Precompression Stress Research Articles

In search of a sound scientific basis for quantification of soil precompression stress

AbstractSoil compaction is a serious threat to soil functions and ecosystem services. Persistent soil deformation takes place when mechanical stress exceeds soil strength. Risk assessment models typically assume soil to be elastic to a precompression stress level and plastic above this threshold. Currently used procedures for estimating soil precompression stress imply applied stress in a logarithmic form that has been criticized. We performed uniaxial, confined compression tests on 117 soil samples with a well‐defined stress history. Strain and stress were recorded at 200 levels of stress in the range of 0–1 MPa. Soil compressibility was calculated as incremental strain per incremental stress, using stress in arithmetic scale. For a given sample, a local minimum in compressibility appeared close to the preload applied to the sample prior to the compression test. This yield stress is suggested as an expression of soil precompression stress. Not all samples displayed a yield stress. Primarily soil exposed to a high preload did not exhibit a clear stress level with change in compressibility. This indicates that a physically based stress level pointing out a transition to plastic conditions will not exist for all soils. Our observation calls for new concepts in risk assessment. Tests with interpolation between a limited number of data points indicate that the yield stress—if existing—may be detected from classical compression data.

Development of a novel crack-resistance technique for concrete slab in the hogging moment region of continuous composite beam

Composite steel-concrete beams offer distinct mechanical advantages. However, concrete cracking in the hogging moment region limits the composite performance of the material. This study presents an innovative technique for enhancing the crack resistance of continuous steel-concrete composite beams, which involves the prestressing of the concrete slab in the hogging moment region through post-tensioning. Following the completion of the concrete slab in the sagging moment region, the prestress is released, thereby preserving pre-compression stress in the hogging moment region without the need for long-term prestressing. This technique is enhanced using uplift-restricted and slip-free connectors, which improve the efficiency of pre-stress introduction. Experimental tests were conducted on composite beams employing this novel technique, alongside numerical simulations. The results indicated that the proposed technique significantly mitigated concrete cracking in the hogging moment region. Specifically, the cracking load of the specimen using the new technique increased by 467 % compared to the traditional composite beam specimen, accompanied by a substantial reduction in both the quantity and width of cracks. Other primary mechanical performance indicators remained relatively similar; however, the new technique exhibited a 14 % increase in the ductility coefficient compared with the traditional method. Additionally, this technique influenced interface slip, moment redistribution, and strain response along the cross-section in both the hogging and sagging moment regions. The numerical results aligned closely with the experimental data, confirming their accuracy and effectiveness. The simulations provided solutions for various construction stages by incorporating different connection constitutive models with adequate precision. A parametric analysis was conducted, revealing a design method for the innovative technique.

Assessing the compression properties of Gravel-bearing forest soil in northeast China’s seasonally frozen regions under Freeze-thaw cycles and varying gravel content

Due to climate change, human activities and natural disturbances in high-latitude permafrost and seasonally frozen areas are gradually increasing, attracting more attention from scholars. However, research primarily focuses on soil biology and chemistry in these regions, with limited exploration of their mechanical properties, especially compression properties. This study aims to evaluate the effects of gravel content and freeze–thaw (F-T) cycles on the compression properties of coarse-grained layered forest soil from northeast China’s seasonally frozen regions, with the goal of predicting the soil’s compressive changes under heavy mechanical loads. Specifically, using uniaxial confined compression tests (UCCT) on 252 disturbed soil samples (including two soil layers: AB and Bhs; six gravel contents; and seven F-T cycles), three characteristic compression coefficients—precompression stress (σpc), compression index (Cc), and swelling index (Cs)—were measured. Additionally, scanning electron microscopy (SEM) was used to analyze the mesostructure evolution of coarse-grained gravel-bearing soil. Volume changes of samples were measured after 15F-T cycles with varying gravel contents. Results indicate non-linear effects of gravel content and F-T cycles on σpc. Gravel content below 50% positively influences σpc, while content above 50% increases soil pore content, decreasing σpc. Cc and Cs exhibit an approximately negative correlation with gravel content and initially increase followed by a decrease with more F-T cycles. Moreover, the σpc and Cc of the AB layer are higher than those in the Bhs layer, likely due to differences in clay and organic carbon contents. Notably, the observed trends differ from previous studies on other soil types such as farmland and paddy fields. This study fills a gap in understanding the compression characteristics of layered gravel-bearing forest soil in seasonally frozen regions, providing valuable insights for evaluating soil compression in both seasonally frozen and permafrost regions, and understanding mechanical vehicle-soil interactions. It also lays the theoretical groundwork and provides data support for constructing compression models of layered gravel-bearing forest soil.

