WO2003023152A2

WO2003023152A2 - Apparatus and methods for trenching

Info

Publication number: WO2003023152A2
Application number: PCT/US2002/028917
Authority: WO
Inventors: Franck K. Bonar
Original assignee: Rocksaw Technology, Inc.
Priority date: 2001-09-11
Filing date: 2002-09-11
Publication date: 2003-03-20
Also published as: WO2003023152A3; AU2002324960A1

Abstract

A trenching apparatus (1) adapted for underwater trenching that includes a flushing (11) device and a mechanical loosening device (31). The flushing device of the underwater trencher is provided with two sets of nozzles (25f, 25b), one set being oriented in a direction toward a flushable cover layer for flushing the flushable material from the cover layer to allow the flushing device to move downwardly onto a base layer and the other set of nozzles being oriented in the direction the flushing device is moved once it rests on the base layer. One or more riser sections are provided for conveying water, air, or a combination of water and air to the flushing device from a pump located on the surface of the water and for positioning the flushing device in the water. The mechanical loosening device (31) for use with both an underwater trencher and on dry land is a chain-milling device (35) that is provided with adjustable chain tensioning. A sled (69) is provided that is pivotable to maintain close contact with the surface of the stratum/strata being trenched and a tool bar assembly is pivotable with respect to the sled for maintaining the optimum cutting angle of the chain tool comprising the chain-milling device. Depth of cut is adjusted by moving the chain tool up and down relative to the tool bar assembly and by pivoting the tool bar assembly relative to the sled.

Description

APPARATUS AND METHODS FOR TRENCHING

BACKGROUND OF THE INVENTION The present invention relates to apparatus and methods for trenching. More specifically, the present invention relates to a method for progressively producing an underwater laying-out channel for an object to be laid out, like a cable or pipe, in an underwater ground by flushing and by mechanically loosening ground formations which are resistive against flushing, by means of a mechanical loosening device having a given maximum working depth. The invention furthermore relates to an apparatus for performing the method, the apparatus comprising a flushing device, like a flushing colter, movable through flushable ground areas of the underwater ground, and a mechanical loosening device for loosening ground formations which are resistive against flushing. The invention furthermore comprises an apparatus for trenching on land. In prior art underwater methods and trenching apparatus, the flushing and the mechanical loosening proceed from a base, for instance a vehicle that is progressively advanced across an underwater ground (an example of the latter is disclosed in German Patent No. 29 22 410). It is furthermore known to provide mechanically acting ripping teeth or the like at the front side of a flushing colter (German disclosure letter No. 14 84 692, German publication letter No. 11 71 968). Furthermore, apparatuses are known which comprise only a flushing device or only a mechanical loosening device (prospectus of the company Simec Z.I. La Malle, Bouc Bel Air, France, printing mark IPS 13160).

Although known methods and devices operate satisfactorily in many applications, in the case of underwater grounds in which flushable ground formations alternate with ground formations which are resistive against flushing, it has occurred that the laying-out channel did not permit sufficiently deep embedding of the laid-out object, and cables laid out in accordance with such methods became damaged by ship anchois even though a trench of depth of sufficient depth to avoid such damage had been projected. U.S. Patent No. 4,787,777 describes a method and device for progressively producing an underwater laying-out channel comprising a flushing device that is said to be movable through any flushable ground area of the underwater ground above a base layer that consists of a mechanical loosening device arranged in the lower end area and to the rear of the flushing device that addresses the limitations of these prior art devices, and the present invention is, among other things, an improvement to the device and method described in that patent. In the case of trenching on land, the conventional approach -o deeper, faster trenching is to utilize bigger, heavier, and higher horsepower trenchers. The cost of building and operating such trenchers, however, is such that there is a need for an apparatus and method for digging/cutting such trenches that is capable of deeper trenches and faster rates of speed. It is, therefore, an object of the present invention to provide a method and apparatus that is capable of digging/cutting deep trenches at relatively high rates of speed and to increase penetration for excavating rock and other hard materials.

Another object of the present invention is to provide an underwater trenching apparatus by which the produced laying-out channel ensures an always sufficiently deep embedding of the object into ground formations which are resistive against mechanical impacts, for instance by ship anchors, that improves upon the device and method disclosed in U.S. Patent No. 4,787,777.

It is also an object of the present invention to provide a mechanical loosening device to an underwater formation that is resistive against flushing, and advancing, in an advancing direction, the mechanical loosening device through the underwater formation which is resistive against flushing, with the working depth being effective from the surface of the formation.

Another object of the present invention is to provide an underwater trenching method in which the working depth of the mechanical loosening device is counted only from the maximum flushing depth obtainable, whereby the working depth achieved with the mechanical loosening device is completely available as a protection depth in a mechanically solid underwater formation.

Another object of the present invention is to provide an underwater trenching method and apparatus in which the flushing device acts, so to speak, as a probe that guides the mechanical loosening device along on the non-flushable solid underwater formation, whereby the working depth of the mechanical loosening device becomes fully effective in that solid underwater formation.

Yet another object of the present invention is to provide an apparatus for producing an underwater trench in which the loosening of the underwater formation is performed in a rear section of the flushing area, in the sense of the advancing direction, and a forward section of the flushing area remains free of the influence of the mechanical loosening device. Accordingly, the mechanical loosening device is arranged in a rear section of the flushing area produced by the flushing device. Thus, the effect of the loosening device is supplemented by an additional flushing in the area where the loosening device is effective. In doing so, the flushing is preferably done at least partly also with air; thereby, an area of reduced density forms in the range of the loosening device that facilitates the removal of ground material from the laying-out channel. To this end, the mechanical loosening device is provided with flushing nozzles for water and/or air. If the loosening device comprises a chain tool, i.e. is designed for instance as a chain milling device or the like, it is appropriate to provide flushing nozzles beneath the chain tool, thereby effectively rinsing the loosened material from the loosening device.

Another object of the present invention is to provide apparatus and methods for laying out an underwater trench of defined width, rather than a wide furrow in the sediment on the underwater floor of the type laid out by certain known prior trenchers, such that the trench that is cut in the hard subsoil or rock on which the sediment lies is cut to a precise width and depth to better insure that the pipe and/or cable is protected and secure.

