High Friction Angle Research Articles

NUMERICAL MODELING OF RETAINING STRUCTURES MADE OF BLOCKS WITH SOIL INFILL

The relevance of the study is driven by the expanding use of numerical models in the design practice of retaining structures and the need for their verification. A promising design solution for retaining walls is a stepped structure, sequentially constructed from hollow-body box type blocks infilled with crushed stone. This solution has several features that require the adaptation of existing calculation methods. A numerical model of a retaining structure made of thin-walled blocks infilled with soil has been developed based on the analysis of the interaction between the structure's components under load, taking into account the work of the foundation and surrounding soil. The SiO2D finite element modeling computer software was used as a modeling tool. The calculation results for the proposed numerical models are compared with corresponding results for analytical solutions. The parameter values of the main physico-mechanical properties of the numerical models were determined as a result of field and laboratory tests in accordance with standard methodologies considering the scale of the tests. The features of the design solution and construction technology of retaining structures made of thin-walled reinforced concrete blocks infilled with crushed stone were examined. Numerical models of retaining structures made of soil-infilled blocks were constructed using the domestic software package SiO2D. Laboratory and field tests established the parameters of the numerical model of the retaining structure. The research demonstrates high values of the structural cohesion («interlocking») parameter c (up to 60 kPa), alongside a high internal friction angle value φ (up to 60°), ensuring high shear stability of the infilled blocks. The study, using numerical models, proposes a calculation basis for retaining structures made of soil-infilled blocks forming a stepped construction, where the blocks are not rigidly connected but are held in their design position by the internal resistance forces of the soil against shear.

The Uses of Lightweight Material in Civil Engineering : A Review

A lightweight aggregate (LWA) is a group of aggregates with a relative density lower than normal density aggregates (natural sand, gravel, and crushed stone), sometimes referred to as low density aggregate. It is utilized for its reduced weight and exceptional qualities in sound reduction, fire resistance, insulation, and geotechnical applications LWA, or lightweight aggregate, is a cutting-edge construction material that is employed to decrease the overall weight of tall structures. Despite being lighter, it possesses a strength that is comparable to that of regular concrete. In recent times, there has been a significant surge in the use of lightweight aggregate in the field of building, mostly because of its exceptional performance in seismic situations. In addition, substituting natural aggregate with other industrial by-products and trash enables us to minimize the adverse environmental consequences. Laser wavelength ablation (LWA) has also been employed to address a wide range of geotechnical engineering challenges, including the transformation of soft and unstable soil into a suitable and usable property. Lightweight fillings have a weight that is around 50% less than fills made using typical materials. The load reduction, along with the high internal friction angle of the lightweight aggregate, can decrease vertical and lateral pressures by almost 50%, potentially resulting in less settling. This literature study examines the use of lightweight materials, including LECA, Bonza, and Thermostone, in geotechnical engineering applications. The results demonstrate a significant emphasis on improving slope stability and minimizing stresses on susceptible soils. Nevertheless, several knowledge gaps exist regarding the efficacy of these materials under challenging conditions and when subjected to dynamic loads. A growing inclination towards using these lightweight aggregates is observed because of their advantageous environmental and mechanical properties. Further investigation is needed to examine the extended-term performance and interactions of these materials with different soil types in order to enhance their performance in diverse geotechnical situations.

Numerical prediction on frictional characteristics of binary mixtures consisting of flexible cylindrical particles and rigid spheres

