arXiv subjects

V. Y. Chertkov

Publications and source records attributed to V. Y. Chertkov.

10 recordsLinked to original sources

arXiv2014

Shrinkage anisotropy characteristics from soil structure and initial sample/layer size

The objective of this work is a physical prediction of such soil shrinkage anisotropy characteristics as variation with drying of (i) different sample/layer sizes and (ii) the shrinkage geometry factor. With that, a new presentation of the shrinkage anisotropy concept is suggested through the sample/layer size ratios. The work objective is reached in two steps. First, the relations are derived between the indicated soil shrinkage anisotropy characteristics and three different shrinkage curves of a soil relating to: small samples (without cracking at shrinkage), sufficiently large samples (with internal cracking), and layers of similar thickness. Then, the results of a recent work with respect to the physical prediction of the three shrinkage curves are used. These results connect the shrinkage curves with the initial sample size/layer thickness as well as characteristics of soil texture and structure (both inter- and intra-aggregate) as physical parameters. The parameters determining the reference shrinkage curve (relating to the small samples) and initial sample size/layer thickness are needed for the prediction of the above soil shrinkage anisotropy characteristics. Using the available data on two soils and samples of two essentially different sizes, illustrative estimates of the relative sample sizes, new characteristic of the shrinkage anisotropy, and shrinkage geometry factor are given as the physically predicted values.

physics.geo-ph↗

arXiv2014

The geometry of soil crack networks

The subject of this work is the modification and specification of an approach to detail the estimation of soil crack network characteristics. The modification aims at accounting for the corrected soil crack volume based on the corrected shrinkage geometry factor compared to known estimates of crack volume and shrinkage geometry factor. The mode of the correction relies on recent results of the soil reference shrinkage curve. The main exposition follows the preliminary brief review of available approaches to dealing with the geometry of soil crack networks and gives a preliminary brief summary of the approach to be modified and specified. To validate and illustrate the modified approach the latter is used in the analysis of available data on soil cracking in a lysimeter.

physics.geo-ph↗

arXiv2014

Water retention of rigid soils from a two-factor model for clay

Water retention is one of the key soil characteristics. Available models of soil water retention relate to the curve-fitting type. The objective of this work is to suggest a physical model of water retention (drying branch) for soils with a rigid matrix. "Physical" means the prediction based on the a priori measured or estimated soil parameters with a clear physical meaning. We rely on the two-factor model of clay that takes into account the factors of capillarity and shrinkage. The key points of the model to be proposed are some weak pseudo shrinkage that the rigid soils demonstrate according to their experimental water retention curves, and some specific properties of the rigid grain matrix. The three input parameters for prediction of soil water retention with the rigid grain matrix include inter-grain porosity, as well as maximum and minimum grain sizes. The comparison between measured and predicted sand water retention curves for four different sands is promising.

physics.geo-ph↗

arXiv2014

Two-Factor Model of Soil Suction from Capillarity, Shrinkage, Adsorbed Film, and Intra-aggregate Structure

The objective of this work is to derive the soil water retention from the soil structure without curve-fitting and only using the physical parameters found irrespective of an experimental retention curve. Two key points underlie the work: (i) the soil suction at drying coincides with that of the soil intra-aggregate matrix and contributive clay; and (ii) both the soil suction and volume shrinkage at drying depend on the same soil water content. In addition the two following results are used: (i) the available two-factor (capillarity and shrinkage) model of clay suction enables one to connect a clay suction and clay water content using the clay matrix structure; and (ii) the recent reference shrinkage curve model based on the concepts of intra-aggregate soil structure permits one to connect the soil water content at shrinkage with the water content of the contributive clay. With that the available two-factor model was essentially modified and, in particular, the effect of adsorbed water film was taken into account. The developed model includes the following input parameters: the solid density, relative volume of contributive-clay solids, relative volume of contributive clay in the oven-dried state, soil clay content, aggregate/intra-aggregate mass ratio, and specific volume of lacunar pores in the aggregates at maximum swelling. The validation of the model is based on available data of water retention and the above input parameters for six soils. A promising agreement between the predicted and observed water retention curves was found.

physics.geo-ph↗

arXiv2014

Physical modeling of the soil swelling curve vs. the shrinkage curve

Physical understanding of the links between soil swelling, texture, structure, cracking, and sample size is of great interest for the physical understanding of many processes in the soil-air-water system and for applications in civil, agricultural, and environmental engineering. The background of this work is an available chain of interconnected physical shrinkage curve models for clay, intra-aggregate matrix, aggregated soil without cracks, and soil with cracks. The objective of the work is to generalize these models to the case of swelling, and to construct the physical-swelling-model chain with a step-by-step transition from clay to aggregated soil with cracks. The generalization is based on thorough accounting for the analogies and differences between shrinkage and swelling and the corresponding use, modification, or replacement of the soil shrinkage features. Two specific soil swelling features to be used are: (i) air entrapping in pores of the contributing clay; and (ii) aggregate destruction with the formation of new aggregate surfaces. The input for the prediction of the swelling curve of an aggregated soil coincides with that of the available model of the shrinkage curve. The analysis of available data on the maximum shrink-swell cycle of two soils with different texture and structure, accounting for sample size is conducted as applied to swelling curves and to the residual crack volume and maximum-swelling-volume decrease after the shrink-swell cycle. Results of the analysis show evidence in favor of the swelling model chain.

physics.geo-ph↗

arXiv2014

An integrated approach to soil structure, shrinkage, and cracking in samples and layers

