Ground freezing method and apparatus with geothermal gradient compensation

Abstract

A ground freezing method and apparatus compensates for geothermal gradients by supplying more refrigerant to deeper parts of the earth. One or more metal freeze pipes are installed in a bore and equipped with one or more feed pipes. The feed pipes extend to different depths with the longer feed pipes being larger to supply more refrigerant to greater depths and achieve uniform top to bottom ground freezing despite the effects of geothermal gradients.

1 . Apparatus for freezing ground adjacent to a bore, said apparatus comprising:
 a freeze pipe in said bore extending therein from the surface;   a first feed conduit in said freeze pipe extending therein to a preselected depth and having a first diameter, said first feed conduit having an upper inlet end and a lower discharge end;   a second feed conduit in said freeze pipe extending therein to a depth greater than said preselected depth and having a second diameter greater than said first diameter, said second feed conduit having an upper inlet end and a lower discharge end;   a supply for supplying refrigerated heat transfer fluid to the inlet ends of said first and second feed conduits for flow therein to the discharge ends of said first and second feed conduits and upwardly through said freeze pipe to freeze the ground adjacent to said bore; and   a collection arrangement for collecting the fluid from said freeze pipe.   
   
   
       2 . Apparatus as set forth in  claim 1 , wherein said first and second feed conduits extend side-by-side in said freeze pipe. 
   
   
       3 . Apparatus as set forth in  claim 1 , wherein:
 said freeze pipe has an upper section with a selected diameter and a lower section with a diameter greater than said selected diameter; and   said second feed conduit is a dual diameter pipe having said second diameter within the lower section of said freeze pipe and a diameter less than said second diameter within the upper section of said freeze pipe.   
   
   
       4 . Apparatus as set forth in  claim 3 , wherein:
 said freeze pipe has a transition between said upper and lower sections thereof, and   said discharge end of said first feed conduit is in proximity to said transition.   
   
   
       5 . Apparatus for freezing ground adjacent to a bore, comprising:
 a first freeze pipe in said bore extending therein from the surface;   a first feed conduit extending in said first freeze pipe to a preselected depth and having a first diameter, said first feed conduit having an upper inlet end and a lower discharge end in said first freeze pipe;   a second freeze pipe n said bore extending therein from the surface;   a second feed conduit extending in said second freeze pipe to a depth greater than said preselected depth and having a second diameter greater than said first diameter, said second feed conduit having an upper inlet end and a lower discharge end in said second freeze pipe;   a supply for applying refrigerated heat transfer fluid to the inlet ends of said first and second feed conduits for flow therein to the discharge ends of said first and second feed conduits and upwardly through the respective first and second freeze pipes to freeze the ground adjacent to said bore; and   a collection arrangement for collecting the fluid from said first and second freeze pipes.   
   
   
       6 . A method of freezing ground adjacent to a bore extending from the ground surface, comprising:
 applying refrigerated heat transfer fluid in a first quantity to a first depth in the bore and then upwardly from said first depth to the ground surface for freezing the ground adjacent to the bore from said first depth to the surface; and   applying refrigerated heat transfer fluid in a second quantity greater than said first quantity to a second depth in said bore greater than said first depth and then upwardly from said second depth to the ground surface for freezing the ground adjacent to the bore from said second depth to the surface.   
   
   
       7 . A method as set forth in  claim 6 , wherein:
 said first and second quantities of fluid are applied through respective first and second feed pipes in the bore; and   said second feed pipe has a larger size than said first feed pipe.   
   
   
       8 . A method of freezing ground comprising the steps of:
 forming a bore into the ground from the surface thereof;   applying a first quantity of refrigerated heat transfer fluid to a first depth in the bore and upwardly in the bore to the surface for freezing the ground adjacent to the bore from said first depth to the surface;   applying a second quantity of refrigerated heat transfer fluid to a second depth in the bore greater than said first depth and upwardly in the bore to the surface for freezing the ground adjacent to the bore from said second depth to the surface, said second quantity of fluid being greater than said first quantity to compensate for thermal gradients in the ground and enhance uniformity to ground freezing in the depth of the bore.   
   
   
       9 . A method as set forth in  claim 8 , wherein:
 said first and second quantities of fluid are applied through respective first and second feed pipes in the bore; and   said second feed pipe has a larger size than said first feed pipe.