Soil Volume Change Research Articles

Geometric Factor as the Characteristics of the Three-Dimensional Process of Volume Changes of Heavy Soils

During simulation of a water regime of heavy soils, it is necessary to know the isotropy parameters of any volume changes. Volume changes appear in both vertical and horizontal directions. In vertical directions, they appear as a topsoil movement, and in horizontal directions as the formation of a crack network. The ratio between horizontal and vertical change is described using the geometric factor, rs. In the present paper, the distribution of volume changes to horizontal and vertical components is characterized by the geometric factor, in selected soil profiles, in the East Slovakian Lowland. In this work the effect of soil texture on the value of the geometric factor and thus, on the distribution of volume changes to vertical and horizontal components was studied. Within the hypothesis, the greatest influence of the clay soil component was shown by the geometric factor value. New information is obtained on the basis of field and laboratory measurements. Results will be used as inputs for numerical simulation of a water regime for heavy soils in the East Slovakian Lowland.

VOLUME CHANGE BEHAVIOR OF PHOSPHOGYPSUM TREATED CLAYEY SOILS CONTAMINATED WITH INORGANIC ACIDS – A MICRO LEVEL STUDY

Soils exhibit undesirable volume changes when exposed to high concentrations of acids, which is manifested most frequently in the beds of foundations of industrial establishments associated with their production or use. However, control of this phenomenon has received less attention than it deserves. This paper aims to investigate the mineralogical and micro-structural changes occurred during the volume change behavior of phosphogypsum treated clayey soils contaminated with sulfuric acid and phosphoric acid solutions. Oedometer test results showed high swelling and low compressibility for acid contaminated soils than that of water. The change in microstructure towards flocculated fabric along with mineralogical transformations are responsible for the volume changes in soils. The mineralogical changes that affected the volume change behavior are discussed with FT-IR, XRD and SEM analysis. Phosphogypsum treatment was found to be effective in controlling volume changes in soils with phosphoric acid, whereas in the case of sulfuric acid found to be futile.

Control of phosphoric acid induced volume change in clays using fly ash

Volume changes of soils induced by inorganic acids cause severe foundation and superstructure failures in industrial buildings. This study aimed to assess the potential of fly ash to control volume changes in soils under acidic environment. Two soils such as black cotton soil predominant with montmorillonite and kaolin clay predominant with kaolinite were used for the present investigation. Both soils exhibited an increase in swelling subjected to phosphoric acid contamination. Ion exchange reactions and mineralogical transformations lead to an increase in swelling and a decrease in compressibility in black cotton soil, whereas phosphate adsorption and mineral dissolution lead to an increase in swelling and compressibility in case of kaolin clay. Different percentages of Class F fly ash obtained from Ramagundam national thermal power station were used for soil treatment. Fly ash treatment leads to significant reduction in swelling and compressibility, which is attributed to the formation of aluminum phosphate cements in the presence of phosphoric acid.

Investigation of immersion influence on dynamic properties of high-speed railway subgrade with semi-rigid waterproof functional layer through field-excitation testing

The subgrade below the under-construction Kunming–Shanghai high-speed railway faces serious stability problems induced by considerable swelling and shrinkage volume change of expansive soil along with variation of moisture content. To prevent the occurrence of potential damage, reasons for the frequent occurrence of drainage ditch breakage and platform damage along the railway corridor in expansive soil areas were analyzed. A novel integral ancillary facility and semi-rigid waterproof functional layer were developed. Large-scale field dynamic tests were carried out to investigate the fatigue performance of the waterproof functional layer and the influences of different service environments (relatively dry condition and immersion condition) on the dynamic response of the subgrade. Results show that the fatigue property and waterproofing capability of the waterproof functional layer can fulfill the standard requirements for the high-speed railway subgrade. There was an enlargement phenomenon of the dynamic stress and vibration velocity when the service environment of subgrade changed from a relatively dry condition to an immersion condition. The vibration velocity seemed to increase along the depth of the graded broken stone surface layer and decrease linearly with further depth increase from the bottom surface of the waterproof functional layer.

