Appraisal of Anchor Arrangement and Size On Sand-Geogrid Interaction In Direct Shear

Soil – reinforcement interaction is a major factor in the analysis and design of reinforced earth structures. In current research the effects of attaching elements of different size and numbers as anchors on enhancement of interaction at soil - geogrid interface under direct shear conditions were studied. Poorly and well graded sands (SC & Sf), a high density polyethylene geogrid, anchors with three different size and numbers (layouts) and clamping length of 2cm from shear surface were used. Samples were prepared dry at a relative density of 80% in a 30×30cm direct shear box and subjected to normal pressures of 12.5, 25 and 50kPa with the shear load applied at a rate of 1mm/min. Results of the assessment show that anchored geogrids improve shear resistance at interface mainly due to mobilization of passive soil resistance that is significantly influenced by the magnitude of the normal pressure and the number and size of anchors. Interaction enhancements achieved varied between a minimum of 8% and a maximum of 42%.

A mechanical insight into the triggering mechanism of frequently occurred landslides along the contact between loess and red clay

The triggering mechanism and movement evolution of loess-red clay landslides, which occurred frequently along the contact between the loess and red clay on the Loess Plateau, are closely related to the mechanical properties of the contact surface. This work presents an experimental investigation on loess, clay and loess-red clay interlaminar (LRCI) samples obtained from a typical loess-red clay landslide in northern part of Shaanxi province of China, using a series of ring shear tests, microscopic observation and scanning electron microscopy tests, in an attempt to explore the mechanical behavior of loess, clay and LRCI samples with variation in moisture content, normal stress and shear rate. The results revealed that for all specimens, both the peak shear strength $$\tau_{p}$$ τ p and the residual shear strength $$\tau_{r}$$ τ r decreased with increasing moisture content, among which, moisture content has the greatest influence on the $$\tau_{p}$$ τ p and $$\tau_{r}$$ τ r of red clay, followed by the LRCI specimen, and the loess specimen is least affected by moisture content. Meanwhile, exponential functions describing the correlations between shear strength and moisture content of LRCI, red clay and loess specimens were proposed. Furthermore, the macroscopic morphological characteristics and the microstructure of shear surface obtained from the LRCI specimens showed that a localized water accumulation was built up within the shear surface as the water content increases to some extent, and a high degree of liquefaction developed within shear surface when the moisture content reached to the saturate degree. The microstructural observation on LRCI specimen suggested that the shear surface became smoother and the larger percentage of small-sized pores was observed with moisture content. Accordingly, the built-up excess pore water pressure during shearing is difficult to be dissipated due to a close structure of small-sized pores. Due to the low permeability, high pore-water pressure built up within the shear zone and the increase in the fine particle content, the LRCI soils with a high saturation degree shows the potential for the localized liquefaction within shear zone, which further provides a scientific explanation for the triggering mechanism of loess-red clay landslides with high-speed and long- run out.

Physical experiment investigation on progressive deformation of shear slip surface of the soil slope

<p>The sliding surface deformation of the soil slope mainly presents progressive failure characteristics, and serial acoustic emission (AE) signals are generated during the deformation process of progressive landslide. A model test aiming at reproducing the typical shear surface deformation of a soil slope is designed. The displacement, AE data and corresponding time-frequency characteristics are comprehensively analyzed to evaluate the progressive deformation behavior. Comparisons with different granular backfills measurements show that cumulative AE count increase proportionally with the shear surface displacement, and the experiments demonstrate that the glass sand backfill exhibits remarkable AE detection characteristics and stronger correlation results. Significantly, AE signal exhibits variational dominant frequencies at different deformation stages, and there is the significant phenomenon that not only the low frequency signals generated with a significantly increase number, at the same time the continuous high frequency signals appear during the accelerating deformation stage. Furthermore, from the statistical trend of the energy percentage of the high frequency band into 312.5~500 kHz, it’s found that the correlative energy proportion occupies up to 15%, or even higher during the accelerating stage, indicating that the landslide may be about to enter a severely dangerous stage. The experiments show that the frequency characteristic of the AE signal can be effectively used as the early warning index, which may be the promising reference of the field warning monitoring for the soil progressive landslides.</p>

Parametric study of aluminum bar shearing using Johnson-Cook material modeling

Previous studies of the shearing process demonstrated that clearance and shear rate are the most influential parameters on the geometry of sheared billets. This paper illustrates a parametric numerical study of the impact of these parameters on the quality of the shear surface using the finite element simulation of shearing. In order to account for interactions between stress state evolution and the associated heating during shearing, a fully coupled thermo-mechanical simulation method was adopted. The influence of stress state, strain rate, and temperature on the material behavior were taken into account by using Johnson-Cook plasticity and ductile failure models. Many simulations were carried out involving diverse shear rates and shear clearances. The relationship between the parameters of shear surface geometry and the temperature was illustrated and proven. Contrary to the expectation of high-speed shearing performance, a burr free smooth shear surface was found using a low shear rate. This study illustrates a numerical strategy to determine the best shear clearance-rate set for aluminum alloy Al7075-T6 bars that minimizes the shear surface defects.

