Characterization of Micaceous Sand for Investigation of...

Characterization of Micaceous Sand for Investigation of a Subsea Mass Movement

T. Langford and S. Perkins

Abstract A recent project involved a shallow slope failure of a deposit of loose sand and a site investigation and laboratory test program was initiated to investi-gate the cause of the slide and evaluate the likelihood of any further movement. The sand was found to have an elevated mica content, which affected the density, compressibility and shearing behavior. Existing correlations between relative den-sity and cone resistance were evaluated to better understand the in-situ density of the soil. Undrained triaxial tests were used to investigate the static strength and material anisotropy, while static and cyclic direct simple shear tests helped study behavior during undrained cyclic loading. The test results are summarised and key conclusions are presented which are of relevance for sites worldwide where mica-ceous sands are prevalent.

Keywords Submarine landslide • geotechnical site investigation • laboratory testing

1 Offshore Investigation

A recent project offshore Norway involved a shallow slope failure of a deposit of loose sand. An initial geophysical survey of the slope revealed a classic ‘fan’ shape failure. A detailed site investigation and laboratory test program was initiated to investigate the cause of the slide and evaluate the likelihood of further movement. The investigation included geophysical techniques to investigate the bathymetry and shallow stratigraphy, eight geotechnical vibrocore (VC) samples to obtain

T. Langford (�)NGI, P.O. Box 3930 Ullevål Stadion, NO-0806 Oslo, Norwaye-mail: [email protected]

S. Perkins (�)Montana State University, 205 Cobleigh Hall, Bozeman MT 59717, USA e-mail: [email protected]

D.C. Mosher et al. (eds.), Submarine Mass Movements and Their Consequences, 79Advances in Natural and Technological Hazards Research, Vol 28,© Springer Science + Business Media B.V. 2010

80 T. Langford and S. Perkins

material for laboratory testing and 28 Cone Penetration Tests with measurement of pore pressure (CPTU) to investigate the in-situ properties of the soils. The geo-physical investigation clearly revealed a debris fan, as shown in Fig. 1.

A corresponding cross-section after the slide shows how the sand has accumu-lated at the lower end of the slope. The following describes the general stratigraphy (descriptions of sand density are qualitative):

Unit Ia very loose to medium dense sand, micaceous, shells and shell fragmentsUnit Ib loose to medium dense sand inter-layered with soft to fi rm clayUnit II till, consisting of fi rm to stiff sandy clay with inclusions of sand and

gravel

The geophysical and geotechnical data confirmed the slide had occurred within the upper loose sand deposit on a shallow gradient of around 5° to 10°. The project’s main focus was therefore to characterise this loose sand deposit, and investigate its cyclic behavior for potential seismic loading.

2 General Characteristics of Upper Sand

The fact that the slide occurred in micaceous sand was reminiscent of the well-documented ‘Jamuna Bridge’ project in Bangladesh (Hight et al. 1998), where a series of failures occurred due to dredging of shallow slopes formed of loose sand. Subsequent testing of material from the bridge site revealed how the sand’s behav-ior was affected by the mica content. Mica particles are flat and platy, resulting in loose packing and a significant increase in voids ratio when compared with other ‘additives’, as illustrated in Fig. 2.

The upper sand was found to be well graded, with few fines (see Fig. 3). Examination of the sand from the current project in the onshore laboratory revealed that it was indeed micaceous. The minimum and maximum void ratios were also

0Distance along slope, m

100100

120

140

160

180

200

200 300 400 500 600 700 800

Dep

th b

elow

MS

L, m slope = 3 to 9° blue line

shows seabed

CPTU/VC locations

direction of slide

dashed red line showstop of underlying till

Fig. 1 Seabed bathymetry and cross section through slope showing approximate thickness of overlying sand

Characterization of Micaceous Sand for Investigation of a Subsea Mass Movement 81

investigated and these are presented in Table 1 together with data for other ‘well-tested’ sands, based on information from Lunne et al. (1997).

The voids ratios measured for the current site are high compared with other sands in the literature, and much higher than those for Hokksund and Ticino sands which were used to develop the widely-used correlations between CPT cone resistance and relative density based on calibration chamber testing. Note that measurement of minimum and maximum voids ratio involves a degree of uncertainty, depending on the method used. The values in Table 1 are mainly based on the ASTM approach.

