Soil displacement hammer

The invention provides a steerable soil displacement hammer for driving holes in the ground. This comprises a substantially cylindrical body (1) and a soil displacement head (2) at a forward end of the body. The head is of larger diameter than the body so as to tend to create an enlarged hole around the body when the head is driven through the ground. At the rear end of the body a pivotable member is provided for directing said rear end away from the center of this hole.

This invention relates to a soil displacement hammer. More particularly, 
the invention relates to a steerable soil displacement hammer for driving 
holes in the ground. 
Soil displacement hammers, commonly referred to as "moles", can be used to 
install pipes, cables or conduits in the ground without the necessity for 
excavating a continuous trench. Soil displacement hammers of this kind are 
described, for example, in GB-A-2 134 152 and GB-A-2 147 035. 
WO 87/03924 describes a steerable soil displacement hammer. This is 
characterised by a retractable baffle member mounted adjacent the forward 
end of the body. When the baffle member projects transversely from one 
side of the body, the soil displacement hammer is caused to describe a 
curved path in the ground. 
An object of the present invention is to provide a soil displacement hammer 
with improved steering means. 
The present invention thus provides a soil displacement hammer for driving 
holes in the ground, comprising a substantially cylindrical body, a soil 
displacement head at a forward end of the body, a longitudinally 
reciprocable striking member housed within the body, and an anvil member 
within the body adjacent its forward end and adapted to receive hammer 
blows from the striking member to cause the body to be driven forward, 
characterised in that the head is of larger diameter than the body so as 
to tend to create an enlarged hole around the body when the head is driven 
through the ground, and means are provided at the rear end of the body for 
directing said rear end away from the centre, i.e. towards the side, of 
the enlarged hole. 
In one embodiment a thrust-providing member is arranged off-centre at the 
rear end of the body. When a machine of this kind is to be driven in a 
straight line through the ground, the steering means at the rear end in 
effect cause the rear end to describe a circular path around the periphery 
of the enlarged hole. When the machine is to be steered, the rear end is 
directed only toward one side of the enlarged hole. This results in the 
machine turning in the direction away from the side to which the rear end 
has been steered.

With reference to FIG. 1, the machine is a pneumatically operated soil 
displacement hammer operating in conventional manner from an external air 
supply via a flexible hose. The construction of such a machine is well 
known to those in the art and therefore does not need to be further 
described here. The machine comprises a cylindrical body 1 and a soil 
displacement head 2 at a forward end of the body. The head 2 is of larger 
diameter than the body 1 so that, as the machine is driven through the 
ground, an enlarged hole is created around the body. Linked to the rear 
end of the body is a solid tube 3. The tube 3 has a universal joint 4 near 
the rear end of the body, and is attached off-centre to the rear end. The 
machine is driven through the ground in conventional manner by pneumatic 
thrust, but in addition extra thrust is applied to the machine via the 
tube 3. In view of the off-centre mounting of the tube, the rear end of 
the machine is directed away from the centre of the hole. This will tend 
to result in the machine turning in the direction away from the side to 
which the rear has been steered. The machine is driven in a straight line 
by causing the entire machine, including the tube 3, to rotate about the 
central longitudinal axis as shown by the arrows 5. Such turning is 
powered by conventional mechanical arrangements. As the machine rotates, 
the rear end is directed by the tube 3 in a circular path (when viewed 
from the end) around the periphery of the enlarged hole. 
The arrangement illustrated in FIG. 2 is somewhat similar to that in FIG. 
1. The machine has a cylindrical body 11 and enlarged head 12. A solid 
tube 13, having a universal joint 14, is mounted off-centre on the rear 
end. However, in FIG. 2, the machine as a whole does not revolve, but only 
a section 16 at the rear end, which is connected to the remainder of the 
machine by bearings 17, which permit the section 16 to rotate as shown by 
the arrows 15. Again, extra thrust is applied to the machine via the tube 
13. Straight line boring and steering are carried out in analogous manner 
to that described for FIG. 1. 
The machine shown in FIG. 3 also comprises a cylindrical body 21 and 
enlarged head 22. It also has a back-end 23 which is enlarged to around 
the same diameter as the head. The back-end is pivoted about a central 
point 24 and can move through an arc in any direction across the back of 
the machine. This movement of the back-end of the machine is achieved by 
suitable power operated devices and is controlled by the operator of the 
machine. The machine and back-end do not revolve and no extra thrust is 
necessary to the back; only the air hose, power supply to the movable rear 
end and tracking equipment are connected to the machine. When the machine 
is to be driven in a straight line the swivelling back-end 23 is held in a 
central position by the powered controls. When the machine is to be 
steered the operator causes the back-end 23 to move across an arc towards 
one edge of the mole. This will cause the rear end of the cylindrical part 
of the machine to move towards the corresponding side of the bored hole. 
The head of the machine will then turn in a direction away from that edge.