Worked example
From soil profile to surcharge removal
This is the path a drain project takes through PVDCal. Every project in the app can be loaded as a ready-made example, so you can reproduce each step rather than read about it.
STEP 01
Describe the ground
A two-layer soft-clay profile goes in with its compression indices, preconsolidation pressures and permeabilities. Where a parameter is uncertain, a low and a high value are given instead of one number. The water table sets the in-situ effective stress profile.
STEP 02
State the target and the construction
Ninety per cent consolidation within a year, under fill placed in two stages with a rest period. Vacuum can be added here, and drains can be told to stop above the base of the profile.
STEP 03
Get a spacing band, not a single number
Each sample of the uncertain parameters runs its own complete spacing search, so the result is the spread of answers the ground allows: the P10, P50 and P90 spacing for square and triangular patterns, and the drains per hectare each implies.
STEP 04
Check what the answer depends on
The consolidation curve shows how the ground gets there, and a tornado — What moved the spacing — shows how far each declared range, on its own, moved it. That is where another borehole or laboratory test is worth its cost.
STEP 05
Once built, let the ground correct you
Settlement plates and piezometers go in as they are read. The search finds the ground that explains the record, reports how well it fits, and forecasts what is still to come with a credible range — the number that decides when surcharge comes off.
The design case
What was asked, and what came back
A spacing on its own cannot be checked. These are the inputs of the Design example beside the answer it produced, both taken from the two files published below — the project file and the report it generated.
Input
- Target
- Us = 90 % at t = 365 days
- Profile
- Two soft-clay layers, 4 m + 6 m; water table at the surface
- Loading
- One stage, Δp = 100 kPa, ramped over 30 days
- Drains
- Band (I-shape) 100 × 4 mm, converted to its equivalent diameter; square pattern
- Smear
- kh/ks = 2, rs = 75 mm, transition to rt = 150 mm
- Vacuum
- Off
- Creep
- On — Cα/Cc = 0.04 in both layers
- Vertical drainage
- Off (cv = 0): radial only, which tightens the spacing
- Sampling
- 100 Latin-Hypercube samples, seed 20260929
Answer
| Percentile | re (mm) | Square S (mm) | Triangular S (mm) | Drains/ha |
|---|---|---|---|---|
| P10slowest tenth of profiles — the conservative design basis | 644 | 1,141 | 1,226 | 7,680 |
| P50median | 754 | 1,337 | 1,437 | 5,595 |
| P90fastest tenth — unconservative unless justified | 908 | 1,609 | 1,729 | 3,863 |
The design is taken to the P10: a square spacing of 1,141 mm, 7,680 drains per hectare. The report also prints the sampling interval on that percentile — 591–674 mm, the range a fresh set of 100 samples would be expected to give — which is the uncertainty of the sampling rather than of the ground, and the reason a P10 should not be quoted to the millimetre.
The deliverable
A report you can issue, not a screenshot
A run that lives on your screen is not something you can hand to a client. One button turns the whole analysis into a report written to be checked. Page one answers the question the report exists for — the spacing, its pattern and drains per hectare, with smear, vacuum, creep and well resistance stated on or off — and then come every input echoed back, the method, vector figures with the numbers behind them, and a document-control block with the revision, the signatures and the software build that produced the numbers.
Download the examples
Three worked examples, each published as the project file that was run and the report that run produced, with a workbook of the numbers behind its charts beside them. Open the project in PVDCal, press Calculate, and you get them back — the sampling seed travels with the file, so the numbers are the same ones, not merely similar ones.
- DesignFind the drain spacing that reaches 90 % consolidation by a target date. Probabilistic: a P10 / P50 / P90 spacing band, with the conservative basis recommended. Report (PDF, 11 pp, 672 kB) Project file (.pvdproj.json, 25 kB) Workbook (.xlsx, 12 sheets, 51 kB)produced by build 2026-10-01 07:35:33
- SimulateForward the consolidation and settlement for a spacing you choose — how far, how fast, and when the surcharge can come off. Report (PDF, 12 pp, 726 kB) Project file (.pvdproj.json, 25 kB) Workbook (.xlsx, 12 sheets, 45 kB)produced by build 2026-10-01 07:35:33
- Back-calculation & forecastFit the ground to 26 readings from two settlement plates and a piezometer, then forecast ahead with a credible range. Report (PDF, 12 pp, 748 kB) Project file (.pvdproj.json, 28 kB) Workbook (.xlsx, 12 sheets, 73 kB)produced by build 2026-10-05 19:13:32
To open a project file: start PVDCal, choose Project › Open › My projects — or just drag the file onto the window. The same three examples are also built into the app under Project › Open › Example projects. The project files are plain readable JSON, so you can also inspect every input without opening the app at all.
The names in the document-control block are fictional; the soil, the analysis and every number come from these very files, run for real.
Also exports as a workbook
One sheet per chart: the consolidation curve, the settlement curve, the effective-stress profile, every sample behind the band, the tornado of what moved the spacing and the adverse corner built from it — and in back-analysis, a sheet per settlement plate and piezometer with the readings, the fitted curve, the P5–P95 band and the residuals side by side. A checker can re-plot or difference any of it without transcribing a number off a PDF.
The first sheet is a contents saying what each of the others holds, its units, and which result card it came from. Alongside it: document control, the inputs, the soil profile and the loading schedule, so the workbook stands on its own.
The workbooks above came from the same runs as the reports beside them. In the application it is Workbook (Excel), next to Report (PDF) on the results overview of every task.
Written to be checked
The soil profile, drain and smear geometry, the loading schedule stage by stage, the hydrology, the boundary conditions and the discretisation are all tabulated. A reviewer can reproduce the run from the document alone.
Limitations included
The report states what the analysis does not cover, and adapts to your run: if vertical drainage was off, or smear disabled, or a parameter left fixed in a probabilistic run, it says so rather than leaving you to notice.
Traceable to a build
Job and document number, revision, purpose of issue, prepared–checked–approved, and the software build stamp on every page. When a number is queried a year later, the report answers which version produced it.
Does it work?
A named field case: the Ballina trial embankment
The Ballina National Field Testing Facility in New South Wales is a published, instrumented full-scale embankment on soft estuarine clay with vertical drains. PVDCal was calibrated on the early part of its settlement record and asked to forecast the rest.
Ballina, New South Wales
| Record given | Forecast error | Range |
|---|---|---|
| 200 days | 9.4 % low | missed |
| 400 days | 1.5 % low | contained the truth |
| 700 days | 0.8 % low | contained the truth |
Scored against the last reading of the M0 extensometer, 1,427 mm. From 200 days the record was simply too short, and the guide reports that beside the successes. The same embankment has been back-analysed in the literature by Bayesian updating; the guide sets the two side by side.
A site whose truth was known
On a synthetic test site built from a hidden soil, the typed laboratory values alone drifted to a final settlement about 14 % too high. Given only the noisy record up to the halfway point, the calibrated answer tracked the hidden truth beyond the cut, and the design range of 993 to 1,168 mm contained the true 1,113 mm. It is one case from the campaign of hundreds summarised on the method page, shown because its arithmetic can be followed.
The method behind these numbers is on the method and validation page.
Run this example yourself
Download the project file above, open it in PVDCal and press Calculate. The run you get is the one on this page — the sampling seed travels with the file.