Geologic models and simulations are once removed (at least) from the input data. Stratamodel
has been producing models of various geologic phenomenon and simulating subsurface processes
for more than ten years. Models include numerical groundwater models using MODFLOW, three
dimensional stratigraphic models using Techbase, and pile load models using software developed
in house. This page demonstrates some of those models and the theoretical basis for their implementation.
Pile Load Models From Cone Penetration Test Data
A Cone Penetration Test (CPT) can be viewed as a scale model of a structural pile. CPT measures
tip resistance (analogous to pile end bearing) and sleeve friction (analogous to shaft friction)
and in the case of a piezocone, dynamic pore pressure. Stratamodel's in house modeling software
has been calibrated against instrumented pile load tests and validated by successfully predicting
pile failure in subsequent pile load tests.
CPT produces the initial input data to the model but must be adjusted for effective stress with depth
and then the combination of stress corrected parameters linked to sediment type via the empirical
model developed by Robertson and Campanella and later revised by Robertson (Robertson, P.K.,
1990, Soil classification using the cone penetration test, Can. Geotech J. 27, pp. 151-8)
.
CPT data must be corrected for effective stress.
Raw CPT data must be corrected or normalized for effective stress based on
depth and saturated overburden thickness before pile load modeling.
Empirical correlation of sediment type with normalized tip and sleeve data yield
a final sediment type. This correlation was first proposed by Robertson and
Campanella and later revised by Robertson.
After the raw CPT data are corrected, each interval is assigned a sediment type and the
downhole traces represent values corrected for effective stress.
A number of pile load models based on CPT data have been proposed over the years. Stratamodel
implemented the method desribed by Bustamante and Gianeselli in 1982 (Bustamante, M. &
L. Gianeselli,1982, Pile bearing pile capacity predictions by means of static penetrometer CPT,
Proceedings of the Second European Symposium on Penetration Testing, (ESOPT II), Amerstdam, A.A.
Balkema, 2, pp. 493-500) and calibrated the model against four pile load tests instrumented at
three or more intervals with continuously monitored strain meters. The model was validated against
over twenty subsequent pile load tests and found to be accurate to within 10% of pile failure
(plunged pile) for cast piles.
From CPT to a load model tracked by monitored drilling during production drilling.
The three logs below are fictional data produced with Stratamodel's Site Investigator software to preserve
client data confidentiallity. The log on the left is normalized CPT data that serves as input to a load
model. The log in the center is the model load for a 14 inch diameter partial displacement pile. The end
bearing component of the total load capacity is shown in red, the cumulative friction component in green
and their cummulative sum in blue. The right hand log is a simulated production auger instrumented with
a Jean Lutz system. The energy used to auger the
hole is tracked in blue.