Another object of the present invention is to provide a method and apparatus for underwater trenching that makes it possible to lay the object to be laid out into the laying- out channel during the production of the laying-out channel. The device is provided with laying-out devices for laying out the object during the production of the laying-out channel. The laying-out devices can be designed in the usual manner, for instance with a gradually curved cable guide, with the object, for instance a cable, being guided therethrough. Another object of the present invention is to provide a method and apparatus for trenching that is adaptable enough to allow pre-trenching, post-trenching or simultaneous trenching and installing of cable or pipe into the underwater floor depending on the specific condition of the underwater floor. Another object of the present invention is to provide a method and apparatus for underwater trenching that increases the likelihood that the cable or pipe will be sufficiently embedded into the subsea soil, rock, or other strata so that it is secure and safe from impact from anchors and other objects that may be dragged along the subfloor, or ice layers, all of which could cut or gouge into the subfloor and injure exposed cable or pipes. It is also an object of the present invention to provide a mechanical chain excavating device operable against a formation that is resistive against plowing and through which known trenchers are not able to trench because of the hard subsoil, rock, etc., in an advancing direction. The mechanical chain cutter device trenches through such formations with the working depth being effective from the surface of the formation. Another object of the present invention is to provide an underwater trenching apparatus which is characterized in that the mechanical trenching device is arranged in the lower end area of the flushing device so that the water jet assisted plow is able to first excavate through the softer material on the sea floor to the harder sub-surfaces and the chain cutter will cut its full depth in the harder material underneath. Another object of the present invention is to provide a method and apparatus for underwater trenching in which the working depth of the mechanical chain cutter device is counted only from the maximum plowable and flushing depth obtainable, whereby the full depth of the trench cut in the solid underwater formation by the mechanical trenching device is available to protect the cable and/or pipe laid in the trench. Another object of the present invention is to provide a method and apparatus for underwater trenching in which the plow device acts to guide the mechanical chain cutter device along on the plowable or jetable solid underwater formation, whereby the working depth of the mechanical trenching device becomes fully effective in that solid underwater formation. Yet another object of the present invention is to provide an apparatus for producing an underwater trench in which the trenching of the underwater formation is performed in a rear section of the plow, in the sense of the advancing direction, and the forward section of the flushing area remains free of the influence of the mechanical chain- cutting device, which is then able to cut the subsoil from which the plowable/jettable material has been removed by the plowing device with the mechanical chain-cutting device in the flushed area so as to allow the mechanical cutter to trench the hard subsoil. Thus, the effect of the water jet enhanced plow is supplemented by additional flushing/jetting directed in both the area where the mechanical chain cutter device is about to cut and against the cutter device itself to remove cut material, thereby making the cutter device more effective. The flushing/jetting is preferably done at least partly also with air, thereby creating an area of reduced density in the range of the plow and chain cutting device that facilitates the removal of ground material from the underwater trench. To this end, the mechanical trenching device is provided with flushing nozzles for water and/or air to enhance and facilitate movement of the material as the chain cutter excavates the material. If the trenching device comprises a chain tool, i.e. is designed for instance as a chain milling device or the like, is appropriate to provide flushing nozzles beneath the chain tool. Thereby, the chain tool is more effectively rinsed free of the loosened material and the material is flushed up and out of the trench, increasing the efficiency of the trenching apparatus.

Another object of the present invention is to provide a method and apparatus for trenching that makes is possible to lay the object to be laid out into the trench during the trenching operations. The device is provided with laying-out devices for laying out the object during the production of the laying-out channel. The laying-out devices can be designed in the usual manner, for instance with a gradually curved cable or pipe guide, with the object (for instance a cable or pipe) being guided into the trench directly behind the trencher, directly following the trencher into the trench.

Another object of the present invention is to provide a method and apparatus for both surface and underwater trenching that is capable of maintaining the trench at a specified depth. Another object of the present invention is to provide a method and apparatus for both surface and underwater trenching that includes a chain tool-type cutting device that is able to maintain an optimal cutting angle of that cutting device so as to maximize the efficiency of the apparatus. This list of several of the objects of the present invention is not intended to be all- inclusive. Other objects, and the advantages, of the present invention will be made clear to those skilled in the art by the following description of several embodiments thereof.

SUMMARY OF THE INVENTION These objects are achieved by providing an underwater trenching device comprising a flushing device movable in a selected direction through a flushable ground area of an underwater formation above a base layer, a plurality of flushing nozzles arrayed on said flushing device and oriented in the selected direction, and a plurality of flushing nozzles arrayed on said flushing device and oriented in a downward direction toward the flushable ground area. Means is provided for directing either water or air, or a combination of water and air through either or both of the flushing nozzles oriented in the selected direction or the flushing nozzles oriented downwardly toward the flushable ground area.

The present invention also provides a method of progressively producing an underwater laying-out channel for an object to be laid out in an underwater channel comprising the steps of lowering a flushing device into water and into proximity to a flushable ground area under the water and pumping either water, air, or a combination of water and air through an array of nozzles directed toward the flushable ground area to flush the flushable ground area from under the flushing device, thereby allowing the flushable device to be lowered down into the flushable ground area. The flushing device is thereafter moved through the flushable ground area while pumping either water, air, or a combination of water and air through an array of nozzles directed toward the direction of movement of the flushing device to flush the flushable ground area from in front of the flushing device, thereby creating a laying-out channel in the flushable ground area.

The present invention also provides an apparatus, and a method, for underwater trenching that incorporates three modes of action into a single trenching system: a plow with a "V" cut section in front which would cut through plowable material to a precise width and variable depth up to ten feet (10') and with side plates to hold a flat smooth trench face or wall; a first set of water jets at the far front in the "V" plow section to enhance the plowing system by flushing the plowed material outward and around to the side of the plow face and a second set of water jets for flushing downwardly to allow the plow jet system to be lowered into the plowable material to a hard base rock or other hard material; and a chain cutter system mounted to the rear of the plow that is capable of excavating rock and other hard materials (which are not plowable or jetable) to variable depths and widths of fifteen feet (15') or more depending on the material to be trenched.

The performance of this third mode of action is enhanced by installing water jets to flush the cutter system clean and to push or move the excavated material out and away from the trencher, moving the material to a desired location for backfilling the trench, thereby increasing the likelihood that pipe or cable has been safely buried in the rock or other hard material deep in the seabed.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a partially schematic view of an embodiment of an underwater trenching apparatus constructed in accordance with the teachings of the present invention. Figure 2 is a partially schematic view of the underwater trenching apparatus of Fig. 1 as it is being utilized in underwater trenching operations.

Figure 3 is a perspective view of the flushing colter and underwater trenching apparatus of Fig. 1. Figure 4 is a perspective view of a second embodiment of an underwater trenching apparatus constructed in accordance with the teachings of the present invention.

Figure 5 is a perspective view of an apparatus constructed in accordance with the teachings of the present invention for use in trenching on dry land. Figures 6A and 6B are perspective views of the apparatus of Fig. 5 showing the manner in which the cutting device comprising a portion thereof is moved to maintain optimal cutting angles and a pre-determined depth of the trench.

Figure 7 is a perspective view of the sled that comprises a portion of the trenching apparatus of the present invention, removed from the apparatus for clarity of illustration.