Hybrid multilayer magnetoelectric coupling based on magnetostrictive materials

Multiferroic materials have a unique ability to combine two or more ferroic orders within the same phase. Specifically, magnetoelectric (ME) materials exhibit a unique combination of three ferroic orders in their response to magnetic, elastic, and electric fields. This study focuses on a finite element investigation of a hybrid multilayer ME coupling, incorporating two different magnetostrictive materials in a single composite. The composite includes Nickel, exhibiting negative magnetostriction, leading to an increase in pre-compressive stress, easy machinability, and cost-effectiveness. Additionally, Terfenol-D is utilized due to its characteristic property of high magnetostrictive strain when exposed to an external magnetic field. The result of this study shows that this hybrid ME structure has an ME coefficient of 804 mV/cm ⋅ Oe without pre-stress and ME coefficient is increased to 32.64 V/cm ⋅ Oe by applying pre-stress while retaining cost-effectiveness. The analysis in this particular work also suggests promising applications for energy harvesting and magnetic field sensing.

Research on topology optimization strut-and-tie model and prestress construction for cable-pylon anchorage zone of Fengshuba Bridge

To address the challenges associated with accurate load-bearing capacity calculation and prestress design for the cable-pylon anchorage zone of cable-stayed bridges, a case study focusing on the Fengshuba Bridge is conducted. Utilizing the Solid Isotropic Material with Penalization (SIMP) variable density topology optimization method, a strut-and-tie model (STM) is constructed for the cable-pylon anchorage zone. This model is subsequently employed to verify load-bearing capacity of the struts and nodes within the cable-pylon anchorage zone, as well as to calculate the required quantity of circumferential prestressing tendons. Additionally, a spatial segmental finite element model is established for the cable-pylon anchorage zone to perform a detailed analysis of prestressed structural optimization. This analysis determines various structural details, including the arrangement of prestressing tendons along the height, the design for prestressing blind zones, and the quantity of prestressing tendons. Subsequently, the optimized model is subjected to stress verification. The research results indicate that the adoption of dispersed tendon arrangement results in reduced principal tensile stress within the cable-pylon anchorage zone, in contrast to the concentrated tendon arrangement. The introduction of short prestressing steel bundles within the conduit of prestressing blind zones uniformly enhances the pre-compressive stress on the cable-pylon side wall. Due to the Poisson effect of materials, it is necessary to arrange prestressing tendons appropriately within the cable-pylon anchorage zone. Arranging prestressing steel bundles according to the proposed STM and structural optimization method adequately fulfills the structural force requirements of the cable-pylon anchorage zone.

Mechanical Resistance to Penetration for Improved Diagnosis of Soil Compaction at Grazing and Forest Sites

