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CONTENTS
Volume 12, Number 5, May 2017
 

Abstract
We would like to present the special issue on Innovative and Eco-friendly Soil Treatment Technologies of the Geomechanics and Engineering, An International Journal (ISSN: 2005-307X). As Geomechanics and Engineering has strong reputation for quality in the field of soil and geotechnical engineering, this special issue also devotes itself to introducing validated emerging technologies on soil treatment. This special issue is an extension of the success of the 2016 International Conference on Geomechanics and Engineering (ICGE16) held in August 2016, Jeju, Korea. Papers which devote themselves to innovative and environmentally-friendly soil treatment researches from laboratory scale attempts to practical implements were selected after the conference, with accompanying fully updated paper submission and peer review processes. Emerging innovative technologies through multidisciplinary (geotechnical; chemical; and biological) convergences is the main topic of this special issue. In this spirit, 9 scientific articles are presented in this volume as:
- Evaluation of the grouting in the sandy ground using bio injection material
- Polylysine biopolymer for coagulation of contaminated water
- Factors affecting waterproof efficiency of grouting in single rock fracture
- Strength and slake durability characteristics of biopolymer-treated sand of Al-Sharqia desert, Oman
- Application of magnesium to improve uniform distribution of precipitated minerals in 1-m column specimens
- Dynamic properties of gel-type biopolymer-treated sands evaluated by Resonant Column (RC) tests
- Geotechnical shear behavior of xanthan gum biopolymer treated sand from direct shear testing
- In situ viscoelastic properties of insoluble and porous polysaccharide biopolymer dextran produced by Leuconostoc mesenteroides using particle-tracking microrheology
- Measuring elastic moduli of bacterial biofilms in a liquid phase using Atomic Force Microscopy (AFM)
Each article provides valuable findings and recommendations on innovative and eco-friendly soil treatment. We appreciate all authors for their faithful research and reviewers for their sincere contribution to peer reviews.
It is our hope that this fine collection of the articles will be a valuable resource for Geomechanics and Engineering readers and will stimulate further research into the vibrant area of innovative and eco-friendly soil treatment.

May 2017

Key Words


Address


Abstract
This study was intended to evaluate the improved strength of the ground by applying the bio grouting method to a loose sandy ground. The injection material was prepared in the form of cement-like powder, with the bio injection material produced by microbial reactions. The grouting test was conducted under the conditions similar to the field where the bio injection material can be applied. In addition, the injection materials (cement and sodium silicate No. 3) used for Labile Waterglass (LW) method and the conventional grouting methodwere prepared through a two-solution one-step process. The injection into the specimens was done at a pressure of 150 kPa and then, with a bender element, their moduliof elasticity were measured on the 7th, 14th, 21st and 28th curingdays to analyze their strengths according to the duration of curing. It was confirmed that in all injection materials the moduli of elasticity increased over time. In particular, when 30% of the bio injection material was added to 100% cement, the modulus of elasticity tended to increase by about 15%. This confirmed that the applicability became higher when the bio injection material was used in place of the conventional sodium silicate.

Key Words
grouting; bio injection material; loose sandy ground; modulus of elasticity; microbial reactions

Address
Department of Civil Engineering, Chosun University, 501-759, Republic of Korea.

Abstract
The coagulation or flocculation of cohesive clay suspensions is one of the most widely used treatment technologies for contaminated water. Flocculated clay can transport pollutants and nutrients in ground water. Coagulants are used to accelerate these mechanisms. However, existing coagulants (e.g., polyacrylamide, polyaluminum chloride) are known to have harmful effects in the environment and on human health. As an alternative, eco-friendly coagulant, this study suggests ε-polylysine, a cationic biopolymer fermented by Streptomyces. A series of sedimentation experiments for various ε-polylysine concentrations were performed, and the efficiency of sedimentation with ε-polylysine was estimated by microscopic observation and light absorbance measurements. Two types of sedimentation were observed in the experiments: accumulation sedimentation (at 0.15%, 0.20%, 0.25% ε-polylysine) and flocculation sedimentation (at 0%, 0.1%, 0.5%, 1.0%, 2.0% ε-polylysine). These sedimentation types occur as a result of the concentration of counter ions. Additionally, the performance of ε-polylysine was compared with that of a previously used environmentally friendly coagulant, chitosan. The obtained results indicate that flocculation sedimentation is appropriate for contamination removal and that ε-polylysine functions more efficiently for clay removal than chitosan. From the experiments and analysis, this paper finds that polylysine is an alternative eco-friendly coagulant for removing chemical contaminants in groundwater.

