¦ An Alternat~ Embodiment of the Trenching Method and Apparatus :
The trenching apparatus of the preferred embodiment may be modified to include a greater or fewer number of cutting assembli ~s than the two longitudinally and laterally offset assemblies of Figs. 1-8. In particular, referring to Fig. 9, in an alternate particular embodiment of the invention, one cutting assembly 210 is provided, and the trenching apparatus 212, thus configured, may operate as follows~ The single cutting assembly 210 is supported for movement in a laterally directed plane and extends away from the path of travel of trenching apparatus 212. The cutting assembly 210 is supported by a cutting assembly support ¦I means 214. Support means 214 pivots on an extended portion of ¦ the frame member, support arm 216, around a pivot line 218 which extends parallel to the longitudinal axis of the trenching apparat tus. The cutting assembly support means is controlled in its Ij pivotal movement around. pivot line 218 by a hydraulically ¦l actuated and cbntrolled cylinder 220 having an extending piston l! rod 222.
I~ The support means and cutting assembly extend to one side 20 '! only of apparatus 212 and create an asy~mnetry in weight distri-ij bution. Hence a counterweight 224 is provided on the other sideof apparatus 212 and the counterweight extends outward over the i other side of the apparatus to provide a balanced and stable operating system. Under the control and guidance of an operator I in a single atmosphere control module 226, and using various measurement and sensory devices such as sonar range me~suring ¦ device 204, and a television camera system 206 mounted for examp I on support means 214, the apparatus cuts a trench beneath an 30 I elon a ~ed member 230 from one side of the member. he spoil and l i l Il llZ~55 ( debris created during the cutting or trenching operation are removed from the trench either simultaneously with the trenching step or in a separate pass through a spoil removal system which is preferably identical to that described in connection with Figs. 1-7. After a complete "pass" has been made, that is, ¦ including the trenching and subsequent or simultaneous spoil removal steps, the trenching appar~tus 212 may make another pass, if necessary, from the other side of the elongated member 230 to complete the trenching operation~ Alternatively, two apparat~ s ~10 ¦ can be deployed, one on each side of the elongated member, for j simultaneously trenching from both sides of the member.
¦¦ The steps of the second pass are the same as the steps of the first pass. Thus, spoil and debris may be removed simulta-neously with or subsequent to the trenching or cutting step.
However, during the second pass, the cutting swath or width may I be the same as or different than the cutting swath during the ¦I first pass. Similarly, the cutting depth during the second pass may be the same as, deeper, or shallower than the cutting ll, depth during the first pass. In the il.ustrated embodiment, ~I where the solid portion of the figure indicates the first pass il and the phantom portion, the second pass, the cutting swath has il been reduced on the second pass and the depth of the cutters !~ has been increased. In practice, as the second trenching operatic n Il proceeds, thè elongated member 230 will fall into the resulting ji trench and rest beneath the bottom surface 232 of the body of Il water.

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7~5~ii SUMMARY OF THE ADVANTAGES OF THE INVENTION
A~D NO~i-oBV~oU~

The invention advantageously provides a unique and highly ef~ective approach to the use of mechanical cutting apparatus for deep water applicationQ. Also, the invention can be used advantageously in shallow water applications.
The invention advantageously provides a pair of offset mechanical cutting devices which can be easily maneuvered ~o a position beneath an elongated member whereln the mechanical cutters provide a significantly high rate of forward progress.
The cutt;ng assemblies are advantageously independently position-able and provide a maximum flexibility and maneuverability for the assembly. The cutting devices can be advantageously mounted together on a self-propelled unit, offset both laterally and longitudinally from the center of the unit, to provide two separate maneuverable cutting swaths, each of which can be adjusted to a preselected width.
The flexibility of the method of the invention is evidenced by an alternate embodiment of the invention which has only one cutting assembly and makes two or more passes along the elongated member, one on each side of the member, in order to provide the two trenching operations necessary to bury the member. In this embodiment, the apparatus is advantageously removed somewhat from the immediate vicinity of the elongated member.
In a preferred embodiment of the apparatus according to the invention, there is advantageously provided a pressure stabilized control module whereby an operator may be stationed to control or supervise the operation o~ the trenching apparatus.

