Geokon 4300 Series User manual

Instruction Manual
Model 4300 series
Vibrating Wire Stressmeter (EX, BX, NX)
No part of this instruction manual may be reproduced, by any means, without the written consent of Geokon®.
The information contained herein is believed to be accurate and reliable. However, Geokon®assumes no responsibility for errors,
omissions or misinterpretation. The information herein is subject to change without notification.
Copyright © 1984-2019 by Geokon®
(Doc Rev I, 1/09/2019)

Warranty Statement
Geokon warrants its products to be free of defects in materials and workmanship, under normal
use and service for a period of 13 months from date of purchase. If the unit should malfunction,
it must be returned to the factory for evaluation, freight prepaid. Upon examination by Geokon,
if the unit is found to be defective, it will be repaired or replaced at no charge. However, the
WARRANTY is VOID if the unit shows evidence of having been tampered with or shows
evidence of being damaged as a result of excessive corrosion or current, heat, moisture or
vibration, improper specification, misapplication, misuse or other operating conditions outside of
Geokon's control. Components which wear or which are damaged by misuse are not warranted.
This includes fuses and batteries.
Geokon manufactures scientific instruments whose misuse is potentially dangerous. The
instruments are intended to be installed and used only by qualified personnel. There are no
warranties except as stated herein. There are no other warranties, expressed or implied, including
but not limited to the implied warranties of merchantability and of fitness for a particular
purpose. Geokon is not responsible for any damages or losses caused to other equipment,
whether direct, indirect, incidental, special or consequential which the purchaser may experience
as a result of the installation or use of the product. The buyer's sole remedy for any breach of this
agreement by Geokon or any breach of any warranty by Geokon shall not exceed the purchase
price paid by the purchaser to Geokon for the unit or units, or equipment directly affected by
such breach. Under no circumstances will Geokon reimburse the claimant for loss incurred in
removing and/or reinstalling equipment.
Every precaution for accuracy has been taken in the preparation of manuals and/or software,
however, Geokon neither assumes responsibility for any omissions or errors that may appear nor
assumes liability for any damages or losses that result from the use of the products in accordance
with the information contained in the manual or software.

TABLE of CONTENTS
1. THEORY OF OPERATION ..................................................................................................................................1
2. INSTALLATION ....................................................................................................................................................3
2.1 BOREHOLE REQUIREMENTS .................................................................................................................................3
2.2 PRELIMINARY CHECKS ........................................................................................................................................3
2.3 ATTACHING THE WEDGE/PLATEN ASSEMBLY .....................................................................................................4
2.4 SETTING THE STRESSMETER (RECOVERABLE TYPE) ............................................................................................4
2.5 RECOVERING THE STRESSMETER .........................................................................................................................5
2.6 SPLICING AND JUNCTION BOXES..........................................................................................................................6
3. TAKING READINGS.............................................................................................................................................7
3.1 GK-404 READOUT BOX.......................................................................................................................................7
3.2 GK-405 READOUT BOX.......................................................................................................................................8
3.2.1 Connecting Sensors with 10-pin Bulkhead Connectors Attached ...............................................................8
3.2.2 Sensors with Bare Leads .............................................................................................................................8
3.2.3 Operating the GK-405 ................................................................................................................................8
3.3 GK-403 READOUT BOX (OBSOLETE MODEL)......................................................................................................9
3.3.1 Connecting Sensors with 10-pin Bulkhead Connectors Attached ...............................................................9
3.3.2 Connecting Sensors with Bare Leads..........................................................................................................9
3.3.3 Operating the GK-403 ................................................................................................................................9
3.4 MEASURING TEMPERATURES...............................................................................................................................9
4. DATA REDUCTION ............................................................................................................................................10
4.1 CHANGE IN STRESS CALCULATION ....................................................................................................................10
4.2 ENVIRONMENTAL FACTORS...............................................................................................................................10
4.3 GAUGE SENSITIVITY FACTORS ..........................................................................................................................11
4.4 CORRECTIONS FOR TEMPERATURE CHANGES ....................................................................................................12
5. TROUBLE SHOOTING.......................................................................................................................................13
APPENDIX A. SPECIFICATIONS.........................................................................................................................15
A.1MODEL 4300 STRESSMETER .............................................................................................................................15
A.2 THERMISTOR (SEE APPENDIX BALSO) ..............................................................................................................15
APPENDIX B. THERMISTOR TEMPERATURE DERIVATION.....................................................................16
APPENDIX C. BIAXIAL STRESS CHANGES .....................................................................................................17

