The engineering description of chalk: its strength,
hardness and density
A.J. Bowdenl, T.W. Spink2 & R.N. Mortimore3
lMouchel Consulting Limited, West Hall, Parvis Road, West Byfleet, Surrey, KTI46EZUK
2Mott MacDonald Group, St Anne House, Wellesley Road, Croydon, Surrey, CRg 2UL UK
3School ol the Environment (Civil Engineering), University of Brighton, Moulsecoomb, Brighton,
Sussex, BN2 4GJ UK
The contribution on the subject from CIRIA (Lord
et al. 1994) uses a very similar scale and descriptive
terminology to that of Mortimore et al. but simplifies
the scale into four units and replaces the term'hardness'
with 'density'. Lord et al. argue that the scatter of the
intact dry density test results is too high to obtain the
Abstract
description of chalk for engineering purposes
is reviewed and recommendations are made for
a refined method for the field determination of
chalk strength, hardness and density. The proposed method incorporates field descriptions, the current
CIRIA intact dry density divisions and the strength terms
of BS5930:1999. The recommendations arise from work
on chalk tunnels where it was lound that the previous
methods of field assessment gave unreliable results.
Specific fieldwork was carried out to develop the proposed system on a wide range of Middle and Upper white
chalks in southern England.
Th"
I
I
I
accuracy implied by the more finely divided Mortimore
el a/. scheme. which has some subdivisions with an intact
dry density range of only 0.05 Mg/mr. The CIRIA scale
uses hand breakability and hammer breakability tests
for each density class.
The above publications have variously used the
terms 'strength' (Spink & Norbury 1990), 'hardness'
Keywords: chalk, engineering description, strength, hardness, intact
dry density
Following the investigations at Mundford (Ward et al.
1968) chalk was classified for engineering purposes using
a grading scheme based on fracture spacing, fracture
aperture, lithology, degree of weathering and hardness
(although the latter two terms were poorly defined).
Ward el al. had made it clear that the Mundford scale
was specific to the Mundford site which is an upland
area of Middle Chalk with the Melbourn Rock at the
base of the sequence investigated. However, the classification was widely used elsewhere in various types of
chalk and it became apparent that the hardness terms
were insufliciently defined and did not correlate well
with the Mundford grades. This raised problems such as
how to apply the classification.
This problem was resolved for most practitioners by
dropping the hardness term from the classification,
thereby defining the grades principally on fracture
spacing and aperture. This practice was formalized in a
paper by Spink & Norbury (1990) who gave ranges of
strength (instead of hardness) which were typicalof each
grade rather than being used to define the grade. The
strength terms used were those of BS 5930 based on the
breakability of the chalk, using hand breakability at low
strengths and hammer breakability at higher strengths.
At the same time Mortimore et al. (1990) defined a
sevenfold field 'hardness' scale for chalk and related it to
intact dry density. Their descriptive system used both
breakability and rock pick and rock pin penetration
criteria for each hardness class.
Quurterly Journal o/ Engineering Geobgy and Hydrogeology,35, 355
361
(Mortimore et all990) and'density'(Lord et al.1994)to
describe an inherent physical property of the intact
chalk material. In this present paper it is considered that
strength, hardness and density, as used in the field
description of the white Middle and Upper Chalks are
all related to the intact dry density and uniaxial compressive strength. Therefore, this paper uses the field
term strength/hardness/density to mean the same. single,
field parameter. Different relationships may apply to the
marly Lower Chalk, and possibly also to the Northern
Province Chalks.
It is now generally accepted that there is not necess-
arily an increase in strength/hardness/density with depth
or improving grade, as implied in the Mundford and
Spink and Norbury schemes, except where the
stratigraphy/sedimentology dictates this, as it does at
Mundford (Mortimore et al. 1990). Strength/hardness/
density is considered to be primarily dependent on
stratigraphy. This is supported by studies for the
Southwick Hill tunnel, Brighton where it has been
shown that the intact dry density is dependent on the
stratigraphic level within each bedding unit rather than
depth or weathering grade, see Figure l, (Bowden el c/.
1998). The Bastion Steps Beds and the chalk at the Old
Nore Beds/Splash Point Beds junction were at similar
depths at opposite portals. At this site solution features
and deeper weathering occurred exclusively in the lower
density chalks whatever the direction of slope of the
hillside. This leads to the conclusion that the variation
in the weathering depth is dependent, to a significant
degree, on the strength/hardness/density, rather than
vice versa.
