Testing Swelling Rocks 1999

International Journal of Rock Mechanics and Mining Sciences 36 (1999) 291±306

0148-9062/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved.

PII: S0148-9062(99 )00005 -4

INTERNATIONAL SOCIETY FOR ROCK MECHANICSCOMMISSION ON SWELLING ROCKS AND COMMISSION

ON TESTING METHODS

SUGGESTED METHODS FOR LABORATORY TESTING OF SWELLING ROCKS

CONTENTS

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293

2. Part 1: suggested methods for sampling, storage and preparation of test

specimens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294

3. Part 2: suggested method for determining axial swelling stress . . . . . . . . . . . . . . . 295

4. Part 3: suggested method for determining axial and radial free swelling strain. . . 299

5. Part 4: suggested method for determining axial swelling stress as a function of

axial swelling strain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302

6. Final comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305

Co-ordinator

F.T. Madsen (Switzerland)

Suggested methods for laboratory testing of swelling rocks

F.T. Madsena

Accepted 2 January 1999

ISRM SUGGESTED METHODS (SMs): SECOND SERIES

A Second Series of Suggested Methods is being produced by the ISRM Commission on Testing Methods from 1998 onwards.In this Second Series, for each SM two versions are published:

1. A Draft SM written by the Working Group Co-ordinator(s);2. A Final SM also produced by the Working Group Co-ordinator but with amendments resulting from the Draft SM review by

the Working Group Members and other comments received after publication of the Draft SM.

A suite of the new Suggested Methods is currently being published in this Journal. These started with an IndentationHardness Index SM written by T. Szwedzicki and published in June 1998. Several more will be published in 1999.However, the following SM results from a Working Group of 14 members, is already in the ®fth draft stage and thus can be

considered to be in its ®nal form.

Please send written comments on this SM to thePresident of the ISRM Commission on Testing Methods:

Professor J A Hudson, 7 The Quadrangle,Welwyn Garden City, Herts AL8 6SG, UK

1. Introduction

The engineering problems caused by swelling rocks

are widely recognized, as is the need to test these rocks

to determine the type and extent of their swelling

behavior and to measure this for purposes of design.

The ISRM Commission on Swelling Rock was

formed in 1980 to provide a systematic treatment of

the swelling rock problem. It is emphasized that the

purpose of `suggested methods' is to specify rock test-

ing procedures and to achieve some degree of stan-

dardization without inhibiting the development of

improvement of techniques. This is particularly perti-

nent in the case of swelling rocks which, because of

their variability, often require special non-standard

treatment during both specimen preparation and test-

ing which di�ers from what is proposed here.

This particular document treats laboratory testing of

argillaceous swelling rocks and swelling rocks contain-

ing clay and anhydrite and consist of four parts:

Part 1: sampling, storage and preparation of test

specimens

Part 2: determining the axial swelling stress

Part 3: determining the axial and radial free swelling

strain

Part 4: determining axial swelling stress as a func-

tion of axial swelling strain

These `suggested methods' are intended to replace

and update those published in [1]. It is important to

note the di�erence in procedure of specimen testing for

argillaceous and for clay±anhydrite rocks as the swel-

ling mechanism is of di�erent nature.

The tests described here are intended for practical

use. For research on swelling behavior, other tests may

have to be used.

aGeotechnical Engineering, Laboratory for Clay Mineralogy, Swiss

Federal Institute for Technology, CH-8093, Zurich, Switzerland.

F.T. Madsen / International Journal of Rock Mechanics and Mining Sciences 36 (1999) 291±306 293

2. Part 1: suggested methods for sampling, storage andpreparation of test specimens

2.1. Scope

1. These suggested methods describe techniques forsampling, storing and preparing specimens for labora-tory swelling tests of argillaceous rocks and rocks con-taining clay and anhydrite1.

2.2. Sampling

2. (a) To obtain meaningful results from swellingtests, the samples2 are to have, as far as possible, thesame density and water content as those in situ at thetime of sampling.

(b) Rock samples are to be collected preferably fromcore borings. Borings should be performed with airpressure or, with an antiswelling admixture (such asAntisol) in the cooling (¯ushing) water, whichever isbest to keep the sample as close to its natural state aspossible.

(c) Coring is to be accomplished using either adouble tube or triple tube core barrel. The core diam-eter should be at least NX but preferably closer to 100mm. The sample length shall be su�cient to prepare atleast three undisturbed specimens, and contain enoughadditional material for identi®cation tests.

(d) Block sampling is another possibility. Thedimensions of the block sample are to be su�cient forpreparation of at least three undisturbed specimens,and contain enough additional material for identi®-cation tests.

