Friction Angle Values Research Articles

Closure to “Shaft Resistance of Drilled Shafts in Clay” by Tanusree Chakraborty, Rodrigo Salgado, Prasenjit Basu, and Mônica Prezzi

Closure to “Shaft Resistance of Drilled Shafts in Clay” by Tanusree Chakraborty, Rodrigo Salgado, Prasenjit Basu, and Mônica Prezzi

Effect of Confining Stress on Soil Water Retention Curve and its Impact on the Shear Strength of Unsaturated Soils

To predict the shear strength of unsaturated soils, several equations have been proposed in the literature. The majority of these equations have the air entry value as the controlling parameter. In this study, an experimental program is planned to investigate the effect of confining stress on the air entry and air expulsion values, in the drying and wetting process, respectively. To evaluate the influence of stress state on these parameters, the soil water retention curve (SWRC) of the soil is determined under two different applied net stresses. For this purpose, a novel miniature pressure plate apparatus was designed to determine the SWRCs under different net stresses. The soil specimens are sheared in a suction‐controlled triaxial apparatus, and the shear stress of the soil is measured. The measurements are performed under net confining stresses identical to the net stresses for which the SWRCs are obtained. Furthermore, the shear strength behavior of unsaturated soil samples are investigated in drying and wetting branches, and the values of effective internal friction angle and cohesion are determined for each path. Comparison of the obtained values to those of saturated samples revealed a rather significant difference. Finally, the shear strength values obtained from these measurements are compared with the predicted shear strength from some of the existing equations. In addition, variations of the χ parameter during drying and wetting processes and its dependence on the air entry/expulsion value were investigated and compared with reported equations. Moreover, a relationship is proposed for the effective stress parameter that can better capture the effect of net stress and, consequently, results in better predictions for the considered soil type.

Reassessing rock mass properties and slope instability triggering conditions in Valles Marineris, Mars

The rock walls of the Valles Marineris valleys (VM) in the equatorial area of Mars exhibit several gravitational failures which resulted in a series of large landslides up to several hundred cubic kilometers in volume. Questions arise as to forces at play and rock strength in the stability of the walls of VM. In this work we address the stability analysis of the walls of VM by considering the strength of the materials of the walls and the causes of landslides. Using finite element calculations and the limit analysis upper bound method, we explore the range of cohesion and friction angle values associated with realistic failure geometries, and compare predictions with the more classical Culmannʼs translational failure model. Our analysis is based both on synthetic, simplified slope profiles, and on the real shape of the walls of VM taken from the MOLA topographic data. Validation of the calibrated cohesion and friction angle values is performed by comparing the computed unstable cross sectional areas with the observed pre- and post-failure profiles, the estimated failure surface geometry and ridge crest retreat. This offers a link between rock mass properties, slope geometry and volume of the observed failure, represented in dimensionless charts. The role of groundwater flow and seismic action on the decrease of slope stability is also estimated. Pseudo-static seismic analyses provide another set of dimensionless charts and show that low seismicity events induced by meteoroid impacts, consistent with the size of craters, could be a cause for some of the observed landslides, if poor rock properties for VM are assumed. Analyses suggest that rock mass properties are more similar to their earth equivalents with respect to what has been previously supposed.

Stabilization of clay soils using lime and effect of pH variations on shear strength parameters

This paper presents the results of geotechnical and mineralogical investigations on lime treated clay soils from Hamedan City, Iran, and effects of pH variations on their shear strength parameters. Initially, lime was added in different percentages and laboratory experiments were conducted after curing times. The results indicate that these soils can be stabilized satisfactorily with the addition of about 7 % lime. Also, investigation of the relationship between lime-treated geotechnical properties and lime percentage and curing time demonstrates high regression coefficients for the proposed relationships. Several laboratory tests were performed on treated and untreated clay soils with lime mixed with pore fluids with different pH values including 3, 5, 7 and 9. The results of shear strength tests indicated that the undrained shear strength parameters for untreated clays increased considerably if the pore fluid had a high pH (pH = 9) or a low pH (pH = 3). It can also be found that for lime-treated soils, maximum cohesion and friction angle values are achieved at pH = 9.