1470-9236102 $l 5.00
e
2002 Geological Society
of London
BOWDEN ET AL.
356
the intact dry density typically by 0.05 to 0.10 Mg/m3.
Also, laboratory investigations showed that a block of
chalk 300 to 400 mm square typically had a range of
laboratory determined densities 0.05 Mg/m3 either side
of the mean density for the block, even when the
block was apparently homogeneous (Lamont-Black &
55
>)}
50
>D)
D>-}
:
45
40
E
6
a-
a aa
Mortimore, 1996). It was therefore considered that the
hardness/density could not be estimated with sufficient
accuracy from field penetration tests to justify the
sevenfold subdivisions of the Mortimore el a/. scheme.
a
35
-9
.9
30
CL
rE
E,,
/;
25
Channel Tunnel
G
.o
oDo
20
b>
F
On the investigations for the Channel Tunnel Rail Link
the CIRIA scheme was used by a large number of
geologists from four different contractors involved in the
logging of chalk trial pits, core and undisturbed samples.
15
B
B
*
'tb
't0
<F
\
5
1.5
1.6
'|'.7
,1.8
1.9
2.0
lntact dry density (Mg/m3)
>
<
.
Bastion Steps Beds
Meeching Beds
Peacehaven Beds
> Old Nore Beds
< Splash Point Beds
\Trend line
Fig. 1. Variation in intact dry density with stratigraphic
level for Southwick Hill tunnel, Brighton (from Bowden
et al. 1998).
Problems with the previous
descriptive schemes
Whilst working independently on tunnelling projects in
the SE of England the flrst two authors have tried to
work with the above descriptive schemes of chalk
strength/hardness/density whilst supervising a number
of other geologists engaged in chalk description and
classification.
Southwick Hi!!
On the Southwick Hill site the Mortimore et ql. scheme
was used to estimate hardness when logging excavations
and tunnel faces (Bowden 2003). It was found that there
was a wide variation between the geologists in their
interpretation of the Mortimore et al. descriptive terms
such as 'some penetration of the pick' and the size of the
rock pin that should be used, which was not deflned.
There was also an apparent miss-match between the
results from pick penetration and the manual breakability tests. The penetration tests gave a scatter of
results, with the estimated dry density typically up to
0.1 Mg/m3 either side of the laboratory measured mean
value. The pick penetration test was the most consistent
method of estimating hardness, but although relatively
consistent estimates could be made, they over estimated
Despite training of the loggers and supervision of
the logging, there was a poor correlation between the
visually assessed CIRIA density and the laboratory
determined intact dry density, with over half of the field
estimates indicating the wrong CIRIA density class. It
was also found that the CIRIA definitions for hand
breakability were incompatible with the hammer breakability terms which indicated stronger chalk than the
corresponding hand breakability terms.
These problems with the existing descriptive schemes
lor strength/hardness/density have led to the research for
the present paper, with the aim of finding an improved
method for the field assessment of strength/hardness/
density.
Fieldwork for
stren gt h/hard ness/density
assessment
The requirement of any field descriptive scheme is that it
should be capable of easy, consistent, repeatable use on
site, that it should be verifiable by laboratory testing and
that it should predict useful engineering properties
which can be related to engineering behaviour. Previous
experience with the use of the intact dry density test
shows that it can be related to many aspects of engineer-
ing behaviour and should form the foundation of the
scheme. The fourfold subdivision of density used in
the CIRIA scheme is considered to reflect significant
changes in engineering behaviour (Table 1) and has been
retained. The aim of the field tests described below is to
allow any logger, after a limited amount of training, to
be able to correctly identify the CIRIA density class the
majority of the time. Obviously, chalk that is borderline
may be misclassified, however, the field tests should not
be carried out as a replacement for the laboratory
determination of intact dry density, but as a supplement
to it.
ENGINEERING DESCRIPTION OF CHALK
Table
l.
357
Engineering behuviour relutcd to CIRIA chalk density class.