(e) The cores or blocks are to be logged by a geol-ogist and photographed. In rocks containing clay andsulphate minerals (anhydrite and gypsum), fabric andthe clay±sulphate minerals ratio is of special interest asboth are related to the swelling parameters. Prior tologging, the cores or blocks are to be cleaned byremoving the mud cake. Their condition, such asmechanical breakage, presence of mud cake on the sur-faces of the core or block, and presence of seams shallbe noted. Natural ®ssures, if any, are to be clearlyidenti®ed.

(f) The samples are then to be wrapped with awaterproof liner such as a thin plastic sheet, followedby aluminum foil and sealed with a mixture consistingof 75% para�n and 25% beeswax. The time betweensampling and sealing should be as short as possible.

(g) The sealed cores or blocks are to be labelled giv-ing details of the sampling location, depth and el-evation.

(h) To reduce breakage of cores or blocks duringtransportation from the ®eld site to the testing labora-tory, the samples are to be placed in containers, andthe space between cores and the container wall is to be®lled with suitable material such as straw, shreddedfoam or paper.

(i) Samples are to be protected from frost andextreme heat at all times during sampling and trans-portation. Sample temperature is to remain in therange 5±308C.

2.3. Storage of samples

3. (a) Storage time should be minimized.(b) Storage in a constant temperature room (208C)

is preferred.(c) The samples must not be exposed to direct sun-

light.(d) If long-term storage is necessary, humidity in the

storage room should be such as to minimize anymoisture change of the samples.

2.4. Specimen preparation

4. (a) The sampling logs and photographs are to beexamined to select cores or blocks that will yieldrequired sizes, shapes and numbers of specimens.

(b) Multiple specimens are to be prepared from thesame sample. At least two are used for testing and oneas a reference specimen for determination of watercontent3, grain density, density and degree of satur-ation. The particular number of specimens for each of

1 Depending on the depth below surface this type of rock may also

contain gypsum. Normally, as these rocks originate in an evaporitic

environment other salts such as halite [NaCl] and dolomite

[CaMg(CO3)2] are also present.2 For the purpose of these suggested methods, the term `sample'

refers to the drill core, the block or other representative piece of

rock received in the laboratory, while the term `specimen' refers to

the individual test specimen prepared from the sample.3 Rocks containing clay and anhydrite (CaSO4) may also contain

gypsum (CaSO4�2H2O). At least this will be the case after the swel-

ling tests have been performed. For rocks containing gypsum the

normally used method for determining the water content by drying

the specimen at 1058C will produce erratic results. This is so because

not only pore water and water connected to clay particles is removed

from the specimen but also some of the crystal water of the gypsum.

Using the following method for determining the water content in

two steps has several advantages. In the ®rst step pore water and

water connected to the clay particles is removed by drying the

crushed specimen over P2O5 in a desiccator for 3 days. The water

content determined in this way is equal to the normally used water

content in soil and rock mechanics. The water content is calculated

as: w%=((M2ÿMP)/MP)�100, where: M2 is the mass of specimen

after testing, before drying over P2O5 and MP the mass of specimen

after drying over P2O5. In the next step the specimen is heated in an

oven for 24 h at 2008C. During this procedure the gypsum releases

all crystal water. The gypsum crystal-water content is calculated as:

w%gypsum=((MPÿMG)/MG)�100, where: MP is the mass of speci-

men after drying over P2O5 and MG the mass of specimen after dry-

ing at 2008C. It is then possible to calculate the amount of gypsum

(weight %) in the specimen as: gypsum %=(1 mol gypsum/2 mol

water)�w%gypsum, gypsum%=4.78�w%gypsum.

F.T. Madsen / International Journal of Rock Mechanics and Mining Sciences 36 (1999) 291±306294

the tests depends on the availability of material and onthe testing program Ð see Section 1. One undisturbedspecimen should be kept in storage for mineralogicalinvestigations.

(c) Specimens are to be prepared as rapidly as poss-ible. If machining (cutting, recoring to a smaller diam-eter) of the specimen is required this must be donewith air-cooling or with an antiswelling medium (suchas Antisol) in the cooling water, whichever is best tokeep the specimen as close to its natural condition aspossible. In general recoring is to be avoided. Forswelling rocks that can break easily, the special pro-cedure described in Appendix A is to be used.Remaining samples must be properly sealed againaccording to 2(f).

