AU656862B2 - Method and apparatus for removing debris from an excavated pier hole - Google Patents

Description

The present invention relates to excavations for concrete piers, and in particular, to a method of removing debris from an excavated pier hole which ensures that substantially all the debris within the hole is removed.

In the construction industry, a pier hole is often dug by a grab or drill which is operated by a crane. When the pier hole is dug lower than the water table the sides of the hole are prone to collapse due to the pressure of the water on the sides of the hole. To prevent the side walls of the hole collapsing, the hole can be filled with a suspension of bentonite mixed in water, while the hole is being dug. The percentage of bentonite which is dissolved in the water is approximately Bentonite suspension is a thixotropic or gel like substance and it forms a coating which is more or less impervious to water on the inside surface of the walls of the hole. This coating of deposited bentonite, and the maintaining of the water level within the hole above the level oW the water table, prevents the side walls of the hole from collapsing and thereby facilitates the formation of the concrete pier.

When the excavation of the hole reaches its final depth, there is a small amount of debris or sediment which settles at the bottom of the hole. Such debris or sediment is undesirable at the bottom of the hole, as the concrete pier which is to be formed within the hole should have a solid foundation. Therefore, it is desirable that the debris or sediment be removed from the base of the hole and that the bentonite suspension remain in the hole prior to the introduction of the concrete into the hole.

It is also desirable that the owner of the structure being built be able to be assured thc't the pier hole is free of debris prior to the commencement of the concrete pier.

One known way of attempting to remove the debris and sediment includes the method of squirting air into the bentonite suspension at the base of the pier to stir up the debris or sediment which then can be sucked out by a slurry pump whilst adding fresh (or filtered) bentonite suspension at the top of the pier hole. This procedure is continued until the output from the pump is clear of debris. This method has not proved successful as the introduction of air under pressure in the bentonite suspension tends to destabilise the bentonite suspension and can precipitate collapse of the side walls of the hole. Any collapse of the sides of the hole increases the fine debris in suspension in the HRN/ 1161 c bentonite suspension which, after a period of time will form further sediment as it reaches the bottom of the hole after the removal process has been completed. Thus this fine sediment is liable to interfere with the success of the pier base cleaning operation.

It is also known to attempt to photograph the bottom of the pier hole by complicated video equipment which is lowered into the hole. Such expensive equipment has hitherto been used as a means of attempting to prove to the structure owner that the hole is free of debris prior to the concrete pour.

It is an object of the present invention to provide a method and apparatus for removing debris from an excavated pier hole which removes substantially all debris from the hole in a repeatable and convincing fashion.

According to one aspect of the present invention there is disclosed a method of removing debris from an excavated pier hole, or the like, which extends well below the water table and which is filled with a pressure stabilizing liquid to a height above that of, the water table, said method comprising the steps of: lowiering down the hole a pump to locate said pump adjacent the hole bottom, forming a plurality of nozzles around said down-the-hole pump in a frame attached to the pump body, operating said down-the-hole pump to suck said liquid from the bottom of the hole, 25 pumping said liquid from a clean supply thereof at ground level into said nozzles to form a plurality of debris stirring jets of said liquid at said hole bottom, whereby debris disturbed by the turbulence of said jets is entrained in said liquid pumped from the bottom of said hole by down-the-hole pump, and 30 continuing steps and until the output at the surface of said down-the-hole pump is substantially free of debris, at all times maintaining the level of the liquid in the pier hole above the ground water table.

According to another aspect of the present invention there is disclosed apparatus for removing debris from an excavated pier hole, or the like, which extends well below the water table and which is filled with a pressure stabilizing liquid to a height above that of, the water table, said apparatus comprising a down-the-hole pump having an outlet HRN/1161c conduit extending the depth of said hole and carrying a frame of pipes containing a plurality of nozzles directed towards the hole bottom; and a liquid supply line connecting said pipes with a source of said stabilizing liquid under high pressure. Preferably a peripheral skirt is formed around said nozzles.

One embodiment of the present invention will now be described with reference to the drawings in which: Fig. 1 is a cut away side view of the apparatus of the preferred embodiment illustrated within a pier hole, Fig. 2 is a partial side view of the apparatus of Fig. 1 illustrating a down-the-hole pump, and Fig. 3 is an inverted plan view of the down-the-hole pump of Fig. 2 illustrated within the hole: The apparatus 1 of the preferred embodiment as illustrated in Fig.

