Method and apparatus for simultaneous trenching and pipe laying in an arctic environment

Disclosed is an apparatus for simultaneously trenching and laying a submarine pipeline within the bed of a body of water covered with a relatively thick ice mass. The apparatus comprises a pipeline construction spread which precedes a trenching and pipe installation spread, both of which traverse the ice mass. The pipe installation vehicle advances toward the constructed pipeline, elevates the pipeline, forms a slot-like opening in the ice and directs the pipeline into the water through the slot. A submersible dredging assembly extends from a installation vehicle which forms part of the installation spread. As the vehicle advances, the dredging assembly forms a trench in the sea bed. At the same time the dredging assembly guides the pipeline into the trench and provides support to a submerged component of the pipeline which is threaded through a slot in the dredging assembly.

BACKGROUND OF THE INVENTION 
This invention relates to the laying of submarine pipelines. More 
particularly, the invention is directed to simultaneous trenching and pipe 
laying in an arctic environment. 
Offshore oil production and storage facilities are typically linked to 
onshore facilities by at least one pipeline which has been laid upon the 
bed of a body of water. Because of the potential for vast offshore oil 
deposits in arctic regions many such pipelines will have to be constructed 
in bodies of water which are covered with a relatively thick ice mass for 
much of the year. Such pipe laying operations may take place during a 
winter season when the water is covered with a thick ice mass, or during a 
summer season when the water is open. 
Arctic pipe laying operations which are restricted to the short open water 
season rarely provide sufficient time to lay a pipeline of appreciable 
length. Economic hardships are thus incurred as a result of delays in the 
flow of production revenues, and consequently, less opportunity for rapid 
installation cost reduction. 
Alternatively, pipelaying operations conducted during an arctic winter 
season present the special problems associated with such a harsh 
environment. One noteworthy problem is that it is necessary to penetrate 
an ice mass of substantial thickness in order to gain access to the body 
of water in which the pipeline is to be laid. Moreover, it is often 
difficult to conveniently support the dredging and laying apparatus upon 
the ice mass or water. 
There are several known techniques for arctic trenching and pipelaying. For 
example, U.S. Pat. Nos. 3,822,558, issued July 9, 1974, and 3,924,896, 
issued Dec. 9, 1975, each disclose an arctic-type pipelaying and burying 
arrangement. These patents disclose a buoyant platform, supported on a 
cushion of air, which is operable to form a slot in the ice through which 
ice laying and burying equipment extend. A trencher mechanism extends 
beneath the surface of the water from the bow end of the platform while a 
stinger for supporting the pipeline to be laid extends from the stern of 
the platform. Other arctic pipelaying arrangements are disclosed in U.S. 
Pat. Nos. 3,681,927, issued Aug. 8, 1972, 3,744,259, issued July 10, 1973, 
3,844,129, issued Oct. 29, 1974, and 3,900,146, issued Aug. 19, 1975. 
Conventional pipelaying and burying arrangements in which a pipeline or 
cable being laid passes through or across a trencher mechanism are 
disclosed in U.S. Pat. Nos. 734,615, issued July 28, 1903, 737,021, issued 
Aug. 25, 1903, 956,604, issued May 3, 1910, and 3,641,780, issued Feb. 15, 
1972. 
The methods and apparatus described in the prior art fail to provide 
convenient and reliable means for laying and burying pipe on the bed of a 
body of water covered with an ice mass. Moreover, the prior art fails to 
disclose a simultaneous method and apparatus for laying and burying a 
submarine pipeline in which the pipeline to be laid receives adequate 
support while submerged, but prior to being received in a trench 
It is accordingly a primary object of this invention to provide a reliable 
method and apparatus for the simultaneous trenching and laying of a 
submarine pipeline. Another object of the invention is to provide a method 
and apparatus for trenching and laying a pipeline within a seabed during 
an arctic winter season in which the body of water is covered with an ice 
mass of substantial thickness. It is also an object of this invention to 
provide a novel apparatus for supporting simultaneous trenching and laying 
operation. A further object of this invention is to provide a submersible 
apparatus for conducting dredging operations while providing adequate 
lateral support for a submerged portion of the pipe. Other objects of this 
invention will be apparent to those skilled in the art upon reading this 
disclosure. 
