3115
Geotechnical Assessment for the Restoration of Garandoya tumulus
with the Naked Stone Chamber
Évaluation géotechnique de la restauration du tumulus de Garandoya et grottes en pierres nues
Mimura M.
Graduate School of Engineering, Kyoto University, Kyoto, Japan
Yoshimura M.
Soil and Rock Engineering Co. Ltd., Osaka, Japan
ABSTRACT: Garandoya Tumulus was constructed on the terrace of Mikuma River and famous for mural paintings. The soil mound
that originally covered the stone chamber has been destroyed. Due to instability of the naked stone chamber, it has been decided to
restore the tumulus with the construction of round soil mound with a diameter of 25 to 30m. The necessary strength together with the
compacted density of the restored mound soils are investigated through various laboratory tests. A series of laboratory test results
confirm that the stability of the restored mound is achieved with the possible in-situ density. Water resistant and adiabatic structure is
required to protect the mural paintings inside the stone chamber. Based on the chamber model test results, the double-layered earth
mound has been introduced for the restored tumulus mound, namely, the well compacted soil with the enough strength to stabilize the
restored tumulus mound underlain by the well permeable gravel layer to support the drainage for rainfall water. The heat conduction
chamber tests on the mound soils are carried out to investigate the capacity to protect the heat transfer into the chamber. A series of
the stability and environmental assessments has successfully assisted to develop the design of the restored tumulus mound.
RÉSUMÉ : Le tumulus de Garandoya, très connu pour ses peintures murales dans ses grottes, est construit sur le banc de la rivière
Mikura. Le monticule de terre qui recouvrait les grottes est désormais dénudé, ce qui mène à l’instabilité des pierres nues des grottes,
ainsi que la vulnérabilité des peintures murales à l’eau. On propose des travaux de restauration du tumulus en construisant un
monticule de forme circulaire de diamètre de 25 à 30m pour le recouvrir. On étudie la résistance du sol compacté et la restitution de la
densité in situ en faisant des tests au laboratoire. La texture du sol compacté doit être étanche pour protéger les peintures murales
contre l’infiltration des eaux dans la grotte. Les résultats de tests sur un modèle réduit de la grotte préconisent une bi-couche pour
restaurer le tumulus, càd une couche de sol compacté recouvrant une sous-couche de gravier pour permettre le drainage. On a aussi
fait des tests de conductivité thermique sur le sol compacté pour évaluer l’isolation de la grotte. Des études de la stabilité
environnementale du monticule ont aussi fait partie du design de la restauration du tumulus.
KEYWORDS: heritage, tumulus, mound, water retention characteristic, capillary barrier, heat conduction
1 INTRODUCTION
Tokyo
Hita
The Garandoya Tumuli, the national heritage are located at Hita
city in Oita prefecture (Figure 1) with the mural paintings in the
stone chamber. Although three tumuli were discovered, all of
them have lost their earth mound and the stone chambers are
exposed. The tumuli have been determined to be restored to
conserve the stone chamber as well as the colored mural
paintings drawn on the surface of the chamber stones. In order
to protect the mural paintings from deterioration, the water
resistant and adiabatic structure is strongly required because the
main factor for the damage of the mural paintings is luxuriant
growth of mold due to dew condensation induced by the
intruded water by rainfall and the rise in heat by solar radiation.
In the present paper, the geotechnical assessment for the
conservation of the tumuli including the mural paintings
through the in situ and laboratory tests is reported. The behavior
of underground water at the site is investigated through the in
situ tests with emphasis on the possibility of suction-induced
water intrusion. The necessary drainage function against the
rain water is also discussed. The layered structure such as the
compacted earth underlain by the permeable coarse gravel for
the restored earth mound is proposed considering the assisting
effect of capillary barrier at the border of these layers.
Discussion is extended to the adiabatic structure of the earth
mound, which is expected with the heat conduction
characteristics of soils. For the purposes, a series of chamber
model tests are conducted.
Figure 1. Location of Garandoya tumulus
2 GENERAL VIEW OF THE RESTORATION PROJECT
2.1 Restoration plan
In order to keep the preferable environment for the mural
paintings on the chamber stones as well as to enable general
public presentation of the stone chamber, the Hita Municipal
Board of Education has determined to construct the shelter
building which covers the stone chamber covered by the
restored earth mound as shown in Figure 2. The shelter building
