2961
Settlements of Earth Fills on Thick Layers of Overconsolidated Soft Clays
without Geodrains
Tassements des remblais sur d’épaisses couches d'argile molle, surconsolidée, sans géodrains
Massad F.
EPUSP – São Paulo, Brasil
Teixeira A.H.
A.H. TEIXEIRA CONSULTORIA E PROJETOS– São Paulo, Brasil
Carvalho C.T., Grangé L.F.A.
ODEBRECHT INFRAESTRUTURA – Brasil
ABSTRACT: The monitoring of earth fills built on soft clays has been done frequently through the Brazilian coastline. As the most
common measurement is the settlement along time, the interpretation of the results is usually done by Asaoka’s Method, generally
involving extrapolations that have given rise to doubts (for instance, about the secondary consolidation effect) and to a double
interpretation, and even to controversies, especially when it comes to evaluating the effectiveness of vertical geodrains to accelerate
settlements. Doubts about the soil disturbances around the geodrains that have been of concern among us and abroad. The paper is
based on data from a work in Santos Harbor, in São Paulo State, Brazil, in which 3 experimental fills were built and monitored, one of
them partially with geodrains. Many laboratory and field tests were available besides local experience that proved decisive in the
evaluation of the measurements and in making decision. It is shown that the controversies can be overcome with information of the
soil and of similar works in the region and details of geodrain installation, confirmed by the behavior of the landfills of the work.
RÉSUMÉ: La surveillance des remblais construits sur argiles molles a souvent été effectuée le long de la côte brésilienne. Comme la
mesure la plus courante est le tassement au cours du temps, l'interprétation des résultats est généralement faite par la méthode
d´Asaoka, impliquant généralement des extrapolations qui ont donné lieu à des doutes (par exemple, à propos de l'effet de la
consolidation secondaire), à une double interprétation, et même à des controverses, surtout quand il s'agit d'évaluer l'efficacité des
géodrains verticaux pour accélérer les tassements. Ces doutes sur les remaniements du sol autour des géodrains ont été une
préoccupation pour nous et à l'étranger. L´article est basé sur les données de travaux au Port de Santos, dans l'État de São Paulo, au
Brésil, au cours duquel trois remblais expérimentaux ont été construits et surveillés, l'un d'entre eux avec des géodrains. De nombreux
essais en laboratoire et in situ étaient disponibles en plus de l'expérience locale qui s'est avérée décisive dans l'évaluation des mesures
et en prise de décisions. Il est démontré que les controverses peuvent être surmontées avec la connaissance des sols,des travaux
similaires dans la région, et le mode d´installation des géodrains. Ceci est confirmé par le comportement des remblais en service.
1 INTRODUCTION
A port terminal (Embraport) is under construction in the left
side of the Santos Harbor Channel, close to the Barnabe Island,
as shown in Figure 1. The total area that is being filled, roughly
800,000m², is delimited by Sandi and Diana Rivers. The Area 3
of Figure 1, alongside the Santos Channel, will be used for
containers storage and part of it was reclaimed underwater. The
final level of the earth fills in the area will be 3.5m.
2 GEOLOGICAL AND GEOTECHNICAL ASPECTS
Many geological evidences show that the sedimentary clays of
the Santos Coastal Plain (“Baixada Santista”) were formed
during two Quaternary depositional cycles, with an intermediate
erosive process. This gave origin to two different types of clays:
the Pleistocene (Transitional) Clays and the Holocene Clays.
The former ones, also called Transitional Clays (AT), deposited
100,000 to 120,000 years BP (Before Present), are medium to
hard clays, pre-consolidated due to a sea-level lowering of 130
m at the peak of the last glaciation (15,000 years BP); as a
consequence, these sediments were also deeply eroded. The
latter ones, also called SFL clays (from Sediments-Fluvial-
Lagoon-Bay), originated since 10,000 years BP by
sedimentation where the Pleistocene sediments had been
eroded, are very soft to soft clays, lightly over consolidated due
to such occurrences as short negative sea-level oscillations (i.e.,
bellow present sea level) or dune action. Included in this last
category are the mangrove sediments, which are still forming.
Santos City
Santo Amaro
Island
Area 3
Quay
Area 2
Area 1
Barnabé
Island
Diana
River
Figure 1.Embraport site delimited by
Sandi and Diana Rivers
.
In the site of the terminal occur fluvial sediments, originating
alternate and discontinuous layers of sand and clay. But it is
close to Santo Amaro Island, where a lagoon-bay type of
sedimentation took place, with deep layers of SFL (SPT ~1 to
4). This way, both characteristics were found.
In fact, an extensive field investigation, including SPT
percussion borings, Vane Tests and CPTUs, revealed: a) a
fluvial sedimentation that led to a sandy or clayey mangrove
deposition, 0 to 2m width (SPT=0); b) an intermediate
sedimentation of a fluvial-bay type, 25 to 35m width, in a mix
environment (turbulent and calm), that gave origin to layers of
clay with sand lenses, with SPTs varying from 1 to 4; c) the
presence of layers of Transitional Clay (AT) at greater depths,
with SPTs>5; and d) at last, the occurrence of sands with gravel
