Geotechnical Borehole Data

Two imports on a log's Import menu (Data tree, right-click a log) bring in the borehole data a geotechnical investigation produces:

• RQD Intervals (CSV)...: RQD, and core recovery and fracture counts when given, per core run, as curves on the log.
• Televiewer / Core Picks (CSV)...: discontinuities picked on a televiewer (acoustic or optical image) log, or measured on oriented core, as plane measurements placed along the log.

Both need the log's path, its trajectory in 3D: import its geophysical log tracks (a LAS file with a deviation survey, see Importing LAS Well Logs) or build it first. Depths are measured depths from the collar, in metres, in the same reference as the log's LAS depths.

Geomechanics

The picks become orientation measurements like any others: plot them on the stereonet, cluster them into sets with Auto-cluster, use them in slope stability and block size, or invert slickensided faults for the stress.

RQD intervals

One row per run:

from,to,rqd,tcr,fractures
1.50,3.00,40,90,12
3.00,4.50,62,95,7

• Columns by header, ignoring case: from (or top, depth from), to (or base, bottom, depth to), RQD; optionally recovery or TCR, and fractures (or count, FF). Without a header row: from, to and RQD, in that order.
• Rows with to not below from, or an RQD outside 0–100, are skipped and counted.

The runs become curves among the log's digital curves, drawn as steps (each run gives a row at its top and one at its base):

Curve	What it holds
RQD	% per run.
TCR	Total core recovery, %, when the file gives it.
FF	Fracture frequency per metre — the count over the run's length — when the file gives counts.

The curves join the log's LAS curves on their shared depth column; the LAS rows inside a run take its values. Importing again replaces the curves of the same name. Show them as a log track like any other curve. An RQD of 0 is drawn as a gap.

Televiewer and core picks

One row per discontinuity:

md,dip,dip direction,type,aperture,set
12.30,65,120,open,0.8,J1
14.10,20,300,bedding,,

• Depth: a depth or MD column.

• Orientation: either a true dip and dip direction (also dipdir or azimuth; the depth column may be depth, md or measured depth) (an oriented televiewer log), or alpha and beta from oriented core:

  • α is the acute angle between the core axis and the plane (90° for a plane across the core);
  • β is measured clockwise, looking down the hole, from the bottom-of-hole line to the down-hole end of the long axis of the plane's ellipse.

  Each α–β pair is turned into a dip and dip direction with the hole's direction at that depth, from the log's path. A hole within half a degree of vertical has no bottom-of-hole line, so there β is read clockwise from north looking down the hole (the reference line taken as north): dip = 90° − α and dip direction = β. If the core was marked against another reference line, add its azimuth to β before importing.

• Optional type (bedding, fault, foliation or cleavage set the plane type; anything else is a fracture), set and aperture (mm).

Each pick becomes a plane measurement at its depth along the log, in a new orientation group log picks, with these attributes:

Attribute	What it holds
Depth (MD)	m.
Terzaghi Weight	1 / |cos θ|, θ the angle between the plane's pole and the hole, capped at 10: how much a plane the hole meets obliquely is under-sampled (Terzaghi 1965).
Aperture (mm)	When given.
Pick Type	The type, when given.

A set label tags the plane with that Set, making it if the project has none of the name. The picks' frequency per metre is added to the log as the curve PICK_FF.

Core runs, boxes and photographs

The core itself can be recorded on the log as well: its runs with their recovery, its boxes, a depth shift from core to log depths, and photographs of the core boxes laid along the log. See Core in the geological logging guide.

Method

Core orientation. With a the hole's direction down the hole, the bottom-of-hole line b is the downward vertical with its component along a removed, and c = a × b lies 90° clockwise from it looking down the hole. The ellipse's down-hole end lies along e = cos β b + sin β c, and the plane's normal is

$$\mathbf n = \sin\alpha\,\mathbf a - \cos\alpha\,\mathbf e .$$

RQD (Deere 1964) is the percentage of a run in sound pieces at least 10 cm long; VRGS reads it from the file.

References

1. Deere, D. U. (1964). Technical description of rock cores for engineering purposes. Rock Mechanics and Engineering Geology, 1, 17–22.
2. Terzaghi, R. D. (1965). Sources of error in joint surveys. Géotechnique, 15, 287–304.

See also

• Importing LAS Well Logs
• Geological Logs — the log's menu.
• Geomechanics