495
Quality control of Cutter Soil Mixing (CSM) technology – a case study
Contrôle de la qualité des la technologie Cutter Soil Mixing (CSM) – une étude de cas
Bellato D., Simonini P.
University of Padua - Department of Civil, Environmental and Architectural Engineering
Grisolia M., Leder E., Marzano I.P.
Sapienza University of Rome - Department of Civil, Environmental and Architectural Engineering
ABSTRACT: The Cutter Soil Mixing (CSM) is a relatively new Deep Mixing (DM) method that offers versatile construction
solutions suitable for various types of ground improvement. Besides the many advantages compared to the most common DM
methods, CSM has a high level of process control. Quality control and quality assurance (QC/QA) procedures are essential aspects of
each DM project, and a successful treatment is related closely to the professional ability to control and verify the DM construction.
This paper presents the results of laboratory tests carried out on wet grab samples collected from a CSM construction site
characterized by the presence of sandy soil. Similar soil-binder mixture were then produced and tested in the laboratory accordingly,
using the same binder adopted for the in situ panel construction and the sandy soil taken directly from the jobsite. A comparison
between the results obtained by UC tests carried out on the wet grab and the laboratory mixed samples is also presented. The results
obtained using an innovative experimental apparatus underline the influence of the physical and chemical characteristics of the natural
soil on the strength gain of the stabilized material.
RÉSUMÉ : Le Cutter Soil Mixing (CSM), appartenant à des méthodes Deep Mixing, est une technique récente qui offre des solutions
constructives adaptés à différents types d'amélioration du sol. En plus des nombreux avantages sur les méthodes les plus courantes, le
CSM a un niveau élevé de contrôle de processus. Les procédures de contrôle et d'assurance de la qualité (QC/QA) sont des aspects
essentiels du projet, et le succès du traitement est étroitement liée à la capacité de contrôler la phase d'exécution. Cet article présente
les résultats de tests de laboratoire effectués sur des échantillons prélevés “wet grab” d'un site à CSM caractérisé par la présence d'un
sol sableux. Semblables sol-liant mélanges ont ensuite été fabriqués et testés dans le laboratoire avec le même liant adopté pour la
construction des panneaux in situ et le sol sablonneux prises directement à partir du site. En particulier, il est présenté une
comparaison entre les résultats obtenus avec des essais de compression simple, effectuée sur des échantillons prélevés “wet grab” sur
le site et éprouvettes réalisés en laboratoire. Les résultats obtenus par l'utilisation d'un appareil expérimental innovateur ont souligné
l'influence des caractéristiques physiques et chimiques du sol naturel sur l'augmentation de la résistance du matériau stabilisé.
KEYWORDS: deep mixing, cutter soil mixing, sandy soil, unconfined compressive strength.
1 INTRODUCTION
The Cutter Soil Mixing (CSM) offers numerous advantages
over the more traditional methods of mixing soils using
standard rotary tools (Fiorotto et al. 2005), being equipped with
two sets of cutting wheels rotating around horizontal axes
producing treated soil panels of rectangular shape.
Several successful applications in different geotechnical
contexts for various engineering purposes have been recently
documented by Gerressen and Vohs (2012).
The Quality Control/Quality Assurance (QC/QA) programs
have the objective to ensure the compliance between the actual
field performance and the design requirements, therefore special
attention is required.
Due to the significant uncertainties related to the site
activity, most of the mix design and mixing procedure
calibration is performed in the laboratory.
In order to develop a tool for an effective comparison
between laboratory and field values, a specific CSM jobsite
located in the city of Zandvoort (NED) has been selected. The
subsoil condition is characterized by the presence of sandy soil.
Despite the fact that higher performance are usually obtained
in the laboratory (Porbaha et al. 2000), the comparison between
strength tests on wet-grab samples and laboratory specimens
have shown sometimes opposite outcomes (Bellato et al. 2012).
The mechanical properties of in-situ improved soil may be
found larger than that of laboratory specimen when using
cement slurry (wet method) to stabilize loose sandy ground due
to water drainage (Yoshimura et al., 2009).
Three types of water drainage may occur during soil mixing
operations: potential expulsion of part of pore-water contained
in the original soil by the injection of the cement slurry;
bleeding of the soil-binder mixture, i.e. drainage of water due to
sedimentation processes; possible drainage towards the
surrounding soil layer of part of the water in the mixture due to
consolidation under the effective overburden pressure.
In this paper the effect of water drainage was investigated
trough an original laboratory experimental apparatus.
To assess the influence of the granular soil type on test
results, the analysis were replicated on a different marine sand.
Moreover, important considerations regarding the significant
influence of the physical and chemical characteristics of the
natural soil on the strength gain of the stabilized sands are
presented and discussed.
2 SITE DESCRIPTION
A requalification activity was planned in Zandvoort, a small
village next to the North Sea coast at about 30 km west of
Amsterdam. Preliminary geotechnical ground investigations
were performed in the jobsite area. The results show a relatively
uniform sand profile characterized by the prevalence of a
medium to fine sand, generally of medium density, whose grain
size distribution is reported in Figure 1. The groundwater level
ranges around 2.5 m below the ground surface.
