Local Slippage Research Articles

Deep-Seated Deformation Mechanisms of Excavated Slope and Control Methods: A Case Study

High slope stability control is a crucial technical issue in water conservancy and hydropower project construction. This issue is relevant throughout the entire engineering-related survey, design, construction, and operation process. This paper reports a recent case in which significant deep-seated deformation occurred during slope excavation. Several unfavorable structural surfaces were revealed throughout the slope’s undercutting process, particularly fault fz39, which ran diagonally through the entire slope from top to bottom. On the slope surface, damage such as cracking, bulging, and local slippage appeared. The measured value of multipoint displacement meters increased in a stepwise pattern with each blast, and the maximum measured value exceeded 100 mm. The studied slope’s whole excavation and reinforcement process is described in detail. We analyzed the deformation mechanism of the excavation slope by combining the geological conditions, real-time safety monitoring findings, and site deformation characteristics. The slope reinforcement scheme was optimized based on the preceding analyses. We used a three-dimensional numerical calculation program to simulate the slope excavation and unloading process to reproduce the current mechanical state of the slope, evaluate the reinforcement measures, and provide a useful reference for decision making. The analysis shows that the deformation behavior of the studied slope is closely related to fault fz39 and fracture L920, and presents a typical wedge failure mode. The deep-seated deformation of the excavation slope occurs at the junction of the wedge and bedrock, which is mainly affected by unfavorable geological structure surfaces, excavation unloading, and blasting vibration. The reinforcement scheme of unloading at the top of the slope and large-tonnage cables are established. The numerical analysis results showed that the design of the slope reinforcement measures was appropriate and ensured slope stability. The work described in this paper deepens our understanding of the occurrence of large deep-seated deformation on the structural-controlled slope under the action of excavation and improves the design philosophy.

Evolution of the Transient Saturated Zone and Stability Analysis of Slopes under Rainfall Conditions

To study slope stability and instability modes under rainfall conditions, an improved Bishop method is proposed according to saturated-unsaturated seepage flow theory. It can simultaneously consider the depth effect of rock and soil mass shear strength parameters, transient water pressure, groundwater pressure, saturated water softening, unsaturated strength, and pore water unit weight. The variation law of the transient saturated zone, potential slip surfaces and stability coefficient under rainfall conditions are analysed with this method. The results indicate that after rainfall starts, the transient saturated zone of the slope continuously expands, and the stability coefficient gradually decreases. After rainfall stops, the transient saturated zone of the slope dissipates rapidly, and the stability coefficient continues to increase. During the early rainfall period, the slope instability mode is deep-layer integral slippage. During the later rainfall period, the slope instability mode is shallow-layer local slippage. The depth effect and unsaturated strength are beneficial to the slope stability, while the transient water pressure, saturated water softening, and pore water unit weight are not. The application of this method in engineering practice is of great significance to slope stability analysis and protection under rainfall conditions.

Many-body dissipative particle dynamics study of the local slippage over superhydrophobic surfaces

The gas–liquid interface (GLI) over superhydrophobic surfaces (SHSs), where the flow slips, is the key to reduce frictional drag in underwater applications. Many-body dissipative particle dynamics simulations are used to explore the slip behavior of a shear flow over a rectangular grooved SHS, and a flat GLI is obtained by tuning the contact angle of the GLI. Due to the slip, the normal profiles of the local velocity, which are perpendicular to the GLI, are curved and shifted away from the linear form near the GLI. Then, a polynomial function is proposed to fit the velocity profile to extract the local shear rate and calculate the slip length. Based on this fitting method, a hybrid slip boundary condition is derived for both longitudinal and transverse flows. That is, the shear stress and slip length are finite near the groove edge, and the stress is nearly zero and the slip length is infinite in the center region of the GLI. This new hybrid slip boundary condition not only explains the inconsistent slip conditions reported in the literature under different groove length scales, but also unifies the existing exclusive slip assumptions.

Study on local slippage accumulation between thread contact surfaces and novel anti-loosening thread designs under transversal vibration

The accumulation of local slippage between thread contact surfaces has recently emerged as a key reason for the self-loosening of threaded fasteners subjected to transversal vibration. However, the mechanism of local slippage accumulation is still elusive despite intense research. The authors recently proposed modified Iwan models to theoretically analyze local slippage accumulation and identified the principle of anti-loosening, upon which some novel anti-loosening structures were designed. However, simulation validation of the modified Iwan models and deep performance analysis of novel thread structures are lacking. Hence, we developed novel algorithms to simulate the modified Iwan models for the cumulative process of local slippage. These algorithms confirmed that the previous theoretical analytical results are reliable. Additionally, the mechanism of local slippage accumulation was revealed and the critical local slippage accumulation was studied. We also compared systematically the tightening and anti-loosening performances of proposed novel thread structures with other existing anti-loosening products by finite-element analyses and experiments. The novel thread structures exhibited superior anti-loosening performance and were convenient to install and remove.