Figure 8 is a side elevational view of the sled of Fig. 7 having the conveyor removed therefrom, but with the chain-milling device mounted thereto, having a portion of the side plates cut away to show the manner in which the structure of the sled causes the spoil from the trench to be milled into smaller size pieces of rock. Figures 9A and 9B are side elevational and sectional views, respectively, the sectional view being taken along the line A - A in Fig. 9A, of the nose wheel assembly that comprises a portion of the chain-milling device that is utilized in each of the embodiments of the present invention shown in Figs. 1, 4, and 5.

Figures ION 10B, IOC, and 10D are partially schematic, side elevational views of several embodiments of the chain-milling device of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Figs. 1 - 3 show an underwater trenching device constructed in accordance with the teachings of the present invention during progressive production of a laying-out channel 3 in an underwater ground which comprises a flushable cover layer 5, for instance of sand, and therebelow a ground formation 7 that is resistive against flushing. The apparatus 1 works in the advancing direction 9 shown. The apparatus contains a flushing device 11 in the form of a flushing colter that is designed in the usual manner and is hung via a riser 19 on a surface vessel 17 of the water body 15, and which is put under the action of a pulling force 23 by means of a driving device (not illustrated) in the manner known in the art. The flushing device 11 comprises in its lower area, up to a level which approximately corresponds to the maximum height to be expected of the flushable cover layer 5, an arrangement of flushing nozzles 25F and 25B from which pressurized water and/or air are ejected to stir up the flushable cover layer 5 so that the flushing device 11 can pass therethrough. Air, water, or a combination of air and water, is pumped down through the pipes 21 comprising riser 19 from a pump 20 located on the vessel 17. In the particular embodiment shown, water is drawn from the water body 15 through an intake (not shown) for pumping to the flushing device 11. Once the air, water, or air and water reaches flushing device 11, it is routed through pipes 12F or 12B to either a first set of flushing nozzles 25F arrayed on flushing device 11 and oriented in the direction of movement 9 or a second set of flushing nozzles 25B arrayed on flushing device 11 and oriented toward the flushable ground layer 5. When the flushing device 11 is lowered down to the flushable ground layer 5, the air, water, or air and water is routed to the set of nozzles 25B directed toward the flushable ground area 5 to flush the flushable ground area from under the flushing device 11, thereby allowing the flushable device to be lowered down into the flushable ground area 5. Thus, when the air, water, or air and water is routed to the first set of nozzles 25F and the flushing device 11 is moved in the direction 9, flushing device 11 rides with its lower end on the surface 27 of the non-flushable ground formation 7 and is pulled onwards on that surface.

In the lower end area of the flushing device 11, a mechanical loosening device 31 is provided and is effective across an adjustable working depth 33 in the non-flushable ground formation 7. In the illustrated embodiment, the loosening device comprises a chain-milling device 35 having a chain tool 37 that travels around over an upper deflection area 39 and a lower deflection area 41. In order that the working depth 33 of the mechanical loosening device 31 is adjustable, the loosening device 31 is arranged pivotally at the flushing device 11 ; in the illustrated embodiment, the loosening device 31 is pivotable by means of a hydraulic cylinder 43 about the upper deflection area 39. In the illustrated embodiment, the loosening device 31 is driven by means of a hydraulic motor 45 that is arranged in the upper deflection area 39. The plow-shaped housing of flushing device 11 extend at least partially around and shielding the hydraulic cylinder 43, hydraulic motor 45, and other mechanical components of loosening device 31 from material loosened from the flushable ground area 5 by flushing device 11 as flushing device 11 is moved in the selected direction 9. In one embodiment, the chain of chain tool 37 is driven at a speed of approximately 50 rpm, it having been discovered that chain speeds slower than the 100 rpm speeds known in the art increase the useful life of the chain. To facilitate the use of slower speeds while still maintaining efficient mechanical loosening with loosening device 31 , it has been found advantageous to increase the size of the hydraulic motors from the 1200-1300 hp motors known in the art to motors as large as about 1800 hp.

Similarly, to increase chain life, a hydraulic cylinder 40 is provided for maintaining chain tension of the chain tool 37 at an operator selected tension. Tension is maintained by the extension (and/or retraction) of hydraulic cylinder 40 in accordance with the pressure of the hydraulic fluid therein. By using regulated chain speeds and continual tensioning as described herein, chain life is extended and considerable maintenance on the chain tool 37 is effectively automated.

The hydraulic conduits 47 for the hydraulic cylinder 43 and the hydraulic drive motor 45 extend to a manifold 46 mounted on flushing device 11 to which a plurality of flexible hydraulic hoses 48 (only one being shown for purposes of clarity) are connected. Hoses 48 extend upwardly from manifold 46, and are preferably clamped to the pipes 21 of riser 19, to the spools 50 on vessel 17. Hydraulic pressure is generated by an engine that is shown schematically at reference numeral 29 on vessel 17.

The mechanical loosening device 31 must not impede the probe function of the flushing device 11 for detecting the surface 27 of the non-flushable ground formation 7. Therefore, the loosening device 31 is arranged, as illustrated, so that it is provided only in a rear section of the flushing area produced by the flushing device 11. Because of that distance between the loosening device 31 and the flushing device 11 , flushing nozzles 49 for water and/or air are provided at the loosening device 31 to supplement removal of ground material from the laying-out channel 3 and to direct material away from the loosening device 31. In this manner, the trench is formed with walls that are more vertical than the walls of trenches cut by certain known prior trenchers, thereby facilitating the laying of the pipe and/or cable in the trench. Air nozzles show a particularly favorable action because they produce a zone of reduced density in which the excavated material is flushed upwardly in a fluidized manner. In the illustrated embodiment, the flushing nozzles 49 are arranged to facilitate removal of the excavated material from the chain tool 37 and to flush the excavated material, or spoil, from the trench.

Laying-out devices (not shown) for laying out an object, for instance a cable (also not shown), during the production of the laying-out channel 3 may be utilized in conection with the apparatus 1 in a manner described in the above-mentioned U.S. Patent No. 4,787,777, the entire disclosure of which is hereby incorporated herein by this specific reference. The laying-out devices, however, can be dispensed with or left unused as also described in that same patent.

Although shown with a single riser 19, those skilled in the art will recognize that the apparatus 1 of the present invention can operate at water depths greater than that of a single riser section simply by adding a second riser section (not shown), each riser section comprising one or more conduits for conveying power and either water, air, or water and air to the flushing device from the pump 20 located above water. To facilitate the addition of a second riser section, both the top of flushing device 11 and the ends of the riser section 19 are provided with flanges 18A and 19B that mate to make up a rigid connection that puts the pipes 21 comprising the riser section 19 in fluid communication with each other and with the pipes 12F and 12B (as the case may be) in flushing device 11.

