Engineering geology for urban planning and development with an

I B U LLETI N
of the International Association of ENGINEERINGGEOLOGY
de I'Association Internationals de GEOLOGIE DE L'INGENIEUR N ~
37--43
,KREFELD1977
I
ENGINEERING GEOLOGY FOR URBAN PLANNING AND DEVELOPMENT WITH AN EXAMPLE
FROM TENERIFE (CANARY ISLANDS)
LA GEOTECHNIQUE POUR LA PLANIFICATION ET LE DEVELOPPEMENT URBAINS AVEC UN
EXEMPLE DE TENERIFFE (ILES CANARIES)
GONZ,g.LEZDE VALLEJO L., Empresa Nacional ADARO. Serrano, 116-Madrid, Spain.
Summary:
A n a p p r o a c h t o e n g i n e e r i n g geological a s s e s s m e n t f o r u r b a n p l a n n i n g and d e v e l o p m e n t is p r e s e n t e d . T h e e n g i n e e r i n g geological investigations f o r t h e u r b a n p l a n n i n g o f Santa Cruz de T e n e r i f e ( C a n a r y Islands) are used as an e x a m p l e .
R6sum6.
O n p r 6 s e n t e la G~ologie d e l'Ing6nieur c o m m e u n m o y e n d ' 6 t u d e utihsable p o u r la p l a n i f i c a t i o n et le d 6 v e l o p p e m e n t u r b a i n s
e n e m p l o y a n t c o m m e e x e m p l e lee investigations g 6 o t e c h n i q u e s r6alis6es p o u r la p l a n i f i c a t i o n u r b a i n e de Santa Cruz de
T e n e r i f e (lies Canaries).
Introduction
The role of engineering geology in urban planning has started to be
recognized in practice only in the last ten years, (1), (9), (14). More
recently an increasing general concern has been observed, (5), (10),
(13), (11), etc. Engineering Geology can contribute significantly to
the solution of many of the urban problems, as follows:
I. Selection of the most environmentally favourable urban settlements.
II. Selection of the most suitable areas for town development.
III. As a contribution to achieve the most economical and environmentally conservative solution for the Urban Plan.
IV. Specific assistance during the development, design and construction stages of the town.
Geology, geomorphology and hydrogeology must be known and investigated before any engineering geological study is carried out.
The kind of information they can provide should be up-to-date, and
at an adequate scale. After these basic investigations, the following,
engineering geological problems should de considered:
- Foundations
- Ground stability
Excavations
Natural resources
Water supply
Waste disposal.
-
-
-
-
An approach to presentation o f maps for urban planning purposes
could suggest these categories:
-
Basic maps
Engineering geological maps
Influence factor maps
Urban suitability maps
Land system maps.
Basic maps are represented by geological, hydrogeological and geomorphological maps. The engineering geological maps should be presented in the way recommended by (2). Normally they include the
information in one sheet map, but where complex factors occur
multiple maps are used which delineate special factors, hazards and
purposes. These are the influence factor maps. Tables which describe the mapped units and their engineering properties are usually
annexed. Although there is no general agreement as to the number
and type of influence factors to be included, nor how they should
be presented for urban planning purposes, the inclusion of the
following is suggested:
- Slope
Foundation conditions
Groundwater conditions
Construction materials
Slope stability
Waste disposal
Mineral resources
Geological hazards.
-
-
-
-
-
-
The incidence of geological hazards in towns is limited and normally
is restricted to particular areas. However, if these occur the consequences can be catastrophic. This possibility places geological
hazards in a very special position in land-evaluation for urban
planning.
Examples of urban suitability maps are given by (8), (15) and (12).
Land system maps are very useful when the analysis of a great number o f variables or even the whole environment over large areas is
required in a short time (3), (7).
Land use planning based on zoning the area in sectors of different
risk is the only way to cope with geological hazards. A general
approach could be:
T h e S a n t a Cruz d e T e n e r i f e Case
I. Evaluation of the problem.
II. Zoning and rating the area as to different grades of risk.
III. Planning and development in accordance with these zones.
IV. Application of special measures and the avoidance or restriction of development where recommended.
This approach can neither eliminate nor diminish the geological
phenomena, but their effects on lives and property can be dramatically decreased (4).