SUMMARY OF THE INVENTION 
According to this invention, a method and apparatus is provided for the 
simultaneous trenching and laying of pipeline within the bed of a body of 
water covered with a relatively thick ice mass (i.e. 6 to 8 feet) which 
serves as a working platform. The apparatus of this invention comprises 
mobile pipeline construction and installation means which advance on the 
ice mass over the location where the pipeline is to be laid. 
The mobile means has two primary components. A first component, referred to 
as a pipeline construction spread, constructs an integral pipeline of an 
indefinite length by joining together a number of pipe segments. This 
spread is similar to, and utilizes similar technology, as the known 
cross-country and lay barge pipe construction techniques. The assembled 
pipeline is deposited behind the pipe construction spread on supports 
which maintain the constructed pipeline just above the surface of the ice. 
Following immediately behind the pipe construction spread is a pipeline 
installation spread. The installation spread comprises a vehicle which 
traverses the ice mass to support and control the trenching and laying 
operations as well as a series of pipe elevation supports and ice cutting 
and removal means. 
The pipe elevation support means comprise a plurality of skid-supported 
structures which are spaced apart and connected to each other and 
propelled by a tractor or similar means. These structures gradually guide 
the constructed pipeline to a height approximately twenty feet above the 
surface of the ice. Also included is a down ramp, or similar means, also 
supported by skids, which guides the pipe from a position of maximum 
height, downwardly to a position beneath the surface of the ice. 
Disposed between the pipe elevation supports, and under the elevated 
pipeline, is an ice cutting and removal apparatus. In a preferred 
embodiment, this apparatus includes a first machine which forms two 
parallel cuts in the ice which are spaced apart by approximately 8 to 10 
feet. Following behind the first cutting device is an apparatus which 
forms cuts in the ice perpendicular to and between the first parallel 
cuts, thus forming ice blocks. This apparatus also features means for 
gripping the ice blocks and placing them under the lip of the ice mass on 
alternating sides of the ice slot. In one embodiment, a third apparatus, 
such as a gantry crane, removes selected ice blocks for replacement in the 
ice slot behind the installation spread to provide added reinforcement to 
the ice. Preferably, each apparatus is supported by tracks or skids which 
straddle the ice slot and rest upon the ice mass. 
The installation spread follows behind the pipeline elevation system and 
includes a self-propelled lightweight vehicle. The vehicle is supported on 
and propelled over the ice by crawler tracks which straddle the slot in 
the ice. The installation spread is also equipped with a dredging assembly 
which facilitates the formation of a trench in the sea bed and aids in 
laying the constructed pipeline within the trench. As the installation 
spread advances toward the assembled pipeline, the length of the trench is 
advanced by continued dredging. This advancement also results in the 
constructed pipeline being received by the installation vehicle and 
simultaneously laid within the formed trench. In a preferred embodiment 
the spoils of the dredging operation are directed into a discharge pipe 
and diverted back into the trench to bury the laid pipeline. 
In a preferred embodiment the dredging means, such as a cutter suction 
head, is appended to the installation vehicle by way of a support means 
such as a dredging ladder. One end of the dredging ladder is pivotally 
secured to the installation spread, and from this point of attachment the 
dredging ladder extends forwardly at a slight angle beneath the surface of 
the water. The submerged end of the dredging ladder houses the dredging 
means which includes a cutter suction head, a dredging motor and dredging 
pump. In addition, a discharge pipe extends backwardly from the pump of 
the dredging means toward the trench. 
The dredging ladder is movable between a non-operative position directly 
below and substantially parallel to the longitudinal axis of the platform, 
and an operative position in which it is disposed beneath the surface of 
the water. An actuable arm may extend from the vehicle to an intermediate 
location on the dredging ladder to aid in the raising and lowering of the 
dredging ladder. The dredging ladder features a centrally disposed slot 
which is intended to receive and provide sub-sea support to the pipeline 
to be laid. Preferably, the dredging ladder supports the submerged 
pipeline at a critical location between the midpoint of the submerged 
component of the pipeline and the surface of the water. 
In a preferred embodiment, power is supplied to both the pipe construction 
spread and the pipe laying spread from a remote facility (or facilities) 
which traverses the ice mass alongside the spreads. A power supply cord is 
connected between the power supply vehicle and the spreads. 