Referring now to Fig. 4, a second embodiment of an underwater trenching apparatus constructed in accordance with the teachings of the present invention is indicated generally at reference numeral 51. Underwater trenching apparatus 51 is self- propelled in the sense that it is mounted on a vehicle 53 that rides on tracks (or other suitable drive system) powered by appropriate hydraulic motors (not shown) as known in the art. A buoyancy compensator/tank 55 is provided on the vehicle 53 for assistance in raising and lowering the apparatus 51 from the surface of the water to the floor of the particular body of water in which the trench is being laid out and for facilitating travel on the subfloor on which soft sediment may be accumulated in which the tracks of vehicle 53 may sink. The hydraulic motors of apparatus 51 are powered by a hydraulic pump(s) that are connected to apparatus 51 by a suitable number of hydraulic hoses (not shown in Fig. 4 for purposes of clarity), apparatus 51 being provided with a hose ring 57 through which the hoses are fed (and appropriate strain reliefs provided) as known in the art. Apparatus 51 may also be provided with the same forwardly- and downwardly-directed nozzles for flushing a flushable cover layer as described above in connection with the description of the apparatus shown in Figs. 1 - 3, and to the extent that the component parts of the apparatus 51 are the same as those comprising the apparatus 1 shown in Figs. 1 - 3, like reference numerals are utilized to designate those parts.

The mechanical loosening device 31 of apparatus 51 comprises the same type of chain-milling device 35 as shown in connection with the apparatus 1 shown in Figs. 1 - 3.

However, the particular chain-milling device 35 shown in Fig. 4 is of actually comprised of side-by-side chain tools 37 or links of various widths for trenching at wider widths with the mechanical loosening device of apparatus 1 shown in Figs. 1 - 3. Side-by-side chain tools 37 are driven from a common drive shaft by hydraulic motors 45 in the same arrangement as shown in connection with the chain-milling device 35 shown in Figs. 1 - 3.

Although it is directed, and often pulled, by a cable, the apparatus 51 provides at least some its own tractive power. As a result of irregularities in the floor of the body of water, the apparatus 51 has a tendency to deviate from the predetermined line of the trench in a way that the apparatus shown in Figs. 1 - 3, which is guided by a surface vessel that the determines the direction of arrow 9 (see Fig. 2), does not deviate. Apparatus 51 is therefore provided with a guidance system that is operably connected to, and interacts with, the hydraulic motors and controls of apparatus 51 to maintain the intended line and depth of the trench that is being laid out by the mechanical loosening device 31. The system (the components of which are so small as to be impractical to show in Fig. 4) includes: means for providing the location of the apparatus 51 at any given time such as, for instance, a global positioning system; means for sensing a change in the pitch of apparatus 51 such as is caused by a change in the slope of the floor of the body of water on which the apparatus 51 rests that would cause the bottom of the trench that is being laid out by apparatus 51 from to deviate from level (or from an intended depth if, for instance, it is intended that the depth of the trench change for the purpose of sloping the bottom of the trench), for instance, gyroscopes; means for sensing a change in the attitude of apparatus 51 such as is caused by an uneven floor of the body of water on which the apparatus 51 rests and that would cause deviations from vertical in the walls of the trench being laid out by apparatus 51 , for instance, gyroscopes; means for sensing a change in the angle of chain-milling device 35 relative to vehicle 53 that would cause a change in the depth of cut of the chain-milling device, and therefore, deviation of the bottom of the trench from level, for instance, linear position transducers (LPTs) in the hydraulic cylinders 59 that pivot chain-milling device 35 relative to vehicle 53 or pressure sensors in fluid communication with the hydraulic lines that are operably connected to the hydraulic cylinders 59 that pivot chain-milling device 35 relative to vehicle 53; means for sensing a change in speed of one or both of the tracks of vehicle 53 that would cause a change in direction of vehicle 53 and/or that might result from a change in pitch or attitude caused by irregularities in the floor of the body of water on which the apparatus 53 rests, for instance, pressure sensors in fluid communication with the hydraulic lines that are operably connected to the hydraulic motors that drive the tracks of vehicle 53; means for sensing a change in the speed of the chain of chain tool 37 such as may result from the bearing of the chain tool 37 against rock or other hard soil that may cause a change in the angle of the chain tool 37 relative to vehicle 53; and means for (a) continuously monitoring the outputs of the location sensing means, pitch sensing means, attitude sensing means, track and chain speed sensing means, and angle sensing means, (b) continuously comparing the outputs of these sensors to an acceptable range of operating parameters selected to insure that the trench laid out by apparatus 51 follows an intended line and maintains an intended depth, and (c) means for adjusting the hydraulic pressure in the lines to the hydraulic motors that drive the tracks of vehicle 53 and the hydraulic cylinders 59 for changing the angle of chain-milling device 35 relative to vehicle 53 to maintain the intended line and depth, for instance, a computer and software for operating the computer in the manner described. Many of the components of the system for maintaining an intended line and depth of the trench that is being laid out by the apparatus 51 are actually located on the surface vessel with the pumps that operate the hydraulic motors and cylinders of apparatus 51 and from which the hydraulic hoses 48 connected to the motors and cylinders of apparatus 51 are spooled. However, if LPTs are utilized for sensing the angle of the chain tool 37 relative to vehicle 53, those LPTs are located in the hydraulic cylinders 59 on vehicle 53 and the output cable from the LPTs is run up to the surface through the hydraulic hoses 48 and connected to the computer that operates the vehicle 53.

Those skilled in the art who have the benefit of this disclosure will recognize that this same system for maintaining the intended line and depth of trench may also be provided for use in connection with the apparatus 1 shown in Figs. 1 - 3. For instance, a control panel 61 is shown mounted to the engine 29 of underwater trenching apparatus 1 in Fig. 1 that is connected to the means for sensing the hydraulic pressure in each respective hydraulic hose 48 by cable 63. The control panel 61 provides appropriate gauges and read-outs for monitoring operating conditions and a computer for comparing the pressures in the hoses and the angle sensing means to the acceptable range of operating parameters, and adjusting the hydraulic pressure in the hoses 48 to the hydraulic motors and cylinders on vehicle 53.

