Borehole dilatometer with intensifier

Apparatus for use in testing the mechanical behaviour and deformation characteristics of rocks and the like at various locations in a borehole comprises a pressure intensifier used in conjunction with a dilatometer head, the two being rigidly interconnected so as to be lowered into the borehole. The pressure intensifier comprises a cylindrical housing providing upper and lower cylinders, and a double action piston which provides a 6 to 1 differential between the input pressure side and the output pressure side. Pressure changes are measured by means of a pressure transducer, and volumetric changes are determined from measurements of the linear displacement of the piston. Such linear displacements are measured by means of a shaft encoder coupled to a motion translating device for translating linear displacement into rotary displacement.

This invention relates to an apparatus for use in testing the mechanical 
behaviour and deformation characteristics of rocks and like materials at 
various locations in a borehole. 
The apparatus is used in conjunction with a dilatometer, which is lowered 
into the borehole to a selected depth, the dilatometer head being 
internally pressurized by hydraulic fluid so as to be expanded radially 
against the wall of the borehole. Rock properties can be determined by 
correlating the volumetric changes of the dilatometer head with the 
applied hydraulic pressure. Hitherto, in such procedures, difficulties 
arising from several causes have been encountered. In the first place, the 
high hydraulic pressures often required cause hazardous working conditions 
above ground where the pressure source is located. Another difficulty, 
particularly in the case of deep borehole measurements where highly 
viscous fluids cannot be used satisfactorily, is that the use of a less 
viscous liquid such as water detracts from the stiffness of the system, 
owing to the compressibility of the liquid, rendering the system 
unsuitable for testing hard rocks such as granite. 
The present invention relates to an apparatus which largely overcomes these 
difficulties. Essentially, the invention provides a pressure intensifier 
which can be interconnected with the dilatometer head and lowered with it 
as a unit into the borehole, thereby eliminating the need for high working 
pressures above ground and so allowing safer working conditions for 
personnel. 
Another feature of the apparatus is that it allows highly viscous fluids 
such as oil, with its low compressibility, to be used instead of water 
since the need for high pressure tubing with its characteristic small 
inner diameter is eliminated. 
An apparatus according to the present invention basically comprises a 
pressure intensifier to be used in conjunction with a dilatometer head 
which is lowered into the borehole to the required location. The 
dilatometer head has a radially expandable body portion defining an 
internal cavity for receiving hydraulic fluid under pressure. The pressure 
intensifier comprises, in combination: a housing defining first and second 
axially aligned interconnecting cylinders, the first cylinder being of 
larger diameter than the second cylinder; connecting means for 
establishing fluid communication between the second cylinder and the 
internal cavity of the dilatometer head; a piston having a head portion 
mounted for non-rotational linear reciprocation within the first cylinder 
so as to define a first chamber of variable volume ahead of the head 
portion, and a rearwardly extending plunger portion mounted for 
simultaneous linear reciprocation within the second cylinder so as to 
define a second chamber of variable volume rearwardly of the plunger 
portion; means for introducing a first hydraulic working fluid into the 
first chamber; means for pressurizing the first working fluid within the 
first chamber so as to displace the head portion of the piston linearly in 
the rearward direction, thereby pressurizing a second working fluid in the 
second chamber; means for measuring the linear displacement of the piston 
and for providing an electrical signal indicative thereof; and transducer 
means for measuring pressure changes of the second hydraulic fluid and for 
providing an electrical signal indicative thereof. 
The invention is characterized by the fact that the linear displacement 
measuring means comprises a shaft encoder fixedly mounted in the housing, 
the shaft encoder being coupled to an axially extending shaft journalled 
for rotation within the housing. The shaft is coupled to the piston by 
motion translating means for effecting rotational displacement of the 
shaft is response to linear displacement of the piston. In a preferred 
embodiment of the invention the shaft has a helically threaded portion 
which is engaged by a ball screw assembly connected to the piston so as to 
be displaceable axially therewith thereby effecting rotational 
displacement of the shaft in response to linear displacement of the 
piston. 
The second hydraulic working fluid may be water, at least if high system 
stiffness is not essential. However, the apparatus makes it possible to 
use highly viscous fluids such as oil, which is about half as compressible 
as water, in applications where system stiffness is important. 