Deformation Characteristics of the Shear Zone and Movement of Block Stones in Soil–Rock Mixtures Based on Large-Sized Shear Test

Soil–rock mixtures (SRM) have the characteristics of distinct heterogeneity and an obvious structural effect, which make their physical and mechanical properties very complex. This study aimed to investigate the deformation properties and failure mode of the shear zone as well as the movement of block stones in SRM experimentally, not only considering SRM shear strength. The particle composition and proportion of specimens were based on field samples from an SRM slope along national highway 318 in Xigaze, Tibet. Shear zone deformation tests were carried out using an SRM-1000 large-sized geotechnical apparatus controlled by a motor servo, considering the effects of different stone contents by mass (0, 30%, 50%, 70%), vertical pressures (50, 100, 200, 300, and 400 kPa), and block stone sizes (9.5–19.0, 19.0–31.5, and 31.5–53.0 mm). The characteristics of the shear zone deformation and block stone interactions were monitored by placing aluminum wires and dry ash in holes in the specimens. The results showed that the stone content 30% and 70% were two critical thresholds to determine the deformation characteristics of SRM. Under the conditions of high stone content and large particle size, the stones throughout the shear surface tended to extrude and roll during the shear process. The block stones around the shear surface were mainly affected by dilatancy and exhibited extrusion, particle breakage, and redistribution. The deformation pattern could be considered as be analogous to push-type shear deformation from the back to front or composite shear deformation from the front and back to the middle of the slope. It is of great importance to study the shear characteristics and deformation evolution of SRM to understand the progressive shear process of the sliding zone and the failure mode of landslides.

Numerical Evaluation of the Perfobond (PBL) Shear Connector Subjected to Lateral Pressure Using Coupled Rigid Body Spring Model (RBSM) and Nonlinear Solid Finite Element Method (FEM)

An analytical investigation focusing on the concrete damage progress of the PBL shear connector under the influence of various lateral pressures, employing a coupled RBSM and solid FEM model was carried out. The analytical model succeeded in simulating the test shear capacities and the failure modes adequately. The internal failure process was also clarified; the two horizontal cracks occurred near the top of the concrete dowels through the hole of the perforated steel plate, and afterward, the two vertical cracks also initiated and propagated along with the shear surface. In a low lateral pressure case, the shear strength was determined by the vertical cracks propagated along the shear surface. While as the amount of applied lateral pressure increased, the shear strength of the two vertical cracked surfaces was enhanced, and the shear strength of the PBL was characterized by the occurrence of the splitting cracks and caused the splitting failure into the side concrete blocks. Moreover, the combined effects of lateral pressure and hole diameters were also evaluated numerically, and it was found that the increase in shear strength was more in a large diameter case subjected to high lateral pressure because of the wide compressive regions generated around the concrete dowel.

Lateral variability in strain along the toewall of a mass transport deposit: a case study from the Makassar Strait, offshore Indonesia

Contractional features characterize the toe domain of mass transport deposits. Their frontal geometry is typically classified as frontally confined or frontally emergent. However, it remains unclear how the style of frontal emplacement and contractional strain within a mass transport deposit vary along-strike. We use bathymetry and 3D seismic reflection data to investigate the lateral variability of frontal emplacement and strain within the toe domain of the Haya Slide in the Makassar Strait, offshore Indonesia. The slide originated from an anticline flank collapse and the toe domain is characterized by a radial fold–thrust belt that reflects southwestwards emplacement. The frontal geometry of the slide changes laterally. It is frontally confined in the south and is associated with a deep, c. 200 m b.s.f. planar basal shear surface. The frontal geometry gradually changes to frontally emergent in the west, associated with a shallow, c. 120 m b.s.f., c. 3° NE-dipping basal shear surface. Strain analysis shows c. 8–14% shortening, with the cumulative throw of the thrusts increasing along-strike westwards from c. 20–40 to c. 40–80 m. We show that even minor horizontal translation of mass transport deposits (c. 1 km) can result in marked lateral variability in the frontal geometry and strain within the failed body, which may influence their seal potential in petroleum systems.

Hybridized Love Waves in a Guiding Layer Supporting an Array of Plates with Decorative Endings

This study follows from Maurel et al., Phys. Rev. B 98, 134311 (2018), where we reported on direct numerical observations of out-of-plane shear surface waves propagating along an array of plates atop a guiding layer, as a model for a forest of trees. We derived closed form dispersion relations using the homogenization procedure and investigated the effect of heterogeneities at the top of the plates (the foliage of trees). Here, we extend the study to the derivation of a homogenized model accounting for heterogeneities at both endings of the plates. The derivation is presented in the time domain, which allows for an energetic analysis of the effective problem. The effect of these heterogeneous endings on the properties of the surface waves is inspected for hard heterogeneities. It is shown that top heterogeneities affect the resonances of the plates, hence modifying the cut-off frequencies of a wave mathematically similar to the so-called Spoof Plasmon Polariton (SPP) wave, while the bottom heterogeneities affect the behavior of the layer, hence modifying the dispersion relation of the Love waves. The complete system simply mixes these two ingredients, resulting in hybrid surface waves accurately described by our model.