ICE Manual of Geotechnical Engineering Vol 1: Geotechnical Engineering Principles, Problematic Soils and Site Investigation

202 Pages·2012·22.67 MB·English

by  John Burland

Partial Saturation in
Compacted Soils
Ge´ otechnique Symposium in Print 2011
Edited by
Domenico Gallipoli
Chair, Ge´otechnique Symposium in Print 2011 sub-committee
Copyright © ICE Publishing, all rights reserved.
Ge´otechnique Advisory Panel Sub-Committee for the Symposium in Print 2011:
Chair:
Professor Domenico Gallipoli, Universite´ de Pau et des Pays de l’Adour, France
Members:
Professor Eduardo Alonso, Universitat Polite`cnica de Catalunya, Spain
Dr Lennart Bo¨rgesson, Clay Technology AB, Sweden
Professor Federica Cotecchia, Politecnico di Bari, Italy
Professor Pierre Delage, Ecole Nationale des Ponts et Chausse´es, France
Professor Cristina Jommi, Politecnico di Milano, Italy
Professor Claudio Mancuso, Universita` degli Studi di Napoli Federico II, Italy
Dr John McDougall, Napier University, UK
Dr Andrew Ridley, Geotechnical Observations, UK
Professor Tom Schanz, Ruhr-Universta¨t Bochum, Germany
Professor Alessandro Tarantino, University of Strathclyde, UK
Professor David Toll, Durham University, UK
Professor Simon Wheeler, University of Glasgow, UK
Related titles from ICE Publishing:
Geotechnical Engineering Principles, Problematic Soils and Site Investigation.
J. Burland, T. Chapman, H. Skinner and M.J. Brown (eds). ISBN 978-0-7277-5707-4.
UK Specification for Ground Investigation, Second edition (Site Investigation in
Construction Series). Site Investigation Steering Group. ISBN 978-0-7277-3506-5
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Preface
This book contains the proceedings of the Ge´otechnique Electron Microscopy or Mercury Intrusion Porosimetry, have
Symposium-in-Print 2011, which was held on the theme of provided new insight into the link between stress-strain
Partial Saturation in Compacted Soils at the Institution of behaviour and material fabric in compacted soils. Some of
Civil Engineers on 20 June 2011. The Symposium attracted the contributions in this book emphasize the ‘living nature’
around 70 delegates, from both industry and academia, of soil fabric, which evolves during wetting–drying cycles
representing countries such as Australia, Czech Republic, and induces corresponding changes of macroscopic mechani-
France, Hong Kong, Italy, New Zealand, Portugal, Spain, cal properties over time.
Switzerland and UK. Significant improvements of design practice have often
The book contains the two keynote addresses delivered by originated from the formulation of general constitutive laws
Prof. Eduardo Alonso and Mr Tony O’Brien, respectively, and principles of soil behaviour, underpinned by an under-
together with the nine papers and one technical note pub- standing of material properties at the microscopic scale.
lished in the April and May 2011 issues of Ge´otechnique During recent years, engineers and scientists have advanced
and presented by authors during the Symposium. These nine fundamental knowledge of mechanical and retention behav-
papers and one technical note were selected, following iour of compacted soils; however, this research momentum
standard Ge´otechnique peer-review, from a total of 98 must be sustained over time to achieve the detailed under-
articles offered in response to a thematic call in the summer standing of soil behaviour which is essential to produce a
2009. They are grouped in this book under four topics step change in geotechnical models and a leap in analytical
corresponding to the four Symposium sessions, namely capabilities.
Material Characterization, Experimental Observation and As highlighted by some of the contributions in this book,
Modelling, Benchmarking of Techniques and Models, and there are still significant challenges ahead for unsaturated
Application to Engineering Problems and Case Studies. The soil modellers. As already known from saturated soil mech-
book also contains a selection of questions posed by dele- anics, the accurate prediction of irreversible volumetric
gates after presentations during the Symposium, together strains during shearing is a particularly arduous task for
with relative answers by presenters. constitutive modellers and well-known saturated models,
The idea of devoting the 16th Ge´otechnique Symposium- such as Modified Cam-Clay, significantly overestimate volu-
in-Print to the theme of Partial Saturation in Compacted metric strains at critical state. This assumes even greater
Soils was instigated by recent advances in the study of significance in unsaturated soils where water retention be-
geomaterials with multiphase or immiscible pore fluids. One haviour is intrinsically linked to volumetric straining. In this
application of this study relates to the design and analysis of case, any error in the calculation of volumetric strains will
earth structures/fills (e.g. dams and embankments, clay bar- have an impact on the computed water retention response,
riers) made of compacted soils that are unsaturated at the i.e. on the predicted variation of degree of saturation and on
time of placement (i.e. pores are partly filled by water and its effect on strength and deformation.