Penetrometers and penetrographers are widely used to measure soil resistance to penetration, but the results are associated with other soil properties (such as bulk density, water content, and particle size distribution). Thus, for an adequate interpretation of results, site-specific studies are necessary to identify which properties are more related to soil resistance. We aimed to measure the resistance to penetration of a Typic Paleudalf under distinct soil uses and to identify soil properties that influence soil resistance. The soil uses in this study included anthropized forest (composed of tree and shrub species), pasture (5-year-old pasture), Eucalyptus 20 (a 20-year-old Eucalyptus saligna stand), and Eucalyptus 4.5 (a 4.5-year-old Eucalyptus saligna under the second rotation). Soil resistance to penetration was measured with an impact penetrometer, and the data were correlated with other physical and mechanical properties of soil, such as the particle size, soil moisture, air permeability, saturated hydraulic conductivity, porosity, bulk density, precompression stress, and compressibility index. We observed that a resistance of 1.3 MPa matches with other soil property values corresponding to soil compaction, and values greater than 1.3 MPa were verified at depths of 0–8 cm for pasture and 8–30 cm for Eucalyptus 4.5. Analyzing all soil uses together, the correlation was significant (p < 0.05) with gravel (r = 0.34), silt (r = −0.32), clay (r = 0.26), gravimetric moisture (r = −0.27), macroporosity (r = 0.24), and soil bulk density at the end of the compressibility test (r = 0.27). The penetrometer is useful for evaluating the physical conditions of soil, but we highlight that soil resistance is influenced by factors such as particle size and soil moisture, as examples. We recommend using a set of soil properties for a better interpretation of penetration resistance data and to support decision-making regarding soil management.

Current limitations and future research needs for predicting soil precompression stress: A synthesis of available data

Precompression stress, compression index, and swelling index are used for characterizing the compressive behavior of soils, and are essential soil properties for establishing decision support tools to reduce the risk of soil compaction. Because measurements are time-consuming, soil compressive properties are often derived through pedotransfer functions. This study aimed to develop a comprehensive database of soil compressive properties with additional information on basic soil properties, site characteristics, and methodological aspects sourced from peer-reviewed literature, and to develop random forest models for predicting precompression stress using various subsets of the database. Our analysis illustrates that soil compressive properties data primarily originate from a limited number of countries. There is a predominance of precompression stress data, while little data on compression index or recompression index are available. Most precompression stress data were derived from the topsoils of conventionally tilled arable fields, which is not compatible with knowledge that subsoil compaction is a serious problem. The data compilation unveiled considerable variations in soil compression test procedures and methods for calculating precompression stress across different studies, and a concentration of data at soil moisture conditions at or above field capacity. The random forest models exhibited unsatisfactory predictive performance although they performed better than previously developed models. Models showed slight improvement in predictive power when the underlying data were restricted to a specific precompression stress calculation method. Although our database offers broader coverage of precompression stress data than previous studies, the lack of standardization in methodological procedures complicates the development of predictive models based on combined datasets. Methodological standardization and/or functions to translate results between methodologies are needed to ensure consistency and enable data comparison, to develop robust models for precompression stress predictions. Moreover, data across a wider range of soil moisture conditions are needed to characterize soil mechanical properties as a function of soil moisture, similar to soil hydraulic functions, and to develop models to predict the parameters of such soil mechanical functions.

Risk assessment of soil compaction due to machinery traffic used in infield transportation of sugarcane during mechanized harvesting

Soil stress imposed by tire-soil contact from transshipment vehicles used in mechanized sugarcane harvesting results in increase in the degree of compactness. In this study we aimed to: (i) estimate the magnitude and propagation of vertical stress into soil caused by sugarcane transshipment wheeling; and (ii) assess the risk and occurrence of soil compaction in an Oxisol of southeastern Brazil. Three tractor-trailers with a carrying capacity of 10, 21, and 30 Mg, and an autonomous truck-trailer with a carrying capacity of 20 Mg were evaluated as field traffic treatments. For each treatment, magnitude and distribution of vertical soil stress (σz) and soil strength (precompression stress, σp) were predicted by modeling estimation and risk of compaction was assessed by σp/σz relationship. The occurrence of soil compaction was evaluated based on measured changes in the bulk density and macroporosity (equivalent pore diameter > 50 μm) up to 0.70 m deep after wheeling. Estimates indicated that the autonomous truck applied stresses that reached 595 kPa at the soil surface beneath the centerline of the tire, imposing the greatest risk of compaction up to a depth of 0.35 m depth. The stresses at the soil surface beneath the centerline from the tractor-towed trailer tires ranged from 275 to 279 kPa, imposing a risk of compaction that did not exceed 0.29 m depth. All assessed transshipment configurations promoted soil compaction, detected by increases in the soil bulk density and decreases in the macroporosity, even at greater depths where risk prediction had not alerted to the soil compaction. The most significant impact on soil compaction was observed for the autonomous truck-trailer and the tractor-towed trailer with a carrying capacity of 30 Mg, also affecting subsoil, as evidenced by a relative increase in soil bulk density of 5 % and 7 % in the 0.30−0.50 m and 0.50−0.70 m layers, respectively, and a relative reduction in macroporosity of 40 % and 50 % in these same soil layers.

