STANDARD VIBRATING WIRE PIEZOMETER User Manual
Contents
1. units K is the period gauge factor for units of calibration taken from the calibration sheet PO is the installation period base or zero reading P1 is the current period reading This method of calculation is used by Soil Instruments Vibrating Wire Loggers models RO 1 VW 1 or 2 and with serial numbers starting VL or TVL internal processors for calculating and displaying directly on the oggers LCD screen the required engineering based units The loggers require period base or zero reading units for entering into their channel ables to calculate and display the required engineering units correctly fan engineering based unit is required other than the units of calibration hen the correct K factor will have to be calculated using the standard relationship between engineering units For example if the units of engineering required were in inches and the calibration units were millimetres we can find out that 1mm is equal to 0 03937 so we would derive the K factor for inches by multiplying the K factor for millimetres by 0 03937 29 30 CALCULATION USING LINEAR UNITS LINEAR UNIT CALCULATION USINGA POLYNOMIAL EOUATION The following formula is used for readings in linear units E G R0 R1 Where E is the resultant engineering unit G the linear gauge factor for the units of calibration taken from the calibration sheet RO is the instal2. Soil Instruments VWnote are programmable to give a direct reading in the appropriate engineering units VWnote is also able to store a series of readings in a non volatile memory for future ransfer to a PC Please refer to Datasheets RO 1 VW NOTE Vibrating Wire Note and RO 1 VW READ Vibrating Wire Readout for details on Soil Instruments Vibrating Wire handheld readouts Standard Vibrating Wire Piezometer Components Cable Stainless Steel housing Porous element Watertight flexible cable gland Watertight flexible oa cable gland Water block lt Stainless Steel housing potting Waterproof connection block Detachable nose piece VW transducer Coil magnet ensing wire Rubber washers 9 i diaphragm E Porous element sg E Filter end piece Nylon washer 11 Part Il VW Piezometer Preparation Guide Contents This section contains the following topics TOPIC SEE PAGE Preparation of Equipment Prior to Installation 14 Removal and Assembly of Filter 14 14 Preparation of Eguipment Prior to Installation Follow the precautions outlined in this manual at all times to ensure the correct working order of your instrument It is essential that the eguipment covered by this manual is handled operated and maintained by competent and suitabl
3. indirect lightning strikes The transducer is fitted with either a low air entry sintered steel or a high air entry ceramic filter and is manufactured from high quality 316 grade Stainless Steel providing long term stability and reliability A cone shaped nose piece is available for push in installations Contents PART OVERVIEW Introduction Important Information Product Changes Warranty Disposal System Description Things You Need to Know About the Vibrating Wire Piezometer Features Benefits System Components Overview Standard Vibrating Wire Piezometer Components PART Il VW PIEZOMETER PREPARATION GUIDE Preparation of Equipment Prior to Installation Removal and Assembly of Filter Pre Installation Base Reading PART III VW PIEZOMETER INSTALLATION GUIDE Standard Vibrating Wire Piezometer Installation Procedure Drilling the Borehole Installing the Piezometer Borehole Installation Installation in Fill Installation of Heavy Duty Push In Piezometer Installation and Termination of Cable Overview Installation in Trenches Termination of Cables Oo O O O 00 o UAR NN NODS BCom COMO 20 20 21 21 2 23 PART IV TEMPERATURE amp PRESSURE EFFECTS 8 DATA REDUCTION 25 Effect of Temperature and Pressure 2 Temperature Change DI Effect of Barometric Pressure 28 Data Interpretation 29 Data Reduction 29 Calculating Engineering Units From Frequency Based Units 29 Calcu
4. test 1EC61000 4 5 2005 Surge immunity test IEC61000 4 6 2008 Immunity to conducted disturbances induced by radio frequency fields IEC61000 4 11 2004 Voltage dips short interruptions and voltage variations immunity tests I hereby declare that the equipment named above has been designed to comply with the relevant sections of the above referenced specifications The items comply with all applicable Essential Requirements of the Directives Philip Day VP xu Date 30 July 2015 HIT Manufacturing Manager Issued in Bell Lane Uckfield East Sussex TN22 1QL United Kingdom 37 SUPPORT www soilsupport co uk 44 0 1825 765044 soil Bell Lane Uckfield East Sussex N STR U M E NTS TN22 1QL United Kingdom t 44 0 1825 765044 e info soilinstruments com W www soilinstruments com Soil Instruments Limited Registered in England Number 07960087 Registered Office 3rd Floor Ashley Road Altrincham Cheshire WA14 2DT