CIRIA density term
Earthworks
behaviour
Low densitv
The chalk readily
Medium densitv
High density
Very high density
The chalk behaves
like a rock and
requires rock
methods of
excavation when
encountered in layers
> lm thick
degrades to fines
under engineering
stresses, releasing
pore water and
The chalk does not
readily generate
The chalk behaves as
a moderately weak
putty if handled
correctly. Excavation
rock with a cemented
structure that does
not readily break
generating putty
plant and
with the correct
down in normal
earthworks
operations
compaction in a
single process is
required
Shallow loundations
Allowable bearing
(Lord ct ul. 1994\
pressure 225 kN/m2
Allowable bearing pressure 300 kN/m'?
(Grades A, B, C and Dc)
(Grade Dc)
240
kN/m2 (Grades
A, B and C)
For the current research intact dry density testing was
carried out on 40 chalk samples collected from both
in situ exposures and large diameter cores. covering
most of the range of densities found in the white Upper
and Middle Chalks of southern England. At
each
sample location the authors each assessed the strength/
hardness/density by as many
of the four field tests as
possible:
o The ease of breaking small lumps by hand
. The amount of penetration of the sharp pointed end
of a new geological rock pick
o The amount of penetration of the blunt pointed end of
a well used geological rock pick
e The amount of penetration of a 150 mm nail when hit
three times with a geological rock pick
It was found that the hand breakability varied significantly with the size and shape of chalk lump, not only in
terms of the thickness of the lump but also its length, as
this affected the leverage that could be applied. A
standard size of 30 to 40 mm thick, by 30 to 40 mm
wide, by 60 to 80 mm long was chosen, as the force
required to break it fitted with the existing BS 5930
(1999) hand breakability strength definitions. A few
moments spent shaping a lump of chalk to the required
dimensions significantly improved the consistency of the
results. This method was the only test that could be
carried out on small fragments of chalk from fragmented core or rock face samples. The standardized
breakability procedures are given in Table 2.
The sharpness ofthe point ofthe geological rock pick,
its shape, the hammer's total weight, the distribution of
weight in the hammer and the force of the swing, all
influenced the amount of penetration. A new, sharp pick
penetrated further than a well used pick with a blunted
end. An Estwing type rock pick rather than a chisel
headed geological hammer was used for consistency of
results (Fig. 2). The swing of the hammer was standard-
ized
to obtain
as constant
a force for each blow as
possible. The hammer was not raised further than ear
level when hammering an exposure at waist level and
the swing was from the elbow, not the shoulder, again
for consistency. The measured penetration test results
and corresponding intact dry densities are plotted in
Figure 3a, b.
The geological rock pick penetration test did not work
it tended to split the core. The nail
penetration test was preferred on large diameter core,
with the hand breakability test being used if only small
diameter core or non-intact core was available. A standard, new 150mm (6 inch) long nail was hit three times
well on core as
with the geological hammer, and the penetration measured. The hammer was swung through about 300 mm
and the reluctance to risk serious damage to ones hand
in the event of a missed hit was found to sufficiently
regulate the force of the blow. The test was most
successful when carried out on the ends ofa short length
of core resting on a concrete floor. Tests carried out on
the side ofthe core were less successful as the core had a
greater tendency to split. It was found that if the core
was struck whilst still in the core box, or on a bench, or
non-concrete floor, then some of the force of the blows
was lost, and the nail penetration was reduced by as
much as 25%. If a concrete floor is not available then
specific calibration of the nail penetration against intact dry density tests would be required, or the hand
breakability test should be used. The measured nail
penetration test results and corresponding intact dry
densities are plotted in Figure 3c.
The pick and the nail penetration methods were found
density,
but were not particularly precise, showing a significant
to be reasonable predictors of the intact dry
scatter
in the results. The trends are
seen most clearly
358
BOWDEN ET AL.
Table 2. Revised field identiJication procedures
CIRIA density term
for CIRIA chalk density
Low density
clusses
(
I)
High density
Medium density
Md*'
Very high density
Intact dry density (2)
<
Approximate UCS (3)
< 3 MN/m2
3-5 MN/m2
5
BS5930 strength term
Very weak and lower
end of weak
Upper end of weak
Moderately weak
Moderately strong
Ease ol breaking
lragments (9)
30 to 40 mm thick
30 to 40 mm thick
30 to 40 mm thick
lragments can be
fragments can be
broken in half using
both hands. but
cannot be crushed
between finger and
fragments cannot be
broken in half (4).