Referring now to Figs 5 - 7, there is shown an apparatus 65 for laying out a trench on dry land. As for the embodiments described above, the component parts of apparatus 65 that are common to the embodiments shown in Figs. 1 - 4 are referenced by like numerals. Trenching apparatus 65 is comprised of a vehicle 67 to which a chain-milling device 35 is mounted that is powered by an engine that is shown schematically, like the engine of the embodiment shown in Figs. 1 - 3, as being contained within the housing shown at reference numeral 29. In the embodiment shown, chain-milling device 35 is not mounted directly to vehicle 67; instead, chain-milling device 35 is mounted to a sled 69 that is pivotally mounted to vehicle 67. Sled 69 is comprised of a frame 70 that is adapted for mounting a conveyor 71 and a tool bar assembly 73 thereto, all as best shown in Fig. 7. In the embodiment shown in Figs. 5 - 7, the conveyor 71 is mounted to the frame 70 of sled 69 on a rail (not visible in the figures) to allow the conveyor to slide from side-to-side under control of a double-acting hydraulic cylinder (also not visible). In this manner, the spoil that is pulled up from the trench by chain-milling device 35 can be deposited either immediately adjacent the trench or at a distance from the edge of the trench, as may be desired, and on either side of the trench. Further control of the spoil is achieved by using a variable speed hydraulic motor (also not visible in the figures) for powering the conveyor, operation of the motor at higher speeds having the result of spreading, or throwing, the spoil to one side or the other of the trench.

Those skilled in the art who have the benefit of this disclosure will recognize from this description of the apparatus 65 that the sled 69 is not required for the apparatus 65 to function for its intended purpose and that the chain-milling device 35 may also be mounted directly to vehicle 67 in the same manner as shown, for instance, in the embodiments shown in the Figs. 1 - 3 (in which the vehicle is replaced by the flushing apparatus 11). However, when mounted with the contact plate 77 positioned adjacent the surface of the ground to be trenched, sled 69 does serve several functions as described below and therefore comprises a significant improvement over prior art trenching apparatus. For that reason, the present invention also contemplates that a sled 69, with or without a conveyor, can be mounted to the flushing apparatus 11, and as described below, a second embodiment of the sled of the present invention is mounted to the apparatus 51 shown in Fig. 4. Although the pivot point is not visible in the view shown in Fig. 5, it will be apparent from the location of the hydraulic cylinders 75 (only one of which is shown for purposes of clarity) that sled 69 pivots relative to vehicle 67 to continually force the contact plate 77 that is integral with the frame 70 of sled 69 against the surface of the ground that is being trenched as the pitch and attitude of vehicle 67 changes as it advances across the surface of the ground that is being trenched. The pivoting of sled 69 relative to vehicle 67 is accomplished by continually sensing the pressure in the hydraulic lines (not shown), comparing that pressure to a pre-selected set pressure, and adjusting the extension of the rams comprising hydraulic cylinders 75 to force the contact plate 77 against the surface of the ground that is being trenched in the same manner as described above in connection with the control system described for the apparatus 51 shown in Fig. 4. This continual forcing of the contact plate 77 of sled 69 against the surface of the ground being trenched serves the function of reacting the upward force resulting from operation of chain-milling device 35. In other words, as the chain-milling device 35 bears against the strata in which the trench is being laid out, the strata is ripped and torn out of the trench and the spoil from that ripping action is carried upwardly by the chain tool 37 thereof. This upwardly-acting force has the result of causing the strata to be ripped out of the trench in large, irregularly-shaped pieces, with considerable, almost instantaneous variations in force on the chain comprising chain tool 37 such that the chain is continually being subjected to violent changes in force in many different directions during operation of the chain-milling device 35. The result of these continuous changes is continual vibration in the apparatus 65. Continual downward forcing of contact plate 77 against the surface of the ground that is being trenched by action of the hydraulic cylinders 75 (under control of the above-described hydraulic pressure monitoring system) reacts the upwardly-acting force of the chain tool 37. As a result of the reaction of the upwardly-directed force from chain tool 37 by contact plate 77, chain tool 37 is able to cut the trench in a more controlled fashion, and vibration and wear on the chain comprising chain tool 37, as well as the other components of apparatus 65 are decreased, thereby significantly prolonging the life of the chain and decreasing maintenance costs for the entire apparatus 65.

Those skilled in the art who have the benefit of this disclosure will recognize that, by the use of the term "continuous" in the previous paragraph, it is not intended that the hydraulic pressure of hydraulic cylinders 75 must be changing at all times for the cylinders 75 to be effective in forcing the contact plate 77 downwardly against the surface of the ground through which the apparatus 65 is trenching. The term "continuous," when used in reference to the downward forcing of contact plate 77 against the surface of the ground, is instead intended to convey the concept of changing the hydraulic pressure to hydraulic cylinders 75 to change the angle of sled 69 relative to vehicle 67 so as to push contact plate 77 against the ground during trenching operations in such a way as to react some or all of the upwardly-directed force of the teeth mounted on the chain of chain tool 37 as the teeth bear against a stratum (or strata) comprising a formation in the ground to be trenched. An unanticipated benefit of forcing the contact plate 77 against the surface of the ground to be trenched to react the upwardly-directed force created by the ripping action of the teeth of chain tool 37 against the stratum/strata being trenched was the discovery that the trailing edge 79 of contact plate 77 acts as a bearing, or crush, point against which the stratum/strata engaged by the teeth (not shown) comprising the chain (not shown) of chain tool 37 bear as the teeth contact the stratum/strata comprising the ground to be trenched. As a result of this crush point provided by the trailing edge 79 of contact plate 77, the effective force brought to bear against the strata comprising the ground to be trenched is increased such that the apparatus 65 is able to trench at faster speeds and through harder rock formations than previous known trenching apparatus while reducing the rock fragments in the spoil to smaller pieces as they contact the crush point so that the teeth mounted on the chain of chain tool 37 can mill the fragments into smaller pieces instead of larger, unmanageable chunks. As might be expected, the trailing edge 79 of contact plate 77 is subjected to severe forces as a result of its function as a crush point and, for this reason, in one embodiment, the contact point, or at least the trailing edge 79 and the portion of contact plate 77 adjacent the trailing edge, is comprised of a hardened, impact resistant material for increased durability.

As best shown in Fig. 7, the tool bar assembly 73 comprising a portion of the sled 69 is pivotally mounted to sled 69 on the pivot axis 83 and bushings 85. Referring to Figs. 5 and 6B, it can be seen that tool bar assembly 73 is pivoted relative to sled 69 by hydraulic cylinders 87 that are mounted to sled 69 for a purpose to be described below.

