INSTRUCTION MANUAL BOREHOLE DILATOMETER (ROCK PRESSUREMETER)

Model PROBEX

© Roctest Limited, 2008. All rights reserved.

This product should be installed and operated only by qualified personnel. Its misuse is potentially dangerous. The Company makes no warranty as to the information furnished in this manual and assumes no liability for damages resulting from the installation or use of this product. The information herein is

subject to change without notification.

Tel. : 1.450.465.1113 • 1.877.ROCTEST (Canada, USA) • 33 (1) 64.06.40.80 (Europe) • www.roctest.com • www.telemac.com

E10037-081009

PROBEX Quick Start a

Quick Start

PROBEX with the ACCULOG-IX

Turn on the Acculog-ix.

From the main menu select “Configuration”.

- Measurement unit → MPa (default)

- Transducers → New transducer → Name: PROBEX (for example) → Serial number: No. 370001 → Calibration Fct: F = Mx + B → Pressure: M = +6.5848 (Example)

B = -3.2924 (Example) → Volume: M = +73.7412 (Example)

B = +324 (Example)

The Acculog-ix is now ready to read the Probex

Return to “Configuration” menu.

- Select → Boreholes → NEW Name: CAL (Example) Type: select calibration Probe: PROBEX

- In the “Borehole” menu, select NEW

Name: HOLE (for example) Type: measurement Probe: PROBEX

You are now ready to run a set of calibration and after, to run some tests in a borehole.

TO RUN A CALIBRATION

Connect the pressure transducer and potentiometer cables to the Acculog-ix. Turn on the Acculog-ix.

From the main menu, select “Measurement”.

Select: CAL (for calibration). Depth: 1.0 m, do not change.

Delay: 060 sec. (default value). You may change it if you want to use a different time base.

Wait for the initialization.

PROBEX Quick Start b

You will have the volume and pressure reading on the display. Just follow the messages on the bottom of the display to proceed to a calibration.

For a test in a borehole, follow the same procedure as for a calibration. The only difference is that you have to indicate, when prompted, the depth of the test.

When you have finished the test, turn off the Acculog-ix and disconnect all the cables.

DATA TRANSFER AND PROCESSING Install Probex companion on your PC, if you get a message about “older

file”, click “Yes”.

Turn on your Acculog-ix.

Connect your Acculog-ix to your PC using the special cable provided with your Acculog-ix. Display on Acculog-ix will indicate “Cable connect”.

Start Probex companion

Select “Data Retrieving”. Choose a name for the file that will be transferred from the Acculog-ix. This file will have the extension .ALX and will include all the information and data stored in the Acculog-ix. Click on “Save” to start the transfer. When the transfer is completed, click on “Close”. You may disconnect the cable from the Acculog-ix. In the main menu of Probex companion, select “Graphic display”.

On the right side of the screen, there is a pull down menu called “Borehole”. Select the test that you want to process. The calibration tests do not appear in that menu but they appear in the second pull down menu. Once you have selected a borehole, the graphic is plotted on the screen.

The next step consists in selecting the calibration that is linked to this test. More than one calibration is run before proceeding to the test in a borehole. These volume calibrations must be done until we get repeatable calibration values. Up to 5 calibrations are normally required. Then, click on “Calculate”. This operation calculates the intrinsic deformation of the system ‘’c’’.

Finally, 2 points must be selected on the chart. These 2 points correspond to the linear portion of the curve (pseudo-elastic phase). Just click on the 2 points you want to select and then, click on “Calculate E”. You will get the deformation modulus E. You may print your result.

