STUDI EKSPERIMENTAL PENGARUH KEDALAMAN GEOMEMBRAN DI BAWAH LAPISAN TANAH PASIR

DIAN ANNISA FITRI, Ir. Agus Darmawan Adi, M.Sc, Ph.D.; Prof. Dr. Ir. Hary Christady Hardiyatmo M.Eng., DEA

2016 | Tesis | S2 Teknik Sipil

Tanah pasir lepas dengan gradasi seragam merupakan tanah berbutir kasar yang rentan terhadap masalah pada struktur. Permasalahan utama pada tanah pasir lepas adalah penurunan dan daya dukung yang rendah apabila diberikan pembebanan di atasnya. Pengaplikasian material geosintetik berupa geomembran yang ditanam dalam massa tanah granular dapat menjadikan solusi untuk permasalahan penurunan dan akan memiliki nilai rasio kedalaman optimum yang mampu meningkatkan daya dukung tanah. Penanaman material geomembran pada tanah pasir juga akan disimulasikan ke dalam program Plaxis, dengan tujuan untuk mengimplementasikan pengujian di laboratorium ke dalam program Plaxis, agar didapatkan perilaku tanah pasir pada setiap kedalaman geomembran. Penelitian ini menggunakan tanah berjenis pasir kering gradasi seragam dan material geomembran tipe HDPE ketebalan 1,5 mm. Peralatan pengujian diantaranya alat pembebanan manual yang berupa dongkrak CBR modification, proving ring, dial gauge indicator, pelat fondasi dengan ukuran 12 cm x 12 cm, box uji ukuran 1.2 m x 1.2 m x 1.2 m, stamper, dan waterpass. Tahapan pengujian meliputi pengujian pendahuluan sifat fisik-mekanik tanah pasir dan pengujian utama yakni pengujian pembebanan dengan sistem loading-unloading. Pengujian sifat fisik tanah pasir yang dilakukan adalah pengujian kadar air, berat jenis tanah, analisa saringan, dan kerapatan tanah. Pengujian sifat mekanis tanah pasir berupa uji geser langsung. Pengujian utama dilakukan melalui uji pemodelan di laboratorium dengan pembebanan konstan menggunakan model beban telapak bujur sangkar di dalam kotak uji yang berisi tanah pasir yang telah ditentukan kepadatan relatifnya. Variasi pengujian terdiri dari kondisi tanah tanpa geomembran yakni kedalaman geomembran 0 B, serta kondisi tanah dengan geomembran yakni kedalaman geomembran 0,5 B; 1 B; 2 B; dan 3 B. Hasil pengujian pendahuluan sifat fisik dan sifat mekanik tanah pasir didapatkan kadar air 0,24 %; berat jenis butiran 3,243; kohesi 0 kN/m�²; dan sudut gesek 40,30�°. Hasil pengujian utama menunjukkan besarnya kapasitas dukung ultimit tanah pasir tanpa geomembran sebesar 327,007 kN/m�² dengan penurunan 9,04 mm. Kondisi optimum penanaman geomembran di tanah pasir berada pada variasi 0,5 B dengan kapasitas dukung ultimit sebesar 668,875 kN/m�²; penurunan 7,36 mm; dan BCR 1,27. Hasil Plaxis didapatkan nilai EPlaxis 13.160 kN/m2 (plane strain) dan 6.130 kN/m2 (axisymmetry); serta nilai axial force 0,79242 kN/m (plane strain) dan 0,20296 kN/m (axisymmetry). Kedalaman perletakan geomembran di tanah pasir berpengaruh pada tingkat keoptimalan penggunaan geomembran, semakin dekat penanaman geomembran dari permukaan tanah pasir, akan semakin besar kapasitas dukung tanah, mengurangi penurunan tanah, meningkatkan nilai EPlaxis dan axial force pada Plaxis.

Loose uniform sand is coarse grained soil which is prone to problems in terms of the structure. The main problems in the loose sand are the settlement and bearing capacity of the weak when given for applying loads. Application of geosynthetic materials such as geomembrane planted in the loose sand can be a solution for the problems of the settlement. It will have the optimum depth ratio value that can improve bearing capacity. Planting geomembrane material in sand will also be simulated in Plaxis program. The objective of implementing the testing in the laboratory into Plaxis program is to get the behavior of sand at any depth of geomembrane. This study uses the loose uniform sand and geomembrane material type HDPE with thickness of 1.5 mm. Testing equipment includes the manual loading tool in the form of jacks of CBR modification, proving ring, dial gauge indicator, the model test with a size of 12 cm x 12 cm, testing box size of 1.2 m x 1.2 m x 1.2 m, stamper, and waterpass. Preliminary stages of testing include testing of physical-mechanical characteristic of sand and the main testing is the loading test with loading-unloading system. The conducted testing of sand physic characteristic is testing the water content, specific gravity, grain size distribution, and the relative density of the soil. Testing of sand mechanic characteristicis in the form of direct shear tests. The main testing is conducted through modeling test in a laboratory with constant loading using the loading of squares model on the test box containing sand with predetermined relative density. Variations of testing consist of soil conditions without gemomembrane (0 B), and soil conditions with geomembrane with the depth of geomembrane 0.5 B, 1 B, 2 B, and 3 B. The results of preliminary testing of the physical and mechanical characteristics sand show water content of 0.24%, specific gravity of 3.243, cohesion of 0 kN/m�², and the friction angle of 40.30�°. The main test results show that the extent of ultimate bearing capacity of sand without geomembrane is 327.007 kN/m�² with the settlement of 9.04 mm. The optimum conditions of geomembrane planting in sand is at 0.5 B with the variation of ultimate bearing capacity of 668.875 kN/m�², settlement of 7.36 mm, and BCR of 1.27. The EPlaxis values are 13,160 kN/m2 (plane strain) and 6,130 kN/ m2 (axisymmetry), and the values of axial force are 0.79242 kN/m (plane strain) and 0.20296 kN/m (axisymmetry). Geomembrane placement depth in the sand influences the level of optimization level of geomembrane usage. The closer the geomembrane planting from the surface of sand, the bigger the bearing capacity, the less of settlement, and the higher EPlaxis and axial force on Plaxis.

Kata Kunci : geomembran, geomembrane