Shale is the most abundant among sedimentary rocks and covers about 70 % of the earth's crust. The shale also covers a significant portion of the Chittagong region, Bangladesh. The field strength (hammer value) for the shale of the Bhuban Formation showed a more considerable variation than that for other rocks in the region, revealing a high potential for weathering susceptibility. This research aims to evaluate the potential use of sodium carboxymethyl cellulose (Na-CMC) to increase the stability of the shale at slopes. Alkali metals were produced due to slaking, indicated by the increased pH and resistivity. The K+ and Na+ concentration increased in durability cycles, and the increase in concentration was higher in K+ than in Na+, suggesting K+ dissolution from the illite layer. The shear strength of the Poly specimen (grained and mixed with Na-CMC solution to solidify) was higher with brittle characteristics than the No-poly specimens (water was used instead of Na-CMC) in the dry condition. It was almost the same under the lowest normal stress with ductile characteristics and higher under increased normal stresses than the No-poly specimens in the wet condition. The critical shear strain of the Poly specimens was more extensive than those of the No-poly specimens in both conditions. The intact specimen immersed in the polymer solution at atmospheric pressure and the room temperature was unbroken and showed less penetration, whereas that immersed in the distilled water was broken and showed more penetration. The Poly specimen immersed in water was relatively stable and showed blocky disintegration with contraction. The No-poly specimen was unstable with grainy disintegration and showed expansion. The Na+ and K+ concentration of the immersed water was lower for the Poly specimen than for the No-poly specimen, indicating relatively higher stability by the sodium CMC solution. Sodium CMC may increase the strength of the shale with increased critical shear strain. It should be further investigated how to use it to increase the stability of in-situ rock slopes.

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