5. the electrical cable i should be tested using a multimeter Check the resistance across i the two conductors either at the end of the cable if available or at the corresponding terminals if wired into a Datalogger i The resistance across the two conductors should be approximately i 1200 to1800 The majority of this resistance will come from the sensor i approximately 1300 with the remainder from the electrical cable connected to the transducer for 22 gauge copper resistance is i approximately 10 15m Before proceeding the continuity should be checked between i conductors and the earthing screen of the electrical cable If continuity exists a damaged cable is confirmed Appendix B Troubleshooting Guide Continued STEP ACTION i Ifthe resistance across the two conductors is much higher than i the values quoted in STEP 1 or is infinite a severed cable must 2 i be suspected i If the location of the cable damage is found the cable can be i spliced in accordance with recommended procedure If the resistance across the two conductors is much lower than the i values quoted in STEP 1 less than 80 O it is likely that cable i damage has occurred causing a short in the circuit i Itis possible to calculate approximately how far from the cable end 3 i or readout location the suspected fault is If the resistance of a i known length of conducting cable is measured a resistance length i unit can be found This f
6. body keeping both sections immersed H PRE INSTALLATION Please refer to Datasheets RO 1 VW NOTE Vibrating Wire Note and BASE READING RO 1 VW READ Vibrating Wire Readout for details on Soil Instruments Vibrating Wire handheld readouts It is necessary to establish a base reading for each instrument prior to installation STEP ACTION Ensure that the piezometer is totally immersed in clean water to a i depth of a few centimetres only and is shielded from direct sunlight Connect the instrument cable to Vibrating Wire Readout such 2 i as VWnote or VWread and record the reading in frequency i or period units Wait for 15 minutes for the transducer to adjust to the temperature i ofthe water and repeat the reading operation A value identical to the first reading indicates that the transducer has adjusted to the water temperature i Continue reading if necessary until stability is observed Record the reading with the current barometric pressure i and water temperature Part III VW Piezometer Installation Guide Contents This section contains the following topics TOP SEE PAGE Drilling the Borehole Installing the Piezometer Borehole Installation eleten in JON S 18 Standard Vibrating Wire Piezometer Installation Procedure Follow the precautions outlined in this manual at all times to ensure the correct working order of your inst
7. ch applications where such relatively small variations are considered to be significant correction of reading errors due to barometric pressure changes should be applied respectively For this purpose a note of barometric pressure on the day of the pre installation base reading is required and also an accurate barometer must be available on site Data Interpretation DATA REDUCTION CALCULATING ENGIN UNITS BASED USING UNITS EERING FROM FREOUENCY UNITS CALCULATION PERIOD The mathematical relationship between the freguency of vibration of a tensioned wire and the force applying the tension is an approximate straight line relationship between the sguare of the measured freguency and the applied force Engineering units of measurement maybe derived from the freguency based units measured by vibrating wire readouts in 3 traditional ways From period units and from linear f 1000 units using two methods a simple linear equation or a polynomial equation Engineering units of measurement maybe derived from the freguency based units measured by Vibrating Wire readouts in three traditional ways From period units t x 107 and from linear P 1000 units using two methods a simple linear equation or a polynomial equation The following formula is used for readings in period units E K 10 7 PO 2 10 7 P1 2 Where E is the pressure in resultant engineering
8. d anti rotation recovered w rod The left hand right hand threaded adaptor will be ith the drill rods for reuse The filter tip should be saturated prior to installation as per the standard piezometer See diagram of Installation by pusing into soft soils for more details Installation by Pushing Into Soft Soils Borehole tese Drill Rod as Piezometer Cable Left Right Hand Threaded Adaptor Anti Rotation Blades Anti Rotation Rod 1m or 2m Long Piezometer Filter Housing Installation and Termination of Cable OVERVIEW Connecting cable is laid in a trench deep enough to provide protection from mechanical damage In certain situations the cables may be run in protective conduits or cast into concrete however great care should be taken to protect cables at interfaces between such relatively rigid conduits and flexible soil areas if this method is used The choice of suitable protection material surrounding the cable along the trench ength will depend on local factors but in all cases should be fine grained with a particle size less than 0 5mm and not contain any sharp particles Fine sand is preferable in free draining areas but should be replaced by screened silt or clay based soil where lower permeability is required Failure to use the correct protection material may result in piping along the trench lines 21 22 INSTALLATION IN TRENCHES You MUST