Investigation into the seamless construction for hundred-meter scale super-length raft structure based on magnesia expansive agent concrete

This research introduces an innovative construction method based on magnesia expansive agent concrete for the seamless construction of hundred-meter scale super-length raft structures, corroborated by the on-site test. The basic principle of this construction method is to use the pre compression stress generated by magnesia expansive agent to offset temperature and shrinkage stress. A temperature-strain monitoring system was employed to gather data, affirming the technique’s applicability and safety. Through the examination of temperature and strain dispersion trends in super-length raft structure, recommendations for the configuration of temperature-strain sensors have been put forth. Through the scrutiny of the temporal evolution pattern of temperature, the specific temporal and spatial coordinates that warrant particular vigilance during the surveillance of the raft’s inner-surface temperature difference were identified. Upon evaluating the correlation between strain dispersion and strain-temperature differential in the raft’s thickness dimension, a novel temperature control index (the bottom-surface temperature difference) was introduced. The threshold for this metric was established at 30°C, derived from empirical test outcomes conducted on-site. Furthermore, the critical regions for monitoring the bottom-surface temperature difference were specified.

Evaluation of electrochemical performance of supercapacitors from equivalent circuits through cyclic voltammetry and galvanostatic charge/discharge

Conventional methods used to analyze electrochemical performance of supercapacitors are complex and cannot illustrate the asymmetrical behavior of charge and discharge curves and the variation of resistance with scan rate and current density. In this work, we propose a simple method to calculate total capacitance and internal resistance of supercapacitors with equivalent circuits and discuss the mechanisms responsible for the asymmetry of galvanostatic charge discharge (GCD) curves. Using the equivalent circuits, we demonstrate the feasibility of analyzing electrochemical performance of supercapacitors from the current-voltage curve for cyclic voltammetry (CV) and the GCD curves for galvanostatic cycling. A series of supercapacitors are constructed, in which the electrodes are pre-compressed under a compressive stress in a range of 1– 7.5 MPa. The experimental results reveal that the total capacitance of the supercapacitors increases with increasing the pre-compressive stress and validated the proposed method. Increasing the pre-compressive stress likely can improve the electrochemical performance of supercapacitors. The results from the analysis with the analytical relations for the resistance of the resistor in parallel connection in the three-element circuit approaching infinity exhibit similar trends to the corresponding ones from the conventional methods in contrast to the results from the three-element circuit, which exhibit different trends. The three-element circuit with the resistor in parallel connection approaching infinity can be used to analyze the electrochemical performance of supercapacitors for both the CV and GCD operational conditions.

Stress state analysis and symmetrical optimization of double-row non-symmetrical arrangement of anchorage slot in concrete lining structure

The role of the anchorage slot is to fix the anchorage and tension anchor rope, which is the weakest link of the concrete lining structure. The stress state of the anchorage slot area in the construction and operation stages of the 2# sand discharge of the Xiaolangdi Project was analyzed by modeling in this paper. The results showed that the stress state of the anchorage slot area was the most complex. The tensile stress was generated in the radial direction of the concrete lining during the construction period, and the circumferential pre-compression stress was unevenly distributed along the thickness direction. During the operation period, when the backfill concrete at the anchor slot and the lining jointly bore the internal water pressure, a tensile stress of 0.89 MPa was generated in the inner anchorage slot area of the lining, which was less than the tensile strength of the concrete itself. Finite element calculation results were compared with the field-measured data, and the results were essentially the same. Finite element analysis software was used to optimize the double-row asymmetric arrangement of the anchorage slots into a single-row symmetrical structure. The results showed that the angle of the complex stress area of the lining is reduced by about 75%. The optimized single-row symmetrical anchorage slot layout was safer, and the pre-stressing distribution was more uniform.

