Clay shale merupakan hasil dari batuan yang telah diendapkan dan lapuk secara mekanis, dengan tanah lempung sebagai komponen utama. Clay shale ini sering memunculkan berbagai masalah geoteknik, termasuk stabilitas lereng konstruksi bawah permukaan, daya dukung pondasi, dan kesulitan dalam memilih material timbunan. Selain banyak menimbulkan masalah, para pakar juga kesulitan dalam menentukan klasifikasinya. Hal ini dikarenakan clay shale mempunyai karakteristik yang berbeda dari material lempung biasa. Jika clay shale terkena air, udara, dan sinar matahari, maka dalam waktu singkat akan cepat lapuk dan berubah menjadi lempung lunak. Hal ini menyebabkan clay shale mudah mengalami penurunan durabilitas dan penurunan kuat geser (Strength Degradation) sehingga menimbulkan masalah di bidang geoteknik. Perbaikan tanah diperlukan untuk meningkatkan daya dukung tanah. Pada penelitian ini, studi kasus yang diambil adalah clay shale yang telah mengalami pelapukan yang dijumpai di daerah pembangunan Gedung DPRD Provinsi Kalimantan Utara, Tanjung Selor. Sampel clay shale diamati selama 14 hari, 21 hari, dan 28 hari dengan campuran semen 10%, 15%, dan 20%, serta variasi kadar air yang ditambahkan sebanyak 10% dari kadar air optimum. Hasil penelitian didapatkan bahwa nilai CBR menunjukkan peningkatan hingga 193,02% dan nilai UCT hingga 53,43% dari tanah asli dengan variasi penambahan semen 20% dan masa peram 28 hari.

Kata Kunci: clay shale, CBR, stabilisasi tanah, semen Portland, kuat tekan beba

Clay shale is the result of rocks that have been precipitated and weathered mechanically with clay soil as the main component. This clay shale often raises various geotechnical problems, including the stability of subsurface construction slopes, the bearing capacity of the foundation, and the difficulties in selecting the backfill material. In addition to causing many problems, experts also have difficulty in determining the classification. This is because clay shale has different characteristics from ordinary clay materials. If clay shale is exposed to water, air, and sunlight, then in a short time it will quickly weather and turn into soft clay. It caused clay shale to easily experience a decrease in durability and a decrease in strength degradation, causing problems in the geotechnical field. Soil improvement was needed to increase the carrying capacity of the soil. In this study, the case study taken is clay shale that has undergone weathering which was found in the construction are of North Kalimantan Provincial Parliament Building, Tanjung Selor. Clay shale samples were observed for 14 days, 21 days, and 28 days with a mixture of 10%, 15%, and 20% cement, as well as a variation in added moisture content of 10% of the optimum moisture content. The result of the study showed that the CBR value showed an increase of up to 193,02% and the UCT value of up to 53,43% of the original soil with a variation 0f 20% cement addition and a 28-day fermentation period. Keyword: Clay Shale, CBR, Soil Stabilization, Portland Cement, Free Compressive Strength