Abstract:
The Samigaluh area, Kulon Progo, Indonesia, is composed of rocks from the Old Andesite and Jonggrangan
Formations, with very different physical properties. The difference in physical properties indeed results in the
engineering properties of rocks, for example, in terms of compressive strength. Studying the relationship
between physical properties and rock compressive strength in these two different formations is exciting to
find out the extent of the relationship between physical properties and rock engineering. A geological
engineering survey was carried out simultaneously with the collection of six rock samples representing
intrusive andesite, andesite (breccia and lava fragments), and tuff of the Old Andesite Formation (OAF),
limestone (reef/calcarenite) Jonggrangan Formation. Furthermore, rock samples were analyzed physically
(petrographically) and mechanically (compressive strength) in the laboratory.
The results of field surveys and analysis of laboratory data yield knowledge about the relationship between
the physical properties of rocks and their compressive strength. The intrusion andesites and OAF andesites
generally have a porphyroaphanitic texture, anhedral - subhedral, hypocrystalline, inequigranular crystal
form, with a massive structure, and the composition of plagioclase, quartz, and accessory minerals
(hornblende). Fine-textured tuff, hypocrystalline, in the form of glass and crystal tuffs. The Jonggrangan
limestones are fine to medium textured, well-sorted, grain supported, with variations of wackestone –
packstone. The compressive strength of andesite is 39.98 – 49.36 MPa, calcarenite is 43.32 MPa, reef
limestone is 20.44 MPa, and tuff is 11.15 MPa. The compressive strength of rock is influenced by texture
(grain size/crystal) with a correlation coefficient of 68% (strong correlation). In comparison, rock
composition (percentage of quartz) has a very weak correlation (correlation coefficient of 18%). |