Other objectives, features and advantages of this invention will be readily 
apparent from the following description of a preferred embodiment thereof, 
taken in conjunction with the accompanying drawings. It is to be 
understood that variations in and modifications to this invention may be 
effected without departing from the spirit and scope of the novel concepts 
of this disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 illustrates a preferred embodiment of the present invention in which 
an apparatus 10 is provided for simultaneously forming a trench within the 
bed of a body of water covered with an ice mass 11 and laying a pipeline 
14 within the trench. The apparatus 10 comprises two basic components, 
both of which are adapted to traverse a relatively thick ice mass covering 
the body of water. A pipeline construction spread 12 is provided for 
joining pipe segments 13 to form an integral pipeline 14 of indeterminate 
length. Spaced a predetermined distance behind the pipe construction 
spread 12 is a pipe installation spread 16 which simultaneously dredges 
the sea bed and lays the pipeline within the dredged trench. The 
installation spread 16 includes a forward section having a number of pipe 
elevation supports 18, and cutting means 20, 22 for creating an opening in 
the ice, a rearward section which includes an installation vehicle 24. 
In a preferred embodiment, the construction and installation spreads are 
immediately adjacent each other. However, it is to be understood that the 
construction spread 12 may precede the installation spread 16 by a 
substantial distance. 
The construction spread 12 may span a distance of approximately 160 to 200 
feet or more, depending upon the characteristics of the pipe being 
assembled. The installation spread 16 spans a distance of approximately 
one-eighth mile. The installation vehicle itself is about 120 to 160 feet 
or more in length depending upon the characteristics of the pipeline being 
laid. The weight of both the construction and installation spreads will of 
course vary depending upon the materials from which they are constructed, 
and their overall length. One skilled in the art may easily determine the 
materials from which spreads are to be constructed, the length of the 
spreads and the safety limits of the weight of the entire load which may 
rest on a given ice mass. 
ln a preferred method of operation the surface of the ice mass under which 
the pipeline is to be located is cleared of snow and other obstacles. Pipe 
segments 13 may then be disposed at various supply caches along the 
cleared route. The pipe construction spread 12 travels over the ice along 
the cleared route and joins the pipe segments to form an integral 
constructed pipeline 14 of indeterminate length. The constructed pipeline 
14 is deposited on supports 26 which elevate the pipeline 14 a slight 
distance (i.e. approximately three feet) above the surface of the ice. In 
a preferred embodiment, the pipe construction spread 12 is propelled by 
acting against the constructed pipeline. Alternatively, spread 12 may be 
pulled in tow by a tractor (not shown) or similar means able to provide 
traction on the ice surface. 
The installation spread 24, following immediately behind the construction 
spread 12, advances toward the constructed pipeline 14. The pipeline 14 is 
further elevated by an inclined up ramp 32 which serves as the lead 
component of spread 16. As ramp 32 advances, the pipeline 14 is 
progressively elevated and is eventually deposited upon pipe elevation 
supports 18 which maintain pipeline 14 at a height of approximately 20 
feet above the ice surface. In one embodiment a first ice cutting means 20 
travels behind up ramp 32 and beneath the elevated pipeline 14 to form two 
parallel grooves in the ice which fully penetrate the ice mass and are 
spaced apart by a distance of approximately 8 to 10 feet. A second ice 
cutting means 22 travels over the ice closely behind the first ice cutting 
means 20 and forms an additional cut, or cuts, in the ice mass which are 
oriented perpendicular to and run between the parallel grooves formed by 
cutting means 20, thus forming ice blocks 34. The ice blocks 34 thus 
formed are removed from the ice hole to provide a slot-like opening in the 
ice mass. In a preferred embodiment, the ice blocks 34 may be placed 
beneath the surface of the ice by ram means 23 carried on cutting means 
22. Preferably, the ice blocks 34 are placed on alternating sides of the 
slot beneath the lip of the ice to provide added support to the ice mass. 
As the installation spread 16 advances, pipeline 14, elevated by supports 
18A, 18B and 18C, is directed downwardly toward the slot in the ice by 
down ramp 36. 
