A study of the correlation between soil-rock

sounding and column penetration test data

Johan Fransson

Master of Science Thesis 11/04 Division of Soil and Rock Mechanics

Department of Civil Architecture and the Built Environment Stockholm 2011

© Johan Fransson 2011 Master of Science Thesis 11/04 Division of Soil and Rock Mechanics Royal Institute of Technology (KTH) ISSN 1652-599X

Preface This is the final thesis for my master degree as a civil engineer at the Royal Institute of Technology, Stockholm, Sweden. The idea for this thesis came from my supervisor Professor Stefan Larsson who has many years experience working with lime-cement columns both in his profession and at an academicals level. I worked closely with D. tech student Niclas Bergman, who helped me with general input, knowledge and his time. The thesis would never have been finished without the help from lecturer Pär Näsman at the Royal Institute of Technology, who helped with the statistical aspects of this thesis, geotechnical engineer Gunnar Nilsson at NCC Teknik, who gave me some useful input about the total sounding method and its use with lime-cement columns, Anders Lundman at LCM, who not only helped with some well needed field trips but found one further test site to sound, field geotechnical engineers Hans-Ola and Ingemar Engström at Tyréns, conducted most of the soundings and came with great ideas and lastly my closest family, namely Thord, Inger, Shana and Emmin gave me moral support and help with some language aspects. Johan Fransson, Stockholm 2011.

Abstract Lime-cement columns have been used in Sweden to improve poor soil conditions since the 1970’s. The method is inexpensive and flexible, but is difficult to test since the columns are manufactured in-situ. Many test-methods have been developed for testing the column strength during the years. Most of them need to be evaluated using an empirical correction-factor known as the cone factor. The column penetration test, KPS, is the most commonly used method in Sweden, it is considered to be reliable since a large part of the column cross-section is tested. The problem is that the probe easily deviates out of the column to the softer surrounding soil. Today a pre-drilled guiding-hole, a soil-rock sounding, helps the probe to stay vertical. Although the soil-rock sounding is commonly not used for evaluation of column strength, the penetration resistance is recorded. A visual comparison between the plotted penetration resistances from the two methods shows similarities in both hard and soft areas of the columns. The relation can be measured using statistics, such as the correlation coefficient. A strong correlation was also found, suggesting that a similar equation used to evaluate the undrained shear strength from the column penetration tests can be applied with the data from the soil-rock soundings. The statically pushed column penetration test probe and the rotated soil-rock sounding bit bore are likely to cause different failure modes in the column. This means that different empirical cone factors are needed when the undrained shear strength is evaluated. By evaluating the ratio between the cone factors of the column penetration test and the data from the soil-rock soundings from three sites, E-road E18 north of Stockholm, E-road E45 outside Gothenburg and at a construction site at Lidingö, the following aspects of the ratio was investigated: if the ratio was site-specific; the sensitivity to the binder content; the sleeve friction and; the sensitivity to rotational speed and rate of penetration. Average columns formed from the penetration resistance at depth from each site were used during the evaluations. The Swedish geotechnical society has standardised two methodologies that can be used for pre-drilling. The soil-rock sounding methodology which has no fixed rate of penetration or rotational speed, and the total sounding methodology, based on the Norwegian total sounding methodology which has fixed rate of penetration and rotational speed. The latter is to prefer when comparing results between sites. To remove the sleeve friction, the data from the soil-rock soundings needed to be de-trended. The amount of de-trending needed to find a constant cone factor varied at the sites between 0.5 kN/m and 1.0 kN/m. This however caused high interference, partly from scaling the variation. The cone factor for the total sounding methodology was found to be between 0.30-0.45 times the cone factor for the column penetration test.

Sammanfattning Kalkcementpelare har använts i Sverige för att förstärka dåliga markförhållanden sedan 1970-talet. Metoden är billig och flexibel, men skapar sämre möjligheter för kontroll eftersom pelarna skapas in-situ. Många olika testmetoder har utvecklats för att kontrollera pelarnas hållfasthet under åren, men gemensamt för de flesta är att de måste utvärderas med en empirisk korrektionsfaktor kallad bärighetsfaktorn. Kalkpelarsonden, KPS, är den vanligaste metoden i Sverige. Den anses tillförlitlig eftersom den provar en stor area av pelaren. Problemet är att den lätt styr ur pelaren till den kringliggande jorden som är betydligt lösare. Idag förborras ofta sonderna med jord-bergsondering för att de inte ska styra ut. Trots att Jb-sonderingen idag inte används för att utvärdera KC-pelare registreras sonderingsmotståndet. En visuell jämförelse mellan det plottade sonderingsmotståndet från KPS:en och dess förborrning visar tydliga likheter vad gällande hårda och mjuka partier i pelarna. Likheten kan jämföras statistiskt med hjälp av korrelationskoefficienten. En stark korrelation hittades, vilket tyder på att en liknande ekvation som används för att utvärdera hållfastheten från KPS:en kan appliceras på data från Jb-sonderingen. Den fysiska skillnaden mellan metoderna där KPS:en trycks statiskt och jord-bergsonderingens borrstål roterar betyder troligen att olika brottsmoder inträffar i pelaren. Detta i sin tur betyder att den empiriska bärighetsfaktorn som används då pelarnas odränerade skjuvhållfasthet utvärderas sannolikt är skilda från varandra. Genom att utvärdera förhållandet mellan KPS:ens och Jb-sonderingens bärighetsfaktorer från tre olika platser, E18 vid Stockholm, E45 utanför Göteborg samt ett bostadsområde på Lidingö, kunde följande aspekter på förhållandet undersökas: hur platsspecifikt det var, känsligheten till bindemedelsmängd, påverkan av mantelfriktion samt rotationshastighet och sjunkhastighet vid borrandet. Då bäst korrelation mellan metoderna fanns när medelpelare skapades från penetrationsmotståndet över djupet användes dessa vid utvärderingen.. SGF har två standarder som används vid förborrning. Jb-sondering som saknar fast sjunkhastighet och rotationshastighet, samt totalsonderingen, baserad på den norska totalsonderingen, som har fast sjunkhastighet och rotationshastighet. Den sistnämnda är att föredra när data ska jämföras mellan olika platser. För att kompensera för mantelfriktion måste sonderingsmotståndet från förborrningen avtrendas. Mellan 0,5 kN/m och 1,0 kN/m behövde avtrendas för att få ett konstant förhållande mellan bärighetsfaktorerna för Jb-totalsonderingen och KPS:en, detta skapade dock stora störningar, bland annat eftersom variationen förstorades upp. Bärighetsfaktorn för Jb-totalsonderingen var mellan 0,30–0,45 gånger bärighetsfaktorn för KPS:en.

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Contents Introduction ............................................................................................................................ 11

Lime-cement columns ............................................................................................................ 13

Production ............................................................................................................................ 13

Testing methods ................................................................................................................... 14

Column penetration test and pre-drilled column penetration test (KPS) ......................... 15

Cone penetration test (CPT)............................................................................................. 16

The total sounding method (Jb-total sondering) .............................................................. 17

Test sites .................................................................................................................................. 19

E-road E18............................................................................................................................ 19

Residential area at Lidingö, Stockholm ............................................................................... 20

E-road E45............................................................................................................................ 21

Methods ................................................................................................................................... 23

Statistical analysis ................................................................................................................ 23

Coefficient of variation .................................................................................................... 23

Correlation and correlation coefficient ............................................................................ 24

Null hypotheses ................................................................................................................ 25

Hypothesis: the population correlation coefficient is zero........................................... 25

Confidence intervals for the correlation coefficient..................................................... 26

Hypothesis: two samples have an equal mean-value ................................................... 27

Individual columns ............................................................................................................... 27

Average column ................................................................................................................... 28

The cone factors ................................................................................................................... 28

Deviating column penetration probes .................................................................................. 28

Evaluating the ratio of cone factors on three sites................................................................ 29

De-trending........................................................................................................................... 29

Results and discussion............................................................................................................ 31

Previous results from the use of soil-rock sounding ............................................................ 31

The E18 site.......................................................................................................................... 31

Low-correlating columns ................................................................................................. 33

Forming an Average Column........................................................................................... 34

The Lidingö site ................................................................................................................... 35

The E45 site.......................................................................................................................... 36

The ratio of the cone factors................................................................................................. 40

De-trending for sleeve friction ......................................................................................... 40

The effect of different binder content............................................................................... 42

Summary .............................................................................................................................. 43

References ............................................................................................................................... 45

Appendix A – tested columns at E18 .................................................................................... 47

Appendix B – the evaluated undrained shear strength at Lidingö.................................... 51

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11

Introduction The need to develop less suitable areas, e.g. areas with poor soil conditions, such as low

bearing capacity, creates geotechnical challenges. Piling with wooden-, steel- or concrete-

piles is an option for buildings with a limited surface area. Roads and railroads have a far

greater spatial extent which makes the majority of them unsuitable for piling. On top of this

roads are commonly located in low-points, and those areas are in south of Sweden often

covered by a layer of clay with low bearing capacity. This produced the lime-column method

in the early 1970’s (Larsson 2005).