A Novel and Facile Method for Characterizing Shrinkage Geometry along the Granitic Soil Profile

Core Ideas A simple and facile approach was proposed for measuring the anisotropic shrinkage. Subsidence was dominant for soils in the loose and aggregated structure. Horizontal shrinkage was predominant for soils with the horizontal arrangement of plate particles The shrinkage behavior of granite soils was controlled by clay content and pore structure. Soil volume change resulting from frequent drying–wetting cycles leads to severe erosion and landslides in granite regions. Limited attempts have been made to investigate the shrinkage geometry of these soils. Here, a new method was proposed for characterizing soil shrinkage behavior by testing cylindrical specimens of undisturbed granitic soils sampled separately in vertical and horizontal directions at the pedogenic layers (i.e., surface [L1], lateritic [L2 and L3], sandy [L4], and detritus [L5] layers). For L1, the coefficient of linear extensibility (COLE) was larger in the vertical than in the horizontal direction, whereas it was the opposite for L2 and L3. For L4 and L5, the COLE showed no significant differences between the two directions. A modified van Genuchten equation fitted well with the COLE curves (p < 0.01). The shrinkage potential decreased in the order of L3 > L2 > L1, L4 > L5. Subsidence was dominant for the L1 soil due to the loose‐aggregated structure, whereas cracking was dominant in the lateritic layer soils due to the horizontal arrangement of clay particles. The shrinkage geometry for L4 and L5 was largely determined by soil structure inherited from the configuration of granite rock. The shrinkage behavior of granite soils was controlled by clay content and pore structure. This new method of measuring shrinkage geometry is accurate, low cost, nondestructive, and labor saving but remains to be improved and validated on a wide range of soil types.

Study of the behavior of mechanically stabilized earth (MSE) walls subjected to differential settlements

The limit equilibrium (LE) analysis has been used to design MSE walls. Presumably, the deflection of MSE walls can be limited to an acceptable range by ensuring sufficient factors of safety (FOSs) for both external and internal stabilities. However, unexpected ground movements, such as movements induced by excavations, volume changes of expansive soils, collapse of sinkholes, and consolidations of underlying soils, can induce excessive differential settlements that may influence both the stability and the serviceability of MSE walls. In this study, a numerical model, which was calibrated by triaxial tests and further by a specially-designed MSE wall tests, investigated the behavior of an MSE wall as well as the influence of various factors on the performance of the MSE wall when the wall facing settled relatively to the reinforced zone. The numerical results showed that the differential settlement would cause substantial vertical and horizontal movements for the MSE wall, as well as an increase in lateral earth pressure and geosynthetic reinforcement strain. The maximum horizontal movement and increase of the lateral earth pressure occurred at about 1.0 m above the toe. The differential settlement resulted in a critical plane that coincided with the plane of 45°+ϕ/2. The maximum increase of the strain for each geogrid layer occurred in that plane, and the bottom layer had the greatest strain increase among all layers of reinforcement. The study further indicated that the surcharge, backfill friction angle, tensile stiffness of geogrid, reinforcement length and MSE wall height had noticeable influences on horizontal and vertical movements, and strain in geosynthetics. According to the results, the MSE wall that had a higher factor of safety would have less movements and geosynthetic strain increase. In contrast, only the friction angle, tensile stiffness and MSE wall height showed some degree of influence on the lateral earth pressure due to differential settlements.