The various ramps, supports and cutting means, which form a forward portion 
of spread 16, may be tethered to each other and towed by tractor 30 or a 
similar means for facilitating movement over the ice. These components 
move in concert with and are connected to installation vehicle 24 by cable 
40. Preferably, installation vehicle 24 is self-propelled. 
The advancing installation vehicle 24 includes equipment which is adapted 
to create a submarine trench 42 of approximately 15 feet in depth in the 
bed of the body of water. At the same time, vehicle 24 lays pipeline 14 
within trench 42, in a manner more fully described below. Preferably, the 
laid pipeline 14 may be covered with the spoils of the trenching operation 
which are redirected to the trench through discharge pipe 126. 
In a preferred embodiment the trenching and pipe laying operation is 
conducted during an arctic winter season when the ice mass is of 
sufficient thickness, such as 6 to 8 feet, to support the weight of the 
apparatus 10 of this invention. To extend the pipe laying season, it is 
sometimes possible to increase the ice mass thickness to provide a working 
ice surface of sufficient strength to support the apparatus 10 of this 
invention. Such ice thickening techniques are well known to those having 
ordinary skill in the art. In a preferred embodiment, the components of 
the pipe construction spread 12 and the installation spread 16 are 
supported on snow skids, if towed by another vehicle, or crawler tracks, 
if self-propelled. In either case, the skids or tracks are supported by 
the ice and typically straddle the slot formed in the ice. 
The pipe construction spread 12, as illustrated in FIG. 1, comprises a 
plurality of environmentally controlled work stations 44 which are 
supported on snow skids. The work stations 44 are serially connected and 
aligned along the longitudinal axis of the spread 12. A pipe conveyor 
system (not shown) extends along the entire length of the spread. A 
control room 46 is located at the head of the spread and contains a diesel 
generator room, fuel storage facility and a control room. The design 
parameters for such an apparatus, which may vary for a given pipe laying 
run, are easily developed by one of ordinary skill in the art. 
The pipeline 14 is constructed by placing a pipe segment 13 on the pipe 
conveyor system and aligning it with the existing pipeline or pipe segment 
to which it is to be joined. The pipe segments may be joined by a variety 
of known techniques. Preferably, however, the pipe segments are joined by 
automatic welding techniques which are performed within the 
environmentally controlled work stations 44. In a preferred embodiment it 
is also desirable to have one or more work stations equipped with x-ray 
equipment to ensure the integrity of the welded joints. Also, it is 
desirable to have audio and visual linkage between the work stations and 
the control room. 
In a preferred embodiment, the construction spread 12 is propelled as a 
result of using the pipe conveyor system to react against the constructed 
pipeline thus resulting in forward movement of spread 12. This method of 
propulsion may be replaced or supplemented by any one of a number of 
propulsion means well known to those skilled in the art. For example, the 
construction spread 12 may be towed by a tractor (not shown) or similar 
means which is able to provide traction over the ice surface. The speed at 
which construction spread 12 travels depends on the dimensions of the 
pipeline being constructed and laid, and typically ranges between 1 mile 
per day and 3 miles per day. 
As the constructed pipeline 14 leaves the construction spread 12 it is 
deposited on pipe supports 26 which maintain the pipeline at a height of 
about three feet above the ice. The supports 26 prevent the pipeline 14 
from freezing to the ice surface. Supports 26 are spaced apart by 
approximately 40 foot intervals. 
The pipeline 14 laid with the apparatus of this invention may be of any 
type which is typically used in arctic, submarine applications. 
Preferably, the pipeline has an inside diameter ranging from several 
inches to several feet. The wall thickness of the pipe may range from 
approximately one quarter inch to a few inches. 
The installation spread 16 simultaneously trenches and lays the pipeline 
within the sea bed. This spread spans approximately one-eighth of a mile 
and is adapted to move at a minimum rate of between one to three miles per 
day. The installation spread 24 includes three components: a pipeline 
support system, an ice slotting and removal system, and an installation 
vehicle 24. 
A pipeline elevation system, towed by a tractor 30, or similar means 
capable of operating in an arctic climate and providing traction on an 
iced surface, serves as the forward portion of the installation spread 16. 
