2981
Prediction of and countermeasures for embankment-related settlement in ultra-soft
ground containing peat
Prédiction et contre-mesure sur les tassements de remblais dans les sols ultra-meubles contenant
de la tourbe
Tashiro M.
Nagoya University, Japan
Inagaki M.
Central Nippon Expressway Company Limited, Japan
Asaoka A.
Association for the Development of Earthquake Prediction, Japan
ABSTRACT: In the Mukasa area of the Maizuru-Wakasa expressway in Japan, delayed settlement as large as 11 m has occurred by
test embankment loading on a ground that includes approximately 50 m of ultra-soft sediment layers containing peat and clay. In this
paper, based on deductions of the initial in-situ soil conditions, simulations were carried out on the settlement and pore water pressure
observed until now at the site, and predictions were made of the settlement that could occur in the future. In addition, the effects of
countermeasures such as ground improvement by sand drain, replacement of the existing embankment with lightweight materials, and
reduction of the loading rate, were also investigated using numerical analysis. These analyses were performed using the soil-water
coupled finite deformation analysis program
GEOASIA
, in which the SYS Cam-clay model was mounted as the constitutive equation
for the soil skeleton. The results showed that improvement of the mass permeability and the slow or lightweight banking are effective
means of improving the stability during loading and reducing the residual settlement after entry into service. The results analyzed in
this paper were applied to the actual construction design of a culvert and the lightweight embankment surrounded it.
RÉSUMÉ : Sur l'autoroute Maizuru-Wakasa au Japon, un tassement différé de près de 11m s'est produit suite à des essais de
chargement de remblai sur un terrain incluant près de 50 m de couches de sédiments ultra-meubles contenant de la tourbe et de
l'argile. Dans cet article, des simulations de tassement et de pression de l'eau interstitielle observées jusqu'à maintenant sur le site ainsi
que des prédictions de tassement pouvant survenir dans le futur ont été réalisées en déduisant les conditions initiales de sols in situ. En
outre, les effets des contre-mesures, comme l'amélioration du sol par drain de sable, le remplacement des remblais existants avec des
matériaux légers, et la réduction de la vitesse de chargement, ont également été étudiés par analyse numérique. Ces analyses ont été
employées en utilisant le programme d'analyse de déformations finies sol-eau couplées
GEOASIA
. Les résultats ont montré que
l'amélioration de la perméabilité de masse, un tassement lent et léger sont des méthodes efficaces pour atteindre la stabilité pendant le
chargement et la diminution du tassement résiduel après l'entrée en service. Les résultats analysés dans ce document ont été appliqués
à la conception de la construction réelle d'un ponceau et du léger remblai qui l'entourait.
KEYWORDS: peat, prediction of settlement, soil-water coupled analysis
1 INTRODUCTION
In the Mukasa area of the Maizuru-Wakasa expressway, the
ground consists of ultra-soft sediment layers comprising peat
and clay with N-values on the order of 0 to 1 and a maximum
depth of 50 m. Delayed settlement in excess of 11 m has
occurred due to test embankment loading for approximately
four years. While the construction of the embankment did not
induce catastrophic sliding failure, it did dramatically impact
the surrounding ground, causing substantial lateral displacement
of up to 2 m and ground upheaval of up to 1 m (Inagaki et al
2010b).
In this paper, we simulated the large-scale ground settlement
behavior observed in the region based on soil-water coupled
finite deformation analysis, and in addition to predicting future
settlement, we demonstrated that ground improvement by drain,
and reduction in loading rate and weight are effective means of
improving stability during embankment loading and reducing
residual settlement of ultra-soft sediments containing peat.
Numerical analyses were conducted using the SYS CAM-clay
model (Asaoka et al. 2002) as an elasto-plastic constitutive
equation mounted on the
GEOASIA
analysis program (All Soils
All States All Round Geo-Analysis Integration: Asaoka and
Noda 2007, Noda et al. 2008). The simulation results were
applied to the actual construction design of a culvert and the
lightweight embankment surrounding it.
2 SUMMARY OF THE TEST EMBANKMENT
Figure 1 presents a longitudinal cross-section of the soil strata
underlying the test embankment that is the subject of this study.
Three types of test embankments were established utilizing the
Elevation(m)
-0.0
-10.0
-20.0
-30.0
-40.0
-50.0
CBD (50m)
SD (50m)
Unimproved (50m)
Embankment
Apt
Ac
As
Dpt
Dg
Figure 1. Schematic of test embankment and underlying soil strata (longitudinal cross section).
