Document an open trench

Record buried utilities while the trench is open. The utility types, their depth and quality-level fields, and the evidence check before backfill.

On this page

An open trench is the only time a buried utility can be seen and measured directly. Once it's backfilled, that chance is gone for the life of the pipe or cable. OpenSurvey3D includes a set of utility types for this job. Their forms ask for what the GNSS position can't tell you, and a check before saving warns you about anything you won't be able to capture later.

Before you start

  • An active project, and ideally an RTK receiver. Phone GPS is metres out, which isn't enough to locate a buried utility. See Phone GPS vs. a receiver.
  • The correct antenna height set, so the elevation is at the rod tip.
  • A tape measure for the depth of cover.

The utility types

The utility types appear at the end of the type chooser, under Lines and Points:

Type Kind Code · layer Fields (required marked *)
Trench Edge Line TRCH · V-TRCH-EDGE Trench width (m), Surface, Reinstatement
Duct Line DUCT · V-COMM-DUCT Buried-run fields, plus Ways, Occupied
Conduit Line COND · V-COMM-COND Buried-run fields
Cable Line CBL · V-COMM-CBL Buried-run fields, plus Cables in run, In a duct
Pipe Line PIPE · V-UTIL-PIPE Buried-run fields, plus Pressure
Warning Tape Line WTAP · V-UTIL-TAPE Utility*, Depth of cover*, Measured to*, Legend, Detectable (tracer)
Splice Point SPL · V-COMM-SPLC Buried-run fields, plus Splice ID, Fibre count
Cabinet Point CAB · V-COMM-CAB Utility*, Cabinet ID, Size, Owner, Installed, Quality level*

The buried-run fields, in the order you'd fill them in standing at the trench:

Field What to enter
Utility * Which utility, using the same categories as the locate paint: Electric; Gas / oil / steam; Communications; Potable water; Reclaimed water / irrigation; Sewer / drain; Unknown.
Depth of cover * Depth below grade, in metres, measured with a tape.
Measured to * Which part of the utility you measured: Top of utility, Invert, Centreline or Ground surface.
Material A pick list suited to the type (for example PVC, HDPE, Ductile iron… for a pipe; Fibre, Copper, Coaxial, Armoured… for a cable).
Diameter In millimetres.
Owner Free text.
Quality level * The ASCE 38 quality level: QL-A — exposed and measured; QL-B — geophysically located; QL-C — surveyed surface features; QL-D — records only. For a utility you can see in an open trench, it's QL-A.
Abandoned Switch this on for a dead line. An abandoned duct looks just like a live one to the next crew.

Why "Measured to" matters

The receiver records the elevation of whatever the rod tip touched, to the centimetre. It can't know whether that was the top of the pipe, its invert or its centreline, and on a 600 mm main those are more than half a metre apart. Measured to records which one it was. Depth of cover is measured from grade, which on a construction site may not be the finished grade yet, so it's a tape measurement rather than something the app can work out from the position.

Document the trench

  1. On the Survey tab, tap the type button and choose the utility type, for example Pipe.
  2. Walk the run and collect it, vertex by vertex, with the rod on the part of the utility you'll name in Measured to. See Collect lines and areas. A Splice or Cabinet is a single point.
  3. When the form opens, fill in Utility, Depth of cover, Measured to and Quality level, then anything else you know.
  4. Under Photos, tap Camera and photograph the open trench, with the utility and bedding visible.
  5. Tap Save.
  6. Optionally, collect the Trench Edge as a separate line, with its width and surface.

Add a 3D capture of the trench

A 3D scan records the whole exposed run: the utility, its neighbours, the bedding and the trench walls. After saving:

  1. Open the asset from the map or the asset list.
  2. In 3D scans, tap Add 3D capture and choose Points (LiDAR devices) or Photogrammetry.
  3. For a line such as a pipe, choose which vertex the capture documents. The capture is anchored at that vertex's position.

See LiDAR point clouds and Photogrammetry.

The evidence check before backfill

For the types that have a Depth of cover field (Duct, Conduit, Cable, Pipe, Warning Tape and Splice), tapping Save first checks for missing evidence. It sorts what's missing into two groups:

Can't be recovered once backfilled Can be filled in later from records
A photo of the open trench Which utility
Depth of cover Material
What the depth was measured to Quality level

Only fields the type actually has are checked. If anything is missing, a dialog explains it. The title reads like "2 things here can't be recovered once this is backfilled", or, when only record-type fields are blank, "2 fields still blank". The message lists what's missing, explains that without it the utility can only be described from records (quality level D), and says "Saving records what was missing on the observation."

  • Go back and fill it in returns to the form.
  • Save anyway saves the asset as it is.

What the app records

When you save past the check, the list of what was missing is stored permanently on the asset's observations. The QA report counts every buried utility filed without irrecoverable evidence, under "… buried utilities were filed without evidence that cannot be recaptured". Unlike the report's other warnings, these can't be fixed by going back and re-measuring.

Blank required fields also show as Required — blank in the asset's Attributes. Fill in the recoverable ones later from the utility's records, from the asset's details.