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TABLE OF CONTENTS

1 INTRODUCTION ..................................................................................................... 1 2 OPERATING PRINCIPLE ....................................................................................... 1 3 CHARACTERISTICS .............................................................................................. 2 3.1 THE DILATOMETER PROBE ...............................................................2 3.2 THE DUAL-ACTION HYDRAULIC MODULE .........................................3 3.3 THE MEASURING MODULE................................................................3 3.4 THE READOUT UNIT ..........................................................................4 3.5 THE HYDRAULIC SYSTEM..................................................................4 4 OPERATING INSTRUCTIONS ............................................................................... 5 4.1 SATURATION PROCEDURE ................................................................5 4.2 CALIBRATION PROCEDURE ...............................................................7 4.2.1 PRESSURE CORRECTION ..................................................................7 4.2.2 VOLUME CORRECTION......................................................................7 4.3 TESTING PROCEDURES .....................................................................9 4.3.1 INSERTION OF THE DILATOMETER ...................................................9 4.3.2 TESTING .......................................................................................... 10 5 INTERPRETATION ............................................................................................... 12 5.1 EXAMPLE OF MODULUS CALCULATION .......................................... 14 5.2 NOTE ON “AT REST VOLUME OF THE PROBE (vo) ............................ 15 6 REPLACEMENT OF THE MEMBRANE .............................................................. 16 7 RADIAL EXPANSION OF THE PROBE .............................................................. 17 8 FIGURES ............................................................................................................... 18

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1 INTRODUCTION

The PROBEX is a borehole dilatometer (rock pressuremeter), which consists of a cylindrical, radially expandable borehole probe used mainly to determine the short-term deformability of rock in situ. Its use may also be extended to the measurement of the creep properties of creep-like materials such as salt or potash.

The PROBEX operates in 76 mm (N size) boreholes and has a maximum working pressure of 30 000 kPa. By measuring the total volume change of the probe upon loading, a mean modulus of the rock may be calculated.

A particularity of the PROBEX is that pressurization of the dilatable membrane is done immediately upstream from it by the movement of a piston actuated from a manual pump at the surface. By recording the displacement of that piston, volume changes may be calculated. This configuration allows the use of the dilatometer at substantial depths and eliminates the parasitic expansion of the tubing and pumping system.

2 OPERATING PRINCIPLE

The complete probe is shown schematically on Figure 1. Reference to this figure helps understand the operation principle of the PROBEX.

The dilatometer probe is basically composed of three main elements:

- An expandable dilatometer probe - A dual-action hydraulic module - A measuring module

A manually operated hydraulic pump together with hydraulic tubing and a digital readout unit complete the PROBEX dilatometer system.

The dilatometer probe shown on figure 1 is mounted on a steel core (C), which is fitted with a saturation plug at its downstream extremity. Water saturation of the system fills the annular space between the dilatable membrane and the steel core as well as cylinder E.

In order to inflate or deflate the dilatometer probe, the manual hydraulic pump acts on the dual-action, hydraulic module. The dual piston identified by letters F, G, and H is the moving part responsible for the expansion or deflation of the probe. Figure shows this piston in its fully retracted position.

The hydraulic module contains two cylinders in which the piston travels. When the piston is fully retracted cylinder E is completely filled with water and the cylinder is fully oil-saturated. With the small handle of the manual pump in the inflation position (No. 1), oil is pumped immediately behind extremity F and the

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whole piston moves downstream pushing water into the dilatometer probe. Simultaneously, the oil contained within the cylinder is returned to the hydraulic pump via the deflation line.

To deflate the probe, the small handle on the manual pump is placed in the deflation position (No. 2) and the oil is pumped into the cylinder. The oil previously pumped into cylinder E is returned to the pump via the inflation line and the water is brought back into cylinder E.

WARNING: The hydraulic pump and hydraulic module constitute a closed circuit for the oil flow. The user must ensure that all 4 connections to the pump and to the dilatometer probe are properly made to avoid potential damage to the hydraulic system.

It must be noted that prior to using the dilatometer probe for testing, complete water and oil saturation of the circuit is necessary. The dilatometer is shipped without water and with the piston F in retracted position.

The measuring module of the PROBEX consists of a linear potentiometer. It is fixed to the upstream end H of the dual piston and follows its displacement throughout the loading and unloading process. The readout unit is programmed in factory with his calibration constant converting potentiometer output into volume.

3 CHARACTERISTICS

3.1 THE DILATOMETER PROBE

The dilatometer probe basically consists of a portable membrane made of flexible material mounted on heat-treated, stainless steel ends.

The nominal overall length of the membrane including the steel ends is 749 mm. The nominal length of the expandable membrane is 457 mm and the diameter is 73,7 mm. This configuration gives an L/D ratio for the dilatable portion of the probe greater than 6.

