Biomimetic Rotary Tillage Blade Design for Reduced Torque and Energy Requirement

A rotary cultivator is a primary cultivating machine in many countries. However, it is always challenged by high operating torque and power requirement. To address this issue, biomimetic rotary tillage blades were designed in this study for reduced torque and energy requirement based on the geometric characteristics (GC) of five fore claws of mole rats, including the contour curves of the five claw tips (GC-1) and the structural characteristics of the multiclaw combination (GC-2). Herein, the optimal blade was selected by considering three factors: (1) the ratio ( r ) of claw width to lateral spacing, (2) the inclined angle ( θ ) of the multiclaw combination, and (3) the rotary speed ( n ) through the soil bin tests. The results showed that the order of influence of factors on torque was n , r , and θ ; the optimal combination of factors with the minimal torque was r = 1.25 , θ = 60 ° , and n = 240 rpm . Furthermore, the torque of the optimal blade (BB-1) was studied by comparing with a conventional (CB) and a reported optimal biomimetic blade (BB-2) in the soil bin at the rotary speed from 160 to 320 rpm. Results showed that BB-1 and BB-2 averagely reduced the torque by 13.99% and 3.74% compared with CB, respectively. The field experiment results also showed the excellent soil-cutting performance of BB-1 whose average torques were largely reduced by 17.00%, 16.88%, and 21.80% compared with CB at different rotary speeds, forward velocities, and tillage depths, respectively. It was found that the geometric structure of the five claws of mole rats could not only enhance the penetrating and sliding cutting performance of the cutting edge of BB-1 but also diminish the soil failure wedge for minimizing soil shear resistance of BB-1. Therefore, the GC of five fore claws of mole rats could inspire the development of efficient tillage or digging tools for reducing soil resistance and energy consumption.

Lateral Spreading and Stability of Embankments Supported on Fractured Unreinforced High-Modulus Columns

Construction of column-supported embankments (CSEs) with unreinforced high-modulus elements is now common practice to accelerate fill placement. These brittle columns are susceptible to column fracturing and CSE designs often limit the degree of lateral spreading such that tensile rupture will not occur, which stems from salient concerns that fracturing may trigger uncontrolled lateral spreading and/or the cessation of intended vertical load transfer. However, tensile rupture is unlikely to coincide with full mobilization of available passive resistance at the toe. Thus, it is disputed in industry whether some degree of column fracturing is tolerable. The objective of this study is to elucidate the influence of column fracturing on lateral spreading and stability of CSEs. A collective examination of available performance data is accompanied by a parametric 3D finite element study of hypothetical embankments, which considers the cessation of column bending resistance due to tensile rupture at discrete crack locations. A factor of safety, which reflects development of a passive failure wedge at the embankment toe, is used as a proxy for lateral stability. Factors of safety are linked to the magnitude of lateral spreading to address whether adequate confinement can be provided by foundation soils when fracturing occurs in unreinforced high-modulus columns that support embankments.

Calculation of active earth pressure on retaining walls with line surcharge effect and presentation of design diagrams in cohesive – frictional soils

