Passive Thrust Research Articles

Large-scale direct shear testing for assessing interfacial parameters of natural and recycled sand with geosynthetic reinforcements

The demand for infrastructure projects is being driven by urbanization, which led to scarcity of natural sand (NS), which prompts exploration of alternative sustainable construction materials due to environmental concerns. Recycled sand (RS), processed from construction and demolition waste (C&DW), is an alternative material in infrastructure applications. Investigating interfacial shear behaviour between geosynthetic reinforcements with RS as a sustainable alternative material is crucial for infrastructure projects. This study presents the comprehensive large-scale direct shear testing (LSDST) on RS, NS, and its interfaces with ten types of geosynthetic reinforcements (i.e., polypropylene geogrids (GRD1 – GRD3), polyester geogrids (GRD4 – GRD6), and geotextiles (GT1 – GT4). LSDST were carried out using self-fabricated direct shear testing equipment of size equal to 500 mm x 500 mm x 300 mm (L x B x H). The findings indicate that the RS and NS exhibit similar shear strength parameters, sand-GRD interface demonstrates greater resistance compared to the sand-GT interface. RS and NS-GRD4 - GRD6 interfaces with transverse ribs and rough texture and NS-GRD1 interface with triangular apertures, exhibit significant shear strength parameters than the unstabilized case due to the mobilization of passive thrust. Interfacial shear coefficients for NS and RS range from 0.94 – 1.27 and 0.80 – 1.15 for GRD interfaces, and 0.89 – 1.06 and 0.86 – 0.99 for GT interfaces, respectively. Therefore, the RS can be a sustainable alternative for NS.

Mono-objective Optimization of Retaining Wall Using Genetic Algorithm

Abstract This paper examines the importance of geotechnical optimization techniques for soil engineering applications, with a particular emphasis on evaluating geotechnical structures. Due to its prevalence in civil engineering, the complex interplay of geotechnical, structural, and financial considerations necessitates a trial and error approach. The study focuses on design elements, geometric dimensions, and volume considerations in order to highlight the economic viability of reinforced concrete retaining walls. Three code files are created using MATLAB to analyze their impact on active and passive thrusts and, as a result, the structure’s volume. The slope angle, backfill overload, and friction angle are varied. The results demonstrate the effectiveness of using evolutionary algorithms to precisely optimize a single goal and demonstrate that this approach can enhance the design of retaining walls in reinforced concrete. This method demonstrates the ability to improve design procedures in this crucial area, which makes it an invaluable resource for structural engineering researchers and civil engineers.

Auto-updating model-based control for thrust variation mitigation and acceleration performance enhancement of gas turbine aero-engines

Model-based control shows promising potential for engine performance improvement and future aero-propulsion requirements. In this paper, an auto-updating thrust variation mitigation (AuTVM) control approach using on-board model strategies is proposed for gas turbine aero-engines under in-service degradation effects, which aims at active thrust regulation and acceleration protection in a simultaneous way. The AuTVM control is integrated with an on-line block, based on a reliable on-board engine model, and an off-line part for the periodical update of control parameters via post-flight engine monitoring data. The core feature of the AuTVM control is a set of auto-updating loops within the on-line part, including thrust regulation loop, surge margin loop, turbine entry temperature loop, and the steady loop, whose control parameters are periodically adjusted with increasing flight cycles. Meanwhile, an industrial sensor-based baseline controller and two tailored model-based controllers, i.e., a thrust variation mitigation (TVM) controller with fixed gains and a self-enhancing active transient protection (SeATP) controller with pro-active transient protection and passive thrust control, are also developed as comparison bases. Numerical simulations for idle to full-power acceleration tests are carried on a validated aero-thermal turbofan engine model using publicly available degradation data. Simulation results demonstrate that both new engines and severely degraded engines regulated by the AuTVM controller show significant thrust response enhancement, compared to the baseline controller. Moreover, thrust variation at the maximum steady state of degraded engines, which exists within the SeATP controller and the baseline controller, is suppressed by the proposed AuTVM controller. Robustness analysis against degradation uncertainties and sensor accuracy confirms that the AuTVM controller owns a closer maximum steady-state thrust distribution to the desired value than those of the SeATP and the baseline controller while utilizing transient margins of controlled engines more effectively. Hence, the control performance of the AuTVM controller for in-service engines is guaranteed.