Steel tubes subjected to combined axial compression and bending

The bending response characteristics of ten tubes subjected to axial pre-compressive stresses ranging from 0 to 45 % of the tube wall yielding stress (σr) were investigated experimentally. The tubes had different diameter-to-thickness ratios of 42 and 56 and length-to-diameter ratios of 15 and 20. The results showed up to a 31 % reduction in the bending capacity of tubes when σr increased from 0 to 45 %. Experimental interaction diagrams for axial pre-compression and bending moment capacity were compared with the proposed relationships in different codes, with the results showing a substantial load-bearing capacity of tubes beyond the codes' predictions.

Estimating pre-compression stress in agricultural Soils: Integrating spectral indices and soil properties through machine learning

Soil compaction resulting from heavy machinery use in agricultural and forestry operations poses a significant threat to sustainable agriculture. Advancements in remote sensing technology have enabled the acquisition of vegetation, water, and soil spectral indices, which offer valuable insights into soil properties. This study focuses on estimating the pre-compression stress (Pc) by developing pedotransfer functions (PTFs) using Sentinel-2 satellite-derived spectral indices and soil properties (clay, CaCo3, and bulk density) as inputs. Two machine learning methods, Random Forest (RF) and Boosted Regression Tree (BRT), are employed for the estimation. A total of 140 surface soil samples were collected randomly from agricultural areas in Qazvin province, Iran. The results indicate that the BRT method outperforms the RF method in terms of accuracy. The estimation of Pc achieved better results when the Redness Index (RI) was used as the soil spectral index and the Surface Water Capacity Index (SWCI) was employed as the water spectral index, along with the soil properties as inputs for PTF3 and PTF11. In the training and testing steps, the root mean square error (RMSE) decreased from 0.100 and 0.114 (kPa) in PTF1 to 0.071 and 0.098 in PTF3, and 0.072 and 0.097 in PTF11, respectively. These outcomes demonstrate the practical applicability of estimating Pc through the integration of soil properties and spectral indices. The findings highlight the potential of remote sensing technologies, such as spectral indices, as effective and cost-efficient tools for studying soil compaction. The proposed methodology contributes to our understanding of soil compaction processes and provides valuable insights for developing sustainable land management strategies. This study has implications for the agricultural sector and offers practical solutions to mitigate soil compaction and its detrimental effects on agricultural productivity.

Effect of pre-stress on surface integrity in micro milling: Modelling and experimentation

Recent years have witnessed rapid growth in microscale manufacturing, particularly in the biomedical, electronics and aerospace industries. Therefore, it is required to improve the capabilities of micro-cutting processes such as micro-milling to generate intricate features with high surface quality. The surface integrity of the machined materials is influenced by the cutting conditions, tool geometry and material properties. The novelty of the proposed work is to improve the surface finish and compressive residual stress of the milled slot by tailoring the pre-compressive stress condition. Ultrasonic-assisted abrasive peening is used to tailor the residual stress and obtained grain refinement on the surface. The micro-milling is performed on the peened surface of Ti-6Al-4V, Al-6061, and OFHC-Cu to investigate the surface roughness and residual stress. A hybrid model is developed to estimate the surface roughness considering the effect of tool geometry, process parameters, size effect and workpiece microstructure. Induced residual stress at the machined surface is simulated through the finite element (FE) method. Moreover, the FE model simulated the minimal chip thickness and contact pressure at the flank face and is deployed as an input to the analytical model for estimation of surface roughness. The pre-deformed material by peening reduced the surface roughness by 35 to 42 % on different materials and improved compressive residual stress due to grain refinement. The predicted average surface roughness and residual stress are validated with experimental results.