Assessment of Soil Disturbance Caused by Forest Operations by Means of Portable Laser Scanner and Soil Physical Parameters

Core Ideas Forest operations may cause severe soil disturbances. Soil impacts are usually assessed by time consuming methods. Our study investigated the use of a portable laser scanner to assess forest soil disturbance. Forest operations can cause compaction and rutting, resulting in soil degradation processes. Soil damage is usually assessed through costly and time‐consuming manual field measurements. The aim of this study is to investigate the impact of logging operations on soil using traditional ground surveys integrated with laser scanning data acquired by a terrestrial portable laser scanner (PLS). This approach provides an alternative to soil rut manual measurements. Two skid trails, that differed by the numbers of machine passes and slope were sampled. Data collection was performed before and after forest operations. The specific objectives were to: (i) assess soil compaction, and (ii) determine rutting by way of multi‐temporal high‐resolution digital terrain models (DTM) generated by PLS data. This is the first study to assess changes in soil volume via the PLS. Significant logging impacts were detected using both investigation methods (i.e., physical parameters from traditional surveys and rutting from multi‐temporal spatial analysis based on DTM). The PLS method provides a very high sampling density of the soil surface, permitting detailed spatial analysis of terrain changes. Moreover, the pre‐processing cost for PLS‐generated DTM is low in comparison to the time needed for traditional survey based on manual field measurements. PLS may be a useful instrument for soil sampling in forest monitoring applications.

Pedotransfer function for calculating the potential of volume changes in soils

The volume changes in the soils are manifested both by the formation of cracks and by the vertical movement of the soil surface. Both of these could be generally negative for engineering constructions. The Coefficient of Linear Extensibility (COLE) is used to quantify volume changes. In this work a pedotransfer function was designed to calculate the COLE potential. Calculation is based on the texture of the soil. This function was designed on the basis of 169 samples of soil samples taken at 11 locations in the East Slovak lowland.

Effect of zeolite utilization on volume change and strength properties of expansive soil as landfill barrier

A sand–Na–bentonite mixture is widely used as engineering barrier material, which usually possesses hydraulic conductivity below the regulatory limit (10−7 cm/s). However, in some areas natural Na–bentonite is not readily available; instead, an abundantly prevailing local expansive soil can be an alternative. This study assesses the suitability of a local expansive soil mixed with zeolite, easily obtained from natural reserves in Turkey, proposed to be used as a landfill liner in a semi-arid climate. The choice of zeolite is due to its already well-understood high adsorption capacity for heavy metals as well as its pozzolanicity. The volume change, strength, and hydraulic conductivity characteristics were studied with respect to durability through ageing. When an expansive soil to zeolite ratio of 0.5 was used, the results indicated improved properties with curing. Swell potential was observed to decrease by 85% within a 90 day curing period, while a 30%–34% reduction was noted in shrinkage and compressibility characteristics. The hydraulic conductivity was observed to remain below the regulatory limit under all confining pressure ranges studied, provided the curing time was at least 90 days. Moreover, the mixture attained improved strength characteristics with time, and proved to be sustainable over the period studied. Therefore, it was concluded that expansive soil mixed with zeolite could be a good alternative to sand–Na-bentonite, mainly in developing areas of growing population and environmental degradation.

A new approach to interpret the mechanical behaviour of unsaturated soil using effective stress and degree of saturation

Unsaturated soil shows complex mechanical behaviours compared to saturated soil. A number of constitutive models for unsaturated soil have been proposed. However, these models suffer limitations. In this paper, a new constitutive model has been proposed in terms of effective stress and degree of saturation based on the modelling assumption about the relationship between hardening effect and degree of saturation. The proposed volume change equation gives a new explanation for the volume change of unsaturated soil. Then, an alternative approach to simulate coupled hydraulic hysteresis and the influence of the volume change on soil–water characteristic curves is suggested. Finally, this paper presents comparisons between the model simulations and experimental data. It is shown that the proposed model represents great ability to reproduce the mechanical and hydraulic response of unsaturated soil.

