PERILAKU SISTEM PELAT TERPAKU PADA TANAH EKSPANSIF

WILLIS DIANA, Prof. Dr. Ir. Hary Christady Hardiyatmo, M.Eng., D.E.A; Prof. Ir. Bambang Suhendro, M.Sc.,Ph.D

2018 | Disertasi | S3 Ilmu Teknik Sipil

Tanah lempung ekspansif adalah tanah yang dapat mengembang dan menyusut karena perubahan kadar air. Perkerasan jalan yang dibangun di atas tanah ini akan menerima tekanan pengembangan yang besar karena mengembangnya tanah, sehingga diperlukan suatu inovasi sistem perkerasan yang mampu mengatasi permasalahan ini. Sistem pelat terpaku merupakan salah satu inovasi sistem perkerasan yang diusulkan karena kemudahan aplikasi di lapangan dan biaya keseluruhan konstruksi yang relatif murah. Sistem pelat terpaku berupa pelat perkerasan dengan ketebalan 15 cm -20 cm yang didukung oleh tiang-tiang mini berdiameter 15 cm - 20 cm, dan panjang tiang 1,5 m - 2,0 m. Pada tanah lunak, sistem pelat terpaku menunjukkan kemampuan yang lebih baik dalam mendukung beban, tetapi perilaku sistem pelat terpaku pada tanah ekspansif mengembang belum diketahui, sehingga perlu untuk diteliti lebih lanjut. Tujuan utama penelitian ini adalah untuk mengetahui perilaku deformasi sistem pelat terpaku pada tanah ekspansif, pengaruh dimensi tiang, ikatan tiang dengan pelat, dan analisis prediksi pengembangan tanah dan deformasi sistem pelat terpaku. Pemodelan skala kecil di laboratorium dan analisis numeris dengan metode elemen hingga dilakukan untuk menyelidiki perilaku sistem pelat terpaku pada tanah ekspansif. Variasi pengujian model skala kecil meliputi variasi panjang tiang, diameter tiang, spasi antar tiang, hubungan antara pelat dengan tiang, penggunaan koperan, dan jenis bahan pelat. Tanah lempung ekspansif yang digunakan berasal dari Ngawi, Jawa Timur. Perkiraan pengembangan volume vertikal dilakukan dengan menggunakan data hasil uji pengembangan dengan alat oedometer dengan menggunakan hubungan variabel perubahan kadar air, tegangan, dan regangan. Perkiraan perubahan volume juga dilakukan dengan menggunakan kurva permukaan konstitutif yang menghubungkan variabel angka pori, kadar air, tegangan, dan matric suction. Analisis numeris elemen hingga dilakukan menggunakan software Plaxis dan Abaqus. Hasil penelitian ini menunjukkan bahwa displacement yang dialami sistem pelat terpaku lebih kecil dibandingkan pelat tanpa dukungan tiang. Semakin panjang tiang, semakin besar diameter tiang dan semakin rapat spasi antar tiang displacement sistem pelat terpaku lebih kecil, tetapi memperpanjang tiang lebih efektif daripada memperbesar diameter tiang. Ikatan antara pelat dan tiang pengaruhnya sangat signifikan terhadap kemampuan sistem dalam menahan pergerakan ke atas karena mengembangnya tanah dasar, ikatan pelat dan tiang yang monolit akan menghasilkan displacement pelat yang lebih kecil dibandingkan tanpa adanya ikatan antara pelat dengan tiang. Sistem pelat terpaku mampu mereduksi 30% pergerakan ke atas (displacement) pelat dibandingkan pelat tanpa perkuatan tiang. Secara umum sistem pelat terpaku memperlihatkan perilaku yang lebih baik dibandingkan pelat tanpa tiang. Tahanan terhadap pergerakan ke atas akibat mengembangnya tanah dasar diperoleh dari komponen berat sendiri pelat, berat sendiri tiang, dan interaksi yang terbentuk antara pelat-tiang-dan tanah ekspansif disekeliling tiang. Perkiraan heave dari data pengujian pengembangan dengan oedometer menunjukkan perkiraan perubahan volume yang lebih besar dibandingkan hasil pengukuran. Pada analisis dengan menggunakan Plaxis, perilaku model hasil pengujian di laboratorium mendekati hasil simulasi pada volumetric strain kurang lebih 30%. Hasil simulasi pengembangan tanah memperlihatkan hasil perubahan volume yang lebih kecil dibandingkan hasil pengukuran di laboratorium.

