From the environmental point of view, application of bioengineering techniques in civil projects such as landslide stabilization is given priority in recent years. In this paper, the influence of the diameter of tree roots on the increase of shear resistance of soil was investigated by means of series of in-situ direct shear tests. Thirty tests were carried out on a natural deposit CL soil containing midow roots by means of a set up designed in soil laboratory of SCWMRI. Since the existing roots in natural deposits have different diameters, a no dimensional index referred to as Root Diameter Ratio (RDR) was defined as the ratio of the mean root diameter to the maximum root diameter. The results showed, in general, the increased shear resistance of the soil due to the presence of roots was inversely proportional to the root diameters. In fact the apparent cohesion of soil increases considerably as the root diameter increases, while at the same time the INTERNAL FRICTION ANGLE decreases smoothly. However, the shear resistance growth stops at a given diameter, then stabilizes after a slight declination. A similar behavior was observed for the soil cohesion, while the INTERNAL FRICTION ANGLE showed a completely opposite behavior.

The FRICTION properties of granular materials play an important role in the determination of specifications for designing hoppers, transporting passages, dryers, silos and machines through which grain flows. In this study, the ANGLE of repose and INTERNAL FRICTION coefficient were determined for three common wheat varieties (Sardary, Gaspard and Saysoter) at four moisture contents (12, 15, 18, 21 w.b.%). Four contact surfaces (black, mild, aluminum and galvanized sheets) were used to measure the ANGLE of repose. The tests were done in five replications. Analysis of variance was used to analyze the data and Duncan’s multiple range test was used to compare the effect of the means (P<5%). The results showed that the effects of moisture content, variety and contact surface were significant for the ANGLE of repose. The effects of grain moisture content and variety were significant for the INTERNAL FRICTION coefficient (P<1%). When moisture content of the grain increased, the ANGLE of repose and INTERNAL FRICTION coefficient increased significantly. Only where grain moisture level changed from 18 to 21% w.b. the INTERNAL FRICTION coefficient did not change significantly. The highest and lowest INTERNAL FRICTION coefficients belonged to the Sardary and Saysoter varieties, respectively. The highest and lowest the ANGLEs of repose belonged to the Gaspard and Sardary varieties, respectively.

Determination of cohesion and ANGLE of INTERNAL FRICTION of the asphalt is of special importance for designing and estimating the bearing capacity of asphalt mixtures. This is usually done by performing the triaxial test. To perform such experiment, however, advanced experimental equipments and experienced people are needed.In the present study, a new method to determine the cohesion and ANGLE of INTERNAL FRICTION parameters of the asphalt is introduced. This method is based on using the unconfined compression and indirect tensile tests instead of triaxial test to measure the shear strength parameters (C,f). In the present study, asphalt samples with different size distribution, percentage of filler, percentage of fracturing and percentage of bitumen were made and tested against Unconfined and indirect tensile experiments. Based on the results obtained from these experiments, the Mohr- Coulomb circles were plotted and cohesion and ANGLE of INTERNAL FRICTION of asphalt were determined using Mohr- Coulomb theory. To assess the validity of the results, the Hveem test was performed on the samples with similar characteristics as tested samples with unconfined and indirect tensile experiments and the relation among the results was obtained and analysed.

In this paper, numerical methods are utilized to investigate the analyses of the elastic and inelastic cyclic behavior of nine reinforced concrete columns having various reinforcement configurations under cyclic compressive load. The response curves of the columns are compared with that of experimental results. In this research, tow main and important concrete mechanical properties "cohesion" and "INTERNAL FRICTION ANGLE" are used for the analysis. To evaluate these parameters it is possible to utilize the only one single parameter as the concrete compression strength and the relevant equation proposed in this work. The results exhibit that the specimen's behavioral model for the complete period of loading and unloading regime, is affected by the complete stress-strain curve of concrete under monotonic load.

Since its simplicity and availability, direct shear test is a current one. This test, compared to the triaxial test, provides different values for the parameters of the gravel due to the specific shape of the test device and the test approach. Triaxial testing, due to the feasibility of providing conditions similar to the natural behavior of gravel in a natural state, can provide more realistic values of material strength parameters. Due to being time consuming, costliness, problems in performing a triaxial test and the difficulty of sample preparation, direct shear test is still used more than triaxial test. In this paper, by studying the results of direct shear test and triangular experiments on gravel material, the stress paths in p - q space and the INTERNAL FRICTION ANGLE of these two tests are compared and the relation between them is obtained. To ensure the obtained results, large-scale triaxial and direct shear tests are used. The values of j, тf and бn are calculated in every direct shear test, and using different lateral pressure coefficients (k), the failure points in the space p and q are obtained. Using the points, failure envelope is depicted in these graphs and then, using the relationships, the gradient of the failure envelope is converted to the FRICTION ANGLE of the sample; and, it is compared with the triaxial test results. Subsequently, the stress path is studied via the results, and it is compared with the stress path of the triaxial test. Finally, it can be concluded that, when the INTERNAL FRICTION ANGLE of the gravel in direct shear test is analyzed via lateral pressure coefficient (kp), it is approximately the same with the INTERNAL FRICTION ANGLE obtained by the triaxial test in p- q space.

Foundation design is conventionally practiced by deriving the allowable bearing capacity in terms of shear strength and compressibility. Shear strength refers to the individual or combined contribution of drained ANGLE of INTERNAL FRICTION and undrained cohesion, at one of the three instances of peak (failure), residual, or critical (softened) states. Compressibility refers to the elastic and consolidation settlements; the predominance of which is a factor of soil permeability. Soil is conventionally examined by confined stressing on the wet stress-state surface, for the coefficient of volume compressibility to be determined. Ultimate bearing capacity is then reduced to a certain total settlement, and an arbitrary factor of safety of 3 is finally applied to cover uncertainties. Such a conservative approach however does not always successfully restrict the settlements beneath foundation. Although the shear strength has become a much-practiced subject, there has been a certain lack of emphasis on a fundamental understanding of shear strength parameters, and even greater neglect of the correct choice of stress path for individual soil types so to derive such parameters in the most critical stress-hydraulic environment. For that reason, this work aims to critically review the shear strength literature for a better understanding of the INTERNAL ANGLE of FRICTION and c-intercept.