1 is used to remove debris which has formed as sediment on the bottom of a pier hole 2. The pier hole 2 as illustrated in the drawings is a rectangular hole and has been dug using a grab (not illustrated) operated by a crane (not illustrated). As the pier hole 2 is being dug, the pier hole 2 is filled with a bentonite in water suspension 21. The bentonite comprises 5% of the suspension and is a thixotropic or gel like substance which is deposited on in the side walls 16 of the the pier hole 2 to form oo a bentonite coating 17 which is substantially impervious to water. The bentonite suspension 21 is continually introduced into the pier hole 2 while the hole 2 is being dug. The level 22 of the bentonite suspensior 25 21 is maintained at approximately ground level 10. This ensures that the level 22 of the bentonite suspension 21 remains above the water table of the ground.

The bentonite coating 17 which forms on the side walls 16 of the pier hole 2 assists in ensuring that the side walls 16 do not collapse 30 and that the pier hole 2 remains substantially rectangular or circular in cross section.

Nhen the pier hole 2 reaches its final depth, there is some loose material etc on the hole bottom and a residual amount of particulate debris suspended in the bentonite suspension 21. This particle charged bentonite is replaced by clean bentonite by means of reverse circulation. The debris 18 remaining should then be removed from the pier hole 2 in order that the concrete foundations which are to be formed are formed on a solid base.

HRW/1161c The apparatus 1 includes a down-the-hole pump 3 which is lowered down the pier hole 2. Connected to the body of pump 3 is a framework of pipes 7 which receive clean bentonite suspension from an outlet 5 of a liquid supply line 23 with the other end of the liquid supply line 23 being connected to a BIGDO (trade mark) pump 20 connected to in a supply tank 14 at ground level The down-the-hole pump 3 has an outlet 9 which is connected to an outlet conduit 4 which rises from the hole bottom 8 to above the ground level 10. The outlet conduit 4 and supply line 23 are both suspended by a crane 15 and have ties 27 to maintain their relative positions. The outlet conduit 4 has an outlet 25 which is directed away from the pier hole 2 to de-sanding plant (not illustrated).

The pipes 7 include a plurality of nozzles 6 which are directed downwardly. The pipes 7 are in addition to the frame 26 of the down-the-hole pump 3. The down-the-hole pump 3 further includes an impeller 13 which is used to direct flow downwards at the base of the hole. A skirt 11 with a scalloped bottom surrounds the pipes 7 where they contain nozzles, the frame 26 and the impeller 13. The skirt 11 is preferably made of sheet metal and attached to the body of the down-the-hole pump 3. As illustrated in the drawings, the skirt 11 is square in transverse cross section and, of a width which, corresponds substantially to the cross section of the pier hole 2.

To commence operations, the down-the-hole pump 3 is lowered into the bentonite suspension 21 within the pier hole 2. The skirt 11 is positioned at the hole bottom 8. The down-the-hole pump 3 is started, and the impeller 13 provides a turbulence, and commences to remove the bentonite suspension 21 from the area around the hole bottom 8 and send it through the outlet conduit 4 to above ground level As the bentonite suspension 21 is being removed from the area 30 around the hole bottom 8, extra clean bentonite suspension 21 is introduced via a supply pipe 29 from storage, at the top of the hole to maintain the level 22. While the down-the-hole pump 3 is sucking the bentonite suspension 21, a further relatively small volume, of clean bentonite suspension is also introduced via the BIGDO pump 20 down the supply line 23 to the pipes 7. The clean bentonite from the supply tank 14 passes through the plurality of nozzles 6 in a downwards direction.

This clean bentonite suspension is preferably under a high pressure of HRI'fI 11 l r 35-50 bars and causes a substantial amount of agitation at the hole bottom 8 to stir up the debris 18 which has settled there.

Once the debris 18 has been stirred, the down-the-hole pump 3 is able to remove the debris 18 within the bentonite suspension at the hole bottom 8. The suction is a continuous process and therefore the level 22 of the bentonite suspension 21 within the pier hole 2 must be continually maintained via top-up at ground level.

The bentonite suspension 28 ejected from the outlet conduit 4 initially includes the debris 18 which is being removed. When the bentonite suspension 28 is substantially clear of debris 18, it is apparent that substantially all the debris 18 has been removed from the hole bottom 8.

The preferred rate of removal of the bentonite suspension 21 via the down-the-hole pump 3 is 2.5 m 3 /min and the preferred introduction rate of bentonite suspension by the BIGDO pump 20 is 0.25 m 3 /min at a pressure of 40 bars which gives a net removal rate of the bentonite suspension of 2.25 m 3 /min from the hole bottom 8. The action of the skirt 11 assists in the agitation of the debris 18 as it is thought that the velocity of the bentonite suspension 21 across the skirt perimeter is 0.625 m/sec. The bentonite suspension 21 is sucked from the area enclosed by the skirt 11, therefore the bentonite suspension which passes across the perimeter of the skirt 11 aids in the agitation action within the skirt 11.