Thorough understanding on the mechanism of vibration-induced loosening of threaded fasteners based on modified Iwan model

Under transversal vibration, the local slippage on the thread and bearing surfaces is typically nonlinear and its gradual accumulation with vibration cycles contributes to the loosening of threaded fasteners. The classical Iwan model is used widely to model the nonlinearity of contact interface, but not appropriate for analyzing the local slippage accumulation on the thread and bearing surfaces. In this paper, we proposed modified Iwan model to represent the nonlinear local slippage behavior. The acting forces on the internal thread were decomposed into three component forces along different directions. The effect of each component on the local slippage accumulation was analyzed theoretically based on the modified Iwan model. It was found that the cyclic component force along the radial direction dominates the local slippage accumulation of thread surface and other two cyclic component forces have no effects on it. Then, we also analyzed the local slippage accumulation on the bearing surface using the modified Iwan model and developed a thorough understanding on loosening mechanism. Based on the loosening mechanism, we proposed that the key to preventing local slippage accumulation and sustained loosening was to inhibit the slippage or relative motion occurring on the thread surface along the radial direction. Thus, several novel thread structures were designed for resisting loosening based on above findings. Finally, their superior anti-loosening abilities were validated by FEA method.

A numerical study on the effect of restrained shrinkage on rapid hardening plain and recycled clean steel fibre concrete overlays

This article presents FE numerical studies on restrained shrinkage of plain and fibre reinforced rapid hardening mortars. Moisture diffusivity analysis is coupled with structural analysis to calculate the evolution of hygral stresses, strains and cracking over time. The numerical results are validated against results from analytical models and compared to measured experimental values. Parametric studies are carried out to examine the effect of the interface stiffness, moisture content of the substrate layer and overlay depth on restrained shrinkage strain and stresses of overlays. Fibre inclusion is shown to reduce the risk of deterioration by slowing down the evolution of local slippage and controlling crack widths. It is also found that the uniform shrinkage strain distribution that is assumed in analytical models underestimates the hygral tensile stresses of overlays compared to real non-linear strain distribution. A modification to account for this effect is proposed through shrinkage amplification factor. This approach is expected to provide a better estimation of the risk of cracking in overlays.

Shape recognition of CAD models via iterative slippage analysis

A new slippage analysis method for recognizing basic primitive surfaces of CAD models is presented in this paper. Obtaining the exact normal and searching the appropriate local region of each point are found to be the key steps for determining the local slippage motion type. First, the tensor voting-based boundary point recognition method is integrated to preprocess the original points. Then, the local slippage analysis method is used to initialize the point type. Furthermore, the appropriate region of each point is acquired by the region growing method. Meanwhile, the middle level information (the basic primitive surface types and the representative parameters) is found, guiding the modification of the normal of each point and the iterative detection of the surface types. Finally, the middle level information-based smooth method is introduced to refine the boundary of each basic primitive surface. The empirical results show that the proposed algorithm is efficient and robust for recognizing primitive shapes from CAD models of mechanical parts.

Centrifuge model tests of deformation and failure of nailing-reinforced slope under vertical surface loading conditions

A series of centrifuge model tests was conducted on a nail-reinforced slope under vertical surface loading conditions considering different slope gradients and nail lengths. The ultimate load of the slope decreased significantly with the increasing gradient of the slope or the decreasing nail length. The slope exhibited significant progressive failure that was captured by a displacement-based analysis. At first, the vertical load caused local slippage near the slope toe and the inner edge of the loading plate. Then, it extended to the interior of the slope and eventually to an entire slip surface. The H-surface was obtained according to the measured displacement to distinguish the zone where the surface load influenced the horizontal displacement of the slope. The H-surface and the position where the peak vertical displacement occurred in a horizontal line moved from the internal slope to the slope surface from the slope top to the slope bottom. This demonstrates the dispersion of the surface load application within the slope. The deflections of nails can be obtained from the corresponding soil deformation. The deflection of nails increased with the increasing load pressure, and exhibited diverse features in its distribution in the upper and the lower parts of the slope.

