Installation and removal of subsea foundations

Abstract

An underwater pile foundation comprises a pump in fluid communication with an internal chamber of the pile to pump water out of or into the chamber. This reduces or increases the pressure of water in the chamber relative to ambient pressure of water outside the chamber during installation or removal of the pile. While that pumping phase is ongoing, and potentially before or after that pumping phase, a pressure variator in fluid communication with the chamber imparts oscillations in the pressure of the water in the chamber. The resulting pressure waves in water within the chamber reduce resistance to movement of the pile relative to soil in which the pile is embedded.

1 .- 35 . (canceled) 
     
     
         36 . A method of reducing resistance to movement of a pile relative to soil during installation or removal of the pile underwater, the method comprising:
 pumping water out of or into an internal chamber of the pile, defined between a top plate of the pile, a skirt of the pile and the soil, to reduce or to increase a level of pressure of water in the chamber relative to ambient pressure of water outside the chamber; and   while that pumping is ongoing, imparting additional oscillations in the pressure of the water in the chamber via a pressure variator pump, wherein the pressure variator pump is in fluid communication with the chamber.   
     
     
         37 . The method of  claim 36 , comprising employing the oscillations to vibrate a wall of the pile in contact with the soil. 
     
     
         38 . The method of  claim 36 , comprising employing the oscillations to drive oscillatory vertical movement of the pile relative to the soil. 
     
     
         39 . The method of  claim 38 , comprising driving the oscillatory vertical movement by cyclically expanding and contracting the chamber in response to the oscillations. 
     
     
         40 . The method of  claim 36 , comprising employing the oscillations to drive pressure waves through the water in the chamber to impact against soil in the chamber. 
     
     
         41 . The method of  claim 40 , comprising directing the pressure waves downwardly within the chamber. 
     
     
         42 . The method of  claim 36 , wherein the pressure variator pump imparting the oscillations is distinct from a pump that pumps the water. 
     
     
         43 . The method of  claim 42 , comprising effecting fluid communication with the chamber through a common port shared by the pump and the pressure variator pump. 
     
     
         44 . The method of  claim 43 , comprising effecting fluid communication with the chamber through the pump and the pressure variator pump in series. 
     
     
         45 . The method of  claim 43 , comprising effecting fluid communication with the chamber through the pump and the pressure variator pump in parallel. 
     
     
         46 . The method of  claim 43 , comprising directing a fluctuating output of the pressure variator pump into the pump as a motive fluid to drive oscillatory flow in the pump 
     
     
         47 . The method of  claim 42 , comprising effecting fluid communication with the chamber through separate ports, at least one of those ports communicating with the pump and at least one other of those ports communicating with the pressure variator pump. 
     
     
         48 . The method of  claim 42 , wherein the pressure variator pump and the pump are disposed outside the chamber. 
     
     
         49 . The method of  claim 42 , comprising effecting fluid communication between the pressure variator pump and the water outside the chamber. 
     
     
         50 . The method of  claim 42 , comprising enclosing the pressure variator pump within the chamber. 
     
     
         51 . The method of  claim 36 , wherein the pressure variator pump pumps the water to reduce or to increase the level of pressure of water in the chamber and the method comprises imparting the oscillations by oscillating flow passing through the pressure variator pump. 
     
     
         52 . The method of  claim 36 , performed when installing the pile, comprising maintaining pressure within the chamber continuously below the ambient pressure of the water outside the chamber. 
     
     
         53 . The method of  claim 36 , performed when installing the pile, comprising employing the oscillations to generate a series of pressure pulses within the chamber, each pulse being above the ambient pressure of the water outside the chamber and the pulses being separated by a period in which pressure within the chamber is below that ambient pressure. 
     
     
         54 . The method of  claim 36 , comprising imparting the oscillations with a frequency of from 5 Hz to 50 Hz. 
     
     
         55 . The method of  claim 36 , wherein the oscillations follow a waveform in which pressure varies continuously. 
     
     
         56 . The method of  claim 36 , wherein the oscillations follow a waveform with step-change transitions. 
     
     
         57 . The method of  claim 36 , comprising varying any of the following parameters during installation or removal of the pile: frequency of the oscillations; amplitude of the oscillations; and/or an average level of water pressure in the chamber about which the water pressure oscillates. 
     
     
         58 . The method of  claim 57 , comprising increasing any of said parameters in accordance with depth of penetration of the pile into the soil. 
     
     
         59 . An underwater pile, comprising:
 a pump in fluid communication with an internal chamber of the pile defined between a top plate of the pile, a skirt of the pile and the soil, the pump being configured to pump water out of or into the chamber during installation or removal of the pile, thus reducing or increasing a level of pressure of water in the chamber relative to ambient pressure of water outside the chamber; and   a pressure variator pump in fluid communication with the chamber for imparting oscillations in the pressure of the water in the chamber, wherein the pressure variator pump is configured to apply negative pressure to the water in the chamber.   
     
     
         60 . The pile of  claim 59 , wherein the pump and the pressure variator pump are in fluid communication with the chamber through a common port. 
     
     
         61 . The pile of  claim 60 , wherein the pump and the pressure variator pump are disposed in series. 
     
     
         62 . The pile of  claim 60 , wherein the pump and the pressure variator pump are disposed in parallel. 
     
     
         63 . The pile of  claim 60 , wherein the pump is a jet pump and an outlet of the pressure variator pump communicates with a motive fluid inlet of the pump. 
     
     
         64 . The pile of  claim 59 , wherein the pump and the pressure variator pump are in fluid communication with the chamber through respective separate ports. 
     
     
         65 . The pile of  claim 60 , wherein the or each port opens downwardly into the chamber in opposition to soil that closes a lower end of the chamber. 
     
     
         66 . The pile of  claim 59 , wherein the pressure variator pump and the pump are disposed outside the chamber. 
     
     
         67 . The pile of  claim 59 , wherein the pressure variator pump is in fluid communication with the water outside the chamber. 
     
     
         68 . The pile of  claim 59 , wherein the pressure variator pump is enclosed within the chamber. 
     
     
         69 . The pile of  claim 59 , wherein the pressure variator pump is a positive-displacement pump. 
     
     
         70 . The pile of  claim 69 , wherein the pressure variator pump comprises a reciprocating element that is movable to draw water from the chamber and to expel water into the chamber in alternation.