Method for prudent penetration of a casing through sensible overburden or sensible structures

In a subterranean drilling operation, a drill stem and drill bit are advanced downwardly while conducting compressed air downwardly through the drill stem. A minor part of the air flow is discharged from the drill bit downwardly against the sensible overburden, and a major part of the air flow is discharged upwardly through passages in the drill stem. A casing is disposed around the drill stem and advanced therewith so that the sensible overburden is shielded from the air discharged from the upwardly directed passages. The upwardly directed passages contain removable inserts which can be exchanged for different inserts in order to vary the amount of air discharged from the upwardly directed passages, and thereby vary the amount of air discharged downwardly from the drill bit against the overburden. In that way, the amount of air acting against the overburden can be adapted to the type of material in the overburden in order to control the amount of disruption to the overburden.

BACKGROUND OF THE INVENTION 
The present invention relates to a method and a device for driving down 
casings to undisturbed ground without essentially displacing or spoiling 
sensible overburden and sensible structures. In the casings piles or the 
like can be driven down for foundation or anchoring in more solid ground. 
Sensible overburden is for instance cultural layers from earlier 
civilizations that can be found under the ground surface having a 
thickness of up to 3 m. The cultural layers are a source of knowledge for 
the archeologist to learn about life and human beings during earlier 
epoches. The cultural layers are in some countries protected by law and 
must not be ruined. 
Sensible structures are for instance walls of unhewn stone for older 
buildings, especially while works are going on for reinforcing the 
fundament or sheet piling in or adjacent to the structures. These works 
must be carried out very carefully if no permanent damage shall occur. 
The main characteristics of the invention are that a drilling device that 
is operated by compressed air is surrounded by a casing, said drilling 
device at its lower end being provided with adjustable exhaust channels 
that direct the major part of the compressed air upwards to lead it away 
between the drill stem and the casing together with the cuttings. Due to 
the fact that the exhaust channels are adjustable, the intensity of the 
part of the compressed air directed downwards toward the drill bit can be 
adapted to the nature of the material that is penetrated. By jet action 
said part of the compressed air can be led upwards along the grooves on 
the side walls of the drill bit. The invention also relates to the design 
of these grooves having a lower narrow inlet and an upwards continuously 
increasing area. Said design makes it impossible for the cuttings to stick 
on their way upwards.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION 
FIG. 1 discloses in section a device for overburden drilling comprising a 
rotating drill 1, that is surrounded by a casing 2. The lower part of the 
drill, i.e. the drill bit, is shown in the figures as a separate detail. 
The drill bit is assembled of a guiding device 11, reamer 12 and pilot bit 
13. The drill also comprises an exhaust channel 14 for the compressed air 
operating the drill. These details are known per se. According to the 
invention the exhaust channel 14 is provided with a control valve 141. 
Above this control valve 141 there are exhaust channels 142 for the main 
part of the compressed air, said exhaust channels 142 being provided with 
flow conducting inserts 143 having passages whose areas are adapted to the 
material that the device is to penetrate. The inserts 143 are accessible 
for exchange in order to carry out a coarse adjustment, if necessary, 
before starting a new drilling cycle. The minor part of the compressed 
air, that passes through the control valve 141 for prudent flushing around 
the drill tip, thereafter is sucked upwards along grooves 144 on the side 
walls of the drill bit through jet action from the compressed air that is 
rushing out directed upwards from the exhaust channels 142 through the 
inserts 143. By having the grooves 144 designed with a narrow lower inlet 
and a gradually upwards increasing area, the cuttings can never stick 
anywhere on their way upwards and obstruct the channels. 
FIG. 2 discloses in section the way of the compressed air through the 
drill. The compressed air is with great power rushing through the exhaust 
channel 14 (arrow A) and is to a major extent pushed backwards by the 
constriction in the control valve 141. The air then continues through the 
upwards inclined exhaust channels 142 having inserts 143 (arrow B) and 
then further upwards together with the cuttings between the drill shank 
and the casing (arrow C). The minor part of the compressed air, that flows 
through the control valve 141 (arrow D) for prudent flushing around the 
drill tip, is sucked upwards along the grooves 144 in the side walls of 
the drill bit (arrow E) through jet action from the compressed air that is 
rushing out in an upward direction from the exhaust channels 142 through 
the inserts 143. 
FIG. 3 discloses the different working phases when the casing and the drill 
is driven down into the overburden 15 to a level just below the lower edge 
of the cultural layer. After the drill has been drawn up piling can take 
place through the casing without disturbing the cultured layer. 
Phase 1 
Mobile drill tower with casing 2 and drill 1 mounted, the tower being moved 
to the drill site. 
Phase 2 
The casing 2 is displaced downwards into the overburden through the 
cultured layers. 
Phase 3 
The casing 2 is driven down in the overburden to a level just below the 
lower edge of the cultural layers. 
Phase 4 
A pile 16 is lowered into the casing. 
Phase 5 
The pile 16 is driven down into the overburden to a predetermined depth. 
Phase 6 
The pile 16 has reached the predetermined depth (driven to a stop in 
friction material) and then cemented 18 in the casing. 
FIGS. 4A to 4D disclose the different working phases when the casing and 
the drill are driven down through a fundament of unhewn stone. 
Phase 1 (FIG. 4A) 
When the fundament 19 has been reinforced in certain areas 20 the drilling 
device can be entered on the floor above the base fundament. 
Phase 2 (FIG. 4B) 
Casings 2 are driven through the fundament 19 down to a level just below 
the lower edge of the fundament 19. 
Phase 3 (FIG. 4C) 
Steel piles 21 are driven down through the casings 2 until the end 22 of 
the piles 21 bear against the rock. 
Phase 4 (FIG. 4D) 
After the steel piles have been driven down to a stop the drilling device 
is taken away. The damages of the fundament caused by the drilling are 
filled with concrete 23. 
The invention is of course not restricted to the above described 
embodiments but many modifications are possible within the scope of the 
appending claims.