Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Investigations on the influence of HPMC on the mechanical response of sandy soil
Jann-Eike Saathoff, Norman Goldau, Martin Achmus
Institute for Geotechnical Engineering, Leibniz Universität Hannover
Hannover, Germany

investigate excess pore pressure build-up beneath a gravity-based
foundation. Partially drained conditions are critical for realistic analysis
and shall be generated by using substituted pore fluids. Due to higher
viscosity, the excess pore pressure needs more time to dissipate and alower effective permeability arises. Partially drained conditions are
created due to slower dissipation with simultaneous equal excess porepressure generation from the mechanical properties of the soil. The massconcentration of the additive will be kept as low as possible in the model
tests. The potential use of Hydroxypropylmethylcellulose (HPMC) for
practical estimation of excess pore water pressures in sandy soils wasinvestigated. The results of the comprehensive study are summarized
below. In the tests, mass concentrations of up to 2 % are used, althoughsignificantly lower concentrations are aimed for in the subsequent
application. However, if the mechanical behaviour of the sand sample is
not affected at 2%, this is also the case for lower concentrations.

ABSTRACT
A comprehensive study was carried out on the influence ofHydroxypropylmethylcellulose (Methocel F50 - HPMC) on themechanical properties of a reference sand. It was found that the nonlineardependence of viscosity on HPMC content is in agreement with literaturedata. As far as the mechanical properties are concerned, no additionalcohesion is generated. There is also no significant effect on the friction
angle determined in the shear box and triaxial tests. The effective
permeability of sand specimens can be significantly affected by changing
the viscosity and thus reduced accordingly. The mechanical influence on
the overall stress-strain relationship (strength as well as stiffness
parameters) in the triaxial device is marginal when the pore fluid isreplaced with an HPMC solution.

KEY WORDS: accumulation; excess pore pressure; HPMC; model

Substituted pore fluids have already been used for many years. In manycases, centrifuge tests are used for excess pore water pressure
investigations, in which a special polymer fluid is used and the test is
carried out under multiple accelerations higher than gravity. However,centrifuge tests are considerably more complex and cost-intensive than
1g-model tests. Nevertheless, for both applications, there are somerequirements that need to be met. Allard et Schenkeveld (1994)(Dewoolkar et al. (1998), Stewart et al. (1998)) identify several
requirements for a substitute pore fluid. The general soil behaviour witha specific stress-strain behaviour, the pore pressure development and theshear strength need to be unchanged. The substituted pore fluid musthave a density close to that of water. The pore fluid must have the same
compressibility as water. It should be available for a wide range ofviscosities to allow experiments with models of different sizes and beeasy to produce with consistent properties between different batches.
Ideally, the pore fluid should be water-soluble and harmless to health andthe environment.

testing; partial drainage; pore fluid

INTRODUCTION
Offshore foundations are particularly exposed to cyclic loads. Cyclicloads generally lead to the accumulation of soil deformations and thus tochanges in the stress conditions in the soil - which in turn induces achange in the load-bearing behaviour of the foundation. The loads also
lead to an accumulation of excess pore water pressures with acorresponding reduction in strength and load-bearing capacity.
Accordingly, the design of foundations must focus strongly on the effectsof cyclic loads. For an investigation of partially drained conditions,which may arise during a storm event, 1g-small-scale tests can be carriedout. The main problem with 1g-model tests is that for realistic drainage
conditions, smaller permeabilities are needed compared to the available
grain size for cohesionless soils. Problems in measuring excess porewater pressure build-up and cyclic accumulation result from therelatively short drainage paths and the still comparatively highpermeability of the fine sand. A remedy can be the use of biodegradable
and non-corrosive water thickeners. These increase the viscosity of thewater in a controlled manner and produce a lower permeability of thesand body with the same mechanical properties.

There are different possible pore fluids with glycerol-added water orsilicone oil available. Allard et Schenkeveld (1994) ruled out silicone oil
because of the limitation of the models to sand and its lower density thanwater, and glycerol because of difficulties in manufacturing (Stewart etal. (1998)). The density of silicone oil and glycerol-water is 4 – 10 %lower and 10-15 % higher than that of water, respectively (Dewoolkar etal. (1999)).

At the institute of the authors, 1g-small scale tests are planned to1498