Tiêu chuẩn iso 22476 7 2012

© ISO 2012 Geotechnical investigation and testing — Field testing — Part 7 Borehole jack test Reconnaissance et essais géotechniques — Essais en place — Partie 7 Essai au dilatomètre rigide diamétral[.]

Terms and definitions

For the purposes of this document, the following terms and definitions apply.

3.1.1 equipment for borehole jack test borehole jack, hydraulic pump, measuring unit and cables to connect the borehole jack to the measuring unit and the hydraulic pump

3.1.2 borehole jack sounding series of successive operations necessary to perform borehole jack testing at a given location, i.e forming a borehole and performing borehole jack tests in this borehole

3.1.3 pocket for jack test circular cylindrical cavity drilled in a borehole in which to insert the borehole jack device

The borehole jack is a circular cylindrical instrument featuring two curved plates positioned diametrically opposite each other These plates are separated by the application of hydraulic pressure to one or more small jacks situated between them.

3.1.5 borehole jack test process of jacking two cylindrical loading plates diametrically outwards against the borehole wall and measuring their associated expansion as a function of pressure and time

When conducting tests in a borehole, it is crucial to account for situations where the hydraulic head in the instrument supply line may surpass that of the borehole fluid To ensure accurate results, measures should be taken to limit the instrument's expansion prior to entering the pocket and upon completing the test.

3.1.6 depth of test distance between the ground level and the centre of the loading plates measured along the borehole axis NOTE See Figure 2.

3.1.7 operator qualified person who carries out the test

Copyright International Organization for Standardization

Provided by IHS under license with ISO Licensee=University of Alberta/5966844001, User=sharabiani, shahramfs

Symbols and abbreviations

For the purposes of this International Standard the symbols and abbreviations of Table 1 apply.

A Projected area of the cylindrical loading plates on the plane normal to the axis of expansion m 2

The cross-sectional area of a jack cylinder is measured in square meters (m²), while the width of the loading plates is specified in millimeters (mm) The design diameter of the jack is denoted as $d$ mm, with $d_0$ representing the initial diameter of the test pocket and $d_c$ indicating the current diameter The diameter of the pocket at the start of the test is referred to as $d_s$ mm Additionally, the associated loading plate expansion is measured in mm, with $e_1$ and $e_2$ representing the loading plates' expansion at specific times $t_1$ and $t_2$ or pressures $p_1$ and $p_2$ respectively The change in loading plates expansion, denoted as $\Delta e_i$, corresponds to the diametral displacement of the borehole wall in mm.

E B Modulus of borehole jack test for loading condition MPa

The E U Modulus of the borehole jack test under unloading conditions is measured in MPa, with a specific device factor denoted as $ k $ The time-dependent strain parameter is expressed in mm, while the axial length of the loading plates and the transducer centre-to-centre length are also measured in mm The applied pressure is indicated in MPa, along with the calculated average contact stress, maximum contact stress, initial contact pressure, and pressures at specific times $ t_1 $ and $ t_2 $ Hydraulic pressure in the jack is measured in MPa, with maximum and starting pressures defined Friction resistance in one jack cylinder is also expressed in MPa The test depth and groundwater depth are measured in meters, with tilt and opening angles of the loading plates specified in degrees The change in calculated average contact stress is noted in MPa, and Poisson’s ratio is included as a relevant parameter.

The principle of the borehole jack test is shown in Figure 1.

Figure 1 — Example of a borehole jack test

The equipment to carry out borehole jack tests shall consist of the components shown in Figure 2.

4 pressure gauge d 0 initial diameter of test pocket

5 hydraulic pump b width of loading plate

7 sediment collection tube B-B cross section

Figure 2 — Diagram of borehole jack equipment (depth less than 100 m)

The following components are obligatory:

— borehole jack (No 8 in Figure 2);

— pressure line (No 6 in Figure 2);

— signal cable (No 2 in Figure 2);

— measuring unit (No 3 in Figure 2);

— hydraulic pump (No 5 in Figure 2);

— pressure gauge (No 4 in Figure 2);

The following components are recommended:

— setting rods (No 1 in Figure 2).

