2371
The new remediation technique for buried pipelines under permanent ground
deformation
Une nouvelle technique de pose des conduites enterrées soumises à des déformations
permanentes du sol
Moradi M., Galandarzadeh A., Rojhani M.
Department of Soil Mechanics and Foundation Engineering of Collage of Civil Engineering, University of Tehran
ABSTRACT: One part of lifelines is buried pipelines such as gas, water and oil pipelines. Permanent ground deformation such as
fault crossing and lateral spreads is one of the more important threats for pipelines. In this research, a new remediation technique for
buried pipeline system subject to permanent ground deformation is proposed. Also this new technique has been evaluated by
centrifuge modeling of buried pipelines subjected to concentrated PGD. In proposed technique, the high porosity gravels are used as
low-density backfill to fill the trench around the pipe near the susceptible area to PGD, thereby reducing soil resistance and soil-pipe
interaction forces and also pipeline strains. Previously, the expanded polystyrene (EPS) geofoam proposed to reduce density of
pipelines backfill. However, the high porosity gravel is better than expanded polystyrene geofoam from many cases such as
workability to construct, environmental effect, durability and cost. In this technical paper, described the proposed technique and also
two centrifuge modeling have been done to evaluate its performance. The comparisons of responses of remediated pipeline with
unremediated pipeline have been shown that the proposed technique is effective considerably.
RÉSUMÉ : Une partie des réseaux nécessaires au transport du gaz, de l’eau et du pétrole est constituée de conduites enterrées. Les
déformations permanentes du sol dues à des tassements ou à des mouvements latéraux sont l'une des menaces les plus importantes
pour les conduites enterrées. Dans cet article, une nouvelle technique de pose des conduites enterrées soumises à des déformations
permanentes du sol est proposée. Cette nouvelle technique a été évaluée par des essais en centrifugeuse sur des canalisations enterrées
soumises à des déformations permanentes du sol. Pour la technique proposée, des matériaux sableux dont la porosité est élevée sont
utilisés pour le remplissage des tranchées. Ils réduisent les efforts induits par l’interaction sol-tuyau. Auparavant, c’est le polystyrène
expansé geofoam qui était utilisé. Le matériau proposé est meilleur que le polystyrène expansé geofoam en ce qui concerne la mise en
œuvre, l'effet sur l'environnement, la durabilité et le coût. Dans ce papier, la technique proposée est décrite ainsi que deux modèles en
centrifugeuse réalisés pour évaluer sa performance. Les résultats obtenus montrent que la technique proposée est plus efficace que
celle utilisée précédemment.
KEYWORDS: Centrifuge Modeling, Faulting, Lifelines, Pipeline, Earthquake
1 INTRODUCTON
Buried pipelines often serve as lifelines in that they may carry
resources that are essential to the support of human life and this
is the reason to retain them in serviceable condition in every
situation. Among various kinds of natural hazards, earthquakes
happen to be the most serious threats for lifelines serviceability.
They can damage lifelines through faulting, permanent ground
deformation (PGD) and deformations due to seismic wave’s
propagation. Faulting can affect pipelines in various ways (Fig.
1) and cause severe damages (Fig. 2) depending on faulting
movement direction.
Considering mentioned hazards, lots of statistical, analytical
and numerical studies have been conducted since 1970s in order
to predict pipelines response and vulnerability level and also to
investigate methods of damage mitigation; but it has been a
difficult and somehow impossible way to evaluate theoretical
and analytical research results due to loss of accurate and
efficient records about pipelines response to faulting in actual
case histories of earthquakes (Choo et al. 2007). In order to
compensate such a gap, studies turned towards applying
experimental and physical modeling of this phenomenon. Since
2003, significant researches have been started in U.S.A. and
Japan with support of companies and institutes such as Tokyo
Gas Company, US lifelines Agency, National Science
Foundation in U.S.A, Earthquake Engineering Research Center
and etc. Most of mentioned conducted studies have been
focused on strike-slip faulting. So, still there is lack of studies
on normal and reverse faultings’ effects and this puts them in
prime importance of research priority.
Herein, the authors investigated the pipeline response due to
reverse faulting and also investigated the use of high porosity
gravel as low-density backfill in pipeline response. It is
expected that low-density backfill for will reduce soil-pipe
interaction and reduce the pipe train.
Table 1. Centrifuge Facility Properties
Property
Unit
Quantity
Exerted acceleration
g
5 – 130
Acceleration accuracy
g
+ 0.2
Rotational velocity range
rpm
38 – 208
Rotation radius
m
3
Maximum model weight (up to 100 g)
kg
1500
Maximum model weight (up to 150 g)
kg
500
1.1
Faulting simulator split box
Experimental setup provision in order to use in centrifuge
instrument has its own limitations; for instance, weight and
dimensions of the box is thoroughly tied to the used centrifuge
facility properties and it is of prime importance for the box to
have the minimum weight and dimensions possible together
with having enough strength for high magnitude forces caused
due to high exerted accelerations. Regarding these limitations,
the group-7000 aluminum alloy which has low density and high
strength is used to build up the faulting simulator split box in
