2425
Time-dependent behaviour of foundations lying on an improved ground
Temps-comportement dépendant de fondations reposant sur un sol amélioré
Alupoae D., Aşuencei V., Răileanu P.
"Gheorghe Asachi” Technical University of Iasi, Faculty of Civil Engineering and Building Services, Department of Roads
and Foundations,43 Dimitrie Mangeron Bd, 700050, Iasi, Romania
ABSTRACT: The paper presents some aspects concerning time-dependent behaviour of the improved foundation soils. The
foundation soils can develop favourable or inappropriate resistance properties under the loads submitted by constructions. Engineers
and investors encounter more and more difficult foundation soils, in their desire to efficiently use the construction sites. In this case,
physical and mechanical properties of the soil have to be improved, in order to sustain the infrastructure and structure of a building.
The paper reviews some improvement methods, after presenting difficult foundation soils from Iaşi area. The paper presents a case
study regarding problems caused by difficult foundation soils that are present in the region, during the operating period of structures.
The presence of water in the foundation soil created a negative impact in its behaviour, which led to differential settlements and,
consequently, the buildings were switching from their initial vertical position. The study also analyzes time-dependent settlements of
a construction. Finally the paper presents some conclusions resulting from studies both bibliographic and practical.
RÉSUMÉ : Le document présente quelques aspects concernant le comportement en temps des sols améliorés pour les fondations. Le
terrain de fondation peut avoir un comportement favorable ou par contre défavorable sous l’action des charges donner par les
constructions. Pour utiliser efficacement les terrains des constructions, les ingénieurs et les investisseurs rencontrent souvent des sols
de fondation de plus en plus difficile. Dans ce cas, les propriétés physiques et mécaniques du sol doivent être améliorées, afin
d’assurer des bonnes conditions d’appuis pour l'infrastructure et la structure d'un bâtiment. Le document passe en revue les sols de
fondation difficiles de la zone de Iaşi et des méthodes de les améliorées. Il est aussi présenté une étude de cas concernant les
problèmes qui peuvent apparaitre au cours de la période d'exploitation de structures, a cause des ces sols de fondation difficiles. La
présence de l'eau dans le terrain de fondation a eu un impact négatif sur son comportement, ce qui a produit des tassements
différentiels, ca veut dire que les bâtiments furent commutés de leur position initiale, verticale. Pour conclure, le document présente
des conclusions issues de l’étude bibliographique et pratique à la fois.
KEYWORDS: leaning structure, expansive clay, loess, differential settlement.
1
INTRODUCTION
As a result of the analysis performed over time on a large
variety of soils and taking into account soil behaviour in the
presence of external factors, the foundation soils can be divided
in two categories, considering their capacity to support loads
from constructions: good and difficult foundation soils.
The entire existence of the building system depends on the
stability and strength of the foundation soil and this is the main
reason why a special interest is given to the second category of
soils and therefore to the specific issues that must be considered
in the design, execution and operating period of a construction.
2
DIFFICULT FOUNDATION SOILS
The sites that have a construction soil with good geotechnical
characteristics are rapidly decreasing. Large urban areas are a
particular problem because, due to the lack of space, it is
necessary to reconsider the possibility of placing a building on a
soil that was unsuitable for constructions until now.
2.1
Difficult foundation soils - classification
These soils are classified as follows:
macroporous soils (present large cavities in their
structure and have the ability to suffer large settlements
when are subjected to a wetting process);
collapsible soils (are characterised by the fact that when
in high humidity develop large deformations);
liquefiable soils (especially non-cohesive soils
consisting of saturated fine sand which under the action
of a dynamic load suddenly loose their shear strength);
expansive soils (cohesive soils such as clays, which
change their volume when water content varies);
soils that during the freezing and thawing phenomena
change their structure and properties;
peaty soils (organic matter is present in its structure,
have a high and very high compressibility and a low
shear strength);
eluvium (formed as a result of decomposition and
alteration of existing rocks);
saline soils (are characterized by the settlement
phenomena that occurs during a long lasting wetting);
fillings (occur as a result of unconsolidated alluvial
deposits) (Iliesi 2012).
2.2
Methods of soil improvement
Given the frequency of soils that present unfavourable
characteristics for constructions over time were developed
methods to improve their mechanical properties, such as:
soil compaction which can be made on surface (rolling,
dynamic, cushions) or in depth (columns, pre-wetting,
dynamic);
chemical soil stabilization (cementation, silicatization,
jet grouting, bentonite etc.);
electrochemical
methods
(electrophoresis
and
electroosmosis);
thermal treatment of soils.
