Internal Friction Angle Values Research Articles

Numerical simulation of soil–cone penetrometer interaction using discrete element method

One of the most common methods to measure soil strength in-situ is cone penetrometers. In this paper the development of a three dimensional (3D) discrete element model (DEM) for the simulation of the soil–cone penetrometer interaction in a slightly cohesive loamy sand soil is presented. The aim was to investigate the effects of the soil model’s geometrical (e.g., soil model cross section shape and size and model’s height) changes on variations in the soil penetration resistance. The model area ratio and height ratio values were adopted to analyse the effects of the cross section size and the model’s height, respectively. The results of penetration resistance of the DEM simulations were compared with the in-situ measurement with a cone penetrometer of the same geometry. This comparison allowed the derivation of the contact properties between the elements. To simulate the soil material the so-called Parallel Bond and Linear Models were used in the 3D version of the Particle Flow Code (PFC) software. Finally the mechanical properties of the soil, namely the cohesion and internal friction angle were estimated by DEM simulation of direct shear box.Results showed that the penetration process can be simulated very well using the DEM. The model’s calculated penetration resistance and the corresponding in-situ measurement were in good agreement, with mean error of 14.74%. The best performing models were a rectangular model with an area ratio of 72 and a height ratio of 1.33 and a circular model with an area ratio of 32 and a height ratio of 2. The simulation output of soil material properties with direct shear box resulted in representative values of real loamy sand soils, with cohesion values range of 6.61–8.66kPa and internal friction angle values range of 41.34–41.60°. It can be concluded that the DEM can be successfully used to simulate the interaction between soil and cone penetrometers in agricultural soils.

Numerical evaluation of the bearing capacity factor N’c of circular and ring footings

ABSTRACTRing footings are widely used to support structures like silos and storage tanks. Analytical design of safe and economical shallow footings requires the knowledge of the bearing capacity factors N’c and N’γ. The geotechnical design Eurocode 7 provides such factors only for simple geometric shapes like squares, circles or rectangles. Furthermore the N’γ factor has been extensively carried out but the research on the N’c factor hasn’t yet been performed. Thus, the present study aims to provide the first numerical N’c values of a ring footing laying on general c-φ Mohr-Coulomb soil. The results, carried out by using FLAC code, indicate that for rough footings there is an optimal ring which is also dependent of the friction φ. The optimal value of ri/r0 is found to be almost equal to 0.26, 0.33 and 0.46 corresponding respectively to a low, medium and high friction soil. The results also indicate that the soil dilation angle influences the value of N’c when the soil displays high non-associativity for large internal friction angle values. The computational results are presented in the form of design tables and graphs, and compared with previous published results available in the literature.

Experimental determination of Drucker-Prager yield criterion parameters for normal and high strength concretes under triaxial compression

In this study, parameters which define Drucker-Prager yield criterion were investigated experimentally for both normal strength concrete (NSC) and high strength concrete (HSC) by triaxial compression tests. Total 16 concrete series with different concrete strength were produced. While 8 concrete series were produced as NSC (20MPa<fcm<55MPa), other 8 series were produced as HSC (55MPa<fcm<85MPa). Each series contains 16 specimens. Triaxial compression tests were performed on these concrete specimens. Concrete compressive strength of the specimens were measured under 4 different lateral compression level (0, 1, 2 and 4MPa). After Mohr circles were drawn by using the data obtained from triaxial compression tests, the values of cohesion were determined between 5MPa and 13MPa for NSC and 13MPa and 19MPa for HSC. The values of internal friction angle were also obtained between 27° and 34° for NSC, 34° and 39° for HSC from the Mohr circles. The parameters defining the Drucker-Prager yield criterion were determined by using the values of cohesion and internal friction angle. Finally, after some equations were proposed to calculate the parameters by using concrete compressive strength, the validation of these equations were also proved in this study.

The Effects of High Alkaline Fly Ash on Strength Behaviour of a Cohesive Soil

Contemporarily, there are 16 coal-burning thermal power plants currently operating in Turkey. This number is expected to rise to 46 in the future. Annually, about 15 million tons of fly ash are removed from the existing thermal power plants in Turkey, but a small proportion of it, 2%, is recyclable. Turkey’s plants are fired by lignite, producing Class C fly ash containing a high percentage of lime. Sulfate and alkali levels are also higher in Class C fly ashes. Therefore, fly ash is, commonly, unsuitable as an additive in cement or concrete in Turkey. In this study, highly alkaline fly ash obtained from the Yeniköy thermal power plants is combined with soil samples in different proportions (5%, 10%, 15%, 20%, and 25%) and changes in the geomechanical properties of Ankara clay were investigated. The effect of curing time on the physicomechanical properties of the fly ash mixed soil samples was also analyzed. The soil classification of Ankara clay changed from CH to MH due to fly ash additives. Free swelling index values showed a decrease of 92.6%. Direct shear tests on the cohesion value of Ankara clay have shown increases by multiples of 15.85 and 3.01 in internal friction angle values. The California bearing ratio has seen a more drastic increase in value (68.7 times for 25% fly ash mix).