An inclined ramp 32 is the lead element of spread 16 and travels under the 
constructed pipeline, thereby raising it a greater distance above the 
surface of the ice. Additional elevation means 18A, 18B and 18C follow 
behind inclined ramp 32 and are connected to ramp 32, and each other, by 
cables 40. As the installation spread 12 advances, the constructed 
pipeline 14 is further elevated and is supported by the top surface of 
supports 18A, 18B and 18C at a height of approximately 20 feet above the 
surface of the ice. A down ramp 36 is spaced behind the last support 18A 
and gradually directs the constructed pipeline 14 downwardly toward the 
surface of the ice. 
Inclined ramp 32 comprises a support frame of suitable strength and design 
to support the weight of the constructed pipeline 14. The support frame is 
mounted upon snow skids which may be spaced relatively close together or, 
alternatively, spaced apart by approximately 8 to 10 feet so that, if 
necessary, the skids may straddle the slot in the ice. Typically, however, 
it is not necessary for the skids of ramp 32 to straddle the ice slot as 
ramp 32 precedes the slot. The top surface of inclined ramp 32 is 
typically inclined at a slight angle sufficient to gradually elevate the 
pipeline to the desired height. This angle is, of course, dependent upon 
the physical properties of the pipeline and may be easily determined by 
one skilled in the art. Ramp 32 may feature a groove of sufficient width 
to supportingly receive the constructed pipeline 14. The interior surface 
of the groove may be constructed from a self-lubricating polymer, or may 
be lined with rollers or bearings to provide the necessary low friction 
seating to facilitate the easy passage of pipe over the ramp. 
Alternatively, the surface of the ramp may be constructed without a groove 
and may be lined with a self-lubricating polymer or may feature bearings 
or rollers to decrease friction. In such case it may be advantageous to 
provide a guide means on the surface of ramp 32 to ensure that pipeline 14 
is properly positioned. 
Elevation support means 18 may comprise approximately three structures 
(18A, 18B and 18C) which are each spaced apart by a distance (e.g. 
approximately 40 to 80 feet) which will vary depending upon the 
characteristics of the pipeline. Preferably, structures 18A, B and C are 
of non-uniform height with structure 18B being the tallest and structures 
18A and 18C being of a substantially equal height and slightly shorter 
than structure 18B. In another embodiment, structures 18A, 18B and 18C may 
all be of uniform height. Ultimately, structures 18A, B and C elevate 
pipeline 14 to a height of approximately 20 feet above the surface of the 
ice. 
In a preferred embodiment, where structures 18A, B and C are of non-uniform 
height, structure 18C follows a predetermined distance behind inclined 
ramp 32 and has a top surface which is slightly inclined to enable the 
pipeline to be gradually elevated to rest on structure 18B. Structure 18B 
follows a predetermined distance behind structure 18C and is approximately 
20 feet in height. Following behind structure 18B is structure 18A which, 
like structure 18C, is slightly less than 20 feet in height. Structure 18C 
has a top surface which slopes downwardly away from structure 18B at an 
angle which is opposite but approximately equal to that of structure 18A. 
Structures 18A, B, and C are all constructed of a support frame of 
sufficient strength to support the weight of the constructed pipeline. The 
support frames of structures 18A, 18B and 18C are each mounted upon snow 
skids, spaced approximately 8 to 10 feet apart which preferably are 
adapted to straddle the slot in the ice. 
The top surfaces of structures 18A, B and C may all be constructed as 
described with respect to ramp 32. 
A down ramp 36 follows a predetermined distance (e.g. approximately 40 to 
80 feet) behind structure 18A. The top surface of ramp 36 is declined in a 
direction away from structure 18A at an angle sufficient to gradually 
direct the pipeline beneath the surface of the water. Like ramp 32, ramp 
36 is constructed of a frame which is mounted upon skids spaced apart by a 
distance sufficient to straddle a slot cut in the ice. The top surface of 
ramp 36 is constructed in such a way as to facilitate the low friction 
passage of the constructed pipeline 14 over the top surface of the ramp, 
and may be constructed as described with respect to the top surface of 
ramp 32. 