A Discrete Element Method (DEM) model for deformable cylindrical particles is established to investigate the Jenike shear process of binary mixtures consisting of flexible cylindrical particles and rigid spheres. The effects of the shape of flexible cylindrical particles and the proportion of cylindrical particles to spherical ones on the friction behavior of the mixture are discussed. Numerical results show that both the shear stress and internal friction angle increase with the aspect ratio (Ar) of the flexible cylindrical particles but decrease with the increase of the proportion of spherical particles. The role of Ar becomes slight when when the amount of spheres are much higher than the cylindrical particles (double or higher). For the mono-system containing flexible cylindrical particles of Ar=6 but without spheres, the strong interlocking packing structure leads to high shear stress and internal friction angle. It is indicated that the inclusion of rigid spheres disrupts the interlocking structure between flexible cylindrical particles and acts as a lubricant during the shear process. Based on the numerical results, a predictive correlation is established to predict the frictional characteristics of binary mixtures consisting of flexible cylindrical particles and rigid spheres considering the effect of particle shape and proportion. Furthermore, through a microscopic analysis of the numerical results, a deeper understanding of this phenomenon is gained. It is confirmed that the spherical particles can fill the voids between the flexible cylindrical particles, increasing the compactness of the mixture and promoting lubrication effects. The current research contributes to the better understanding of the mechanism of particle flow and is of paramount importance to improve the kinetic theories for complex granular flows.

A pressure-sensitive rheological origin of high friction angles of granular matter observed in NASA–MGM project

Abstract An abnormally high peak friction angle of Ottawa sand was observed in (National Aeronautics and Space Administration) NASA–(Mechanics of Granular Materials) MGM tests in microgravity conditions on the space shuttle. Previous investigations have been unsuccessful in providing a constitutive insight into this behavior of granular materials under extremely low effective stress conditions. Here, a recently proposed unified constitutive model for transient rheological behavior of sand and other granular materials is adopted for the analytical assessment of high peak friction angles. For the first time, this long-eluded behavior of sand is attributed to a hidden rheological transition mechanism, that is not only rate-sensitive, but also pressure-sensitive. The NASA–MGM microgravity conditions show that shear-tests of sand can be performed under abnormally low confining stress conditions. The pressure-sensitive behavior of granular shearing that is previously ignored is studied based on the μ(I) rheology and its variations. Comparisons between the model and the NASA microgravity tests demonstrate a high degree of agreement. The research is highly valid for pressure-sensitive and rate-dependent problems that occur during earthquakes, landslides, and space exploration.

Mechanical properties of reaction mediums in permeable reactive barriers

The mechanical properties of reaction media in permeable reactive barriers (PRB) is vital in geoenvironmental applications. Bentonite, activated carbon and zeolite, recognized for their excellent adsorption capabilities, are employed as the main reaction media in PRB for the treatment of contaminated underground water. The compaction test and the undrained and unconsolidated triaxial test were carried out to investigate the compression and shear strength of the activated carbon-zeolite mixture and activated carbon-bentonite mixture at various composition ratios. The impact of compaction degree on samples' shear strength was analyzed. The influence of different composition ratios on the mechanical properties and the permeability of each reaction medium were also evaluated. The results show that the mechanical performance of most activated carbon-zeolite (AZs) is not satisfactory compared to natural soil and activated carbon-bentonite mixtures. Activated carbon‑sodium bentonite (ANBs) and activated carbon‑calcium bentonite (ACBs) present similar compaction characteristics and shear properties. In ANBs and ACBs, the cohesion of mixes with a mass ratio of 1:2 (ANB2 and ACB2) was found lower than that of mixes with mass ratios of 1:1 (ANB1 and ACB1) and 1:3 (ANB3 and ACB3). And in most ANB and ACB mixes, 100 % compaction produced higher moisture content and higher friction angle, but lower cohesion, compared to 92 % compaction degree. And the shear strength behavior of ANBs is dominated by both bentonite and activated carbon. The permeability of ACB1, AZ3 and ACB1-sand are at 1.31 × 10−6 m/s, 1.37 × 10−6 m/s and 7.72 × 10−7 m/s, respectively. These results provide valuable insights into the selection and optimization of reaction media for PRBs in geoenvironmental engineering applications.

