Cranfield University

Soil Compaction Models
VCL parameters. The predicted soil displacement was highly accurate. The models of
Gupta and Larson (1982) and Bailey and Johnson (1989) which require more input pa-
rameters can hardly be more accurate, however, the larger amount of input parameters
these need make them unsuitable for such an in-situ approach. Chi et al. (1993) point out
that the derivation of critical state soil mechanics parameters is the largest source of error
when comparing soil compaction model predictions to real data. This source was reduced
here due to the small number of necessary parameters and the large sample size.
It was possible to use a soil mechanics model based on critical state soil mechanics theory
(Schofield and Wroth, 1968) and gain its soil specific soil physical parameters from simple
empirical measurements. This allowed qualitative but more importantly quantitative cor-
rect predictions.
The output from COMPSOIL is more distinct than for models such as TASC (Diserens
and Spiess, 2004) or SOCOMO (van den Akker, 2004) which only predict soil stresses.
Although the screw driver test for TASC is easier to perform than gaining an in-situ VCL,
the additional information gained from COMPSOIL due to the accurate soil displacement
and soil density increase prediction with depth make the additional effort worthwhile. Thus
the in-situ VCL approach improves considerably the user-friendliness of COMPSOIL due
to the ability to adapt easily to different soil types.
Considering the different approaches taken to derive VCL parameters, the approach de-
scribed here to gain an in-situ VCL has the advantage of easily accessible information and
very large sample size compared to any laboratory based approach. The large sample size
and in-field test avoids the major issue of variations with small sample testing for critical
state soil mechanics models as pointed out by Chi et al. (1993) when investigating the ac-
curacy of soil compaction models. The sample size is of concern for the approach taken by
Gurtug and Sridgaran (2002) who obtained compaction characteristics from plastic limit
tests for fine grained soils as these are usually carried out with only a few grams of soil.
Compared to the improvement of Kirby et al. (1998) who derive all critical state soil me-
chanics parameters from one constant cell volume triaxial cell test, the field test only pro-
vides the information for soil compaction, but without any laboratory equipement. No pedo
- transfer functions as for example included by Keller et al. (2007) in SOILFLEX are nec-
essary as the approach can be repeated on any soil type and the resulting in-situ VCL will
Ph.D. Thesis Dirk Ansorge (2007)
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