Download engineering geological mapping applied to the regional and urban

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Session number – Oral or poster presentation
ENGINEERING GEOLOGICAL MAPPING APPLIED TO THE REGIONAL AND URBAN
PLANNING OF THE ÁGUEDA REGION (PORTUGAL).
Isabel Duarte (1); António Pinho (2) and Fernando Ladeira (3)
(1) Department of Geosciences, University of Évora,7000-Évora-Portugal; Research Centre ”Industrial
Minerals and Clays”; E-mail: [email protected]
(2) Department of Geosciences, University of Évora,7000-Évora-Portugal; Research Centre ”Industrial
Minerals and Clays”; E-mail: [email protected]
(3) Research Centre ”Industrial Minerals and Clays”, FCT, University of Aveiro, Portugal; E-mail: ladeira.
[email protected]
KEY WORDS: Engineering Geological Mapping,
Urban Planning, Geotechnical Unities.
INTRODUCTION
The intention of this study is to contribute to the
geological and geotechnical knowledge of the
terrains of the Águeda region, where urbanindustrial development is one of the largest in the
country.
To this end, there were undertaken in the
region
a
photo-geological
study
and
reconnaissance of the surface, a collection of
samples for laboratory experimentation, tests in
the field and the collection of information contained
in the reports of geological and geotechnical
studies already done.
In the present work, it is intended to highlight to
what extent the existing geological and
geotechnical characteristics in the area under
study might influence:
a) decisions that relate to the better use of
space;
b) decisions about the suitability of the terrain
for the construction of different types of structures.
In making use of new areas that are sometimes
less suitable for construction purposes or which
have little known construction capacity, the urban
planner is confronted with questions of cost, of
security and safety and of prevention against
natural risks. In this context, Engineering Geology
provides essential information for the organisation
and development of the territory (Gonzalez de
Vallejo, 1977).
Underestimating or being unaware of
geotechnical conditions is often responsible for
heavy economic consequences, whereas prior
knowledge is, as a rule, a factor for economy and
security in the choice of location, in the
conception, in the project itself and in any
construction work that is undertaken. At the same
time, because of industrial development, the ever
increasing consumption of natural resources, the
growing levels of pollution, etc., the occupation of
land and the factors responsible for environmental
degradation have come to assume an increasing
importance in regional and urban planning.
Indeed, geological and geotechnical data have
a fundamental role at the level of primary decisionmaking as far as the occupation of new areas is
concerned. Use of these data by planning teams
helps to resolve a range of problems and allows
the following objectives to be achieved
(Golodkovskaya, 1979):
a) economy in the implementation of
engineering work;
b) security in construction, and the prediction
and prevention of natural risks;
c) rational use of the geological environment
together with the protection of natural resources.
The analysis of the geological and geotechnical
conditions of the area throws into relief the
dominant importance of geology above other
factors. It is certain that hydrological and
geomorphological conditions and the manifestation
of geodynamic phenomena are basically controlled
by lithology and by geological structure. For this
reason, lithology is in a privileged position as the
criterion for zoning purposes.
At the level of the lithological types which
comprise
each
geotechnical
unity,
their
characterisation
embraces
geotechnical
classification and classification with respect to
workability, to behaviour in relation to landfill, to
the behaviour of the layer under the road surface
and to the ground for building foundations (Duarte,
1993). The geotechnical zoning that is thus
obtained results, however, from a compromise
between general zoning (a description of the
properties of the terrain independent of its use)
and a zoning in terms of its utilisation (an
interpretation of the suitability of a terrain for a
given use).
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GENERAL
CHARACTERISTICS
ÁGUEDA REGION
OF
THE
The region under study belongs to the district
of Aveiro, in the north of Portugal, and occupies an
area of 80 Km2 (Figure 1).
•
•
mainly homogeneous and schist and greywacke in
nature.
In the selected area, two large geomorphological
unities are considered: Low Aluvial (low levels <15m and declivities less than 5%) and the
Elevated Zone (levels between 50 and 120 m and
declivities between 5% and 15%).
The hydrographic basin of the River Águeda is the
major feature represented in the area. The major
drainage follows an E-W orientation. The runoff of
surface water is high and there are dense
hydrographic networks, dendritic in appearance.
METHODOLOGY AND TESTS
The methodology used encompasses four
phases, each realising different work:
Figure 1 – Location of the Region.
The principal reasons for choosing this area
are as follows:
•
•
•
•
It is a region in full economic and industrial
development, with a recent increase in all types of
industry in locations that are not always
appropriate.
As a consequence of the growing numbers of
inhabitants and industrial installations, the need has
arisen for the planning and location of a waste
water treatment plant and a sewage treatment
plant.
Due to its geographical position, the town of
Águeda is situated at the point where important
roads meet, of which the IP5 and the A1 motorway
are of particular importance, together with the EN1,
the EN333 and the EN230.
The River Águeda flows through the town and has
influenced its urban plan, as well as environmental
problems related to it such as basic waste disposal,
adjacent infrastructures, among others.
