3271
Simplified Prediction of Changes in Shear Strength in Geotechnical Use of Drinking
Water Sludge
Prédiction simplifiée de changements dans la force du ciseau dans usage Geotechnical de boue de
l'eau potable
Watanabe Y.
Central Research Institute of Electric Power Industry
Komine H.
Ibaraki University
ABSTRACT: Drinking water sludge is the aggregation of clay and organic compounds which is formed in flocculation and
sedimentation process. This study focused on the decomposition of the bonding by flocculating agent and organic matter, and
proposed a simplified method for the prediction of changes in shear strength caused by DWS decompositions. The changes in shear
strength of DWS were investigated by triaxial compression tests. The specimens were produced using the DWS which was mainly
decomposed by H
2
O
2
solutions. As a result, volumetric strain became large in the large axial strain range, and the maximum deviator
stress decreased concomitantly with the decrease in ignition loss. After the organic matter was decomposed until 1.38%, the internal
friction angle decreased from approximately 38.8° to 37.6°. The changes of shear strength were related to the substantial period in
geotechnical works such as road infrastructures. The decompositions of the mechanical bridging and organic matter were described
based on diffusion-controlled Al leaching and aerobic biodegradation, respectively.
RÉSUMÉ : La boue de l'eau potable est l'agrégation d'argile et composés organiques qui sont formées dans le flocculation et
processus de la sédimentation. Cette étude s'est concentrée sur la décomposition de la liaison par agent du flocculating et matière
organique et a proposé une méthode simplifiée pour la prédiction de changements dans la force du ciseau causée par les
décompositions DWS. Les changements dans la force du ciseau de DWS ont été enquêtés par les épreuves de la compression du
triaxial. Les spécimens ont été produits utiliser le DWS qui était principalement décomposé par les solutions H
2
O
2
. En conséquence,
la tension volumétrique est devenue grande dans la grande gamme de la tension axiale, et le stress du déviateur maximal a diminué de
façon concomitante avec la baisse dans la perte de l'ignition. Après que la matière organique ait été décomposée jusqu'à 1.38%, l'angle
de la friction interne a diminué d'approximativement 38.8° à 37. 6°. Les changements de force du ciseau ont été mis en rapport avec
période substantielle dans le geotechnical travaille tel qu'infrastructures de route. Les décompositions de la mécanique qui lie et la
matière organique a été décrite basé sur Al diffusion-contrôlé qui lessive et biodégradation aérobique, respectivement.
KEYWORDS: waste, sludge, reuse, organic matter, decomposition, aluminum, leaching, shear strength
1 INTRODUCTION
Drinking water sludge (DWS) which is discharged during
water purification is presently classified as industrial waste in
Japan. A microphotograph of DWS is represented in Fig. 1.
DWS is the aggregation of clay and organic compounds which
is formed in flocculation and sedimentation process. Reuse and
disposal of DWS are an important viewpoint in the sound
material-cycle society.
The geotechnical use of DWS such as a road infrastructure
material is greatly anticipated. So far, mechanical and leaching
characteristics of DWS have been investigated (Roque and
Carvalho, 2006; Watanabe et al., 2009). Specifically, it is
presumed that Al leaching results from the Al-type flocculating
agent. Watanabe et al. (2011) showed that the organic matter
decomposition decreased in shear strength of DWS. To reuse
DWS safely, the evaluation of the durability is strongly
required. Therefore, this study focused on the decomposition of
the bonding by flocculating agent and organic matter, and
proposed a simplified method for the prediction of changes in
shear strength caused by DWS decompositions in geotechnical
works.
Figure 1. Microphotograph of DWS.
2 DECOMPOSITION MECHANISM
The DWS formation during water purification process is
based on two phases in Fig. 2. Less than 10
-6
m diameter
particles including organic matter were flocculated by
chemicals as first binding, and floc settled and consolidated
(Montgomery, 1985). Bonding force is generated by the
Figure 2. Schematic DWS formation process.