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- :~2 -Various features of the apparatus disclosed herein are ; no~ new. Thus, a self-propelled apparatus for burying elongated members is not new. Nor is it new to provide a burying apparatus with a laterally pivotable rotary cutter in combination with an eductor type spoil removal system. An example of such an :~ apparatus is DeVries, U.S. Patent No. 3~583,170, issued June 8, 1971.
Similarly, apparatus wherein the individual cutting tools can be characterized by cylinders supporting circumferenti~lly mounted cutter teeth is disclosed, for example, in Fig. 8 of Breston et alJ U.S. Patent No. 3,670,514, issued June 20, 1972.
(For a related cutting system see Martin, U.S. Patent No. 3,429,132¦, issued February 25, 1969.) Also, various apparatus have been disclosed which have means for varying the cutting depth of the soil removal elementsl.
For example, Tittle, U.S. Patent No. 3"338~059, issued August 29,i 1967, Perot, Jr., U.S. Patent No. 3,751,927, issued August 14,19,,3, and ~ood et al, U,S. Patent No. 3,786,642, issued January 22, 1974, all disclose embodiments wherein the cutting members are vertically adjustable. They do not however contemplate the continuously operable telescoping system claimed herein.
Other related references include Lynch, U.S. Patent No.
1 3,732,700, issued May 15, 1973, which has a single, off-center mounted, rotary cutter carried by a self propelled sled body;
and Lecomte, U.S. Patent No. 3,978,679, issued September 7, 1976, which describes a burying apparatus having a single mechanical cutting tool which is laterally directed to a position beneath ~he elongated member, the apparatus being positioned to one side of the elongated ~ember and having a releasable command sphere.

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1, ! `, These references however simply do not describe~ disclose, or suggest the invention claimed herein. Thus,the references totally lack disclosure regarding a self-prcpelled burying ¦ apparatus having two cutting tool axes which define the rotatabl~
cutting plane and means to vary the width of the cut as describec I and claimed herein; a burying apparatus further incorporating ¦I the telescoping apparatus of the present invention or the il bifurcated support arm of the present invention to provide, in ¦ part, the variable width cutting capability; or an apparatus I having at least two cutting assemblies offset from the center of~
I the apparatus both longitudinally and laterally. Not only are !I these claimed features not suggested or shown in the prior art ~ i li but they provide a burying apparatus having uniquely advan~ageou i! cutting abilities beyond that previously known.
¦ Other embodiments of the invention, including additions, ~
Il subtractions, deletions, or other modifications of the disclosed~ ;
¦! preferred particular embodiments will be obvious to those skilledl I¦ in the art, and are within the scope of the following claims. !

I, .

~1

Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. An apparatus for trenching the bottom of a body of water comprising a movable frame member, at least one cutting assembly, means secured to said frame member for supporting each cutting assembly and for moving each assembly at least in a laterally directed plane normal to a direction of movement of said frame, and each cutting assembly comprising a rotatable bifurcated cutting tool support arm for supporting two generally upright, downwardly directed, rotatable cutting tools, and means actuatable to rotate said tools about respective tool rotating axes.

2. The trenching apparatus of Claim 1 wherein each cutting assembly further comprises means for rotating said bifurcated arm about a longitudinal axis of said cutting assembly, thereby rotatably positioning said rotatable cutting tools, as a unit, about said assembly axis and varying the cutting width of said assembly.

3. The trenching apparatus of Claim 2 further comprising means for selectively translating each said cutting assembly in a direction parallel to its longitudinal axis, whereby the cutting depth is vertically adjustable.

4. The trenching apparatus of Claim 1 wherein there are two cutting assemblies, and wherein said supporting and moving means comprises means for offset mounting said cutting assemblies in a spaced apart relationship both laterally and longitudinally with respect to the center of said frame member, and means for independently adjusting each cutting assembly according to the conditions under which the apparatus is operating.

5. The trenching apparatus of Claim 1 wherein said cutting assembly support means comprises for each cutting assembly and extendable support structure, connected to and supporting said cutting assembly, a longitudinally extending connecting means defining a pivot axis parallel to the longitudinal axis of said frame member for supporting the cutting assembly and said extendable support structure for pivotal movement thereof about said pivot axis, and means connected between the extendable support structure and the frame member for selectively pivoting said cutting assembly about said pivot axis.