The nominal diameter of the borehole shall be some millimetres larger than the external diameter of the closed borehole jack.

NOTE In the case of a borehole diameter of 101 mm, a borehole jack with an external diameter of 95 mm has been shown to be suitable.

Annex A shows the geometrical parameters for various instruments.

The hydraulic pressure exerted on the jacking cylinders located between the loading plates will be monitored using an electric transducer, as illustrated in Figure 3 Additionally, this pressure can be recorded by an appropriate measuring device positioned at the ground surface.

1 displacement transducer d design diameter of the jack

2 hydraulic cylinders (variable No.) l axial length of loading plates

3 spherical bearing surface l T centre-to-centre distance of transducers

5 axis of cylinder expansion B-B cross section b width of the loading plate

The monitoring of loading plate expansion requires one or more electric transducers When hydraulic cylinders operate in parallel to move the loading plates, a minimum of two transducers is necessary to detect any tilting However, if tilting is not a concern, a single transducer will suffice.

The downhole instrument is linked to surface measuring and control units via a pressure line and a signal cable The pressure line connects to a hydraulic pump and a pressure gauge, while the signal cable connects the instrument's transducers to the measuring unit.

Calibration of the testing device

Before testing, it is essential to calibrate the equipment and determine any necessary corrections, as outlined in Annex B Calibration documents must be readily available at the job site, and the specific components of the equipment that require calibration should be clearly identified.

If any part of the system is repaired or exchanged, the calibration shall be verified.

Pocket drilling and device placing

A sample shall be recovered according to ISO 22475-1 at the test depth before the borehole jack test is carried out.

In unstable boreholes, it is essential to install a casing with an appropriate diameter up to 1.0 m above the intended test location Following this, a central hole or pocket approximately 3 m in length should be cored at the nominal diameter required for the instrument.

The pocket must be drilled, and the downhole instrument should be positioned at the test site with minimal ground disturbance It is essential to consider the potential impact of sedimentation within the borehole.

The borehole jacking device must be promptly positioned into the pocket, and if needed, the setting rods can be used to orient the instrument It is essential that the upper edges of the jacking plates remain at least 0.5 m from the pocket entry, while the lower edges of the loading plates should not be closer than 0.5 m from the bottom of the pocket.

Borehole jack tests should not be carried out in ground where the stability of the borehole wall is not guaranteed.

Loading programme

The maximum hydraulic pressure, q max, to be used shall be decided considering the maximum stress expected to be applied to the ground by the proposed structure.

Two procedures may be chosen from to carry out the test:

— tests including load, unload and reload phases;

— tests in which time-dependent effects are important These tests shall be individually designed according to the exact data requirements.

During the loading phase of operation, a minimum of three unload/reload loops must be performed The schedule for these loops will be determined by either the test specifications or the observed progress of the test The initial load reversal point should be established based on the initial contact stress Prior to starting the descent phase of a reload loop, sufficient time must be allowed for time-dependent effects to diminish.

During the test initiation, the loading plates are gradually jacked until they make contact with the wall of the test pocket, signaled by a sudden increase in hydraulic pressure, known as the initial contact pressure, $ p_s $ Subsequently, additional pressure is applied until it reaches $ q_s $, which should be set between 2% and 5% of the planned maximum pressure.

The soil or rock is subjected to incremental pressure loads, with each hold lasting between 1 to 3 minutes During this process, simultaneous measurements of pressure and loading plate expansion are taken Each loading phase consists of five to eight increments Prior to each unloading in the unload/reload cycle, the pressure is maintained at a constant level until time-dependent effects diminish to an acceptable level.

Deviations from the test procedure shall be reported in each individual case and their influence on the test results shall be explained.

Key a First loading phase. b Second loading phase. c Third loading phase.

Figure 4 — Example of a loading test programme

After having reached the maximum hydraulic pressure of the loading phase, the load shall be decreased in steps with pressure and loading plate expansion being recorded.