Does no-tillage mitigate the negative effects of harvest compaction on soil pore characteristics in Northeast China?

Optimizing tillage management is one way to reduce the risk of soil compaction due to traffic load in Northeast China. In this study, we aimed to examine the responses of precompression stress (σpc), compression index (Cc), pore morphology (>30 µm), air-filled porosity (εa60), air permeability at matric potential of − 60 hPa (ka60) and saturated hydraulic conductivity (Ks) to harvest traffic on soil from two contrasting tillage practices using a 10-yr old field experiment. After the crop was harvested with a combine harvester, undistributed soil cores were collected in the 0–10 and 10–20 cm layers from non-traffic and traffic zones of no-tillage (NT) and moldboard plough (MP) plots. In the non-traffic zone, the MP management showed greater total porosity (εtotal), εa60 and macroporosity (εX-ray) than the NT. There were no differences in pore connectivity, mean pore size and ka60 of the 0–10 cm layer and in Ks of the 0–20 cm layer between the two tillage practices, however, more biopores were observed under NT. Harvest traffic showed no significant effects on NT soil. In the MP plots, the εtotal, εX-ray, and pore connectivity, were decreased and pores larger than 0.15 mm were preferentially compacted. As a result of traffic, MP soil displayed lower ka60 in the 0–20 cm layer and lower εX-ray and connectivity in the 10–20 cm layer. In the NT management, the pore system had greater water and air conduction efficiencies and stable properties. Thus, compared to MP, NT can mitigate the negative effects of harvest compaction on soil in Northeast China.

Impact of sulfate attack on flexural behaviour of CFRP strengthened concrete beams

The effect of exposing concrete beams (150 × 250 × 1600 mm), retrofitted with parabolic and straight profiles of near-surface-mounted (NSM) carbon-fibre-reinforced polymer (CFRP) ropes, to mild and moderate stages of cyclic sulfate treatment (CST) is investigated as a part of an ongoing comprehensive study. A total of 16 beams were used to evaluate structural performance for strengthened beams before and after exposure to CST for about 4 and 11 months when free concrete expansions of about 2008 and 8690μ strain, respectively, were attained. Mechanical tests on concrete cylinders showed increased brittleness of concrete as a result of the CST, with 6% and 15% reductions in compressive strength after exposure to mild and moderate stages of CST, respectively. The load capacity and stiffness for beams exposed to the mild stage of CST were slightly decreased, yet were noticeably increased for those exposed to the moderate stage of CST, owing to the significant precompressive stresses induced in concrete. In contrast, rotational ductility and toughness were progressively decreased as the treatment progressed. Generally, concrete beams, strengthened with curved and straight NSM CFRP ropes, cannot retain their overall structural performance under moderate levels of sulfate attack.

Effective stress and shear strength parameters of unsaturated soils as affected by compaction and subsequent shearing

AbstractWheeling induced compression and shearing forces are main stresses accounting for soil deformation and changes of hydraulic, gaseous and thermal properties. There are reports about the combined effects of compaction and subsequent shearing on soil hydraulic properties, but their consequences on soil strength properties (i.e., effective stress and shear strength) need to be further analysed. This study investigated the dynamics of soil mechanical properties as affected by pore water pressure () during compaction and shearing. Soil samples from an A‐horizon of Gleysols derived from glacial sediment and a Stagnic Luvisol from loess were analysed. The repacked and structured samples were compressed under static and cyclic loading and then sheared at two speeds (0.3 and 2.0 mm min−1) with three loading levels (50, 100, and 200 kPa). During each stress application, the , chi factor (χ) and effective stress () were measured and calculated. The shear strength (), angle of internal friction () and cohesion (), were determined and fitted by the Mohr–Coulomb failure criterion. The results showed that compaction and shearing increased and χ in all homogenized soils while on structured soils this phenomenon only occurred when the applied loading stress exceeded the soil precompression stress. The increased resulted in soil hydraulic and mechanical stresses, which ultimately reduced the , especially at −6 kPa initial matric potential. Soils with finer texture, higher loading stresses and faster shear speed normally exhibited more reduced values. The structured soil had higher values with higher and compared to the homogenized soils. The changes of at high loading stress (i.e., 200 kPa) may overlap the normal pattern of the Mohr–Coulomb failure line that results from the theoretical Mohr envelope. Thus, to minimize the destruction of soil structure and stability induced by wheeling, it is important to consider field water content, traffic loading and wheeling speed.