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.

Numerical evaluation of the bearing capacity factor [formula omitted] of ring footings

In this paper, numerical computations using FLAC code are carried out to evaluate the soil bearing capacity factors Nγ′ for both smooth and rough ring footings for low and high friction associated and nonassociated Mohr–Coulomb soils. The results indicate a significant decrease in the value of Nγ′ with an increase in the ratio of internal radius to external radius of the ring. They also indicate that the soil dilation angle influences the value of Nγ′ when the soil displays high nonassociativity for large internal friction angle values. The values of Nγ′ for a rough footing base, especially with greater values of φ, are shown to be significantly higher than those for a smooth footing base. The computational results are presented in the form of design tables and graphs, and compared with previous published results available in the literature.

An empirical approach for estimating shear strength of decomposed granites in Galicia, Spain

Decomposed granites are often found in Galicia, Spain, where they are referred to as jabres. Similar decomposed granites are also found in many other parts of the world. Granite weathering rarely produces an homogeneous altered rock mass with all material decomposed to the same degree – or even a simple weathering profile where the degree of alteration decreases progressively with depth. This paper presents an empirically based approach that allows estimation of the shear strength of this type of materials in terms of Mohr–Coulomb cohesion and internal friction angle values. The approach is based on back analysis of failed slopes in decomposed granites, and it is implemented through simple in-situ testing and classification of the weathered granite, treating it as a soil material. An advantage of the used approach is that it allows prediction of shear strength values at different locations within the deposit in a quick and economical way, from which average values of shear strength parameters can be computed. This is particularly important when considering the heterogeneous nature of decomposed granite formations in relation to the scale of the engineering work involved. Analysis of three slopes instability cases in jabres in Galicia, illustrating the approach are described in detail. These correspond to a road cut, a natural slope and the wall of an open pit mine.

Shape factor sγfor shallow footings

The results of FLAC3D-based numerical evaluation of the bearing capacity shape factor <TEX>$s_{\gamma}$</TEX> are presented for square and rectangular footings on granular soils. The results confirm a peculiar effect found earlier by Zhu and Michalowski (2005), where for large values of internal friction angle, <TEX>$s_{\gamma}$</TEX> exhibits a peak at some aspect ratio of the footing, and then decreases towards unity at large aspect ratios. The Zhu and Michalowski's results were derived using the finite element program ABAQUS, and the results presented in this note corroborate their earlier findings.

NUMERICAL ANALYSIS OF CONTROLLED MODULUS COLUMN FOUNDATION SYSTEM SUPPORTED EMBANKMENTS

The objective of this research is to present the numerical analysis of deep foundation system namely controlled modulus columns (CMC) for support of embankments. This paper describes the analysis modeling used for CMC foundation system using the finite element method. The elasto-plastic finite element model used to simulate the embankment soil foundation has been verified against field data. The results obtained from this study showed that the effect of CMC could be negligible when the soil strength increased in terms of its angle of internal friction. With low values of internal friction angle, the CMC reduce the potential of surface deformation about 12%. The values of surface deformation decreased with column diameter until it reach constant value at (0.5m) where less than this values the reduction in deformation could be negligible or have insignificant effect. The maximum deformation was observed at the middle of embankment, also the deformation at the embankment foundation reduce by about (17%) when take into consideration the CMC in soil embankment foundation.

Passive and active earth pressures in the presence of groundwater flow

This paper deals with the effect of seepage flow on the lateral earth pressures acting on deep sheeted excavations in cohesionless soil. The computation of the passive and active earth pressures in the presence of hydraulic gradients is performed using the explicit finite difference method implemented in Fast Lagrangian Analysis of Continua (FLAC) code. The available effective passive earth pressure coefficients in the presence of upward seepage forces are given for both associative and non-associative material. The present solutions show that the soil dilation angle influences the effective passive earth pressures for large internal friction angle values of the soil. They also show that the effective passive pressures diminish with the hydraulic head loss. Good agreement is observed between the present results and those using an upper-bound approach in limit analysis for an associative material. For the active case, the effect of downward seepage forces on the active earth pressures is investigated. The numerical results show a significant increase in the effective active earth pressures due to a hydraulic head loss. It is also shown that the dilation angle influences the effective active earth pressures for large internal friction angle values.