FIGURES
FIGURE 1-VIBRATING WIRE STRESSMETER.................................................................................................................. 1
FIGURE 2-VIBRATING WIRE STRESSMETER INSTALLATION TOOL ASSEMBLY ............................................................. 4
FIGURE 3-LEMO CONNECTOR TO GK-404 ................................................................................................................... 7
FIGURE 4-LIVE READINGS –RAW READINGS............................................................................................................... 8
FIGURE 5-MODEL 4300EX SENSITIVITY FACTOR VS.ROCK MODULUS ......................................................................11
FIGURE 6-MODEL 4300BX SENSITIVITY FACTOR VS.ROCK MODULUS......................................................................11
FIGURE 7-MODEL 4300NX SENSITIVITY FACTOR VS.ROCK MODULUS .....................................................................12
TABLES
TABLE 1-SAMPLE CALCULATIONS ..............................................................................................................................10
TABLE 2-SAMPLE RESISTANCE ...................................................................................................................................14
TABLE 3-RESISTANCE WORK SHEET...........................................................................................................................14
TABLE 4-SPECIFICATIONS ...........................................................................................................................................15
TABLE 5-THERMISTOR RESISTANCE VERSUS TEMPERATURE ......................................................................................16
EQUATIONS
EQUATION 1-CHANGE IN STRESS ................................................................................................................................10
EQUATION 2-TEMPERATURE CORRECTION .................................................................................................................12
EQUATION 3-RESISTANCE TO TEMPERATURE .............................................................................................................16
EQUATION 4-PLANE STRESS .......................................................................................................................................17
EQUATION 5-STRESS IN ANY DIRECTION.....................................................................................................................17
EQUATION 6-SECONDARY PRINCIPLE STRESSES AND ANGLE .....................................................................................17

1
1. THEORY OF OPERATION
Geokon vibrating wire stressmeters are designed primarily for long-term measurements of stress
changes in rock, by utilizing a vibrating wire transducer to measure the deformation of a thick-
walled steel ring preloaded into a borehole by a wedge and platen assembly as shown in Figure
1.
Figure 1 - Vibrating Wire Stressmeter
In use, changing rock stresses impose changing loads on the gauge body causing the body to
deflect, and this deflection is noted as a change in tension and resonant frequency of vibration of
the vibrating wire element. The square of the vibration frequency is directly proportional to the
change in diameter of the gauge and, by calibration, to the change in stress in the rock.
The actual calibration of the gauge depends upon many factors including the host rock elastic
constants, the prestress applied during installation, the orientation of the stressmeter with respect
to the principal rock stress direction and platen contact area. Thus, the accuracy of the gauge
reading is largely indeterminate and the indicated stress magnitude can only be approximate.
A coil and magnet assembly located close to the wire is used to both excite the wire and sense
the resultant frequency of vibration. When the gauge is connected, a pulse of varying frequency
is applied to the coil and magnet assembly, and this causes the wire to vibrate at its resonant
frequency. The wire continues to vibrate, and a signal, at the gauge frequency, is induced in the
pickup coil and transmitted to the readout box where it is conditioned and displayed.
In theory, where the effective modulus of the stressmeter (approximately 28 GPa (4 x 106 PSI))
is more than two times the modulus of the host rock, conversion of the readings to changes in
stress does not require and accurate knowledge of the rock modulus, and this is the reason for
using the term stressmeter for this device. However, in most rocks, and especially in harder
rocks, the modulus must be known to improve the accuracy of the stress measurements, and
calibration curves provided herein give sensitivity factors for materials of different moduli. It
should be noted that as the rock modulus changes by a factor of 10, the gauge factor changes
only by a factor of two.

2
The stressmeter is a uniaxial device. To completely evaluate stress changes in a given plane,
three stressmeters, installed at 0°, 45°, and 90°orientations, are required.
The gauge wire in the Model 4300 Series stressmeters runs perpendicular to the direction in
which the gauge body is loaded in an effort to minimize the effects of point loading, off center
loading, etc. This gives the gauge a very high range and, since as the load increases the wire gets
tighter, the wire never goes slack.
Gauge installation is accomplished by driving a wedge between the gauge body and the platen,
which contacts the borehole walls. Preloading to desired levels is accomplished by further
driving of the wedge with the setting tool. In soft rocks, a soft rock platen and soft rock shoe are
used to increase the area of contact.
The gauge is constructed of corrosion resistant materials and should have an indefinite lifetime
under even the most severe conditions.