Expansive soils are clay that swells and shrinks with changing moisture content. The structure that constructed on these soils is subjected to large uplifting forces caused by swelling. Hence, there is need to counteract the problem posed by these soils by devising innovative pavement technique. An attempt to develop a simple, easy to install and cost-effective alternative pavement system, the nailed slab system was developed, wherein slab pavement will be connected to a reinforced concrete mini piles. Nailed slab system is a pavement system, which consists of a thin plate (thickness 12 cm-20 cm) reinforced with mini piles with a diameter of 15 cm-20 cm and a length ranging from 1.5 m - 2.0 m. On soft soil, the nailed slab system can increase the modulus of subgrade reaction and shows better performance than conventional rigid pavement systems in their ability to support the load. However, behavior nailed slab system on expansive soil still unknown and needs to be researched. Hence, the focus of this study was to explore the behavior of the nailed slab system on the expansive soil. Small-scale experimental models and numerical simulation have been done. Nailed slab system models with a variation in the length, diameter, a spacing between piles, types of connection between pile and slab, types of slab material, and application of coverage at the edge of slab have been investigated. The disturbed expansive soil sample was collected from Ngawi, East Java. The soil was air dried and pulverized into passing no.4 sieve, and then used as soil media. The heave prediction was done by using the correlation between change in moisture content, surcharge pressure, and vertical strain from oedometer test data. The volume change prediction also doing by using constitutive surfaces of void ratio, water content, mean mechanical pressure, and matric suction. Plaxis and Abaqus finite element software were used to simulate the behavior of expansion of this soil. The swell of the expansive clay was modeled in Plaxis by applying a volumetric strain to the soil element. The soil hydro-mechanical process (swelling) for expansive soil on Abaqus has been explained by thermal-stress analogy. The results of this study indicate that the nailed slab system experiencing smaller upward movement than an unsupported slab (a slab without pile). The longer pile and the smaller spacing between piles produce the smaller vertical slab displacement. However, extending the pile lengths is more effective in reducing the heave rather than increasing the diameter of the pile. The connection between the pile and the slab has a significant effect on the system ability to withstand the upward movement of expansive soil. When pile and the slab were monolithically connected, the system shows the better performance than those the slabs with the free head pile. The nailed slab system can reduce upward displacement of the slab 30% lower than unsupported slab. Soil expansion causes decreased modulus of subgrade reaction, with increasing piles length (L) the difference in its modulus of subgrade reaction due to soil expansion decrease. The result found that not all soil deformation dispersed as slab displacement caused slabs has stiffness. The application of coverage at the edge of slab made the slab stiffer. In general, on the expansive soils, the nailed slab system showed better performance than the conventional pavement system. The Resistance of upward movement of the nailed slab system was obtained from the weight of pile, the weight of slab, the interaction between slab, pile, and soil around the perimeter of the pile. Thereafter a heave prediction analysis provided the amount of heave that slightly overestimates, but still good enough for a rough estimation. The numerical simulation showed that the behavior of model tested on laboratory similar with the model simulated on 30% volumetric strain in Plaxis. The underestimate volume change prediction result are shown in numerical simulation using Abaqus.

Kata Kunci : Tanah ekspansif, Sistem pelat terpaku, Pengembangan tanah, Displacement pelat, Prediksi heave