Currently, in the middle of the period for my postgraduate study enrolment, I join a geotechnical investigation for a karst hill in Palimanan. The area is Kesultanan Cirebon's heritage site. So, ITP, a cement producer who has the permit for the area, cannot mine the hill for its limestone. Yet, since last year, there is an indication that the structure is moving. It is shown by the fact that a grave located near the hill becomes closer to the hill. So, this project is to prove the movement, and if there is a movement, whether it is from the hill or the ground around the grave.
Is general, this work is divided into several parts which are surveying, geotechnical (structure mapping), geophysics (modelling), and vibration monitoring. Due to my experience in blasting monitoring, I got responsibilities to do vibration monitoring with one of my junior in mining department taking his final assignment this year. But, I also able to learn other kinds of work because in this project we also apply a "knowledge sharing" method.
Firstly, I learnt about GPR. GPR (Ground-Penetrating Radar) is a geophysics method to detect the subsurface structures. It is using electromagnetics wave that able to differentiate each layer of soils or rocks. Actually, I never do this test before. When I was studying mining engineering, I just learn how to make a geological model based on borehole data. And l was lucky to know this method because I found in the master programme syllabus that I applied, GPR is used in geotechnical engineering to detect the cracks or other structures in the subsurface. Although I haven't known how to process the data yet, I think it's a good thing to learn this method directly from the experts on the field.
Is general, this work is divided into several parts which are surveying, geotechnical (structure mapping), geophysics (modelling), and vibration monitoring. Due to my experience in blasting monitoring, I got responsibilities to do vibration monitoring with one of my junior in mining department taking his final assignment this year. But, I also able to learn other kinds of work because in this project we also apply a "knowledge sharing" method.
Firstly, I learnt about GPR. GPR (Ground-Penetrating Radar) is a geophysics method to detect the subsurface structures. It is using electromagnetics wave that able to differentiate each layer of soils or rocks. Actually, I never do this test before. When I was studying mining engineering, I just learn how to make a geological model based on borehole data. And l was lucky to know this method because I found in the master programme syllabus that I applied, GPR is used in geotechnical engineering to detect the cracks or other structures in the subsurface. Although I haven't known how to process the data yet, I think it's a good thing to learn this method directly from the experts on the field.
GPR uses high-frequency (usually polarized) radio waves, usually in the range 10 MHz to 1 GHz. A GPR transmitter emits electromagnetic energy into the ground. When the energy encounters a buried object or a boundary between materials having different permittivities, it may be reflected or refracted or scattered back to the surface. A receiving antenna can then record the variations in the return signal. The principles involved are similar to seismology, except GPR methods implement electromagnetic energy rather than acoustic energy, and energy may be reflected at boundaries where subsurface electrical properties change rather than subsurface mechanical properties as is the case with seismic energy. (en.wikipedia.org/wiki/Ground-penetrating_radar).
Secondly, I tried the structures mapping. I have learnt this in college. But, to be honest, it was my first experience trying this mapping directly in the field. The method named scanline. Things that needed to do in the scanline is spanning a line (with scale) that crossing the structures both minor and major. Then, each structure needs to be identified. The identification includes the dip and dip direction, filling materials, opening, water conditions, and the weathering.
Besides these new things, like what I said before, I also do vibration monitoring using Minimate. It's really funny how I knew this device at first and until now I have got many experiences from this device; becoming the assistant for Explosives and Blasting Techniques, Person in charge for Blasting Vibration Analysis competition, Jury for the same competition, team for blasting monitoring, and the latest, in this project for vibration monitoring. The best things from this monitoring are you just need a few minutes to do the work, and sometimes you can watch the blasting activity!
There is another situation that gets me a flashback to my former project in South Sumatera. It is about liquefaction. Most of the fresh graduates mining engineer who choose geotechnical as their specialisation will not familiar with this term. Liquefaction is more studied by the civil engineer because liquefaction happens in soil layer. As far as I know (from the former project and youtube video :p), this condition happens in saturated soil that makes the soil lost its strength in response to applied stress. So, this case might have a condition where the saturated soil with a "makam keramat" on the surface gets stress from blasting or heavy vehicle vibration in a long period and so the liquefaction happens. But, I don't know for sure...
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