Site investigation · In-situ testing
CPTu dissipation test: ch and kh calculator
Horizontal coefficient of consolidation from the time to 50 % dissipation, with an optional estimate of horizontal permeability from the constrained modulus.
Standard: Teh & Houlsby (1991): ch = T50·r²·√Ir / t50, T50 = 0.245 (u2)
Open the live calculator → All site investigation calculators
Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Time to 50 % dissipation t50 | 950 | s |
| Rigidity index Ir = G/cu | 150 | |
| Cone area | 10 cm² | cm² |
| Constrained modulus M (for kh) | 3 | MPa |
| Dissipation reached at end of test | 60 | % |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Cone radius √(A/π) | 0.018 | m |
| ch = 0.245 r²√Ir/t50 | 0.000 | m²/s |
| kh = ch·γw/M | 0.000 | m/s |
| ch per year | 31.73 | m²/yr |
- ✓ Test held to at least 50 % dissipation
Method, formulas and assumptions
- Cone radius √(A/π) = SQRT(10/10000/PI()) = 0.017841 m
- ch = 0.245 r²√Ir/t50 = 0.245*0.017841^2*SQRT(150)/950 = 1.005e-6 m²/s
- kh = ch·γw/M = 1.005e-6*9.81/(3*1000) = 3.288e-9 m/s
- ch per year = 1.005e-6*31557600 = 31.728 m²/yr
- Field ch from the piezocone is for horizontal flow in the over-consolidated range of remoulded soil around the cone; adjust before using for vertical consolidation of normally consolidated clay.
Related site investigation calculators
- SPT corrections & correlations — Raw N to N60 and (N1)60 with energy, rod, borehole and overburden corrections, and common correlations…
- CPT interpretation (Robertson SBTn) — Normalised cone resistance and friction ratio, Ic, soil behaviour type plotted on the Robertson chart and as…
- DCP to CBR — Penetration per blow by layer and estimated in-situ CBR, plotted with depth.
- Plate load test — Pressure–settlement curve to deformation modulus and modulus of subgrade reaction.
- Ménard pressuremeter: modulus, bearing and settlement — Ménard modulus from two points on the pseudo-elastic part of the test curve, net limit pressure, soil class…
- Flat dilatometer (DMT) data reduction — Corrects the A and B readings, then gives the intermediate parameters ID, KD, ED, soil description…
- Borehole log builder — Draws a borehole log from a layer table (base depth, soil type code, SPT N, description) with groundwater…
For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.