The mixing process when manufacturing the lime-cement columns are very complex (Larsson

2005). It involves many phases and factors that affects the result. Because of this it is not

possible to estimate the strength of the columns prior to execution. Different test methods

have been developed during the years. In common for most in situ tests is that they need

empirical correlation between measured penetration resistance and true shear strength

(Liyanapathirana and Kelly 2010). There is however still uncertainties about this correlation

(Axelsson 2001). Absolute measured shear resistance may be obtained from unconfined

compression tests or triaxial tests (Liyanapathirana and Kelly 2010). Since it is neither

reasonable nor economically feasible to test entire column-sections at labs, these tests are

performed on small samples that are likely not representing the entire column.

The most commonly used method for testing the strength of lime-cement columns in Sweden

is the pre-drilled column penetration test (Larsson 2006, Axelsson and Larsson 2003), The

reason is the large volume tested and the simplicity of the test. A special developed probe that

spans almost the entire diameter of the column is pushed down into the column. This design

of the probe is believed to reflect a better interpretation of the entire column width. The test

can be performed in two manners, either by recording the resistance at the surface, meaning

that the sleeve friction is also incorporated into the reading, or by using a modern cone

penetration probe integrated with the column penetration probe which records only a small

sleeve friction from the probe.

The big drawback with the column penetration test is that the large probe easily deviates to

the surrounding soil. Axelsson and Larsson (2003) and Larsson (2006) suggest that the

maximum depth at which the column penetration test can be utilised is as little as 8 meters

even with columns with the modest undrained shear strengths of 150 kPa. Some methods have

been suggested to deal with this problem, the reversed column penetration test have been

developed where the probe is been pulled up through the column. The method was reviewed

by Axelsson and Larsson (2003), which concluded that the installation of the probe disturbed

the column why the evaluated results likely is not representing the surrounding columns and

the usage of the reversed column penetration test in Sweden has since decreased. Another

solution is to drill a guiding hole for the column penetration probe. By doing this, columns

with a length of 12 to 15 meters and undrained shear strength of 300-350 kPa can be tested

(Ekström 1994, Larsson 2006). Additional pre-drilling of the tests significantly increases the

time consumption when testing, which turn increases the costs. Soil-rock sounding, in Sweden

known as Jord-bergsondering is commonly used as pre-drilling.

A subjective visual comparison between the recorded penetration resistance from the column

penetration test and recorded penetration resistance from the soil-rock soundings shows many

similarities concerning the resistance at depth. A report by Ekström (1994) concluded that

soil-rock sounding could not be used to evaluate the strength of the columns. Ekström also

suggest that further special sounding in the bores could give some indication of the strength of

12

the columns. A more recent study (Jelisic and Nilsson 2005) examined the possibility to use

the data from the pre-drilling, which was performed according to the total sounding

methodology to evaluate the strength of the columns. The study concluded that harder and

softer areas correlated between the two methods when average columns were formed.

However the individual columns showed poor correlation.

Nilsson (2008b) later re-examined this as an internal report for the Swedish Transport

Administration, formerly known as Vägverket in an internal report. The report is unpublished,

but with permission from the author it is summarized in the results section.

In this thesis the relation between the recorded penetration resistance from the soil-rock

sounding and the penetration resistance from the column penetration test has been evaluated

using statistics. Data from three sites was used. The idea was that the undrained shear strength

of the columns could be evaluated via the penetration resistance from the soil-rock sounding

with the equations used with the column penetration tests. The statistical evaluation included

the coefficient of correlation to determine the relation, coefficient of variation to determine

the variability and null hypothesis to make conclusions objectively.

If a sufficiently good correlation was found, the results from the soil-rock sounding could be

used as a complement to the column penetration test for harder and longer columns where it is

not possible to use the column penetration test. However the different failure modes of the

column concerning a stationary probe or a rotating drill probably results in different cone

factors for the two methods. This reasoning assumes that there exists a significant relation

between the penetration resistance from the soil-rock sounding and the shear strength in the

column.

A relation between the cone factors, used to evaluate the strength of the columns, from the

column penetration test and the soil-rock sounding was compared between a test site at E-road

E18, just north of Stockholm, one test site at E-road E45 outside Gothenburg and one test site

at a construction project at Lidingö in Stockholm.

The Swedish soil-rock sounding (SGF 1999) does not suggest a rotational speed and rate of

descent. This made it difficult to compare the penetrations resistance from different columns,

since the penetration resistance likely depends on both rotational speed and rate of

penetration. The total sounding methodology (SGF 2006), which is mainly based on the soil-

rock sounding however have both fixed rotational speed and rate of penetration. The pre-

drilling was performed according to the soil-rock methodology at the E45 site and according

to the total sounding methodology at the E18 site and the Lidingö site. This indicated whether

the rotational speed and the rate of penetration had a major impact on the ratio of the cone

factors.

Because more and more emphasis is put into the use of probability based design, for instance

with the introduction of Eurocode 7, and thereby taking the variability into consideration, the

variability with respect to the penetration resistance was evaluated. The variability is

important also when deciding how many column that needs to be tested in a control program.

The variability with respect to the coefficient of variation was compared between the column

penetration test and the soil-rock sounding.

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Lime-cement columns The lime-column method, also known as the deep mixing method DMM, was developed in

Sweden and Japan in the 1970´s (Larsson 2005). In the beginning lime alone was used as

binder in Sweden, but later cement was added to the mix to construct harder columns

(Larsson 2006). The methodology can be divided into mainly two sub-groups, the wet method

and the dry method. The wet method was developed in Japan in the mid 1970’s. The dry

method is often divided into the Japanese- and the Nordic method (Larsson 2005).

The dry method has solely been used in Sweden (Larsson 2006). It is most suitable for soft

soils with a high natural water-content. The lime-cement mix is distributed into the soil

through a mixing tool using pressurized air. The wet method uses a lime-cement slurry mixed

above surface and pumped down to the mixing tool (Larsson 2005 and Larsson 2006). The

wet method can be used in soils with lower natural water content and the slurry can have

higher cement content (Larsson 2006).

Production

Specialised equipment is used to manufacture dry-mix lime-cement columns. The machine is

usually based on a large excavator with a high boom (figure 1, left). The boom holds the long

kelly bar with a mixing tool attached at the bottom. The mixing tool consists of wings or

paddles covering the width of the column.

The lime-cement binder is normally premixed at the factory and transported to the worksite as

a bulk cargo in a trailer. A smaller quantity is loaded onto the holding wagon (figure 1, right).

It is there kept under pressure between 200 and 1000 kPa (Larsson 2005) and fed to the

excavator using a pressure hose. The compressed air forces the binder down through the Kelly

bar and is emitted from the mixing tool above the paddles.

The kelly bar is rotated and pushed to the desired depth of the column without any binder

being incorporated. The rotation is then reversed and the speed is increased to about 150-200

rpm (Larsson 2005) and incorporates the binder into the ground, while the kelly bar is

retrieved at a speed of about 20-25 mm/s.

During the mixing process, depth, retrieving-rate, rotational speed, incorporated amount of

binder as well as binder remaining in the holding wagon are measured and monitored

(Carlsten 2000). The data from every column is recorded in a log-file.

14

Figure 1. Lime-cement column production by LCM at Lidingö, Stockholm 2010.

Testing methods

Testing, sometimes known as quality assessment, can be divided into both testing that the

design is fulfilled and to ensure the manufacturing process (Larsson 2005). Ensuring the

manufacturing process is however not further discussed in this thesis. The aim of the columns

determines which parameters are to be tested (Axelsson 2001). Axelsson also implies that

almost all lime-cement columns in Sweden are used in mechanical problems, e.g. settlement-

reduction or increased soil-stability, where the strength properties are of great interest

(Larsson 2005), however there are also hydrological problems or environmental problems

(Axelsson 2001) where permeability might be of greater interest. The undrained shear

strength is the major parameter used to describe the strength of the columns (Larsson 2005).

A wide range of special probes have been developed to evaluate the undrained shear strength.