3
2. INSTALLATION
2.1 Borehole Requirements
Stressmeters are designed to be used in smooth-walled diamond drill holes. Stressmeters can be
installed in percussively drilled holes and drag bit drilled holes, provided that care is taken to get the
proper hole diameter with a smooth wall. If the walls are rough, the gauge response (calibration) can
be radically affected.
After drilling, the hole should be thoroughly cleaned by washing out with water or blowing out
with compressed air. The borehole diameter should then be checked with the GO-NO-GO gauges
supplied with the installation tool. If the borehole diameter is correct, the installation can
proceed.
Standard hole configurations for each of the models is as follows:
Model 4300EX Stressmeters are designed for use in EX diamond drill holes 38 mm (1.5”), and
the hole can range in diameter from 37 mm (1.45”) to 39 mm (1.55”) when using the standard
wedge and platen assembly.
Model 4300BX Stressmeters are designed for use in BX diamond drill holes 60 mm (2.36”), and
the hole can range in diameter from 59 mm (2.30”) to 61 mm (2.40”) when using the standard
wedge and platen assembly.
Model 4300NX Stressmeters are designed for use in NX diamond drill holes 76 mm (2.98”), and
the hole can range in diameter from 75 mm (2.95”) to 77.5 mm (3.05”) when using the standard
wedge and platen assembly. Oversize platens are available for oversize boreholes (consult
factory).
2.2 Preliminary Checks
Before installing the gauges in the field, perform a preliminary check by completing the
following
1) Connect the gauge to a readout box. (See Section 3 Readout instructions.)
2) Take a reading. Zero readings at the site should coincide with the factory readings within a
few digits after corrections for temperature are made. (See Section 4.4 for information on
temperature correction.)
3) A check of electrical continuity can be made using an ohmmeter. The resistance between the
two lead wires (usually red and black) should be around 180 ohms for Models 4300BX and
4300NX, 90 ohms for Model 4300EX. Remember to add the cable resistance at
approximately 14.7Ω/1000' (48.5Ω/km) at 20 °C. Multiply this factor by two to account for
both directions.
4) Using an ohmmeter check the resistance between the two thermistor wires (usually white and
green). Using Table 5 in Appendix B, convert the resistance to temperature. Compare the
result to the current ambient temperature.

4
2.3 Attaching the Wedge/Platen Assembly
The wedge/platen assemblies are shipped separately. They are held together by a nylon screw
and nut. Remove the nut and then use the nylon screw to attach the wedge/platen assembly to the
Stressmeter Body. Orient the wedge so that the narrow end is facing in the same direction as the
cable, (see Figure 2 in the next section). Tighten the nylon screw into the threaded hole in the
body. Do not overtighten the screw as it may break; it is made of nylon so that it can be
sheared easily later in the installation.
(Note: The BX size stressmeter and the NX size stress meter both use the same wedge. However,
there are two holes in the wedge. The one nearest the tip is for the BX size, the one farthest from
the tip is for the NX size).
2.4 Setting the Stressmeter (Recoverable Type)
Mount the stressmeter on the setting tool by pushing the nylon threaded pieces into the matching
holes in the setting tool head. Feed the gauge leads through the slot in the setting head. (See
Figure 2 below.)
Connect the first section of 1/4” rod to the yoke attached to the thin end of the wedge. Note that
the first section of rod has one end with a ¼-20 left handed thread on it. This will connect to the
left-handed thread in the yoke.
Attach the first section of the 3/4” positioning rod to the back of the setting tool head. Push the
stressmeter into the hole using the positioning rod. The buttons on the setting rod connectors
indicated the orientation of the wedge/ platen assembly, e.g., for taking measurements in a
vertical direction, keep the buttons to the top of the rod.
As the 3/4” positioning rod is pushed into the hole, add new sections of both 3/4” and 1/4” rod
until the desired depth has been reached. It is advisable to wear gloves during this procedure
to protect the thumb while depressing the buttons on the 3/4 inch rods.
Slide the slide-hammer over the last section of 1/4” rod and then thread the anvil block onto the
outer end of the 1/4” rod. Connect the readout box to the lead wires and take initial readings.
(See Section 3 for readout instructions.)
Figure 2 - Vibrating Wire Stressmeter Installation Tool Assembly