Tool bar assembly 73 is provided with a pair of opposed side plates 89 having tracks 91 formed therein (see Fig. 7) for receiving complementary-shaped rails 92 (best shown in Fig. 6 A) integral with chain- milling device 35. Although only the butt plates 93 to which they are mounted are visible in the figures (see Fig. 7), hydraulic cylinders are mounted between the chain-milling device 35 and tool bar assembly 73 for slidably moving the chain-milling device 35 up and down relative to vehicle 67. As best shown by comparison of Fig. 5 to Figs. 6A and 6B, by action of hydraulic cylinders 87 and the hydraulic cylinders mounted in the tracks 91, the cutting angle of chain-milling device 35 (shown by the arrow 97 in Fig. 5) and the depth of cut (arrow 95) of chain-milling device 35 are changed either by operator intervention and/or by continuous adjustment as a result of the monitoring of the hydraulic pressure in the various lines in the manner described above. The ability to change the cutting angle of chain-milling device 35 and the ability to move the chain-milling device 35 up and down relative to vehicle 67 also provides the trenching apparatus 65 with the unique operating capability of "rocking" the chain-milling device 35 to concentrate cutting power on a particular difficult stratum/strata in a manner similar to the way that a carpenter rocks a handsaw to concentrate the cutting force of the saw on wood as it is sawn. This rocking function can be accomplished under operator control using the above-described means for changing the depth of cut and/or the angle of chain-milling device 35 or by programmed operation that is activated either by the operator or automatically when sensed changes in the hydraulic pressure to the hydraulic cylinders 75 and 87 exceed a preselected degree of change, indicative of a particular hard stratum or strata that has been encountered by chain- milling device 35. As best shown in Fig. 5, it can also be seen that the chain tool 37 comprising chain-milling device 35 is comprised of three sections 37A, 37B, and 37C, and that the depth of cut of the trench can also be adjusted by changing the length of the chain tool 37 by inserting one or more center sections 37B (only one such section being shown in Fig. 5) or removing the center section 37B.

Referring again to Figs. 5 and 7, it can be seen that as the chain tool 37 cuts the stratum/strata through which a trench is being cut, the spoil that is ripped upwardly and crushed or sheared against the trailing edge 79 of contact plate 77 is carried upwardly along the length of the lower deflection area 41 of chain-milling device 35 into the area between the sled 69 and the chain-milling device 35. Because the tool bar assembly 73 to which chain-milling device 35 is mounted is pivotally mounted to sled 69 on the pivot axis 83 and bearings 85 above the frame 70 of sled 69, the chain tool 37 and the front of sled 69 are not parallel to each other. Instead, the space between the chain-milling device 35 and the front of sled 69 decreases at points closer to pivot axis 83. As spoil is carried upwardly to drop onto conveyor 71, this decrease in the space between chain-milling device 35 and sled 69, indicated by the arrow 72 in Fig. 8, acts to further crush the spoil. To maximize the crushing action of this decrease in the space 72 between sled 69 and chain tool 37 as the spoil is carried upwardly toward the pivot axis 83, the front of sled 69 is provided with a hardened face, or anvil, 99 that is provided with one or more ridges 101, each of which act to provide further crush points as the spoil is swept further upwardly along the anvil 99. In another embodiment (not shown), the ability of the sled 69 to process the rock spoil cut from the ground to be trenched by chain-milling device 35 is enhanced by mounting a second conveyor to the sled 69 to catch the spoil as it falls off of conveyor 71, the second conveyor being provided with a screen having a mesh size selected for separating the milled rock spoil into particles of sizes suitable for padding and back-filling the trench after the cable and/or pipe is laid therein and depositing the processed, separated rock spoil in parallel rows along the trench as the vehicle to which the sled 69 is mounted progresses along the intended path. If necessary, a vibratory shaker may be added to this second conveyor for insuring that the material is moved and separated as desired.

One disadvantage of known trenchers, regardless of whether they are utilized on dry ground or underwater, is wear and tear on the nose wheel 103 comprising chain- milling device 35 around which the chain of chain tool 37 rotates. The trenching apparatus of the present invention addresses that disadvantage by providing continuous lubrication of nose wheel 103. As shown in Figs. 9A and 9B, nose wheel 103 is journaled between two side plates 105, the side plates 105 being received within a box (not shown in Figs. 9A or 9B) formed in the end of chain tool 37 for moving in and out to maintain the tension of the chain on hydraulic cylinder 40 (see Fig. 3). A groove 107 is milled into the surface of one of the side plates 105 for receiving a line (not shown) that connects to a fitting (not shown) through the hole 109 in that same side plate 105 at one end and a bearing capsule 1 1 1 at the other end for supplying a continuous flow of lubricant to the nose wheel 103.

Referring now to Figs. 10A - 10D, several embodiments of the chain-milling device 35 of the present invention are shown detached from the sled 69 and/or apparatus 1 or 51. The chain-milling device 35A in Fig. 10A is shown with the side plates 89 of tool bar assembly 73 to provide a point of reference to the other figures. Chain-milling device 35 A is provided with a roller 113 located proximate the nose wheel 103 around which the chain (not shown so as not to obscure the view of roller 113) of chain tool 37 rotates. Roller 113 provides two benefits, the first being a reduction in friction of the chain against the chain tool 37, thereby decreasing wear on the chain and increasing useful horsepower. The second benefit is an increase in the angle of attack on the point of maximum pressure of the teeth mounted on the chain against the stratum/strata being trenched at the bottom of the trench where the teeth first engage the stratum/strata.

Figure 10B shows a chain-milling device 35B that is provided with a plurality of 115 mounted on ears 117 at intervals along the length of chain tool 37. Just as the roller 1 13 (Fig. 10A) reduces friction in the case of chain-milling device 35A, the sprockets 115 of chain-milling device 35B reduce friction by holding the links comprising the chain away from chain tool 37 for at least a portion of the travel of the chain, thereby increasing useful horsepower. A second benefit of the sprockets 115 is an increase in the pressure exerted against the stratum/strata by the cutting teeth located on any link of the chain as that link travels over the tooth sprocket of each sprocket 115. In an alternative embodiment of the chain-milling device 35B, a high-pressure air jet (or, if chain-milling device 35B is mounted to flushing device 11 shown in Fig. 1 or vehicle 53 shown in Fig. 4, a high- pressure water jet or high-pressure air/water jet) is directed into the gap between each sprocket and the underside of the chain for the purpose of decreasing the likelihood of rock particles interfering with the interaction between the teeth comprising the sprocket 115 and the links comprising the chain of chain tool 37. Figure IOC shows a variation of the chain-milling device 35B wherein the chain-milling device 35C is provided with a plurality of rollers 119, rather than sprockets 115, so that the interaction of the teeth of the sprockets 115 and the chain of chain tool 37 is not complicated by, for instance, interference from rock particles. Although not visible in Fig. IOC, in a preferred embodiment, each roller is shaped so as to contain the chain comprising chain tool 37, thereby reducing any racking or side-to-side movement of the chain as the teeth mounted thereto encounter hard strata, thereby decreasing wear on the chain.