Interface strength behavior of expanded polystyrene EPS geofoam

In the present investigation, the interface strength behavior of expanded polystyrene EPS geofoam with EPS geofoam and with various other construction materials such as jute geotextile, geogrid, and fly ash are presented. A series of large direct shear tests were conducted with shear box of dimensions 305mm length, 305mm width, and 175mm height. The experimental investigations were carried out by using four different densities of EPS geofoam blocks, 015, 020, 022, and 030kNm3 under four different normal stresses 25, 50, 75, and 100kPa. The effects of density of EPS geofoam and the applied normal stresses on the interface strength parameters were investigated. The results of the interface strength are expressed in the form of shear stress versus normal stress and the direct shear failure envelopes were found to be linear. The experimental results indicate that the density of EPS geofoam does not have significant effect on its interface strength behavior. For all densities of EPS geofoam, it was observed that there was no significant variation in interface friction angle values. However, a slight increase in adhesion Ca was observed with the increase in the density of EPS geofoam.

Experimental study on mechanical properties of weathered rock covered by loess

Based on dynamic triaxial test, the mechanical properties of the weathered rock covered by loess were studied. The cohesion value of weathered mudstone is far below that of the weathered sandstone, while the internal friction angle values are basically equivalent, about 30°. Compared with the undisturbed sample, the cohesion value of remodeling weathered rock sample decreases significantly. With the increase of moisture content, the strength of weathered mudstone is obviously decreased due to the influence of the water softening effect. This results illustrate that the bearing stratum is not easily affected by external disturbance in comparison to weathered mudstone. In the engineering, in order to ensure the good mechanical properties of the soil, more attention should be paid to keeping the water content constant, even to reducing the water content. The experiments show that the relations between shear stress and strain of weathered rock were nonlinear and the behavior of weathered rock can be expressed by the hyperbolic model. The initial modulus of undisturbed weathered rock, under the same consolidation conditions, is much greater than that of remodeling samples. Meanwhile, the initial dynamic elastic modulus of sandstone is also greater than that of the mudstone. The dynamic shear modulus ratios of the undisturbed sandstone, the undisturbed mudstone, as well as the remodeling mudstone have the normalization characteristics with the increase of dynamic shear strain. The damping ratio of mudstone is larger than that of the sandstone, and the damping ratio of remolding sample is also greater than that of the undisturbed mudstone. The mudstone has the bad mechanical properties as bearing stratum.

Influence of water content on the shear strength parameters of clayey soil in relation to stability analysis of a hillside in Brno region

Shear strength of soils is highly affected by moisture conditions (i.e. water content), especially if the soil contains clay materials. Usually the laboratory specimen, which are used to determine shear strength of soil are prepared at water content and dry density same as in the field conditions, without respect to the fact, that the conditions in the future might not remain the same. For the purpose of this study soil specimen were compacted and the optimum moisture content was identified. After compaction soil was tested at the dry side of optimum water content at w = 9 %, 10 % and 11 %. Parameters of shear strength were obtained and used for stability analysis with software GEOSLOPE/W 2012. According to referenced literature, it was expected for the shear strength of the soil to decrease with increasing water content. This hypothesis was not proven for clayey soil from Brno region. Development of values of friction angle and cohesion exhibited anomalous behaviour and such development was found also for values of Factor of safety (FOS) obtained from stability analyses. Results proved the necessity of taking moisture conditions into account, when processing stability analyses, in order to achieve reliable and safe constructions.

Closure to “Assessment of Reinforcement Strains in Very Tall Mechanically Stabilized Earth Walls” by Armin W. Stuedlein, Tony M. Allen, Robert D. Holtz, and Barry R. Christopher

In the course of analyzing data collected from two exceptionally tall mechanically stabilized earth (MSE) walls constructed for the third runway at Seattle-Tacoma International Airport (SeaTac), the authors failed to understand three fundamental points regarding MSE wall design: 1. The authors ignore both the mandated design friction angle and the fact that the actual backfill internal friction angle was not known when the wall was designed. Instead, they assess the accuracy of the MSE design methods using selected in-place values of the soil friction angle, 40 and 44 , which are substantially higher than the mandated design friction angle, 37 . 2. The authors also ignore the fact that MSE walls are designed for the finished condition, not for the partially constructed condition. Instead, they condemn the validity of the Coherent Gravity and Simplified design methods based on those methods’ underprediction of reinforcement loads at intermediate stages of construction. Postconstruction stresses in the soil reinforcements at SeaTac are consistent with those predicted by the Coherent Gravity and Simplified methods using the mandated design friction angle, 37 . 3. The earth pressure distribution behind an MSE wall is triangular, not trapezoidal as assumed by the K-Stiffness method.

