Geotechnical engineering behaviors of gellan gum biopolymer treated sand

Abstract

Biological approaches have recently been explored as environmentally friendly alternatives to engineered soil methods in geotechnical engineering practices. The use of microbial induced calcite precipitation, reactive enzymes, and microbial polymers, such as biopolymers, in soil improvement has been studied by researchers around the world. In the present study, gellan gum, a microbial polysaccharide generally used in the food industry due to its hydrogel rheology, was used to strengthen sand. The effects of gellan gum on the geotechnical behaviors of cohesionless sand were evaluated through a series of experimental programs including an unconfined compression test, direct shear test, falling head permeability test, and scanning electron microscopy. The geotechnical properties (friction angle, cohesion, and unconfined compressive strength) of gellan gum–treated sands were determined based on varying moisture conditions: initial, dried, and re-submerged. Gellan gum has a distinct strengthening effect on cohesionless sands through artificial cohesion that varies with the moisture conditions. The strengthening effect of gellan gum on sand appears to be a result of the combination of enhanced bonding between unreactive sand particles and the agglomeration of sand particles through hydrogel condensation, in which the agglomerated sand particles behave as enlarged aggregates in soil.

Shear strength behavior and parameters of microbial gellan gum-treated soils: from sand to clay

“…4(a). However, the / d will increase when the gellan gum gels are fully dried, by forming a surface coating and enlarging interparticle contact areas [21].…”

“…These results suggest the potential utility of these biopolymers as a new construction material for environmentally friendly geotechnical engineering [5,13,14,18,19]. Among biopolymers suitable for soil treatment, gel-type biopolymers, such as gellan gum, agar gum, and xanthan gum, have several advantages, including quick (rapid) setting (gelation) [17], the ability to reduce hydraulic conductivity via bio-clogging [21], improving the shear resistance of soils [38,52] and a unique gel-structure formation process that reveals high gel strength even under fully saturated conditions [22]. Soil type and soil particle composition (i.e., coarse and fine composition) are basic properties that affect soil index parameters, such as Atterberg limits [67,80], and geotechnical engineering behaviors, such as undrained shear strength [73,82], soil stiffness and compressibility [12,15] and hydraulic conductivity [56].…”

“…Cement-treated sand consists of a solid phase (sand grains and C-S-H hydrates) only after cement hydration, while gellan gum-treated sand contains solid grains and hydrogels in voids. The presence of gellan gum hydrogels in sand pores only affects c d depending on the gel concentration, without any effect on the mechanical behavior (w d , / d ) of sand [21]. Thus, the shear behavior of gellan gum-treated sand should be interpreted differently than that of cement-treated sands.…”

“…For biopolymertreated soils, the elapsed time of horizontal shearing must be at least 49250 s due to the high water holding capacity and low coefficient of consolidation (C v ) values of biopolymer-treated clays (i.e., C v = 0.2 9 10 -7 m 2 /s, at void ratio = 0.9 for beta-glucan-treated clay) [14,58]. However, although horizontal shearing has been applied slowly, it is hard to present a perfect drained condition during a direct shear test on gel-type biopolymer-treated soils due to the high water holding capacity of gellan gum hydrogels [17,21]. Thus, the direct shear test results from this study have been interpreted in terms of direct shear strength, direct shear dilation angle, direct shear cohesion and direct shear friction angle where notations become s f , w d , c d , and / d , respectively.…”

“…The interactions between gel-type biopolymers and clay particles result in greater strengthening due to direct ionic or hydrogen bonding and matrix formation, while neutral sand particles undergo no direct bonding with biopolymers. For sand, gellan gum biopolymer provides strengthening to gellan gum-sand mixtures due to the condensation and aggregation effects of the high tensile gellan gum hydrogels among the sand particles [21]. However, a detailed understanding of the interactions between gellan gum and soils and their strengthening behavior, especially for sand-clay mixtures with different clay contents, has yet to be achieved.…”