US3365894A - Caisson construction - Google Patents

Description

Jan. 30, 1968 E MURA-rl CAISSON CONSTRUCTION Filed March 9, 1966 INVENTOR MURATI l L .L x

EFRAHIM United States Patent O 3,365,894 CAISSON CONSTRUCTION Efrahim Murati, Puerto Rico Testing Services, Inc., BX 588, Roosevelt Station, San Juan, Puerto Rico, 00929 Filed Mar. 9, 1966, Ser. No. 533,048 Claims. (Cl. 61-53.6)

ABSTRACT OF THE DISCLOSURE The construction of caissons or the like, in non-cohesive water-permeated earth, wherein the construction includes the steps of boring a hole or shaft in the earth; forcing a water-tight liner into the shaft to support its walls; rearning out a laterally enlarged cavity, which may be bell-shaped, below the liner; sealing off the cavity. A freezant is uniquely fed under pressure through the seal and into the cavity for a dual purpose: (l) the freezant forces evacuation of water and/or slush in the cavity upwardly through another conduit passing through the seal; and (2) the freezant freezes the walls of the cavity. Finally, the cavity and shaft are filled with waterirnpermeable material such as concrete.

In conventional construction of foundations and similar earth working operations in water-permeated earth, a caisson is formed by boring a hole, stem or shaft, then forcing water-tight liners into place against the walls of the shaft down to a predetermined level, and a bell-shaped cavity is` reamed out below the liners.

By the time this work is done, the bell and the lined shaft above it are at least partly filled by inflowing ground water, or by water purposely pumped into the shaft to block inliow of ground water when it is necessary to preserve the ground water level in the nearby area. Subsequently, tremie concrete is .poured to till the ooded bell and shaft of the caisson, and to displace the water therein.

The presently employed tremie process or underwater emplacing of concrete is not only costly, but it does not assure the same quality of construction as obtained when the walls of the caisson are dry, as occurs in dry formations, when concrete is poured to ll it. Further, with the water-filled caisson and caisson bell, prior to tremie concreting, it is manifestly impossible to effect a dry inspection of the bell for the purpose of effecting reaming finish of the bell as required. The efforts necessary in caisson construction in water-bearing formations are large and commonly present considerable `problems for the contractor as is evident, for example, from an article dealing with caisson construction in a water-bearing formation appearing in the Engineering News Record for Dec. 2, ,1965, pages 30-32.

With increasing caisson construction being necessarily effected in water-bearing formations, or indeed in underwater or ocean sites, efforts are being made to reduce the need for tremie concreting as, for example, by utilization of larger precast units as disclosed in an article on bell pier construction in the October 1965 issue of the Journal of the American Concrete Institute.

It is therefore an important object of the present invention to provide a method and means whereby a caisson, formed in water-permeated earth, may be filled with concrete without recourse to the relatively undesirable tremie process. This object is uniquely achieved by emptying the caisson of water, and thereafter freezing the waterpermeated walls to a depth suicient to prevent the further Cil ICC

inflow of ground water while the dry frozen walls are subsequently covered as the caisson is filled with concrete.

Another object of the invention is the provision of a method and means wherein a uid freezant, such as liquid petroleum gas, is admitted to the caisson to freeze the water permeated walls.

Still another object of the invention is the provision of means such as an inflatable and deiiatable stopper for temporarily sealing a lower portion of the caisson while the freezant is pressure fed into the sealed olf portion, and a conduit is provided to condut excess water from the bottom of the caisson to a point remote from the caisson, under the pressure exerted on the water by the freezant.

Yet another signicant object of the invention is the provision of a method and means for freezing the walls of the caisson so that they may be inspected while dry and any finishing operations performed thereon, if the inspection indicates this to be desirable or necessary.

Numerous other objects and advantages of the instant invention will become apparent as the same is better understood from the following description thereof taken in connection with the accompanying drawing.

Referring to the drawings:

FIG. 1 is a schematic sectional view of a caisson and adjunct formation-freezing equipment according to the present invention; and

FIG. 2 is a schematic sectional view showing the pouring of concrete into the caisson.

With further refe-rence to the drawing, the caisson 1t) comprises a conventional shaft 11 and a bell 12 reamed out below the shaft in a water-permeable earth formation, as often occurs, so that seepage through the walls of the caisson would normally indicate use of the hitherto necessary tremie process to ll the caisson with cement.