During the unloading phase, hydraulic pressure must not drop below the specified level, q s The design of a reload loop should be determined based on test specifications or the observed progress of the test It is essential to have enough data points in the reload loop to accurately define the entire system.

The loading phase shall be stopped when either:

— the maximum hydraulic pressure is reached; or

— the maximum admissible expansion of the loading plates is reached; or

``,,,``,,`,```,,,,`,```,```,,,-`-`,,`,,`,`,,` - tanα = difference between transducers and

Back-filling of borehole

After completion of the tests, each borehole shall be back-filled and the site shall be restored according to the specifications given in ISO 22475-1.

Safety requirements

National safety regulations shall be followed; e.g for:

— personal health- and safety equipment;

— clean air if working in confined spaces;

— ensuring the safety of the equipment.

Basic equations

6.1.1 Calculation of average contact stress

The average contact stress, p c, between the loading plates and the borehole wall shall be determined by p F c = A (1) where

A is one loading plate projected area;

F is the force exerted by the jacks on one loading plate:

F nA= c ( q r− c ) (2) where n is the number of cylinders; q is the hydraulic pressure;

A c is the cross-section area of one cylinder of the jack; r c is a friction-effect correction which must be determined by a calibration (see B.4).

6.1.2 Modulus of borehole jack test, E B

The modulus of the jack test, E B, shall be determined by the general formula

∆ ∆ (3) where f is the specific device factor dependent on the opening angle of the loading plates β and on

Device-specific factors for instruments are detailed in Annex A The current diameter of the pocket is denoted as \$d_c\$ The change in loading plates expansion is represented by \$\Delta e_i\$, which is influenced by the change in calculated average contact stress, denoted as \$\Delta p_i\$.

E B is always specific to the stress range considered.

Loading tests

The test data will be illustrated in Figure D.1, where the loading plate expansion, denoted as \$e\$, is represented as a function of the calculated average contact stress, \$p_c\$ The loading modulus of the jack test, \$E_B\$, will be calculated from the test data using the changes in expansion and contact stress, represented as \$\Delta e\$ and \$\Delta p_c\$ according to Formula (3).

When assessing borehole jack tests, it is essential to choose Δp c within the specific range of a single loading or unloading phase, as this selection dictates whether the measured modulus is for loading or unloading Additionally, a distinction must be made between the first loading modulus and the various reloading moduli, as illustrated in Table D.1 and Figure D.2 All modulus values should be calculated and reported separately, with results presented to three significant figures.

Constant load test

To assess time-dependent ground deformation under constant stress conditions (p₁ = p₂), the expansion of the measured loading plate should be graphed against the logarithm of time The resulting slope represents the time-dependent strain parameter $ k_f $ This parameter can be analytically calculated using Formula (4) for a specified stress level $ p $.

(lg −lg ) (4) where e 2 is the loading plate expansion at time t 2 ; e 1 is the loading plate expansion at time t 1 ; with p 1 = p 2

General

Test results should be presented in a manner that ensures easy accessibility, utilizing formats such as tables or standard archive schemes Digital presentation is also acceptable to facilitate smoother data exchange.

Subclause 7.2 describes which information shall be in:

— the field record of test results;

— every table and every plot of test results.

The field report and test report from the project site must include the information specified in section 7.2 Additionally, the test results should be presented in a manner that allows a third party to verify and comprehend the findings.

Reporting of test results

1.a Reference to this part of ISO 22476 and to ISO 22475-1 x x

1.c Name and signature of the equipment operator executing the test x

1.d Name and signature of the field manager responsible for the project x

1.e Depth to the groundwater table (if recorded) and date and time of recording x x

1.f Description of the material cuttings according to ISO 14688-1 and

1.g Type and composition of any medium used to support the borehole wall x x

1.h Depth and possible causes of any stoppages in the borehole jack testing x x

1.i Stop criteria applied, i.e target pressure, maximum pressure, maximum diameter x x

1.j Observations done in the test: drops of pressure, diameter or volume, incidents, changes in zero/reference readings, etc. x x

