ISO 22476-7:2012 Geotechnical investigation and testing Field testing — Part 7: Borehole jack test

Standard Number
BS EN ISO 22476-7:2012
Title
Geotechnical investigation and testing. Field testing. Borehole jack test
Publication Date
International Relationships
EN ISO 22476-7:2012, ISO 22476-7:2012
Descriptors
This part of ISO 22476 specifies the equipment requirements, execution of and reporting on borehole jack tests.
NOTE This part of ISO 22476 fulfils the requirements for borehole jack tests as part of geotechnical investigation and testing according to EN 1997-1 and EN 1997-2.
Keywords
Site investigations, Construction operations, Soils, Soil surveys, Soil sampling, Soil testing, Ground water, Rocks, Safety measures, Occupational safety, Field testing, Excavations, Soil drilling, Aerial photography, Geological analysis, Sampling methods, Sampling equipment, Test specimens, Samples, Surveys, Soil-testing equipment, Geophysical measurement, Industrial, Planning, Mining, Land pollution, Land, Ecology, Extraction (minerals), Quarries, Quality assurance, Defects, Log sheets, Reports, Classification systems, Symbols, Laboratory testing, Personnel, Physical testing, Mechanical testing, Density measurement, Selection, Geology, Hydrology, Design
Title in French
Reconnaissance et essais géotechniques. Essais en place. Essai au dilatomètre rigide diamétral
Title in German
Geotechnische Erkundung und Untersuchung. Felduntersuchungen. Seitendruckversuch
Pages
28

CONTENTS

 

Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 22476-7 was prepared by the European Committee for Standardization (CEN) Technical Committee CEN/TC 341, Geotechnical investigation and testing, in collaboration with Technical Committee ISO/TC 182, Geotechnics, Subcommittee SC 1, Geotechnical investigation and testing, in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).

ISO 22476 consists of the following parts, under the general title Geotechnical investigation and testing — Field testing:

Introduction

The results of borehole jack tests are used for ground deformation calculations provided that the range of stresses applied in the test are representative of the stresses caused by the proposed foundation. Local experience normally improves the application of the results.

For identification and classification of the ground, the results of sampling (according to ISO 22475-1) from each borehole are available for the evaluation of the tests. In addition, identification and classification results (ISO 14688-1 and ISO 14689-1) are available from every separate ground layer within the desired investigation depth (see EN 1997-2:2007, 2.4.1.4(2) P, 4.1(1) P and 4.2.3(2) P).

1 Scope

This part of ISO 22476 specifies the equipment requirements, execution of and reporting on borehole jack tests.

NOTE This part of ISO 22476 fulfils the requirements for borehole jack tests as part of geotechnical investigation and testing according to EN 1997-1 [1] and EN 1997-2 [2].

This part of ISO 22476 specifies the procedure for conducting a borehole jack test in ground stiff enough not to be adversely affected by the drilling operation. Two diametral cylindrical steel loading plates are placed in the ground and opened by pressure. Pressure applied to, and associated opening of the probe are measured and recorded so as to obtain a stress-displacement relationship of the ground for the range of the expected design stress.

This part of ISO 22476 applies to test depths of ≤ 100 m and to testing either on land or off-shore.

2 Normative references

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including amendments) applies.

ISO 10012, Measurement management systems — Requirements for measurement processes and measuring equipment

ISO 14688-1, Geotechnical investigation and testing — Identification and classification of soil — Part 1: Identification and description

ISO 14689-1, Geotechnical investigation and testing — Identification and classification of rock — Part 1: Identification and description

ISO 22475-1, Geotechnical investigation and testing — Sampling methods and groundwater measurements — Part 1: Technical principles for execution

ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in measurement (GUM: 1995)

3 Terms, definitions and symbols

3.1 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

3.1.4

borehole jack

circular cylindrical instrument in which two diametrically opposed curved plates on the outside are forced apart by the application of hydraulic pressure to one or more small jacks located 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

NOTE 1 See Figure 1.