Cannot be broken by
hand. 100 mm
diameter lump can
be broken by a single
hammer blow when
held in the palm of
1.55 Mg/m3
crushed between
finger and thumb,
and remoulds to
lorm a putty (4)
1.55-1.70
thumb (4)
Mdrr'
>
1.95 Mg/m3
MN/m2
>
12.5
1.70-1.95
-
12.5
Only thin slabs
< l0 mm thick. and
corners and edges of
lumps can be broken
MN/m2
the hand (5)
with difficulty using
both hands
15 25 mm
6
> 30mm
Chalk splashes
1l
2 ll
> 35mm
Chalk splashes
18-35 mm
150 mm nail
penetration (6) (7) (10)
(12)
> 25mm
Used rock pick
penetration (7) (8) (l l)
(12)
New rock pick
penetration (7) (8) (l
l)
15mm
<6mm
Putty lormed around
nail
30 mm
mm
< 2mm
Gl8 mm
<6mm
(t2)
Notes: (l) The field procedures apply to the white chalks of southern England and to material that is > 90%n saturated. They may
not apply to grey marly chalks or northern province chalks, or where the chalk is < 90'2, saturated. Most rn situ chalk has > 90%
saturation, except where a face has been exposed for some time. Core or samples must be prevented from drying out prior to
logging. (2) Intact dry density should be measured by the method of BS1377:1990. (3) The relationship to uniaxial compressive
strength (UCS) is at natural moisture content. It is approximate and has been derived from Fig 4. (4) Fragments should be shaped
using a chisel headed hammer, paint scraper or chisel to be 30 to 40 mm thick, 30 to 40 mm wide and 60 to 80 mm long. (5) Extreme
hand pressure could break corners or thin slabs, but only at the risk ol a bruised thumb. The hammer blow should not be painlul
to the hand. (6) A new 150 mm (6 inch) standard carpenter's nail with a four lacetted approximately 40 degree point should be used,
and hit three times with a geological rock pick. The hammer should be swung through about 300 mm. The reluctance to risk serious
damage to the hand sufficiently regulates the force of the blow. Mark the penetration with the thumb nail, and measure with a mm
scale. Repeat the test several times. (7) A steel handled geological rock pick of the Estwing type or similar, of approximately 0.9 kg
total weight should be used. Hammers of signiflcantly different weight, or wooden handled hammers where most of the weight is in
the hammer head, should not be used. (8) The hammer should be swung from about ear level by moving the elbow only, not the
shoulder. Mark the penetration of the rock pick with the thumb nail. and measure with a mm scale. Repeat the test several times.
Protective glasses are recommended. particularly in low density chalk. (9) This method is particularly suited to logging small
diameter or poor quality core and samples where only small lumps are available. Repeat the test several times. (10) This method is
particularly suited to logging large diameter core (of approximately 100 mm diameter or more). A section of core about 100 mm
long should be taken out of the core box, and the ends squared off with a chisel headed hammer. paint scraper or chisel. The core
piece should be stood on its end on a concrete floor and the test carried out on the ends. The nail should be in the centre ofthe core
and should not break the core. Repeat the test several times avoiding previous nail holes. Il the core is tested in the core box or on
a soil surflace, bench or wooden floor. some of the energy is absorbed and the nail penetrations may be up to 25o/olowet, and would
require specific calibration against intact dry density tests. (l l) This method is particularly suited to logging in situ chalk in trial pits,
excavations or exposures. (12) The penetrations are obtained from the mean lines in Figure 3 and should be considered as
approximate guides only; there is a significant scatter in the results. All field tests should be supported by laboratory intact dry
density testing.
when plotting the log of the penetration. The pene-
in Table 2. These relationships have been based on a
trations indicated by the mean lines on Figure 3a, b, c, at
each of the CIRIA density boundaries are summarized
relatively small number of test results and may need to
be revised as more data becomes available. Also, it is
BOWDEN ET AL.