A recent model showed how a clay shrinkage curve is step-by-step transformed into the shrinkage curve of an aggregated soil at any clay content if it is measured on samples so small that cracks do not occur at shrinkage. Such a shrinkage curve was called a reference curve. The present work generalizes this model to any soil sample size or layer thickness, i.e., to any crack contribution to the shrinkage curve. The approach is based on: (i) recently suggested features of an intra-aggregate structure; (ii) detailed accounting for the contributions to the soil volume and water content during shrinkage; and (iii) new concepts of lacunar factor, crack factor, and critical sample size. The following input parameters are needed for the prediction: (i) all parameters determining the basic dependence of the reference shrinkage curve; (ii) parameters determining the critical sample size (structural porosity and minimum and maximum aggregate size at maximum swelling); and (iii) initial sample size or layer thickness. A primary experimental validation of the new model concepts is conducted using the relevant available data on the shrinkage curves of four soils with different texture and structure that were obtained utilizing the samples of two essentially different sizes. The results show evidence in favor of the model.

physics.geo-ph↗

arXiv2014

The physical effects of an intra-aggregate structure on soil shrinkage

Clay and soil containing it have shrinkage curves that are qualitatively different in shape. The objective of this work is to qualitatively show with maximum simplicity, how a clay shrinkage curve turns into a soil shrinkage curve. Because of the crack volume the measured shrinkage curve is not the single-valued feature of a soil. We use a concept of the reference shrinkage curve that is only stipulated by soil shrinkage without cracking, single-valued, and qualitatively similar to an observed shrinkage curve. We also use new concepts of an intra-aggregate soil structure: (i) a rigid superficial layer of aggregates that loses water during shrinkage; and (ii) lacunar pores (micro-cracks) inside an intra-aggregate clay that change in volume during shrinkage. Then, through a series of consecutive steps, illustrating each step by a separate graphic presentation, we move from a clay shrinkage curve to a soil shrinkage curve with predicted qualitative features that coincide with those experimentally observed in numerous soil shrinkage publications. We thereby demonstrate the qualitative physical impact of the intra-aggregate structure on soil shrinkage.

physics.geo-ph↗

arXiv2014

Estimating the aggregate/intraaggregate mass ratio of a shrinking soil

A recently introduced parameter, the ratio of an aggregate solid mass to a solid mass of an intraaggregate matrix (K ratio) is connected with the mean thickness of a deformable, but non-shrinking surface layer of aggregates and is a fundamental property of aggregated soils that essentially influences their shrinkage. The objective of this work is to suggest and validate an approach to estimating the K ratio at any soil clay content through characteristics of soil texture and structure. We derive an equation that reflects the interrelation between the K ratio and soil texture and structure. The K ratio can be estimated as the solution of the equation and is determined by the mean size of soil solids and the maximum size of soil aggregates in the oven-dried state, independently of a measured shrinkage curve. To validate the approach we use available data for eight soils.

physics.geo-ph↗

arXiv2014

Physical modeling of shrink-swell cycles and cracking in a clayey vadose zone

Physical understanding of the crack origin and quantitative physical prediction of the crack volume variation far from the clay soil surface are necessary to protect the underlying aquifers from pollutants. The basis of this work is an available physical model for predicting the shrinkage and swelling curves in the maximum water content range (the primary curves) and crack volume variation. The objective of the work is to generalize this model to the conditions of the deep layer of a clayey vadose zone with the overburden pressure, multiple shrinkage-swelling, and variation of water content in a small range. We aim to show that the scanning shrinkage and swelling curves, and steady shrink-swell cycles existing in such conditions, inevitably lead to the occurrence of cracks and a hysteretic crack volume. The generalization is based on the transition to the increasingly complex soil medium from the contributive clay, through the intra-aggregate matrix and aggregated soil with no cracking, to the soil with cracks. The results indicate the single-valued physical links between the scanning shrink-swell cycles and crack volume variation of the four soil media on the one hand, and primary shrinkage and swelling curves of the media on the other hand. The predicted cycles and crack volume hysteresis can be expressed through the physical properties and conditions of the soil at a given depth. The available observations of the cracks and crack volume variation in the clayey vadose zone give strong qualitative experimental evidence in favor of the feasibility of the model.

physics.geo-ph↗

arXiv2014

The soil reference shrinkage curve

A recently proposed model showed how a clay shrinkage curve is transformed to the soil shrinkage curve at the soil clay content higher than a critical one. The objective of the present work was to generalize this model to the soil clay content lower a critical one. I investigated (i) the reference shrinkage curve, that is, one without cracks; (ii) the superficial layer of aggregates, with changed pore structure compared with the intraaggregate matrix; and (iii) soils with sufficiently low clay content where there are large pores inside the intraaggregate clay (so-called lacunar pores). The methodology is based on detail accounting for different contributions to the soil volume and water content during shrinkage. The key point is the calculation of the lacunar pore volume variance at shrinkage. The reference shrinkage curve is determined by eight physical soil parameters: (1) oven-dried specific volume; (2) maximum swelling water content; (3) mean solid density; (4) soil clay content; (5) oven-dried structural porosity; (6) the ratio of aggregate solid mass to solid mass of intraaggregate matrix; (7) the lacunar factor that characterizes the rate of the lacunar pore volume change with water content; and (8) oven-dried lacunar pore volume. The model was validated using available data. The model predicted value of the slope of the reference shrinkage curve in the basic shrinkage area is equal to unity minus the lacunar factor value, and is between unity and zero in the agreement with observations.

physics.geo-ph↗