This planning and design of site investigations to tackle the abovementioned engineering geological problems depends largely on the
purpose and stage of the urban planning and development and on
the geological complexity of the area. Fig. 1 is a suggestion of the
different stages and purposes of the site investigations and how they
are influenced by the urban planning conditions;
Engineering geological investigations were carried out to provide information on the physical environment and engineering geological
characteristics of the urban planning of Santa Cruz de Tenerife
(Canary Islands). The area studied has a surface of approximatly
100 sq.km with present population of 250,000 inhabitants, estimated to reach 350,000 in the next fifteen years.
Santa Cruz and La Laguna are the largest towns. These have experienced a rapid peripheral expansion over a region of particular
and complex geological and morphological conditions.
The area (Fig. 2) is composed of three main lithological formations:
The borders of the Anaga Massif, the alluvial clays of La Laguna,
and the Basaltic Series III. The Anaga Massif, which is the oldest formation, extends through the north and north eastern borders of the
area. It is formed of basaltic lava flows and large masses of pyroclastic flows. The alluvial clays, located in the centre of the area, are
the consequence of the filling of a valley which was clogged by besalts and pyroclasts coming from near-by volcanoes. The Basaltic
38
I
N~ TO~I
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STAGE OF
INVESTIGATIONS
t
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GENERAL
PURPOSESOF THE
INVESTIGATIONS
URBAN
SUITABILITY
~
EVALUATION
SPECIFIC URBAN
SUITABILITY
EVALUATION
PLANNINGOF
INTBRSUIT. &
CONFLICTING
AREAS
SPECIFIC URBAN
SUITABILITY
EVALUATION
PLANNING OF
INTERSUIT. &
CONFLICTING
AREAS
SPECIFIC STUDIES
EXISTING TOWN
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SPECIFIC URBAN
SUITABILITY
EVALUATION
PLANNING OF
INTERSUITA8. &
CONFLICTING
AREAS
SPECIFIC STUDIES
SCALE OF
INVESTIGATIONS
Fig. 1 : Stages and purposes of site investigations in the urban environment.
Series III, which cover the rest of the area, consist of lava flows of
scoriaceous basalts. Quaternary volcanoes crossing this formation
have built many cinder cones of lapilli and ashes (Fig. 3). In the
northern areas residual soils have been developed by the weathering
of pyroclasts and basalts.
Site
Investigations
All the available information concerning geology, hydrogeology and
seismology of the region was collected, before carrying out any site
investigation. It was possible to get a summary log of 325 boreholes
drilled on basaltic lavas during previous work. To obtain field information on geological, hydrogeological and geomorphological characteristics of the area a detailed survey was carried out. At the same
time a geophysical survey using the electric resistivity m e t h o d was
performed to determine the thickness of the overburden, and the
composition and structure of the most geologically complex areas.
Soft samples were taken from 40 trial pits. Rock and water samples
were also collected from outcrops and wells, respectively.
Site investigations for engineering geological purposes were carried
out after the geological conditions of the area were known. Eightytwo boreholes were drilled in soils by the shell- and auger method
at an average depth of 10 m, although a depth of 25 m was reached
in some boreholes. S.P.T. tests, water level measurements, 77 dynamic penetration tests using the "Borro" penetrometer, and 42 trial
pits, completed the site investigation on soils. Ten boreholes were
drilled on basalts to a depth of 10 m , j u s t to complete the information provided by the summary logs. Soil laboratory tests consisted
o f classification, compaction and swelling tests. Strength and compressibility tests were carried o u t on selected samples. Rock laboratory tests consisted o f density, porosity and uniaxial compressive
strength determinations. The point load test was extensively used.
Engineering Geological Aspects Considered in this Case
The following subjects were considered in the engineering geological
investigations for the urban planning o f this area:
- Geology
- Geomorphology
- Hydrology and hydrogeology
- Construction materials
- Geological hazards
- Engineering geology
- Waste disposal and ground water pollution.
Just to give a general idea of the engineering geological conditions of
the site, some of the main aspects will be briefly described. Soil for-
mations are covering the northern a n d western parts of the area.
They consist of transported and residual soils both of volcanic origin
formed by the weathering of pyroclasts and basatts.
Transported soils were deposited u n d e r alluvial conditions and they
fill the La Laguna valley to variable thickness, as indicated by isopachous lines in Fig. 4. The middle o f this valley was occupied by a
lake which was desiccated in the year 1873.
The hydrogeological conditions determined an initial high water
table which has been progressively lowered. Based upon index and
classification tests it was possible to identify ten different soil units.
