Penggunaan bakteri bacillus amyloliquefaciens dalam perbaikan tanah lempung ekspansif. = utilization of bacillus amyloliquefancies bacteria in repairing expansive soil.

Lawalata, Yoses (2018) Penggunaan bakteri bacillus amyloliquefaciens dalam perbaikan tanah lempung ekspansif. = utilization of bacillus amyloliquefancies bacteria in repairing expansive soil. Bachelor thesis, Universitas Pelita Harapan.

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Abstract

Tanah lempung ekspansif memiliki permasalahan berupa sifat kembang susut yang tinggi, kuat geser yang rendah, tingkat plastisitas yang tinggi, dan lain-lain. Oleh karena itu, dilakukanlah upaya untuk memperbaiki permasalahan-permasalahan tersebut. Salah satu metode yang dapat digunakan untuk memperbaiki tanah lempung ekspansif adalah dengan penggunaan kalsium. Berdasarkan penelitian-penelitian sebelumnya, pemberian kalsium melalui bahan stabilisasi berupa limestone telah terbukti mampu untuk mengurangi sifat kembang susut dan meningkatkan kuat geser tanah lempung ekspansif. Penelitian ini menggunakan metode stabilisasi biogrouting. Biogrouting memanfaatkan mikroorganisme berupa bakteri Bacillus amyloliquefaciens beserta medium kulturnya untuk membentuk kristal kalsium karbonat (CaCO3), yang dapat menstimulasi proses sementasi. Dengan adanya proses sementasi, tanah lempung ekspansif diharapkan akan mengalami perbaikan berupa penurunan pada sifat kembang susut dan peningkatan pada kuat gesernya. Perbaikan dilakukan dengan cara menyiramkan kultur cair Bacillus amyloliquefaciens pada sampel tanah. Masa pemeliharaan pada setiap sampel tanah adalah selama 14, 28, 60, dan 90 hari. Tanah yang diuji merupakan tanah lempung berjenis CH (fat clay), dengan indeks pengembangan tanah sebesar 103,7% dan nilai kuat geser sebesar 0,0175 kg/cm2 dan 0,2270 kg/cm2 untuk UU direct shear test dan unconfined compression test. Berdasarkan hasil pengujian, didapatkan peningkatan kuat geser terbesar setelah masa pemeliharaan 90 hari, yaitu sebesar 160,748% dan 77,528% untuk UU direct shear test dan unconfined compression test. Sementara itu, hasil pengujian terhadap indeks pengembangan tanah menunjukkan adanya penurunan sebesar 33,368%. Hasil tersebut mempengaruhi tingkat derajat pengembangan tanah, dari yang semulanya berderajat pengembangan tinggi turun menjadi berderajat pengembangan sedang./ Expansive clay soil has some weaknesses such as high swelling potential, low shear strength, high plasticity level, high volume change, and others. Various methods can be used to overcome these weaknesses, one of them is by using calcium. Previous studies had shown that addition of limestone containing calcium to stabilize, reduce swelling potential and increase shear strength of expansive clay soil. In this research, biogrouting was used by utilizing Bacillus amyloliquefaciens and its culture medium for the formation of calcium carbonate (CaCO3), which stimulates sementation process. It is hoped that sementation process could reduce swelling potential and increase shear strength. Bacteria liquid culture was added to the soil sample by sprinkling method. Maintenance period for every samples were 14, 28, 60, and 90 days. Soil sample tested was expansive clay soil type CH (fat clay), with free swell index of 103,7% and shear strength of 0,0175 kg/cm2 and 0,2270 kg/cm2 based on UU direct shear test dan unconfined compression test respectively. After maintenance period of 90 days, its shear strength increased 160,748% for UU direct shear test and 77,528% for unconfined compression test. In addition, its free swell index decreased by 33,368%. It can be concluded that the addition of calcium carbonate could decrease swelling potential of expansive clay soil; from high to medium degree of potential swelling.

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