Underwater trenching apparatus

1. Underwater trenching apparatus comprising:

a soil cutting arrangement having a forwardly disposed cutting portion and a rearwardly disposed non-cutting portion;

a soil removal device configured to remove soil from a location forward of the soil cutting arrangement; and

a barrier device located in front of the soil cutting arrangement; and

a crumber unit;

wherein the barrier device extends in a travel direction beyond an outer periphery of the forwardly disposed cutting portion, and is configured substantially to prevent passage of soil to the non-cutting portion of the soil cutting arrangement;

wherein the soil removal device comprises an inlet and an outlet, the outlet is provided substantially tangential to the direction of rotation of the soil cutting arrangement or of the travel direction; and

wherein the crumber unit is located at the lower part of the rearwardly disposed non-cutting portion to assist preventing re-circulation of the soil.

2. The underwater trenching apparatus as claimed in claim 1 , wherein the barrier device is constructed to prevent passage of solid materials contained in the soil having a maximum dimension greater than a selected threshold dimension.

3. The underwater trenching apparatus as claimed in claim 1 , wherein the soil removal device conveys soil in fluidized form.

4. The underwater trenching apparatus as claimed in claim 3 , wherein the soil removal device is an eductor.

5. The underwater trenching apparatus as claimed in claim 4 , wherein the barrier device is configured to prevent or deter entry of solid materials to an inlet of the eductor, where such solid materials have a dimension greater than a selected threshold dimension.

6. The underwater trenching apparatus as claimed in claim 1 , wherein the soil cutting arrangement includes a plurality of soil cutting elements arranged for movement about an endless path.

7. The underwater trenching apparatus as claimed in claim 6 , wherein the soil cutting arrangement is a rockwheel.

8. The underwater trenching apparatus as claimed in claim 1 , wherein the soil cutting arrangement is an auger.

9. The underwater trenching apparatus as claimed in claim 1 , wherein the barrier device is disposed substantially at soil level.

10. The underwater trenching apparatus as claimed in claim 1 , wherein the soil removal device is arranged above the barrier device.

11. The underwater trenching apparatus as claimed in claim 4 , wherein an eductor driving jet is directed towards the soil cutting arrangement, thereby to displace soil accumulated on the soil cutting arrangement.

12. The underwater trenching apparatus as claimed in claim 4 , wherein the path of fluid exiting the eductor is configured to be substantially tangential to the direction of rotation of the soil cutting arrangement.

13. The underwater trenching apparatus as claimed in claim 4 , wherein the eductor includes a diffuser portion arranged to slow the fluidized flow velocity of the soil conveyed by the eductor, whereby denser material contained within the soil falls back into the trench.

14. The underwater trenching apparatus as claimed in claim 1 further comprising means for propelling the apparatus in a desired direction for trench forming.

15. The underwater trenching apparatus as claimed in claim 14 further comprising control means for controlling the operation of the underwater trenching apparatus.

16. The underwater trenching apparatus as claimed in claim 3 , wherein the soil removal device is a dredge pump.

17. Underwater trenching apparatus comprising:

a soil cutting arrangement having a forwardly disposed cutting portion and a rearwardly disposed non-cutting portion;

a soil removal device configured to remove soil from a location forward of the soil cutting arrangement;

a barrier device located in front of the soil cutting arrangement, extending in a travel direction beyond an outer periphery of the forwardly disposed cutting portion, and configured substantially to prevent passage of soil to the non-cutting portion of the soil cutting arrangement;

means for propelling the apparatus in a desired direction for trench forming, wherein the soil removal device comprises an inlet and an outlet, the outlet is provided substantially tangential to the direction of rotation of the soil cutting arrangement or of the travel direction; and

a crumber unit located at the lower part of the rearwardly disposed non-cutting portion to assist preventing re-circulation of the soil.

18. The underwater trenching apparatus as claimed in claim 17 , wherein the soil cutting arrangement includes a plurality of soil cutting elements arranged for movement about an endless path;

wherein the soil removal device is an eductor that conveys soil in fluidized form;

wherein the barrier device is constructed to prevent passage of solid materials contained in the soil having a maximum dimension greater than a selected threshold dimension; and

wherein the barrier device is configured to prevent or deter entry of solid materials to an inlet of the eductor, where such solid materials have a dimension greater than a selected threshold dimension.

19. The underwater trenching apparatus as claimed in claim 18 , wherein the soil cutting arrangement is a rockwheel;

wherein the soil removal device is an eductor that conveys soil in fluidized form;

wherein the barrier device is disposed substantially at ground level;

wherein the eductor is arranged above the barrier device;

wherein an eductor driving jet is directed towards the soil cutting arrangement, thereby to displace soil accumulated on the soil cutting arrangement;

wherein the path of fluid exiting the eductor is configured to be substantially tangential to the direction of rotation of the soil cutting arrangement; and

wherein the eductor includes a diffuser portion arranged to slow the fluidized flow velocity of the soil conveyed by the eductor, whereby denser material contained within the soil falls back into the trench.