Transverse compression behavior of polyamide 6.6 rovings: Experimental study

The purpose of the present work is to understand physical phenomena occurring in roving structures under transverse compression. In order to reach this aim, transverse behavior of prototype rovings featuring a small number of polyamide 6.6 filaments are studied using an experimental device developed in our laboratory. Moreover, the effect of roving characteristics on their transverse compression behavior is examined. The studied characteristics are filament diameter and number, roving twist and tension. It is found that the roving behavior under compression shows plateaus separated by a significant increase of compression force, indicating discontinuous changes in the roving structures. This fact may be attributed to a reorganization of rovings followed by a local slippage between filaments. Transverse properties of rovings are affected by contact-friction inter filaments and the initial filament section fraction. In fact, it is more difficult to compact high-twisted rovings. Rovings with a greater number of filaments require a higher force in order to be compacted. The pre-tension of the rovings has no noticeable effect on their compression behavior.

Flexural behavior of reinforced concrete beams strengthened with a hybrid inorganic matrix - steel fiber retrofit system

The aim of this study was to investigate the flexural behavior of reinforced concrete beams strengthened with a novel strengthening system. Concrete beams were strengthened with a hybrid retrofit system consisting of high strength steel cords impregnated in an inorganic fireproof matrix (Geopolymer). The strengthened reinforced concrete beams along with non-strengthened control beams were tested monotonically under four point bending loading conditions. Moreover, an analytical model is introduced, that can be used to analyze the flexural performance of the strengthened beams. The experimental results indicate that the failure of the strengthened beams was based on the yielding of the reinforcement in the tension face of the beams, followed by a local slippage of the steel cords. The flexural stiffness of the strengthened beams was significantly improved compared to the stiffness of the non-strengthened beams. In conclusion, the strengthening system can provide an effective alternative to commercially available systems.

Experimental research on distributed fiber sensor for sliding damage monitoring

A distributed optical fiber sensor (DOFS) with the principle of microbend loss has been developed for concrete or rock-sliding damage measurement. The combination of multiple microbend sensors can form a sensor array for distributed sensing application in monitoring local slippage or deformation along the rock mass of the high slope, and the optical time-domain reflectometry (OTDR) can be conveniently used for interrogation of each sensor point. The sensor sensitivity can be obtained at a specific range according to the requirement of the model test condition. Connected with multiplexed sensing processing schemes, its sliding range of dynamic sensing response reached 0–3.6 mm and semi-empirical formula was fitted according to data from model tests. The DOFS array may find a potential application in real-time monitoring and damage detection of large and critical slope engineering structures.

522 ボールネジ内部のボール/ネジ溝間の力学的相互作用(OS17.計算力学と最適化(3),オーガナイズドセッション)

Ball-Screw is composed of Screw-Rod, Nut and a number of Balls, which has a smooth motion due to the rolling friction instead of the sliding friction. While the balls are moving, they show a complex motion rather than a simple revolution, due to the local slippage, which has a significant influence on its smooth motion transmission and its durability. In the case of ball bearings, rolling bodies show a complex motion even in a 2/D ring slot, whereas in the case of ball-screw, they show a more complex motion due to the spiral slot shape and reaction from ball circuit. In this paper, with the practical use of the tool for multi body dynamics, the motion of balls in a slot is numerically verified, as well as the level of friction force.

Using Three-dimensional Plant Root Architecture in Models of Shallow-slope Stability

The contribution of vegetation to shallow-slope stability is of major importance in landslide-prone regions. However, existing slope stability models use only limited plant root architectural parameters. This study aims to provide a chain of tools useful for determining the contribution of tree roots to soil reinforcement. Three-dimensional digitizing in situ was used to obtain accurate root system architecture data for mature Quercus alba in two forest stands. These data were used as input to tools developed, which analyse the spatial position of roots, topology and geometry. The contribution of roots to soil reinforcement was determined by calculating additional soil cohesion using the limit equilibrium model, and the factor of safety (FOS) using an existing slope stability model, Slip4Ex. Existing models may incorrectly estimate the additional soil cohesion provided by roots, as the spatial position of roots crossing the potential slip surface is usually not taken into account. However, most soil reinforcement by roots occurs close to the tree stem and is negligible at a distance >1.0 m from the tree, and therefore global values of FOS for a slope do not take into account local slippage along the slope. Within a forest stand on a landslide-prone slope, soil fixation by roots can be minimal between uniform rows of trees, leading to local soil slippage. Therefore, staggered rows of trees would improve overall slope stability, as trees would arrest the downward movement of soil. The chain of tools consisting of both software (free for non-commercial use) and functions available from the first author will enable a more accurate description and use of root architectural parameters in standard slope stability analyses.

Study on Velocity Characteristics and Mechanics of Paper Feeding with Rubber-Covered Roller Drive.

