Abuahsan’s Weblog

The stability of underground mining was influenced by some factor, such like the strength of material, cracked, underground water, vibration include the earthquake, etc. If the opening hole area in the underground mining need support, the support will give contribution to that mining stability. One of the other kind of support is rock bolt.

Rock bolt is one of the supporting that if we use will be a part of rock mass. The research area at block 1A and block 2 south, part of 500 Ciurug’s level, tendon UBPE Pongkor. This area have a stope form with widht 25 m and height 5 m. This research have a purpose to find the installing model of split set that have more effective with separation be 5 model.

Analysis of the programming resulted to find the best rock bolt installing model with analysing displacement in the observation point, normal and shear displacement, axial force and axial strain, and the last shear force on yhe split set added safety factor that calculated by analytic. B and C model can’t supported rock block, that the final analysis do to the A, D and E model.

Displacement result in the horizontal axis show that A model getting displacement on the first and second observation point is 0,46 mm, and 0,453 mm. D model getting displacement on the first and second observation point is 49,9 mm, and 49,9 mm. E model getting displacement on the first and second observation point is 41,8 mm, and 41,6 mm. The same things happened in the vertical axis show that displacement on the first and second observation titik in the A model is 20,7 cm, and 14,8 cm, D model is 15,6 cm and 12,5 cm, and the last E model is 12,2 cm and 11,1 cm

Oppener crack on the left side in the A model is 76,96 mm, D model is 5,056 mm and E model is 2,018 mm. Closure crack on the right side in the A model is 0,108 mm, D model is 0,100 mm, and E model is 0,0977 mm. Shear left crack show the same trend that in the A model is 204,6 mm, D model is 169,4 mm, and E model is 131 mm. The biggest axial strain happened in the E model that value is -8,429 x 10-2 MN. Minus is way and that axial force holded the force to the split set. The last, the biggest value of safety factor happened to E model 3,12. A and D model is 2,58 and 3,02. Tha conclusion E model is relatively more effective beside the other model.

Gumilar (Bandung Instituted of Technology, Indonesia)

One of the methods used to determine the long term shear strength is accomplished by conducting creep test at the laboratory. Usually the creep test is conducted by one direction loading system, which is known as uniaxial creep test. The test is very suitable when applied to the determination of long term strength of underground pillar and at roof or wall of the tunnel. But it is not representative to be applied for the determination of long term strength of the rock mass around underground opening. With three direction loading system, the laboratory creep test would be more suitable to simulate the rock mass loading condition in its natural state; hence the long term strength obtained from this test would be more appropriate. Based on this assumption, the triaxial creep test needs to be carried out. From the triaxial creep test result obtained, the axial strain condition is constant with time. Axial strain only occurred when axial load was increased (immediate strain), after that, primer, secondary and tertiary strain did not occur during constant loading within + 48 hours. The creep process did not take place because the stress and temperatures in this experiment were inadequate to induce deformation dependent to time. Hoek and Brown commented that the rock specimen used in this experiment is categorized as High Strength, so that the rock would not result in creep when subjected to axial load of 30 MPa to 132, 38 MPa and temperature of 26°-28° C. Several factors must be taken into account to acquire long term strength parameter from triaxial creep test for andesit breccia; such as the determination of preliminary axial load, constant axial load and temperature.

Yudianto (Bandung Institute of Technology, Indonesia)

Two phases α2-TiAlγ-TiAI intermetalic alloy is developed for high temperature operation in oxidation enviroments. Its oxidation is relatively high due to the formation of TiO2 oxide scale which is not protective. Utilization of this material in a gas turbine engine can result in cracking and spelling of the oxide scale. The halide activated pack cementation method was used to deposit aluminize coatings on α2-TiAlγ-TiAI intermetalic alloy to enhance the oxidation resistance of α2-TiAlγ-TiAI intermetalic alloy. The aluminizes were deposited from a pack of aluminum powder, NH4CI, and alumna powder, the composition of the pack used variation was 10, 15, 20 wt % Al, 1, 1,5 2 wt % NH4C1, and Al2O3 as inert balance. All coatings were deposited tested at 900°C during 10 hours an argon atmosphere. Both coatings were subsequently at 1100°C under cyclic condition. X-ray diffraction (XRD), energy dispersive analysis of x-ray (EDAX), scanning electron microscopy (SEM) and optical microscopy were used to evaluate the coating deposition, morphology and oxidation behavior. The aluminide coating deposited in this study was of a compact duplex structure, the processes formed two layers, they are TiAl2 and TiAl3. During cyclic oxidation testing the aluminide coating at two phases α2-TiAlγ-TiAI intermetalic alloy substrate form by oxide scale is α-Al2O3 and TiO2. Forming And growth of TiO2 oxide faster by increasing cycle at temperature 1100°C. Substrate which is coated will give better oxidation resilience if is thick of coating above 48,66 gm with TiAl3 phases.

Ganda Putra (Bandung Institute of Tecnology, Indonesia