Average values showed that they are o f fine grain size, passing more
than 80 % by the 200 sieve (ASTM), liquid limits between 35 and
55 %, plastic limits from 20 to 35 %, plasticity index from 15 to
22 %, and dry densities from 1.1 to 1.4 gr/cm 3 .
Overeonsolidated clays were formed in the higher levels of these
clays as a result of the desiccation a n d lowering o f the water table.
It was also possible to recognize the presence of expansive clays permitting an evaluation in terms o f swelling potential and swelling
pressures (Fig. 4).
Rock formations cover more than 60 % of the total investigated area.
T h e y mainly consist of flows of basalts, 1" to 2 m thick, alternating
with scoria. Basalts are generally fresh, highly fissured, and with
occasional cavities, holes and tubes o f very variable size. Inclusions
of irregular bodies of scoria and/or pyroclasts are also present. In
this formation there was a great variation in geotechnical properties.
Lapilli generally build up cinder cones. T h e y showed practically no
cohesion and the average angle o f internal friction was about 30 ~ .
The bulk density was between 1.2 a n d 1.5 gr/cm 3 . Lapilli can be
weathered very quickly to clayey soils.
The following points were considered in the description of the engineering geological characteristics o f t h e area:
Classification o f the area into engineering geological soils and rock
units. Extent, distribution and thickness o f each unit. Characteristics of the engineering geological units based on classification,
strength and compressibility properties. Identification, origin, engineering properties and distribution o f the expansive clays. Evaluation o f foundation conditions. Slope stability and excavation evaluations.
Presentation
of
Data
The information was presented in t h e form of maps and plans ac-
39
c o m p a n i e d by a 1 0 , 0 0 0 ,~ord r e p o r t . The f o l l o w i n g list o f c o l o u r e d
m a p s , aU a t a scale o f 1 : 2 5 , 0 0 0 , were included in a n atlas:
II.
- Site investigations l o c a t i o n m a p
- Engineering geological m a p
- Table o f e n g i n e e r i n g g e o l o g i c a l c h a r a c t e r i s t i c s
Basic Maps
-
G e o l o g i c a l m a p a n d geological cross sections
G e o l o g i c a l m a p o f surface f o r m a t i o n s
Geomorphological map
Hydrogeological map
Construction materials resources map
9
11I. U r b a n S u i t a b i l i t y M a p s
- Slope steepness e v a l u a t i o n m a p
- Engineering geological e v a l u a t i o n m a p
- Waste disposal a n d g r o u n d w a t e r p o l l u t i o n e v a l u a t i o n m a p
~
,.~'L~-__
.,~,-'a..-"
Sandy r
E n g i n e e r i n g G e o l o g i c a l Maps
and boulders
'
2-~2-
--•
---42~-:-
.~:'~'------: :: ? ,: -:----:-::~--~&- :---5
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Old Basaltic S~rie~ I
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Phonolite lava flo~
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Fig. 2 : G e o l o g i c a l m a p o f a n area f r o m Tenerife
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The following information was included in the engineering geological map: each soil/rock unit was represented by a different colour.
Location of expansive clays and their related problems were represented by symbols. Isopaehous lines of thickness of soils were
shown by coloured lines. A table of engineering geological characteristics to accompany the engineering geological map was presented.
This table was produced in a similar manner as the one carried out
by the IGS at Milton Keynes (2). The table was divided in 10 main
subjects, as follows:
Name of the unit
- Equivalent geological unit
Qualitative descriptions and thickness
- Geotechnical parameters
- Foundation stability
- Slope stability
- Workability
- Hydrogeological characteristics
Waste disposal suitability
- Uses
-
-
-
'tT
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Fig. 3 : Geomorphological map of an area from Tenerife
Conmx slope in delores
Pediment
41
vourable conditions. Figs. 2, 3, 4 and 5, are shown just to illustrate
some aspects of these maps, although in the figures only a part of
the total investigated area is presented. These figures are shown
without the original colours, due to the obvious printing limitations
of this paper.
The urban suitability maps were produced principally in order to
assist planners - not necessarily for experts in Earth Sciences - and
to give a quick idea of the most suitable or unsuitable areas for different factors. A "traffic light" code colour system was used to indicate green for favourable, yellow for restricted, and red for unfa-
;'~
Distribution of Expansive Soils.
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Swellin~l potenfial
Probable S~elling prealmures
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Very critical
Subindex 1 means<225 KN/m 2> 147 KN/m 2
;
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[]Critical
Subindex 2 means< 147 KN/m2> 78 KN/rn2 !
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Margina,
Subindex 3 . . . .