(d) The specimens required for the tests described inParts 2, 3 and 4 (Sections 3±5) below are to be in theshape of a right circular disc. Experience has shownthat for specimen diameters between 50 and 100 mm,a thickness between 20 and 30 mm is most suitable.The test described in Part 3 Section 4 can also be per-formed with other specimen shapes, such as entirelyirregular pieces which have undergone no preparationat all. The apparatus and procedure have then to beadapted to such specimen shapes.

3. Part 2: suggested method for determining axialswelling stress

3.1. Scope

1. The test is intended to measure the time depen-dent axial swelling stress of a radially con®ned rockspecimen when immersed in water4. If possible themaximum swelling stress is to be determined5.

3.2. Apparatus

The apparatus6 is to include the following as sche-matically shown in Fig. 1.

2. (a) A stainless steel ring ((1) in Fig. 1), for rigidradial restraint of the specimen. The inner surface ofthe ring is to be polished and smooth. The wall thick-ness of the ring depends on its other dimensions andhas to be calculated based on those dimensions andthe maximum lateral stress to be expected. Not morethan 10ÿ4 radial strain is allowed. Thicknesses between5 and 10 mm are usually satisfactory. Several ringsshould be available to ®t all desired specimen dimen-sions.

(b) Two porous plates ((2) in Fig. 1). The porousplates should be made of high modulus material.Porous stainless steel plates are most suitable.Alternatively, stainless steel plates into which a num-ber of small holes (dia 0.1 mm) have been drilled arealso suitable. In the latter case, small channels con-necting the small holes to the water supply arerequired.

(c) One porous plate is to be on top of the specimenand the other at its bottom. The lower plate is to havea diameter of approx. 5 mm greater than the outer di-ameter of the specimen ring, and the upper plate hasto be of a size just ®tting the inside of the ring withoutrestraining its movement.

Fig. 1. Apparatus for measuring the axial swelling stress: (1) stain-

less-steel ring, (2) porous metal plates, (3) stainless-steel loading

plate, (4) container, (5) dial gages (attached to the bottom of con-

tainer (4), attachment not shown), (6) load measuring device, (7)

rigid frame and (8) loading piston, (9) stainless steel plate.

4 For argillaceous rocks, distilled water is normally used. Water

from the sampling site, or water with a special chemical composition

may also be used. For rocks containing clay and anhydrite using dis-

tilled water may cause uncontrolled dissolution of sulphates in the

specimen. Normally a calcium-sulphate solution of 2.4 g CaSO4 per l

distilled water is used to minimize dissolution of the sulphate from

within the specimen into the container water.5 In the swelling process of clay±anhydrite rocks two di�erent swel-

ling mechanisms are involved: the swelling of clay due to hydration

of clay particles (an osmotic process) and the swelling due to trans-

formation of anhydrite into gypsum (chemical process which involves

dissolution and precipitation). Normally clay swelling takes place in

the ®rst days after immersion in water or calcium-sulphate solution,

whereas anhydrite±gypsum swelling goes on for years.6 Since nearly every institution working on swelling rocks has

developed its own apparatus for measuring the swelling stress, the

apparatus described here is only an example. The advantage of this

apparatus is the possibility to use steel rings of various diameters,

depending on the diameter of the specimen. This reduces time and

e�ort for preparation and lessens the risk of disturbing the specimen.


(d) A stainless-steel loading plate ((3) in Fig. 1) ofthe same bottom diameter as the upper porous plate,but slightly conically shaped, and placed on top of theporous plate. The loading plate has to be thick enoughto ensure rigid strain application; for specimen diam-eters of between 50 and 100 mm a 10-mm thick plateis adequate.

(e) A rigid frame ((7) in Fig. 1) with a loading devicecapable of continuous adjustment.

(f) A loading piston or rod ((8) in Fig. 1) with ahemispherical end or a separate sphere to rest on theloading plate.

(g) Two mm dial gauges ((5) in Fig. 1) with a sensi-tivity of 2.5 mm to measure the axial swelling or com-pressive displacement of the specimen. The dial gaugesare attached to the bottom of the container (4).

(h) A sti� load measuring device7 ((6) in Fig. 1), forinstance an electromechanical load cell capable ofmeasuring to an accuracy of 20.5% of the maximumrating of the load measuring device.

(i) A container ((4) in Fig. 1) (dia 15 cm) for thespecimen assembly, and ®lled with water to a levelabove the top of the specimen.

3.3. Procedure

3. (a) The test is to be conducted in an environment

where the ambient temperature can be maintained con-stant at 20228C.

(b) The thickness h0 of the specimen which was pre-pared as described in Part 1 (Section 2, Specimen prep-aration) is to be measured in at least three locationsbetween specimen ends, to an accuracy of20.1 mm.