The most common test methods for soft to semi-hard columns in Sweden are according to

Larsson (2006);

• Column penetration test (KPS)

• Pre-drilled column penetration test

• Reversed column penetration test (OPS)

• Pre-installed reversed column penetration test (FOPS)

• Vane tests

And for harder columns

• Cone penetration test (CPT)

These methods are thoroughly described in The Swedish Deep Stabilizations Research

Centre’s Rapport 17 (Larsson 2006). This thesis focuses on two testing methods, the column

penetration test and the total sounding method. The column penetration test is performed

using a cone penetration probe, CPT, integrated with the column penetration probe.

15

Column penetration test and pre-drilled column penetration test (KPS)

The column penetration test, in Sweden known as traditionell pelarsondering, kalkpelarsond

or KPS, is most widely used test method for lime-cement columns in Sweden (Larsson 2006).

It can be applied for 500 – 800 mm diameter columns, with a length of 8 meters and a

maximum undrained shear strength of 150 kPa. When harder or longer columns are tested, the

probe often deviates from the column. If a guiding hole is pre-drilled it is possible to test

longer columns with a maximum undrained shear strength of 300 – 350 kPa (Axelsson 2001,

Larsson 2006). The probe is formed with two large wings that interact with almost the entire

width of the column (figure 2, left). The width of the probe is usually 100 mm less than the

diameter of the column. The probe to the left in Figure 2 is used with diameter 600 mm

columns and has a width 500 mm.

Figure 2. Column penetration test probe (left), CPT probe (right).

The probe is pushed down with a constant rate of 20 mm/s ± 20 % and the penetration

resistance is registered (Carlsten 2000). If the penetration resistance it measured at the surface

a reduction is have to be made for the sleeve friction, otherwise the strength of the columns

will be overestimated (Axelsson and Larsson 2003). A more modern version of the column

penetration test utilising the cone penetration test probe, CPT, integrated with the column

penetration probe is sometimes used. The penetration resistance is recorded at the tip of the

probe. Because of this almost no sleeve-friction is recorded when using a CPT probe. The

undrained shear strength is evaluated using equation (1) (Larsson 2006).

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Equation 1. Evaluating the undrained shear strength using KPS.

(1)

c

fuN

AFc =

Where

=fuc Undrained shear strength (Pa)

=F Probe resistance force (N)

=A Probe area (m²)

=cN Empirical cone factor (-)

The empirical cone factor represents the correlation between the recorded force and the shear

strength of the lime-cement column. The equation is simplification of the equation for the

Swedish Geotechnical Institutes Iskymeter, a sounding method developed for soft soils

(Axelsson 2001). A rigorous calibration of the Iskymeter was performed in Sweden between

the 1930´s and the 1960´s. Axelsson and Larsson (2003) suggests a cone factor between 10

and 15.

Cone penetration test (CPT)

Cone penetration test uses a conic shaped probe that measures the cone penetration resistance

and the local unit side friction (figure 2, right). It can be used on harder columns than the

column penetration test, but a much smaller part of the column is tested (Larsson 2006). The

CPT also has the disadvantage of easily deviate from the column.

The undrained shear strength can be evaluated using one of the equations (2), (Larsson 2006).

If the pore-water pressure is measured, with a Piezocone penetration test CPTU, the measured

point pressure can be corrected to the total point pressure. Then the left equation is used.

Otherwise the right equation is used.

Equation 2. Evaluating the undrained shear strength using CPT.

(2)

kt

vt

fuN

qc 0σ−

= or

c

vc

fuN

qc 0σ−

=

Where

=fuc Undrained shear strength (Pa)

=tq Cone penetration resistance corrected for

pore water pressure effects (Pa)

=0vσ Initial total vertical overburden stress at the depth

under consideration (Pa)

=ktN Empirical cone factor for point resistance (-)

=cq Cone penetration resistance and the local unit side

friction (Pa)

=cN Empirical cone factor for point resistance (-)

17

The empirical factors ktN and cN are fairly uncertain for stabilized soil. Porbaha, Yamane

and Taguchi (2001) suggest empirical factors between 18 and 23. Larsson (2006) states that

values between 15 and 25 have been suggested for normal lime-cement columns and values

up to 30 have been recommended for hard columns. The large uncertainties concerning the

cone factors have been pointed out for instance by Larsson (2005).

The total sounding method (Jb-total sondering)

The total sounding method, in Sweden known as Jb-total sondering, is based on the

Norwegian total sounding method that was developed in the 1980´s (SGF 2006). It is a further

development of the Swedish soil-rock sounding 2nd

class. The difference between the

Norwegian total sounding method and the total sounding is that the rate of penetration was

lowered from 50 mm/s to 20 mm/s (SGF 2006), which is the same descent that is suggested

for the CPT by the Swedish Geotechnical Society. The requirement to record the pressure of

the spool medium was also removed.

The sounding is performed with a constant rate of penetration of 20 mm/s and a constant

rotational speed of 25 rpm (SGF 2006). When the drill-rig has reached its maximum

penetration resistance, i.e. compressive force capacity, usually 10-30 kN, hammer-drilling is

used. For softer lime-cement columns in Sweden hammer-drilling is not necessary since 10

kN of penetration resistance corresponds to a shear strength higher than most lime-cement

columns when a 57 mm drill bit is used.

Figure 3. A button bit bore, 57 mm diameter.

18

19

Test sites

E-road E18

The initial statistical analysis was based on data from the E-road E18 between Hjulsta and

Kista just north of Stockholm. The geotechnical data for the site is presented in table 1

(Karlsson 2008).

Table 1. Geotechnical data from the test site at E-road 18. Layer Level Undrained

shear strength Senstivity Natural water

content Liquide limit

Surface +8 m

Clay +7 m 30 kPa 4 70 % 80 %

Clay +6 m 9 kPa 3 55 % 50 %

Clay +5 m 12 kPa 5 >80 % > 80 %

Clay +3 m 9 kPa 6 60 % 50 %

Non-cohesive soil

+1 m

Bedrock -4 m >

A test-area of 15 x 15 meter was selected for testing. The columns were placed in a grid

pattern with a spacing of approximately 1 m. The 600 mm diameter columns were

manufactured with a binder content of 29 kg/m, 25 mm/s retrieval rate and a 100-200 rpm

rotational speed. Thirty randomly selected columns were tested using pre-drilled column

penetration tests (figure 4). The column penetration test was carried out using a CPT probe

integrated with the 500 x 15 mm column penetration probe. Penetration resistance used while

drilling and while pushing the column penetration probe was recorded to data-logs. The

limited area made it possible to assume that the properties of the soil were approximately

homogeneous.

Figure 4. Testing in progress at E18, March 2010.

20

The guiding holes were drilled according to the total sounding methodology (SGF 2006) with

a 57 mm button bit drill, a rate of penetration of 20 mm/s and a rotational speed of 25 rpm.

Great emphasis was however not put on maintaining the rotational speed which varied

between 20 and 30 rpm, with a total average of 26.2 rpm. During testing all columns were

between 16 and 20 days of age.

Residential area at Lidingö, Stockholm

JM AB has developed a residential area at Lidingö, north of Stockholm. LCM has performed

the ground improvements. Lime-cement columns were installed to support the access roads

during the later construction. Two test groups of four columns each were conducted in close

proximity. The 600 mm diameter columns were manufactured using an average binder

content of 23.5 kg/m and a rotational speed of 200 rpm. The columns were tested using pre-

drilled column penetration test. The pre-drilling was performed according to the total

sounding methodology and the column penetration test was performed using a CPT probe

integrated in the column penetration probe. During the testing all columns were between 18

and 24 days old. It was also made possible to evaluate the sleeve friction from the total

sounding tests. The total sounding methodology (SGF 2000) suggests that the drill can be

lifted 0.5 m with constant rotational speed of 25 rpm and retrieval rate of 20 mm/s while the

pulling resistance is registered, however this was not possible due to software limitations,

instead the drill was lifted about 0.5 meter and pushed down a second time. The penetration

resistance was then recorded over a distance of 0.5 meter, and an average sleeve friction per

meter was calculated. Table 2 presents the geotechnical data from the site (Bard 2007).

Table 2. Geotechnical data at Lidingö Layer Depth Undrained shear

strength Senstivity Natural water

content

Filling ~1,5 m - - -

Clay 2 m 13 kPa 20 >80 %

Clay 3 m 12 kPa 24 76 %

Clay 5 m 15 kPa 20 62 %

Clay 7 m 20 kPa 20 65 %

Non-cohesive soil 10 m - - -

Bedrock 11 m - - -

21

E-road E45

The Swedish Transport Administration was upgrading the existing roads and railroads on E-

road 45 from Gothenburg to Trollhättan (Wahlqvist 2010). The road was heavily used and

out-dated. The data used was taken from a pre-production test area. The geotechnical data for

the test area is presented in table 3.

