Soil compaction by agricultural machinery in general by and tractors in particular is an important problem in modern agricultural production. Such compaction destroys the soil structure, creates unfavorable physical parameters of the soil, and as a result, reduces crop yields. Therefore, it is important to clearly establish how the tractor wheels affect the soil. The experiments were conducted on the sandy loam soil by using CLAAS Xerion 5000 tractor with TRELLEBORG IF 900/60 R42 tires with internal pressures varying from 0.08 to 0.24 MPa in 0.04 MPa increments. To determine the stress propagation a developed simulation model was adapted to the parameters of the tractor in use. The iterative method was used for the numerical determination of the soil stress state. The impact of soil compaction starting from a 40 cm depth is not noticeable following the tractor's pass. In fact, from a depth of 40 cm, the normal stresses reach equilibration according to the developed mathematical model. From a depth of 20 cm, the soil compaction pattern is similar for all tire widths tested. Tires with a width up to 10 cm, 0.92 m wide tires compact the soil 25.4% less on average than tires with a width up 0.872 m wide tires. To the depth of 20 cm, tires with a width up the 0.92 m wide tires compact the soil 18.9% less on average than the tires with a width up 0.872 m, and to a depth of 30 cm - only 5.1% less. The tractor with a working tire width of 0.92 m and an axle load of 119.5 kN generate contact stresses on the field surface of up to 150 kPa, which is a permissible load for soil structure safety. Thus, the suggested simulation model of the soil stress state is suitable for use, and studies and modeling advance the idea that using wider tires results in a more equitable distribution of loads. The proposed model for analyzing stress propagation in soil enables to estimate the potential adverse impacts of wheeled or tracked agricultural machinery on soil structure by assessing stress levels that may disrupt or damage soil integrity, with the stresses varying according to the specific physical and chemical properties of each soil type.

This study presents a novel approach to forecasting the evolution of hysteresis stress-strain response of different types of soils under repeated loading-unloading cycles. The forecasting is made solely from the knowledge of soil properties and loading parameters. Our approach combines mathematical modeling, regression analysis, and Deep Neural Networks (DNNs) to overcome the limitations of traditional DNN training. As a novelty, we propose a hysteresis loop evolution equation and design a family of DNNs to determine the parameters of this equation. Knowing the nature of the phenomenon, we can impose certain solution types and narrow the range of values, enabling the use of a very simple and efficient DNN model. The experimental data used to develop and test the model was obtained through Torsional Shear (TS) tests on soil samples. The model demonstrated high accuracy, with an average R 2 value of 0.9788 for testing and 0.9944 for training.

BackgroundThe theory of stress distribution in soil based on continuum mechanics introduces a stress concentration factor (xi) of 3 for a purely elastic soil and larger than 3 for an elastic-plastic soil material. However, the experimental estimation of xi as a function of loading geometry and soil properties is a challenge. Furthermore, the insertion of a stress probe into the soil exacerbates the stress concentration due to the arching effect.ObjectiveThe aim of this study is to model xi under circular surface (uniform) loading as a function of soil strength, loading area, and depth using finite element method.Materials and MethodsThe simulations were performed using a model of stress propagation under circular uniform loading in two parts: with and without a stress probe. Simulations were carried out for combinations of 21 soil properties of varying water content and cone index (CI), surface loading radius (R), soil depth (z), and surface stress (q). For each combination, the stress at a given depth (sigma z) and the resulting concentration factor (xi) were analyzed.ResultsA total of 1512 values were obtained for xi from simulations. Regression models were developed and validated for with-probe and without-probe xi as a function of CI, R, z, soil yield stress (sigma yield), and vertical stress (sigma z). Experimental data of stress measurements under plate sinkage loading for samples of a clay loam soil at two levels of water content each at two levels of bulk density were used to validate the with-probe regression model.ConclusionThe values obtained from the model and those from the experimental tests showed a relatively good correlation with R2 of 0.7. xi varied between 3.5 and 14 which is much larger than the values obtained for the without-probe model or reported in the literature.