(c) The specimen diameter d is to be measured atleast at three locations along the circumference.Measuring accuracy is again to be better than 20.1mm.

(d) The mass of the specimen M1 is to be determinedto 0.1 g.

(e) The specimen ring is to be cleaned and its massM0 determined.

(f) The specimen is inserted into the ring. The speci-men must ®t snugly into the ring.

(g) The apparatus is assembled. The ring with thespecimen is placed on the lower porous plate, followedby the upper porous plate and the steel loading plate.The plate is placed with the smaller diameter facingupwards. The piston is brought into contact with thetop plate and centered.

(h) A seating load corresponding to an axial stressof 25 kPa is to be applied. The initial readings of themicrometer dial gages are noted.

(i) The container is ®lled with water to cover the topporous plate.

(j) The container is covered with a plastic disc tominimize evaporation of the container water.

(k) The axial force N and the axial displacement dare measured and recorded as a function of elapsedtime t8.

(l) Depending on the mineralogical composition ofthe specimen small amounts of strain are to be com-pensated in a stepwise manner by increasing the axialforce9. The steps should be kept as small as possible.

(m) The test should be continued until the maximumaxial force developed by the specimen can be deter-mined or estimated.

(n) The ring with the specimen is then to beremoved from the container (after removing of thecontainer-water and unloading), the excess waterwiped o� and the mass M2 determined. For stronglyswelling rock, the water is drained o� before unload-ing. At this stage the specimen condition is logged.

(o) If the tested rock is purely argillaceous (no gyp-sum), the specimen with the ring is heated in an ovento constant mass at a temperature of 105228C. Thespecimen with the ring is allowed to cool in a dessica-tor. The oven-dry mass M3 is determined.Alternatively the specimen can be oven heated withoutthe ring10.

(p) If the tested rock contains clay and anhydrite/gypsum, a part of the specimen is used for the determi-nation of the water content after testing as earlierdescribed.

7 Normally, load cells of a capacity of 20 kN and de¯ecting less

than 10ÿ8 are suitable. For very high swelling stresses, load cells of

50 kN may be required. The accuracy of 0.5% is related to the maxi-

mum rating of the load cell.8 In argillaceous rocks rapid changes in strain take place during

the ®rst hours. Also, most of the changes usually occur within the

®rst few days, and the total test duration strongly depends on the

dimensions of the specimen. On the contrary, the transformation of

anhydrite into gypsum is a rather slow process and the determination

of the maximum swelling stress may take several years. These facts

should be considered when scheduling the test.9 The swelling heave (axial strain) due to clay swelling is reversible

and for specimens containing only clay minerals (no anhydrite and

gypsum) the original thickness of the specimen may be kept constant

by increasing the axial stress. The steps should be kept as small as

possible, particularly toward the end of the test (see Fig. 2b); this is

necessary to obtain an accurate measurement of the maximum axial

force and thus maximum axial swelling stress. An axial strain of

0.05% in the last increment is usually adequate. The transformation

of anhydrite into gypsum cannot be reversed by increasing the axial

stress (at least not for the range of stresses which normally occurs in

tunnelling problems). For rocks containing anhydrite the axial strain

of the specimen caused by transformation of anhydrite into gypsum

is not to be compensated as a compensation will lead to an unreason-

able high swelling stress. In some cases it may however be sensible to

compensate the strain occurring during the ®rst days of the test as

this is usually caused by the clay-swelling process. After this time

however, no compensation is to be made.10 In all tests, an alternative approach is to remove a part of the

specimen before drying to determine its mineralogical composition.

The mass M2 and M3 determination applies then to the remainder of

the specimen.


Fig. 2. (a) Plot of axial stress vs. time of argillaceous rock. s �=maximum axial stress. (b) Plot of axial stress vs. compensated axial swelling

strain of argillaceous rock. s �=maximum axial stress.


Fig. 3. (a) Plot of axial stress vs. time of clay±sulphate (anhydrite) rock. (b) Plot of axial swelling strain due to noncompensation of the specimen

height vs. time of clay±sulphate (anhydrite) rock.


3.4. Calculations

4. (a) The following test parameters are calculated:the area of cross section of the specimen A; the axialstress s; the compensated swelling strains eclay and thenoncompensated swelling strains egypsum.

(b) The area of cross-section A of the specimen iscalculated as

A � pd2

4,

where d is the specimen diameter.(c) The axial stress s is calculated as

s � N

A,

where N is the measured axial force.(d) The compensated clay swelling strain increment

Declay is calculated as

Declay � Ddclay

h0,

where Ddclay is the displacement increment caused byclay swelling and h0 the original thickness of the speci-men.