Calibration chamber testing has been performed by several institutions, including ENEL CRIS (Bellotti et al. 1988), ISMES (Baldi et al. 1986), NGI (Parkin and Lunne 1982), and Oxford University (Houlsby and Hitchman 1988)

0.0

0.5

1.0

1.5

2.0

2.5

0 5 10 15 20

void

s ra

tio

% mica, silt or kaolin by weight

mica inhibits packing

sand-sized micaangular siltkaolin

Fig. 2 Effects of mica content on voids ratio (adapted from Hight et al. 1998)

0.0

0.2

0.4

0.6

0.8

1.0

0.0

Com

pres

sion

inde

x, C

c

Voids ratio, e

Hokksund

Ticino

Dogs Bay

L. Buzzard

Quiou

Current site

Highcompressibilityfor current site

0

20

40

60

80

100

0.01

Per

cent

age

pass

ing

Grain size, mm

Hokksund

Ticino

Dogs Bay

L. Buzzard

Toyoura

Quiou

Current site

0

1

2

3

4

5

0 1 2 3

Pen

etra

tion,

m

Cone resistance, qc, MPa

0 20 40 60Pore pressure, u, kPa

0.5 1.0 2.5 3.01.5 2.0 0.1 1 10

Fig. 3 Grain size distribution and compression index for different sands; typical CPTU data for the site


and Southampton University (Last et al. 1987). Although many of the tests were performed on low to medium compressibility sands, some highly compressible sands were also tested, such as Dogs Bay and Quiou Sand. Research into highly compressible sands has generally focused on materials with a large proportion of ‘carbonate’ or ‘calcareous’ particles, whereas the engineering properties of the current sand appear to be governed by both the mica and carbonate particles.

Many calibration chamber test results are presented in Lunne et al. (1997) together with descriptions of the equipment. Grain size curves for some of the sands are shown together with the compressibility measured in oedometer tests on Fig. 3. A typical profile of cone resistance and pore pressure from the slide material is also shown.

Figure 4 shows the range in CPTU cone resistance measured at locations before (or outside) the slide and after (within) the slide. Very low values were measured within the slide and the average profile is much lower than that measured before the slide.

Table 1 Properties of sand for current sites and sands from calibration chamber tests

Sand name Gs

emin

, emax

Mineralogy (for guidance) Compressibility

Current site 2.70 0.9–2.1 10% mica, 40% quartz, 50% shells HighHokksund 2.70 0.5–0.9 35% quartz, 10% mica MediumTicino 2.67 0.6–0.9 30% quartz, 5% mica MediumToyoura 2.64 0.6–1.0 90% quartz LowL. Buzzard 2.65 0.5–0.7 Quartz LowDogs Bay 2.75 1.1–1.8 90% carbonate HighQuiou 2.71 0.5–1.3 74% shell fragments, 12% quartz HighSand A 2.70 0.8–1.6 Carbonate HighH. Mines 3.02 0.6–1.1 Feldspar, quartz, mica HighMonterey 2.65 0.6–0.8 Quartz with feldspar Low

0 2 4 6 8 10 12Cone resistance, qc, MPa

5

4

3

2

1

0

Dep

th b

elow

sea

bed,

m

0 2 4 6 8 10 12Cone resistance, qc, MPa

5

4

3

2

1

0

Dep

th b

elow

sea

bed,

m

Before/outside slide After/within slide

0 20 40 60 80 100Relative density, Dr, %

5

4

3

2

1

0

Dep

th b

elow

sea

bed,

m

0 20 40 60 80 100Relative density, Dr, %

5

4

3

2

1

0

Dep

th b

elow

sea

bed,

m

Before/outside slide After/within slide

Fig. 4 Profiles of CPTU cone resistance and relative density before (or outside) the slide and after (within) the slide


3 Interpretation of Relative Density

The cone penetration test is an excellent tool for evaluating the variability in soil strength or density across a site. For sands, relative density is typically used as a reference parameter, where this is the relationship between the current in-situ voids ratio and the maximum and minimum voids ratios, e

max and e

min, referring to

the loosest and densest possible states. The use of relative density as a design parameter itself is questionable. However, the parameter is used in the geotechni-cal laboratory during preparation of reconstituted sand specimens to the in-situ density since it is extremely challenging to obtain an ‘undisturbed’ sand sample during a site investigation.