Also shown in Fig. IOC are a plurality of arrows 121, each arrow 121 being oriented at a right angle, or at an oblique angle, relative to the direction of movement of the chain and representing a controllable force vector at the axes of the rollers 119. The controllable force vectors 121 are shown schematically in this manner because they are generated in any of several ways. For instance, in one embodiment, eacn set of ears 117 on which the rollers 119 mounted are mounted on a heavy duty coil spring that biases the roller toward the chain of chain tool 37 and the amount of bias can be changed by changing springs or by changing the degree of compression of the coil spring. In another embodiment, each of the ears 117 is mounted to a respective hydraulic cylinder set to exert a selected pressure or controlled by the operator so as to produce the desired controllable force vector 121. It will also be recognized by those skilled in the art who have the benefit of this disclosure that the entire set of ears 1 17 and roller 119 need not be movable under the influence of controllable force vector 121. In one embodiment (not shown), the axis on which the rollers 119 rotate is confined not to a round hole in the ears 117 but in a slot, the axis of which is normal to the long axis of chain tool 37 so that the axle pin travels to and from the chain tool 37 depending upon the magnitude of the controllable force vector 121. The chain-milling device 35D shown in Fig. 10D is similar to the device 35C shown in Fig. IOC except that in the case of the chain-milling device 35D, each of the means for creating the controllable force vector 121 is individually controlled by the operator and/or by programmed operation that is activated either by the operator in response to certain operating conditions and/or automatically when a selected set of operating conditions is sensed, the controllable force vectors 121 applied to each roller 119 being shown as different lengths to illustrate that different amounts of force may be applied to each roller 119 and/or at different times. In this manner, enhanced control of the stress distribution among the teeth along the chain tool 37 at any given time is provided. Thus, if it is determined, for instance, that the stratum/strata at a particular depth is significantly harder than the other strata, the operator can cause a controllable force vector to be exerted at the depth forward of that stratum by, for instance, extending the hydraulic cylinder to which the roller 119 is mounted to increase the force exerted by the teeth mounted on the chain of chain tool 37 as the teeth pass over that particular roller 1 19. In another embodiment, each of the hydraulic cylinders is activated in sequence and at different times to provide a continuously changing point at which the impact of the teeth on the stratum/strata in concentrated. It will, of course, be apparent from this description of the several embodiments of chain-milling device 35 that the various embodiments can be combined in different combinations. For instance, the roller 1 13 shown in Fig. 10A can be utilized with any of the embodiments shown in Figs. 10B, IOC, and 10D. Similarly, any of the embodiments for which controllable force vectors 121 have been described may utilize sprockets or rollers, and so on.

Those skilled in the art who have the benefit of this disclosure will recognize that certain changes can be made to the component parts of the apparatus of the present invention without changing the manner in which those parts function to achieve their intended result. For instance, as has already been described, the chain-milling device 35 may be mounted to any of the embodiments shown in Figs. 1, 4, or 5 directly or to a sled (such as is shown in Fig. 5). Similarly, either of the embodiments shown in Figs. 1 or 4 may be provided with a conveyor such as the conveyor 71 shown in Fig. 5 and either of the embodiments shown in Figs. 4 and 5 may be provided with air, water, or combination air/water nozzles for flushing or blowing particulate spoil away from the chain of chain tool 37 during operation such as the nozzles 49 shown in Figs. 2 and 3. It will also be recognized that the speed at which the chain tool 37 operates and the horsepower of the hydraulic motors set out above are approximate speeds and horsepower, and that actual speed and horsepower may be varied by +35% while still accomplishing the intended results. All such changes, and others which will be clear to those skilled in the art from this description of the preferred embodiments of the invention, are intended to fall within the scope of the following, non-limiting claims.

Claims

WHAT IS CLAIMED IS:

1. An underwater trencher comprising: a flushing device movable in a selected direction through a flushable ground area of an underwater formation above a base layer; a first set of flushing nozzles arrayed on said flushing device and oriented in the selected direction; a second set of flushing nozzles arrayed on said flushing device and oriented in a downward direction toward the flushable ground area to flush the flushable ground from the flushable ground area to lower said flushing device down onto the base layer; and means for selectively directing either water, air, or a combination of water and air through either or both of the first or second sets of flushing nozzles.

2. The underwater trencher of claim 1 wherein said flushing device comprises a plow-shaped housing.

3. The underwater trencher of either of claims 1 or 2 additionally comprising a mechanical loosening device arranged in the lower end area and to the rear of the flushing device relative to the selected direction for loosening the material comprising the base layer, said loosening device being supported at least in part on the upper surface of the base layer by said flushing device, the housing of said flushing device extending at least partially around and shielding the mechanical components of said loosening device from material loosened from the flushable ground area by said flushing device as said flushing device is moved in the selected direction.

4. The underwater trencher of claim 3 additionally comprising a plurality of nozzles arrayed on said flushing device and oriented in a direction toward said mechanical loosening device.

5. The underwater trencher of claim 1 additionally comprising a flange on said flushing device for attaching a riser section thereto, said riser section comprising one or more conduits for conveying either water, air, or water and air to said flushing device from a pump located above water.

6. The underwater trencher of claim 5 additionally comprising a second riser section connected to the end of said first riser section for operating said flushing device at water depths greater than the depth of a single riser section.

7. The underwater trenching device of claim 5 wherein said mechanical loosening device comprises a chain milling device powered by hydraulic motors and said flushing device additionally comprises a manifold for receiving flexible lines for conveying hydraulic fluid to said hydraulic motors, said hydraulic lines being unwound from a spool located above water.

8. The underwater trenching device of claim 7 wherein said mechanical loosening device comprises hydraulic means for adjusting the tension of the chain comprising said chain milling device.

9. A method of progressively producing an underwater laying-out channel for an object to be laid out in an underwater channel comprising the steps of: lowering a flushing device into proximity to a flushable ground area under water; pumping either water, air, or a combination of water and air through an array of nozzles directed toward the flushable ground area to flush the flushable ground area from under the flushing device, thereby allowing the flushable device to be lowered down into the flushable ground area; and thereafter moving the flushing device through the flushable ground area while pumping either water, air, or a combination of water and air through an array of nozzles directed toward the direction of movement of the flushing device to flush the flushable ground area from in front of the flushing device, thereby creating a laying-out channel in the flushable ground area as the flushing device moves.

10. The method of producing an underwater laying-out channel of claim 9 additionally comprising mechanically loosening the material comprising a base layer on which the flushable ground area rests during movement of the flushing device.

1 1. The method of producing an underwater laying-out channel of claim 10 wherein the material comprising the base layer is mechanically loosened with a chain milling device driven at various speeds by a driveshaft operating at a speed of approximately 50 rpm.