Key Words
ε-polylysine; sedimentation; biopolymer; coagulation; flocculation

Address
(1) Yeong-Man Kwon, Jooyoung Im, Gye-Chun Cho:
Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology (KAIST), 34141 Republic of Korea;
(2) Ilhan Chang:
School of Engineering and Information Technology, University of New South Wales, Canberra, ACT 2600, Australia.

Abstract
Using a transparent fracture replica with aperture size and water-cement ratio (w/c), the factors affecting the penetration behavior of rock grouting were investigated through laboratory experiments. In addition, the waterproof efficiency was estimated by the reduction of water outflow through the fractures after the grout curing process. Penetration behavior shows that grout penetration patterns present similarly radial forms in all experimental cases; however, velocity of grout penetration showed clear differences according to the aperture sizes and watercement ratio. It can be seen that the waterproof efficiency increased as the aperture size and w/c decreased. During grout injection or curing processes, air bubbles formed and bleeding occurred, both of which affected the waterproof ability of the grouting. These two phenomena can significantly prevent the successful performance of rock grouting in field-scale underground spaces, especially at deep depth conditions. Our research can provide a foundation for improving and optimizing the innovative techniques of rock grouting.

Key Words
waterproof efficiency; penetration pattern; rock grouting; aperture sizes; water-cement mixed ratio (w/c)

Address
(1) Hang Bok Lee, Tae-Min Oh, Eui-Seob Park:
Center for Deep Subsurface research, Korea Institute of Geoscience and Mineral Resources, Daejeon 305-350, Republic of Korea;
(2) Jong-Won Lee, Hyung-Mok Kim:
Department of Energy & Mineral Resources Engineering, Sejong University, Seoul 143-747, Republic of Korea.

Abstract
Biopolymer treatment of geomaterials to develop sustainable geotechnical systems is an important step towards the reduction of global warming. The cutting edge technology of biopolymer treatment is not only environment friendly but also has widespread application. This paper presents the strength and slake durability characteristics of biopolymer-treated sand sampled from Al-Sharqia Desert in Oman. The specimens were prepared by mixing sand at various proportions by weight of xanthan gum biopolymer. To make a comparison with conventional methods of ground improvement, cement treated sand specimens were also prepared. To demonstrate the effects of wetting and drying, standard slake durability tests were also conducted on the specimens. According to the results of strength tests, xanthan gum treatment increased the unconfined strength of sand, similar to the strengthening effect of mixing cement in sand. The slake durability test results indicated that the resistance of biopolymer-treated sand to disintegration upon interaction with water is stronger than that of cement treated sand. The percentage of xanthan gum to treat sand is proposed as 2-3% for optimal performance in terms of strength and durability. SEM analysis of biopolymer-treated sand specimens also confirms that the sand particles are linked through the biopolymer, which has increased shear resistance and durability. Results of this study imply xanthan gum biopolymer treatment as an eco-friendly technique to improve the mechanical properties of desert sand. However, the strengthening effect due to the biopolymer treatment of sand can be weakened upon interaction with water.

Key Words
desert sand; bio-soil improvement; Xanthan gum; biopolymer; strength; durability

Address
(1) Mohsin U. Qureshi, Khaloud Al-Sadarani:
Faculty of Engineering, Sohar University, P.O. Box 44, PC, 311, Sohar, Sultanate of Oman;
(2) Ilhan Chang:
School of Engineering and Information Technology, University of New South Wales (UNSW), Canberra, ACT 2600, Australia.