To gain access to the bed of the body of water, it is necessary to create 
an opening in the ice mass 11. In the present invention this is 
accomplished by forming a slot-like opening of indeterminate length in ice 
mass 11. A first cutting device 20 is located behind inclined ramp 32 and 
below the elevated pipeline 14. Cutting device 20 contains plural cutting 
means 48 which are disposed side-by-side and spaced apart by approximately 
8-10 feet. Cutting device 20 forms parallel grooves in the ice of 
sufficient depth to fully penetrate the ice mass. The cutting means 48 may 
comprise conventional cutters of the type well known in the art, e.g. 
rotary blade saws, endless blade cutters, hydraulic saws, shaped charge 
explosives, laser cutters, or other means suitable for such an 
application. Cutting device 20 is preferably a self-propelled vehicle such 
as a tractor 51 or similar means which is able to provide traction over an 
iced surface. 
As illustrated in FIG. 1, second cutting device 22 travels a predetermined 
distance behind first cutting device 20 and is situated beneath elevated 
pipe 14. As best shown in FIGS. 4A and 4B second cutting device 22 
includes cutting means 50 which is pivotally mounted on one side of 
cutting device 22. Cutting means 50 may comprise a cutting tool such as a 
saw or similar means which is able to penetrate an ice mass having a 
thickness of approximately 6 to 8 feet or more. Cutting means 50 is 
adapted to form a cut in the ice which runs perpendicular to and between 
the grooves formed by first cutting device 20, thus forming blocks 34. In 
an alternative embodiment, cutting device 22 may contain the means for 
both forming slots in the ice and forming ice blocks. It is also 
understood that cutting means 50 may comprise any of the various devices 
described above with respect to first cutting means 48. 
After cutting an ice block from the ice, ram means 52, which may form part 
of second cutting device 22, grips the cut ice block 34 and disposes it 
under the surface of the water beneath the lip of the ice mass. 
Preferably, the cut ice blocks 34 are disposed on alternating sides of the 
ice slot. 
As is best shown in FIGS. 4A and 4B, second ice cutting device 22 comprises 
a frame-like support structure 58, formed of a strong, light weight 
material mounted upon crawler tracks 60. Alternatively, support structure 
58 may be mounted upon snow skids. As illustrated in FIG. 4A, cutting 
means 50 utilizes a cutting tool such as a saw or or other such tool, 
which is pivotally mounted to a flange 62 appended to one side of support 
structure 58. The cutting means 50 is partially shielded by a protective 
plate 64 mounted above the cutting means. As illustrated in FIG. 4B, 
cutting means 50 is preferably mounted at the forward end of the cutting 
device 22. Cutting device 22 is oriented such that the cutting means 50 is 
able to form a cut in the ice which is perpendicular to and runs between 
the grooves cut by cutting device 20. Upon being activated, cutting means 
50 will pivot downwardly about point 66 to penetrate the ice thus forming 
an ice block 34. 
In another embodiment, the cutting means 50 may include twin saws, or 
similar cutting tools which are spaced apart by approximately 8-10 feet. 
Such an arrangement may increase the cutting efficiency of cutting device 
22. 
Referring to FIGS. 4A and 4B, a preferred embodiment of cutting device 22 
also includes ram means 52 for grasping ice blocks 34 and disposing the 
blocks beneath the surface of the ice on alternating sides of the slot in 
the ice. Ram means 52 is centrally located on cutting device 22 and is 
mounted on a cross bar structure 56 which enables the ram means 52 to be 
suspended over the slot to be formed in the ice. Ram means 52 includes 
approximately four telescopingly extensible arms 54 which are each mounted 
in the vicinity of one of the corners of a generally square flange 56. 
Extensible telescoping arms 68 are received in sleeves 69 such that arms 
68 are able to extend from sleeves 69, downwardly beneath the surface of 
the water. The lower ends of each of arms 68 are pivotally attached at 
point 72 to a gripping means 70. Gripping means 70 is adapted to securely 
grasp a cut ice block once it has been cut. After the ice block has been 
firmly grasped, arms 68 extend from sleeves 69 and force the ice block 
downwardly beneath the surface of the water as shown in FIG. 4A. When arms 
68 are fully extended the ice block is pivoted (either clockwise or 
counterclockwise), as shown in FIG. 4B, to place the ice block beneath the 
surface of the ice. After the ice block is properly located beneath the 
surface of the ice, the grasping means is released and arms 68 are 
retrieved. The exact design of ram means 52 may vary depending upon the 
goals of a particular pipelaying operation. One skilled in the art may 
easily choose a design for ram means 52 which will suit the objectives of 
a particular operation. 