360
30
Low
Medium
Very High
High
N
E
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25
Vy
=
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20
(t,
o
o
.=
o
o
(u
V
V
a
V
15
VV
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a
V
CL
o
o
Moderately
Strong
a
10
.g
5
f
o
- aaY
Moderately
Weak
I
4r
GI
'=
12.5
a
V
od
a
-4r I _)_
e"ffi
5
3
1.25
0
1.4
1.5
1.6
1.7
1.8
1.9
2.0 2.1
lntact dry density (Mg/m3)
a
v
'
Southwick Hill, Brighton,
Hull, Humberside
North Kent
Sussex o
2.2
Weak
Very Weak
855930
Strength
Terms
Channel Tunnel Rail Link (Kent and London)
. Bell et al (mean values Yorkshire, Nortolk and Kent)
\equation of trend line UCS = 0.01{6 x e(3.58 x IDD)
Fig. 4. Intact dry density versus uniaxial compressive stren-uth.
times. In the field each penetration or hand breakability
result should be recorded, but on the log the CIRIA
density class derived from the average of the results
should be reported in words eg'medium density', or'low
to medium density' if the results are close to a density
boundary. However, common sense is needed when
averaging results. Some parts of the chalk succession
contain units of alternating denser and less dense material in beds 200 300 mm thick. Averaging results from
such beds may be misleading. In such cases the range
of density values found in each layer will provide
a more realistic estimate of the range of engineering
it is more usual to also determine natural moisture content, and hence degree of
saturation. In this case the chalk lumps should be
wrapped in several layers of cling film or aluminium foil
and placed in a sealed plastic bag or plastic tub. Cling
fllm alone has been found to be inadequate. The samples
should be tested within a few days, as otherwise they
may sweat and partially dry out. Sections of core that
are also to be used for strength testing require additional
physical protection and improved sealing, for example
by wrapping in aluminium foil and coating with wax
be determined. However,
impregnated muslin.
behaviour.
The field assessment of the CIRIA density class
should always be supported by laboratory determinations of intact dry density using the method of BS
1377 (1990) for the determination of saturated moisture
content. It should be noted that the BS 1377 (1990) test
method should strictly only be used on lumps about
75 mm across. If only smaller lumps are available
the more accurate test method of Lamont-Black &
Mortimore (1996) may be used.
The samples collected for laboratory testing do not
require special protection if only intact dry density is to
Relationship between intact dry
density and uniaxial compressive
strength
Data collected during a research project to investigate
the relationship between the point load test and uniaxial
compressive strength of chalk has shown a convincing
relationship between intact dry density and the uniaxial
compressive strength (Bowden et al. 1998). This data is
shown in Figure 4, together with data collected for the
ENGINEERING DESCRIPTION OF CHALK
(a)
100
\Lo*.
c
,\
E
c
.9
359
Med
\t
E
-
o
co
Very High
High
30
lE
11
t0
A.
{
J
.9
IL
J
a.,
!,
l
1.1
tl
2
1.6 1.8 2.O
2.2
2.4
lntact dry density (Mg/nP)
\/
(b)
100
150
mm nails
Lo\
\
E
E
o
noted that the majority of points falling outside a dry
density band about * 0. I Mg/m3 from the mean (shown
dashed on Fig. 3a, b, c) were from chalk that was less
than 9C.h saturated. The majority of in situ chalk has a
saturation of greater than 90ok, even when above the
water table. Saturations of less than 90ok are generally
only found on faces that have been exposed to drying
conditions for some time (as was probably the case in
this study), or in core that has not been adequately
prevented from drying out. Tests should therefore be
carried out on chalk in freshly excavated faces or on
fresh samples and core.
.E
o
o
High
Med
;t't.
Very High
35
I
rO
a'
18
t
10
CL
T
6
a'
.9
CL
!
o
P
zo=
1
1.4
1.6 1.8 2.O
2.2
2.4
lntact dry densigr (Mg/m3)
(c)
100
Summary of proposed method for
determination of
stren gth/hard ness/density
The results of the fieldwork are presented in Table 2 as
revised field procedures for identifying the CIRIA chalk
density classes. The notes in the table describe the field
procedures and are designed to achieve consistency. At
first sight the procedures may appear cumbersome, but
with a little practice, they soon become routine and easy
to apply. The inclusion of these procedures in normal
commercial logging will not add significantly to the
logging time. The scheme has been tested on the white
Middle and Upper Chalks of southern England. It is
suspected that the marly Lower Chalks, and possibly
also Northern Province Chalks, may show different
relationships.
It is recommended that when
(
ol
1
li
Fig. 2. Suitable rock picks (new and used) and
for the field assessment of chalk density.