Causes of the high friction angle of diatomaceous soil: microscale and nanoscale insights

Diatomaceous soil has geotechnical properties that differ fundamentally from those of common non-diatomaceous soils due to the presence of diatom microfossils with biological origins. Despite its dominant fines content, diatomaceous soil usually has high frictional shear resistance (approaching that of sand). Currently, the exact role of diatoms in controlling soil strength and underlying mechanisms remain obscure. Here, the frictional strength of diatomaceous soil is evaluated by way of angle of repose and direct simple shear tests on diatom–kaolin mixtures with differing diatom content. The microscale and nanoscale structures are characterised in detail using scanning electron and atomic force microscopy to establish how soil structure evolves with diatom content and shear. For the studied diatom–kaolin mixtures, the angle of repose and internal frictional angle are high and increase with diatom content, especially when the diatom content exceeds 20%. Diatom content controls the frictional strength through its intricate morphology (cylindrical, saucer and disc shapes), very rough surface (hundreds of times rougher than flaky minerals) and stiff frustules with high Young's modulus. These features increase the particle coordination number and produce interparticle interlockings, both of which prevent particle rearrangement during shear and improve the frictional strength. This paper provides new insights into the multiscale structure of diatoms and improves understanding of the shear strength of diatomaceous soils.

A Mechanistic Model and Experiments on Bedrock Incision and Channelization by Rockfall

AbstractRockfall and rock avalanches are common in steep terrain on Earth and potentially on other planetary bodies such as the Moon and Mars. Since impacting rocks can damage exposed bedrock as they roll and bounce downhill, rockfall might be an important erosive agent in steep landscapes, even in the absence of water. We developed a new theory for rockfall‐driven bedrock abrasion using the ballistic trajectories of rocks transported under gravity. We calibrated this theory using laboratory experiments of rockfall over an inclined bedrock simulant. Both the experiments and the model demonstrate that bedrock hillslopes can be abraded by dry rockfall, even at gradients below the angle of repose, depending on the bedrock roughness. Feedback between abrasion and topographic steering of rockfall can produce channel‐like forms, such as bedrock chutes, in the absence of water. Particle size has a dominant influence on abrasion rates and runout distances, while the hillslope angle has a comparatively minor influence. Rockfall transport is sensitive to bedrock roughness; terrain with high friction angles can trap rocks creating patches of rock cover that affect subsequent rockfall pathways. Our results suggest that dry rockfall can play an important role in eroding and channelizing steep, rocky terrain on Earth and other planets, such as crater degradation on the Moon and Mars.

Characterization of the Ngouache Landslide by Geotechnical Survey (Bafoussam, Cameroon)

The heavy rainfall during the night of October 28-29, 2019, caused a landslide in the Ngouache 4 neighborhood in Bafoussam in the West Cameroon region. This landslide caused 43 deaths, several missing persons and the destruction of several houses and plantations. The present investigation attempts to find the causesof this landslide. First, the landslide area was identified and heavy dynamic penetrometer surveys were conducted. Next, intact and reworked samples were taken and, finally, slopes were measured on the slide area to determine the soil parameters. The results of the heavy dynamic penetrometer showed the presence of altered clay layers which, when saturated, exert hydrostatic pressure and unbalance the soil. The granulometric analysis noted a soil with more than 50% of grains of ϕ>80µm with liquidity limits between (50-65.3%), a consistency index between (1.01-1.24), a low cohesion between (0.22-0.30 bars) for a high internal friction angle (20.72°-23.86°), slopes between 48° and 56° and a degree of saturation Sr between (80.5° and 139.9°). These characteristics associated with the large water columns of the night of October 28 to 29, 2019 demonstrated that the water had exerted a hydrostatic pressure having made the clay material reach the limit of plasticity to the creep and raised the level of the water table. Thistherefore promoted the saturation of the substrate yet the increase in the water content reduces the cohesion of the materials and that triggered the saturation at the origin of this deadly slide. The results of the present research may help the public authorities in the decision making regarding the characterization and the securing of risk zones.