Cyclic testing was planned for the current site to investigate liquefaction susceptibility of the sand and a reasonable estimate of the relative density was required to reconstitute the specimens, since the vibrocore method caused significant densification of the original material. The low cone resistance measurements were initially correlated with the relative density using the general correlation presented by Baldi et al. (1986) for normally consolidated deposits of clean sand:

' 0.550

1. ln

2.41 157c

rv

qD

s⎡ ⎤

= ⎢ ⎥⋅⎣ ⎦ (1)

Where Dr is relative density, q

c is cone resistance and s¢v0 is the in-situ vertical

effective stress. The corresponding profiles of relative density as calculated above are shown in Fig. 4. The Baldi correlation is probably the most widely used within current engineering practice and therefore serves as a reference for other correlations between cone resistance and relative density.

The relative density profiles inside the slide are greatly reduced, as are the cone resistance profiles shown in Fig. 4. The lowest interpreted relative densities for some locations are below 10% for some locations between 1 and 4 m penetration. These values are extremely low when compared with previous experience in both hydraulic fills and natural soils. Several studies suggest a minimum relative density around 25% in sand deposits (e.g. Lee et al. 1999). The same general figure applies in the laboratory where it is difficult to prepare a stable specimen in a looser state. These low calculated densities were therefore treated with caution.

The Baldi correlation is accepted to give reasonable results for deep deposits of uniform soils that match well with ‘standardised’ and less compressible materials in the literature (i.e. Ticino and Hokksund sands). Unfortunately, the correlation is less reliable for other types of soil. Differences in grain size distribution, angularity and especially mineralogy will affect the measured cone resistance for a given rela-tive density. Furthermore, the existing correlations generally provide a less reliable indication of actual soil density for shallow soils (the upper 5 m) since the lowest confining stress used in the calibration chamber tests was 50 kPa.

Compressibility has previously been used as a qualitative factor to explain some of the scatter in the data from calibration chamber testing. Jamiolkowski et al. (1985)


show how correlations between relative density and cone resistance are seen to change with varying compressibility. The results confirm the intuitive trend that more compressible sand will give a lower cone resistance for a given relative den-sity when compared with less compressible sand. Kulhawy and Mayne (1990) suggest an empirical correlation accounting for compressibility:

2 1

305c

rC OCR A

qD

Q Q Q=

⋅ ⋅ ⋅ (2)

Where qc1

is the normalised cone resistance = (qc/p

a)/(s¢v/pa

)0.5, QC is a compressi-

bility factor, QOCR

is an overconsolidation factor = OCR0.18 and QA is an ageing

factor. The compressibility factor is based on qualitative evaluation as opposed to any specific measurement with suggested values of 0.91 for high compressibility, 1.0 for medium compressibility and 1.09 for low compressibility, corresponding to the trend mentioned above.

Wehr (2005) presents another correlation based on a series of recent calibration chamber tests from Karlsruhe University (unpublished), including compressible calcareous sands. The correlation modifies the cone resistance using a ‘shell cor-rection factor’, f

shell. The updated cone resistance is then given by q

c,shell = q

c . f

shell

and the relative density may be recalculated.

0.0046 1.3629shell rf D= ⋅ + (3)

These relationships are compared on Fig. 5 with data for different sands from cali-bration chamber testing. The Baldi correlation tends to the lower bound of relative density for low values of normalised cone resistance (q

c1 < 50).

110

100

90

80

Rel

ativ

e D

ensi

ty, D

r

70

60

50

40

30

20

100 50 100 150

Normalised cone resistance, qc1

200 250 300

Correlations formore compressible(calcareous) soils

Range fromJamiolkowski et al

CC data

Baldi

K&M

Wehr

Jamiolkowski

Range fromKulhawy and Mayne

Fig. 5 Relative density versus normalised cone resistance, comparing empirical relationships with calibration chamber test data


Figure 5 shows clear scatter in test data which may be predominantly attributed to sand type. The high compressibility of the sand for the current site is demon-strated in Fig. 3. Uncertainty on how to reliably interpret the relative density for laboratory testing meant that the project chose to re-evaluate calibration chamber test data, including more recent experience with calcareous sands (see Table 1). The data points from Figure 5 are divided into sand type on Fig. 6 using a logarithmic plot to provide more detail at low values of normalised cone resistance.

Figure 6 suggests that the data for more compressible sands (Dogs Bay, Quiou and Sand A) indeed plot ‘above’ the Baldi line, agreeing with the trend indicated by the various published correlations. Furthermore, a fitted line through all data for low, medium and high compressibility sands also plots above the Baldi correlation, which is based predominantly on Ticino and Hokksund sands. Since no calibration chamber testing was performed for the current site, this ‘best-fit’ correlation is compared with the Baldi correlation in Fig. 7 for the range of CPTU data shown previously in Fig. 4.