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Non --critical
00-
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ll~pachyiei ot overburden soils
< 58 KN/m2> 19 KN/m 2 !
-.*~ ; ~
-/ .....
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7t'..~: :--
Residual soils lea than 2 m thick, " - ~ - - ~ -
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9 :~::~'---:~- ~ : :f:!~,~ ::::::::::::::::::::::
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6--Dark brown and reddiah, soft to firm, silty CLAY of high
plasticity (MH) with lapilli.
7--Reddish brown, firm and occasionally soft, sandy and silty
CLAY. of high plasticity (MH), with some gravels.
8~Reddish brown, firm to soft. sandy and silty CLAY, of high
~
o
"~--Redd~shb
_
........ dya.do,ay.~S,~r.o.o.~,.stic~._..
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5 - - Dark brown, and greyish blue, firm to soft, silty CLAY, of high
plasticity (M H), with t hin layers of yellowish sands.
:
iiiiii !iiiiiii
wth
4 - - Reddish brown, firm, sandy CLAY, of low plasticity (ML).
~ii~:
:IT~I~
i ~
.
l--Dark b. . . . . nd reddish fi . . . .
dy CLAY, of lOW piasticity
CL withinclusionsofbasalticbouldersandlapilli.
~==-= . --somepyrobl'ast,
o . . b r - - ~ .rm . , , . ~LA~ o, ,ow . , . c d y , ~ - . ~ ,
a'ndba~blticl~uld . . . . . lopes.
,",'
-
J
9--Dark brown, firm to soft, CLAY, of high plasticity (MH) with
some basaltic boulders,
10 - - Boulders and CObbleswith sands and silty clays
(GM, GC, ML, CL).
11 ~ 1 to 2 m thick tava flows of fresh, highly fissured BASALTS
=;~=,,,aGngwith scona.
~
12 - - Weakly warded ashes and [apigi forming cinder cones.
~
13 - - Less than 2 m thick, fresh pumice flows
Fig. 4 : Engineering geological map of an area from Tenerife
I
42
!
,
:
340
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9:
"?-'!
EJ~EEEEEE~E~
....
'
". i : ' - ' - .
I
i:iii:iii!i!! ;:i:ili, ,',
Favourable.- Rocks of hi~l to ~
high b41arirKjcaipaci W with'
great variationl of geotechnical proplrfiis.
Favourable.-- Soils of moderate bearing capacity w i t h rock
zubctratum at I ~ thzlm 4 m depth.
Restricted.-- Potentially un~Jd3llzIdop~ and soils o f high
beadng cspaciw.
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Restricted.- Soils of low bearing cepaciW with rock
~Jbstritum at lira than 8 m depth.
Restricted.-- Soils of low bearing c~paciW with rock Ir
9 at less than 6 m depth and high water level.
Restricted.- Soils of low bearing r
expamive,
~ t h rock ~absl~tum at l m than 6 rn depth.
RestrictlKI.-- Soils of low bearing r
dlgh~lv e X l ~ V q l ,
bad drain~3e and deep substratum.
Unfavourable.- Soils of low bearing capacity, high Iv expandve,
bad d~inlRe deeD substratum~ and area lubjectld to floodl.
UnfavourabhL- LipillL of low bNring capacity, e a r l y to densely
mainly under dynamic loads.
"
o
S(l~
Unfa~arabla.-- Unstable colluvild SOilS,
I
Fig. 5 : Urban suitability map for engineering geological conditions of an area from Tenerife
Discussion and Conclusions
Engineering geology can provide essential information for urban
planning and development as follows:
I. Recognition of the problem
II. Evaluation of the problem
III. Anticipation of a general behaviour of the materials in relation
to the engineering properties
IV. Prediction of general problems affecting the same engineering
geological unit
V. Zoning the area in different ranges of urban suitability or risk
VI. Planning and development according to the characteristics of
each zone
VII. Recommendation for detailed studies in order to apply remedial measures, and/or avoid or restrict development in appropriate areas.
The complexity of the urban environment, where no factor can be
considered separately, makes it necessary to take into account some
of the following questions when an evaluation o f influence factors is
carried out:
-
-
Problems derived from intrinsic suitability evaluation, in which
each factor is analysed independently, and restrictive criteria are
applied, allowing the rating of different parameters.
The evaluation of conflictive areas where there may be factors of
the land in conflict at times with each other.
