Interface Friction Angle Research Articles

Passive earth pressure of vegetation rooted soils based on limit analysis and quasi-static approach

Although it has been recognized that vegetation roots have a positive effect on the stability of geotechnical structures, few quantitative studies have been performed on the effects of vegetation roots on earth pressures. In this paper, based on the upper bound limit analysis theory and quasi-static method, a new method for calculating the seismic passive earth pressure of vegetation rooted soils is proposed, which considers both the hydrological and mechanical effects of vegetation roots on the passive earth pressure. The proposed method is validated by some existing solutions. The effects of root parameters of shrubs (root transpiration rate, root tensile strength, and root depth), angle of the soil slope surface with the horizontal, and wall interface friction angle on the seismic passive earth pressure coefficient are also investigated. The results show that the passive earth pressure coefficient increases with the increase of root transpiration rate, root tensile strength, root depth, angle of the soil slope surface with the horizontal, and wall interface friction angle. Compared with the mechanical effect, the hydrological effect of vegetation roots on the passive earth pressure coefficient is more obvious. The effects of root parameters on the passive earth pressure ranked in descending order of sensitivity are root transpiration rate, root tensile strength, and root depth. In addition, the effect of vegetation roots on the passive earth pressure becomes more significant with the increase of internal friction angle. The proposed method can provide a reference for the local reinforcement of multi-stage slopes with vegetation.

Seismic pseudo-static active earth pressure of narrow c-φ soils on gravity walls under translational mode

This study utilises adaptive finite element analysis to investigate the failure mechanisms of narrow cohesive backfill under seismic conditions, and five classical failure modes are summarized. The pseudo-static solution is developed for the case when a narrow cohesive backfill is behind a gravity retaining wall and experiences seismic conditions. Our analytical solution uses the limit equilibrium method, Rankine's theory and the horizontal differential layer method. It considers the effect of soil cohesion, the interface friction angles, backfill geometries, seismic acceleration, the soil arching effect and the effect of shearing forces between adjacent elements on seismic active earth pressure. We propose a new approach that utilises the finite difference method to determine the tension crack depth of the narrow cohesive backfill, and an iterative calculation to determine the critical failure angle of the backfill wedge.

Effect of one cycle of heating-cooling on the clay-concrete pile interface shear strength parameters

This study investigated the effect of applying a one heating-cooling cycle on the interface strength parameters of saturated clay soil in contact with concrete, and the potential use of heating to improve/increase the pile capacity. A large direct shear test device with inner dimensions of 300 mm, 300 mm, and 200 mm for width, length, and height, respectively, was modified to perform the soil-concrete interface tests. A concrete block was built and placed in the bottom section of the shear device. Heating rods system were used to heat the circulating water that heated the specimens. The experimental tests were conducted on low plasticity soil with PI = 12, medium plasticity soil with PI = 29, and high plasticity soil with PI = 60. The specimens were first consolidated to a target normal stress prior to shearing. Two tests were performed for each normal stress and clay type with one test performed without heating-cooling cycle at ∼20 °C and the other test performed at ∼20 °C after a heating-cooling cycle up to 70 °C. The specimens were tested under different normal stresses ranging from 30 to 150 kPa. The specimens' temperature was increased gradually during the heating process from room temperature (∼20 °C) to ∼70 °C. The specimens were then gradually cooled back to room temperature. The test results showed significant increase in both the peak and residual interface friction angles by a percent ranges from 13.6% to 35.5%. The specimens subjected to a one heating-cooling cycle during shear experienced significant volumetric reduction by a percent ranges from 11.3% to 96%. The thermally induced “contraction” volumetric strain (TIVS) was found to increase with increasing temperature loading and the plasticity index, PI, but independent of the applied normal stress.

Earth pressure in narrow cohesive-fictional soils behind retaining walls rotated about the top: An analytical approach

There is currently a lack of an available design approach to estimate the earth pressure in narrow backfills behind retaining walls rotated about the top (RT). The considerations of some significant factors, primarily load transfer mechanisms (soil arching effect and horizontal shear stress in soils), failure mechanisms (shape and number of slip surfaces) and soil cohesion are often neglected for brevity in routine design. Such simplifications may lead to significant deviations from reality. This paper first uses the finite element limit analysis (FELA) technique to identify the underlying failure mechanisms and load transfer mechanisms. The results observed in FELA models indicate that active rotation of walls about the top develops one curved slip surface, which can be approximated by the log-spiral function. Under the soil arching effect, the upper intermediate passive zone with major principal stress rotation trajectory and the lower active zone with minor one can be defined. The arched differential element method (ADEM) is then introduced to formulate the earth pressure calculation. The results from newly published tests, existing analytical approaches, and FELA are compared to validate the accuracy of the proposed approach in both purely-frictional and cohesive-frictional soils. Parametric studies are further conducted to thoroughly understand the earth pressure problems, considering the effects of sensitive design variables (e.g. aspect ratio, soil strength parameters, and wall-soil interface friction angle). The analytical approach presented here would be a great extension to the design guidelines for the retaining structures with narrow backfills.