The working pressure of the PROBEX dilatable membrane is a function of the diameter of the borehole. Risk of bursting the membrane will increase with pressure level and borehole size. The test is normally stopped either after 30 000 kPa of pressure is injected or a volume of about 350 cc is injected. When positioning the probe in the borehole, a special attention must be paid at the core samples in order to avoid clay seam or weak zone in rock where the probe could bulge locally and burst.

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It cannot be overly emphasized that dilatometer tests should be run in well calibrated, N size boreholes having diameters of 76 mm. Performance of the PROBEX dilatometer will then be enhanced and the risk of damaging a probe greatly reduced.

3.2 THE DUAL-ACTION HYDRAULIC MODULE

As explained in section 2 above, it is the oil pumped right behind extremity F of the dual piston that displaces it downstream, pushing water into the probe. The internal diameter of cylinder E shown on Figure 1 is 60,122 mm and the overall travel of the dual piston is set at 238.125 mm. This geometrical configuration allows a total theoretical volume of water equal to around 676 cc to be injected into the probe. The area on the water side of the piston F is slightly larger than the area of the hydraulic oil side by a ratio of 95.5%, this due to the area of rod G, which represent 4.5% of the piston area.

The water pressure which acts inside the dilatometer probe, may be obtained with the following equation

pb = 0.955 pg

where: pb = water pressure in the probe (kPa or psi) pg = oil pressure read on the pressure gauge (kPa or psi)

This equation must be applied only when the pressure is read on the analogic pressure gauge. The pressure value displayed by Acculog readout is already corrected in order to take into account this difference of pressure.

3.3 THE MEASURING MODULE

The measuring module consists of an electrical transducer (Potentiometer) enclosed in a watertight casing. It gives the displacement of the piston F which is proportional to the injected volume in the probe. The module is mounted in a section of BW casing (K on Figure 1).

Type Potentiometer Recti-P12

Rn 22 kilo ohms +/- 20%

Range 25 cm

Linearity 0.5% F.S.

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3.4 THE READOUT UNIT

The model ACCULOG-IX is a portable datalogger equipped with rechargeable batteries. It directly provides the volume and pressure changes of the probe. The Acculog-ix can read different types of transducers. In order to read the PROBEX, the user must select the “PROBEX” transducer on the readout. The user should refer to the instruction manual specific to the ACCULOG-IX for information about the readout specifications and operation.

3.5 THE HYDRAULIC SYSTEM

The hydraulic system consists of the following elements:

- the hydraulic hand pump - the pressure gauges (and a pressure transducer on the inflation line) - the tubing - A cyclic test valve located on the inflation circuit between the gauge block and the pump (this valve must always be kept opened except when doing a cyclic load test).

The hydraulic pump is mounted with a 4-way control valve (2 positions). The right position No. 1 is used to inflate the probe and the left position No. 2 to deflate the probe. Its characteristics are:

- Pressure rating 68 900 kPa - Reservoir capacity 7 500 cc - Weight 14.5 kg

Two pressure gauges are mounted on the hydraulic pump. The gauge controlling testing pressure is installed on a block mounted on the inflation circuit (position No. 1) and has a pressure range of 35 000 kPa, accuracy of 1 % Full Scale. A second gauge is also fixed to a block mounted on the deflation circuit. It has a smaller pressure range than the testing gauge and is provided as a safety feature to prevent over-pressurization of the return cylinder (See Figure 1) upon complete retraction of the dual-acting piston.

WARNING: The user should stop pumping when the deflation circuit pressure gauge reaches 7000 kPa (1 000 psi.).

In addition to the 35 000 kPa pressure gauge, the inflation line is equipped with the 35 000 kPa pressure transducer. The main specifications of the transducer are as follows:

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Operating pressure range: 35 000 kPa

Excitation 0-30 VDC

Output 0.5 – 5.5 VDC

The pressure transducer comes with a set of quick connect to install it on the inflation manifold of the hydraulic pump.

Dual high-pressure hydraulic lines connect to the hydraulic pump. The inflation line has a working pressure of 68 000 kPa and the deflation line a maximum working pressure of 32 500 kPa.