Figure 7 shows the mean for all locations together with the mean ±1 standard deviation for the Baldi and ‘best-fit’ correlations. There is relatively little differ-ence in the relative density for CPTUs performed before or outside the slide zone where the average is around 70% (medium dense). However, there is a marked increase for the CPTUs performed within the slide zone where the relative density is significantly lower. This fits with the trend shown on Fig. 6, where the intersec-tion between the Baldi correlation and the logarithmic fit to calibration chamber test data is for a relative density of around 70% (or a normalised cone resistance just over 100).

Based upon the profiles shown in Fig. 7, the project agreed that the likely in-situ relative density of the sand was higher than predicted by the Baldi correlation.

Fig. 6 Relative density versus normalised cone resistance, showing data for different sand types

110

100

90

80

Rel

ativ

e D

ensi

ty, D

r

70

60

50

40

30

20

0

10

5 50

Correlations formore compressible(calcareous) soils

ToyouraL BuzzardHokksundTicinoDogs BayQuiouSand ALog fit (all data)K & MWehrBaldiJamiolkowski

Normalised cone resistance, qc1

500


Nonetheless, a range of 20% to 25% was conservatively applied for much of the advanced laboratory testing due to remaining uncertainties.

4 Laboratory Testing of Sand

An extensive laboratory test program at NGI and Montana State University was undertaken to investigate the behavior of the sand. A series of Anisotropically Consolidated Undrained triaxial (CAU) tests sheared in compression and extension were used to evaluate anisotropy. Cyclic constant volume Direct Simple Shear (DSS) tests were used to investigate the liquefaction potential.

The CAU triaxial tests were performed at the lowest achievable relative density, ranging between 25% and 45%, with a consolidation stress coefficient K

0 around

0.5. Figure 8 shows normalised stress paths for a total of ten tests, with six sheared in compression and four in extension. The mean and shear stresses have been normalised by the mean consolidation stress, p¢

0.

The results are compared with the range given by Hight et al. (1998) for Jamuna Bridge sand with a mica content of 0% to 40%. The results agree well with these previous findings, showing clear anisotropy with a much weaker response during initial shearing in extension than compression. According to the Jamuna Bridge results, the addition of a relative small proportion of mica (less than 2.5% by weight) resulted in a more unstable response, whereas larger proportions actually increased the stability of the sand. No detailed quantitative evaluation of the mica content was performed for the current site, but an estimate was made of 10% con-tent by volume which is equivalent to a much lower proportion of the weight. Hight et al. (1998) discuss the importance of sample preparation and grain orientation on results. Moist tamping was used exclusively for preparing samples for the current site, although care was taken to keep the relative density as uniform as possible,

Relative Density, Dr %

00

1

2

3

Dep

th, z

, m

4

5

20

Best fit, av

Best fit, +/– stdev

Before/outside After/inside

Baldi, +/– stdev

Baldi, av

40 60 80 100

Relative Density, Dr %

00

1

2

3

Dep

th, z

, m

4

5

20 40 60 80 100

Fig. 7 Profiles of relative density before (or outside) the slide and after (within) the slide, based on Baldi and ‘best fit’ correlations for all calibration chamber test data


with the lowest practical achievable relative density around 25% for the triaxial specimens and 20% for the DSS tests.

The results for the current site suggest static stability would be low for a trigger mechanism involving unloading at the base of the slope, similar to the Jamuna Bridge case. However, in the absence of the trigger mechanism, the slope stability was found to be adequate.

Cyclic DSS tests were performed for two levels of relative density, namely around 20% and 50%. The samples were sheared with different levels of normal-ised cyclic shear stress, t

cy /s¢vc, and an average shear stress t

cy /s¢vc = 0. Results are

summarised on Fig. 9 in terms of normalised cyclic shear stress versus number of cycles to failure. The scatter in data around t

cy /s¢vc = 0.25 is thought to be due to

natural variability in the material.The resulting ‘strength’ of the material with the relative density of 50% is much

greater than that with the lower relative density. The DSS testing was used to evaluate the liquefaction potential of the soils during seismic loading, where this can be evaluated by comparing the Cyclic Stress Ratio (CSR) and Cyclic Resistance Ratio (CRR) so that the resulting factor of safety is given by CRR/CSR.