Table 3. Geotechnical data from E-road 45. Layer Level Undrained

shear strength Senstivity Natural water

content

Surface +2 m

Clay 0 m 12 kPa 11 100 %

Clay -2,5 m 15 kPa 31 92 %

Clay -5 m 17 kPa 30 73 %

Clay -7,5 m 20 kPa 28 72 %

Clay -10 m 18 kPa 33 60 %

Clay -12,5 m 16 kPa > 40 70 %

Clay -15 m 18 kPa > 40 68 %

A total of 21 columns were tested to evaluate the relation between the cone factors for the

column penetration test and the soil-rock sounding. The area tested had three different binder

contents that were tested. The binder content was 25-, 30- and 35 kg/m, with 7 columns each.

All of the columns were manufactured with a 600 mm diameter and a retrieval rate of 20

mm/s. The binder type was Lime-cement 50/50. The columns were all tested at an age

between 12 and 16 days using pre-drilled column penetration tests. A column penetration

probe with an integrated CPT probe was used. The pre-drilling was performed using soil-rock

sounding (SGF 1999). It was performed with a rate of penetration of 30-40 mm/s until a

penetration resistance of approximately 8 kN was reached, the rate of penetration was then

lowered to prevent the drill rods from bending. Full rotational speed was used, which was

about 50 rpm. The rotational speed dropped gradually as the sleeve friction increases by

depth. During the pre-drilling a 58 mm drill bit was used.

22

23

Methods The data from the test sites was statistically evaluated to find the relation between the data

from the column penetration test and the data from the soil-rock sounding. Using statistics, it

was possible to quantify the relation. The use of a statistical tool known as null hypotheses

helped to change the subjective conclusions to objective conclusions.

Before the evaluation the data was prepared using a visual inspection. The aim was to find

singularities that came from changing drill rods. When the drill rods were changed, the data-

log was paused and the first value was often almost zero when the drilling resumed. This was

manually corrected.

The recorded resistance from both methods was synchronized at depth. The synchronization

can be done by manually by visually lining up the data to match high strength areas and low

strength areas. The correlation coefficient can also be calculated before and after shifting one

data pair up or down. In this thesis the visual synchronization was primarily used, but when a

visual interpretation was not possible the second method was utilized.

Statistical analysis

Some assumptions were made to make the statistical analysis possible. The data was firstly

assumed to be normal distributed with a mean and a standard deviation. Secondly the data in

the distribution was independent and random. It is an empirical fact that many physical

quantities are normal distributed. (Blom et al. 2005). A common way to test for normal

distribution is to use the Kolmogorov-Smirnov one sample test. Although the test is good for

smaller data series it will not give a reliable answer for large data sets. The central limit

theorem states that the distribution of X is approximately normal with the mean µ and

variance n2σ when n is large (Johnson 2005). The distribution is normal when n is as low

as 25 or 30. Since n in this case was much more than 30, it was assumed that the data was

normal distributed. The data was also visually evaluated using histograms generated with

PASW. The soil is likely not independent, there is a spatial correlation, which has earlier been

investigated in a master thesis by Nilsson (2008a), but since the majority of the evaluation in

this thesis was performed on average columns the assumption about randomness and

independence was valid.

The large amount of data made it difficult to calculate the statistics by hand why the statistical

calculations were made in PASW Statistics 18 (formerly known as SPSS) and Microsoft

Excel.

Coefficient of variation

The variation gave some indication of a measured value relative to the entire population. A

low variation indicated that the population was uniform and any measured value was a good

approximation of the population mean. The standard deviation is an absolute measurement of

the variation, hence it depends of the scale of measurement (Johnson 2005).

The coefficient of variation, CoV is a measurement of the relative variation of a dataset

compared to the mean value. The CoV gives the standard deviation as percentage of the mean

value, see equation (3). In this thesis the CoV was evaluated as a moving average of 0.5 m on

an average column formed from all columns at a test site.

24

Equation 3. Coefficient of variation (3)

%100⋅x

s x

Where

xs = sample standard deviation

x = sample mean

Correlation and correlation coefficient

Correlation is a measurement of the relation between two data series. It is used in science to

understand how different physical quantities and phenomena relate. In this thesis the

relationship between the measured penetration resistances from the two tests, the column

penetration test and the soil-rock sounding were investigated. When a correlation is found

between two data series where there are no obvious relation a third variable, called a lurking

variable (Johnson 2005) causes the correlation. This means that the two data sets have

variables at a higher lever that is directly related. Since the two methods have physical

dissimilarities there was no obvious relation between them. The best candidate for the lurking

variable that may cause the correlation is considered to be the strength of the soil.

The correlation between the column penetration tests and the soil-rock sounding has a true

correlation coefficient ρ also known as the population correlation coefficient. This true

correlation can never be measured, since the population is infinite. The best estimation of ρ is

the sample correlation coefficient r that can be calculated (Johnson 2005). The same author

states that r is not an unbiased estimator of the population correlation coefficient, but is

widely used. This means that there might be a high correlation between the two test methods,

although it is not easily measured since both tests are done in situ. When testing in situ, there

are lots of interference obscuring the results. These can be weather related, human error,

machinery error etc.

By plotting the two data sets against each other in a scatter plot, a visual impression of the

correlation can be made. If the two data sets are (linear) related the points will form against a

straight line in the plot. The better fit to the line the better correlation (figure 5). To get a

mathematical interpretation of this, r can be calculated. This requires the data to be in

standardized form according to equation (4).

Equation 4. Standardize data (4)

x

i

s

xx −

Where

ix = observation i

x = sample mean

xs = sample standard deviation

r is the sum of products of the standardized variables divided by the sample size minus one

according to equation (5), (Johnson 2005).

25

Equation 5: The Sample Correlation Coefficient (5)

−

−

−= ∑

= y

in

i x

i

s

yy

s

xx

nr

11

1

The correlation coefficient can take values between -1 and 1. The value 1 indicates a perfect

positive linear relation, and -1 indicated a perfect negative linear relation. The value 0

indicates no linear relation and thus applies that the data sets have no linear relation (Blom et

al. 2005). An r -value around 0.5 is usually considered a weak correlation (figure 5).

9.0≈r 5.0≈r 0≈r

Figure 5. Typical correlation coefficients.

Null hypotheses

A useful tool in statistics is the null hypothesis test. It is used to answer questions while

dealing with uncertainties. A null hypothesis focus not on proving if a statement is true, but

rather determines if it is probable that the statement is not true. Think of the phrase “Innocent

until proven guilty”. When deciding if it is probable that the statement is not valid, a level of

significance is chosen. The level of significance α is usually set to 0.05, 0.01 or 0.001,

referring to the probability that the hypothesis was proven by chance or randomly (Blom et al.

2005). Table 4 present the most commonly used significance levels. At significance 0.05 five

out of one hundred hypnoses are falsely rejected whiles at 0.001 level of significance only one

out of one thousand hypotheses are rejected although they are true. Which significance is

chosen depends on the consequences of making a false statement.

Table 4. The two-tailed significance levels

025.02 =α 005.02 =α 0005.02 =α

σ96.1 σ58.2 σ29.3

Hypothesis: the population correlation coefficient is zero

Forming a null hypothesis that stated that the population coefficient was zero suggest that

there was no relation between the column penetration tests and the soil-rock soundings. The

alternate hypothesis was that the population correlation coefficient was not zero. Since the

Quantity x

Quantity

y

Quantity x Quantity x

Quantity

y

Quantity

y

26

correlation coefficient can only take values between -1 and 1, a Fisher Z transformation was

required to calculate the statistics (Johnson 2005). See equation (6).

Equation 6. Fisher Z transformation (6)

r

rz

−

+=

1

1ln

2

1

The Fisher Z transformation forms a random variable having an approximately normal

distribution with the mean r

rz

−

+=

1

1ln

2

1µ and the variance

3

1

−n. This variable can then be

used when calculating the statistics according to equation (7).

Equation 7: Statistics for the null hypothesis (7)

znZ ⋅−= 3

The null hypothesis states that ρ equals zero, and was set up as follows:

1. The null hypothesis is that 0=ρ .

The alternate hypothesis is that 0≠ρ .

2. The level of significance α = 0.05 (table 4).

3. Criterion: Reject the null hypothesis if 96.1−<Z or 96.1>Z .

4. Calculations: The Z is calculated with equations (6) and (7).

5. Decision: If 96.1−<Z or 96.1>Z the null hypothesis is rejected. It is then concluded

that there is a relationship between the column penetration test and the soil-rock

soundings at a 95 % significance level.