4 OPERATING INSTRUCTIONS

4.1 SATURATION PROCEDURE

An adequate water saturation of the dilatometer probe and cylinder E is necessary before conducting any test on rock. This saturation must be undertaken every time the membrane is dismounted from the probe and when the dilatometer is used for the first time.

The following saturation procedure must be followed:

STEP 1. The dilatometer is connected to the manual pump with the two hydraulic lines. The electrical cable leading from the probe to the readout unit is also connected.

The hydraulic pump and hydraulic module constitute a closed circuit for the oil flow.

WARNING: The user must ensure that all 4 connections to the pump and to the dilatometer probe are properly made to avoid potential damage to the hydraulic system.

Note: In order to properly connect quick connects, one must align the slot and the spherical button, which are located on the side of each connector

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STEP 2. The stainless steel, conical end cap identified as A is removed from the probe.

STEP 3. The whole dilatometer probe is inclined at about 20 degrees the saturation plug being at its uppermost point. The probe is then turned until the small notch made at the end of the steel core (C) is in the upper position. This notch being in line with two small holes made in the steel core to allow the flow of water to cylinder E indicates that the two holes are also in the upper position. The plug is then completely unscrewed.

STEP 4. A 1-m nylon tubing is screwed in place of the saturation plug.

STEP 5. Place the small handle on the manual pump in the inflation position No. 1 and activate the pump to displace the dual piston to the end of its range (maximum travel) or until water starts to come out from the nylon tubing (the latter situation assumes that some water was left in cylinder E).

NOTE: Maximum travel is reached when the volume displayed on the readout unit stops changing (at approximately 676 cc). Do not continue pumping at this stage to avoid possible damage to the probe.

STEP 6. Put the end of the tubing in a container filled with clean water or anti-freeze solution (50% glycol – 50% water). If possible, use deaired water.

STEP 7. Change the position of the small handle on the pump to the deflation position No. 2 and activate the pump to bring back the dual piston to its fully retracted position indicated by a constant reading on the readout. In doing so, water in the tubing will be sucked into the probe.

To prevent air from entering, the tubing level must be maintained sufficiently deep into the water during this entire procedure.

NOTE: Again, to avoid damage to the probe, stop pumping when the zero reading is obtained on the readout unit or when a slight pressure increase (7000 kPa/1 000 psi approx.) is seen on the deflation circuit pressure gauge.

STEP 8. Return the small handle on the pump to the inflation position No. 1 and activate the pump. If air is present in the probe, it will be expelled and bubbles will be seen out of the tubing. This is continued until the bubbling stops and the water starts coming out of the tubing. At this stage, Step 7 is repeated. If, from the fully retracted position, downstream movement of the piston does not expel air bubbles out of the tubing, saturation is complete.

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STEP 9. Remove the tubing and screw the saturation plug back onto the steel core taking care to use Teflon tape on the plug's threads. Screw the stainless steel, conical end cap back onto the probe.

4.2 CALIBRATION PROCEDURE

The calibrations are done in two steps and have the following purposes:

1. The pressure correction is used to annul the influence of the inertia of the membrane on load transfer to the rock. It is the pressure necessary to dilate the probe to a specific volume under atmospheric pressure.

2. The volume correction corresponds to the intrinsic volumetric expansion of the probe and the hydraulic module when the probe is pressurized in a medium of infinite rigidity. This is the small difference between the injected volume that is read on the readout unit and the real volume increase due to the deformation of the rock tested.

4.2.1 PRESSURE CORRECTION

The pressure correction curve is also called the inertia curve of the membrane. To determine the pressure correction curve, proceed as follows:

STEP 1. Once the whole system is saturated, place the probe horizontally at ground level next to the pump. Inflate and deflate the probe 5 times in order to knead the membrane, each time displacing the dual-action piston through its full range.

STEP 2. Bring the dual-action piston to its completely retracted position.

STEP 3. Inflate the probe from the deflated state in steps of 50 cc.

Following each volume increment, the corresponding pressure is read after one minute.

Draw the inertia or pressure correction curve as shown on Figure 2. The determination of this curve must be done for each new membrane mounted on the dilatometer.

In most cases of rock modulus testing, the pressure correction will have negligible influence on the end results.