Analysis of passive thrust near slope toe in laterally confined slopes lying on inclined bedding plane

Analysis of passive thrust near slope toe in laterally confined slopes lying on inclined bedding plane

Air-Jet Levitation of Continuum Robots: Stable Head Floating by Passive Thrust Vectoring for Enhancing Mobility

Flexible, continuum-type robots can access narrow spaces in debris areas during search-and-rescue missions. However, their current problem is the lifting capability of the head, which is necessary to surmount the rubble. This study proposes a passive-thrust vectoring method to stabilize head levitation for air-jet-actuated, long, continuum robots, and thus enhance their step-climbing abilities. An air jet can generate a thrust force that is sufficient for head levitation. A critical issue in levitation involves the backward bending of the head without using any air-jet control; however, thrust control is inappropriate because of the delay caused by the long channel. Therefore, the proposed method maintains the thrust direction constant. Sufficient conditions for global stability are derived and confirmed via dynamic simulations. The proposed method is simple and can be mechanically realized with a passive head-bending mechanism, thus contributing to a lightweight design. Experiments demonstrated that the developed air-floating-type, 7-m long robot, can achieve stabilized head levitation, and that the robot can climb a step with a height of 250 mm. Robot demonstrations in rubble justify the robot’s capacity to surmount the rubble. This passive-thrust vectoring method is expected to contribute to the future enhancement of the mobility of continuum robots owing to its simplicity and practicality.

Lithofacies and Depositional Environments of the Garubathan Alluvial Fan, North Bengal, India

Abstract The sedimentology of the Garubathan alluvial fan of north Bengal foothills is a product of Himalayan neotectonics and monsoon climate. The active neo-tectonics of the Main Central Thrust (MCT), Ramgarh Thrust (RT) and Ghis Transverse Fault (GTF) produce a huge amount of angular clasts in the upper reaches of the river Chel and Mal. During the wet season, either sediment flow by gravity or turbulent stream flow or both, move the clasts to the downhill. The tectonic zone of Main Boundary Thrust (MBT) and Main Frontal Thrust (MFT) are relative passive thrusts than the MCT, RT and GTF in the study area. A very low angle slope is observed in the area of MBT and MFT of the study area. So, the downhill deposition occurred in MBT and MFT zones of the study area. The river Chel and Mal are perinial rivers. During dry periods (pre-monsoon and post-monsoon), in the absence of sediment flow by gravity or turbulent stream flow, the low stream competency deposit the fine sediments. To identify the depositional environments three, seven and six lithofacies varieties were identified in the upper, middle and lower fan surfaces, respectively. The non-cohesive sediment flows by gravity deposited large angular boulders, cobbles and pebbles in the upper fan area. These deposits are either chaotic, unsorted, un-imbricated or graded and imbricated. Deposition of sand is scanty. Both, sediment flow by gravity and fluvial processes deposited angular to round clasts with matrix in the middle fan area. In this area the deposits are reverse graded, reverse to normally graded, laminated and cross-bedded. The high facies diversity of this area indicates highly variable nature of the depositional environments. In the lower fan area, presence of both clast-supported chaotic and matrix-supported laminated or cross-bedded layers suggests a complex nature of the depositional environment of sediment flow by gravity and fluvial processes.

