Demo Valley: A Complete Worked Site Project With Free Online Tools
Every tool on this site has its own worked example, but real projects never arrive one calculation at a time. Demo Valley is a complete fictional site with one coherent dataset, built so that every number agrees with every other number. Work through it start to finish and you will touch survey mapping, borehole logging, cross sections, soil classification, aquifer analysis, and cost risk, ending with a single report. Nothing to download: copy each block of data below straight into the linked tool.
The scenario
A small town wants two things at the mouth of Demo Valley: a new water supply well and a modest housing scheme. You have a topographic survey of the valley, five boreholes drilled along a line across it, laboratory results on the soils, a 24 hour pumping test on a trial well, and a budget from the quantity surveyor. Your job is to turn that pile of numbers into a defensible story.
Dataset 1: the topographic survey
Forty two survey points on a grid, coordinates in meters, elevations in meters above datum. The valley floor runs up the middle and the ground climbs steeply on both flanks.
x,y,z 0,0,125.0 100,0,109.0 200,0,101.0 250,0,100.0 300,0,101.0 400,0,109.0 500,0,125.0 0,100,128.0 100,100,112.0 200,100,104.0 250,100,103.0 300,100,104.0 400,100,112.0 500,100,128.0 0,200,131.0 100,200,115.0 200,200,107.0 250,200,106.0 300,200,107.0 400,200,115.0 500,200,131.0 0,300,134.0 100,300,118.0 200,300,110.0 250,300,109.0 300,300,110.0 400,300,118.0 500,300,134.0 0,400,137.0 100,400,121.0 200,400,113.0 250,400,112.0 300,400,113.0 400,400,121.0 500,400,137.0 0,500,140.0 100,500,124.0 200,500,116.0 250,500,115.0 300,500,116.0 400,500,124.0 500,500,140.0
Step 1. Paste the points into the Contour Map Generator and contour at a 5 meter interval. You should see smooth contours wrapping a north trending valley, tightest on the flanks where the gradient is steepest. This map becomes the base figure of the report.
Dataset 2: the boreholes
Five holes across the valley at northing 250, depths in meters below ground. The sequence is the same in every hole: topsoil over alluvial sand and gravel, over firm becoming stiff clay, over weathered granite, onto strong granite. The sand and gravel thickens toward the valley center, exactly what the contour map would lead you to expect from an old river course.
| Borehole | x | Ground level | Topsoil base | Sand and gravel base | Clay base | Weathered granite base | Hole ends |
|---|---|---|---|---|---|---|---|
| BH1 | 50 | 123.5 | 0.5 | 4.0 | 9.0 | 11.5 | 15.0 |
| BH2 | 150 | 111.5 | 0.5 | 7.0 | 12.0 | 14.5 | 18.0 |
| BH3 | 250 | 107.5 | 0.6 | 9.5 | 14.0 | 17.0 | 20.0 |
| BH4 | 350 | 111.5 | 0.5 | 7.5 | 12.5 | 15.0 | 18.0 |
| BH5 | 450 | 123.5 | 0.4 | 4.5 | 9.5 | 12.0 | 15.0 |
Step 2. Build a graphic log for BH3 with the Borehole Log Creator. Groundwater was struck at 3.5 meters below ground in BH3 and near 4 meters in the others, so mark the water strike on the log.
Step 3. Feed all five holes to the Cross Section Maker. The section shows a classic buried valley: a lens of sand and gravel thickest under the middle of the valley, pinching out against rising granite on both sides. That lens is both the aquifer and the bearing stratum, which is why the rest of the project revolves around it.
Dataset 3: soil tests
Standard penetration tests were run in BH3 and the clay was tested for plasticity. Liquid limit 42, plastic limit 21.
| Depth in BH3, m | Stratum | SPT N value |
|---|---|---|
| 1.5 | sand and gravel | 6 |
| 3.0 | sand and gravel | 12 |
| 4.5 | sand and gravel | 18 |
| 6.0 | sand and gravel | 22 |
| 7.5 | sand and gravel | 24 |
| 10.5 | clay | 14 |
| 13.5 | clay | 17 |
Step 4. Run the clay through the USCS Soil Classification Tool. The plasticity index is 21, which plots above the A line with a liquid limit under 50, so the clay classifies as CL. The N values of 14 and 17 make it stiff, comfortable for house foundations. In the sand, N climbs from 6 near the surface to 24 at depth: loose at the top, medium dense to dense where it matters.
Dataset 4: the pumping test
The trial well was pumped at 1200 cubic meters per day for 24 hours while an observation well 50 meters away was monitored.
| Time since pumping began, hours | Drawdown at 50 m, meters |
|---|---|
| 1 | 1.14 |
| 2 | 1.33 |
| 4 | 1.52 |
| 8 | 1.71 |
| 12 | 1.82 |
| 24 | 2.01 |
Step 5. Notice that drawdown climbs by about 0.63 meters for every tenfold increase in time. That straight line on a log time plot is the Cooper Jacob signature, and it corresponds to a transmissivity near 350 square meters per day with a storativity around 0.0002. Open the Groundwater Flow Simulator, enter those aquifer properties with the same pumping rate, and watch the cone of depression grow: it predicts very close to 2.0 meters of drawdown at 50 meters after one day, matching the observed 2.01, and about 2.9 meters if pumping runs for a month. The aquifer can support the town supply with drawdown staying well above the top of the clay.
Dataset 5: the budget
The quantity surveyor priced the housing scheme in thousands, with honest uncertainty on every line.
| Cost item | Minimum | Most likely | Maximum |
|---|---|---|---|
| Earthworks | 180 | 220 | 320 |
| Substructure | 380 | 450 | 600 |
| Superstructure | 820 | 900 | 1150 |
| Services | 310 | 350 | 470 |
| External works | 190 | 230 | 340 |
Step 6. The most likely figures sum to 2,150 thousand, but nobody should promise that number. Put the five lines into the Construction Cost Risk Calculator and let it run thousands of trials. The spread between the median and the 80th percentile is the contingency the project actually needs, and the tornado view shows the superstructure line dominating the risk, which tells you where sharper quotes are worth chasing.
Step 7: pull it together
Along the way, each tool can save its inputs and results to the project workspace in your browser. Finish in Report Studio, where the saved pieces assemble into one document: site plan with contours, borehole log, cross section, soil classification, aquifer analysis, and a costed risk position. That is a complete site appraisal produced with nothing but a browser.
Why a fictional valley is worth your time
Because the dataset is coherent, the checks work in every direction. The thickest sand sits where the contour map says the valley floor is. The water strike depths match the aquifer the pumping test measures. The drawdown the simulator predicts matches the observation well to a centimeter. When you later run your own site through the same sequence, you will know what agreement between independent lines of evidence looks like, and you will notice quickly when something disagrees.
Related Calculators and Reference
- How to Plan a Site Investigation: choosing borehole spacing and depth before you drill.
- How to Make a Contour Map from Survey Data: the mapping side of this project in more depth.
- Site Investigation Planner: scope holes and budget for a site like Demo Valley.
- Probabilistic STOIIP Calculator: the same Monte Carlo thinking applied to resources.
- USGS on aquifers and groundwater: background reading on the water side of the project.