Generation of microcracks in molded soils by rapid wetting

Soil Research ◽  
1989 ◽  
Vol 27 (1) ◽  
pp. 169 ◽  
Author(s):  
CD Grant ◽  
AR Dexter
Keyword(s):  
Water Management ◽  
Tensile Strength ◽  
Natural Regeneration ◽  
Soil Structure ◽  
Initial Water ◽  
Fracture Surfaces ◽  
Water Contents ◽  
Wetting Rate ◽  
Soil Tensile Strength

Tillage of compacted or of puddled and remoulded soils is a major agronomic problem internationally. The natural regeneration of microcracks (tilth mellowing) prior to the cultivation of such soils can reduce the energy needed to work them. Rapid wetting, under certain conditions, plays a major role in developing cracks in structurally damaged soils. This study reports the use of different initial water contents and wetting rates to examine the development of 'new' soil structure, described mechanically by tensile strength, and optically by measurements of the relief of fractured soil surfaces. New terminology is introduced to describe the rate of wetting needed to induce mellowing and to describe the rugosity of soil fracture surfaces. Rapid wetting was found to induce microcracking in soils, even with initial matric potentials as wet as -1.0 to -1.5 MPa. Implications for water management are briefly considered. Visual and analytical evidence from photographs and computer images indicates that internal microcracking is almost always detectable whenever the wetting rate is sufficiently high to reduce the soil tensile strength.

scholarly journals Modified Liu-Carter Compression Model for Natural Clays with Various Initial Water Contents

2016 ◽  
Vol 2016 ◽  
pp. 1-8 ◽  
Author(s):  
Sen Qian ◽  
Jian Shi ◽  
Jian-wen Ding
Keyword(s):  
Water Content ◽  
Soil Structure ◽  
Initial Water Content ◽  
Initial Water ◽  
Compression Behaviour ◽  
Compression Model ◽  
Proposed Model ◽  
Natural Clays ◽  
Water Contents ◽  
Carter Model

The initial water content has a significant effect on the compression behaviour of reconstituted clays. This effect has to be considered in the Liu-Carter model to ensure the addition voids ratio only related to soil structure. A modified Liu-Carter compression model is proposed by introducing the empirical equations for reconstituted clays at different initial water contents into the Liu-Carter model. The proposed model is verified against the experimental results from the literature. The simulations by the proposed method are also compared with that by old method where the influence of initial water content is not considered. The results show that the predicted virgin compression curves of natural clays are similar, but the values ofbandΔeymay be very different.

scholarly journals Tensile strength, friability and organic carbon in an oxisol under a crop-livestock system

2009 ◽  
Vol 66 (4) ◽  
pp. 499-505 ◽  
Author(s):  
Rachel Muylaert Locks Guimarães ◽  
Cássio Antonio Tormena ◽  
Sérgio José Alves ◽  
Jonez Fidalski ◽  
Éverton Blainski
Keyword(s):  
Tensile Strength ◽  
Organic Carbon ◽  
Soil Compaction ◽  
Soil Structure ◽  
Soil Depth ◽  
Limiting Factor ◽  
Surface Layers ◽  
Livestock Systems ◽  
Livestock System ◽  
Soil Tensile Strength

The crop-livestock system can promote soil compaction in surface layers, mainly due to animal trampling. However, plants and their root growth, in interaction with animal trampling, can decrease the deleterious changes in soil structure caused by this system. Up to the present time, the physical soil modifications in crop-livestock systems, including oat and ryegrass crops for winter animal forages are unknown. The objective of this study was to quantify and to relate tensile strength, friability and soil organic carbon in an Oxisol under a crop-livestock system. The study was conducted in Campo Mourão - Paraná, Brazil. Four forage heights were used for the winter forages: 7, 14, 21 and 28 cm. For each forage height, five soil blocks were randomly collected from each layer of 0 - 0.1, 0.1 - 0.2 and 0.2 - 0.3 m of depth. The increase in carbon content promotes an increase in soil tensile strength at the 0.1 - 0.2 m soil depth, this layer having the highest values for tensile strength. The forage height of 21 cm was found to be the best height for soil friability, and the soil was very friable at this height. Despite a decrease in friability in the upper layers of the soil, the crop-livestock system was not found to be a limiting factor for the subsequent cultivation of annual crops.

scholarly journals Compressibility behaviour of remoulded, fine-grained soils and correlation with index properties

2000 ◽  
Vol 37 (3) ◽  
pp. 712-722 ◽  
Author(s):  
A Sridharan ◽  
H B Nagaraj
Keyword(s):  
Liquid Limit ◽  
Plasticity Index ◽  
Engineering Properties ◽  
Test Results ◽  
Index Properties ◽  
Initial Water ◽  
Fine Grained ◽  
Wide Range ◽  
The Relationship ◽  
Water Contents

Correlating engineering properties with index properties has assumed greater significance in the recent past in the field of geotechnical engineering. Although attempts have been made in the past to correlate compressibility with various index properties individually, all the properties affecting compressibility behaviour have not been considered together in any single study to examine which index property of the soil correlates best with compressibility behaviour, especially within a set of test results. In the present study, 10 soils covering a sufficiently wide range of liquid limit, plastic limit, and shrinkage limit were selected and conventional consolidation tests were carried out starting with their initial water contents almost equal to their respective liquid limits. The compressibility behaviour is vastly different for pairs of soils having nearly the same liquid limit, but different plasticity characteristics. The relationship between void ratio and consolidation pressure is more closely related to the shrinkage index (shrinkage index = liquid limit - shrinkage limit) than to the plasticity index. Wide variations are seen with the liquid limit. For the soils investigated, the compression index relates better with the shrinkage index than with the plasticity index or liquid limit.Key words: Atterberg limits, classification, clays, compressibility, laboratory tests.