In this study, a formulation and models have been proposed to calculate the active earth pressure on the wall and to determine the angle of failure wedge with line surcharge effect and taking into account the soil cohesion. The proposed method has the advantage of taking into account soil parameters such as cohesion, the angle of friction between the soil and the wall, the surcharge effect in the elasto-plastic environment, and the range that determines the critical surcharge. This paper presents dimensionless diagrams for different soil specifications and surcharges. According to these diagrams, it is easy to determine the distribution of excess pressure caused by surcharge, the distribution of the total active earth pressure on the wall, the angle of the failure wedge as well as the minimum and maximum active coefficient of the pressure with respect to surcharge distance. Furthermore, all soil parameters, surcharge and the results have been addressed. In general, the results indicated that increasing the angle of internal friction of the soil and cohesion would result to a nonlinear reduction in the active earth pressure coefficient, contrary to the line surcharge, which increases the active earth pressure of the soil and ultimately increases the active earth pressure coefficient. In this research, a diagram has been presented that expresses the surface that the active earth pressure coefficient changes with respect to the surcharge distance. The lower limit of each graph expresses the minimum active earth pressure coefficient (kas (min)) at the minimum surcharge distance, whereas the upper limit indicates the maximum active earth pressure coefficient (kas (max)) at the maximum surcharge distance from the wall. Comparison of the results of the proposed method with previous methods, codes and numerical software shows that in general, the proposed method is able to simplify the analysis of walls with surcharge effect in cohesive-frictional soils. In addition to the formulation and diagrams, a computer program in MATLAB software has been written. Using the results of these codes, the pressure on the wall with the linear surcharge effect, angle of failure wedge and pressure distribution on the wall in the cohesive-frictional soils can be calculated for all scenarios.

An analytical model for predicting the natural frequency of retaining structures

The importance of the retaining structures is crucial in geotechnical engineering and the accurate determination of static and seismic earth pressures and natural frequency is important for study the dynamic behavior of these structures. Usually analytical formulas which do not consider the earth pressures behind retaining structure are used. An analytical model for predicting the natural frequency of retaining structures including the earth pressures by failure wedges is proposed in the present analysis. The model considers the effect of Coulomb and Mononobe Okabe failure wedges. Backfill material is considered in the analysis as cohesionless. The failure wedge is an important factor which should be considered in determining the natural frequency of retaining structures. As the weight of failure wedge increases the natural frequency decreases significantly. The current model is validated using several analytical models reported in the literature of the earlier researcher.

Design Diagrams for the Analysis of Active Pressure on Retaining Walls with the Effect of Line Surcharge

In this study, a formulation has been proposed to calculate the pressure on wall and determine the angle of failure wedge based on limit equilibrium method. The mentioned formulation is capable of calculating active pressure coefficient, culmination of forces in failure surface, and pressure distribution on wall with the effect of line surcharge. In addition, based on the proposed method, a simple formula has been proposed to calculate the angle of failure wedge by the effect of surcharge. Moreover, the proposed approach has the advantage of taking into account the effect of surcharge on elastoplastic environment by considering the parameters of soil and determining the extent to which the surcharge is effective in pressure distribution on the wall. However, in most previous methods and specifications, resultant lateral pressure from surcharge in elastic environment had been considered. Finally, based on the obtained results, the design diagrams for different soils and different surcharges have been proposed. According to these diagrams, pressure on wall, pressure distribution on wall, and angle of failure wedge will easily be achieved. Also, a computer program has been written in MATLAB software environment. Using the results of these codes, the pressure on wall with the effect of surcharge, the angle of failure wedge, and pressure distribution on wall will be determined.

Pseudo-static lateral earth pressures on broken-back retaining walls

Displacement of retaining walls during earthquakes causes damage to the structures founded on their backfill. The displacement of the wall can be reduced by decreasing the lateral earth pressure applied on its back. This can be achieved in a broken-back wall as the size of the failure wedge formed behind the wall is reduced; therefore, the calculation of lateral earth pressures is essential in assessing the safety of and designing broken-back retaining walls. In this study, a series of reduced-scale shaking table model experiments were performed on broken-back quay walls composed of concrete blocks with two different rear-face shapes. In comparison with a vertical-back wall, earth pressures increased at the upper forward (i.e., seaward) leaning rear-face segments of the wall, whereas they decreased at lower backward (i.e., landward) leaning elevations. Because of the wide application of the pseudo-static method of Mononobe–Okabe in engineering practice and design codes, lateral earth pressures have also been estimated using this approach. The comparison between the measured lateral earth pressures and those calculated using the Mononobe–Okabe method shows fairly good agreement in predicting the overall distribution of lateral active earth pressure during and after the shaking.