Worked example: a fill and clay borehole
An annotated end-to-end log through fill into residual clay.
A worked example of a straightforward borehole through fill into residual clay — the most common hole most technicians will log.
Location tab
| Field | Value |
|---|---|
| Location ID | BH11 |
| Type | Borehole |
| Field status | Complete |
| Final depth | 20.00 m |
| Ground level / RL | 556.5 m |
| Logged by | ES |
| Drilling method | Auger, washbore and NMLC coring |
| Contractor | (drilling contractor) |
Lithology
| Depth | Description |
|---|---|
| 0.00–0.35 m | dry to moist, dark brown, TOPSOIL FILLING, with some gravel and rootlets |
| 0.35–3.00 m | well compacted, dry to moist, brown, low to medium plasticity sandy CLAY FILLING, fine to coarse grained sand, trace fine to coarse angular gravel, trace cobbles — from 0.6 m abundant gravel and cobbles, from 0.7 m inferred boulders, moist to wet |
| 3.00–5.00 m | very stiff, moist, grey with light orange/red mottling, medium to high plasticity CLAY, trace ironstone gravel |
What to notice
- No gaps. Each interval starts where the last ended.
- Depth-referenced changes within an interval. The fill changes character at 0.6 m and 0.7 m without becoming a separate layer. Noting from 0.6 m keeps the detail without fragmenting the log.
- Fill is identified as fill. CLAY FILLING, not CLAY. Whether material is engineered fill or natural ground is often the single most important thing on the log.
- Consistency on the natural clay, compaction on the fill. Different materials, different descriptors.
Samples
| Sample | Depth | Type |
|---|---|---|
| E1 | 0.10 m | Environmental |
| E2 | 0.50 m | Environmental |
| S1 | 2.25–2.45 m | SPT — 4,7,4; N=11 |
| S2 | 3.05–3.25 m | SPT — 4,8,7; N=15 |
Environmental samples near surface, SPT samples through the fill and into the natural clay. Individual increments recorded, not just the totals.
Field tests
| Test | Depth | Result |
|---|---|---|
| SPT | 2.35 m | 11 blows |
| SPT | 3.15 m | 15 blows |
Groundwater
| Type | Depth | Observed |
|---|---|---|
| Standing | 0.60 m | 6 Nov 2014 |
Standing level recorded with its date. Note the contrast with the lithology, which records the fill becoming moist to wet from 0.7 m — the two observations corroborate each other.
Why this log works
Someone who never saw the hole can tell: there is roughly 3 m of fill of variable quality over stiff natural clay, groundwater is shallow at about 0.6 m, and the fill contains obstructions from 0.6 m down. Those three facts drive the foundation and excavation decisions, and all three are legible at a glance.