NOTE 2 When testing in a borehole where the hydraulic head in the instrument supply line is likely to exceed the hydraulic head of the fluid in the borehole, consideration must be given to restricting the expansion of the instrument before it enters the pocket and at the conclusion of 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

3.2 Symbols and abbreviations

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

Table 1 — Symbols
Symbol Description Unit
A Projected area of the cylindrical loading plates on the plane normal to the axis of expansion m2
Ac Cross section area in one jack cylinder m2
b Width of the loading plates mm
d Design diameter of the jack mm
d0 Initial diameter of test pocket mm
dc Current diameter of test pocket mm
ds Diameter of the pocket at the start of the test mm
e Associated loading plate expansion mm
e1 Loading plates expansion at time t1 or pressure p1 mm
e2 Loading plates expansion at time t2 or pressure p2 mm
Δei Loading plates expansion change equals diametral displacement of borehole wall mm
EB Modulus of borehole jack test for loading condition MPa
EU Modulus of borehole jack test for unloading condition MPa
f Specific device factor
kf time-dependent strain parameter mm
l axial length of loading plates mm
lT transducer centre-to-centre length mm
p applied pressure MPa
pc calculated average contact stress MPa
pmax maximum contact stress MPa
ps initial contact pressure MPa
p1 pressure at time t1 MPa
p2 pressure at time t2 MPa
q hydraulic pressure in a jack MPa
qmax maximum hydraulic pressure to be used MPa
qs starting pressure of the test MPa
rc friction resistance in one jack cylinder MPa
t time min
t1 time 1 of a constant stress test min
t2 time 2 of a constant stress test min
z test depth m
zW groundwater depth m
α tilt angle of the loading plates º
β opening angle of loading plates º
Δpc change of calculated average contact stress MPa
v Poisson's ratio

4 Equipment

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

Example of a borehole jack test

Key

  • 1 ground surface
  • 2 borehole
  • 3 test pocket
  • 4 loading plates
  • p applied pressure
  • A—A axial section
  • B—B cross section
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.

Diagram of borehole jack equipment

Key

  • 1 setting rods
  • 2 signal cable
  • 3 measuring unit
  • 4 pressure gauge
  • 5 hydraulic pump
  • 6 pressure line
  • 7 sediment collection tube
  • 8 borehole jack
  • 9 loading plate
  • β opening angle
  • d0 initial diameter of test pocket
  • b width of loading plate
  • z test depth
  • 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:

  • sediment collection tube to protect from caving (No. 7 in Figure 2);
  • 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 applied to the jacking cylinders between the loading plates shall be measured by an electric transducer in the instrument (see Figure 3). The pressure may be recorded by a suitable measuring device at the ground surface.

Sketch of expanded borehole jack: axial section and cross section

Key

  • 1 displacement transducer
  • 2 hydraulic cylinders (variable No.)
  • 3 spherical bearing surface
  • 4 loading plate
  • 5 axis of cylinder expansion
  • b width of the loading plate
  • d design diameter of the jack
  • l axial length of loading plates
  • lT centre-to-centre distance of transducers
  • A—A axial section
  • B—B cross section
Figure 3 — Sketch of expanded borehole jack: axial section and cross section

The expansion of the loading plates shall be monitored by one or more electric transducers. If the loading plates are moved by hydraulic cylinders connected in parallel, at least two such transducers should be provided so that any tilt of the loading plates is recorded. If the plates cannot tilt then a single transducer is sufficient.

The pressure line and the signal cable shall connect the downhole instrument to the measuring and control units at the surface. The pressure line shall be connected to a hydraulic pump and a pressure gauge. The signal cable shall connect the transducers in the instrument to the measuring unit.

5 Test procedure

5.1 Calibration of the testing device

Before testing, the equipment shall have been calibrated and applicable corrections determined (see Annex B). Copies of the calibration documents shall be available at the job site. The following components of the equipment shall be calibrated:

  • displacement measuring system;
  • pressure measuring system.

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

5.2 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, a casing with a suitable diameter shall be placed down to a level 1,0 m above the desired test location. A central hole or pocket of about 3 m in length shall then be cored at the nominal diameter for the instrument.

The pocket shall be drilled and the downhole instrument shall be placed in the test location with the minimum of disturbance to the ground to be tested (see Annex E). Careful attention should be paid to the possible effects of any sedimentation in the borehole.

The borehole jacking device shall be set into the pocket without delay. If necessary the instrument may be orientated in the pocket by rotating the setting rods. The instrument shall enter the pocket so that the upper edges of the jacking plates are at least 0,5 m from the pocket entry. The lower edges of the loading plates shall 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.

5.3 Loading programme

5.3.1 General

The maximum hydraulic pressure, qmax, 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.

In the first procedure, at least three unload/reload loops shall be carried out during the loading phase of operation. The programme for these unload/reload loops shall be either given by the specifications for the test or decided according to the observed progress of the test. The position of the first load reversal point has to be decided by reference to the initial contact stress (see 6.1.1). Before commencing the descent phase of a reload loop, enough time shall be allowed for time-dependent effects to become insignificant.