GCL-LLDPE geomembrane interface friction angle evaluation and stability analysis of a valley fill leach pad project

The Los Chancas mining project, initiated in 1998, is a copper mine focused on extracting copper sulfides and oxides. In 2020, a mine plan update required a review of the constructability design and an evaluation of the Permanent Leach Pad and Filtered Waste/Rock Dump's physical stability. This paper presents results from an evaluation study regarding friction angles at the liner interface and stability analysis in the VLF pad. Previously, an internal friction angle of 23° was established for the basal liner interface (LLDPE-GCL) to meet stability requirements. However, due to the high required friction angle, the pad design was updated with lower slopes. The study evaluated various GCL materials from two suppliers using direct shear tests, revealing that the GCL from the second supplier achieved a high friction angle of 22.3° at the interface. Stability analysis considered two critical sections, examining three types of failure under both static and pseudo-static conditions. Results showed a need for a minimum friction angle of 16° in static conditions and 20.5° in pseudo-static conditions to ensure compliance. These results suggest the potential use of high strength geosynthetic materials in the studied areas, with a preference for the GCL material offering the highest friction angle.

Mechanism of hydraulic fracture vertical propagation in deep shale formation based on elastic–plastic model

Deep shale reservoirs exhibit strong plasticity, and the simulation results from previous fracturing simulations based on elastic models may not adequately account for the effects of plastic. Therefore, the research objective is to develop a 3D finite element method (FEM) model of hydraulic fracture vertical propagation in multilayer reservoirs. The model simultaneously considering Drucker-Prager elastic–plastic rock model and bedding plane. To investigate the impact of various parameters on the vertical propagation pattern of fracture, it is crucial to consider factors such as friction angle, yield strength, interlayer strength, and vertical stress. This study quantitatively characterizes the mechanical parameters such as ground stress, matrix strength, and interface strength on hydraulic fracture morphology. Additionally, a new integrated control diagram is established to provide a comprehensive understanding of these effects. The results indicate that rocks with high friction angles and low yield strength are more resistant to cracking, and hydraulic fractures tend to have narrower fractures. Fracturing from high-strength and high-stress zones to lower zones promotes vertical fracture propagation. The high vertical stress plays a crucial role in preventing the fracturing fluid from entering the interface. Moreover, the strength of the formation interface greatly influences the vertical extension of hydraulic fractures. The bedding plane interface with a high cementation level can enhance the possibility of fracture vertical connection with multiple reservoirs. Conversely, breaking through low strength cemented interfaces in the formation can pose challenges for hydraulic fractures. The present simulation conditions determine that the fracture's ability to cross the layer depends on the ratio of interface strength to matrix strength, which should be between 0.25 and 0.5. These findings offer valuable theoretical guidance on the vertical propagation of fractures in deep multilayer fracturing.

Application of electrical resistivity tomography and geotechnical techniques for identification and characterization of collapsible soils in Bafoussam (Western, Cameroon)

Road failure catastrophes have increased in frequency in the West Cameroon area. The collapsed soil characteristics that contribute to these phenomena in Bafoussam have been investigated using the geophysical investigation combined with geotechnical tests. The result of electrical resistivity tomography shows water conditions and heterogeneity of road foundation materials: resistivity values higher than 200 Ωm indicate dry materials, values between 30 and 200 Ωm define wet materials, and values lower than 30 Ωm indicate the very wet or water-saturated materials. These water-saturated materials can therefore move, bounded by a sliding surface of high-resistivity materials. Geotechnical properties analysis shows that these materials are clayey-sensitive water (64% clay fraction; A-7-6), very plastic (liquid limit: 46–63% plasticity limit: 29–39%), compressible, with high porosity (e > 0.8), low shear strength, and high friction angle (24–37°). The quality of foundation materials associated with high slopes (> 40°) and heavy rainfall in wet seasons (July–October) means that seepage water is the main factor responsible for the mass movement observed on the road of Western Cameroon. The construction or rehabilitation of these roads should be carried out in compliance with the natural conditions of the project site.Article highlights- 2D Electrical Resistivity Tomography method is able to determine the nature, subsurface structure and water conditions of road foundation soils.- Geotechnical test can be used to define the physical and mechanical properties of road foundation soils.- These two techniques complement each other to understand the mass movement observed on two sections of road failures caused by seepage water.