partly filled by air). Unlike saturated soils whose pores are Moreover, the sensitivity of predictions to parameter cali-
entirely filled by water, the presence of two immiscible pore bration poses an additional challenge to engineers wishing to
fluids gives rise in unsaturated soils to capillary actions on apply unsaturated models to practical problems. The adop-
the solid skeleton that affect both deformation and strength. tion of different strategies in selecting parameter values,
During service life, the compacted soil will alternate be- even for the same model and from the same set of experi-
tween unsaturated and saturated conditions, or remain per- mental data, can result in different computations of soil
manently unsaturated, depending on prevailing environmental behaviour, partly because of the large number of parameters
actions. involved. This raises doubts about the usefulness of develop-
Some key engineering properties of compacted soils (e.g. ing ever more sophisticated constitutive laws without propos-
strength, stiffness and permeability) depend on current ing, at the same time, robust methods for parameter
moisture content, which will change as a consequence of the calibration.
interaction with the surrounding environment. It is therefore The book also includes results from two benchmark exer-
not surprising that, since the early 30s, civil engineers have cises undertaken by several European Universities within the
devoted considerable effort to the study of unsaturated ‘‘Marie Curie’’ Research Training Network MUSE (Mech-
compacted soils. Ralph Proctor, from the Los Angeles anics of Unsaturated Soils for Engineering). A salient activ-
Bureau of Waterworks and Supplies in the USA, performed ity of the MUSE Network has been the comparison of
a wide laboratory campaign of compaction tests on more experimental/modelling techniques used by researchers
than 200 soils, driven by the necessity of developing suitable across the world. This activity had the twofold objective of
construction protocols to maximise stability and minimize improving current procedures and, where possible, formulat-
permeability of earth dams. This resulted in the definition of ing accepted standards. In this spirit, these two benchmarks
the ‘optimum moisture content’, i.e. the water content that make use of easily accessible data or commercially available
produces the highest soil dry density for a given compaction materials so that they can be readily repeated by other
effort. researchers.
Today, routine geotechnical design still relies on Proctor’s I would like to thank all members of the Symposium sub-
definition of optimum water content. Nevertheless, modern committee, namely Eduardo Alonso, Lennart Borgesson,
experimental techniques, such as Environmental Scanning Federica Cotecchia, Pierre Delage, Cristina Jommi, Claudio
Copyright © ICE Publishing, all rights reserved.
iv PREFACE
Mancuso, John McDougall, Andrew Ridley, Tom Schanz, anics, ranging from material testing to modelling and analy-
Alessandro Tarantino, David Toll and Simon Wheeler, for sis of engineering boundary value problems. This knowledge
their contribution in organizing the Symposium and review- will contribute to improve design of earth structures/fills by
ing manuscripts within a very tight timescale. I would also maximizing the use of locally sourced soils, with consequent
like to thank the Ge´otechnique Advisory Panel, and in gains in safety, cost and sustainability of future building
particular the then Chairman, Prof. Chris Clayton, for sup- practice. I wish you enjoyable reading and hope that this
porting the proposal of a Ge´otechnique Symposium-in-Print volume will become a valuable reference for engineers and
on the theme of Partial Saturation in Compacted Soils and researchers in future years.
for their continued help throughout the organization.
This book provides a comprehensive overview of recent Domenico Gallipoli
advances in the fast growing area of unsaturated soil mech- Chair, Ge´otechnique Symposium-in-Print 2011
Copyright © ICE Publishing, all rights reserved.
