Search

In addition to creating environmental threats, the leakage and entrance of chemical fertilizers into soil, which is possible in various ways, dramatically changes the physical and mechanical properties of soil. Furthermore, clay soils in the vicinity of monoammonium phosphate (MAP) contamination show substantially negative behavior, thus, improving the engineering geological factors of soil has become a huge challenge for engineers. Extensive programs such as triaxial compression test, consolidation test, compaction test, Atterberg limits, and collapse tests, in addition to X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) were performed on samples containing 10%–30% MAP over 7 days, 1, and 3 months. The mentioned trend was repeated when 0.5%–3% nano A (Al2O3 in alpha phase), nano F (Fe2O3 in alpha phase), and AF in form of a nanohybrid were added to soil which had been contaminated by MAP. Gained reports demonstrated significant declines in maximum dry density, plasticity index, and shear strength of contaminated soil when compared with natural soil. Conversely, increases in liquid limit, plastic limit, consolidation settlement, as well as soil collapse index were observed. Furthermore, a decrease in the amount of minerals in the XRD results and the formation of a flocculated structure in the SEM images in MAP-contaminated soil are evident. According to microstructural analysis, adding nano A, nano F, and AF nanohybrid as an improvement phase caused remediation of the soil structure and created cementation bonds between soil particles, thereby increasing the maximum dry density and soil shear strength, and decreasing the consolidation settlement and soil collapse index. Therefore, the use of AF as an efficient additive to remediate physical and mechanical properties of soils that have been contaminated with MAP, and to decrease the geological hazards of these kinds of contamination is recommended. [ABSTRACT FROM AUTHOR]

In this paper, a constitutive model is presented to model the behavior of various soils (sand and clay) in different loading conditions and the minimum required parameters are obtained. Although some practical features (concepts) of the bounding surface framework and modified Cam-Clay have been employed in its formulations, the model is developed mainly based on the generalized plasticity framework. Moreover, some concepts such as dilatancy relation and loading history surface are redefined. Finally, the proposed constitutive model is evaluated using the experimental data related to two different sandy soils and three different clays under different loading conditions. Finally, it is concluded that the proposed constitutive model can easily be calibrated for various clayey and sandy soils. It can depict different behavioral aspects of these soils under different monotonic and cyclic loading conditions. [ABSTRACT FROM AUTHOR]

This paper presents an iterative horizontal method of slices (iterative HMS) for the global stability analysis of a slurry trench in layered cohesive-frictional soils. The iterative HMS differs from existing HMS models in terms of the assumptions on interslice forces. Preceding HMS techniques postulate that normal interslice forces can be evaluated from overburden pressures, which can lead to the violation of failure criteria along interslice boundaries. The iterative HMS ensures that a limit equilibrium system is established without violating the failure criterion throughout the entire soil mass. This is achieved by iteratively adjusting interslice forces by means of enforcing the failure criterion for the aforementioned problematic slice boundaries violating the failure conditions. The performance of the iterative HMS is evaluated in example problems of a slurry trench in uniform clayey soils and cohesive-frictional strata. The results are compared against solutions obtained using finite-element limit analysis (FELA) and a shear strength reduction FEM (SSRFEM). This comparative analysis shows that the adjustment in interslice forces is important for reasonably assessing trench stability conditions. A parametric analysis is performed by using the iterative HMS to show under what trench construction parameters the adjustment of interslice forces cannot be neglected in the stability analysis of a slurry trench. [ABSTRACT FROM AUTHOR]

In this paper, the compressive and tensile ultimate bearing capacity of helical piles, in the load range required for designing 63-kV transmission towers, are studied by conducting analytical and numerical investigations. In this light, an explicit easy-to-use analytical framework was developed by considering the unsaturated soil condition that was validated against experimental records. Also, finite-element models were constructed for fully saturated and fully dry soil conditions. Then, to validate the analytical and numerical solutions in fully saturated and fully dry soil conditions, three compressive and one tensile field tests were carried out, and the results were compared quantitatively with analytical and numerical calculations. Comparative studies showed that the analytical, numerical, and experimental results have a high level of conformity. In accordance with the load ranges of transmission towers, analytical parametric studies were conducted for different geometrical aspects of the helical piles in different soils. Also, for two typical unsaturated sand and clay soils, the ultimate load of helical piles was calculated versus matric suction. Moreover, a vast numerical parametric study was performed to investigate the role of the geometrical aspects of helical piles and soil characteristics on the load-transfer mechanism and ultimate bearing-capacity values for helical piles driven in sandy and undrained saturated clayey soils. Results showed that the maximum load capacity of helical piles occurred in a matric suction less than that of a fully dry soil. In addition, the soil type and the geometrical aspects of the helical pile were shown to have significant effects on the load–displacement behavior and ultimate bearing-capacity values. [ABSTRACT FROM AUTHOR]