An approach for modelling volume change of fine-grained soil subjected to thermal cycles

As a result of cyclic heating and cooling around the ambient temperature under drained conditions, normally consolidated and lightly overconsolidated fine-grained soils experience accumulation of irreversible volumetric contraction. Most existing thermomechanical models were developed for one heating–cooling cycle and are not suitable for multiple thermal cycles. An approach is proposed to simulate the volume change of fine-grained soil induced by thermal cycles. In the proposed approach, a thermal stabilization line is introduced to control the stabilized volumetric contraction under thermal cycles. Comparison with experimental results shows that the proposed approach can reproduce well the cumulative feature of volumetric contraction of fine-grained soil subjected to thermal cycles.

Soil organic matter accumulation in relation to changing soil volume, mass, and structure: Concepts and calculations

Change in soil organic matter (SOM) stocks over time is a critical issue for soil fertility, soil development (pedogenesis) and the global carbon (C) cycle. Measuring such change typically relies on sampling to constant depth (CD) which is well known to be inaccurate if bulk density (BD) has changed between sampling sites or times. The usual solution to this problem is to sample an equivalent mass (EM), but in most cases soil mass also changes over time. Indeed, the whole point in measuring ΔSOM is to quantify a change in C mass. As SOM accumulates, soil volume increases (soil dilation) unless all added SOM fills in existing pores. Soil dilation as a result of root ingrowth is well documented in the geological literature but has rarely been considered in conjunction with studies of ΔSOM. Other processes that can alter soil volume include eluviation, bioturbation and dissolution/decomposition of both mineral and organic soil particles.Here, we present a method (the volume/mass corrected or VMC method) for calculating potential effects of processes that alter soil volume (V) and/or mass (M) on calculated values for ΔC and other soil characteristics. We first present a hypothetical example to illustrate the expected differences in soil V, M, bulk density (BD), porosity and ΔC when determined via CD, EM, and VMC methods. We then compare these three approaches for assessing the actual changes in soil characteristics across four soil chronosequence studies in which ΔV was actually measured, allowing ΔC to be calculated correctly. Results show errors of −75% to +49% in ΔC had the profiles been sampled via the CD method and even larger errors (−87% to +54%) had they been sampled via the EM method. Studies where V had increased (dilation) generally showed underestimates for ΔC for both CD and EM methods, whereas those where V had decreased (collapse) over time showed overestimates for ΔC for the CD and EM methods. Results are discussed in light of the few laboratory, field, and simulation studies comparing effects of changes in soil volume on ΔC measurements as well as the processes that cause changes in soil V.We hope that the VMC method provides a conceptual framework for addressing the interplay between changes in soil volume, porosity, and structure, one that will provide the foundation for a new set of mechanism-based SOM models that take into account changes in soil volume, mass, and physical structure across a wide range of spatial and temporal scales.

Volume Change Measurement in Triaxial Tests by Monitoring Cell Fluid Volume Based on Viscoelastic Behavior of the Test Setup

A novel procedure was developed to measure the total volume change of the unsaturated soils in triaxial testing. The principle of the proposed method was based on cell fluid volume measurements corrected by the assumption of viscoelastic behavior for the triaxial setup. Calibration and parameter determination procedures of the model are devised, and the presented model is implemented into a MATLAB code. The proposed method was validated through a series of consolidated drained triaxial tests on saturated specimens, by comparing the changes in volume measurement of proposed method and conventional measurement (pore fluid). The accuracy in volume measurement during consolidation and shear stages of these tests was between 0.09 and 0.32 cm3, which is on par with or better than more complex and expensive alternatives found in the literature. Repeatability of the proposed technique in measurement of the volume change was also investigated through a series of suction controlled unsaturated soil tests.