Abstract
This study discussed the possible optimization of enzyme-mediated calcite precipitation (EMCP) as a soil-improvement technique. Magnesium chloride was added to the injection solution to delay the reaction rate and to improve the homogenous distribution of precipitated minerals within soil sample. Soil specimens were prepared in 1- m PVC cylinders and treated with the obtained solutions composed of urease, urea, calcium, and magnesium chloride, and the mineral distribution within the sand specimens was examined. The effects of the precipitated minerals on the mechanical and hydraulic properties were evaluated by unconfined compressive strength (UCS) and permeability tests, respectively. The addition of magnesium was found to be effective in delaying the reaction rate by more than one hour. The uniform distribution of the precipitated minerals within a 1-m sand column was obtained when 0.1 mol/L and 0.4 mol/L of magnesium and calcium, respectively, were injected. The strength increased gradually as the mineral content was further increased. The permeability test results showed that the hydraulic conductivity was approximately constant in the presence of a 6% mineral mass. Thus, it was revealed that it is possible to control the strength of treated sand by adjusting the amount of precipitated minerals.

Key Words
precipitation; magnesium; uniformity; reaction rate; soil improvement

Address
(1) Heriansyah Putra, Hideaki Yasuhara, Naoki Kinoshita:
Department of Civil and Environmental Engineering, Ehime University, 3, Bunkyo-cho, Matsuyama, Japan;
(2) Akira Hirata:
Department of Applied Chemistry, Ehime University, 3, Bunkyo-cho, Matsuyama, Japan;
(3) Heriansyah Putra:
Faculty of Engineering, Jambi University, KM 11 Jambi - Palembang, Jambi, Indonesia.

Abstract
Due to numerous environmental concerns in recent years, the search for and the development of sustainable technologies have been pursued. In particular, environmentally friendly methods of soil improvement, such as the potential use of biopolymers, have been researched. Previous studies on the use of biopolymers in soil improvement have shown that they can provide substantial strengthening efficiencies. However, in order to fully understand the applicability of biopolymer treated soils, various properties of these soils such as their dynamic properties must be considered. In this study, the dynamic properties of gel-type biopolymer treated soils were observed through the use of resonant column tests. Gellan gum and Xanthan gums were the target gel-type biopolymers used in this study, and the target soil for this study was jumunjin sand, the standard sand of Korea. Through this study it was demonstrated that biopolymers can be used to enhance the dynamic properties of the soil, and that they offer possibilities of reuse to reduce earthquake related soil failures.

Key Words
biopolymer treatment; gellan gum; xanthan gum; shear modulus; damping ratio

Address
(1) Jooyoung Im, An T.P. Tran, Gye-Chun Cho:
Department of Civil Engineering, Korean Advanced Institute for Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea;
(2) Ilhan Chang:
School of Engineering and Information Technology, University of New South Wales, Canberra, ACT 2600, Australia.

Abstract
Conventional geotechnical engineering soil binders such as ordinary cement or lime have environmental issues in terms of sustainable development. Thus, environmentally friendly materials have attracted considerable interest in modern geotechnical engineering. Microbial biopolymers are being actively developed in order to improve geotechnical engineering properties such as aggregate stability, strength, and hydraulic conductivity of various soil types. This study evaluates the geotechnical engineering shear behavior of sand treated with xanthan gum biopolymer through laboratory direct shear testing. Xanthan gum-sand mixtures with various xanthan gum content (percent to the mass of sand) and gel phases (initial, dried, and re-submerged) were considered. Xanthan gum content of 1.0% sufficiently improves the inter-particle cohesion of cohesionless sands 3.8 times and more (up to 14 times for dried state) than in the untreated (natural) condition, regardless of the xanthan gum gel condition. In general, the strength of xanthan gum-treated sand shows dependency with the rheology and phase of xanthan gum gels in inter-granular pores, which decreases in order as dried (biofilm state), initial (uniform hydrogel), and re-submerged (swollen hydrogel after drying) states. As xanthan gum hydrogels are pseudo-plastic, both inter-particle friction angle and cohesion of xanthan gum-treated sand decrease with water adsorbed swelling at large strain levels. However, for 2% xanthan gum-treated sands, the re-submerged state shows a higher strength than the initial state due to the gradual and non-uniform swelling behavior of highly concentrated biofilms.