A log-spiral limit equilibrium analysis for passive earth pressure under the effect of unsaturated seepage conditions

In the current state of the study regarding passive earth pressure, the majority of literature was limited in scope to dry or saturated cases. However, most soils in practical engineering are unsaturated. Based on the log-spiral failure mechanism, this paper develops a limit equilibrium (LE) analysis to evaluate the passive earth pressure under the effect of steady unsaturated seepage conditions. For assessing the effect of suction stress on passive earth pressure, a suction stress-based effective stress representation is incorporated into a limit equilibrium analysis. The analytical formula of passive earth pressure coefficient is derived using the moment equilibrium equation for the backfill defined by a log-spiral slip surface. An optimization procedure is developed to search for the minimum passive earth pressure coefficient and the critical failure surface via MATLAB. A parametric analysis is performed to investigate the effects of some key parameters on passive thrust. Besides, examples of two different cases are given to verify the effectiveness of theoretical results. Results indicate that suction stress can increase the magnitude of the passive earth pressure coefficient and the suction-induced effect highly depends on the seepage conditions and soil types.

Passive Thrust of “Imperfect” Prisms of Soil Thrust and Placement of Anchor Supports Relative to the Retaining Walls

This study proposes a solution to determine the passive thrust of “imperfect” prisms of soil thrust. This study also analyzes the regulatory directives for the designation of the distance between anchor supports and retaining walls.

Analytical solution to estimate the point of application of resultant passive earth thrust against unsaturated retaining structures

ABSTRACT This paper describes a simplified analytical solution for computing the magnitude and the point of application of the resultant passive earth thrust, as well as the passive earth pressure distribution against inclined walls retaining unsaturated soils under different steady flow conditions. The present analysis was performed based on the assumptions consistent with the Coulomb approach within the framework of the limit equilibrium method. Possible modifications of induced negative pore pressure or matric suction within the unsaturated zone above the water table have been considered depending upon the steady flow conditions, soil types, and groundwater table positions. Results of the parametric study showed considerable alterations in the passive earth pressure of unsaturated soils due to different parameters and highlight the importance of incorporating suction stress changes directly in the stability analysis of earth-retaining structures.

Earth Pressure behind a Retaining Wall under Linearly Varying Geotechnical Parameters

Objectives: The present study discuss estimation of active and passive earth pressure behind a smooth vertical retaining wall with horizontal backfill under linearly varying geotechnical properties, i.e., cohesion (c), angle of internal friction (φ) and unit weight (γ) of backfill vary linearly with depth.It is noted that the earth pressure behind the retaining wall is nonlinear and its variation can be established through regression analysis that follows 2nd order polynomial in the form of pa = -az2+bz+c; where z is the depth below the backfill surface, a, b & c are constants. Methods/Statistical Analysis: Regression analysis incorporating least square error approach option is available in Microsoft excel in data analysis tool pack. The total amount of thrust (active or passive ) estimated through non-linear distribution of earth pressure behind retaining wall is compared with the corresponding values computed through most widely used Rankine’s earth pressure theory in which average values of geotechnical parameters are taken. Findings: It is noted that there is 5-7% reduction in the active earth thrust although not much reduction is achieved in the moment. In passive case, the increase in passive thrust is almost 20%. Application/Improvements: Consideration of non-linear earth pressure distribution is useful in situations where base width of the retaining wall is controlled with respect to base shear. It will ultimately lead to reduction in the total cost of construction of the retaining wall and will help in achieving economy when the length of the retaining wall is large.

Numerical Study on Passive Earth Pressures Using Kötter's Equation

AbstractA numerical protocol was developed to compute the passive earth pressure coefficients, Kpγ, for the case of an inclined rigid wall retaining an inclined cohesionless backfill. A complete log-spiral failure surface is assumed in this study. Kotter's equation is used in the analysis to obtain the resultant soil reaction on the failure surface. In addition, a limit-equilibrium approach is used to identify the unique failure surface, which fulfils all three equilibrium conditions, viz., ∑H = 0, ∑V = 0, and ∑M = 0, with the passive thrust located at the lower one-third height of the retaining wall. The analysis is further extended to evaluate the bearing capacity factor, Nγ, for the case of a centrally loaded rigid rough strip footing resting on a cohesionless soil medium. For this purpose, particular failure mechanisms are considered. The computed Nγ values are found to be in good agreement with most of the available theoretical solutions.