4.2.2 VOLUME CORRECTION

The volume correction is subtracted from the injected volume shown on the readout unit. It is the volume loss due to the intrinsic system dilatation.

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NOTE: For a representative volume correction factor to be determined, the user is advised to conduct immediately prior to testing and in the same environmental conditions, a series of five volume calibrations.

The procedure to determine the volume correction is as follows:

STEP 1. Once the whole system has been saturated, place the deflated probe in a calibration tube, which may be any thick wall metallic tube with an interior diameter of around 76 mm.

STEP 2. Three or four times in a row, inflate the probe up to its maximum working capacity of 30 000 kPa and deflate.

NOTE: This operation mechanically sets the components of the dilatometer probe subjected to pressure.

STEP 3. Inflate the probe in steps of 3000 kPa to the maximum working pressure of the dilatometer. At each step of pressure, note the corresponding volume reading displayed on the readout unit after one minute.

STEP 4. Repeat step 3 until a series of 5 calibrations has been completed.

STEP 5. The five volume correction curves (pb versus injected volume) are drawn as shown on figure 3. The correction factor "a" is calculated from the linear part of the curves and an average value (a) is determined.

Two deformation components contribute to the value of "a". They are the intrinsic volumetric expansion of the dilatometer system known as "c" and the small expansion undergone by the calibration tube during pressurization. The expansion of the thick wall metallic tube is determined theoretically and is expressed by the "b" parameter.

The volume correction factor "c" is given by the following equation:

c = a - b (4.1)

The "b" parameter is calculated with equation 4.2:

[ ]e) x E(

m) + (1 e +r V2 = b m

(4.2)

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Where:

V: volume taken by the dilatable membrane of the PROBEX when in contact with the metallic calibration tube

r: internal radius of the calibration tube e: wall thickness of calibration tube m: Poisson's ratio of calibration tube material Em: Modulus of elasticity of calibration tube material

The PROBEX dilatometer is supplied with a standard, steel calibration tube having the following characteristics:

• nominal I.D.: 76.2 mm

• nominal O.D.: 101.6 mm

• Em (modulus of elasticity): 207 x 106 kPa (30 x 10⁶ psi)

• m (Poisson's ratio): 0.20

Using these values in the previous equation and assuming a dilatable length of the PROBEX membrane equal to 457 mm, one obtains the following "b" value:

b = 84.57 x 10-6 cc/kPa

or b = 35.624 x 10-6 in.³/psi

IMPORTANT CONSIDERATIONS ON VOLUME CORRECTION

As will be seen in the section dealing with interpretation, the volume correction factor "c" enters the equation used to calculate the modulus of deformation of the rock. A high level of confidence in the modulus calculated therefore depends on the exactness of the "c" value and of its representativeness of the actual intrinsic deformation of the dilatometer probe during the tests. This is particularly the case when testing highly stiff rock.

The user is therefore encouraged to run as many volume calibration tests as possible prior to testing. As indicated at the beginning of this section, a series of 5 calibrations appears adequate. It is also recommended to run a volume calibration after a series of test has been completed in order to make sure that the calibration factor ‘’c’’ has not changed significantly.

4.3 TESTING PROCEDURES

4.3.1 INSERTION OF THE DILATOMETER

As previously stated, it is of the uppermost importance to run the tests in well calibrated boreholes having a diameter between 75 mm and 78 mm.

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To avoid the risk of damaging or losing the probe in unstable boreholes, the electrical cable and tubing are threaded in a BW casing (or NW rods) before inserting the probe in the borehole. The probe has a female BW casing thread at its upper end. The distance between the centre of the probe and the upper end of the dilatometer is 2.0 m.

STEP 1. Connect the two hydraulic tubing and the electrical cable to the probe and protect their free ends with dust caps and electrical tape.

STEP 2. Thread cable and tubing through the sections of casing required to reach the depth of testing.

Be sure that the male thread of each section is well at the lower end of the string of casings. Sections of 1.5 or 3 m length may be used. Leave enough slack at the borehole mouth to allow insertion in the hole.

STEP 3. Make hydraulic and electrical connections to the manual pump and readout unit and check that the whole system is working well by inflating and deflating the probe. Check the battery charge.

