Pengaruh variasi kadar air terhadap deformasi lereng di Kilometer 15,9 saluran irigasi Kalibawang Kulon Progo

DWIDJAKA, Agus, Dr.Ir. Hary Christady Hardiyatmo, M.Eng.,DEA

2006 | Tesis | S2 Teknik Sipil

Gerakan tanah yang terjadi pada lereng-lereng sering mengakibatkan kerusakan dan korban jiwa yang relatif besar. Gerakan tanah pada lereng sekitar saluran induk Kalibawang Kabupaten Kulon Progo, Daerah Istimewa Yogyakarta khususnya di penggal kilometer (km) 15,9 diperkirakan penyebabnya adalah perubahan kadar air. Bertolak dari hal tersebut dilakukan penelitian geoteknis di laboratorium terhadap tanah dari lokasi di atas dengan memvariasikan kadar air dan kemudian menganalisis deformasinya. Tujuan dari penelitian ini adalah untuk mengetahui parameterparameter geoteknis tanah, akibat perubahan kadar air tanah di lereng dan pengaruhnya terhadap deformasi/gerakan tanah. Bahan yang digunakan untuk penelitian ini adalah tanah yang diambil dari Dusun Klepu, Desa Banjar Arum, Kecamatan Kalibawang, Kabupaten Kulon Progo, Daerah Istimewa Yogyakarta, di lokasi lereng sekitar kilometer 15,9 Saluran Induk Kalibawang. Variasi kadar air 20%, 30%, 40% untuk uji pengembangan, 20%, 30% dan 54% (jenuh) untuk mendapatkan parameter-parameter tanah. Data yang diperoleh dari pengujian selanjutnya dianalisis menggunakan program plaxis untuk memodelkan deformasi. Hasil penelitian menunjukkan tanah dengan kadar air awal rendah dibandingkan dengan kadar air awal tinggi mempunyai perubahan volume, pengembangan (swelling) dan tekanan pengembangan lebih besar juga menghasilkan kohesi dan sudut gesek dalam yang lebih besar. Tanah akan mengalami deformasi dan pergerakan semakin besar seiring dengan bertambahnya kadar air pada tanah, ditunjukkan dari hasil analisis deformasi, dan diperkirakan tanah akan kehilangan kuat gesernya seiring dengan penjenuhan yang terjadi. Berdasar analisis deformasi, lokasi lereng km 15,9 Saluran Induk Kalibawang akan mengalami deformasi yang agak besar jika terjadi penjenuhan pada tanah dan deformasi lebih kecil jika tanah dalam kondisi lebih kering.

Soil movement that occured at slopes often caused victim and damages in great volume. The soil movement that was analyzed was around Kalibawang irrigation channel at km 15.9 in Kulon Progo district, special Province of Yogyakarta, Indonesia. This soil movement was approximately caused by the change in soil water content. Based on that condition, geotechnical research was carried out in laboratory to soil taken from that area. The variations applied were soil water contents and soil deformations were then analized. The aims of this research were to determine some geotechnical properties due to the changes in soil water content at the slopes and the effect of them to soil deformation. The soil was taken from Klepu, village Banjar Arum, Kalibawang, Kulon Progo district, special province of Yogyakarta at km 15.9 of Kalibawang irigation channel. The variations of soil water content were grouped based on the purposes of laboratory testing.The first group was for swelling test, the variations of soil water content were 20%, 30%, and 40%. The second one was for getting geotechnical parameters and the variations of soil water content were 20%, 30% and 54% (saturated) to get soil parameters. The data obtained were then analyzed with Plaxis software to modelling the soil deformation. The results showed that soil with low water content compared with soil with high water content possessed greater volume changes, swelling degrees and swelling pressures. It also possessed bigger cohesion values and internal friction angle values. The soil would deform and the movement was getting greater when the soil water content increased. This condition led to the loss of stress strength in soil due the increasement of soil saturation. Based on the deformation analysis, the deformation of slope at km 15.9 of Kalibawang irrigation channel was getting bigger when the saturating condition occured in soil. The deformation would be smaller when the soil was in dry condition.

Kata Kunci : variasi kadar air, pengembangan, deformasi, lereng, variation of moisture contents, swelling, deformation, slope