Analysis of passive earth thrust in an unsaturated sandy soil using discontinuity layout optimization

This paper addresses a numerical study into passive earth pressure in an unsaturated sandy soil. The computational limit analysis method, discontinuity layout optimization (DLO), is extended to take into consideration the effect of saturation and suction on strength. The extended analysis was utilised to model a retaining wall case study using a sandy soil as a simulated backfill material and the results were compared with Rankine equations which were modified to take into account the capillary rise effect. The numerical results demonstrated that an increase of the total passive thrust up to 47%, for a frictionless wall, at ϕ ′ = 30° due to the effect of partial saturation in the sandy soil.

Determination of passive earth pressure coefficients using limit equilibrium approach coupled with the Kötter equation

A numerical method is developed to evaluate the passive earth pressure coefficients for an inclined rigid retaining wall resting against a horizontal cohesionless backfill. A composite failure surface comprises a log spiral, and its tangent is assumed in the present study. The unique failure surface is identified based on the limit equilibrium approach coupled with the Kötter equation (published in 1903). Force equilibrium conditions are used to evaluate the magnitude of the passive thrust, whereas the moment equilibrium condition is employed to determine the location of the passive thrust. The distinctive feature of the present study is that no assumption is required to be made regarding the point of application of the passive thrust, which would otherwise be an essential criterion with respect to the several limit equilibrium based investigations available in the literature. The passive earth pressure coefficients, Kpγ, are evaluated for various values of soil frictional angle [Formula: see text], wall frictional angle δ, and wall inclination angle λ, and compared with the existing results.

Immediate effects of upper thoracic manipulation on the skin surface temperature of the vertebral region in healthy women

Manipulation of the spinal column is a manual therapeutic resource characterized by passive thrust of a given joint at a high velocity and low amplitude within the limits of anatomic integrity. The objective of the present study was to assess the immediate effects of upper thoracic manipulation on skin temperature in the vertebral region in healthy women. Thus, a randomized controlled blind trial was realized in the university community. Twenty-six healthy women were randomly allocated into an experimental group (n=13) and a placebo group (n=13). A single session of upper thoracic spine manipulation (segment T3) was performed. Infrared thermography was used to determine changes in skin temperature in the vertebral region. Images were taken prior to, immediately after and both five and 10 minutes after manipulation. Two-way repeated measures analysis of variance with post hoc Bonferroni test was used for inter and intragroup comparisons. The level of significance was set to 5%. No significant differences were found between the different evaluation times in either group (p>0.05). In the intergroup analysis, no statistically significant differences were found in any of the comparisons (p>0.05). Based on the method employed, thoracic spine manipulation of the T3 vertebral segment does not promote changes in skin surface temperature in the region manipulated in asymptomatic individuals.

受動磁気軸受を活用する5軸能動制御形ベアリングレスキャンドモータポンプの小型・低損失化の検討

Bearingless canned motor pumps, which employ 5-axis active electromagnetic control, have been developed. In this paper, two types of 5-axis active control type bearingless canned motor pump are introduced and explained about the difference of each structure. One is a conventional structure which was investigated in the past research, the other is a novel structure which was newly proposed. One of the most important difference between these two types is the machine size. To realize miniaturization, the structure of suspension stator core was optimized to insert radial gap sensors into slots. In addition, suspension rotor cores were also used as gap sensor targets. Thus, the area of the radial gap sensors and the gap sensor targets which was arranged to the both ends of the electromagnetic machine could be deleted. Furthermore, a passive thrust magnetic bearing was effectively inserted in the dead space of an active radial magnetic bearing arranged at the buttocks side. As a result, the whole machine size could be miniaturized. Although the machine size was miniaturized, the experimental results demonstrated that the proposed novel structure has enough output power and suspension force. In addition, the proposed structure could reduce the flow loss, because the rotor length was decreased through the miniaturization. Accordingly, whole input power also could be reduced. In this paper, these advantages will be shown by the pump experiments with water.