Effect of snakeskin-inspired patterns on the shear response of soil - continuum interfaces

ABSTRACT The interface shear responses of soils and 3D printed continuum surfaces with patterns inspired by three distinctive snake-scale morphologies are studied. Interface shear tests are conducted under low normal stresses in cranial (where soil shears against the scales) and caudal (where soil shears along with the scales) directions. The experiments show that the snakeskin-inspired surfaces with different heights and shapes of the scales exhibit different shear responses and mobilize frictional anisotropy (difference in peak interface friction angles) in the range of 3–9 degrees. In the cranial direction, all the snakeskin-inspired patterns mobilize the peak internal friction angle of the neighbouring soil at the interface after a critical normalized roughness of the surfaces. Further, the snakeskin-inspired patterns exhibit significant strain-softening behaviour in comparison to an unpatterned surface. Rounded soil particles exhibit a lower frictional resistance and stick-slip phenomenon in the post-peak interface shear response, unlike angular soil particles.

Non-limit passive earth pressure against cantilever flexible retaining wall in foundation pit considering the displacement.

A series of model tests are carried out on flexible retaining walls such as cantilevered piles, continuous walls, and sheet pile walls in the foundation pit to study the deformation, failure surface, and earth pressure distribution of soils in a passive zone. The shape, displacement, and shear strain of slip failure surface of sand in a passive area are analyzed by Particle Image Velocimetry. The slip failure surface is a broken line, the upper end slides out from the top of the soil, and the lower end is close to the zero displacements of the retaining wall. With the increase of the flexural deformation and horizontal displacement of the wall, the shear strain of the soil increases, and the shear fracture zone in the upper part of the sliding surface is more prominent. Based on the broken line rupture surface in the test results, the passive area can be divided into two zones, the limit state zone and the non-limit state zone. Then the mechanical models are set up respectively. Considering soil displacement, the upper and lower soil layer’s internal friction angle and wall-soil interface friction angle mobilize differently. The relationship between mechanical parameters along the retaining wall and horizontal displacement is estimated. Finally, the earth pressure distribution is obtained by using the horizontal differential layer method. The calculation results of this paper are consistent with the existing research results and the model test results in terms of earth pressure distribution. With the increase of depth, the unit earth pressure increases in the limit state zone. Still, after entering the non-limit state zone, the unit earth pressure rises to a certain extent and decreases rapidly.

Limit Analyses of the Active Earth Pressure on Rigid Retaining Walls under Strip Loading on Backfills

Recent studies of retaining walls include experimental studies, numerical analysis and analytical models. Although active earth pressure against retaining structures has received much attention, the evaluation of active earth pressure of backfill when loaded by a strip foundation, has been slightly studied. This paper studies the effect of a strip load on the active pressure force and the distribution of the horizontal stresses on a rigid wall, using a finite element limit analysis. The strip loading is located at different distances from the vertical face of the wall. The OptumG2 code is used to analyze the effect of width of strip surcharge (soil-wall), interface friction angle and soil internal friction angle. New interesting results are demonstrated and presented here: the dependency of the active earth pressure coefficient on both position and width of the strip load, in one hand, and the effect of the internal friction angle of the soil, the soil-wall interface, and the position of the strip loading on the failure mechanism, in the other hand.

