What belongs on a borehole log, and what quietly gets left off

Updated: 2026-08-13 · ISKRIT

A borehole log is read by three people with different questions. The designer wants layer boundaries and test results, the contractor wants what the excavator will meet, and the reviewer wants to know whether to believe either. A log that serves only the first is half a log.

The elements

The water record

A single line reading "water at 3.2 m" is close to useless. Three facts are needed and usually only one is written: the depth at which water was first struck, the depth it stood at after the hole was left, and how long it was left. Water struck at 3.2 m that rises to 1.4 m overnight is a confined layer under pressure, which is a different excavation problem from a water table at 3.2 m, and the two are indistinguishable from the single line.

This is the item most often lost when logs are retyped from field sheets, because it lives in the margin rather than in the depth column.

Description before classification

The field description and the laboratory classification are separate statements and both belong on the log. The description is what the logger saw: colour, consistency, structure, secondary constituents, inclusions. The classification is what the tests later said. When they disagree, the disagreement is information, and collapsing them into one line hides it.

Scale and honesty

A log drawn at 1:100 cannot show a 50 mm silt parting, so the parting either gets exaggerated to be visible or disappears. Both are lies of a kind, and the usual convention is to draw it at minimum visible thickness and say so in the description. What must never happen is a boundary drawn straight because the drawing looks better that way.

The borehole log tool keeps the strike level, the rest level and the standing time as three separate fields, and carries the field description alongside the classification rather than in place of it.