Simultaneous Measurements of Spiracular and Cuticular Water Losses in Periplaneta Americana: Implications for Whole-Animal Mass Loss Studies

1991 ◽  
Vol 161 (1) ◽  
pp. 439-453 ◽  
Author(s):  
J. MACHIN ◽  
P. KESTLER ◽  
G. J. LAMPERT
Keyword(s):  
Water Loss ◽  
Periplaneta Americana ◽  
Water Losses ◽  
Initial Water ◽  
Variable Activity ◽  
Cuticular Permeability ◽  
Order Of Magnitude ◽  
Animal Mass ◽  
Principal Contributor ◽  
Water Contents

Spiracular and cutaneous water loss through the cuticle and spiracles of Periplaneta americana was measured in animals of differing initial water contents under controlled temperature, humidity and airflow conditions, by continuous weighing (resolution ±10μg). Stable water loss rates (2.09×10−8 to 3.47×10−8gh−1cm−2Pa−1) were as much as an order of magnitude less than those reported in earlier studies employing intermittent weighing techniques. We suggest that increased water loss caused by substantial increases in ventilatory water loss during the episodic disturbances required by intermittent weighing is the principal contributor to this discrepancy. Water losses, as well as the interval between spiracular ventilations, decreased with water content. However, greater variation was primarily due to interruptions of the regular cyclic pattern of ventilation by highly variable, activity-related bouts of increased ventilatory loss. Variations in water loss appear to be too large and too rapid to be convincingly explained in terms of cuticular conductance. Our results suggest that previous experiments using 5% CO2 anaesthesia, linking changes in total water loss to the conducting properties of the cuticle, were not valid. There seems to be no adaptive value for the proposed voluntary increases in cuticular permeability in an animal where ventilatory water losses can be so high.

Effects of differential drying rates on viability retention of recalcitrant seeds of Ekebergia capensis

1998 ◽  
Vol 8 (4) ◽  
pp. 463-471 ◽  
Author(s):  
N. W. Pammenter ◽  
Valerie Greggains ◽  
J. I. Kioko ◽  
J. Wesley-Smith ◽  
Patricia Berjak ◽  
...  
Keyword(s):  
Water Content ◽  
Exponential Function ◽  
Time Course ◽  
Drying Rate ◽  
Recalcitrant Seeds ◽  
Tissue Water ◽  
Initial Water ◽  
Viability Loss ◽  
Drying Rates ◽  
Water Contents

AbstractThe drying rate of whole seeds of Ekebergia capensis (Meliaceae) was shown to influence the response to desiccation, with rapidly dried seeds surviving to lower water contents. Short-term rapid drying (to water contents higher than those leading to viability loss) actually increased the rate of germination. The form of the time course of decline of axis water content varied with drying rate; slow drying could be described by an exponential function, whereas with rapid drying initial water loss was faster than predicted by an exponential function. These observations suggest that slow drying brought about homogeneous dehydration and that the rapid drying was uneven across the tissue. This raised the possibility that the different responses to dehydration were a function of different distributions of water in the axis tissue under the two drying regimes. However, ultrastructural observations indicated that different deleterious processes may be occurring under the different drying treatments. It was tentatively concluded that a major cause of viability loss in slowly dried material was likely to be a consequence of aqueous-based processes leading to considerable membrane degradation. Uneven distribution of tissue water could not be rejected as a contributory cause of the survival of rapidly dried seeds to low bulk water contents. The differential response to dehydration at different drying rates implies that it is not possible to determine a ‘critical water content’ for viability loss by recalcitrant seeds.

Determination of the tensile strength of unsaturated tailings using bending tests

2015 ◽  
Vol 52 (11) ◽  
pp. 1874-1885 ◽  
Author(s):  
Bibiana Narvaez ◽  
Michel Aubertin ◽  
Faustin Saleh-Mbemba
Keyword(s):  
Tensile Strength ◽  
Water Content ◽  
Water Retention ◽  
Water Retention Curve ◽  
Initial Water Content ◽  
Ambient Conditions ◽  
Initial Water ◽  
Bending Tests ◽  
Retention Curve ◽  
Apparent Cohesion

Bending tests were conducted on specimens of unsaturated tailings from three hard rock mines to evaluate their tensile strength. Saturated samples were prepared at an initial water content, w0, of 40% and then naturally dried under ambient conditions to pre-selected degrees of saturation, Sr, which can be related to the corresponding suction using the water retention curve. The basic interpretation of the bending tests results is based on an elastic–brittle behavior. The results show how the tensile strength, σt, of unsaturated tailings varies with water content, w (and Sr). The experimental data are also used to evaluate Young’s modulus in tension, Et, and to estimate the apparent cohesion, capp, as a function of Sr. Predictive equations are also applied to estimate the values of σt of unsaturated tailings using the water retention curve.

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