9. igure can be used to calculate the length of i theconductor cable in between the readout location and the break in the circuit If the location of the cable damage is found the cable i can be spliced in accordance with recommended procedure This method is only applicable if the short occurs between the two conductors of the electrical cable Since cables are generally buried or hidden it is may not be possible to confirm a short is of this nature using this method ACTION i If the resistance is within the values quoted in STEP 1 and no i continuity exists between the conductor and the earth screen A i AND the reading from the sensor is unstable or wildly fluctuating i it must be assumed that the integrity of the circuit is good and i the fault lies within the crackmeter In this case please contact our i support team at soilsupport co uk 35 36 Appendix C Sample Calibration Certificate soil INSTRUMENTS Bell Lane Uckfield East Sussex TN22 1QL United Kir t 444 0 1 trument Ltd Registered in England Number 079600 25765044 e Registered Period Gauge Factor K 1627 8840000 info soil co uk w www soil co uk ffice 34 Bell Lane Uckfield East Suss Barometric Pressure TN22 1QL UK VIBRATING WIRE INSTRUMENTS CALIBRATION CERTIFICATE Instrument Type W9 Vibrating Wire Piezometer Serial No 053048 Instrument Range 0 00 to 300 0 kPa Calibration Date 05 08 2015 Gauge Factor
10. illing is generally a b into place completed to ground level with an impervious grout entonite cement mix through a tremie pipe positioned above the bentonite plug and withdrawn as grouting proceeds If more than one instrument is being installed it is vitally important to clearly identify the cables using colour coded P V C adhesive tapes This is essentially similar to installation in shallow soil foundations filter sand n clay fill the piezometer may either be placed in a sand pocket or in direct contact with the fill material This latter operation is performed using a mandrel to form an impression into which the piezometer is placed In rock fill the tip should be surrounded by clean coarse Installation of Heavy Duty Push In Piezometer IMPORTANT INSTALLATION INFORMATION The push in Piezometer is designed for pushing into soft soils using drill rods either by hand or using the hydraulics of the rig The Piezometer should be m onitored during the pushing process to ensure that pressures do not exceed the calibrated range of the piezometer Should the pressure be stopped s reach or exceed the calibrated range the process should o allow the pressure to dissipate before continuing If the drill rods are to be removed then a bladed anti rotation rod with a left hand ri ght hand threaded adaptor should be used This will allow the drill rods to be rotated clockwise and detached from the blade
11. lation linear base or zero reading RT is the current linear reading Again the linear gauge factor for units other than the units of calibration would need to be calculated using the same principles as stated in the last paragraph of the period unit section Linear units may be applied to the following polynomial equation for calculation of engineering units to a higher order of accuracy E AR142 BR1 C Where E is the resultant engineering unit A B and C the polynomial gauge factors A B and C taken from the calibration sheet R1 is the current linear reading The value C is an offset value and relates to the zero value experienced by the transducer at the time of calibration This value should be recalculated at the installation time as follows C AROA2 BRO Where A and B are as above RO is the installation linear base or zero reading Please note that the sign of the recalculated value of C should be the same as the original value of C so if the original is negative then the recalculated value should also be a negative Conversion to engineering units other than the units of calibration would best be done after conversion using a factor calculated using the same principles as stated in the last paragraph of the period unit section Part V Appendices 32 Contents This section contains the following topics SEE PAGE i