Confidence intervals for the correlation coefficient

The Fisher Z transformation above can also be used to determine a confidence interval for the

ρ. 2az refers to the level of significance (see table 4). The confidence interval then needs to

be transformed back to r using equation (9) (Johnson 2005).

Equation 8: Confidence interval for the population correlation coefficient

(8)

33

22

−+<<

−−

n

zz

n

zz z

ααµ

27

Equation 9: Transformation back to r . (9)

−+−

−+

−+−

−+

−−−

−−

−−−

−−

+

−<<

+

−

33

33

33

33

22

22

22

22

n

zz

n

zz

n

zz

n

zz

n

zz

n

zz

n

zz

n

zz

ee

eer

ee

eeαα

αα

αα

αα

Hypothesis: two samples have an equal mean-value

The second null hypothesis focuses on the variation of the data sets. Since the sample

correlation coefficient is calculated using standardized data the mean value of the series is not

taken into consideration. See equations (4) and (5). This means that although the variation

correlates between the two data sets, the mean value can be different. Since one aim of this

thesis is to find an empirical cone factor a null hypothesis has to be formed concerning the

mean-values as well. The two populations have the mean 1µ and 2µ and the variance 2

1σ and 2

2σ the null hypothesis 021 ≠− µµ is formed. The alternate hypothesis will then

be 021 =− µµ . Since the samples are normal distributed and both data sets have n more than

30 the following statistics in equation (10) can used (Johnson 2005).

Equation 10: Statistics for large sample test concerning difference between two means

(10)

2

2

2

1

2

1

21

n

s

n

s

XXZ

+

−=

Where X is the sample mean and s is the sample standard deviation

The null hypothesis was set up as follows:

1. The null hypothesis is that 021 =− µµ .

The alternate hypothesis is that 021 <− µµ or 021 >− µµ .

2. The level of significance α = 0.05 (table 4).

3. Criterion: Reject the null hypothesis if 96.1−<Z or 96.1>Z .

4. Calculations: The Z is calculated with equations (10).

5. Decision: If 96.1−<Z or 96.1>Z the null hypothesis is rejected. It is then concluded

that the mean value of the two evaluated undrained shear strengths is not equal at a 95

% significance level.

Individual columns

The correlation coefficient was first calculated for the individual columns. The main reason to

do this was to identify columns with low correlation. These columns were then investigated in

order to find the cause for the low correlation. If most of the columns have a high correlation

coefficient and only a few columns stands out with low correlation, there are reasons to

believe that there is an underlying problem with these columns. If the cause for the low

correlation can be found and explained, the columns can be excluded from the analysis.

28

Average column

In order to cancel out some of the individual variation in the columns an average column was

formed. The average columns were formed as an average of the registered penetration

resistance from every column at each depth at one site. Calculating r gave an indication if the

two methods related. A null hypothesis about the population correlation coefficient was

formed and a confidence interval for the sample correlation coefficient was calculated.

The cone factors

The cone factor Nc is an empirical factor used for the evaluation of the undrained shear

strength from the measured penetration resistance from the column penetration test. The

equation to calculate the undrained shear strength is presented as equation (1). It was the

authors believe that the same equation could be used to evaluate the undrained shear strength

from the penetration resistance recorded while drilling. The total sounding method was

calibrated against the column penetration test and a ratio of the cone factor between the

column penetration test and the total sounding methodology was calculated. The equation to

evaluate the undrained shear strength for both the column penetration test and the total

sounding method are presented as equation (11).

Equation 11: Equations to evaluate the undrained shear strength.

(11)

(a) Column penetration test:

KPSc

KPSKPS

fuN

AF

,

=τ

(b) Total sounding method:

drillc

drilldrill

fuN

AF

,

=τ

As suggested earlier the difference in failure modes between the methods likely means

different cone factors are needed. By combining equation (11a) and (11b) a ratio between the

cone factors could be formed as equation (12). If it was later found that if the same cone

factor would apply to both methods this ratio would be one.

Equation 12: Relation between the cone factors (12)

KPS

KPS

drill

drill

KPSc

drillc

KPSc

KPSKPS

drillc

drilldrill

F

A

A

F

N

N

N

AF

N

AF⋅=→=

,

,

,,

Deviating column penetration probes

At the E45 site there were inclination data available from the column penetration tests. This

made it possible with a good degree of accuracy to determine the amount of probe deviation

from the column centre. Multiplying the tangent β for the inclination with the distance since

the last data point ∆z gave the distance the probe had deviated from the centre of the column

since the last recording, see equation (13).

29

Equation 13: Probe deviation (13)

( ) xz ∆=⋅∆ βtan

Where:

β is the incline

∆z is the distance in z since last registration ∆x is the deviation in x since last registration

When the probe starts to deviate from the column centre the probe will gradually leave the

column giving a value that is no longer fully representing the column. When the probe has

deviated enough to stop representing the column is a subjective evaluation.

Evaluating the ratio of cone factors on three sites

Two additional sites were used to evaluate the ratio of the cone factors. This would dismiss

the results as being coincidental. It would also prove if the ratio was site-specific. The data

from all sites were first visually inspected. The r was then calculated for the individual

columns. Average columns were then formed to evaluate both r and the variation, visually

and calculated as CoV.

The construction area at Lidingö was chosen where the columns were tested with the

specifications used at the E18 site. The way the total sounding test was executed at Lidingö

also made it possible to evaluate the effect of the sleeve friction. During the execution of the

total soundings the drill was lifted by 0.5 meters at the bottom of the bore holes and pushed

down a second time. The idea was that this would be an estimation of the sleeve friction at

that depth, why an average sleeve friction per meter was calculated for the individual columns

and the removed as a linear function.

The construction of E-road 45 was chosen as a third location. At E45, the total sounding

methodology was not utilized. As discussed earlier, the penetration resistance from the soil-

rock sounding might not be compatible between sites, because the cone factors might be

dependent on the rotational speed and/or the rate of penetration. Three groups of columns

with different binder content were also tested. This made it possible to evaluate the effect of

different binder content on the ratio of the cone factors.

The final evaluation of the ratios was done by plotting the ratios of all three sites as a function

of depth.

De-trending

The penetration resistance was recorded at the surface during the soil-rock soundings, this

meant that the sleeve friction generated from the drill rods was incorporated into the reading.

Since the sleeve friction is a cumulative quantity and the sleeve area is linearly related to the

depth of the hole it was assumed to be linear distributed over the depth of the hole. This made

it possible to remove the sleeve friction by de-trending the data using a linear function. The

amount of de-trending needed was visually determined using the ratio of the cone factors,

which needed to be constant at depth and then compared with the evaluated sleeve friction at

the Lidingö site.

30

31

Results and discussion The results are divided into two parts. The first presents the analyses of the correlation

between the penetration resistances from the column penetration test and the soil-rock

sounding. The second part compares the ratio of the cone factors from all three sites based on

average columns formed from each site.

Previous results from the use of soil-rock sounding

Nilsson (2008b) has previously investigated the use of the total sounding methodology with

lime-cement columns. The report is unpublished but here summarized with permission from

the author.

The test site was located at Lidatorp on road 73 from Stockholm to nearby Nynäshamn.

Twenty lime-cement columns, 800 mm diameter were manufactured. The columns were

divided into four groups with specifications according to table 5.

Table 5. The groups of columns manufactured at road 73.

Group Columns Binder content Retrieval rate Rotational speed Length

1 5 80 kg/m3

20 mm/s 200 rpm 13,5 m

2 5 80 kg/m3 25 mm/s 200 rpm 13,4 -13,8 m

3 5 100 kg/m3 20 mm/s 200 rpm 13,4 -13,8 m

4 5 100 kg/m3 25 mm/s 200 rpm 13,5 -14,0 m

In each group two columns were tested after 7 days, two columns were tested after 14 days

and 1 column was tested after 30 days. The columns were tested with the pre-drilled column

penetration test. The guiding holes were drilled according to the total sounding methodology

(SGF 2000) with a rotational speed of 25 rpm and a rate of penetration of 20 mm/s. If a

penetration resistance of 20 kN was reached, hammer-drilling was used. The undrained shear

strength was evaluated for the column penetration tests using a cone factor of 10. The same

cone factor was also used to evaluate the undrained shear strength from the total sounding

thus the ratio between the cone factors was 1. Some emphasis was also put on minimizing the

sleeve friction. Every time the drill rod was spliced, the drill was lifted 0.5 m and the bore

hole was lubricated with water.