Assessment of bauxite refining residue (red mud) as a liner for waste disposal facilities

Red mud (RM), a waste arising from the bauxite refining, was studied to assess its suitability as a compacted liner material. The geotechnical and hydraulic conductivity (K) characteristics of the RM, as well as the effect of desiccation, were evaluated. RM has index properties satisfying the requirements to achieve low K. The compaction–permeability studies showed that RM may be compacted to a dense homogeneous mass using a moderate compactive effort, while lowest K (⩽1 × 10−7 cm/s) was achieved for RM compacted slightly (0.4–4%) wet of optimum. Shear strength test revealed high values of friction angle and cohesion for compacted RM, and its tight structure was also evidenced by its low compressibility and maximum settlement under load. Desiccation adversely affected the permeability of compacted RM, but to a lesser extent than generally observed for clays. These results suggest that RM could be potentially utilised as a low-permeability barrier to be laid down under engineered landfill sites.

Seismic pullout capacity of vertical anchors in sand

The horizontal pullout capacity of vertical anchors embedded in sand in the presence of pseudo static horizontal earthquake body forces has been determined by using the lower bound finite element limit analysis. The variation of the pullout factor Fγ with changes in embedment ratio of the anchor plate for different values of horizontal earthquake acceleration coefficient (αh) has been established. The effect of the anchor-soil interface friction angle on the results has also been examined. The pullout capacity decreases quite significantly with an increase in αh. The pullout capacity becomes higher for greater values of embedment ratio and interface friction angle. The normal pressure distribution along the front surface of the anchor plate and the development of failure patterns have also been examined.

Bearing Capacity of Circular Footings on Reinforced Soils

A method is presented for determining the ultimate bearing capacity of a circular footing reinforced with a horizontal circular sheet of reinforcement placed over granular and cohesive-frictional soils. It was assumed that the reinforcement sheet could bear axial tension but not the bending moment. The analysis was performed based on the lower-bound theorem of the limit analysis in combination with finite elements and linear optimization. The present research is an extension of recent work with strip foundations reinforced with different layers of reinforcement. To incorporate the effect of the reinforcement, the efficiency factors eta(gamma) and eta(c), which need to be multiplied by the bearing capacity factors N-gamma and N-c, were established. Results were obtained for different values of the soil internal friction angle (phi). The optimal positions of the reinforcements, which would lead to a maximum improvement in the bearing capacity, were also determined. The variations of the axial tensile force in the reinforcement sheet at different radial distances from the center were also studied. The results of the analysis were compared with those available from literature. (C) 2014 American Society of Civil Engineers.

Influence of Natural Variation on flow Behavior of Wormy Compost

Dependence on chemical fertilizer continually is increasing. Continual increasing of using chemicalfertilizer causes nature pollution (e.g. water contamination). This has led researchers to aggressively investigate renewable fertilizer resources, biomass, to produce organic crops and reduced wastage. Wormy compost is a bulk solid and biomass feed stocks. Wormy compost flow is obstacle as it often becomes confined by Clogging and bridging which occurs during storage and processing. The objective of this study was to review the primary factors affecting flow-ability and wall friction characteristics of granular solids and powders, as well as devote testing methodologies for this biomass material. It can be said that high moisture content and small particle size has an adverse effect on the flow property of wormy compost. Increasing the moisture content and decrees particle size of the wormy compost reduced its flow-ability from free flowing at moisture content of 25% (w.b.) and 1.18mm in particle size to cohesive at moisture content of 35% (w.b.) and 0.3mm in particle size. The maximum values of friction angle were occurred for Steel, Galvanized and Aluminum surface, respectively.

Municipal solid waste shear strength parameters defined through laboratorial and in situ tests

This paper presents the parameters of municipal solid waste shear strength determined in the laboratory (triaxial tests) and by in situ tests: standard penetration tests (SPT) and cone penetration tests (CPT). The results analyzed here are part of a study carried out on the Santo Tirso landfill (north of Portugal) between 2001 and 2007. The influence of the strain levels, waste composition, and waste age on the shear strength parameters is presented, as well as an attempt to establish some correlations between the SPT and CPT tests and to estimate municipal solid waste (MSW) friction angles from the SPT tests. The results indicate that the aging of the waste, which is characterized by a decrease in fibrous and organic materials and an increase in inert materials and fine fraction, leads to an increase in frictional resistance and to a decrease in cohesion. The results of the SPT and CPT tests indicate higher penetration resistance in older and deeper waste. Estimating the frictional resistance from the SPT test seems to obey an empirical relationship expressed by a power function, which depends on the strain level. Implications: Comparison of shear strength parameters of municipal solid waste (MSW) determined through laboratory (triaxial tests) and in situ tests (SPT and CPT) showed that the greater amount of fibrous and granular elements leads to an increase in “cohesion” and in friction angle values, respectively. Waste aging results in an increase in frictional resistance and in a decrease in “cohesive” resistance. This is consistent with the composition changes with aging: increase of the relative quantity of inert materials and fine fraction, and decrease in particle size, in organic matter content, and in fabrics and plastics.