WARNING: The user must ensure that all 4 connections to the pump and to the dilatometer probe are properly made to avoid potential damage to the hydraulic system.

STEP 4. Conduct five volume calibrations as per section 4.2.2.

STEP 5. Insert the dilatometer into the borehole and support it with a pipe vise or a casing clamp.

NEVER SUPPORT THE INSTRUMENT BY ITS TUBING OR CABLE.

STEP 6. Position the deflated probe at the testing location, based on core examination. The dilatable membrane must not straddle large cracks or rock types of significantly different mechanical properties.

4.3.2 TESTING

STEP 1. Turn on the readout unit and wait long enough for the probe to reach temperature equilibrium with the surrounding rock.

STEP 2. The dual-action piston must be in the completely retracted position.

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STEP 3. Set the manual pump control valve handle to position 1, make sure that cyclic test valve is opened, and pump until the probe expands against the sides of the borehole.

STEP 4. The pressure is increased in increments. Eight to ten increments are usually sufficient for an accurate calculation of modulus. The recommended pressure step is 3 000 kPa. This step can be smaller when working in a very soft rock.

Maintain the pressure constant at each pressure stage and record the volume display every minute. Continue until the volumetric deformation becomes constant to within some predetermined value of the reading at the beginning of the test. A five percent (5%) margin is adequate.

STEP 5. If an unloading phase is required, close the cyclic test valve and strike the handle of the pump valve in the direction of position 2 (See Figure 1). Proceed to gradual unloading using the cyclic test valve. The pressure and volume readings are recorded. Re-open test cyclic test valve and start pumping at the same time in order to start re-loading.

STEP 6. When the test is over, completely deflate the probe by pumping with the control valve handle in position 2. The dual-action piston will be fully retracted when the readout shows a zero reading.

STEP 7. Withdraw the dilatometer from the hole or move it to the next testing location.

WARNING: Take note of the volume reading at which the pressure starts increasing. This value can give an indication of the borehole diameter prior to loading. For a quick evaluation of the borehole diameter, the user can prepare a graph of the equivalent PROBEX membrane diameter as a function of the volume reading. The working pressure of the PROBEX dilatable membrane is a function of the diameter of the borehole. Risk of bursting the membrane will increase with pressure level and borehole size. The test is normally stopped either after 30 000 kPa of pressure is injected or a volume of about 350 cc is injected. When positioning the probe in the borehole, a special attention must be paid at the core samples in order to avoid clay seam or weak zone in rock where the probe could bulge locally and burst.

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5 INTERPRETATION

The data obtained during the tests are used to construct the pressure versus injected volume curves from which the rock modulus can be determined. The basis for the interpretation method is given in the following.

Lamé in 1852 expressed the radial expansion of an internally pressurized cylindrical cavity made in an infinitely elastic medium by the following equation:

where G: the elastic shear modulus V: the volume of the cavity p: the pressure in the cavity

When doing tests with the PROBEX dilatometer, the variation in the cavity volume (ΔV) corresponds to the additional volume (Δv) injected into the dilatable membrane and the applied pressure is "pb ". The equation becomes:

The ratio Δpb/Δv corresponds to the slope of the pressure-volume curve obtained during a dilatometer test. Modulus determination from the pressure-volume curve is done over the pseudo-elastic phase of the test, on a pressure range where the curve is linear. Thus, while over this phase Δpb/Δv is constant, the volume of the cavity (V) is not and so is the case for "G".

In his development of the soil mechanics pressuremeter technique, Louis Ménard of France was the first to propose that the value of "G" be determined at the midpoint of the pressure range chosen for modulus determination. This value of "G" is referred to as "GM " and a mean volume of the cavity "Vm" is also considered at the midpoint. The equation becomes:

To convert the shear modulus "GM" to an elastic modulus equivalent to Young's modulus, the following well-known elasticity relation is used:

⎟⎠⎞

⎜⎝⎛ΔΔ

vp x V =G

⎟⎟⎠

⎞⎜⎜⎝

⎛ΔΔ

vp

x V =G b

⎟⎟⎠

⎞⎜⎜⎝

⎛ΔΔ

vp

x V =G bm

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where ER: modulus of deformation of the rock υR: Poisson's ratio of the rock

Combining these equations and solving for ER, one obtains:

The term "Vm " is the total cavity volume at the midpoint of the pressure range over which the rock modulus is determined. It is the sum of two volume components as defined hereunder:

where vo: nominal initial or "at rest" volume of the deflated probe; this volume is approximately equal to 1 950 cc (see note on "vo" at the end of this section 5).

vm: mean additional volume (up to the selected pressure range midpoint) injected into the probe from the "at rest" condition.

