جستجوی مقالات مرتبط با کلیدواژه « sandy slope » در نشریات گروه « عمران »

Foundations are sometimes located either on a sloped surface or near the crown of a slope. Obvious examples can be seen in the footings of bridges abutments, foundations near excavations, retaining walls, and electric transmission towers built on mountain slopes. When the footing is placed near the edge of sloping ground, the bearing capacity may be significantly reduced, depending on the location of the footing concerning the slope. Therefore, the bearing capacity and stability of a slope is one of the most important research issues in geotechnical engineering. The adjacent soil's bearing capacity and the slope's stability can be increased by installing continuous confining structures like skirts. Skirted foundations are a type of shallow foundation with internal or lateral skirts made of steel or reinforced concrete. Using a skirt due to confinement of the soil beneath the foundation and transmitting the shear Failure at the level of the skirt tip. In this research, a series of laboratory tests were conducted on strip footing models adjacent to sand slope whit one side vertical skirt to evaluate the load-settlement response subjected to vertical compression loading. The effects of skirt depth (Hs) and setback distance (b) of the model on the bearing capacity and settlement of skirted foundations were studied. The results of the model tests have shown that using skirts improves the bearing capacity and settlement values of skirted foundations compared with shallow foundations without a skirt. The ultimate bearing capacity of skirted foundations increases up to about 104 to 232% with increasing the ratio of skirt depth to foundation width. To investigate the effect of setback distance on the skirted foundation behavior, three different distances of footing from crest to the width of the footing of 0, 1, and 2 were used. The results showed that the increase in the ratio of the distance of footing from the crest to the width of footing caused to increase in the ultimate bearing capacity of only footing. The results showed when the skirted footing is placed directly at the crest (b=0), increasing the depth of skirts leads to a significant increase in the bearing capacity. By increasing the edge distance from the slope crest to the footing, the effect of utilized skirts decreases. The Settlement Reduction Factor (SRF) decreased from 4 to 72% with the increase in the depth of the skirt and with a decrease in setback distance. Furthermore, the effect of a single-side skirt strip foundation resting on the top of the sand slope was investigated on the values of foundation tilting and failure mechanism. Evaluating results showed that strip footing near the slope has a clockwise tilt angle and after using one single skirt the tilt angle got changed. It was observed that in setback distance b/B=0 under s/B=15% with an increase in skirt depth (Hs=1b, 3B), the reduction values of footing tilt were from 46 to 24%, respectively. In the end, utilized skirts affect the failure mechanism and dependent on skirt length and setback distance change the failure pattern of the soil, face failure to toe, or base failure.

In this research, the free vibration or natural frequency analyzes have been performed with the help of small-scale physical models. Laboratory modeling in the geotechnical engineering can be performed in the acceleration field of 1g.  In each of the physical modeling modes, the relationship between the model and prototype frequencies is very essential. In this paper, with the help of hammer impact pulse tests (HIPTs) -dynamic experiments- the optimal frequency ranges and the best geometric scales for physical modeling are investigated by a strongbox. The frequency range studied has been selected according to the study of shaking table models between 0.001Hz and 150Hz. To perform impact pulse tests, the physical models of dry sandy slope with different inclination angles from 25 to 60 degrees (and a constatnt slope height) have been instrumented by the piezoelectric acceleration sensors.  The relative density of the sandy slope models is medium dense and about 50% to 52%. In addition to 8 physical models of sandy slopes, two models of level-ground and empty box have also been investigated. The time-history of the acceleration function of the input excitation shock at the slope floor (base point) and the response acceleration at the slope crest are recorded by the acceleration sensors.  These acceleration time responses last for a short stroke (short impact) of less than 1.0 second duration. After extracting temporal responses, the frequency analyzes including transfer function (TF), Fourier response spectrum ratio (RFRS), and spectral energy density function (PSD-function) are derived from the temporal results. Using the transfer function or RFRS, quantitative values of natural frequencies of the physical model of the sandy slope and the storngbox are extracted in different vibration modes. According to the findings of the present study, for a constant slope model the frequencies at which the maximum seismic or dynamic energy is emitted are quite different from the frequencies with the maximum magnified response amplitude. The results of the present study prove the existence of a logic relationship between the sandy slope inclination angle (physical model natural frequencies) and the model response amplification frequency. So that by increasing the angle of inclination of the model slopes at a constant height, the magnification values of the impact acceleration response decrease. Because in general, the amount of sandy materials magnifies or weakens the amplitude of frequency responses. The presence of low sandy materials (on steep slope models) reduces the magnification range of the acceleration response and high sandy materials (on gentle slopes) increase the response range. Optimal frequencies in strong box modeling in the 1g acceleration field are frequencies that do not interfere with acceleration magnifications before or during seismic excitation (pre-seismic mode). Acceleration magnification causes resonance and premature failure in the physical model, which is generally undesirable and unmeasurable in laboratory studies. In this research, the optimal frequency range according to the measurements is proposed for the physical modeling of the 1g acceleration field. These ranges and frequency values are presented according to the various constraints such as the type of strong box, slope angle, relative density of sand, the actual frequency effect of the horizontal components of earthquakes, and so on.

One of the efficient ways in order to reinforce the earth slopes is Geogrid Encased Stone Column (GESC). This technique can increase bearing capacity and decrease settlement rate of slopes. The aim of this study is to perform a three dimensional finite difference method (FLAC3D) for GESC in the stabilization of sand slopes. According to the results of 3D numerical analysis, the existence of geogrid-encased stone column, increases stability to an ideal level compared with ordinary stone column-reinforced slopes. Different parameters including stone column diameter, the coupling spring stiffness, coupling spring cohesion, coupling spring friction, S/D ratio, and the layout of encasements evaluated and discussed in this paper. The influential parameter in geogrid in order to reinforce stone column, is coupling spring cohesion. By increasing the parameter, slope bearing capacity of reinforced slope increases linearly. This indicate that use of geogrid reinforced stone column, based on type of geogrid characteristics, can enhance earth slope bearing capacity up to 1.8 times of slope reinforced by ordinary stone column. The maximum bearing capacity with a row of stone columns was obtained for S/D=2. However, the reduction of S/D does not necessarily imply the increase of bearing capacity of slopes.