Influence of Soft Soil Samples Quality on the Compressibility and Undrained Shear Strength – Seven Lessons Learned From the Vistula Marshlands

Jakub Konkol

doi:10.2478/sgem-2023-0012

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Influence of Soft Soil Samples Quality on the Compressibility and Undrained Shear Strength – Seven Lessons Learned From the Vistula Marshlands

Studia Geotechnica et Mechanica

Volume 45 (2023): Issue s1 (December 2023)

By: Jakub Konkol

Open Access

|Sep 2023

Figures & Tables

Schematic presentation of soft soil sample quality influence on (a) compressibility behavior and (b) undrained shear strength (Note: σ_v′ = effective vertical stress; ɛ_v = axial strain; σ_p′ = preconsolidation pressure; q = deviatoric stress according to Cambridge notation; p′ = effective mean stress according to Cambridge notation; p₀′ = initial mean stress; CSL = critical state line).

Table 1:

Vistula Marshlands soft soils basic physical properties.

Physical/index properties	Soil			Standard
Physical/index properties	Organic clay	Organic silt	Peat	Standard
LOI	10%<LOI<30%	5%<LOI<10%	LOI>30%	ASTM D2974 or PN-ISO 10694
Fines	~50% of Cl and Si	~95% of Si	N/A	Laser diffraction method
wc	63.5±21.0	45.5±18.5	261±110.4	ASTM D2216 or PN-EN ISO 17892-1
ρ	1.58±0.16	1.74±0.18	1.17±0.27	ASTM D854 or PN-EN ISO 17892-2
G_s	2.61±0.06	2.60±0.06	2.04±0.32	ASTM D7263 or PN-EN ISO 17892-3
LL	82.5±32.1	52.0±21.0	268.9±115.7	ASTM D4318 or PN-EN ISO 17892-12
IP	50.1±25.1	29.4±13.8	159.4±87.5	ASTM D4318 or PN-EN ISO 17892-12
Casagrande's chart	Along and above A-line	Above A-line	N/A	ASTM D2487 or PN-EN ISO 14688-2

[i] Note: LOI = loss on ignition (equivalent to organic matter content); w_c = water content; ρ = soil density; G_s = specific gravity; PL = plastic limit; LL = liquid limit; ± indicates standard deviation values

Table 2:

Soil specimens used in soil sample quality evaluation.

Soil	Time of tests after sampling [number of tests]*
Soil	*1 day*	*Up to 1 week*	*2–3 weeks*	*Above 3 weeks*
Organic clay	8	7	3	4
Organic silt	6	4	4	7
Peat	6	1	4	—

* The information is gathered from the soil investigation reports.

Table 3:

Soil specimens used in soil sample quality evaluation.

SQD (Terzaghi et al., 1966)	Δe/e₀ criteria (Lunne et al., 1997)				C_r/C_c (deJong et al., 2018)
*ɛ_vol at σ′_vo[%]*	*SQD class*	*OCR 1–2*	*OCR 2–4*	*Rating*	C_r/C_c	*Rating*
<1	A	<0.04	<0.03	v. good to excellent (A)	<0.15	High
1–2	B	0.04–0.07	0.03–0.05	good to fair (B)	0.15–0.4	Moderate
2–4	C	0.07–0.14	0.05–0.1	Poor (C)	>0.4	Low
4–8	D	>0.14	>0.1	Very poor (D)	-	-
>8	E	-	-	-	-	-

Soil sample quality according to different rating systems for peats (a,b,c), organic clay (d,e,f), and organic silt (g,h,i).

Relationships between different SQD criteria for peats (a,b,c), organic clay (d,e,f), and organic silt (g,h,i).

Influence of sample quality on oedometric modulus and compression index.

Table 4:

Natural variability of the organic silt samples for oedometric tests.

Sample no	*Boring no*	*Sample depth [m]*	*Test method*	*w_c [%]*	*ρ [g/cm³]*	*G_s [−]*	*Notes*
1	O3	10.5–11	24h IL	50.6	1.46	2.58	Sample few cm to no.2
2	O3	10.5–11	24h IL	59.9	1.29	2.58	Sample few cm to no.1
3	O1	9.5–10	24h IL	51.4	1.57	2.57	O1 borehole is at distance of 10 m from O2
4	O2	9.5–10	24h IL	42.9	1.71	2.54	O2 borehole is at distance of 10 m from O1
5	O3	9.3–9.8	24h IL	48.0	1.80	2.58
6	O3	10–10.5	24h IL	91.0	1.39	2.46	Very variable water content and plasticity of soil in the tube
7	O4	10–10.5	24h IL	103.5	1.37	2.26	Very variable water content and plasticity of soil in the tube
8	O4	10.5–11	24h IL	55.8	1.53	2.52	-
9	O2	9.5–10	CRS*	41.2	1.68	2.57	-

[i] Note: w_c = water content; ρ = soil density; G_s = specific gravity; IL = incremental loading oedometer test

Local relations of (a) C_c, (b) C_s, (c) C_s/C_c and (d) C_α with ρ_d0

Table 5:

Variability of constrained modulus and compression index for first group of soils (samples No. 1, 2, 3, 6, 7, and 8).