Water permeable subsoil is shown at 15 and the caisson shaft 11 is lined in conventional manner with one or more tubular sections 16, which may be steel plate cylinders, or tubing of other suitable material to block lat eral inflow or seepage.

The bell 12 may be formed in conventional manner, such as by use of a bucket that is provided with laterally extensible blades which cut and ream the walls to the desired shape, and which in a water-bearing formation would liltely be performed under water.

In accordance with the instant invention, instead of displacing the water with tremie concrete, the lower, water lled portion 18 of the caisson is largely sealed off and a iiuid freezant, such as liquid nitrogen or liquitied petroleum gas` (LPG), is fed under pressure into this sealed off portion of the caisson so that at least some water is forced back into the subsoil and the excess water and/or slush is forced upwardly and outwardly through a conduit. The fluid freezant also freezes the walls of the caisson as the water recedes, and the freezing operation is continued after the water and/or slush is evacuated, and until the walls and subsoil 15 are frozen to a desired depth.

Means for sealing off the lower portion 18 of the cais son may 4be a transverse seal including an `annular distensible stopper 20 made of rubber, or the like. The stopper is inflatable by an air pump 21 which forces air into the stopper through a conduit 22. When inated, the outer wall 23 of the stopper is in sealing contact with the caisson liner 16, and the inner wall 24 of the stopper is pressed into sealing engagement with the outer wall of the vertical leg of freezant conduit or pipe 25. When desired, deflation of the stopper 20 is effected by venting7 air from the stopper by opening a suitable control valve 26 in the conduit 22.

Disposed substantially concentrically within the ver- B tical pipe leg is a vertical section 29 of a discharge conduit or pipe which extends downwardly through and below the lower and open end of the freezant pipe 25 upwardly to a point close to the bottom of the caisson bell 18 where it terminates in an inlet or head 31. Section 29 of the discharge pipe also extends upwardly, through a wall of the freezant pipe 25 and enters a T juncture at 33 with a waste section 34 and a tank section 35 of the discharge pipe 30. A two-way and closing valve 37 at the junction 33 permits direction of the upward flow of either water, slush or freezant from section 29 to either section 34 or 35 for purposes more fully explained below.

With the stopper 20 inflated to sealing position, the fluid freezant, such as LPG stored in a tank or other source 40, is withdrawn therefrom through a conduit 42 lby a suitable pump 44 which forces the freezant, under pressure, through the pipe 225 and into the sealed off lower portion 18 ofthe caisson.

Where the inifiowing freezant contacts the side walls of the bell it forces some of the water on the wall back while freezing it, thus stopping further seep-age. Simultaneously, the freezant applies pressure and freezing action to the surface of the rseepage water in the bell. The freezing action will inherently produce some slush, a mixture of water and ice particles, and the pressure will cause the seepage water and/or slush to enter inlet 31 and then to pass upwardly through section 29 of the discharge pipe to the valve 37, which at this time, is turned to direct water to and through the discharge section 34 to a discharge point remote from the caisson. The inlet 31 is, of course, spaced sufficiently above the bottom of the bell so that it will lie above solidly frozen water and/or slush at the bottom of the bell.

Hereinafter, the term water is intended to include slush where the water may carry particles of ice.

When the water is substantially fully evacuated from the caisson, fluid freezant will follow the water upward through section 29, at which time valve 37 is turned either to closed position for a time and/or turned to direct the freezant through section 3'5 of conduit 30 back to the tank 40.

While water is being evacuated from the caisson and usually for some time interval after such evacuation, the fluid freezant continues to be fed into the bell until the water-permeated walls are frozen to a desired length. The inward flow or seepage of water from the formation is thus effectively blocked.

The stopper 20 is then deflated and the stem 11 sufiiciently cleared to permit visual inspection of the dry frozen walls `by the use of lconventional mirrors, television, or other suitable means. If indicated by the inspection, additional reaming or other .finishing operations may be performed to give the dry, frozen walls a desired shape or form before the caisson is cleared and then filled with concrete. This filling is shown schematically in FIG. 2 wherein concrete 46 is lbeing poured by conventional means which may include an inclined conduit 47 leading to the open end of the caisson where the concrete is received by a second conduit 48 which directs it to a lower level in the caisson. When desirable or necessary, heat may tbe introduced into the poured concrete by electric `heating coils 49 or other conventional means used to facilitate setting of concrete under freezing conditions.