I
t
e
o
o
a
using any of the four
procedures described here for field determination of the
CIRIA density class, the test should be repeated several
E
E
\
.t
tr
.9
6
E
o
co
A
Low Med
10
High
Very High
'.o
$
t
25
=G
z
6
a
E
E
o
ra,
1
1.4
1.6
1-8
2.O
2.2
2-4
lntact dry density (Mg/m3)
+
o
> 90% aaturation in situ / in cora, with sprcad
of results from the three authors
< 90% saturation in situ / in core
Fig. 3. Intact dry density versus penetration (log scale) lor (a)
used rock pick. (b) new rock pick and (c) 150 mm nail.
ENGINEERING DESCRIPTION OF CHALK
present study. The scatter of the data is highest for the
high and very high density Northern Province Chalks
(results from Hull and averaged results from Yorkshire,
Norfolk and Kent after Bell et al. 1990). The trend line
through the data can be used to obtain an approximate
correlation between intact dry density and uniaxial
compressive strength. The mean strength values corresponding to the CIRIA density boundaries are given in
Table 2.
From Figure 4 and Table 2 it should be noted that the
CIRIA high and very high density terms are equivalent
to the BS 5930 (1999) strength terms moderately weak
and moderately strong. However, for CIRIA low and
medium densities there is not a direct equivalence with
the BS 5930 (1999) strength terms, with the low/medium
density boundary falling in the middle of the BS 5930
(1999) weak strength range. Because of this lack of
equivalence the CIRIA density terms should be used
throughout
all chalk logging; the BS
strength terms can be given in addition,
if
5930 (1999)
required.
361
Acknowledgements. The authors gratefully acknowledge the
support ol the lormer Union Railways in sponsoring the
laboratory testing for this research and for allowing the use of
the Channel Tunnel Rail Link data. The data for Southwick
Hill tunnel is included with the permission of Mouchel
Consulting Ltd and the Highways Agency. with some of the
work reported being supported by Taylor Woodrow Civil
Engineering. Other data is included with acknowledgements to
the Mott MacDonald Group and Kent County Council.
References
Bplr-, F.G., Cnrpps, J.C.. EouoNos, C.N. & Curssnw. M.G.
1990. Chalk labric and its relation to certain geotechnical
properties.
In:
Bunr-eNu. J.B., Monrrlrone. R.N..
Rosnnrs, L.D., JoNes, B.L. & Consnm, B.O. (eds) Chulk.
Proceedings
of the
Internutional Chulk
Symposiuttr,
Brighton Polytechnic. Thomas Telford. London. 187 194.
BoworN, A.J. 2003. Tunnelling in tlte chalk oJ Southtick Hill.
Proceedings Symposium on Tunnelling in Chalk. in press.
BoworN, A.J.. LeuoNr-Blacr, J. & Ullvorr. S. 1999. Point
load testing of weak rocks with particular reference to
chalk. Quarterly Journul oJ Engineuing Geologv,
95 103.
Conclusions
The CIRIA intact dry density divisions have been
found to relate to engineering behaviour for the white
BS 1377 British srandard nrcthods of test jbr
soils
31.
/br dfil
engineering purposes, 2. British Standards Institution.
BS 5930 Code of'practice for site iwestigotion,\. British Stand-
Middle and Upper Chalks and can be determined with
reasonable accuracy in the field using the standardised
procedures given in this paper. There is a good correspondence between the CIRIA medium/high and high/
very high density boundaries and the BS 5930 (1999)
ards Institution.
LelroNr-Br-acx, J. & Monrrnonr, R.N. 1996. Determination
ol the intact dry density of irregular chalk lumps: a new
method. Quurterly Jourrutl of Enginearing Geology, 29,
strength boundaries. However, this correspondence does
Funders Report/CP/13. CIRIA Project Report.
Monrrrvronr. R.N.. Rosrnrs. L.D. & JoNes. D.L. 1990. Logging olchalk lor engineering purposes. 1r.' BunraNo. J.B.,
not hold for the low/medium density boundary. Therefore, it is recommended that CIRIA density classes
should be assessed in all chalk descriptions; the BS 5930
(1999) strength can be given in addition, if required.
Field assessments of CIRIA density class should be
supported by laboratory determinations of intact dry
density. The assessment of CIRIA density class should
be carried out as part of a full engineering geological
description of the chalk generally following the CIRIA
procedures, but as amplified by Spink (2002). The chalk,
as seen in boreholes, trial pits or exposures, must be
evaluated within the broader picture of the geology of
the site including the stratigraphy, weathering profile
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a