The report concluded that there were a fairly good correlation between the column penetration

test and the total sounding method when an average column were evaluated from group 1,

group 2 and group 4. The correlation at group 3 was lower. However this might be explained

by the difficulty to sound the 30-day column in that group. The author also points out that it

was very hazardous to evaluate the undrained shear strength from individual columns using

the total sounding methodology since the correlation of individual columns varied a lot.

The E18 site

The data was used to evaluate the correlation between the two test methods. Histograms for

the column penetration test and the guiding holes, carried out according to the total sounding

methodology were generated using PASW (figure 6). They give the visual appearance that the

32

data sets are approximately normal distributed, thus making the following statistical

evaluation valid.

Figure 6. Histograms calculated from the data at the E18 site.

The sample correlation coefficient for the individual columns is presented in figure 7. There

are clearly a number of columns with high correlation coefficients around 0.8 and even 0.9. In

fact the median value was 0.742. Eight columns had a correlation of less than 0.5 and four of

those columns have an almost non existing correlation of 0.2 or less (column 26 had a

negative correlation). All of the columns from the E18 site are presented in Appendix A.

Figure 7. The sample correlation coefficient in different columns at E18.

r

Column penetration tests Soil-rock soundings

33

Low-correlating columns

As shown in figure 7, columns 1,4,26 and 30 have an exceptionally low correlation

coefficient. The column penetration test and the guiding holes for column 1, 4, 26 and 30 are

presented in figure 8. There is also an average based on all of the columns for comparison.

Since the earth pressure increases at depth, it was expected that the columns strength increases

and accordingly the measured penetration resistance. This was observed for the evaluated

average column for both the column penetration tests and the total sounding test (figure 8a).

This was also the case for all of the soil-rock soundings in columns with low correlation

(although very slightly in column 30). However this was not the case for column 1, 4 and 26

where the penetration resistance for the column penetration test decreased while the

penetration resistance kept increasing for the total sounding tests. Since this was only

occurring in the column penetration test it is the authors believe that this was caused by the

probe leaving the column for the surrounding soil with lower strength. Columns 1, 4 and 26

were excluded from the subsequent analyses. The cause for the low correlation of column 30

could not be found, and it was therefore not removed from the study.

Soil-rock sounding

Column penetration tests

a) Average columns 1-30

0

2

4

6

0 20 40

P enetrat io n resistance

(kN )

Dep

th (

m)

b) Column 1

0

2

4

6

0 20 40

P enetrat io n resistance

(kN )

Dep

th (

m)

c) Column 4

0

2

4

6

0 20 40

P enetrat io n resistance

(kN )

Dep

th (

m)

d) Column 26

0

2

4

6

0 20 40

P enetrat io n resistance

(kN )

Dep

th (

m)

e) Column 30

0

2

4

6

0 20 40

P enetrat io n resistance

(kN )

Dep

th (

m)

Figure 8. Plots showing the average column and columns with low correlation at E18.

34

Forming an Average Column

When plotting the average column penetration tests and the average total sounding tests a

clear similarity was visible (figure 9). At the depth of seven meter, there was a sudden drop in

penetration resistance for both methods. It was the authors believe that this was caused by

either the end of the column or both the total sounding tests and the column penetration test

deviating the column. At this depth the data was based on only two columns making it more

uncertain. For this reason the average column was only be formed to a depth of seven meters.

At this depth, nine columns were present. When average columns were formed the r was

calculated to 0.91. The correlation was null hypothesis tested. The null hypothesis states that

the population correlation coefficient is zero, hence that there was no relation.

The null hypothesis was calculated using equations (6) and (7). This gave a Z -value of 26.4.

Since 26.4 was considerably more than 1.96, the null hypothesis was rejected. Calculating the

confidence interval with equations (6), (7), (8) and (9) with a 95 % significance interval

gave 93.089.0 << r .

The variation was also evaluated both by plotting the individual columns and by calculating

the coefficient of variation, figure 9. It was concluded that the variation of the total sounding

tests was generally five to ten percent points higher than the column penetration test. This

might be caused by the smaller area tested.

All column

penetration tests

0

1

2

3

4

5

6

7

8

0 10 20 30 40

P enetratio n resistance

(kN )

Dep

th (

m)

All total sounding

tests

0

1

2

3

4

5

6

7

8

0 5 10

P enetrat io n resistance

(kN )

Dep

th (

m)

Variance moving

average 0.5 m

0

1

2

3

4

5

6

7

8

0 10 20 30 40 50

CoV (%)

Dep

th (

m)

Average column

All columns

Average column

All columns

Soil-rock sounding

Column penetration test Figure 9. Measured penetration resistance for all columns and average columns and CoV for both methods at E18.

35

The Lidingö site

The r between the two tests methods were all above 0.5 for the individual columns at the

Lidingö site. The median correlation coefficient was 0.73. Figure 10 presents r for all columns

at Lidingö.

0

0,5

1

144 145 146 147 2595 2601 2603 2607

Columns

Co

rrela

tio

n c

oeff

icie

nt

r

Figure 10. Sample correlation coefficient for individual columns at the Lidingö site.

When an average column was formed the correlation coefficient was 0.92, which indicated a

high correlation. The 95 % confidence interval for the correlation coefficient is presented in

table 6. The variation was evaluated by plotting the data from all columns and the CoV was

calculated, figure 11. The CoV for the total sound tests was here considerably higher than the

column penetration tests, but comparing with the E18 site the CoV for the total sounding test

were fairly equivalent. The CoV for the column penetration test was however much lower at

the Lidingö site.

Table 6. Results for the average column formed at the Lidingö site.

Sample correlation coefficient r 92.0

95 % confidence interval for r 94.090.0 << r

Null hypothesis: There is no correlation Rejected ¹

¹ At a 95 % significance level

36

All column

penetration tests

2

3

4

5

6

7

0 10 20 30

P enetratio n resistance

(kN )

Dep

th (

m)

All total sounding

test

2

3

4

5

6

7

0 2 4 6 8

P enetrat io n resistance

(kN )

Dep

th (

m)

Variance moving

average 0.5 m

2

3

4

5

6

7

0 10 20 30 40 50

CoV (%)

Dep

th (

m)

Average column

All columns

Average column

All columns

Soil-rock sounding

Column penetration test Figure 11. Measured penetration resistance for all columns and average columns and CoV for both methods at Lidingö.

The sleeve friction during the total sounding at Lidingö was also evaluated. This was possible

since the drill was lifted about 0.5 m at the bottom of the holes and pushed down a second

time. The sleeve friction varied among the individual holes between 0.4 kN/m and 1.3 kN/m

with an average of 0.85 kN/m. At a depth between 5 and 6 meters on the average column

formed, the sleeve friction accounted for 50 % of the penetrations resistance registered while

drilling.

The E45 site

The correlation between the two methods was also evaluated on a site which did not utilise

the total sounding methodology. The columns at the E45 site were formed into three groups

constructed with different binder content, 25 kg/m, 30 kg/m and 35 kg/m. This would indicate

the ratio of the cone factors sensitivity to binder content as well as rotational speed and rate of

penetration. The effect of the binder content was distinguished by first comparing the cone

factor-ratios between the three groups.

Visually comparing the penetration resistance gave the clear indication that there was a low

correlation at very shallow depth. This was likely caused by the methods not correlating at the

dry clay crust above the water table. There was also a low correlation at higher depth where

the penetration resistance from the column penetration test decreased at a depth around 7-8.

This was likely caused by the column penetration probe deviating from the column. Using

equation (13) it was possible to calculate the deviation from the column centre. Table 7

presents the depth at which the probe has deviated by 0.3 m (the radius of the columns).

37

Knowing this and since the cone factor was formed from data down to a depth of 7 meters at

E18, the columns at E45 was statistically evaluated at a depth of 2 to 7 meters.

Table 7. Depth at which the column penetration probe had deviated the column centre by 0.3 m. Columns: (25 kg/m)

Depth: Columns: (30 kg/m)

Depth: Columns: (35 kg/m)

Depth:

25292 7.1 m 25199 > 11 m 25141 7.0 m

25296 12.1 m 25203 9.0 m 25142 9.5 m

25297 9.2 m 25204 7.8 m 25146 > 9.5 m

25323 10.8 m 25208 7.7 m 25168 8.5 m

25327 9.9 m 25234 > 10 m 25172 > 11 m

25328 12.5 m 25235 8.1 m 25173 10.5 m

25331 8.7 m 25239 7.4 m 25177 9.1 m

Average 10 m ~9 m ~9 m

Table 7 also shows that the column penetration probe had deviated the column fully at a depth

of 9 to 10 meters even thought it has been suggested that the method can be used with

columns down to 12-15 meters (Ekström 1994, Larsson 2006). This opens for the possibility

to test deeper columns using soil-rock sounding since the rotation likely helps guiding the

drill.

