Geokon 4800 Series User manual

©2021, GEOKON. All rights reserved.
Document Revision: Z | Release date: 06/23/21
Model 4800 Series
VW Earth Pressure Cells
Instruction Manual

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 specifi-
cation, misapplication, misuse or other operating conditions outside of GEOKON's
control. Components that wear or 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 merchant-
ability 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 instal-
lation 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.
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.
The GEOKON® wordmark and logo are registered trademarks with the United States Patent and Trademark Office.

I
TABLE OF CONTENTS
1. INTRODUCTION............................................................................................................................................1
1.1 THEORY OF OPERATION...............................................................................................................1
1.2 EARTH PRESSURE CELL DESIGN.........................................................................................2
1.3 EARTH PRESSURE CELL CONSTRUCTION ..................................................................3
1.3.1 MODEL 4800 EARTH PRESSURE CELLS.................................................................................3
1.3.2 MODEL 4810 CONTACT ("FAT BACK") PRESSURE CELL.................................................4
1.3.3 MODEL 4815 HYDRAULIC LOAD CELL ...................................................................................4
1.3.4 MODEL 4820 EARTH PRESSURE "JACKOUT" CELL ..........................................................5
1.3.5 MODEL 4830 PUSH-IN PRESSURE CELL ................................................................................5
2. INSTALLATION..............................................................................................................................................6
2.1 PRELIMINARY TESTS......................................................................................................................6
2.2 PRESSURE CELL INSTALLATION .........................................................................................6
2.2.1 INSIDE FILLS AND EMBANKMENTS ........................................................................................6
2.2.2 INSTALLATION OF MODEL 4810 CONTACT ("FAT BACK") PRESSURE CELL.........8
2.2.3 INSTALLATION OF MODEL 4815 HYDRAULIC LOAD CELL ....................................... 10
2.2.4 INSTALLATION OF MODEL 4820 JACKOUT PRESSURE CELL IN SLURRY
TRENCHES........................................................................................................................................ 10
2.2.5 INSTALLATION OF CELLS TO MEASURE EARTH PRESSURE AT THE BASE
OF FOOTINGS, FLOOR SLABS, PAVEMENTS, ETC......................................................... 11
2.2.6 INSTALLATION OF PUSH-IN PRESSURE CELLS TO MEASURE LATERAL
EARTH PRESSURES ..................................................................................................................... 12
2.3 CABLE INSTALLATION AND SPLICING ...................................................................... 13
2.4 ELECTRICAL NOISE ....................................................................................................................... 14
2.5 INITIAL READINGS ........................................................................................................................ 14
3. TAKING READINGS ............................................................................................................................. 15
3.1 OPERATING THE GK-404 ......................................................................................................... 15
3.2 GK-405 VIBRATING WIRE READOUT............................................................................ 15
3.2.1 CONNECTING SENSORS WITH 10-PIN BULKHEAD CONNECTORS
ATTACHED ....................................................................................................................................... 16
3.2.2 CONNECTING SENSORS WITH BARE LEADS................................................................... 16
3.2.3 OPERATING THE GK-405 ........................................................................................................... 16
3.3 MEASURING TEMPERATURES ........................................................................................... 16
4. DATA REDUCTION ................................................................................................................................17
4.1 PRESSURE CALCULATION...................................................................................................... 17
4.2 TEMPERATURE CORRECTION ............................................................................................. 18
4.3 BAROMETRIC CORRECTION ................................................................................................. 18
5. TROUBLESHOOTING .......................................................................................................................... 20
APPENDIX A. SPECIFICATIONS .................................................................................................. 21

II
A.1 EARTH PRESSURE CELLS ....................................................................................................... 21
A.2 STANDARD TEMPERATURE THERMISTOR............................................................. 21
APPENDIX B. THERMISTOR TEMPERATURE DERIVATION ....................... 22
APPENDIX C. TEMPERATURE EFFECT ON EARTH PRESSURE
AND CONCRETE STRESS CELLS........................................................ 23
C.1 FORMULAS............................................................................................................................................ 23
C.2 EXAMPLES............................................................................................................................................. 25
APPENDIX D. IMPROVING CALCULATED PRESSURE ACCURACY... 27

