Soil consolidation apparatus, tool and method

In order to consolidate soil, a hole is drilled therein by advancing downwardly through the soil a rotary percussive drill bit disposed at the end of a drill string. Water is pressurized at the ground surface and is conducted to actuate a hydraulically driven down-the-hole hammer disposed above the drill bit. While vertically retracting and rotating the drill string, grout, which is pressurized at the ground surface, is conducted downwardly through the drill string and ejected laterally outwardly through a lateral opening in the drill string to produce a console of mixed soil and grout surrounding the hole. The water and grout are pressurized in respective chambers of a pump.

FIELD OF THE INVENTION 
The present invention relates to a soil consolidation apparatus, as well as 
a tool and a method for soil consolidation. 
BACKGROUND OF THE INVENTION 
The technique of soil consolidation has been used for the static retrofit 
of existing structures for several years. Soil consolidation is ideally 
suited for solving foundation problems in areas of tight access, low 
overhead or difficult geology conditions. A typical method of soil 
consolidation is to drill a bore by rotating a rotary drill bit by means 
of a tube string, opening a free end of the string and inserting a ball 
that gravitates onto a seat in the drill string located adjacent to the 
drill bit. Thus a check valve is created shutting the channel to the 
rotary drill bit and allowing jet grouting of the soil adjacent to the 
hole during retraction of the string and the drill bit. When the soil to 
be consolidated includes big boulders (e.g., having diameters of 0.3 to 
1.0 m) the known method becomes ineffective in terms of penetration speed. 
When that kind of boulder-containing soil is to be consolidated it is often 
necessary to use a top hammer equipment wherein the hammer impacts on a 
sealed drill string which transfers the resulting shock waves to a 
percussive drill bit. When the drill bit has reached its predetermined 
position down into the soil, jet grouting is commenced at 300 to 500 bars 
of internal pressure. However, the shock waves will eventually impair the 
function of the seals mounted in every drill string joint, whereupon the 
grout will leak and abrade holes in the expensive drill tubes. Also, the 
leakage will result in the jet grouting being performed at a lower 
pressure than intended. As soon as the leakage is discovered the drill 
tube is exchanged. 
Disclosed in U.S. Pat. No. 5,219,247 is a soil consolidation apparatus 
utilizing an air-driven down-the-hole hammer. However, that apparatus 
requires the use of at least two pressurizing means, i.e., one compressor 
to pressurize air and one pump for jet grouting. Furthermore, the air has 
to be pressurized to a high level by the compressor for lifting the 
cuttings, and thus the soil surrounding the hole will be eroded by the 
high-pressure air. 
OBJECTS AND SUMMARY OF THE INVENTION 
One object of the present invention is to provide an improved soil 
consolidation apparatus, and a tool and method for soil consolidation that 
retain the advantages of the prior art. 
Another object of the present invention is to provide a soil consolidation 
apparatus which is environment friendly. 
Still another object of the present invention is to provide a soil 
consolidation apparatus which needs only one pressurizing means to 
function. 
Still another object of the present invention is to provide a soil 
consolidation apparatus which can penetrate the soil at a high production 
rate without impairing the drill tubes. 
These and other objects are attained by a method of consolidating soil 
comprising the steps of: 
A) drilling a hole by advancing downwardly through the soil a rotary 
percussive drill bit disposed at the end of a drill string; 
B) pressurizing hydraulic fluid at the ground surface and conducting the 
pressurized hydraulic fluid downwardly through the drill string during 
step A to actuate a down-the-hole hammer disposed above the drill bit for 
applying percussive impacts thereto; 
C) retracting the drill string upwardly while rotating the drill string; 
and 
D) pressurizing grout at the ground surface and conducting the pressurized 
grout downwardly through the drill string during step C and ejecting the 
pressurized grout laterally outwardly through a lateral opening in the 
drill string whereby the opening rotates with the drill string to produce 
a console of mixed soil and grout surrounding the hole. 
The present invention also relates to a soil consolidation apparatus which 
comprises a drill rig and a drill string mounted to the drill rig to be 
rotated, lowered and raised thereby. A percussive drill bit is mounted at 
an end of the drill string. A down-the-hole hammer is mounted above the 
drill bit for applying percussive impacts thereto. A source of hydraulic 
fluid, and a source of grout are provided. Pressurizing apparatus is 
provided for selectively pressurizing the hydraulic fluid and the grout. 