CA–MQL grinding of zirconia engineering ceramics under precompressive stress

CA–MQL grinding of zirconia engineering ceramics under precompressive stress

Structure dependent changes in pore water pressure due to stress application and consequences on the effective stress

Divergent processes in soils affect the pore systems and alter hydraulic, gaseous and thermal fluxes as soon as the internal soil strength (= the precompression stress) is exceeded. Especially the intense changes of the hydraulic flux properties during soil deformation result in retarded soil settlement due to their dependency on time and stress dependent changes in pore water pressure as well as the water saturation degree. These processes depend besides on texture and bulk density especially on aggregation level, but the linkage between changes in effective stress and soil structure in various soil horizons defined by the precompression stress is still not analyzed and is therefore subject of this investigation. In this study, stress strain and pore water pressure data from almost 900 (predrained to −60 hPa) samples from arable top- and subsoil horizons subjected to oedometer compaction tests are evaluated. Among others, hydraulic stress parameters like the effective stress and χ-factor are calculated and linked to the precompression stress values. Results are presented for 6 differently aggregated soil horizons. Ap horizons with a very weak soil structure document no defined soil rigidity due to a reduced functionality of the pore systems and a stress dependent weakening, while especially the soil deformation behavior of sandy Bw horizons is less controlled by the precompression stress and the calculated effective stresses. The E and Bg horizons indicate anthropogenic impacts on structure properties and the related stress-strain behavior. While it could be documented that the enhanced strain coincides with an increase in the calculated χ-factor, it does not coincide in correspondingly enhanced effective stresses due to the non- equilibrated pore water pressure even after 45 h of increasing stress application. We conclude that further investigations are needed to quantify the highly dynamic interactions between the stress dependent hydraulic conductivity / pore water pressure ratio and the impact on the stress affected pore water pressure reequilibration. Furthermore, the contribution of the sorptive potential in soils with more negative initial matric potential on these changes would elucidate also the physico chemical impacts on soil strength more clearly especially under drier soil conditions.

Soil water diffusivity as function of the pore size distribution and precompression stress

The idea of the study was to combine the saturation-dependent hydraulic conductivity, K(Se), as intensity parameter with the volume fraction related to the fractional capillary potential for each of the characteristic pore size classes that based on the matric flow potential, φ, and the soil water diffusivity, D(θ). The analysis is focused on the soil hydraulic properties of differently textured soils with differences in the pore size distribution, PSD. The soil-moisture retention, θ(h), and K(Se) as function of the effective saturation were determined with undisturbed samples for each soil profile and horizon and fitted by Mualem–van Genuchten type analytical function. The results indicate a strong linear relationship between φ values and the soil water diffusivity, D(θ), of soils with its volume fractions of macropores (r2: 0.65–0.91), wide coarse pores (r2: 0.55–0.77), and medium pores (r2: 0.83–0.85). The precompression stress, Pc, as mechanical soil strength parameter affects the soil water diffusivity of the chosen datasets especially in the wide coarse pore range (r2: 0.85). The results suggest that the PSD’s-related φ and D(θ) values are affected by both textural and structural effects. The soil water diffusivity itself strongly depends on the PSD and is an effective link between soil’s intensity and capacity parameter.