E3S Web of Conferences 415, 06005 (2023)
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https://doi.org/10.1051/e3sconf/202341506005

Debris flow mitigation by using biopolymers as a soil stabilizer
Hadi Fatehi1, Dominic Ong1, Jimmy Yu1, and Ilhan Chang2
1School of Engineering & Built Environment, Griffith University, Nathan, Australia
2Department of Civil System Engineering, Ajou University, Suwon-si, Korea

Abstract. Towards rising the attention to the use of green materials in geotechnical applications, this studyaims
to introduce carrageenan as a new environment-friendly polymer for slope surface stabilization. A set ofexperiments were conducted to evaluate the performance of the biopolymer-treated soil to form a resistantsurface
against the surface erosion and debris flow. samples were tested by changing a variety of effective parameters
including biopolymer content, moisture content, curing time, soil type, and durability under wet- dry cycles.
Kaolinite soil along with river sand in different combinations were employed and treated by various biopolymer
proportions to optimize the biopolymer and soil parameters. Subsequently, the optimum mixture of eachbiopolymer-treated soil was subjected to 5 cycles of wetting and drying. A broad microstructural study byperforming FTIR analysis and scanning electron microscopy (SEM) images was conducted and an analyticalmodel was developed to clarify how biopolymer stabilize the slope surface. Theresults confirm the successful
performance of carrageenan in connecting soil grains, increasing mechanical strength and durability of soil
against surface erosion. It can be concluded that carrageenan can be consideredas a sustainable alternative toconventional materials such as cement and lime.

1 Introduction
Whereas conventional materials enhance theengineering properties such as strength, stability,workability as well as the hydraulic features, they
adversely affect the surrounding environment [1].
Cement is responsible for approximately 5% of global
CO2 emissions, causing detrimental damages tobiodiversity and environment [2]. Among several
methods and materials which have been developed tominimize the impacts of cement, biopolymer haveshown to have a significant impact on soil improvement
and reducing harm to the environment. Biopolymers area type of natural polymer produced by living organisms.
They can be divided into three major types:
polynucleotides, polypeptides, and polysaccharides [3].
Sustainability, low carbon emission, renewable
resource, and being biodegradable are the benefits ofusing biopolymers towards reaching a greener planet[4].
An annual cost of eight billion dollars is incurred by
the global economy due to soil erosion caused by water.
Biopolymer have been utilized for a variety ofgeotechnical applications including erosion prevention,
hydraulic barriers, slope stability, and subgrade
improvement [5]. The governing parameters that control
the behaviour of the biopolymer-treated soils arebiopolymer content, biopolymer concentration, curingtime, soil type, and temperature. It has been shown thatincorporating biopolymer into soil enhances its
resilience to erosion and critical shear strength. Its
strong erosion resistance is the result of boosting soil
cohesion and decreasing soil permeability and void ratio[6].

Carrageenan is a biopolymer produced from naturallinear
sulphated polysaccharides [7]. Addition of a small
quantity of Carrageenan reduced the soil lossimposed bywater flow and wind by creating a resistantlayer on thesurface of soil [8].
In this study, carrageenan is introduced as a novel
biopolymer to improve the slope surface stabilization.A
set of laboratory tests were used to evaluate thecharacteristics of carrageenan treated soil. Durability
under wetting and drying cycles were studied. Soil andbiopolymer interactions were explained by providing
SEM pictures and a schematic model.

2 Materials and methods
2.1 Soil
Kaolinite silt and sand were employed in this study.
Kaolinite main chemical component is aluminumsilicate. The soil is classified as high-plasticity kaolinite
silt based with Skempton activity of 0.77%. A poorlygraded sand was the other soil used in this study.
2.2 Carrageenan
Carrageenan is a linear polysaccharide comprising long
chains of sugar molecules. It is typically produced fromred seaweed and utilized as thickener and stabilizer infood products. The biopolymer used in this work was
Kappa-Carrageenan manufactured by the Tokyo
Chemical Industry (TCI).

© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0(https://creativecommons.org/licenses/by/4.0/).

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2.3 Experimental Program

2000

16

1800

14

Unconfined compressive strength test was used toassess the effect of biopolymer content, dehydration
time, and soil type in slope surface stability. Durabilityof the treated samples was tested after 5 cycles ofwetting and drying. SEM images were taken to visually
express the interaction of the biopolymer and soil
through a chemical model.
A labelling pattern was used to name different
samples. K as kaolinite, S as sand, a number from 0 to 4
for kaolinite-sand mixture. For example, K1S3 shows amix of 25% kaolinite and 75% sand.

