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The piezocone penetration test (CPTu) is a common geotechnical field test to evaluate soil properties. In interpreting the CPTu field measurements, soil drainage conditions are mostly considered completely drained or undrained; however, partial drainage conditions govern for such soils as silts or clayey sand mixtures. Previous studies show that neglecting partial drainage conditions causes incorrect estimation of soil geotechnical parameters. Most studies have been conducted using calibration chambers and centrifuge tests on clayey soils. Due to the complications in modeling the piezocone test, few numerical studies have been performed under partially drained conditions, especially on coarse-grained soils. Among the challenges of numerical modeling of CPTu, one can mention the difficulty of modeling soil structure in large strain mode and soil–water interaction behavior. In this paper, piezocone penetration tests were modeled using the advanced hypoplastic constitutive model and finite-element method. The behavior of Firoozkooh sandy soil under different drainage conditions and relative densities was analyzed. Then, the effect of cone penetration on the surrounding soils was discussed. It was shown that drainage conditions and the soil relative densities significantly affected the trend of variations in excess pore-water pressure (EPWP) generated around the piezocone. [ABSTRACT FROM AUTHOR]

Eucalyptus (Eucalyptus spp.) leads to depletion of nutrients from the soil due to its fast growing nature. Therefore, a pot experiment was conducted to study the effect of zinc (Zn) application on clonal eucalyptus growth, biomass output and its uptake, as well as response of eucalyptus to Zn in soils of three textures. The treatments consisted of eight levels of Zn (0, 5, 10, 15, 20, 25, 30, and 35 mg kg−1 applied through ZnSO4.H2O) in a completely randomized design triplicated in soils of three distinct textures (loamy sand, sandy loam and sandy clay). The plant height, collar diameter, dry weight of shoot and roots, soil plant analysis development (SPAD) readings, Zn concentration and uptake by leaves, stem+branches and roots increased significantly with Zn application. Average dry weight of shoot and roots (31.93 and 15.12 g plant−1, respectively) was significantly highest at 15 mg Zn kg−1 whereas Zn concentration and uptake (18.35 mg kg−1 and 286.2 µg plant−1, respectively) by roots were highest at 20 mg Zn kg−1. The above parameters differed significantly among soils as sandy clay>sandy loam>loamy sand except Zn content and uptake by roots and SPAD values which were highest in sandy loam soil. Loamy sand and sandy loam soil exhibited higher Zn use efficiency, shoot biomass response and uptake response to applied Zn than sandy clay soil. It is concluded to apply 20 mg Zn kg−1 in light soil and 15 mg Zn kg−1 in heavy textured soil for better growth and productivity of eucalyptus. [ABSTRACT FROM AUTHOR]

In this letter, the authors propose a microwave sensor capable to detect soil moisture content parameter for use in precision agriculture and agricultural smart monitoring applications. The novel sensor is based on complementary split‐ring resonator metamaterial topology, microstrip line and was built under biodegradable dielectric substrate of polylactic acid for sustainable purposes. The sensing mechanism relates the sensor's resonant frequency to the soil moisture content changes over time. For experimental validation purposes, a compact sensor prototype (75 mm × 35 mm × 1.55 mm and 12 g) with fundamental resonant frequency at 958 MHz was built and submitted to calibration process on typically sandy and clay soils to get fitting models capable to estimate soil moisture content. Simulated and experimental results are presented together and show good agreement with each other. The calibration data for both soil types were processed using the least‐squares method and the proposed curve‐fitting models are capable to estimate soil moisture content levels from 5% to 20% for sandy soil and from 12% to 23% for clay soil with satisfactory accuracy, proving the device viability. [ABSTRACT FROM AUTHOR]

• GeoWATCH performs statistically better in certain soil textures. • Bias correction models were applied to the raw GeoWATCH values. • The bias correction models significantly improved performance of GeoWATCH. The US Army is required to be a good steward of the land per US Army regulation AR 200-1. Based on this regulation, Army installations need to manage lands, to reduce potential damage and impacts to water quality and habitat that may occur from training. Maneuver training does impact the vegetation and soil and this damage is directly related to soil moisture. Soil moisture is an important factor for understanding the potential for soil surface disturbance due to vehicle impacts and predicting soil resilience to vehicle traffic, however, producing accurate estimates of the spatial and temporal variation of soil moisture has historically been elusive. GeoWATCH, which stands for Geospatial Weather-Affected Terrain Conditions and Hazards (formerly DASSP), simulates soil moisture world-wide, at relatively small spatial and temporal scales. GeoWATCH uses a physics-based downscaling approach that uses weather-scale land surface model estimates of soil moisture and land surface water and energy fluxes, with high resolution geospatial data. GeoWATCH soil moisture outputs coupled with vehicle impact models, are anticipated to be useful for near-real-time estimation of ground disturbance, but will require ground validation. To validate GeoWATCH soil moisture estimates, we utilized Soil Climate Analysis Network (SCAN) gauge network soil moisture data from 127 sites across 34 states. Statistical analysis of the raw GeoWATCH output indicated the model performs statistically better in certain soil textures. Model bias is largest for sandy soils, whereas clayey soils were least biased. As a result, bias correction models were applied to the raw GeoWATCH simulated values using linear regression to predict correction factor (CF) values based on physical site characteristics. The bias correction models significantly improved the performance of the GeoWATCH soil moisture model in terms of average performance statistics and number of statistically cally unbiased sites. This process could easily be incorporated into GeoWATCH, allowing for a capability to rapidly estimate vehicle impacts and determine rehabilitation requirements by installation land managers. [ABSTRACT FROM AUTHOR]

