ACADSTAFF UGM
| Title | : | GEOPHYSICAL INVESTIGATIONS IN GROUNDWATER AND LOCAL SITE EFFECT FOR GEOTECHNIC APPLICATION |
| Author | : |
Boko Nurdiyanto (1) A D Guntara (2) Drs. Imam Suyanto, M.Si. (3) Suherman (4) Sigit Pamungkas (5) Fatkhul Muin (6) Said Sabbeq (7) Achmad Sri Fadli (8) Ihsan A Yunandra (9) |
| Date | : | 2018 |
| Keyword | : | groundwater,site effect,geotechnic groundwater,site effect,geotechnic |
| Abstract | : | Since geothermal projects are at high risk and require substantial funds, therefore prior to a developing geothermal field a careful assessment is needed to assess whether the prospect area is safe for the construction of the facility. Environmental and development potential risk (Construction risk) occurs in the construction process of Geothermal Power Plants (GPP) site, with the discovery of several groundwater manifestations that arise on the surface due to excavation and development activities. 22 lines of dipole-dipole configuration of Electrical Resistivity Tomography (ERT) and 3 point of Schlumberger configuration of Vertical Electrical Sounding (VES), 8 lines of Seismic Refraction Tomography and 17 point of Mikrotremor surveys have been done to investigate these risks. This investigation was intended to identify the type, pattern and distribution of groundwater based on the measured resistivity data, as well as provide information about the rock structure and dynamic characteristics of the local geological conditions in favor of the necessary engineering geotechnical. In general, based on its resistivity value, the rock layers obtained from VES measurements are divided into 4 layers, Soil, uppermost with varying resistivity value. Lava, has a resistivity value above 45 ohm meters. Breksi Laharik has resistivity value 14.7 sd 19.3 ohm meter. And Clay has resistivity value above 5.5 sd 8.5 ohm meter. The 3D modeling results based on ERT data processing and interpretation results on the existence of aquifer that correlated with geological outcrop and refraction seismic concluded that the presence of aquifers are determined by anomalous form, true resistivity and its velocity value, where the aquifers value range are in the range of 15 to 25 ohm meters, and have wave velocity in the range of 1000 m/s. Aquifers are in the lava breccia zone as reservoir of water, while the impermeable layer are lava and clay (an alteration zone). Aquifer forms two unrelated channels on the surface at higher elevations, but at lower elevations, the aquifer merges into one. Channeling on the subsurface is based on the same anomaly obtained on the measurement lines. The channel connectivity at a lower elevation is based on the interpolation of geoelectric measurement data showing the similarity of aquifer pattern on each north-trending lines. From the results of microtremor data analysis using HVSR method to microtremor signal concluded that GPP site area has seismic vulnerability index (Kg) and ground shear strain (?) generally shows very low values. The low value in this area is due to the geological conditions in this area composed of andesite breccia material on the surface, with the threshold value occurs deformation and liquefaction is ? ? 10- 2 and Kg ? 30 then the location of LB-12, LB-11 and LB-05 have a moderate level of vulnerability so it is necessary to be anticipated if it will be developed for the building structure. So location of the GPP site is relatively safe from earthquake shocks except at the location of LB-12, LB-11 and LB-05 until geotechnical engineering is done |
| Group of Knowledge | : | |
| Level | : | Internasional |
| Status | : |
Published
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