12. lation Using Period Units 29 Calculation Using Linear Units 30 Linear Unit Calculation Using a Polynomial Equation 30 PART V APPENDICES 31 Appendix A Conversion Table 33 Appendix B Troubleshooting Guide 34 Appendix C Sample Calibration Certificate 36 Appendix D CE Declaration 97 PRECISELY MEASURED instrumentation and monitoring Part Overview Contents This section contains the following topics TOPIC SEE PAGE i Introduction Introduction Important Information The following symbols are used throughout this manual A999 WARNING PRODUCT CHANGES WARRANTY DISPOSAL IMPORTANT QUESTION INFORMATION Important Failure to adhere to the warnings in this manual may result in network disruption and possible data loss Failure to observe the warning may result in injury product malfunction unexpected readings or damage to the product that may invalidate its warranty Tips give additional information that may be helpful when using a Standard Vibrating Wire Piezometer Soil Instruments Limited has an on going policy of design review and reserves the right to amend the design of their product and this instruction manual without notice Please refer to Soil Instruments Limited terms and conditions of sale for warranty information Batteries are a consumable item and are excluded from any warranty Products marked with the mam symbol are subject to the following disposal r
13. ld excessive voltages be induced into the connecting cable during electrical storms The transducer consists of a rigid cylinder sealed at one end by a watertight bulkhead and at the other by a thin diaphragm which serves as an elastic force sensing member A thin steel wire strung between these two points is tensioned and firmly anchored during manufacture A coil magnet assembly set at the mid position on the wire provides the means of exciting the wire into oscillation the freguency of which is dependent on wire tension Pore water pressure acting on the diaphragm causes it to deflect changing the tension of the wire and the resonant freguency The readout unit supplies an electrical pulse to the coil magnet assembly which plucks the wire causing it to vibrate at its resonant freguency The coil magnet assembly acts as a pickup as the oscillations of the wire through the magnetic field induce an alternating current in the coil which is detected by the readout The readout converts the sinusoidal alternating voltage to a square waveform which may easily be timed using a frequency oscillator In this way the period of oscillation may be accurately measured The relationship between a change in the period of oscillation and he strain of the wire is non linear Basic readout units simply give a reading in period units which must be manually converted to the appropriate units by use of formulae More sophisticated readout units such as
14. on Table Convers Appendix A T OIXSOIL OLXL68 7 0 vi X88 v V 0LXE88 Y COLX88ZY i SO euo zw edl Edil zw ql waliosd zy jua GH uu OZHY OLHW we aeq yyjiody J0ZW NY JO ZW NW 34 Appendix B Troubleshooting Guide Before any of the steps below are followed a Vibrating Wire readout unit should be used to verify the stability of the reading The method used to verify the signal will be dependent on which type of VW readout is being used all Soil Instruments readouts use FFT analysis where as some other manufacturers use audio signal Please refer to the manufacturers user manual for details on the method reguired for verifying signal strength Please refer to Datasheets RO 1 VW NOTE Vibrating Wire Note and RO 1 VW READ Vibrating Wire Readout for details on Soil Instruments Vibrating Wire handheld readouts Wildly fluctuating readings from the sensor or an unsteady audio signal are both indications of possible problems with the instrument or related electrical cables If the readout is giving faulty readings or audio signals from all of the sensors a faulty readout unit and or lead must be suspected Another lead readout unit should be used to check the readings If there is a fault with the readout unit please contact www soilsupport co uk for assistance ACTION i The resistance across the two conductors of
15. rmistor coil in each transducer or the separate installation of another temperature measuring device in order to provide the temperature data reguired for corrections to be applied Temperature gradients across the unit triggered by rapid changes in ambient temperature will produce considerable reading error For this reason it is essential that pre installation base readings are only taken after sufficient time has been allowed for the transducer to stabilise at the ambient temperature Piezometers MUST be immersed in shallow water and shaded from direct sunlight until readings settle 27 28 EFFEGT OF BAROMETRIC PRESSURE External pressure applied to the diaphragm of the transducer modifies the wire tension and therefore its resonant frequency Such a change is used to determine the magnitude of the applied pressure Since the unit is evacuated and sealed during manufacture subsequent external variations in barometric pressure will cause a differential force to act across the diaphragm which will affect the tensioned wire proportionally The effect is most significant with thin diaphragms low range units For example For a 50mH20 transducer a 10 millibar change in ambient barometric pressure equivalent to 100 mm of water head relative to the encased pressure within the unit will modify the reading by the equivalent of 100 mm of water head even though the external water head to be measured remains constant In su