(e) The noncompensated anhydrite into gypsumswelling strain increment Degypsum is calculated as

Degypsum � Ddgypsum

h0,

where Ddgypsum is the displacement increment causedby the transformation of anhydrite into gypsum and h0the original thickness of the specimen.

(f) Density, initial and ®nal water contents anddegree of saturation are calculated according to [2].

3.5. Reporting of results

5. The test report is to include the following foreach specimen.

(a) A unique identi®cation of the sample and ofeach individual specimen.

(b) Information on geographic origin, lithology, fab-ric and, if possible, mineralogy and pore water chem-istry of the sample and specimen.

(c) Date and method of sampling; date(s) of testing.(d) Method of sealing and storage.(e) Method of specimen preparation for testing.(f) Orientation of the specimen axis relative to speci-

men anisotropy speci®cally with respect to beddingplanes and relative to in situ directions.

(g) Dimensions of the test specimen.(h) Density, water content, grain density and degree

of saturation of the test specimen before the swellingtest11.

(i) Final density, water content and degree of satur-ation of the test specimen after the swelling test.

(j) Test temperature.(k) Applied seating-load.(l) Speci®cation of water used for immersion.(m) A plot of axial stress vs. elapsed time, such as

Fig. 2a and Fig. 3a.(n) A plot of axial swelling strain vs. elapsed time,

such as Fig. 3b.Additional for argillaceous rock:(o) A plot of axial stress vs. compensated swelling

strain such as Fig. 2b.(p) Total compensated swelling strain (optional).

4. Part 3: suggested method for determining axial andradial free swelling strain

4.1. Scope

1. The test is intended to measure the axial andradial free swelling strain developed when an uncon-®ned, undisturbed rock specimen is immersed in water.

Fig. 4. Apparatus for measuring the swelling strain: (1) container, (2)

dial gauge, (3) glass plate, (4) stainless-steel band and (5) specimen.

11 Density and water content of the test specimen are determined in

the specimen next to the test specimen (having similar mineralogical

composition) in the drilling core or block.


4.2. Apparatus

2. The apparatus12 is to include the following asschematically shown in Fig. 4:

(a) A container (dia 15 cm) for the specimen ((1) inFig. 4).

(b) A mm dial gauge (or equivalent) with a sensitivityof 2.5 mm, mounted to measure the swelling displace-ment in the central axis of the specimen ((2) in Fig. 4).

(c) A glass plate, positioned at the point of gaugingto prevent indentation of the specimen ((3) in Fig. 4).

(d) A thin (0.1 mm) ¯exible, stainless steel band ((4)in Fig. 4) attached to the specimen by an elastic rubberband. The steel band is calibrated at 0.1-mm intervalsand is used to determine the radial swelling13 defor-mation.

4.3. Procedure

3. (a) The test is to be conducted in an environmentwhere the ambient temperature can be maintained con-stant at 20228C.

(b) The thickness h0 of the specimen which was pre-pared as described in Part 1 Section 2 is to bemeasured in at least three locations between specimenends, to an accuracy of20.1 mm.

(c) The specimen diameter d0 is to be measured atleast at three locations along the circumference, to anaccuracy of20.1 mm.

(d) The mass of the specimen M1 is to be determinedto 0.1 g.

(e) The stainless-steel band is attached and the speci-men with the dial gauge (or equivalent) is mounted inthe container.

(f) The container is to be ®lled with water to coverthe specimen.

(g) The container is covered with a plastic disc tominimize evaporation of the container water.

(h) The axial swelling displacement dax is recordedas a function of time elapsed14.

(i) The swelling displacement is recorded until amaximum (or constant) value has been reached or canbe estimates15.

(j) After swelling strain is determined, and beforethe specimen is removed from the container, theincrease in circumference DC is measured with thestainless-steel band.

(k) The specimen is then to be removed from thecontainer, the excess water wiped o�, the stainless-steelband removed from the specimen, and the mass M2

determined. At this stage the specimen condition islogged.

(l) If the tested rock is purely argillaceous, the speci-men is heated in an oven to constant mass at a tem-perature of 105228C. The specimen is then allowed tocool in a dessicator. The oven-dry mass M3 is deter-mined.

(m) If the tested rock contains clay and anhydrite/gypsum a part of the specimen is used for the determi-nation of the water content after testing as describedearlier.

4.4. Calculations

4. (a) The axial swelling strain eax and the radialswelling strain erad are determined.

(b) The axial swelling strain is calculated as

eax � dax

h0,

where dax is the axial displacement and h0 the initialthickness of the specimen.