Deformation and strength of embankments on soft Dutch soil

Embankment and dyke stability in the Netherlands has always been evaluated by effective stress analysis. The subsoil of most of these structures is organic, weak and soft, but the internal friction angle of these soils is surprisingly high. Empirical methods are used to obtain acceptable, reduced values of friction angle from triaxial tests for use in stability analyses. It appears possible, however, to do full justice to the peculiar combination of low strength and stiffness and high friction angle by means of the finite-element method using a viscous version of the Cam-clay model. All parameters of the model are found from a single test in a constant-rate-of-strain K0 oedometer. The approach is illustrated by two case histories, after first providing insight into the peculiar properties of the Dutch soils, and the manner in which they are dealt with.

Laboratory shear strength parameters of cohesive soils: variability and potential effects on slope stability

The study quantified laboratory geotechnical variability by analyzing compacted alluvial fine-grained soils commonly used to backfill exhausted quarries in Central Italy. Repeating the test 4 times and combining the relevant results, 256 pairs of friction angle and cohesion values were obtained, with mean values of 27.0° ± 0.8° and 19.22 ± 4.08 kPa, respectively in the shear stress range 100–250 kPa. The influence of the variability of laboratory drained shear strength parameters on the long-term stability of artificial saturated slopes was examined, taking into account both deterministic and probabilistic approaches. In many cases, when the deterministic approach indicates stability, the probabilistic one indicates a certain probability of instability, even for the lowest slope height (5 m) and a slope angle higher than 15°.

이차원 개별요소 수치해석을 통한 화강풍화토의 평균입자크기와 전단강도의 관계 규명

본 연구에서는 개별요소법을 적용하여 화강암 기원의 풍화토에서 입자 크기와 입자크기 분포 특성 중 최대입경/최소입경의 비가 강도정수에 미치는 영향을 살펴보았다. 입자크기와 입도분포가 변화할 때의 전단강도 특성 변화를 규명하기 위하여 개별요소법 수치해석을 실시하였다. 점착력이 0.25MPa, 내부마찰각이 <TEX>$29^{\circ}$</TEX>인 강도특성을 갖는 기준시료를 수치해석적으로 구현한 후, 간극률을 기준시료와 동일하게 유지하면서 입자의 크기와 입도분포를 바꾸어 가며 점착력과 내부마찰각의 변화를 살펴보았다. 수치해석결과 평균입자의 크기가 커질수록 점착력의 현저한 감소가 관찰되었으며, 내부마찰각의 변화는 미미하지만 증가하는 경향을 보였다. 이러한 연구결과는 입도만을 이용하여 간편하게 화강풍화토의 강도정수 산정 시 활용될 수 있을 것으로 판단된다. 특히 풍화상태가 점이적으로 변화하는 화강풍화토의 경우, 현장시험과 실내시험을 통하여 일부 구간에서 측정된 입도-강도 자료가 있을 때, 이러한 시험들이 수행되지 않은 구간에 대해서도 입도분포를 통해 간편하게 강도특성을 규명할 수 있을 것으로 여겨진다. We have carried out a series of numerical experiments to study the effect of average particle size on the mechanical properties of granite-derived weathered soils. A distinct-element method was adopted to study the changes in macro-scale mechanical properties with particle size and maximum-to-minimum particle size ratio. The numerical soil specimen with cohesion values of 0.25 MPa and internal friction angle of 29 degrees was prepared for reference. While keeping the porosity values constant, we varied particle size and size distribution to study how cohesion and internal friction angle changes. The experimental results show that the values of cohesion apparently decrease with increasing particle size. Changes in the values of internal friction angles are small, but there is a trend of increase in internal friction angle as the average particle size increases. This study demonstrates a possibility that the results of numerical experiments of this type may be used for rapid estimation of mechanical properties of granite-derived weathered soils. For example, when mechanical properties obtained through in situ tests and particle size data obtained through lab analysis are available for a site, it is expected that the mechanical properties of weathered granite soils with varying degrees of weathering (thus, varying particle size) may be estimated rapidly only with particle size data for that site.