16. rument It is essential that the equipment covered by this manual is handled operated and maintained by competent and suitably gualified personnel To guide you in the competence reguired for installing each instrument in our product range Soil Instruments provide you with a recommended skill level in all of our manuals and datasheets ovr Soil Instruments recommend an intermediate skill level for installing a Standard Vibrating Wire Piezometer DRILLING THE A borehole with the diameter of 75 150mm is either driven into BOREHOLE soils using shell and auger drilling or into rock using rotary water flush drilling Air flushing and subsequent entrapment of air in the ground should be avoided The sides of the borehole in the vicinity of the piezometer tip should be free from mud cake and debris If the hole requires casing this should be withdrawn to keep pace with the installing operation oF On completion of the borehole it is strongly recommended to flush with fresh water to remove any silt or debris that may be present in the borehole A head of water will ease installation of the piezometer however this is not appropriate in highly impermeable soils If the borehole is completely dry add a little water to cover the instrument during installation Installing the Piezometer BOREHOLE INSTALLATION A Place coarse clean filter sand through the water ideally with a tremie pipe and compact to
17. s in kPa Ambient Temperature 225 C 1011 mbar Linear Gauge Factor G kPa digit 0 1627900 Calibration Technician Steve Hill Polynomial Gauge Factor A 0 000000746368600 i i Mensor APC 600 Polynomial Gauge Factor B 0 1550534000 AVW200 Data Logger Polynomial Gauge Factor C 974 044300 Regression Zero 6105 1 Applied Reading Reading Calculated Error FS Linear kPa Period F 1000 Linear Linear Calculated Error FS Increment Polynomial Polynomial 0 00 4048 0 6102 8 0 369 0 12 0 0 0 013 0 00 30 00 4110 0 5919 8 30 159 0 05 183 0 30 004 0 00 60 00 4175 2 5736 5 59 998 0 00 183 3 60 020 0 01 90 00 4243 6 5553 1 89 853 0 05 183 4 90 002 0 00 120 00 4315 6 5369 4 119 758 0 08 183 7 119 983 0 01 150 00 4391 6 5185 1 149 759 0 08 184 3 150 011 0 00 180 00 4471 8 5000 7 179 778 0 07 184 4 180 005 0 00 210 00 4556 8 4815 9 209 861 0 05 184 8 210 012 0 00 240 00 4646 8 4631 1 239 944 0 02 184 8 239 969 0 01 270 00 4742 8 4445 6 270 141 0 05 185 5 269 988 0 00 300 00 4845 2 4259 7 300 403 0 13 185 9 300 021 0 01 Formulae Linear E G R0 R1 Polynomial E ARI BRI C The zero reading should be established on site by the user on installation The site value of C must be calculated using the formula C AR0 BRO The instrument detailed hereon has as applicable been tested and calibrated in accordance with procedures which are part of our ISO 9001 2008 Quality Management Sys
18. soil INSTRUMENTS Man 106 STANDARD VIBRATING WIRE PIEZOMETER User Manual Soil Instruments Limited has an ongoing policy of design review and reserves the right to amend these specifications without notice Man106 Vibrating Wire Piezometer Standard MN1114 Rev1 2 0 What s this manual about This manual tells you about the Standard Vibrating Wire Piezometer and how to use it to measure pore water pressures in fully or partially saturated soil Who does this apply to Installers field engineers and technicians who need to acguire pore water pressure measurements in fully or partially saturated soil Welcome Thank you for choosing the Standard Vibrating Wire VW Piezometer This manual has been written to provide you with relevant information and to guide you in best practice when using a Vibrating Wire Piezometer in order for you to gain the most from our product Please read this manual thoroughly before use to help avoid any problems and keep it handy during installation Standard Vibrating Wire Piezometer The Standard Duty Vibrating Wire Piezometer accurately measures pore water pressures in fully or partially saturated soil and is designed for pressure ranges from 50 to 4 000 kPa The small diameter piezometer is hermetically sealed and combines in built temperature compensation with an integral thermistor for temperature monitoring and an over voltage surge arrestor to offer protection from