The drill string includes a lateral opening formed therein. A first 
channel is disposed in the drill string and is connected to the hammer for 
conducting pressurized hydraulic fluid to the hammer for actuating the 
hammer during a drilling operation. A second channel is disposed in the 
drill string separate from the first channel, for conducting pressurized 
grout to the lateral opening for ejection therethrough during upward 
retraction of the drill string. 
The invention further relates to a soil consolidation tool which comprises 
a drill string and a percussive drill bit mounted at an end of the drill 
string. A hydraulically driven down-the-hole hammer is mounted above the 
drill bit. A first channel is disposed in the drill string and is 
connected to the hammer for conducting pressurized hydraulic fluid 
thereto. A lateral grout-ejecting opening is disposed in the drill string. 
A second channel is formed in the drill string separate from the first 
channel and connected to the grout-ejecting opening for conducting 
pressurized grout to the opening.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE PRESENT INVENTION 
In FIG. 1 is generally shown a set-up of equipment 10 needed for soil 
consolidation according to the present invention. The equipment comprises 
a silo 11 for cement, a mixer 12 for mixing water and cement into a grout, 
a pressuring device in the form of a pump 13 having at least two chambers 
for respectively pumping hydraulic fluid (preferably water) and the grout, 
a control panel 14 for controlling the parameters of the equipment 10, and 
a drill rig 15. That equipment is conventional and readily available on 
the market. The setup shown in FIG. 1 is different from a conventional 
soil consolidation set-up in that a two-chamber pump 13 is used in place 
of a pump and separate air compressor, and no air is compressed. 
The present invention is further different from a prior art soil 
consolidation set-up in that the drill rig 15 carries a hydraulically 
(liquid) driven down-the-hole hammer 16 instead of an air (pneumatically) 
driven down-the hole hammer. Now referring to FIG. 2, the hydraulic 
down-the-hole hammer 16 is shown which is adapted to be raised and lowered 
by the rig 15. The hammer 16 is connected to a one-way (non-return) valve 
39, which in turn is connected to a jet grouting monitor 18, which in turn 
is connected to a drill string 17. The drill string 17 comprises a number 
of double-lead, high pressure drill tube sections 17A duly sealed in the 
thread areas. The hammer 16 is a conventional hydraulic (preferably 
water-driven) hammer preferably of the type disclosed in U.S. Pat. No. 
5,107,944 the disclosure of which is incorporated herein by reference. The 
water driven hammer carries a percussive drill bit 19 preferably of the 
type disclosed in U.S. Pat. No. 5,645,132, the disclosure of which is also 
incorporated herein by reference. 
As is conventional, the rearward end of the hammer 16 is provided with a 
drive piston 20 reciprocable in a cylinder. The front end of the piston is 
guided for reciprocation in a bearing located adjacent an anvil of the 
drill bit. Between the cylinder and the bearing, the hammer is elongated 
and enlarged diametrically relative to the piston. A port is provided in 
the rear end for supplying pressurized hydraulic fluid from the drill 
tube. The enlarged hammer portion reciprocates freely in a chamber formed 
by an outer casing 21. The casing is mounted to the front end of the drill 
rod. The drill bit is slidably received and retained by the front end of 
the casing having a channel extending longitudinally therethrough. Drive 
water is expelled from the cylinder and flushes the hole drilled by the 
bit 19. An open ended tubular valve reciprocates to control a duct 
connecting the interior of the valve to a coaxial through-flushing passage 
23 formed in the hammer and the drill bit. 
The percussion drill bit 19 includes a drill body having the fluid passage 
23 for conducting flushing fluid to a front drilling face of the drill 
bit. The fluid passage includes a main portion extending from a rear end 
of the bit and terminating short of the drilling face, and a plurality of 
branch lines extending from a front end of the main portion to the 
drilling face. Front and rear axially spaced seats are disposed in the 
main portion of the fluid passage. A check valve in the form of a ball 24 
is freely movable within the main portion of the fluid passage between 
contact with the front and rear seats. When the drill bit is subjected to 
external over-pressure or when it is oriented upwardly and no flushing 
water is supplied, the ball moves rearwardly into sealing contact with the 
rear seat so that no water or contamination can flow rearwardly past the 
rear seat. When flushing fluid is conducted, the flushing fluid pushes the 
ball forwardly, into non-sealing contact with the front seat and travels 
past the ball into the branch lines. During downwards drilling, if the 
density of the ball is less than that of backflowing water, the ball will 
float upwardly upon the backflowing water and into sealing contact with 
the rear seat. 