Replacing Vm in previous equations, we obtained:

Figure 4 is a schematic representation of a dilatometer pressure-volume curve. It helps understanding the interpretation procedure described herein.

The two values of Δpb and Δv must be corrected firstly, due to the inertia of the membrane and secondly, because of the volume losses related to the intrinsic system dilatation, as previously defined in the calibration procedure. When these corrections are applied to the previous equation, the resulting expression becomes:

) + (1 2E = G

R

rm

ν

⎟⎟⎠

⎞⎜⎜⎝

⎛ΔΔ

vp

x V x ) + (1 2 = E bmRR ν

v + v = V mom

⎟⎟⎠

⎞⎜⎜⎝

⎛ΔΔ

vp

x )v + v( x ) + (1 2 = E bm0RR ν

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The value of Δpi is the change of the pressure of inertia of the dilatable membrane corresponding to the applied pressure increment Δpb. Parameter "c" is the volume correction factor of the dilatometer, as defined in section 4.2.2.

For most rock dilatometer tests, the relative importance of the inertia of the membrane in relation to the applied pressures attained during the tests will be such that the values of Δpi will be negligible. Accordingly, the previous equation may be simplified to the following:

This equation is the basic equation used for rock modulus calculation when the PROBEX dilatometer is used. If relatively soft material is tested, the user has to use the previous equation enclosing the Δpi.

5.1 EXAMPLE OF MODULUS CALCULATION

Given:

- Equation (3.2) applies - Poisson's ratio υR = 0.20 - At rest volume of probe: vo = 1 950 cc - Thick wall steel tube calibration a = 1.19 x 10-3 cc/kPa b = 0.087 x 10-3 cc/kPa - Volume correction factor "c" c = a - b = 1.103 x 10-3 cc/kPa - Pressure range selected for modulus calculation:

c- p - p

v1 x )v + v( x )+ (1 2 = E

ib

m0RR

⎟⎟⎠

⎞⎜⎜⎝

⎛ΔΔ

Δν

c- pv1 x )v + v( x )+ (1 2 = E

b

m0RR

⎟⎟⎠

⎞⎜⎜⎝

⎛ΔΔ

ν

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pg1 = 13 788 kPa (2 000 psi) pg2 = 20 682 kPa (3 000 psi)

Calculations:

1) Injected volumes: v1 = 252.8 cc v2 = 312.4 cc vm = 0.5 (v1 + v2) = 282.6 cc Δv = v2 - v1 = 59.6 cc 2) Applied pressures in the probe pb1 = 0.955 x 2 000 psi = 1 910 psi (13 167 kPa) pb2 = 0.955 x 3 000 psi = 2 865 psi (19 751 kPa) Δpb = 955 psi (6 584 kPa) 3) Modulus (ER)

ER = 667 964 kPa (96 880 psi)

5.2 NOTE ON “AT REST VOLUME OF THE PROBE (VO)

The nominal initial volume of the PROBEX dilatable membrane is 1950 cc. This value is based on a nominal dilatable length of 457 mm and a nominal diameter of 73.7 mm. The fabrication process of the dilatable membranes used with the dilatometer may cause slight differences, particularly in the length of the dilatable membrane. These differences could mean changes in the value of the initial volume. For a precise value to be used, the user is advised to measure directly the length of the dilatable portion (length between the steel ends) on the specific membrane used in testing.

0.00103- 658459.6

1 x 282.6) + (1950 x 0.2) + (1 2 = E R

⎟⎠⎞

⎜⎝⎛

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6 REPLACEMENT OF THE MEMBRANE

Figure 5 shows the details of the dilatometer probe mounted on the steel core. Every time the probe already mounted on the dilatometer probe is damaged or needs to be changed, the replacement procedure given below must be followed.