Numerical study on influence of particle shape and deformation on friction behavior of flexible cylindrical particle flows

AbstractA discrete element method (DEM) model for deformable particles is established and adopted to investigate the Jenike shear process of flexible cylindrical particles with different aspect ratios (4 < < 6). The DEM model is firstly validated against both experimental data and analytic solutions. Then, numerical simulations are carried out and the effects of particles shape and deformation on their friction behavior are investigated through a particle‐scale analysis on particle deformation, coordinate number, contact forces, orientation and internal friction angle. Comparative results between flexible and rigid particles under the same conditions show that the shear stress increases almost linearly with the normal load regardless of particle stiffness or shape. For both rigid and flexible particles, the shear stress and internal friction angle increase with . The shear stress and internal friction angle of the flexible particles are higher than those of the rigid ones especially when = 6. The latter has more inter‐particle contacts but the former has stronger contact forces. When = 4 and 5, the flexible particles without many initial deformations will deform significantly during the shear process with a complex reconfiguration taking place. However, when = 6, the initial deformation and internal forces of the flexible particles only change slightly during the shear process. It is thus believed that the high shear stress and internal friction angle of the flexible particles with = 6 are caused by their solid packing structure which strongly enhances the capability of the particle flow to resist shear. The current knowledge will be helpful for improving the kinetic theories for granular flow for complex irregular particle flows.

Evaluation of lightweight aggregate to reduce vertical stresses and improve load transfer in pile-supported embankments

Lightweight aggregate has unique characteristics of light self-weight, high friction angle, and good interaction with geosynthetics, and may be used as a fill material in load transfer platforms (LTP) over piles to support embankments on soft soils. This study included five plane-strain trapdoor tests to evaluate the use of lightweight aggregate to improve the performance of load transfer platforms over piled beams to support embankments on soft soils. These model tests consisted of trapdoor downward movement (settlement) and surface loading to investigate the mobilization and degradation of soil arching above the trapdoor. The surface loading was applied locally using a hydraulic jack through a footing. The vertical stresses on the trapdoor and the stationary supports were measured using earth pressure cells and the settlement of the footing was measured using a displacement transducer. Test results showed that soil arching mobilized with the settlement of the trapdoor and degraded with the footing loading. The geosynthetic reinforcement hindered the degradation of soil arching and increased the bearing capacity of the embankment under footing loading. Overall, the lightweight aggregate had favorable soil arching behavior with low vertical stresses on the trapdoor and the stationary supports as compared with the river dand. Lightweight aggregate is proven to be a good alternative material for load transfer platforms in pile-supported embankments.

Experimental study on the behavior of single pile foundation under vertical cyclic load in coral sand

The bearing behaviors of piles in coral sand are critical for project safety due to the unique physical and mechanical properties of coral sand, such as high void ratio, high compressibility, high friction angle and easy to break. A series of model experiments were carried out in this study to evaluate the vertical behavior of single pile in coral sand foundation under cyclic dynamic load with the consideration of the influence of the amplitude of cyclic load, the static biased load and the number of cyclic. Load-settlement relationships, settlement-cyclic number relationships, pile tip and pile side resistances have been thoroughly investigated. Results showed that the load in coral sand foundation will transfer to the pile tip more obviously compared with the pile foundation in quartz sand. Therefore, the pile side resistance will be reduced while the corresponding pile tip resistance will be increased. Particularly, the weakening of side resistance mainly occurs in the first 500 cycles. The development of cyclic cumulative settlement is affected by the combination of the magnitude of static biased load and cyclic amplitude. The existence of static biased load is conducive to restrain the cyclic cumulative settlement when the amplitude of cyclic load is less than static load.