Weighting different factors when considering a wide range o f aspacts; e.g. foundation conditions, waste disposal, earthquake
hazards. In these cases it is quite difficult to establish rating
systems and jointly to evaluate t h e m as a whole. The suggested
approach is:
43
ENGINEERING GEOLOGY
FOR URBAN
ANO DEVELOPEMENT
PLANNING
I
I GEQMO
GEOLOGY
&
RPHQLOGY
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DATA
OF
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NAND
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MANAGEMENT
Fig. 6 : Engineering geology assesstmcnt for urban planning and development
a) to evaluate in a first category those geological hazards which
involve loss of life, and property loss and damage.
b~ to establish a second category considering those factors
which can severely affect environmental conditions.
c) to evaluate the remaining factors in economic terms when
they do not substantially affect environmental conditions.
Engineering geological investigations should be carried out in the
early stages of planning and during all the development and design
stages. These investigations are particulary important for new towns,
the peripheral expansion of existing towns and re-development. The
"flow-chart" shown in Fig. 6 is a summary of the main stages of
engineering geology for urban planning as discussed in this paper.
An engineering geology plan should always try to achieve the
following goals:
-
To optimize the whole environment
To get the most economical solution for the urban plan.
Emphasis is laid on the importance of two aspects that need closer
investigation and which should be included in all engineering geological investigations for urban planning:
I. The investigation of trends of engineering properties, and the degree of confidence in extrapolation of geotechnical data.
II. The changes, interferences or alterations that urbanization can
produce on the geological environment.
Engineering Geology. Eng. Group of the Geological Soc. of
London. Q. J1. Engng. Geol. 5 , 2 9 3 - 3 8 1 .
3. AITCHISON G.D. - GRNAT K. (1968) : Terrain Evaluation
for Engineering. CSIRO Symposium Aust. Div. S. Mech.
Paper 2.
4. ALFORS J.T. - BURNETT J.L. - GAY T.E. (1973) : Urban
Geology: - Master Plan for California. California Div. Min.
and Geol. Bull. 198.
5. CRATCHLEY C.R. - DENNESS B. (1972) : Engineering Geology in Urban Planning with an Example from the New City
of Milton Keynes. 24th. Inter. Geological Congress. See. 13,
13-22.
6. GONZALEZ DE VALLEJO L. (1975) : Engineering Geology
for Urban Planning and Development. M.Se. Thesis, Imperial
College London.
7. GRANT K. (1974) ; A systematic Approach to Mapping Engineering Geology. 2nd. Inter. Congress IAEG, Theme 3,
PMC 2, 9 p.
8. HACKETT J.E. - McCOMAS M.R. (1969) :Geology for
Planning in McHenry County, lllinois, lllinois State Geological Survey, Cir. 438.
9. KNILL J.L. - PRICE D . G . - HIGGINBOTTOM I.E. (1968) :
Aspects of the Engineering Geology of the City of Bristol.
23rd. Inter. Geol. Congress. See. 12, 7 7 - 8 8 .
10. LEGGET R.F. (1973) : Cities and Geology. McGraw Hill.
Acknowledgement
The author is most grateful to Prof. J.L. Knill of the Engineering
Geology Division, at Imperial College, for helpful comments
during the preparation o f the manuscript. Thanks are also due to
J.L. Berzal and A. Linares-Rivas of ENADIMSA, for assistance in
the site investigations in Tenerife. Gratitude is expressed to the
Empresa Nacional ADARO and the Geological and Mining Institute
of Spain for permission to publish this paper.
R e f e r e n c e s :
1. ANON. (1965) : Geology and Urban Development. Assoc. Eng.
Geologists. Special Pub.
2. ANON.(1972) : The preparation of Maps and Plans in Terms of
11. MATULA M. (1974) : Engineering Geology in Country and
Urban Planning 2nd. Inter. Congress IAEG, Theme 3, GR,
20 p.
12. McHARG I. (1969) : Design with Nature. Natural History
Press for the American Museum of Nat. History, New York.
13. MORAN D.E. - SLOSSON J.E. - STONE R.O. - YELVERTON CH. A. (Editors) (1973) : Geology, Seismicity and Environmental lml~act. - Assoc. Eng. Geologists. Special Publ.
14. POLLARD W.S. - MOORE D.W. (1969) : The State of the
Art of Planning. Proc. ASCE, U.P. 95, 27-41.
15. TURNER A.K. - COFFMAN D.M. (1973) :Geology for
Planning: A Review of Environmental Geology. Q. Colorado
Sch. of Mines, Vol. 68, No 3.