Abstract: The fragmentation of larger soil aggregates to smaller fractions is a fundamental physical process that may occur naturally or be imposed. Soils that naturally re-structure themselves following structural damage from a homogeneous mass into a heterogeneous matrix of fine, granular and stable aggregates and pores are of great benefit. A key driving force is shrink–swell processes, particularly wet–dry cycles. Models of dynamic fragmentation have been devised. A promising model based on a threshold limiting size distribution of aggregates, with temporal- and scale-invariance, has been developed recently. We sought to assess this model with soil fragmentation test data. We sampled 12 soils from a 2km transect (Bedfordshire, UK), subjected them to physical damage by shearing and kneading, and then imposed up to 3 or 5 wet–dry cycles. We measured the aggregate size distribution and mean weight diameter (MWD) of both the whole soil fraction and the fine-scale (<5mm) aggregate fraction, selected as a key threshold size, as they fragmented. A subset of four soils was examined in more detail to assess the model predictions. Clayey soils fragmented considerably more than sandy soils, and resulted in an accumulation of fine-scale aggregates. This suggested that fragmentation was induced by shrinkage and swelling stresses impacting upon the clay fraction and that the wet–dry cycles were not able to reverse the structural damage imposed on the sandy soils. In the clayey soils the form of the distribution of fine-scale aggregates showed clear signs of temporal invariance over the wet–dry cycles. In addition, as the cumulative distributions of the fine-scale aggregates followed a power law relationship, this suggested invariance in scale. In fragmenting soils, the MWD of the fine-scale aggregates was a convincing asymptote for the MWD of the whole soil fraction. We demonstrated temporal- and scale-invariance in clayey soils that fragment upon wetting and drying and the accumulation of a resistant set of fine-scale aggregates. Such soils are likely to be better-able to recover naturally from any physical damage to their structure and will require less remedial work, and hence a lower energy input, compared to non-fragmenting sandy soils. [Copyright &y& Elsevier]

A new method of estimating the permeability of soils using an acoustic technique is proposed in this technical note. Biot’s coupled theory of mixtures from the mid-1950s, which addresses the relationship between the permeability of saturated soils and the characteristic frequency of elastic waves, is used. The characteristic frequency is determined from the attenuation versus frequency curves obtained by acoustic sweep tests. This study presents the experimental technique for measuring the characteristic frequency of soils and calculation procedure for estimating the permeability of sandy soils. This technical note holds discussion for silty or clayey soils. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) can form symbiotic relationships with roots of plants and potentially affect nitrogen (N) cycling in cropping systems. However, it is unclear how AMF influence N 2 O emissions and crop N assimilation, two key N cycling steps which are closely related to climate change and food production, under different soil management regimes. A microcosm experiment was conducted to test the effects of AMF on N 2 O emission and plant N assimilation, with wheat as a model crop, under organic (straw) amendment in soils with different textures. We found that AMF suppressed N 2 O emissions, promoted mycorrhizal N uptake and remobilization to grains and increase grain biomass under organic amendment in the sandy soil. However, AMF did not affect N 2 O emission, although increased plant N uptake, but inhibited mycorrhizal N remobilization to grains under organic amendment in the clay soil. These findings highlight that AMF have different effects on N 2 O emission and N translocation between sandy and clay soils. Appropriate soil management for mycorrhizal symbiosis in the cropping system can combat climate change and ensure food production. • AMF only reduced N 2 O in sandy soils, but not for clay soils. • AMF could promote N uptake irrespective of soil texture. • Organic amendment could promote N foraging from mycorrhizae remobilized to grains. [ABSTRACT FROM AUTHOR]

The paper examines the influence of soil strength and stiffness on the end resistance mobilised by a cone or displacement pile in a two-layered soil profile (i.e. strong soil overlying or underlying weak soil). The investigation involved a series of numerical analyses that idealise pile/ cone penetration assuming the spherical cavity expansion analogue. It is shown how the end resistance mobilised by a penetrometer in a dense sand (i.e. strong soil) varies with the number of penetrometer diameters (D) from a weak soil (assumed here to be either a loose sand or soft clay), and depends on the ratio of the steady-state penetration resistances of the strong and weak layers. The penetrometer resistance in the weak soil is not affected by an adjacent strong layer at penetrations greater than 2D. A design procedure based on a numerical parametric study is proposed, and this is subsequently shown to compare well with centrifuge test data and with previous numerical research. [ABSTRACT FROM AUTHOR]

A viscoplastic cap model of the Perzyna type was developed for simulating high strain rate behaviors of soils. An associative viscous flow rule was used to represent time-dependent soil behaviors. The viscoplastic cap model was validated against experimental data from static and dynamic soil tests. The model was also compared with soil behaviors under creep and stress relaxation with good agreement. However, the model was unable to represent tertiary creep where strain softening became significant. The model was subsequently integrated into LS-DYNA for finite-element simulations of high strain rate behaviors of sandy and clayey soils in explosive tests. The significance of strain rate effect on the soil responses is presented herein. It is concluded that the viscoplastic cap model is adequate for simulations of soil behaviors under high strain rate loading, creep, and stress relaxation, covering a wide range of time-dependent problems. [ABSTRACT FROM AUTHOR]