Docs / Borehole Logging / Worked example: a trial pit

Worked example: a trial pit

Logging an exposed face, excavatability, bulk sampling and photography.

A trial pit differs from a borehole in one important way: you can see the ground, so your description should be better, not worse.

Location tab

Field	Value
Location ID	`TP01`
Type	Trial pit
Field status	Complete
Final depth	3.20 m
Ground level / RL	558.2 m

Setting Type to Trial pit changes how the location is drawn on the log, the site plan and the 3D model, and which layer it falls under on the GIS Map.

Lithology

Depth	Description
0.00–0.25 m	dry, dark brown, silty TOPSOIL, with rootlets
0.25–1.60 m	loose to medium dense, moist, mixed brown and grey, sandy GRAVEL FILLING, with brick and concrete fragments, angular to sub-angular
1.60–3.20 m	stiff, moist, grey-brown, medium plasticity sandy CLAY, trace fine gravel

What to notice

Inclusions are described. Brick and concrete fragments identify this as uncontrolled fill and may carry contamination implications.
Particle angularity is recorded — visible in a pit face and worth capturing while you can see it.
The fill/natural boundary is sharp and observed, not inferred from cuttings. That is the advantage of a pit, and the log should say so.

What only a pit gives you

Record in the additional observations, and photograph:

Face stability — whether the sides stood or ravelled, and at what depth
The boundary itself — whether sharp or gradational, and how it varies across the face
Seepage — where water entered the face, which is directly observable in a pit
Excavatability — what plant was used and how hard it worked

Excavatability is often the reason the pit was dug. Excavated readily with 5 t excavator to 1.6 m; slower progress in stiff clay below answers the question the client asked.

Samples

Sample	Depth	Type
B1	0.80 m	Bulk — fill
B2	2.00 m	Bulk — natural clay
D1	2.40 m	Disturbed

Bulk samples from each material. Pits allow large samples that a borehole cannot recover — take them if the laboratory will need them.

Photographs

Photograph the face with a scale, each material, and the spoil. Include the pit ID in frame. Once the pit is backfilled the photographs are all that remains.

Before backfilling

Confirm depths, the boundary depth, samples and photographs are all recorded. A pit cannot be revisited.

# Worked example: a trial pit

A trial pit differs from a borehole in one important way: you can see the ground, so your description should be better, not worse.

## Location tab

| Field | Value |
|---|---|
| Location ID | `TP01` |
| Type | Trial pit |
| Field status | Complete |
| Final depth | 3.20 m |
| Ground level / RL | 558.2 m |

Setting **Type** to *Trial pit* changes how the location is drawn on the log, the site plan and the 3D model, and which layer it falls under on the GIS Map.

## Lithology

| Depth | Description |
|---|---|
| 0.00–0.25 m | *dry, dark brown, silty TOPSOIL, with rootlets* |
| 0.25–1.60 m | *loose to medium dense, moist, mixed brown and grey, sandy GRAVEL FILLING, with brick and concrete fragments, angular to sub-angular* |
| 1.60–3.20 m | *stiff, moist, grey-brown, medium plasticity sandy CLAY, trace fine gravel* |

### What to notice

- **Inclusions are described.** Brick and concrete fragments identify this as uncontrolled fill and may carry contamination implications.
- **Particle angularity is recorded** — visible in a pit face and worth capturing while you can see it.
- **The fill/natural boundary is sharp and observed**, not inferred from cuttings. That is the advantage of a pit, and the log should say so.

## What only a pit gives you

Record in the additional observations, and photograph:

- **Face stability** — whether the sides stood or ravelled, and at what depth
- **The boundary itself** — whether sharp or gradational, and how it varies across the face
- **Seepage** — where water entered the face, which is directly observable in a pit
- **Excavatability** — what plant was used and how hard it worked

Excavatability is often the reason the pit was dug. *Excavated readily with 5 t excavator to 1.6 m; slower progress in stiff clay below* answers the question the client asked.

## Samples

| Sample | Depth | Type |
|---|---|---|
| B1 | 0.80 m | Bulk — fill |
| B2 | 2.00 m | Bulk — natural clay |
| D1 | 2.40 m | Disturbed |

Bulk samples from each material. Pits allow large samples that a borehole cannot recover — take them if the laboratory will need them.

## Photographs

Photograph the face with a scale, each material, and the spoil. Include the pit ID in frame. Once the pit is backfilled the photographs are all that remains.

## Before backfilling

Confirm depths, the boundary depth, samples and photographs are all recorded. A pit cannot be revisited.