1.k Borehole back-filled according to ISO 22475-1 (if applicable) x

7.2.2 Location of the test Field report

2.d Coordinate reference system and tolerances x

2.e Elevation of ground surface referred to a stated datum x x

3.c Description of the drilling works according to ISO 22475-1 x

3.e Measuring ranges of the sensors x

3.f Date of last calibration of the sensors (recommended) x

3.g Inside diameter, wall thickness and material of the calibration cylinder x

4.e Starting time of the test x x

4.f Clock time of the events during the test x x

4.g Depth of the borehole jack test, measured to the centre of the expanding plates x x x

4.h Fluid (water or drilling mud) level in the borehole x x

7.2.5 Measured and calculated parameters Field report

5.a Applied pressures p and diametral displacements of borehole wall Δe with time x x

5.b Zero and/or reference readings of pressure, and diameter before and after the test x x

5.c Zero drift (in engineering units) x

5.d Corrections applied during data processing (e.g drifts, system compliance, etc.) x

5.e Borehole jack moduli and the methods used to obtain them x

Choice of axis scaling

All graphical results shall be presented at a scale which results in the graph sensibly filling the space on the paper.

Presentation of test results

The presentation of borehole jack test results must include specific data as outlined in section 7.2, which encompasses the specifications of the displacement and pressure measuring systems, including type, manufacturer, and serial number; details of the borehole jack, such as type, manufacturer, and serial number; a table and graphs illustrating applied pressures alongside corresponding diametral pocket displacements; a comprehensive table of all moduli derived from the test results; a plot depicting diametral displacement, Δe, against corrected pressure, p; and a time-load diagram showing applied pressure, p, as a function of time, t.

Dimensions of borehole jacks and related device factors

The standardized dimensions of borehole jacks and related device factors are given in Table A.1.

NOTE These factors were established from finite element calculations (FEM) For further information on the device factors see Bibliography [3] and [4].

Table A.1 — Dimensions of borehole jacks and related device factors Type No.

Design diameter Specific device factor β (°) l

All control and measuring systems must undergo verification each time they are utilized Comprehensive calibration against reference standards, in line with ISO 10012, is required both prior to and following each contract.

The resolution of the displacement transducer must be 10 àm or better.

The allowable error is 0,5 % of the indicated pressure or 0,1 % of the full scale pressure, whichever is the greater.

The hydraulic cylinders actuating the loading plates are subject to friction which reduces the forces acting on the ground This represents a pressure correction, r c, which must be determined by a calibration.

The instrument should be held vertically in free air with the cylinders completely closed Gradually increase the pressure until the cylinders begin to move The pressure, denoted as \$r_c\$, at which movement occurs indicates the friction resistance and must be deducted from all future pressure measurements.

A check shall also be made that the friction effect at large expansion does not differ significantly from the value determined above. © ISO 2012 – All rights reserved ``,,,``,,`,```,,,,`,```,```,,,-`-`,,`,,`,`,,` - 15

While the content of the report contains normative minimum requirements, the format may be freely chosen.

Borehole jack test field report

Coordinate: Job site: Borehole No.:

Drilling rig: Drilling tool: Drilling completed between _ _ m and

Loading test £ Constant pressure test £

Pilot hole from m to m back-filling (if applicable) £

Measuring direction: Groundwater level zw = _ _ m

Loading plate expansion Difference between transducers No 1 and

(maximum allowable loading plate expansion difference)

Remarks (cause of any stoppages, stop criteria, incidents):

Name and signature of the operator in charge:

The result of a borehole jack test is shown in Figure D.1.

Key p c average contact stress (kPa) e loading plate expansion (mm)

Figure D.1 — Result of a borehole jack test; expansion diagram; average contact stress, p c , versus loading plate expansion, e

3 unloading 70 %/30 % p c average contact stress e loading plate expansion

Placing the borehole jack in the ground

Borehole jack testing and drilling are interconnected, as the integrity of the borehole wall directly impacts test quality To ensure accurate borehole jack parameters, the operator must choose the appropriate drilling technique based on the specific soil or rock type.

Any placing technique not listed in Table E.1 must be validated by the operating organization to ensure that it produces borehole jack results of acceptable quality.

