Determination of parameter properties for failure analysis based on Atterberg test in East Wall area, Batu Hijau open pit, Sumbawa, Indonesia

Abstract

PT. Newmont Nusa Tenggara is a major copper and gold mines company located in West Sumbawa, Indonesia. It has a mine site named Batu Hijau. From 2001–2012 there were several slope failures occurred in this site. Failure X is one of the slope failure spot in East Wall Open Pit of Batu Hijau. Failure X is composed by altered rock which is called Feldspar Destruction and generally, in the field it consists of altered clay materials. Due to the condition of Feldspar Destruction in this area, the value of Factor of Safety is critically important and can be obtained by using the soil mechanics approach to get the angle of internal friction. The soil sampling is carried out in the field. Afterwards, the Atterberg Test is carried out in the laboratory to obtain the Plasticity Index values, correlating between the Plasticity Index values and the angle of internal friction, and carry out the slope stability simulation. The result of this research shows that the value of the angle of internal friction from Feldspar Destruction Zone is 33°. Besides that, rain has a quite big effect on the Ru value which has a direct impact to the Factor of Safety value and became the trigger of the last slope failure. Based on the simulation, when the Ru value is bigger than 0.27, the wall is not stable anymore This value can be used to another simulation in the next phase. Therefore, it is necessary to pay an intensive attention to the wall in the location of Failure XX and surrounding area (especially in Feldspar Destruction Zone) when the rain is coming. .