(c) The radial swelling strain is calculated as

erad � drad

d0,

where d0 is the initial specimen diameter and

drad � DCp

,

where DC is the increase in specimen circumference asmeasured with the stainless-steel band (see 3f).

(d) Density, initial and ®nal water contents anddegree of saturation are calculated according to [2].




(b) Information on geographic origin, lithology, fab-

12 This apparatus represents a possible example. If the swelling

strain has to be measured in three directions the specimens should

preferably be cube shaped. It should be possible to mount the dial

gauges (or equivalent) in three directions.13 A number of possibilities exist to conduct both continuous and

more precise measurements of radial strain. Given the purpose of the

swell test, which is to provide as quick information as possible on

the swelling strain, such sophistication may not be justi®ed.14 Some swelling rocks may start to disintegrate after a short period

of immersion in water by developing open ®ssures along their bed-

ding planes. In such cases, applying a small axial surcharge may be

advisable.15 The time for reaching the ®nal (maximum) strain depends on the

mineralogical composition of the tested specimen. For argillaceous

rock this usually takes a few days. For rocks containing anhydrite it

may take several years to reach the ®nal strain, as the transformation

of anhydrite into gypsum is a rather slow process.


Fig. 5. (a) Axial swelling strain vs. time (example for an argillaceous specimen). e �=maximum axial strain. (b) Axial swelling strain vs. time

(example for a clay±sulphate (anhydrite) specimen). e �=maximum axial strain.


ric and, if possible, mineralogy and pore water chem-istry of the sample and specimen.

(c) Date and method of sampling; date(s) of testing.(d) Method of sealing and storage.(e) Method of specimen preparation for testing.(f) Orientation of the specimen axis relative to speci-

men anisotropy speci®cally with respect to beddingplanes and relative to in situ directions.

(g) Dimensions of the test specimen.(h) Density water content, grain density and degree

of saturation of the test specimen before the swellingtest.


(j) Test temperature.(k) Applied load (if any).(l) Speci®cation of water used for immersion.(m) A plot of axial strain vs. elapsed time, such as

Fig. 5a or b.(n) Maximum axial swelling strain.(o) Maximum radial swelling strain.(p) Volumetric strain, either computed from axial

and radial swelling strain for regularly shaped speci-mens, or determined by the liquid displacementmethod.

5. Part 4: suggested method for determining axialswelling stress as a function of axial swelling strain

5.1. Scope

1. The test is intended to measure the axial swellingstrain necessary to reduce the axial swelling stress of aradially constrained rock specimen immersed in waterfrom its maximum value to a value which is acceptablein the particular application. It is intended for appli-cation to cases where analogous boundary conditionsprevail. The test is practicable only on purely argillac-eous specimens.

5.2. Apparatus

2. The apparatus16 is to include the following asschematically shown in Fig. 6.

(a) A stainless-steel ring for rigid radial restraint ofthe specimen ((1) in Fig. 6). The inner surface of thering is to be polished and smooth. The wall thicknessof the ring depends on its other dimensions and has to

be calculated based on these dimensions and the maxi-

mum lateral stress to be expected. Not more than 10ÿ4

radial strain is allowed. Thicknesses of between 5 and

10 mm are usually satisfactory. Several rings should be

available to ®t all desired specimen dimensions.

(b) Two porous plates ((2) in Fig. 6). The porous

plates should be made of a high modulus material.

Porous stainless-steel plates are most suitable.

Alternatively, stainless-steel plates into which a num-

ber of small holes (dia 0.1 mm) have been drilled are

also suitable. In the latter case, small channels con-

necting the small holes to the water supply are

required.

(c) One porous plate is to be on top of the specimen

and the other at its bottom. The lower plate is to have

a diameter approx. 5 mm greater than the outer diam-

eter of the specimen ring, and the upper plate has to

be of a size just ®tting the inside of the ring without

restraining its movement.

(d) A stainless-steel loading plate of the same bot-

tom diameter as the upper porous plate but slightly

conically shaped, and placed on top of the porous

Fig. 6. Apparatus for measuring the axial swelling stress as a func-

tion of axial swelling strain: (1) stainless-steel ring, (2) porous metal

plates, (3) stainless-steel loading plate, (4) container, (5) dial gauge

(attached to the bottom of container (4)), attachment not shown and

(6) loading frame.

16 The apparatus described here is essentially a modi®ed oedometer,

as used in soil mechanics. The di�erence and advantage of this par-

ticular apparatus is the possibility to use steel rings of various diam-

eters, depending on the diameter of the specimen. This reduces time

and e�ort for specimen preparation and lessens the risk of disturbing

the specimen.


plate. The loading plate has to be thick enough toensure rigid strain application ((3) in Fig. 6). For spe-cimen diameters of between 50 and 100 mm a 10-mmthick plate is adequate. An indentation in the center ofthe plate for placing the load transfer sphere (see (e)below) is required.