12. Apparatus for trenching comprising: a vehicle; a sled adapted for pivotally mounting to said vehicle; and a tool bar assembly mounted to said sled and having a chain-milling device pivotally mounted thereto.

13. The apparatus of claim 12 wherein said chain-milling device is slidably mounted to said tool bar assembly.

14. The apparatus of either of claims 12 or 13 additionally comprising means for forcing said sled into contact with the ground to be trenched.

15. A sled for mounting to a vehicle and to which a chain-milling device is mounted for trenching the ground on which the vehicle rests comprising: a frame adapted for mounting to a vehicle; a contact plate integral with said frame for positioning adjacent the surface of the ground to be trenched when said frame is mounted to a vehicle; an anvil integral with said frame; and said frame further comprising a pivot point to which a chain-milling device is mounted.

16. The sled of claim 15 wherein said pivot point is located on the side of said frame proximate said anvil.

17. The sled of claim 16 wherein said pivot point is located above said anvil.

18. The sled of any of claims 15 - 17 additionally comprising a ridge formed in said anvil.

19. The sled of any of claims 15 - 17 wherein said contact plate comprises a trailing edge proximate said anvil.

.

20. The sled of any of claims 15 - 19 wherein said frame is additionally adapted for mounting a conveyor thereto.

21. The sled of claim 20 wherein said frame is additionally adapted for mounting means for separating the spoil from the ground to be trenched according to size.

22. The sled of claim 15 wherein said frame is adapted for pivotally mounting to a vehicle.

23 The sled of claim 15 additionally comprising a tool bar assembly mounted to said pivot point, the chain-milling device being mounted to said tool bar assembly.

24. The sled of claim 23 wherein the chain-milling device is slidably mounted to said tool bar assembly.

25. A mechanical loosening device adapted for mounting to a trenching apparatus comprising: an elongate chain tool having a nose wheel positioned at one end thereof around which a chain rotates, the links of the chain being provided with teeth for cutting into a stratum to be trenched, the chain being rotated under power provided from the trenching apparatus; opposed side plates slidably mounted to said chain tool, said nose wheel being journaled in said side plates; and means for selectively sliding said side plates relative to said chain tool for changing the tension on the chain of said chain tool.

26. A mechanical loosening device adapted for mounting to a trenching apparatus comprising: an elongate chain tool having a nose wheel positioned at one end thereof around which a chain rotates, the links of the chain being provided with teeth for cutting into a stratum to be trenched, the chain being rotated under power provided from the trenching apparatus; opposed side plates slidably mounted to said chain tool, said nose wheel being journaled in said side plates; and a groove communicating with a hole in one of said side plates for receiving a lubrication line therein and connecting at one end to a fitting received in the hole and to a bearing capsule at the other end for lubricating the nose wheel mounted thereto.

27. In a mechanical loosening device adapted for mounting to a trenching apparatus comprising an elongate chain tool having a nose wheel positioned at one end thereof around which a chain of links rotates, the links of the chain being provided with teeth for cutting into a stratum to be trenched, the chain being rotated under power provided from the trenching apparatus, the improvement comprising either a roller or a sprocket for holding the chain away from the chain tool during a portion of the travel of the chain to reduce friction between the chain and the chain tool.

28. The mechanical loosening device of claim 27 further comprising means for creating a controllable force vector on said roller or said sprocket at an oblique angle to said chain.

29. The mechanical loosening device of either of claims 27 or 28 additionally comprising means for preventing the racking of the links comprising said chain.

30. In an apparatus for laying out a trench through ground or an underwater floor comprising a vehicle and a chain-milling device, the improvement comprising: means for providing the location of the vehicle at a given time; means for sensing a change in the pitch of the vehicle on the ground or the underwater floor on which the vehicle rests that would cause the bottom of the trench that is being laid out to deviate from level or from an intended depth; means for sensing a change in the attitude of the vehicle on the ground or the underwater floor on which the vehicle rests that would cause deviations from vertical in the walls of the trench being laid out apparatus; means for sensing a change in the angle of chain-milling device relative to the vehicle that would cause a change in the depth of cut of the chain-milling device, and therefore, deviation of the bottom of the trench from level; and means for (a) continuously monitoring the outputs of the location sensing means, pitch sensing means, attitude sensing means, and angle sensing means, (b) continuously comparing the outputs of these sensors to an acceptable range of operating parameters selected to insure that the trench being laid out follows an intended line and maintains an intended depth, and (c) means for changing the direction of the vehicle and for changing the angle of the chain-milling device relative to the vehicle to maintain the intended line and depth of the trench.

31. The apparatus of claim 30 additionally comprising means for sensing a change in the speed of the chain of the chain- milling device that may affect the angle of the chain-milling device relative to the vehicle.

32. The apparatus of claim 30 wherein said means for monitoring, comparing and changing comprises a microprocessor.

33. The apparatus of claim 32 wherein said microprocessor is located remotely from the vehicle.

34. In a method of trenching with a vehicle to which a chain-milling device is mounted, wherein the chain-milling device is mounted to the vehicle by mounting to a sled that is pivotally mounted to the vehicle, the improvement comprising continually forcing the sled into contact with the ground to be trenched to react the upward force created by the bearing of the teeth of the chain on the chain-milling device as the teeth bear against a stratum in the ground to be trenched.

35. The method of claim 34 additionally comprising sensing either the amount of extension or the pressure of a hydraulic fluid of a hydraulic cylinder mounted between the vehicle and the sled and continually changing the extension of the hydraulic cylinder to pivot the sled relative to the vehicle.

36. The method of claim 34 additionally comprising crushing the spoil from the trench against a contact point formed on the sled.

37. The method of any of claims 34 - 36 additionally comprising milling the spoil from the trench to decrease the size of the particles.

38. The method of any of claims 34 - 36 additionally comprising grinding the spoil from the trench against a surface of the sled to decrease the size of the particles.

39. The method of claim 38 additionally comprising sorting the ground particles by size and conveying the sized particles to separate piles along the trench during trenching.

40. The method of claim 34 additionally comprising either (a) sliding the chain- milling device up or down relative to the vehicle, (b) changing the angle of the chain- milling device relative to the vehicle, or (c) sliding the chain-milling up or down relative to the vehicle and changing the angle of the chain-milling device relative to the vehicle to maintain a desired depth in the trench.

41. The method of claim 40 wherein the up and down position of the chain- milling device and the angle of the chain-milling device are sensed and controlled by a microprocessor.

42 The method of claim 41 wherein the microprocessor is preprogrammed to cause a sequence of changes in the up and down position and the angle of the chain- milling device when either activated by an operator or when the sensors output a preselected set of output readings indicative of an operating condition.

43. The trenching apparatus substantially as disclosed herein.

44. The method for laying out a trench substantially as disclosed herein.