5.3.2 Loading phase

When starting the test, the loading plates shall be jacked slowly until they contact the wall of the test pocket. This contact is indicated by an abrupt rise in the hydraulic pressure. This shall be the initial contact pressure, ps. Further pressure shall then be applied until it equals qs, which shall be chosen between 2 % and 5 % of the planned maximum pressure (see Figure 4).

Starting from this initial pressure, the soil or rock shall be loaded by stepped increments of pressure. The duration of these pressure holds shall be chosen to be between 1 min and 3 min. Simultaneous readings of pressure and loading plate expansion are recorded. Each loading phase shall be performed in five to eight increments. Before the start of each unload in an unload/reload loop, the pressure shall be held constant until time-dependent effects have declined to an acceptable value.

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

Example of a loading test programme

Key

  • a First loading phase.
  • b Second loading phase.
  • c Third loading phase.
Figure 4 — Example of a loading test programme

5.3.3 Unloading phase

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.

The hydraulic pressure in an unloading phase shall never fall below qs. The exact design of a reload loop shall either be given by the specifications for the test or decided according to the observed progress of the test. Sufficient data points shall be available in a reload loop to give a good definition of the whole loop.

5.3.4 End of loading

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
  • the tilt angle α of the loading plates is more than 3°. The tilt angle is defined as:

5.4 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.

5.5 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.

6 Test results

6.1 Basic equations

6.1.1 Calculation of average contact stress

The average contact stress, pc, between the loading plates and the borehole wall shall be determined by

(1)

where

A is one loading plate projected area;

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

F = nAc(q – rc)
(2)

where

n is the number of cylinders;

q is the hydraulic pressure;

Ac is the cross-section area of one cylinder of the jack;

rc is a friction-effect correction which must be determined by a calibration (see B.4).

6.1.2 Modulus of borehole jack test, EB

The modulus of the jack test, EB, 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 Poisson's ratio v,

NOTE Device specific factors/for instruments in use are given in Annex A.

dc is the current diameter of the pocket;

Δei is the loading plates expansion change due to Δpi;

Δpi is the change of calculated average contact stress;

EB is always specific to the stress range considered.

6.2 Loading tests

The test data shall be plotted as shown in Figure D.1. The loading plate expansion, e, is plotted as a function of the calculated average contact stress, pc. The loading modulus of jack test, EB, shall be determined from the test data Δe and Δpc according to Formula (3).

When evaluating borehole jack tests, Δpc shall only be selected within a range of any one loading or unloading phase. Whichever phase is selected determines whether the modulus measured is a loading or an unloading one. There is a further distinction between the first loading modulus and various reloading moduli (see Table D.1 and Figure D.2). All moduli shall be calculated and reported individually (Table D.1). Modulus values shall be reported to three significant figures.

6.3 Constant load test

To evaluate the time-dependent ground deformation at constant stress (p1 = p2), the measured loading plate expansion shall be plotted as a function of the logarithm of time. The slope corresponds to a time-dependent strain parameter kf. Analytically, kf can be determined according to Formula (4) for a stated stress level p:

(4)

where

e2 is the loading plate expansion at time t2;

e1 is the loading plate expansion at time t1;

with p1 = p2;

7 Reporting

7.1 General

In the presentation of test results, the information should be easily accessible, for example in tables or as standard archive scheme. Presentation in digital form is permissible for easier data exchange.

Subclause 7.2 describes which information shall be in:

  • the field record of test results;
  • the test report;
  • every table and every plot of test results.

The field report, completed at the project site, and the test report shall include the information given in 7.2. The test results shall be reported to enable a third party to check and understand the results.

During the test, particulars or deviations from this part of ISO 22476 which can affect the results of the measurements shall be recorded and reported.