In a preferred embodiment of the invention a block removal device 73, for 
example a gantry crane 75 mounted upon snow skids as shown in FIGS. 1 and 
5, is included as part of the installation spread 16 for removing selected 
ice blocks from within the ice slot. Ice blocks removed in this manner may 
be placed on the surface of the ice for subsequent replacement within the 
slot to add additional reinforcement to the ice mass and to facilitate 
quick mending of the ice surface. Preferably, block removal device 73 is 
located between elevation supports 18A and 18B and is mounted upon snow 
skids which straddle the ice slot. Further, removal device 73 is 
preferably connected by cable to the support structures 18 and moves in 
concert with these components as they are towed by tractor 30. In a 
preferred embodiment, every tenth block is removed by device 73 for 
replacement in the slot. It is understood, however, that in the practice 
of the present invention the ice blocks selected to be removed may be 
other than every tenth block. 
Although block removal device 73 may comprise virtually any suitable 
crane-like structure, a gantry crane 75 such as that shown in FIG. 5 is 
preferred. Gantry crane 75 comprises a rectangular support frame 76, as is 
well known in the art. In an alternative embodiment the gantry crane 75 is 
self propelled and traverses the ice on crawler tracks 78 which straddle 
the slot in the ice. 
Suspended from a top cross-bar 77 of rectangular frame 76 is a crane means 
80 for raising and lowering the ice blocks. Secured to the lower portion 
of the crane means 80 is a block receiving frame 82 which securely holds 
the ice blocks to be removed. The crane means 80 mounted upon the top 
cross-bar 77 of frame 76 includes an extensible cable 84 for raising and 
lowering the block. Crane means 80 is adapted to move horizontally across 
the top cross-bar 77 of frame 76 to facilitate placement of the ice block 
on the surface of the ice mass for subsequent replacement within the ice 
slot. Crane means 80 is powered by a motor capable of lifting the ice 
blocks which are to be removed from the slot. 
The installation vehicle 24 follows behind the pipe support structures and 
the ice cutting equipment as shown in FIG. 1. Platform 24 comprises two 
primary components--a support platform 86 and a dredging means 88. 
Referring to FIGS. 2A, 2B, 2C and 3, support platform 86 comprises a high 
strength, light weight frame 90, the design of which may be easily 
developed by one having ordinary skill in the art. Frame 90 is mounted 
upon crawler tracks 92. The top deck 94 of platform 86 includes control 
rooms 96 and 98, and service crane means 100. Dredging vehicle 24 is 
self-propelled upon crawler tracks 92 and receives power from a remote 
source (not shown) which travels alongside vehicle 24. As best shown in 
FIG. 3, support platform 86 features at least one guide means 102, which 
is height-adjustable through pulley system 104, for providing guiding 
support for pipeline 14 in both submerged and surface positions. 
Appended from platform 86, and oriented along the longitudinal axis of 
platform 86, is dredging assembly means 88 which is operably disposed 
through the slot in the ice. Dredging assembly 88 is preferably pivotally 
attached to the rear end of the platform 86 at points 106. As such, the 
dredging assembly may be raised to an inoperative surface position or 
lowered to a operative submerged position. To aid in the raising and 
lowering of dredging assembly 88, and to provide additional stability, the 
support platform 86 is equipped with an actuable arm 108 which is 
pivotally connected to and extends between an intermediate portion of the 
dredging assembly 88 and the support platform 86. 
Dredging assembly 88 comprises a dredging support ladder 110, one end of 
which is pivotally secured to a rear end of support platform 86 at points 
106 as noted above. Ladder 110 extends forwardly from its point of 
attachment on platform 86, and is pivotable between an inoperative surface 
position and operative submerged position. In the surface position (shown 
in phantom in FIG. 2A) the ladder 110 is nested just below the lower deck 
90 of platform 86. In such a position ladder 110 is substantially 
horizontally oriented along the longitudinal axis of platform 86 and is 
disposed above the slot in the ice. In the operative position the ladder 
110 is disposed at a slight angle with the lower deck 90 and extends 
downwardly through the slot in the ice to the sea bed. An actuable arm 108 
facilitates the lowering of ladder 110 and also provides additional 
support to the ladder during trenching operations. 