Contents Preface iii
Keynote speeches
Compactedsoilbehaviour:initialstate,structureandconstitutivemodelling 3
E.E.Alonso,N.M.PinyolandA.Gens
Theassessmentofoldrailwayembankments-timeforachange? 19
A.S.O’Brien
Session 1: Material Characterisation
Papers
Effectsofthemaximumsoilaggregatessizeandcyclicwetting-dryingonthestiffnessofalime- 35
treatedclayeysoil
A.M.Tang,M.N.VuandY.-J.Cui
Technical Note
Someaspectsofthebehaviourofcompactedsoilsalongwettingpaths 45
S.Taibi,J.M.Fleureau,N.Abou-Bekr,M.I.Zerhouni,A.Benchouk,K.LachgueurandH.Souli
Session 2: Experimental Observation and Modelling
Papers
Aninsightintothewaterretentionpropertiesofcompactedclayeysoils 55
E.Romero,G.DellaVecchiaandC.Jommi
Hydromechanicalbehaviourofcompactedgranularexpansivemixtures:experimentaland 71
constitutivestudy
E.E.Alonso,E.RomeroandC.Hoffmann
Experimentalobservationsofthestressregimeinunsaturatedcompactedclaywhenlaterally 87
confined
J.L.BoydandV.Sivakumar
Session 3: Benchmarking of Techniques and Models
Papers
Benchmarkofconstitutivemodelsforunsaturatedsoils 109
F.D’Onza,D.Gallipoli,S.Wheeler,F.Casini,J.Vaunat,N.Khalili,L.Laloui,C.Mancuso,
D.Masˇ´ın,M.Nuth,J.-M.PereiraandR.Vassallo
Benchmarkofexperimentaltechniquesformeasuringandcontrollingsuction 129
A.Tarantino,D.Gallipoli,C.E.Augarde,V.DeGennaro,R.Gomez,L.Laloui,C.Mancuso,
G.ElMountassir,J.J.Munoz,J.-M.Pereira,H.Peron,G.Pisoni,E.Romero,A.Raveendiraraj,
J.C.Rojas,D.G.Toll,S.TombolatoandS.Wheeler
Session 4: Application to Engineering Problems and Case Studies
Papers
Hydromechanicalbehaviourofaheterogeneouscompactedsoil:experimentalobservationsand 141
modelling
A.Gens,B.Valleja´n,M.Sa´nchez,C.Imbert,M.V.VillarandM.VanGeet
ModellingtheresponseofLechagoearthandrockfilldam 161
E.E.Alonso,S.Olivella,A.Soriano,N.M.PinyolandF.Esteban
Physicalmodellingofwetting-inducedcollapseinembankmentbase 183
L.Thorel,V.Ferber,B.CaicedoandI.M.Khokhar
Selected Questions and Answers 195
Copyright © ICE Publishing, all rights reserved.
Keynote Speeches
Copyright © ICE Publishing, all rights reserved.
Copyright © ICE Publishing, all rights reserved.
Alonso, E. E. et al. Ge´otechnique [http://dx.doi.org/10.1680/geot.11.P.134]
Compacted soil behaviour: initial state, structure and constitutive
modelling
(cid:2) (cid:2) (cid:2)
E. E. ALONSO , N. M. PINYOL † and A. GENS
The paper explores the behaviour of compacted soils throughout the (dry density–water content)
compaction plane by means of a conceptual framework that incorporates microstructural information.
The engineering properties of compacted soils are described by an initial state in terms of a yielding
stress, soil suction and a microstructural state variable. Microstructure is defined by the ratio of
microvoid volume to total void volume. The pattern of variation of the microstructural parameter
within the compaction plane has been determined, for some compacted soils, by analysing mercury
intrusion porosimetry data. The microstructure of wet and dry compaction conditions can then be
quantified. To ensure consistency, the framework is cast in the form of a constitutive model defined in
terms of an effective suction and a constitutive stress that incorporate the microstructural variable.
The model is shown to be consistent with a number of experimental observations and, in particular, it
explains the intrinsic collapse potential of compacted soils. It predicts, for a common initial suction, a
higher collapse potential for dry of optimum conditions than for wet compaction. It also predicts in a
natural manner the observed evolution of soil compressibility during drained or undrained loading.
Model capabilities are illustrated by application to a testing programme on statically compacted
samples of low-plasticity silty clay. The compression behaviour of samples compacted wet and dry of
optimum and the variation of collapse strains with confining stress have been successfully reproduced
by the model.