A preferred feature of the invention is that the pressure intensifier is 
releasably connected to the dilatometer head in such a way that, should 
the dilatometer head become lodged in the borehole, the pressure 
intensifier can be hoisted out separately and the dilatometer head can be 
retrieved subsequently by drillrods.

Referring to FIG. 1, a hoist 10 at ground level is used to lower the 
dilatometer head 11 to the selected location in a borehole 12, the 
borehole 12 being drilled vertically into the ground. The dilatometer is 
of the type having an expandible body portion defining an internal cavity, 
which can be internally pressurized by hydraulic fluid so as to expand the 
body portion radially against the wall of the borehole. One such 
dilatometer head for this purpose is disclosed in our copending 
application Ser. No. 790,234 filed Oct. 18, 1985, the contents of which 
are incorporated herein by reference. A hydraulic pump 13 is used to 
supply hydraulic fluid under pressure to a pressure intensifier 14, the 
latter being rigidly interconnected with the dilatometer head 11 and 
operable to internally pressurize the latter. As hereinafter described, a 
pressure transducer mounted in the pressure intensifier housing is 
operable to measure pressure changes on the high pressure side of the 
intensifier and to provide an electrical signal indicative thereof. 
Volumetric changes of the dilatometer are determined from linear movements 
of a piston within the intensifier housing, means being provided for 
producing an electrical signal indicative thereof. The electrical signals 
are transmitted to a signal processing apparatus 15 whereby the signals 
are processed to obtain the required measurements of rock properties. 
By reason of the fact that the dilatometer head and the pressure 
intensifier are rigidly interconnected and lowered into the borehole as a 
unit, the high working fluid pressures are confined below ground, only the 
fluid on the low pressure side of the intensifier being taken above ground 
level. Furthermore, pressure changes and volume changes are measured 
directly within the intensifier housing and converted to electrical 
signals which are safely transmitted by cable to the signal processing 
apparatus 15. 
As shown in FIG. 2, the pressure intensifier 14 is hydraulically and 
mechanically connected to the dilatometer head 11 by a yoke fastening 16 
at the lower end of the intensifier. At the upper end of the intensifier 
14 is a coupling assembly 17 which carries both the hydraulic connections 
18 on the low pressure side of the intensifier 14, and the electrical 
connections 19 which transmit signals to the signal processing apparatus 
15 of FIG. 1. 
Referring now also to FIGS. 3 to 8, the pressure intensifier 14 comprises 
an elongate cylindrical housing 20, within which a hollow insert 21 is 
located adjacent the lower end of the housing. The insert 21 defines 
together with the housing an upper cylinder 22 and a lower cylinder 23 
interconnected with it. The cylinders 22 and 23 are axially aligned, the 
upper cylinder being of larger diameter than the lower cylinder 23. A 
piston having a head portion 24 and a downwardly directed plunger portion 
25 is mounted in the housing 20 for linear reciprocation therein. The 
piston is constrained not to rotate by means of axially extending guide 
tubes 29 rigidly mounted within the housing, the guide tubes 29 
registering with, and extending through, cooperating bores in the head 
portion 24 of the piston. The head portion 24 of the piston is thus 
constrained to reciprocate linearly within the upper cylinder 22 so as to 
define a first chamber of variable volume above the head portion. The 
plunger 25, being integral with the head portion of the piston, is 
constrained for simultaneous linear reciprocation within the lower 
cylinder 23, so as to define a second chamber of variable volume below the 
plunger. 
A first hydraulic fluid is introduced into the first or upper chamber via a 
fluid passage 26 communicating with an inlet tube 27, the first hydraulic 
working fluid being introduced under pressure by the pump 13. A return 
fluid passage (not shown) communicates with an outlet tube 28. The tubes 
27, 28 are interconnected with the pressure source represented by the pump 
13. 