A new bounding surface model for thermal cyclic behaviour

Summary To accurately predict soil volume changes under thermal cycles is of great importance for analysing the performance of many earth structures such as the energy pile and energy storage system. Most of the existing thermo-mechanical models focus on soil behaviour under monotonic thermal loading only, and they are not able to capture soil volume changes under thermal cycles. In this study, a constitutive model is proposed to simulate volume changes of saturated soil subjected to cyclic heating and cooling. Two surfaces are defined and used: a bounding surface and a memory surface. The bounding surface and memory surface are mainly controlled by the preconsolidation pressure (a function of plastic volumetric strain) and the maximum stress experienced by the soil, respectively. Under thermal cycles, the distance of the two surfaces and plastic modulus increase with an accumulation of plastic strain. By adopting the double surface concept, a new elastoplastic model is derived from an existing single bounding surface thermo-mechanical model. Comparisons between model predictions and experimental results reveal that the proposed model is able to capture soil volume changes under thermal cycles well. The plastic strain accumulates under thermal cycles, but at a decreasing rate, until stabilization. Copyright © 2017 John Wiley & Sons, Ltd.

Modelling volume changes of sand under thermal loads: a preliminary attempt

Within the critical state framework, some thermo-mechanical models have been developed to simulate thermal volume changes of saturated soils. Most of the existing models are verified through the experimental results of silt and clay, and they cannot well capture the behaviour of sand under thermal loads. In this study, an elastoplastic model is newly proposed to predict thermally induced volume changes of saturated sand. The key component of the new model is the introduction of a state-dependent threshold temperature, TR, which can be determined experimentally. The TR is found to increase with an increase in the state parameter, which is defined as the difference between the current void ratio and the critical state void ratio. Depending on the state parameter, heating would induce overall contraction at temperatures below TR, but only cause overall expansion when the temperature is higher than TR. When the maximum temperature experienced by the soil specimen, Ty, is lower than TR, heating would induce not only elastic but also plastic strains. The plastic modulus becomes larger when the difference between Ty and TR is smaller. When Ty is larger than TR, sand response becomes essentially elastic. The new model is applied to simulate the behaviour of Toyoura sand under heating at different stresses and densities. It is shown that the measured and computed results are fairly consistent. The new model is able to capture well the state-dependent volume changes of sand under thermal loads.

Coupled infiltration model of unsaturated porous media for steady rainfall

Unsaturated soil slopes introduce complex hydro-mechanical coupled processes which greatly alter matric suction distribution of an unsaturated soil during rainfall. In order to investigate matric suction and volume change of unsaturated soils, a two-dimensional hydro-mechanical coupled infiltration model (YS-Slope) is developed by incorporating the hydraulic and mechanical characteristics of unsaturated soils, such as the soil-water characteristic curve, permeability function, shear strength, and porosity. Special attention is given to the porosity-dependent permeability function of unsaturated soils. In addition, in order to highlight effectiveness of YS-Slope and coupling effects of hydro-mechanical processes on the infiltration behavior of unsaturated soils, a series of infiltration analyses for a soil column under various soil properties is conducted and their results are compared with those of commercial software, GEO-SLOPE (2012). The results of the numerical analyses show good agreement with data from the analytical solution and laboratory tests, which indicates that the proposed model is appropriate for use in the simulatfion o the infiltration of rainwater into deformable soils. The transient seepage and rainwater flow in deformable soils are influenced by the volume change of the soil. The change in matric suction on a slope due to rainfall infiltration influences change in effective stress while the effective stress alters seepage processes according to hydraulic properties. The results indicate that hydro-mechanical coupled behavior of soils has a positive effect on the stability of unsaturated soil slops during rainfall.

A contribution to understanding the origin of platy structure in silty soils under no tillage