KEYWORDS: clays; compaction; constitutive relations; fabric/structure of soils; partial saturation; plasticity;
suction
INTRODUCTION the 1950s and 1960s (Leonards, 1955; Lambe, 1958; Seed &
A significant proportion of the published research on unsatu- Chan, 1959; Lambe & Whitman, 1969). This idea is recov-
rated soil mechanics concerns compacted soils. It could be ered here, but the focus now is to incorporate advances in
inferred that examining the current state of development of unsaturated soil mechanics reported in the last two decades.
unsaturated soil research would provide detailed information Significant recent contributions involve the search for appro-
on compacted soil behaviour. This is only partially true, priate constitutive stress formulations, the development of
however. Often, basic research is conducted in silty mater- elasto-plastic frameworks, and the increasing recognition of
ials, statically compacted at a low density. These soils the role played by soil microstructure.
exhibit an open structure, sensitive to suction-induced Microstructure, in particular, was very early identified as a
effects. Compacted soils in practice span a much wider key feature in any explanation of compacted soil behaviour
range of grain-size distributions. Proctor (1933) was able to associating dispersed microstructure with compaction on the
show the fundamental relationship between attained density wet side (wetter than optimum) and flocculated microstruc-
and water content for a given compaction energy. This ture with compaction on the dry side (drier than optimum)
finding defined the compaction plane (in terms of dry unit (Lambe, 1958; Lambe & Whitman, 1969). However, direct
weight, ª , against water content, w) which is a very observations of soil fabric by means of scanning electron
d
convenient procedure to represent the compaction states of a microscopy, and the interpretation of mercury intrusion
given soil. This plane remains the basic representation for porosimetry tests reported from the 1970s (Sridharan et al.,
investigating the properties of compacted soils. 1971; McGown & Collins, 1975), led to significant changes
This is also the starting point of the study reported in this in this initial microstructural interpretation. It was observed,
paper. Instead of focusing on a given initial state of a for instance, that clay tended to form aggregated structures
compacted soil, the main objective is to explore the compac- that behaved as much larger particles, especially when
tion plane. This approach will hopefully provide a wider compacted on the dry side. It was soon accepted that water
perspective on soil compaction. The properties of compacted was trapped inside the clay aggregations, even if the mixture
soils (permeability, stiffness, strength) were linked to the remained relatively dry. These ideas have been widely con-
compaction state in some classical contributions published in firmed by subsequent studies (Delage et al., 1996; Romero
& Simms, 2008; Lee & Zhang, 2009; Monroy et al., 2010).
The debate on effective stress has been a recurrent topic
in unsaturated soil mechanics research since the early intro-
duction by Bishop (1959) of an effective stress equation.
Manuscript received4November2011; revised manuscript accepted
This topic will be discussed further below. The unavoidable
3September2012.
fact is, however, that modern constitutive laws for unsatu-
Discussion onthispaperiswelcomedbytheeditor.
(cid:2)Department of Geotechnical Engineering and Geosciences, rated soils that attempt to provide a comprehensive descrip-
tion of soil behaviour (and not just of a specific property)
UniversitatPolite`cnica deCatalunya,Barcelona, Spain.
†International Centre for Numerical Methods in Engineering have been always formulated in terms of two ‘stress states’
(CIMNE),Barcelona, Spain. or ‘constitutive stresses’ (Jommi, 2000; Gens, 2010). One of
3
Copyright © ICE Publishing, all rights reserved.
4 ALONSO, PINYOL AND GENS
them is generally a function of soil suction, often the soil regarding the effects of microstructure on the engineering
suction itself. behaviour of compacted soils. The incorporation of such
The development of elasto-plastic constitutive models effects is a key aspect of the work presented here.
provides an alternative way to characterise the initial state of In summary, the goal of this paper is to present a unified
compacted soils by associating model parameters and vari- but general picture of compacted soil behaviour incorporat-
ables with the pair dry unit weight and water content (ª , ing recent developments in unsaturated soil mechanics and
d
w), which defines the ‘as-compacted’ condition. For instance, microstructural considerations.
