International Journal of Civil Engineering
Volume:11 Issue: 1, Apr 2013

For calculating the natural frequency of structures such as buildings, chimneys, bridges and silos appropriate analytical formulas exist. However, in the case of retaining walls undergoing the soil pressure at one side, calculating the natural frequency is not a straightforward task and requires the effects of soil-structure interactions to be considered. By modeling the soil as series of linear springs, a new formulation is presented in this article, to calculate the natural frequency of retaining walls. This formula considers the vertical cross sectional width change, and hence, enables us to calculating the natural frequency of retaining walls with different types of backfill. The geometrical properties of the retaining walls and its bending rigidity together with the soil’s modulus of elasticity and its Poisson’s ratio are the most important parameters to calculate. A comparison of the results for retaining walls with constant cross section obtained from the suggested method with those of the software analyses was carried out and good agreement was detected. A second comparison of the results with those of other researchers revealed that the natural frequency of flexible retaining wall is an upper bound for natural frequency of rigid walls. The Selected shape function is also very close to the real shape mode.

Owing to the proximity of certain locations to the thermal power stations, it has always been efforts of Engineers to enhance the flyash utilization rate in various Civil Engineering Constructions adopting suitable strategies. In the present study, a soilflyash interface mechanism has been evolved using different soil-flyash ratios to upgrade significantly stabilization of supporting medium based on CBR tests. The study confirms soundness of approach when a particular interface arrangement gives high flyash utilization rate along with many fold increase CBR values. A study was carried out to investigate the interface effect of soil-flyash layered system in terms of CBR values so that an optimum arrangement can be achieved by using flyash in combination with soil. In this study, 18 samples of different ratios of soil and flyash (1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3) with three sets of interfaces N = 2, 4 and 6 were tested to arrive at the most optimized combination of soil and flyash. The results indicate that the CBR value optimized at soil-flyash ratio 1:2.5 and number of interface N = 4. The present study reveals that soil with flyash when used in layered system with various numbers of interfaces gives considerable improvement in CBR values. In the above arrangement about 71 % of flyash and 29 % of soil thus contributing significantly in utilization of flyash in subgrade of flexible pavements. In the overall study, three equations for number of interfaces N = 2, 4 and 6 have also been developed in terms of soil-flyash ratio and CBR value, so that CBR value can directly be obtained by substituting the value of soil-flyash ratio at a particular number of interfaces.

Spatial Variation of Earthquake Ground Motion (SVEGM) is clearly indicated in data recorded at dense seismographic arrays. The main purpose of this paper is to study the influence of SVEGM on the seismic response of large embankment dams. To this end, the Masjed Soleyman embankment dam, constructed in Iran is selected as a numerical example. The spatially varying ground motion time histories are generated using spectral representation method. According to this methodology, the generated time histories are compatible with prescribed response spectra and reflect the wave passage and loss of coherence effects. To investigate the sensitivity of the dam responses to the degree of incoherency, three different coherency models are used to simulate spatially variable seismic ground motions. Finally, the seismic response of the dam under multi-support excitation is analyzed and compared to that due to uniform ground motion. Also, the Newmark's method is used to estimate seismic-induced permanent displacements of the embankment dam. The analysis results reveal that the dam responses can be sensitive to the assumed spatial variation of ground motion along its base. As a general trend, it is concluded that the use of multi-support excitation, which is more realistic assumption, results in lower acceleration and displacement responses than those due to uniform excitation

Among the different ways of in-situ soil investigation, cone penetration test data are selected to evaluate the spatial variability of geomaterials and the scale of fluctuations is chosen to evaluate the correlation structure of CPT data. In this regard six case studies in sandy materials from Australia, U.S.A. and Iraq are selected. Various techniques for the calculation of the scale of fluctuation of geotechnical parameters are suggested in literature e.g. VXP, SAI, AMF, BLM and VRF without any preference or privilege for any specific procedure. In order to isolate the stochastic portion of cone tip resistance, deterministic trend was first removed by regression analysis. This study suggests that quadratic trend removal is more suitable for selected CPT data soundings. The closeness of the estimated scale of fluctuation using different approaches is assessed too. Mean value of the scale of fluctuation by five established methods ranges between 0.44 to 1.52 meter for six different cases and the coefficient of variation for the scale of fluctuation calculated by these methods varies between 12 to 27 % showing that available established methods produce almost compatible and comparable results.

The occurrence of piping failures in earth structures demonstrates the urgency and importance of studying piping. With this intention, a new piping model was developed in the framework of continuum mixture theory. Assuming that porous media are comprised of solid skeleton phase, fluid phase and fluidized fine particles phase, the fluidized fine particles phase is considered to be a special solute migrating with the fluid phase. The three phases interact while being constrained by the mass conservation equations of the three phases, and a sink term was introduced into the mass conservation equation of the solid skeleton phase to describe the erosion of fluidized fine particles, then a new continuum fluid-particle coupled piping model was established and validated. The validation indicates that the proposed model can predict the piping development of complicated structures under complex boundary and flow conditions, and reflect the dynamic changes of porosity, permeability and pore pressure in the evolution of piping.