This paper examines the accuracy of a new elastic–thermoviscoplastic (E-TVP) constitutive model developed based on critical state soil mechanics. The model can be used for simulating the temperature-dependent and strain-rate-dependent behavior of clay soils. The study compares the E-TVP behavior of a single soil element with previously published thermo-mechanical experimental results performed on saturated clay specimens at different temperatures. Suggestions regarding unloading and reloading at constant temperatures as well as thermal consolidation under constant loads are presented. A modification for unloading–reloading adds a new criterion to the volumetric thermoviscoplastic strain rate formulation. A physics-based term is added to the current specific volume of the soil to include the viscous effect induced by temperature change. These modifications improve the convergence of laboratory data and simulated model responses. Comparisons of results from an earlier E-TVP model and the newly improved model provide evidence of improved predictive capabilities. [ABSTRACT FROM AUTHOR]

This paper presents an analytical three-dimensional rotational mechanism for the limit analysis on the overall stability of slurry trenches in layered cohesive soils. The proposed mechanism differs from the traditional torus mechanism in terms of the assumption on the shapes of cross section. The proposed rotational mechanism can have cross section with arbitrary shapes that are described by a smooth rotation radius function. The factor of safety for the overall stability of slurry trenches is obtained by using the new kinematic mechanism. The performance of the proposed mechanism is evaluated by analyzing the overall stability of trenches in single-layered, uniform and nonuniform clayey soils. The computed results are compared with the solutions given by finite-element limit analysis (FELA), which show that the proposed mechanism can give better solutions than the traditional torus mechanism when the length-to-depth ratio of the trench is relatively small. Based on the proposed mechanism, the stability of slurry trenches in layered undrained clay is investigated. The results show that, for trenches in two-layered undrained clay, the strength ratio between the shallow and deep layers can significantly influence the depth of the collapse mechanism. For trenches in three-layered undrained clay with a weak interlayer, the thickness of the interlayer can greatly affect the modes of failure in terms of global or local instability. [ABSTRACT FROM AUTHOR]

This paper analytically investigates the postconstruction load-carrying capacity of a cast-in-place pile in clayey soil. The stress release induced by borehole excavation, the slurry supporting effects, and the dissipation of the negative excess pore-water pressure after construction, all of which have significant effects on the effective stresses of the soil around the pile, are the main concerns of this study, which aim to establish a method to reasonably evaluate the load-carrying capacity of a cast-in-place pile after construction. The stress release due to borehole excavation is modeled by cylindrical cavity contraction theory, which employs a K0-consolidated anisotropic modified Cam-clay (K0-AMCC) model to represent the mechanical behavior of the soil. Considering the dissipation of the negative excess pore pressure, the load-carrying capacity after construction is determined by the total stress method, with consideration of the three-dimensional strength of the soil adjacent to the pile. The proposed method was verified by finite-element (FE) numerical simulations. The results indicate that the soil properties and the factors involved in pile construction, such as the stress release due to borehole excavation, the slurry supporting effects, and the dissipation of negative excess pore-water pressure, have substantial influences on the postconstruction load-carrying capacity of the pile. [ABSTRACT FROM AUTHOR]

Pressure-dispersed compression anchor consists of several anchor units fitted with an end plate. Limited field tests have been conducted to investigate the performance of a pressure-dispersed compression anchor system in cohesive soil. This paper conducted a series of field pullout loading test of pressure-dispersed compression anchors in clay soils, considering the following influence factors of stressing sequence, grouting method and compensation load. The simultaneous stressing yielded less pullout capacity than the individual stressing because of the relatively large interaction between the units. With the increase of the load level, the movement ratio decreased with a gradually decreased rate, followed by a slight increase when the load level exceeded 0.7. The rebound stiffness declined as the load level increased and the individual stressing yielded smaller reduction in the rebound stiffness than the simultaneous stressing. The back calculation indicated that the effective anchor diameter was enlarged by 10% due to the post grouting with a grouting factor of 0.2. [ABSTRACT FROM AUTHOR]

In most geotechnical construction works, compacted soils of cohesive-frictional nature are expected to remain mostly under partially saturated conditions and hence experience continuous changes in the suction state (negative pore-water pressure) stemming from seasonal weather and temperature variations throughout any given year. Over the last decade, a few studies have demonstrated that the suction stress characteristic curve (SSCC) can be used to describe the state of stress in partially saturated soils and therefore assess, with reasonable accuracy, the additional shear strength contribution resulting from matric or total suction. However, limited experimental data are available to conclusively verify the magnitude of suction stress at rather high values of suction, especially well beyond the residual suction. In the present work, the SSCC for compacted silty sand has been thoroughly assessed in light of recent experimental data obtained from suction-controlled triaxial testing over a wide range of matric and total suction values (0.05–300 MPa). The suction stress in the test soil was observed to increase with increasing suction even beyond the residual suction state, in contrast with findings from previous works reported in the literature for predominantly sandy or clayey soils. In addition, experimental data from suction-controlled true triaxial, ring shear, and plane strain (biaxial) tests, recently conducted on six different types of cohesive-frictional soils in the low-to-medium matric suction range, were also analyzed to obtain the corresponding SSCCs. Finally, suitable model equations are presented in order to best fit the multiple experimental data sets and hence predict the SSCC for each of the test soils under the different suction-controlled testing techniques. [ABSTRACT FROM AUTHOR]