the dry density achieved by compaction can be related to the The paper is organised as follows. First, a summary of
position of the initial yield surface after compaction. Water some relevant experimental work devoted to isolate the
content, on the other hand, is controlled mainly by the effect of microstructure on compacted soil behaviour is
current suction, s, and to a lesser extent by the void ratio. In presented. Then a constitutive stress expression that incorpo-
the context of the simple elasto-plastic BBM model (Alonso rates explicitly soil microstructure is introduced. This is
et al., 1990), the yield surface is essentially defined by the done through the definition of a single microstructural state
isotropic yield stress for saturated conditions, p(cid:2): Therefore, variable. The interpretation of testing programmes providing
0
as a starting point, the pair (p(cid:2), s) may provide equivalent data on pore size distribution has allowed this microstructur-
0
information to (ª , w), with one added advantage: they al state variable to be mapped onto the compaction plane,
d
supply fundamental information for constitutive modelling. and general trends of behaviour to be established. Compres-
An analysis of a limited number of soil compaction sibility and its relationship with suction and microstructure
testing programmes led to the p(cid:2)–ª relationship given in are then discussed, because this leads to a consistent descrip-
0 d
Fig. 1 (Alonso & Pinyol, 2008). It can be noted that the tion of collapse behaviour, one of the key aspects of
saturated isotropic yield stress increases rapidly with dry unsaturated soil behaviour. To ensure consistency, the de-
unit weight. Also, for a given dry unit weight, the yield scription of behaviour is cast in the form of a new constitu-
stress p(cid:2) increases significantly with soil plasticity. The plot tive framework that incorporates the developments and
0
in Fig. 1 may help to select p(cid:2) in the absence of specific concepts described previously. Its predictive capabilities are
0
tests. On the other hand, many s(w, ª ) relationships can be checked against experiments.
d
found in the literature (e.g. Gens et al., 1995; Li, 1995;
Romero et al., 1999; Tarantino & Tombolato, 2005).
Thus the pair (p(cid:2), s) provides key information MICROSTRUCTURE AND COMPACTED SOIL
0 as-compacted
concerning the compacted state of a given soil, but it does BEHAVIOUR
not include any information on its microstructure. A review In this paper, information on microstructure is derived
of microstructural effects on the compacted soil behaviour, from MIP tests performed both after compaction and after
given below, indicates that microstructure is also a signifi- the application of a given stress–suction path.
cant aspect that should be introduced in a realistic modelling Consider, in Fig. 2, the pore size density function of a
of compacted soils. The generalisation of techniques (parti- sample of low-plasticity Barcelona silty clay (w ¼28%,
L
cularly mercury intrusion porosimetry, MIP) to examine the IP¼9.3%), statically compacted at a high void ratio
evolution of soil microstructure has provided information (e¼0.82) and then isotropically loaded in a triaxial cell to a
substantially lower void ratio (e¼0.57) (Buenfil et al.,
2004). The observation of two dominant pore sizes during
2·2
High-plasticity Boom clay compaction, especially dry of optimum, is a characteristic
(Romero, 1999) feature, widely observed. These two dominant pore sizes
2·0 Medium-plasticity soil w (cid:2)56% will be referred to as microporosity and macroporosity.
(Hondaet al., 2003) L
IP(cid:2)27% Volumetric deformation upon isotropic loading results in a
1·8 Medium-low-plasticity soil reduction of the size and volume of the macropores. In
(Hondaet al., 2003)
contrast, the micropores retain their partial volume and their
Morainic soil
1·6 (Cuisinier & Laloui, 2004) size. Clay aggregates are readily observed in the micropho-
tographs for e¼0.82 and, to a lesser extent, for e¼0.57,
Low-plasticity silty clay
1·4 from Barcelona where it can be observed that the size of the macropores has
Pa (Barrera, 2002) clearly reduced.
M
p*: 01·2 N(Boanlm-palacsetdica s, i1lt9y 9s1a)nd chaAngseescoisndgiveexnaminplFeigo.f3tfhoer Befofeocmt colfayloianditiinagllyancdomspuacctitoedn
Yield stress, 01··80 MSclaaenya sSuarlevda dvoarlu seil toyf wL(cid:2)33·5% mactoneeldlen.¼twhTea0hns.e9w3dsretiartetenedsdds–aSatrstu¼cccoot0inno.ss4ntta4annp(ttaRtvvoheomrltuaeipmcropaelliee(stsdtwraeleis.sl,sli2nsi0nkg1e1ptac)rnh.eesTosdhuederieonsmppFaeetctihegi-)r.