Drucker-Prager型構成則を用いた円柱コンファインドコンクリート供試体の圧縮破壊FEM解析

Main purpose of the present study is to discuss the effect of parameters (e.g. internal friction angle and dilatancy angle) of the constitutive law of Drucker -Prager type on the result of simulation analysis of confined concrete under compression. Two series of 3-D FEM analyses have been carried out. Firstly, the optimum values of the internal friction angle and dilatancy angle, used in the Drucker-Prager type plasticity model with the strain softening effect, have been discussed for a set of compressive strength data of concrete specimens with different shapes. As a result, reasonable value as the internal friction angle has been found to be approximately 30 degrees for a condition of rather high equivalent lateral pressure. Secondly, simulation analyses have been carried out for the compressive behavior of cylindrical concrete specimens confined by steel tubes or reinforcing bars, introducing interface element and different values of the internal friction angle. As a result, it has been pointed out that the distribution of equivalent confining pressure along the longitudinal direction of a specimen and the progress of the degree of damage in horizontal sections differ to a large extent by the value of internal friction angle applied.

ブリーディングによる強度変動を考慮した円柱コンクリートの一軸圧縮FEM解析

Purpose of the present study is to discuss the compressive failure state and the effectiveness of internal friction angle used in the Drucker-Prager model, based on the uniaxial compression 3-D FEM analysis of plain concrete with the strength variation due to bleeding. As a result of analyses which introduced the different values of internal friction angle (30 and 53 degree), it has been pointed out that 1) the failure zone along the longitudinal direction of specimen shows tendency of proportional reduction with the increase in the size of a specimen, and 2) the distribution of equivalent strain inside a specimen obtained from the analysis with internal friction angle of 53 degree can represent the ordinary failure pattern.

Mechanical properties in relation to vehicle mobility of Sepang peat terrain in Malaysia

An analytical framework for determining the mechanical properties of peat and predicting the tractive performance of tracked vehicle is presented. It takes into account the load-sinkage and shearing characteristics of peat as well as all major design parameters of tracked vehicle. An experimental study on the mechanical properties of peat soil was conducted at Sepang area, Selangor, Malaysia. The stiffness values of surface mat and underlying weak peat deposit from load-sinkage test were determined by specially made bearing capacity apparatus. The mean values of surface mat stiffness before and after drainage were found to be 31 and 45.62 kN/m 3, respectively and the mean values of underlying peat stiffness before and after drainage were found to be 252 and 380.20 kN/m 3, respectively. The mean value of the internal frictional angle, cohesiveness and shear deformation modulus of the peat soil sample were determined using a direct shear box apparatus in the laboratory. The mean values of internal friction angle, cohesiveness and shear deformation modulus before and after drainage were found to be 22.80° and 24.31°, 2.63 and 2.89 kN/m 2, and 1.21 and 1.37 cm, respectively.

Mechanical behaviour of the upper layers of a sandy loam soil under shear loading

The mechanical behaviour of the upper layers of a sandy loam soil was studied under standard triaxial compression and direct shear box tests. Variations of soil material properties were investigated at four different initial dry bulk densities of 1410, 1520, 1610 and 1670 kg/m 3. Soil deformation and volume change under the triaxial compression loading were also studied at these bulk densities. Results from the two tests showed increases in the soil mechanical properties with the initial dry bulk density. The internal friction angle values measured with the triaxial compression apparatus exceeded those measured with the direct shear box. In contrast, the soil cohesion values measured with the direct shear box exceeded those measured with the triaxial compression apparatus. Under the triaxial compression test, the loose soil samples underwent contraction and volume reduction, whereas the dense samples swelled and failure cracks appeared clearly at various planes. The soil contraction for the former case characterizes the occurrence of soil compaction, whereas the cracks propagation and volume increase in the latter case characterizes the breaking up and loosening of soil during tillage operations. For the loose and moderately compacted states, the engineering Poisson's ratio increased with the axial strain until loading was completed. It also increased at the compacted and very compacted states until reaching given loading stages, after which its value started to decrease. This shifting in the engineering Poisson's ratio during loading may provide another identification of the moment of soil failure occurrence, in addition to that of the maximum shear stress.

Probe to measure friction coefficient of cohesion-less soils. Technical note : Kolbe, E; Corell, R W; Nielsen, J P Geotech Test J, V5, N1–2, March–June 1982, P42–46

A probe is designed to measure the in-place value of internal friction angle for cohesionless soils. The behavior of the blunt probe is similar to that of a rough footing forced into the soil. The face of the probe is split and capable of measuring shear forces which vary with the internal friction angle of the soil. A series of static penetration tests in dry sand show the variation of the ratio of shear and normal forces on the probe face (R/N) with soil friction angle phi. (Author)

A Probe to Measure Friction Coefficient of Cohesionless Soils

Abstract A probe is designed to measure the in-place value of internal friction angle for cohesionless soils. The behavior of the blunt probe is similar to that of a rough footing forced into the soil. The face of the probe is split and capable of measuring shear forces which vary with the internal friction angle of the soil. A series of static penetration tests in dry sand show the variation of the ratio of shear and normal forces on the probe face (R/N) with soil friction angle φ.