In use of the apparatus, the second chamber defined by the plunger 25 and 
lower cylinder 23 is filled with a second working hydraulic fluid, which 
may be the same as or different from the first working fluid. The head 
portion 24 and plunger portion 25 are dimensioned so as to provide a 6 to 
1 double action piston differential between the input pressure side of the 
intensifier and the output pressure side. The pressure intensifier 14 is 
rigidly interconnected with the dilatometer head 11 by means of a rigid 
shaft 30 providing an internal passageway 31 communicating with the 
internal cavity of the dilatometer head. The shaft has a coupling head 32 
at its upper end, the coupling head being formed with an annular detent 
33. The lower end of the cylindrical housing 20 of the intensifier has a 
circular opening 34 through which the coupling head extends, the coupling 
head being retained in cooperative engagement with an external socket 35 
provided on the underside of the lower end of the insert 21. The insert 21 
is formed with an internal passageway 36 communicating with the second 
chamber formed by the lower cylinder 23, and the coupling head 32 and 
socket 35 provide respective cooperating ports which interconnect the 
passageways 31 and 36 when the coupling head and socket means are mutually 
engaged as shown in FIG. 3. Thus, fluid communication between the lower 
cylinder 23 of the intensifier and the internal cavity of the dilatometer 
head is established by the passageways 31 and 36, and the cooperating 
ports. 
The hydraulic pressure on the high pressure side of the intensifier, that 
is, in the cylinder 23 which communicates with the dilatometer head is 
measured by means of a pressure transducer 37 mounted in the intensifier 
housing. The transducer 37 is interconnected with the lower chamber formed 
by cylinder 23 by means of a passageway 38 extending through one of the 
guide tubes 29. A high pressure seal 39 engages the side of the plunger 25 
immediately above the lower end of the passageway 38, there being a small 
clearance between the plunger and the cylinder wall forming, in effect, an 
extension of the passageway 38 to the chamber formed in cylinder 23. The 
pressure transducer 37, which may be of the ET/ETM-375 series manufactured 
by Kulite. provides output leads 40 for transmitting the 
pressure-dependent electrical output signal to the processing unit 15. 
Volumetric changes of the dilatometer head are determined from measurements 
of the linear displacements of the plunger 25 in the cylinder 23. Such 
linear displacements are measured by means of an incremental shaft 
encoder, which may be of type LC-23 of Durham Instruments, a division of 
Buchan Instruments Inc. The shaft encoder 41 is fixedly mounted within the 
housing 20 near its upper end, and is coupled to an axially extending 
shaft 42 which is journalled within the housing for rotation about its 
axis. The shaft is coupled to the piston 24, 25 by means of a ball screw 
assembly 43. The ball screw assembly 43 may be of a type manufactured by 
Warner Electric Brake & Clutch Company. The axially extending shaft 42 has 
a helically threaded portion 42', the balls of the ball screw assembly 
engaging the helically threaded portion 42'. The housing of the assembly 
43 is connected to the piston 24, 25 so as to be diplaceable axially 
therewith thereby to effect rotational displacement of the shaft 42 in 
response to linear displacement of the piston. The rotational displacement 
of the shaft 42 is converted to an electrical signal by the shaft encoder 
41, the signal being transmitted through leads 44 to the processing unit 
15. 
As shown in FIG. 3, the piston 24, 25 has an axially extending bore 45 
which opens into the upper chamber 22 at its upper end and is closed at 
its lower end. The shaft 42 extends into the bore 45, the housing of the 
ball screw assembly 43 having a threaded portion 46 which is threaded into 
the upper end of the piston. 
The structure of the pressure intensifier further comprises a spring-loaded 
releasable fastening means located at the bottom of the cylindrical 
housing 20. The fastening means comprises a ball assembly 47 retained in a 
race 48 (FIG. 5), and a spring-loaded washer 49 which biasses the balls 47 
radially inwardly into fastening engagement with the detent. With this 
arrangement, should the dilatometer head become lodged in the borehole, 
the intensifier can be readily released from it and hoisted from the 
borehole. The shaft 30, which is connected to the dilatometer head by the 
yoke fastening 16, has a helically threaded portion 50 which is adapted 
for engagement by a suitable retrieval tool, such as a drill rod, for 
retrieving the dilatometer head from the borehole. 
Although the invention has been particularly described with reference to a 
dilatometer head which is lowered into a vertical borehole, it is to be 
understood that, so far as the structure of the pressure intensifier is 
concerned, the orientation of the borehole is immaterial. The subject of 
the present invention is the pressure intensifier as defined by the claims 
herein.