Among the main geological, geomorphological
and hydrological characteristics, the following are
of note:
•
The region is in the Central-Iberian Zone (Julivert et
al., 1974) and is situated in a place of transition
between two of the principal morpho-structural
unities of Portugal: the Western Meso-Caenozoic
Terranes and the Iberian Massif. The formations of
post-Paleozoic Terranes are essentially composed
of sands, clays, gravel beds and sandstone,
although in the Iberian Massif, the formations are
Phase 1 – Collection of bibliographical data,
photo-interpretation and the recording of boreholes
and “in situ” tests .
Phase 2 – Geological reconnaissance of the
surface, collection of samples and drawing up of a
Sampling Map .
Phase 3 – Drawing up of a Geological Map and
completion of geotechnical field and laboratory
tests.
Phase 4 – Definition of geotechnical unities
based on lithological types and geotechnical
parameters. Drawing up of a Geotechnical Map.
The main laboratory tests that were undertaken
on the samples of soil collected with the objective
of characterising the geotechnical unities were:
moisture content, grain size distribution, liquid and
plastic
limits,
particle
density,
swelling,
permeability, sand equivalent, shear strength,
uniaxial and triaxial tests, compressibility and
compaction tests. Among the field tests of note
are: DPL-Dynamic Penetration Light, SPT –
Standard Penetration Test and Vane Test. From
the data obtained it was possible to establish
intervals of variation for the geotechnical
parameters for each geotechnical unity (Duarte et
al, 1994; Duarte, 1995).
.
GEOTECHNICAL UNITIES AND ENGINEERING
GEOLOGICAL MAP
In this work, the concept of “geotechnical
unity”, proposed by Gwinner (1954), was used in
the sense of comprising a group soils with identical
mechanical behaviour, although inside each unity
there can occur different types of soil.
At the same time, a basic principle of
Geotechnical Cartography refers to the fact that
geological history determines the geotechnical
properties of soils and rocks (UNESCO/IAEG,
1976). Thus, in drawing up the map of
geotechnical unities, the lithogenetic criterion was
used (UNESCO/IAEG, 1976), which consists of
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Session number – Oral or poster presentation
recognising terrains which have the same genesis
and identical geological history (represented by
diagenisis,
tectonics
and
phenomena
of
alteration). Based on this principle, the following
geotechnical unities were defined:
Al – Alluvial Deposits;
Q – Gravelly Formations;
P – Sandy-Silty Complex;
TC – Residual soils of sandstones and
siltstones from Triassic and Cretaceous Complex;
XG – Residual soils of schists and greywackes
Complex.
From the analysis and interpretation of the data
obtained in the tests that were made and
compiled, it was possible to characterise each
geotechnical unity, as well as to evaluate and
compare the geotechnical unities in relation to
expected geomechanical behaviour relative to
different requirements, particularly with reference
to aspects of the workability of the soil, the
behaviour in relation to landfill and on the layer
under road surface, excavatability and, finally, the
suitability of soils for urban occupation and for the
construction of roads. All of these aspects are
represented in diagrammatic synthesis which
complements the interpretation of the Engineering
Geological Map.
Finally, the Engineering Geological Map of the
Águeda Region is presented, initially drawn up to
the scale of 1/10 000. A reduction of this is
presented in Figure 2.
Figure 2 – Engineering Geological Map of the Águeda
Region.
REFERENCES
DUARTE, I. M. R (1993) - Contribution to the
Engineering geological mapping of the Águeda
region. Msc. Thesis (FCT/UNL), 153p.
DUARTE, I. M. R. & LADEIRA, F.L. (1994) - "Regional
planning in Águeda country through engineering
geological mapping". Proceedings 7th International
Congress International Association of Engineering
Geology. Lisboa, 1994, Vol. II, pp.1261-1266.
DUARTE, I. M. R. (1995) – Geotechnical characteristics
of residual soils from the Agueda region. Proc. 5º
Nat. Cong. Geot., Coimbra. Vol 1, pp.167-172.
GOLODKOVSKAYA, G.A. et al.(1979). Engineering
geological mapping in the URSS. Proc.XXIII
Int.Geol.Cong., Prague, Vol.12, pp.57-64.
GONZALEZ de VALLEJO, L. (1977). Engineering
geology for urban planning and development with an
example from Tenerife (Canary Islands). Bull.IAEG,
nº15, Krefeld, pp. 37-43.
GWINNER, M. (1954). Die Anwendung der genetischemorphologischen Bodenkund in der Ingeneur
geologie, insbesondere zur Klassifizierung des
Baugunds
auf
BaugrundKarten.
Mitt.Arb.Geol.Min.Inst. TH Stuttgart, 12.
JULIVERT, et al (1974). Mapa tectónico de la Peninsula
Iberica y Baleares. Int.Geol. y Min. de España,
Madrid. 101p.
UNESCO/IAEG (1976). Guide pour la préparation des
cartes géotechniques. Les Presses de l`Unesco,
Paris.