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Multi-Sleeve Axial-Torsional-Piezo Friction Penetration System for Subsurface
Characterization
Système de pénétromètre à friction axial-torsional-piezométrique à manchons multiples
pour la reconnaissance des sols superficiels
Frost J. D., Martinez A.
Georgia Institute of Technology
ABSTRACT: The multi-sleeve penetration system is an in-situ testing device that is derived from the cone penetration test. It
incorporates a series of friction sleeves with varying surface texture along with a series of pore pressure sensors, in addition to the
standard smooth friction sleeve and pore pressure sensor located directly behind the tip in the conventional CPT device. The
multiple measurements made with this device allow it to provide new insight into soil type and stratigraphic variations as well as
in-situ shear strengths as a function of sleeve texture height. This paper describes a third generation version of this device that
incorporates torsional load sensing capabilities in addition to the standard axial load sensing capabilities. In this manner, the
effects of different vertical and horizontal stress states on measured sleeve stresses can be explored. This multi-sleeve technology
offers benefits over devices which are used to measure the mechanical response of soils.
RÉSUMÉ : Le système multi-manchon de pénétration est un dispositif de test in situ qui est dérivée à partir de l'essai de
pénétration de cône. Il comporte une série de manchons de friction avec plus ou moins de surface le long d'une série de capteurs
de pression de pore, en plus de la douille de friction lisse et standard de capteur de pression de pore situé directement derrière
l'extrémité dans le dispositif de CPT classique. Les multiples mesures effectuées avec cet appareil permettent d'apporter un
nouvel éclairage sur le type de sol et les variations stratigraphiques ainsi que in situ la résistance au cisaillement en fonction de la
hauteur de la texture manche. Cet article décrit une version de troisième génération de ce dispositif qui intègre la charge de
torsion capacités de détection, en plus de la charge axiale norme capacités de détection. De cette manière, les effets des différents
états de contraintes verticales et horizontales sur les contraintes manches mesurées peuvent être explorées. Cette technologie
multi-douille offre des avantages par rapport à d'autres appareils qui sont utilisés pour mesurer la réponse mécanique des sols.
1 INTRODUCTION
The general trend followed for in-situ site characterization
practice has been to utilize devices that incorporate only one
sensor of a given type to measure desired engineering
properties. While a number of different sensor types may be
incorporated into a single device, they typically measure
different properties and then rely on empirical correlations
to predict engineering properties. The primary reason for
this single sensor approach has been historical precedent as
opposed to any compelling technical limitations. While this
approach has proven to yield generally acceptable results for
many projects, opportunities remain to improve practice. For
example, as the complexity and uniqueness of investigation
projects increase, the merit of conventional single sensor in-
situ tools decreases. Hence, recent efforts have sought to
develop new tools for subsurface characterization studies
configured with multiple sensors, which have the ability of
providing more reliable information as part of more detailed
investigations.
As noted above, invasive site characterization tools have
traditionally followed the approach of using “single-sensor”
configurations. An example is the cone penetration test
(CPT). The CPT measures, as a minimum, the penetration
resistance of a conical tip inserted into the ground, the
frictional force that the soil exerts on a smooth sleeve
located just above the cone tip, and the pore pressure
(assuming the pores are fluid filled) recorded at a location
also typically close to the penetrating tip as the probe is
inserted into the subsurface. Such an in-situ tool can provide
a robust set of data in the sense that it measures the bearing
and frictional resistances of the soil being tested. However,
one shortcoming is that it only measures the frictional
response of the soil when sheared against a surface of fixed
and specified low roughness. Studies by Frost and DeJong
(2005) have shown that friction measurements of soil
against smooth surfaces are more indicative of soil particle
sliding along the surface and not of shearing against the
sleeve surface. A more robust characterization of interface
strength can be achieved when the soil is sheared against a
range of surfaces of different roughnesses (DeJong et al.,
2001).
2 MULTI-SENSOR IN-SITU TOOLS
Among the new generations of more specialized in-situ tools
that exploit the multiple sensor approach are the “multi
sleeve penetrometer attachments” developed at the Georgia
Institute of Technology (DeJong, 2001; DeJong and Frost,
2002; Hebeler, 2005; Hebeler and Frost, 2006; Frost et al.,
2012). These attachments are designed to be used behind a
regular 15cm
2
CPT, or as a stand-alone device behind an
instrumented tip. The first and second generation devices
were described in detail by DeJong and Frost (2002) and
Hebeler and Frost (2006), respectively, and are briefly
summarized below. The third generation device is under
development and is introduced herein.
