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Sampling method and pore water pressure measurement in the great depth (-400m)
Méthode de mesure de pression interstitielle de l'eau d'échantillonnage en grande profondeur
(– 400m)
Rito F.
OYO Corporation
Emura T.
Kansai International Airport CO.,LTD
ABSTRACT: Pleistocene clay and sand layers are deposited in the great depth under Holocene soft clay layer at Kansai international
airport area. Since the weight of the reclamation soil is heavy because of its depth of sea water which is reached -20m, it has become
the very important issue that the characteristics of Pleistocene clays are investigated correctly. For this reason, the new type sampling
method which has been called ‘Koken wire line system’ was developed and the undisturbed samples were obtained by this sampling
system. Sample quality which obtained from great depth was estimated using the range of the strain which was re-consolidated to in-
situ effective stress by constant strain rate consolidation test. As a result, it was confirmed that the sample quality of these samples had
good quality. On the construction phase of reclamation, cone type measuring equipment of pore pressure for Pleistocene clay and new
type measuring equipment of pore pressure for sand were developed and the excess pore water pressure was measured. As a result of
the examination of these data, the measured value has been had high accuracy. Therefore, the consolidation characteristic of
Pleistocene deposit of Kansai international airport area has been estimated more correct by these useful data.
RÉSUMÉ :
L’argile Pléistocène et couches du sable sont déposées dans la grande profondeur sous Holocene couche de l'argile
douce à Kansai région aéroportuaire internationale. Depuis le poids du sol de la réclamation est lourd à cause de sa profondeur d'eau
de mer qui en est atteinte -20m, il est devenu la question très importante que les caractéristiques d'argiles Pléistocène sont enquêtées
sur correctement. Pour cette raison, la nouvelle méthode de l'échantillonnage du type qui a été appelée 'Koken installent le système de
la ligne' a été développé et les échantillons non dérangés ont été obtenus par ce système de l'échantillonnage. Goûtez la qualité qui a
obtenu de grande profondeur a été estimée utiliser la gamme de la tension qui a été réconsolidée à in-situ stress efficace par épreuve
de la consolidation du taux de la tension constante. En conséquence, il a été confirmé que la qualité de l'échantillon de ces
échantillons avait la bonne qualité. Sur la phase de la construction de réclamation, matériel de la mesure du type du cône de pression
du pore pour argile Pléistocène et nouveau matériel de la mesure du type de pression du pore pour le sable a été développé et la
pression de l'eau du pore en excès a été mesurée. Par suite de l'examen de ces données, la valeur mesurée a été eue la haute exactitude.
Par conséquent, la caractéristique de la consolidation de dépôt Pléistocène de Kansai que la région aéroportuaire internationale a été
estimée plus correct par ces données utiles.
KEYWORDS: Pleistocene clay, Koken wire-line system, Pore water pressure measurement.
1 INTRODUCTION
Kansai international airport has constructed in the Osaka bay
area. In this area, Pleistocene clay and sand layers are
deposited into the great depth under a Holocene soft clay
layer. Since the weight of the reclamation soil is heavy
because of its depth of sea water which is reached 20m in
depth, it has become the very important issue that the
characteristics of Pleistocene clays are investigated correctly.
Therefore, it has been required high quality sampling and
high-precision consolidation test for the samples deposited
such great depth of 400m in depth.
On the construction phase of reclamation, the measurement of
pore water pressure for Pleistocene clay and sand layers has become a
important issue to improve settlement analysis in addition to the
measurement of settlement. As the target depth of the measurement of
pore water pressure reaches 300m in depth, the piezometer and the
permeability test equipment which are usually used in shallow depth
can not use such great depth. The cone type measuring equipment of
pore water pressure for Pleistocene clay named GD-CONE and the
new type measuring equipment of pore water pressure for sand
named H-MHT have been developed. We have been able to measure
the pore water pressure in great depth using these new equipment.
2 SAMPLING FROM GREAT DEPTH USING KOKEN
WIRE LINE METHOD
Port and Airport Research Institute has tried to improve wire
line boring method for the investigation method at the port
and harbor area (Matsumoto K., et al.1981). As a result, new
wire line method called Koken wire line method has
developed. The characteristic of this method is to be able to
obtain undisturbed samples which are stiff clay and sand in
great depth. Koken wire line method has applied for boring
and sampling method of Kansai international reclamation
project.
The system of Koken wire line method is shown in Figure
1 (Okumura T., et al.1982). Three types of specific samplers
have made for Koken wire line method. The structure of these
samplers is shown in Figure 2 and Table 1. Thin-walled tube
sampler with fixed piston is used for soft and stiff clay whose
unconfined compressive strength is under 2MN/m
2
.
Denison
sampler which is rotary double-tube sampler is used for more stiff
clay whose unconfined compressive strength is over 2MN/m
2
. Rigid
sampler which is double-tube sampler fixed outer tube and inner tube
is used for stiff sand and gravel.
