Geokon Stressmeter 4300 Series User manual

Instruction Manual
Vibrating Wire
Stressmeter
4300 Series (EX, BX, NX)
No part of this instruction manual may be reproduced, by any means, without the written consent of Geokon, Inc.
The information contained herein is believed to be accurate and reliable. However, Geokon, Inc. assumes no responsibility for
errors, omissions or misinterpretation. The information herein is subject to change without notification.
Copyright © 1984, 2004 by Geokon, Inc.
(Doc Rev C, 04/07)

Warranty Statement
Geokon, Inc. 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, Inc. 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, Inc. or any breach of any warranty by Geokon, Inc. shall not exceed the purchase price paid by the
purchaser to Geokon, Inc. 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, Inc. 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.

Contents
1. SPECIFICATIONS.............................................................................................................................................1
2. THEORY OF OPERATION..............................................................................................................................2
3. INSTALLATION ................................................................................................................................................3
3.1 BOREHOLE REQUIREMENTS..............................................................................................................................3
3.2 PRELIMINARY CHECKS .....................................................................................................................................3
3.3 ATTACHING THE WEDGE/PLATEN ASSEMBLY ..............................................................................................3
3.4 SETTING THE STRESSMETER (RECOVERABLE TYPE).........................................................................................4
3.5 RECOVERING THE STRESSMETER......................................................................................................................5
3.6 SPLICING AND JUNCTION BOXES ......................................................................................................................5
4. TAKING READINGS.........................................................................................................................................6
4.1 OPERATION OF THE GK-403 OR GK-401 READOUT BOX .................................................................................6
4.2 OPERATION OF THE GK404 READOUT BOX ..................................................................................................6
5. DATA REDUCTION..........................................................................................................................................7
5.1 GAGE SENSITIVITY FACTORS............................................................................................................................7
5.2 CORRECTIONS FOR TEMPERATURE CHANGES...................................................................................................9
5.3 ENVIRONMENTAL FACTORS............................................................................................................................10
6.TROUBLE SHOOTING....................................................................................................................................10
TABLE 1: THERMISTORS ................................................................................................................................11
APPENDIX 1: BIAXIAL STRESS CHANGES .................................................................................................12
REFERENCES......................................................................................................................................................13

LIST of FIGURES, TABLES and EQUATIONS
FIGURE 1. VIBRATING WIRE STRESSMETER............................................................................................................... 2
FIGURE 2. VIBRATING WIRE STRESSMETER INSTALLATION TOOL ASSEMBLY. ........................................................... 4
FIGURE 3. MODEL 4300EX VIBRATING WIRE SRESSMETER SENSITIVUTY FACTOR VS. ROCK MODULUS ................ 8
FIGURE 4. MODEL 4300BX VIBRATING WIRE SRESSMETER SENSITIVUTY FACTOR VS. ROCK MODULUS ................ 8
FIGURE 5. MODEL 4300NX VIBRATING WIRE SRESSMETER SENSITIVITY FACTOR VS.ROCK MODULUS.................. 9

1
1. Specifications __________________________________________________
General Specifications EX BX NX
Nominal Range Mpa (psi) 135 - 100 (5000 - 15000) 35 - 100 (5000 - 15000) 35 - 100 (5000 - 15000)
Resolution KPa (psi) 2 - 15 (0.3 - 2) 10 - 30 (1.5 - 4) 35 - 140 (5 - 20)
Accuracy ±220 % 20 % 20 %
Operating Temperature °C 3–30 to +90 –30 to +90 –30 to +90
Thermal Zero Shift % F.S./°C 0.02 0.04 0.04
Resonant Frequency Range Hz 3000 - 5000 2000 - 3500 1500 - 2500
Length mm (inches) 44 (1.75) 70 (2.75) 76 (3.0)
Outer Diameter mm (inches) 29 (1.125) 48 (1.875) 64 (2.50)
Inner Diameter mm (inches) 13 (0.5) 22 (0.875) 32 (1.25)
Weight kgm (lbs.) 0.45 (1) 0.9 (2) 1.4 (3)
Borehole Diameter mm (inches) 38 (1.485) 60 (2.36) 76 (2.98)
Gage Materials 17-4 SS, 304 SS 17-4 SS, 304 SS 17-4 SS, 304 SS
Cable 2 conductor or 4 conductor shielded 22 gage. PVC jacket, 5mm dia. or 6mm dia.
1Depends on rock modulus
2Accuracy depends to a large extent on the roughness of the borehole walls; on the degree to which the platens bed into the
surrounding material thus increasing the area of contact and on the gage stiffness; and also on the accuracy with which the
host rock elastic constants are known.
3High temperature versions are available (
− 20 ° C to 200 ° C)