E.2 Time between drilling and testing

Borehole jack testing shall be carried out immediately (no more than 2 h) after the borehole pocket has been drilled and during the same working shift.

Groundwater level, z w, shall be measured in the borehole pocket before placing the probe It must be checked after pulling up the probe.

To ensure stability in boreholes drilled in weathered rock or stiff soils, especially when extending below the groundwater level, it is essential to use casing and drilling mud for stabilization.

The casing installation can be achieved through driving or drilling to a depth of 0.5 m above the expected probe top When driving the casing, essential tools include a driving hammer, driving shoe, driving guide, and an assembly for casing extraction For drilling, the choice of a carbide, saw tooth, or diamond casing shoe bit depends on the geological conditions Additionally, a fluid circulation system is necessary to remove material from the casing, ensuring that the borehole remains clean after the casing is installed.

When using a hollow stem flight auger for simultaneous drilling and casing, it is essential to keep the auger end closed Additionally, it is crucial to ensure that the test pocket remains undamaged by suction during the auger's withdrawal.

The following rotary drilling techniques according to ISO 22475-1 should be used to prepare the test pocket depending on the ground type encountered (see Table E.1):

When determining the diameter of the necessary cutting tool for the pocket, three factors shall be considered:

— diameter of the pocket required;

— overcutting of the pocket resulting from wobble of the cutting tool or wall erosion by the mud circulation or both; and

— inward yielding that occurs between the removal of the cutting tool and the jack placement.

Inward yielding or swelling can be reduced by the use of an appropriate drilling fluid.

The tool diameter shall not be more than 1,08 × d

When choosing site equipment, it is essential to have a variety of bit sizes on hand to accommodate adjustments for overcutting or inward yielding.

When choosing a testing tool, it is crucial to ensure that the wall of the test pocket is smooth and that the diameter $ d_i $ remains consistent throughout its length Significant variations in diameter, such as those caused by ravelling or non-cylindrical shapes, can negatively affect the quality of the test results.

Table E.1 — Guidelines for borehole jack probe placement techniques

Medium dense and dense sandy soils ∗∗∗ ∗ c ∗∗

CFA Continuous flight auger (in dry ground)

CD core drilling involves rotary percussion with mud, where the rotation speed must not exceed 60 r/min, and the tool size should allow for a radial clearance of 2 mm to 3 mm This section is not covered by ISO 22476 For slurry circulation, the pressure should remain below 500 kPa, with a flow rate of 15 l/min, although the flow may be temporarily interrupted if necessary.

F.1 Resolution of the measuring devices

Pressure and displacement readings, whether recorded manually or through transducers, rely on the resolution of the display for manual recordings or the data logger for automatic recordings.

The minimum requirements for the measuring devices as given in Annex B shall be adhered to.

It shall be considered that the accuracy of the measurements depends on the equipment and the type of measuring devices of pressure and displacement employed.

The uncertainty, defined as the interval within which the true measure of the magnitude will be encountered, shall be calculated by reference to ISO/IEC Guide 98-3.

The uncertainties in borehole jack testing have the following possible sources amongst others:

— ambient and transient temperature effects;

— zero shifts of the measuring devices during testing;

— quality of the test pocket;

[1] EN 1997-1, Eurocode 7: Geotechnical design — Part 1: General rules

[2] EN 1997-2, Eurocode 7: Geotechnical design — Part 2: Ground investigation and testing

[3] Smoltczyk, U and Seeger, H., 1980, Erfahrungen mit der Stuttgarter Seitendrucksonde, Geotechnik,

Vol 3, VGE Verlag GmbH Essen, pp.165-173

[4] Heuze, F E and Amadei, B., 1985, The NX-Borehole Jack: a Lesson in Trials and Errors, International

Tiêu đề	Geotechnical Investigation And Testing — Field Testing — Part 7: Borehole Jack Test
Trường học	University of Alberta
Chuyên ngành	Geotechnical Engineering
Thể loại	Tiêu chuẩn
Năm xuất bản	2012
Thành phố	Switzerland

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