Mechanical and hydraulic compatibility of RAP with geosynthetics used in MSE walls

Mechanical and hydraulic properties of recycled asphalt pavement (RAP) as backfill in mechanically stabilized earth (MSE) walls were evaluated. Woven and nonwoven geotextiles and uniaxial and biaxial geogrids were used as reinforcements. Results of interface direct shear tests showed that the interface friction angle (δ) of RAP-geogrid was higher than that of RAP-geotextile. On average, the δ for RAP-biaxial geogrid was 15% higher than δ for RAP-uniaxial geogrid. For geotextile reinforcement, the δ for RAP-woven geotextile was 20% higher than δ for RAP-nonwoven geotextile. Compaction of RAP at elevated temperatures only slightly affected δ. Pullout capacities of RAP-uniaxial geogrid and RAP-woven geotextile are comparable to those of sand-uniaxial geogrid at different overburden pressures. The compacted RAP reinforced with uniaxial geogrid, however, exhibited significant creep strains at a range of sustained pullout forces that led to failure of the RAP-uniaxial geogrid. Reducing the pullout capacity by 40% is recommended for design to reduce the potential of creep failure. Long-term filtration tests showed that in all cases RAP-geosynthetic systems were able to drain freely and this behavior could be predicted with the existing clogging criteria that have been previously developed for sands and gravels.

Geosynthetic Interface Friction at Low Normal Stress: Two Approaches with Increasing Shear Loading

The evaluation of geosynthetic interface friction is a key parameter for the stability of coupled geosynthetics, as in landfill capping liner. At the present time, few types of tests are suitable for measuring the interface friction at low normal stress: one of these is the inclined plane, usually carried out under a vertical stress of 5 kPa. This type of test is not without critical aspects, mainly due to the nonuniform normal stress state induced by the inclination of the plane, but, on the other hand, the most widespread direct shear test generally cannot be performed at such low values of normal stress. After a short discussion on the pros and cons of these two types of test, the paper presents a comparison of the interface friction angles obtained, for three interfaces, by means of an inclined plane and an unconventional direct shear apparatus, under the same low normal stress. The peculiarity of this latter device is of ensuring a gradual increase of the mobilized strength, in a way similar to what occurs during the inclined plane test. The good correspondence of the results of the two types of tests confirmed the validity of both the test approaches.

Effect of Soil and Rock Interface Friction on the Bearing Capacity of Strip Footing Placed on Soil Overlying Hoek–Brown Rock Mass

Abstract In the present study, the ultimate bearing capacity of a strip footing placed on a soil layer overlying a rock mass layer is determined by considering the interface friction angle (δsr) be...

INFLUENCE OF SWELLING ON SHEAR STRENGTH OF SHALE-LIMESTONE INTERFACE

Rock slope stability is almost controlled by the behaviour of the interface between rock layers. The presence of shale layers between limestone layers complicates this behaviour. As the shale layer undergoes swelling with moisture, it causes the shear interface properties to change with a specific behaviour different from the dry state. The behaviour will depend on the shale’s degree of saturation, swelling percentage, and stress level over shale. An experimental program was carried out to determine the shear interface behaviour parameters of shale-limestone during swelling phenomena to guide stability checks. The interface cohesion and friction angle results are reported along the swelling process and compared with the dry state condition. These results help engineers assign adequate and accurate values for joint shear and normal stiffness in jointed rock slopes, including swelling layers.

Influencing Factors of Interfacial Behavior between Geogrid and Coal Gangue

Coal gangue is a type of solid waste that is generated in the process of coal mining and washing. This concept can be effectively used in reinforced engineering fillings. The influences of shear rates and geogrid transverse ribs were studied using a large indoor direct shear test. The test results showed that the relationship between shear stress and shear displacement of geogrid‐coal gangue is nonlinear, and the shear process is accompanied by the crushing of coal gangue particles. The addition of geogrid significantly improved the shear stress and interfacial quasi‐cohesion of geogrid‐coal gangue, whereas the interfacial quasi‐friction angle remained almost unaffected. When normal stress was greater than 25 kPa, the shear stress gradually increased as the shear rate was increased from 1 to 5 mm/s. With an increasing shear rate, the interfacial quasi‐friction angle increased, whereas the interfacial quasi‐cohesion decreased. The interfacial shear stress, interfacial adhesion, and interfacial friction angle decreased with the number of geogrid ribs; the contribution of the middle transverse rib to the interfacial shear strength was smaller than that of the transverse rib at the far end in the shearing direction.