For clarification purposes, the user should note that when the dilatometer probe is taken off the steel core of the probe, he has in his hands a unit composed of elements No. 8, 9 , 10, 11 and 14 shown on Figure 5. The replacement probes are also composed of the same elements.

STEP 1. Remove the stainless steel, conical end cap No. 1 from the probe.

STEP 2. Unscrew the hexagonal nut No. 4 from the steel core (No. 3).

STEP 3. Using the 4-prong tool supplied, remove locking nut No. 7 from the steel core (No. 3).

STEP 4. Using strap wrenches on the upstream steel end of the probe (part No. 11), completely unscrew it from the probe.

STEP 5. Carefully pull the probe away from the steel core. It will slide on the 'O' rings (No. 5) mounted at both ends of the steel core (No. 3) and the water contained in the annular space between the core and the membrane (No. 14) will flow out of the upstream end.

STEP 6. To reassemble a probe, the reverse procedure is followed and care must be taken with respect to the following details:

- Put a small amount of grease provided in the tool kit on the 'O' rings and on the internal surface of parts No. 10 and No. 9 in the probe.

- Tightening nuts No. 9 should be checked and screwed tightly against spacers No. 8 with the 4-prong tool supplied.

- The probe should be slid gently over the steel core to prevent damaging the 'O' rings No. 5.

- Locking nut No. 7 and the hexagonal nut No. 4 are screwed back in position without tightening them. Good contact is all that is needed.

- Water saturation of the probe must be undertaken following the procedure given in this manual.

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E10037-081009 Probex

7 RADIAL EXPANSION OF THE PROBE

Some applications require determining the exact radial expansion of the probe’s membrane during a test. One example of this is the pile lateral deflection analysis based on P-y curves developed with rock pressuremeter tests. These P-y curves are obtained by re-interpreting rock pressuremeter results in term of radial strain and pressure. Then, the radial strain component is multiplied by the pile half-width and the pressure component by the pile width*.

These P-y curves’ plotting requires knowing the corrected volume and pressure test data, which can be obtained as follows :

• Corrected Pressure = Pressure read with the readout unit + Hydrostatic pressure (normally negligible) – Membrane resistance at corresponding volume.

• Corrected Volume = Volume read with the read out unit – Volume correction at corresponding pressure.

Each corrected pressure data can be obtained with PROBEX COMPANION V2.04 by clicking on each point of the corrected curve. The corrected volume must be calculated using the volume correction factor ‘’c’’ determined during volume calibration (ref: sect. 4.2.2.). This factor is automatically calculated with PROBEX COMPANION.

Then the volume reading is converted into radial expansion using cylinder volume equation : V = (pi x D2 / 4) x L

With : L = Length along which the membrane can expand (nominal value = 457 mm). D = Diameter of the membrane (nominal value = 73,7 mm).

*Robertson P.K., Campanalla R.G., Brown P.T., Grof I., Hughes J.M. (1985) Design of Axially and Laterally Loaded Pile Using In Situ Tests: A Case History. Canadian Geotechnical Journal, 22 (4), 518-527.

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E10037-081009 Probex

8 FIGURES

FIGURE 1: Schematic representation of the PROBEX dilatometer

Potentiometer

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E10037-081009 Probex

Typical Membrane Resistance

0,000

0,500

1,000

1,500

2,000

2,500

3,000

0,000 200,000 400,000 600,000 800,000

Volume (cc)

Pres

sure

(MPa

)

Test 1Teat 2Test 3Mean of tests 1, 2, 3

FIGURE 2: PROBEX Typical membrane resistance (inertia)

Figure 3 :

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E10037-081009 Probex

Figure 4 :

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E10037-081009 Probex

FIGURE 5: PROBEX Dilatometer probe components detail

1- Conical end cap 7- Locking nut 2- Saturation plug 8- Washers 3- Steel core 9- Tightening nut 4- Hexagonal nut 10- Internal probe sleeve 5- O’rings 11- Outer probe steel ring 6- Washer 14- Dilatometer membrane