Geotechnical investigation guide for building in volcanic environments - Volcanic Rock Mechanics - page 232

The Department of Public Works and
Transportation of the canarian Government has
drafted a guide to assist the correct interpretation
and implementation of national code in the canar-
ies: The Geotechnical investigation Guide for Build-
ing Projects in the canary islands (GeTcan-10).
The guide, presented in this article, articulates the
basic appropriate methodology for the planning of
geotechnical prospecting in building projects and
for conducting geotechnical studies concerned, in
accordance with current regulations and canarian
terrains.
logically, the guide is a very extensive document
and in this paper only aspects relating to the plan-
ning of geotechnical survey are presented.

2 GeoTechnical UniTs

The geology around the canary islands is domi-
nated almost entirely by a succession of volcanic
materials and structures.
Geotechnical mapping of the entire archipelago
has been made as first step of the guide project.
a geotechnical units classification of the canar-
ian terrain was necessary in order to establish areas
and groups of terrains with similar geomechanical
behaviour ( Table 3 ) . These units have been further
classified into groups of terrains that define the
cTe ( Table 2 ) .
Geotechnical areas of behavior more or less
homogeneous have been considered, with the

Table 2. Groups of terrains according to the cTe.

Group Description

T-1 Favourable terrains : those with little variability, and where the usual practice in the area

is direct foundation by isolated elements.

T-2 Intermediate terrains : those who show variability, or that the area does not always

happen the same foundation solution, or where it can be assumed to have some rel-
evance
anthropic filled, although probable it not exceed 3.0 m.

T-3 Unfavourable terrain : those who do not qualify in any of the previous types. it is

especially this group will be considered in the following areas:
a) expansive soils
b) collapsible soils
c) soft or loose soils
d) karstic terrains in gypsum or limestone
e) Variable terrains in composition and condition
f) anthropic filled with more than 3 m thick
g) Terrains in susceptible areas to landslides
h) Volcanic rocks in thin layers or with cavities
i) land with slope greater than 15º
j) Residual soils
k) land of marshes

Table 3. Geotechnical units of the canary islands and their classification according to cTe terrains.

Units subunits cTe terrains

Unit i: Basal complex T3e

Unit ii: salic lava flows and salic
massif

T1

Unit iii: altered basaltic massif T3h

Unit iV: Fresh lava flows iVa: “aa” lava flows little scoriaceous T1

iVb: “Pahoehoe” lava flows and “aa” lava flows very
scoriaceous

T3e

Unit V: Pyroclastic deposits Va: ignimbrites y tuffs T2

Vb: loose or weakly cemented pyroclastic deposits T3b

Unit Vi: Volcanic breccias T2

Unit Vii: alluvial-colluvial deposits T3c

Unit Viii: coastal sands T3c

Unit iX: clay and silt soils T3j

Unit X: anthropic filled T3f