DEGREE OF WEATHERING CHARACTERIZATIONS ANDESITE AND ITS GEOMECHANICS BEHAVIOR IN PURWAKARTA

• Main Author: Setiadji, Prihananto
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/69662
• Institution: Institut Teknologi Bandung

In tropical region of Indonesia, weathering phenomena are very common processes which are occurred when the rocks exposed to the atmosphere and hydrosphere. From geological point of view, weathering is long-term processes; however, it can be clearly recognized by using whether field observations or laboratory tests. Moreover, weathering of rock is very important from engineering point of view. Weathered rocks will have specific engineering properties which are difference from fresh rocks and residual soils. Studied area is located in Kecamatan Sukatani, Kabupaten Purwakarta, West Java, and physiographically is a part of Bogor Zone. Due to the fact that the extensive use of andesite in Purwakarta for the main source of construction materials on region of West Java and DKI Jakarta, the existence of weathered andesites are very interesting to be studied. From aforementioned point of view, the main objective of this study is to characterize of weathered andesites and its geomechanical behavior. An ideal sequence of weathering sequences can be significantly observed using test pits and in-situ tests, consisting of residual soils (grade VI), upper completely weathered (grade Va), lower completely weathered (grade Vb, highly weathered (grade IV), moderately weathered (grade III), slightly weathered (grade II) and fresh rock (grade I). Meanwhile, penetration values as results of hand penetrometer test tend to increase with the increasing of weathering grade. Rock hardness obtaining from Schmidt hammer test tends to linearly decrease due to weathering. iv Based on petrographical analyses, studied andesite can be divided into two type which are andesite pyroxen (G. Patapan) and andesit hornblende (G. Kacapi and G. Cupu). Andesite pyroxen tends to be more easily weathered comparing to andesite hornblende. Results of physical or index property tests show that some soil/rock physical properties tend to increase due to weathering, such as water content (w), porosity (n) and degree of saturation (Sr). However, wet density (?w) and specific gravity (G) do not show any certain pattern of change, having values of 1.54 - 1.73 gr/cm3 for wet density and 2.41 - 2.60 for specific gravity. Results of mechanical property analysis show that there is an exponential relationship between modulus elasticity (Et(50)), point load index (Is), Schmidt hammer value (SHV) and compressive strength value (?c). The relationship can be expressed with equation of Et(50) = 2530e0.0201?c ( R2 = 0.9248), ?c = 26.017e0.5528Is ( R2 = 0.9881) and ?c = 16.964e0.0527SHV ( R2 = 0.9349). Finally, an engineering classification scheme of weathered andesite and its geomechanical behavior are presented in detail using three patterns of stress-strain curve model and failure mode from each degree of weathering.