In this paper, an advanced formulation of a time-domain two-dimensional boundary element method (BEM) is presented and applied to calculate the response of a buried, unlined, and infinitely long cylindrical cavity with a circular cross-section subjected to SV and P waves. The applicability and efficiency of the algorithm are verified with frequency-domain BEM examples of the effect of cylindrical cavities on the site response analysis. The analysis results show that acceptable agreements exist between results of this research and presented examples. For a shallow cavity, the numerical results demonstrate that vertically incident SV wave reduces the horizontal components of the motion on the ground surface above the cavity, while it significantly increases the vertical component for a dimensionless frequency (η) of 0.5 and h/a=1.5. The maximum values of normalized displacements in vertical component of P waves are larger than horizontal component of SV waves for η=1.0. For a deeply embedded cavity, the effect of the cavity on the surface ground motion is negligible for incident SV wave, but it increases the vertical component of the displacement for incident P wave. Additionally, far and near distances from the center of the cavity show different amplitude patterns of response due to the cavity effect. Increasing the distance from the center of the cavity, the amplitude of displacement and the effect of the cavity attenuates significantly.

An important concern in rock mechanics is non-homogeneity as joints or fault. This noticeable feature of failures in rock is appearance of slip surfaces or shear bands, the characteristics of that are associated with deformation being concentrated in a narrow zones and the surrounding material remaining intact. Adopting the joints as fractures, fractures are well known for their effects on the mechanical and transport properties of rock. A damaged pro-elasticity multi-plane based model has been developed and presented to predict rock behavior. In this multi-plane model, the stress–strain behavior of a material is obtained by integrating the mechanical response of an infinite number of predefined oriented planes passing through a material point. Essential features such as the pro-elasticity hypothesis and multi-plane model are discussed. The methodology to be discussed here is modeling of slip on the local and global levels due to the deformation procedure of the existing/probable joints of rock and this method has a potential of using different parameters on different sampling planes to predict inherent anisotropy of rocks. Upon the presented methodology, more attention has been given to slip initiation and propagation through these joints. In particular, softening in non-linear behavior of joints in going from the peak to residual strengths imparts a behavior often associated with progressive failure. The predictions of the derived stress–strain model are compared to experimental results for marble, sandstone, Quartz mica schist and anisotropic schist. The comparisons demonstrate the capability of this model to reproduce accurately the mechanical behavior of rocks.

Geometrical profile (roughness) of joint surfaces influences the behaviour of rock joints under shear loading. With regard to the dilation, there are two models of direct shear test that may simulate the original loading condition existing in the location from where the specimens have been sampled. The first model in which the normal load is constant (CNL) and the discontinuity is free to dilate in shearing, represents typical situations such as movement of a block on a surface slope as a result of its own weight. The second model in which the dilatancy is prohibited (VNL), simulates the condition of a block confined in a rock mass in an underground opening. A shear test conducted under restricted normal displacement (dilation) will generally yield considerably higher shear strength than one conducted under constant normal stress. In this research, both types of tests were conducted on smooth and rough surfaces of specimens made from rock like material. The results of the VNL and the CNL direct shear tests on regular teeth-shaped profile discontinuities indicates that at all levels of normal load, the linear Mohr-Coulomb criterion was not valid for rough surfaces that subscribed to the power law equations. Increasing normal load emphasized the difference between the results obtained from two methods, although for lower normal loads the results were nearly similar.

In a rare engineering experience throughout the world, we successfully stabilized relatively coarse materials of drain using cement grouting. The grouting work was performed at the Karkheh earth dam, southwest Iran, and was part of the efforts to extend the dam’s cut-off wall. Since the dam was completed, the execution of the new cut-off wall from the dam crest was inevitable. Hence, one of the main difficulties associated with the development of the new cut-off wall was trenching and execution of plastic-concrete wall through the relatively coarse materials of drain in the dam body. Due to high permeability of drain, the work was associated with the possible risk of excessive slurry loss which could result in the collapse of the trench. In order to achieve an appropriate grouting plan and to determine the mix ratio for the grouting material, a full-scale test platform consisting of actual drain materials was constructed and underwent various tests. Results of the testing program revealed that a grouting plan with at least 2 grouting rows and a Water/Cement mix ratio of 1/ (1.5-2) can successfully stabilize the drain materials. After finalizing the technical characteristics of the grouting work, the method was applied on the drain materials of the Karkheh dam body. The results were satisfactory and the drain materials were stabilized successfully so that the cut-off wall was executed without any technical problem.