The CSR represents the relative shear stress caused by the seismic event, whereas the CRR represents the relative shear resistance of the soil to a given event.

Seed and Idriss (1971) suggest a procedure for evaluating the CSR (here excluding the depth reduction coefficient):

Fig. 8 Normalised stress paths from anisotropically consolidated undrained triaxial tests

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Normalised mean stress, p'/p'0

Nor

mal

ised

she

ar s

tress

, τ/p

' 0Range in behaviour

from Hight et al. (1998)for sands with differentmica content (0 to 40%)

CAUC-1

CAUC-2

CAUC-3

CAUC-4

CAUC-5

CAUC-6

CAUE-1

CAUE-2

CAUE-3

CAUE-4Results show significant anisotropy, much weaker

response in extension than compression


max' '

0.65h v

v v

aCSR

g

t ss s

= = ⋅ ⋅ (4)

Where th is the horizontal shear stress caused by the seismic event, s¢v is the vertical

effective stress, sv is the vertical total stress and a

max is the seabed acceleration.

Two seismic events were evaluated for the site: a 100 year event and more extreme 10,000 year event. This allowed the CRR to be evaluated from the cyclic DSS tests. The 100 year event assumed an equivalent number of cycles (N

equiv) of 3,

giving the CRR as 0.4. The Peak Ground Acceleration (PGA) at bedrock was given as 0.02 g. The 10,000 years assumed N

equiv as 5, giving the CRR as 0.2. The PGA in

this case was given as 0.1 g. A site response analysis suggested the accelerations in the sand layer could be amplified by a factor of around 1.0 to 1.5. The total unit weight of the soil is taken around 16 kN/m3, which is equivalent to a relative density around 20%.

The CSR for the 100 year event is found to be between 0.04 and 0.06 for the 100 year event, which is far lower than the CRR of 0.4. The corresponding CSR for the 10,000 year event is found to be between 0.18 and 0.28 compared with the CRR of 0.2. The resulting safety factor suggests a possibility of failure for the extreme 10,000 year seismic event. However, additional analyses showed the pre-dicted maximum displacements resulting from the extreme seismic event to be minimal, which suggest that a catastrophic failure would be unlikely. Furthermore, the DSS results presented here are based upon a conservatively low relative density.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1 10 100 1000 10000

Nor

mal

ised

cyc

lic s

hear

str

ess,

τcy

/σ' v

c

Number of cycles to failure, N

Dr around 50%

Dr around 20%

N for gcy = 10%, thenstatic shear, estimated

N = 15 for gcy = 15%

Fig. 9 Summary of results from cyclic DSS tests at two levels of relative density


The prior evaluation of calibration chamber CPTU data suggests that these low values are likely to underestimate the in-situ field density.

The very shallow (<5°) slope at the base of the slide area where the loose sand is currently deposited gives an additional normalised average shear stress t

av/ s¢v =

sin 5° = 0.07. This shear stress acts permanently on the slope and can therefore be taken to act drained. Although no specific tests were performed in this case, experi-ence with other sands indicates that a small degree of drained average shear stress does not reduce the resistance to undrained cyclic stress.

Additional tests were performed to investigate the post-cyclic static strength of the sand, in order to evaluate the sand’s behavior after the unlikely event of seismic failure. Figure 10 shows the normalised cyclic shear stress versus shear strain and normalized effective vertical stress. The tests were run as before up to a limit of 10% cyclic shear strain at which point the cyclic stress was set to the zero point. Without allowing any intermediate drainage, the specimens were then sheared stati-cally to failure in either the ‘forwards’ or ‘reverse’ directions.

The cyclic tests show the typical trend of increasing shear strains with number of cycles, which would usually lead to failure for a cyclic test. The post-cyclic static test appears to follow a similar path as the final cycle of the cyclic tests. The aver-age effective vertical stress for the cyclic tests gradually reduces towards zero, although the response of the static test for larger strains forms an envelope due to dilation of the sand. This suggests that the sand would develop additional capacity at larger strains. This means that even if a slide were to occur due to a seismic trig-ger, the slope would likely stabilize after limited displacements.

The results from the in-situ and laboratory testing were then implemented in analyses to evaluate the static and cyclic stability of the slope as part of an ongoing investigation. Initial results suggest that the current stability is within acceptable levels.

