Adamcová R., Kondrcová M., Ottner F. & Wriessnig K., 2020: Adobe material of the Temple of the Sun, Pachacamac, Peru: Engineering geological classification and sustainability assessment as a challenges. Acta Geologica Slovaca, 12, 2, 153–160.

Adobe material of the Temple of the Sun, Pachacamac, Peru: Engineering geological classification and sustainability assessment as a challenges

Renáta Adamcová¹, Magdaléna Kondrcová¹, Franz Ottner² & Karin Wriessnig²

¹Comenius University in Bratislava, Faculty of Natural Sciences, Department of Engineering Geology, Ilkovičova 6, 842 15 Bratislava, Slovakia
²BOKU - University of Natural Resources and Life Sciences, Peter-Jordan-Straße 82, 1190 Vienna, Austria

Abstract

Only two small pieces of an ancient adobe from an important archeological site near Lima were available for a laboratory research, making the engineering geological soil classification challenging. An experienced engineering geologist is able to assess the most important physical properties of the soil if it is properly classified according to STN EN 72 1001: 2011. However, less than 100 g of the material are insufficient for standard classification tests common in Slovakia. How to carry out the engineering classification of such a small sample? The answer to this question is the main goal of this study. Searching for an alternative, a SEDIGRAPH was used instead of the Casagrande hydrometer method for the grainsize analysis, and water adsorption by the Enslin - Neff method gave input data for both the liquid limit and plasticity index calculations according to Dieng (2006). This allowed the engineering geological classification of the material as a clayey sand, class S4, symbol SC (STN 72 1001:2011). Additional mineralogical analyses confirmed the low content of clay minerals and explained the low plasticity also due to the low amount of the expandable vermiculite in the bulk sample. Consequently, several conclusions can be made about other physical properties of that adobe based on general experience with the soils from the class S4. To take advantage of the available test results, an approximate sustainability assessment of the adobe became the secondary goal of the case-study. The low content of cohesive particles makes the adobe quite brittle, loadsensitive, but minimizes destructive volume changes when saturated with water. The related higher hydraulic conductivity and erodibility, higher than in a typical adobe with high content of fines, are a matter of concerns due to the specific local climate with occasional heavy rains. The less known laboratory methods applied in this case-study are a good alternative if the size of the soil sample is too small for standard classification tests (objects protected by law etc.). This is the most important outcome, because a proper engineering geological classification can tell a lot about the physical properties of the soil, as illustrated in this case-study.

Key words: Pachacamac Temple of the Sun, adobe, engineering geological classification, grain size analysis, Enslin – Neff, mineralogical analysis, clayey sand

Manuscript received: 2020-10-09

Revised version accepted: 2020-11-12