Last Wednesday (03 June 09), I had a chance for monitoring the ground condition inspection by Geotech FI, because from the last inspection conducted by Christ said in GVD 3 North from XC 8 lot of void inside the current rock.
Currently I worked at GVD Project, GVD mean Grasberg Ventilation Decline which the goal of this projects are:
• Accelerate the schedule for the development and production of the Grasberg Block Cave Mine.
• Establishes access for the Grasberg Block Cave Mine Development.
• Provides alternative access and materials handling while the AB Adits are closed for rail installation.
• Provides increased geological knowledge for the excavation and construction of the Grasberg Infrastructure.
• Provides ventilation during the development phases of the Grasberg Block Cave Mine.
We drive currently 3 Tunnels where are straight ahead to North and 1 active heading to Exhaust Access. Look at the picture below regarding on orientation of heading location.
GPR is a geophysical instrument that is nondestructive and produces a continuous cross-sectional profile of different subsurface features. It is often used to investigate subsurface conditions and features such as the depth to bedrock, different soil layers and subsurface voids. Subsurface profiles are collected by towing the radar instrument over the ground surface and observing the underlying geologic features as profiles on a computer screen.
The electrical conductivity of the subsurface materials is one of two factors determining the depth to which the radar waves can penetrate. In low conductivity materials, such as dry sand or granite, deeper depths may be obtained. In highly conductivity materials, such as clay and shale, the radar waves are attenuated and absorbed, which greatly decreases the depth of penetration. The frequency of the radar antenna is the other factor determining the depth to which the radar waves can penetrate. Antennas with low frequencies (100 MHz) have lower resolutions but obtain reflections from deeper depths, about 10 to 30 meters, while higher frequency antennas (500 MHz) have greater resolution but less depth penetration. GPR operates by transmitting pulses of radio waves down into the ground through an antenna. The transmitted energy is reflected from contacts between different earth materials. When the transmitted signal enters the ground, it contacts subsurface strata with different electrical conductivities and dielectric constants. Portions of the radar waves are reflected off a subsurface interface, while the rest of the waves pass through to the next interface. The digital control unit receives the reflected waves after they
have returned through the antenna. The control unit registers the reflections against a two-way travel time, then amplifies the signals and sends them to a computer. The computer takes the output signals, representing reflected surfaces, and plots them on the radar profile as different color bands.
Why the Geotech used the GPR methods?
Ground penetrating radar locates almost anything underground
Ground penetrating radar makes an underground "picture"
GeoModel, Inc. conducts ground penetrating radar surveys anywhere in the world
Low cost ground penetrating radar surveys
Geotech conducts ground penetrating radar surveys with various frequencies. Depths of ground penetrating radar (GPR) can be as deep as 30 to 40 feet (10 to 15 meters) in sandy or silty soils, using a low frequency ground penetrating radar antenna. A higher frequency antenna can examine the near surface, from 0 to 10 feet (0 to 3 meters), in great detail.
• Establishes access for the Grasberg Block Cave Mine Development.
• Provides alternative access and materials handling while the AB Adits are closed for rail installation.
• Provides increased geological knowledge for the excavation and construction of the Grasberg Infrastructure.
• Provides ventilation during the development phases of the Grasberg Block Cave Mine.
We drive currently 3 Tunnels where are straight ahead to North and 1 active heading to Exhaust Access. Look at the picture below regarding on orientation of heading location.
GPR is a geophysical instrument that is nondestructive and produces a continuous cross-sectional profile of different subsurface features. It is often used to investigate subsurface conditions and features such as the depth to bedrock, different soil layers and subsurface voids. Subsurface profiles are collected by towing the radar instrument over the ground surface and observing the underlying geologic features as profiles on a computer screen.The electrical conductivity of the subsurface materials is one of two factors determining the depth to which the radar waves can penetrate. In low conductivity materials, such as dry sand or granite, deeper depths may be obtained. In highly conductivity materials, such as clay and shale, the radar waves are attenuated and absorbed, which greatly decreases the depth of penetration. The frequency of the radar antenna is the other factor determining the depth to which the radar waves can penetrate. Antennas with low frequencies (100 MHz) have lower resolutions but obtain reflections from deeper depths, about 10 to 30 meters, while higher frequency antennas (500 MHz) have greater resolution but less depth penetration. GPR operates by transmitting pulses of radio waves down into the ground through an antenna. The transmitted energy is reflected from contacts between different earth materials. When the transmitted signal enters the ground, it contacts subsurface strata with different electrical conductivities and dielectric constants. Portions of the radar waves are reflected off a subsurface interface, while the rest of the waves pass through to the next interface. The digital control unit receives the reflected waves after they
have returned through the antenna. The control unit registers the reflections against a two-way travel time, then amplifies the signals and sends them to a computer. The computer takes the output signals, representing reflected surfaces, and plots them on the radar profile as different color bands.
Why the Geotech used the GPR methods?
Ground penetrating radar locates almost anything underground
Ground penetrating radar makes an underground "picture"
GeoModel, Inc. conducts ground penetrating radar surveys anywhere in the world
Low cost ground penetrating radar surveys
Geotech conducts ground penetrating radar surveys with various frequencies. Depths of ground penetrating radar (GPR) can be as deep as 30 to 40 feet (10 to 15 meters) in sandy or silty soils, using a low frequency ground penetrating radar antenna. A higher frequency antenna can examine the near surface, from 0 to 10 feet (0 to 3 meters), in great detail.
The result: 16 – 20 m ahead of current heading, it’s defined as fractured rock zone with lenses of void. Fractured zone could be shears zone (?) or fault zone (?), which associate with water .
Not much clay content observed at the heading, but the rock mass is very fragile as blocky material within shears zone.
There is no potential squeezing on this area. 
Based on information from Hydrology, refer to Drill hole CI3 04-01, the water around the heading will decrease in time.
For geographic reference I did survey pick up into sounding location by total station with resection mode.
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1 comments:
wuih,,TS model apa tuw..
pinjem dong,,hahaha
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