7.2 Reporting of test results

7.2.1 General information Field report Test report Every plot
1.a Reference to this part of ISO 22476 and to ISO 22475-1 × ×  
1.b Company executing the test × × ×
1.c Name and signature of the equipment operator executing the test ×    
1.d Name and signature of the field manager responsible for the project   ×  
1.e Depth to the groundwater table (if recorded) and date and time of recording × ×  
1.f Description of the material cuttings according to ISO 14688-1 and ISO 14689-1 × ×  
1.g Type and composition of any medium used to support the borehole wall × ×  
1.h Depth and possible causes of any stoppages in the borehole jack testing × ×  
1.i Stop criteria applied, i.e. target pressure, maximum pressure, maximum diameter × ×  
1.j Observations done in the test: drops of pressure, diameter or volume, incidents, changes in zero/reference readings, etc. × ×  
1.k Borehole back-filled according to ISO 22475-1 (if applicable) ×    
7.2.2 Location of the test Field report Test report Every plot
2.a Test No. × × ×
2.b Depth of test   × ×
2.c Local or general coordinates   × ×
2.d Coordinate reference system and tolerances   ×  
2.e Elevation of ground surface referred to a stated datum   × ×
7.2.3 Test equipment Field report Test report Every plot
3.a Borehole jack type ×   ×
3.b Geometry and dimensions × ×  
3.c Description of the drilling works according to ISO 22475-1 ×    
3.d Identification of borehole jack × × ×
3.e Measuring ranges of the sensors   ×  
3.f Date of last calibration of the sensors (recommended)   ×  
3.g Inside diameter, wall thickness and material of the calibration cylinder ×    
7.2.4 Test procedure Field report Test report Every plot
4.a Test type × ×  
4.b Test specifications × ×  
4.c Method of test control × ×  
4.d Date of the test × × ×
4.e Starting time of the test × ×  
4.f Clock time of the events during the test × ×  
4.g Depth of the borehole jack test, measured to the centre of the expanding plates × × ×
4.h Fluid (water or drilling mud) level in the borehole × ×  
7.2.5 Measured and calculated parameters Field report Test report Every plot
5.a Applied pressures p and diametral displacements of borehole wall Δe with time × ×  
5.b Zero and/or reference readings of pressure, and diameter before and after the test × ×  
5.c Zero drift (in engineering units)   ×  
5.d Corrections applied during data processing (e.g. drifts, system compliance, etc.)   ×  
5.e Borehole jack moduli and the methods used to obtain them   ×  

7.3 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.

7.4 Presentation of test results

Presentation of the results of a borehole jack test shall include data according to 7.2:

  • a) specifications of the displacement and pressure measuring systems (type, manufacturer, serial number);
  • b) specifications of the borehole jack (type, manufacturer, serial number);
  • c) table and graphs of applied pressures and related diametral pocket displacements (see Annex D);
  • d) table of all moduli calculated from the test results;
  • e) plot of the diametral displacement, Δe, against the corrected pressure, p;
  • f) plot of the applied pressure, p, as a function of time, t (time-load diagram).

Annex A

(normative)

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 relateddevice factors
Type No. Opening
angle
β
(º)
Load plate length
l
(m)
Design diameter
d
(m)
Specific device factor
f   for v = 0,25 f   for v = 0,3 f   for v = 0,4
1 120 0,195 0,146 0,792 0,785 0,749
2 120 0,220 0,146 0,827 0,822 0,785
3 120 0,490 0,146 0,960 0,949 0,898
4 130 0,490 0,146 0,894 0,885 0,834
5 120 0,785 0,146 1,017 1,005 0,946
6 130 0,340 0,096 0,820 0,808 0,748
7 120 0,490 0,101 0,986 0,972 0,904

Annex B

(normative)

Calibration and correction

B.1 Measuring devices

All the control and measuring systems shall be checked every time they are used. Full calibration against reference standards in accordance with ISO 10012 shall be performed before and after each contract.

B.2 Displacement transducers

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

B.3 Hydraulic pressure

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

B.4 Friction effect

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

The instrument shall be supported vertically in free air and with the cylinders fully closed. The pressure shall be then increased gradually until the cylinders start to move. The pressure, rc, at which this happens represents the friction resistance and must be subtracted from all subsequent pressure readings.

A check shall also be made that the friction effect at large expansion does not differ significantly from the value determined above.

Annex C

(normative)

Field report example

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

Borehole jack test field report
Contractor: File number: Enclosure:
Client/name of project:
Coordinate: Job site: Borehole No.:
Date:
Drilling rig: Drilling tool: Drilling completed between _____ m and _____ m
Test date:
Starting time:
Test depth
z = _____m
Formation:
Type of soil/rock:
Type No.
(see Table A.1):
Device serial No.:
Test specification:
Loading test □
Constant pressure test □
Pilot hole from _____ m to _____ m back-filling (if applicable) □
  Measuring direction:
Groundwater level
zw = _____m
Date:
 
Time
min
Average contact stress
MPa
Loading plate expansion Difference between transducers No. 1 and No. 2
mm
(maximum allowable loading plate expansion difference)
Transducer No. 1 mm Transducer No. 2 mm Mean value
mm
           
           
           
           
           
           
           
           
           
Remarks (cause of any stoppages, stop criteria, incidents):
Name and signature of the operator in charge:

(informative)

Test example

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

Key

pc average contact stress (kPa)

e loading plate expansion (mm)

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

The corresponding moduli EB for the example test result are given in Table D.1.