The verification of the cleanliness of the bentonite suspension 28 which is being removed via the outlet conduit 4 is preferably demonstrated by a bentonite density test result of less than l.lOg/ml.

When the debris 18 has been substantially removed from the hole bottom 8, the down-the-hole pump 3 is removed from the pier hole 2. The pier hole 2 is then in a condition ready for formation of the concrete 30 pier which is to be formed therein.

The foregoing describes only one embodiment of the present invention, and modifications obvious to those skilled in the art can be made thereto without departing from the scope of the present invention.

For example, the skirt 11 of the preferred embodiment has a rectangular or square cross sectional shape, but obviously, this shape can be varied according to the shape of the pier hole. It is also envisaged that the bottom surface of the skirt 13 can have scallops which HRN/ll61c vary in size and can assist in the increase in velocity of the bentonite across the perimeter of the skirt.

Further, for holes of relatively large cross sectional area, the area under the skirt 11 can be many times less than the cross sectional area of the pier hole. Under these circumstances the entire pump 3 can be moved backwards and forwards over the hole bottom to thoroughly clean the entire hole.

HRpNlIfilr

Claims (9)

1. A method of removing debris from an excavated pier hole, or the like, which extends well below the water table and which is filled with a pressure stabilizing liquid to a height above that of, the water table, said method comprising the steps of: lowering down the hole a pump to locate said pump adjacent the hole bottom, forming a plurality of nozzles around said down-the-hole pump in a frame attached to the pump body, operating said down-the-hole pump to such said liquid from the bottom of the hole, pumping said liquid from a clean supply thereof at ground level into said nozzles to form a plurality of debris stirring jets of said liquid at said hole bottom, whereby debris disturbed by the turbulence of said jets is entrained in said liquid pumped from the bottom of said hole by down-the-hole pump, and continuing steps and until the output at the surface of said down-the-hole pump is substantially free of debris, at all times maintaining the level of the liquid in the pier hole above the ground water table.

2. A method as claimed in claim 1, wherein the pressure stabilizing liquid is a bentonite suspension.

3. A method as claimed in claims 1 or 2, including the step for providing additional turbulence by an impeller.

4. A method as claimed in any one of the preceding claims where extra liquid is supplied to the pier hole at the top, via a supply pipe.

Apparatus for removing debris from an excavated pier hole, or the like, which extends well below the water table and which is filled with a pressure stabilizing liquid to a height above that of, the water table, said apparatus comprising a down-the-hole pump having an outlet conduit extending the depth of said hole; said pump carrying a frame of pipes containing a plurality of nozzles directed towards the hole bottom; and a liquid supply line connecting said pipes with a source of said stabilizing liquid under high pressure.

6. Apparatus as claimed in claim 5, wherein a peripheral skirt is formed around the nozzles of said frame of pipes. HRW/1161 c -8-

7. Apparatus as claimed in claims 5 or 6, wherein said down-the-hole pump includes a means to provide turbulence at the bottom of said hole.

8. Apparatus as claimed in claim 7, wherein said turbulence means is an impeller.

9. A method of removing debris from an excavated hole, or the like, which extends well below the water table and which is filled w'th a pressure stabilizing liquid to a height above that of, the water table, said method being substantially as described with reference to the accompanying drawings. Apparatus for removing debris from an excavated pier hole, or the like, which extends well below the water table and which is filled with a pressure stabilizing liquid to a height above that of, the water table, said apparatus being substantially as described with reference to the accompanying drawings. DATED this TNENTY-SECOND day of JUNE 1993 S.I.F. Enterprise Bachy Patent Attorneys for the Applicant SPRUSON FERGUSON *o HRN/1161c Method and Apparatus for Removing Debris from an Excavated Pier Hole Abstract A method of and apparatus for removing debris from an excavated pier hole is disclosed. The method includes the steps of lowering down the hole a pump to locate the pump adjacent the bottom of the hole The pump has attached to its body a frame work of pipes (7 which have nozzles directed downwardly. The pipes (7) cause turbulence at the bottom of the hole and the pump sucks the liquid from the bottom of the hole which has entrained therein the debris. The method is continued until the output of the pump is substantially free from any debris. Fig. 1. 9*rS9* *f HRH/l61lc