Rheological Parameters as Affected by Water Tension in Subtropical Soils

Pértile, Patricia; Reichert, José Miguel; Gubiani, Paulo Ivonir; Holthusen, Dörthe; Costa, André da

doi:10.1590/18069657rbcs20150286

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Division 2 - Soil Processes and Properties • Rev. Bras. Ciênc. Solo 40 • 2016 • https://doi.org/10.1590/18069657rbcs20150286 copy

Rheological Parameters as Affected by Water Tension in Subtropical Soils

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

Rheological parameters have been used to study the interaction between particles and the structural strength of soils subjected to mechanical stresses, in which soil composition and water content most strongly affect soil resistance to deformation. Our objective was to evaluate the effect of water tension on rheological parameters of soils with different mineralogical, physical, and chemical composition. Surface and subsurface horizons of four Oxisols, two Ultisols, one Alfisol, and one Vertisol were physically and chemically characterized; their rheological parameters were obtained from amplitude sweep tests under oscillatory shear on disturbed soil samples that were saturated and subjected to water tension of 1, 3, 6, and 10 kPa. In these samples, the rheological parameters linear viscoelastic deformation limit (γ_L), maximum shear stress (τ_max), and integral z were determined. By simple regression analysis of the rheological parameters as a function of soil water tension, we observed increased mechanical strength with increasing water tension up to at least 6 kPa, primarily due to increased capillary forces in the soil. However, increased elasticity assessed by γ_L was not as expressive as the increase in structural rigidity assessed by τ_max and integral z. Elastic deformation of the soil (γ_L) increases with the increase in the number of bonds among particles, which depend on the clay, total carbon, expansive clay mineral, and cation contents; however, maximum shear resistance (τ_max) and structural stiffness (integral z) mainly increase with clay, kaolinite, and oxide content by increasing the strength of interparticle bonds. A decrease in mechanical strength occurs for water tension of 10 kPa (the lowest water content evaluated) in sandy horizons or in horizons with a high proportion of resistant microaggregates (pseudosand), when associated with low bulk density, due to fewer points of contact between soil particles and therefore lower capillary force.

soil mechanics; rheometry; cohesion; water content; capillary forces

SiBCS/USDA⁽¹⁾	Symbol	Coordinates	Horizons⁽²⁾	Depth	Sand	Silt	Clay	TC	Al³⁺	Ca²⁺	Mg²⁺	PL	LL	PI	ρ_s⁽⁵⁾
				m	---------g kg^-1---------				---cmol_c kg^-1---						Mg m^-3
Latossolo Vermelho Distrófico típico/Oxisol	LVd1	28°58’43,81”S 53°38’38,11”W	Ap	0.00-0.35	774	71	155	11.0	0.3	1.1	1.9	16	21	4	1.33
Latossolo Vermelho Distrófico típico/Oxisol	LVd1	28°58’43,81”S 53°38’38,11”W	Bw₁	1.05-1.52	649	77	274	4.2	1.2	0.5	1.1	18	25	7	1.43
Latossolo Vermelho Distrófico típico/Oxisol	LVd2	28°38’17,83”S 53°5’6,91”W	A₁	0.00-0.26	160	237	603	23.2	1.6	2.4	1.8	38	48	10	0.91
Latossolo Vermelho Distrófico típico/Oxisol	LVd2	28°38’17,83”S 53°5’6,91”W	Bw₁	1.00-1.38	84	114	802	6.4	1.0	2.2	1.3	41	54	13	1.18
Latossolo Bruno Distroférrico rúbrico/Oxisol	LBdf1	28°22’34,00”S 51°4’52,43”W	Ap	0.00-0.30	63	232	705	34.4	1.3	4.6	3.2	37	54	16	0.98
Latossolo Bruno Distroférrico rúbrico/Oxisol	LBdf1	28°22’34,00”S 51°4’52,43”W	Bw₁	0.95-1.50	48	143	809	5.0	0.8	0.7	1.2	50	62	12	1.08
Latossolo Bruno Distroférrico típico/Oxisol	LBdf2	28°30’38,09”S 50°52’46,15”W	A₁	0.00-0.26	70	381	549	33.6	0.2	6.4	4.9	41	56	16	1.10
Latossolo Bruno Distroférrico típico/Oxisol	LBdf2	28°30’38,09”S 50°52’46,15”W	Bw₁	0.80-1.00	39	178	783	11.4	1.4	0.5	0.9	40	51	11	1.13
Argissolo Vermelho Distrófico típico/Ultisol	PVd1	29°51’59,41”S 52°50’23,13”W	A	0.00-0.40	671	170	159	5.7	1.0	0.6	1.5	14	18	4	1.62
Argissolo Vermelho Distrófico típico/Ultisol	PVd1	29°51’59,41”S 52°50’23,13”W	Bt	1.10-1.55	429	146	425	5.4	1.6	1.4	2.0	24	34	10	1.48
Argissolo Vermelho Distrófico arênico/Ultisol	PVd2	30°41’25,23”S 55°7’50,11”W	A₁	0.00-0.20	844	99	57	6.2	0.1	1.1	0.8	-	13	-	1.66
Argissolo Vermelho Distrófico arênico/Ultisol	PVd2	30°41’25,23”S 55°7’50,11”W	Bt₁	0.77-0.98	507	73	420	5.0	1.4	2.9	1.3	23	38	14	1.67
Planossolo Háplico Eutrófico êndico/Alfisol	SXe	30°15’44,10”S 54°32’23,89”W	A₁	0.00-0.30	624	267	109	9.5	3.1	1.6	1.3	16	18	2	1.50
Planossolo Háplico Eutrófico êndico/Alfisol	SXe	30°15’44,10”S 54°32’23,89”W	Btg	0.70-1.20	417	188	395	4.5	0.7	8.1	2.7	24	41	17	1.48
Vertissolo Ebânico Órtico típico/Vertisol	VEo	30°43’9,00”S 55°47’38,56”W	A	0.00-0.30	41	406	553	44.1	0.1	33.8	8.6	49	90	41	0.94
Vertissolo Ebânico Órtico típico/Vertisol	VEo	30°43’9,00”S 55°47’38,56”W	Biv	0.30-1.15	28	305	667	32.1	0.1	47.8	8.5	42	98	56	1.06

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[1] * Corresponding author: E-mail: patricia_pertile@hotmail.com From these results, the storage modulus (G’, Pa) and loss modulus (G”, Pa) were calculated according to equations 3 and 4, respectively; and the loss factor (tan δ, dimensionless) was calculated by the ratio of G” and G’ (Equation 5).