Kajian stabilisasi tanah lempung ekspansif dari ruas jalan Surakarta-Purwodadi menggunakan semen

ANANTA, Dr.Ir. Hary Christady Hardiyatmo, M.Eng.,DEA

2007 | Tesis | Magister Sistem dan Teknik Transportasi

Kerusakan jalan yang disebabkan oleh tanah dasar (Subgrade) yang mempunyai kembang susut besar merupakan persoalan yang serius, jenis kerusakan ini setidaknya terjadi pada beberapa ruas jalan Surakarta-Purwodadi. Kondisi tanah dasar merupakan salah satu hal yang penting mengingat tanah dasar merupakan tumpuan yang akan menerima seluruh beban dari lapis perkerasan maupun beban lalulintas yang diatasnya. Penelitian stabilisasi tanah lempung ekspansif menggunakan semen dilakukan pemeriksaan kadar air, analisa ukuran butiran, berat jenis tanah, batas-batas Atterberg, potensi pengembangan (potential swell), dengan maksud untuk mengetahui sifat fisik tanah lempung dan klasifikasinya. Kemudian diuji CBR yang sebelum diuji CBR direndam dalam bak perendaman selama 4x24 jam sambil pemeriksaan swelling. Selanjutnya dibuat benda uji dengan variasi kadar semen 3%, 6%, 9%, dan 12% terhadap berat kering tanah lempung, dilakukan pencampuran hingga tercampur secara homogen dan ditambahkan air sesuai dengan kadar air optimum dari masing masing campuran yang diperoleh dari percobaan pemadatan standar. Pengujian sesuai dengan peraturan Bina Marga dan AASHTO. Hasil penelitian menunjukkan bahwa stabilisasi tanah lempung ekspansif dengan menggunakan semen 3% meningkatkan nilai CBR dari 1,73% menjadi 19,3% sudah memperbaiki daya dukung tanah dari jelek menjadi kategori baik. Penambahan kadar semen 6%, 9%, 12% menjadi 30,6%, 37,1%, dan 56,4% tergolong sempurna (excellent) untuk lapisan subgrade. Nilai Batas cair (LL) tanah lempung ekspansif 75%. Penambahan semen 3% mengalami penurunan menjadi 73%, kadar semen 6%,70%, kadar semen 9% menjadi 64,21%, dan kadar semen 12%, 63,88%. Indeks plastisitas (PI) turun 45,05% lempung ekspansif menjadi 29,94% pada penambahan semen 3%, 27,22% kadar semen 6%, 21,57% kadar semen 9%, 21,44% penambahan kadar semen 12%, masih melebihi batas yang dianjurkan dalam proses stabilisasi sehingga tidak mendapatkan hasil yang baik dan ekonomis. Menurunkan potensi pengembangan (swell potential) dari 33% tanah asli menjadi 10% penambahan semen 12% masih tergolong tinggi. Diperlukan penanganan lebih lanjut selain metode stabilisasi seperti metode pemadatan dan pengendalian kadar air (moisture control ).

Road damages caused by a highly swelling and shrinking subgrade are serious problems, and such damages had occurred on at least several strips of Surakarta-Purwodadi road. The condition of a subgrade is important since it is the foundation of the entire load of the upper hardening layer or of the traffic of the road. A study on the stabilization of expansive clay soil using cement was carried out by examining the content of water, the size of soil grains, soil specific gravity, Atterberg thresholds, and potential swell to find out the physical characteristics of the clay soils and their classifications. CBR tests on the soils were performed after they were immersed in a container for 4x24 hours while checking their swell. Then, the test object was made with variations of cement concentration of 3%, 6%, 9%, and 12% against the dry mass of the clay soil, mixing up until they were homogenous and the water was added according to the optimum concentration of water of each mix obtained from the standard hardening experiments. The tests were carried out in accordance with the regulations of directorate general of highway construction and maintenance and AASHTO. The results of study showed that stabilization of expansive clay soils using 3% cement could increase the value of CBR from 1.73% to 19. 3%. Such an increase was able to improve a poor supporting capacity of soil into a good one. The addition of cement concentration from 6%, 9%, and 12% to 30.6%, 37.1%, and 56.4% was considered excellent for the subgrade. The liquid limit value of expansive clay soil was 75%. The addition of 3% cement caused a decrease of LL to 73%, cement concentrations of 6%, 70%, and 9% resulting in 64.21% LL, and cement concentration of 12% resulting in 63.88% LL. Plasticity index (PI) decrease of 45.05% expansive clay decreased to 29.94% at the cement addition of 3%, 27.22% at the addition of cement 6%, 21.57% at the addition of 9%, and 21.44% at the addition of cement concentration 12%. This was still beyond the advised limit in the process of stabilization so that no good and economic results were achieved. The lowering of swell potential from 33% of the original soil to 10% with the addition of cement of 12% was still considered as high. Further treatment was needed besides stabilization method, such as hardening and moisture control methods.

Kata Kunci : Jalan Raya,Stabilisasi Tanah,Tanah lempung Ekspansif,expansive clay soil, stabilization