Dredging ladder 110 is preferably constructed of a strong, light weight 
material such as alloys, composites and advanced polymers. It is expected 
that ladder 110 should be of sufficient strength to withstand the stresses 
associated with dredging from a moving surface vehicle in a corrosive 
arctic environment. The dredging ladder 110 may be described as an 
elongate member having a length sufficient to extend from platform 86 to 
the sea bed. Although its length will vary with particular applications, 
the length of ladder 110 is generally in the range of 110 to 150 feet. The 
width of ladder 110 must, of course, be small enough to enable it to fit 
within an 8 to 10 foot wide ice slot in the ice. In addition, as best 
shown in FIG. 6, ladder 110 features a central, elongate slot 112, the 
dimensions of which will vary depending upon the dimensions and physical 
properties, including the bend radius, of the pipeline being laid. In any 
event, the slot 112 should be of such size as to enable the pipeline to be 
easily threaded through the slot, while at the same time provide lateral 
and vertical support to the pipeline. One skilled in the art may easily 
determine the proper dimensions and placement of slot 112 for a given 
pipelaying operation. 
Slot means 112 preferably is positioned so as to allow a submerged 
component of the pipeline to pass through the slot means 112 such that the 
slot provides support to the submerged component of the pipeline at a 
location between the midpoint of the submerged component and the surface 
of the water. 
As illustrated in FIGS. 2A and 6, the forward end of ladder 110 houses a 
dredging means 114 which creates the trench within the sea bed. Dredging 
means 114 includes a cutter suction head 116, a cutter motor 118, 
reduction gear 120, dredging pump 122, pump motor 124 and a discharge pipe 
126. 
In a preferred embodiment the dredging operation is accomplished using a 
cutter suction head 116 having a generally circular shape, with a diameter 
of approximately 10 feet and sufficient power to create a trench of up to 
15 feet in depth. It is believed that a wide variety of cutter suction 
heads may be used in the practice of the present invention. Preferably the 
cutter suction head features interchangeable teeth to accommodate dredging 
operations in a variety of soils. The cutter head 116 preferably is 
powered by a 1000 horsepower motor 118 which enables the cutter head to 
break up the seabed to form the trench 42. Through the action of pump 122, 
which is approximately 30.times.30 inches, and is powered by a 1000 
horsepower motor, the dredging spoils are pumped into discharge pipe 126. 
Discharge pipe 126 is mounted to the side of ladder 110 and extends 
upwardly with the ladder to the rear of platform 86. After reaching the 
platform 86, pipe 126 is redirected downwardly into the water to 
facilitate the backfilling of the trench after the pipe has been laid, as 
shown in FIG. 1. 
To commence the trenching and pipe laying operation of this invention, the 
ice over the area in which the pipeline is to be laid is cleared of snow 
and other obstacles, and the pipeline is constructed as described above. 
As the installation spread 16 advances toward the constructed pipeline 14, 
the pipeline is raised on supports 18 to a height of approximately 20 feet 
above the ice surface. Ice cutting device 20, operates beneath the 
elevated pipe to create a slot-like opening of approximately 8 to 10 feet 
in width. A second cutting device 22 cuts blocks 34 in the ice and, 
through the action of ram means 52, disposes the blocks under the surface 
of the ice. Subsequently the pipe 14 is directed downwardly toward the 
slot cut in the ice. 
With dredging assembly 88 and guide 102 in the raised position, pipeline 14 
is threaded first through guide 102 and then through slot 112 of dredging 
ladder 110. The guide 102 and dredging assembly 88 are then lowered 
through the slot in the ice (along with the pipeline) into the water. 
After cutter suction head 116 contacts the seabed, dredging is commenced 
and trench 42 is created. Installation vehicle 24 advances along the 
predetermined path while extending the length of trench 42. As the vehicle 
24 advances it gathers additional length of pipeline 14 and simultaneously 
deposits the pipeline within the trench. After the pipeline 14 is laid it 
is covered with the spoils of the dredging operation which issue from the 
discharge pipe 126. The trenching and laying operation continues in this 
manner until a sufficient length of pipeline is laid. 
Although the invention has been described in connection with a preferred 
embodiment thereof, it will be appreciated by those skilled in the art 
that additions, modifications, substitutions and deletions not 
specifically described may be made without departing from the spirit and 
scope of the invention as defined in the appended claims.