(e) A loading frame ((6) in Fig. 6), with suitable fea-tures to apply incremental loads up to a total load of10 kN. Direct loading or indirect loading via a leverusing lead plates are possibilities. The loading frametransmits the load to the top steel plate via a 2-cm di-ameter polished steel sphere.

(f) A mm dial gauge (or equivalent) with a sensitivityat 2.5 m attached to the bottom of container (4) anmounted in such a way as to measure compressionand swelling along the central axis of the specimen ((5)in Fig. 6).

(g) A container ((4) in Fig. 6) (dia 15 cm) for thespecimen assembly, which is ®lled with water to a levelabove the top of the specimen.

5.3. Procedure

3. (a) The test is to be conducted in an environmentwhere the ambient temperature can be maintained con-stant at 20228C.

(b) The thickness h0 of the specimen, which was pre-

pared as described in Part 1 (Section 2, Specimen prep-

aration) is to be measured in at least three locations

between specimen ends, to an accuracy of20.1 mm.

(c) The specimen diameter d is to be measured in at

least three locations along the circumference.

Measuring accuracy is again to be better than 20.1

mm.

(d) The mass of the specimen M1 is then to be deter-

mined to 0.1 g.

(e) The specimen ring is to be cleaned and its mass

M0 determined.

(f) The specimen is inserted into the ring. The speci-

men must ®t snugly into the ring.

(g) The apparatus is assembled. The ring with the

specimen is placed on the lower porous plate, followed

by the upper porous plate, the loading plate and the

sphere. The load frame is then placed on the sphere.

(h) The specimen is loaded in a stepwise manner up

to a load corresponding to a desired axial stress s. Astress level comparable to the overburden stress at the

sample location is reasonable. This load and the corre-

sponding ®nal compression of the specimen are

recorded (Fig. 7, curve l).

(i) The container is the ®lled with water to cover the

top porous plate.

(j) Initial swell heave is recorded (curve segment 3 in

Fig. 7).

Fig. 7. Axial stress vs. total axial strain: (1) compression curve (without water supply), (2) water applied at the stress sA (in this example=2

MPa), (3) swelling at the stress sA, (4) unloading to sB (in this example=1.5 MPa), (5) swelling at the stress sB, (6) matrix deformation strain

Des and (7) swelling strain Des.


(k) The axial load is reduced in consistent decre-ments17. It is usual to reduce the load by 50% in eachstep. However, other decrements can also be chosen.

(l) The swell heave for each load decrement ismeasured until no displacement can be observed forthe particular load decrement. The load decrement andthe displacement are recorded.

(m) Steps (k) and (l) are repeated down to a loadcorresponding to 25 kPa18. Complete unloading is notrecommended because upward bulging may occur pro-ducing displacements which are not representative ofswelling.

(n) The ring with the specimen is then to beremoved from the container (after removing of thecontainer water and unloading), the excess waterwiped o� and the mass M2 determined and recorded.For strongly swelling rock the container water isdrained o� before unloading. At this stage the speci-men condition is logged.

(o) The specimen with the ring is heated in an ovento constant mass at a temperature of 105228C.

(p) The specimen and the ring and is allowed to

cool in a desiccator. The oven-dry mass, M3 is deter-mined and recorded. Alternatively the specimen can beoven heated, without the ring.

5.4. Calculations

4. (a) The following test parameters are calculated:the area of cross section of the specimen, A, the axialstress s, the axial matrix deformation strain Des andaxial swelling strain Des.

(b) The area of cross-section A of the specimen iscalculated as

A � pd2

4,

where d is the specimen diameter.(c) The axial stress s is calculated as

s � N

A,

where N is the measured axial force.(d) The matrix deformation strain Des, which is re-

lated to the axial stress decrement, is calculated as:

Des � dsh0

,

where ds is the instantaneous axial displacement due

Fig. 8. Axial stress vs. swelling strain.

17 This procedure is expected to produce lower bound swelling stres-

ses for a particular swelling strain. The method is appropriate for

determining heave resulting from unloading.18 For applications in which the stress on the swelling rock is lower

than 25 kPa, such as foundations of light buildings or excavated

slopes, lower ®nal loads have to be selected.


to matrix deformation per decrement Ds and h0 theoriginal thickness of the specimen.

The swelling strain Des at each stress level is calcu-lated as

Des � ds

h0,

where ds is the axial displacement due to swelling perdecrement Ds and h0 the original height of the speci-men.

