• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.3
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• pp.209-222
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• 2024

The Earth Pressure Balance (EPB) shield Tunnel Boring Machine (TBM) is widely used for underground tunnel construction for its advantages, such as eliminating the need for additional facilities compared to the slurry shield TBM, which requires Slurry Treatment Plant (STP). During EPB shield TBM excavation, a soil conditioning technique is employed to enhance the physical properties of the excavated soil by injecting additives, thus broadening the range of applicable ground conditions to EPB shield TBMs. This study explored the use of xanthan gum, a type of biopolymer, as an alternative to the commonly used polymer additive. Biopolymers, derived from biological sources, are fully biodegradable. In contrast to traditional polymers such as polyacrylic acid, which contain environmentally harmful components, xanthan gum is gaining attention as an eco-friendly material due to its minimal toxicity and environmental impact. Test conditions with similar workability were established through slump tests, and the rheological characteristics were assessed using a laboratory pressurized vane shear test apparatus. The experiments demonstrated that, despite exhibiting similar workability, the peak strength in the flow curve decreased with increasing the content of xanthan gum. Consequently, a correlation between the xanthan gum content and peak strength was established. Replacing the traditional polymers with xanthan gum could enable stable EPB shield TBM operation by reducing equipment load, in addition to offering environmental benefits.

• Economic and Environmental Geology
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• v.51 no.4
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• pp.359-370
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• 2018

The batch and column experiments were performed to overcome the limitation of the neutralization process using the $scCO_2$-water-recycled aggregate, reducing its treatment time to 3 hour. The waste cement mortar and two kinds of recycled aggregate were used for the experiment. In the extraction batch experiment, three different types of waste mortar were reacted with water and $scCO_2$ for 1 ~ 24 hour and the pH of extracted solution from the treated waste mortar was measured to determine the minimum reaction time maintaining below 9.8 of pH. The continuous column experiment was also performed to identify the pH reduction effect of the neutralization process for the massive recycled aggregate, considering the non-equilibrium reaction in the field. Thirty five gram of waste mortar was mixed with 70 mL of distilled water in a high pressurized stainless steel cell at 100 bar and $50^{\circ}C$ for 1 ~ 24 hour as the neutralization process. The dried waste mortar was mixed with water at 150 rpm for 10 min. and the pH of water was measured for 15 days. The XRD and TG/DTA analyses for the waste mortar before and after the reaction were performed to identify the mineralogical change during the neutralization process. The acryl column (16 cm in diameter, 1 m in length) was packed with 3 hour treated (or untreated) recycled aggregate and 220 liter of distilled water was flushed down into the column. The pH and $Ca^{2+}$ concentration of the effluent from the column were measured at the certain time interval. The pH of extracted water from 3 hour treated waste mortar (10 ~ 13 mm in diameter) maintained below 9.8 (the legal limit). From XRD and TG/DTA analyses, the amount of portlandite in the waste mortar decreased after the neutralization process but the calcite was created as the secondary mineral. From the column experiment, the pH of the effluent from the column packed with 3 hour treated recycled aggregate kept below 9.8 regardless of their sizes, identifying that the recycled aggregate with 3 hour $scCO_2$ treatment can be reused in real construction sites.