The above described technique finds utilization in a number of similar environments. Thus the same is workable in sand subsoil to establish a load-bearing concrete column where heretofore it has not been possible to provide a reamed out caisson bell. Thus a vertical hole can be made below a liner as at 16 in such a sand subsoil using a betonite or drill mud thick density suspension. The suspension is then displaced upwardly by the LPG which in turn freezes the sandlike walls close thereto. Thereafter reaming into the iced sand is effected with alternating LPG freezing to successively enlarge the hole i while preventing any tendency to collapse, resulting in a bell as at 12 in a sandy subsoil for receiving a conventional concrete footing.

I have described my invention as principally applied to mfachine-'reamed caissons and bells in non-cohesive water-permeated earth, as is commonly encountered and wherein my invention finds frequent utility. It should be noted that in addition thereto as well as to non-cohesive sandy and relatively waterless soils as discussed in the preceding paragraph, my invention may with similar benet be employed in connection with virtually any earth formation, as for example decomposed rock soils, whether cohesive or non-cohesive, or whether water-permeated or Water-permeable. In like manner, my invention is obviously not restricted to machine-reamed bell caissons, but may be employed with larger man-made bells and excavations as for example in connection with bridge pier caissons.

Further, under particular operating conditions as may occur in a given installation, or with specific concrete formations in connection therewith, it is possible that the low caisson bell or wall temperatures may unduly retard or interfere with setting of the concrete. Such an eventuality may be overcome as for example by the introduction through shaft 11 of flexible or rigid heating coils or conduits to insure proper temperature conditions for the concrete, while the poor thermal conductivity thereof coupled with the low-temperature, radial-depth freeze of the surrounding earth will preclude any significant difficulty with water seepage-control.

It is thought that the invention and many of its attendant advantages will be understood from the foregoing description, and it is obvious that various changes may be made in the form, construction and arrangement of parts without departing from the spirit and scope of the invention.

What is claimed is:

1. In the construction of caissons in water permeable earth, a method comprising the steps of:

sinking a shaft in the earth;

lining said shaft to a predetermined depth with a water impermeable material;

sealing off a lower portion of said shaft below said lined portion with a transverse seal;

feeding a liquid freezant under elevated pressure through said seal and freely into said sealed off lower portion of the shaft to freeze water present in the surrounding earth walls thereof;

unsealing and opening said lower portion of the shaft;

and

filling said lower portion and said upper lined portion of the shaft with a water impermeable material while said surrounding earth walls are still sufficiently frozen to prevent undesirable water seepage.

2. The method set forth in claim 1, wherein said freezant is a liquified gas.

3. The method set forth in claim 1 including the further step of reaming said frozen walls to enlarge said shaft lower portion to a desired shape before filling it with said water impermeable material.

4. The method set forth in claim 1 including the further steps of successively and alternately reaming and freezing said frozen walls to enlarge said shaft lower portion to the desired dimensions before filling it with said material.

5. The method set forth in claim 1 wherein said lower portion of the shaft is formed as an enlarged cavity.

6. The method set forth in claim 5 wherein said cavity is reamed to bell shape before the walls are frozen.

7. The method set forth in claim 1 wherein the water impermeable material is concrete and said cavity and shaft above it are lled with concrete.

8. The method set forth in claim 11 wherein the cavity is bell shaped and its dry frozen walls are inspected, and

5 a inishing operation is performed on the Walls when and Where indicated by the inspection.

9. The method set forth in claim 1 wherein said step of feeding frcezant under pressure includes forcing at least some of the Water in said shaft lower portion back into the soil While freezing it, and also forcing any excess water at the bottom of the cavity upwardly through a discharge conduit passing through said seal and away from said shaft.

10. The method set forth in claim 9 wherein the tinal freezing stage is effected with the freezant circulated be tween the source and the cavity.

References Cited UNTED STATES PATENTS Perin 61-36 Sooysinith 61--36 Schmidt 61-36 Miller 61-36 Goldsiborough 61-53.6 Dunn et al. 61-36 Sanger 61-.5

JACOE SHAPIRO, Primary Exmtainer.

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