III
FIGURES
FIGURE 1: STRESS REDISTRIBUTION, WEAK SOIL WITH STIFF CELL ..........................1
FIGURE 2: STRESS REDISTRIBUTION, STRONG SOIL WITH STIFF CELL ......................2
FIGURE 3: STRESS REDISTRIBUTION, STIFF SOIL WITH WEAK CELL ..........................2
FIGURE 4: MODEL 4800 RECTANGULAR EARTH PRESSURE CELL ..............................3
FIGURE 5: MODEL 4800 CIRCULAR EARTH PRESSURE CELL .......................................3
FIGURE 6: MODEL 4810 CONTACT PRESSURE CELL .....................................................4
FIGURE 7: MODEL 4815 HYDRAULIC LOAD CELL .........................................................4
FIGURE 8: MODEL 4820 JACKOUT LOAD CELL ..............................................................5
FIGURE 9: MODEL 4830 PUSH-IN PRESSURE CELL ......................................................5
FIGURE 10: MODEL 4800 EARTH PRESSURE CELL INSTALLATION .............................7
FIGURE 11: ATTACHMENT OF MODEL 4810 TO CONCRETE FORM .............................9
FIGURE 12: MODEL 4810 CONTACT PRESSURE CELL INSTALLATION ........................9
FIGURE 13: MODEL 4815 HYDRAULIC LOAD CELL MEASURING LOADS .................10
FIGURE 14: MODEL 4820 JACKOUT PRESSURE CELL INSTALLATION ......................11
FIGURE 15: MODEL 4800-1-1P EARTH PRESSURE CELL INSTALLATION ..................12
FIGURE 16: GK-404 READOUT .......................................................................................15
FIGURE 17: LEMO CONNECTOR TO GK-404 .................................................................15
FIGURE 18: GK-405 READOUT .......................................................................................15
FIGURE 19: SAMPLE MODEL 4800 CALIBRATION SHEET ..........................................19
FIGURE 20: RADIUS (R) AND THICKNESS (D) ..............................................................23

IV
TABLES
TABLE 1: RATIOS FOR TWO GROUT MIXES....................................................................8
TABLE 2: 4830 WIRING CHART.......................................................................................13
TABLE 3: ENGINEERING UNITS MULTIPLICATION FACTORS.....................................17
TABLE 4: EARTH PRESSURE CELL SPECIFICATIONS...................................................21
TABLE 5: 3KΩ THERMISTOR RESISTANCE....................................................................22
TABLE 6: TYPICAL VALUES OF VARIOUS CELL PARAMETERS ..................................25

V
EQUATIONS
EQUATION 1: TERZAGHI’S PRINCIPLE OF EFFECTIVE STRESS..................................... 1
EQUATION 2: DIGITS CALCULATION .............................................................................. 17
EQUATION 3: CONVERT DIGITS TO PRESSURE ............................................................ 17
EQUATION 4: TEMPERATURE CORRECTION................................................................. 18
EQUATION 5: 3KΩ THERMISTOR RESISTANCE............................................................. 22
EQUATION 6: EXPANSION OF LIQUID FOR A 1° C TEMPERATURE RISE .................. 23
EQUATION 7: COMPRESSION OF LIQUID...................................................................... 23
EQUATION 8: EXPANSION OF LIQUID............................................................................ 23
EQUATION 9: DEFORMATION AT THE CENTER ............................................................ 23
EQUATION 10: DEFORMATION AT THE EDGE .............................................................. 24
EQUATION 11: DIFFERENCE IN DEFORMATION .......................................................... 24
EQUATION 12: AVERAGE TOTAL EXPANSION OF THE CELL....................................... 24
EQUATION 13: COMBINED EQUATIONS ....................................................................... 24
EQUATION 14: TOTAL EMBEDMENT.............................................................................. 24
EQUATION 15: TOTAL EMBEDMENT FOR CONTACT PRESSURE CELLS ................... 24
EQUATION 16: PRESSURE CALCULATION WITH SECOND ORDER POLYNOMIAL .. 27
EQUATION 17: “LINEARITY (%F.S.)” ON CALIBRATION SHEET .................................. 27
EQUATION 18: CALCULATING C USING THE ZERO PRESSURE READING ................ 27

VI