Sample no	E^oed [kPa]	E^oed_corr [kPa]	C_c^100–200kPa [−]	C_c^200–400kPa [−]	ρ_d0 [g/cm³]	C_c^eq.(5) [ −]	RE [%]
1	1468	1304	0.601	0.557	0.973	0.511	14.9
2	1342	1125	0.788	0.687	0.811	0.783	0.5
3	1565	1351	0.525	0.434	1.037	0.432	17.7
6	983	843	1.141	1.077	0.728	0.976	14.4
7	1175	973	0.951	0.816	0.673	1.127	18.6
8	1462	1240	0.583	0.536	0.982	0.499	14.4
AVG	1332	1140	0.764	0.684	-	-	-
SD	198	181	0.221	0.213	-	-	-
COV	0.14	0.16	0.29	0.31	-	-	-

[i] Note: E^oed = oedometric (constrained) modulus; E^oed_corr = oedometric (constrained) modulus corrected due to sample disturbance; C_c = compression index, number in brackets indicated stress range; ρ_d0 = initial dry bulk density; RE = relative error; AVG = average; SD = standard deviation; COV = coefficient of variation.

Table 6:

Variability of constrained modulus and compression index for second group of soils (samples No. 4, 5, and 9).

Sample no.	E^oed [kPa]	E^oed_corr [kPa]	C_c^100–200kPa [−]	C_c^200–400kPa [−]	ρ_d0 [g/cm³]	C_c^eq.(5) [−]	RE [%]
4	2949	2679	0.239	0.215	1.196	0.283	18.4
5	3311	3058	0.213	0.203	1.216	0.269	26.3
9	3125	2905	0.243	0.291	1.189	0.288	18.6
AVG	3128	2881	0.232	0.236	-	-	-
SD	147	155	0.013	0.039	-	-	-
COV	0.05	0.05	0.06	0.16	-	-	-

(a) Raw oedometer results (lab selected seating stress level is the reference one; usually approx. 5 kPa) and (b) “corrected” plots due to soil sample disturbance (in situ stress level is the reference one, here 100 kPa).

General picture of undrained shear strength of soft soil in Vistula Marshlands: (a) UUC test results, (b) FVT tests, and (c) specific location values (Jazowa testing site).

Table 7:

Jazowa testing site—different c_u estimates.

Sample no	Type (Δe/e₀)	Sampling/Testing depth [m]	Soil type	Test method	c_u [kPa]	Rate	c_u normalized to 1%/h ⁽¹⁾ [kPa]
1	In situ (B)	8	orSi	UUC	24.2	70%/h	18.9
2	In situ (B)	9	orSi	UUC	27.3	70%/h	21.3
3	In situ (B)	10	orSi	UUC	28.2	70%/h	22.1
4	In situ (B)	10	orSi	UUC	29.3	70%/h	22.9
5	In situ (N/A)	8.5	orSi	FVT	30.7⁽²⁾	0.1°/s (700%/h)	30.7⁽²⁾
6	In situ (N/A)	9	orSi	FVT	30.1⁽²⁾	0.1°/s (700%/h)	30.1⁽²⁾
7	In situ (N/A)	9	orSi	FVT	28.5⁽²⁾	0.1°/s (700%/h)	28.5⁽²⁾
8	In situ (N/A)	10	orSi	FVT	33.5⁽²⁾	0.1°/s (700%/h)	33.5⁽²⁾
9	Reconstituted (A)	9	orSi	CK₀UC	32.7	1%/h	32.7
10	Reconstituted (A)	9	orSi	CK₀UC	29.3	1%/h	29.3
11	Reconstituted (A)	9	orSi	DSS	27.2	20%/h	22.8
12	Reconstituted (A)	9	orSi	DSS	29.3	20%/h	24.5

[i] Note: (1) Rate dependency of organic silt was observed in lab and field tests. These tests indicates that c_u increases of about 15% in one log cycle due to strain rate increase; (2) FVT tests were already corrected due to rate effects according to equation (2).

Different estimates of c_u for Jazowa site.

Table 8:

Organic clay—different estimates of c_u (location No. 2).

Sample no.	Type (Δe/e₀)	Sampling/Testing depth [m]	Soil type	Test method	c_u [kPa]	Rate
1	In situ (D)*	2–3	orCl	CK₀UC	17.0	1%/h
2	In situ (D)*	2–3	orCl	CK₀UC	23.4	1%/h
3	In situ (D)*	2–3	orCl	CK₀UE	15.2	1%/h
4	N/A	2–3	orCl	SHANSEP	18.2±9.5	N/A

* In K₀ (or anisotropic) consolidation triaxial tests, the influence of sample disturbance is marginal due to sample restoration to in situ conditions.

Table 9:

Organic clay—different estimates of c_u (location No. 3).

Sample no.	Type (SQD)	Sampling/Testing depth [m]	Soil type	Test method	c_u [kPa]	Rate
1	In situ (D)	9–10	orSi	CK₀UC	26.4	1%/h
2	In situ (D)	9–10	orSi	CK₀UC	32.7	1%/h
4	N/A	9–10	orSi	SHANSEP	25±5.2	N/A

* In K₀ (or anisotropic) consolidation triaxial tests, the influence of sample disturbance is marginal due to sample restoration to in situ conditions.

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DOI: https://doi.org/10.2478/sgem-2023-0012 | Journal eISSN: 2083-831X (formerly 0137-124X) | Journal ISSN: 0137-6365

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Language: English

Page range: 262 - 281

Submitted on: Jan 15, 2023

Accepted on: Jun 23, 2023

Published on: Sep 30, 2023

Published by: Wroclaw University of Science and Technology

In partnership with: Paradigm Publishing Services

Keywords:

soft soils,

soil sample quality,

constrained modulus,

deformation properties,

undrained shear strength

Related subjects:

Physics,

Mechanics and fluid dynamics

© 2023 Jakub Konkol, published by Wroclaw University of Science and Technology
This work is licensed under the Creative Commons Attribution 4.0 License.

Volume 45 (2023): Issue s1 (December 2023)

Influence of Soft Soil Samples Quality on the Compressibility and Undrained Shear Strength – Seven Lessons Learned From the Vistula Marshlands

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