A new approach for the computation of bearing capacity factor Nc: Terzaghi and Prandtl mechanisms

A new approach is suggested for the computation of bearing capacity factor, Nc considering Terzaghi and Prandtl failure mechanisms. The proposed analysis makes use of Kötter’s equation coupled with limit equilibrium conditions. It successfully demonstrates the applicability of Kötter’s equation to the solution of limit equilibrium problems involving plane or curved failure surfaces. Kötter’s equation also enables using moment equilibrium condition to locate the point of application of the passive thrust.

Pseudo-dynamic methods for seismic passive earth pressure behind a cantilever retaining wall with inclined backfill

The designing of retaining walls requires the complete knowledge of earth pressure distribution. Under earthquake conditions the design needs special attention to reduce the devastating effect, but under seismic conditions, the available literature mostly uses the pseudo-static analytical solution as an approximate to the real dynamic nature of the complex problem. This paper shows a detailed study on the seismic passive earth thrust behind a cantilever retaining wall with inclined backfill surface by pseudo-dynamic analysis. A planar failure surface has been considered. The effect of variation of parameters such as soil friction angle, wall friction angle and back fill inclination have been explored. A complete analysis shows that the time dependent non-linear behaviour of the pressure distribution obtained in the present method results in more realistic design values of earth pressures under earthquake conditions. Results are provided in tabular and graphical non-dimensional form and compared thoroughly with the existing values in the literature.

Pullout capacity of vertical plate anchors in cohesion-less soil

In this paper, the ultimate pullout capacity of a vertical plate strip anchors in cohesion-less soil is analyzed with the consideration of active and passive state of equilibrium in the soil. Ktter`s equation is used to compute the active and passive thrusts (along with their point of application) which are subsequently used in the analysis in which, all the equation of equilibrium are properly interpreted. A comparison of the results with the experimental results vis--vis available theoretical/empirical solutions shows that, the proposed analysis provides a better estimate of the pullout capacity.

Pullout Capacity of a Vertical Plate Anchor Embedded in Cohesion-less Soil

In this paper, the ultimate pullout capacity of a shallow laid vertical plate strip anchor in cohesion-less soil is analyzed with the consideration of active and passive states of limit equilibrium in the soil. Kotter’s equation is used to compute the active and passive thrusts, which are subsequently used in the analysis in which, all the equation of equilibrium are properly interpreted. The unique failure surfaces under active and passive states of limit equilibrium are identified on the basis of force equilibrium conditions. One distinguishing feature of the proposed method is its ability to compute the point of application of active/passive thrust using moment equilibrium. Another distinguishing feature is the prediction of distribution of soil reactions on the failure surface. Comparison of the results of the proposed method with the available experimental results vis-a-vis other theoretical methods shows that, up-to embedment ratio of 3.0, the proposed method is capable of making reasonably good predictions.

Passive Magnetic Bearing Design for a Small Wind Generator System

A passive magnetic thrust bearing for a small vertical wind generator system is considered in this paper. The passive magnetic bearing is designed to reduce the axial load of the rotor system. The load capacity of the passive magnetic bearing is analyzed by finite element analysis software. From the simulation results, a suitable solution for the passive magnets of the test wind generator system is verified to be 225.6N with about a 2mm air gap. The experiment results show that a wind generator system with the additional passive magnetic bearing can start at a lower wind speed and transfers more power to the generator. The proposed hybrid bearing system can increase efficiency by 20%~50%, as compared with a traditional system supported by roller bearings at the same wind speed.