The Effect of Uniaxial Pressure on Development on 3D Fracture and Its Properties of Clay Cap Rock on One Potential Geothermal Area in Candi Umbul-Telomoyo, Semarang, Central Java, Indonesia Sumarni (a*), Selly Feranie (a), N D Ardi (a), F D E Latief (b)
a) Digital Rock Physics and Soil Mechanical Laboratory, Departement of Physics Education, Faculty of Education Mathematics and Natural Sciences
Indonesian University of Education
Jalan Setiabudhi no. 229, Bandung 40154, Indonesia
*sumarnis093[at]gmail.com
b) Physics of Earth and Complex System, Faculty of Mathematics and Natural Sciences
Institut Teknologi Bandung
Jalan Ganesha no. 10, Bandung 40132, Indonesia
Abstract
The geothermal potential of Candi Umbul-Telomoyo is very interesting to be observed due to the emergence of geothermal manifestations. A sample of clay cap rock on geothermal area in Candi Umbul-Telomoyo, Semarang has been digitized to the observe 3D fracture development due to the influence of uniaxial pressure. The 3D fracture were analyzed using digital image processing and analysis method. The sample is an altered ceses andesite breccia with diameter of 4.4 cm and height of 4.3 cm. The rock sample was collected from well at 590 m. Rock sample was given uniaxial pressure treatment of 59 bar, 75 bar, 91 bar, 107 bar, 123 bar and 156 bar. The results show that 3D fracture develops as pressure increase are total orientation {\(\theta\) (P)}, aperture {e (P), fracture density {\(\Phi\) (P)}, fracture intensity {I (P)} and fractal dimension {D (P)}. Total orientation and fracture intensity have polynomial to relative to the given pressure. Aperture and fractal dimension are linearly proportional to the give pressure, while the fracture density is exponentially proportional to the give pressure. The effect of increasing pressure to the safety of this geothermal clay cap was studied by conducting a continuous uniaxial compressive test on the sample. From this test, it is observed that the sample broken at the pressure of 478 bar. The results of this study are expected to provide an overview of the characteristics of the clay cap rock and the clay cap stability on Geothermal Area Candi-Umbul Telomoyo.
Keywords: fracture characteristics, uniaxial pressure, clay cap
