فصلنامه رویکردهای نوین در مهندسی عمران
سال دوم شماره 2 (تابستان 1397)

In previous studies, it has been found that utilization of various supplementary cementations materials has significant effect on rheological properties of self-consolidating concrete. The present study aims to extend the role of water film thickness on rheological characteristics of self-consolidating concrete containing silica fume. For this purpose, relation between T50 flow time, V-funnel flow time and plastic viscosity with water film thickness of self-consolidating concrete mixtures containing different amounts of silica fume has been investigated. Results, showed that the rheological parameters can be closely related to the thickness of excess water around the solid particles.

The main aim of this study is an investigating the effect of using geogrid layers in the reinforcement of soil under the foundation to estimate the reaction of industrial machines’ foundations under periodic loading based on finite element method using ABAQUS software. Also, the effect of the number of geogrid layers, the effect of depth and width of geogrid, different loading frequencies along with the effect of using geogrid layers on the first to the third modes of frequency values of the soil were evaluated. The results showed that as the number of geogrid layers increases, bearing capacity of foundation rises and the optimum depth of geogrid layers for dynamic mode is equal to 0.6 times the width of the foundation strip. Furthermore, increasing frequency of dynamic load does not lead to a significant change in capacity.

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 φ, τf 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.

The rapid growth of construction in urban areas has resulted in building structures on soft and weak soils. These soils possess the low bearing capacity and high settlements. One of the common ways to increase bearing capacity in weak soils is to use granular trench. Trenching can be built easier, faster and cheaper than deep foundations. The function of granular trench is similar to stone columns. However, the difference is that instead of a column of granular material, a large area of granular material is used. In this research, we compare the results of static bearing capacity for shallow foundation with and without trench obtained from numerical modeling using FLAC2D. Furthermore, the effect of depth of granular trench on bearing capacity has been studied and finally the optimum depth is presented.

In recent years, a new type of fiber reinforced concrete (FRC), called hybrid FRC, comprised of fibers of the same material but with different geometry has been developed. The aim of this paper is to investigate the influence of volume fraction and aspect ratio of steel fibers on the basic engineering properties of hybrid steel fiber reinforced concrete. To this end, steel fiber reinforced concrete composites, comprised of different combinations of fiber volume fraction and fiber size/shape, are experimentally tested and compared in terms of compressive, splitting tensile strengths and flexural toughness by four-point bending tests. The results indicate that both micro and macro size steel fibers generally improve various engineering properties of concrete, despite advantages of one on the other for different mechanical properties. Straightforward relations are proposed relating the significant mechanical properties of hybrid steel FRC to the volume fraction of micro and macro steel fibers in the composite.