Weighted Joint Density
- Luis Yanez
- Luisa Herrmann
- Sam Johnson
This document details Datarock’s product Weighted Joint Density (wJd).
wJd was developed by Palmström et al with the aim of better characterising the degree of jointing and the block size than other common methods. The method is based on the understanding that joints perpendicular to a bore hole will be more frequently intersected than other joints.
Contents
Literature
This product is based on the following literature:
Title | Author | Year |
The weighted joint density method leads to improved characterization of jointing | A Palmström et al | 1996 |
Dependent Models
The outputs of the following models are used:
Model Name | Model Type |
Fracture Detection and Classification | Object Detection |
Drillers Break | Object Detection |
Fracture Mask | Instance Segmentation |
Data Processing
The following steps are taken to determine the Weighted Joint Density of a given interval:
Take the output of the fracture detection model, “simple” classes only
Run a segmentation model to extract the fracture profile
Measure the angle of each fracture with respect to the core axis
For a given interval, calculate the Weighted Joint Density
where
L = length of the measured section along the core
δ = the intersection angle, the angle between the drill core and the individual joint
This method provides a more nuanced understanding of joint density, leading to potentially more accurate characterisation of the rock mass. The image below shows an example of measured Weighted Joint Density along side row imagery.
Further Information
The Weighted Joint Density quantifies the joint density in rock masses, adjusted for joint orientation:
Variability: It shows the distribution of joints, indicating rock mass strength and stability.
Engineering Impact: High wJd values may signal potential weak zones, influencing design strategies.
Hydrogeology: Similar to engineering impact, wJd can indicate permeability and fluid flow, important for groundwater management and resource extraction.
In summary, wJd can be used as a key factor in geotechnical and engineering analyses, affecting project safety and effectiveness.
Product Configuration Options
There are no configuration aspects to this product.
Output Data
Default interval length: 1.0m
Customisable interval available: Yes.
User Data
User data may be provided to the Datarock team via csv in the following format:
· HoleID_sampling_intervals_WJD.csv
CSV file to contain the following headers:
File Header | Description |
depth_from | Start of interval |
depth_to | End of interval |
Data Output
Results from this product is delivered in a batch nature.
Integration of the required technologies into Datarock production is ongoing.
The available CSV files include the following:
ProjectID_HoleID_WJD_3m.csv
ProjectID_HoleID_WJD_by_user_intervals.csv
Both CSVs contain the following headers:
File Header | Description |
hole_id | Customer’s Hole ID |
depth_from_m | Start of interval (metres) |
depth_to_m | End of interval (metres) |
depth_from_ft* | Start of interval (feet) |
depth_to_ft* | End of interval (feet) |
wjd | Weighted joint density |
wjd_measurable | Weighted joint density using only “measurable” fractures |
*Only included if project depths are in feet.
Product Limitations
Limitations | Comments |
Dimensional Limitation | The wJd method relies on measurements taken from drill cores or scanlines, which are essentially one-dimensional. This can limit the accuracy of joint characterization because it may not capture the true three-dimensional spatial distribution of joints within the rock mass. |
Sampling Bias | The data derived from wJd is dependent on the orientation and location of the borehole or scanline relative to the joint sets. If the sampling is not representative of the entire rock mass, it could lead to skewed results. |
Impact of Unseen Joints | There could be joints that are not intersecting the core or scanline but could be critical for the stability of the rock mass. The wJd may underestimate the density and impact of such joints. |
Technological Limitations | The accuracy of wJd is dependent on the technology used for measuring and analyzing the rock joints. Imperfections in imaging or data processing can lead to errors in the final analysis. |
Document Version
Version | Date | Author | Rationale |
1.0 | 19 Dec 2023 | L Yanez | Initial release |