PARAMETERS CONTROLLING THE GEOMETRY OF DETACHMENT AND FAULT‐BEND FOLDS: INSIGHTS FROM 3D FINITE‐ELEMENT MODELS APPLIED TO THE AHWAZ ANTICLINE IN THE DEZFUL EMBAYMENT, SW IRAN

Fault‐related folds are present in most tectonic settings and can serve as structural traps for hydrocarbons. These structures have therefore been widely studied by both structural and petroleum geologists using a range of techniques. Approaches include field‐ and seismic‐based methods, and numerical and analogue modelling. Geomechanical models attempt to examine the mechanical and geometric features of folds.This study investigates the effects of variations in a range of parameters, including detachment and ramp geometry, friction coefficient and internal friction angle, on the geometry and development of detachment folds and fault‐bend folds. For this purpose, we ran seven series of numerical, 3D elastic‐plastic finite element models using ABAQUS software (26 model runs in all). Each model set‐up consisted of five layers whose mechanical properties were based on those of stratigraphic units in the Zagros fold‐and‐thrust belt, SW Iran. The models were labelled series A to F and series H. Models in series A investigated the impact of concave, convex, wavy and oblique detachment surfaces on the development of detachment folds; those in series D examined the role of ramp dip and of listric, oblique and wavy ramps on the development of fault‐bend folds. Models in series B and E, and series C and F, examined the effects of variations in the friction coefficient and of the internal friction angle, respectively, on the development of these two classes of folds. Finally, hybrid models in series H were provided to evaluate the results.Major results were as follows. Firstly, the geometry of modelled detachment and fault‐bend folds was found to be influenced by the geometry of the associated ramps and detachment faults. Thus the crests of anticlines and the trough lines of synclines were located at points of maximum curvature and at inflexion points on a wavy detachment fault or wavy ramp, respectively. Second, two important additional factors controlling fold style were identified: the friction coefficient, and the presence of along‐strike geometric variations in the ramp or the detachment fault. Layers with low friction coefficients and high internal friction angles formed detachment folds with thick hinges and thin limbs; conversely, layers with high friction coefficients and low internal friction angles created detachment folds with thick limbs and thin hinges. Application of the results to modelling of the Ahwaz anticline in the Dezful Embayment, SW Iran, was successful, and in general the modelled structure was consistent with that observed in the field.

Unsaturated shear strength parameters for a compacted iron ore tailings

The use of iron mining tailings in compacted landfills is expected to expand more and more to replace the placement of tailings in dams. With this, the unsaturated condition of these materials becomes of great importance for the safety of the structures executed with them. In addition to tests in the saturated condition, and with the objective of simplifying the determination of strength parameters in the unsaturated condition, direct shear tests with constant water content were performed. Data of physical and chemical characterization of the tailings, and the water retention curve at the compacted state and continuously disturbed condition are also presented. The latter aims to evaluate the effect of the shear process on the final suction of the material. The results suggest that there are no significant variations in suctions during the failure process and that, in this case, the initial suction can be assumed to be the same as the one at failure. The shear strength parameters indicate a high friction angle, which does not vary with suction. With the data obtained, it was possible to apply the model of Vilar (2006) to obtain the shear envelope with suction. The results presented aim not only to expand the database of iron ore tailings parameters, but also to present a procedure for the application of tests with constant water content.

Interpretation of CPTu and SPT data about sandy soils in the Plovdiv region

CPTu (Piezocone Penetration Test) and Penetration tests – SPT (Standard Penetration Test) are the most used in situ tests in order to map a soil stratigraphy and determine the geotechnical parameters of construction soils. A comparison has been made between the relative density values obtained on the basis of the two types of field trials. The soils examined are classified according to well-established classification diagrams. The sandy soils are described in the range of dense to very dense. They have good strength and deformation characteristics – with a high friction angle and high Young’s modulus but the presence of a high level of groundwater is a prerequisite for their liquefaction under dynamic impacts.