Traffic-induced cyclic loading generates repetitive stresses and cumulative deformations on the GRS abutments, which affect the serviceability of GRS abutments. To evaluate the stress distribution of GRS abutments under cyclic traffic loading, this paper presents reduced-scale GRS abutment models constructed with sand backfill and geogrid reinforcements. The GRS abutment models were subjected to staged cyclic loading with different cyclic loading amplitudes to investigate the influences of cyclic loading amplitude, bridge superstructure load, and reinforcement vertical spacing on the dynamic soil stress distributions. The results indicate that the increase in residual stresses due to stress redistribution induced by cyclic loading is most pronounced at the top of the abutment, while there is little stress redistribution down to the foundation level. Increasing the static load of bridge superstructure or the amplitude of cyclic loading results in an increase in the incremental dynamic vertical soil stresses. Reinforcement vertical spacing does not significantly impact the incremental dynamic vertical soil stresses under cyclic loading, while the cyclic load has the most significant influence. Closer reinforcement vertical spacing could provide stronger lateral confinement, resulting in larger dynamic lateral soil stresses behind wall facing.

The bearing and deformation characteristics of embankments with rigid-flexible long-short pile composite foundations (RLPCFs) in thick collapsible loess strata are not yet accurately understood. In this study, a large-scale field experiment was conducted, and screw (long) and compaction (short) piles were employed to reinforce a of the foundation of the Lanzhou-Zhangye high-speed railway in thick collapsible loess. The pile load transfer, foundation settlement, pile-soil stress distribution, and load sharing characteristics were analyzed to reveal the bearing properties of the composite foundation. The results show that negative friction arises along the upper part of the pile, and the neutral points of the short pile and long pile are located at 2/5 and 1/3 down the pile lengths, respectively. The short pile eliminates the collapsibility of the shallow loess and enhances the foundation's bearing capacity. The long pile transfers the load of the shallow foundation and pile top to the deep foundation through lateral friction, which reduces the settlement of the shallow foundation. When the soil arch in the embankment is fully formed, the short pile bears approximately 20% of the load, while the long pile and the soil between piles bear 80%. With the increase in embankment filling height, the load borne by the long pile rises, and the load borne by the soil between piles decreases gradually. The top settlement of the cross- of the composite foundation is distributed in a concave basin shape, and the maximum settlement occurs in the center of the embankment. The parameters of the short pile can be obtained on the basis of the collapsibility grade and bearing capacity of the loess foundation, the length and area replacement rate of the long pile can be obtained based on the settlement control requirements of the superstructure of the composite foundation, and the lateral friction of the long pile can be increased by increasing the roughness of the pile and setting the screw.

Bank failures in alluvial rivers are a typical soil-water interaction problem, which is related to many factors including the direct action of flow, river stage change, and human actions (such as bank revetment). To investigate the failure mechanism of protected riverbanks and possible factors affecting their stability, we analyzed data measured from a typical reach of the Middle Yangtze River. Furthermore, we performed numerical simulations of seepage and stress variation inside the riverbank. The field observation and simulated results indicated that: (1) Hydraulic erosion by near -bank flow remains the primary factor influencing the erosion of the protected riverbank. However, the bank protection works effectively limit the lateral bank retreat but increase the incision of the nearby riverbed, with the largest erosion depth of 10.6 m during August to November in 2020. (2) The initial damage in protected banks may be triggered by local tensile stress concentration during the water-rising period, under the combined actions of hydrostatic confining force, pore water pressure and gravity. This initial damage will progress into more severe bank failure events, particularly during the flood period. (3) After the regulation of the Three Gorges Project, the increased changing rate of river stage (similar to 1.6-2.5 fold) could potentially increase the risk of damage to protected riverbanks in the Middle Yangtze River.

Machinery traffic is associated with the application of stress onto the soil surface and is the main reason for agricultural soil compaction. Currently, probes are used for studying the stress propagation in soil and measuring soil stress. However, because of the physical presence of a probe, the measured stress may differ from the actual stress, i.e. the stress induced in the soil under machinery traffic in the absence of a probe. Hence, we need to model the soil -stress probe interaction to study the difference in stress caused by the probe under varying loading geometries, loading time, depth, and soil properties to find correction factors for probe -measured stress. This study aims to simulate the soil -stress probe interaction under a moving rigid wheel using finite element method (FEM) to investigate the agreement between the simulated with -probe stress and the experimental measurements and to compare the resulting ratio of with/without probe stress with previous studies. The soil was modeled as an elastic -perfectly plastic material whose properties were calibrated with the simulation of cone penetration and wheel sinkage into the soil. The results showed an average 28% overestimation of FEM-simulated probe stress as compared to the experimental stress measured under the wheel loadings of 600 and 1,200 N. The average simulated ratio of with/without probe stress was found to be 1.22 for the two tests which is significantly smaller than that of plate sinkage loading (1.9). The simulation of wheel speed on soil stress showed a minor increase in stress. The stress over -estimation ratio (i.e. the ratio of with/without probe stress) noticeably increased with depth but increased slightly with speed for depths below 0.2 m.