Table D.1 — Calculated moduli, EB
Loading phase
No.
Range of applied pressure
[kPa]
Moduli, EB
[MPa]
First loading Reloading Unloading 70 %/30 % (see Figure D.2)
1 100 to 500 2,24
500 to 100 26,2
2 100 to 500 20,8
500 to 1 000 8,82
1000 to 100 27,4
3 100 to 1000 22,4
1 000 to 1 500 12,1
1 500 to 100 26,9
4 100 to 1 500 22,9
1 500 to 2 000 13,2
2 000 to 100 26,2
5 100 to 2 000 22,5
2 000 to 2 600 7,8
2 600 to 100 24,8

Key

  • 1 first loading
  • 2 reloading
  • 3 unloading 70 %/30 %
  • pc average contact stress
  • e loading plate expansion

     

Figure D.2 — Schematic expansion diagram of a borehole jack test: average contact stress, pc, plotted against loading plate expansion, e

Annex E

(normative)

Placing the borehole jack in the ground

E.1 General considerations

Borehole jack testing and borehole drilling shall be considered together. The quality of the borehole wall governs the quality of the test. In order to place the probe in the ground and to obtain valid borehole jack parameters, the drilling technique shall be selected by the operator according to the type of soil or rock (see Table E.1).

If any other placing technique which is not included in Table E.1 is used, the operating organization shall be able to prove that the technique yields borehole jack results of satisfying 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.

E.3 Groundwater level

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

E.4 Probe placement techniques

For boreholes in weathered rock or stiff soils or when the boring is extended below the groundwater level, steps shall be taken to stabilize the borehole with casing and the pocket with drilling mud.

The casing may be advanced by driving or by drilling to the desired depth, that is 0,5 m above the expected depth of the probe top. If the casing is driven, a driving hammer, a driving shoe, a driving guide, and an assembly to extract the casing shall be used. For drilling the casing into the ground, a carbide, saw tooth, or diamond casing shoe bit shall be used, depending on the geological conditions. In addition to the casing and shoe bit, a fluid circulation system shall be in place to remove material from the casing. After the casing has been placed, the borehole shall be clean.

When a hollow stem flight auger is used for simultaneous drilling and casing of the initial hole, the auger end shall be kept closed. Great care shall be taken that the test pocket is not damaged by suction when the auger is withdrawn.

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):

  • continuous flight auger (CFA);
  • core drilling (CD);
  • rotary percussion drilling (RPM).

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 selecting equipment for the site, several bits of various sizes should be available so as to adjust the size of the bit depending on whether overcutting or inward yielding occurs.

When selecting the tool, important considerations are that the wall of the test pocket should be as smooth as possible and that the diameter di should be as constant as possible over the length of the pocket. If this diameter varies significantly, e.g. because of ravelling or if the pocket is not cylindrical, the quality of the test will be impaired.

Table E.1 — Guidelines for borehole jack probe placement techniques
Soil type Boring technique
CFAa CD RPM
Stiff clayey soils *** ***c **
Medium dense and dense sandy soils *** *c  
Weathered rock, Soft rock ** **c **
Rock  b ***c ***
*** Recommended
** Suited
* Acceptable
CFA Continuous flight auger (in dry ground)
CD Core drilling
RPM Rotary percussion with mud
a Rotation speed should not exceed 60 r/min and tool size should give 2 mm to 3 mm radial clearance.
b Not covered by this part of ISO 22476.
c Slurry circulation: pressure should not exceed 500 kPa and the flowrate 15 l/min. The flow may be temporarily interrupted if necessary.

Annex F

(normative)

Resolutions and uncertainties

F.1 Resolution of the measuring devices

Since readings for pressure and displacement are either recorded manually or by transducers, it shall be considered that their resolution depends on either the display (data recorded manually) or the data logger (data recorded automatically).

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

F.2 Uncertainties of the measurements

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;
  • data acquisition;
  • zero shifts of the measuring devices during testing;
  • quality of the test pocket;
  • ground variability;
  • operator effects.

Bibliography

[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 Journal of Rock Mechanics and Mining Sciences, Vol. 22, Elsevier, pp.105-112