IP(cid:2)13·2%
3(a). Pore size distribution tests were performed at points 1,
0·6 2 and 3, and the results are given in Fig. 3(b). The first
loading–wetting path results in a significant reduction in the
0·4 IwPL(cid:2)(cid:2)1320%% IwPL(cid:2)(cid:2)1310··85%% wL(cid:2)28% soifzethoefmthaecrmopaocrreosp,obreust. tFhuertmheircrdorpyoirnogsitryedsueceemdsthteovroemluamine
wL(cid:2)43% IP(cid:2)8% largely unchanged throughout.
0·2 IP(cid:2)13·4% NP Figure 4 shows the change in pore size distribution of a
sample of Barcelona silty clay, statically compacted on the
0 dry side (sample DD), when it is wetted under a small
1·0 1·2 1·4 1·6 1·8 2·0 confining stress and taken to the position DW close to
Dry unit weight,γd: g/cm3 saturation conditions. Some changes are observed, but in this
case the ‘as compacted’ pore size distribution seems to be
Fig.1. Relationship between isotropic yield stress at saturated
conditions and dry density of several soil types. From Alonso & largely preserved after wetting.
Pinyol (2008). # 2008 Taylor & Francis Group, London, UK. This is consistent with the results of Thom et al. (2007)
Usedwithpermission testing statically compacted kaolin, dry of optimum, which
Copyright © ICE Publishing, all rights reserved.
COMPACTED SOIL BEHAVIOUR: INITIAL STATE, STRUCTURE AND CONSTITUTIVE MODELLING 5
60 μ m s
e(cid:2)0·82
D)
g 1 3
o 19 μ m
/ (lδδe0·8
(cid:3) e(cid:2)0·57
n,
o
cti
sity fun0·4 455 nm pSrwepseasltlhuinrge Drying
n
e
d
e
z
si
e
or
P 2 σ
0 (a)
10 100 1000 10000 100000
Entrance pore size,D: nm
(a) D) As-compacted
g e (cid:2)0·41
/ (loδδe0·8 Scowantusrtaantiot nvo alutme 2
(cid:3)
on, Dried after 1
cti saturation
n
u
y f 0·4
sit
n
e
d
e
z
si
e
or 3
P
0
10 100 1000 10000 100000
Entrance pore size,D: nm
(b)
Fig.3. Evolution of pore size distribution of compacted high-
plasticity Boom clay during loading and suction changes: (a)
stress path; (b) pore size distribution at three stress–suction
pointsindicatedin(a).FromRomeroetal.(2011)
indicated that the bimodal domain of voids induced by soil
compaction is essentially maintained upon the application of
(b) significant stress and suction changes. However, this is not
always the case. Wetting tests reported by Monroy et al.
(2010) on statically compacted high-plasticity London Clay
indicate that changes in micropores may also be significant
on wetting. The higher activity of the clay probably explains
the enhanced sensitivity of microporosity to suction changes.
The variation of engineering properties of a given soil
when compacted at different dry densities and water contents
has been often reported (Cox, 1978; Rese´ndiz, 1980; Lawton
et al., 1989, 1991; Alonso et al., 1992; Benson et al., 1992;
Fredlund & Rahardjo, 1993; Tinjum et al., 1997; Vanapalli
et al., 1999; Simms & Yanful, 2002; Santucci de Magistris
& Tatsuoka, 2004; Jotisankasa et al., 2007, 2009). However,
it is not feasible to isolate microstructural effects in many of
these contributions, mainly because compacting dry or wet
of optimum implies not only a different microstructure, but
also a different suction. In addition, compacting at different
void ratios implies both a variation in macroporosity and a
change in the initial yield locus. Hence conventional testing
of compacted samples mixes the effects of the initial state
(p(cid:2), s) and of the microstructure. Therefore specifically
0
designed testing programmes are required to isolate micro-
structural effects.
An interesting example of such programmes is provided
(c) by Santucci de Magistris & Tatsuoka (2004), who tested
dynamically compacted specimens of low-plasticity silty
Fig.2. Evolution of microstructure during loading. (a) Pore size
sand (a residual granitic soil) in a triaxial cell. Once
distribution. (b), (c) ESEM observations, statically compacted
low-plasticityBarcelonasiltyclay:(b)e 0.82;(c)e 0.57.After compacted, all samples were taken to a saturated state before
Buenfilet al.(2004) testing. Because it is a low-plasticity soil, it was expected
Copyright © ICE Publishing, all rights reserved.