Paper feeding systems with rubber-covered roller drive are widely used in information processing devices such as copy machines, printers and ATM. It is important in their designs to control the paper velocity with precision. Accordingly, the experimental verification is carried out to estimate the effects of the normal load between two rollers, the back tension of a paper sheet and also the change of the frictional coefficient on the velocity ratios of the paper translation to the roller rotation. Next, the behaviors of a rubber-covered roller driving a loaded paper sheet together with a rigid roller are simulated in transition from the micro-slip contact to the rolling contact with non-linear finite element analyses. And furthermore, the variations of the shearing stress distributions and the deformations of the rubber as well as the local slippage in the various kinds of conditions are investigated by enforcing the rotating condition on the rubber-covered roller. As a result, the effects of the normall load, the tension force and the driving configuration on the velocity ratios are studied by using the presented mechanical model, which is based on the deformation mode and the micro-slip zone in the contact nip.

A special technique for determining the bond strength of micro-fibres in cement matrix by pullout test

The complete relationship between the pullout load and the displacement of a fibre when it pulls out of the matrix serves as an important parameter in the design of composite materials. Many analytical models for the prediction of the behaviour of composite materials are based on the assumption of a constant friction load between the fibre and the matrix, regardless of the displacement of the fibre. Based on this assumption test techniques were developed [1, 2] in which the critical length of the fibre was determined. The bond strength was calculated from the critical length assuming that the fibre strength and diameter are known. The two techniques are quite similar, and were found by [1] as inapplicable for extremely brittle fibres such as carbon fibres. In addition, some pullout tests suggest an interface friction which depends on the amount of local slippage [3]. Such slip-dependency cannot be identified by test methods based on measuring the critical fibre length only.

The physics of very large landslides

In 1881 the alpine village of Elm, Switzerland, was nearly wiped out by an enormous rockslide that flowed 2 km down the valley. This disaster made geologists and engineers aware that large masses of rock debris may sometimes behave like a fluid with a low internal resistance to deformation. Since 1881 many other instances of fluidized rockslides have been found, both contemporary and prehistoric. The discovery of such rockslide deposits on Mars and the Moon make it clear that neither air nor water play an essential role in the fluidization process, although they may enhance it. The fluid-like flow of large rock debris masses, evenin vacuo, may be explained by the presence of strong acoustic waves or ‘noise’ within the slide mass. Acoustic waves, generated by the shear flow, diffuse though the strongly-scattering rock debris. Because rocks in the slide remain largely in contact during flow, these waves may transmit large pressure fluctuations elastically without simultaneously transporting large amounts of energy. The pressure fluctuations allow the dry rock debris to yield under a differential stress much smaller than the average overburden. The overburden is briefly relieved by any unusually large pressure fluctuation and a local slippage may take place in the debris mass. If such local slippages are frequent enough, the debris may creep forward under an anomalously small mean shear stress. The theoretical prediction, that rock debris may be fluidized by strong acoustic waves, was tested experimentally in sand subjected to strong ultrasonic shaking. Preliminary observations are consistent with the theory. As predicted, the flow is highly non-Newtonian for weak acoustic fields (strain rate is proportional to the eighth power of the stress), but approaches Newtonian flow as the acoustic intensity increases. Rockslides involve so much strain that the acoustic energy produced during the initial fall cannot last long enough to keep the mass fluidized during the last stages of motion. Acoustic fluidization can account for the mobility of large masses of rock debris only if the acoustic energy is regenerated during flow. It is plausible that shear flows may generate large amounts of acoustic energy and thus regenerate the field, but the efficiency of the process is still uncertain. Theoretical studies suggest that regeneration is adequate to acount for the principal features of large rockslides, but more experimental work is required. Despite these uncertainties, fluidization by sound is the only theory that accounts for the major features of the large rockslides orSturzstrom that have occured on earth and the other planets of our solar system. This theory also accounts for the collapse of large impact craters, the formation of central peaks, and the formation of the multiple ring systems that characterize impact basins.

The Rolling Contact of Two Elastic-Layer-Covered Cylinders Driving a Loaded Sheet in the Nip

A circular stress function is used for the steady rolling contact of two cylinders. Each cylinder has an elastic layer bonded to a hard core, and an elastic thin sheet is compressed in the contact arc and being driven by the system. An asymmetric stress distribution is caused by a pushing or pulling force acting at the tail end of the sheet. The effect of the normal load and the tail force on the speed ratios of the two cylinders and the sheet, and also the local slippage in the contact arc are studied by enforcing the exact conditions at the contact zone. The resulting equations are solved by the collocation method and an iterative procedure which stepwisely unlocked the nonslip contacting points whenever the calculated interface shear exceeds the local Coulomb friction.