In silty soils under no tillage (NT), platy (P) soil structure is widespread and constrains water infiltration. Our objectives were (i) to evaluate how traffic and the presence of crop residues influence P structure development in the field and (ii) to characterize changes in soil structure caused by alternation of wetting and drying (w-d) periods for two topsoil layers of a silty soil and two compaction levels in the laboratory. The five-year field experiment was carried out on a Typic Argiudoll under NT and the structure of the A horizon was analyzed using visual soil evaluation (VSE) both before and five years after two traffic levels were applied to four crop sequences. The laboratory experiment of w-d cycles was carried out with two disturbed layers of a Typic Argiudoll, which was repacked to achieve two different bulk densities, and the columns were subjected to 5, 10, or 15 w-d cycles. In the field experiment, the P structure was clearly identified by VSE and corroborated by shear strength and bulk density measurements. The proportion of P structure increased until about 50% of the A horizon after 5 years, irrespective of the traffic or presence of crop residues at the expense of the Φ structure proportion. In the laboratory, consecutive w-d cycles caused changes in soil volume, cracking of the soil surface, and formation of P structure of variable thickness up to 20mm, confirming that alternation of w-d periods can cause structural modification of the silty soil, in particular horizontally oriented cracks. The number of w-d cycles increased the thickness of the P structure in the upper layer (R2=0.55) and in the compacted treatment (R2=0.81). The results obtained constitute important progress in the understanding of the evolution of P structure of silty soils under NT.

Volume changes of an unsaturated clay during heating and cooling

Thermally induced soil volume changes can have significant influence on many geotechnical structures. So far, research on thermal volume changes of unsaturated soil is very limited, particularly at temperatures lower than typical room temperature (23°C). The principal objective of this study is to investigate the volumetric behaviour of normally consolidated intact and recompacted low-plasticity clay specimens (loess soil) over a wide thermal cycle ranging from 5 to 53°C using a modified double-cell triaxial apparatus. It is found that contractive volumetric strain increases as the temperature increases. During the cooling process, soil volume keeps contracting until the temperature decreases to 5°C. Different from previous studies in the literature on saturated remoulded illite and natural silty clay, a plastic contraction at a much higher rate is observed from 13 to 5°C for both recompacted and intact loess specimens. The plastic volume changes during cooling are probably because cooling-induced contraction of soil particles leads to particle rearrangements in loess. Moreover, the cooling-induced plastic volume change, which only occurs when the cooling temperature is less than a critical value (13°C for the test conditions considered in this study), cannot be captured by the existing thermo-mechanical models, which predict elastic contraction during cooling. A new yield surface (temperature decrease) is proposed to simulate the observed elastoplastic behaviour during cooling.

Particle‐scale effects on global axial and torsional interface shear behavior

SummaryAn extensive literature on the shear behavior of continuum–particulate interfaces has been developed during the last four decades. However, relatively limited work regarding the behavior of interfaces under different loading conditions has been published. This paper presents a discrete element modeling study, along with comparisons from experimental data, of interface behavior under axial and torsional drained loading conditions. Detailed studies allow for links between micro‐scale particle behavior and observed global response to be developed and for the latter to be evaluated in light of particle–particle and particle–continuum interactions. The results of this study indicate that axial and torsional interface shear induce inherently different loading conditions, as shown by the different failure envelopes, stress paths, and induced soil volume changes and deformations. Furthermore, the results presented in this paper indicate that particle‐level mechanisms, such as particle rotations and contact slippage, play different roles in axial and torsional shear. Coordination number, polar histograms, particle displacements, particle rotations, and local void ratio measurements provide further insights into the fabric evolution, loading conditions, and failure mechanisms induced by these two shear modes. This study expands the current understanding of interface behavior and discusses potential improvements to geotechnical systems that leverage the characteristics of different imposed loading conditions. Copyright © 2016 John Wiley & Sons, Ltd.

Thermal volume change of poorly draining soils II: Model development and experimental validation

This study presents the development of an alternative constitutive model for predicting the thermal volume change of saturated and unsaturated soils using the concept of thermally-accelerated secondary compression. The model requires observation of the secondary compression response prior to drained heating to estimate the coefficient of secondary compression. The model was found to successfully capture the trends in thermal volume change arising from accelerated secondary compression resulting from prior mechanical loading for unsaturated, compacted Bonny silt. The model was also used successfully to represent data from the literature for normally consolidated and heavily overconsolidated soils prepared with different loading paths.