TOMOGRAFI GEOLISTRIK UNTUK IDENTIFIKASI LITOLOGI PADA LOKASI RENCANA BENDUNG DAN TEROWONGAN DI SULAWESI UTARA

Abstract

Geoelectric measurements have been conducted to identify the lithology and aquifers based on rock resistivity at a dam and tunnel site plan in North Celebes using three-lines survey with 32 electrodes (a= 5,5 m) dipole-dipole configuration and 9 electrode extension cables (a=20 m). Based on electrical resistivity tomography (ERT), it can be interpreted that the survey area is composed of soil in the form of sandy clay (low resistivity), breccia Tondano (30- 1000 Ωm), weathered of Tondano tuff (30-80 Ωm) and tondano tuff(<30 Ωm). In the area of the dam, there are thin soil, a layer of tuff and breccia tondano on the river banks. Tondano layer in the tunnel area has experienced weathering into sandy clay with a thickness of up to 15 m, while layers below it has took the form of breccia, which has weathered into sandy loam with fragments of gravel (40-125 Ωm) to boulder (200-2000 Ωm) with a thickness of 10 - 35 meters. Andesite intrusion was found at a depth of 50 m, with cracks on andesite filled by water. There are at least five of the aquifers at a depth of about 50 meters between the location of surgetank to the powerhouse plan.