19. tem and unless otherwise indicated performs within 0 10 Polynomial as specified Thus the instrument conforms in all respects to our relevant specifications and drawings Certified MK E Line MANAGER Appendix D CE Declaration soil INSTRUMENTS EC Declaration of Conformity Soil Instruments Ltd located at 34 Bell Lane Uckfield East Sussex TN22 1QL United Kingdom We hereby declare that the devices described below are in conformity with the directives listed In the event of unauthorised modification of any devices listed below this declaration becomes invalid Type STANDARD VIBRATING WIRE PIEZOMETER Product Model W9 series Relevant EC Directives and Harmonized Standards 2004 108 EC Electromagnetic Compatibility directive as amended by EN61326 1 ed3 The product s to which this declaration relates is in conformity with the essential protection reguirements of 2004 108 EC Electromagnetic Compatibility directive as amended by EN61326 1 ed3 The products are in conformity with the following standards and or other normative documents EMC Harmonized Standards EN 61326 1 2006 Lab Eguipment EMC 1EC61000 6 3 2007 Emission standard for residential commercial and light industrial environments 1EC61000 4 2 2008 Electrostatic discharge immunity test 1EC61000 4 3 2006 Radiated radio frequency electromagnetic field immunity test IEC61000 4 4 2012 Electrical fast transient burst immunity
20. the proposed base of the piezometer tip Allow a suitable amount of time for the sand to settle particularly if the water level is high When marking the proposed depth of the piezometer make sure you take into account the borehole casing above ground level Mark the proposed depth of the tip on the piezometer cable using coloured PV C adhesive tape remembering to take account of any borehole casing remaining above ground level Just prior to installation measure the water level in the borehole Very carefully lower the piezometer down the borehole until the tape mark coincides with the top of the casing Take a reading on the piezometer allowing time for temperature equilibrium to be established Compare the calculated head of water with the measured water level Comparing the calculated head of water with the measured water level is a very useful operational test Place further filter sand until the tip is covered by at least 150mm If using a punner to compact the filter material take extra precaution not to damage the cable 19 20 INSTALLATION IN FILL Remember to allow time for the sand to settle as it is difficult to remove surplus sand without causing considerable disturbance A plug to prevent entry of grout into the filter should be placed in the form of bentonite pellets or alternatively balls of stiff bentonite no larger than 50mm diameter may be dropped through the water and tamped Backf
21. ules in European countries This product is designated for separate collection at an appropriate collection point Donotdispose of as household waste For more information contact Soil Instruments Limited or the local authority in charge of waste management System Description Things You Need to Know About the Standard Vibrating Wire Piezometer FEATURES Small diameter Uses proven Vibrating Wire VW technology e Manufactured from high grade 316 Stainless Steel for extended operation Inbuilt temperature compensation e Hermetically sealed e Suitable for long term monitoring Noelectronic components in sensor module e Capable of measuring negative pore pressures to 50 kPa e Fitted with thermistors for temperature monitoring BENEFITS Accurate repeatable readings over long cable lengths Long working life long term stability and reliability Fast response to pressure changes Design prevents case stresses from affecting readings Over voltage surge arrestor protects against electrical damage Connecting cable is strong screened and flexible 10 System Components OVERVIEW The piezometer comprises a porous tip element connected toa Vibrating Wire VW Transducer The transducer body is constructed throughout from high integrity materials the sensing wire diaphragm and anchor are enclosed in an independent unit An electrical surge protector is included in the design to prevent coil damage shou
22. und movements might be anticipated and may also be looped at cable joints to avoid any unnecessary stresses The cables should be identified using coloured PVC tape applied at regular intervals The correct functioning of the instrument MUST be checked before backfilling the trench TERMINATION OF CABLES Compaction of backfill should be carried out using only hand operated eguipment It may be advisable to clearly mark out or survey the position of the instrument trench particularly if there is to be further excavation or borehole drilling in the vicinity A record of the trench position and depth should be kept and pegged out The cables are normally terminated in multi channel terminal units The terminal units have a hinged cover secured by two screws and the cables enter through waterproof glands Please refer to Datasheet RO TB JB TJ Terminal and Junction Boxes for details on Soil Instruments terminal and junction boxes 23 24 To wire the cables into a terminal unit follow the step guide below STEP ACTION i Unscrew the four fixing screws holding the terminal panel and 2 i carefully remove it without straining the connecting leads 3 Prepare the cables by stripping and cutting back approximately 20mm of the outer insulation and screen a i Remove the inner sheath and strip back 5mm of the nductor insulation i Connect the readout unit to each instrument in t
