Dear RG members,
I see in many papers, the authors use various techniques to indirectly gather the information of joints (that can be observed in a outcrop), such as LiDaR, X-ray CT scan, and DigitalTerrestrialPhotogrammetry. Honestly, these mesurements are extremely promising, because we are difficult to set a scanline or a sampling window in some dangerous areas, e.g. rock cliff.
However, I am confused that how these researchers determine the joint orientations using these techniques. The photograph of a rock exposure is 2D (I know the apparent dip angle can be determined from such a photo). I doubt that if the true dip direction/dip angle can be determined from 2D rock exposure photo. I have seen many authors, they use their joint data (obtained from those afore-mentioned indirect methods) to do a lot of things with confidence, e.g., DFN modelling and rock slope stablity assessment (these works need accurate joint orientation data). I guess there must be some uncertainties.
We all know that, in practice, the fracture patterns in rocks are 3D phenomena, and the outcrop centainly has a topographical variation, therefore, we can use compass to determine the dip angle and dip direction of a joint.
Regards!
TC Yin
Dear Tingchang,
I want to talk about my own experiences here.
We tried to explore the structural information of the tunnel excavation surface by the technology of three-dimensional binocular digital photography or three-dimensional laser scanning.
Indeed, information such as grouping, dip direction, dip angle and position of joint outcrop, and length, opening and position of traces can be obtained. However, I think this information is not very accurate (perhaps I do not understand the theories enough), and requires direct tests (such as a compass) to verify.
When constructing a discrete fracture network (DFN) in a numerical model, I just need the main joint information (verified by the direct methods) and uses the probabilistic method to generate the randomly discrete fractures (background fractures).
I hope this information is useful to you.
Regards,
Chunchi Ma
Dear Yin,
Your response is the next sentence:
'However, I am confused that how joint orientations are determined using these techniques. In practice, the fracture patterns in rocks are 3D phenomena, and the outcrop certainly has a topographical variation, therefore, we can use compass to determine the dip angle and dip direction of a joint. '
To use an indirect method for your purpose, you have to make lot of tests in available zone... The parameters which you determine indirect, they have objective sign in outcrops ... they have to observed in well available zone ... and you can make for yourself such tools like in case of determination of microscope...
Regards,
Laszlo
Dear Tingchang,
I want to talk about my own experiences here.
We tried to explore the structural information of the tunnel excavation surface by the technology of three-dimensional binocular digital photography or three-dimensional laser scanning.
Indeed, information such as grouping, dip direction, dip angle and position of joint outcrop, and length, opening and position of traces can be obtained. However, I think this information is not very accurate (perhaps I do not understand the theories enough), and requires direct tests (such as a compass) to verify.
When constructing a discrete fracture network (DFN) in a numerical model, I just need the main joint information (verified by the direct methods) and uses the probabilistic method to generate the randomly discrete fractures (background fractures).
I hope this information is useful to you.
Regards,
Chunchi Ma
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