5 Conclusions

A detailed site investigation and laboratory testing program was used to study the properties of a loose micaceous sand involved with a shallow slope failure offshore Norway. The soil exhibited elevated voids ratios and higher compressibility than many other documented sands. A subsequent re-evaluation of existing correlations between cone resistance and relative density suggested that the common Baldi cor-relation would not be valid, and a higher range of relative densities was used for reconstitution of samples in the laboratory.

Anisotropically consolidated undrained triaxial test results showed that the sand responded in a similar fashion to the well-documented Jamuna Bridge sand. The elevated voids ratio and platy mica particles promote a significantly anisotropic response during static undrained shearing. Direct simple shear testing revealed that the current sand would develop additional capacity at larger strains during post-cyclic static shear.


–0.6

–0.5

–0.4

–0.3

–0.2

–0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

–14–12–10 –8 –6 –4 –2 0 2 4 6 8 10 12 14Shear strain, g, %

DSS-12-cy

DSS-13-cy

DSS-12-st

DSS-13-st

–0.6

–0.5

–0.4

–0.3

–0.2

–0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

–0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Normalised effective vertical stress, s'v/s'vc

Nor

mal

ised

she

ar s

tres

s, t

/s' vc

Nor

mal

ised

she

ar s

tres

s, t

/s' vc

Fig. 10 Results from cyclic and post-cyclic static DSS tests in forward and reverse directions


For the Jamuna Bridge project, the failure was found to be initiated by a trigger mechanism with excavation at the base of the slope. A similar mechanism is antici-pated to be responsible for the failure at the current site; an investigation is ongoing and the laboratory testing results have been implemented in analyses to evaluate the static and cyclic stability of the slope. The results for this material may also be relevant for other sites worldwide where micaceous sands are encountered.

Acknowledgments The authors would like to acknowledge the input of David Hight and Steve Kay for advice and initial discussions during the planning and testing stage, based on experience with the Jamuna Bridge project. Colleagues at NGI and Montana State University are also thanked for assistance with laboratory testing and interpretation. The reviewers are acknowledged for timely and useful comments to the draft manuscript.

References

Baldi G, Bellotti R, Ghionna N, Jamiolkowski M and Pasqualini E (1986) Interpretation of CPTs and CPTUs. 2nd Part: Drained Penetration of Sands. 4th International Geotechnical Seminar, Field Instrumentation and In-Situ Measurements, Singapore

Bellotti R, Crippa V, Pedroni S and Ghionna VN (1988) Saturation of Sand Specimen for Calibration Chamber Tests. Proceedings of the 1st International Symposium on Penetration Testing, Orlando, FL

Hight DW, Georgiannou VN, Martin PL and Mundegar AK (1998) Flow Slides in Micaceous Sand. Problematic Soils, Sendai, Japan

Houlsby GT and Hitchman RC (1988) Calibration Tests of a Cone Penetrometer in Sand. Géotechnique, 38:39–44

Jamiolkowski M, Ladd CC, Germaine JT and Lancellotta R (1985) New Developments in Field and Laboratory Testing of soils. Theme Lecture. Proceedings of the 11th International Conference on Soil Mechanics and Foundation Engineering, San Francisco, CA

Kulhawy FH and Mayne PH (1990) Manual on estimating soil properties for foundation design. Electric Power Research Institute, EPRI, August 1990

Last NC, Butterfield R and Harkness RM (1987) An Investigation of Full-Scale Penetrometers in a Large Triaxial Calibration Chamber – March 1983 to February 1986, Civil Engineering Department, University of Southampton, Final Report to SERC

Lee KM, Shen CK, Leung DHK and Mitchell JK (1999) Effects of Placement Method on Geotechnical Behavior of Hydraulic Fill Sands. ASCE J Geotech Geoenviron Eng 132:832–846

Lunne T, Robertson PK and Powell JJM (1997) Cone Penetration Testing in Geotechnical Practice, Spon Press, London

Parkin AK and Lunne T (1982) Boundary Effects in the Laboratory Calibration of a Cone Penetrometer in Sand. Proceedings of the 2nd International Symposium on Penetration Testing, Amsterdam

Seed HB and Idriss IM (1971) Simplified Procedure for Evaluating Soil Liquefaction Potential. J Soil Mech Foundations Div, ASCE, 97(9):1249–1273

Wehr W (2005) Influence of the Carbonate Content of Sand on Vibro-compaction, 6th International Conference on Ground Improvement Techniques, Coimbra, Portugal

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