23. urn to i check connections Please refer to Datasheets RO 1 VW NOTE Vibrating Wire Note and RO 1 VW READ Vibrating Wire Readout for details on Soil Instruments Vibrating Wire handheld readouts Part IV Temperature amp Pressure Effects amp Data Reduction 26 Contents This section contains the following topics TOPIC SEE PAGE i Effect of Temperature and Pressure Temperature Change i Data Interpretation Data Reduction Calculation Using Period Units Calculation Using Linear Units Effect of Temperature and Pressure TEMPERATURE CHANGE The materials used in the construction of the transducer are carefully chosen and controlled in order to reduce the effect of ambient temperature changes on readings In addition the strain wire assembly is evacuated when it is sealed during manufacture which considerably reduces internal air pressure on the diaphragm when the piezometer is heated which might give rise to false negative readings in extremes The significance of temperature change is always with respect to the temperature difference between the current time and the time of the pre installation base reading As a rule of thumb installed temperature changes of less than 10 C are not for practical purposes significant If large temperature changes are to be expected in the ground where the piezometers are to be installed then consideration must be given to specifying the incorporation of a the
24. use screened connecting cable and use an electrical jointing kit ensuring you follow the manufacturer s instructions precisely The screened connecting cable is compacted within the trench ensuring that it is protected by 150mm of stone free material normally sand silt or clay above and below the cable itself Although sand is often the most convenient to use only silt clay or clay should be used where the creation of a drainage path would be undesirable If the trench passes through an impervious clay core of an embankment dam additional cut offs across the trench may be necessary If the trench is to be backfilled using rock fill or coarse granular material the thickness of the protective layer over the cables should be increased to 250mm The trench cable must be connected to the borehole cable by use of a proper electrical jointing kit It is strongly recommended to avoid any cable joints however if this is not possible the same jointing kit must be used The effectiveness of these joints largely depends on the care with which the jointing operation is carried out The cables should be laid loosely within the trench and snaked to prevent any strain due to ground movements in most cases a wavelength of 3m and amplitude of 200mm should be sufficient In certain cases it may be advisable to separate the cables from each other within the base of the trench The cables should be looped on crossing an interface where differential gro
25. y gualified personnel To guide you in the competence reguired for installing each instrument in our product range Soil Instruments provide you with a recommended skill level in all of our manuals and datasheets Soil Instruments recommend an intermediate skill level for installing a Standard Vibrating Wire Piezometer The ceramic filter MUST be soaked in clean water for a minimum of 24 HOURS prior to installation gt Seb REMOVAL 8 As soon as the equipment arrives check that all the necessary parts ASSEMBLY are in correct working order even if the installation is not going to OFFILTER be carried out immediately Prior to installation the following tasks are necessary ACTION Locate a suitable clean container large enough to immerse the entire piezometer and fill with clean water Unscrew the detachable nose piece containing the filter from the main sensor body i Immerse the nose piece containing the filter upright in the container of clean water and soak for a minimum of 24 hours STEP ACTION Shortly before proceeding with the installation immerse the E i piezometer body in the same container of water and invert IE i to expel any air repeat if neccesary to ensure that all the air i hasbeen removed Invert the detachable nose piece containing the filter 5 i to expel any air and screw the nose piece back on to i in the water during attachment In the piezometer
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