Fig. 2. UCS and moisture content variation with time

3 Results

3.3 Soil type

12UCS (kPa)

1400
K1S3

1200

10qmaxK1S3-Ca

1000

8

K1S3

800

6Moisture content
K1S3-Ca

600

Moisture content (%)

1600

4400
220000051015202530

Curing time (day)Fig. 3 depicts the UCS test results for several sandkaolinite combinations treated with 0.5% carrageenan
and kept for 14 days. In sand-kaolinite combinations, thequantity of sand varies by 0, 25, 50, 75, and 100 percent.
All samples had a moisture level of less than 1%, hence
the impact of moisture may be disregarded.
As expected, the soil combination with 25% kaolinite
and 75% sand (K1S3) provided the maximum strength.
The small particles of kaolinite were distributed
throughout the sand spaces to produce a dense soil mass,
allowing K1S3 to reach the maximum dry density of all
soil combinations.

3.1 Biopolymer content

UCS (kPa)

Figure 1 displays the compressive strength values for
untreated and treated soils with varying quantities ofcarrageenan and xanthan (0, 0.25, 0.5, 1, and 1.5% byweight to dry soil). The treated samples were stored for
14 days in a controlled environment with a temperatureof 23 °C and a relative humidity of 50-60%. On the basisof compaction test, the initial moisture content of K4S0
and K1S3 samples was estimated to be 35% and 15%,respectively.
As seen in Fig. 1, carrageenan increased the strength andstiffness of samples up to 0.5%, after which a reduction
was observed. The highest improvement in terms of thesoil type was for K1S3 due to its higher relative densityand better soil particle size distribution.

02010080

Kaolinite Content (%)
406080

100

200

2000
1800
1600
1400
1200
1000
800
600
400
200
06040

Sand Content (%)
Untreated Soil

Ca-treated soil

Fig. 3. UCS value by different soil type

3.4 Leaching capacity under wetting and drying
Figure 4 depicts the change in compressive strength andstiffness of untreated soil and carrageenan-treated soil
(0.5% biopolymer) after cyclic wetting and drying
operations. It reduces the strength and elasticity
modulus of both untreated and treated soils. The
reduction rate in UCS values was significant for
untreated soil, with almost 50% after 3 and 80% after 5wetting and drying cycles, whereas carrageenan
maintained a viable level of strength after five cycles ofwetting and drying, with carrageenan retaining 19.3% of
the strength reduction. This suggests that, despite thefact that soaking in water adversely effect the strength,
most of the bonds and interactions rebound substantiallyafter drying.
The mass loss of the biopolymer lowered the amountof soil washed during the process of wetting and drying.
Figure 5 indicates the shape of sample over the wet-dry
cycles. Mass loss was reduced from around 80% forFig. 1. UCS of untreated and carrageenan-treated soil bydifferent biopolymer contents

3.2 Time
The effect of curing time on the compressive strength ofcarrageenan-treated soil was studied after 0, 1, 3, 7, 14,
and 28 days of curing in a controlled environment. As
per Fig. 2, after 24h from preparation, a growing trend
in strength was started. More than 90% of thecompressive strength was attained within the first 7 days
from preparation, and the strength of the treated samples
reached their maximum on day 14 and remained almost
constant until the day 28. Therefore, in subsequent
phases, 14 days was deemed to be the optimal duration.

2

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UCS (kPa)

untreated soil to 19% for carrageenan treated soil after 5cycles.
2000
1800
1600
1400
1200
1000
800
600
40020001829

1823
1684
1536

407

3670260

1211

21476

88
3

5

Wet-Dry Cycle No.
Untreated Soil

Carrageenan

Fig. 4. Durability over wetting and drying cycles
Fig. 6. SEM of carrageenan treated K1S3

Fig. 5. Stability under cycle of wetting and drying

3.5 Microstructural Analysis

Fig. 7. Schematic figure of the biopolymer-kaolinite
interaction

Figure 4 shows how carrageenan bind the soil particles
through complex physiochemical interactions. There areseveral strong hydrogen interactions between oxygen
atoms of tetrahedral silicate sheets and hydroxyl groupsof octahedral aluminium hydroxide sheets in theinterlayer region of kaolinite. Intermolecular hydrogenbonding is an interaction in kaolinite/k-carrageenan
composite formation due to the presence of abundanthydroxyl functional groups on the surface of kaolinite(inner surface –OH) and organic functional groups,
namely –OH and –SO4, in the structure of kcarrageenan. A schematic figure of the existing
interactions is provided in Figure 7.
The interfacial mechanical contact of the sand/kcarrageenan polymeric chain is the major driving factor
for the production of the sand/k-carrageenan composite.
The second driving factor in the composite structure ishydrophobic bonding between the uncharged surface ofsand and the carbon chain of k-carrageenan.

4 Conclusions
This study introduces carrageenan as a new sourceof sustainable material with the aim of soilimprovement. Detailed research was performed topresent the performance of the biopolymer. Carrageenan
indicated a significant growth in the compressive
strength in terms of biopolymer content, moisture
content, and durability. Therefore, more research isencouraged to be done using carrageenan combinedwith various soil types.

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