2
2. 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 gage 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 gage and, by
calibration, to the change in stress in the rock.
The actual calibration of the gage depends upon many factors including the host rock elastic constants, the pre-
stress 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 gage 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 both to excite the wire and sense the resultant
frequency of vibration. When the gage 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 gage 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 28Gpa (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

3
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 gage factor changes only by a factor of 2.
The stressmeter is a uniaxial device, and to completely evaluate stress changes in a given plane, three
stressmeters, installed at 0°, 45°, and 90°orientations, are required.
The gage wire in the Model 4300 Series stressmeters runs perpendicular to the direction in which the gage body is
loaded in an effort to minimize the effects of point loading, off center loading, etc. This gives the gage a very high
range and, since as the load increases the wire gets tighter, the wire never goes slack.
Gage installation is accomplished by driving a wedge between the gage 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 gage is constructed of corrosion resistant materials and should have an indefinite lifetime under even the
most severe conditions.
3. Installation______________________________________________________
3.1 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 gage response (calibration) can be radically affected.
The Model 4300EX Stressmeter is designed for use in EX diamond drill holes 38mm (1.5”), and the hole can
range in diameter from 37mm (1.45”) to 39mm (1.55”) when using the standard wedge and platen assembly.
The Model 4300BX Stressmeter is designed for use in BX diamond drill holes 60mm (2.36”), and the hole can
range in diameter from 58.5mm (2.30”) to 62mm (2.44”) when using the standard wedge and platen assembly.
The Model 4300NX Stressmeter is designed for use in NX diamond drill holes 76mm (2.98”), and the hole can
range in diameter from 74mm (2.91”) to 78mm (3.07”) when using the standard wedge and platen assembly.
Oversize platens are available for over-size boreholes (consult factory).
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 gages supplied with the installation tool.
If the borehole checks out the installation can proceed.
3.2 Preliminary Checks
Upon receipt of the stressmeter the zero reading should be checked and noted along with the temperature if a
thermistor is included in the gage. Gage connections are normally red to red and black to black, although with the
GK-401 Readout Box these can be reversed without changing the readings. Zero readings at the site should
coincide with the factory readings within a few digits after corrections for temperature are made.
3.3 Attaching the Wedge/Platen Assembly

4
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). Tighten the nylon screw
into the threaded hole in the body. Do not over-tighten – the screw is made of nylon so that it can be sheared
more easily. (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).
3.4 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 gage leads through the slot in the setting head. (See figure 2 on page 5).
Connect the first section of ¼” 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 Hand Thread on it. This will connect to the left-hand thread in the yoke.
Attach the first section of the ¾” 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. Thus for making measurements in a vertical direction keep the buttons to the top of the rod, etc.
As the ¾” positioning rod is pushed into the hole, add new sections of both ¾” and ¼” rod until the desired depth
has been reached. It is advisable to wear gloves during this procedure to protect the thumbwhile depressing
the buttons on the ¾ inch rods. Now slide the slide hammer over the last section of ¼” rod and then thread the anvil
block onto the outer end of the ¼” rod. Connect the GK-403 or GK-401 readout box to the lead wires and switch to
position “F” for EX size or “B” for BX and NX size. Take initial readings.
Figure 2. Vibrating Wire Stressmeter installation tool assembly.
Holding the positioning rod firmly at its correct depth and orientation, slide the slide hammer back up the ¼” rod,
then side it quickly back to the anvil striking it a sharp firm blow. This will shear the rivet holding the wedge to