Determination of the vertical extent of transition zones based on the dispersion measures of CPTu tests and the impact of excluding these zones in estimating characteristic values of parameters

Wojciech Janecki

doi:10.2478/sgem-2026-0008

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Determination of the vertical extent of transition zones based on the dispersion measures of CPTu tests and the impact of excluding these zones in estimating characteristic values of parameters

Studia Geotechnica et Mechanica

Volume 48 (2026): Issue 2 (June 2026)

By: Wojciech Janecki

Open Access

|Oct 2026

Figures & Tables

Correction q_t in thin layers. Sand layer sandwiched between clay layers (left, quoted after [12,14]) and hypothetically symmetrically, a clay layer sandwiched between sandy layers (right). Formula (7) is defined only for the left-hand case.

Correction factor (K_H vs layer thickness H_S) – (7).

Hypothetical dynamics of q _c change in the neighborhood of the boundary between layers.

Hole E1. Determination of transition zones based on CPT soundings. The black plot next to q _c, named on graph as CVqc, is the local coefficient of variation V _L(X) (13) of the q _c parameter. Gray background indicates transition zones. Classification by Robertson 1990.

Hole E2. Determination of transition zones based on CPT soundings. The black plot next to q_c, named on graph as CVqc, is the local coefficient of variation V_L(X) (13) of the q_c parameter. Gray background indicates transition zones. Classification by PN-EN ISO 14688-1:2018 [19].

Table 1

CPT test E1. General characteristics.

Averaged borehole profile. 5 sandy layers and 5 cohesive layers	Average for the hole E1
	Layer thickness (m)	Central zone thickness (m)	Transition zone thickness (m)	Share of central zones	Share of transition zones
Coarse soils	0.76	0.48	0.28	62.63%	37.37%
Fine soils	0.77	0.50	0.28	64.08%	35.92%

Source: Author’s contribution.

Table 2

CPT test E2. General characteristics.

Averaged borehole profile. 4 sandy layers and 2 cohesive layers	Average for the hole E2
	Layer thickness (m)	Central zone thickness (m)	Transition zone thickness (m)	Share of central zones	Share of transition zones
Coarse soils	1.91	1.65	0.26	86.61%	13.39%
Fine soils	0.79	0.67	0.12	84.81%	15.19%

Source: Author’s contribution.

Table 3

Hole E1. Relative changes in selected parameters after omitting transition zones

Hole E1	Parameters	Average values in the hole	Relative changes in selected parameters after excluding transition zones
Hole E1	Parameters	Average values in the hole	Mean value μ	Std dev s	Pop dev σ	Coeff of var V	Value acc. EC7 μ-1.645σ	CIL m- $\frac{t}{\sqrt{n}} s$	Value acc. to Duncan μ-1.645σ σ=⅙(X_max-X_min)	Value acc. to Schneider μ-s/2
			%	%	%	%	%	%	%	%
Coarse soils	Point resistance q _c (MPa)	6.42	9.11	−29.69	−30.33	−33.05	81.35	14.46	34.00	18.33
	Sleeve friction resistance f _s (MPa)	0.03	15.41	−50.37	−50.37	−49.82	254.75	20.99	46.25	29.42
	Relative density I _D (%)	59.87	1.38	−34.42	−35.10	−35.31	12.79	2.68	9.68	4.03
	Constr. modulus M ₀ (MPa)	25.52	9.12	−32.05	−33.34	−34.64	80.53	14.83	32.87	18.56
Fine soils	Point resistance q _c (MPa)	0.51	−8.79	−54.11	−54.40	−52.18	63.42	−3.42	40.00	1.24
	Sleeve friction resistance f _s (MPa)	0.02	−8.96	−39.12	−40.25	−38.39	1.89	−4.08	16.40	−1.19
	Relative density I _D (%)	30.15	−10.62	−53.72	−54.36	−51.46	120.79	−3.95	64.67	1.94
	Constr. modulus M ₀ (MPa)	3.57	−9.88	−54.58	−55.26	−51.64	108.76	−4.01	56.95	−0.49

Source: Author’s contribution.

Table 4

Hole E2. Relative changes in selected parameters after omitting transition zones

Hole E2	Parameters	Average values in the hole	Relative changes in selected parameters after excluding transition zones
Hole E2	Parameters	Average values in the hole	Mean value μ	Std dev s	Pop dev σ	Coeff of var V	Value acc. EC7 μ-1.645σ	CIL m- $\frac{t}{\sqrt{n}} s$	Value acc. to Duncan μ-1.645σ σ=⅙(X_max-X_min)	Value acc. to Schneider μ-s/2
			%	%	%	%	%	%	%	%
Coarse soils	Point resistance q _c (MPa)	16.12	7.94	−4.63	−4.69	−11.57	65.54	10.26	26.18	11.68
	Sleeve friction resistance f _s (MPa)	0.26	6.51	−12.37	−12.05	−17.10	27.09	8.52	15.61	9.56
	Relative density I _D (%)	78.98	3.66	−16.37	−16.41	−19.22	12.75	5.01	12.46	5.70
	Constr. modulus M ₀ (MPa)	48.98	6.48	−7.76	−7.53	−13.20	27.52	8.44	19.65	9.45
Fine soils	Point resistance q _c (MPa)	3.09	1.30	−13.63	−13.58	−14.95	16.39	2.71	6.82	3.51
	Local friction resistance f _s (MPa)	0.10	−1.47	−16.84	−15.46	−15.44	5.49	−0.47	4.76	−0.52
	Undrained shear strength S _u (MPa)	99.30	1.23	−13.70	−13.92	−15.11	17.85	2.76	7.20	3.56
	Constr. modulusM (MPa)	24.57	1.29	−14.83	−12.75	−15.28	18.29	2.73	7.01	3.91

Source: Author’s contribution.

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DOI: https://doi.org/10.2478/sgem-2026-0008 | Journal eISSN: 2083-831X (formerly 0137-124X) | Journal ISSN: 0137-6365

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Language: English

Page range: 1 - 15

Submitted on: Nov 6, 2025

Accepted on: Jun 15, 2026

Published on: Oct 17, 2026

Published by: Wroclaw University of Science and Technology

In partnership with: Paradigm Publishing Services

Keywords:

Characteristic values,

CPTu,

Related subjects:

Physics,

Mechanics and fluid dynamics

© 2026 Wojciech Janecki, published by Wroclaw University of Science and Technology
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

Volume 48 (2026): Issue 2 (June 2026)

Determination of the vertical extent of transition zones based on the dispersion measures of CPTu tests and the impact of excluding these zones in estimating characteristic values of parameters

Figures & Tables

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Table 1

Table 2

Table 3

Table 4

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