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Geomechanics and Engineering
  Volume 20, Number 2, January25 2020 , pages 165-174

Stiffness loss in enzyme-induced carbonate precipitated sand with stress scenarios
Jun Young Song, Youngjong Sim, Sun Yeom, Jaewon Jang and Tae Sup Yun

    The enzyme-induced carbonate precipitation (EICP) method has been investigated to improve the hydro-mechanical properties of natural soil deposits. This study was conducted to explore the stiffness evolution during various stress scenarios. First, the optimal concentration of urea, CaCl2, and urease for the maximum efficiency of calcite precipitation was identified. The results show that the optimal recipe is 0.5 g/L and 0.9 g/L of urease for 0.5 M CaCl2 and 1 M CaCl2 solutions with a urea-CaCl2 molar ratio of 1.5. The shear stiffness of EICP-treated sands remains constant up to debonding stresses, and further loading induces the reduction of S-wave velocity. It was also found that the debonding stress at which stiffness loss occurs depends on the void ratio, not on cementation solution. Repeated loading-unloading deteriorates the bonding quality, thereby reducing the debonding stress. Scanning electron microscopy and X-ray images reveal that higher concentrations of CaCl2 solution facilitate heterogeneous nucleation to form larger CaCO3 nodules and 11-12 % of CaCO3 forms at the inter-particle contact as the main contributor to the evolution of shear stiffness.
Key Words
    enzyme; CaCO3; debonding; shear stiffness; stress relaxation; X-ray CT
Jun Young Song: Korea Polar Research Institute, Incheon 21990, Republic of Korea

Youngjong Sim: Land and Housing Institute, Korea Land and Housing Corporation, Daejeon 34047, Republic of Korea

Sun Yeom: Korea Institute of Civil Engineering and Building Technology, Gyeonggi-Do 10223, Republic of Korea

Jaewon Jang: Department of Civil and Environmental Engineering, Hanyang University, Seoul 04763, Republic of Korea

Tae Sup Yun: Department of Civil and Environmental Engineering, Yonsei University, Seoul 03722, Republic of Korea

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