The fluid passage can also be sealed against back flow at a location above 
the hammer by means of a check valve device 39 having a movable ball 39A 
which is movable upwardly against a seat 39B to block fluid flow. 
In FIG. 2 is shown the tool in the consolidation apparatus and also shown 
are the pump 13, manual shut off valves 26,27,41, a maximum pressure 
relief valve 28, a manual relief valve 29, a pressure gage 30, a filter 
31, high pressure hoses 32, 33 and a rotation unit 34. 
The tool is mounted by threading the check valve device 39 onto the 
threaded upper end of the hammer 16. The jet grouting monitor 18 is 
threaded onto the check valve 39, and the drill tube is threaded onto the 
jet grouting monitor 18. An inner pipe or channel 38 is mounted 
substantially simultaneously with the drill tube. 
When the drill rig 15 has been positioned at the drilling site as shown at 
step I in FIG. 3, with the tool connected to the rotation unit 34 of the 
drill rig, the valve 26 is opened. Thus, high pressurized water from the 
pump 13, pressurized up to 80 to 200 bar, will run through the hose 32 and 
the filter 31, and successively through a swivel 35, the water channel 38 
in the drill string 17, forcing open check valve 39 and entering the 
hammer 16. The piston 20 of the hammer will then impact on the rear end of 
the drill bit 19, thereby transferring shock waves to the bit buttons 
impacting on the soil or the rock. If boulders 37 are present in the feed 
direction of the drill string there will be no stoppage of the drilling 
operation since the down-the-hole hammer is adapted for hard rock 
drilling. Spent drive water is used to cool the drill bit and to remove 
drill cuttings in front of the drill bit upwardly outside the drill string 
and carry the cuttings to the surface. When additional tool length is 
required as drilling progresses, the water supply is cut off via the valve 
26 and an additional inner pipe 38 and an external tube section 17A are 
mounted, usually every 2 m of drilling advancement. When the drill bit has 
reached its predetermined depth as shown at step II in FIG. 3 the manual 
shut off valve 26 is closed and the pressure in the hose 32 is relieved. 
When the water supply is thus cut off, any back-flow of fluid occurring in 
the bit 19 causes the ball 24 to ascend to the rear seat and seal the 
hammer from any back-flowing fluid. To minimize said back-flow through 
channel 23 the additional check valve 39 seals the water pipe 38 above the 
hammer to create a counter pressure if backflow starts. 
Then, the drill bit is withdrawn upwardly while the hole is grouted. The 
grout is introduced into the pump 13 and pressurized up to maximum 500 
bar. Then the valve 27 is opened and the highly pressurized grout will run 
through the hose 33 and the pressure relief valve 28, and successively 
through the swivel 35, a grout channel 36 in the drill string 17 and out 
through openings or grout channel ejectors 40 of the jet grouting monitor 
18. The grout will not enter the hammer 16 since the hammer and the water 
chamber 38 are sealed and separate from the grout channel 36. The rotation 
unit 34 is started, to rotate the drill string while retracting it. The 
lateral jet stream of grout exiting from the openings 40 will mix with the 
surrounding soil to a diameter of one meter maximum and produced a console 
C of mixed soil and grout extending about as high as the depth of the 
drilled hole as shown in steps II-V of FIG. 3. After completion of the 
consolidation process, the drill string is completely retracted from the 
drilled hole and often the jet line 33, 36, 40 is flushed with water 
before the valve 27 is closed. During retraction of the tool the grout 
supply is periodically cut off via the valve 41 such that the inner pipes 
38 and external tube sections 1 7A can be dismounted. Then the 
consolidation apparatus is ready to drill a new hole by opening the valve 
26 for a new drill cycle. 
It should be noted that the present invention provides numerous additional 
advantages relative to prior art devices. A water driven hammer will not 
affect the surrounding soil as much as air driven tools with respect to 
erosion, oil pollution and noise, For example, with respect to erosion, 
the speed of water to drive the water driven hammer is about 1 m/s as 
compared to an air driven hammer wherein the air speed is about 20 m/s. 
The apparatus according to the present invention obviates the need for an 
air compressor. Furthermore by using a water driven hammer the hammer will 
not be heated and thus the grout will not dry on the hammer to counteract 
extraction of the hammer. 
The invention can be varied freely within the scope of the appended claims. 
Although the present invention has been described in connection with a 
preferred embodiment thereof, it will be appreciated by those skilled in 
the art that additions, deletions, modifications, and substitutions not 
specifically described may be made without departing from the spirit and 
scope of the invention as defined in the appended claims.