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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)
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Summary of Contents for Geokon 4300 Series
- Page 1 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 ®...
- Page 3 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.
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Page 5: Table Of Contents
TABLE of CONTENTS 1. THEORY OF OPERATION ..........................1 2. INSTALLATION ..............................3 2.1 B ..........................3 OREHOLE EQUIREMENTS 2.2 P ............................3 RELIMINARY HECKS 2.3 A ..................... 4 TTACHING THE EDGE LATEN SSEMBLY 2.4 S ) .................... 4 ETTING THE TRESSMETER ECOVERABLE 2.5 R... - Page 6 FIGURES 1 - V ........................1 IGURE IBRATING TRESSMETER 2 - V ............. 4 IGURE IBRATING TRESSMETER NSTALLATION SSEMBLY 3 - L GK-404 ........................7 IGURE ONNECTOR TO 4 - L – R ....................... 8 IGURE EADINGS EADINGS 5 - M 4300EX S ..............11 IGURE...
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Page 7: Theory Of Operation
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... - Page 8 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.
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Page 9: Installation
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. -
Page 10: Attaching The Wedge/Platen Assembly
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). -
Page 11: Recovering The Stressmeter
Holding the positioning rod firmly at its correct depth and orientation, slide the slide-hammer back up the 1/4” rod, then side it quickly back to the anvil striking it a sharp firm blow. This will shear the rivet holding the wedge to the platen and will pull the wedge into the platen thereby expanding it against the wall of the borehole. -
Page 12: Splicing And Junction Boxes
Contact Geokon for splicing materials and additional cable splicing instructions. Junction boxes and terminal boxes are available from Geokon for all types of applications. In addition, portable readouts and dataloggers are also available. Contact Geokon for specific... -
Page 13: Taking Readings
20 hours continuously on two AA batteries. It is designed for the readout of all Geokon vibrating wire gauges and transducers, and is capable of displaying the reading in either digits, frequency (Hz), period (µs), or microstrain (µε). The GK-404 also displays the temperature of the transducer (embedded thermistor) with a resolution of 0.1 °C. -
Page 14: Gk-405 Readout Box
3.2.2 Sensors with Bare Leads Attach the GK-403-2 flying leads to the bare leads of a Geokon vibrating wire sensor by connecting each of the clips on the leads to the matching colors of the sensor conductors, with blue representing the shield (bare). -
Page 15: Gk-403 Readout Box (Obsolete Model)
3.3.2 Connecting Sensors with Bare Leads Attach the GK-403-2 flying leads to the bare leads of a Geokon vibrating wire sensor by connecting each of the clips on the leads to the matching colors of the sensor conductors, with blue representing the shield (bare). -
Page 16: Data Reduction
4. DATA REDUCTION 4.1 Change in Stress Calculation To obtain the change in stress at any given time the following equation applies: σ = (R – R Equation 1 - Change in Stress Where; σ = Stress change, in psi. = Initial reading after the gauge has been set in place. -
Page 17: Gauge Sensitivity Factors
4.3 Gauge Sensitivity Factors The graphs in Figure 5, Figure 6, and Figure 7 are used to determine the stress sensitivity or gauge factor for rocks of different moduli. Sensitivity factors are based on experimental data conducted on rock samples and can only serve as a guide. For more accurate determinations of stress sensitivity, calibrations must be performed in samples of the rock being monitored. -
Page 18: Corrections For Temperature Changes
Figure 7 - Model 4300NX Sensitivity Factor vs. Rock Modulus 4.4 Corrections for Temperature Changes The materials used in the construction of the stressmeter are affected by changes in ambient temperature. Since these gauges are normally installed underground in constant temperature environments, corrections are not normally applied. -
Page 19: Trouble Shooting
Return any faulty gauges to the factory. Gauges should not be opened in the field. For additional troubleshooting and support, contact Geokon. Symptom: Thermistor resistance is too high: There may be an open circuit. Check all connections, terminals, and plugs. If a cut is located in the cable, splice according to instructions in Section 2.6. -
Page 20: Table 2 - Sample Resistance
Vibrating Wire Sensor Lead Grid - SAMPLE VALUES Black White Green Shield BX and NX≅ 180Ω infinite infinite infinite EX ≅90Ω BX and NX ≅180Ω Black infinite infinite infinite EX ≅90Ω 3000Ω at White infinite infinite infinite 25°C 3000Ω at Green infinite infinite... -
Page 21: Appendix A. Specifications
APPENDIX A. SPECIFICATIONS A.1 Model 4300 Stressmeter Model Nominal Range 35 - 100 MPa (5000 - 15000 psi) Resolution KPa (psi) 2 - 7 (0.25 - 1) 10 - 30 (1.5 - 4) 35 - 140 (5 - 20) Accuracy ±20 % Operating Temperature –20 to +80 °C... -
Page 22: Appendix B. Thermistor Temperature Derivation
APPENDIX B. THERMISTOR TEMPERATURE DERIVATION Thermistor Type: YSI 44005, Dale #1C3001-B3, Alpha #13A3001-B3 Resistance to Temperature Equation: A+B ( LnR ) +C(LnR) -273.2 Equation 3 - Resistance to Temperature Where; T = Temperature in °C. LnR = Natural Log of Thermistor Resistance A = 1.4051 ×... -
Page 23: Appendix C. Biaxial Stress Changes
APPENDIX C. BIAXIAL STRESS CHANGES The relationship between the radial deformation of a borehole, U, and two principle stresses in the plane of a borehole has been given by Hast (1958) and Merrill and Peterson (1961). The equation for Plane Stress is: U = d/E [(σ... - Page 24 For Example: Three gauges are set in borehole. The first is at 0° (σ ), the second at 45° (σ ) and the third at 90° (σ ), measured counterclockwise from 0. The uniaxial stress changes for each gauge are determined by the reading change times the calibration factor.
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