Numerical Simulation on Borehole Instability Based on Disturbance State Concept

This paper carries out a study on the numerical simulation of borehole instability based on the disturbance state concept. By introducing the disturbance damage factor into the classical Mohr–Coulomb yield criterio, we establish a finite element hydro-mechanical coupling model of borehole instability and program the relevant field variable by considering elastic–plastic deformation in borehole instability, the distribution of the damage disturbance area, the variation of porosity and permeability with the disturbance damage factor, etc. Numerical simulation shows that the borehole stability is related to the action time of drilling fluid on the wellbore, stress anisotropy, the internal friction angle of rock, and borehole pressure. A higher horizontal stress difference helps suppress shear instability, and a higher rock internal friction angle enhances shear failure around the borehole along the maximum horizontal principal stress. When considering the effect of the internal friction angle of rock, the rock permeability, disturbance damage factor, and equivalent plastic strain show fluctuation characteristics. Under the high internal friction angle of rock, a strong equivalent plastic strain area and disturbance damage area occur in the direction of the maximum horizontal principal stress. Their cloud picture shows the mantis shape, where the bifurcation corresponds to the whiskers of the shear failure area in borehole instability. This study provides a theoretical basis for solving the problem of borehole instability during drilling engineering.

Precipitation Amounts Triggering Landslide Processes in the Western Part of the Nałęczów Plateau (Lublin Upland, Poland)

Abstract This study covers the western part of Poland’s loess Nałęczów Plateau (Kazimierz Dolny, Zbędowice). Mass movements in the Lublin Upland occur during periods of increased precipitation or after a snowy and cold winter. To date, there are no comprehensive studies on active (precipitation, hydrology, vegetation, land use, anthropogenic factors) or passive factors (lithology, slope angle) causing such geohazards in this region. This area’s formations are characterised by high sensitivity to even small changes in moisture content; thus, their geotechnical parameters deteriorate as a result of precipitation or rising groundwater levels. The calculations in this study were chosen to determine the time necessary for ground response to external factors, in addition to determining the impact of these factors on decreases in the factor of safety (FS). Based on calculations in GeoStudio software, the impacts of rainfall totals and duration on slope failure, interpreted as an event where the FS falls below 1.0, were analysed. Accordingly, the threshold rainfall value was determined as the total rainfall at the time of slope failure. The study’s results indicate that loess covers are characterised by average water permeability, relatively high internal friction angles and low cohesion, which, combined with high slope inclination, favour landslide formation even when the slope is only partially saturated. The most unfavourable stability conditions occur at the beginning of spring, indicating that loess stability is significantly affected by snowmelt and precipitation at the beginning of the vegetation season, as well as the occurrence of episodic intense precipitation during the summer.

The effects of target density, porosity, and friction on impact crater morphometry: Exploratory experimentation using various granular materials

AbstractThe dimensions of relatively small‐scale impact craters are undoubtedly sensitive to the physical properties of the target. Studying gravity‐controlled crater formation at the laboratory scale often relies on cohesionless, granular materials, which, by their nature, make it difficult to separate the individual contributions to this process from all of the relevant target properties. Here, we conduct a suite of impact experiments to isolate and evaluate the effects of density, porosity, and internal friction on impact crater morphometry. Each made from one of four different granular materials, targets were impacted vertically with 4.76 mm aluminum projectiles at an average speed of ~1.55 km s−1. Two different methods were used to load these materials into the target bucket (pouring and sieving), resulting in targets that varied in bulk density and internal friction. The experimental results indicate that depth–diameter ratios of the craters are largely influenced by the loading method of the target material and are sensitive to the friction and porosity of the targets. Sieved targets (relatively higher density, lower porosity, and higher friction angle) produce craters that are markedly shallower, have notably smaller volumes, and exhibit a flat‐floored morphology, with some possessing small central mounds. Flat‐floored craters are typically attributed to a strength‐layered target; in these experiments, however, they were produced in cohesionless targets. This study demonstrates that a flat floor is not necessarily diagnostic of strength layering in a target and, in some instances, might be the consequence of greater shear strengths in granular materials with high coefficients of static friction.