Computations of Seismic Passive Resistance and Uplift Capacity of Horizontal Strip Anchors in Sand

In this paper, the limit equilibrium method is used to compute seismic passive earth pressure coefficients and the vertical uplift capacity of horizontal strip anchors in presence of both horizontal and vertical pseudo-static earthquake forces. By considering a simple planar failure surface, distribution of soil reaction is obtained through the use of Kotter’s equation. Presence of pseudo-static seismic forces induces a considerable reduction in the seismic passive earth pressure coefficients. The reduction in seismic passive earth pressure coefficients increases with increase in magnitude of the earthquake accelerations in both horizontal and vertical directions and with increase in wall friction angle. The vertical uplift capacity of horizontal strip anchor is obtained for various values of soil friction angle, embedment ratio and seismic acceleration coefficients in both horizontal and vertical directions by using rigorous computational optimization. Proper justification for selected value of wall friction angle is established. Results are presented in the form of non-dimensional breakout factor for anchor. A significant reduction in breakout factor is observed in presence of both the seismic acceleration coefficients whereas breakout factor increases with increase in soil friction angle and embedment ratio even under the seismic condition. Angles of failure planes keep changing with change in seismic acceleration coefficients and failure zone shifts towards the critical direction of seismic acceleration coefficients. Present results are compared and found in good agreement with some specific available results in literature.

DIPANALYST: A computer program for quantitative kinematic analysis of rock slope failures

Kinematic analysis is used to analyze the potential for the various modes of structurally controlled rock slope failures (plane, wedge, and toppling failures) due to the presence of unfavorably oriented discontinuities. Traditionally kinematic analysis is performed after plotting discontinuity orientations, slope angle, slope azimuth and representative friction angle value on a stereonet. Due to large number of discontinuities, only representative orientation values (dip/dip direction) for identified cluster sets are considered. This stereonet-based analysis is qualitative in nature and requires the presence of tight data clusters for which a reasonable representative orientation value can be assigned. However, there are cases when a tight circular clustering of discontinuity orientations does not exist, making stereonet-based analysis unreliable. Also, variability of discontinuity data in cluster sets is not easy to consider using the stereonet-based method.To overcome these problems, an application software, DIPANALYST, has been developed by the first author to perform quantitative kinematic analysis based on not just representative discontinuity values, but all discontinuities and their possible intersections. The software calculates ratios of discontinuities or their possible intersections that can potentially cause failures (plane, wedge or toppling) to the total number of discontinuities or their possible intersections. The calculated ratios are known as failure indices, and the method is termed as the quantitative approach for kinematic analysis. DIPANALYST is also capable of performing the traditional stereonet-based method.

Bearing Capacity of Strip Foundations in Reinforced Soils

AbstractA method is proposed to determine the ultimate bearing capacity of a strip footing placed over granular and cohesive-frictional soils that are reinforced with horizontal layers of reinforcements. The reinforcement sheet is assumed to resist axial tension but not bending moment. The analysis was performed by using the lower bound theorem of the limit analysis in combination with finite elements. A single layer and a group of two layers of reinforcements were considered. The efficiency factors ηγ and ηc that need to be multiplied with the respective bearing capacity factor Nγ and Nc to account for the inclusion of the reinforcements were established. The results were obtained for different values of the soil internal friction angle (ϕ). The critical positions of the reinforcements, which would result in a maximum increase in the bearing capacity, were established. The required tensile strength of the reinforcement to avoid its breakage during the loading of the foundation was also computed. The resu...

Static and dynamic analyses of the stability of mining wastes (Ravaneti) in the Carrara marble area (Apuan Alps, Italy) / Analiza statyczna i dynamiczna stabilności hałd odpadów górniczych w regionie wydobycia marmurów Carrara (Alpy Apuańskie, Italia)

Abstract The problem of the stability of “ravanetos” (debris piles of mining waste material extracted from the Apuan Alps, Italy) is very relevant, because of the consequences a landslide would have on the people and the existing civil infrastructures throughout the territory. In this work, the stability of two ravanetos that can be considered as representative of those in the Carrara area has been studied: the Polvaccio ravaneto, a recent type of debris pile and the Torrione-Tecchione, an old debris pile at present undergoing re-naturalisation. The study using the LEM (Limit Equilibrium Method) in a static and pseudo-static field, has made it possible to first carry out a back-analysis to define the most probable apparent cohesion and friction angle values of the material that makes up the ravanetos. Subsequently, it was possible to determine the intensity of the seismic wave that would be able to lead the two ravanetos to limit stability conditions and to determine the probability of such a seismic wave occurring in the next 50 years. A more accurate analysis, carried out with a numerical method in the dynamic field, of the most critical condition (the Polvaccio ravaneto) has led to more conservative results (higher safety factors) than those obtained with the LEM. This result allows us to reveal how the LEM can be considered a cautionary instrument to judge the stability of debris piles during a seismic event and that the likelihood of a landslide occurring in the two studied representative ravanetos over the next 50 years is very slim.