0

0,5

1

25

29

2 *

25

29

6

25

29

7

25

32

3

25

32

7

25

32

8

25

33

1

25

19

9

25

20

3

25

20

4

25

20

8

25

23

4

25

23

5

25

23

9

25

14

1

25

14

2

25

14

6

25

16

8

25

17

2

25

17

3

25

17

7

25 kg/m 30 kg/m 35 kg/m

Columns, groups

r

* Column 25292 has a negative correlation here presented as positive.

Figure 12. Sample correlation coefficient for individual columns at E45.

The sample correlation coefficient was calculated for the individual columns at E45 using

equation (5) and is presented in figure 12. The correlation of the individual columns varied a

lot, similar to the individual columns from E18 (figure 7). The majority of the columns had a

high correlation and only a few had a low correlation. All columns manufactured with 30

38

kg/m and 35 kg/m showed a high correlation. Two columns constructed with 25 kg/m still had

a low correlation (column 25292 had a negative correlation).

Next step was to form average columns from each concentration group. The correlation

coefficient and a 95 % significant confidence interval for the sample correlation coefficient

were calculated. The r was good for all the groups. The null hypotheses that the correlation

was coincidental were rejected and a narrow confidence interval for r was found (table 8).

Table 8. Results for the average columns formed at E45. Group of 25 kg/m

Sample correlation coefficient r 88.0

95 % confidence interval for r 91.085.0 << r

Null hypothesis: There is no correlation Rejected ¹

Group of 30 kg/m

Sample correlation coefficient r 95.0

95 % confidence interval for r 96.094.0 << r

Null hypothesis: There is no correlation Rejected ¹

Group of 35 kg/m

Sample correlation coefficient r 98.0

95 % confidence interval for r 99.098.0 << r

Null hypothesis: There is no correlation Rejected ¹

¹ At a 95 % significance level

39

The variation was evaluated by plotting the data from all columns and the CoV was calculated

as a moving average of 0.5 m, figure 13. The CoV for the soil-rock sounds were generally 10

to 15 percentage point higher than for the column penetration tests.

All column

penetration tests

2

3

4

5

6

7

0 10 20 30

Penetration resistance (kN)

Dep

th (

m)

All total sounding

tests

2

3

4

5

6

7

0 5 10

Penetration resistance (kN)

Dep

th (

m)

Variance moving

average 0.5 m

2

3

4

5

6

7

0 10 20 30 40 50

CoV (%)

Dep

th (

m)

Average column

All columns

Average column

All columns

Soil-rock sounding

Column penetration test Figure 13. Measured penetration resistance for all columns and average columns and CoV for both methods at E45.

40

The ratio of the cone factors

Figure 14 shows the ratio of the cone factors, calculated with equation (12), as a function of

depth. It was clear that the ratio at all three sites increased by depth. The incline was however

fairly similar for all three sites and might be caused by the sleeve friction, this was later dealt

with using de-trending. The curve from the Lidingö site was not stationary which might be

caused by the fact that only eight columns were tested. The three groups at the E45 site were

combined to a total of twenty-one columns.

Figure 14. The ratio of the cone factors at depth at the three test sites.

The average columns used for the evaluation of the cone factors were formed from data at a

depth between 1 and 6 meters beneath the surface. This was done because the manufacturing

gives uneven quality close to the surface partly caused by the fact that pneumatic fracturing of

the soil occurs. A possible shortage of water for the chemical reaction above the water table

also causes large variability. The lower limit of 6 meters was chosen since the number of

columns then dropped dramatically. The shorter columns at Lidingö was only possible to

evaluate to a depth of 5,5 m.

De-trending for sleeve friction

A depth-dependant cone factor is not used with the column penetration tests and contradicts

the theory that the undrained shear strength is directly related to the penetration resistance.

The increase of the cone factor at depth might however be caused by the sleeve friction being

incorporated in the registered penetration resistance from the soil-rock sounding. As

mentioned previously the possibility to evaluate the sleeve friction from the soil-rock

sounding was given at the Lidingö site. The sleeve friction was recorded over a distance of

KPSc

drillc

N

N

,

,

41

about one meter at the bottom of the drill-hole. Figure 15 presents the recorded sleeve friction

as well as the estimated sleeve friction as a linear function. The average sleeve friction at

Lidingö was 5.7 kN at a depth of 6.7 meters, thus giving an average de-trending of 0.85

kN/m. The last graph in figure 15 shows the average penetration resistance from the soil-

rocksoundings at Lidingö before and after de-trending.

Figure 15. Evaluation of the sleeve friction at the Lidingö site

In order to find a constance ratio of the cone factors at depth the soil-rock soundings at E18

and E45 was de-trended by 0.5 kN/m and the soil-rock sounding at Lidingö was de-trended by

1.0 kN/m, presented in figure 16 as a moving average of 0.5 m.

42

Figure 16. The ratio of the cone factor with de-trended total sounding tests.

The use of different de-trending for the sites suggests that the sleeve friction varies between

sites. It was obvious that the ratio of cone factors evaluated from the E45 site differed from

the ratio evaluated from the E18 site, although the same de-trending was used. This might be

caused by the different specifications used while drilling. Faster rotational speed and rate of

penetration might alter the failure mode of the columns why the same relation was not valid.

The ratio between the cone factors from the E18 site was 0.42 and the ratio from the Lidingö

site was 0.30. These two average ratios was null hypothesis tested and it was found that they

did not have an equal mean-value at a 95 % level of significance, meaning that the sleeve

ratio was different at the two sites. The ratio of the cone factors at the E45 site was 0.23 when

the penetration resistance was de-trended by 0.5 kN/m. Since the de-trending was linear the

variation was also scaled up proportionally. If the total sounding method is to be used to

evaluate the undrained shear strength the sleeve friction must be evaluated for each individual

column either by using the method utilized at the Lidingö test site of better evaluate the sleeve

friction with its own variation. The latter could perhaps be accomplished by drilling the entire

hole twice thus theoretically only recording the sleeve friction during the second pass,

however further research is needed on this subject. Nilsson (2008b) suggested lubricating the

bore hole with water to minimize the sleeve friction. He then used the same cone factor

suggested for the column penetration test without de-trending the data. This was not examined

during this thesis.

The effect of different binder content

The E45 site made it possible to evaluate the effect of different binder contents on the ratio of

the cone factors. The site had three groups of seven columns manufactured using 25 kg/m, 30

KPSc

drillc

N

N

,

,

43

kg/m and 35 kg/m of lime-cement binder. Figure 17 presents the effect on the ratio of the

cone factor using the different binder contents. The soil-rock soundings were not de-trended

but it was clear that the cone factors were almost equivalent between the three groups. It was

therefore concluded that the ratio of the cone factors was not dependent of the amount of

binder used at the interval 25-35 kg/m, which is about 88-124 kg/m³.

Figure 17. Ratio of the cone factors of the three binder content groups at the E45 site.

Summary

The good relation between the two test methods means that it was likely possible to evaluate

the undrained shear strength of lime-cement columns from the soil-rock sounding data.

However the sleeve friction has to be evaluated, preferably on each column individually. To

get reliable result average columns needs to be formed. More studies about the effect of the

sleeve friction for the soil-rock sounding used with limecement columns are needed before it

can be used solely to evaluate the undrained shear strength.

It is desirable that a standardized methodology such as the total sounding methodology is used

when pre-drilling. This would make it possible to compare the recorded penetration resistance

between columns and test sites. If for instance difficulties with the column penetration test

was found at one site the site-specific ratio of the cone factors could be evaluated from the

existing soil-rock soundings at that site, eliminating extra soundings.

The rate of penetration and the rotational speed likely have an impact on the cone factor. The

similar inreace in penetration resistance with depth at all three sites suggest that the sleeve

friction is rougly equal. However the sleeve friction is dependent on many factors, such as the

earth pressure, water pressure, soil type etc. The binder content had a minor effect on the ratio

in the span of 25- to 35 kg/m used at the E45 site.

The variation for the soil-rock soundings data was larger than for the column penetration tests.

This was likely caused by a smaller area tested. However it was unknown how big part of the

KPSc

drillc

N

N

,

,

44

variation that derived from the sleeve friction since it was evaluated as a linear function. It

should also be mentioned that the sleeve friction is a cumulative quantity.