(e) Density, initial and ®nal water contents anddegree of saturation are calculated according to Ref.[2].




(b) Information on geographic origin, lithology, fab-ric and, if possible, mineralogy and pore water chem-istry of the sample and specimen.

(c) Date and method of sampling; date(s) of testing.(d) Method of sealing and storage.(e) Method of specimen preparation for testing.(f) Orientation of the specimen axis with respect to

specimen anisotropy, speci®cally with respect to bed-ding planes and relative to in situ directions.

(g) Dimensions of the test specimen.

(h) Density, water content, grain density and degreeof saturation of the test specimen before the swellingtest.


(j) Test temperature.(k) Speci®cations of water used for immersion.(l) A plot of axial stress vs. total axial strain similar

to Fig. 7. The plot has to distinguish between Des ((6)in Fig. 7), which is the instantaneous strain directly re-lated to the axial stress decrement through matrix de-formation, and Des ((7) in Fig. 7), which is the swellingstrain caused by adsorption of water. The total strainat a certain stress is thus

Detot � Des � Des:

(m) A plot of swelling strain vs. axial stress such asFig. 8. This graph is obtained by plotting the swellingstrain, Des for the corresponding stress decrements.The resulting curve can be used to estimate the poten-tial swelling strains which need to be considered in de-sign.

6. Final comments

. The methods are relatively simple and have beenextensively used in practice.

. Future development of laboratory testing will benecessary, particularly regarding 3-D testing.

. The maximum possible swelling stress developingfrom the transformation of anhydrite into gypsum isnot known at the present time. Swelling stresses upto 8 MPa have been reported from laboratory tests.

Acknowledgements

The Commission members responsible for preparingthese suggested methods were: C. Amstad,Switzerland, G. Anagnostou, Switzerland N. Bischo�,Switzerland; H.H. Einstein, USA; E. Fecker,Germany; L. Hauber, Switzerland; J.R. Kiehl,Germany; D. Kirschke, Germany; F.T. Madsen,Switzerland; G. Mesri, USA; R. NuÈ esch, Switzerland;H. Santos, Brazil; W. Steiner, Switzerland; B. VoÈ gtli,Switzerland.

Appendix A. Specimen preparation for rocks that caneasily break

(a) The intact specimen is trimmed into a sharp-edged, approx. 65 mm diameter and 20 mm tallhighly-polished stainless-steel con®ning ring. Thesample is hand-carved in a humidity-controlled room

Fig. 9. (1), (5)=bearings, (2)=upper adapter, (3)=trimming ring;

(4)=lower adapter and (6)=specimen.


using sharp and pointed (for instance, Bard-ParkerNo. 10) stainless-steel surgical blades.

(b) A slice approx. 30 mm thick is to be cut ¯atfrom an undisturbed cylindrical (or block shaped)sample. If necessary, the slice-ends are to be re®nished¯at and nearly parallel to each other using a sharp,straight edge.

(c) The slice is to be placed and centered on thelower adapter of a manual press (Fig. 9). The manualpress is modi®ed from a U-116 Field Classi®cationTester (Soiltest, Inc), using two adapters and bearingsso that the swelling rock slice can be rotated freelyduring the trimming process.

(d) After removing any rock from outside the ring,the trimming ring is to be pressed down in small incre-ments (generally less than 2 mm) using the manualpress. Prior to each increment the part of the specimenjust below the trimming ring is to be handcarved asclose as possible to the ®nal dimension but withoutundercutting, so that only a thin annular layer isremoved by the advancing ring. This is to be continueduntil the specimen completely occupies the 20 mm highring.

(e) The face of the specimen at the sharp end of thering is to be cut ¯at using a sharp, straight edge.

(f) For testing the specimen, height must be lessthan the ring height. A spacer approx. 5 mm thick isto be placed against the ¯at surface, and using themanual press the trimmed specimen is pushed out inthe direction opposite to the one it has been pushed in.

(g) The specimen is then to be cut ¯at at this oppo-site end using a sharp straight edge as it extrudes outof the ring, such that the desired specimen thickness isreached.

References

[1] Suggested methods for laboratory testing of argillaceous swelling

rocks. ISRM Commission on Swelling Rocks, 1989.

[2] ISRM Commission on Standardisation of Laboratory and Field

Tests. Suggested methods for determining water content, poros-

ity, density, absorption and related properties and the swelling

and slake durability index. In: Brown ET, editor. Rock charac-

terisation, testing and monitoring. Oxford: Pergamon Press, 1981

document No. 2, First Revision.


Testing Swelling Rocks 1999

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