Effect of Chemical Composition of Fine Aggregate on the Frictional Behavior of Concrete–Soil Interface under Sulfuric Acid Environment

Through direct shear tests, this paper aimed to research the effect of fine marble aggregate on the shear strength and fractal dimension of the interface between soil and concrete corroded by sulfuric acid. More realistic concrete rough surfaces than the artificially roughened surfaces were formed by immersing four concrete plates in plastic buckets filled with sulfuric acid for different periods of time. The sand was adopted to imitate the soil. 3D laser scanner was employed to obtain the digital shapes of concrete plates subjected to sulfuric acid, and the rough surfaces were evaluated by fractal dimension. Large direct shear experiments were performed to obtain the curves of the interface shear stress and shear displacement between sand and corroded concrete plate. The method of data fitting was adopted to calculate the parameters of shear strength (i.e., friction angle and the cohesive) and the parameters of the Clough–Duncan hyperbolic model. The results indicated that as the corrosion days increased, the surface of the concrete plate became rougher, the surface fractal dimensions of the concrete corroded by sulfuric acid became bigger, and the interface friction angle became greater. The friction angle of the interface and the fractal dimensions of the surface of the concrete plate containing crushed gravel and marble sand were smaller than that of the concrete plate containing crushed gravel and river sand.

Strength Model of Backfill-Rock Irregular Interface Based on Fractal Theory

In the two-step open stope subsequent filling mining method, the determination of the strength model for the backfill-rock interface is of great engineering significance to study the stress distribution and stability of the backfill in the stope. Considering the deformation mechanism of the interface and the interaction of the asperities, a strength model for backfill-rock with irregular interface has been proposed based on fractal theory, which can effectively describe the shear mechanical behavior of interfaces with random roughness. The model has been compared with the two-body mechanistic model and good agreements have been achieved. The results show that the shear strength of the interface changes non-linearly with increasing fractal dimension D, when the fractal dimension D is in the range of 1∼1.12. The complete relationship between the interface shear strength and the fractal dimension is given, as the fractal dimension increases from 1 to 2 based on the presented model. At the same time, the quantitative relationship between the interface and backfill friction angles during direct shear testing is analyzed.

Characterisation of geomembrane and geotextile interface short-term creep behaviour in a dry condition

This study aims to characterise the interface creep behaviour between geomembrane and geotextile (i.e. GM-GT) in the liner system. Two types of GM (i.e. smooth SGM and textured TGM) and two types of GT (i.e. nonwoven NWGT and woven WGT) were investigated using the conventional direct shear apparatus for four combinations of GM-GT. The interface friction angles (φin) between GM-GT were firstly determined at the normal stresses (σn) of 25, 50, 100 and 200 kPa. The results show that TGM-NWGT has a much larger φin (23.9°) than the other three combinations which ranged from 9.5° to 11.1°. Subsequently, creep tests were conducted at three shear stress (τ) levels (i.e., 30, 50 and 70% of the peak stress (τp) under each normal stress). The creep test results of the four combinations were analysed and a power equation of time was used to estimate creep displacement (δcp). The coefficients A and B in the power equation were found to be functions of Young's modulus of the composite material (Ec), time, σn, τ, τp, and φin. The tertiary creep stage was not observed in the test and it is recommended that longer duration GM-GT interface creep tests should be conducted for in-depth understanding of the interface creep mechanism.

Effects of Axial Relative Ground Movement on Small Diameter Polyethylene Piping in Loose Sand

Small diameter (42 mm) medium density polyethylene (MDPE) pipes are widely used in the gas distribution system in Canada and other countries. They are sometimes exposed to ground movements resulting from landslides or earthquakes. The current design guidelines for evaluating the pipes subjected to ground movement were developed for steel pipes of larger diameters and may not apply to flexible MDPE pipes. This paper evaluates 42 mm diameter MDPE pipes buried in loose sand under axial relative ground movement for developing a design method for the pipes. MDPE is a viscoelastic material; therefore, the behaviour of MDPE pipes exposed to landslides would depend on the rate of ground movements. In this research, full-scale laboratory tests were conducted to investigate the responses of buried pipes under various rates of relative axial displacement. Finite element modelling of the tests was used to interpret the observed behaviour using the continuum mechanics framework. The study revealed that the pulling force on the pipe depends on the rate of relative ground displacement (pulling rate). The nondimensional pulling force possessed a nonlinear relationship with the pulling rate. A rate-dependent interface friction angle could be used to calculate the maximum pulling forces using the conventional design guidelines for the pipes in loose sand. Based on the pulling force, the pipe wall strains can be estimated using the methods available for larger diameter pipes.