The report by Nilsson (2008b) implies that the same cone factor can be used for the totals

sounding method as the column penetration test. This present investigation on the other hand

implies that a lower cone factor might be needed. The difference between the studies was that

a column penetration test without a CPT probe was used in Nilsson’s study why a sleeve

friction was recorded from both of the two test methods. The bore hole was also lubricated

with water to minimize the sleeve friction. Furthermore the test was carried out on 800 mm

diameter columns. An obvious reason for the difference was not found.

45

References

Axelsson, M. 2001. Djupstabilisering med kalkcementpelare – metoder för

produktionsmässig kvalitetskontroll i fält, Report 8, Swedish Deep Stabilization Research

Centre, Linköping, 163p. (in Swedish).

Axelsson, M. and Larsson, S. 2003. Column penetration tests for lime-cement columns in

deep mixing – experiences in Sweden. ASCE Geotechnical Special Publication No. 120, Vol.

1, p. 681-694.

Bard, G. 2007. Lidingö Stad. Dalénium östra, Planerade bostäder, gator och ledningar. PM

Geoteknik. Projekteringsunderlag. WSP Stockholm, 9p. (In Swedish).

Blom, G., Enger, J., Englund, G., Grandell, J. and Holst, L. 2005. Sannolikhetsteori och

statistikteori med tillämpningar. Studentlitteratur. Lund. 426p. (In Swedish).

Carlsten, J. 2000. Kalk- och kalkcementpelare. Vägledning för projektering, utförande och

kontroll. Swedish Geotechnical Society. Linköping, 111p. (In Swedish).

Ekström, J. 1994. Kontroll av kalkcementpenare – Slutrapport. Med redovisning av

fältförsöken i Ljungskile. Report 1994:3, Chalmers University of Technology. Gothenburg.

(In Swedish).

Jelisic, N. and Nilsson, G. 2005. Testing of the shear strength of cement columns by using the

total sounding method. Proc. Int. Conf. on Deep Mixing Best Practice and Recent Advances,

Stockholm, Vol. 1, p. 527-531.

Johnson, R. A. 2005. Miller & Freund’s Probability and Statistics for Engineers. Seventh

Edition. International Edition. Pearson Prentice Hall. London, 642p.

Karlsson, D. 2008. E18 Hjulsta – Kista. Ursvik 300 gemenstamt. Tolkad geoteknik km 4/900-

5/120. [construction document] Vägverket, Sweco, Grontmij. (In Swedish).

Larsson, R. 2006. Djupstabilisering med bindemedelsstabiliserade pelare och

masstabilisering – en vägledning. Report 17, Swedish Deep Stabilization Research Centre.

Linköping, 381p. (In Swedish).

Larsson, S. 2005. State of Practice Report Session 6: Execution, monitoring and quality

control. Proc. Int. Conf. on Deep Mixing, Best Practice and Recent Advances, Stockholm,

Vol. 2, 54p.

46

Liyanapathirana, D. S. and Kelly R. B. 2010. Interpretation of lime column penetration test.

IOP Conference Series: Materials Science and Engineering, Vol. 10, No. 1. 10p.

Nilsson, A. 2008a. Rumslig korrelation avseende hållfastheten i en pelarförstärkning. Royal

institute of Technology, Stockholm, 45p. (In Swedish).

Nilsson, G. 2008b. Rapport: Markförstärkning vid tpl Lidatorp. WSP Samhällsbyggnad.

Stockholm 12p. (In Swedish)

Porbala, A, Yamani, N. and Taguchi, H. 2001. In situ measurement of artificially cemented

ground properties. International Conference on Insitu Measurment of Soil Properties and

Case Histories. Bali, p. 219-223.

SGF. 1999. Metodbeskrivning för Jord-bergsondering. Report 2:99, Swedish Geotechnical

Society. Linköping, 30p. (In Swedish).

SGF. 2006. Metodbeskrivning för JB-totalsondering. Report 1:2006, Swedish Geotechnical

Society. Linköping, 11p. (In Swedish).

Wahlqvist, K. 2010. E45 Bohus-Nödinge, entreprenad E33.

http://www.skanska.se/sv/Projekt/Visa-projekt/?pid=1248 [accessed 2010-11-11] (In

Swedish)

Photographs

Al-Naqshabandy, M. S. 2010. Figure 4.

Bergman, N. 2010. Figure 2.

Fransson, J. 2010. Figure 1 and figure 3.

47

Appendix A – tested columns at E18 Appendix A contains all of the tested columns from E18. The penetration resistance from the

column penetration test and the soil-rock soundings is presented for comparison. The lower

penetration resistance from the soil-rock soundings is only partially explained by the lesser

area of the drill bit.

Column penetration test

Soil-rock sounding

a) Column 1 b) Column 2 c) Column 3

d) Column 4 e) Column 5 f) Column 6

48

Column penetration test

Soil-rock sounding

g) Column 7 h) Column 8 i) Column 9

j) Column 10 k) Column 11 l) Column 12

m) Column 13 n) Column 14 o) Column 15

49

Column penetration test

Soil-rock sounding

p) Column 16 q) Column 17 r) Column 18

s) Column 19 t) Column 20 u) Column 21

v) Column 22 w) Column 23 x) Column 24

50

Column penetration test

Soil-rock sounding

y) Column 25 z) Column 26 za) Column 27

zb) Column 28 zc) Column 29 zd) Column 30

51

Appendix B – the evaluated undrained shear strength at Lidingö This appendix was formed as an experiment to evaluate the undrained shear strength of the

columns at Lidingö from both the column penetration tests and the soil-rock soundings,

according to the total sounding methodology. Eight columns were evaluated. In the first eight

figures there was no reduction for the sleeve friction during the total sounding. A cone factor

of 12.5 was chosen for the column penetration tests andKPScdrillc

NN ,, 6.0 ⋅= for the soil-rock

soundings. The last eight figures were evaluated with a reduction for the sleeve friction soil-

rock sounding andKPScdrillc

NN ,, 5.0 ⋅= .

No reduction for the sleeve friction. Column penetration test

Soil-rock sounding

1

2

3

4

5

6

7

8

9

0 100 200 300 400

Undrained shear strength (kPa)

Dep

th (

m)

1

2

3

4

5

6

7

8

9

0 100 200 300 400

Undrained shear strength (kPa)

Dep

th (

m)

a) Column 144 b) Column 145

52

1

2

3

4

5

6

7

8

9

0 100 200 300 400

Undrained shear strength (kPa)D

ep

th (

m)

1

2

3

4

5

6

7

8

9

0 100 200 300 400

Undrained shear strength (kPa)

Dep

th (

m)

c) Column 146 d) Column 147

1

2

3

4

5

6

7

8

9

0 100 200 300 400

Undrained shear strength (kPa)

Dep

th (

m)

1

2

3

4

5

6

7

8

9

0 100 200 300 400

Undrained shear strength (kPa)

Dep

th (

m)

e) Column 2595 f) Column 2601

Column penetration test

Soil-rock sounding

53

1

2

3

4

5

6

7

8

9

0 100 200 300 400

Undrained shear strength (kPa)D

ep

th (

m)

1

2

3

4

5

6

7

8

9

0 100 200 300 400

Undrained shear strength (kPa)

Dep

th (

m)

g) Column 2603 h) Column 2607

Reduction for the sleeve friction in the soil-rock soundings.

1

2

3

4

5

6

7

8

9

0 100 200 300 400

Undrained shear strength (kPa)

Dep

th (

m)

1

2

3

4

5

6

7

8

9

0 100 200 300 400

Undrained shear strength (kPa)

Dep

th (

m)

i) Column 144 j) Column 145

Column penetration test

Soil-rock sounding

54

1

2

3

4

5

6

7

8

9

0 100 200 300 400

Undrained shear strength (kPa)D

ep

th (

m)

1

2

3

4

5

6

7

8

9

0 100 200 300 400

Undrained shear strength (kPa)

Dep

th (

m)

k) Column 146 l) Column 147

1

2

3

4

5

6

7

8

9

0 100 200 300 400

Undrained shear strength (kPa)

Dep

th (

m)

1

2

3

4

5

6

7

8

9

0 100 200 300 400

Undrained shear strength (kPa)

Dep

th (

m)

m) Column 2595 n) Column 2601

Column penetration test

Soil-rock sounding

55

1

2

3

4

5

6

7

8

9

0 100 200 300 400

Undrained shear strength (kPa)D

ep

th (

m)

1

2

3

4

5

6

7

8

9

0 100 200 300 400

Undrained shear strength (kPa)

Dep

th (

m)

o) Column 2603 p) Column 2607

Column penetration test

Soil-rock sounding