Key Words
Xanthan gum; biopolymer; direct shear; inter-particle; friction angle; cohesion

Address
(1) Sojeong Lee, Moon-Kyung Chung:
Geotechnical Engineering Research Institute (GERI), Korea Institute of Civil Engineering and Building Technology (KICT), 283 Goyangdae-ro, Goyang 10223, Republic of Korea;
(2) Ilhan Chang:
School of Engineering and Information Technology, University of New South Wales (UNSW), Canberra, ACT 2600, Australia;
(3) Yunyoung Kim:
Inha University, 100 Inha-ro, Incheon 22212, Republic of Korea;
(4) Jong Kee:
Hanyang University, 55 Hanyangdaehak-ro, Ansan 15588, Republic of Korea.

Abstract
With growing interests in using bacterial biopolymers in geotechnical practices, identifying mechanical properties of soft gel-like biopolymers is important in predicting their efficacy in soil modification and treatment. As one of the promising candidates, dextran was found to be produced by Leuconostoc mesenteroides. The model bacteria utilize sucrose as working material and synthesize both soluble and insoluble dextran which forms a complex and inhomogeneous polymer network. However, the traditional rheometer has a limitation to capture in situ properties of inherently porous and inhomogeneous biopolymers. Therefore, we used the particle tracking microrheology to characterize the material properties of the dextran polymer. TEM images revealed a range of pore size mostly less than 20 μm, showing large pores > 2 μm and small pores within the solid matrix whose sizes are less than 1 μm. Microrheology data showed two distinct regimes in the bacterial dextran, purely viscous pore region of soluble dextran and viscoelastic region of the solid part of insoluble dextran matrix. Diffusive beads represented the soluble dextran dissolved in an aqueous phase, of which viscosity was three times higher than the growth medium viscosity. The local properties of the insoluble dextran were extracted from the results of the minimally moving beads embedded in the dextran matrix or trapped in small pores. At high frequency (ω > 0.2 Hz), the insoluble dextran showed the elastic behavior with the storage modulus of ~0.1 Pa. As frequency decreased, the insoluble dextran matrix exhibited the viscoelastic behavior with the decreasing storage modulus in the range of ~0.1–10-3 Pa and the increasing loss modulus in the range of ~10-4–1 Pa. The obtained results provide a compilation of frequency-dependent rheological or viscoelastic properties of soft gel-like porous biopolymers at the particular conditions where soil bacteria produce bacterial biopolymers in subsurface.

Key Words
complex shear modulus; biopolymer; dextran; particle tracking micro-rheology

Address
(1) Min-Kyung Jeon, Tae-Hyuk Kwon:
Department of Civil Engineering, Korean Advanced Institute for Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea;
(2) Jin-Sung Park, Jennifer H. Shin:
Department of Mechanical engineering, Korean Advanced Institute for Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea.

Abstract
With the increasing interest in using bacterial biofilms in geo-engineering practices, such as soil improvement, sealing leakage in earth structures, and hydraulic barrier installation, understanding of the contribution of bacterial biofilm formation to mechanical and hydraulic behavior of soils is important. While mechanical properties of soft gel-like biofilms need to be identified for appropriate modeling and prediction of behaviors of biofilm-associated soils, elastic properties of biofilms remain poorly understood. Therefore, this study investigated the microscale Young\'s modulus of biofilms produced by Shewanella oneidensis MR-1 in a liquid phase. The indentation test was performed on a biofilm sample using the atomic force microscopy (AFM) with a spherical indentor, and the force-indentation responses were obtained during approach and retraction traces. Young\'s modulus of biofilms was estimated to be ~33–38 kPa from these force-indentation curves and Hertzian contact theory. It appears that the AFM indentation result captures the microscale local characteristics of biofilms and its stiffness is relatively large compared to the other methods, including rheometer and hydrodynamic shear tests, which reflect the average macro-scale behaviors. While modeling of mechanical behaviors of biofilm-associated soils requires the properties of each component, the obtained results provide information on the mechanical properties of biofilms that can be considered as cementing, gluing, or filling materials in soils.

Key Words
elastic modulus; biofilm; hertz contact model; AFM

Address
(1) Yong-Min Kim, Tae-Hyuk Kwon:
Department of Civil and Environmental Engineering, Korean Advanced Institute for Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea;
(2) Seungchul Kim:
Department of Optics and Mechatronics Engineering, College of Nanoscience & Nanotechnology, Pusan National University, Pusan, Republic of Korea.

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