Towards an improved analytical framework to estimate active earth pressure in narrow c – ϕ soils behind rotating walls about the base

Retaining walls are sometimes unavoidably constructed near existing stabilized structures to maintain stability of narrow retained c-ϕ soils. Although some analytical approaches have been presented to estimate active earth pressure on the wall undergoing rotation about the base (RB), the contributions of soil cohesion and horizontal shearing forces in c-ϕ soils are typically neglected for brevity. Hence it is always expected to be improved, and to seek a more economical design framework used in the retaining wall with narrow c-ϕ soils. This paper first uses finite element limit analysis (FELA) to study the developed failure mechanisms under RB mode, which provides a basis to establish a calculation model. An analytical framework using arched differential element method is further presented with overall considerations of soil cohesion, soil arching effect, shearing forces between adjacent elements and the studied failure mechanism. The calculation flowchart is mapped and executed under C++ environment. The results from centrifuge test, existing analytical approaches and FELA are compared for validation in both purely-frictional and cohesive-frictional soils. A parametric study considering the effects of sensitive variables (e.g. aspect ratio, soil strength parameters and wall-soil interface friction angle) on the design is carried out. For the use of proposed analytical framework in practice, two simplified design equations are provided to correlate standard Coulomb’s solutions.

Numerical study of strain development in high-density polyethylene geomembrane liner system in landfills using a new constitutive model for municipal solid waste

Tensile strain development in high-density polyethylene (HDPE) geomembrane (GMB) liner systems in landfills was numerically investigated. A new constitutive model for municipal solid waste (MSW) that incorporates both mechanical creep and biodegradation was employed in the analyses. The MSW constitutive model is a Cam-Clay type of plasticity model and was implemented in the finite difference computer program FLAC™. The influence of the friction angle of the liner system interfaces, the biodegradation of MSW, and the MSW filling rate on tensile strains were investigated. Several design alternatives to reduce the maximum tensile strain under both short- and long-term waste settlement were evaluated. Results of the analyses indicate that landfill geometry, interface friction angles, and short- and long-term waste settlement are key factors in the development of tensile strains. The results show that long-term waste settlement can induce additional tensile strains after waste placement is complete. Using a HDPE GMB with a friction angle on its upper interface that is lower than the friction angle on the underlying interface, increasing the number of benches, and reducing the slope inclination are shown to mitigate the maximum tensile strain caused by waste placement and waste settlement.

An Investigation of Geomechanical and Microstructural Properties of Full-Scale Jet Grout Column Constructed in Organic Soil

Jet grouting methods have recently become one of the soil enhancement technologies utilized to provide strength improvement and solve most problems of weak soils. In this study, a full-scale 1 m diameter and 5 m length jet grout (soilcrete) column was constructed in the field with a water-to-cement ratio of 1 and 400 bar pressure injections. A mechanical, physical, and microstructural investigation was performed on jet grout samples taken from six different depths (0.0, 0.5, 1.0, 1.5, 2.0, and 2.5 m) and at the same depth at five different locations, including the center. For normal conditions, samples were prepared for six periods to study dry and saturated conditions. The following tests are performed on each sample: compressive strength index (Is) in all conditions, water absorption, density, porosity, and interface friction. Additionally, SEM was performed on selected samples to investigate the microstructures of jet grout columns (JGCs). The test results showed that the Is varies with depth, and within the same depth, the variation is approximately 20%. Other properties also vary with depth and location; for example, the average percentage of water absorption and porosity are considered minimum values at the same location, which are 53 and 30%, respectively. However, the interface friction angle of organic soil–cement grout gains 48° and 10 kPa cohesion. The theoretical part of this study is to predict the diameter of JGC in organic soil.

Effect of geotextile ageing and geomembrane surface roughness on the geomembrane-geotextile interfaces for heap leaching applications

A series of large scale direct shear experiments is used to investigate the effect of the geomembrane (GMB) surface roughness, geotextile (GTX) properties, and GTX ageing, on the GMB-GTX interface shear behaviour. Interfaces involving smooth, coextruded textured, and structured surface GMBs underlying four different nonwoven needle-punched staple fibres (GTXs) with mass per unit areas between 200 and 2400 g/m2, and a geocomposite drain (GCD) are examined at normal stresses between 250 and 1000 kPa. The results showed that the interlocking between the GMB and GTX increased with increasing the GMB asperity height and/or decreasing the mass per unit area of the GTX. For the interfaces that involved GTXs preaged prior to the shear box experiments for up to 2 years at 85 °C, it was found that the 2400 g/m2 heat bonded two-layered GTX exhibited internal shear failure at low shear displacements. However, all the highly aged single layered GTXs showed an increase in the peak interface friction angles with the increase in their ageing. For these single layered GTX, the results suggest that assessing the interface friction angles using unaged GTXs for the stability analysis is conservative as long as the GTX remains intact in the field.